Author(s)

R. K. Thapa & B. M. Halvorsen

Abstract

Dual fluidized bed gasification reactors are used in a wide range of biomass conversion processes. Some of the important processes are steam gasification of biomass for combined heat and power (CHP) production and synthesis processes leading to production of liquid and gaseous biofuels. Gas-solid multiphase flow and thermochemical processes are responsible for overall performance of the reactor. The multiphase flow involves reacting flow of solids (biomass and bed materials) with gases (steam and product gas components). The thermochemical process involves devolatilization of wood followed by steam gasification, CO2 gasification, methanation, water gas shift and methane reforming. In order to optimize the performance of the reactor, it is important to study each of the global reaction and their reacting flow separately. A computational model has been developed to study the reaction kinetics and the reacting flow in a dual fluidized bed gasification reactor. The model has been validated against the measurements of gas composition in an operating plant for biomass gasification. The reactions are simulated individually using commercial Computational Particle Fluid Dynamic (CPFD) software Barracuda VR 15. The results of simulations such as product gas compositions (CO, CO2, CH4, and H2), wood particle volume fraction and char particle volume fractions are compared for each individual reaction. The results show each of the global reaction contributes to the product gas composition differently. The volume fractions of wood and char particles show that the residence time of wood and char particle in the reactor is different for different reactions. The contribution of devolatilization, steam gasification and water-gas shift in the product gas heating value is more significant than others. Keywords: biomass gasification reactor, dual fluidized bed, CPFD, steam gasification, reaction kinetics, reacting flow.

Keywords

biomass gasification reactor, dual fluidized bed, CPFD, steamgasification, reaction kinetics, reacting flow.