Coal-char gasification with steam and steam-oxygen mixtures

Thermochimica Acta, 85 (1985) 315-318 Elsevier Science Publishers B.V., Amsterdam

COAL-CHAR

E.

GASIFICATION

PILARCZYK,

K.

WITH

STEAM

KNOBLAUCH

Bergbau-Forschung

GmbH,

315 -Printed

and

in The Netherlands

AND

H.

STEAM-OXYGEN

MIXTURES

JDNTGEN

Franz-Fischer-Weg

61,

4300

Essen

13

(FRG)

ABSTRACT The kinetics and pore development in steam and steam/oxygen gasification of a special coal-char derived from a German bituminous hard coal have been studied in a temperature range of 1023-1213 K. The steam gasification occurs under kinetic control causing the pore volume to grow with increasing burn-off. The reaction order with respect to the remaining carbon is Z/3, the activation energies applying a Langmuir-Hinshelwood equation are 266 resp. 51 kJ/ to steam the reaction rate is enmol. Adding 0.5 i 5.0 % oxygen hanced and becomes limited by the film diffusion-resistance. In this case lower pore volumes are obtained than in absence of oxygen.

INTRODUCTION In

activation

often for

used high

moved

in

of order

the

reaction

regime,

In

external

loss

of

the mainly

tics

study

and

the

pore

steam

a suitable During exterior

kinetic,

kinetic

porous

inner

gasification surface

pore

control

gasification structure

carbon

depending

diffusion

is

and

desired

in

is

is

on

film

order

re-

the

diffusion to

avoid

carbon.

materials

impurities, to

and/or

(ref.l-4)

applications

was

develop

namely

general

papers

materials

capacities.

interior

control.

starting

to

adsorptive

at

Many

carbonaceous

concerning have

been

steam

steam/carrier-mixture oxygen.

of

development

in

low

in

this

often

Therefore,

influence

activation

published

the

amounts

steam

of

different

field.

In

contains

technical

different

objective

of

this

of

on

the

oxygen

work kine-

activation.

EXPERIMENTAL The German

char

used

in

bituminous

(C:

88.0%,

The

kinetics

0040~6031/85/$03.30

H:

0.9%, were

this

hard N:

study

coal

was

by

1.5%,

determined 0 Elsevier Science

derived

from

devolatilization

0:

1.5%,

by

TGA-technique

Publishers

S:

B.V.

0.7%,

a special in ash:

N,

at

6.6%,

measuring

oxidized 1173

K

wf). continous

316 weight

changes

3 mm)

pressure. and

oxygen

different

isothermal

Helium

was

(O-50

different and

of

during

chosen

hPa).

burn-offs

steam/oxygen

grains

of

the

gasification as

carrier

Besides

were

in

these

prepared

gasification

for

(aO.1,

0.3

steam

(100-500

structure

3 mm

- 0.5,

at

TGA-experiments

for

of

char

a thermobalance

chars

analysis

granules

normal hPa)

in

with by

steam

a fluidized

bed. Hg-penetration to

determine

gasified

and

the

adsorption

pore

size

of

methanol

distribution

(T=293

resp.

K)

pore

were

volume

used of

the

chars.

RESULTS

AND

First action

DISCUSSION

of

all

rates

means

the

the

rate

be

oxygen-free

obtained

reaction

glecting can

for

were

is

steam

for

under

the

gasification

three

kinetic

different

control.

influence

of

the

gaseous

formulated

by

the

following

In

products

similar

re-

grains,

that

this the

case

and

ne-

gasification

Langmuir-Hinshelwood

equation:

-

dm, 1 _--.-_=_

dXc

dt

rn!

ki

1

1

dt

(l-Xc)n

= kio

exp

(-Ei/RT)

m,

the

actual

(1)

klCH,O

(m;)"-'

I+k2CH,0

with

Where weight

is

of

respect

carbon,

to

frequency

Xc

carbon,

(2) weight

the

CH

o the

EiZthe

factors,

of

carbon

burn-off,

at

n the

steam

time

t,

reaction

concentration,

activation

energies

rn: the order

initial

with

Iki o the and

T'the

tempera-

ture. The sus

reaction

(l-Xc)

different slope tion

of

on

order

n can

log-log

paper.

steam 0.66

energies

Ei

gression

after

measured

burn-off/

neously.

The

ted

parameters

and

the

result are:

is

Fig.1

time-data of

this

of

For

method different

fitting

plotting

such

parallel

factors

squares

by

shows of

obtained.

frequency

least

obtained

A set

pressures. (n=0.66)

be

is

plots lines

evaluation ki

dXc/

dt

for

four

with of

o a nonlinear

WAS

computed

experiments shown

in

Fig.2.

an the

ver-

average activa-

refitting

the

simultaThe

evalua-

317

kl,O

k2,0

= 4.7.10'

m3gl'3/mo1

= 82.4

m3/mol

min

E1

= 265.6

E:! =

50.9

kJ/mol kJ/mol

* 0.6 8 0 0. 4 k 2

0.00

Fig.1

I

I111114

l-Xc

C-l

I

, 1

1.

Determination tion order n +200,x300,050~

Adding

0.5-5%

O2

gasification very

much

other pore

(see it

the

external is

sion

steam

is

be

On

the by

burn-off due

to

that of

car-

film

diffu

control.

During used

a bimodal

with

micro-

developed.

resp.

100

150

200

Cminl

Influence of temperature on the rate of steam oasification (500 hPa H,OTexp: +1083,x1133,*1183,o1213 K; solid lines: talc.)

1.0

z

0.8

2

0.6

rc 7 0.4 E 2 0.2

gasification

(rp (10

Fig.2

the

shown

analysis

raised

50

enhanced

Fig.3). can

structure

bon

to

0

time t

of the reac(T=1173K/*lOO. hPa H26)

rate

hand

0.2

of

pore

and

the

char

0. 0

structure

time t

macropores

rp>

10

Cminl

rim) is Fig.3

Influence of 0, on the rate of steam gasification (100 hPa H,O,T=1173 K/*0, +5,x10,025,#50 hPa 0,)

318

Fig.4

and

Fig.5

burn-off

for

cation

no

there

the

different

pore

is

show

pore

of

of

experimental

development

a raise

volume

the

is pore

these

conditions.

observed volume

at

T

In

1023

K,

as

function

H20/02-gasifiwhereas

I

,

4o

‘;; > 20

L”

8.0

9 macro

s

At

';; > 20

J “?I a-0

Xc

not

occur,

the

outside

interior. interior

temperature only

oxygen

surface At

the

surface

burn-off.

steam

will

diminish

(see

Fig.5),

with

without

pore in

it volume

the

water-gas

carbon

the is

for

Xc

the

creating

reacts

pore

evident

micropore

I

I

I

C-l

reaction

burning or

steam

consequently

the

I

I

that

a given

pellets pores

too,

volume

does

but

at in

at

increases adding

burn-off

oxygen level

region.

REFERENCES

1 2 3 4

I

Influence of 0, on the development of microand macropore volume in steam gasification (T=1173K/ *lOO hPa Hz0 no oxygen, +lOO hPa HZO+10 hPa 0,)

widening

temperature,

Therefore

especially

Fig.5

endothermic

reacts

area,

increasing

I

I

burn-off

the

area

higher

I

0 0.2 0.4 0.6 0.8 1. 0

C-l

Influence of temperature on the development of microand macropore volume in H,O/O,-gasification (100 hPa H,O, 10 hPa O,/ + 1023, *1173K)

lower

?z?

B,

0 0.2 0.4 0.6 0.8 1.0

the

#

pl

,

K

I

macro /

40

burn-off Fig.4

1173

/”

8

5

at

I

60

al

of

(Fig.4).

80

% 8

pores

K. Hashimoto, K. Miura et al., Ind. Eng. Chem. Process Des. Dev., 18, 1 (1979) 72-80. H. Juntgen, Carbon, 6 (1968) 297-308. H.E. Klei, J. Sahagian and D.W. Sundstrom, Ind. Eng. Chem. Process Des. Dev., 14, 4 (1975) 470-473. 5.3. Kipling, and 6. MC Enaney, Papers 2nd Conf. on Ind. Carbon and Graphite, London, 7.-9.4.65, 380-389.

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