Design concepts of a scaled-down autothermal membrane reformer for on board hydrogen production

Michael Patrascu*, Moshe Sheintuch

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The design of an on-board autothermal membrane reactor producing pure hydrogen at atmospheric pressure, while recuperating heat, is analyzed mathematically. The suggested design incorporates two reactors exchanging heat; an endothermic methane steam-reforming (MSR) reactor embedding Pd membranes to separate pure H2, and an exothermic methane oxidation (MOx) reactor fed by the MSR effluent. The analysis is conducted at three levels of details: (i) Thermodynamics reveals that the minimum operating temperature for high thermal efficiency under adiabatic conditions with full recycle of MSR effluents is 550 °C. Feeding the oxidation reactor with added fuel does not improve efficiency. (ii) A kinetic model that accounts for the permeance of the Pd membranes suggests even higher temperatures should be considered when operating with limited membrane area. The effect of catalytic kinetics is small. (iii) A transient detailed one-dimensional model considering heat exchange between the reactors, heat losses to surroundings and axial distribution of the MOx feed is used to study the performance of a 1.3 L system in terms of thermal efficiency and permeate flow rate. Efficiency and H2 output are favored by higher flow rates, which result in higher temperatures. Combustion of recycled effluent produces hot spots, but distributing the feed axially mitigates the non-uniformity, and improves efficiency and permeate flow rate. Some distinct dynamical aspects are presented. We conclude that such a nonadiabatic autothermal system can operate at efficiencies of ∼66% and expected power density of 0.5 kW/L at maximum MSR temperature of 700 °C, when feeding the MSR reactor with liquid H2O instead of pre-vaporizing it. This represents significant improvement over previous designs, and is currently tested experimentally.

Original languageEnglish
Pages (from-to)123-136
Number of pages14
JournalChemical Engineering Journal
Volume282
DOIs
StatePublished - 15 Dec 2015
Externally publishedYes

Keywords

  • Autothermal reforming
  • Exothermic and endothermic reactions coupling
  • Hydrogen production
  • Membrane reactors
  • Modeling
  • Process integration

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