Numerical investigations of the impact of inflow conditions on characteristics of a large-scale pyrolysis unit

This work is devoted to the 3D numerical study of the process of co-combustion of biomass volatiles, premixed with air, and non-premixed air-propane burner in the combustion chamber of an industrial biochar reactor. This chamber provides indirect heat for the production of biochar from wood planer shavings using a continuous feeding process running on a slat chain conveyor. A variety of inflow conditions, such as the co-injection of wood pyrolysis gases are investigated with consideration given to different excess air inlets. For each case the heat transfer rate through the plate separating the combustion chamber and the pyrolysis section is calculated and compared to the experimental configuration, which entails the combustion of propane and injection of pyrolysis gas through a large side duct. It was shown that co-injection of pyrolysis gas reduces the required propane flow rate without reducing the overall thermal energy of the unit, while maximizing the heat transfer rate between the combustion chamber and the pyrolysis section. The Finite Rate model/Eddy Dissipation model coupled with k-epsilon Realizable RANS model were used to render turbulence-chemistry interactions. Validation against experimental data published in the literature and measured in the system demonstrated reasonable agreements.