Reduced-Order Modeling (ROM) of a Segmented Plug Flow Reactor (PFR) for Hydrogen Separation for Integrated Gasification Combined Cycles (IGCC)

A reduced-order model (ROM) procedure for a one-dimensional steady plug-flow reactor (PFR) is developed and used to investigate the performance of a membrane reactor (MR), or membrane module (MM), for hydrogen separation from syngas that may be produced in an integrated gasification combined cycle (IGCC). A feed syngas enters from one side into a retentate zone, while a sweep gas of nitrogen enters from the opposite side into a neighbor permeate zone. The two zones are separated by permeable palladium membrane surfaces that are selectively permeable to hydrogen. After analyzing the hydrogen permeation profile in a base case (300 °C uniform temperature, 40 atm absolute retentate pressure, and 20 atm absolute permeate pressure), the temperature of the module, the retentate-side pressure, and the permeate-side pressure were varied individually and their influence on the permeation performance is investigated. In all the simulation cases, fixed targets of 95% hydrogen recovery and 40% mole-fraction of hydrogen at the permeate exit are demanded. The module length is allowed to change in order to satisfy these targets. Other dependent permeation-performance variables that are investigated include the logarithmic mean pressure-square-root difference, the hydrogen apparent permeance, and the efficiency factor of the hydrogen permeation. Various linear and nonlinear regression models are proposed based on the obtained results. This work gives general insights into hydrogen permeation via palladium membranes in a hydrogen membrane reactor (HMR). For example, the temperature is the most effective factor to improve the permeation performance. Increasing the absolute retentate pressure from the base value of 40 atm to 120 atm results in a proportional gain in the permeated hydrogen mass flux, with about 0.05 kg/m2.hr gained per 1 atm increase in the retentate pressure; while decreasing the absolute permeate pressure from the base value of 20 bar to 0.2 bar causes the hydrogen mass flux to increase exponentially from 1.15 kg/m2.hr. to 5.11 kg/m2.hr.