Correlations Between Petrographical Properties, Chemical Structure

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2 Correlations Between Petrographical Properties, Chemical Structure, and Technological Behavior of Rhenish Brown Coal E. A. WOLFRUM Rheinische Braunkohlenwerke AG, Stüttgenweg 2, 5000 Köln 41, Federal Republic of Germany

The brown coal reserves in the Federal Republic of Germany amount to approx. 56 billion metric tons, 55 billion metric tons of which are in the Rhenish brown coal district located west of Cologne. About 35 billion metric tons of that reserve are considered to be technologically and economically mineable today (1). Rhenish brown coal is now mined in five opencast mines with an average depth of about 280 m. Modern mining equipment having a daily capacity of some 240,000 m is used. About 119 million metric tons of brown coal were mined in 1981. Of that output, 84.5 % was used for power generation, 7.9 % for briquette production in 4 briquetting plants of the Rheinische Braunkohlenwerke and 4.2 % for powdered brown coal production in two grinding mills. A low portion, viz. 0.3 %, was used in a Salem-Lurgi rotary hearth furnace to produce about 96,000 metric tons of fine coke in 1981. About 2.7 % of the brown coal output was used for other purposes, inter alia in test plants for processes like gasification and hydrogenation. Mining in greater depths leads to a change of the geotectonic conditions and hence a natural change in the brown coal quality characteristics. This has varying and graduated effects on the individual refining processes (2). 3

0097-6156/84/0264-0015$06.00/0 © 1984 American Chemical Society In The Chemistry of Low-Rank Coals; Schobert, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

T H E CHEMISTRY OF LOW-RANK COALS

The p e t r o g r a p h i c a l and chemical i n v e s t i g a t i o n s presented i n the f o l l o w i n g s e c t i o n s were c a r r i e d out i n order to describe the behaviour of the c o a l types c h a r a c t e r i s t i c s of the Rhenish brown coal area during r e f i n i n g processes.


STRUCTURE AND COMPOSITION OF RHENISH BROWN COAL Rhenish brown coal c o n s i s t s of a v a r i e t y of l i t h o t y p e s which are already d i s c e r n i b l e i n the coal seam by brightness v a r i a t i o n s . Recent p o l l e n a n a l y t i c a l i n v e s t i g a t i o n s proved that the bright and dark l a y e r s r e s u l t mainly from changing conversion and decomposition c o n d i t i o n s . The bog f a c i e s has only a l i m i t e d i n f l u e n c e . The gradation from dark to b r i g h t l a y e r s r e f l e c t s the degree of brown coal d e s t r u c t i o n ( 3 , 4 ) . Only a model can e s t a b l i s h the complex, heterogeneous s t r u c t u r e of brown c o a l . Figure 1 shows a model that interconnects the various s t r u c t u r a l components, namely l i g n i n , humic a c i d and aromatic s t r u c t u r a l elements. The high content of f u n c t i o n a l groups causes high r e a c t i v i t y . Figure 2 shows how oxygen-containing f u n c t i o n a l groups are d i s t r i b u t e d i n the Rhenish brown c o a l . Macropetrographical

characterization

Based on macropetrographical c r i t e r i a ( d e t e r mination of the l i t h o t y p e s by v i s u a l examination with the naked eye) 15 brown coal l i t h o t y p e s were s e l e c t e d for the i n v e s t i g a t i o n s described i n the f o l l o w i n g ; they represent more than 90 % of the main seam. Figure 3 shows these 15 brown c o a l l i t h o t y p e s arranged according to s t r a t i f i c a t i o n (unhanded to banded coal) and texture (plant t i s s u e c o n t e n t ) . Micropetrographical

characterization

Micropetrography evaluates the c o a l components a s c e r t a i n a b l e by microscopy. Figure 4 shows an extract of the r e s u l t s obtained from the combined m a c e r a l - m i c r o l i t h o t y p e a n a l y s i s a f t e r the I n t e r n a t i o n a l Handbook of Coal Petrography of the 15 brown c o a l l i t h o t y p e s . Based on the q u a l i t a t i v e assignment of the i n d i v i d u a l coal components, Rhenish brown coal can be divided i n t o four groups having s i m i l a r

In The Chemistry of Low-Rank Coals; Schobert, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


lignin

Figure

1.

Schematic

humic acids composition

of

the

brown

coal

structure.

structural aromatic elements


•-4

18

T H E CHEMISTRY O F LOW-RANK COALS

oxygen(°/o w t ) r e f e r e n c e : maf c o a l


r a n g e of variations

meanvalue "

30· 27,8 25, A 23,4 2018.1

10-

11,8

10,6 9,2 75

97

5,3 3,5 0

1.6

3,5

J

total oxygen 0

carboxyl groups -C00H

F i g u r e 2. D i s t r i b u t i o n i n R h e n i s h brown c o a l .

of

methoxyl groups -OCH3 the

hydroxyl

remainder-0

groups -OH

ether*ketone

oxygen-containing

functional


groups


6

8

9

10

11

12

13

14

15

18,5 *

9,2 %

3,0 «

5,7 *

1,9 *

2,5 *

2,2 %

2,0 «

5

7

4

12,8 %

5,8 %

3

5,5 *

15,0 %

7,8 %

1

2

4,2 %

no.

sample

3,9 *

percentage of a seam section

3.

from

Ref.

lithotypes

Figure 2.

the

(Reproduced Schriftleitung

area.

1981,

Rhenish

Copyright

from

Macropetrographical

stratified coal stratified coal stratified coal coal

coal Braunkohle.)

permission

15 b r o w n with

of

sub. heavily textured,bright texture,resinous heavily textured,xylite and fusite nests heavily textured,xylite,gelled heavily textured,fusite texture

medium-bright dark dark dark (black)

heavily heavily heavily fibrous

stratified stratified stratified stratified

classification

textured,xylite and resinous substance textured,xylite and bright texture xylite and gelled,textured textured,xylite and fusite nests

coal coal coal coal

medium-bright medium-dark dark dark

slightly slightly slightly slightly

xylite-and mineral-free, matrix granular gelification nests, xylite xylite-containing slightly textured and xylite slightly textured,xylite,surface gel slightly textured,xylite-free siightly textured,xylite,gel,fusite

bright dark medium-bright medium-bright medium-dark medium-bright dark

coal coal coal coal coal coal coal

unstratified unstratified unstratified unstratified unstratified unstratified unstratified

accessory intercalations

gelification rate

and coluor

brightness

matrix / texture

structure


SO


20

THE CHEMISTRY OF LOW-RANK COALS

maceral

groups,

maceral

subgroups,

microlithotypes

maceral

group no. lith. no.

1

2

1,2

4

3

9,11,12,

5,8,10

3,4,6,7

13,14,15

groups

liptinite

% vol.

26 - 28

20 - 26

6 - 11

3 - 12

huminite

% vol.

67 - 69

72 - 79

87 - 92

80 - 90

inertinite

% vol.

5

maceral

1 -

1 -

3

4

2 - 17

subgroups

humodetrinite

% vol.

54 - 58

31

- 43

12 - 31

humotelinite

% vol.

3 -

5

10 -

17

26 - 33

34 - 50

humocollinite

I

6 -

7

3 -

8

vol.

56

- 59

19

- 26

17

- 31

microlithotypes

56 - 67

lipto-humodetrite

% vol.

79 - 80

telo-humodetrite

% vol.

3

telo-humocollite

% vol.

9 - 15

detro-humocollite

% vol.

3 -

gelo-humotelite

% vol.

Figure into

4.

1981,

(Reproduced with Schriftleitung

3 - 17

- 30

permission

10 - 30

8-15

3 - 17

7

3

10 - 12

3

Micropetrographical classification

4 groups.

Copyright

3

21

of

15

10 - 39

lithotypes

from Ref.

2.

Braunkohle.)


WOLFRUM

Rhenish Brown Coal


micropetrographical p r o p e r t i e s which correspond with the macropetrographical features ( p r i n c i p l e of c l a s s i f i c a t i o n : s t r a t i f i c a t i o n and t e x t u r e ) . The c l a s s i f i c a t i o n i n t o four main groups r e s u l t s i n the c o r r e l a t i o n s shown i n the f o l l o w i n g F i g u r e s . Figure 5 shows the l i p t i n i t e content as a f u n c t i o n of the group c l a s s i f i c a t i o n s 1 to 4. With r i s i n g group number, corresponding to stronger s t r a t i f i c a t i o n and texture, the l i p t i n i t e content d e c l i n e s . Figure 6, which shows the huminite as a f u n c t i o n of the group numbers, i n d i c a t e s that the huminite content r i s e s with i n c r e a s i n g s t r a t i f i c a t i o n and texture. Chemical and p h y s i c a l

composition

Subsequent to the p e t r o g r a p h i c a l coal a n a l y s i s , both a chemical and a chemo-physical i n v e s t i g a t i o n were c a r r i e d out. Figure 7 shows the chemical and p h y s i c a l p r o p e r t i e s of the i n v e s t i g a t e d brown coal lithotypes. Rhenish brown coal has an average ash content of about 4 % (mf), a v o l a t i l e matter of about 52 % (maf) and a lower heating value of 25.6 MJ/Kg of coal (maf). The f i n a l a n a l y s i s of the coal under maf c o n d i t i o n s shows the f o l l o w i n g average composition : 69 % carbon, 5 % hydrogen, 1 % nitrogen and approx. 25 % oxygen; the sulphur content amounts to about 0.35 % (maf), about 50 to 70 % of which i s bound to the ash during the combustion process since approximately h a l f of the mineral components of Rhenish brown coal c o n s i s t of basic a l k a l i and a l k a l i n e earth compounds - p r i m a r i l y those of calcium. CORRELATIONS BETWEEN PETROGRAPHICAL STRUCTURE, CHEMICAL COMPOSITION AND REFINING BEHAVIOUR OF RHENISH BROWN COAL The c o r r e l a t i o n s between the chemical brown coal data, p e t r o g r a p h i c a l parameters and the r e f i n i n g behaviour are described i n the f o l l o w i n g discussion. A d i r e c t c o r r e l a t i o n among the q u a l i t y of the raw m a t e r i a l , the r e f i n i n g c o s t , and the q u a l i t y of the desired products i s a p p l i c a b l e to nearly a l l brown coal r e f i n i n g processes. Hence, i t i s i n d i s p e n s i b l e for any r e f i n i n g operation to know and assess the composition of the raw m a t e r i a l and i t s behaviour during the r e f i n i n g process.


22

THE CHEMISTRY O F LOW-RANK COALS

group c lassif ication

4-

•V

0

3


0

000

0 0

\

2

0 0

oo\

00

\

y=A,b5-0,116x \

0

5

10

15

20

25

30

r2=0,80

35 »

Figure

5.

Liptinite

classification. Copyright

content

as

(Reproduced

a function

with

1981, S c h r i f t l e i t u n g

40

45

50

l i p t i n i t e (*/· vol.) of

permission

micropetrographical from R e f . 2.

Braunkohle.)

group classification

^huminite(Vol.°/o) Figure

6.

Huminite

classification. Copyright

content

as

(Reproduced

a function with

1981, S c h r i f t l e i t u n g

of

permission

micropetrographical from R e f .

2.

Braunkohle.)


WOLFRUM

Rhenish Brown Coal


The u s a b i l i t y of the r e s u l t s obtained from the raw m a t e r i a l c h a r a c t e r i z a t i o n i n everyday p r a c t i c e depends on - the spacing of d r i l l i n g s usable for q u a l i t y assessment - the l e v e l of g e o l o g i c a l knowledge of the coal forming c o n d i t i o n s - a representative sampling i n the opencast mine, taking i n t o account the c u t t i n g geometry of the excavator ( p o s i t i o n of the excavator cuts to the d e p o s i t ) , the rate of mining advance and the high volumes i n v o l v e d . C o r r e l a t i o n s between chemical and p e t r o g r a p h i c a l parameters Heating value Figure 8 shows that the heating value d e c l i n e s with i n c r e a s i n g coal s t r a t i f i c a t i o n . A comparison of the heating value of coal and i t s hydrogen content i n Figure 9 i n d i c a t e s that according to expectation the heating value of the c o a l r i s e s p a r a l l e l to an increase i n i t s hydrogen content. This again i s due to the p o r t i o n of hydrogen-rich m a c é r a i s , such as l i p t i n i t e , d e c l i n i n g i n the s a i d order - a c o r r e l a t i o n c l e a r l y evident i n Figure 10. The heating value of the c o a l obviously r i s e s i n proportion to i t s l i p t i n i t e content. The oxygen-rich l i g n i t i c coal components, such as huminite, have the opposite e f f e c t on the heating value: Figure 11 shows that the heating value of the coal i s down sharply with an increase i n the p o r t i o n of t h i s maceral group. Volatile

content

The i n d i v i d u a l coal c o n s t i t u e n t s c o n t r i b u t e d i f f e r e n t portions to the v o l a t i l e matter of the coals ( 5 ) . With increased s t r a t i f i c a t i o n , the v o l a t i l e matter decreases, caused by the r e l a t i v e d i s t r i b u t i o n of the various maceral groups. Figure 12 gives an example how the content of v o l a t i l e matter and that of the hydrogen-rich l i p t i n i t e maceral c o r r e l a t e . Hydrogen content Figure 13 shows that also the hydrogen content c l o s e l y corresponds to the p e t r o g r a p h i c a l prope r t i e s . Figure 14 shows the c o r r e l a t i o n between



heating

-

-

C-fix

paraffin

bitumen

Extraction

hydrogen

carbon

analysis

analysis

content

content

Elementary

value

volatiles

content

coal (raw)

analysis

"

ash

brown

Short

~

-

l i t h o t y p e no.

maf

maf

maf

maf

maf

maf

màf

from Ref.

Braunkohle.)

permission

19.

to

8,79 4,93

68,2 5,19

52,0 3,90 52,42 47,58 25,85

5

6,S3

7,43

69,3 5,21

25,97

56,6 4,42 52,09

6

Copyright

the

7,29 6,00

65,7 4,71

60,0 4,27 52,98 47,02 25,27

8 9

10

coal

5,40 3,93

68,4 4,92

55,1 3,52 49,76 50,24 25,43

Schriftleitung

with

brown

7,10 5,77

68,5 5,10

53,4 3,04 49,65 50,35 25,55

(Reproduced 1983,

investigation.

of

8,96 7,48

69,6 5,25

54,0 3,55 51,91 *9,00 26,30

7

characterization

12,04 10,00

68,9 5,56

55,6 3,86 54,70 45,30 26,69

4

Chemo-physical

10,96 9,00

67,8 5,24

2,78 55,11 44,89 25,89

60,1

3

subjected

7.

Figure

12,25 9,46

67,5 5,60

60,4 2,44 55,25 44,75 25,87

2

lithotypes

12,87 10,19

69,6 5,89

52,2 6,53 59,68 40,32 27,99

%

%

% %

MJ/kg

%

% % %

an *

mf

1


9,18 5,90

68,9 4,69

54,0 3,73 48,36 51,64 25,31

11

7,20 5,93

67,4 4,91

59,7 2,73 53,72 46,28 24,96

12

9,65 8,20

66,3 4,79

eo,6 3,56 51,74 48,26 25,43

13

5,11 4,19

6",4 4.8Γ:

58,6 3,38 51,77 48,23 25,36

14

7,31 3,16

69,5 4,51

49,0 3,92 48,79 51,21 24,99

15


2.

Rhenish Brown Coal

WOLFRUM

1

Figure

8.

Heating

function with

of

value

2

of

3

4

the

from Ref.

2.

29-ι

5

brown

macropetrographical

permission

25

6

7

8

coal

9

10

classification.

Copyright

11

12

lithotypes

1981,

13

as

14

15

a

(Reproduced Schrif t leitung Braunkohle. )

3 22,784, 0,02236 χ ° 0,81

Φ Ο

Ξ Ε

h y d r o g e n content( /ewt) r e f e r e n c e : mat c o a l _ e

ι

6,0

Figure

9.

contents

C o r r e l a t i o n between of

permission

the

15

lithotypes

from R e f .

19.

y r

the

heating

values

investigated.

Copyright

1983,

and

hydrogen

(Reproduced

with

Schrif t leitung Braunkohle. )

=24,777.0,0697 2

= 0,62

α Ε

a*

α» Φ .c »-

I iptinite (/ο vol) β

25

Figure

10.

Heating

of

15

lithotypes

the

from

Ref.

19.

value

as

a

function

investigated.

Copyright

1983,

of

the

liptinite

(Reproduced with

Schriftleitung

I 30

content

permission

Braunkohle.)



h e a t i n g v a l u e (MJ/kg) r e f e r e n c e : mat c o a l


29-1

y

= 5 0 , β 8 β - 5,715

r = 2

In χ

0,57

1

90

» huminite(°/oVol) Figure

11.

contents

C o r r e l a t i o n between

of

permission

the

15

from

lithotypes

Ref.

19.

heating

values

investigated.

Copyright

1983,

and

huminite

(Reproduced

with

Schriftleitung

Braunkohle.) volatiles (maf) ( /,wt) e

• liptinite( /o vol) e

Figure

12.

content. right

1983,

Volatile

portion

(Reproduced

with

Schriftleitung

as

a

function

permission

from

of

the

Ref.

liptinite 19.

Copy

Braunkohle.)


Rhenish Brown Coal

WOLFRUM

v o l a t i l e s (mat) ( /,wt)

hydrogen(maf )

e

60-1

(/o w t ) e

volatiles —

hydrogen

58·


•5,5

-4,0

t

π—ι—ι—r τ—ι—ι—ι—ι—ι—ι—ι—ι—ι—I 1 2

Figure

13.

of

lithotypes,

the

3

4

5

6

7

8

(Reproduced

with

Schriftleitung

10

11

12

13

14

15

lithotype no.

C o r r e l a t i o n between and

9

the

volatile

matter,

macropetrographical

permission

from

Ref.

2.

hydrogen

content

classification.

Copyright

1981,

Braunkohle.)

h y d r o g e n content ( ° / o w t ) reference: maf c o a l |6,0n y = 4,803. 0,01026 χ

y

r=

r

2

0,79

= 6,2 59 - 0,386 In χ = 0,72

2

5,5-

4.5->

π— 10

)

1

1

1

1

1

1

30

40

50

60

70

80

^ ( x) H u m o - T e l i n i t e (% vol) ^ ( Δ )

Lipto - Humodetrite ( /evol) and H u m o - T e l i n i t e e

Figure and from

14.

C o r r e l a t i o n between

Lipto-Humodetrite Ref.

2.

Copyright

portions. 1981,

hydrogen

(Reproduce

Schriftleitung

with

permission

Braunkohle.)



the hydrogen content and the l i p t o - h u m o d e t r i t e and/or the humotelinite content of the i n v e s t i gated l i t h o t y p e s . A higher amount of l i p t o humodetrite leads to an increased hydrogen content. The content of the humotelinite maceral, however, has a t o t a l l y d i f f e r e n t e f f e c t : This component has a high p o r t i o n of oxygen-rich molecular groups which causes the hydrogen content of the brown coal to drop.


C o r r e l a t i o n s between coal q u a l i t y r e f i n i n g behaviour

and

B r i q u e t t i n g and coking There are many i n v e s t i g a t i o n s and p u b l i c a t i o n s a v a i l a b l e on the b r i q u e t t i n g behaviour of brown c o a l s , both from the GDR and the Rhenish area (6 to 9 ) . In order to e s t a b l i s h s t a t i s t i c a l l y usable data on the b r i q u e t t i n g behaviour of Rhenish brown c o a l s , the 15 brown coal l i t h o t y p e s were briquetted under i d e n t i c a l c o n d i t i o n s (water content, g r a i n s i z e d i s t r i b u t i o n and mould pressure) with a laboratory press. For a s s e s s i n g the b r i q u e t t a b i l i t y of these c o a l s , a number of b r i q u e t t i n g parameters were c o r r e l a t e d with the p e t r o g r a p h i c a l p r o p e r t i e s of the brown coal types. A s t a t i s t i c e v a l u a t i o n of these b r i q u e t t i n g parameters and the micropetrographical composition of the coals reveals only a minimal degree of interdependence. Figure 15 c l e a r l y shows that the humotelite content c o r r e l a t e s with the height and volume expansion of the b r i q u e t t e s . The b r i q u e t t i n g expenditure i s r e l a t e d to the t e l o humocollite content. The c o r r e l a t i o n c o e f f i c i e n t (r) v a r i e s between 0.76 and 0.82, and i s compara t i v e l y low. A l l the other c o r r e l a t i o n s between the b r i q u e t t i n g parameters ( e . g . d i a m e t r i c a l expansion) and the p e t r o g r a p h i c a l coal composition turned out to be rather i n s i g n i f i c a n t so that they need not be taken i n t o c o n s i d e r a t i o n . These i n v e s t i g a t i o n s on c o r r e l a t i o n s e s t a b l i s h e d between the raw m a t e r i a l p r o p e r t i e s and b r i q u e t t a b i l i t y of Rhenish brown coal led to the following r e s u l t s : 1. A macro- and m i c r o p e t r o g r a p h i c a l a n a l y s i s with a view to before t e c h n o l o g i c a l problems involved i n the b r i q u e t t i n g process allows one at the most to judge the b r i q u e t t a b i l i t y of Rhenish brown coal on the basis of trend data.


2.

height expansion form

29

Rhenish Brown Coal

WOLFRUM

yield

20 1

,

8

(·/.) 16 14 12 10 β

y = 5,005 • 0.4018 χ , r2 = 0.67


6 4 2 0 0

Τ — I — I — I — I — I — I — I — I — I 2 4 6 8 10 12 14 16 18 20 • Humorelite content ( % v o l )

volume expansion form

yield

20-j 1

(·/.)

8

16 -

y= 8,805*0,4217 χ , r*= 0.58

H u mo tel i te content ( % vol) expended

20-

briqetting

work

(Nm/g)

1

8

_

16 14 12 10 y = 11,296*0.3139 χ , f2 = 0,66

8 6 4 2 0 0 Figure

τ—I—I—I—I—I—I—I—I—I 2 4 6 8 10 12 14 16 18 20

15. C o r r e l a t i o n

between

microlithotypes

and v a r i o u s

with

from

permission

the contents

briquetting

R e f . 19.

Copyright

^Telo-Humocollite content ( % v o l ) of

results. 1983,

various (Reproduced Schriftleitung

Braunkohle.)




2.

A c o r r e l a t i o n a n a l y s i s of the chemo-physical parameters of Rhenish brown coal and i t s b r i q u e t t a b i l i t y gives only trend data as w e l l . Therefore g e n e r a l l y an a n t i c i p a t e d q u a l i t y assessment of the b r i q u e t t e s i s r e s t r i c t e d to the following points: 1· Macropetrographical assessment of the coal seam and e v a l u a t i o n of the b r i q u e t t a b i l i t y on the basis of values gained by experience. 2. Laboratory production of b r i q u e t t e s and determination of t h e i r compression s t r e n g t h . 3. Determination of the ash content as an essent i a l f a c t o r for the assessment of brown coal briquettability. Numerous p u b l i c a t i o n s (10 to 12) have appeared, p r i n c i p a l l y from the GDR, on the required q u a l i t y p r o p e r t i e s of brown coal and t h e i r i n f l u e n c e on the q u a l i t y c h a r a c t e r i s t i c s of formed coke. Since the Rheinische Braunkohlenwerke AG i s not engaged in formed coke production at present, raw m a t e r i a l q u a l i t y and coking behaviour are of i n t e r e s t only f o r the production of f i n e coke using the rotary hearth furnace ( 1 3 » 14). This technology i s dependent only to a small extent on the s p e c i f i c raw m a t e r i a l composition. The p e t r o g r a p h i c a l f a c t o r s of the feedstock have an impact p r i n c i p a l l y on g r a i n s i z e and g r a i n s i z e distribution. Gasification Two g a s i f i c a t i o n processes under development, namely High Temperature Winkler G a s i f i c a t i o n (HTW) and h y d r o g a s i f i c a t i o n of l i g n i t e (HKV), encouraged to study the g a s i f i c a t i o n behaviour of various brown coal l i t h o t y p e s (15). HTW process p r i n c i p l e : F i n e - g r a i n e d dry brown coal i s g a s i f i e d i n a f l u i d i z e d bed with oxygen/steam or a i r under pressure and at a high temperature i n t o a gas r i c h i n carbon oxide and hydrogen. HKV process p r i n c i p l e : F i n e - g r a i n e d dry brown coal is g a s i f i e d i n the f l u i d i z e d bed with hydrogen under high pressure and at a higher temperature i n t o a CHi|-rich gas. The r e a c t i v i t y of the r e s i d u a l char i s the r a t e - c o n t r o l l i n g f a c t o r for brown coal hydrogasif i c a t i o n (16). L a b o r a t o r y - s c a l e i n v e s t i g a t i o n s on the g a s i f i c a t i o n behaviour of various types of brown coal coke showed that the mode of pretreatment has a



WOLFRUM

Rhenish Brown Coal

greater i n f l u e n c e on the g a s i f i c a t i o n process than do the raw m a t e r i a l p r o p e r t i e s . To give an example, thermal pretreatment of the coke i n an i n e r t atmosphere l i k e helium at g a s i f i c a t i o n temperature (900 ° C ) has a very favourable e f f e c t on g a s i f i c a t i o n . With one exception only, g a s i f i c a t i o n degrees c l o s e to 100 % were achieved. D i f f e r e n c e s i n g a s i f i c a t i o n rates are due to the heterogeneous pore s t r u c t u r e and the inhomogeneous i r o n d i s t r i b u t i o n i n the coal matrix. I r r e g u l a r l y l o c a l i z e d i r o n groupings contained i n cokes of the l i t h o t y p e s 1 and 8 show a varying r e a c t i v i t y behaviour. Cokes of the l i t h o t y p e s 4, 5, 9, 11, 13 and 15 with s i m i l a r g a s i f i c a t i o n behaviours have a comparatively homogeneous d i s t r i b u t i o n of a l l ash components ( F i g . 16). No c o r r e l a t i o n was e s t a b l i s h e d between the maceral composition and the r e a c t i v i t y behaviour of the cokes (17). As was the case with the mentioned h y d r o g a s i f i c a t i o n process, the r e s u l t s obtained with HTW g a s i f i c a t i o n did not show any s t a t i s t i c a l l y s i g n i f i c a n t c o r r e l a t i o n s between the p e t r o g r a p h i cal composition of the l i t h o t y p e s and t h e i r g a s i f i c a t i o n behaviour. Liquefaction To determine p o t e n t i a l raw m a t e r i a l impacts on brown coal h y d r o l i q u e f a c t i o n , the 15 l i t h o t y p e s were converted i n t o l i q u i d products using various techniques (18): 1. moderate i n d i r e c t h y d r o g é n a t i o n with t e t r a l i n as a h y d r o g e n - t r a n s f e r r i n g solvent 2. d i r e c t h y d r o g é n a t i o n with hydrogen and d i f f e rent c a t a l y s t s s i m i l a r to o p e r a t i o n a l c o n d i tions . I n d i r e c t h y d r o g é n a t i o n using t e t r a l i n at a r e a c t i o n temperature of 410 ° C , a pressure of 400 bar and an o v e r a l l r e a c t i o n time of 2 h produced carbon conversion rates from 50 to 79 ( Î w t ) and l i q u i d product y i e l d s from 43 to 69 (%wt). Of the multitude of c o r r e l a t i o n s e s t a b l i s h e d between the r e s u l t s of the h y d r o g é n a t i o n t e s t s and the micropetrographical composition of the coal types only a few examples are given. Figure 17 shows the product y i e l d s of i n d i r e c t brown coal h y d r o g é n a t i o n with t e t r a l i n as a f u n c t i o n of s t r a t i f i c a t i o n and texture ( l i t h o t y p e



40 bar

H /900°C 2

pretreatment: 0.5 h, 1 bar (helium ). 900° C


Figure

16. of

from

Ref.

-,

n

C o n v e r s i o n as brown c o a l 19.

Copyright

0

L

B

texture

function

of

time

(Reproduced

1983

with

with

Schriftleitung

hydrogasifi-

permission Braunkohle.)

heavy texture

slight texture

1

n

m

a

cokes.

72 80 120 30 46 240 34 390

93,3 92,5 88,3 82,1 82,4 87 34,1 100

9 13 5 4 15 11 1 8

cation

time (mi η

burn-out

lith.no.

0

stratification

"~ Γ*

Ifibrous heavy stratification 5rTycoal"]

slight stratification

100η

80-

60-

ο a

40-

«

20-

V ~1

° • χ Figure with

2

ο -· x 17.

(lithotype

4

5

6

7

8

9

10

11

12

Product as

achieved

a function

number). 1983,

yields

13

14

15

- l i t h o t y p e no.

l i q u i d produkt residue gas

tetralin

Copyright

3

of

through

(Reproduced with

Schriftleitung

indirect

stratification

and

permission

hydrogénation

texture

from R e f .

Braunkohle.)


19.

WOLFRUM

Rhenish Brown Coal


number). It i s obvious that with i n c r e a s i n g s t r a t i f i c a t i o n and texture, i . e . with r i s i n g l i t h o t y p e number, the l i q u i d product y i e l d drops and the p o r t i o n of h y d r o g é n a t i o n residue i n c r e a s e s . Regarding the f i n e s t r u c t u r e of the coal the f o l l o w i n g c o r r e l a t i o n s r e s u l t : Figure 18 represents the carbon conversion rate as a f u n c t i o n of the l i p t i n i t e and huminite maceral p o r t i o n s . It can be seen that an increase i n the hydrogen-rich l i p t i n i t e c o n s t i t u e n t improves carbon conversion while the oxygen-rich huminite reduces the carbon conversion r a t e . These trends a l s o apply to the y i e l d of l i q u i d products. During d i r e c t h y d r o g é n a t i o n with molecular hydrogen and c a t a l y s t , the i n f l u e n c e of the raw m a t e r i a l was expected to weaken using hydrogen and a c a t a l y s t under the c o n d i t i o n s s i m i l a r to those in the r e a l h y d r o l i q u e f a c t i o n process. An increase in the carbon conversion rate up to a maximum of 96 (%wt) shows that brown c o a l s with high or low carbon-to-hydrogen r a t i o s achieve high product y i e l d s . D i s t i n c t impacts of the raw m a t e r i a l on the l i q u e f a c t i o n r e s u l t s are no longer observed. Summarizing, i t can be s a i d that the extent of h y d r o g é n a t i o n r i s e s i n d i r e c t proportion to carbon conversion. The r e s u l t i s that nearly a l l brown coal types mineable i n the Rhenish area can be converted i n t o l i q u i d products with high y i e l d s . The i n v e s t i g a t i o n s showed that i n general p r a c t i c e no importance i s a t t r i b u t e d to a m i c r o p e t r o g r a p h i c a l assessment of the coal types as a c r i t e r i o n f o r s e l e c t i n g s p e c i f i c brown coals from the Rhenish a r e a . In g e n e r a l , brown c o a l s from various areas that meet the q u a l i t y parameters given i n Figure 19 have s a t i s f a c t o r y h y d r o g é n a t i o n properties . SUMMARY For the purpose of an assessment with a view to r e f i n i n g , the p e t r o g r a p h i c a l , chemical and p h y s i c a l p r o p e r t i e s of l i t h o t y p e s of Rhenish brown coal were e s t a b l i s h e d and compared with one another. The i n v e s t i g a t e d coal types cover more than 90 % of the coal types determined by boring i n the Rhenish d e p o s i t . A c o r r e l a t i o n of the r e s u l t s shows a d e s c r i b a b l e , sometimes m u l t i d i m e n s i o n a l , dependancy.


34


C-conversion( /e wt )

C - c o n v e r s i o n (°/owt)


e

^liptinite(°/*vol) Figure

18.

Carbon

conversion

génation

with

huminite

contents.

Copyright

tetralin

1983,

1.

as

a

*-huminite(°/ovol ) achieved

function

(Reproduced

with

Schriftleitung

humodetrinite inertinite

content

content

content

%

vol

>50

%

vol

>50

%

vol

J> % v o l

< 6 %

vol

> 7 %

>11

content

% wt

(mf)

>

7 % wt

(maf)

hydrogen content

>

5 % wt

(maf)

ratio

Under the

conditions

seam o f

the

7 8 % wt

of

1983,

20

Correlations Between Petrographical Properties, Chemical Structure

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