CFD simulation of a fluidized bed reactor for biomass chemical looping gasification with continuous feedstock

Abstract

Integrating the gasification process with the chemical looping technology presents a promising route for biomass conversion with the objective to obtain high quality syngas without air separation. In this study, the biomass gasification with iron-based oxygen carrier and continuous feedstock in the bubbling fluidized bed (BFB) fuel reactor has been investigated based on the computational fluid dynamics (CFD). The solid phases including fuel and oxygen carriers are modeled based on the pseudo-fluid assumption. The numerical model integrates the multi-fluid model and the chemical reaction models involving the decomposition and gasification of biomass and the heterogeneous reactions between gases and metal oxides. The predicted time-varying outlet concentrations of five gas components agree well with the experimental data from the literature. The impacts of the mixing and segregation behaviors between two solid phases on the gas composition distribution are analyzed. The effects of operation temperature, fuel feeding rate and steam content on the chemical looping gasification (CLG) performance are also investigated. The concentrations of CO and H2 as well as the gas yield and gasification efficiency increase while the concentrations of hydrocarbons and CO2 decrease with the escalating temperature because of the facilitation of higher temperature on the endothermic reactions. Raising the feeding rate of biomass leads to a higher gasification efficiency with more valuable syngas but a lower carbon conversion efficiency due to the relatively lower OC-fuel ratio. The gasification atmosphere containing 10–50% of steam also brings remarkable enhancements on the H2 concentration, gas yield and gasification efficiency.