Analysis of the energy efficiency of an integrated ethanol processor for PEM fuel cell systems

Abstract The aim of this work is to investigate the energy integration and to determine the maximum efficiency of an ethanol processor for hydrogen production and fuel cell operation. Ethanol, which can be produced from renewable feedstocks or agriculture residues, is an attractive option as feed to a fuel processor. The fuel processor investigated is based on steam reforming, followed by high- and low-temperature shift reactors and preferential oxidation, which are coupled to a polymeric fuel cell. Applying simulation techniques and using thermodynamic models the performance of the complete system has been evaluated for a variety of operating conditions and possible reforming reactions pathways. These models involve mass and energy balances, chemical equilibrium and feasible heat transfer conditions (ΔTmin). The main operating variables were determined for those conditions. The endothermic nature of the reformer has a significant effect on the overall system efficiency. The highest energy consumption is demanded by the reforming reactor, the evaporator and re-heater operations. To obtain an efficient integration, the heat exchanged between the reformer outgoing streams of higher thermal level (reforming and combustion gases) and the feed stream should be maximized. Another process variable that affects the process efficiency is the water-to-fuel ratio fed to the reformer. Large amounts of water involve large heat exchangers and the associated heat losses. A net electric efficiency around 35% was calculated based on the ethanol HHV. The responsibilities for the remaining 65% are: dissipation as heat in the PEMFC cooling system (38%), energy in the flue gases (10%) and irreversibilities in compression and expansion of gases. In addition, it has been possible to determine the self-sufficient limit conditions, and to analyze the effect on the net efficiency of the input temperatures of the clean-up system reactors, combustion preheating, expander unit and crude ethanol as fuel.

[1]  S. Devotta,et al.  Integrated Fuel Cell Processor for a 5-kW Proton-Exchange Membrane Fuel Cell , 2005 .

[2]  Z. Önsan,et al.  Investigation of ethanol conversion for hydrogen fuel cells using computer simulations , 2005 .

[3]  Theophilos Ioannides,et al.  Thermodynamic analysis of ethanol processors for fuel cell applications , 2001 .

[4]  François Maréchal,et al.  Optimization of a fuel cell system using process integration techniques , 2003 .

[5]  A. Dalai,et al.  Synthesis, characterization and performance evaluation of Ni/Al2O3 catalysts for reforming of crude ethanol for hydrogen production , 2005 .

[6]  Lanny D. Schmidt,et al.  Catalytic partial oxidation of ethanol over noble metal catalysts , 2005 .

[7]  Sibel Ozdogan,et al.  Simulation study of a proton exchange membrane (PEM) fuel cell system with autothermal reforming , 2006 .

[8]  Chunshan Song,et al.  Low-temperature reforming of ethanol over CeO2-supported Ni-Rh bimetallic catalysts for hydrogen production , 2005 .

[9]  X. Verykios,et al.  Renewable Hydrogen from Ethanol by Autothermal Reforming , 2004, Science.

[10]  Agus Haryanto,et al.  Current status of hydrogen production techniques by steam reforming of ethanol : A review , 2005 .

[11]  M. Lyubovsky,et al.  A reforming system for co-generation of hydrogen and mechanical work from methanol , 2006 .

[12]  François Maréchal,et al.  Thermo‐Economic Modelling and Optimisation of Fuel Cell Systems , 2005 .

[13]  Ilie Fishtik,et al.  A thermodynamic analysis of hydrogen production by steam reforming of ethanol via response reactions , 2000 .

[14]  P. C van der Laag,et al.  Benchmarking of chemical flowsheeting software in fuel cell applications , 2001 .

[15]  R. Arjona,et al.  Bio-ethanol steam reforming: Insights on the mechanism for hydrogen production , 2005 .

[16]  Alírio E. Rodrigues,et al.  Insight into steam reforming of ethanol to produce hydrogen for fuel cells , 2006 .

[17]  A. Ersöz,et al.  Reforming options for hydrogen production from fossil fuels for PEM fuel cells , 2006 .

[18]  James Larminie,et al.  Fuel Cell Systems Explained , 2000 .

[19]  M. A. Laborde,et al.  Hydrogen production by the steam reforming of ethanol: Thermodynamic analysis , 1991 .

[20]  S. Douvartzides,et al.  Exergy analysis of an ethanol fuelled proton exchange membrane (PEM) fuel cell system for automobile applications , 2005 .

[21]  P. Umasankar,et al.  Steam reforming of ethanol for hydrogen production : thermodynamic analysis , 1996 .