Numerical simulation of reactive gas-particle flow in a solar jet spouted bed reactor for continuous biomass gasification

Abstract

Solar steam gasification of beech wood biomass in a novel solar conical jet spouted bed reactor was studied. A 3D numerical model of the reactive two-phase gas-particle flow was developed and the model was experimentally validated. The cavity-type solar reactor was operated in both direct and indirect heating configurations at a constant wall temperature of 1200 °C with a biomass feeding rate that varied from 1.2 g/min to 2 g/min. Experiments showed that directly heating the particles increases the H2 yield and the carbon conversion efficiency. The Computational Fluid Dynamics (CFD) model was developed to thoroughly investigate the biomass conversion process inside the conical jet spouted bed subjected to direct or indirect solar irradiations. The desired vigorous cyclic flow pattern of the biomass particles was accurately predicted by the model with peak particles velocity of 2 m/s in the spout region. The maximum temperature reached by the indirectly-irradiated particles is about 1200 °C while it is above 1500 °C when considering directly-irradiated particles. Direct heating thus increases both particles gasification rates and carbon conversion efficiency. Furthermore, simulations reveal that the reaction zone temperature is 100 °C higher for the direct heating configuration. This promotes the H2 formation at the expense of CH4. The steam oxidant concentration, gas products distribution and particles trajectories inside the cavity were also investigated to identify improvement strategies for enhancing the phase mixing and the gas/solid residence time.