Page 172 - Entrophy Analysis in Thermal Engineering Systems

Entropy and chemical equilibrium 167

Fig. 10.9 Comparison of the measured and predicted syngas molar composition using
the modified model at various air ratios. Data are obtained for various feedstock types
gasified at 1100K. (From X. Li, J.R. Grace, A.P. Watkinson, C.J. Lim, A. Ergudenler, Biomass
gasification in a circulating fluidized bed, Biomass Bioenergy 26 (2004) 171–193.)

where n C and n H denote the moles of carbon and hydrogen, respectively.
In this model, it is assumed that all elements, except carbon and hydro-
gen, are completely converted. The predictability of the modified model is
examined using a set of biomass gasification experiments obtained from a
pilot-scale circulating fluidized bed gasifier. Fig. 10.9 provides a comparison
between the measured and predicted dry-gas molar contents of the main
species (except water) of the gasification products. The modified model pre-
dicts the CH 4 content with a good accuracy, but the predicted concentra-
tions of hydrogen are notably higher than the experiments. Furthermore,
the modified model captures the measured CO 2 contents very well, whereas
it underpredicts the CO concentrations with a relative difference of 20%–
25%. The authors stated that the modified model provides better predictions
than the traditional Gibbs energy minimization model.

References
[1] R. Bain, Material and energy balances for methanol from biomass using biomass gas-
ifiers, National Renewable Energy Laboratory, 1992. Report No: TP-510e17098.
[2] X. Ku, T. Li, T. Løva ˚s, CFD–DEM simulation of biomass gasification with steam in a
fluidized bed reactor, Chem. Eng. Sci. 122 (2015) 270–283.
[3] C. Di Blasi, Dynamic behaviour of stratified downdraft gasifiers, Chem. Eng. Sci.
55 (2000) 2931–2944.