Numerical study of the biomass pyrolysis process in a spouted bed reactor through computational fluid dynamics

Abstract

Physical and thermochemical characteristics of biomass pyrolysis in a lab-scale spouted bed reactor are studied by means of a reactive multiphase particle-in-cell approach in which gas and solid motions are respectively resolved under the Eulerian and Lagrangian frameworks. Model validation is first conducted, followed by exploring the reactor hydrodynamics and spatial distributions of gas thermochemical properties. The results show that the preferential distribution of biomass particles at the annulus top affects the distribution pattern of gas thermochemical properties. The vertical flux of solid phase in the spout region is at the scale of 100 kg/(m2s), which is nearly one order of magnitude larger than the horizontal one. The turbulent viscosity of gas phase is at the scale of 10−4 m2/s, and the temperature difference within the apparatus is nearly 100 K. The intensively turbulent flow of gas phase exists in the spout region, which will be enhanced as gas inlet velocity and pyrolysis temperature increase. The preferential distribution of biomass particles gives rise to the large content of non-condensable gas and tar in the primary reaction, low temperature, and large density of gas phase in this region. The large content of non-condensable gas in the secondary reaction exists in the upper part of the bed. The results obtained provide a deep understanding of the hydrodynamics and thermochemical properties of gas-solid flows in spouting apparatuses for biomass pyrolysis.