External Circulating Countercurrent Moving Bed Reactor With Solid Heat Carrier And Its Application To Biomass Gasification

The novel catalytic gasification process with solid heat carrier is called External Circulating Countercurrent Moving Bed gasification system. The system is composed of three reactors, a gas-solid countercurrent moving bed gasifier, a moving bed pyrolysis reactor and a riser-type combustor. The atmosphere of combustor is isolated in relation to pyrolysis reactor and the gasifier. A circulation loop of bed material is achieved among the three reactors. The circulating bed material acts as not only solid heat carrier from the combustor to the gasifier, which supplies the required energy for gasification reactions of biomass, but also catalyst in tar reduction. Fast pyrolysis of biomass in the pyrolysis reactor and catalytic steam reforming of tar in the gasifier occurs in sequence. In the combustor, reheating of solid heat carrier and regenerated catalyst are made by burning off the residual char and coke on catalyst. During the process, fast pyrolysis of biomass, reforming of tar, heating of solid carrier and catalyst regeneration occur simultaneously and continuously. In this way, a hydrogen-rich gas with low tar content is produced. A lab-scale facility of 1kg/h biomass was established to demonstrate this process concept. The operation conditions including bed material, the temperatures of gasifier and pyrolysis reactor, the steam/biomass ratio, bed height and particle size are investigated. The H2 content of 35 mol% in dry gas and the tar yield of 2.5 g/Nm3 dry gas can be obtained at the pyrolysis reactor temperature of 650℃and S/B ratio (steam/biomass mass ratio) 1.2 g/g with calcined olivine as catalyst. The results verify the new concept of biomass gasification for hydrogen-rich gas is feasible. Countercurrent moving of pyrolysis gas and catalyst in the gasification zone is a good solution that enhances the efficiency of the process and decreases the tar yield.