PEM Fuel Cell Simulation On Hysys Platform [PDF]

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PEM Fuel Cell – A case Study in Hysis Platform



Vinay K Sachan & Subhasish Mitra Department of Chemical Engineering IIT Kanpur



Motivation:
Faster depletion of fossil fuels coupled with global warming issue.
Hydrogen appears to be the most promising fuel which is inherently clean & green.
With changing demands, distributed hydrogen economy is envisaged.
Fuel cell drawing attention in various application areas e.g. micro-power, auxiliary power, transportation power, stationary power etc. as an efficient device for utilizing hydrogen potential.



Fuel Cell Principle:
First demonstrated in principle by British Scientist Sir Willliam Robert Grove in 1839. The invention was based on idea of reverse electrolysis.
In general, a fuel cell consists of two electrodes Anode and Cathode.
Hydrogen and Oxygen are fed into the cell.
Catalyst at Anode causes hydrogen atoms to give up electrons leaving positively charged protons.



Fuel Cell Principle (Contd.):
Oxygen ions at Cathode side attract the hydrogen protons.
Protons pass through electrolyte membrane.
Electrons are redirected to Cathode through external circuit.
This leads to production of electrical power.



Fuel Cell Working Mechanism:



Fuel Processor:



[1]



Catalyst: ATR: PdO on Al2O3/CeO2 HTS : Fe/Cr LTS : Cu/Zn/Al PROX : Ru/Pt



[1]. Simulation study of a PEM fuel cell system with autothermal reforming, Atilla Ersoz, Hayati Olgun, Sibel Ozdogan, Energy 31 (2006), 1490 - 1500



Simulation Flow Sheet Data:



[1]



Active cell area is 400 cm2



[1]. Simulation study of a PEM fuel cell system with autothermal reforming, Atilla Ersoz, Hayati Olgun, Sibel Ozdogan, Energy 31 (2006), 1490 - 1500



Simulation Flow Sheet Data:



[1]



P1,P2,P3: Pumps, AC : Air Compressor, E : Power Turbine, HE : Heat Recovery Hx, COM : Combustor, C : Exhaust Stack



[1]. Simulation study of a PEM fuel cell system with autothermal reforming, Atilla Ersoz, Hayati Olgun, Sibel Ozdogan, Energy 31 (2006), 1490 - 1500



Modeling Strategy: Process Simulator: Hysis Version: 2006



Thermodynamic model: Vapor phase : Peng-Robinson EOS (suitable for hydrocarbons)



Unit operations: ATR, HTS, LTS, Combustor : Gibbs reactor PROX, Fuel Cell Cathode : Conversion Reactor Fuel Cell Anode : Separator



Fuel Processor Plant Simulation Diagram: CO clean up section



Heat recovery-II



Heat recovery-I



PEM Fuel Cell



Feed section Fuel Cell Cooling Unit



PEM Fuel Cell Simulation Diagram: Cooling loop



Anode block



Cathode block



Combustor block



System Efficiency Calculations:



[1]



[1]. Simulation study of a PEM fuel cell system with autothermal reforming, Atilla Ersoz, Hayati Olgun, Sibel Ozdogan, Energy 31 (2006), 1490 - 1500



Fuel Cell Polarization Curve:



Generalized polarization curve for a fuel cell showing regions dominated by various types of losses.



The single cell polarization curve taken for calculation.



[1]. Simulation study of a PEM fuel cell system with autothermal reforming, Atilla Ersoz, Hayati Olgun, Sibel Ozdogan, Energy 31 (2006), 1490 - 1500



Fuel Cell Polarization Curve – Curve Fitting: PEM fuel cell characteristics y = -9E-10x 3 + 2E-05x 2 - 0.1076x + 1006.4 R2 = 0.9921 1200



Cell Voltage (mV)



1000 800 600 400 200 0 0



2000



4000



6000



8000



Current density (A/m 2)



10000 12000



A third order polynomial is fitted to describe cell voltage and current density relationship.



Overall System Efficiency Comparison: •Total energy generated (PEMFC + Power Turbine) by the system is 100 Kw – claimed in the reference [1] •PEMFC power calculation as a function of H2 generated not shown. • PEMFC power (Pcell) is calculated using the following reference [2] Pcell = Molar flow rate of H2 X LHV of H2 X electrochemical efficiency



Using this with electrochemical efficiency 0.6 Pcell : 54.21 kW , Ppower turbine : 16 kW, Total energy : 70.21 kW Global system efficiency : 0.2473 Pe : Power generated by the fuel cell system Pa : Auxiliary power consumption Molar flow rate & LHV will be for liquid fuel instead of CH4 [2]. L. Salemme, L. Menna, M. Simeone, Analysis of energy efficiency of innovative ATR based PEM fuel cell system with hydrogen membrane separation, International journal of hydrogen energy 34(2009) 6384-6392.



Section Wise System Efficiency Comparison: No of cells Section



1000 Ref-efficiency



No of cells Simulated - efficiency



Section



500 Ref-efficiency



Simulated - efficiency



1



0.77



0.768



1



0.77



0.768



2



0.76



0.8072



2



0.76



0.8072



3



0.745



0.8016



3



0.745



0.8016



4



0.74



0.7806



4



0.74



0.7806



5



0.735



0.7687



5



0.735



0.7687



6



0.501



0.5584



6



0.434



0.5352



7



0.344



0.3816



7



0.344



0.3657



No of cells



1250



No of cells Section



750 Ref-efficiency



Simulated - efficiency



Section



Ref-efficiency



Simulated - efficiency



1



0.77



0.768



1



0.77



0.768



2



0.76



0.8072



2



0.76



0.8072



3



0.745



0.8016



3



0.745



0.8016



4



0.74



0.7806



4



0.74



0.7806



5



0.735



0.7687



5



0.735



0.7687



6



0.484



0.5447



6



0.517



0.5699



7



0.344



0.3722



7



0.368



0.3894



System Efficiency Comparison: Comparison of system efficiency - No of Cells 750



1



1



0.8



0.8



0.6



Ref-efficiency



0.4



Simulated efficiency



Efficiency



Efficiency



Comparison of system efficiency - No of Cells 500



0.2



0.6



Ref-efficiency



0.4



Simulated efficiency



0.2



0



0



1



2



3



4



5



6



7



1



2



System section



Comparison of system efficiency - No of Cells 1000



4



5



6



7



Comparison of system efficiency - No of Cells 1250



1



1



0.8



0.8



0.6



Ref-efficiency



0.4



Simulated efficiency



0.2 0



Efficiency



Efficiency



3



System section



0.6



Ref-efficiency



0.4



Simulated efficiency



0.2 0



1



2



3



4



5



System section



6



7



1



2



3



4



5



6



7



System section



Efficiency : Ratio of outlet & inlet heat content in a section. Section 1:Liquid fuel, Section 2: ATR, Section 3: HTS, Section 4: LTS, Section 5: PROX



System Power Consumption Comparison: Power Consumption /Generation Source



Power (W) (Reference)



Power (W) (Simulated)



Liquid fuel (P1)



4.3



3.68



Water pump (P2)



5.87



5.88



Cooling loop pump (P3)



210



200.4



Air Compr (AC)



15430



15180



Expander (E)



16700



16000



Stack Voltage Efficiency Comparison: Comparison of stack voltage efficiency



No of cells



Ref-efficiency



Simulated - efficiency



500



0.542



0.669



750



0.605



0.681



1000



0.626



0.698



1250



0.646



0.712



Efficiency



Stack voltage efficiency



0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0



Ref-efficiency Simulated efficiency



0



500



1000



No of cells in stack



Higher simulated values obtained due to •Probable error in fitting voltage/current density curve •Mismatch in Fuel Cell feed flow rate. (Reference: 6 kmol/hr, Sim:8.385 kmol/hr)



1500



Wind up:




Fairly close agreement is obtained between simulated and reference efficiencies of various section of the fuel cell system.








Fairly close agreement is obtained between simulated and reference power consumptions in various sections of the fuel cell system.








Stack voltage efficiency is observed to increase with number of cells in the stack. Simulated stack voltage efficiency is found to be on higher side than reference values.








The obtained net electrical efficiency (7) varies in the range of 34% – 37% which is comparable with the conventional gasoline based IC engine.








To make fuel cell more appealing, volume & mass of reformer system need to be compact by material & catalyst improvement .



Thanks for your attention!