Fuel Cells – Innovative Systems for Power Generation Fuel Cells For Power Generation.

Fuel Cells – Innovative Systems for Power GenerationFuel Cells – Innovative Systems for Power Generation

Fuel CellsFuel Cells

For Power GenerationFor Power Generation


Dr.-Ing. Hartmut Krause 211/2005

1.1. General aspectsGeneral aspects

2.2. Design and function of fuel cellsDesign and function of fuel cells

3.3. Hydrogen generation for fuel cellsHydrogen generation for fuel cells

4.4. Fuel cell applicationsFuel cell applications

ContentContent



Principle of a fuel cell Principle of a fuel cell compared tocompared to

conventional power generationconventional power generation

ChemicalChemicalenergy of fuelenergy of fuel

Thermal Thermal EnergyEnergy

Mechanical Mechanical EnergyEnergy

ElectricalElectricalenergyenergy

fuel cellfuel cellfuel cellfuel cell

Steam power station / combustion enginesSteam power station / combustion engines

Direct electrochemical conversionDirect electrochemical conversion



AdvantagesAdvantages

High efficiency in small and large power unitsHigh efficiency in small and large power units

High efficiency over the whole control rangeHigh efficiency over the whole control range

Therefore fuel cells are suitable for Therefore fuel cells are suitable for

distributed power supplydistributed power supply

in domestic applicationsin domestic applications



Comparison of theoretical electrical efficiency between Comparison of theoretical electrical efficiency between fuel cell process and combustion processesfuel cell process and combustion processes

en

outenel T

TT

Combustion processCarnot cycle

Fuel cell process

R

Rel H

G



Electrical efficiency of different power generation systemsElectrical efficiency of different power generation systems



Electrical efficiency in the part load rangeElectrical efficiency in the part load range



General parts of a fuel cell systemGeneral parts of a fuel cell system

Fuel processing unitFuel processing unit Fuel cell unitFuel cell unit

primary fuel: natural gas

desulphurization

reformerwater

air

CO - converting

heat heat

hydrogen rich gas

off gas alternating current

digital current

inverter

fuel cell




2.2. Construction and function of fuel cellsConstruction and function of fuel cells



ContentContent



Maximum obtainable work of a chemical reactionMaximum obtainable work of a chemical reaction

HH22 + + ½O½O22 HH22OO HHrr = = GGrr + T + T SSrr

G = - n F EG = - n F E00 H = - n F EH = - n F E00HH

Ideal efficiency of a reactionIdeal efficiency of a reaction

Real conditionsReal conditions

Fuel cell discharge mode:Fuel cell discharge mode: G + n F E < 0G + n F E < 0Electrolysis mode:Electrolysis mode: G + n F E > 0G + n F E > 0

Fundamentals:Fundamentals:

0

0

1H

th E

E

H

ST

H

G



Dependence of cell voltage E on the currant loadDependence of cell voltage E on the currant load

0

*

Hload E

E



Thermodynamic data for fuel cell reactions under Thermodynamic data for fuel cell reactions under standard conditions (1,013 bar, 298 K)standard conditions (1,013 bar, 298 K)

Fuel Reaction n-H0

[kJ/mol]-G0

[kJ/mol]E00

[V]th

[%]

Hydrogen H2 + ½O2 H2Ol 2 286,0 237,3 1,229 83,0

CO CO + ½O2 CO2 2 283,1 257,2 1.066 90,9

Formic acid HCOOH + ½O2 CO2 + H2Ol 2 270,3 285,5 1,480 105,6

Methanol CH3OH + 1½O2 CO2 + 2H2Ol 6 726,6 702,5 1.214 96,7

Methane CH4 + 2O2 CO2 + H2Ol 8 890,8 818,4 1.060 91,9



Thermodynamic cell voltage and ideal efficiency Thermodynamic cell voltage and ideal efficiency under different temperaturesunder different temperatures

Fuel Reaction298 K

E00 [V] th [%]600 K

E00 [V] th [%]1000 K

E00 [V] th [%]

Hydrogen H2 + ½O2 H2Og 1,18 94 1,11 88 1,00 78

CO CO + ½O2 CO2 1,34 91 1,18 81 1,01 69



General characteristics of fuel cellsGeneral characteristics of fuel cells



Principle Principle ofoffuel cellsfuel cells

fuel air

anode off gas cathode off gas

anode cathode

electrolyte

gas permeable catalyst

collector with gas feeder



Types of fuel cellsTypes of fuel cells

type electrolyte ion fuel working temperature

AFC Alcaline FC KOH + water OH- H2 60 – 80°C

PEMFC Polymer Electrolyte Membrane FC

proton feeding membrane, water

H+ H2 60 – 80°C

PAFC Phosphoric Acid FC molten phosphoric acid H+ H2 170 – 200°C

MCFC Molten Carbonate FC molten carbonates (K2CO3, Li2CO3)

CO32- H2, CO 650°C

SOFC Solid Oxide FC ceramic (ZrO2) O2- H2, CO 800 – 1000°C

DMFC Direct Methanol FC proton feeding membrane, water

H+ CH3OH 60 – 80°C

Zoxy Zinc-air-batery KOH OH- Zn 60°C



Electrical characteristic of Hydrogen PEM-FCElectrical characteristic of Hydrogen PEM-FC• maximum voltage 1,23 V at 25°C, 1 bar• minimum voltage 0,33 V (possible electrolysis)• typical current density 0,75 A/cm²

Dependence of cell performance on media pressure



Electrical characteristic of Hydrogen PEM-FC-StackElectrical characteristic of Hydrogen PEM-FC-Stack



Requests to the fuelRequests to the fuel

– maximum hydrogen in the fuel gas

– sulfur content < 0,1 ppm

– free of halogens

– free of particles

Type Fuel Oxidant

AFC – Poor H2 – Poor O2

PEMFC – CO < 15 ppm – O2, Air

PAFC – CO < 1 % – Free of NH3 or minimum N2 in primary gas

– O2, Air

MCFC – internal reforming of CH4 is possible – water additions are necessary

– O2, Air, – CO2-Adition

SOFC – internal reforming of CH4 is possible – water additions are necessary

– O2, Air



Construction types of fuel cellsConstruction types of fuel cells



stack with end stack with end plates and contactsplates and contacts

cellcell

Assembly Assembly of a PEMof a PEMfuel cellfuel cellstackstack



PEMPEM Fuel Cell Stack, Performance: 4 kW Fuel Cell Stack, Performance: 4 kWel.el.



PEMPEM fuel cell stack from insight fuel cell stack from insight




2.2. Construction an function of fuel cellsConstruction an function of fuel cells



ContentContent



• There is no existing up to now a sustainable There is no existing up to now a sustainable hydrogen supply systemhydrogen supply system

• There is an existing natural gas infrastructureThere is an existing natural gas infrastructure

• Natural gas can be converted into hydrogen by Natural gas can be converted into hydrogen by reforming technologiesreforming technologies

Why hydrogen generation by reforming of natural gasWhy hydrogen generation by reforming of natural gas



Natural gas

Desulphurization

ReformingWater

Air

CO - cleaning

Heat Heat

Hydrogen gas



Types of reforming processes of natural gas

Steam-Reforming Autothermic-Reforming Partial Oxidation

Reforming-Reactions

CH4 + H2O CO + 3H2 CH4 + 2H2O CO2 + 4H2

CH4 + H2O CO + 3H2 2CH4 + O2 2CO + 2H2

2CH4 + O2 2CO + 2H2

CO-Conversion (Shift-Reaction)

CO + H2O CO2 + H2

Heat of Reaction Q > 0, endothermic Q = 0, autothermic Q < 0, exothermic.

Hydrogen concen-tration - maximum - typical

80 % 75 %

45 % 40 %

34 % 31 %



eva

po

rato

rre

form

er

CO - conversionand fine cleaning

HT TT SelOx

burner

water

air

des

ulp

hu

r.

nat. gas

compressor moistening

off gas return

heat buffer or heating system

inve

rte

r

con

dit

ion

ing

fu

el c

ell

sta

ck



Low temperature desulphurization with activated carbon:

is necessary for sulfur sensitive catalysts (most) adsorbs also higher hydrocarbons ( odor substances)

High temperature desulphurization with oxidic absorbents (ZnO):

using non sulfur sensitive catalysts for prereforming convert all sulfur compounds into H2S. forming ZnS (higher capacity of desulphurization)

Desulphurization

sulfur content, input : natural gas < 5 mg/m³ reforming gas < 3,5 ppm



Advantages of Steam Reforming

High hydrogen concentration high utilization of the reforming gas

By separate supply of energy and raw gas the energetic use of the off gas from the fuel cells, in the reforming process is possible.

Steam reforming offers the possibility to using the calorific value.

High technical complexity for the facilities because of the heat transfer.

Disadvantages



Steam Reformer

Objectives: - Catalytic splitting methane to hydrogen- With smallest expenditure of energy- With low carbon monoxide content in the product

gasMain reactions:

CH4 + H2O CO + 3H2 HR= 206 kJ/mol

CH4 + 2H2O CO2 + 4H2 HR= 165 kJ/mol

Energy supply:- Over an external surface burner- Recycling of the residual reforming-gas from the fuel cell - Heat recovery from the reformat gas to the raw gas



Equilibrium Concentrations of Steam Reforming Process

73%

74%

75%

76%

77%

78%

600 650 700 750 800 850 900

Temperatur in °C

H2-G

eh

alt

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

CH

4,

CO

, C

O2-G

eh

alt

H2CH4COCO2

p = 1,2 bar p = 1,8 bar

temperature, [°C]

CH

4,

CO

, C

O2 -

co

nc e

ntr

a tio

n

H2 -

co

nc e

ntr

a tio

n



Power Consumption for Hydrogen Generation by Steam Reforming

Without heat recovery

5900

6000

6100

6200

6300

6400

6500

6600

6700

6800

600 650 700 750 800 850 900

Temperatur in °C

En

eg

ieb

ed

arf

be

zog

en

au

f W

as

se

rsto

ffin

kJ

/m³

p = 1,8 bar

p = 1,2 bar

temperature, [°C]

Po

wer

re

qu

ire m

ent

rela

ted

to

H2

[

k J/m

3]



CO - Shift - Conversion

Objectives: - Catalytic transformation of carbonmonoxid With free water from the reforming process- After the reaction: carbonmonoxid concentration < 1 %

Main reaction:

CO + H2O CO2 + H2 HR= - 41 kJ/mol

Use of energy:- provide for heating



Equilibrium Concentration of CO-Shift-Conversion

Specifications for dry Reformat

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

100200300400500

Temperatur °C

CO

, C

O2-G

eh

alt

75%

76%

77%

78%

79%

80%

H2-G

eh

alt

CO

CO2

H2

Reformat = 700°Cp = 1,8 barS/C = 3,0

H2 -

co

nc e

ntr

a tio

n

CO

, C

O2 -

con

cen

trat

i on

temperature, [°C]



Preferential Oxidation

Objectives: - catalytic transformation of carbonmonoxid with oxygen (air) - after the reaction: carbonmonoxid concentration < 10 ppm

Main Reactions:

CO + ½ O2 CO2 HR= - 283 kJ/mol

H2 + ½ O2 H2O HR= - 246 kJ/mol

Energy recovery: - disposition for heating



Change of the Gas Composition durning the Steam Reforming Process and Gas Purification

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%N2

H2

CH4

CO2

C

Reformer CO-Shift Selektive Oxidaton

Composition of gas H2 = 73 Vol%, CO2 = 19 Vol% CH4 = 5 Vol%, N2 = 4 Vol% CO < 5 ppm

Preferential OxidationCO-Shift-ConverterSteam-Reformer

O



Different forms Different forms of catalystsof catalysts




2.2. Construction an function of fuel cellsConstruction an function of fuel cells



ContentContent



Motor vehicles Motor vehicles with PEMFCwith PEMFC

DaimlerChrysler DaimlerChrysler

GM Opel GM Opel Ford Ford

Fiat Fiat

Toyota Toyota

Volkswagen Volkswagen

DaimlerChrysler Ballard DaimlerChrysler Ballard

MAN Siemens MAN Siemens



H Power Corporation H Power Corporation

Fraunhofer Institut Fraunhofer Institut für Solare für Solare Energiesysteme Energiesysteme

IndependentIndependentpower supplypower supplyof portable of portable appliancesappliances



Howaldswerke Howaldswerke DeutscheDeutsche

WerftWerft

Poewer supply of space Poewer supply of space craft and submarines craft and submarines with fuel cellswith fuel cells

International Space Station ISS International Space Station ISS

Space Shuttle Space Shuttle



Heat and Electricity ConsumptionHeat and Electricity Consumption in a Standard Domestic Application in Germanyin a Standard Domestic Application in Germany



PlugPower PlugPower

Sulzer HexisSulzer Hexis

HGC (Energiepartners)HGC (Energiepartners)

Fuel Cell Systems for Fuel Cell Systems for Domestic ApplicationsDomestic Applications

VaillantVaillant



Vaillant BZHVaillant BZH

Electric Power: 1 - 4,6 kW Thermal Power: 1,5 - 7 kWElectrical Efficiency: 30 % Overall Efficiency: > 80 %Working Temperature: 70 / 55 °C



Sulzer HexisSulzer HexisHXS 1000 PremiereHXS 1000 Premiere

Elektrische Leistung: max. 650 WThermische Leistung, ges.: 15/19/25 kW(mit integriertem Brennwertgerät)

Brennstoffzelle:elektr. Wirkungsgrad: 20 %Gesamtwirkungsgrad: 85 %

Fuel Cells – Innovative Systems for Power Generation Fuel Cells For Power Generation.

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Transcript of Fuel Cells – Innovative Systems for Power Generation Fuel Cells For Power Generation.