Pilot scale conical spouted bed pyrolysis reactor: Draft tube selection and hydrodynamic performance

Abstract

A study has been conducted on the selection of a draft tube and its performance on a pilot scale conical spouted bed reactor used in the fast pyrolysis of biomass waste. The nonporous draft tube confers high stability to the bed and, furthermore, reduces the fluidizing agent flow rate, which means significant energy saving. The goal of the study is the optimization of the geometrical factors of the internal device in order to achieve suitable operating conditions, given that they have a great influence on bed hydrodynamics and, therefore, on heat transfer characteristics, residence time of the volatiles in the reactor and pyrolysis kinetics.The criteria for the selection are based on a compromise between gas flow rate and solid circulation rate in a bed operating under stable conditions. Moreover, studies have also been carried out on the performance of wood/sand mixtures and the critical elutriation diameter. The results show that a draft tube conical spouted bed operated with a suitable flow rate gives way to very good mixing, elutriation of light particles and short gas residence times.