Determination of Biogenic Energy, Fossil Energy and Mass Fractions in Refuse Derived Fuels

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1 CONTACT Determination of Biogeni Energy, Fossil Energy and Mass Frations in Refuse Derived Fuels Helmut Rehberger, Vienna University of Tehnology, Austria Johann Fellner, Vienna University of Tehnology, Austria Oliver Ceni, Vienna University of Tehnology, Austria Philipp Ashenbrenner, Vienna University of Tehnology, Austria Helmut Rehberger Vienna University of Tehnology Institute for Water Quality, Resoure and Waste Management Karlsplatz 13/ Vienna, Austria Tel.: Fax: helmut.rehberger@tuwien.a.at EXECUTIVE SUMMARY A method to determine the mass, energy and arbon ontent of biogeni and fossil matter in refuse-derived fuel (RDF) is desribed. The method ombines standard hemial information about biogeni and fossil material with data from a hemial analysis of the RDF. The data are used to solve a set of equations that deliver the mathematially and statistially derived final result. For the hemial analysis representative samples of the RDF are assessed in a CHNSO elemental analyser. The proposed method is validated by haraterizing defined referene mixtures of plastis and biomass (e.g., polyethylene and ardboard). The orrelation between the measured and referene values is exellent. If ombined with representative sampling a reliable and easy appliable haraterization of RDF is available. INTRODUCTION Refuse-derived fuel (RDF) proessed from muniipal solid waste and/or ommerial waste is usually an unknown mixture of biogeni and fossil organi matter. Due to various European regulations (e.g., Diretive 2003/87/EC on establishing a sheme for greenhouse gas emission allowane trading; Diretive 2001/77/EC on the promotion of eletriity produed from renewable energy soures in the internal eletriity market) produers and users of RDF are interested in reliable and ost-effetive methods for determining the biogeni and fossil organi matter, energy, and arbon ontent of RDF. In reent years, different methods for haraterizing the biomass ontent of RDF have been established: sorting analysis, the seletive dissolution method (van Dijk & Steketee 2002) and the radioarbon method (Kneissl 2001, Norton & Devlin 2006, Palstra & Meijer 2010). A detailed desription of all methods is given in Staber et al. (2008) and the European Standard pren 15440:2008. In addition to these standardized methods operators of waste inineration plants an haraterize the biomass ontent of their waste feed using the balane method (Fellner et al. 2007). This method ombines standard data on the

2 hemial omposition of biogeni and fossil organi matter with routinely measured operating data from the inineration plant by the ompilation of several mass balanes and one energy balane, whereby the result of eah balane desribes a ertain waste harateristi (e.g., ontent of organi arbon, heating value, ash ontent, ). Today the balane method is routinely implemented in several European Waste-to-Energy plants (Obermoser et al. 2009). However, the balane method has a major disadvantage in the analysis of refuse-derived fuels, sine it only allows post-ombustion haraterization of the fuel or waste. For RDF analysis this is unsatisfatory, as reliable information about the omposition of the fuel (e.g., ontent of fossil organi arbon) is required prior to its utilization. Therefore in this study a CHNSO analyser, whih guarantees routine and highapaity appliation, is used in onjuntion with the balane method, whih is appropriately adapted. The developed method is validated by analyses of defined mixtures of biogeni and fossil organi matter (e.g., mixtures of wood, paper, polyethylene, polystyrene). The present paper gives a detailed desription of the method and summarizes the results of the validation proess. MATERIALS AND METHODS The method is based on the distint hemial omposition of moisture- and ash-free biogeni and fossil organi matter in RDF and on the differenes in the omposition of the two materials (Rehberger et al. 2007, Kost 2001). Suh data are used to ompile balane equations for different substanes (C, H, O, N and S). The dry matter of RDF is virtually subdivided into inert m inert, biogeni m biogeni and fossil m fossil matter. Inert matter inludes all inombustible solid residues suh as metals, stones, ash or other inorgani matter from biowastes and plastis (e.g. kaolin in paper). Biogeni and fossil organi matter refers only to the moisture- and ash-free organi material. Balane equations a) Carbon balane: The total organi arbon ontent TOCRDF of the RDF equals the sum of biogeni arbon ( mb C b ) and fossil organi arbon ( mf C f ). m + m = TOC = TC TC m (1) b Cb f Cf RDF RDF i i The other balane equations are organized analogously to the arbon balane. b) Hydrogen balane: m + m = TOH = TH TH m b Hb f Hf RDF RDF i i ) Oxygen balane: m + m = TOO = TO TO m b Ob f Of RDF RDF i i d) Nitrogen balane: m + m = TON = TN TN m b Nb f Nf RDF RDF i i e) Sulphur balane: m + m = TOS = TS TS m whereby m b m f b Sb f Sf RDF RDF i i Moisture- and ash-free biogeni mass fration of the RDF [kg/kg] Moisture- and ash-free fossil organi mass fration of the RDF [kg/kg] (2) (3) (4) (5)

3 m i Ash ontent of the moisture-free RDF [kg/kg],,,, : Carbon, hydrogen, oxygen, nitrogen and sulphur ontent of moisture- Cb Hb Ob Nb Sb and ash-free biogeni matter [g/kg],,,, : Carbon, hydrogen, oxygen, nitrogen and sulphur ontent of moisture- Cf Hf Of Nf Sf and ash-free fossil organi matter [g/kg] TOCRDF, TOHRDF, TOORDF, TONRDF, TOS RDF : Total organi ontent of arbon, hydrogen, oxygen, nitrogen, and sulphur in the RDF with referene to dry matter [g/kg] TCRDF, THRDF, TORDF, TNRDF, TS RDF : Total arbon, hydrogen, oxygen, nitrogen, and sulphur ontent in the RDF with referene to dry matter [g/kg] TCi, THi, TOi, TNi, TS i: Total ontent of arbon, hydrogen, oxygen, nitrogen, and sulphur in the ash [g/kg] The single mass frations (m b,m f ) represent the only two unknowns in a set of five nonlinear equations. The other parameters (TC RDF, TH RDF, TO RDF, TN RDF, TS RDF, m i, TC i, TH i, TO i, TN i, TS i ) are determined by laboratory analyses of the RDF or are based on published data in the ase of the moisture- and ash-free omposition of biogeni and fossil organi matter (,,,,,,,,, ) (see Table 1). Cb Hb Ob Nb Sb Cf Hf Of Nf Sf In addition to the five substane balane equations the following onditions (equations 6 to 9) need to be fulfilled: The sum of biogeni matter m b and fossil organi matter m f and inert matter m i must equal 1: mb + mf + mi =1 (6) For biogeni matter it an be assumed that the sum of the C, H, O, N and S ontent must equal almost 1000 g/kg water- and ash-free matter, whereas for fossil organi matter (plastis) this summation results in a slightly smaller value than 1000 g/kg (depending on the fration of PVC and Polytetrafluoroethylene, and thus the Cl and F ontent, respetively): (7) Cb Hb Ob Nb Sb ± 20 (8) Cf Hf Of Nf Sf In addition the sum of the total organi ontents of C, H, O, N and S should amount to almost 1000 g/kg, whereby again aording to the fration of hlorinated and fluorinated plastis, a value slightly smaller than 1000 g/kg must be assumed. TOC + TOH + TOO + TON + TOS 1 m RDF RDF RDF RDF RDF i 985 ± 15 In order to obtain the required input data (TC RDF, TH RDF, TO RDF, TN RDF, TS RDF, m i, TC i, TH i, TO i, TN i, TS i ) for alulating the biomass ontent and ontent of fossil organi matter, respetively, the following onditioning proesses and analyses are required. 1. Representative sampling of RDF (This is not reported in this paper sine representative sampling is also required to determine other standard harateristis of RDF suh as heating value, and hlorine and heavy metal ontent.) 2. Drying of the samples at 105 C to a onstant weight. The loss of mass of the samples is used to alulate the water ontent of the RDF. (9)

4 3. Conditioning of the samples for elementary analyses and the measurement of ash ontent. In partiular the grain size of the samples and their mass are redued. The final grain size depends on the sample size for the elementary analysis. 4. Part of the sample material is used to determine the ash ontent m i and loss on ignition of the RDF (at 550 C). 5. Determination of the elementary omposition (TC RDF, TH RDF, TO RDF, TN RDF, TS RDF ) of the RDF and of the ignition residue (TC i, TH i, TO i, TN i, TS i ). TABLE 1. Typial hemial omposition of biogeni and fossil organi matter in RDF that is proessed from household and ommerial waste (derived from data given in Fellner et al. 2007). Moisture and ash free Biogeni matter* Fossil organi matter ontent of unit symbol bc av sd symbol FC av sd C g/kg bh H g/kg bo O O g/kg bn N N g/kg bs FS S g/kg * Differenes in the elementary omposition in omparison to data given in Fellner et al. (2007) are due to the different omposition of the biogeni materials in RDF in omparison to household waste (e.g., inreased paper and ardboard, dereased kithen waste). av average value, sd. standard deviation The mathematial solution of the set of equations is desribed in Rehberger et al and more speifi in Fellner et al.(submitted). Validation of the model In order to validate the developed method defined mixtures of biogeni and fossil organi materials were made. Polyethylene (PE), polystyrene (PS), ardboard and wood were mixed together in different ratios ranging from 80% biogeni matter to 80% fossil organi matter. These referene mixtures were subsequently analysed in terms of their fossil organi matter ontent using the methodology desribed above. Finally, the obtained results were ompared with the known omposition of the referene mixtures and the 2 quality of the math was evaluated using the oeffiient of determination r. r 2 n ( O = i O) ( Pi P i 1 ) = n 2 n 2 = ( ) = ( ) O i 1 i O P i 1 i P 2 (10) n represents the number of material mixtures analysed, O i is the fossil organi matter ontent aording to the material mixtures and P i represents the alulated ontent of fossil organi matter. Fresh (unontaminated) pakaging materials is used to produe the defined material mixtures. The different materials (PE, PS, wood, and ardboard) are milled in two steps using a utting mill (Retsh Shneidmühle SM 2000) and an ultra-entrifugal mill (Retsh Ultrazentrifugalmühle ZM200) to a final grain size of 0.2 mm. The powder obtained is dried to onstant weight (at 105 C) and after that mixed to different ratios of biogeni and fossil organi matter (mixtures of PE and ardboard, PS and ardboard, PE and wood, and PS and wood). Prior to mixing, the single materials are analysed for their elementary

5 omposition (C, H, O, N, and S ontent). Thereto around 30 mg of material (per measurement) are analysed using a CHNSO Analyser (vario MACRO CHNSO), and about 10 g (per measurement) are used to determine the ash ontent (ignition at 550 C over 6 hours). In addition the ignition residues are also analysed for their C, H, O, N and S ontent. Altogether six repliates for eah analysis are onduted in order to obtain information about the repeatability and unertainty of the analyses. The elementary omposition of moisture- and ash-free ardboard, wood, PE and PS is alulated from the measured data (see Table 2). These data are subsequently utilized as material speifi input data ( C,,,, b H b O b N b S,,,, b C f H f O f N f S ) for biogeni matter and fossil organi f matter. TABLE 2 Elemental omposition (with referene to moisture- and ash-free matter) and ash ontent of the materials used Biogeni matter Fossil organi matter Moisture- and ash free Cardboard Wood PE PS ontent Symbol Symbol Unit av sd av sd av sd av sd of C H O N g/kg (moisture and ash free) bc bh bo bn bs S BiomassA Ash g/kg DS ontent av average value, sd. standard deviation, DS... dry substane C FH FO FN S fossila RESULTS AND DISCUSSION Mixtures of PE & ardboard Cardboard and PE are mixed in ratios of around 20:80, 50:50 and 20:80 to form samples of about 5 g, of whih 30 mg are used for the CHNSO analyser and the remaining material for determining the ash ontent. The results of the analyses are summarized in Table 3. The remaining ashes were subsequently analysed for their C, H, O, N and S ontent. Sine the ashes of the material mixtures stem almost exlusively from ardboard (ashes of mixtures with only 20% of ardboard onsist of more than 80% of the inert matter of ardboard), the omposition of ashes varied within small ranges. Thus, average values for the PE & ardboard mixtures and subsequently also for the other material mixtures investigated were used (see Figure 2). TABLE 3 Ratio between ardboard PE [g/100 g mixture] Analyses of mixtures of PE and ardboard TC TH TO TN TS [g/kg DS] Ash ontent

6 DS... dry substane TABLE 4 Analyses of ashes from different material mixtures (mean value and 95% onfidene interval) Material mixtures of PE PS PE PS ardboard ardboard wood wood TC i TH i TO i TN i TS i [g/kg ash] 57 ± ± ± ± ± ± ± ± ± ± 0.2 The data shown in Table 3 and 4 are applied in onjuntion with the methodology explained above to determine the omposition of the defined mixtures of PE & ardboard. The values thereby obtained for the moisture- and ash-free biogeni mass fration m b are used to alulate the ratio of PE m plasti as follows CA biomass mb mplasti = 1 mb CA biomass (11) where C A biomass [g/kg DS] represents the ash ontent of the biogeni material (in the present ase the ash ontent of ardboard see Table 2). In Figure 1 the alulated ratios of PE are ompared with the defined ratios. The fit between the alulated and defined values is exellent, as expressed by a oeffiient of 2 determination r of more than The maximum differene is less than 1.1% (absolute values).

7 100% Calulated mass fration of PE [%] 80% 60% 40% 20% 0% 0% 20% 40% 60% 80% 100% Given mass frations of PE [%] FIGURE 1: Calulated fration (y-axis) of PE for the mixture of PE & ardboard versus defined fration (x-axis) of PE Mixtures of PS & ardboard, PE & wood, and PS & wood The results of the analyses of the other material mixtures investigated (PS & ardboard, PE & wood, and PS & wood) are summarized in Figure 2. For these data the oeffiient of 2 determination r is also greater than 0.99 and the maximum deviation between referene and measured values is less than 1.0% (absolute value). Only a single data point for the PE & wood mixture showed a larger deviation (alulated value of 40.0% in ontrast to a defined value of 49.2%). However, this an be attributed to an apparent error in the analysis of the H ontent of the mixture. (A) (B) (C) 100% 100% 100% Calulated mass fration of PS [%] 80% 60% 40% 20% Calulated mass fration of PE [%] 80% 60% 40% 20% Calulated mass fration of PS [%] 80% 60% 40% 20% 0% 0% 20% 40% 60% 80% 100% Given mass fration of PS [%] 0% 0% 20% 40% 60% 80% 100% Given mass fration of PE [%] 0% 0% 20% 40% 60% 80% 100% Given mass fration of PS [%] FIGURE 2. Calulated fration (y-axis) of PS for the material mixture of PS & ardboard (A), of PE for the material mixture of PE & wood (B), and of PS for the material mixture of PS & wood (C) versus defined frations (x-axis) of PS and PE, respetively Sensitivity analysis To evaluate the impat of variation in eah input parameter (C, H, O, N and S ontent of RDF and ignition residue, ash ontent, and omposition of biogeni and fossil organi matter) on the results, a two-step sensitivity analysis is onduted. In the first step the mean value of every parameter is separately varied by 1% and the results are reorded in order to identify the sensitivity. During the seond step of the analysis the effets of atual measurement unertainties are evaluated. Information about these unertainties is derived from repliate analyses of the single materials (see Table 2). In addition the effets of expeted unertainties in the hemial omposition of moisture- and ash-free biogeni and

8 fossil organi matter in real RDF are evaluated using the data shown in Table 1 (relative standard deviation of,,,, and,,,, ). Cb Hb Ob Nb Sb Cf Hf Of Nf Sf Relative error of final results due to a theoretial error of 1% of the hemial omposition of organi matter S-fossil N-fossil Relative error of final results due to the standard error of the hemial omposition of organi matter O-fossil H-fossil C-fossil S-biogeni N-biogeni O-biogeni H-biogeni C-biogeni 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% -0.5% -1.0% -1.5% -2.0% -2.5% Relative error of fossil C ontent [%] Relative error of final results due to a TIN Relative error of final results due to theoretial error of 1% of analysis data TIS atual unertainties of analysis data TIO TIH TIC Ash ontent TN TS TO TH TC 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% 0.5% 1.0% 1.5% 2.0% 2.5% Relative error of fossil C ontent [%] FIGURE 3. Results of sensitivity analysis of input parameters (relative error of fossil C ontent due to hanges in the omposition of organi matter (top) and analysis data (bottom)), whereby C-biogeni represents C b, H-biogeni represents, and C-fossil represents, H b C f Figure 3 shows the orresponding hanges in fossil C arbon ontent due to the variation of input data. The outomes of the analysis indiate first that the sensitivity of the final results (e.g., fossil arbon ontent) to unertainties in single input data is less than 2.5% (relative error), thereby demonstrating the robustness of the methodology. Seond the results onfirm the onlusion of Fellner et al. (2007) that of the input parameters haraterizing the omposition of the organi matter, the C, H and O ontent of the fossil material are most sensitive followed by the C, H and O ontent of biogeni matter. And third, the relative error due to unertainties of the elementary analysis (CHNSO analysis) is less than 2%, whereby the ontents of TH, TC, and TO as well as TIO are the most determinant variables. Considering the potential inauray of all input parameters the maximum error of the final result is less than 5% (relative error).

9 Limitations of the method The developed method is generally based on a distint differene in the hemial omposition of biogeni and fossil organi matter. Thus, biomass whose omposition approximates that of fossil organi matter is spuriously assigned to fossil materials (e.g., bioplastis, vegetable oil), and, ontrariwise, plastis of typial biogeni elementary omposition are assigned to biomass (e.g., sodium polyarylate, whih is used as an absorbent in diapers). However, due to the minor ontent of materials suh as bioplastis, vegetable oil, or the polymer sodium polyarylate in RDF, this error is at most negligible. A future inrease in the use of materials suh as bioplastis an be aounted for by simply orreting the results using statistial information about the share of bioplastis or polyarylate in total plastis onsumption. CONCLUSION We have reported the development, appliation and suessful validation of a new method for determining the mass, energy and arbon ontent of the biogeni and fossil material frations of mixed wastes and RDF. The method is based on the onept of the balane approah (Fellner et al., 2007), whih uses information about the hemial omposition of biomass and fossil organi matter and operating data from waste ininerators. Unlike the latter method the presented approah uses information obtained by the elementary analysis (TOC, TOH, TOO, TON, and TOS ontent) of waste or RDF samples, respetively. This allows measurement of the fration of biomass or fossil matter, respetively, of fuels prior to their thermal utilization. This method is suessfully validated by analysing defined mixtures of biomass and plastis (PE, PS, ardboard, and wood). The observed differenes between the defined and alulated frations of fossil matter are at most far less than 1%. Sine the input data required for the developed method are obtained by laboratory analyses, whih are to a large extent fundamental for the standard haraterization of RDF (e.g., C-ontent, ash ontent), the analysis effort and thus additional osts are minimal in omparison to alternative methods. The sensitivity analysis shows the importane of reliable data about the hemial omposition of moisture- and ash-free biogeni and fossil organi matter, in partiular regarding the C, H and O ontents. However, errors in the final results (e.g., fossil organi arbon ontent) due to reported unertainties in the omposition of the biogeni and fossil organi matter of household waste for instane (e.g., Fellner et al., 2007) are below 5% (relative error), thereby indiating the robustness of the developed method. ACKNOWLEDGEMENT The authors wish to thank voestalpine AG for finanial support. The Chair of Resoure Management is finanially supported by the Altstoff Reyling Austria AG. REFERENCES CEN, Solid reovered fuels Method for the determination of biomass ontent, European Committee for Standardization CEN, Brussels, 2008, pp. 63. European Parliament, Diretive 2001/77/EC on the Promotion of Eletriity Produed from Renewable Soures in the Internal Eletriity Market, Offiial Journal of the European Communities, L283 (2001) European Parliament, Diretive 2003/87/EC on the Establishing a Sheme for greenhouse gas emission allowane trading within the EU, Offiial Journal of the European Union, L275 (2003)

10 Fellner J., Ceni O., Rehberger H., A New Method to Determine the Ratio of Eletriity Prodution from Fossil and Biogeni Soures in Waste-to-Energy Plants, Environ. Si. Tehnol., 41 (2007) Fellner J., Ashenbrenner P., Ceni O., Rehberger H., Determination of the Biogeni and Fossil Organi Matter Content of Refuse-Derived Fuels based on Elementary Analyses, submitted. Kneissl P., Method for Determining the Relationship of Renewable to Non-Renewable Soures of Engery. WO 02/06730 A1, in, Austria, 2001, pp. 21. Kost T., Brennstofftehnishe Charakterisierung von Haushaltsabfällen, Institut für Abfallwirtshaft und Altlasten, Tehnishe Universität Dresden, Dresden, Mohn J., Szidat S., Fellner J., Rehberger H., Quartier R., Buhmann B., Emmenegger L., Determination of biogeni and fossil CO2 emitted by waste inineration based on 14CO2 and mass balanes, Bioresoure Tehnology, 99 (2008) Norton G.A., Devlin S.L., Determining the modern arbon ontent of biobased produts using radioarbon analysis, Bioresoure Tehnology, 97 (2006) Obermoser M., Fellner J., Rehberger H., Determination of reliable CO2 emission fators for waste-to-energy plants, Waste Management & Researh, 27 (2009) Palstra S.W.L., Meijer H.A.J., Carbon-14 based determination of the biogeni fration of industrial CO2 emissions - Appliation and validation, Bioresoure Tehnology, 101 (2010) Rehberger H., Fellner J., Ceni O., Verfahren zur Ermittlung der Anteile biogener und fossiler Energieträger sowie biogener und fossiler Kohlendioxidemissionen beim Betrieb von Abfallverbrennungsanlagen, Müllhandbuh, (artile 9312), Berlin, Staber W., Flamme S., Fellner J., Methods for determining the biomass ontent of waste, Waste Management and Researh, 26 (2008) van Dijk E.A., Steketee J.J., Cuperus J.G., Feasibility Study of Three Methods for Determining the Biomass Fration in Seondary Fuels, TAUW, Deventer, 2002, pp. 51.

Effect of Variation of Fuel Composition on Gas Turbine Off-Design Performance

Effect of Variation of Fuel Composition on Gas Turbine Off-Design Performance Applied Mehanis and Materials Submitted: 2014-08-28 ISSN: 1662-7482, Vol. 666, pp 194-198 Aepted: 2014-08-28 doi:10.4028/www.sientifi.net/amm.666.194 Online: 2014-10-20 2014 Trans Teh Publiations, Switzerland