Biochar-assisted gasification of raw biomass: a review on the reactivity and synergistic effect on tar reforming

Abstract

The thermal conversion process known as biomass gasification has the potential to produce environmentally friendly fuels such as hydrogen. However, tar generation during the gasification remains an issue, affecting operational efficiency and environmental health. Biochar has been confirmed as an inexpensive and efficient catalyst for tar removal. The challenge lies in creating a highly reactive biochar which can be applied for different types of biomass with varying properties. This review discusses the factors that affect biochar's reactivity as a catalyst for tar reforming. Additionally, incorporating biochar into a gasification scenario with raw biomass offers a practical solution by leveraging the synergistic behavior. However, this synergy could be either positive or negative: the positive synergy enhances tar removal while the negative synergy has the opposite effect. The numerous factors affecting the results of gasification are presented in this review. It is concluded that the positive synergistic effect resulted from the balance between the available reactants from biomass and biochar, the optimal gas flowrate and the active sites on the carbon surface. Understanding these interactions is crucial for optimizing biochar performance for tar removal. Ultimately, this research provides insights into biochar's role in biomass gasification and suggests improvements for future studies to enhance the feasibility of biomass gasification with the assistance of biochar.