CHEMICAL EQUILIBRIUM MODELING OF ENTRAINED FLOW GASIFICATION OF TORREFIED TOMATO PEELS

Pre-treating biomass by torrefaction could be beneficial for entrained flow gasification due to the lower milling energy consumption, the improved powder characteristics, the increased heating values and the smaller particle sizes, which enhances fuel conversion. Nevertheless, studies on entrained flow gasification of torrefied fuels are still limited and, so it is not certain if torrefaction pre-treatment is a suitable solution for biomass gasification. The purpose of the present study was therefore to quantify the impact of such a treatment on the quality of the product gas arising from the oxygen-steam gasification in high-temperature entrained flow reactors. To this aim, a chemical equilibrium model for biomass gasification was developed, which allowed to predict the product gas composition as a function of process temperature, equivalence ratio, steam-to-biomass ratio and biomass elemental composition. A global sensitivity analysis with respect to the model input parameters was performed to assess the impact of torrefaction and gasification operating conditions on the product gas quality in terms of heating value and composition metrics typically adopted in the chemical industry (H2/CO ratio, stoichiometric module, etc.). In particular, the gasification of raw tomato peel residues and torrefied solids resulting from their thermal under light (200 °C and 30 min), medium (240 °C and 30 min) and severe (285 °C and 30 min) conditions was investigated using ultimate analysis data in the model. The alternative scenario of steam gasification was also investigated for comparison. Results of this analysis highlighted that the quality of product gas arising from the oxygen-steam gasification of torrefied and untreated tomato peels did not differ very much, although torrefied feedstocks produced more H2 and CO and less CO2 than the parent one. Outcomes of this study provide a useful tool to predict controlling variables in high temperature oxygen-steam entrained flow gasifier.