A Novel Process Of Catalytic Gasification Of Biomass For Hydrogen Production With Solid Heat Carrier

For optimizing the energy utilizations and reducing environmental problems, more and more people paid much attention to hydrogen energy. Gasification of the renewable biomass for hydrogen production is a promising technology. However, there are still many obstacles required to resolve until the commercial breakthrough could be obtained, such as high tar content in dry gas and low hydrogen yield. The addition of steam and catalyst favor hydrogen production and tar reduction. In this thesis, a novel process of catalytic gasification of biomass with solid heat carrier is proposed, which is called ECCMB (External Circulating Concurrent Moving-Bed) gasification system. The ECCMB gasification system is composed of two reactors, a gas-solid concurrent moving-bed gasifier and a riser-type combustor. A circulation loop of bed material is achieved between the two reactors. The circulating bed material acts as not only solid heat carrier from the combustor to the gasifier, which supplies the required energy of gasification reactions of biomass, but also catalyst in tar reduction. In gasifier, fast pyrolysis of biomass, catalytic reforming of tar and gasification of char sequently occurs. A dry gas with low tar content and high hydrogen content should be obtained in the ECCMB process. In the combustor, reheating of solid heat carrier and regenerated catalyst are made by burning off the residual char and coke on catalyst.For developing the ECCMB process, investigations were conducted in this thesis as follows:As a part of the ECCMB process, fast pyrolysis of biomass influences greatly the product distribution. As a preliminary work, fast pyrolysis and steam gasification of biomass were studied in a free fall reactor. Effects of reactor temperature, particle size, fuel type and S/B ratio (steam to biomass mass ratio) on product distribution were investigated. It has been shown that the occurrence of the in-situ steam reforming of tar, the steam gasification of char and the water-gas shift reaction after the primary fast pyrolysis of the biomass took place even in a short gas residence time in the free fall reactor. Fast pyrolysis favors biomass conversion for tar reduction and hydrogen production. In addition, during steam gasification of biomass, water-gas shift reaction influences greatly the gas composition at higher temperature. In the free fall reactor, only a limited conversion of tar was achieved because of the short contact time between the catalyst and volatiles.