A reactor-scale CFD model of soot formation during high-temperature pyrolysis and gasification of biomass

Tao Chen,Tian Li,Jonas Sjöblom,Henrik Ström

doi:10.1016/j.fuel.2021.121240

Tao Chen, Tian Li + Show 2 more

Open Access

https://doi.org/10.1016/j.fuel.2021.121240

Copy DOI

Abstract

Soot generation is an important problem in high-temperature biomass gasification, which results in both air pollution and the contamination of gasification equipment. Due to the complex nature of biomass materials and the soot formation process, it is still a challenge to fully understand and describe the mechanisms of tar evolution and soot generation at the reactor scale. This knowledge gap thus motivates the development of a comprehensive computational fluid dynamics (CFD) soot formation algorithm for biomass gasification, where the soot precursor is modeled using a component-based pyrolysis framework to distinguish cellulose, hemicellulose and lignin. The model is first validated with pyrolysis experiments from different research groups, after which the soot generation during biomass steam gasification in a drop-tube furnace is studied under different operating temperatures (900–1200 °C) and steam/biomass ratios. Compared with the predictions based on a detailed tar conversion model, the current algorithm captures the soot generation more reasonably although a simplified tar model is used. Besides, the influence of biomass lignin content and the impact of tar and soot consumptions on the soot yield is quantitatively studied. Moreover, the impact of surface growth on soot formation is also discussed. The current work demonstrates the feasibility of the coupled multiphase flow algorithm in the prediction of soot formation during biomass gasification with strong heat/mass transfer effects. In conclusion, the model is thus a useful tool for the analysis and optimization of industrial-scaled biomass gasification.

Highlights

Biomass gasification is one of the most promising technologies that plays an important role in the energy supply system of many countries [1,2,3]
Existing studies illustrate that soot formation in biomass pyrolysis is mainly caused by the tar generation from lignin, while cellulose and hemicellulose only contribute to a small amount of soot
A new biomass gasification model is established by integrating an Eulerian-Lagrangian multiphase flow algorithm with a two-equation soot formation model that considers the evolution of both soot mass fraction and soot particle size

Summary

Introduction

Biomass gasification is one of the most promising technologies that plays an important role in the energy supply system of many countries [1,2,3]. There are still some practical issues (e.g., tar genera tion) in industrial-scale biomass utilization [4,5,6]. Among various ways of improving the conversion efficiency, high-temperature operation and pulverization of the feedstock are the most commonly used strategies such as in entrained flow gasification [7,8]. Increasing the operating temperature results in additional problems, in particular soot formation, which has an adverse impact on the subsequent cleaning of the bio-syngas and in the maintenance of the gasification equipment [9]. Understanding the mechanism of soot formation is important

Objectives

Methods

Results

Discussion

Conclusion