THE COUPLING OF CATALYTIC STEAM REFORMING AND OXIDATIVE REFORMING OF METHANE TO PRODUCE PURE HYDROGEN IN A NOVEL CIRCULATING FAST FLUIDIZATION BED MEMBRANE REFORMER
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Introduction Steam reforming of natural gas represents the principal commercial route to hydrogen production. The classical industrial steam reformer (1 generation) consists of hundreds of parallel catalyst tubes of about 10 inches diameter, surrounded by a very large furnace. This process suffers from a number of limitations making it extremely inefficient e.g.: (1) Diffusion Limitations: The effectiveness factors of the large catalyst pellets have been found to be as low as 10 – 10. 1,2 (2) Thermodynamic Limitations: The reversibility of the reforming reactions limits the conversion to thermodynamic equilibrium. (3) Catalyst Deactivation: Carbon formation increases with the increase in the temperature, leading to catalyst deactivation. The most successful milestone to date in the development of a more efficient reformer was the bubbling fluidized bed membrane steam reformer (BFBMSR) for natural gas, where powdered catalyst was used to overcome the diffusion limitations and hydrogen selective membranes were used to overcome the thermodynamic equilibrium barrier. Roy et al have experimentally studied the addition of oxygen to the BFBMR to provide all of the heat required for the endothermic reforming reactions, and found that autothermal conditions could be reached and maintained. The BFBMSR, although very efficient, still suffers from a number of important limitations. The present work suggests a novel, more efficient and flexible process consisting of a fast fluidization riser reactor where steam reforming and partial oxidation reactions are carried out. The riser reactor also has a number of hydrogen selective membranes for hydrogen removal and oxygen selective membranes to introduce a part of the oxygen into the reactor for partial oxidation of the feed. A gas solid separator is used to separate the solids and they are recycled to the riser reactor after regeneration of the catalyst. A preliminary schematic diagram of the proposed novel reformer is shown in Figure 1.