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Keywords:

  • circulating fluidized bed;
  • fuel;
  • higher hydrocarbon;
  • hydrogen;
  • membrane reformer;
  • modeling;
  • optimization;
  • steam reforming

Abstract

In the present investigation optimization is classified into configuration optimization on one hand and optimization of the design and operating parameters for each configuration on the other hand. The process investigated is that of hydrogen production by steam reforming of higher hydrocarbons. Heptane is used as a model component for higher hydrocarbons. The proposed novel reforming process is basically a circulating fluidized-bed membrane reformer (CFBMR) with continuous catalyst regeneration and gas–solid separation. Composite hydrogen-selective membranes are used to remove the product hydrogen from the reacting gas mixture, thus driving the reversible reactions beyond their thermodynamic equilibria. Dense perovskite oxygen-selective membranes are also used to introduce oxygen for the exothermic oxidation of hydrocarbons and carbon. Four configurations are investigated, two of which relate to the catalyst regeneration before the gas–solid separation and the other two related to the catalyst regeneration after the gas–solid separation. The optimization of the performance of each configuration is carried out for a number of design and operating parameters as optimization parameters and under both non-autothermal and autothermal conditions. Results show that the autothermal operation with direct contact between cold feeds (water and heptane) and hot circulating catalyst can be the best configuration for efficient hydrogen production with minimum energy consumption. The maximum net hydrogen yield is 16.732 mol of hydrogen per mol of heptane fed, which is 76.05% of the maximum theoretical hydrogen yield of 22 when the final reforming products are carbon dioxide and hydrogen. Previous investigations never exceeded 70.82% of this theoretical value. © 2005 American Institute of Chemical Engineers AIChE J, 2005