Rice Husk Gasification Using N2 and Air-Steam for Partial Oxidation

Abstract

The concern for the reduction of the environmental impact caused by greenhouse emissions (CO2) from fossil fuel combustion processes is growing around the world. This has increased research on new energy technologies to produce clean fuels. One of them is the use of biomass as feedstock in gasification processes. The rice agriculture industry around the world produces a great amount of rice husk wastes (RHW) which show the potential for water, soil, and air pollution (including global warming by way of potent greenhouse emissions such as CH4) since waste handling system and structures for storage and treatment frequently are not appropriate. However, the concentration of the rice husk in industrial units makes this low Btu feedstock a viable source for locally based thermal gasification. The current paper presents results on both HRW adiabatic gasification modeling using air-steam blends for partial oxidation and pyrolysis kinetic model to determine, by thermogravimetric analysis (TGA), the RHW activation energy (E). The Chemical Equilibrium with Applications program (CEA), developed by NASA, was used to estimate the effect of both the equivalence ratio (ER) and the steam to fuel ratio (S:F) on adiabatic temperature, gas quality (gas composition and energy density), and energy recovery of an unlimited number of species (∼150). The thermogravimetric analysis (TGA) was carried out using N2 as carrier gas and under different heating rates (β: 10, 20, 40, and 50 °C/min). Furthermore, the activation energy (E) was estimated based in the results from TGA and using the isoconversional method (i.e., free-model). In general, for the range of parameters studied (0.2 < S:F < 0.8 and 1.5 < Φ < 6), the results from equilibrium adiabatic modeling (CEA) showed that increased ER and (S:F) ratios increase the production of H2 and CO2 but decrease the production of CO. Equilibrium temperature decreases with increased ER until ER = 3.0 whereas at ER > 3.0, the effect of ER on equilibrium temperature is negligible. Also, the activation energy average value, estimated from the kinetics model, results to be 233 kJ/kmol.