Catalytic Gasification Of Biomass In External Circulating Radial Flow Moving-Bed Reactor System

In this thesis, a novel process of catalytic gasification of biomass with solid heat carrier is proposed, which is mainly based on the radial flow moving-bed gasifier. This gasification system consist of a gas-solid crosscurrent radial flow moving-bed gasifier, a solid-solid cocurrent and gas-solid countercurrent pyrolyzer and a riser-type combustor. The circulation of bed material, which acts as catalyst and heat carrier, is achieved through the three reactors. The gas in combustor is separated with that in the other reactors. The required heat for gasification reactions is provided by combustion of the pyrolysis char and coke on catalyst, which transferred to the process by heat carrier. The tar and light hydrocarbons in product gas reduce markedly by using radial flow moving-bed gasifier, making it possible to obtain high heat value fuel gas and synthesis gas.Biomass gasification was carried out in the lab-scale facility of lkg/h biomass to demonstrate the system performance, including stability, repeatability and regenerability of catalyst. It has been shown that temperature, pressure and product gas can maintain stability in long time experiment. The product gas fluctuation is less than 5%. Catalyst is reused and regenerated well.A series of experiments were seriously conducted with calcined olivine as the solid heat carrier. The operation conditions including the temperatures of pyrolyzer, steam/biomass mass ratio, fuel type and particle size were investigated. The results show that gas yield and hydrogen content greatly increase with increasing pyrolyzer temperature and S/B, but tar content is opposite. Pine sawdust is better than apricot shell for hydrogen-rich gas production. Under the preferable process parameters, a dry gas of 0.90 Nm3/kg with the content of 50.5vol%(H2+CO) and tar content of 4.3 g/Nm3 has been obtained. Experiment results verified the feasibility of this process.Based on NiO/olivine catalyst prepared in laboratory, steam gasification of Pine sawdust was carried out in the same facility. The effects of gasifier temperature, S/B, circulating amount of bed material(C/B), Z418 catalyst and different amounts of NiO/olivine on product distribution and gas composition has been determined. The NiO/olivine catalyst showed a high activity in the steam and carbon dioxide reforming of methane and tars. With 40wt% catalyst in the bed, the gas yield is 1.27 Nm3/kg, the (H2+CO) content is 73.9vol%, methane content reduced to 0.8vol%, and tar content is 1.46g/Nm3.