Analysis of energy balances in low and high temperature air gasification systems of pelleted biomass

Energy balance in low and high temperature air gasification of biomass for practical implementation has been carried out based on modeling technique, that involved computation emulating practical gasification processes. The model prediction is based on the first law of thermodynamics analysis of mass species and energy conservation in the gasification systems. In this work, biomass based on sawdust pellets was used to investigate the effect of variation of gasification temperature on the mass flow rate of biomass fuel and the gasification gases (syngas) produced and its quality. The range of temperature deployed is 450 °C to 1200 °C which covers those encountered in the low and high temperature air gasification processes of biomass, and the mass flow rate used in this study ranged from 5 to 50 kg/h. The temperature and biomass mass flow rate influence on the amount, composition, heating value of syngas together with energy balances of each system component were evaluated. Model results obtained predicted that the gasification process is more efficient at gasification temperature ranging from 850 °C to 1000 °C corresponding to an equivalence ratio of 0.283. At this ratio the mass flow of sawdust pellets required to run a 30-kW power plant was 45 kg/h at 600 °C and 40 kg/h at 1000 °C. The computed low heating value (LHV) of the syngas at these temperatures was 3.0 MJ/kg and 7.6 MJ/kg respectively. The results from the model can be used for simulation of syngas composition, LHV, tar and char yield, mass and energy balances and power output of gasification of pelleted sawdust. These results compare well with those obtained from the literature with percentage error of ± 10.