Tar conversion of biomass syngas in a downstream char bed (original) (raw)

Abstract

The catalytic conversion of biomass-derived tars over char during long tests (over 6 hours) is studied. The syngas is generated in a steam-blown fluidized-bed gasifier employing wood pellets and conducted to a second tubular reactor where non-activated char particles are fluidized. The gasifier operated at 750 °C whereas the temperature of the secondary reactor was varied between 750 °C and 875 °C. The evolution of the tar conversion, gas composition and internal structure of the used catalysts were studied. At 750 °C, the initial catalytic activity of the char was low and deactivation occurs rapidly. However, as the reactor temperature increased, the catalytic activity of the char improved significantly. At 875 °C, the initial conversion of tar was above 70 % and over 64 % after 5 h of operation. Moreover, the conversion of the heaviest tars was above 80 % during the entire test. At this temperature, the decrease in tar conversion is attributed to the consumption of the char by steam gasification since its catalytic activity increased during of the test. In these conditions the char bed with an initial weight of 32 g converted approximately 12 g of tars (benzene not included) after 5 h of operation. 1-Introduction Gasification is a thermo-chemical route for conversion of solid fuels, such as biomass and wastes, into a syngas that can be used in a variety of applications [1,2]. Fluidized bed (FB) gasification has several advantages over that in fixed/moving bed or entrained-flow for distributed energy production [3]. However, in all types of FB gasifiers the process temperature must be kept relatively low to prevent agglomeration and sintering of bed material. The low temperature results in incomplete carbon conversion and a high concentration of heavy tars in the gas. The condensation of heavy tars in downstream equipment is the main bottleneck for the use of the syngas in any application where the gas needs to be cooled down. During the last decades, different methods have been developed to reduce the tar concentration in the gas based on physical separation (wet/physical methods) or reforming/cracking of the tar in the hot gas. Wet methods have been tested using water [4,5] or organic solvents [6], and have been reported to be technically efficient. However, this way to clean the gas seems to be too complex and expensive for small or medium-size plants [1]. The reforming/cracking of tar using metallic catalysts (mainly Ni-based) in a downstream vessel is also efficient [7,8] but the presence of certain contaminants in the syngas causes their rapid deactivation. The fast

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References (38)

  1. A. Gómez-Barea, B. Leckner. Gasification of biomass and waste, in: M. Lackner, F. Winter, A.K. Agarwal (Eds.), Handbook of Combustion, vol. 4, Wiley-VCH, Weinheim, 2009, pp. 365-397.
  2. C. Higman, M. van der Burgt. Gasification, second ed. Gulf Professional Publishers/Elsevier Science, Amsterdam, 2008.
  3. Gómez-Barea A, Leckner B, Villanueva Perales A, Nilsson S, Fuentes-Cano D. Improving the performance of fluidized bed biomass/waste gasifiers for distributed electricity: a new three-stage gasification system. Appl Therm Eng 50 (2013) 1453- 1462.
  4. D.J. Stevens. Hot Gas Conditioning: Recent Progress with Larger-Scale Biomass Gasification Systems, NREL, Golden, CO, USA, 2001, Report no. NREL/SR-510-29952.
  5. P. Hasler, T. Nussbaumer. Gas cleaning for IC engine applications from fixed bed biomass gasification, Biomass Bioenergy 16 (1999) 385-395.
  6. H. Boerrigter, "OLGA" Tar Removal Technology, The Energy Research Centre of the Netherlands, 2005, ECN-C-05-009.
  7. D. Sutton, B. Kelleher, J.R.H. Ross. Review of literature on catalysts for biomass gasification, Fuel Process. Technol. 73 (2001) 155-173.
  8. P. Simell, Catalytic Hot Gas Cleaning of Gasification Gas, VTT Publication No 330 (1997).
  9. Z. Abu El-Rub, E.A. Bramer, G. Brem, Fuel 87 (2008) 2243-2252
  10. S. Hosokai, K. Kumabe, M. Ohshita, K. Norinaga, C.Z. Li, J.I. Hayashi. Mechanism of decomposition of aromatics over charcoal and necessary condition for maintaining its activity, Fuel 87 (2008) 2914-2922.
  11. P. Brandt, E. Larsen, U. Henriksen. High tar reduction in a two-stage gasifier, Energy Fuels 14 (2000) 816-819.
  12. D.M.L. Griffiths, J.S.R. Mainhood. Cracking of tar vapor and aromatic compounds on activated carbon, Fuel 46 (1967) 167-176.
  13. D. Fuentes-Cano, A. Gómez-Barea, S. Nilsson, P. Ollero. Decomposition kinetics of model tar compounds over chars with different internal structure to model hot tar removal in biomass gasification, Chem. Eng. J. (2013) 1223-1233.
  14. G. Ravenni, Z. Sárossy, J. Ahrenfeldt, U.B. Henriksen. Activity of chars and activated carbons for removal and decomposition of tar model compounds -A review. Renew Sust Energ Rev 94 (2018) 1044-1056
  15. T. Matsuhara, S. Hosokai, K. Norinaga, K. Matsuoka, C.Z. Li, J.I. Hayashi. In-situ reforming of tar from the rapid pyrolysis of a brown coal over char. Energy Fuels 24 (2010) 76-83.
  16. U. Henriksen, J. Ahrenfeldta, T.K. Jensena, B. Gøbela, J.D. Bentzenb, C. Hindsgaula, L.H. Sørensenc. The design, construction and operation of a 75 kW two-stage gasifier. Energy 31 (2006) 1542-1553.
  17. R.Ø. Gadsbøll, Z. Sarossy, L. Jørgensen, J. Ahrenfeldt, U.B. Henriksen. Oxygen-blown operation of the TwoStage Viking gasifier. Energy 158 (2018) 495-503.
  18. R. Moliner, I. Suelves, M. Lazaro, O. Moreno. Thermocatalytic decomposition of methane over activated carbons: influence of textural properties and surface chemistry, Int. J. Hydrog. Energy 30 (2005) 293-300.
  19. D. Fuentes-Cano, F. Parrillo, G. Ruoppolo, A. Gómez-Barea, U. Arena. The influence of the char internal structure and composition on heterogeneous conversion of naphthalene. Fuel Process. Technol. 172 (2018) 125-132
  20. H. Marsh, F. Rodríguez-Reinoso, Activated Carbon, Elsevier, Oxford, 2006.
  21. F. Nestler, L. Burhenne, M.J. Amtenbrink, T. Aicher. Catalytic decomposition of biomass tars: the impact of wood char surface characteristics on the catalytic performance for naphthalene removal, Fuel Process. Technol. 145 (2016) 31-41.
  22. Y. Song, Y. Wang, X. Hu, J. Xiang, S. Hu, D. Mourant, T. Li, L. Wu, C.Z. Li. Effects of volatile-char interactions on in-situ destruction of nascent tar during the pyrolysis and gasification of biomass. Part II. Roles of steam, Fuel 143 (2015) 555-562.
  23. D. Feng, Y. Zhao, Y. Zhang, S. Sun, S. Meng, Y. Guo, Y. Huang. Effects of K and Ca on reforming of model tar compounds with pyrolysis biochars under H2O or CO2, Chem. Eng. J. 306 (2016) 422-432.
  24. D. Feng, Y. Zhao, Y. Zhang, J. Gao, S. Sun. Changes of biochar physiochemical structures during tar H2O and CO2 heterogeneous reforming with biochar, Fuel Process. Technol. 165 (2017) 72-79.
  25. D. Feng, Y. Zhang, Y. Zhao, S. Sun, J. Gao. Improvement and maintenance of biochar catalytic activity for in-situ biomass tar reforming during pyrolysis and H2O/CO2 gasification. Fuel Process. Technol. 172 (2018) 106-114
  26. C. Choi, K. Shima, S. Kudo, K. Norinaga, X. Gao, J-I Hayashi. Continuous monitoring of char surface activity towards benzene, Carbon Resources Conversion. 2 (2019) 43-50.
  27. A. Korus, A. Samson, A. Szlek, A. Katelbach-Wozniak, S. Sładek, Pyrolytic toluene conversion to benzene and coke over activated carbon in a fixed-bed reactor, Fuel 207 (2017) 283-292.
  28. Y-L Zhang, Y-H Luo, W-G Wu, S-H Zhao, Y-F Long. Heterogeneous cracking reaction of tar over biomass char, using naphthalene as model biomass tar, Energy Fuels 28 (2014) 3129-3137.
  29. G. Ravenni, O.H. Elhami, J. Ahrenfeldt, U.B. Henriksen, Y. Neubauer. Adsorption and decomposition of tar model compounds over the surface of gasification char and active carbon within the temperature range 250-800 °C, Appl. Energy 241 (2019) 139-151
  30. M. Morin, X. Nitsch, M. Hémati. Interactions between char and tar during the steam gasification in a fluidized bed reactor, Fuel 224 (2018) 600-609.
  31. Y. Zhang, S. Kajitani, M. Ashizawa, Y. Oki. Tar destruction and coke formation during rapid pyrolysis and gasification of biomass in a drop-tube furnace, Fuel 89 (2010) 302-309.
  32. D. Buentello-Montoya, X. Zhang, S. Marques, M. Geron. Investigation of competitive tar reforming using activated char as catalyst, Energy Procedia 158 (2019) 828-835
  33. J. Karl, T. Pröll. Steam gasification of biomass in dual fluidized bed gasifiers: A review, Renew. Sust. Energ. Rev. 98 (2018) 64-78
  34. Guideline for sampling and analysis of tar and particles in biomass producer gases. ECN 2002. ECN-C-02-090.
  35. van Paasen SVB. Tar formation in a fluidised-bed gasifier. Impact of fuel properties and operating conditions. 2004. ECN-C-04-013.
  36. D. Fuentes-Cano, A. Gomez-Barea, S. Nilsson. generation and secondary conversion of volatiles during devolatilization of dried sewage sludge in a fluidized bed. Ind. Eng. Chem. Res. 52 (2013) 1234-1243.
  37. L. Jiang, S. Hu, J. Xiang, S. Su, L. Sun, K. Xu, Y. Yao. Release characteristics of alkali and alkaline earth metallic species during biomass pyrolysis and steam gasification process. Bioresour. Technol. 116 (2012) 278-284
  38. A. Dieguez-Alonso, A. Funke, A. Anca-Couce, A. G. Rombolà, G. Ojeda, J. Bachmann, F. Behrendt. Towards biochar and hydrochar engineering-influence of process conditions on surface physical and chemical properties, thermal stability, nutrient availability, toxicity and wettability, Energies. 11 (2018) 496