ABSTRACT. Professor Ashwani K. Gupta Department of Mechanical Engineering

Transcription

1 ABSTRACT Title of Document: HIGH TEMPERATURE STEAM GASIFICATION OF SOLID WASTES: CHARACTERISTICS AND KINETICS Islam Ahmed Gomaa, Docto of Philosophy, Diected by: Pofesso Ashwani K. Gupta Depatment of Mechanical Engineeing Geate use of enewable enegy souces is of pinnacle impotance especially with the limited eseves of fossil fuels. It is expected that futue enegy use will have inceased utilization of diffeent enegy souces, including biomass, municipal solid wastes, industial wastes, agicultual wastes and othe low gade fuels. Gasification is a good pactical solution to solve the gowing poblem of landfills, with simultaneous enegy extaction and nonleachable minimum esidue. Gasification also povides good solution to the poblem of plastics and ubbe in to useful fuel. The chaacteistics and kinetics of syngas evolution fom the gasification of diffeent samples is examined hee. The chaacteistics of syngas based on its quality, distibution of chemical species, cabon convesion efficiency, themal efficiency and hydogen concentation has been examined. Modeling the kinetics of syngas evolution fom the pocess is also examined. Models ae compaed with the expeimental esults. Expeimental esults on the gasification and pyolysis of seveal solid wastes, such as, biomass, plastics and mixtue of cha based and plastic fuels have been povided. Diffeences and similaities in the behavio of cha based fuel and a plastic sample has been discussed. Global

2 eaction mechanisms of cha based fuel as well polystyene gasification ae pesented based on the chaacteistic of syngas evolution. The mixtue of polyethylene and woodchips gasification povided supeio esults in tems of syngas yield, hydogen yield, total hydocabons yield, enegy yield and appaent themal efficiency fom polyethylene-woodchips blends as compaed to expected weighed aveage yields fom gasification of the individual components. A possible inteaction mechanism has been established to explain the synegetic effect of co-gasification of woodchips and polyethylene. Kinetics of cha gasification is pesented with special consideation of sample tempeatue, catalytic effect of ash, geometic changes of poes inside cha and diffusion limitations inside and outside the cha paticle.

3 HIGH TEMPERATURE STEAM GASIFICATION OF SOLID WASTES: CHARACTERISTICS AND KINETICS By Islam Ahmed Gomaa Dissetation submitted to the Faculty of the Gaduate School of the Univesity of Mayland, College Pak, in patial fulfillment of the equiements fo the degee of Docto of Philosophy Advisoy Committee: Pofesso Ashwani K. Gupta, Chai Pofesso Nam Sun Wang, Dean s Repesentative Pofesso Michael Zachaiah Pofesso Gegoy Jackson Pofesso Bao Yang

4 Copyight by Islam Ahmed Gomaa

5 Dedication I would like to dedicate this thesis to my wife, Tahanie Thabet, and my paents, Pofesso Ibahim Gomaa and Ms. Sohei Saleh. They have been a geat suppot fo me thoughout the yeas of my PhD study. ii

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7 Acknowledgments I would like to acknowledge my adviso, Pofesso A. K. Gupta fo his help and suppot. Pofesso A. K. Gupta opened my eyes to the meaning of had wok. I am also thankful fo his help in publishing a good numbe of jounal papes. Also, I would like to thank my wife and paents fo thei suppot. My wife tuned down numeous job offes in ode to stay next to me duing the yeas of my study. My paents accepted the fact that I will be living away fom them fo yeas. Finally, I would like to expess my sincee gatitude to the Office of Naval Reseach (ONR), who suppoted this wok. iv

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9 Table of contents Dedication ii Acknowledgments iv Table of Contents. vi List of Tables.. viii List of Figues... ix Nomenclatue... xii Chapte I: Intoduction... Motivations and Objectives.... What is Gasification? Chaacteistics of syngas evolution Kinetics of cha gasification... 3 Chapte II: Liteatue eview.7.. Chaacteistics of syngas evolution duing pyolysis and gasification..7.. Kinetics of cha gasification Kinetics of syngas evolution duing pyolysis...4 Chapte III: Expeimental setup and expeimental conditions Desciption of expeimental setup Cha pepaation Pocedues of eactivity detemination Expeimental conditions and samples popeties.48 Chapte IV: Results and discussion...5 vi

10 4.. Chaacteistics of syngas evolution fom wastes gasification and pyolysis Kinetics of syngas evolution fom cha gasification and pyolysis 4.3. Kinetics of syngas evolution duing pyolysis of solid wastes...54 Chapte V: Expeimental uncetainty analysis Flow ates uncetainty [Systematic eo] Data epeatability [Random eo] Vaiation in gasifying agent patial pessue Expeiments with diffeent sample mass and diffeent chips size...7 Chapte VI: Conclusions Chaacteistics of syngas evolution fom cha based samples Chaacteistics of syngas evolution fom Polystyene Chaacteistics of syngas evolution fom mixed samples Kinetics of cha gasification.79 Chapte VII: Recommendations fo futue wok Design pocedues of small scale gasifie fo expeimental investigations Inteaction between diffeent samples Liquid fuels poduction by themal/hydothemal cacking of plastics..85 Appendix A: Fomulation of the finite element poblem 87 Appendix B: List of Publications.9 Refeences...9 vii

11 List of Tables Table II-. Steps of cellulose pyolysis as suggested by Balat Table III-. Tested samples and expeimental conditions Table III-. Opeational conditions fo cha gasification kinetics expeiments Table III-3. Sample popeties; ultimate and poximate analysis Table IV-. Activation enegies and pe-exponential facto at diffeent degees of convesion fo X =. to.9 Table IV-. Activation enegies and pe-exponential factos at diffeent degees of convesion fom.93 to.98 Table IV-3. Rate constants and stuctual paametes fo both steam and CO expeiments Table IV-4. Kinetic paametes of steam cha eaction Table IV-5. Examples of f(x), g(x) and the coesponding ate-detemining mechanism Table IV-6. Kinetic paametes fo the thee heating ate. Table IV-7. Kinetic paametes of the paallel fist ode eactions model viii

12 List of Figues Figue I-. Reaction sequence fo gasification Figue I-. Pogess of food waste sample though pyolysis and gasification Figue I-3. Schematic of gasifying agent concentation pofiles inside diffeent cha paticles; (a) geneal case of medium poosity paticle, (b) vey low poosity paticle and (c) highly poous paticle Figue II-. Cellulose eaction mechanisms Figue II-. Reactions sequence duing PDE, DPM, stilbene and TPE pyolysis. Figue III-. A photogaph of the expeimental facility Figue III-. Schematic diagam of the expeimental setup Figue III-3. Detailed dawing of the eacto Figue IV-. Syngas flow ate fom pyolysis and gasification at (a) 6 o C and (b) 7 o C Figue IV-. Syngas flow ate fom pyolysis and gasification at (a) 8 o C and (b) 9 o C Figue IV-3. Syngas flow ate fom pyolysis and gasification at o C Figue IV-4. Hydogen flow ate fom gasification Figue IV-5. Hydogen flow ate fom pyolysis Figue IV-6. Hydogen yield fom pyolysis and gasification Figue IV-7. H and CO mole faction fo pyolysis and gasification at (a) 6 and (b) 7 o C Figue IV-8. Evolution of H and CO mole faction duing pyolysis and gasification at (a) 8 and (b) 9 o C Figue IV-9. Equilibium mole faction fo H O/CO eaction Figue IV-. Pecentage of Cha esidues fom pyolysis and ash esidues fom gasification Figue IV-. Cha leftove fom pyolysis (left) and ash leftove fom gasification (ight) ix

13 Figue IV-. (a) Enegy yield fom pyolysis and gasification and (b) appaent themal efficiency of pyolysis and gasification Figue IV-3. Evolution of H mole faction fo eacto tempeatues (a) 8, (b) 9 and (c) o C Figue IV-4. Evolution of CO mole faction fo eacto tempeatues (a) 8, (b) 9 and (c) o C Figue IV-5. Total yield of H, CO and CO fom (a) pyolysis and (b) gasification Figue IV-6. Reaction mechanism of biomass gasification. Blue line epesents pyolysis oute which ae acceleated with incease in eacto tempeatue. Red line epesents cha fomation oute and consequent CO poduction oute though cha gasification. This oute is favoed at lowe tempeatues Figue IV-7. Evolution of syngas flow ate fo eacto tempeatues 8, 9 and o C Figue IV-8. Evolution of H flow ate fo eacto tempeatues 8, 9 and o C Figue IV-9. Reaction mechanism of biomass gasification. The dotted line epesents outes which ae favoed at high heating ates and high eacto tempeatues. Figue IV-. Evolution of sample tempeatue with time fo eacto tempeatues 8, 9 and o C Figue IV-. Evolution of CO/CO atio (mola basis) Figue IV-. Enegy yield at eacto tempeatues of 8, 9 and o C Figue IV-3. Enegy yield at eacto tempeatues of 8, 9 and o C Figue IV-4. Syngas and hydogen yield at eacto tempeatues of 8, 9 and o C Figue IV-5. Cumulative syngas yield at eacto tempeatues of 8, 9 and o C Figue IV-6. Cumulative hydogen yield at eacto tempeatues of 8, 9 and o C x

14 Figue IV-7. Cumulative enegy yield at eacto tempeatues of 8, 9 and o C Figue IV-8. Evolution of syngas flow ate fom pyolysis and gasification fo eacto tempeatues (a) 7 o C, (b) 8 o C and (c) 9 o C Figue IV-9. Evolution of hydogen flow ate fom pyolysis and gasification fo eacto tempeatues (a) 7 o C, (b) 8 o C and (c) 9 o C Figue IV-3. Evolution of output powe fom pyolysis and gasification at eacto tempeatues of: (a) 7 o C, (b) 8 o C and (c) 9 o C Figue IV-3. Oveall syngas yield fom pyolysis and gasification Figue IV-3. Oveall hydogen yield fom pyolysis and gasification Figue IV-33. Condensable hydocabons fom PS gasification Figue IV-34. (a) Enegy yield and (b) appaent themal efficiency fo pyolysis and gasification Figue IV-35. Oveall hydogen mole faction fo pyolysis and gasification Figue IV-36. Oveall pue fuel pecentage in syngas fo pyolysis and gasification Figue IV-37. Evolution of syngas flow ate duing ubbe gasification Figue IV-38. Evolution of syngas flow ate duing ubbe pyolysis Figue IV-39. Evolution of hydogen flow ate duing ubbe pyolysis Figue IV-4. Evolution of hydogen flow ate duing ubbe gasification Figue IV-4. Syngas yield fom ubbe gasification and pyolysis Figue IV-4. Hydogen yield fom ubbe gasification and pyolysis Figue IV-43. Enegy yield fom ubbe gasification and pyolysis Figue IV-44. Syngas yield fom had wood, wood chips and ubbe gasification Figue IV-45. Hydogen yield fom had wood, wood chips and ubbe gasification Figue IV-46. Enegy yield fom had wood, wood chips and ubbe gasification xi

15 Figue IV-47. Hydocabons yield fom gasification of had wood, wood chips and ubbe Figue IV-48. Evolutionay behavio of syngas chemical composition (a) gasification at steam flow ates of 4. g/min (b) gasification at steam flow ates of 5. g/min and (c) Pyolysis at same tempeatue (9 o C) Figue IV-49. Change of sample tempeatue with time Figue IV-5. Evolutionay behavio of H flow ate at diffeent steam flow ates Figue IV-5. Evolutionay behavio of CO mole faction at diffeent steam flow ates Figue IV-5. Evolutionay behavio of CH 4 mole faction at diffeent steam flow ates Figue IV-53. Evolutionay behavio of H /CO atio at diffeent steam flow ates Figue IV-54. Evolutionay behavio of Fuel % in syngas at diffeent steam flow ates Figue IV-55. Evolutionay behavio of syngas LHV (kj/m 3 ) at diffeent steam flow ates Figue IV-56. Effect of steam flow ate on syngas composition Figue IV-57. Effect of steam flow ate on pue fuel yield and pue fuel % Figue IV-58. Effect of steam flow ate on appaent themal efficiency and enegy yield Figue IV-59. Effect of steam flow ate on oveall LHV, (kj/m 3 ) and (kj/kg) Figue IV-6. Effect of steam flow ate on H yield and oveall H /CO atio Figue IV-6. Effect of steam flow ate on cabon convesion (%) and syngas yield (lites) Figue IV-6. Effect of steam flow ate on coefficient of enegy gain (CEG) at diffeent sample esidence time in the eacto Figue IV-63. Evolution of syngas chemical composition at eacto tempeatue of 8 C Figue IV-64. Evolution of syngas chemical composition at eacto tempeatue of C Figue IV-65. Evolution of syngas flow ate at diffeent eacto tempeatues Figue IV-66. Evolution of H flow ate at diffeent eacto tempeatues xii

16 Figue IV-67. Evolution of output powe at diffeent eacto tempeatues Figue IV-68. Evolution of H /CO atio at diffeent eacto tempeatues Figue IV-69. Evolution of LHV (kj/kg) fo diffeent eacto tempeatues Figue IV-7. Effect of eacto tempeatue on syngas composition Figue IV-7. Effect of eacto tempeatue on syngas and H yields Figue IV-7. Effect of eacto tempeatue Enegy yield (kj) and appaent themal efficiency Figue IV-73. Effect of eacto tempeatue on oveall H /CO atio and ta yield (gams) Figue IV-74. Cellulose pyolysis mechanism Figue IV-75. Evolution of syngas flow ate (a) fom to 5 minutes and (b) fom 5 to 5 minutes Figue IV-76. Evolution of hydogen flow ate (a) fom to 5 minutes and (b) fom 5 to 5 minutes Figue IV-77. Evolution of (a) ethylene flow ate and (b) total hydocabons flow ate Figue IV-78. Evolution of (a) output powe and (b) cabon flow ate Figue IV-79. Evolution of cabon flow ate (a) fom to 5 minutes and (b) fom 5 to 5 minutes Figue IV-8. Syngas yield (left axis) and hydogen yield (ight axis) Figue IV-8. Total hydocabons yield (left axis) and ethylene yield (ight axis) Figue IV-8. Enegy yield (left axis) and appaent themal efficiency (ight axis) Figue IV-83. Oveall cabon yield (based on cabon content in the syngas) Figue IV-84. Aangement of PE and WC sample in the eacto Figue IV-85. Possible volatiles-cha inteaction mechanism Figue IV-86. Cumulative syngas yield xiii

17 Figue IV-87. Cumulative hydogen yield Figue IV-88. Cumulative enegy yield Figue IV-89. Time of 99% syngas convesion Fig IV-9. ln(-x) vesus time Fig IV-9. ln(k) o ln( cha ) vesus /T Figue IV-9. Pogess of food waste sample though pyolysis and gasification Figue IV-93. Cabon flow ate vesus time fo tempeatues 75, 8, 85 and 9 o C Figue IV-94. Convesion vesus time fo tempeatues 75, 8, 85 and 9 o C Figue IV-95. Cha eactivity vesus convesion fo tempeatues 75, 8, 85 and 9 o C Figue IV-96. Ahenius plot at diffeent degees of convesion; fom. to.9 Figue IV-97. Ahenius plot at diffeent degees of convesion; fom.93 to.98 Figue IV-98. Ahenius plot fo convesions fom.93 to.98 showing the isokinetic tempeatue and isokinetic eactivity Figue IV-99. Ln(A) vesus E act fo the convesion fom.93 to.98 Figue IV-. Evolution of eaction ate at gasifying agent patial pessue of.5 bas Figue IV-. Evolution of eaction ate at gasifying agent patial pessue of. bas Figue IV-. Evolution of eaction ate at gasifying agent patial pessue of.9 bas Figue IV-3. Evolution of eaction ate at gasifying agent patial pessue of.6 bas Figue IV-4. Reaction ate vesus convesion and RPM fitting fo gasifying agent patial pessue.5 bas Figue IV-5. Reaction ate vesus convesion and RPM fitting fo gasifying agent patial pessue. bas xiv

18 Figue IV-6. Reaction ate vesus convesion and RPM fitting fo gasifying agent patial pessue of.9 bas Figue IV-7. Reaction ate vesus convesion and RPM fitting fo gasifying agent patial pessue of.6 bas Figue IV-8. Reaction ates vesus convesion and aveage RPM fitting fo steam expeiments Figue IV-9. Reaction ates vesus convesion and aveage RPM fitting fo CO expeiments Figue IV-. A schematic diagam of a chemically contolled suface eaction Figue IV-. -(-X) -ncha /(-n cha ) vesus time Figue IV-. Ln(K obseved ) vesus /T Figue IV-3. Pogess of total convesion with time fo expeimental and numeical esults at o C Figue IV-4. Concentation pofiles fo a lage Da numbe case. Figue IV-5. Convesion pofiles fo a lage Da numbe case. Figue IV-6. Pogess of gasifying agent concentation inside the cha paticle fo a lage Da numbe case. Figue IV-7. Pogess of the cha paticle convesion with time fo lage Da numbe case. Figue IV-8. Concentation pofiles fo a small Da numbe case. Figue IV-9. Degee of convesion fo a small Da numbe case. Figue IV-. Gasifying agent concentation inside the cha paticle fo a small Da numbe case. Figue IV-. Pogess of the cha paticle convesion with time fo a small Da numbe case. Figue IV-. Concentation pofiles fo an intemediate Da numbe case. xv

19 Figue IV-3. Convesion pofiles fo an intemediate Da numbe case. Figue IV-4. Pogess of gasifying agent concentation inside the cha paticle fo intemediate Da numbe case. Figue IV-5. Pogess of the cha paticle convesion with time fo intemediate Da numbe case. Figue IV-6. Total convesion vesus time fo diffeent paticle sizes, fom p =.4 to 4 mm in.4mms steps. Figue IV-7. Total convesion vesus time fo diffeent initial poosities, fom ε ο =.7 to.7 in.7 steps. Figue IV-8. Total convesion vesus time fo diffeent ate constants, fom K obseved =. to /min in. /min steps. Figue IV-9. F(X) vesus (/T) fo heating ate (a) 8, (b) and (c) o C/min. Figue IV-3. Convesion (X) vesus tempeatue (T) fo heating ates (a) 8, (b) and (c) o C/min. Figue IV-3. Expeimental convesion ates of main gases duing pyolysis and thei fist ode model fit; (a) H, (b) CO, (c) CO and (d) CH 4 Figue V-. Vaiation of pecentage of uncetainty eo due to uncetainty in MC eading as a function of syngas constituent mole faction. Figue V-. (a) Syngas flow ate and (b) H flow ate at o C fo two uns Figue V-3. Syngas flow ate, (b) hydogen flow ate and (c) output powe fo thee uns at 8% PE-%WC mixtue conditions Figue V-4. Vaiation of (a) steam and (b) CO patial pessues with sample convesion xvi

20 Figue V-5. Reaction ate vesus sample convesion fo fine chips sample and smalle mass sample Figue VII-. Algoithm of the gasification numeical simulations and gasifie design xvii

21 Nomenclatue A pe-exponential facto (/sec) o (/min) C Gasifying agent concentation (mol/m 3 ) C cabon is the initial cabon concentation in the cha paticle (mol/m 3 ) C s Gasifying agent concentation at the cha paticle suface (mol/m 3 ) C Gasifying agent concentation fa fom the cha paticle (mol/m 3 ) Da Damkohle numbe (-) D effective effective diffusivity inside the paticle in the definition of Damkohle numbe (m /sec) D ga-b binay diffusion coefficients of the gasifying agent in gas B (m /sec) D ga-c binay diffusion coefficients of the gasifying agent in gas C (m /sec) D o is the gasifying agent diffusivity in the gas phase (m /sec) D p is effective diffusion coefficient of the gasifying agent inside the paticle (m /sec) E act Activation enegy (kj/mol) E yield enegy yield fom PS gasification o pyolysis (kj) E i mean activation enegy value in the distibuted activation enegy model (kj/mol) f(x) is a function of convesion (X), (-) K eaction ate constant K i Reaction ate constant fo pseudo eaction (i), (/min)o (/sec) K obseved obseved eaction ate constant in a chemically contolled expeiment (/sec) L chaacteistic length in the definition of Damkohle numbe (m) m cha mass at time t (kg) N e numbe of moles in each element n e N H numbe of hydogen moles evolved at time (t) fom pape pyolysis expeiments xviii

22 N * H total numbe of hydogen moles evolved fom the sample duing pape pyolysis N total total numbe of moles in the paticle N o initial numbe of moles in the cha paticle n cha eaction exponent with espect to cha (-) n e numbe of elements in the FEM solution n ga is the ate exponent with espect to gasifying agent n eaction is the eaction ate exponent with espect to the gasifying agent in the definition of Damkohle numbe n time numbe of time intevals in the finite diffeence solution q sample heating ate ( o C/min) R Univesal gas constant (J/kmol.K) R cd coefficient of detemination (-) adius (m) cha cha eactivity (/sec) o (/min) e adius to the fist node of element numbe (e) iso isokinetic eactivity (/sec) o (/min) p paticle adius (m) t time (sec) o (min) T tempeatue (K) o ( o C) T iso isokinetic tempeatue (K) o ( o C) T o initial eacto tempeatue (K) V CH4 amount of CH 4 evolved at time (t) V * CH4 maximum potential amount of CH 4 xix

23 w i weight of pseudo eaction (i) in pape pyolysis kinetics, (-) X Cha convesion, (-) X e degee of convesion at the fist node of element numbe (e) X total Total convesion of the cha paticle (-) y B mole faction of gas B (-) y C mole faction of gas C (-) y ga gasifying agent mole faction (-) ρ density (kg/m 3 ) Ψ is a dimensionless stuctual paamete in the andom poe model (-) α j oveall convesion of main syngas constituent (j) at time (t) fom pape pyolysis α i convesion of main syngas constituent fom pape pyolysis fom pseudo eaction i η app. Appaent themal efficiency (-) λ totuosity facto (-) ε poosity of cha at a given () and (t), (-) ε ο initial poosity of the cha paticle (-) σ ι width paamete of the distibution in the distibuted activation enegy model (kj/mol) Subscipt it index fo time intevals H O steam CO Cabon dioxide Supescipt je index fo numbe of nodes xx

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25 .. Motivations and Objectives Chapte I: Intoduction Many cities woldwide, in paticula densely populated cities ae confonted with the poblem of acceptable means of disposing-off lage quantities of municipal solid waste (MSW). Cuently, landfills ae the pimay means of MSW disposal and account fo about 8% of the esidential waste geneated in the USA. Howeve, ising landfill tipping fees and thei poven detimental envionmental impact have led enginees and scientists to seach fo cleane and inexpensive altenatives fo the disposal of municipal waste. Enegy ecovey fom MSW, known as wasteto-enegy (WTE), is one such altenative. One moe motivation towads the WTE ecovey is govenmental egulations and plans such as, the Solid Waste Disposal Act of 976 [] (also known as Resouce Consevation and Recovey Act-RCRA), which equies all states to implement 'Solid Waste Plans' that maximize waste eduction and ecycling. Clean waste-to- Enegy educes the amount of mateials sent to landfills, assists in peventing ai/wate contamination impoves ecycling ates and lessens the dependence on fossil fuels fo powe geneation. Gasification of solid wastes is a good solution fo not only the enegy poblem but also offes envionmentally benign solution fo waste destuction and management []. Specific poblems ise fom diffeent types of solid waste. Dumping food waste in a landfill causes envionmental poblems. By volume, the dumped landfill waste causes the lagest contibution to methane gas poduction [3]. It causes odo as it decomposes to cause public annoyance in addition to foming gems, and attacting flies and vemin. Anothe seious poblem of food wastes is the geneation of landfill leachate. Landfill leachate is liquid that leaks fom the landfill and entes the envionment. Once it entes the envionment the leachate is at

26 isk fo mixing goundwate nea the site which then tanspots to some distances. Futhemoe it has the potential to add biological oxygen demand (BOD) to the goundwate. BOD measues the ate of oxygen uptake by mico-oganisms in a sample of wate at a tempeatue of C and ove an elapsed peiod of five days in the dak. Despite poblems that aise fom food wastes, they ae biodegadable and can be decomposed easily. Howeve, plastics and ubbe ae not biodegadable, but photo-degadable. Photodegadation is a pocess in which the mateial bakes down by sunlight into smalle and smalle pieces, all of which ae still polyme molecules, eventually becoming individual molecules of plastic, which ae still difficult fo the envionment to accommodate. Automobile ties alone ae big poblems not only in the USA but many counties woldwide. It is estimated that about billion ties lie as tash in the USA and additional amounts woldwide. In addition ove million ties ae added annually in the USA as wastes. It is estimated that about 8 to 9% of the plastics is disposed off impopely. The use of plastics in the cas has incease significantly ove the yeas. Fo example in 98 aveage amount of plastics in cas was 86 kg/vehicle, while in 99 it was 63 kg/vehicle. The use of plastics is expected to incease in the futue not only in cas in the tanspotation secto but also in othe applications, such as appliances, toys and selected industial and consume applications. Geate use of enewable enegy souces is of pinnacle impotance especially with the limited eseves of fossil fuels. It is expected that futue enegy use will have inceased utilization of diffeent enegy souces, including biomass, municipal solid wastes, industial wastes, agicultual wastes and othe low gade fuels. The diffeent types of wastes povide not only unique challenges fo enegy utilization, but also the enegy yield and gas composition fom gasification o pyolysis is stongly impacted by the feed mixtue composition. Development of

27 sustainable enewable enegy technologies fo thei use in cuent and new powe plants is of geate impotance now than eve befoe due to seveal easons. Some of these easons include enegy secuity and availability, independency fom foeign oils and eduction of geenhouse gas emissions to povide cleane envionment fo bette health and plant and animal life. These easons dictate the development of altenative and sustainable enegy technologies. Gasification povides pat of the solution towads dependable enewable enegy souce. Gasification is a obust solution to solve the gowing poblem of landfills, since enegy can be fully extacted and the waste is destucted with minimum esidue and with the popely developed pocess the emaining esidue is non-leachable. On the othe hand, gasification povides an excellent solution to the poblem of plastics and ubbe in landfills by getting id of the plastic and ubbe wastes and ecoveing enegy in the same time [4-7]. The goal of the new stategies in handling wastes must be gabage in and enegy out in an envionmentally acceptable manne [8]. The potential of gasification is attibuted to seveal key advantages of the gasification pocess. Fo example, the IGCC powe plants povide a vey high themal efficiency. Beside the high themal efficiency of IGCC powe plants, the gasification pocess can utilize a wide ange of cabonaceous mateials as feedstock (such as coal, biomass and wastes) and the gases poduced can be used as fuel in powe plants. The esidue emaining fom gasification, especially ash, can be used as constuction mateial. Syngas fom gasification can possess low, medium o high hydogen content, with the emaining as cabon monoxide. Pope mixtue of the two gases povides a potential of poducing liquid fuels. Altenatively sepaating out hydogen fom the syngas can be used as good clean fuel in hydogen engines o fuel cells. 3

28 Residues emaining fom gasification ae mainly ashes. Ash is not destucted by gasification o combustion. The ash emaining afte the gasification pocess is a valuable poduct. Fo example, it can be used in the poduction of cement and othe constuction mateials. The emission of hazadous pollutants is also eliminated o minimized. Fo example; NO X fomation is eliminated if steam and/o oxygen ae used as gasifying agents. NO X fomation is also minimized even if ai is used as the gasifying agent due to the lowe eacto tempeatue as compaed to that encounteed in diect combustion of waste mateials. Note that gasification tempeatues ae lowe than the tempeatues at which themal NO X is fomed (8 o C). Such high tempeatues ae common in combustion systems that have stoichiometic mixtues at selected egions of combustion chambe but not in the gasification studies conducted hee. Howeve, ai gasification systems, uns on vey ich equivalence atios and the gasification tempeatues ae much lowe. A consideable advantage of gasification ove combustion is the eduction of volumetic gases poducts by a facto 5 to which in tun educes the size of gas conditioning/cleaning equipment [9]... What is Gasification? Gasification is heating-up of solid o liquid cabonaceous mateial with some gasifying agent to poduce gaseous fuel. The heating value of the gases poduced is geneally low to medium. This definition excludes combustion, because the poduct flue gas has no esidual heating value fom complete combustion of the fuel. It does include patial oxidation of fuel o fuel-ich combustion, and hydogenation. In patial oxidation pocess the oxidant (also called the gasifying agent) could be steam, cabon dioxide, ai o oxygen, o some mixtue of two o moe gasifying agents. The gasifying agent is chosen accoding to the desied chemical composition of the syngas and efficiency. 4

29 Pyolysis and gasification ae impotant to efom solid and liquid hydocabons to clean gaseous fuel which can be futhe pocessed to obtain clean and pue gaseous fuel o liquid fuel. Pyolysis is a themal degadation pocess of oganic compounds in the absence of oxygen o ai to poduce vaious gaseous component yield as well as yield of ta and cha esidues. The heating ate of the sample, pyolysis tempeatue, and paticle size and distibution has an impotant effect on the poducts evolved and thei distibution duing pyolysis []. Cha gasification eactions have elatively high activation enegy as compaed to pyolysis eactions. This diffeence in activation enegies eveals highe sensitivity of gasification on the eacto tempeatue than that of pyolysis. Highe values of activation enegy in case of gasification esult in longe gasification time. Consequently, cha gasification is consideed to be the ate limiting step in the oveall gasification pocess []. Steam is usually used as a gasifying agent to achieve high hydogen yield. Steam has been used as gasifying agent in this study to investigate the behavio of syngas duing steam gasification and effect of steam flow ate on main syngas popeties. The final composition of the syngas is a function of the gasification tempeatue, steam to cabon atio and pessue. Consequently, adjustment of these paametes should be taken into consideation to optimize themal efficiency. Duing the pocess of gasification of solid cabon, whethe in the fom of coal, coke, o cha, the pinciple chemical eactions ae those involving cabon, cabon monoxide, cabon dioxide, hydogen, wate (o steam), and methane []. These include Combustion eactions: C+½O =CO, H = MJ/kmol CO+½O =CO, H = 83 MJ/kmol 5

30 H +½O =H O, H = 4 MJ/kmol The Boudouad eaction: C+CO CO H = +7 MJ/kmol () The wate gas eaction: C+H O CO+H, H = +3 MJ/kmol () The methanation eaction: C+H CH 4 H = -75 MJ/kmol (3) Reactions fom (), () and (3) ae the most impotant eactions in the cha-gasification step and both ae endothemic eactions. These eactions ae educed to the following two homogeneous gas eactions. Wate-gas shift eaction: CO + H O CO + H, H = 4MJ / kmol (4) The steam methane efoming eaction: CH 4 + H O CO + 3H, H = +6MJ / kmol (5) A simplified eaction sequence fo the gasification of cabonaceous mattes is shown in Figue I-. Figue I- shows the pogess of a sample unde pyolysis and gasification conditions Solid Cabonaceous Mateial Pyolysis Pyolysis gases (CO, H, H O etc.) Ta, Oil, Naphtha Oxygenated compounds (Phenols, Acid) Cha CO, H Gas phase eactions, CH 4, CO, H O and (Cacking, efoming, Cacking poducts Combustion CO shift) Cha-Gas eactions Gasification, Combustion, CO shift CO, H, CH 4, CO, H O Figue I-. Reaction sequence fo gasification [] 6

31 Food waste (Simulated as dog food) Cha + Ash Ash (~5.75%) Pyolysis Cha gasification (~.75%) (~5 9 o C) (~35 9 o C) Gasification (~38 9 o C) Figue I-. Pogess of food waste sample though pyolysis and gasification.3. Chaacteisticss of syngas evolution.3.. Intoduction Samples othe than coal have stated to attact attention of eseaches in the gasification field. Chaacteistics of syngas evolution fom waste samples, such as, cadboad [], pape [], plastic [3] and food wastes [4] have been investigated. Results show thatt thee is a geat potential of using these mateials as well as othe waste mateials as fuel fo powe geneation in gasification powe plants..3.. Gasification of cha based fuel Since cadboad foms a big pecentage of MSW, gasification of cadboad has been investigated with specific focus on the evolutionay behavio of syngas chemical composition and its chaacteistics. The investigation povides infomation on the evolutionay behavio of main gaseous poduced in the syngas, such as hydogen flow ate, hydogen concentation, hydogen to cabon monoxide atio, syngas heating value and othe popeties concening themal efficiency and effectiveness 7

32 of the pocess. The effect of steam flow ate on the evolutionay behavio of syngas chemical composition and flow ates of main species has also been investigated. Infomation of the time dependent popeties have been used to detemine the oveall yields and popeties of the syngas, such as syngas yield, hydogen yield, oveall hydogen to CO atio, combustible pat of the syngas (yield of pue fuel as pecentage), heating values and othe factos that descibes the oveall themal effectiveness of the pocess. The effect of steam flow ate on the oveall yield, syngas popeties and appaent themal efficiency has also been detemined. Pape epesents appoximately /3 of the waste composition in the municipal solid wastes. Theefoe, pape has been investigated unde gasification and pyolysis conditions fo eacto tempeatues up to o C. Studies on pape will help assist in bette design of advanced waste to enegy convesion systems. By definition, gasification of solid wastes includes a devolatilization pocess at beginning of the pocess. At high heating ates, the sample undegoes pyolysis and gasification in paallel; howeve, at low heating ates the sample undegoes pyolysis and gasification in seies in the ode of pyolysis then cha gasification (see figue I-). Pecentage of ovelap between gasification and pyolysis can be obseved by plotting the evolution of syngas flow ate fo both gasification and pyolysis in the same figue. Ou pesent esults have shown an ovelap between syngas flow fom cha gasification and gaseous yield fom pyolysis of 7% at low eacto tempeatue of 8 o C to ~ 95% ovelap at high ( o C) tempeatue. The main diffeences between the gasification and pyolysis pocesses ae examined hee with special focus on the evolution of syngas flow ate, hydogen flow ate and oveall hydogen yield, enegy yield, appaent themal efficiency, evolution of H and CO mole factions and the esidue emaining fom the pocess at tempeatues of 6, 7, 8, 9 and o C. The main 8

33 diffeence between gasification and pyolysis is absence of a gasifying agent in case of pyolysis. Consequently, cha inheently poduced in the pyolysis pocess emains in the poduct steam while steam-cha eactions diminish the fixed cabon in sample with steam gasification. Chaacteistics of food waste gasification and pyolysis have been investigated as well. Main chaacteistics which have been investigated ae syngas yield, hydogen yield, enegy yield and appaent themal efficiency. The esults show that food wastes offes a good potential fo themal teatment of the waste with the specific aim of powe geneation Gasification of plastics and ubbe Plastics have the advantage of highe heating value when compaed to aveage heating value of cellulosic mateial. Plastics have the aveage LHV of 4 MJ/kg. Howeve, the LHV fo cellulosic wastes such as cadboad is 6 MJ/kg. Not only the plastics have the advantage of highe heating value than that of othe components in municipal wastes but also, it has the potential of poducing highe hydogen yield when undegoing pyolysis o gasification. Plastics behave diffeently than othe solid fuels such as coal, pape, cadboad o biomass when undegoing a gasification pocess. Plastics diffe in the sense that thee is no cha o fixed cabon content in it. On the othe hand, sample such as pape o biomass have on the aveage 8% fixed cabon and some ash depending on the sample heating ate. Based on this fact, when a biomass o cellulose based mateial undego a pyolysis pocess of slow o medium heating ate, only the volatile pat of the sample evolves and the cha emains in the eacto. Howeve, unde the same pyolysis conditions, plastics will yield almost 99% of its mass as volatile poducts, leaving aound % of ash and cabonaceous mateial. Since thee is no cha content in plastics, gasifying agents does not have the chance to eact with the solid phase sample at low tempeatues and the 9

34 benefit of syngas poduction is not gained unless the eacto tempeatue is high enough to acceleate the gasifying agent-sample eaction to a compaable ate to pyolysis eaction ates. Most of the eseach conducted in this aea focus on the monomes yield fom the polymes, such as the effect of opeating conditions on olefins yield as compaed to the paaffins eithe in the liquid phase o gaseous phase. Less attention has been devoted to the gaseous yield specially the hydogen yield. The focus of this eseach is to detemine the chaacteistics gaseous yield fom the gasification o pyolysis of polystyene. Specific attention is given to effect of opeating conditions on syngas yield, syngas quality, enegy yield and specially hydogen yield. Main investigated opeating conditions examined ae the eacto tempeatue and the pesence of a gasifying agent, namely steam. Enegy ecovey fom polystyene fom its solid phase to gaseous phase equies that the investigation should be conducted at highe tempeatue ange than that in the eseach aiming fo monomes and liquid hydocabons ecovey. Rubbe wastes also have the advantage of high heating value and high hydogen content. Rubbe heating value is appoximately 37. MJ/kg, which is close to the aveage heating value of plastic (~ 4 MJ/kg) and significantly highe than that of the biomass, which is about 8 MJ/kg. The gasification of ubbe has been investigated hee with specific focus on the evolution of syngas flow ate, hydogen flow ate in the syngas, amounts of syngas yield, hydogen yield and enegy yield fom a given amount of mateial. Results of syngas chaacteistics obtained fom the gasification pocess have been compaed to that obtained fom the pyolysis. The chaacteistics of syngas fom ubbe gasification have been compaed to that fom woody biomass samples, namely had wood and wood chips Gasification of a mixtue of a cha based fuel and a plastic fuel

35 Gasification systems may un on single o multiple souces of feedstock. Howeve, in many cases the gasification systems often encounte the poblem of unsteady souce of biomass feed thoughout the yea so that the biomass composition is aely fixed. Duing off-season of a given biomass, anothe feedstock has to be mixed with the feedstock in ode to maintain a steady supply of feedstock to the gasifie fo seeking the desied output powe fom the gasification powe plant. On the othe hand, a gasification system might be designed to un on solid wastes, which consists of a mixtue of diffeent cabonaceous mateials. Howeve the composition of the waste can change both tempoally and spatially. The fate of multi-components as feed stock to the gasifie might be much diffeent than the expected fate of single components. Misleading infomation might aise fom the assumption that the syngas chaacteistics esulting fom gasifying a mixtue of mateials ae diectly popotional to the weighted aveage popeties of syngas evolved fom individual components of mateials in the gasification pocess. This assumption ignoes the possibility of mateialmateial inteaction between the mixed multi-component feed stock samples. An inteaction might occu between the volatile mattes evolved fom each sample o between the volatile matte of a cetain sample and the fixed cabon of anothe sample o both. Most pobably an inteaction on the volatiles evolved between the samples will occu among simila mateials, such as two o moe biomass samples. Howeve, the inteaction between volatiles fom a cetain mateial and fixed cabon fom anothe mateial most pobably occus between diffeent types of mateials, such as, plastics and biomass o biomass and coals. The volatiles fom plastics geneally stat to evolve at a highe tempeatue ange (3~5K) as compaed to those fom biomass o coals (~4K). Having an ovelapping tempeatue ange of gasification fom the

36 two diffeent mateials suggest the existence of a combination of inteactions between the volatiles eleased and fixed cabon. Fo example, volatile matte evolving fom coal pyolysis is known to contain species of low molecula weight in the fom of fee adicals. On the othe hand, hydocabon species oiginated fom cleavage of plastics bond contibutes in stabilizing the adicals geneated fom the coal, esulting in highe weight loss of coal and lowe yield of cha. Howeve, in tems of volatile-cha inteactions, the hydogen deficient active sites of cha extact hydogen fom the plastic esulting in the fomation of liquid molecule sites [5]. Some eseach in the aea of mixtue co-pyolysis and/o co-gasification has been conducted at the low tempeatue ange. Consequently, the eseach was focused on synegistic effect on liquid hydocabons yield [5, 6]. Othe eseaches have focused on the behavio of mixed sample fom a pue themogavimetic point of view that involves weight loss as a function of tempeatue of the sample. Not much attention has been given to the synegistic effect of mixed samples on the chaacteistics of syngas yield at high tempeatue gasification. Consequently, this section foms a basis fo investigating the behavio of two compounds in the sample feedstock on the evolved syngas behavio. Mixtues of diffeent amounts of plastics in the biomass sample to fom a mixtue of woodchips and polyethylene is investigated unde high tempeatue steam gasification conditions at atmospheic pessue. Chaacteistics of syngas have been evaluated based on the evolution of syngas flow ate/yield, evolution of hydogen flow ate/yield, output powe and enegy yield, evolution of hydocabons flow ate/yield, and appaent themal efficiency. The esults obtained clealy showed that popeties of syngas geneated fom a mixed sample ae not

37 a weighted aveage of syngas popeties obtained fom sepaate gasification of each sample, which suggests synegistic effect due to co-gasification of woodchips and polyethylene..4. Kinetics of cha gasification.4.. Intoduction Cha gasification is slowe than pyolysis and is the ate limiting step in the oveall gasification pocess. Kinetics of biomass cha and food wastes cha gasification has not eceived the same attention as kinetic of coal cha gasification. Kinetic paametes fo coal cha gasification ae abundant in the liteatue, while kinetic paametes fo biomass cha and food wastes gasification ae scace. It is impotant to develop a ate expession fo biomass and food wastes chas gasification which can be used in modeling the oveall gasification pocess. The pogess of cha paticle gasification is a function of the paticle size, poosity [7], gasifying agent chemical composition [8], gasifying agent patial pessue[9, ], eacto tempeatue [-], geomety of the paticle, poe stuctue [3], numbe of active sites, numbe of eactive sites [4], ash content[5-7], inhibitos patial pessue [8, 9], total pessue [3, 3] and themal histoy of cha which emanates fom the heating ate duing the pyolysis pocess [3]..4.. Gasification kinetics of Woodchips cha The objective of this pat of the investigations is to compae the behavio of woodchips cha duing gasification using steam o CO as the gasifying agents. The compaison will be conducted in tem of geometic evolution of sample poes duing the pocess, gasification duation, aveage eaction ate and effect of patial pessue of the gasifying agent. Reacto 3

38 tempeatue and total pessue wee held constant at 9 o C and bas, espectively. Steam and CO flow ates was adjusted to have equal oxygen content fo accuate compaison Random poe model is well known to be used in modeling coal cha gasification; howeve, vey few numbes of investigations used the RPM in modeling kinetics of chas fom biomass samples. Kinetic paametes of the andom poe model have been detemined fo woodchips cha gasification using steam and CO as the gasifying agents Catalytic effect of ash on cha gasification One of the most impotant paametes which have been investigated is the catalytic effect of ash content on cha gasification. Catalytic effect of ash on cha gasification has been investigated fo seveal biomass samples. Kinetics of food waste cha gasification did not daw the attention of eseaches in this field. Since food waste has consideable ash content, its catalytic effect must be investigated. Results show that ash has a positive effect on cha eactivity. Kinetic paametes have been calculated fo diffeent degees of convesion. Values of kinetic paametes wee found to be affected by the degee of convesion. Quantitative analysis of kinetic paametes dependency on sample convesion has been examined hee. Quantifying the catalytic effect of ash on cha kinetics will help assist impoving gasifies design Kinetics of cha gasification unde diffusion esistance conditions In this section, the effect of paticle size, poosity and eacto tempeatue/eaction ate constant on the pogess of paticle convesion is investigated by numeically solving the tanspot equation inside a eacting cha paticle. These ae the main paametes affecting the convesion of cha paticle. 4

39 Figue I-3 shows diffeent cases of a eacting cha paticle. The fist case, figue I-3a, shows the geneal case whee, the chemical eaction ate and diffusion ate play an equal ole in the pocess. Figue I-3b shows the exteme case of a diffusion contolled cha gasification pocess, in which the eaction ate is vey fast and the paticle has low poosity. In this case the eaction occus in oute shell of the paticle and the gasifying agent concentation is almost zeo at the paticle suface. Figue I-3c show exteme case of a chemically contolled pocess, in which the eaction ate is vey low and the paticle is poous enough to allow fo high effective diffusivity inside the paticle. The gasifying agent concentation, in this case, is a hoizontal line paallel to the X-axis. C C C C S C C C S = C C S ~ Figue I-3. Schematic of gasifying agent concentation pofiles inside diffeent cha paticles; (a) geneal case of medium poosity paticle, (b) vey low poosity paticle and (c) highly poous paticle The model used in this section is the exposed coe model [33]. In this model the gasifying agent has to diffuse fom the suounding to the suface of the paticle and into the paticle. In ode to calculate the degee of convesion as a function of time and space, X(, t), the distibution of gasifying agent concentation inside the paticle has been calculated. The concentation pofiles 5

40 wee detemined by numeically solving the tanspot equation inside the paticle using the finite element method. The Rayleigh-Ritz method has been used to detemine the weight function and the appoximation function [34]. The degee of convesion, X(, t), has been calculated by numeically solving the cha eaction ate equation using the finite diffeence method. The assumption of constant effective diffusion coefficient is usually used to solve the tanspot equation inside the paticle analytically. The finite volume method is usually used fo obtaining numeical solution of the Stum Liouville equation to assist with the poblem of unknown coefficients. Solving the poblem using the finite element method is pesented hee as a diffeent appoach. In the solution pesented hee, the assumption of constant diffusion coefficient was eliminated as well as the assumption of constant gasifying agent concentation outside the paticle. Pesented also is the expeimental method fo detemining the kinetic paametes and expeimental validation of the model. Numeical simulations have been conducted fo thee cases of two exteme cases and one geneal case, Da = The two exteme cases coespond to lage Damkohle numbe and small Damkohle numbe. The high Damkohle numbe coesponds to a high eaction ate, lage paticle size and low poosity paticle. The small Damkohle numbe coesponds to a low eaction ate, small paticle size and highly poous paticle. The thid case coesponds to an intemediate value of Damkohle numbe. 6

41 Chapte II: Liteatue eview.. Chaacteistics of syngas evolution duing pyolysis and gasification... Gasification of cha based fuel... Reaction mechanisms of cellulose and lignin pyolysis Cellulose is a main constituent of biomass and has been investigated by seveal investigatos in tems of eaction mechanisms and behavio unde pyolysis and gasification conditions. Shin et al. [35] investigated the kinetics of cellulose deived poducts, such as, levoglucosan, unde pyolysis conditions. They modeled the pyolysis of levoglucosan using a thee compound model; pimay, seconday and tetiay compound. The pimay compound, levoglucosan, deceases with the incease in tempeatue, the seconday compounds peaks at a cetain tempeatue and the tetiay compounds inceases with the incease in tempeatue. The seconday compounds whee found to be cabonyl compounds and hydoxyl deivatives, such as, methanol, acetaldehyde, acolein, glyoxal and fuans compounds. Tetiay compounds wee found to be cabon monoxide and othe gaseous hydocabons. Balat [36] categoized the steps at which cellulose eacts duing pyolysis in tems of the following tempeatue anges: Table II-. Steps of cellulose pyolysis as suggested by Balat [36]. Tempeatue eaction poducts < 575 K elimination of wate, and Fomation of cabonyl and caboxyl, evolution of depolymeization CO and CO, and mainly a chaed esidue 575<T<75K Beaking of glycosidic Mixtue of levoglucosan, anhydides, and 7

42 linkages of polysacchaide oligosacchaides in the fom of a ta faction > 75 K scission of suga units Fomation of cabonyl compounds such as acetaldehyde, glyoxal, and acolein > 775 K mixtue of all above pocesses A mixtue of all above poducts Condensation condense and cleave to cha Cha A eview of the mechanistic pathways of cellulose pyolysis is shown in figue II- [37-43]. Boido-shafizadeh [37] and modified Boido-Shafizadeh models [38] ae based on an activation step followed by paallel competing eactions between cha fomation and evolution of gas and volatiles. In the modified mechanism [38] levoglucosan is added as an intemediate befoe cha fomation. The Vatihegyi model [39] eliminated the active cellulose step based on the absence of any vaiations in mass duing TGA expeiments and wose fit if the activation step is not eliminated. The Vatihegyi mechanism is based on paallel competing eactions of oligomes fomation and a seies of solids and gases fomation. Luo et al [4] consideed the fomation of cha fom dehydation of active cellulose. Active cellulose then undegoes paallel depolymeization eactions and fagmentation eactions. Ta is fomed by epolymeization of levoglucosan. Banyasz et al [4] pesented a mechanism in which CO and CO ae fomed fom competing paallel outes. CO is favoed at high heating ates and high tempeatues. Lin et al. [43] pesented a mechanism in which fagmented compounds, such as, aldehydes and ketones ae fomed fom dehydated sugas in contast to thei fomation by diect fagmentation fom active cellulose. Cellulose Active Cellulose Cha + gas Volatile 8

43 Levoglucosan Cha + Gas Cellulose Activated Cellulose Cha + gas Aldehydes, Ketones, fuans, ta, gas Cellulose Solid intemediates + volatiles Solid intemediates + volatiles Solid intemediates + volatiles Oligomes Cellulose Active Cellulose Cha + gas Levoglucosan Fagment Ta + gas Fast Hydoxyacetaldehyde + - Hydoxy--popanone + ta + gas Seconday gas Seconday ta Cellulose Active Cellulose Pimay vapo Cha + wate Cha + wate Hydoxyacetaldehyde Cellulose Cellulose (Low degee of polymeization) Intemediates Fomaldehyde + CO Cha + H O Levoglucosan/ ta (l) Levoglucosan/ ta (g) +CO 9

44 Cellulose Active Cellulose Levoglucosan Isomeisation -H O -H O,4:3,6 dianhydo-α-dglucopyanose -H O levoglucosenone -H O -H O,6-anhydo-α-Dglucofuanose Aldehydes + ketones Fagmentation -[CO+CO +H O] Cha Fuans -[CO+CO +H O] Figue II-. Cellulose eaction mechanisms [37-43] Petocelli and Klein [44] investigated initial steps of lignin pyolysis using model compounds;, -diphenylethane (DPE) [C 6 H 5 -CH -CH -C 6 H 5 ], stilbene [C 6 H 5 -CH=CH-C 6 H 5 ], diphenylmethane (DPM) [C 6 H 5 -CH -C 6 H 5 ], and tiphenylethylene (TPE) [C 6 H 5 -CH=C-(C 6 H 5 ) ]. Reacto tempeatue anged fom 4 to 6 o C. DPE initially decomposed to hydogen ich benzene and toluene accompanied with the hydogen deficient ethylbenzene [C 6 H 5 -CH -CH 3 ], styene [C 6 H 5 -CH=CH ] and stilbene. Stilbene and styene undegoes futhe decomposition and oligomeization to fom hydogen deficient species and hydogen adicals. Hydogen adical in tun, combines with benzyl and phenyl adicals to fom moe toluene and benzene. DPM decompose to fom phenyl adical, benzyl adical in paallel with hydogen deficient species, fluoene [C 6 H 4 -CH -C 6 H 4 ] and hydogen adicals. Hydogen adical in tun, combines with benzyl and phenyl adicals to fom toluene and benzene. On the othe hand, initial steps of TPE pyolysis involve thee outs; the fist is unimolecula decomposition to fom toluene and DPM. The second is decomposition of TPE to fom benzene and stilbene o DPE. Figue 4 shows eactions sequence duing PDE, DPM, stilbene and TPE pyolysis.

45 DPE Toluene + Stilbene Benzene + ethylbenzene + styene Stilbene decomposition Styene decomposition Hydogen deficient species + H adical Hydogen deficient species + H adical Phenanthene DPM Phenyl + Benzyl adicals Benzene + Toluene DPM Fluoene Hydogen deficient species + H adical H adical DPE Toluene + DPM Stilbene DPM TDE Benzene + Stilbene Toluene Benzene + DPE Figue II-. Reactions sequence duing PDE, DPM, stilbene and TPE pyolysis.... Effect of opeational conditions... Effect of steam flow ate Gil et al. [45] investigated the effect of steam to oxygen atio in the gasifying agent on the syngas popeties and concluded that LHV deceases with decease in H O/O atio, because of in-situ combustion of some gas components with the addition of O fed to the eacto. Howeve, when gasifying agent-to-biomass atio (fo a given H O/O atio) is inceased, the LHV

46 deceases by the same eason (since moe O is intoduced) [45, 46]. Consequently the themal efficiency deceases with incease in gasifying agent-to-biomass atios [45]. The geneal tend of incease in the steam to sample atio is to incease the yield of total syngas, H, and CO, while the yield of CO and CH 4 deceases [47-5]. The incease in H and CO yield and the decease in CO yield ae attibuted to the acceleation of the fowad eaction ate of the wate gas shift eaction (CO + H O CO + H ) [47, 49-5]. On the othe hand the incease in steam to sample atio inceases the methane efoming eaction to cause a eduction in the yield of methane [48]. Theefoe, incease in steam to sample atio esults in a diect incease in the atio of H /CO [48, 5]. Chaudhai et al [53] studied effect of steam flow ate on total amount of gas poduced, and its composition fom bagasse cha and commecial cha gasification. Fomation of poduct gas was, appoximately, doubled when steam flow ate incease fom.5 to g/h/g of cha. They attibuted this incease in gaseous poducts to the incease in the amount of steam, being one of the eactants, in the eaction leads to highe convesion as well as highe gas poduction. H /CO atio in the synthesis gas obtained fo bagasse cha was deceased while it was inceased fo commecial cha with inceasing the steam flow ate fom.5 to g/h/g of cha. heating value of the poduct gas did not change much and anged between 7 and 9 Btu/scf fo bagasse cha and fom 5 to 8 Btu/scf fo commecial cha.... Ai vesus steam gasification Steam gasification favos steam efoming eactions, while the ai gasification pomotes combustion eactions. The yield of H and hydocabons with steam gasification ae highe than those with ai injection, wheeas CO and CO ae lowe, since the extent of combustion of cha and volatiles is educed by eplacing ai with steam. It is also expected that CH 4 and othe

47 hydocabons concentations would be lowe, since the equilibium of wate gas-shift eaction favos H poduction. Steam efoming of tas (Ta + H O xh + zco) and of hydocabons (C n H m + nh O (n+m/) H + nco) favos H poduction, accompanied with a decease in hydocabons content in the exit gas [54, 55]. Ocampoa et al. [56] investigated expeimentally the gasification of Colombian coal in a fluidized bed. Expeimental esults showed a maximum in the highe heating value (HHV) cuves vesus ai to coal atio. The highest gas heating value of 3.3 MJ/m 3 was obtained using a steam/coal atio of.7 and an ai/coal atio of Reacto tempeatue Gil et al. [45] investigated the effect of diffeent opeational condition on the syngas chemical composition and popeties. As pat of thei investigation, they examined the effect of eacto tempeatue on themal efficiency of the pocess which inceased with incease in eacto tempeatue. This is attibuted to the endothemicity of the gasification pocess. The yields of H and CO incease with incease in eaction tempeatue since the gasification eactions ae endothemic. The data showed that the incease in gas yield with eaction tempeatue is patly achieved at the expense of ta and liquids [5, 5]. The LHV inceases a little with incease in eacto tempeatue due to incease in the yields of C H, H, and CO. The C H m species ae fomed by the (steam) cacking of aomatic components of the ta [46]. Demibas [57] investigated gaseous poducts fom biomass by pyolysis and gasification. In thei study they intoduced the effect of eacto tempeatue on gaseous, liquid and cha yield fo the 3

48 pyolysis pocess. Inceasing the eacto tempeatue deceased the liquid and cha yield. Howeve, inceasing eacto tempeatue inceased the gaseous yield Catalytic gasification The low heating value (LHV, kj/m 3 ) of the gas deceases somewhat when dolomite is used in the gasifie bed. This decease can be due to the decease in the amounts of light hydocabons in the flue gas. Howeve, it is again veified how some dolomite in the bed has a positive effect; it inceases the themal efficiency fom 86 pecent to about 96 pecent [5, 54]. Coella et al. [58] investigated the effect of placing the dolomite in a seconday eacto downsteam fom the pimay gasifie on popeties of the syngas evolved. The study povided no impotant diffeences between the two locations of the dolomite (i.e., inside the pimay gasifie o downsteam of the pimay gasifie). This finding eveals that incease in the amount of H in the flue gas is compensated with the decease in amount of CO and also by the nonimpotant vaiation in the amounts of CH 4 and othe hydocabons (C H n ) in the flue gas. Theefoe, thee is no diffeence between locating the dolomite in the same gasifie bed o at a downsteam position in the eacto fom the point of view of LHV of the gas Effect of heating ate Milosavljevic et al [59] investigated themal effects in cellulose pyolysis. They investigated the effect of heating ate on cha fomation and pyolysis heat absoption. A linea elationship between mass loss and heat absoption, obseved at high heating ate, 6 K/min. They concluded that the pocesses esponsible fo net heat absoption ae appaently quite constant thoughout the pocess of apid heating. In contast to high heating ate the esults obtained at lowe heating ates show a deviation fom a steady heat absoption cuve, at some point. This deviation occus at pogessively lowe extents of mass loss as the heating ate is loweed. They suggested that the 4

49 heats of pyolysis depend upon the exothemic natue of cha fomation. They concluded that a lage potion of the exothemic cha fomation is delayed to pogessively late times duing the pyolysis pocess at highe heating ates Gasification using Supecitical wate Supecitical wate mixes with most of the oganic compounds so that apid and homogeneous eactions of oganic compounds ae possible in supecitical wate. Matsumua [6] investigated the enegy efficiency, poduct gas composition and economic feasibility fom supecitical wate gasification. They showed that cellulose decomposes much moe apidly in supecitical wate than in sub-citical wate. They concluded that this high eactivity can be used to decompose oganic mateials into gases without any peteatment of dying the feedstock. Theefoe, supecitical wate gasification is consideed a pomising technology fo the gasification of wet biomass since it does not equie dying of feedstock befoehand. Sepaation of the gas and wate occus afte complete gasification, cooling down and depessuization of the pocess.... Gasification of plastics and ubbe Encina et al. [6] investigated the themal decomposition of natual polystyene. The fist ode eaction model has been used to descibe the eaction ate. These investigatos detemined Kinetic paametes using multiple linea egession appoach. The activation enegy and peexponential facto vaied with the heating ate. The activation enegy anged fom 86.5 to 68. kj/mol fo the heating ates anging fom 5 to 5 K/min. On the othe hand Westehout et al. [6] used the fist model to intepet the expeimental data. In thei investigation the use of the fist ode powe law model was esticted to the 7-9% of the convesion ange. They attibuted the eason fo this estiction to the fact that the actual eaction ode vaies with the convesion. And this desciption is valid mostly in this convesion ange fom 7 to 9%. 5

50 Lin et al. [63] investigated the pyolysis kinetics of a efuse-deived fuel (RDF) which consists of high plastic content: wt.% of polystyene, 3 wt.% of Polyethylene, wt.% of PVC, and 4 wt.% of pape. The nth ode eaction model was used and individual activation enegies wee detemined. The polystyene activation enegy was found to be.9 kj/mol. The global pyolysis eaction ate was calculated fom the weighed sum of the component factions of RDF. Two stages have been identified to descibe the convesion ate of the plastics mixtue. The obtained activation enegy and eaction ode fo the fist stage wee 83.6 kj/mol and.9, espectively. Howeve, fo the second stage the activation enegy and eaction ode wee 38 kj/mol and.7, espectively. In a simila study by Cozzani et al. [64], RDF pyolysis has been investigated. They identified two weight loss steps as well. Tempeatue of the fist step anged fom 3 to 4 o C and the second step anged fom 45 to 5 o C. The fist step coesponded to the degadation of cellulosic mateials while the second step coesponded to plastics. Simila conclusions wee obtained when sawdust-polyethylene mixtue was investigated. Sawdust degadation took place at eacto tempeatue between 3 to 43 o C; howeve, polyethylene degadation took place between 43 to 53 o C [65]. Bockhon et al. [66] calculated the degee of convesion fo a mixtue of PVC, PS and PE (:: by weight) fo stepwise low tempeatue pyolysis (33, 38 and 44 o C). Calculations wee conducted based on isothemal kinetic paametes fom the liteatue. At 33 C about % of the polystyene decomposes (eaction time 3 min). At 38 C depolymeization of the majo pat of polystyene into its monome takes place and about % of the PVC decomposed (eaction time 6 min). At highe tempeatues (44 C) the decomposition of polyethylene and of the majo pat of the esidue fom of PVC occus. 6

51 Ponzio et al. [67] investigated the effect of steam injection on hydogen yield in the gasification of plastic containing waste. Compaed to ai gasification, the elative popotion of H in syngas fo steam gasification expeiments was highe. This was attibuted to steam efoming (C+H O => H +CO) and wate gas shift (CO+H O => H +CO ) eactions. In a simila study by He et al. [5] on catalytic steam gasification of municipal solid waste (MSW), an incease in syngas flow ate and decease in gasification peiod was obseved by inceasing the eacto tempeatue. Gasification peiod at 7 o C was 9 minutes and 39 minutes fo eacto tempeatue 95 o C. Kaminsky et al. [68] investigated the pyolysis of mixed plastics (Polyolefins 57%, Polystyene 9%, PVC 3.7%, and othe mateials.3%) in a fluidizing medium, namely steam, in the tempeatue ange of 6 to 8 o C. They found vey inteesting esults concening the distibution of gaseous yield in this tempeatue ange. At 7 o C, the highest yield of C, C 3 and C 4 alkenes was obseved. On the othe hand the amount of cabon oxides and the highly hydogenated gases such as methane and hydogen inceased with incease in eaction tempeatue. In a simila study by Simon et al. [69] on the pyolysis of polyolefins with steam, the investigatos noticed that high amounts of olefins ae obtained at tempeatues aound 7 o C, with -3 % ethene, 4-8 % popene, and 3-6 % butenes. Clealy the ole of tempeatue and mateial popeties ae citical fo the amounts of hydogen and othe gas yield in the syngas. Theefoe, the focus of ou eseach is to povide futhe insights on the pyolysis and gasification of polystyene at diffeent eacto tempeatues and detemine the kinetics paametes fo thei futue use in modeling the pocess. Tongamp et al. [6] developed a pocess to poduce hydogen fom polyethylene [ CH ] n (PE) by milling with Ca(OH) and Ni(OH) followed by heating the milled poduct. Diffeent mixtues wee heated fom to 7 o C at a heating ate of o C/min. H elease occued 7

52 between 4 and 5 o C, and H concentation of 95% was obtained fom the mixtue of PE/Ca(OH) /Ni(OH) (C:Ca:Ni = 6:4:) sample. The ole of milling, Ca(OH) and Ni(OH) was descibed as follows. Milling is necessay to avoid sepaate decomposition of PE and hydoxides and to stimulate inteaction between them when heat is applied. With the well milled samples, heating at a low tempeatue simply leads to the fomation of calcium cabonate, and elease of hydogen at the same time. When nickel hydoxide is well dispesed within PE and calcium hydoxide, this pocess allows fo the onsite fomation of fine nickel paticles that function as catalyst to facilitate the fomation of hydogen. The oveall pocess eaction was given as: 6[CH ] + Ca(OH) + Ni(OH) = 6CaCO 3 + 8H + 6CaO + H O + Ni Seveal eseaches have investigated the kinetics of weight loss of ubbe containing samples [7-7]. The esults eveal that the kinetics of ubbe gasification can be descibed using paallel fist ode independent eactions. The esults obtained on activation enegies depended on the heating ate and the ange of investigated tempeatues. The activation enegy value anged fom 4 to kj/mol. Castaldi et al. [73] poposed a eaction mechanism of Styene Butadiene Rubbe (SBR) decomposition unde pyolysis conditions. The mechanism suggested was based on simultaneous themogavimetic analyze (TGA) and gas chomatogaph/ mass spectomete (GC/MS) measuements. These investigatos have suggested the following decomposition steps fo SBR; fist, thee is a beakage between the ligand and butadiene backbone, which esults in some hydogen libeation. The backbone continues to be hydogenated to fom butane and n-butane. The styene ligand undegoes vaious tansfomations, hydogenation and emoval of methylene goups, leading to the substituted polycyclic aomatic hydocabons (PAHs), such as, ethylbenzene and toluene. 8

53 Seveal eseaches have investigated the poosity of cha obtained fom ubbe pyolysis. San Miguel et al. [74] found that cha obtained fom pyolysis of scap ties developed poo poosity and limited intenal poes suface aea. On the othe hand, Helleu et al. [75] concluded that the poo poosity of the obtained cha was enhanced by futhe cabonization using steam and CO activation. Using steam at 9 o C fo thee hous poduced an activated cabon with good suface aea (3 m /g). Steam was obseved to geneate a naowe but moe extensive mico-poosity than cabon dioxide [76, 77]. On the othe hand, Vizuete et al. [78] concluded that chemical teatment of esidual ubbe using HNO 3 esulted in lage poe stuctue in the mateial...3. Co-gasification and Co-pyolysis of mixed fuels Azna et al. [79] investigated the gasification of a mixtue of plastic waste, pine wood sawdust and coal in an ai fied fluidized bed gasifie. Among othe paametes they studied the effect of feed stock composition on syngas yield, enegy content, syngas LHV and syngas chemical composition. Mixtue atios of 8%-%-%, 6%-4%-%, 6%-%-4% and 6%- %-% of coal-biomass-plastic wee investigated. A peak value of enegy content and LHV was obtained at a mixtue atio of 6% coal - 4% plastic while syngas yield was minimal fom the same mixtue. The peak value of enegy yield and syngas LHV is attibuted to the high LHV of plastics. In a simila study, pinto et al. [5] investigated steam gasification of biomass mixed with plastic wastes in a fluidized bed gasifie. Pesence of % polyethylene (PE) inceased H concentation fom 8% to 5% and deceased the CO concentation fom 38% to 8%. Pesence of PE is effective only up to % PE. Any futhe incease in PE pecentage did not incease the H concentation o decease the CO concentation. Constant concentation of H and CO was etained. 9

54 Vélez et al. [8] investigated co-gasification of Colombian coal and biomass in a fluidized bed gasifie. Seveal samples of these blends wee used in the expeiments by mixing 6% o 5% of biomass, (sawdust, ice o coffee husk), with coal. The themal efficiency was calculated fo the six investigated mixtues. Inceasing the mass pecentage of ice and coffee husk fom 6 to 5% inceased the themal efficiency; howeve, inceasing the sawdust pecentage did not change the themal efficiency of the pocess. The enegy efficiency of the pocess eached a peaked value of appoximately 6%. Shaypov et al. [8] investigated the co-pyolysis of wood biomass and synthetic polyme mixtues. Chaacteistics of themal degadation of sepaate biomass and plastic samples and thei mixtue wee investigated using a themogavimetic analyze (TGA). The mutual influence of biomass and plastics duing the themal decomposition was not appaent fom the esults obtained. In othe wods, the degadation of single components in biomass and plastic mixtues wee clealy evealed to be independent. The influence of biomass/plastic mixtue composition on the poducts yield fom the copyolysis was investigated at 4 C [8]. Yields of both light and heavy liquid factions inceased with the pesence of plastic mateial. A maximum yield of light liquids was obtained fo a mixtue of % biomass and 8% plastic. One inteesting esult obseved was that moe than two times highe yield of light liquid hydocabons was obtained fom the -8% biomassplastic mixtue as compaed to the expected yield fom individual mateials, i.e., the sum of light liquid factions poduced fom the pyolysis of each sepaate component. They supposed that the olefinic poducts fom plastics themal convesion eact with some poducts fom the biomass depolymeization to esult in the fomation of light liquids. 3

55 Kumabe et al. [8] examined co-gasification of woody biomass and coal with ai and steam using a downdaft type fixed bed gasifie at 73 K. The biomass to coal atio was vaied fom to based on the cabon content. The convesion to syngas inceased with incease in biomass in the feedstock. Howeve, the convesion to cha and ta deceased with incease in biomass. The incease in biomass faction esulted in a decease in H composition and incease in CO composition. The cold gas efficiency inceased fom 65% to 85% when biomass faction inceased fom to. Simila esults wee obtained by Lapueta et al. [83] on the themal efficiency of an ai blown ciculating flow gasifie who epoted exponential incease of cold gas efficiency fom ~5% to 4% with the addition of biomass to coal. The eason fo highe themal efficiency fom the use of biomass was attibuted to diffeent C-C bonds in the two mateials. The coal stuctue (cha) consists of mainly C=C bonds deived fom its significant heavy polycyclic aomatic hydocabons (PAH's) content which equies high activation enegy to beak such bonds. Howeve, the cellulose and lignin content of the biomass consists mainly of weake bonds, such as, R O R (phenols, aldehydes, ketones, etc.), which can easily be boken. Shaypov et al. [6] investigated the inteaction between coal and polyolefinic plastic (PP) duing co-pyolysis using TGA, GC-MS and HPTLC diagnostics. Fom the TGA expeiments it was established that the mass looses ae non-additive fo the blends examined so that it can be assumed that plastic coal inteaction occu duing the themal teatment. Pedicted values fo co-pyolysis of the coal/pp mixtues wee calculated based on additive contibution of the suitable value of coal o PP obtained fom the expeiments. The yield of liquid hydocabons was identified accoding to thei boiling point. Hydocabons with boiling point below 8 o C epesented faction, hydocabons with boiling point in the ange 8 to 35 o C epesented faction and distillate esidues epesented faction 3. It is to be noted that the amounts of 3

56 faction ae non-additive. Expeiments lead to an ovepoduction of liquids. Second, the obseved inceases coespond to a decease of faction 3. This phenomenon could be explained fom the change in distibution of the hydocabons poduced by the degadation of polymes. The inteaction between coal and plastic was explained as follows; coal pomotes adical fomation leading to the poduction of lighte hydocabons fom the polyme. On the othe hand, polyme plays the ole of hydogen dono to enhance convesion of coal. Radicals that pomote the coal-plastic inteaction ae alkyl aomatic compounds and contibute to mainly liquids of faction. These alkyl aomatic compounds ae not found in the poducts of coal o plastic when eacted alone. These compounds wee consideed as molecula pobes fo chemical inteactions between the coal and polymes. Caia et al. [5] investigated the synegistic effect between the low volatile coal (LVC) and plastic (polypopylene, PP, low density polyethylene, LDPE and high density polyethylene, HDPE). A diffeence in weight loss ( W) was defined as the diffeence between the weight loss fo a blend and the theoetical weighted aveage loss of each sample examined sepaately. W was less than ±% befoe 4 C, since at this tempeatue plastic did not decompose and no inteaction occued between LVC and plastic. The weight loss ( W) eached..7% at eacto tempeatue highe than 53 C, which indicates synegistic effect duing pyolysis at high tempeatues. The kinetic paametes (activation enegy and pe-exponential facto) of coal and plastic pyolysis wee detemined by assuming a fist ode eaction. Results showed that activation enegy and pe-exponential facto of the coal/plastic blends ae diffeent fom those of the individual mateials. This diectly suggests that the pyolysis mechanism of coal/plastic blends is diffeent than that fo the individual components pesent in the mixtue. 3

57 Sakuovs [84] investigated the effect of adding polypopylene (PP), polystyene (PS), polyacylonitile (PAN), (CH -CH-CN) n ) o polyphenylene sulfide (PPS) to thee diffeent Austalian coking coals on the coal fluidity (plasticity). Polystyene stongly educed the fluidity of coal. Polypopylene did not affect the fluidity in two of the coking coals. Polyphenylene sulfide (PPS) educed the fluidity of the coals at tempeatues nea the solidification tempeatue of the coals. Polyacylonitile (PAN) inceased the coal fluidity at tempeatues nea the softening tempeatue. Sakuovs [84] attibuted this change in coal fluidity to chemical inteactions between coal and plastics, which involve tansfe of hydogen, eithe to the coal that esults in an incease in fluidity, o fom the coal that esults in a decease in fluidity. A lot of counties in the EU gained consideable expeience with co-gasification and cocombustion of coal and biomass o coal and sewage sludge because of thei paticipation in the APAS Clean Coal Technology pogam (99-994), (Activite de Pomotion, D'Accompagnement et de Suivi). Synegic effects wee epoted by some eseaches such as Sjostom et al. [85] who epot synegies in Fluidized bed co-gasification of wood and coal mixtues and de Jong et al. [86] who epot synegies with co-gasification of coal, miscanthus and staw in an ai-blown Fluidized bed gasifie. On the othe hand, Rudige et al. [87] epoted an absence of any synegistic effects between the diffeent fuels. They attibuted this absence of synegistic effect to the diffeence in tempeatue anges within which devolatilization of coal and biomass take place. Kuznetsov et al. [88] studied the Co-pyolysis and co-hydopyolysis of biomass/polyolefine mixtues. Expeiments wee held in the tempeatue ange of 3 to 5 o C. They found that hydopyolysis of biomass/plastic mixtue esults in highe degee of convesion and inceased yield of light liquids as compaed to co-pyolysis in an inet atmosphee. They attibuted this 33

58 incease in convesion and liquid hydocabons yield to the hydogen assisted uptue of C-O and C-C bonds. The hydogen atoms can stabilize the adical poducts duing the themal degadation of polyme. A simila study was conducted by Kuznetsov [89] using a coal/polyethylene (PE) mixtue. The following catalytic pocesses wee applied: pyolysis in an inet atmosphee, hydopyolysis and wate steam cacking. The highest degee of coal convesion was achieved in the hydopyolysis pocess at 43 o C and woking pessue 6 MPa. The maximum yield of light distillate poducts was obseved fo the wate steam cacking at 43 o C and MPa. Most eseaches conducted thei expeiments in a continuously fed eacto in ode to undestand the effect of opeational conditions on syngas popeties. The syngas was analyzed at the exit of the eacto, so that the syngas analyzed was a esult of all the eactions that occu inside the eacto. In this study the expeimental setup is designed to esolve this issue of global aveaging by monitoing the evolution of syngas chemical composition in the time domain. This pocedue allows one to also detemine the global composition, if desied. This investigation povides bette undestanding of syngas evolution fom solid fuels while flowing though the space domain in gasifies. Monitoing the evolution of syngas in the time domain allowed fo calculating the cumulative yield of key popeties of the syngas such as cumulative yield of syngas, hydogen, enegy with time, and efficiency... Kinetics of cha gasification... Effect of eacto pessue Robets et al. [] investigated the effect of pessue on appaent and intinsic eaction kinetics. The appaent eaction ate at % convesion fo the cha-co eaction is a function of pessue. The esults showed that pessue inceases the appaent eaction ate of the cha-co. Howeve, this incease is not constant ove the pessue ange -3 atm. As the pessue is inceased to 34

59 above atm., effect of pessue is less and appaent eaction ode is almost zeo at pessues of -3 atm. Howeve, the intinsic eaction ate was not found to be affected by the pessue that much. This suppots that the shift in appaent eaction ode at high pessues is not due to fundamental change in the eaction mechanism. They attibuted this decease in eaction ode due to the following: at atmospheic pessue the suface of the sample is not satuated and the eaction ate is popotional to the numbe of suface complexes. As the pessue inceases, moe suface complexes ae fomed to esult in an incease in eaction ate. At high enough pessues the suface will be satuated with complexes, such that inceases in pessue will not lead to the fomation of futhe suface complexes and the eaction ate will not incease. Consequently, the appaent eaction ode is zeo. Cetin et al.[3] studied the CO gasification kinetics of chas fom biomass species within the tempeatue ange of 8 95 o C and pessues between and ba using themogavimetic analysis (TGA). Pessue has been found to have no effect on eactivity duing cha convesion while it has a damatic effect on the chemical and physical stuctue duing the pyolysis pocess. They found that incease in total pessue deceases the aveage eactivity of gasification of pine chas. Duing these expeiments, patial pessue of CO was kept constant while the total pessue was vaied. The total pessues used in these expeiments wee identical to those used duing pyolysis to geneate the cha samples. They concluded that the diffeence shown in eactivities could be due to the ole of pyolysis pessue on the intinsic eactivity and/o the effect of total gasification pessue on the appaent eactivity. To distinguish the effect of pyolysis pessue on the intinsic eactivity, adiata pine chas geneated at diffeent pessues wee gasified at 85 o C and ba fo compaison with the biomass cha. They suggested that the diffeence in intinsic eactivity can only be assigned to the effect of pyolysis pessue athe 35

60 than the total suface aea effect. They used the x-ay diffaction (XRD) technique to quantify the effect of pyolysis pessue by chaacteizing the atomic stuctue of the cha samples. Results showed that the eactivity diffeence can be linked to the gaphitic stuctue found in chas geneated at pessues geate than atmospheic pessue. Consequently, they concluded that the diffeence in gasification eactivities unde diffeent gasification pessues is mainly due to gaphitization in biomass cha stuctue at highe pessues. Eveson et al [8] investigated the effect of CO pesence in the eacto on the eaction kinetics of pulveized coal-chas. to evaluate the paametes fo the intinsic eaction ate they conducted two sets of expeiments, () with cabon dioxide and an inet (nitogen), and () with cabon dioxide and cabon monoxide. A compaison between cha eactivities fo the two expeiments, CO was found to have an inhibiting effect of cabon monoxide. Reaction ate fo steam gasification was found to be double than that fom CO gasification [8]. A eaction ode of.5 to.8 was found fo H O and CO gasifying agents, espectively. The investigatos have indicated that the eaction ode is not affected by pessue of up to bas. Howeve, it deceased fo eacto pessues above bas []. In geneal, the incease in eacto tempeatue esulted in an exponential incease in eaction ate, especially in the chemically contolled egime. Hydogen and cabon monoxide wee found to have an inhibition effect in both steam and CO gasification. Wall et al [9] confimed that the inhibition effect of CO and H is moe significant at high eacto pessues, highe than bas. They also indicated that the inhibition of H and CO is explained in tems of the Langmiu-Hinshilwood eaction mechanism; CO and H ae adsobed to active cites, esulting in less fee active sites fo the gasifying agent to eact with the cha. 36

61 Cetin et al [3] investigated the effect of total pessue on cha gasification. Cetin et al [3] have shown that total pessue has no effect on intinsic eactivity of cha. They also, investigated the effect of pyolysis pessue on the eactivity of cha. Cetin et al [3] measued the qualitative pesence of gaphite stuctues in chas obtained at high pyolysis pessues. Gaphite stuctues inceased with the incease in pessue. Gaphite stuctues duing pyolysis deceased the appaent eactivity of cha duing gasification.... Effect of geometic changes on kinetics of cha gasification Kajitani et al. [9] investigated the kinetics of coal cha gasification in a pessuized dop tube funace at a high tempeatues ange, fom to 5 o C. The peak eaction ate was at a convesion value of appoximately.4. Reaction ode with espect to CO was found to be.73 and.86 fo steam. The andom poe model (II-E) was used to fit the expeimental data.. ln / (II-E) Stuctual paamete was found to be 3 in case of steam and CO and 4 in case of using oxygen as the gasifying agent. In a simila study by Ochoa et al. [9] the stuctual paamete, ψ, value was 4.7 fo sub-bituminous coal and 7 fo high volatile bituminous coal. Zou et al. [] conducted modeling investigation fo studying the eaction kinetics of petoleum coke gasification with CO. They deduced that highe tempeatues lead to shote time of gasification and highe gasification ate. The andom poe model was used in thei study and they found that the gasification ate inceased with the incease in convesion then followed by a apid decease afte eaching a maximal ate aound a convesion value, X, of.3. They attibuted the lowe gasification ate initially to the poo poosity initially, which is also, the main eason of the occuence of a peak gasification ate. 37

62 The andom poe model has also been used to model the gasification of low ank coal cha, such as, Thai-lignite. Sangtong and Naasingh [9] compaed esults fom the andom poe model with esults obtained fom fitting the homogeneous model fo two types of chas. The andom poe model povided bette fitting than the homogeneous model. Stuctual paametes obtain fom the andom poe model fitting was.6 fo cha sample A and. fo cha sample B. Bhat et al [9] investigated the kinetics of ice husk gasification using steam as gasifying agents. The investigated tempeatue ange was fom 75 o C to 9 o C. They used both the volume eaction model epesented by the convesion time elation; ln(-x) = (KC)t, and the shinking non-eacting coe model epesented by; t = (ρ p /KC)[-(-X) /3 ]. Thei esults show that the gasification eaction of ice husk cha is chemically contolled up to a tempeatue of 85 o C. The activation enegy obtained by volume eaction model and shinking coe model wee close in ageement. The activation enegy calculated was in the ode of 8 to kj/mol. This value is highe than the value obtained fo pape cha gasification in this study using the same eacting volume model. This discepancy may be attibuted to the high ash content of pape which may have a catalytic effect on the pocess. Bhatia and Pelmutte [3] developed a model which accounts fo the change in poe stuctue esulting in a change in intenal suface aea with time/convesion. This change in intenal suface aea esults in a popotional change in the cha convesion ate. The andom poe model developed by Bhatia and Pelmutte [3], is usually used to descibe the pesence of a peak value of eaction ate/convesion ate. Yamashita et al [7] modeled the cha paticle is a thee-dimensional cube. The cube is composed of a lage numbe of small, andomly aanged lattices classified as cha, ash, o 38

63 macopoes. The poosity of the paticle was expessed as a lage void in the cente of the paticle. They indicated that when the poosity is high, the eaction occus on both an intenal void suface and an extenal suface...3. Catalytic effect on cha gasification Tancedi et al. [5] investigated the catalytic effect of ash on cha gasification fo eucalyptus wood chas. The ash content in cha was of the ode of.45% on mass basis. The eactivity of the cha inceases monotonically with convesion. At low and intemediate convesion, it can be attibuted to the incease in suface aea as gasification poceeds. At high convesion levels a steepe incease in eactivity has been obseved, which cannot be explained by the development of suface aea. This egion of the eactivity-convesion cuves can be bette explained as the esult of an incease in catalytic effect of the metallic constituents (mainly Na and K) pesent as inoganic matte in the chas. Hee CO was used as the gasifying agent. Activation enegies detemined wee found to vay within a naow ange of 3 to 57 kj/mol. Ahenius plots showed paallel lines fo diffeent degees of convesion. Paallel line of Ahenius plot indicates simila activation enegies. The incease in eactivity was mainly due to an incease in peexponential facto. In a simila study by Montesinos et al. [6], steam gasification and CO gasification of gape fuit skin cha wee investigated. They also obseved an incease in eactivity at high values of convesion. Howeve, a diffeent tend of activation enegies values was obseved; in the case of CO gasification, as the convesion inceased, a decease in activation enegy was obseved. On the othe hand an incease in activation enegy was obseved in case of steam gasification. This incease in activation enegy was also, obseved by Mas et al. [93]. The decease in activation enegy values in the case of CO gasification was accompanied by a decease in pe-exponential facto as well. This behavio is called the compensation effect 39

64 [94]. Montesinos et al. obtained a value of isokinetic tempeatue of 5 K. The isokinetic tempeatue is the tempeatue at which all eactivities ae equal fo diffeent convesions. An isokinetic tempeatue of 449 K was obtained by Dhupe et al [95] fo CO gasification using catalyzed sodium lignosulfonate. Feistel et al [96] found this tempeatue to be 45 K, obtained using potassium-catalyzed steam gasification. Gokan and Muhlen [97] investigated the gasification of cha using two types of catalysts and a mixtue of both the catalysts. The investigated catalysts wee calcium lignosulfonate and sodium lignosulfonate. The cabon matix was satuated by calcium lignosulfonate at % by weight. Howeve, this satuation did not affect the catalytic effect of sodium lignosulfonate in the mixed catalytic system. Li and Cheng [98] investigated the catalytic gasification of coal cha using Na CO 3 and K CO 3 as catalysts. Effect of catalyst loading was investigated. Incease in catalysts loading was found to be effective until 5% by weight of K CO 3 loading and % by weight of Na CO 3 loading. Futhe incease in catalysts loading esulted in a decease in cha eactivity. The esults of eactivity vesus convesion plots showed an incease in cha eactivity initially. Futhe incease in convesion showed a decease in cha eactivity. They attibuted this decease to the cha poes blocking the catalyst at high degees of convesion. A compensation effect was obseved and an isokinetic tempeatue of 89 o C fo Na CO 3 and 466 o C fo K CO 3 wee obtained. Iwaki et al [99] investigated the catalytic effect of molten cabonates mixtues on waste pape convesion. Li, Na and K cabonates and thei mixtues wee used in thei expeiments. They found that the melting point is an essential facto to be consideed. Usually a mixtue of cabonates has a lowe melting point than a single cabonate compound. The esults show that 4

65 cabon convesion vaies significantly with one, two and thee cabonate components. They attibuted this vaiation in cabon convesion to a lowe melting point associated with the mixtue catalyst as compaed to a single catalyst fom the impoved contact efficiency between the gasifying agent and wastepape using a mixtue. Tomishige et al. [] investigated the cellulose gasification using Rh/CeO /SiO catalysts. They investigated the dependence of cabon convesion (C-convesion) and cold gas efficiency in the gasification of cellulose on CeO content in Rh/CeO/SiO catalysts. Thee was a maximum in the C-convesion and the cold gas efficiency at 35 mass % CeO content. The pesence of a peak was justified as follows. The BET suface aea deceased with incease in CeO content in the catalyst. On the othe hand, using Rh/SiO with no addition of CeO showed low pefomance of the gasification of cellulose and showed an elevated value of ta and solid cabon yield. Howeve, addition of % CeO deceased the yield of ta and solid cabon dastically, and this indicates that CeO pomoted the gasification eaction significantly. On the othe hand, the addition of CeO deceased the catalyst suface aea, and this can make the paticle size of Rh metal lage and educe the activity. So, the addition of CeO has both positive and negative aspects to the gasifie pefomance. In a simila study by Asadullah et al [] Rhodium metal loaded on CeO (Rh/CeO ) was found to be an excellent catalyst fo cellulose gasification at low tempeatues that esulted in % C-convesion to syngas. Watanabe et al [] investigated Catalytic hydogen geneation fom biomass simulated as glucose and cellulose with ZO in supecitical wate. They found that gasification efficiency with ziconia was twice as much as that without catalyst at all the expeimental conditions. Fo compaison, they conducted the expeiments using alkali hydoxide (NaOH) fo glucose and cellulose. Fo all the expeiments, the gasification efficiency with NaOH was the highest and the 4

66 yield of CO was negligibly small. Negligible CO yield was attibuted to the acceleation in the wate gas shift eaction. Most eseaches have used the TGA to investigate the kinetics of cha gasification. The implicit assumption hee is that the cabon steam eactions that occu ae the main souces fo weight loss. It is to be noted that cha contains appoximately 5 % hydogen and oxygen (on a mass basis). In the wok pesented hee, this assumption is eliminated; the eactivity of cabon in the cha paticle is calculated based on monitoing the cabon content in the syngas steam. Consequently, the kinetic paametes obtained ae not subjected to the eo of mass loss due to hydogen and oxygen evolution fom the cha paticle..3. Kinetics of syngas evolution duing pyolysis Heteogeneous substances such as coal and biomass have a complex stuctue. Detailed eaction mechanisms than include necessay elementay eactions fo cellulose, lignin o coal pyolysis ae still unde development. Consequently, coal and biomass pyolysis ae usually modeled using simple semi-empiical models as an appoximation using expeimental data. [3] Pseudo paallel fist-ode model: the heteogeneous sample is thought to be composed of pseudo-components, whee a pseudo-component is a goup of eactive species that exhibit simila eactivity. A fist-ode kinetic equation is assumed fo each pseudo-component. The esulting mass loss ate cuve is the weighted sum of the individual dα i /dt eaction ates: dα j = C dt dα dt i (II-E) i dα = i (II-E3) i dt i and K ( α ) 4

67 whee, α j is the oveall convesion at time t, α i is the convesion fom pseudo eaction i, C i is the weight of eaction i and K i is the eaction ate constant fo eaction i.[4] Pseudo paallel n th -ode model: due to the complex stuctue of the biomass o coal samples, the eactivity of a cetain functional goup may depend on its physical position and concentation of othe goups. The application of n th ode kinetics is a simple way to fit expeimental esults to the model; dαi dt n = K ( α ) (II-E4) i Distibuted activation enegy model (DAEM): The pyolysis pocess sometimes is expessed using infinite numbe of eactions that diffe only in the activation enegy value. This way, the activation enegy can be expessed as a continuous distibution function, D j (E act ). [6] i D i (E act ) = (π) -/ σ i - exp[-(e act -E oi ) /σ i ] (II-E5) whee E i and σ ι ae the mean value and the width paamete (vaiation) of the distibution. 43

68 Chapte III: Expeimental setup and expeimental conditions 3.. Desciption of expeimental setup Figues III-and III- show a photogaph and a schematic diagam of the laboatoy scale expeimental facility used fo pyolysis and gasification expeiments. Pue steam is geneated by stoichiometic combustion of hydogen and oxygen. Steam geneated is then intoduced into the gasifying agent conditione section, an electonically contolle tube funace (LINDBERG/BLUE M MINI-MITET M ). The funace is used to ensue that the gasifying agent tempeatue is at the same tempeatue as that of the main eacto in which the gasification occus. The sample mateial undegoes gasification in the main eacto. The main eacto is a inch tube section of the funace, (LINDBERG/BLUE M C SPLIT-HINGE TUBE FURNACE). The tube funace unit consists of an electic heate and a tempeatue contol unit. The contolle povides unifom tempeatue in the test section of the eacto. The unifomly heated length of the eacto is inches. The sample is placed in a stainless steel mesh then intoduced to the main eacto via a fast connection located at the ea end of the main eacto. The mesh is.8 inches in diamete and 7 inches in length see figue III-3. Steam at a defined tempeatue is then intoduced to the main eaction chambe. The syngas flowing out fom the main eaction chambe is sub-divided into two banches; one passes to the sampling line while the othe is passed though the exhaust system. The bypass line has a non-etun valve and a flow mete to assue a unidiectional flow out fom the eacto. The syngas sample is then intoduced to a condense followed by a low pessue filte and a moiste 44

69 absobe (anhydous calcium sulfate). Syngas flow is then intoduced to a thee way valve that allows one to fill the sampling bottle o intoduce the syngas diectly to the mico GC fo detailed analysis of the syngas poduced. The sampling line, condense and sampling bottles wee puged with agon pio to each expeiment. The Agon puging step ensues that the sampling line, condense and sampling bottles ae fee of ai o syngas samples fom a pevious test un. Sampling bottles ae used only when shot sampling intevals ae needed (.5 to min). Diect sampling and analysis ae caied out by the GC when longe sampling time intevals ae allowed. A constant flow ate of inet gas (nitogen) is intoduced with the oxygen flow in the steam geneation section. The nitogen is detected by the GC and is used to detemine the flow ate of diffeent syngas species by compaing the detected species mole faction with the known nitogen mole faction. In ode to assue that the oxygen to hydogen atio is stoichiometic, steam is condensed and nitogen flow is analyzed in the Agilent 3 mico GC. If tace amounts of hydogen and/o oxygen ae detected, the hydogen and/o the oxygen flow ate ae finely adjusted. These steps ae epeated until the oxygen and hydogen content in the nitogen flow is negligible. Oxygen would esult in a bigge eo in the syngas flow ate and composition, consequently, the H and O flow ates whee finely adjusted to have tace amount of excess hydogen (~.8%) and no detectable oxygen concentation. The semi-batch eacto is vey useful in the pocess analysis and undestanding the chaacteistics of each stage of the pocess fo bette design and development of advanced gasification systems. The semi-batch eacto has the following advantages: 45

70 The system allows one to monito the vaiation in syngas flow ate and chemical composition with time. At the beginning, the high flow ate due to pyolysis is obseved and quantified. The extended low value of syngas flow ate due to cha gasification is obseved as well. The tempeatue can be easily contolled and set to a constant value. Contol unit Bune Steam Heate Reacto Sampling line Mico GC H O +N A Bypassing valves Mass spectomete Figue III-. A photogaph of the expeimental facility 46

71 Moistue Sepaato Gas Sampling Line Figue III-. Schematic diagam of the expeimental setup Steam flow Solid fuel sample 3.. Cha pepaation Figue III-3. Detailed dawing of the eacto Fo cha pepaation, both the main and gasifying agent conditioning eactos wee heated up to 9 o C. A continuous flow of helium was intoduced to both eactos duing and afte heating. Then a sample was intoduced to the main eacto though a fast connection located at the eacto exit. The helium gas was kept flowing though the eacto to povide an inet medium fo chaing and to sweep the volatile mate out of the eacto. The sample was kept at a chaing tempeatue of 9 o C fo an hou. In ode to insue that the pyolysis pocess has been 47

72 completed, a sample of the exit gases was analyzed using the mass spectomete [MKS PPT Quadupole Residual Gas Analyze]. The chaing pocess is consideed complete when the analyzed exhaust contained only helium in the steam flow Pocedues of eactivity detemination In ode to examine the catalytic effect of ash the cha gasification a mass spectomete was used. Data fom the mass spectomete was used to calculate the eactivity of cabon in the sample cha. Cabon in the sample will evolve in the fom of cabon monoxide though the wate gas eaction (C + H O CO + H ) and in the fom of cabon dioxide though the wate gas shift eaction (CO + H O CO + H ). Consequently, monitoing the evolution of CO and CO flow ate helps to calculate the cabon consumption ate fom the sample. Helium was used as an inet gas in the eactivity expeiments to avoid the confusion between CO and N in the mass spectomete. The mass spectomete was used to measue the flow ate of CO and CO obtained by elating the patial pessue of CO and CO with the patial pessue of Helium. Fo this pupose the flow ate of Helium was kept constant at a known flow ate. Fom the cabon flow ate time, elationship one can calculate the total yield of cabon and instantaneous sample mass inside the eacto at time (t) Expeimental conditions and samples popeties Table III-. Tested samples and expeimental conditions Sample Reacto Gasifying agent Tace gas/ Inet (Mass) tempeatue(s) (Flow ate(s)) medium fo pyolysis 48

73 (Flow ate) Cadboad 9 o C Steam - (35 g) (3.3, 4., 5., 6.33, and 8.9 g/min) Pape 6, 7, 8, 9 Steam Nitogen (35 g) and o C (8 g/min) (.6 LPM) Rice husk 8, 9 and o C Steam Nitogen (35 g) (8 g/min) (.33 g/min) Sugacane bagasse 8, 9 and o C Steam Nitogen (5 g) (8 g/min) (.33 g/min) Food waste 8 and 9 o C Steam Nitogen (35 g) (8 g/min) (.6 LPM) Polystyene (C 8 H 8 ) 7, 8 and 9 o C Steam Nitogen (35 g) (8 g/min) (3 g/min) ubbe ties 8 and 9 o C Steam Nitogen (35 g) (8 g/min) (.33 g/min) Polyethylene- 9 o C Steam Nitogen 49

74 woodchips mixtue (7.7 g/min) (.33 g/min) fom % to % in % intevals (35 g) Table III-. Opeational conditions fo cha gasification kinetics expeiments Sample Chaing Pessue Gasifying Reacto Tace gas (mass) tempeatue agent tempeatue (flow ate o and (flow ate) patial pessue) duation* Food waste 9 o C atm Steam 75, 8, 85 Helium (35 g) ( h) (8 g/min) and 9 o C. g/min Woodchips 9 o C bas Steam 9 o C Agon (35 g) ( h) (4.4 g/min).5,.8,. and CO.4 bas (5.4 g/min) Activated - atm Steam 775, 8, 85 Nitogen chacoal (7.7 g/min) and 85 o C (.33 /min) ( g) * A flow of inet gas was used fo chaing the sample 5

75 Table III-3. Sample popeties; ultimate and poximate analysis Sample Volatile matte (%) Fixed cabon (%) Ash (%) C H O N S Heating value (MJ/kg) pape Cadboad [6] Rice husk [7] HHV: 4.89 sugacane bagasse HHV: 7.33 [7] yellow pines woodchips C 5.6 H 7. O 4. N S LHV:.3 [8] Rubbe ties [9] Polyethylene [] Paticle size ~5 µm Activated chacoal popeties Poosity.75(-) Density 3~ 7 kg/m 3 LHV:

76 Chapte IV: Results and discussion 4.. Chaacteistics of syngas evolution fom wastes gasification and pyolysis 4... Pape gasification and pyolysis In this section, main chaacteistics of gaseous yield fom steam gasification have been investigated expeimentally. Results of steam gasification have been compaed to that of pyolysis. The tempeatue ange investigated wee 6 to o C in steps of o C. Results have been obtained unde pyolysis conditions at same tempeatues. Investigated chaacteistics wee evolution of syngas flow ate with time, hydogen flow ate, chemical composition of syngas, enegy yield and appaent themal efficiency. Residuals fom both pocesses wee quantified and compaed as well. Mateial destuction, hydogen yield and enegy yield wee bette in case of gasification as compaed to that of pyolysis. This advantage of the gasification pocess is attibuted mainly to cha gasification pocess. Cha gasification was found to be moe sensitive to the eacto tempeatue than pyolysis. A patial ovelap between gasification and pyolysis has been obseved. This patial ovelap inceases with incease in tempeatue Syngas flow ate Figues IV-, IV- and IV-3 show the syngas flow ate fo both pyolysis and gasification at diffeent tempeatues. Flow ates fom pyolysis and gasification show simila tend at the fist few minutes. The values ae almost the same in both cases. Pyolysis shows a apid incease in flow ate at the beginning of the pocess followed by a apid decease in flow ate until the flow ate eaches an asymptotic value of zeo. In contast, esults fom gasification pocess show positive values of flow ate fo longe peiod of time, indicating the pesence of cha-steam 5

77 eaction. The aea confined between the pyolysis cuve and the gasification cuve eveals pesence of cha gasification. One can see this aea is almost zeo in the case of 6 o C. This indicates less contibution fom cha gasification pocess at this tempeatue. This is futhe confimed by the esults on esiduals emaining given in section Incease in tempeatue deceased cha gasification time as shown in figues IV-, IV- and IV-3. One can notice the patial ovelap in time between gasification and pyolysis at 7 o C. This patial ovelap inceases with the incease in tempeatue. Fo example, at eacto tempeatue of 8 o C, pyolysis ends at about 5 minute while gasification ends at ~ 45 minute. Ovelap between gasification and pyolysis is extended fom the 4 th minute until the 5 th minute. This ovelap at the 8 o C epesents aound 7% of the cha gasification pocess. An examination of the data at 9 o C (figue IV-b), shows that the ovelap exists between the 3 d and the th minute, while cha gasification ends at about 7 th minute. These values eveal a 5% ovelap between gasification and pyolysis. The ovelap at o C tempeatue is almost 95% of the cha gasification time. Flow ate (g/min) Gasification Pyolysis Flow ate (g/min) Gasification Pyolysis Time (min) Time (min) (a) (b) Figue IV-. Syngas flow ate fom pyolysis and gasification at (a) 6 o C and (b) 7 o C 53

78 6 5 Gasification Pyolysis Gasification Pyolysis Flow ate (g/min) 4 3 Flow ate (g/min) Time (min) Time (min) (a) (b) Figue IV-. Syngas flow ate fom pyolysis and gasification at (a) 8 o C and (b) 9 o C Flow ate (g/min) Gasification Pyolysis Time (min) Figue IV-3. Syngas flow ate fom pyolysis and gasification at o C 4... Hydogen flow ate and yield Figues IV-4 and IV-5 show the effect of eacto tempeatue on hydogen flow ate fo both gasification and pyolysis pocesses. The common effect of incease in eacto tempeatue in both pocesses is that incease in eacto tempeatue inceases hydogen flow ate and deceases the time of hydogen elease. This is attibuted to the endothemicity of hydogen elease fo both pocesses and incease in eaction ates with the incease in eacto tempeatue. Howeve, gasification shows highe hydogen flow ates than pyolysis at same pocess 54

79 tempeatue. Additional hydogen poduction is attibuted to gasification of cha with steam and also fom the patial contibution of wate gas shift eaction. One moe impotant esult is that hydogen evolution in case of gasification is elaxed ove a longe peiod of time than hydogen evolution fom pyolysis. This is due to the slowe eaction kinetics of cha gasification, which leads to the extension of the gasification pocess fo a longe time duation. Fo example, at 8 o C the esults fo both pyolysis and gasification shows that hydogen elease in the case of pyolysis is almost zeo at the th minute, while one can see consideable flow ate of hydogen at th minute in case of gasification. Fo the 6 o C case, gasification and pyolysis yielded same amount of hydogen as shown in figue IV-6. This is attibuted to almost negligible gasification eactions at this tempeatue. g/min C 7 C 8 C 9 C C Time (min) Figue IV-4. Hydogen flow ate fom gasification g/min C 7 C 8 C 9 C C Time (min) Figue IV-5. Hydogen flow ate fom pyolysis 55

80 (g) Gasification Pyolysis Tempeatue ( o C) Figue IV-6. Hydogen yield fom pyolysis and gasification Evolution of H and CO mole faction Figues IV-7(a), IV-7(b), IV-8(a) and IV-8(b) show the effect of tempeatue on evolution of H and CO mole faction duing gasification and pyolysis. Except fo the 6 o C data, all othe tempeatues examined hee show the same tend. At the beginning, both gasification and pyolysis show a good ovelap in the mole faction values. Fo example at eacto tempeatue of 7 o C (figue IV-7b) one can see an ovelap in mole faction of H and CO fo the fist five minutes. This ovelap is educed with the incease in eacto tempeatue. Ovelap in the 9 o C un is only fo one minute. This ovelap is attibuted to the time taken by the sample to each eacto nominal tempeatue. Ovelap in mole faction indicates pyolysis of the sample at the beginning of the gasification pocess. Long peiods of ovelap at low tempeatues ae attibuted to slow kinetics of cha gasification at these low tempeatues and indicate the sensitivity of cha gasification to eacto tempeatue. Fo eacto tempeatues highe than 6 o C, H mole factions fo gasification ae highe than that of pyolysis and CO mole factions fo gasification ae lowe than that of pyolysis. The incease in H mole faction in case of gasification is attibuted to cha gasification by steam and the wate gas shift eaction. Howeve, lowe values of mole faction of CO ae attibuted to wate gas shift eaction and 56

81 pesence of tace amount of oxygen emanated fom the steam geneation system. It is impotant to note the elative incease in steam mole faction in the eacto with time and the elative decease in cabon mole faction with time. This esults in the consumption of CO mole faction by the wate gas shift eaction (figue IV-9) and the gain of H at the same time. The 6 o C un does not follow the same tend as in fo the othe tempeatues due to the absence of steam-cha gasification eactions at this low tempeatue. 7 6 H Gasification CO Gasification H Pyolysis CO pyolysis 7 6 H Gasification CO Gasification H Pyolysis CO Pyolysis Mole faction (%) Mole faction (%) Time (min) Time (min) (a) (b) Figue IV-7. H and CO mole faction fo pyolysis and gasification at (a) 6 and (b) 7 o C 7 6 H Gasification CO Gasification H Pyolysis CO Pyolysis 8 7 H Gasification CO Gasification H Pyolysis CO Pyolysis Mole faction (%) Time (min) Mole faction (%) Time (min) (a) (b) Figue IV-8. Evolution of H and CO mole faction duing pyolysis and gasification at (a) 8 and (b) 9 o C 57

82 6 CO+HO<---> H+CO Equilibium Mole faction H CO CO HO/CO atio Figue IV-9. Equilibium mole faction fo H O/CO eaction Residue Mateial afte Pyolysis and Gasification Figue IV- shows esidual mateial leftove afte the pyolysis and gasification pocess. As shown in (figue IV-), pyolysis shows highe pecentage of esidual mateial as compaed to that obtained fom the gasification pocess. Residual mateials fom the pyolysis pocess ae mainly the cha emaining fom the devolatilization pocess. On the aveage the cha pecentages is about % of the initial sample mass fom pyolysis. This value epesents the amount of fixed cabon in the sample as shown by the dak colo mateial collected. In contast, the esidual mateials in the case of gasification ae white ash (no dak colo mateial). Ash epesents about 8~9% in the pape. The esiduals pecentage being of the ode of 8% in case of gasification, confims the gasification of all the cha (fixed cabon) left ove fom the pyolysis pocess. The gasification of all the cabon content in the sample is also confimed by the pesence of only white colo ashes leftove fom the gasification pocess vesus the black colo cha leftove fom the pyolysis pocess (see figue IV-). It is impotant to note the absence of steam-cha eactions at low tempeatues (less than 7 o C). Residuals fom the gasification pocess at 6 o C showed consideably highe values than that at successively inceased tempeatues. Mass of Residuals at 6 o C (fo gasification) was 3% of the initial sample which is compaable to the 58

83 esiduals mass fom a pyolysis pocess. This indicates that only pyolysis took place at this 6 o C tempeatue. (%) Gasification Pyolysis Tempeatue ( o C) Figue IV-. Pecentage of Cha esidues fom pyolysis and ash esidues fom gasification Figue IV-. Cha leftove fom pyolysis (left) and ash leftove fom gasification (ight) Enegy yield Figue IV- shows the effect of eacto tempeatue on enegy yield and appaent themal efficiency fom the pape sample. Incease in eacto tempeatue inceases the enegy yield fom the sample fo both pyolysis and gasification cases. In case of the pyolysis pocess, incease in tempeatue allow fo bette beakdown of long chains of hydocabons and consequently allow the elease of moe gaseous yield fom the pocess. Moe specifically incease in the pyolysis tempeatue inceases the CO yield at the expense of CO yield. This incease in CO yield at the expense of CO yield aises the quality of syngas beside the initial incease in oveall syngas yield. As fo gasification same tend is obseved; incease in the 59

84 eacto tempeatue inceases enegy yield fom the sample. This is attibuted to two easons. Fist, the gasification pocess stats with apid devolatilization of volatile component in the sample (pyolysis) which is enhanced with the incease in eacto tempeatue. Second, it pomotes in bette steam-ta efoming pocess at elevated tempeatues. In geneal, gasification shows highe enegy yields than pyolysis. Howeve, the enegy yields fom gasification and pyolysis at 6 o C ae compaable. Gasification did not show highe enegy yield than pyolysis at this low tempeatue. The same would be expected if the expeiments wee caied out at even lowe tempeatues. This indicates the absence of cha gasification eactions at this tempeatue. This is confimed by the esidual mateial esults shown in figueiv-. The mateial emaining fom the gasification pocess at 6 o C is consideably highe than that obtained at successively inceased tempeatues. 5 Gasification Pyolysis Gasification Pyolysis 4.8 (kj) Tempeatue ( o C) Tempeatue ( o C) (a) (b) Figue IV-. (a) Enegy yield fom pyolysis and gasification and (b) appaent themal 4... Rice husk gasification efficiency of pyolysis and gasification 6

85 Evolution of syngas fom ice husk pyolysis and gasification has been investigated at eacto tempeatues of 8, 9 and o C. Steam has been used as the gasifying agent. Evolution of main syngas constituents has been investigated. Results confim that gasification occus in two stages with the fist stage as pyolysis and the second stage being gasification of cha. Pyolysis expeiments have been conducted at the same eacto tempeatues as gasification to povide diect compaison. Hydogen and CO yields fom pyolysis inceased with the incease in eacto tempeatue. Howeve, fo gasification, hydogen deceased slightly with incease in tempeatue while the CO yield emained almost constant. The behavio of hydogen yield as well as CO yield fom gasification and pyolysis can be explained in tems of hydogen and cabon content in cha, liquid hydocabons (HCs) and syngas Evolution of CO and H mole factions H mole faction at 8 o C H mole faction at 9 o C H mole faction at o C Gasification Pyolysis Gasification Pyolysis Gasification Pyolysis 5 5 Time (min) 5 5 Time (min) 5 5 Time (min) (a) (b) (c) Figue IV-3. Evolution of H mole faction fo eacto tempeatues (a) 8, (b) 9 and (c) o C Figues IV-3a, IV-3b and IV-3c show the evolution of H mole faction fom ice husk at 8, 9 and o C eacto tempeatues. Initially the mole faction of H fom gasification coincides to that fom pyolysis. This ovelap is longe in case of eacto tempeatue 6

86 of 8 o C. Afte the initial stage in which H mole faction fom gasification coincides with that fom pyolysis, H mole faction fom gasification continues to incease until it eaches an asymptotic value. The incease in H mole faction in case of gasification is mainly attibuted to the wate gas eaction and the wate gas shift eaction. Figues IV-4(a), IV-4(b) and IV-4(c) show the evolution of CO mole faction fom gasification and pyolysis at thee diffeent tempeatues. In contay to the behavio of H mole faction in gasification expeiments, CO mole faction fom gasification continues to decease to each an asymptotic value. CO mole faction is affected by two competing eactions in the stage of cha gasification; the CO mole faction tends to incease by the wate gas eaction and tend to decease by the wate gas shift eaction (CO+ H O H + CO ). Howeve, since the steam to CO atio in the late stages of cha gasification is high, the wate gas shift eaction tends to shift towads moe H, CO and less CO. Results of equilibium concentation of the wate gas shift eaction at 9 o C confims the fogoing discussions, see figue IV CO mole faction at 8 o C Gasification Pyolysis 5 5 Time (min) CO mole faction at 9 o C Gasification Pyolysis 5 5 Time (min) (a) (b) (c) Figue IV-4. Evolution of CO mole faction fo eacto tempeatues (a) 8, (b) 9 and (c) o C CO mole faction at o C Gasification Pyolysis 5 5 Time (min) 4... Total yield of main syngas constituents 6

87 Figue IV-5 shows the total yield of main syngas constituents fom pyolysis and gasification of ice husk at the selected 3 eacto tempeatues. Hydogen yield fom pyolysis tends to incease with the incease in eacto tempeatue as shown in figue IV-5(a). CO yield incease with the incease in eacto tempeatue in case of pyolysis. On the othe hand hydogen slightly deceases with the incease in tempeatue in the case of gasification and CO yield is almost constant. The behavio of hydogen yield as well as CO yield fom gasification and pyolysis can be explained in tems of hydogen and cabon content in cha, liquid hydocabons (HCs) and syngas. Unde non-isothemal pyolysis conditions, cha yield is maximized at the conditions of low tempeatue and low heating ates. The liquid hydocabons yield is maximized at the conditions of intemediate eacto tempeatues and high heating ates. The syngas yield is maximized fo the conditions of high heating ate and high eacto tempeatues..35 Total yield fom pyolysis (moles).9 Total yield fom gasification (moles).3.5 H CO CO H CO CO Tempeatue ( o C) Tempeatue ( o C) (a) (b) Figue IV-5. Total yield of H, CO and CO fom (a) pyolysis and (b) gasification 63

88 Based on the above mentioned behavio of cha, liquid hydocabons and syngas yields accoding to eacto conditions, the incease of H and CO with incease in tempeatue is in ode. Howeve, it might look contadictoy to have a decease in hydogen yield fom gasification and a constant CO yield. Hydogen yield fom gasification is attibuted to the pyolysis pat as well the cha gasification pat. The incease in eacto tempeatue tends to incease the hydogen yield in the fom of syngas, but it also tends to incease the hydogen content in the liquid hydocabons and tends to decease the cha fomed. A schematic epesentation of the competing outes duing biomass gasification is shown in figue IV-6. Aldehydes, Ketones, Caboxylic acids and gases (CO, CO, C n H m, H ) Tetiay eactions Gaseous hydocabons (Alkanes, alkenes alkynes) + CO Fagmentation + decabonylation + decaboxylation Aomatization and epolymeization Steam hydocabons efoming eactions Cellulose Hemicellulose and lignin Pecusos (activated compounds) Cha Cha gasification Slow heating ate to low tempeatues Depolymeization Cha and amophous cha (Coke), gases and H O Seconday eactions (ing opening) Repolymeization Wate gas shift eaction CO, H, CO Aomatic cyclic and heteocyclic compounds (Benzene, toluene, styene, xylene, Glucose, fuctose, levoglucosan) Oligomeization Ta (oligomes) + CO Cha gasification 64

89 Figue IV-6. Reaction mechanism of biomass gasification. Blue line epesents pyolysis oute which ae acceleated with incease in eacto tempeatue. Red line epesents cha fomation oute and consequent CO poduction oute though cha gasification. This oute is favoed at lowe tempeatues Having less cha fomed esulted in less yield of hydogen in the syngas fom the cha gasification (C+H O CO + H ). The decease in hydogen yield is mainly attibuted to competing effects of syngas incease due to incease in tempeatue and less cha fomed and in tun less hydogen fomation via the wate gas eaction. Same discussion applies fo the CO behavio; CO yield inceases diectly with the incease in eacto tempeatue and heating ate by pyolysis. Howeve, in contast the cabon yield in fom of cha deceases as the eacto tempeatue inceases. Howeve, the competing effect esults in almost a flat yield of CO. Deceasing yield of CO fom gasification can be explained in tems of the wate gas shift eaction equilibium. The WGS tends to yield moe poducts at the lowe tempeatues. Consequently, CO yield deceases at highe tempeatues Gasification and pyolysis of sugacane Sugacane bagasse gasification stats with pyolysis, followed by the gasification of cha. The chaacteistics of syngas evolved duing gasification stongly depend on the heating ate and the sample tempeatue. The pyolysis pocess consists of a complex seies of hydocabons beakdown, fagmentation, isomeization and epolymeization. At high heating ates and high eacto tempeatues steam gasification and steam efoming eactions occu in paallel with some of the pyolysis eactions. The evolution of syngas chaacteistics will be discussed in lights of a global eaction mechanism which includes the pyolysis step in conjunction with possible steam efoming/gasification eactions. 65

90 Global eaction mechanism of sugacane gasification Figue IV-7 show the evolution of syngas flow ate with time at eacto tempeatues of 8, 9 and o C. The flow ate stats with a high value at appoximately 3 seconds followed by a steep decease in flow ate. In the case of 8 o C expeiment, the steep decease in flow ate is followed by a mild slope of syngas flow ate that is attibuted to cha gasification. Howeve, at 9 o C, the cha gasification peiod is patially meged with the syngas evolution fom pyolysis, which esulted in a local peak at the second minute. In the o C test case, one can see a total meging between the pyolysis step and the cha gasification step. The evolution of hydogen showed simila behavio, see figue IV-8. The behavio of syngas evolution duing gasification can be explained using the eaction mechanism pesented in figue IV-9, and the evolution of sample tempeatue, pesented in figue IV-. Syngas flow ate (moles/min) C 9 C C 5 Time (min) 5 Figue IV-7. Evolution of syngas flow ate fo eacto tempeatues 8, 9 and o C H flow ate (moles/min). 8 C.6 9 C. C Time (min) 5 Figue IV-8. Evolution of H flow ate fo eacto tempeatues 8, 9 and o C In the mechanism pesented below the main constituting blocks of biomass ae; cellulose, hemicellulose and lignin. The fist step is activation of these compounds. Afte activation, the pecusos undego paallel eactions duing initial stages of pyolysis. The pecusos might 66

91 undego fagmentation eactions by cabon bonds scission, decabonylation and decaboxylation, esulting in fagmented hydocabons; ketones, aldehydes and acetic acids. On the othe hand the activated compounds might undego depolymeization to fom cyclic and heteocyclic compounds. The fagmentation oute is favoed at high heating ates and high eacto tempeatues. Howeve, the depolymeization oute is favoed at high/medium heating ates and intemediate eacto tempeatues. Aldehydes, Ketones, Caboxylic acids and gases (CO, CO, C n H m, H ) Tetiay eactions Gaseous hydocabons (Alkanes, alkenes alkynes) + CO Fagmentation + decabonylation + decaboxylation Aomatization and epolymeization Steam hydocabons efoming eactions Cellulose Hemicellulose and lignin Pecusos (activated compounds) Cha Cha gasification Slow heating ate to low tempeatues Depolymeization Cha and amophous cha (Coke), gases and H O Seconday eactions (ing opening) Repolymeization Wate gas shift eaction CO, H, CO Aomatic cyclic and heteocyclic compounds (Benzene, toluene, xylene, styene, Glucose, fuctose, levoglucosan) Oligomeization Ta (oligomes) + CO Cha gasification Figue IV-9. Reaction mechanism of biomass gasification. The dotted line epesents outes which ae favoed at high heating ates and high eacto tempeatues. 67

92 Cyclic compounds might undego fagmentation though seconday eactions to yield gaseous hydocabons and fagmented hydocabons, which in tun, might undego tetiay eactions to yield gaseous hydocabons and cabon monoxide [35]. Tempeatue o C C 4 9 C C Time (Sec) Figue IV-. Evolution of sample tempeatue with time fo eacto tempeatues CO/CO atio.5 8 C 9 C C Time (min) Figue IV-. Evolution of CO/CO atio (mola basis) 8, 9 and o C Cha is fomed by thee outes; the fist is chaing and coke fomation at low heating ates and low tempeatues. The second oute is aomatization and epolymeization fom fagmented hydocabons. The thid oute is epolymeization of cyclic and heteocyclic compounds. Ta and cabon dioxide ae fomed by oligomeization of pecusos such as levoglucosan to fom oligomes. It has been epoted in the liteatue that CO and CO ae fomed fom competing paallel outes [4]. CO poduction oute is favoed at high heating ates at high eacto tempeatues. Howeve CO oute is favoed at intemediate heating ates and intemediate tempeatues. Based on the above mentioned obsevations, CO and CO evolutions in this mechanism ae geneated fom competing outes. This conclusion is confimed fom the 68

93 esults of CO/CO atio shown in figue IV-. CO/CO atio at eacto tempeatue of o C is highe than that at eacto tempeatues of 8 and 9 o C. The behavio of syngas flow ate can be explained in lights of the pesented eaction mechanism. The incease in eacto tempeatue esults in an incease in the heating ate, see figue IV-. Consequently outes of fagmentation, seconday fagmentation, tetiay eactions, steam-hydocabons efoming eactions and cha gasification eactions ae acceleated. As a esult of the acceleation in these outes syngas flow ate is inceased. It is impotant to note that the pecusos fo cha fomation ae the depolymeized cyclic and heteocyclic and fagmented hydocabons, which ae consumed by tetiay eactions and steam efoming eactions as well. Consequently, the incease in eacto tempeatue esults in less cha fomation and shote time duation fo cha gasification. Figue IV-8 shows the evolution of hydogen flow ate fo the investigated tempeatues. The peak value of hydogen flow ate shifts towads a high eacto tempeatue and longe esidence time as compaed to the peak syngas flow ate. Fo example, hydogen flow ate peaks at the second minute fo eacto tempeatues of 8 and 9 o C and peaks duing the fist minute fo eacto tempeatue of o C. Howeve, the syngas flow ate peaks at about 3 second fo the tempeatues epoted hee. Hydogen is mainly poduced by fagmentation, seconday eactions, tetiay eactions, efoming eactions and cha gasification eaction. All these outes ae favoed at high heating ates and high eacto tempeatues Enegy yield and appaent themal efficiency Figue IV- and IV-3 show the enegy yield and the appaent themal efficiency at the thee eacto tempeatues. The incease in eacto tempeatue esulted in an incease in enegy 69

94 yield and appaent themal efficiency. Although the incease in eacto tempeatue did not povide a consistent effect on syngas and hydogen yield, see figue IV-4, the enhancement in syngas quality at the o C case esulted in an incease in the enegy yield. The enhancement in syngas quality is mainly attibuted to the incease in CO and C n H m yields at o C. 8 Enegy yield (kj).8 Appaent themal efficiency (-) Tempeatue ( o C) 8 9 Tempeatue ( o C) Figue IV-. Enegy yield at eacto Figue IV-3. Enegy yield at eacto tempeatues of 8, 9 and o C tempeatues of 8, 9 and o C.7 Hydogen yield Syngas yield CO CnHm*.6.5 Yield (moles) Tempeatue ( o C) Figue IV-4. Syngas, hydogen, CO and C n H m yield at eacto tempeatues of 8, 9 and o C 7

95 Cumulative yield of syngas, hydogen and enegy fom sugacane gasification Figue IV-5, IV-6 and IV-7 show the evolutionay behavio of cumulative yield of syngas, hydogen and enegy. The vetical lines epesent the time at which syngas, hydogen and enegy yields eached 99% of the total yield. The pupose of these figues, figues IV-5 to IV-7, is to set a citeion to define time duation of gasification. The sample might take up to minutes fo its complete convesion o absolute zeo flow ate of syngas. On the othe hand, it took only 8 minutes to each 99% of sample convesion o 99% of total syngas yield. Fom figue IV-6, one can see that the incease in eacto tempeatue esulted in a significant decease in time duation fo enegy convesion, based on the poposed citeion. This definition of time duation is moe significant in detemining the equied esidence time fo a cha paticle to each a cetain degee of convesion. Note that thee was no contol on the esidence time of gaseous and volatile yields duing the expeiment as they follow with the steam flow fom the eacto. Theefoe, the pesented esidence time in figues IV5-7 coesponds to the cha content in the sample. Cumulative syngas yield (moles) C 9 C C 3 Time (min) Figue IV-5. Cumulative syngas yield at eacto tempeatues of 8, 9 and o C Cumulative hydogen yield (moles) C 9 C C 3 Time (min) Figue IV-6. Cumulative hydogen yield at eacto tempeatues of 8, 9 and o C 7

96 Cumulative enegy yield (kj) C 9 C C Time (min) 3 Figue IV-7. Cumulative enegy yield at eacto tempeatues of 8, 9 and o C Polystyene gasification and pyolysis Polystyene (PS) pyolysis and gasification have been examined in a semi-batch eacto at tempeatues of 7, 8 and 9 o C. Chaacteistic diffeences between pyolysis and gasification of polystyene (PS) has been evaluated with specific pefomance focus on the evolution of syngas flow ate, evolution of hydogen flow ate, evolution of output powe, syngas yield, hydogen yield, enegy yield, appaent themal efficiency and syngas quality. Behavio of (PS) unde eithe pyolysis o gasification pocesses is compaed to that of cha based sample, such as, pape and cadboad. In contast to cha based mateials, PS gasification yielded less syngas, hydogen and enegy than pyolysis at 7 o C. Howeve, the gasification of PS yielded moe syngas, hydogen and enegy than pyolysis at 9 o C tempeatue. Gasification of PS is affected by eacto tempeatue moe than PS pyolysis. Syngas, hydogen and enegy yield inceased exponentially with tempeatue in case of gasification. Howeve, syngas and 7

97 enegy yield inceased linealy with tempeatue having athe a mild slope in the case of pyolysis. Pyolysis esulted in highe syngas quality at all tempeatues Evolution of syngas flow ate Figues IV-8a, IV-8b and IV-8c show the evolution of syngas fom polystyene (PS) pyolysis and gasification at thee diffeent tempeatues of 7, 8 and 9 o C. The esults show a peak at cetain time of the pocess. This is attibuted to tansient heating of the sample afte intoduction of the sample into the main eacto. One can clealy see the shift in peak position towads shote times at highe eacto tempeatues. This behavio is moe obvious in the pyolysis uns. This can be explained by assuming that the evolution of volatiles in the case of pyolysis follows an n th ode single step eaction, i.e., dx/dt = K*(-X) n whee X epesents the convesion at time t and K is the eaction ate constant. Incease in the eacto tempeatue is equivalent to inceasing the heating ate of the sample, especially in the fist few minutes of the pocess. Incease in the heating ate means that the sample will each the same tempeatue in shote time. Consequently, the ate constant k will each a highe values in a shote time and the tem epesenting the volatile amount emaining in the sample, (-X) n, will have a highe value. Consequently the eaction ate, dx/dt, will each its peak in a shote peiod of time. The incease in eacto tempeatue has a positive effect on syngas flow ate in both pyolysis and gasification. Howeve, the effect of eacto tempeatue is moe significant in gasification than pyolysis. At 7 o C, the syngas flow ate fo pyolysis is highe than that of gasification. Incease in the eacto tempeatue to 8 o C esulted in incease in the syngas flow ate fo both pyolysis and gasification. In addition, the syngas yield fom gasification was moe than that fom the pyolysis. The incease in syngas flow ate at 9 o C was even moe significant. One can say that the syngas flow ate inceased quasi-linealy with tempeatue fo the pyolysis pocess 73

98 and inceased exponentially fo the gasification pocess ove the investigated tempeatue ange of 7 to 9 o C. These esults can be diectly seen fom the data shown in figue IV-3 whee the oveall syngas yield flow ate is pesented. Of couse these elations ae not expected to hold fo all othe tempeatue values and tempeatue anges. Theefoe, futhe investigations should be caied out in ode to detemine the behavio of syngas evolution at highe (o lowe) eacto tempeatues. Syngas flow ate (g/min) Pyolysis Gasification 7 o C Time (min) Syngas flow ate (g/min) Pyolysis Gasification 8 o C Time (min) Syngas flow ate (g/min) o C Pyolysis Gasification Time (min) (a) (b) (c) Figue IV-8. Evolution of syngas flow ate fom pyolysis and gasification fo eacto tempeatues (a) 7 o C, (b) 8 o C and (c) 9 o C Evolution of hydogen flow ate Figues IV-9a, IV-9b and IV-9c show the evolution of syngas fom the pyolysis and gasification of PS at the thee investigated tempeatues, namely 7, 8 and 9 o C. Simila to the syngas flow ate esults shown above, all cuves show a peak at a cetain time in the pocess. A shift in peak position towads shote time with incease in the eacto tempeatue is obseved. This behavio is seen fo both the pyolysis and gasification expeiments. This shift is attibuted to the incease in sample heating ate, which inceases the eaction ate constant to povide a shote time. On the othe hand, it was expected that the pesence of steam will incease the hydogen flow ate and yield at all tempeatues. Howeve, at eacto tempeatue of 7 o C, hydogen flow ate fom the gasification expeiment was less than that fom the pyolysis 74

99 expeiment. This suggests a competing eaction of PS with steam that foms condensable hydocabons. This competing eaction is moe favoable at eacto tempeatue of 7 o C. The incease in eacto tempeatue inceased the hydogen flow ate fo both pyolysis and gasification. If the goal fom the pyolysis and gasification of PS is the poduction of hydogen gas, then it is not useful to use the gasification pocess unless the eacto tempeatue is highe than 8 o C, see figues IV-9 and IV-3. One can see fom the hydogen flow ate esults, figue IV-9, as well as the oveall hydogen yield esults, figue IV-3, that hydogen yield fom gasification at eacto tempeatue of 7 and 8 o C is lowe than that fom pyolysis. H flow ate (g/min) Pyolysis Gasification 7 o C H flow ate (g/min) Pyolysis Gasification 8 o C H flow ate (g/min) Pyolysis Gasification 9 o C Time (min) Time (min) Time (min) (a) (b) (c) Figue IV-9. Evolution of hydogen flow ate fom pyolysis and gasification fo eacto tempeatues (a) 7 o C, (b) 8 o C and (c) 9 o C Evolution of output powe Figue IV-3a, IV-3b and IV-3c show the evolution of output powe (kj/min) associated with the chemical enegy in the syngas. The figues epesent the output powe fom pyolysis and gasification at eacto tempeatues 7, 8 and 9 o C. Gasification yielded less powe than pyolysis at 7 o C, almost the same powe at 8 o C and moe powe at 9 o C. If chemical enegy fom PS in its oiginal solid fom is to be ecoveed in efomed gaseous fom, it is ecommended to use gasification pocess only at eacto tempeatues highe than 8 o C. 75

100 Powe (kj/min) Pyolysis 7 o C Gasification Time (min) Powe (kj/min) Pyolysis Gasification 8 o C Time (min) Powe (kj/min) Pyolysis 9 o C Gasification Time (min) (a) (b) (c) Figue IV-3. Evolution of output powe fom pyolysis and gasification at eacto tempeatues of: (a) 7 o C, (b) 8 o C and (c) 9 o C Syngas yield Polystyene yields almost 99 % volatile matte unde pyolysis o gasification conditions. Aound % of black cabon has been obseved fo pyolysis expeiment caied out at 7 o C. Besides this all the expeiments yielded negligible amount of black cabon, accounting to less than %. The volatile yield is eithe in the gas phase o condensable phase. The condensable phase contains liquid hydocabons and wax. The change in gaseous yield with eacto tempeatue can help descibe pyolysis and gasification of PS using simple models. One can conside the pyolysis of PS as if it undegoes two paallel competing eactions with two diffeent eaction ates of k and k, whee k coesponds to the eaction yielding gaseous fom and k coesponds to the eaction yielding condensable hydocabons. This model can be epesented as follows: (PS) k k Syngas Condensable hydocabons (liquid + wax) 76

101 Syngas yield (g) Syngas yield (g) Pyolysis Gasification Tempeatue ( o C) Hydogen yield (g) Hydogen yield (g) Pyolysis Gasification Tempeatue ( o C) Figue IV-3. Oveall syngas yield fom pyolysis and gasification Figue IV-3. Oveall hydogen yield fom pyolysis and gasification Examinations of the syngas yield fom pyolysis eveal an incease in both syngas flow ate and yield with incease in tempeatue, see figue IV-3. This behavio indicates that PS pyolysis pocess favos the syngas poduction oute (k ) at inceased tempeatues. Results of syngas flow ate and oveall syngas yield show that at 7 o C, gaseous yield fom gasification is lowe than that of pyolysis; howeve, at 9 o C the yield fom gasification is highe than that of pyolysis, see figue IV-3. This behavio is diffeent fom the behavio of cellulosic based mateial. In a pevious study by the authos, Ahmed and Gupta [3, 7] showed that steam gasification always yielded moe syngas than pyolysis at all tempeatues. One futhe majo diffeence between PS and cellulosic based mateial is the hydogen yield. Steam gasification always inceased the hydogen yield fo cellulosic mateial as compaed to pyolysis, and one would expect simila behavio fo PS also. On the contay a decease in hydogen flow ate and yield was obseved with steam gasification at 7 o C as compaed to pyolysis. Hydogen flow ate and oveall hydogen yield ae shown in figue IV-9 and figue IV- 3, espectively. Putting this infomation togethe eveals that the pesence of a PS-steam eaction that yields condensable hydocabons (liquid + wax). This eaction is competing with 77

102 the gasification eactions. Consequently, in the simplest model, the gasification pocess has to be epesented by fou competing paallel eactions as given below: (PS) k k k 3 Syngas (fom pyolysis) Condensable hydocabons (fom pyolysis) Syngas (fom gasification) k 4 Condensable hydocabons (fom gasification) Fom the esults of syngas yield and hydogen yield shown in figues IV-3 and IV-3, one can conclude the domination of eaction (k 4 ) at eacto tempeatue of 7 o C. Howeve, at eacto tempeatue of 9 o C, the thid eaction (k 3 ), dominates. In ode to suppot this conclusion, a compaison between condensable yield fom pyolysis and gasification has been conducted. The sample size and expeimental conditions was as follows: o Sample: 8 gams of polystyene (PS) o Reacto tempeatue: 7 o C fo both pyolysis and gasification o Steam flow ate fo gasification: 8 g/min o Nitogen flow ate fo pyolysis: 3 g/min The sample mass was educed because the condense was designed to condense only a faction of the flow fo gas analysis. In this expeiment the entie poduct steam was diected to the condense with no bypass of the sample. Condensable hydocabons ae collected in the condense and a small flask was placed afte the condense. Gaseous poducts wee diected to the exhaust system. In the case of gasification expeiments the condensable hydocabons got mixed with the condensed wate. Sepaation of condensable hydocabons fom the condensed wate was pefomed using the diffeence in density in a long column. Condensate fom 78

103 pyolysis was appoximately 4.4 gams o 4.4 % of the initial sample mass. Howeve fo gasification the condensate was appoximately gams, epesenting 6. % of the initial sample mass. Getting moe hydocabons condensate fom gasification than pyolysis emphasize the pesence of eaction fou (k 4 ), which epesents the condensable hydocabons fomation as a esult of steam-ps eactions. An accuate mass balance could not be pefomed due to the eo emanating fom condensate which was not etieved fom the condense as well as the escaped volatiles which wee not condensed. Consideing that the factos causing the eo ae equally affecting the pyolysis and gasification expeiments, the fact that gasification yields moe condensable hydocabons than pyolysis is still tue. Figue IV-33 shows a photogaph of a sample fom the condensed hydocabons and they ae labeled to show the global factionation. Liquid hydocabons (highe seies of hydocabons including Polycyclic aomatic hydocabon compounds) Suspended wax paticles Figue IV-33. Condensable hydocabons fom PS gasification Hydogen yield Figue IV-3 shows the effect of eacto tempeatue on oveall hydogen yield. Hydogen yield fom gasification shows a consistent incease with an incease in eacto tempeatue. Gasification yielded moe hydogen than pyolysis only at the examined eacto tempeatue of 9 o C Enegy yield and appaent themal efficiency Figue IV-34a and IV-34b show the enegy yield and appaent themal efficiency fo gasification and pyolysis at eacto tempeatues of 7, 8 and 9 o C. The appaent themal 79

104 efficiency was based on a LHV of 4 kj/kg.[] The incease in eacto tempeatue inceases the enegy yield and appaent themal efficiency fo both the pocesses of pyolysis and gasification. Fo eacto tempeatue less than 8 o C, gasification yielded less enegy and lowe appaent themal efficiency than pyolysis. At eacto tempeatue of 9 o C, gasification yielded almost thee times the amount of enegy than that fom pyolysis. Enegy yield and appaent themal efficiency inceases quasi-linealy with tempeatue in case of the pyolysis pocess. The incease in enegy yield and appaent themal efficiency with incease in tempeatue fo gasification can be descibed best using an exponential function in tempeatue simila to that of the Ahenius equation. This indicates that the effect of tempeatue on enegy yield is simila to that on the eaction ate. A simple cuve fitting can put these behavios to povide an equation of the fom: E yield (T) =.74T-6.85 {fo 7 o C < T < 9 o C} Pyolysis E yield (T)=.685* *exp[-83/t] {fo 7 o C < T < 9 o C} Gasification η app. =.5T {fo 7 o C < T < 9 o C} Pyolysis η app. = *exp[-8/T] {fo 7 o C < T < 9 o C} Gasification whee, E yield is the enegy yield in kj, T is the eacto tempeatue in K and η app. is the appaent themal efficiency (dimensionless). 8

105 8 6 4 Enegy yield (kj) Pyolysis Gasification Tempeatue (K) (a) Appaant themal efficiency Pyolysis Gasification Tempeatue (K) (b) Figue IV-34. (a) Enegy yield and (b) appaent themal efficiency fo pyolysis and gasification Syngas quality The objective of pat of this study was to detemine the effect of eacto tempeatue on oveall syngas quality and to compae the quality of syngas esulting fom the pyolysis pocess with the gasification pocess. The citeia upon which the syngas quality will be detemined ae based on oveall hydogen mole faction, figue IV-35, and oveall pue fuel pecentage (mola basis), figue IV-36. The pue fuel mole faction is detemined by subtacting CO yield fom the total syngas yield. Pyolysis shows bette syngas quality at all tempeatues based on both the above citeia. It is impotant to note that the citeia hee ae only the mole faction and not the total yield of pue fuel o hydogen. Gasification yields much moe enegy than pyolysis as shown in section ( ) above. Fom the esults on the effect of tempeatue on syngas quality one can see that incease in tempeatue causes a quasi-linea incease in pue fuel pecentage in the case of gasification. On the othe hand, tempeatue has no effect on pue fuel pecentage in the case of pyolysis. The fuel pecentage fo the pyolysis expeiments is almost 99%. This value of fuel pecentage is highe than that epoted by the authos fo cadboad pyolysis, which was 77% and 8% at 8

106 eacto tempeatues of 8 and 9 o C, espectively.[] The pecentage of pue fuel fom gasification at 9 o C was 9.6%. This value is highe than that was epoted fo cadboad gasification, which was appoximately 78% fo simila expeimental conditions.[] Neithe pyolysis no gasification shows a consistent tend of hydogen mole faction yield as a function of eacto tempeatue. Howeve, pyolysis esulted in highe hydogen mole faction than gasification at all tempeatues. H mole faction (%) Oveall H mole faction Pyolysis Gasification Tempeatue ( o C) Figue IV-35. Oveall hydogen mole faction fo pyolysis and gasification Pue fuel pecentage (%) Oveall pue fuel pecentage Pyolysis Gasification Tempeatue ( o C) Figue IV-36. Oveall pue fuel pecentage in syngas fo pyolysis and gasification Rubbe gasification and pyolysis The chaacteistics of syngas evolution duing pyolysis and gasification of waste ubbe have been investigated. A semi-batch eacto was used fo the themal decomposition of the mateial unde vaious conditions of pyolysis and high tempeatue steam gasification. The esults ae epoted at two diffeent eacto tempeatues of 8 and 9 C and at constant steam gasifying agent flow ate of 7. g/min and a fixed sample mass. The chaacteistics of syngas wee evaluated in tems of syngas flow ate, hydogen flow ate, syngas yield, hydogen yield and enegy yield. Gasification esulted in 5% incease in hydogen yield as compaed to 8

107 pyolysis at 8 C. Howeve, at 9 C the incease in hydogen was moe than 7% as compaed to pyolysis. Fo pyolysis conditions, incease in eacto tempeatue fom 8 to 9 C esulted in 64% incease in hydogen yield while fo gasification conditions a 4% incease in hydogen yield was obtained. Results of syngas yield, hydogen yield and enegy yield fom the ubbe sample ae evaluated with that obtained fom woody biomass samples, namely had wood and wood chips. Rubbe gasification yielded moe enegy at the 9 C as compaed to biomass feedstock samples. Howeve, less syngas and less hydogen wee obtained fom ubbe than the biomass samples at both tempeatues Evolution of syngas and hydogen flow ates Figue IV-37 shows the evolution of syngas flow ate with time. The flow ate stats with a high value of syngas followed by a steep decease in the flow ate. This is then followed by an extended peiod of monotonically deceasing syngas flow ate. The initial high value of syngas flow ate and the subsequent steep decease in the flow ate ae mainly attibuted to the evolution of volatile matte fom the ubbe sample. This is also confimed by the similaity in flow ate tend obseved initially on the evolution of syngas flow ate fom gasification and pyolysis, compae Figues IV-38 and IV-39. The extended peiod of monotonically deceasing syngas flow ate is attibuted to the pesence of einfocing fibes in the ties. Figue IV-38 shows the evolution of syngas flow ate fom the pyolysis of ubbe tie. Note the diffeent scales in the two figues IV-37 and IV-38. The syngas flow ate stats at a high value followed by a steep decease in flow ate. The peak value of syngas flow ate at 9 o C was highe than that at 8 o C. This is attibuted to the highe heating ate of volatile matte in the sample in case of the highe eacto tempeatue. The incease in eacto tempeatue shifts the 83

108 peak value of flow ate towad shote esidence time in the eacto and is attibuted to the highe heating ate in case of the high eacto tempeatue. Figue IV-37. Evolution of syngas flow ate duing ubbe gasification Figue IV-38. Evolution of syngas flow ate duing ubbe pyolysis Figue IV-39 shows the evolution of hydogen flow ate fom the pyolysis of ubbe at the same two tempeatues of 8 and 9 o C as that examined unde gasification condition. The esults show the same tend as the syngas flow ate. The hydogen flow stats with a peak value followed by a steep decease in the flow ate. The incease in eacto tempeatue fom 8 to 9 o C inceased the peak value of hydogen fom appoximately.3g/min to.53g/min. and this significant incease of ove 5 pecent is attibuted to enhanced themal beakdown of long chains of hydocabons in the sample with incease in tempeatue. 84

109 3 Figue IV-39. Evolution of hydogen flow ate duing ubbe pyolysis Figue IV-4. Evolution of hydogen flow ate duing ubbe gasification Figue IV-4 shows the evolution of hydogen flow fom the gasification of ubbe at 8 and 9 o C. It is impotant to note the temendous incease in the peak value of hydogen associated with the incease in eacto tempeatue fom 8 to 9 o C in case of gasification. The peak value of hydogen flow inceased fom appoximately.3g/min to appoximately.3 g/min. This clealy indicates that steam hydocabons efoming eactions incease with the incease in eacto tempeatue. The hydogen flow ate cuve fo the 8 o C can be divided into two egions wheein the fist egion is dominated by hydogen evolution due to pyolysis and is chaacteized by a steep incease e in flow ate followed by steep decease in flow ate. The second egion is dominated by hydogen evolution due to cha gasification and is chaacteized by monotonically deceasing flow ate of hydogen. In contast, the hydogen evolution fo the 9 o C un case can be divided into thee egions. The fist egion is dominated by hydogen evolution due to ubbe pyolysis, the thid egion is hydogen evolution due to cha gasification and the middle egion is the hydogen flow ate due to simultaneous evolution on of hydogen fom ubbe pyolysis, steam efoming eactions 85

110 and steam cha eactions A possible eason fo the slow eaction ate, and extended duation fo cha gasification, could be fom the thid egion shown in Figue IV-4 wheein the diffusion limited cha oxidation egion might be hindeed by inceased value of ash with time in the chasteam eaction. One can see that the slope of hydogen flow ate epesents an aveage value of hydogen evolution fom egion one and egion thee Syngas, hydogen and enegy yield The effect of eacto tempeatue on oveall yield of syngas, hydogen and enegy fom gasification and pyolysis conditions ae now discussed. Figue IV-4 show the oveall yield of syngas fom gasification and pyolysis at the two eacto tempeatues of 8 and 9 o C. Gasification always yielded highe syngas as compaed to pyolysis. The incease in eacto tempeatue inceased the syngas yield fom both gasification and pyolysis. Figue IV-4 shows a diect compaison of the oveall yield of hydogen fom gasification and pyolysis at eacto tempeatues of 8 and 9 o C. Gasification esulted in significant incease in hydogen yield at both the tempeatues examined hee. Gasification esulted in 5% incease in hydogen yield as compaed to pyolysis at 8 o C. Howeve at 9 o C, the gasification esulted in moe than 7% incease as compaed to pyolysis. Incease in eacto tempeatue fom 8 to 9 o C unde pyolysis conditions esulted in 64% incease in hydogen yield. Howeve, unde gasification conditions the coesponding incease in hydogen yield was 4%. This suggests that the gasification esults in not only inceased amounts of hydogen in the syngas but also at highe gasification tempeatues the pecent incease of hydogen is highe. The esults suggest that high tempeatue conditions ae favoable fo inceased amounts of syngas yield, enegy yield and hydogen yield in the case of steam assisted 86

111 gasification. At low tempeatue eatue conditions the amounts of enegy yield is simila fom pyolysis and gasification. This is because e the gasification eactions dominate only at highe tempeatues. Fo biomass wastes the gasification ion eactions dominate at tempeatues geate than 7 o C while fo the ubbe sample the gasification eactions become impotant at tempeatues close to 9 o C. Figue IV-4. Syngas yield fom ubbe gasification and pyolysis Figue IV-4. Hydogen yield fom ubbe gasification and pyolysis Figue IV-43 shows the oveall yield of enegy fom the ubbe sample obtained fom gasification and pyolysis at eacto tempeatues of 8 and 9 o C. Gasification yielded almost the same enegy as pyolysis at a eacto tempeatue of 8 o C. This behavio is significantly diffeent fom that obseved fo a cellulosic sample, such as pape, cadboad and woodchips, at this tempeatue. Gasification always yielded moe enegy than pyolysis at 8 o C. Consequently, if enegy yield is the main focus fom a pocess it is impotant to maintain a highe eacto tempeatue (9 o C) fo the gasification of ubbe. At this tempeatue the gasification time is also shote. 87

112 Figue IV-43. Enegy yield fom ubbe gasification and pyolysis Figue IV-44. Syngas yield fom had wood, wood chips and ubbe gasification Compaison with biomass samples A compaison between ubbe gasification and woody biomass samples is now pesented with focus on syngas yield, hydogen yield and enegy yield. Figue IV-44 shows the syngas yield fom the gasification of had wood, wood chips and ubbe at two eacto tempeatues of 8 and 9 o C. The esults show that eacto tempeatue did not affect the oveall syngas yield fom any of the woody samples. On the othe hand, incease in eacto tempeatue inceased the syngas gas yield fom the ubbe sample. This indicates the impotance of eacto tempeatue in enhancing steam hydocabons efoming eactions fo the ubbe sample. Figue IV-45 shows the hydogen yield fom the gasification of had wood, wood chips and ubbe at two diffeent tempeatues of 8 and 9 o C. Incease in eacto tempeatue slightly inceased the hydogen yield in case of the woody biomass samples. Howeve, fo ubbe gasification, incease in eacto tempeatue doubled the hydogen yield. It is to be noted that 88

113 ubbe yielded less hydogen than the biomass samples fo all the cases examined hee. This is because of low hydogen to cabon atio in the ubbe as compaed to woody biomass. (g) Figue IV-45. Hydogen yield fom had wood, wood chips and ubbe gasification Figue IV-46. Enegy yield fom had wood, wood chips and ubbe gasification Figue IV-46 shows the enegy yield fom the two biomass samples and its compaison with the ubbe sample. The enegy egy yield fom all samples was almost the same at gasification tempeatue of 8 o C. Howeve, at the 9 o C ubbe yielded much moe enegy than the two biomass samples. The incease e in enegy in case of the biomass samples is attibuted to enhancement of syngas quality, namely the incease of CO mole faction. This is because the total syngas yield in case of the had wood and wood chips is not affected by the eacto tempeatue. Howeve, the enhancement in enegy yield in case of ubbe gasification is attibuted to both the quantitative and qualitative effects, see figue IV-44. Getting moe enegy fom the ubbe gasification than that fom the biomass sample indicates the geat potential of using ubbe waste as fuel in gasification systems. It also indicated that some amounts of ubbe ae favoable fo the co-gasification of wastes. Ou pevious esults on the gasification of plastics and biomass wastes suggests inceased yield of syngas and enegy fom a mixtue of biomass 89

114 and plastics than the individual gasification of eithe of the mateials. This equies futhe examination with the use of biomass-ubbe mixtues. Figue IV-47 show the mass of hydocabon yield fom the gasification of ubbe and its diect compaison with had wood and wood chips at two diffeent eacto tempeatues of 8 and 9 o C. Rubbe yielded moe hydocabons at both the tempeatues. Incease in eacto tempeatue inceased the hydocabon yield fom ubbe gasification. Howeve, the incease in hydocabons yield with the incease in tempeatue did not have the same effect on had wood and wood chips. These esults indicate that the pecentage of enegy gained fom the ubbe sample that is in the fom of hydocabons is highe than that fom the biomass samples. Figue IV-47. Hydocabons yield fom gasification of had wood, wood chips and ubbe Cadboad gasification and pyolysis Evolutionay behavio of syngas chaacteistics evolved duing the gasification of cadboad has been examined using a semi-batch eacto with steam as a gasifying agent. Evolutionay behavio of syngas chemical composition, mole factions of hydogen, CO and CH 4, as well as H /CO atio, LHV (kj/m 3 ), hydogen flow ate, and pecentagee of combustible fuel in the syngas evolved has been examined at diffeent steam flow ates with a fixed mass of 9

115 cadboad waste. The effect of steam to cabon atio as affect by the steam flow ate on oveall syngas popeties has theefoe been examined. A new paamete, coefficient of enegy gain (CEG), has been intoduced to povide infomation on the enegy gained fom the pocess. This new paamete elaboates the impotance of optimizing the sample esidence time in the eacto Evolutionay behavio of syngas chaacteistics and the effect of steam flow ate The evolutionay behavio of syngas chemical composition (mole faction of H, CO, and CH 4 ) as well as H /CO atio, LHV (kj/m 3 ) and pue fuel pecentage has been examined at steam flow ates of , 5., 6.33, 7.65 and 8.9 g/min. The majo chemical species detemined hee whee: H, CH 4, CO, CO and C n H m (consisting of mainly C H, C H 4, C H 6, C 3 H 8 and C 3 H 6 ). Pue fuel flow ate is defined hee as syngas flow ate minus CO flow ate. Pue fuel pecentage is defined as the pue fuel flow ate divided by the syngas flow ate. Figue IV-48 shows chaacteistic evolutionay behavio of selected majo gases in the syngas duing gasification (Figue IV-48a and b) and duing pyolysis at same tempeatue (Figue IV-48c). The inclusion of pyolysis esults at same tempeatue is to aid explaining the syngas behavio in the fist thee minutes of gasification and fo compaison as well. 6 6 gas composition (%) H CO CnHm CH4 CO gas composition (%) H CO CnHm CH4 CO Time (min) Time (min) (a) (b) 9

116 gas composition (%) H CO CnHm CH4 CO Time (min) (c) Figue IV-48. Evolutionay behavio of syngas chemical composition (a) gasification at steam flow ates of 4. g/min (b) gasification at steam flow ates of 5. g/min and (c) Pyolysis at same tempeatue (9 o C) The esults show that the evolutionay behavio of syngas at all the steam flow ates examined povides the same tend qualitatively. Hydogen in the syngas stats at a elatively small mole faction followed by a steep incease between the fist and the second minute into gasification. Highe gasification times beyond minutes esults in a slow and linea incease in hydogen mola atio. On the othe hand cabon monoxide mole faction stats at a high concentation then expeience a steep decease between the fist and the second minute. This is attibuted to the apid pyolysis pocess occuing at the beginning (the sample tempeatue is aised fom oom tempeatue to eacto tempeatue in a vey shot time). The incease in hydogen fomation is due to the endothemicity of hydogen fomation (fom the wate gas eaction: C + H O CO + H O + 3 KJ/Kmol). The apid incease in hydogen mole faction and apid decease in CO mole faction can be bette explained by consideing pyolysis esults of syngas chemical composition with time (see figue IV-48c). In the pyolysis esults one can see that hydogen stats with a elatively small mole faction and CO stats with a high mole 9

117 faction. Howeve, between the fist and second minute thee is a steep incease in hydogen mole faction accompanied by a steep decease in CO mole faction. This behavio is simila to that of gasification in the fist two minutes. This similaity indicates the domination of pyolysis at the beginning of gasification. On the othe hand, thee is a diffeence in mole factions behavio afte the second minute between gasification and pyolysis. In case of gasification hydogen mole faction keep on inceasing and CO mole faction keep on deceasing. In case of pyolysis, hydogen mole faction is showing a peak and CO mole faction is showing a minimum at the same time. This diffeence in behavio between gasification and pyolysis afte the thid minute is attibuted to pesence of cha gasification in case of steam gasification. The esults show a linea decease in CO mole faction and an incease in the CO mole faction afte the thid minute. This is attibuted to the effect of the wate gas shift eaction (CO + H O CO + H ) which favos the fomation of H and CO at the expense of CO. The wate gas shift eaction has this tendency because of the gadual incease of steam to sample atio with time in the batch eacto. This incease in steam to sample atio inceases the steam concentation in the eacto which acceleates the fowad eaction ate fo the wate gas shift eaction. Mole factions of hydocabons like CH 4 and C n H m ae showing a consideable mole faction at the beginning followed by a apid decease between the fist and thid minute. This behavio is consistent in both gasification and pyolysis uns. Consequently, Hydocabons yield in the gasification pocess is mainly attibuted to sample pyolysis in the initial stage of gasification. 93

118 Tempeatue ( o C) Time (Sec.) Figue IV-49. Change of sample tempeatue with time Figue IV-5 shows the evolution of H flow ate. The hydogen flow ate inceases with incease in steam flow ate. This is because of the incease in fowad eaction ate in the wate gas eaction (C + H O CO + H +3 KJ/Kmol), wate gas shift eaction (CO + H O CO + H ) and steam-hydocabons efoming eactions (C n H x + mh O nco + (m + x/) H ) and steam-ta efoming eactions. The above cuve (Figue IV-5) exhibits a peak in hydogen flow ate between the fist and the second minute. This peak is implicitly a esult of two evolutionay behavios of syngas; the fist is the incease in hydogen mola concentation with time. The second is the decease in bulk flow ate of syngas with time. The incease in hydogen mola faction tends to incease the hydogen flow ate, while the decease of bulk flow ate of syngas tends to decease the hydogen flow ate. Combination of these two behavio esults in a peak flow ate of hydogen at appoximately the second minute. In addition the evolution of H due to pyolysis also occus at elevated tempeatue in the ange of 55 8 O C and the sample is expected to each this tempeatue in about 9 seconds, see figue IV

119 Flow ate (LPM) g/min 4. g/min 5. g/min 6.33 g/min g/min 8.9 g/min Time (min) Figue IV-5. Evolutionay behavio of H flow ate at diffeent steam flow ates CO mole faction g/min 4. g/min 5. g/min 6.33 g/min g/min 8.9 g/min Time (min) Figue IV-5. Evolutionay behavio of CO mole faction at diffeent steam flow ates Figues IV-5, IV-5 and IV-53 show the evolution of CO mole faction, CH 4 mole faction and H /CO atio at diffeent steam flow ates, espectively. CO mole faction fo diffeent steam flow ates is showing same qualitative behavio. As mentioned befoe the geneal tend of CO mole faction is a high mole faction of CO initially then a steep decease between the fist and second minute, then a monotonically decease afte the thid minute. This is attibuted to faste evolution of CO than hydogen duing pyolysis. This is confimed by the tend shown in figue IV-48c. Incease in steam flow ate esulted in a decease in CO mole faction fo the same gasification timing. This is attibuted to the wate gas shift eaction. Evolution of CH 4 mole faction should be intepeted in tems of pyolysis occuing initially, since fomation of methane due to methanation eactions (C + H CH 4 ) is known to be so slow, especially if compaed to fast devolatilization of cellulose duing the pyolysis pocess. Methane mole faction shows a peak at the fist minute (Figue IV-5). This peak indicates pesence of two competitive factos. The fist facto is pesence of high volatile content in the sample initially, which deceases with time. The second facto is the continuous incease in sample tempeatue with time in the fist 9 second. The fist facto tends to favo a high 95

120 methane mole faction initially with a steep decease in mole faction with time, while the second facto tends to incease volatile matte yield, including methane, with time. Inceasing the steam flow ate didn t have a significant effect on CH 4 mole faction. This confims that methane evolution is mainly attibuted to sample pyolysis. The above intepetation can be summaized in the following equation. dvch 4 * = K( V ) CH V 4 CH 4 dt K = A exp[ E / RT] o n Whee V CH4, V * CH4 and K ae the amount of CH 4 evolved, the maximum potential amount of CH 4 and the ate constant espectively. The (V * CH4 V * CH4) tem deceases with time, while the ate constant, K, inceases with time. The evolutionay behavio of H /CO eveals the same qualitative behavio. Howeve, the incease in steam flow ate inceases the H /CO atio (Figue IV-53). This effect is moe ponounced at longe time (minutes) into gasification and not seen in the fist 9 seconds. This is because at the beginning of gasification, pyolysis takes place so that the lone hydocabon chains beaks down into small components of gaseous stuctues. Since all steam flow ates shae the same pyolysis pocess at the beginning of gasification, the H /CO atio has the same value at all steam flow ates examined duing the fist 9 seconds. The monotonically incease in H mole faction and decease of CO mole faction afte the thid minute esults fom the wate gas shift eaction (CO + H O CO + H ). 96

121 CH4 Mole faction g/min 4. g/min 5. g/min 6.33 g/min g/min 8.9 g/min Time (min) Figue IV-5. Evolutionay behavio of CH 4 mole faction at diffeent steam flow ates H/CO mola atio g/min 4. g/min 5. g/min 6.33 g/min g/min 8.9 g/min Time (min) Figue IV-53. Evolutionay behavio of H /CO atio at diffeent steam flow ates Figue IV-54 shows the evolutionay behavio of fuel (i.e., syngas CO in the syngas) at diffeent steam flow ates. High steam flow ates esults in inceased fuel pecentage at longe esidence time (o highe steam/sample atios). Figue IV-55 shows that LHV (kj/m 3 ) stats at a high value and then decays with longe esidence in the eacto. This is attibuted to high concentation of cabon monoxide at the beginning of gasification which tansfoms CO and tas to fuel-ich syngas. At late times into gasification the concentation of cabon monoxide deceases and concentation of hydogen inceases which has less heating value (in kj/m 3 ) as compaed to the heating value of cabon monoxide. On the othe hand inceasing the steam flow ate inceases the LHV (kj/m 3 ) only slightly. Howeve, fuel pecentage emains almost constant with time. Incease in the steam flow ate inceases the pue fuel pecentage slightly due to the incease in hydogen mole faction in syngas. 97

122 Fuel pecentage (%) g/min 5. g/min 6.33 g/min g/min 8.9 g/min Time (min) Figue IV-54. Evolutionay behavio of Fuel % in syngas at diffeent steam flow ates LHV (kj/m 3 ) g/min 5. g/min 6.33 g/min g/min 8.9 g/min Time (min) Figue IV-55. Evolutionay behavio of syngas LHV (kj/m 3 ) at diffeent steam flow Effect of steam flow ate on oveall syngas chaacteistics The above esults have clealy shown that the syngas popeties change with time into gasification. The oveall behavio of syngas, defined as the time integal of syngas popeties, is now pesented. Fo example, the oveall syngas yield (in lites) is the time integal of syngas flow ate (LPM) and oveall syngas heating value is the time integal of output powe (kj/min) divided by time integal of syngas flow ate (kg/min o LPM). Figues IV-56 to IV-6 show the effect of steam flow ate on syngas composition, pue fuel yield (lites) and oveall fuel pecentage in syngas (%), appaent themal efficiency and enegy yield (kj), oveall LHV (kj/m 3 ) and (kj/kg), hydogen yield (lites) and oveall hydogen to cabon monoxide mola atio (Kmol/Kmol), cabon convesion and syngas yield (kj), and coefficient of enegy gain. The majo components in the syngas wee evaluated as a function of the steam flow ate and ae pesented in figue IV-56. The esults show an incease in hydogen mole faction in the syngas with incease in the steam flow ate. On the othe hand both cabon monoxide and cabon dioxide mole faction deceases with incease in the steam flow ate. Almost constant behavio 98

123 of the methane mole faction shows that steam flow ate has insignificant effect on methane mole faction. On the othe hand incease in steam flow ate inceases the pue fuel yield fom lites to 3 lites and slightly inceases the pue fuel pecentage fom 77% to 8% which is a diect esult of steam efoming pocess fom long chains of hydocabons (C n H x + mh O nco + (m + x/) H ), see figue IV-57. The pue fuel yield inceases due to the acceleated eaction ate with incease in the steam concentation in the eacto which in tun inceases the syngas yield. Mole faction Steam flow ate (g/min) H CO CO CH4 CnHm Figue IV-56. Effect of steam flow ate on syngas composition Oveall fuel % Pue fuel yield (lites) Steam flow ate g/min Figue IV-57. Effect of steam flow ate on pue fuel yield and pue fuel % Appaent themal efficiency is defined as enegy yield fom syngas divided by enegy yield fom the solid fuel sample. The esults ae shown in figue IV-58. The appaent themal efficiency inceases with incease in the steam flow ate. This is a diect esult of the pue fuel yield incease with the incease in steam flow ate, which in tun inceases the total out powe accompanied fom the syngas. Note that the themal efficiency is descibed as an appaent themal efficiency because of two easons; fist is that pat of the hydogen geneated in the syngas is a esult of the steam biomass eaction, and the second eason is that the heat equied fo the endothemic gasification eaction is povided by an oute souce of heat supply (in this case an electic heating funace).the incease in steam flow ates inceases the LHV of the 99

124 syngas poduced based on both volume and mass basis, see fig IV-59. At high steam flow ates examined hee the LHV of the syngas obtained was about 4,kJ/m 3. This is a quite high LHV of the syngas as compaed to that epoted in the liteatue fom gasification of cellulose and pape waste Appaent themal efficiency Enegy yield (kj) Steam flow ate g/min Figue IV-58. Effect of steam flow ate on appaent themal efficiency and enegy yield LHV (kj/m3) LHV (kj/kg) Steam flow ate (g/min) Figue IV-59. Effect of steam flow ate on oveall LHV, (kj/m 3 ) and (kj/kg) The incease in oveall H /CO atio and H mola atio with incease in the steam flow ate (figue IV-6) is due to two easons; fist the acceleation of fowad eaction ate of the CO Shift eaction (CO + H O CO + H -4 kj/kmol). Second is due to the acceleation of fowad eaction ate of steam methane efoming eaction (CH 4 + H O CO + 3H + 6 MJ/kmol). On the othe hand inceasing the steam flow ate inceases the LHV on both mass and volume basis (kj/kg) and kj/m 3 ). This is due to the slight incease of pue fuel pecentage in syngas with incease in the steam flow ate.

125 Oveall H yield (lites) Oveall H/CO atio Steam flow ate (g/min) Figue IV-6. Effect of steam flow ate on H yield and oveall H /CO atio Syngas yield (Lites) Cabon convesion Steam flow ate (g/min) Figue IV-6. Effect of steam flow ate on cabon convesion (%) and syngas yield (lites) The cabon convesion is defined as the atio of cabon in syngas to the cabon initially contained in the sample. Incease in steam flow ate has a slight effect on incease in the cabon convesion. This is due to the acceleation of gasification fowad eaction ates with the inceased concentation of steam in the eacto. Both the cabon convesion and syngas yield incease with incease in steam flow ate (see figue IV-6) Coefficient of enegy gain (CEG) The coefficient of enegy gain (CEG) is defined as the atio of enegy gained by syngas to the total enegy utilized in the gasification pocess. The total enegy utilized is the time integal of the aveage powe consumed by the electic heating funace and the estimated enegy needed fo heating up the steam to the desied tempeatue. Despite the fact that moe enegy is needed fo heating up the steam fo highe steam flow ates, inceasing the steam flow ate inceased the CEG. Figue IV-6 shows the effect of steam flow ate on CEG at diffeent esidence time (.5,, 3, 5 and 7 minutes) in the eacto. The esults show that smalle esidence time esults in highe (aveage) CEG which is to be expected due to high flow ate of syngas at

126 the beginning of the pocess. While it is wothwhile to have a high CEG but at the expense of loss of total enegy yield and total hydogen yield since thee will be not enough time to extact all the available enegy in the sample, i.e., this will lowe the appaent themal efficiency and the cabon convesion. 5 CEG (%) Steam flow ate (g/min).5 min min 3 min 5 min 7 min Figue IV-6. Effect of steam flow ate on coefficient of enegy gain (CEG) at diffeent sample esidence time in the eacto Cadboad pyolysis Evolutionay behavio on the yield of vaious gaseous components duing pyolysis of cadboad has been investigated using a semi-batch eacto. Specifically, the behavio of syngas flow ate and chemical composition of syngas have been examined at vaious pyolysis tempeatues with vaiation of cadboad esidence time in the eacto. The syngas popeties detemined include evolutionay behavio of concentations of hydogen, CO, CO and hydocabons in the syngas as well as tempoal behavio of syngas flow ate. The tempoal behavio of syngas heating value, output powe, H /CO atio, pue fuel pecentage in syngas and appaent themal efficiency have also been examined. The esults showed that the eacto

127 tempeatue has distinct effect on the evolutionay behavio of syngas popeties duing pyolysis, specially the peak position of hydogen yield and H /CO mola atio Evolutionay behavio of syngas chaacteistics Mole faction Gas 8 C H CO CnHm CO CH Time (min) Figue IV-63. Evolution of syngas chemical composition at eacto tempeatue of 8 C Mole faction Gas C H CO CnHm CO CH4 3 4 Time (min) Figue IV-64. Evolution of syngas chemical composition at eacto tempeatue of C Figues IV-63 and IV-64 show a change in syngas chemical composition with esidence time of the sample in the eacto. These esults show that the tend is simila fo all gaseous species except H which showed a shap incease in mole faction at the beginning of the pocess. CO, CH 4 and C n H m show a gadual decease with time. Howeve, CO show an initial decease in mole faction followed by steady state levels at eacto tempeatue of 8 C, while at C eacto tempeatue a local minimum in mole faction followed by steady state value is obtained at longe esidence times in the eacto. Compaing figues IV-63 and IV-64 eveals an aveage incease in CO mole faction and an aveage decease in CO mole faction. This incease in CO mole faction with the coesponding decease in CO mole faction can be explained fom the kinetics study of Banyasz et al.[4] which suggests a mechanism that suppot the pesence of competing outes fo CO and CO fomation. Thei study showed that the CO fomation oute acceleates with the incease in heating ate (eacto tempeatue). Howeve CO 3

128 fomation mechanism is not affected equivalently with the incease in eacto tempeatue. Details of this mechanism ae intoduced in section syngas flow ate (LPM) Time (min) 8 C 9 C C Figue IV-65. Evolution of syngas flow ate at diffeent eacto tempeatues H flow ate (LPM) Time (min) 8 C 9 C C Figue IV-66. Evolution of H flow ate at diffeent eacto tempeatues Evolutionay behavio of syngas flow ate shows a high flow ate at the beginning of pyolysis then a steep decease in syngas flow ate between the fist and the thid minute see figues IV-65 and IV-66. The steep decease depends stongly on the nominal eacto tempeatue. In geneal highe eacto tempeatue esults in steepe decease in hydogen and syngas flow ate. Fo example; flow ate deceased fom 6 LPM to LPM in minute at eacto tempeatue of o C, while it deceased fom 6 LPM to LPM in.75 minutes at eacto tempeatue of 8 o C. In contast incease in the nominal eacto tempeatue inceases the syngas flow ate. This effect is moe evident duing the initial fist minute of pyolysis. This is due to the endothemicity of cellulose cacking pocess and the incease in heating ate with the incease in eacto tempeatue. Hydogen flow ate showed a diffeent evolutionay behavio than the syngas flow ate. Evolutionay behavio of hydogen flow ate is chaacteized by a peak value in flow ate. The location of flow ate peak is affected by the eacto tempeatue. The location of peak value of 4

129 flow ate shifts towads shote esidence time at inceased eacto tempeatue. Pesence of a local peak in hydogen flow ate is attibuted to two competing effects. The fist effect is the incease in hydogen flow ate due incease in sample tempeatue and sample heating ate. The second effect is the decease in hydogen flow ate with time due to the decease in hydogen content in the solid sample. Eventually, hydogen content in the sample eaches an asymptotic value of zeo, consequently the hydogen flow ate exhibits a deceasing tend until it eaches zeo Output powe (kj/min) Time (min) 8 C 9 C C Figue IV-67. Evolution of output powe at diffeent eacto tempeatues H/CO mola atio Time (min) Figue IV-68. Evolution of H /CO atio at diffeent eacto tempeatues 8 C 9 C C The output powe is defined hee as the syngas flow ate multiplied by the syngas heating value Output powe eleased as chemical enegy contained in the syngas was examined at vaious pyolysis tempeatues and the esults ae shown in figue IV-67. The output powe obtained show a simila behavio to that of syngas flow ate (high output powe initially then a steep decease between the fist and the second minute), as expected. Incease in eacto tempeatue inceased the conveted enegy fom the solid fuel to the gaseous fuel and hence inceased output powe. 5

130 The mola atio of hydogen to cabon monoxide shown in figue IV-68 eveal a qualitatively simila behavio of local peak occuence at some esidence time fo the thee eacto tempeatues examined hee. The peak value shifts towads lowe eaction time with incease in the eacto tempeatue. At the beginning of pyolysis pocess (fist.75 minutes) incease in eacto tempeatue inceased the atio of hydogen to cabon monoxide slightly, while this tend opposed afte.5 minutes into pyolysis. The oveall effect of eacto tempeatue on H /CO atio will be discussed futhe late on in the pape. 5 LHV (kj/kg) C 9 C C Time (min) Figue IV-69. Evolution of LHV (kj/kg) fo diffeent eacto tempeatues Incease in eacto tempeatue esults in an incease in heating value (HV) of the syngas on mass basis (kj/kg) fo esidence time less than minutes, see figue IV-69. Howeve, the data shows opposite tend afte the second minute. By compaing this data to the plot of H /CO atio data explains this behavio since the H /CO plot shows the same behavio (heating value of hydogen based on units of kj/kg is highe than that of cabon monoxide) Chaacteistics of oveall syngas yield 6

131 Mole faction Effect of eacto tempeatue on syngas composition CO H CO CH4 CnHm Reacto tempeatue (C) Figue IV-7. Effect of eacto tempeatue on syngas composition The eacto tempeatue has a significant effect on the syngas mole faction; incease in the eacto tempeatue inceased the CO mole faction and deceased the CO mole faction. Hydogen showed a slight decease in mole faction. On the othe hand, methane and highe hydocabons mole faction inceased slightly with incease in the eacto tempeatue, see figue IV H yield (lites) & Syngas yield (lites) Synags yield (lites) H yield (lites) Reacto tempeatue (C) Figue IV-7. Effect of eacto tempeatue on syngas and H yields Appaent themal efficiency & Enegy yield KJ Appaent themal efficiency 8 Enegy yield (kj) Reacto tempeatue (C) Figue IV-7. Effect of eacto tempeatue Enegy yield (kj) and appaent themal efficiency The oveall syngas yield is defined as the time integal of syngas flow ate. Incease in the eacto tempeatue inceased the syngas yield, see figue IV-7. This is due to the effective 7

132 beakdown of long chains of hydocabons in cadboad and ta into smalle fagments of gaseous hydocabons with incease in the eacto tempeatue. Similaly, incease in the eacto tempeatue inceased the hydogen yield fom the sample. Incease in the eacto tempeatue assists in cacking of ta duing the seconday ta cacking eaction which esults in highe hydogen yield, see figue IV-7. Appaent themal efficiency is defined as total enegy yield fom syngas divided by the enegy povided by the solid fuel combustion. Figue IV-7 shows that the appaent themal inceases with incease in the eacto tempeatue and is fom the diect esult of inceased enegy yield with incease in the eacto tempeatue. Oveall hydogen to cabon monoxide mola atio deceased fom.54 to.46 with incease in the eacto tempeatue, see figue IV-73. This is due to the incease in CO concentation at the expense of deceased CO as mentioned befoe. Incease in the eacto tempeatue deceased the ta yields, see figue IV-73. This is because highe tempeatues pomote the cacking of ta via seconday eactions to smalle fagments of gaseous poducts Effect of tempeatue on Ta yield & H/CO atio Oveall H/CO atio Ta yield (gams) Tempeatue C Figue IV-73. Effect of eacto tempeatue on oveall H /CO atio and ta yield (gams) 8

133 Banyasz et al.[4] investigated gas evolution and mechanism of cellulose pyolysis in a two heating zone pyolysis system. The two heating zone expeiments indicated that a lage potion of CO is fomed fom the decomposition of pimay volatile poducts (aldehydes) duing seconday eactions. Howeve CO is fomed at ealy stages of cellulose pyolysis duing the pimay eactions. In the two heating zone expeiment, CO fomation was found to be highly dependent on the tempeatue set at the second zone, while CO was not affected by additional heating, thus indicating futhe decomposition of vapo poducts to poduce CO [4, 3]. The behavio of CO is adequately descibed by a single fist ode eaction. The effect of CO fomation equies the incopoation of a competing eaction step into the mechanism. At high tempeatues and fast heating ates k >k (see figue IV-74), so that at faste heating ate takes less time fo convesion to CO while at low tempeatue the competing eaction pefeentially convets the pecuso to the competing poducts (CO and levoglucosan). Theefoe at high heating ates CO is pefeable since k is lage than k at high tempeatues and vice vesa. Levoglucosan/ta is the pobable pedominant poduct of pathway () in the mechanism given below. Pathway one is a majo pyolysis pathway fo cellulose poducing intemediates that undego futhe eactions yielding fomaldehyde, CO and othe gases fomed duing seconday cacking eaction of intemediates geneated in pathway one[4]. 9

134 Hydoxyacetaldehyde (Fast) k Intemediate(s) fomaldehyde, CO Pecuso k Competing Poduct(s), CO Figue IV-74. Cellulose pyolysis mechanism [4] Antal et al. [4] have povided a eview on the cuent state of knowledge on the kinetics of cellulose pyolysis in which they concluded that two majo pathways ae now ecognized to be active duing cellulose pyolysis. The path leading to the fomation of levoglucosan is a elatively stable poduct while the second yields in glycolaldehyde fomation. Highe heating ates and tempeatues favo the glycolaldehyde fomation pathway. This as well as the conclusion fom Banyasz et al. [4] studies confims that the intemediate foming the fomaldehyde and CO is glycolaldehyde and the competing poduct in pathway () is levoglucosan (ta) and CO Mixtue gasification Gasification of polyethylene (PE) and woodchips (WC) mixtues have been investigated in a semi-batch eacto, using high tempeatue steam as the gasifying agent. The eacto tempeatue was maintained at 9 o C. The atio of PE to WC was vaied fom % to % in % intevals. Chaacteistics of syngas wee evaluated based on the yield of syngas, hydogen,

135 enegy, ethylene, total hydocabons and appaent themal efficiency of the pocess. Results show that popeties of syngas evolved duing gasification of PE-WC blends cannot be detemined fom the weighted aveage syngas popeties obtained fom sepaate gasification of WC and PE. Supeio esults in tems of syngas yield, hydogen yield, total hydocabons yield, enegy yield and appaent themal efficiency fom PE-WC blends wee obtained as compaed to expected weighed aveage yields fom gasification of individual components. Results confim synegistic inteaction between PE and WC duing high tempeatue steam gasification of these mixtues. These esults also povide the impotance of mixing two o moe compounds on the pefomance of steam gasification of wastes. Pesented in the fist pat of this section is the evolutionay behavio of syngas popeties (syngas flow ate, hydogen flow ate, output powe, cabon flow ate, ethylene flow ate and total hydocabons flow ate) as affected by PE to WC atio. The second pat pesents esults on the oveall yield of syngas popeties (syngas yield, hydogen yield, enegy yield, appaent themal efficiency, ethylene yield, total hydocabons yield and cabon yield) Evolutionay behavio of syngas popeties Figues IV-75a and IV-75b show the evolution of syngas flow ate fom to 5 minutes and fom 5 to 5 minutes, espectively, as affected by diffeent pecentages of PE in the feed stock. Syngas flow ate stats with a high value, fom zeo to thee minutes, followed by a steep decease in flow ate, fom minute to minute 5, followed by an extended peiod of low flow ate (notice the diffeence in X and Y axis scale between figue IV-75a and IV-75b. The eason fo high syngas flow ate, initially is that the sample was initially at oom tempeatue then injected to the eacto which is at an elevated tempeatue of 9 o C. Consequently the sample is subjected to high heating ate. Besides, the sample initially has its % volatile content as well.

136 Because of the high heating ate and high volatile content, initially, the syngas flow ate stats with a high value. Afte few minutes the sample becomes in equilibium with the eacto tempeatue and a most of the volatile matte has evolved duing the initial stage of the pocess, esulting in a steep decease in syngas flow ate. Syngas flow ate (g/min) 5 5 PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Syngas flow ate (g/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Time (min) Time (min) (a) (b) Figue IV-75. Evolution of syngas flow ate (a) fom to 5 minutes and (b) fom 5 to 5 minutes The incease in PE pecentage tends to decease the maximum value of syngas flow ate. Except fo the % PE test conditions, a decease in the peak value of syngas flow ate is obseved. In contast to the effect of PE% on syngas flow ate, the peak value of hydogen flow ate inceased with incease in the amounts of PE% pesent in the feed stock, see figue IV-76a. The evolution of hydogen flow ate cuve is also chaacteized by the initial high value of flow ate, followed by an extended peiod of lowe flow ate, see figue IV-76b. In figue IV-76b, examination of the time peiod fom minute 7 to minute 6, one can notice a lowe hydogen flow ate fom the % PE un as compaed to the othe woodchips (WC) containing test

137 sample. This is attibuted to the cha - steam gasification eaction (C + H O CO +H ), which takes place in case of WC cha gasification and absent in case of PE. H flow ate (g/min).5.5 PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% H flow ate (g/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Time (min) Time (min) Figue IV-76. Evolution of hydogen flow ate (a) fom to 5 minutes and (b) fom 5 to 5 minutes Figue IV-77a and IV-77b shows the evolution of ethylene flow ate and total hydocabons flow ate, including ethylene, espectively, fo diffeent pecentages of PE in WC in the feed stock sample. As the monome foming the PE plastic, ethylene is an indicato of PE themal degadation. Evolution of hydocabons, including ethylene, did not extend fo moe than five minutes in the gasification pocess. Evolution of hydocabons is mainly attibuted to themal beakdown of long hydocabons chains in both PE and WC. Consequently, one can conclude that the syngas and hydogen flow afte the fifth minute is mainly attibuted to gasification eactions and steam hydocabons efoming eactions. 3

138 Ethylene flow ate (g/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% CnHm flow ate (g/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% 4 6 Time (min) 4 6 Time (min) (a) Figue IV-77. Evolution of (a) ethylene flow ate and (b) total hydocabons flow ate (b) Figues IV-78a and IV-78b show the evolution of output powe fom to 5 minutes and 5 to 5 minutes, espectively, fo diffeent pecentages of PE in the feed stock sample. One can see fom the output powe evolution cuve that most of the enegy is being eleased in the fist fou to five minutes fom the stat of gasification. The incease in PE pecentage tends to incease the peak value of output powe. Figues IV-79a and IV-79b show the evolution of cabon flow ate fom to 5 minutes and 5 to 5 minutes. Cabon flow ate was calculated based on cabon content in the syngas. No appaent effect of PE pecentage in the feed stock sample on the peak value of cabon flow ate could be obseved. 4

139 Output powe (kj/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Output powe (kj/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Time (min) Time (min) (a) Figue IV-78. Evolution of (a) output powe and (b) cabon flow ate (b) Cabon flow ate (g/min) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Cabon flow ate (g/min).5.5 PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% Time (min) Time (min) Figue IV-79. Evolution of cabon flow ate (a) fom to 5 minutes and (b) fom 5 to 5 minutes Oveall yield of syngas popeties Figue IV-8 shows the syngas yield and hydogen yield fo diffeent PE to WC atios, vaying fom % PE to % PE in the feed sample. A peak value of syngas yield is shown at 5

140 PE pecentage of appoximately 8%. The syngas yield fom sepaate gasification of PE o WC yielded less syngas than fo any blend of thei mixtues. Solid line in the figue epesents the weighted aveage value of syngas yield based on sepaate syngas yield fom the gasification of PE and WC. Same behavio is obseved fo the hydogen yield. Results show a peak value of oveall hydogen yield at PE pecentage value of 8%. The solid line in the figue also epesents the weighted aveage yield. Hydogen yield fom the mixed samples was highe than that fom the theoetical weighted aveage yield. Figue IV-8 shows the yield of total hydocabons and ethylene yield at diffeent PE to WC atios, fom % PE to % PE. The incease in PE pecentage inceased both hydocabon yield and ethylene yield, except fo the %PE expeiment. The maximum yields of ethylene and hydocabons wee obtained at the 8%PE expeiment. This indicates the synegistic effect of co-gasification of PE and WC. The incease did not follow the linea tend of weighted aveage yield fom sepaate gasification of PE and WC. Blends of PE and WC always yielded highe values of hydocabons and ethylene. Syngas yield (g) Syngas yield.5 Hydogen yield PE% (g/g) Figue IV-8. Syngas yield (left axis) and hydogen yield (ight axis) 4 3 H yield (g) Ethylene yield (g) Ethylene yield Total hydocabons yield PE% (g/g) CnHm (g) Figue IV-8. Total hydocabons yield (left axis) and ethylene yield (ight axis) 6

141 Figue IV-8 shows the enegy yield and appaent themal efficiency fo diffeent PE to WC atios in the feed stock. Following the tend of pevious popeties, enegy yield and appaent themal efficiency of PE-WC blends showed supeio esults as compaed to weighted aveage values, epesented by the solid line in the figue. Peak values of enegy yield and appaent themal efficiency wee obtained at PE pecentage of appoximately 8%. The PE is expected to yield moe enegy than the WC because of its highe heating value. Howeve, adding small amount of WC, %, esulted in highe enegy yield than that obtained fom the % PE sample conditions. This means that the pesence of a small pecent of WC temendously inceases the enegy gain fom the PE consideing the fact that PE (LHV: 4.98 MJ/kg) was eplaced by high heating value of WC (LHV:.3 MJ/kg). Figue IV-83 shows the cabon yield in gas phase fo diffeent PE to WC atios. The cabon yield was calculated based on the cabon content in the syngas. Highe yield of cabon fom PE-WC blends indicates the pesence of steam-ta efoming eactions. The solid line in the figue epesents the cabon content in the sample. The cabon content in the syngas is close to the theoetical maximum fo the mixed samples expeiments than that fo the single component samples. Based on the esults obtained on the oveall yield of syngas popeties, it can be confimed that thee is a synegistic inteaction between PE and WC duing gasification of the sample feed stock mixtue. Supeio esults in tems of syngas yield, hydogen yield, total hydocabons yield and enegy yield fom PE-WC blends wee obtained as compaed to the expected weighed aveage yield. A possible inteaction mechanism is that PE acts as a hydogen dono to adicals geneated fom WC pyolysis, esulting in stabilizing those adicals and the poduction of highe yield of total hydocabons than that expected by the weighted aveage 7

142 yield. Enhancement in HCs was ~ 4 gams at 8% PE. Howeve the enhancement in syngas yield was ~ 8 gams at the 8% PE un. This means that thee is ~ 4 gams incease in CO, H and CO which is not explained by the hydogen dono mechanism. In ode to explain the enhancement in CO, H and CO yield, the aangement of WC with espect to PE should be consideed. A possible volatiles-cha inteaction mechanism is shown in figue IV-84. PE was always located upsteam fom WC fo all expeiments fo consistency. WC cha might have played a ole in adsobing volatile matte evolved fom PE, and in tun, pomoted steamhydocabons efoming eaction, to esult in excess H, CO and CO than what expected by the weighted aveage yield alone, see figue IV-85. Pomotion of the steam-hydocabons efoming eactions, is also evidenced fom the close cabon yield values to the theoetical maximum in case of mixed samples data points, see figue IV-83. Enegy yield (kj) Enegy yield Appaent themal efficiency PE% (g/g) Figue IV-8. Enegy yield (left axis) and appaent themal efficiency (ight axis) Appaent themal efficiency (-) Cabon yield (g) PE% (g/g) Figue IV-83. Oveall cabon yield (based on cabon content in the syngas) 8

143 Figue IV-84. Aangement of PE and WC sample in the eacto PE Volatile HCs Adsoption WC cha Steam-HCs efoming H + CO Figue IV-85. Possible volatiles-cha inteaction mechanism Cumulative yield of syngas, hydogen and enegy Pesented in this section is the cumulative behavio of main syngas popeties; syngas cumulative yield, hydogen cumulative yield and enegy cumulative yield. The cumulative behavio is vey impotant in quantifying the yield-time elationship. The expeiment might last fo moe than an hou befoe eaching an absolute zeo value of syngas flow ate. On the othe hand, 99% of the syngas might have evolved in a matte of minutes. The cumulative behavio might help in detemining the equied esidence time and consequently gasifie size fo a cetain convesion degee of syngas, hydogen o enegy. Figue IV-86 show the cumulative yield of syngas fo the mixtues investigated. All plots coincide on each othe duing the initial stage, to nd minute. Because of the high value of syngas flow ate initially, a steep slope of cumulative syngas yield is obtained. The steep slope gadually gets less steep until it eaches an asymptotic value appoaching zeo. This is attibuted 9

144 to low flow ate values afte the th minute. The hoizontal solid lines epesent the 99% syngas yield value fo each mixtue condition. The vetical lines epesent the time at which 99% of the syngas has been evolved, see figue IV-89. Although a syngas flow was detected even afte 4 minutes fom the beginning of expeiments, 99% of the syngas has evolved in less than minutes. Figue IV-87 shows the cumulative yield of hydogen fo all mixtues. 99% of hydogen has evolved in the time duation ange of to 9 minutes. The solid hoizontal and vetical lines ae the 99% hydogen yield mak and the time at which 99% of hydogen has been evolved. Fo the woodchips containing expeiments, the cumulative hydogen yield is following the same tend; a steep slope initially followed by a gadual decease in slop, followed by an asymptotic slope value to zeo. The % PE un is showing a fast evolution of hydogen in the fist minutes, consequently a shote peiod of 99% hydogen yield has esulted. Cumulative syngas yield (g) PE% WC% PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% 3 4 Time (min) Cumulative hydogen yield (g) PE% WC% PE% WC8% PE4% WC6% PE6% WC4%.5 PE8% WC% PE% WC% 3 4 Time (min) Figue IV-86. Cumulative syngas yield Figue IV-87. Cumulative hydogen yield

145 Figue IV-88 shows the cumulative enegy yield of all expeiments. 99% of the enegy has evolved aound the 5 th minute. 99% of the enegy has evolved in less than minutes in case of % PE un. One can see a temendous enhancement in enegy yield of the mixed samples as compaed to that of the pue samples. Cumulative E yield (kj) PE% WC% 4 PE% WC8% PE4% WC6% PE6% WC4% PE8% WC% PE% WC% 3 4 Time (min) Time of 99% syngas convesion(min) PE% (g/g) Figue IV-88. Cumulative enegy yield Figue IV-89. Time of 99% syngas convesion 4.. Kinetics of syngas evolution fom cha gasification and pyolysis 4... Gasification kinetics of pape cha The kinetics of cha gasification is usually detemined by monitoing the deteioation of mass of cha with time using a Themogavimetic analyze (TGA). At low eacto tempeatues (< 9 o C) cha gasification is assumed to be chemically contolled and ate constant is calculated based on a single step fist ode eaction, dm =, whee, m, is the sample mass at time t cha and cha is the eaction ate. Afte the end of the pyolysis pocess the syngas yield is totally m dt

146 attibuted to the cha gasification. It takes on the ode of 8 to minutes fo the pyolysis pocess to finish, which is enough time fo the sample to each the eacto tempeatue. This means that the cha gasification pocess is accomplished unde isothemal conditions. Based on the assumptions that the cha gasification is chemically contolled and the eaction occus isothemally, integation of the fist ode eaction ate yields the following expession Kt = ln( X ), whee K is the ate constant and X is the convesion. In the pesent expeiment thee was no possibility to monito the mass deteioation in the eacto with time. Howeve, afte making some assumptions, it is possible to oughly estimate the mass deteioation in the eacto based on the syngas flow ate and its cabon content. These assumptions ae: the cha leftove afte the pyolysis pocess is mostly cabon and the steam cha eaction yields only gas phase poducts. Now, analogues to the fist ode eaction assumed above one can detemine the kinetics of cabon convesion by the same way and unde the same conditions. The ate constant is detemined fom figue IV-9 by calculating the slope of ln(- X) vesus time. The activation enegy and the pe-exponential facto ae detemined fom fig IV- 9, ln(k) vesus /T, whee T is the isothemal tempeatue. The activation enegy obtained is this wok was 49 kj/mol, which is compaable to epoted values in the liteatue fo cabonaceous mateials such as biomass chas [3] (appaent activation enegy fo the steam-cha gasification anges fom 3 to 7 kj/mol).

147 -ln(-x) y =.69x +. 9 C 8 C 7 C y =.6x -.4 y =.3x Time (s) ln(k) y = x /T (/K) Figue IV-9. ln(-x) vesus time Figue IV-9. ln(k) o ln() vesus /T 4...Gasification kinetics of food wastes cha Figue IV-9 shows the pogess of the food waste sample duing pyolysis and cha gasification and coesponding time duation fo each pocess. The cha gasification eaction is slowest in the oveall gasification pocess. So, it is impotant to quantify how fast this pocess is. The main constituent of cha is cabon and main eaction in the cha gasification pocess is the wate gas eaction (C+H O => CO + H ). The cabon-monoxide may undego a wate gas shift eaction CO + H O CO + H ). Theefoe, the cabon eactivity in the cha can be infeed fom the mola flow ate of cabon-monoxide and cabon dioxide. A mass spectomete has been used to calculate the CO and CO flow ate. Fom the CO and CO flow ate, the total cabon yield and cabon convesion histoy can be detemined. Figue IV-93 shows the change of cabon mola flow ate with time fo tempeatues 75, 8, 85 and 9 o C. One can see that highe the tempeatue shote the cha gasification peiod and highe the cabon flow ate. Figue IV-94 shows the cabon convesion vesus time at tempeatues of 75, 8, 85 and 9 o C. The plots ae chaacteized by an initial constant slop. Results show that lowe the tempeatue is longe the convesion time. 3

148 Food waste (Simulated as dog food) (~35 gams) Pyolysis (~5 9 o C) Cha + Ash (~.75%) Cha gasification (~35 9 o C) Ash (~5.75%) Gasification (~38 9 o C) Figue IV-9. Pogess of food waste sample though pyolysis and gasification dm/dt (moles/min).5e-.e-.5e-.e- 5.E-.E Time (min) 9 C 8 C 75 C 85 C 5 8 Figue IV-93. Cabon flow ate vesus Cabon convesion C 85 C 8 C 75 C Time (min) Figue IV-94. Convesion vesus time time fo tempeatues 75, 8, 85 and fo tempeatues 75, 8, 85 and 9 o C dm Cabon eactivity was defined as cha = -. Whee, m is the mass at time (t). Histoy m dt of cabon mass inside the eacto was calculated fom the cabon flow ate histoy. While, dm is dt the cabon mass flow ate measued by the mass spectomete. Figue IV-95 shows the change of cabon eactivity with convesion. Cabon eactivity inceases monotonically with convesion until convesion value of.7 followed by a steepe incease in eactivity. The steepness at lowe tempeatue plots may not be obseved because of the values scale. The food waste cha contains ~7.7% ash, most of which is salt. The inoganic components in cha ae the main 4