A novel circulating fluidized bed membrane reformer for efficient pure hydrogen production for fuel cells from higher hydrocarbons

Steam reforming of hydrocarbon is an important process for hydrogen production. Previous processes suffer from a number of limitations. In this dissertation a novel Circulating Fluidized Bed Membrane Reformer (CFBMR) is suggested for pure hydrogen production. Heptane is used as a model component for higher hydrocarbons. Hydrogen selective membranes are used for removing the product hydrogen and driving the reversible reactions beyond their thermodynamic equilibriums. As a result it improves the hydrogen production significantly. The oxygen introduction by direct feed or through oxygen selective membranes supplies part of heat for the endothermic steam reforming by exothermic oxidation of hydrocarbons and carbon. Counter-current operation provides more efficient hydrogen production at certain conditions. A random carbon deposition and catalyst deactivation model is developed to account for the effects of carbon deposition on the overall reforming performance. An engineering approach with a concept of critical/minimum steam to carbon feed ratio is proposed and used to control the carbon formation in the riser reformer.; The continuous catalyst regeneration recovers the catalyst activity and makes this novel process more flexible with a wide range of hydrocarbon feedstocks. In order to produce hydrogen more efficiently with minimum energy consumption, the heat generated in the catalyst regenerator is utilized to supply the necessary heat for the endothermic process. Autothermal reforming is achievable for the entire adiabatic reformer-regenerator system. Multiplicity of the steady states or Static Bifurcation Behavior (SBB) is found under autothermal operations. Detailed bifurcation behavior and its implications within two possible autothermal configurations are explored over a number of design/operating parameters, which is quite complex and defies the simple logic of non-autothermal processes.; Process parameter and reformer configuration are optimized for the efficient pure hydrogen production with minimum energy consumption under autothermal and non-autothermal conditions. Results show that the autothermal operation with direct contact between the cold feeds (water and heptane) and hot circulating catalyst is the best configuration with a maximum net hydrogen yield of 16.732 moles of hydrogen per mole of heptane fed. Finally, the economics of hydrogen production by steam reforming of hydrocarbons in the Autothermal Circulating Fluidized Bed Membrane Reformer (ACFBMR) is evaluated. Economical analysis shows that this novel process can be a more efficient, more flexible and more economical pure hydrogen producer.