CFD-based coupled multiphase modeling of biochar production using a large-scale pyrolysis plant

Abstract

This paper presents a combined CFD simulation of the thermal conversion of biomass to biochar and the co-combustion of air and biomass volatiles with non-premixed swirl air and volatiles in an industrial pyrolysis plant. The main objective of this study is to investigate thermal conversion process in indirect biochar plants taking into accounts the main challenges associated with biochar production. The model is based on the implementation of calculations on the thermal conversion of biomass in a computational fluid dynamics (CFD) environment. Several sub-models have been introduced to simulate the thermal conversion of biomass to biochar, taking into consideration heat and mass transfer, drying, pyrolysis and volume shrinkage. A non-uniform heat flux obtained by simulating the non-premixed co-combustion of the swirl propane burner and the wood volatile gas has been implemented as an inlet boundary condition in the pyrolysis section. The feasibility of the self-ignition of wood volatiles has been investigated. Uniformity of heat transfer rate between thermal oxidizer and pyrolysis section and lower moisture content in the feedstocks play a remarkable role in producing higher quality of biochar and minimizing residence time in indirect slow pyrolysis plants.