Study On Hydrogen Generation From Biomass Pyrolysis Gas By Packed Bed Technology Based Chemical Looping Process

Hydrogen generation derived from biomass wastes through gasification combined chemical looping process is a novel routine to sovle environment and energy issues. In this study, model gasification gas and its main component(CO) were utilized as fuels. Packed bed reactor system has been set up to achieve high solid and fuel conversion simutaneouly during the reduction period in chemical looping process. Both study of oxygen carriers and reators were carried out with the focus on phase transition characteristics of iron oxides.Based on the calculation of thermodynamics, the characteristic of Fe2O3 reduction played important roles in hydrogen generation.. It was proved that a solid coversion of 20% and a CO conversion of 100% were gained in packed bed reactor through the entire reduction breakthrough curve due to its proper gas-solid contact pattern.The oxygen carrier of 60wt%Fe2O3/40wt%Al2O3 was produced by ball milling method. In a thermogravimetric analyzer, the experiments of sepwise reduction of iron oxides based on the thermodynamics control were implemented. The three steps during the reduction were successfully decoupled. By using Hancock-Sharp method, it was shown that the step of Fe2O3â†'Fe3O4 was fit for nucleation-growth mechanism, the step of Fe3O4â†'FeO was limited by diffusion mechanism, and the step of FeOâ†'Fe was shrinking core mechanism. Among them, the step of Fe3O4â†'FeO was the limitation one. Moreover, the quantitive impact of Al2O3 on the deep reduction of iron oxide was figured out due to the presence of FeAl2O4.The division idea and experiment were applied to directly investigate characteristics of the reduced particles bed in packed bed reactors rather than simply focus on the evolution of effluent gases. This method quantitively released the phase distribution fearture of packed bed technology. By the end of reduction, the reaction zone of Fe3O4â†'FeO took up 80% length of the entire particles bed. Besides, the effect of reator operation parameters has been carried out. For the system built in this study, high efficiencies could be achieved when temperature was 900℃~1000℃, dp/dRwas 0.03~0.09 and the space velocity was about 15min-1。With the modifications, a solid coversion of 28%~30%, a CO conversion of 98.8%~99.6%, a hydrogen generaiotn intensity of 2000~2400μmolH2/gFe2O3, a hydgen generation efficiency of 70%~75% and a hydrogen purity of ~99% were gained. The addition of 5wt%CuO intoFe2O3/Al2O3 managed to increase the amount of Fe and the hydrogen generation intensity was promoted by 30%。Some cases were investigated to assess the potentials of packed bed technology based chemical looping hydrogen generation process for real industrial application. Firstly, a continuous 100-cycle experiments and the regeneration test of used oxygen carrier particles showed the stability of the system. Then, model pyrolysis gas derived from biomass wastes and model coke-oven gas were used as fuels to detect the feasibility of the system for multi-component fuels. The result indicated that packed bed reactors also successfully converted these fuels at high efficiency under proper operation strategies. These satisfying results lay the foundation for this technolyg into industrial application.