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Thermodynamics of autothermal wood gasification

: Mevißen, N.; Schulzke, T.; Unger, C.; Mac an Bhaird, S.


Special topical issue on papers from tchiomass2009. The International Conference on Thermochemical Conversion Science 2009 : Chicago, IL, SEP 16-18, 2009
Chichester: Wiley, 2009 (Environmental progress & sustainable energy 28.2009, Nr.3)
ISSN: 1944-7442
International Conference on Thermochemical Conversion Science <2009, Chicago/Ill.>
Konferenzbeitrag, Zeitschriftenaufsatz
Fraunhofer UMSICHT Oberhausen ()
wood gasification; circulating fluidised bed (CFB); thermodynamic equilibrium; adiabatic condition; carbon; Solid Matter; temperature boundary; cold gas; efficiency; simulation; calculation; Holzvergasung; zirkulierende Wirbelschicht (ZWS); Gleichgewicht(thermodynamisch); adiabatische Bedingung; Kohlenstoff; Feststoff; Temperaturgrenze; Kaltgas; Effizienz; Berechnung

This work extensively studies the thermodynamics of air blown autothermal wood gasification at adiabatic conditions. To this end, the software package HSC Chemistry (R) was used to determine the composition of the synthesis gas at thermodynamic equilibrium. This software operates on the basis of Gibb's energy minimization. In the model, dry and ash-free wood has been represented by CH1.O-44(0.66). Dry air has been modeled as a mixture of oxygen, nitrogen and argon. As the calculations were carried out with respect to adiabatic conditions, it was necessary to determine the adiabatic flame temperature via beat and mass balances. This approach of adopting adiabatic conditions, though generally not taken into consideration in thermodynamic studies, is seen as beneficial, providing additional information with regard to the gasifier operating point. A sensitivity analysis was conducted. The influence of parameters; like equivalence ratio, water content of wood fuel and air preheating on adiabatic flame temperature and cold gas efficiency is discussed. For air at ambient temperature, the highest cold gas efficiency is achieved with an equivalence ratio of about 0.28. This was dependent to some small degree on the water content of the fuel wood. With increased air preheating, the maximum cold gas efficiency is increased and shifted to lower equivalence ratios. For wet wood, it transpired to be more efficient to use the sensible beat from the synthesis gas for drying of the fuel rather than preheating of the air. Finally, calculated values are compared to measurements from a circulating fluidised bed gasifier.