PEM Fuel Cell Simulation on Hysys Platform

PEM Fuel Cell – A case Study in Hysis Platform

Vinay K Sachan & Subhasish MitraDepartment of Chemical EngineeringIIT 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.

� 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 Principle (Contd.):

Fuel Cell Working Mechanism:

Fuel Processor: [1]

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

Catalyst:

ATR: PdO on Al2O3/CeO2

HTS : Fe/Cr

LTS : Cu/Zn/Al

PROX : Ru/Pt

Simulation Flow Sheet Data: [1]

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

Active cell areais 400 cm2

Simulation Flow Sheet Data: [1]

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

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

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:

PEM Fuel Cell

Fuel Cell Cooling Unit

CO clean up section

Heat recovery-I

Heat recovery-II

Feed section

PEM Fuel Cell Simulation Diagram:

Anode block

Cooling loop

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-10x3 + 2E-05x2 - 0.1076x + 1006.4

R2 = 0.9921

0

200

400

600

800

1000

1200

0 2000 4000 6000 8000 10000 12000

Current density (A/m2)

Cell V

olt

ag

e (

mV

)

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

[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.

Pe : Power generated by the fuel cell system

Pa : Auxiliary power consumption

Molar flow rate & LHV will be for liquid fuel instead of CH4

Section Wise System Efficiency Comparison:

0.38160.3447

0.55840.5016

0.76870.7355

0.78060.744

0.80160.7453

0.80720.762

0.7680.771

Simulated - efficiencyRef-efficiencySection

1000No of cells

0.36570.3447

0.53520.4346

0.76870.7355

0.78060.744

0.80160.7453

0.80720.762

0.7680.771

Simulated - efficiencyRef-efficiencySection

500No of cells

0.37220.3447

0.54470.4846

0.76870.7355

0.78060.744

0.80160.7453

0.80720.762

0.7680.771

Simulated - efficiencyRef-efficiencySection

750No of cells

0.38940.3687

0.56990.5176

0.76870.7355

0.78060.744

0.80160.7453

0.80720.762

0.7680.771

Simulated - efficiencyRef-efficiencySection

1250No of cells

System Efficiency Comparison:

Comparison of system efficiency - No of Cells 500

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6 7

System section

Eff

icie

ncy

Ref-efficiency

Simulated efficiency

Comparison of system efficiency - No of Cells 750

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6 7

System section

Eff

icie

ncy

Ref-efficiency

Simulated efficiency

Comparison of system efficiency

- No of Cells 1000

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6 7

System section

Eff

icie

ncy

Ref-efficiency

Simulated efficiency

Comparison of system efficiency

- No of Cells 1250

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6 7

System section

Eff

icie

ncy

Ref-efficiency

Simulated efficiency

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:

1600016700Expander (E)

1518015430Air Compr (AC)

5.885.87Water pump (P2)

200.4210Cooling loop pump (P3)

3.684.3Liquid fuel (P1)

Power (W) (Simulated)

Power (W) (Reference)

Power Consumption/Generation

Source

Stack Voltage Efficiency Comparison:

0.7120.6461250

0.6980.6261000

0.6810.605750

0.6690.542500

Simulated - efficiencyRef-efficiencyNo of cells

Stack voltage

efficiency

Comparison of stack voltage efficiency

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 500 1000 1500

No of cells in stack

Eff

icie

nc

y

Ref-efficiency

Simulated efficiency

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)

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!