A review on computational fluid dynamics modeling of fixed-bed biomass gasifiers: Recent advances and design analysis

Abstract

Biomass gasifiers, especially fixed-bed type, have been perceived as a promising technology for small-scale power generation from renewable sources. Depending on production capacity and end-use applications, various modifications of fixed-bed gasifiers have emerged to generate clean synthesis gas (syngas) with less waste disposal and higher gasifier efficiency. Recently, H₂-rich and CO₂-free syngas production has been experimented with by modifying operating conditions and gasifier design. Computational fluid dynamics (CFD) modeling, incorporating hydrodynamics, chemical reaction mechanism, reactor development, and process intensification, has been brought to pursue a rigorous investigation of gasifier design and the gasification process. This review presents a recent advance in developing the CFD model of fixed-bed gasifiers. A detailed characterization of the biomass gasification process, including devolatilization, homogeneous gas oxidation and reduction, and heterogeneous char reactions, is highlighted. Design analysis of fixed-bed gasifiers is also discussed. Tar species in the devolatilization reaction and their cracking mechanism are interpreted. In addition, the effects of a gasifier configuration and an equivalence ratio of gasifying agents on the producer gas composition, tar content in the producer gas, and the cold gas efficiency are analyzed as a basis for further improvement of the CFD gasifier models.