Fuel processing for fuel cell power systems

Fuel processing for he1 cell power systems By Shabbit

Ahmed,

Romesh

Kumar

and Michael

Krumpelt,

Argonne

National

Laboratory,

Fuel for transportation

Fuel processors to produce hydrogen from conventional and alternative fuels are being developed for use in fuel cell power generators. The design of these fuel processors hinges on many factors that include the temperature and pressure required for the conversion, the type and level of by-product that the fuel cell can tolerate, and the duty cycle of the fuel cell power system. This article reviews the types of fuels being considered for fuel cell systems, the reformer technologies being pursued, and the suitability of the reformers for specific applications. The various components needed in the fuel processor have been identified, and some results obtained from the fuel processor development work being conducted at Argonne National Laboratory have been reported.

Fuel

cells

and

portable

consumer cell

are being

developed

power

for

generation

applications.

Recent

technology,

such

stack

reduction

in

the

electrodes

and

more

increasingly

for in fuel

as the

IOO-fold

content

of

economic

bipolar

the

plates,

dominant

of the

absence

option

and a hydrogen

fuel

carbon

fuel gas with

readily

power

an

even

lower sulfide.

1 is a schematic

diagram

system,

which

hydrogen

storage

the low-temperature The

polymer

CO

clean-up

monoxide at

a

for

fuel cell

required is determined be used and the type different

types

demonstrated Except

by the type of application.

of for

electric

for the direct

cell types require

fuel

of fuel cell to At least six

cells

have

power

methanol

generation.

fire1 cell, all fuel

which widely

themselves

operate

of the stack.

available

fuels must

be reformed

a fuel

gas containing

hydrogen)

cells.

For

automotive

fuel

conventionaI availability

gasolines and of alternative

other

methanol,

sulfide)

in

(such

the

reformate

by the operating

as ammonia, -

is

hydrogen determined

temperature

of the

fuel

ethanol,

blends.

the fuel systems,

species

of its ready

gas.

For example,

the solid

hydrogen,

to hydrogen

with

being

effect

for

The

conversion

fuel

process

the

basis

comparisons

factors

related

relative

to the

the

cost

per

refueling

on fuel processing. natural

content ($/mile)

availability

in most

vehicle

to

of >90% heating

needs mile,

other some

and

of

their

fuel cell

fuel because areas.

considerable

efficiency.[2] are based

on

capacity sector,

environmental

impact,

etc.

more

than

would entry

twice

the

energy

carbon coke.

fuels

than drivers

gas

monoxide, as gasoline)

amounts of removed,

an

will and

metal can

density.

It

of

700°C over

on-board

eventually

possibly

a strong

because

gas contains

requires

Furthermore,

(such

in

is not

vehicles

cell

the fuel cell. Although these be removed more effectively

decision

energy

produce

of

possibly

that

temperatures

to

amounts

refinery

Natural

market.

tends

damage may

from market regulations.

fuel

the

to hydrogen

sulfur and trace if not effectively

processor,

the

into

and

and

contain which,

allow

>65O”C

petroleum-derived

natural

energy,

than gasoline

production

its conversion

temperatures

fueling

requires

of the automotive the

that

However,

the

as a percentage

gasoline

the

a smoother

at

urban

efficiencies

of methanol, may be less expensive in the US, and has a well-established

the

diesel, with limited fuels, such as

For stationary

for

can be

as the lower

itself

with

has

the

gas is an attractive

methanol

is less attractive

infrastructure

are

compared

start-up

is essential

of a well-to-wheel

Other

systems,

cell vehicles

conversion rapid

hydrogen,

methanol

irreversibly contaminants

gas and various

et all’1

(or

for use in fuel cell

defined

of the product

methane

not be of the

to hydrogen

fuels

natural

Hauer

choices

fuel cell. In general, the higher-temperature fuel cells have greater tolerance to non-hydrogen in the fuel

on

- at least in the near term - will available. Thus, one or more

The extent of fuel processing required - that is, the allowable levels of carbon monoxide and species

of fuel processing.

cells

available

primarily

degree

been

that

infrastructure

commercially

trace

some

processing

a capability

converted

Gasoline

Fuel

fuel

low for

Further,

and perhaps

The

of the

This

is advantageous applications.

on

different

the sulfur removal unit, downstream reformer will not be needed for an SOFC

extent

less.

below

steam-reformed

vehicular

and thus

Fuel of choice depends on application

and

at temperatures

of the lower heating value of the methanol feed). Methanol is produced largely from natural gas.

the

Fuel cell type determines extent of fuel processing required nature

or

(efficiency

ppm)

electrolyte

250°C

of the

convert to to carbon

At

are needed

devices,

and hydrogen

of the reformer,

of carbon

the

the easiest fuels to dissociates

and can be catalytically

temperature

of a fuel cell

that

transportation Methanol

value

(co.1

highlights

components

is unquestionably

potential hydrogen.

fuel cells

oxidise

spectrum, cell needs

content

of hydrogen

fuel processor system.

ppm)

Methanol

400°C

for

electrochemically.

and

concentration

because

at least in the near term.

developed

can

a low (~50

especially

infrastructure,

500°C

monoxide

Figure

marketing

being

other end of the fuel cell temperature the 80°C polymer electrolyte fuel

technology matures, fuel is becoming an

of a viable

(SOFC)

above

monoxide

issue,

cell

operation

the fuel

increased interest in of polymer electrolyte

cells (PEFCs). As the stack the choice of an appropriate

oxide

and

advances

platinum

have led to commercialisation

distributed

USA

of its

government contender

for

relatively

low

requires

reforming

or higher. 90%

fuel emerge

Typically,

methane,

along

Fuel Cells Bulletin No. 12

with

higher

hydrocarbons,

nitrogen.

Converting

be highly

efficient

to-carbon

ratio.

carbon methane

because

dioxide

and

to hydrogen

can

of its high

Methane

is.also

coking during reforming, hydrocarbon fuels.

Air

hydrogen-

less prone

compared

to

to other

Fuel

-J4

Reformer 230-l

Fuel for stationary The

existing

urban

natural

areas

stationary

fuel

developing

fuel cell power

and

small

can

US

200

kW

have

use in

companies

230-35O’C

80%

150-200-C

Water *

power

Burner

Radiator *

are

Exhaust

gas-fueled,

been

Removal *

1

for residential

Natural

acid fuel cell (PAFC)

generate

for

generators

use.

Fuel Cell

co

-w

t-

in most

attractive

Several

business

phosphoric

350-C

fuel cells

it very

cells.

200-C

Shifter

7)

b

gas infrastructure

makes

Sulfur Removal

-w

plants

that

commercially

available for some time. Higher-temperature fuel cells, i.e. the molten carbonate fuel cell (MCFC) and the solid oxide fuel cell (SOFC), demonstrated 200 kW fuel

for stationary

to 2 MW

cell

In almost

applications,

converted

to

reforming, but

the

compartment

natural by

within

not

generation

from

gas

fuel

catalytic

the

fuel

necessarily

is

steam

cell in

stack

the

or

anode

of the fuel cell.

chemical

industries

use

process

and

hydrogen

in

processes,

and

have

decades.

The

conversion

hydrogen

is carried

techniques and

autothermal

the

l

It

these

of the

require

plants.

A

processor

fuel

to major

The

ability

to cycle

vary

from

processing l

Meeting

l

Maintaining

:sponse

needed

Partial

is

are several than

compact

through (one

5%

to

frequent

or more

in and start-

per day).

rate that is in demand, which 100%

of the

10,

rated

strict

cost targets.

+ CO

nd high

co2 method

reforming + H,)

the rapid

:form

for producing

Fuel Cells Bulletin No. 12

+ the

hydrogen

most

less dynamic

results The

is then

remaining and

other

ejecting

an appropriate

in heat

generation

heat generated used

to steam-

hydrocarbons pyrolysis

of steam

his gas mixture. The oxidation step onducted with or without a catalyst. Autothermal

reformers the

partial

reactions

combine oxidation

by feeding

into

may

be

and the fuel,

H,O common

in the chemical

3

the

etermines nd steam team

and

reaction the relative

reforming the

pathways extents reactions.

and

heat

use of an appropriate

will be formed

under air)

oxygen

and water

= 2, then

temperatures

above

Figure

autothermal

illustrates reforming

= 1, then

coke

such

can be avoided

at

advantage

of

the (which

injects

water

in

with the feed) from the standpoint of coking. These equilibrium calculations also show that yields

feed stream,

are higher

because

Of course,

addition

for

to the

when

more

water

hydrogen

the reaction in the

is in the enters

energies

reforming

product

the

have to

process,

distribution

in

obtained

from thermodynamic equilibrium calculations. Regardless of the type of reformer, the initial invariably

contains

carbon

water-gas

reaction

H, + CO,), which a high-temperature

catalyst

feed

isooctane

575°C.

water

shift

low-temperature oxide, catalyst,

of

in the

are doubled

coking

steam

presence

the

different

of only

proportions

that the O/C

to additional

thereby

three

at O/C

can be converted

of the oxidation The

(from

of

2 shows

at 1, the reactor temperature can be lowered to 1025°C before carbon formation occurs. If the

product the

that

to

form at temperatures up to 1175°C. If is added while maintaining the O/C ratio

be accounted by

is likely calculations

Figure

If the feed consists

oxygen

reactor.

(usually

products),

amount

while

approximation

of carbon

hydrogen

from

coking

formation.

of isooctane

The

react the fuel with

amount of oxygen. The reaction (C,H,O, + 0, j

reaction

of

to and

applications.

reformers

methane

ffects

would water

a wall)

and

to

CO,,

equilibrium

a first

conditions. and

or operated,

for carbon

reforming

and kinetics.

(across

provide

heat

nd air together into the reactor. This process is arried out in the presence of a catalyst, which

reliably.

(C,H,O,

is probably

in automotive

+ H,O)

the

by

can

the amount

reformers

start-up

temperatures.

ontrols Steam

transfer

and

of coke.

Thermodynamic

potential

and steam

limited

steam

oxidation

:forming

performance

by a

methanation,

reaction

selectivity

of H,

the formation

designed

occur.

techniques

endothermic,

the

formation

properly

dioxide

reactors are designed and tend to be heavy

heat

sub-stoichiometric litial oxidation

rate. very

indirect

from

that

than

conventional

he oxidation

A hydrogen production responsive to the change can

rather

the

product

on a dry

gas stream

typically

favour

as lower-temperature

greater

relatively

and carbon scrubbing

such

and

The processing of hydrocarbons always has the potential to form coke. If the reactor is not.

(~-70%

is strongly are

benefits,

inhibiting

reaction,

:onsequently, these sromote heat exchange lakes

applications,

that

shift

reaction

technologies

smaller

and

provide

dioxide. These long periods of

the reformate

designs

for

levels

ups and shutdowns l

from

ttractive

cell

monoxide

reacts

operation

and can deliver

of reactions

urge. The

oxidation

lightweight. l

re removed

perhaps

magnitude

chemical

carbon

steam

gas) in the hydrogen,

of hydrogen

asis). The

ransfer, for

of the following:

production of

operation,

.igh concentrations

is

fuel

one or more

Hydrogen orders

l

reforming.

teady-state

eactor

different

one of three partial

to review

perspective

which

using

arbon monoxide and carbon eformers are well suited for

:forming

hydrogen

reforming,

process,

(e.g. natural to produce

10, absorption in amine solutions, iressure swing adsorption. The primary

of hydrocarbons

out

- steam

appropriate

many

In this

uch as water-gas

petrochemical

manufactured

industry.

ariety

Choice of reforming process affected by fuel and application The

lrocess

rith the hydrocarbon lresence of a catalyst

all of these stationary

hydrogen

often

bundle,

have also been

power

the

is very

environment; activated,

most

monoxide.

hydrogen (CO

+

It

via the H,O

3

is conducted in two reactors: shift reactor followed by a shift

reactor.

active

low-temperature

sensitive

to the temperature

it deactivates the catalyst

Copper

needs

above

zinc shift and

250°C.

To be

to be reduced

in situ

0

1 .E-04 p

l.E-08

E

l.E-12

$ E P s $$ 0

,!+I,+ 0,+3.76N,)

:BH,8+2(0,+3.76NJ +4H,O

i.E-16 1 .E-20 C,H&(0,+3.76N,) +aH,O

I.&24

4

10

n 2 a

1 .E-28 1 .E-32

0

1 :oo

0:30

1 .E-36

Experiment 300

100

500

700

900

Temperature,

and thereafter

isolated

from

air. Rapid

1100

1300

weight,

than

oxidation

those

the

the

shutdowns,

but

train,

and

capability.

As these

final

CO

into

largest can

reactors lower

reactors

are usually

in the fuel processing

the CO

reduction

to ~10

by a catalytic CO,)

shift level

to - 1%. The

ppm

is presently

preferential

approached

oxidation

(CO

+ O,a

reformers

may

incorporate

the

reactor, from

a membrane

separator

within

which

hydrogen

is extracted

pure

reformate

gas mixture

using

a palladium

the power

automotive

by

have

settled

the

as the

alloy

temperature

cell

fuel

cell.

hydrogen

For high

membrane

reaction. is made

hydrogen

separators,

In addition,

available

to the

recovery

the

reforming

with

the

must

be

this

easily,

reduction,

and water partial

energy

to the necessary oxidation

compressing pressure

to pressurise

the

or

autothermal

air

feed

of the membrane

very significant high parasitic

high

it takes

the liquid pressures.

to separator

amounts of energy, power consumption.

fuel With

reforming, the

need

and result

in

constraints

strong processor.

of the fuel cell application

bearing

on

For example,

the

generators for residential natural gas and generate severely

constrained

design

stationary

of

respect

scenario

load-following

hh:mm

Its

of

choice. makes

fuel

to size and

operating

it suitable

for

fast

tolerance

for

carbon

sulfide

and

other

the fuel

reformate

processing

removal,

water, oxygen

low

cell systems water-gas

and

a final

the shift

processor must

for such

incorporate

steps, shift

CO

oxidiser). distinctly

including

reactors

removal

for CO

unit

fuel processor

(e.g. a

described oxide reactor,

damaged during

system

must

requires manner.

include

heat-

injection devices high reforming

in

A review

of the state several

Laboratory131 are fact

the

wall),

on partial

oxidation

ones

most This

that

indirect

conclusion

based

applications. this

suited

as is needed

(heat

these

functions

because

can

be achieved

compact fuel processor that For example, during start-up can

be heated

temperatures

rapidly by burning

in a relatively

can fit inside a car. the fuel processor

to its normal a small

amount

operating of fuel

feeding ratio Dynamic

transfer

It allows the

for

reactor

automotive does

can

is used load-following

during

a

This

system enables and lightweight, or media

start-up

be heated

in fuel and air, but at a higher than

need

across

reformers.

materials rapid

on the

not

transferred

in steam

fuel

reforming

was based

of reforming

heat transfer

National that

for

conclusion

type

no heat

technology

led to the

needed.

all of

(or

uses).

of reforming

since

design

be

start-up

years ago at Argonne

needed

system

into not

Catalytic autothermal reformer for gasoline

start-up

use.

would

between

the rapid

appropriate

Issues

by research

to air during

capability

the

shift

earlier.

which

integration

With

water-gas

addressed

catalysts,

feature of the partial oxidation the reformer to be compact

compromise

specific

if a copper-zinc

the

integrate thermal

load-following

models.

mentioned

shutdown

of

detail

and materials in the the start-up protocol

efficiencies, it is important to thermally these various steps. However, high may

in

to any

not work

by exposure

processors

need excess

will

such as these are being

reaction

therefore

be given

is used

shift

type

be examined

for the reasons

alternative

to

This

system-level

must

above

conducted

may

can

catalyst

of

locations

of components.

comprehensive

Each of these reactions different temperatures.

and the preferential oxidiser (air) injection in a controlled

for automobile

fuel cell power

to

through

amounts

at key

limitations for the catalysts fuel processor. For instance,

fuel cell

low

products

Appropriate

be injected

Consideration

(passenger appear

the combustion processor.

air may

with

for a typical

cell

Thus,

and dynamic

use could operate on 2-5 kWe. They are less with

start-up

be hooked

vehicles

fuel

preferential occurs at

have a the

overheating

might

exchangers, and air and water and controls. To maintain

Effect of fuel cell application on fuel cell system The

sulfur

The

cell

hydrogen

Furthermore,

operating would

prevent

electrolyte

contaminants.

employ

little

load-following

on the polymer

a very

automotive several

relatively

excess

manufacturers

of 80°C

has

pressures (20 bar or of liquid fuels can because

continuously start-up and

fuel

cycle. fuel

monoxide,

out at elevated Steam reforming more

passing

the

and its high energy density can make it However, the polymer electrolyte fuel

carried more).

process

and

use.

this dynamic

automobile

fuel

selectivity

of the reforming

some

generators

grid,

light-duty the

start-up, compact.

pure

with

driving

cars),

membrane. The removal of hydrogen helps to increase the fuel conversion and the hydrogen almost

The

automotive

units would operate requiring frequent

For some

for

need not be as severe as that needed

step.

Alternatively,

Time,

‘C

stationary without

The

2100

hh:mmExperiment

1500

of the copper can lead to very high (1OOO’C) temperatures that will at the very least deactivate catalyst.

I:30

Time,

normal

are

capability directly

by

air-to-fuel operation.

is also easier, because

as

long as the air/fuel ratio is constant, the heat generated in partial oxidation reformers is directly

proportional

to the processing

rate.

In

Fuel Cells Bulletin No. 12

H,S is then process. The elemental SO,

sulfur

or, more

and converted

trap

the

any

H,S

reforming then

the

because must

which

the catalyst

In addition

to a simple

as described catalytic has

can overheat

earlier,

autothermal

a number

appropriate higher

system

and

inhibition

benefits

141 lower

The

of an

levels

of carbon

coke

At Argonne, catalyst

that

fuels - including Figure

gasoline,

3 shows

carbon

and

reformate

generated

cylindrical diameter,

reactor 14 inches

pellets

of CO

Argonne reformer

technology

reactor.

reactor

using

a single-stage

the catalyst

would

shift

With

more

shift thermally

oxide, Argonne shift catalyst. This

oxidising

and

well as temperature If

not

hydrocarbon fuel

the

fuels

processor

petrochemical converted to H,S

will

and

in

poison the

catalysts fuel

cell.

includes

will

be

the

fuel

shift

was

of

Technologies.

Laboratory

is owned

government,

and operated under

use

reactor

reformer,

(see Table the carbon

that

isooctane

gas stream

less than

1). With monoxide

4%

at this

can

containing carbon

J.L.

of 30th

Automotive

Myles:

hydrogen applications

in

Depending application

is

processor The

need

under

States of with

contract

W-

H. Friedrich, requirements

W. for

Laboratory

2%.

Robbins:

“Fuel cell

fuel

International Italy,

1998. M.

for

and

fuel

vehicles”. Symposium

&

S. Ahmed,

Report

Illinois,

USA,

Geyer,

monoxide

Powertrain

1999).

Automation

Krumpelt,

the

K.M.

production

of

hydrogen from methanol and alternative fuels for fuel cell powered vehicles”. Argonne National

4. R. Kumar,

improved process control, level could be reduced to

vehicles”,

for

“Reformers

(a

M.

trade-off

ANL-92/31,

R. Ahluwalia, Krumpelt:

E.D.

“Design,

analyses

Doss,

of gasoline-fueled

November

H.K.

integration,

electrolyte fuel cell systems for 1998 Fuel Cell Seminar, California,

Argonne,

1992.

1998;

and

polymer

transportation”. Palm Springs, Abstracts

Book,

226229. Lee, J.D.

Conclusions

as

National

United

of a contract

Technology

Florence,

be 40%

electric

options

3. R. Kumar, a

developed

gasoline)

US

by the University

1) (Winter

Espino,

(ISATA),

that

from

in

2. R.L.

on

results show

the

of Energy

5. S. Ahmed,

the

Argonne by

the provisions

cell powered

Proceedings

and

processor

catalysts

Preliminary

the

of Advanced

References

removal,

autothermal

by

Office

Automotive

reforming

on an engineeringfuel

hardware.

supported

of Energy’s

InternationalZ(

if needed.

conducted

reactor

Fuel processing

The

work

any potential

of sulfur

integrated

the catalytic

also drop.

be capable

methods

hydrogen in compact

is 347 will

zinc oxide bed for the sulfur removal, and a water-gas shift section: Both the reformer and

less than

in the In

fuel processing

has which

31-109-Eng-38.

than

present

industry, organosulfur by hydro-desulfurisation.

Fuel Cells Bulletin No. 12

in this method

with

environments, sulfur

that

at Argonne

to identify

alternative

hydrogen

rugged

oxide

to develop

(6 kWe)

would

conducted

weaknesses

reactor

excursions.

removed,

zinc

to a fuel

of

needed

objective,

converted

has developed an material is active at

reducing

that this

shift

25045O”C, and it appears to be very attractive for fuel cell applications because it can tolerate both

to verify

oxide are being

integrated

where

of

higher temperatures

fuel

of zinc

component

reactor,

Department

the Department

lifetime

principal

the objective

water-gas

can

per gallon

of gasoline

work designs

Acknowledgment

Chicago

over

the

and lightweight

operating

fuel cell power

and reactor

amount

the

H,

content

Component

integration

1. K.-H. Hauer, 0. Duebel, Steiger, J. Quissek: “Technical

A rgonne.

by a low-temperature

at -2OOOC. is much

effluent Conventional

followed

shift

The l/min.

at 80 miles

systems.

cell

at lower

the

technology

and system catalysts

a multi-

towards

processing

demonstrated

This

about

on the assumptions

sulfur

kWe

scale a

was -40 and additional

uses a high-temperature

at 350-4OO”C,

copper-zinc advanced

to CO,

shift

in

catalyst.

output

in the

need to be converted in a water-gas

gasoline

an

the average

Tests are being

in the

(3 inches (7.6 cm) in (35 cm) long) filled with

hydrogen

10%

dioxide

miles

for

that

fuel

development

the

bed (or other

indicate

for

fuel

processor. If the sulfur content of gasoline is reduced to lower levels in the coming years, the

of hydrogen,

carbon from

the

corresponding

process.I51

which

oxide

required

based

and that

meeting

gas and diesel

reforming

km),

Investigations hydrocarbon

the concentration

monoxide

in

a new class of

naturaI

autothermal

are

of 100,000

IO-12

a significant

can convert

in a zinc

gas

permit

in the reformer,

of

has

directed

fuel

of the fuel. is highly

catalyst

development

concentrations

of the

scrubbing

Laboratory

programme

led to newer

trap).

ZnO

Nattonal

have

product

end

would

calculations

l/100

If the

the

hydro-desulfurisation reforming it

Argonne

suitable

of

complicated

to the front

the US average

processing.

we have developed

materials the

results

formation,

in hydrocarbon

8 kg of

ppm

of water

selectivity

from

sulfur

a fuel ahead

sulfur-tolerant,

hydrogen

Preliminary

(3.5

is not

some

of H,S

In

sulfur-tolerant. becomes

be removed

lifetime

including

combination

catalyst

of

advantage

The

use

it

lower-temperature

many

efficiency,

because

The

allows

offers

options.

injection

by

system

itself

because

suitable

oxide.

processor

be recycled

then

the

produced in the reformer, and a wider of materials of construction and

fabrication

-

process

reforming

of advantages.

which

monoxide variety

oxidation has pursued

catalyst

reforming,

partial

Argonne

catalyst

has been to

be removed

fuel

formation

to

in reforming,

processes.

disciplinary

zinc must

is not

desirable,

or “quench”.

with that

processor for A sulfur-tolerant

steam reformers the heating rate (across the wall) has to closely match the processing rate, without

oxidised

the approach

the sulfur

catalyst

generally,

technologies

and separation

to H,S04.

In fuel cell systems, processor,

alternative

converted to sulfur by the Claus sulfur is then recovered as either

“Catalytic

technology

is receiving in

for the generation

a fresh look

fuel

cell

because

power

of

of new

on the type of fuel cell, the specific and the type of fuel, the fuel system for

design smaller,

can change lighter,

fuel processors producing hydrogen-rich gas has created

more

significantly. responsive

a high-purity, opportunities

for

Krumpelt,

partial

Book,

R. Kumar,

R. Wilkenhoener, oxidation

hydrocarbon fuels”. 1998 Palm Springs, California, Abstracts

generation.

M.

Carter,

S.H.D.

C. Marshall: reforming

Fuel Cell November

of

Seminar, 1998;

242-245.

For more information, contact: Dr Shabbir Ahmed, Group Leader for Fuel Processing, Argonne National Laboratory, 9700 South Cass Avenue, Bldg. 205, Argonne, IL 60439, USA. Tel: +l 630 252 4553, Fax: +1 630 952 4553, Email: [email protected]

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