Review of microwave-based treatments of biomass gasification tar

The formation of biomass tar is one of the most serious drawbacks of gasification, because it not only clogs filters and pipelines, but also poses a serious threat to the environment. Tar abatement is indispensable for the commercialisation of gasification and the production of clean and renewable bio-energy. Microwave heating is an emerging method for tar treatment that provides several advantages, including high heating rates, volumetric heating, and thermochemical reaction acceleration. Although some success has been achieved in biomass tar treatment using microwave-based methods, systematic evaluation of these approaches is still required to achieve detailed understanding of these methods. In this review, the fundamental principles of microwave heating are introduced, and microwave effects, such as hot spots and microwave plasma, are described. The performance and mechanisms of in-situ and ex-situ microwave tar treatment processes are presented and compared. The energy consumption is carefully evaluated. Finally, application potential of these techniques is discussed by comparing with other tar treatments. This review focuses on the most recent reports of microwave-based tar treatment in the literature. It is hoped that this review will provide a foundation for, and new insights into, biomass tar treatment using microwaves.