As a flexible energy carrier that can be produced from a variety of resources and with compre­hensive uses, hydrogen is one of the most promising substitutes for fossil fuels. It is certain that renewable-based hydrogen will be quite important in the future, especially hydrogen from biomass which has a series of unique merits. Technologies of hydrogen production from biomass mainly contains two kinds of processes. One is the thermo-chemical route, including biomass/waste gasification, biomass pyrolysis, hydrogen from biomass derived methane/methanol/ethanol; the other is the biological route, including direct bio-photolysis, indirect bio-photolysis photo fer­mentation, hydrogen synthesis via the water gas shift reaction of photo-heterotrophic bacteria, dark fermentation and microbial fuel cells, etc (Chen etal., 2006).

The catalytic hydrogen production technology route of Lu et al. (2004b) research is: CFB and fixed bed are used as reactors, and the catalyst is a mixture of dolomite and nickel-based powder. Dolomite is used as bed material and catalyst, and Ni-based catalyst is placed at outlet of the CFB. The results show that the volume content of hydrogen is more than 50%, and content of CO2 is lower than 1%, gas yield could reach 3.31 Nm3/kg, productivity of hydrogen is 130.28 g/kg biomass.

In the State Key Laboratory of multiphase flow in power engineering of Xi’an Jiao Tong Uni­versity, Yan etal. (2005) have done much work on supercritical water gasification and solar energy catalyzed biomass for hydrogen production. In their study, biomass was used as raw material and an Ni-based alloy tube was taken as reactor. Supercritical water-gasification processed at 650°C under a pressure of 25 MPa. Experimental results indicated that volume content of hydrogen is 41.28%, and the small size of biomass particles favor of the production of hydrogen. Besides, the wall of the reactor could enhance the production of hydrogen (Guo et al., 2005).

The Institute of Coal Chemistry, Chinese Academy of Science has studied the CFB conversion of biomass and supercritical water conversion for hydrogen production. The feasibility of total processing of biomass and coal was investigated in the CFB. Besides, hydrogen production from sawdust was processed under supercritical pressure at 773-923 K, and batch-type supercritical water reactor was used as reaction chamber. It was found that the molar ratio of calcium and carbon has a great influence on the conversion of sawdust. Gas conversion of carbon and the gas yield of hydrogen is doubled when the molar ratio of calcium and carbon equals to 0.48. Besides, reaction temperature also has great impact on gas yield of hydrogen.

Figure 4.10. Polygeneration scheme of cotton stalk system.

The Institute for Thermal Power Engineering of Zhejiang University has developed steam-gas co-production of biomass and coal experiment and a mechanism study which aim at obtaining combustion gas. The synthetic gas was tested in a double CFB circulating system and the calorific value can reach 2800kcal/Nm3, and conversion of fuel is 95%. Based on these results, biomass conversion for hydrogen production is under investigation at present, including the separation of CO2.

Tianjin University is famous for catalytic pyrolyzation of biomass for hydrogen-rich gas, and has proposed the technology route of fast pyrolysis-catalyst steam reforming. A two stage catalyzed gasification hydrogen production system, which includes CFB gasification reactor and fixed bed, was built. The impact of operation parameters, design parameters and catalyst type to the gas yield were investigated, and the results showed that the volume of hydrogen-rich gas can reach 50-65% (Chen etal., 2003b).