In the present work, the sewage sludge from the wastewater treatment plant was acquired as the feedstock. With the amplifying growth of human population, industrial development and urbanization, the nation’s facing an acute challenge related with the management and disposal of sewage sludge. There exists an imperative requisite to ascertain sustainable, energy competent and minimum cost elucidations for the management, treatment and re-utilization of sewage sludge. Amid the thermo-chemical conversion processes, gasification was said to be the most prominent strategy for viable management. Gasification is a thermochemical process that is currently used to produce higher calorific value gases, such as hydrogen, carbon monoxide, carbon dioxide, methane, and other hydrocarbons. In these product gases, the hydrogen and carbon monoxide are called synthesis gas(syngas) which is widely used in heat or power generation and synthesis of fuels and chemicals.
The intention of this work is to propose a model to simulate the gasification of sewage sludge in a fixed-bed downdraft gasifier. The gasification zones were modeled using integrated thermodynamic stoichiometric equilibrium (TSE) and Langmuir-Hinshelwood (LH) kinetic modeling for sewage sludge-based gasification process. The proposed model was compared with formerly published experimentation & modeling on Aspen results. In line with validation of the proposed model, the presented results were in a notable pact with the experimental work. The presented model showed 40% cold gas efficiency (CGE) and 95 % carbon conversion efficiency (CCE). For the developed model, a sensitivity analysis was performed by considering the operating conditions like temperature, pressure, equivalence ratio, steam to biomass ratio and residence time to evaluate the improvement in model for outlet gas composition. In the design of polygeneration process, we divided syngas into combined cycle for power generation and synthesis of hydrogen, natural gas and methanol through simple design with splitter. In the range of splitter, the max power generation is 240 MW, max SNG production is 25900 kg/hr. max hydrogen production is 7760 kg/hr. and max methanol production is 11750 kg/hr.

[1] Syed-HassanSSA, WangY, HuS, SuS, XiangJ. Thermochemical processing of sewage sludge to energy and fuel: Fundamentals, challenges and considerations. Renew Sustain Energy Rev 2017;80:888–913. https://doi.org/10.1016/j.rser.2017.05.262.
[2] KelessidisA, StasinakisAS. Comparative study of the methods used for treatment and final disposal of sewage sludge in European countries. Waste Manag 2012;32:1186–95. https://doi.org/10.1016/j.wasman.2012.01.012.
[3] PecciaJ, WesterhoffP. We should expect more out of our sewage sludge 2015.
[4] YangG, ZhangG, WangH. Current state of sludge production, management, treatment and disposal in China. Water Res 2015;78:60–73. https://doi.org/10.1016/j.watres.2015.04.002.
[5] GaoN, KamranK, QuanC, WilliamsPT. Thermochemical conversion of sewage sludge: A critical review. Prog Energy Combust Sci 2020;79:100843.
[6] KacprzakM, NeczajE, FijałkowskiK, GrobelakA, GrosserA, WorwagM, et al. Sewage sludge disposal strategies for sustainable development. Environ Res 2017;156:39–46. https://doi.org/10.1016/j.envres.2017.03.010.
[7] ZakerA, ChenZ, WangX, ZhangQ. Microwave-assisted pyrolysis of sewage sludge: a review. Fuel Process Technol 2019;187:84–104.
[8] ChenY-C, KuoJ. Potential of greenhouse gas emissions from sewage sludge management: a case study of Taiwan. J Clean Prod 2016;129:196–201.
[9] GaoN, KamranK, QuanC, WilliamsPT. Thermochemical conversion of sewage sludge: A critical review. Prog Energy Combust Sci 2020;79:100843. https://doi.org/10.1016/j.pecs.2020.100843.
[10] LishanX, TaoL, YinW, ZhilongY, JiangfuL. Comparative life cycle assessment of sludge management: A case study of Xiamen, China. J Clean Prod 2018;192:354–63. https://doi.org/10.1016/j.jclepro.2018.04.171.
[11] ZhenG, LuX, KatoH, ZhaoY, LiYY. Overview of pretreatment strategies for enhancing sewage sludge disintegration and subsequent anaerobic digestion: Current advances, full-scale application and future perspectives. Renew Sustain Energy Rev 2017;69:559–77. https://doi.org/10.1016/j.rser.2016.11.187.
[12] MurrayA, HorvathA, NelsonKL. Hybrid life-cycle environmental and cost inventory of sewage sludge treatment and end-use scenarios: A case study from China. Environ Sci Technol 2008;42:3163–9. https://doi.org/10.1021/es702256w.
[13] WertherJ, OgadaT. Sewage sludge combustion. Prog Energy Combust Sci 1999;25:55–116. https://doi.org/10.1016/S0360-1285(98)00020-3.
[14] CantinhoP, MatosM, TrancosoMA, dosSantosMMC. Behaviour and fate of metals in urban wastewater treatment plants: a review. Int J Environ Sci Technol 2016;13:359–86.
[15] PathakA, DastidarMG, SreekrishnanTR. Bioleaching of heavy metals from sewage sludge: a review. J Environ Manage 2009;90:2343–53.
[16] CantinhoP, MatosM, TrancosoMA, dosSantosMMC. Behaviour and fate of metals in urban wastewater treatment plants: a review. Int J Environ Sci Technol 2016;13:359–86. https://doi.org/10.1007/s13762-015-0887-x.
[17] ZhangL, XuC, ChampagneP, MabeeW. Overview of current biological and thermo-chemical treatment technologies for sustainable sludge management. Waste Manag Res 2014;32:586–600. https://doi.org/10.1177/0734242X14538303.
[18] YoshidaH, ChristensenTH, ScheutzC. Life cycle assessment of sewage sludge management: A review. Waste Manag Res 2013;31:1083–101. https://doi.org/10.1177/0734242X13504446.
[19] ZhenG, LuX, KatoH, ZhaoY, LiYY. Overview of pretreatment strategies for enhancing sewage sludge disintegration and subsequent anaerobic digestion: Current advances, full-scale application and future perspectives. Renew Sustain Energy Rev 2017;69:559–77. https://doi.org/10.1016/j.rser.2016.11.187.
[20] StafM, BuryanP. Slow pyrolysis of pre-dried sewage sludge. Chem Pap 2016;70:1479–92. https://doi.org/10.1515/chempap-2016-0089.
[21] RulkensW. Sewage sludge as a biomass resource for the production of energy: Overview and assessment of the various options. Energy and Fuels 2008;22:9–15. https://doi.org/10.1021/ef700267m.
[22] CartmellE, GostelowP, Riddell-BlackD, SimmsN, OakeyJ, MorrisJ, et al. Biosolids - A fuel or a waste? An integrated appraisal of five co-combustion scenarios with policy analysis. Environ Sci Technol 2006;40:649–58. https://doi.org/10.1021/es052181g.
[23] ChenP, XieQ, AddyM, ZhouW, LiuY, WangY, et al. Utilization of municipal solid and liquid wastes for bioenergy and bioproducts production. Bioresour Technol 2016;215:163–72. https://doi.org/10.1016/j.biortech.2016.02.094.
[24] FerrasseJH, SeyssiecqI, RocheN. Thermal gasification: A feasible solution for sewage sludge valorisation? Chem Eng Technol 2003;26:941–5. https://doi.org/10.1002/ceat.200301813.
[25] SamoladaMC, ZabaniotouAA. Comparative assessment of municipal sewage sludge incineration, gasification and pyrolysis for a sustainable sludge-to-energy management in Greece. Waste Manag 2014;34:411–20. https://doi.org/10.1016/j.wasman.2013.11.003.
[26] CaoY, PawłowskiA. Life cycle assessment of two emerging sewage sludge-to-energy systems: Evaluating energy and greenhouse gas emissions implications. Bioresour Technol 2013;127:81–91. https://doi.org/10.1016/j.biortech.2012.09.135.
[27] JiangLB, YuanXZ, LiH, ChenXH, XiaoZH, LiangJ, et al. Co-pelletization of sewage sludge and biomass: Thermogravimetric analysis and ash deposits. Fuel Process Technol 2016;145:109–15. https://doi.org/10.1016/j.fuproc.2016.01.027.
[28] McKendryP. Energy production from biomass (Part 3): Gasification technologies. Bioresour Technol 2002;83:55–63. https://doi.org/10.1016/s0960-8524(01)00120-1.
[29] DeviL, PtasinskiKJ, JanssenFJJG. A review of the primary measures for tar elimination in biomass gasification processes. Biomass and Bioenergy 2003;24:125–40.
[30] GilJ, CorellaJ, AznarMP, CaballeroMA. Biomass gasification in atmospheric and bubbling fluidized bed: effect of the type of gasifying agent on the product distribution. Biomass and Bioenergy 1999;17:389–403.
[31] SchusterG, LöfflerG, WeiglK, HofbauerH. Biomass steam gasification - An extensive parametric modeling study. Bioresour Technol 2001;77:71–9. https://doi.org/10.1016/S0960-8524(00)00115-2.
[32] CampoyM, Gómez-BareaA, VidalFB, OlleroP. Air-steam gasification of biomass in a fluidised bed: Process optimisation by enriched air. Fuel Process Technol 2009;90:677–85. https://doi.org/10.1016/j.fuproc.2008.12.007.
[33] GilJ, AznarMP, CaballeroMA, FrancésE, CorellaJ. Biomass gasification in fluidized bed at pilot scale with steam-oxygen mixtures. Product distribution for very different operating conditions. Energy and Fuels 1997;11. https://doi.org/10.1021/ef9602335.
[34] LvPM, XiongZH, ChangJ, WuCZ, ChenY, ZhuJX. An experimental study on biomass air–steam gasification in a fluidized bed. Bioresour Technol 2004;95:95–101.
[35] PintoF, FrancoC, AndreRN, TavaresC, DiasM, GulyurtluI, et al. Effect of experimental conditions on co-gasification of coal, biomass and plastics wastes with air/steam mixtures in a fluidized bed system. Fuel 2003;82:1967–76.
[36] FontsI, GeaG, AzuaraM, ÁbregoJ, ArauzoJ. Sewage sludge pyrolysis for liquid production: A review. Renew Sustain Energy Rev 2012;16:2781–805. https://doi.org/10.1016/j.rser.2012.02.070.
[37] Atienza-MartínezM, FontsI, LázaroL, CeamanosJ, GeaG. Fast pyrolysis of torrefied sewage sludge in a fluidized bed reactor. Chem Eng J 2015;259:467–80. https://doi.org/10.1016/j.cej.2014.08.004.
[38] Atienza-MartínezM, FontsI, ábregoJ, CeamanosJ, GeaG. Sewage sludge torrefaction in a fluidized bed reactor. Chem Eng J 2013;222:534–45. https://doi.org/10.1016/j.cej.2013.02.075.
[39] PecchiM, BaratieriM. Coupling anaerobic digestion with gasification, pyrolysis or hydrothermal carbonization: A review. Renew Sustain Energy Rev 2019;105:462–75. https://doi.org/10.1016/j.rser.2019.02.003.
[40] LinKH, LaiN, ZengJY, ChiangHL. Temperature influence on product distribution and characteristics of derived residue and oil in wet sludge pyrolysis using microwave heating. Sci Total Environ 2017;584–585:1248–55. https://doi.org/10.1016/j.scitotenv.2017.01.195.
[41] LiuT, LiuZ, ZhengQ, LangQ, XiaY, PengN, et al. Effect of hydrothermal carbonization on migration and environmental risk of heavy metals in sewage sludge during pyrolysis. Bioresour Technol 2018;247:282–90. https://doi.org/10.1016/j.biortech.2017.09.090.
[42] TrinhTN, JensenPA, KimDJ, KnudsenNO, SørensenHR. Influence of the pyrolysis temperature on sewage sludge product distribution, bio-oil, and char properties. Energy and Fuels 2013;27:1419–27. https://doi.org/10.1021/ef301944r.
[43] AlvarezJ, AmutioM, LopezG, BilbaoJ, OlazarM. Fast co-pyrolysis of sewage sludge and lignocellulosic biomass in a conical spouted bed reactor. Fuel 2015;159:810–8. https://doi.org/10.1016/j.fuel.2015.07.039.
[44] ChenQ, LiuH, KoJH, WuH, XuQ. Structure characteristics of bio-char generated from co-pyrolysis of wooden waste and wet municipal sewage sludge. Fuel Process Technol 2019;183:48–54. https://doi.org/10.1016/j.fuproc.2018.11.005.
[45] CaoJP, ShiP, ZhaoXY, WeiXY, TakaradaT. Catalytic reforming of volatiles and nitrogen compounds from sewage sludge pyrolysis to clean hydrogen and synthetic gas over a nickel catalyst. Fuel Process Technol 2014;123:34–40. https://doi.org/10.1016/j.fuproc.2014.01.042.
[46] WangK, ZhengY, ZhuX, BrewerCE, BrownRC. Ex-situ catalytic pyrolysis of wastewater sewage sludge – A micro-pyrolysis study. Bioresour Technol 2017;232:229–34. https://doi.org/10.1016/j.biortech.2017.02.015.
[47] DeAndrésJM, NarrosA, RodríguezME. Air-steam gasification of sewage sludge in a bubbling bed reactor: Effect of alumina as a primary catalyst. Fuel Process Technol 2011;92:433–40. https://doi.org/10.1016/j.fuproc.2010.10.006.
[48] GilC, SebastiánF. Downdraft gasifier modeling 2016:1–63.
[49] BudhathokiR. Three zone modeling of Downdraft biomass Gasification: Equilibrium and finite Kinetic Approach 2013.
[50] RoddyDJ, Manson-WhittonC. Biomass gasification and pyrolysis. vol. 5. 2012. https://doi.org/10.1016/B978-0-08-087872-0.00514-X.
[51] ParthasarathyP, NarayananKS. Hydrogen production from steam gasification of biomass: Influence of process parameters on hydrogen yield - A review. Renew Energy 2014;66:570–9. https://doi.org/10.1016/j.renene.2013.12.025.
[52] Puig-ArnavatM, BrunoJC, CoronasA. Review and analysis of biomass gasification models. Renew Sustain Energy Rev 2010;14:2841–51.
[53] GaoN, LiA. Modeling and simulation of combined pyrolysis and reduction zone for a downdraft biomass gasifier. Energy Convers Manag 2008;49:3483–90. https://doi.org/10.1016/j.enconman.2008.08.002.
[54] Marcio L. de Souza-Santos. Second Edition Solid Fuels Combustion and Gasification. 2010.
[55] HenriksenU, AhrenfeldtJ, JensenTK, GøbelB, BentzenJD, HindsgaulC, et al. The design, construction and operation of a 75 kW two-stage gasifier. Energy 2006;31:1542–53. https://doi.org/10.1016/j.energy.2005.05.031.
[56] RatnadhariyaJK, ChanniwalaSA. Three zone equilibrium and kinetic free modeling of biomass gasifier–a novel approach. Renew Energy 2009;34:1050–8.
[57] ZainalZA, AliR, LeanCH, SeetharamuKN. Prediction of performance of a downdraft gasifier using equilibrium modeling for different biomass materials. Energy Convers Manag 2001;42:1499–515. https://doi.org/10.1016/S0196-8904(00)00078-9.
[58] ChanniwalaSA, ParikhPP. A unified correlation for estimating HHV of solid, liquid and gaseous fuels. Fuel 2002;81:1051–63.
[59] SteuerW. Allgemeine Formel zur Berechnunbdes Heizwertes von festen fossilenBrennstoffen aus des Elementaranalyse. Brennstoff-Chem 1926;7:344–7.
[60] MummeJ, EckervogtL, PielertJ, DiakitéM, RuppF, KernJ. Hydrothermal carbonization of anaerobically digested maize silage. Bioresour Technol 2011;102:9255–60. https://doi.org/10.1016/j.biortech.2011.06.099.
[61] StormC, Ru¨ digerH, SpliethoffH, HeinKRG. Co-pyrolysis of coal/biomass and coal/sewage sludge mixtures 1999.
[62] ParikhJ, GhosalG, ChanniwalaSA. A critical review on biomass pyrolysis. Proc. 12th Eur. Biomass Int. Conf. Netherlands, 2002.
[63] Van deSteeneL, SalvadorS, NapoliA. Rice husk, straw and bark behaviour during pyrolysis, combustion, and gasification: fundamental study, ETA; 2002.
[64] ChanniwalaSA. On biomass gasification process and technology development some analytical and experimental investigations. Bombay” Indian Inst Technol 1992.
[65] GumzW. Gas producers and blast furnaces: theory and methods of calculation. Wiley; 1950.
[66] GardinerWC, BurcatA. Combustion chemistry. Springer; 1984.
[67] SrinivasB, AmundsonNR. A single‐particle char gasification model. AIChE J 1980;26:487–96.
[68] ChoYS, JosephB. Heterogeneous model for moving-bed coal gasification reactors. Ind Eng Chem Process Des Dev 1981;20:314–8.
[69] ThringMW. The science of flames and furnaces. Wiley; 1962.
[70] EvansDD, EmmonsHW. Combustion of wood charcoal. Fire Saf J 1977;1:57–66.
[71] BhagatPM. Wood charcoal combustion and the effects of water application. Combust Flame 1980;37:275–91. https://doi.org/10.1016/0010-2180(80)90096-6.
[72] ReedTB. Biomass gasification: Principles and technology Noyes Data Corporation. Part Ridge, New Jersey, US A 1981.
[73] ReedTB, LevieB, GraboskiMS. Fundamentals, development and scaleup of the air-oxygen stratified downdraft gasifier. Solar Energy Research Inst., Golden, CO (USA); 1987.
[74] TurkdoganET, VintersJV. Effect of carbon monoxide on the rate of oxidation of charcoal, graphite and coke in carbon dioxide. Carbon N Y 1970;8:39–53.
[75] IrvineWM. Langmuir-Hinshelwood Mechanism BT - Encyclopedia of Astrobiology. In: GargaudM, AmilsR, QuintanillaJC, CleavesHJ (Jim), IrvineWM, PintiDL, et al., editors., Berlin, Heidelberg: Springer Berlin Heidelberg; 2011, p. 905. https://doi.org/10.1007/978-3-642-11274-4_863.
[76] TurkdoganET, VintersJV. Kinetics of oxidation of graphite and charcoal in carbon dioxide. Carbon N Y 1969;7:101–17.
[77] AnderssonD, KarlssonM. Investigation of the Effects of Introducing Hydrodynamic Parameters into a Kinetic Biomass Gasification Model for a Bubbling Fluidized Bed 2014.
[78] WenCY, ChenH, OnozakiM. User’s manual for computer simulation and design of the moving bed coal gasifier. vol. 1390. 1982.
[79] SharmaAK. Equilibrium and kinetic modeling of char reduction reactions in a downdraft biomass gasifier: A comparison. Sol Energy 2008;82:918–28.
[80] deAndrésJM, VedrenneM, BrambillaM, RodríguezE. Modeling and model performance evaluation of sewage sludge gasification in fluidized-bed gasifiers using Aspen Plus. J Air Waste Manag Assoc 2019;69:23–33. https://doi.org/10.1080/10962247.2018.1500404.
[81] MarcantonioV, DeFalcoM, CapocelliM, BocciE, ColantoniA, VillariniM. Process analysis of hydrogen production from biomass gasification in fluidized bed reactor with different separation systems. Int J Hydrogen Energy 2019;44:10350–60. https://doi.org/10.1016/j.ijhydene.2019.02.121.
[82] CoutoN, MonteiroE, SilvaV, RouboaA. Hydrogen-rich gas from gasification of Portuguese municipal solid wastes. Int J Hydrogen Energy 2016;41:10619–30. https://doi.org/10.1016/j.ijhydene.2016.04.091.
[83] ZengJ, XiaoR, YuanJ. High-quality syngas production from biomass driven by chemical looping on a PY-GA coupled reactor. Energy 2021;214:118846. https://doi.org/10.1016/j.energy.2020.118846.
[84] PrestipinoM, ChiodoV, MaisanoS, ZafaranaG, UrbaniF, GalvagnoA. Hydrogen rich syngas production by air-steam gasification of citrus peel residues from citrus juice manufacturing: Experimental and simulation activities. Int J Hydrogen Energy 2017;42:26816–27. https://doi.org/10.1016/j.ijhydene.2017.05.173.
[85] ShahbazM, YusupS, InayatA, AmmarM, PatrickDO, PratamaA, et al. Syngas Production from Steam Gasification of Palm Kernel Shell with Subsequent CO2 Capture Using CaO Sorbent: An Aspen Plus Modeling. Energy and Fuels 2017;31:12350–7. https://doi.org/10.1021/acs.energyfuels.7b02670.
[86] HuangX, WuJ, WangM, MaX, JiangE, HuZ. Syngas production by chemical looping gasification of rice husk using Fe-based oxygen carrier. J Energy Inst 2020;93:1261–70. https://doi.org/10.1016/j.joei.2019.11.009.
[87] BaZ, ZhaoJ, LiC, HuangJ, FangY, ZhangL, et al. Developing efficient gasification technology for high-sulfur petroleum coke to hydrogen-rich syngas production. Fuel 2020;267:117170. https://doi.org/10.1016/j.fuel.2020.117170.
[88] GaoW, AslamA, LiF. Effect of equivalence ratio on gas distribution and performance parameters in air-gasification of asphaltene: A model based on Artificial Neural Network (ANN). Pet Sci Technol 2019;37:202–7. https://doi.org/10.1080/10916466.2018.1533864.
[89] FragoulakisV, MitropoulouC, WilliamsMS, PatrinosGP. Advanced Methodological Aspects in the Economic Evaluation. Econ Eval Genomic Med 2015:65–96. https://doi.org/10.1016/b978-0-12-801497-4.00005-9.
[90] AmrullahA, MatsumuraY. Supercritical water gasification of sewage sludge in continuous reactor. Bioresour Technol 2018;249:276–83. https://doi.org/10.1016/j.biortech.2017.10.002.
[91] SahaP, Helal UddinM, Toufiq RezaM. A steady-state equilibrium-based carbon dioxide gasification simulation model for hydrothermally carbonized cow manure. Energy Convers Manag 2019;191:12–22. https://doi.org/10.1016/j.enconman.2019.04.012.
[92] Autoradiographic a N, OfS, TranslocationTHE. And utilization 1970:14–25.
[93] WuW, WenF, ChenJR, KuoPC, ShiB. Comparisons of a class of IGCC polygeneration/power plants using calcium/chemical looping combinations. J Taiwan Inst Chem Eng 2019;96:193–204. https://doi.org/10.1016/j.jtice.2018.11.010.
[94] Puig-GameroM, Argudo-SantamariaJ, ValverdeJL, SánchezP, Sanchez-SilvaL. Three integrated process simulation using aspen plus®: Pine gasification, syngas cleaning and methanol synthesis. Energy Convers Manag 2018;177:416–27. https://doi.org/10.1016/j.enconman.2018.09.088.
[95] Gutiérrez OrtizFJ, SerreraA, GaleraS, OlleroP. Methanol synthesis from syngas obtained by supercritical water reforming of glycerol. Fuel 2013;105:739–51. https://doi.org/10.1016/j.fuel.2012.09.073.
[96] MendesD, MendesA, MadeiraLM, IulianelliA, SousaJM, BasileA. The water-gas shift reaction: From conventional catalytic systems to Pd-based membrane reactors- A review. Asia-Pacific J Chem Eng 2010;5:111–37. https://doi.org/10.1002/apj.364.
[97] RaseHF. Handbook of commercial catalysts: heterogeneous catalysts. CRC press; 2000.
[98] Er-rbibH, BouallouC. Modeling and simulation of CO methanation process for renewable electricity storage. Energy 2014;75:81–8. https://doi.org/10.1016/j.energy.2014.05.115.
[99] KopyscinskiJ. Production of synthetic natural gas in a fluidized bed reactor. Understanding the hydrodynamic, mass transfer, and kinetic effects 2010. https://doi.org/10.3929/ethz-a-006031831.