The Chemistry of Low-Rank Coals - American Chemical Society

1 The Chemical Characteristics of Victorian Brown Coal 1

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G. J. PERRY , D. J. ALLARDICE , and L. T. KISS 1

Victorian Brown Coal Council, 136 Exhibition Street, Melbourne 3000, Australia State Electricity Commission of Victoria, Herman Research Laboratory, Howard Street, Richmond 3121, Australia

Downloaded by UNIV OF COLORADO BOULDER on March 27, 2017 | http://pubs.acs.org Publication Date: September 10, 1984 | doi: 10.1021/bk-1984-0264.ch001

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Extensive deposits of soft brown coal exist i n Tertiary age sediments in a number of areas in Victoria and the largest single deposit occurs in the Latrobe Valley, about 150 kilometers east of Melbourne. In this region the coal seams often exceed 150 metres in thickness, with an overburden to coal ratio usually better than 1:2 making the coal ideally suited for large-scale open-cut mining. A recent study (1) has estimated the State's brown coal resources to be almost 200,000 million metric tons with approximately 52,000 million metric tons defined as usable reserves. About 85% of this coal i s located i n the Latrobe Valley. Since 1920 Latrobe Valley brown coal has been developed for power generation. The State Electricity Commission of Victoria (SECV) wins coal from two major open cuts at Yallourn and Morwell and operates coal fired power stations which presently consume approximately 35 million metric tons per annum. In addition to power generation, small quantities of brown coal are used for briquette manufacture and char production. Brown coal accounts for about 95% of Victoria's non-renewable energy reserves and it i s now recognized that with suitable upgrading, primarily drying, it has the potential to become the basis of the supply of energy in a variety of forms. Currently various studies for major conversion projects proposed by Australian, Japanese and German interests are being undertaken with the cooperation of the Victorian Brown Coal Council, the most advanced project being a 50 metric tons per day hydrogenation pilot plant currently under construction at Morwell, funded by New Energy Development Organization (NEDO) of Japan. The chemical characteristics of Latrobe Valley brown coals have been extensively studied over the last twenty-five years, primarily in relation to the effect of coal quality on combustion for power generation. More recently a research project was initiated with the objective of determining the characteristics and suitability of the State's brown coal resources for uses other than power generation, primarily conversion to liquid fuels. 0097-6156/84/0264-0003$06.00/0 © 1984 American Chemical Society

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

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THE CHEMISTRY OF LOW-RANK COALS

T h i s paper o u t l i n e s t h e c h e m i c a l c h a r a c t e r i s t i c s o f V i c t o r i a n brown c o a l and d i s c u s s e s t h e v a r i a b i l i t y o f t h e c o a l , b o t h between f i e l d s and w i t h i n a seam. The importance o f c h e m i c a l p r o p e r t i e s i n r e l a t i o n t o c o a l q u a l i t y and t h e i m p l i c a t i o n s f o r u t i l i z a t i o n a r e a l s o b r i e f l y addressed. P r o p e r t i e s o f V i c t o r i a n Brown C o a l The development and a d a p t a t i o n o f modern a n a l y t i c a l t e c h n i q u e s f o r a n a l y s i s o f V i c t o r i a n brown c o a l was p i o n e e r e d j o i n t l y i n t h e I 9 6 0 s by t h e Commonwealth S c i e n t i f i c and I n d u s t r i a l Research O r g a n i z a t i o n and t h e S t a t e E l e c t r i c i t y Commission o f V i c t o r i a . As a r e s u l t , the t o t a l c o a l a n a l y s i s time was h a l v e d and t h e d e t e r m i n a t i o n o f t h e ash f o r m i n g c o n s t i t u e n t s d i r e c t l y on t h e c o a l took one s i x t h o f t h e time o f c o n v e n t i o n a l ash a n a l y s i s . More importantly brown c o a l a n a l y s i s was put onto a r a t i o n a l b a s i s t a k i n g i t s unique p r o p e r t i e s i n t o a c c o u n t , t h e r e b y p r o v i d i n g more p e r t i n e n t i n f o r m a t i o n c o n c e r n i n g t h e g e n e s i s , o c c u r r e n c e and use o f V i c t o r i a n brown c o a l .


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Moisture. One o f t h e most i m p o r t a n t c h e m i c a l measurements made on brown c o a l i s t h e bed m o i s t u r e c o n t e n t which i s a l s o a good measure o f p h y s i c a l rank; t h e g r e a t e r t h e degree o f compaction o f t h e c o a l and i t s degree o f c o a l i f i c a t i o n , t h e lower i s t h e m o i s t u r e c o n t e n t . To o b t a i n m e a n i n g f u l r e s u l t s , t h e s a m p l i n g and sample p r e p a r a t i o n have t o be c a r r i e d out q u i c k l y t o a v o i d m o i s t u r e l o s s . The c h o i c e o f t h e method o f d e t e r m i n a t i o n i s i m p o r t a n t as t h e r m a l decomposi t i o n o f f u n c t i o n a l groups can r e s u l t i n l o s s o f C 0 as w e l l as H 0. The p r e f e r r e d methods t h e r e f o r e i n v o l v e d i r e c t measurement o f t h e water r e l e a s e d e i t h e r by a z e o t r o p i c d i s t i l l a t i o n o r a d s o r p t i o n from an i n t e r t c a r r i e r gas r a t h e r than by weight l o s s o f t h e c o a l . I t i s i m p o r t a n t t o r e a l i z e t h a t t h e bed m o i s t u r e c o n t e n t o f s o f t brown c o a l s i s s i g n i f i c a n t l y h i g h e r than t h e e q u i l i b r i u m moisture holding capacity, a parameter which i s used to c h a r a c t e r i z e h i g h e r rank c o a l s . T h i s i s i l l u s t r a t e d i n Table 1 f o r a range o f V i c t o r i a n brown c o a l s . In terms o f m o i s t u r e t h e economic v a l u e o f h i g h - r a n k c o a l s i s b e s t i n d i c a t e d by t h e m o i s t u r e h o l d i n g c a p a c i t y because i t r e f l e c t s the c o n d i t i o n o f t h e c o a l f o r u t i l i z a t i o n . In t h e case o f V i c t o r i a n brown c o a l , t h e bed m o i s t u r e c o n t e n t i s t h e c r i t i c a l v a l u e s i n c e t h e c o a l i s used d i r e c t l y from t h e open c u t . Mineral and Inorganic Content. Ash c o n t e n t has been t r a d i t i o n a l l y used t o a s s e s s t h e magnitude o f combustion r e s i d u e and t o d e r i v e t h e s o - c a l l e d " c o a l s u b s t a n c e " by d i f f e r e n c e which a l l o w s m e a n i n g f u l comparisons o f d i f f e r e n t c o a l s . In t h i s c o n t e x t the ash i s used as an a p p r o x i m a t i o n o f t h e m i n e r a l matter c o n t e n t . The t a c i t assumption made, o f c o u r s e , i s t h a t t h e ash i s d e r i v e d s o l e l y from c o a l m i n e r a l s , and t h i s i s c e r t a i n l y not t h e case f o r V i c t o r i a n brown c o a l where t h e b u l k o f t h e ash f o r m i n g m a t e r i a l o c c u r s as i n h e r e n t i n o r g a n i c m a t t e r i n t h e form o f exchangeable c a t i o n s , a s s o c i a t e d w i t h oxygen c o n t a i n i n g f u n c t i o n a l groups. This i s a l s o t h e case w i t h many o t h e r low-rank c o a l s . U s i n g a c o m b i n a t i o n o f X-ray f l u o r e s c e n c e (XRF) on c o a l p e l l e t s and atomic a b s o r p t i o n (AA) t e c h n i q u e s on a c i d e x t r a c t s , 2


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1.

PERRY ET

AL.

The Chemical Characteristics of Victorian Brown Coal

d i r e c t c h e m i c a l a n a l y s e s o f the ash f o r m i n g elements i n V i c t o r i a n brown c o a l has been performed. A r i s i n g from t h i s , a method o f e x p r e s s i o n o f r e s u l t s has been developed (2) which i s based on c l a s s i f y i n g the m i n e r a l m a t t e r i n brown c o a l i n t o m i n e r a l and i n o r g a n i c matter f r a c t i o n s and e x p r e s s i n g each i n a way which r e f l e c t s t h e i r o c c u r r e n c e i n the c o a l . The I n o r g a n i c s a r e a group o f exchangeable c a t i o n s and water s o l u b l e s a l t s , a n a l y z e d by AA on d i l u t e a c i d e x t r a c t s from the c o a l and e x p r e s s e d i n terms o f c h e m i c a l a n a l y s i s on a c o a l b a s i s as -


I n o r g a n i c s = Na + Ca + Mg + Fe + ( A l ) + ( S i ) + NaCl where Fe r e f e r s t o the n o n - p y r i t i c i r o n and ( A l ) and ( S i ) t o the a c i d s o l u b l e aluminium and s i l i c o n r e s p e c t i v e l y . This expression i s c o m p l i c a t e d by the f a c t t h a t some i r o n and aluminium can be p r e s e n t as a c i d s o l u b l e h y d r o x i d e s , but t h e s e a r e not u s u a l l y significant. The group named M i n e r a l s , which o c c u r s as d i s c r e t e p a r t i c l e s p r i n c i p a l l y o f q u a r t z , k a o l i n i t e and p y r i t e / m a r c a s i t e i s e x p r e s s e d i n terms o f c h e m i c a l a n a l y s i s as Minerals = S i 0

2

+ A1 0 2

3

+ Ti0

2

+ K0 2

+ FeS

2

T h i s e x p r e s s i o n i g n o r e s the water o f c o n s t i t u t i o n o f c l a y s which i s u s u a l l y o f n e g l i g i b l e magnitude f o r V i c t o r i a n brown coals. The t o t a l weight o f M i n e r a l s and I n o r g a n i c s e x p r e s s e d on a d r y c o a l b a s i s g i v e s the b e s t e s t i m a t e c o r r e s p o n d i n g t o " m i n e r a l matter" i n high-rank c o a l technology. In the case o f L a t r o b e V a l l e y c o a l s the I n o r g a n i c s a r e f a r more i m p o r t a n t than M i n e r a l s both i n q u a n t i t y and from a u t i l i z a t i o n p o i n t o f view. From a knowledge o f the c h e m i c a l c o n s t i t u t i o n o f the m i n e r a l m a t t e r , i t i s p o s s i b l e t o c a l c u l a t e and p r e d i c t the c o m p o s i t i o n o f the ash or i n o r g a n i c r e s i d u e r e m a i n i n g a f t e r most t e c h n o l o g i c a l processes. Table 2 i l l u s t r a t e s the comparison between m i n e r a l m a t t e r c o n t e n t and ash c o n t e n t and the s u c c e s s f u l c a l c u l a t i o n o f ash c o n t e n t from m i n e r a l m a t t e r d a t a f o r a number o f t y p i c a l V i c t o r i a n brown c o a l s . Table 3 illustrates the f u t i l i t y of p r e d i c t i n g the q u a n t i t i e s o f ash produced i n modern, p u l v e r i z e d f u e l f i r e d power s t a t i o n s from the e m p i r i c a l ash t e s t r e s u l t s . It i l l u s t r a t e s f o r M o r w e l l and Y a l l o u r n c o a l s the q u a n t i t i e s o f ash produced i n a b o i l e r as opposed t o the ash t e s t ; and i t compares the l a b o r a t o r y ash c o m p o s i t i o n w i t h the p r e c i p i t a t o r ash a c t u a l l y produced. The m i n e r a l m a t t e r c o m p o s i t i o n i s a l s o g i v e n as a guide. Both the l a b o r a t o r y and p r e c i p i t a t o r ash c o m p o s i t i o n s can be c a l c u l a t e d from the c o m p o s i t i o n o f the m i n e r a l matter by a l l o w i n g f o r the d i f f e r e n c e i n the degree o f s u l p h a t i o n o f the Inorganics. By e x t e n d i n g t h i s approach i t s h o u l d a l s o be p o s s i b l e to c a l c u l a t e the c o m p o s i t i o n o f the i n o r g a n i c r e s i d u e o b t a i n e d i n hydrogénation p r o c e s s e s . I t s h o u l d a l s o be noted t h a t oxygen can o n l y be e s t i m a t e d by d i f f e r e n c e i f the m i n e r a l m a t t e r i s known; u s i n g the ash v a l u e w i l l y i e l d misleading results.


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TABLE 1.

BED MOISTURE AND MOISTURE HOLDING CAPACITY FOR SELECTED VICTORIAN COALS


Coal F i e l d (Selected Values)

Bed M o i s t u r e (As R e c e i v e d )

Kg/Kg Dry Coal Yallourn-Maryvale Morwell-Narracan Loy Yang Flynn Y a l l o u r n North E x t Coolungoolun Gormandale Gelliondale Stradbroke Anglesea Bacchus Marsh

1.82 1.54 1.63 1.76 0.98 1.19 1.27 1.83 1.41 0.87 1.53

Moisture Holding Capacity % (Equilibrium Moisture)*

Weight Percent 38.4 38.2 42.1 41.2 41.2 35.0 39.0 35.3 37.1 32.9 31.2

64.2 60.5 61.9 63.5 49.5 54.4 56.0 64.6 58.4 46.6 60.4

* Determined a t 97?o h u m i d i t y and 30°C

TABLE 2.

COMPARISON OF ASH CONTENT AND SELECTED VICTORIAN BROWN COALS

Coal F i e l d (Selected Values)

Yallourn-Maryvale Morwell-Narracan Loy Yang Flynn Y a l l o u r n North E x t Coolungoolun Gormandale Gelliondale Stradbroke Anglesea Bacchus Marsh

MINERAL

MATTER

Mineral Matter*

Ash* Determined C a l c u l a t e d 2.3 2.4 1.0 1.4 4.3 2.3 1.6 5.8 3.9 3.9 7.4

2.4 2.6 1.1 1.5 4.5 2.4 1.6 5.8 3.6 3.4 7.4

1.7 1.5 0.8 0.1 3.0 2.2 1.3 3.4 2.0 2.2 3.5

* Dry C o a l B a s i s


FOR

1.


PERRY ET A L .

TABLE

C O A L - A S H CHEMISTRY

3.

:

MORIAIELL OPEN

CUT

C o a l % Dry B a s i s

Minerals FeS 2 Si0 A1 0 Inorganics Fe Ca Mg Na CI Organic S T o t a l Ash 2


2

3

Ash?o

0.13 0.19 0.04

Si0 A1 0

0.32 0.70 0.24 0.08 0.04 0.25

Fe 0 CaO MgO Na 0 -

2

2

2

3

3

2

SO

3

Laboratory

Boiler Precipitator

6.2 1.3

8.0 1.7

17.6 32.0 13.1 3.6 26.1 3.1

22.7 41.2 16.8 4.6 5.0 2.6

Oxygen F u n c t i o n a l Groups. Oxygen i s one o f t h e major elements p r e s e n t i n t h e o r g a n i c s u b s t a n c e o f V i c t o r i a n brown c o a l . For L a t r o b e V a l l e y brown c o a l s oxygen g e n e r a l l y c o m p r i s e s over 25?ό on a dry m i n e r a l and i n o r g a n i c f r e e ( d m i f ) b a s i s and about h a l f o f t h i s oxygen can be accounted f o r i n t h e a c i d i c f u n c t i o n a l groups p h e n o l i c h y d r o x y l , f r e e c a r b o x y l i c a c i d and c a r b o x y l a t e . The 4050?ό o f t h e oxygen n o t a c c o u n t e d f o r as a c i d i c oxygen i s p r i m a r i l y c o n t a i n e d i n c a r b o n y l g r o u p s , e t h e r l i n k a g e s and h e t e r o c y c l i c r i n g structures. V a r i a t i o n o f Chemical P r o p e r t i e s

W i t h i n a Seam

The v a r i a t i o n o f chemical properties i n a brown c o a l seam i s a t t r i b u t a b l e t o t h e i n f l u e n c e o f two independent v a r i a b l e s , namely c o a l rank and c o a l t y p e . Rank v a r i a t i o n s a r e due t o t h e h u r i a l h i s t o r y o f t h e c o a l , t h a t i s , t h e t i m e , t e m p e r a t u r e and p r e s s u r e i t has undergone s i n c e i t s d e p o s i t i o n . However, t y p e ( o r l i t h o t y p e ) variations also significantly influence brown c o a l properties. Lithotypes a r i s e from v a r i a t i o n s i n t h e p r e v a i l i n g botanical communities, t h e depth and n a t u r e o f t h e swamp water and i n t h e conditions o f decay and d e c o m p o s i t i o n o f p l a n t m a t e r i a l . In Victorian brown coal these lithotypes are macroscopically recognizable bands o r l a y e r s w i t h i n a c o a l seam which become r e a d i l y a p p a r e n t on p a r t i a l l y d r i e d and weathered f a c e s o f open cuts. The b a s i c f a c t o r s on which l i t h o t y p e s a r e c l a s s i f i e d a r e c o l o r and t e x t u r e i n a i r - d r i e d c o a l , w i t h degree o f g e l i f i c a t i o n , w e a t h e r i n g p a t t e r n and p h y s i c a l p r o p e r t i e s used as supplementary c h a r a c t e r i s t i c s which v a r i e s from p a l e t o dark rown. I n t h e case o f L a t r o b e V a l l e y c o a l s , t h e c o l o r o f t h e a i r d r i e d c o a l as measured by i t s d i f f u s e r e f l e c t a n c e and e x p r e s s e d as a C o l o r Index gives a numerical value r e l a t e d t o l i t h o t y p e .


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THE

CHEMISTRY OF LOW-RANK COALS

The v a r i a t i o n i n rank w i t h depth i n the M o r w e l l Open Cut i s i l l u s t r a t e d by the y e a r l y w e i g h t e d averages f o r each o p e r a t i n g level. The g r a d a t i o n i n rank i s c l e a r l y i l l u s t r a t e d i n F i g u r e 1 by the i n c r e a s e i n c a r b o n c o n t e n t , and the a s s o c i a t e d i n c r e a s e i n g r o s s dry s p e c i f i c energy; the v o l a t i l e matter a l s o d e c r e a s e s slightly w i t h depth. These samples were not s e l e c t e d on a l i t h o t y p e b a s i s and the g r a d u a l changes i n these c o a l p r o p e r t i e s are presumed t o a r i s e p r i m a r i l y from the i n c r e a s e i n rank w i t h depth. The v a r i a t i o n o f c o a l p r o p e r t i e s w i t h l i t h o t y p e has been examined w i t h i n c o n t i n u o u s sequences o f samples taken from f i v e L a t r o b e V a l l e y c o a l f i e l d s ( 3 ) . The r e s u l t s i n d i c a t e t h a t the c o a l p r o p e r t i e s r e l a t e d t o the o r g a n i c c o a l s u b s t a n c e , eg: volatile m a t t e r , hydrogen, c a r b o n , oxygen and s p e c i f i c energy v a r y w i t h l i t h o t y p e l a y e r s i n the c o a l seam. The dependence o f carbon and hydrogen on l i t h o t y p e (as measured by c o l o r i n d e x ) i s i l l u s t r a t e d i n F i g u r e 2 f o r a t y p i c a l b o r e . A l l the major c o n s t i t u e n t s o f the o r g a n i c c o a l s u b s t a n c e are l i t h o t y p e dependent and t h e i r v a r i a t i o n w i t h i n a seam i s a d i r e c t consequence o f the changes i n d e p o s i t i o n a l environment which o c c u r r e d d u r i n g f o r m a t i o n o f the seam. The occurrence o f o r g a n i c s u l f u r and o r g a n i c n i t r o g e n i s independent o f l i t h o t y p e a l t h o u g h the c o n c e n t r a t i o n o f n i t r o g e n i s i n f l u e n c e d by the presence o f wood i n the c o a l . G e n e r a l l y s p e a k i n g , the c o n c e n t r a t i o n o f m i n e r a l s i n the c o a l i s h i g h e s t near the overburden and the i n t e r s e a m sediment l a y e r s . Because o f the d i s c r e t e n a t u r e o f the m i n e r a l s t h e i r s p o r a d i c d i s t r i b u t i o n i n a seam cannot be a c c u r a t e l y a s s e s s e d from a s i n g l e t r a v e r s e o f sampling through the seam. The concentration of inorganics, particularly sodium, magnesium, c a l c i u m and n o n - p y r i t i c i r o n show no r e l a t i o n s h i p t o l i t h o t y p e ( F i g u r e 3) i n d i c a t i n g t h a t t h e s e i n o r g a n i c s p e c i e s a r e probably p o s t - d e p o s i t i o n a l i n o r i g i n . However, some depth r e l a t e d g r a d i e n t s are a p p a r e n t ; f o r example, sodium and magnesium o f t e n show a c o n c e n t r a t i o n i n c r e a s e near the top o f a bore w h i l s t the aluminium c o n c e n t r a t i o n tends t o i n c r e a s e near the bottom. T h i s i s b e l i e v e d t o be due t o d i f f u s i o n o f aluminium i n t o the c o a l from the c l a y c o n t a i n i n g sediments below the c o a l seam. On the o t h e r hand c a l c i u m i n the M o r w e l l open c u t has the h i g h e s t c o n c e n t r a t i o n near the m i d d l e o f the p r o f i l e . V a r i a t i o n i n Chemical P r o p e r t i e s between C o a l F i e l d s In a d d i t i o n t o the v a r i a t i o n o f c h e m i c a l p r o p e r t i e s w i t h i n c o a l seams, s i g n i f i c a n t v a r i a t i o n a l s o o c c u r s between d i f f e r e n t c o a l fields in Victoria. An e x t e n s i v e r e s e a r c h program i n which t h i s variation was i n v e s t i g a t e d has been conducted by the State E l e c t r i c i t y Commission o f V i c t o r i a on b e h a l f o f the V i c t o r i a n Brown Coal C o u n c i l . In t h i s Brown C o a l E v a l u a t i o n Programme a sampling philosophy was adopted t h a t would h i g h l i g h t the n a t u r a l v a r i a b i l i t y o f the c o a l and i n d i c a t e the range o f c o a l q u a l i t i e s which may be e n c o u n t e r e d d u r i n g m i n i n g and u t i l i z a t i o n o f the d e p o s i t s .



PERRY ET AL.


TOP OF S E A M

Figure the

1.

Variation

Morwell

Copyright

Open

1982,

Cut.

of

selected

coal

properties

(Reproduced with

Butterworth

& Co.,

with

permission

depth

from

Ref.

Ltd.)



THE CHEMISTRY O F LOW-RANK COALS

60

80

(DARKER)

I

4-1

100 COLOUR

120 INDEX

1

I

4· 5

140

160

I

1

60

6-3

I

50

180 < LIGHTER)

5-5

HYDROGEN ·/. (d.m.i.f.) I

I

I

I

I

64

66

68

70

72

CARBON Figure index

2.

V a r i a t i o n of hydrogen

(lithotype)

in a typical

°/o (d.m.i.f.)

and carbon with

bore

depth

and c o l o r

core.


1.

PERRY ET AL.

DEPTH METRES 761


BORE N°- LY1280 M-l Pa Lt

M-l


Lt M-l Lt M-d M-l M-d M- I

Lt M-l M-d"

M-l Pa

M-d M-l

ft/u M-l Lt* Pa/Lt Lt M-l . , Inferior Coal Ligneous Silt Sandy Silt

I

1

0

0-1 °/o d.b

1 0-2

SODIUM CALCIUM MAGNESIUM IRON Figure iron

3.

with

V a r i â t ion of depth

sodium,

in a typical

(Non P y r i t i c )

calcium,

bore

magnesium,

and n o n p y r i t i c

core.


11


12


The program commenced i n t h e L a t r o b e V a l l e y c o a l f i e l d s by s a m p l i n g open-cut f a c e s and 220 mm d i a m e t e r bore c o r e s and was l a t e r extended t o i n c l u d e major c o a l d e p o s i t s i n V i c t o r i a . Lithotype logs were p r e p a r e d u s i n g q u a r t e r c o r e s e c t i o n s l a i d o u t t o d r y , and s e l e c t e d l i t h o t y p e samples from each c o r e were a n a l y z e d f o r a v a r i e t y o f c h e m i c a l , p h y s i c a l and pétrographie c h a r a c t e r i s t i c s and u t i l i z a t i o n p a r a m e t e r s : 144 p a r a m e t e r s i n a l l . To d a t e , a t o t a l o f 219 c o a l samples have been a n a l y s e d from three open-cut faces and twenty 220 mm d i a m e t e r bore cores, r e p r e s e n t i n g 11 c o a l f i e l d s t h r o u g h o u t V i c t o r i a . C o a l samples from a f u r t h e r s i x bores are p r e s e n t l y being c h a r a c t e r i z e d . The d a t a g e n e r a t e d from t h e s e a n a l y s e s and t e s t s was e v a l u a t e d by statistical methods and c o r r e l a t i o n c o e f f i c i e n t s have been d e t e r m i n e d between a l l p a i r s o f v a r i a b l e s . A n a l y s i s of t h i s data has r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s i n t h e c h e m i c a l p r o p e r t i e s o f the c o a l from d i f f e r e n t f i e l d s and e n a b l e s t h e s e l e c t i o n o f c o a l with specific properties for particular applications. Table 4 i l l u s t r a t e s some o f t h e s e d i f f e r e n c e s by showing t h e range o f v a l u e s d e t e r m i n e d f o r s e l e c t e d c o a l p r o p e r t i e s from 219 samples (11 c o a l fields). T y p i c a l v a l u e s from t h e two open c u t mines c u r r e n t l y o p e r a t i n g i n t h e L a t r o b e V a l l e y a r e shown f o r c o m p a r i s o n . These d i f f e r e n c e s i n c h e m i c a l p r o p e r t i e s between t h e d i f f e r e n t c o a l f i e l d s are g e n e r a l l y more s i g n i f i c a n t than l a t e r a l v a r i a t i o n s w i t h i n a p a r t i c u l a r f i e l d ( i e : between d i f f e r e n t b o r e s w i t h i n a f i e l d ) and they a r e p r i m a r i l y r e l a t e d t o rank. TABLE 4.

VARIATION IN SELECTED CHEMICAL VICTORIAN BROWN COAL FIELDS Yallourn Open Cut

Property M o i s t u r e (wt %) Net wet s p e c i f i c ^ energy (MJ Kg" ) Ash (wt %) M i n e r a l s and I n o r g a n i c s (wt %, db) V o l a t i l e M a t t e r (wt«, d m i f ) H/C Atomic R a t i o Oxygen (wt?o, d m i f ) N i t r o g e n (wt?o, d m i f ) Sulphur (wt%, dmif) S i 0 (wtSS db) C a l c i u m (wtSS db) Magnesium ( w t % db) Sodium (wt/o db) I r o n - t o t a l (wt» db) P h e n o l i c - OH (meq/g) -C00H (meq/g) -COO" (meq/g) 2

66.4

Morwell Open Cut 60.2

PROPERTIES

BETWEEN

Range o f V a l u e s (219 Samples) 43.7

-

71.0

6.87 1.3

8.95 3.5

5.24 0.5

-

13.87 12.8

1.3 52.1 0.86 26.2 0.52 0.27 0.38 0.04 0.18 0.06 0.18 3.72 2.21 0.49

2.7 49.2 0.86 24.2 0.62 0.34 0.14 0.74 0.23 0.13 0.19 3.70 1.90 0.59

0.3 43.3 0.77 17.4 0.36 0.14 0.01 0.01 0.02 0.02 0.01 1.91 0.90 0.03

-

12.8 67.8 1.16 30.0 0.85 5.36 7.6 2.07 0.85 0.47 1.80 4.44 2.94 1.66

dmif - d r y , m i n e r a l and i n o r g a n i c - f r e e b a s i s db - d r y b a s i s


1.

P E R R Y ET AL.


E f f e c t o f Chemical P r o p e r t i e s on

Utilization


As a r e s u l t o f the Brown C o a l E v a l u a t i o n Program, the u n d e r s t a n d i n g o f the v a r i a b i l i t y o f V i c t o r i a n brown c o a l s and i t s i m p l i c a t i o n s for utilization have improved substantially. I t has become apparent t h a t c e r t a i n c h e m i c a l p r o p e r t i e s can have important consequences f o r u t i l i z a t i o n o f the c o a l f o r power g e n e r a t i o n , l i q u e f a c t i o n and o t h e r a p p l i c a t i o n s . A number o f examples w i l l be b r i e f l y d e s c r i b e d Carbonate F o r m a t i o n D u r i n g Hydrogénation. The f o r m a t i o n o f c a r b o n a t e m i n e r a l s d u r i n g hydrogénation o f low-rank c o a l s can cause s e r i o u s o p e r a t i o n a l d i f f i c u l t i e s i n the r e a c t o r systems. A good c o r r e l a t i o n has been found between the c a l c i u m c o n t e n t o f a number of V i c t o r i a n brown coals and the carbonate formed during hydrogénation. However, the r e s u l t s i n d i c a t e d t h a t c a t i o n s o t h e r t h a n c a l c i u m were i n v o l v e d i n the f o r m a t i o n o f c a r b o n a t e . XRD a n a l y s i s has r e v e a l e d the presence o f s e v e r a l d i f f e r e n t t y p e s o f c a r b o n a t e m i n e r a l s i n l i q u e f a c t i o n r e s i d u e s from a number of c o a l s . M i n e r a l s i d e n t i f i e d i n c l u d e d v a t e r i t e and c a l c i t e (two polymorphs o f C a C 0 ) d o l o m i t e ( C a M g [ C 0 ] ) and i n the r e s i d u e from a h i g h s u l f u r c o a l (2.26% d b ) , a n h y d r i t e (CaSO^) was i d e n t i f i e d . The t y p e s o f m i n e r a l d e p o s i t s formed depend not o n l y on the c o a l but a l s o on the r e a c t i o n c o n d i t i o n s . Our d a t a i n d i c a t e s t h a t whilst vaterite forms at low temperatures (380°C), as the temperature i n c r e a s e s , the v a t e r i t e becomes p r o g r e s s i v e l y c o n v e r t e d t o c a l c i t e , the more s t a b l e form. After further increases i n temperature, p a r t i c u l a r l y at long r e a c t i o n times, dolomite begins t o form. The r e a c t i o n t o form a n h y d r i t e , i n the case o f the h i g h s u l f u r c o a l , must compete f o r c a l c i u m w i t h the f o r m a t i o n o f c a l c i u m c a r b o n a t e , and t h i s may have a b e n e f i c i a l e f f e c t . C l e a r l y the t y p e s o f i n o r g a n i c p r e c i p i t a t e s which form d u r i n g hydrogénation o f V i c t o r i a n brown c o a l a r e dependent on the n a t u r e o f the exchangeable c a t i o n s and t o some e x t e n t the a v a i l a b l e c o a l sulfur. 3

3

2

Sodium and B o i l e r F o u l i n g . The c o n c e n t r a t i o n o f sodium i n c o a l i s regarded as the most s i g n i f i c a n t f a c t o r i n the f o r m a t i o n o f troublesome ash d e p o s i t s d u r i n g combustion. Although V i c t o r i a n brown c o a l s a r e g e n e r a l l y low i n ash forming c o n s t i t u e n t s , c o a l s w i t h a h i g h p r o p o r t i o n o f sodium can form ashes which c o n t a i n l a r g e amounts o f low m e l t i n g p o i n t , sodium s u l p h a t e compounds. These are formed d u r i n g combustion from the i n o r g a n i c sodium and o r g a n i c s u l p h u r i n the c o a l . The sodium s u l f a t e condenses on the s u r f a c e o f b o i l e r tubes and t o g e t h e r w i t h f l y - a s h p a r t i c l e s forms s t i c k y d e p o s i t s , which can c o n s o l i d a t e on h e a t i n g and l e a d t o e x t r e m e l y dense h a r d - t o remove d e p o s i t s . The presence o f h i g h sodium s u l f a t e c o n t e n t ash t h u s r e q u i r e s s p e c i a l c o n s i d e r a t i o n d u r i n g the d e s i g n and o p e r a t i o n of b o i l e r s .


13

14


Aluminium and P r e c i p i t a t o r Ash. I n some V i c t o r i a n brown c o a l s s i g n i f i c a n t q u a n t i t i e s o f a c i d - s o l u b l e aluminium a r e found. This i s b e l i e v e d t o be p r e s e n t a s aluminium h y d r o x i d e which i s d i s p e r s e d throughout t h e water phase o f t h e c o a l . D u r i n g combustion o f t h i s c o a l , t h e r e f r a c t o r y aluminium o x i d e formed t a k e s t h e shape o f t h e r e l i c s o f t h e p l a n t m a t e r i a l p r e s e n t i n t h e c o a l , t h u s f o r m i n g an e x t r e m e l y low d e n s i t y a s h ( a p p r o x i m a t e l y 100 kg/m ). Whilst the c o l l e c t i o n o f t h e s e p a r t i c l e s by e l e c t r o s t a t i c p r e c i p i t a t i o n i s p o s s i b l e , t h e problem o f r e e n t r a i n m e n t on r a p p i n g has n e c e s s i t a t e d the use o f l a r g e r s i z e d u n i t s than would o t h e r w i s e be r e q u i r e d . I t i s t h e r e f o r e i m p o r t a n t t o determine t h e a c i d s o l u b l e aluminium f r a c t i o n i n t h e c o a l t o determine i f p r e c i p i t a t i o n o f f l y a s h i s l i k e l y t o be a problem.


3

Acknowledgments The authors wish t o acknowledge t h e support o f the State E l e c t r i c i t y Commission o f V i c t o r i a (SECV), t h e V i c t o r i a n Brown C o a l Council (VBCC), and t h e companies i n t h e VBCC Industrial P a r t i c i p a n t s Group. The a s s o c i a t e d d r i l l i n g , l o g g i n g and s a m p l i n g a c t i v i t i e s were managed by t h e SECV's G e o l o g i c a l and E x p l o r a t i o n D i v i s i o n , and t h e a n a l y t i c a l work was performed by t h e s t a f f a t t h e Herman Research L a b o r a t o r y .

LITERATURE CITED 1. Victorian Brown Coal Resource Development Study, Kinhill Pty Ltd. 9 Volumes. December 1982. 2. Kiss LT and King TN. Fuel 1977, 56, 340-1. 3. King TN, George AM, Hibbert WD and Kiss LT. Variation of Coal Properties with Lithotype Pt 2. SECV Report No. SO/83/55 (1983). 4. Perry, GJ; Allardice, DJ; Kiss, LT Fuel 1982,61,1060. R E C E I V E D March 12, 1984


The Chemistry of Low-Rank Coals - American Chemical Society

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