NITROGEN OXIDES EMISSION CONTROL THROUGH REBURNING WITH BIOMASS IN COAL-FIRED POWER PLANTS. A Thesis SENTHILVASAN ARUMUGAM

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1 NITROGEN OXIDES EMISSION CONTROL THROUGH REBURNING WITH BIOMASS IN COAL-FIRED POWER PLANTS A Thei by SENTHILVASAN ARUMUGAM Submitted to the Office of Graduate Studie Texa A&M Univerity in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE December 004 Major Subject: Mechanical Engineering

2 NITROGEN OXIDES EMISSION CONTROL THROUGH REBURNING WITH BIOMASS IN COAL-FIRED POWER PLANTS A Thei by SENTHILVASAN ARUMUGAM Approved a to tyle and content by: Submitted to Texa A&M Univerity in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE Kalyan Annamalai (Chair of Committee) Jerald A. Caton (Member) John M. Sweeten (Member) Denni O Neal (Head of Department) December 004 Major Subject: Mechanical Engineering

3 iii ABSTRACT Nitrogen Oxide Emiion Control Through Reburning with Bioma in Coal-Fired Power Plant. (December 004) Senthilvaan Arumugam, B.E., Bharathidaan Univerity Chair of Adviory Committee: Dr. Kalyan Annamalai Oxide of nitrogen from coal-fired power tation are conidered to be major pollutant, and there i increaing concern for regulating air quality and offetting the emiion generated from the ue of energy. Reburning i an in-furnace, combution control technology for NOx reduction. Another environmental iue that need to be addreed i the rapidly growing feedlot indutry in the United State. The production of bioma from one or more animal pecie i in exce of what can afely be applied to farmland in accordance with nutrient management plan and tockpiled wate poe economic and environmental liabilitie. In the preent tudy, the feaibility of uing bioma a a reburn fuel in exiting coal-fired power plant i conidered. It i expected to utilize bioma a a low-cot, ubtitute fuel and an agent to control emiion. The ucceful development of thi technology will create environment-friendly, low cot fuel ource for the power indutry, provide mean for an alternate method of dipoal of bioma, and generate a poible revenue ource for feedlot operator. In the preent tudy, the effect of coal, cattle manure or feedlot bioma, and blend of bioma with coal on the ability to reduce NOx were invetigated in the Texa A&M Univerity 9.3

4 iv kw (00,000 Btu/h) reburning facility. The facility ued a mixture of propane and ammonia to generate the 600 ppm NOx in the primary zone. The reburn fuel wa injected uing air. The toichiometry teted were.00 to.0 in the reburn zone. Two type of injector, circular jet and fan pray injector, which produce different type of mixing within the reburn zone, were tudied to find their effect on NOx emiion reduction. The flat pray injector performed better in all cae. With the injection of bioma a reburn fuel with circular jet injector the maximum NOx reduction wa 9.9 % and with flat pray injector wa 6. %. The mixing time wa etimated in model et up a 936 and 407 m. The maximum NOx reduction oberved with coal wa 4.4 % and with bioma it wa 6. % and the reduction with blend lay between that of coal and bioma.

5 v ACKNOWLEDGEMENTS Thi work wa upported by United State Department of Agriculture through The National Center for Manure and Animal Wate Management, North Carolina. With reverence and repect, I expre my incere thank with profound gratitude to Dr. Kalyan Annamalai for providing valuable advice and guidance during thi work. I alo expre my gratitude by acknowledging Dr. Jerald A Caton and Dr. John M. Sweeten who erved on my committee. I expre my thank to Dr. Cady Engler who ubtituted for Dr. Sweeten during my thei defene. I am alo greatly indebted to my friend Soyuz Priyadaran, Vittilapuram Kannan, and Tuan Doan for their upport and encouragement during the experiment.

6 vi TABLE OF CONTENTS Page ABSTRACT...iii ACKNOWLEDGEMENTS...v TABLE OF CONTENTS...vi LIST OF FIGURES...ix LIST OF TABLES...x CHAPTER I INTRODUCTION... Environmental and health effect of NOx emiion... Theorie of NOx formation in combution ytem...4 Control of NOx emiion...6 Bioma...8 II LITERATURE REVIEW...0 Parameter that influence NOx reduction...0 Reburning with different fuel...0 Mixing effect in reburning... III OBJECTIVE AND TASKS...3 IV EXPERIMENTAL FACILITY...4 Furnace...4 Primary NOx generation ytem...9 Reburn fuel upply ytem...9 Exhaut and ah ytem...3 Diagnotic ytem...3

7 vii CHAPTER Page V EXPERIMENTAL PROCEDURE...6 Fuel and furnace preparation...6 Calibrating the fuel feeder...7 Preheating the air and furnace...7 Etablihing the primary zone combution...8 Setting the required primary zone NOx...9 Reburning...9 Sytem hut off...9 Error analyi...30 VI RESULTS AND DISCUSSION...3 Initial trial...3 Fuel analyi...33 Mixing time cale...37 Reburning...43 Effect of reburn air dilution on NOx reduction...45 Effect of reburn injector type on reburn zone temperature...47 Effect of reburn injector type on exit zone temperature...49 Effect of fuel type on NOx reduction...5 Effect of injector type on NOx reduction...58 Effect of ah content of bioma on NOx reduction...63 VII CONCLUSIONS...66 VIII FUTURE WORK...68 REFERENCES...69 APPENDIX A...73 APPENDIX B...76 APPENDIX C...78 APPENDIX D...84

8 viii Page VITA...87

9 ix LIST OF FIGURES Page Fig. IV.: Schematic ketch of the TAMU 9.3 kw (00,000 Btu/h) reburning facility 6 Fig. IV.: Cro ection of the furnace module...7 Fig. IV.3: Sketch depicting the dimenion of the furnace...8 Fig. IV.4: Apiration of ambient air through the venturi eductor... Fig. IV.5: Reburn injector and their cro ection... Fig. IV.6: Blower air upply calibration curve for two different orifice plate [3]...5 Fig. VI.: NO generation from co-firing for different fuel [33]...33 Fig. VI.: Size ditribution of coal and bioma...36 Fig. VI.3: Schematic of the jet in cro flow invere mixing model...39 Fig. VI.4: Schematic ketch of the model facility for mixing time experiment...4 Fig. VI.5: Mixing time correlation...4 Fig. VI.6: NOx reduction due to the dilution with reburn air upply...47 Fig. VI.7: Temperature at reburn zone and exit zone for circular jet injector...50 Fig. VI.8: Temperature at reburn zone and exit zone for flat pray injector...5 Fig. VI.9: Bae cae NOx reduction with coal and circular jet injector...5 Fig. VI.0: NOx reduction with bioma a reburn fuel compared to bae cae coal...54 Fig. VI.: NOx reduction with blend a reburn fuel compared to coal...55 Fig. VI.: NOx reduction with 90-0 blend a reburn fuel compared to coal...56 Fig. VI.3: NOx reduction with circular injector for variou reburn fuel...57 Fig. VI.4: NOx reduction with circular and flat injector for coal reburning...59 Fig. VI.5: NOx reduction with flat injector for bioma reburning...60 Fig. VI.6: NOx reduction with flat injector for blend reburning...6 Fig. VI.7: NOx reduction with flat injector for 90-0 blend reburning...6 Fig. VI.8: NOx reduction with flat pray injector for variou reburn fuel...63 Fig. VI.9: NOx reduction with low and high ah bioma [3]...65 Fig. D.: Schematic of the mixing proce in an eductor...84

10 x LIST OF TABLES Page Table V.: Intrument error...3 Table V.: Error in meaurement...3 Table VI.: Comparion of variou fuel ued for reburning on an a received bai...34 Table VI.: Reburning parametric matrix...44 Table VI.3: Reburning experimental parameter...45 Table VI.4: Comparion of low and high ah bioma propertie...64

11 CHAPTER I INTRODUCTION Power generation i a ignificant ource of pollution that contribute toward the impairment of human health and the environment. The prevailing pattern of wind lead to intertate and long range tranport of emiion that play a ignificant role in thee problem whereby emiion are no longer conidered a point ource problem. The International Energy Outlook project growth in coal ue for power generation at an average annual rate of.5 % (on a tonnage bai) between 00 and 05 []. The combution of coal produce everal type of emiion that adverely affect health and environment. Oxide of nitrogen from coal-fired power tation are conidered to be major pollutant, and there i increaing concern for regulating air quality and offetting emiion generated from the ue of energy. NOx, a generic term for the variou oxide of nitrogen like nitrogen dioxide (NO ), nitric oxide (NO) and nitrou oxide (N O), i a key iue due to it impact on the environment and health. The Intergovernmental Panel on Climate Change pecial report on the emiion cenario rank the United State at thirteenth among the countrie of the world in the total NOx emiion per populated area [] and the Organization for Economic Cooperation and Development rank the United State third in the NOx generated per capita [3]. The United State generate.9 thouand metric ton of NOx per quare kilometer of populated land area and 80 kg weight of NOx per capita. The weighted world average tand at.79 thouand metric ton of NOx per populated land area and Thi thei follow the tyle of Combution and Flame.

12 4. kg weight of NOx per capita. NOx emiion cot ociety billion of dollar annually from illne and death and a uite of year-round environmental problem. Environmental and health effect of NOx emiion The Environmental Protection Agency, United State of America (EPA) ha identified NOx a a pollutant that impact health and environment. Significant concern identified with NOx emiion are generation of ground level ozone, contribution toward acid rain and global warming, production of toxic chemical and fine particle in the atmophere, deterioration of water quality, and impairment of viibility [4]. NOx react with Volatile Organic Compound (VOC) in the preence of unlight to form ground-level ozone, a major component of mog in citie and many rural area. Although naturally occurring ozone in the tratophere provide a protective layer above the earth hielding inhabitant from the hazardou effect of ultraviolet ray from the un, ground-level ozone i detrimental. It irritate the eye, exacerbate athma, lead to chronic lung damage, and increae the uceptibility of young children and the elderly to repiratory infection. It i our mot widepread and intractable urban air pollution problem. Ozone alo reduce agricultural production and the growth rate of tree by impairing their ability to produce and tore food. NOx i a precuror to the formation of acid rain. The interaction of NOx with certain ubtance preent in the atmophere produce acid that may fall to the earth in variou form like rain, fog, or now. Acid rain acidifie enitive oil and water where it fall, killing plant, fih, and the animal that depend on them. Acid rain alo

13 3 caue property damage through accelerated decay of material, paint, building, and cultural artifact uch a hitorical monument, and culpture. Fine particle are formed in the atmophere by the converion of NOx emiion when they react with ammonia, water vapor and other compound. Thee mall particle penetrate into the enitive part of the lung when inhaled and can caue or woren repiratory dieae and aggravate exiting heart ailment. They alo catter light and create hazy condition, decreaing viibility and contributing to a regional haze. Ditinct haze that identify particular pollutant are grey for lead, yellow for ulfur, and brown for nitrogen oxide. Additionally NOx react readily with common organic compound to produce toxic chemical like nitrate radical that trigger biological mutation. Exceive amount of nitrogen in coatal water from atmopheric depoition are thought to be a contributor to nitrification, i.e., over fertilization of wet land and bay. Thi lead to harmful algal bloom, uch a the red tide which upet the balance of nutrient between aquatic plant and animal, killing million of fih each year. A contituent of NOx, nitrou oxide, i a greenhoue ga which contribute to global warming, the gradual increae in the temperature of the earth due to the heattrapping ability of thee gae. The accelerated global warming due to the increaed concentration of thee gae may lead to dratic climatic change. NOx ha alo been found to have an indirect effect on radiative forcing [5]. Radiative forcing i the change in the balance between the radiation entering and leaving the earth atmophere. A poitive radiative forcing tend on an average to warm the earth urface and a negative radiative forcing tend to cool the earth urface.

14 4 Increaed concentration of NOx lead to a decreaed lifetime of CH 4 and HFC via OH and thereby reduce the radiative forcing. The increae in ozone concentration due to the preence of NOx increae the radiative forcing. The radiative forcing i reduced when the NOx emiion increae the N depoition through fertilization and increaed CO uptake. Theorie of NOx formation in combution ytem The combution of fuel and air reult in converion of nitrogen preent in the air or the fuel into variou oxide of nitrogen like nitric oxide (NO), nitrou oxide (N O), and nitrogen dioxide (NO ) that are collectively given a generic name, NOx. The formation of NOx can occur in the pre-combution, combution, and pot-flame region. It i worth noting that NOx can be produced in iolated ection of the flame, and it i not unuual for over 80 % of the combined NOx to be produced in only 0 % of the flame volume. The NO to NOx ratio i approximately 0. in typical methane/air flame and 0.9 in low temperature, low-nox flame with high HNO concentration. The NO formed i very enitive to the fluid dynamic in the flame zone and it formation from NO tend to occur in region where rapid cooling take place (mixing region of hot gae with inlet air). The meaurement proce i enitive to meaurement technique a NO can form inide the ampling probe. N O contribute to the greenhoue effect in the tropophere and participate in ozone depletion in the tratophere. N O emiion are not ignificant in coal combution ytem a they rapidly react with H and OH radical to form N. They

15 5 urvive only in the hotter, fuel-rich, flame region and are detroyed downtream. Peak N O in coal ytem i le than % of peak NO. N O formation in the pot-flame zone (75 K-55 K) i negligible; wherea, it form in fluidized-bed combution due to lower operating temperature. A N O i table only in the high temperature region of the flame and readily convert to N, NOx i generally conidered to be compoed of NO and NO. There are three identified homogeneou ga phae reaction pathway for the formation of NO known a thermal, prompt, and fuel NO mechanim [6, 7]. Thermal NO originate from the nitrogen preent in the air upplied for combution under fuellean condition. The formation of thermal NO ha a trong dependence on temperature, reidence time, and a linear dependence on the concentration of oxygen atom. The generation of thermal NO i decribed by the widely accepted two-tep Zeldovich mechanim given below. N O NO N (I.) N O NO O (I.) In the cae of fuel-rich flame where the OH radical are preent in higher concentration than atomic hydrogen or oxygen, the two-tep mechanim under-predict NO generated, o a third elementary tep that conider the effect of OH radical i ued a given by the extended Zeldovich mechanim. N OH NO H (I.3)

16 6 Prompt NO i formed in fuel-rich environment with hort flame-reidence time; formation being initiated through variou hydrocarbon fuel fragment like CH and CH. The prompt NO formation i decribed by the Fennimore reaction given below: N CH x HCN N (I.4) The cyano pecie react further to form NO though the following reaction. HCN O NO (I.5) The amount of prompt NO i proportional to the number of carbon atom preent in the molecule of the hydrocarbon fuel. Fuel bound nitrogen i releaed during combution through the formation of HCN or NH 3 which then oxidize to form fuel NO or N depending on the local toichiometric condition. The fuel NO i formed in fuel-rich zone. When nitrogen i bound in the fuel, it more readily form fuel NO than thermal NO a the N-C and N-H bond found in fuel are much weaker than the N-N triple bond of the nitrogen molecule. The overall reaction can be repreented a follow. HCN / NH 3 O NO (I.6) Control of NOx emiion The variou technique for the control of NOx emiion fall into two broad categorie namely, combution control and pot-combution control. Combution control refer to technique which aim to regulate the NOx emiion during the formation tage of combution by inhibiting the condition neceary for the production of NOx through the variou mechanim given above. Combution control technique

17 7 achieve reduction of NOx by lowering the flame temperature, creating fuel-rich region at the maximum flame temperature, or by lowering the reidence time under oxidizing condition. Among the variou combution control ytem, low-nox burner, fuel taging, reburning, flue-ga recirculation, over-fire air, and water/team injection provide ubtantial reduction in NOx; wherea, air taging, fuel biaing, burner out-of-ervice, and other operational modification are low cot method with limited reduction capabilitie. The pot-combution control method reduce NOx emiion after the NOx i formed by converting them into N with reagent. Two important pot-combution treatment are Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR). Reburning i an in-furnace, combution control technology for NOx reduction. The reduction i achieved through the taged introduction of fuel into the combution device. Reburn combution control require change to the furnace and the additional operating expene of the reburn fuel but offer the potential advantage of reducing unburned carbon, alo known a Lo On Ignition (LOI) and CO emiion control. The overall reburning proce occur within three delineated phyical zone, namely, primary zone, reburn zone, and burnout zone [8]. The fuel upplied in the primary zone generate % of the total rated heat throughput of the ytem with normal to low exce air condition. The lower fuel firing rate and O concentration lead to reduced fuel and thermal NOx compared to conventional ytem without reburning. At the reburn zone, the remaining 0-30 % heat throughput i generated by the reburn fuel injected into the product from the primary zone combution. The addition of reburn

18 8 fuel create localized fuel-rich region that act a reducing environment to convert NOx from the primary zone into molecular nitrogen through the revere prompt NOx Fennimore mechanim. The extent of thi converion depend on the toichiometry and mixing achieved in the reburn zone. Any unburnt fuel from the reburn zone i conumed in the burnout zone through the upply of overfire air, uually at exce air of 5-5 %. The condition in the burnout zone hould be optimized uch that it i not conducive for generation of thermal NO. The extent of reduction of NOx achieved from reburning varie from 0 to 90 % depending on the operating condition of the ytem. Bioma Another environmental iue that need to be addreed i the rapidly growing feedlot indutry. In the United State, 94 million total head generated 0 million ton of wate in 997 and the increae in animal wate generation wa % for the previou decade [9]. Each animal leave approximately ton of collectible bioma over a 5 month period [0]. In many cae, the production of bioma from one or more animal pecie i in exce of what can afely be applied to farmland in accordance with nutrient management plan, and the tockpiled wate poe economic and environmental liabilitie. Hence, bioma can contribute to urface or ground water contamination and air pollution problem with the releae of greenhoue gae. Dipoal of the vat quantity of manure produced a a by-product of the cattle feeding indutry i one of the major operating tak of the indutry. It i both an economic burden on the indutry and a potential environmental hazard to air, water, and land. The traditional mean of dipoal wa the ue of manure a fertilizer. An alternative and attractive way of

19 9 overcoming thi threat i to develop procee that make ue of manure a a reource. Some of the poible method include utilizing the generated manure a fuel or a raw material in other indutrie. Thee will alleviate the ever increaing burden placed both on the indutry and the natural reource. The ue of bioma a the ole ource of energy reported in the literature [0-3] ha met with limited ucce. In the preent tudy, the feaibility of uing of bioma a a reburn fuel in exiting coal fired power plant i conidered. It i expected to utilize bioma a a low-cot, ubtitute fuel and an agent to control emiion. The opportunity for the adoption of thi technology i particularly attractive in the high plain area where many feedlot are located. Succeful development of technology to ue bioma a a reburn fuel will create an environment-friendly, low cot fuel ource for the power indutry and provide mean for an alternate method of dipoal of bioma and a poible revenue ource for feedlot operator.

20 0 CHAPTER II LITERATURE REVIEW Thi chapter provide a review on reburning fuel and parameter that influence the reburning proce in the literature. Parameter that influence NOx reduction Numerou parameter have been identified in the literature that influence the extent to which NOx reduction may be achieved. Among them, the ignificant factor include the reburning zone temperature, reburning zone toichiometry, mixing between reburning fuel and main combution ga, reidence time, primary zone NOx level, boiler load, reburn fuel percentage of total boiler heat input, reburn fuel compoition, reburn burner toichiometry, reburn burner pulverized fuel finene, reburn ytem characteritic and location, over fire air characteritic and location, economizer outlet O %, flow and combution parameter, and fuel and firing configuration. Reburning with different fuel A wide range of fuel have been conidered for reburning with varying effectivene for NOx reduction. Thee fuel had demontrated NOx reduction from 0-90 % for varying operating and modeling condition. Hydrocarbon Nazeer et al [4] ued natural ga a the reburning fuel and achieved a maximum of 70 % NOx reduction. Spliethoff et al [5] performed reburning experiment with methane and ynthetic pyrolyi gae and found that the concentration of hydrocarbon

21 in the pyrolyi ga had no effect on reburn efficiency. They alo howed a trong influence of reidence time and toichiometry which hould not be conidered eparately, and determined that in pulverized bituminou coal combution, reburning wa uperior to air taging for NOx reduction. Nitrou oxide reduction by hydrocarbon, like methane and ethane, wa evaluated by Rutar et al [6] in fluidized bed combutor. N O detruction wa found to depend more on the amount of reburning fuel added rather than on the abolute reactor temperature. In propane, natural ga, and reidual oil reburning tudie, Chen et al [7] howed that propane and natural ga were the mot effective reburn fuel. They concluded that fuel volatility wa not of firt order importance o long a the rich zone reidence time and toichiometry were adequate to inure overall, fuel-rich condition. Their tudie indicated that the reburning proce wa relatively inenitive to burnout air mixing. Coal and Coal Water Slurry Zarnecu et al. [8] tudied the potential of coal water lurry a a reburn fuel. For a 30 % reburn heat input, they achieved 39 % NOx reduction with coal water lurry. Hardy and Kordylewki [9] ued Polih lignite a reburn fuel in a laboratory cale drop tube furnace and found % effectivene for NOx reduction, depending on the toichiometric ratio of 0.7 to.0. Their experiment howed that volatile matter and calcium content had ignificant role in the effectivene. Bioma Hard and oft wood were utilized a reburning fuel by Hardy and Adam [0, ]. NOx reduction of 70 % wa oberved with approximately 0-5 % of wood heat

22 input. It wa alo oberved that the initial NOx value had a more ignificant effect on the reduction than temperature. In further tudie in a cyclone fired boiler, oppoed injection wa found to be mot effective in reducing NOx emiion with wood reburning. Experimental and modeling tudie in an entrained flow reactor with wheat traw a the reburning fuel were performed by Vila et al [] and Kicherer et al [3]. Mixing effect in reburning Reburning i a mixing-influenced proce due to the relatively fat chemitry time of reburning kinetic which are comparable to the mixing time in full and pilot cale intallation [4]. Mixing effect were identified to be more important in downfired combutor unit than tangentially fired unit a it ha been uggeted that mixing change the electivity of the reaction at the reburn fuel injection and at the rich-lean tranition, control the diperion of the reburning fuel within the furnace, and influence the toichiometry and reidence time [5-8]. Though the quantity of reburn fuel i only a fraction of the primary fuel, the high velocity and momentum aociated with the reburn jet determine the degree of mixing and diperion produced in the reburning zone. Varying degree of mixing may be achieved through variation in the configuration of the reburn fuel injector and the momentum aociated with the reburn fuel. The effect of the injector geometry and configuration have been reported in the literature [9, 30]. The mixing time in the reburning zone depend on everal factor including configuration of the reburning fuel injection, velocitie, temperature of the reburning fuel and flue ga tream, and compoition of each tream [3]. Mixing time i important under low-temperature condition and a limitation with pace limitation.

23 3 CHAPTER III OBJECTIVE AND TASKS The overall objective of thi invetigation i to develop a technology to employ bioma a a reburn fuel. The tak performed to accomplih the overall objective are ummarized a follow:. Invetigate the effect of coal, bioma, and their blend on NOx reduction.. Fabricate a new flat pray injector and intall it in the burner. 3. Etimate the impact of different firing configuration on NOx reduction.

24 4 CHAPTER IV EXPERIMENTAL FACILITY The Texa A&M Univerity experimental facility i a laboratory-cale, downfired, boiler-burner with a rated heat throughput of 9.3 kw (00,000 Btu/h). Pulverized olid fuel like coal, bioma, and blend of coal and bioma were the principal fuel teted. The facility can be adapted to perform co-firing and reburning experiment with minor modification. The ytem wa initially built to perform co-firing experiment and it had inufficient reactor length to include the burnout zone where overfire air i injected to complete combution. Hence, it wa adapted to imulate only the reburning zone of a typical reburning facility. The primary zone wa imulated with the combution of propane and ammonia. Potential for NOx reduction through reburning with coal, bioma, and blend of coal and bioma were tudied. A chematic ketch of the etup i depicted in figure IV.. The facility wa made of five ub-ytem: furnace, primary NOx generation, reburn fuel upply, exhaut, and diagnotic. A brief decription of thee ytem i given below. Furnace The furnace, a modular contruction of 9 tacked ection which, from the top down, are: burner, flame control, reburn fuel upply, reburning, water injection, and exhaut and ah collection. A ectional view of the modular ection and the dimenion of the furnace are given in figure IV. and IV.3. Each modular ection wa made of a ceramic refractory liner encloed by two layer of thermal inulation blanket within a teel caing. The alumina baed ceramic refractory liner, cat from GREENCAST 94,

25 5 had a hollow core of diameter 5.4 mm (6 ) that formed the combution pace. The INSWOOL ceramic blanket provided additional thermal inulation. The ection were bolted together with GRAFOIL gaket between the flange to eal againt ga leak. All the ection except the burner, water injection, and exhaut and ah ection had diametrically oppoite port for ga ampling and temperature meaurement. The port were located every combution chamber diameter (5.4 mm (6 )) from the viewing ection down to the water pray ection. In the burner ection the propane or the propane-ammonia mixture wa ignited with the required amount of air by two igniter torche. The flame from the ignited mixture wa oberved through three quartz view port located in the flame viewing ection. During tartup, the flame wa monitored through the view port and the flow rate of air and propane were adjuted to achieve a table flame at the required toichiometry. The reburn fuel upply ection had two eparate port to accommodate the reburn injector. Fuel injected through the reburn port mixed and reacted with the product of the primary zone along the four reburning ection until the exit plane where the meaurement were made. At the water injection ection, two radial pray of water were directed into the cro flowing tream of reacting gae. The pray trapped the unburnt fuel and burnt ah particulate from the treaming gae and enured that the particle loading in the exhaut tream, which could have damaged the exhaut fan, wa minimal. The particulate collected with the water pray ettled to the bottom of the exhaut and ah ection.

26 Fig. IV.: Schematic ketch of the TAMU 9.3 kw (00,000 Btu/h) reburning facility 6

27 Fig. IV.: Cro ection of the furnace module 7

28 Fig. IV.3: Sketch depicting the dimenion of the furnace 8

29 9 Primary NOx generation ytem The primary NOx generation ytem produced the pecified amount of NOx at the primary zone. The amount of NOx generated wa repreentative of the NO x at the exit of a coal-fired power plant which wa tudied for reduction. It wa imulated through the combution of propane doped with mall amount of ammonia. The ammonia wa aumed to be fully converted into NOx in the primary zone, and by regulating the flow of ammonia different primary NOx concentration were obtained. The propane flow in the primary zone wa regulated to generate 70 % of the rated thermal throughput while the remaining 30 % wa upplied by the reburning fuel. The propane and ammonia, premixed with the requiite quantity of air, wa ignited inide the furnace by mean of two igniter torche fueled by propane at the burner ection of the furnace. The air required for the combution of the propane-ammonia mixture wa upplied from a mechanical blower. The air wa preheated to about 395 K (50 ºF) by a circulation heater to aid eaier ignition. The ammonia upply line were fluhed of any remaining trace gae between experiment with nitrogen purge ga. The nitrogen upply wa alo ued to hold the flow rate of ammonia teady without any fluctuation. Reburn fuel upply ytem The reburn fuel ued in the preent tudy were coal, bioma, and blend of coal and bioma. The fuel wa fed into the fuel line from a commercial dry olid feeding ytem. The feeder had a central auger to dipene fuel and two agitating auger to prevent bridging and creation of dead zone in the hopper. The feeder wa calibrated to

30 0 the required flow rate before every experiment by collecting and weighing the amount of fuel upplied by the feeder over a period of minute. Air wa ued a the carrier medium to convey the fuel from the hopper to the furnace through a venturi eductor valve on the fuel line that facilitated the mixing of the fuel and carrier ga. The venturi valve apirated ambient air that wa about 0.4 to.0 time the motive air upplied. So the carrier ga flow rate wa adjuted to account for thi apiration. The quantity of apirated air wa determined from knowledge of the concentration of oxygen within the reactor. The air upply from the mechanical blower wa diluted with nitrogen ga uch that the concentration of O wa reduced within the furnace. The concentration at the reburn zone and exit zone were meaured. When the reburn air wa turned on, air wa apirated through the venturi eductor valve. The O concentration meaured at the exit zone within the furnace indicated the amount of apirated air. The procedure wa repeated for variou value in the range of motive reburn air upply required during the experiment. The plot of the apirated air for variou value of motive air upply i given in figure IV.4. Another principle that may be ued in thee tudie i given in appendix D. The fuel along with the carrier ga wa injected into the furnace through two reburn injector located at the reburn fuel upply ection. Two type of injector were tudied for the effect of mixing on the reduction of NO x : i) a nozzle with a circular croection and ii) a nozzle with an elliptical cro-ection producing a flat fan haped pray. Thee tainle teel injector produced a velocity of 0 to 5 m/, depending on flow

31 rate, a the fuel wa injected into the furnace. The photograph and cro ection of the two injector i hown in figure IV Primary Air (SCFH) Motive Air (SCFH) Fig. IV.4: Apiration of ambient air through the venturi eductor

32 Fig. IV.5: Reburn injector and their cro ection

33 3 Exhaut and ah ytem The tream of exhaut gae with the particulate material removed by the water pray wa conveyed by duct to an exhaut fan from where they were releaed into the atmophere. The exhaut fan created a light negative preure within the furnace, the extent of which wa controlled by a damper provided in the exhaut duct work. Thi negative preure provided a afety meaure by averting flame leap when the ga port were opened during meaurement. During the coure of the experiment the damper wa adjuted to maintain a negative preure of approximately 0.05 kpa (0. of water). Thi low amount of uction, apart from enuring afety during operation, alo made ure that the negative preure did not draw ambient air into the furnace thereby diluting the required toichiometry of the ytem. The particulate of unburnt fuel and burnt ah, gathered by the mit of water pray, ettled at the bottom of the exhaut and ah ection. The water wa drained out of the furnace and the particulate ettled down. After the experiment were completed the reidue wa collected through the ah port. Analye of the ediment may be performed to determine the fraction of fuel that wa completely burnt and the compoition of ah. Diagnotic ytem The diagnotic ytem conited of intrument to aid in maintaining the condition of the furnace while in operation and for the analyi of the furnace exhaut gae. The flow of gae and air were meaured uing flow meter. An orifice plate calibrated with a water tube manometer wa ued to meaure higher flow rate of air from the mechanical blower. The calibration curve for the blower i given in figure

34 4 IV.6. The 0.75 orifice plate wa ued in the reburning experiment. The temperature inide the furnace and at the air pre-heater were meaured uing thermocouple. A record of the temperature hitory during the coure of the experiment and at every ga concentration meaurement wa obtained with an OMEGA data acquiition ytem. Expoed tip S-type thermocouple and heathed K-type thermocouple were ued. An ENERAC 3000E emiion analyzer wa ued meaure the emiion concentration. The analyzer may be ued to meaure the concentration of O, CO, SO, NO, and NO on a dry bai to an accuracy of about 3 % at every ga port. A the concentration of CO were very high during reburning experiment, which caued the analyzer to malfunction, the CO enor wa iolated and only concentration of O, NO, and NO were meaured. The analyzer wa calibrated before every experiment againt tandard calibration gae.

35 Fig. IV.6: Blower air upply calibration curve for two different orifice plate [3] 5

36 6 CHAPTER V EXPERIMENTAL PROCEDURE The procedure for conducting the reburning experiment i detailed in thi ection. Fuel and furnace preparation The reburn experiment were performed with coal, bioma, and blend of coal with bioma. The proximate and ultimate analye of the fuel were completed at Huffman Lab, CO prior to the trial. The value for the blend of coal and bioma were calculated baed on the blend ratio. The ah from previou experiment wa collected through the ah port and aved to perform ah analyi and determine it compoition. The fuel hopper wa topped and an extra container with the fuel kept handy to refill the hopper if the fuel ran out during the experiment (Thi wa more eential during co-firing than reburning experiment). The blend of coal and bioma were prepared by weighing definite proportion of coal and bioma and then mixing them thoroughly. The thermocouple were withdrawn from the furnace and cleaned of ah depoit on the inulation. The air filter of the mechanical blower wa inpected for clogging and cleaned. All ga, view, and temperature port were cloed with the cover plug and made ure there wa no air leak into the ytem. The ENERAC 3000E emiion analyzer wa calibrated uing the tandard calibration gae.

37 7 Calibrating the fuel feeder The feeder wa diconnected from the fuel feed line. An empty pan of known weight wa placed under the feeder and the feeder motor wa turned on. The fuel wa collected for a period of minute and weighed. If the required feed rate wa not obtained, then the controller wa adjuted accordingly and the proce wa repeated until the required feed rate wa achieved. Then the feeder wa reconnected to the fuel line. Preheating the air and furnace The propane tank for the igniter torche and primary upply were connected. After ga, view, and temperature port were cloed with cover plug, the exhaut fan wa turned on. The blower for the primary air upply wa tarted and et cloe to the required value. The blower wa alway ued in the forward mode. The temperature at location along the axi of the furnace wa recorded in the data acquiition ytem. The air pre-heater wa witched on and et to the maximum value. After the temperature of the primary zone air had reached approximately 395 K (50 ºF), the valve of the propane tank for the igniter torche wa opened uch that the flow rate wa within the afety limit hown on the regulator. The water injection wa turned on o that the lower zone of the furnace wa cooled. The damper wa et uch that uction preure of approximately.54 mm (0. ) of water prevailed inide the furnace. The igniter torche were lit and the furnace wa heated till the temperature in the reburn zone reached approximately 4 K (300 ºF). The flame from the torche wa viewed through the view port. The torche were damaged by burnout of the ignition wire due to long operating duration at very

38 8 high temperature. To overcome thi problem, the torche were witched off and then withdrawn once the primary zone combution wa etablihed and tabilized. The opening for the torche were later properly ealed to prevent any leak of air into the reactor. Etablihing the primary zone combution The valve of the primary propane upply tank wa opened and the flow rate wa et to the required value uing the regulator. If the torche were blown out, then the damper poition wa adjuted, the primary propane upply wa cut off and the torche were reignited. If a table flame wa difficult to be etablihed, the flame wa cautiouly ignited with one of the view port open. Once the flame wa table, the air flow rate wa et to the required value. Following a 30 minute period of primary propane combution, the air for the reburn fuel wa turned on and et at toichiometric condition. The damper wa adjuted to maintain the uction preure. Then the reburn fuel wa turned on. The extent of combution wa oberved from the ah collected by the cooling water pray. The furnace wa heated for a period of 45 minute until the temperature at the reburn zone reached approximately 366 K (000 ºF). The reburn fuel and air were witched off, the damper readjuted and thermal NO and O % reading uing the ENERAC 3000E emiion analyzer were taken at the exit zone. The O % wa enured to be very cloe to % implying that an equivalence ratio of 0.95 exited at the primary zone; any deviation wa annulled by adjuting the propane flow rate or the exhaut damper.

39 9 Setting the required primary zone NOx The ammonia tank wa opened and et to the required flow rate. The flow rate wa adjuted till the required amount of NO wa meaured at the exit zone. The NO generated at the primary zone tabilized after 0-5 minute. The nitrogen purge ga wa ued to tabilize any fluctuation in the ammonia flow. Reburning The reburn air wa upplied at the required flow rate accounting for the apiration of ambient air at the venturi eductor valve. The NO value meaured at the exit zone gave an indication of the reduction with only the upply of air i.e., the dilution effect. The feeder motor wa witched on and the reburn fuel wa fed into the ytem. A teady NO meaurement wa obtained at the reburn zone after 0-5 minute. The temperature wa recorded during all the meaurement tage. The intered filter at the tip of the analyzer probe got clogged with the particulate in the exhaut tream while operating at higher equivalence ratio. It wa cleaned between meaurement by fluhing it with air. The reburning wa tarted at toichiometric condition and after concentration of O, NO, and NO are meaured with ENERAC 3000E emiion analyzer, the reburn motive air upply wa reduced to imulate richer condition of reburn zone toichiometry. Sytem hut off The reburn fuel and air upply were firt turned off. The primary propane upply wa topped by cloing the valve of the propane tank and diconnected from the line.

40 30 The primary air upply wa turned off. All the ga port and temperature port were opened to allow the furnace to cool. The water pray wa continued until the temperature at port ubided to about 4 K (300 ºF). The reburn fuel line were fluhed of trace of ammonia with nitrogen. A period of one day wa allowed before the next experiment wa conducted. Error analyi The error analyi wa performed to quantify the error that might occur in the parameter calculated. Baed on thee value, the error in the meaurement were determined. The error given by the intrument manufacturer and the calculated error are provided in table V. and V.. The error bar in the reult were baed on thee calculation.

41 3 Table V.: Intrument error Parameter Intrument Error Motive air gage ± 3 SCFH Secondary air gage ± 6 % O enor ± 0. % NO enor ± 4 % NO enor ± 4 % Fuel feeder Thermocouple at reburn zone Thermocouple at exit zone ± g/min ±.8 K ±. K Table V.: Error in meaurement Parameter Calculated Error Equivalence ratio.97 % Normalized NOx 5.76 % NOx reduction.6 %

42 3 CHAPTER VI RESULTS AND DISCUSSION Thi chapter preent the reult of the reburning experiment and a dicuion on the reult. Initial trial The Texa A&M Univerity boiler burner facility wa alo ued to perform cofiring experiment with coal, bioma, and their blend. Co-firing i a proce in which coal wa blended with bioma and ued a the fuel in the down-fired reactor. Thee were the firt ever tudie that demontrated the ability of coal blended with bioma to reduce NOx emiion. The detail of the experimental facility, parameter under which the trial were conducted, and dicuion of the reult are provided in reference [3, 33]. The invetigation at different blend ratio indicated that though the fuel nitrogen increaed due to the blending of bioma with coal, the NOx emiion reduced a depicted in figure VI.. The ame trend wa oberved at different exce air value. Thi wa a ignificant finding which directly connoted that blend of coal and bioma can be ued a effective reburn fuel. Fuel bound nitrogen i conidered to be a ignificant ource of NO in coal fired reactor but, thee reult from literature indicate the oppoite. The reduction with bioma i thought to originate from the following factor: higher volatile content of bioma, rapid releae of volatile content, and the releae of fuel bound nitrogen in the form of ammonia. Baed on thee trial it wa decided to tet bioma a a reburn fuel.

43 33 NO at exit zone during co -firing (kg /G J ) % Exce air 5% Exce air 0.00 Coal (0.96) 90:0 Blend (.04) 80:0 Blend (.) Fuel Type (Fuel nitrogen content a ma percentage) Fig. VI.: NO generation from co-firing for different fuel [33] Fuel analyi The fuel ued for the reburning experiment were coal, bioma, and blend of coal and bioma. Two blend ratio of coal: bioma, and 90-0 on a ma bai, were invetigated. Prior to the experiment the ultimate and proximate analye were performed for the coal and bioma. The reult from the analye were ued to

44 34 calculate the value for the blend. Table VI. ummarize the analye and calculated reult for the four fuel ued for the experiment. Table VI.: Comparion of variou fuel ued for reburning on an a received bai Ultimate Proximate Parameter Coal Bioma Blend 90-0 Blend Carbon (ma %) Hydrogen (ma %) Nitrogen (ma %) Oxygen (ma % by difference) Sulfur (ma %) Chlorine (ma %) < Ah (ma %) Dry Lo (ma %) Volatile Matter (ma %) Fixed Carbon (ma %) HHV (kj/kg) From the analye reult in table VI. it wa oberved that bioma wa a low energy fuel. The combution of bioma would generate 30 % lower thermal rating a compared to the ame quantity of coal. Hence, when bioma i ued a the ole ource of energy, the fuel feed rate hould be increaed to achieve imilar heat throughput a achieved with coal burning. The ah content of bioma wa about three time higher than that of coal. The higher ah content, higher fuel feed-rate, and higher chlorine

45 35 content are likely to poe problem of ah depoition on boiler tube wall when bioma i ued a the primary fuel. Fuel bound nitrogen i the principal ource for the generation of fuel NO. A comparion of bioma with coal indicated that the fuel nitrogen in bioma wa about three time higher than that of coal. The reult from cofiring tudie indicated that the higher nitrogen content of bioma did not necearily lead to higher NO production. A comparion of the volatile content of bioma revealed a value two time higher than coal. Thi implie, with bioma, the volatile releae rate would be fater and thu bioma will have better combution characteritic. Thu the comparion of coal and bioma indicated that bioma wa a more volatile, low energy, high ah, and high nitrogen fuel. The ize ditribution of the coal and bioma wa performed adopting the procedure according to the ASTM tandard [34]. Sieve of meh number 35, 00, 00, 50, 0, 6, and 0 with meh ize repectively of 45, 75, 50, 300, 840, 9, and 000 micron were ued. The reult of the ieve analyi of the fuel are illutrated in figure VI.. It may be oberved that coal ha about 70 % of it ma le than 00 µm wherea, in bioma only 50 % of the ma i le than 00 µm. Thu the bioma particle ize ditribution wa coarer than that of coal. The higher fiber content of the bioma during the proce of collection render the grinding proce difficult and finer grain were not produced a the fibrou material of bioma were not broken into powder during the grinding operation but rather compreed. The difference in ize ditribution between coal and bioma might lead to difference in combution characteritic. The preence of a greater fraction of bioma particle over the 300

46 36 micron range led to the problem of clogging at the venturi during the feeding of reburning fuel. 0 Coal Bioma 00 Ma le than Size (%) Meh Size (micron) & Sieve Number Fig. VI.: Size ditribution of coal and bioma

47 37 Mixing time cale The mixing time ditribution within the furnace give a great deal of information about the tate of mixing. The formulation of the mixing model and the decription of the experiment to determine the mixing time ditribution of the furnace are detailed below. Formulation Baed on the work of Zwietering [35] a adapted in Alzeuta et al [36], the mixing of the reburn fuel with the tream of primary gae within the furnace wa defined by a imple approach. The mixing proce in the reburn zone wa modeled a a jet in cro flow problem, where the jet correponded to the injection of the reburn fuel and the cro flow ymbolized the product of primary combution. In thi invere-mixing model, the product of primary combution were gradually entrained and diluted the reburn jet a oppoed to practical condition where the reburn fuel wa injected into the flow of the product of primary combution. Thi may enable the definition of the hitorie in the mixing zone in term of thoe of the reburn fuel rather than on the product of primary combution. A chematic of the mixing model i given in figure VI.3. The model aumed an exponential mixing rate in which the cro flow ma advancing into the jet at a given time wa proportional to the ma of the cro flow. The proportionality contant wa a value that depended on the mixing time, which may be determined by experiment or etimated. Thi approach did not decribe the phyical proce of mixing of the reburn jet and the product of primary combution that take place in the mixing region. Still, it characterized mixing i.e., the reburn fuel react from an initial fuel-rich

48 38 to fuel-lean condition a it wa entrained into the cro flow. Thi characteritic mixing time may be compared with the kinetic time cale. To etimate a mixing time τ mix, the ma flow of the bulk flow at any time, when the reburn and cro flow jet were 97.8 % mixed, i repreented by the following equation [37]. m bulk t ( t) m ( t = 0) m ( t = 0) exp = reburn croflow τ mix (IV.) The relation between the ma flow of the two jet and the mixing time offer a way of determining the mixing time. Rearranging the above equation lead to a relation for the mixing time in term of the concentration of oxygen a hown in the appendix B. t τ mix ( t = 0) N total, reburn 3.85 N total, croflow = ln () 3.85 xo, bulk t (IV.) Conidering a mean value for the velocity of the reburn and cro flow, the variation in oxygen percentage along the length of the ection downtream of the reburn fuel injection can be ued to determine the characteritic mixing time.

49 39 Fig. VI.3: Schematic of the jet in cro flow invere mixing model Tet facility and experiment The mixing time tudie were conducted in a model tet et up built imilar to the Texa A&M Univerity 9.3 kw (00,000 Btu/h) boiler burner facility. Figure VI.4 illutrate the chematic of the model facility. The reacting multiphae flow of the laboratory facility were imulated by cold ga flow ytem in the model. A clear acrylic cat tube model of inner diameter 5.4 mm (6 ) repreented the combution chamber of the actual tet facility with identical dimenion. The main flow compriing the product

50 40 from the combution of propane and ammonia in the tet facility wa replaced in the model facility through ambient air upplied from the mechanical blower. The reburn fuel and air mixture wa ubtituted with a pure nitrogen flow from a regulated cylinder. The reburn port were poitioned at location imilar to that in the tet facility. The main flow rate wa identical to that in the tet facility. The number of meaurement port in the model wa increaed with leer pacing than the laboratory facility. Three port uptream and 4 port downtream of the reburn port, at 5.4 mm ( ) pacing, were ued a meaurement port wherea, the laboratory facility ha port paced every 5.4 mm (6 ). The flow field oxygen concentration wa meaured uing the ENERAC 3000 E emiion analyzer ytem. The initial experiment were conducted in the model that wa not completely operational to tet under the condition imilar to that of the laboratory facility. Reburn flow rate imilar to that for actual tet cae could not be produced with the available configuration of N cylinder. It wa decided to ue a low-momentum reburn jet in order to predict the mixing time. The tet condition of 5.0 m/ air flow and. m/ nitrogen jet were ued that repreented the repectively the cro flow and reburn jet. The main flow from the mechanical blower wa tarted and then the nitrogen upply wa alo et to the required flow rate. The mixing of the main and reburn jet were left to attain a teady mixing for about 5 minute. The oxygen concentration were meaured at the centerline and at the wall, at every meaurement port downtream of the reburn port. Reading above the reburn port were alo made to check for upward mixing at the reburn zone.

51 4 Fig. VI.4: Schematic ketch of the model facility for mixing time experiment Determination of mixing time The experimentally meaured oxygen concentration along the length of the model ection for a pecified reburn and cro flow rate wa correlated a hown in the appendix. The correlation wa ued to determine the mixing time. For two cae of

52 4 mixing, 97.8 % and 90 % thi correlation wa plotted a hown in figure VI.5. The lope of thee curve give an indication of the mixing time. From the value of the reburn and cro flow rate, the mixing time wa etimated a 936 m and 407 m repectively for 97.8 % and 90 % mixed condition. The mixing time of 400 m wa reported in literature for 90 % mixed condition ln(f) % Mixed 90 % Mixed Ditance from reburn port (inch) Fig. VI.5: Mixing time correlation

53 43 Reburning The analyi of the nature of the fuel ued for reburning will enable the interpretation of the reult from reburning trial. Table VI. ummarize the variou reburning trial were conducted. The different reburning fuel ued were coal, bioma, blend, and 90-0 blend on a ma bai. The two injector ued were circular jet and flat pray injector. Thee variou configuration were teted for reburn zone equivalence ratio of.00,.05,.0,.5, and.0 i.e., from toichiometric condition at.00 to lightly fuel-rich condition at.0. The experiment with coal a the reburn fuel and circular jet injector wa conidered the bae cae for all the comparion. The reburn fuel upplied 30 % of the total rated heat throughput of the facility. During all experiment the total heat throughput wa kept identical thu, when the reburn fuel wa changed, the fuel feed rate wa increaed for the ame air flow rate. The reburning experimental condition are given in table VI.3.

54 44 Table VI.: Reburning parametric matrix Experiment Fuel Injector Equivalence Ratio Coal * Circular Jet *.00,.05,.0,.5,.0 Coal Flat Spray.00,.05,.0,.5,.0 3 Bioma Circular Jet.00,.05,.0,.5,.0 4 Bioma Flat Spray.00,.05,.0,.5, Blend Circular Jet.00,.05,.0,.5, Blend Flat Spray.00,.05,.0,.5, Blend Circular Jet.00,.05,.0,.5, Blend Flat Spray.00,.05,.0,.5,.0 * Bae cae experiment

55 45 Table VI.3: Reburning experimental parameter Parameter Value Total Burner Rating 9.3 kw (00,000 Btu/h) Reburn Rating 8.79 kw (30,000 Btu/h) Propane flow rate 7.7 SCFH Reburn Zone Primary Zone Air flow rate 700 SCFH Equivalence Ratio 0.95 O %.00 NOx 600 3% O Fuel flow rate 8-7 g/min Motive air flow rate 8-43 SCFH Apiration ~ 50 % of motive air Equivalence ratio at reburn zone Equivalence ratio of reburn upply.5-.4 Temperature ~ 40 K (00 ºF) Effect of reburn air dilution on NOx reduction The upply of reburn air through the reburn port dilute the toichiometry at the reburn zone, the very nature of which i a change in the local concentration of NOx. Thi peudo-reduction in NOx wa evaluated to iolate the effect of dilution and identify the reduction produced from the reburn fuel. The propane burner wa fired at the total rated heat throughput. The ammonia injection ytem generated pecified amount of NOx in the primary zone. The oxygen concentration at the exit zone wa at %

56 46 implying a primary zone equivalence ratio of With the addition of reburn air, the O concentration and the NOx concentration reduced. The reduction with dilution i calculated uing the formula: NOxwith air NOxwithout air NOx reduction = reburn reburn 00 (VI.3) NOxwithoutreburnair The effect of dilution at different initial NOx level i depicted in figure VI.6. It can be oberved that the reduction in NOx with the addition of reburn air increaed with the increae in primary zone NOx.

57 47 0 NOx reduction with reburn air dilution (% ) Primary zone NOx (ppm) Fig. VI.6: NOx reduction due to the dilution with reburn air upply Effect of reburn injector type on reburn zone temperature The two injector ued in the preent tudy, circular jet and flat pray, differed in the nature of mixing produced in the reburn zone between the reburn upply and primary zone flow. The difference in mixing pattern may caue variation in temperature ditribution at the reburn zone. From prior tudie in literature [4-8], it wa known that the temperature at the reburn zone wa an important factor for NOx reduction ince

58 48 it affect the kinetic time cale. The typical temperature at the reburn zone before the addition of reburn fuel-air mixture wa about 370 K (000 ºF). The hop air upplied along with the reburn fuel wa at ambient condition of about 300 K (80 ºF). Thu the temperature of the mixture between the hot gae and cooler reburn air at the location of the reburn zone may depend on the extent of mixing produced locally. Once the reburn fuel and air were upplied the reburn fuel ignited a the temperature at the reburn zone wa higher that the elf ignition temperature. Thi increaed the temperature at the reburn zone a the combution of the reburn fuel progreed and reached almot teady tate within 45 min. After thi duration, the temperature increaed gradually. It wa oberved that the ue of flat pray injector for reburn fuel injection reulted in a higher reburn zone temperature a compared to the circular jet nozzle. The higher temperature with flat pray wa found to be imilar in all type of reburn fuel teted: coal, bioma, and their blend. Mot NOx control technique aim to achieve lower level of NOx with reduced temperature i.e., by uppreing the environment favorable for the production of thermal NO. In our tudie the temperature were much lower than 800 K (800 ºF) required for ignificant amount of thermal NO to be produced. At thee condition, the overall toichiometry at the reburn zone ha more effect on the NOx reduction proce. The higher temperature at the reburn zone with the flat pray injector implied that there wa a better mixing of the reburn fuel with the tream of primary zone gae. The temperature rie at the reburn zone a the equivalence ratio wa increaed had a linear trend for pure coal and bioma a reburn

59 49 fuel wherea, in the cae of blend the temperature decreaed for the reburn zone equivalence ratio of.0 and then increaed for other value. Effect of reburn injector type on exit zone temperature The exit zone wa located in the lower end of the furnace before the water pray capture the particulate in the exhaut tream and formed the end of reburn zone. The knowledge of the temperature at thi exit plane may give an etimate of the extent of burning achieved. The temperature in the exit zone howed a trend that wa oppoite of that oberved in the reburn zone. The trial with circular injector exhibited higher temperature at the exit that thoe with the flat pray injector indicating that combution occurred a later time. Thi trend wa identical in all type of fuel: coal, bioma, and their blend. There wa a rie in temperature at the exit plane a the reburn zone equivalence ratio wa increaed from toichiometric condition to lightly fuel-rich condition. However, imilar to that oberved at the reburn zone, the temperature dropped to lower value at an equivalence ratio of.0. The lower temperature with the circular injector a compared to the flat injector indicated that the mixing produced by the flat injector wa better and the fuel burned further down the reactor with the circular jet injector than with the flat pray injector. It wa oberved that there wa a temperature difference between the two type of injector. To eliminate the effect of temperature on NOx formation and detruction proce, it wa eential that the variou configuration of the experiment were repeated at imilar temperature condition. Figure VI.7 and VI.8 how temperature in the reburn and exit zone for the different experiment. It may be oberved that the

60 50 temperature in the reburn and exit zone were imilar for the variou fuel at different equivalence ratio both for the circular injector and flat pray injector. The maximum variation in temperature at the reburn and exit zone for the circular injector were repectively, 84 K and 46 K and for the flat pray injector were 9 K and 34 K Average temperature at reburn zone K Temperature (K) Average temperature at exit zone K Coal Reburn Zone Bioma Reburn Zone Blend Reburn Zone 90-0 Blend Reburn Zone 300 Coal Exit Zone Bioma Exit Zone Blend Exit Zone 90-0 Blend Exit Zone Φreburn zone Fig. VI.7: Temperature at reburn zone and exit zone for circular jet injector

61 Average temperature at reburn zone - 58 K Temperature (K) Average temperature at exit zone - 9 K Coal Reburn Zone Bioma Reburn Zone Blend Reburn Zone 90-0 Blend Reburn Zone 300 Coal Exit Zone Bioma Exit Zone Blend Exit Zone 90-0 Blend Exit Zone Φ reburn zone Fig. VI.8: Temperature at reburn zone and exit zone for flat pray injector Effect of fuel type on NOx reduction To tudy the effect of fuel type on their effectivene in NOx reduction four type of fuel were conidered. They were coal, bioma, and blend coal and bioma in the ratio of and 90-0 by ma. Coal a reburn fuel with circular jet injection wa ued a the bae cae for comparion of all the reult. The bae cae NOx reduction obtained when coal wa ued a reburning fuel i hown in figure VI.9. The NOx reduction exhibited an increaing trend with increaed reburn zone equivalence

62 5 ratio. The maximum reduction achieved wa 0.4 % at reburn zone equivalence ratio of.0. The reduction wa calculated baed on NOx value corrected on the bai of 3 % oxygen in the exhaut a given below: ambinet O referenceo ( referenceo ) = NOx ( meaured O ) NOx (IV.4) ambient O meaured O ( referenceo ) NOx ( initial) NOx ( initial) NOx NOx reduction (%) = 00 (IV.5) 0 Circular Jet Injection of Coal Bae cae NOx reduction (%) Φ reburn zone Fig. VI.9: Bae cae NOx reduction with coal and circular jet injector

63 53 It wa oberved that the reduction of NOx by bioma alo increaed with increae in the reburn zone toichiometry. However, at lower equivalence ratio bioma eemed to produce higher NOx and the reduction wa le than that oberved for coal. At higher equivalence ratio, the bioma reduced NOx at a higher rate than coal. The maximum reduction 9.9 % wa achieved at an equivalence ratio of.0. The NOx reduction when bioma wa ued a reburning fuel i hown in figure VI.0. The primary NO generation mechanim wa through fuel NO a the temperature are inufficient to produce ignificant amount of thermal NO. Bioma with a higher percentage of fuel bound nitrogen hould have produced higher NOx. On the contrary, it wa een that bioma reduced NOx better than coal. The form of the releae of fuel bound nitrogen during oxidation play an important role in the amount of reduction. With coal the fuel bound nitrogen may have been releaed in the form of HCN and in the cae of bioma there might have been a higher proportion of NH 3. Both HCN and NH 3 are reducing agent for the converion of NOx into molecular nitrogen but, the reaction rate differ. The NH 3 reduction mechanim proceed at a much higher rate than HCN reaction. Thu, under imilar reidence time for both coal and bioma, bioma exhibited twice a much capacity to reduce NOx. An eential condition for effective reburning i local fuel-richne. At fuel-lean condition, bioma being coarer than coal doe not have ufficient time to burn and reduce NO x. The mixing pattern produced at the reburn zone from the circular injector could have been inufficient to dipere the available fuel appropriately to generate numerou fuel-rich location that were potential ite for NOx reduction.

64 54 40 Circular Jet Injection NOx reduction (%) Coal Bioma Φreburn zone Fig. VI.0: NOx reduction with bioma a reburn fuel compared to bae cae coal The propertie of bioma uch a low heat content, high ah, and high chlorine and phophoru content do not make it a ole ource energy fuel. But if the ame were blended with coal we could exploit the advantage of both the coal and bioma. Thu, bioma blend with coal were alo invetigated. The two blend tudied were and 90-0 on a ma bai. The reult of NOx reduction with a blend of bioma with coal on a ma bai i given in figure VI.. It wa oberved that the behavior of blend wa imilar to coal. The maximum NOx reduction of 6.8 % occurred at an equivalence ratio of.0 which wa about 60 % higher than that obtained with coal a

65 55 the reburning fuel. But the blend did not how higher reduction potential at lower equivalence ratio. At an equivalence ratio of.0, the lower reduction could be due to the reduced temperature at the reburn zone implying there wa incomplete burning of the reburn fuel. 0 Circular Jet Injection NOx reduction (%) 5 0 Coal Blend Φreburn zone Fig. VI.: NOx reduction with blend a reburn fuel compared to coal

66 56 Figure VI. how that the performance of 90-0 blend wa imilar to that of coal. But the maximum reduction with the 90-0 blend wa about 7 % higher than that of coal. 0 Circular Jet Injection NOx reduction (%) 5 0 Coal 90-0 Blend Φreburn zone Fig. VI.: NOx reduction with 90-0 blend a reburn fuel compared to coal A comparion of effect all the different reburn fuel on NOx reduction with the ue of circular injector i hown in figure VI.3. From the figure it may be oberved that at higher equivalence ratio bioma had the ability to reduce NOx wherea, at other value it did not reduce a well a coal. The reduction with blend wa imilar to coal

67 57 and the maximum reduction i about 7 %. Thu, it may be inferred that bioma can be ued a reburn fuel but it i required that the reburn fuel hould be dipered well within the reburn zone. The need for ufficient diperion of reburn fuel implied that when temperature effect were eliminated, the toichiometry of the reburn zone and the generation of local fuel-rich region were ignificant factor to achieve high NOx reduction. 40 Circular Jet Injector NOx reduction (%) Bae Cae Bioma 90-0 Blend Blend Φreburn zone Fig. VI.3: NOx reduction with circular injector for variou reburn fuel

68 58 Effect of injector type on NOx reduction The mixing of the reburn jet into the tream of primary zone combution product ha a major impact on the effectivene of NO x reduction. Trial were performed with a modified injector to tudy thi mixing effect. The initial experiment were performed with circular jet injector. In order to improve mixing, the circular injector wa replaced by a flat pray nozzle. The flat pray pread the reburn fuel at a wider angle of º than the circular injector at the reburn zone. The flattening of the nozzle to produce an elliptical cro ection alo increaed the momentum of the pray. The even preading of the fuel at the reburn zone may have created more region of localized fuel-richne that were ideal ite for NOx reduction. Alo the better diperion with a flat pray led to better combution and fater releae of volatile in the cae of bioma. Thi had an impact on the temperature at the reburn zone a dicued earlier. All the fuel were teted with the flat pray to determine the effect of mixing. A comparion of the NOx reduction with coal injected through the flat pray againt the bae line cae i given in figure VI.4. The ue of flat pray for coal reburning howed that the NOx reduction improved at all equivalence ratio except at near toichiometric condition of the reburning zone.

69 59 0 Bae Cae 6 Coal - Flat Spray Injector NOx reduction (%) Φreburn zone Fig. VI.4: NOx reduction with circular and flat injector for coal reburning The NOx reduction with the flat injector and bioma i compared with the bae cae in figure VI.5. It wa found that bioma howed much higher reduction potential of NOx than coal at all equivalence ratio. The maximum reduction of 6. % occurred at an equivalence ratio of.0 which wa over 5 time higher than that produced with coal a the reburning fuel. The reduction potential of coal level off a the equivalence ratio wa increaed but in the cae of bioma, it howed a continuou increaing trend. Thi may imply that the flat pray created higher mixing within the reburn zone and

70 60 when coupled with the propertie of bioma, very high reduction may have been achieved. When bioma wa dipered within the reburn zone, the higher volatile content of bioma would have been releaed at a higher rate and created localized fuelrich zone Bae Cae Bioma - Flat Spray Injector Coal - Flat Spray Injector NOx reduction (%) Φ reburn zone Fig. VI.5: NOx reduction with flat injector for bioma reburning The effect of flat pray injection of and 90-0 fuel blend are given in figure VI.6 and V.7. The blend alo exhibited higher reduction a compared to coal but, the reduction wa lower at low equivalence ratio. At higher equivalence ratio

71 6 much higher reduction were oberved. The maximum reduction with and 90-0 blend are repectively 44.7 %and 34. %. A comparion of all NOx reduction with different fuel injected a a flat pray i exhibited in figure VI.8. It wa oberved that coal had the leat reduction and bioma howed the highet reduction at all equivalence ratio. The reduction with blend lied between that of bioma and coal. When the percentage of bioma wa higher in the blend then the NOx reduction wa higher at higher equivalence ratio. 50 NOx reduction (%) Bae Cae Blend - Flat Spray Injector Coal - Flat Spray Injector Φ reburn zone Fig. VI.6: NOx reduction with flat injector for blend reburning

72 6 40 NOx reduction (%) 30 0 Bae Cae 90-0 Blend - Flat Spray Injector Coal - Flat Spray Injector Φreburn zone Fig. VI.7: NOx reduction with flat injector for 90-0 blend reburning

73 63 80 Flat Spray Injector NOx reduction (%) Coal Bioma 90-0 Blend Blend Bae Cae Φreburn zone Fig. VI.8: NOx reduction with flat pray injector for variou reburn fuel Effect of ah content of bioma on NOx reduction Thien [3] had performed reburning experiment with bioma that had higher ah content that the one ued in the preent tudie. Table VI.4 compare the propertie of the two bioma fuel. It wa oberved that the low ah bioma of the preent tudie had about 75 % higher heat content, 68 % higher fuel bound nitrogen, and 54 % higher volatile matter. It alo had about 35 % lower ah and 30 % lower chlorine content. The NOx reduction comparion between thee two biomae i given in figure VI.9. It wa

74 64 een that the low ah bioma had lower NOx reduction and exhibited an increaing trend wherea the high ah bioma had a contant reduction at all equivalence ratio. Table VI.4: Comparion of low and high ah bioma propertie Parameter High Ah Bioma [3] Low Ah Bioma Carbon (ma %) Hydrogen (ma %) Nitrogen (ma %) Oxygen (ma % by difference) Sulfur (ma %) Chlorine (ma %) Ah (ma %) Dry Lo (ma %) Volatile Matter (ma %) Fixed Carbon (ma %) Higher Heating Value (kj/kg) Fuel Nitrogen per Heat Content (kg/gj).89.8 Fuel Nitrogen per Heat Content (lb/mmbtu) Ultimate Proximate

75 Fig. VI.9: NOx reduction with low and high ah bioma [3] 65