Development of a microwave-assisted downdraft moving-bed gasifier for continuous processing of lignite and biomass chars

This research illustrates a microwave-assisted downdraft moving-bed gasifier for the first time. This design enables continuous solid gasification processes. An adjustable auger was applied to control the solid removal rate and the gas-solid interaction time. Both lignite and biomass chars were investigated to determine the capability of the current system for low-tar feedstocks with different densities. The presented reactor design was able to operate continuously for 3 h and 20 min under 700 °C and atmospheric pressure, with air as the gasifying agent. For lignite char, the downdraft moving-bed design shows better cold gas efficiency compared to the common fixed-bed design (55.7% vs. 42.3%), due to controllable residence time and more homogeneous microwave heating. For yellow pine char, the processing rate could reach 34.1 grams per hour with decent syngas production. The limitations of the current design and the direction of the novel microwave-assisted chemical reactor design were discussed. This novel reactor design provides a way to improve the efficiency of the microwave-assisted gasification process and shows its potential to be incorporated into other established chemical reaction processes as a modular add-on.