Staging Distribution of Oxygen in Circulating Fast Fluidized-Bed Membrane Reactors for the Production of Hydrogen

详细信息    查看全文

• 作者：Mohamed E. E. Abashar ; Fahad M. Alhabdan ; Said S. E. H. Elnashaie
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2007
• 出版时间：August 15, 2007
• 年：2007
• 卷：46
• 期：17
• 页码：5493 - 5502
• 全文大小：237K
• 年卷期：v.46,no.17(August 15, 2007)
• ISSN：1520-5045

文摘

A mathematical model is used to simulate coupled steam and oxidative reforming reactions of methane forheat integration and to improve the yield of hydrogen in a circulating fast fluidized-bed membrane reactor(CFFBMR). A composite membrane of a very thin layer of palladium silver alloy is used for the removal ofhydrogen, shifting the thermodynamic equilibrium and achieving the production of pure hydrogen that issuitable for fuel cells from one integrated unit. A distributed oxygen feed through discrete injection pointsalong the length of the reformer to control the heat in the reaction medium is compared with oxygen feedingthrough dense perovskite membranes and the conventional direct feeding of oxygen (co-feed). Equispacedand orthogonal injection points for oxygen distribution, as well as uniform and nonuniform oxygen flowdistribution, are investigated. The results indicate that the staging distribution of oxygen enables one to controlthe hot-spot temperatures and to operate the reactor under safer operability conditions in contradistinction tothe possibility of thermal runaway for the conventional co-feed mode of operation. The results also show thatthe nonuniform oxygen flow distribution is superior, with regard to hydrogen yield over uniform oxygenflow distribution, for both equispaced and orthogonal injection systems. This is due to the good control andhigh oxygen fluxes at the injection points. The equispaced injection system gives better hydrogen yield thanthe orthogonal injection system in a certain region of parameter space and vice versa in other regions. Amongthe advantages of distributed oxygen feed is that the reformer can be operated at low feed temperatures.