Experimental Evaluation of Biomass Medium-Temperature Gasification with Rice Straw as the Fuel in a Bubbling Fluidized Bed Gasifier

Abstract

Abstract Our previous pilot-scale studies (Bioresource Technology 2018, 267: 102–109) preliminarily demonstrated the feasibility of performing air gasification with a novel two-stage system, including a medium-temperature bubbling fluidized bed (BFB) reactor and a high-temperature swirl-flow furnace reactor, using rice husk as the fuel. As an extension of that work, this study aims to further investigate the reaction mechanism and application prospect of this technology in the use of a more representative biomass fuel, i. e. rice straw. The operation stability, flow behaviors and reaction characteristics in the first-stage medium-temperature gasification reactor are studied in a lab-scale BFB gasifier. The effects of important operating conditions on the syngas quality, tar yield, compositions of carbon residue, and risk of agglomeration are elucidated in depth. The results have shown that an increase in the gasification temperature can promote syngas quality, gasification efficiency, and carbon conversion, but also increases the risk of agglomeration. An increase in the gasification equivalent ratio leads to positive effects on the syngas yield, carbon conversion, and tar concentration, but also has negative effects on the syngas heating value, tar yield, and especially the restrain of agglomeration. An increase in the raw material moisture content has negative influence on the gasification performance of rice straw, in terms of the gasification efficiency, carbon conversion, tar yield, and so on. However, the increase of moisture content can reduce the cost of raw material drying, and avoid the fluctuation of bed temperature, and therefore, a practical gasification system is recommended to be designed and operated under a certain conditions with moderate moisture contents.