Influence of microlithotype composition on hardgrove grindability for selected eastern Kentucky coals

International Journal of Coal Geology, 7 (1987) 227-244 Elsevier ~cience Publishers B.V., Amsterdam - - Printed in The Netherlands

227

Influence of Microlithotype Composition on Hardgrove Grindability for Selected Eastern Kentucky Coals

JAMES C. HOWER, ANNE M. GRAESE* and JEFFREY G. KLAPHEKE

Kentucky Energy Cabinet Laboratory, Box 13015, Iron Works Pike, Lexington, KY 40512, U.S.A.

(Received February 10, 1986; revised and accepted July 10, 1986)

ABSTRACT

Hower, J.C., Graese, A.M. and Klapheke, J.G., 1987. Influence of microlithotype composition on Hardgrove grindability for selected eastern Kentucky coals. Int. J. Coal Geol., 7: 227-244.

The relationship between Hardgrove grindability and coal microlithotype composition was studied for three coals from two eastern Kentucky mines. The purpose of the study was to further investigate the use of petrographic data as a predictor of mechanical properties important in mining and utilization. Samples were collected according to lithotype divisions. In general, monomaceral microlithotypes increased the grindability while the complex trimaceral microlithotypes decreased grindability. The bimaceral microlithotypes exhibited a varied influence depending upon their maceral composition.

INTRODUCTION

Coal grindability is a complex property related to coal hardness, strength, tenacity, and fracture (Yancey and Geer, 1945). All of these properties are influenced by the coal rank, the megascopic and microscopic coal petrography, and the type and distribution of minerals ( Lawrence, 1978). As an indicator of a number of properties, grindability is important in the consideration of the mining and pulverization of coal.

This study of Hardgrove grindability was developed as part of a study of the influence of lithotype composition on continuous-miner-bit wear in eastern and western Kentucky mines (Lineberry and others, 1984). In addition to three underground operations studied in detail (including analysis of bit wear and float/sink analysis of the mined product from sharp and dull bits), one surface mine and three additional underground mines were included in the

*Present address: Illinois State Geological Survey, Champaign, IL 61820, U.S.A.

0166-5162/87/$03.50 © 1987 Elsevier Science Publishers B.V.

228

study of the relationship between compressive strength and lithotype composition. The two eastern Kentucky mines in the detailed study and the surface mine, located in the same mining complex as one of the underground mines (Fig. 1 ), are discussed in this paper.

In this study the influence of maceral and microlithotype composition on the variation in the Hardgrove grindability index (HGI) between coal lithotypes from two sites in eastern Kentucky is discussed. Each of the high-volatile-A bituminous sites is considered alone, therefore, coal rank is not a factor in this study except in preventing the combination of the two sets. Expanded studies of more coals could provide a continuum of rank, allowing the more complete analysis of the variations in maceral and microlithotype composition across the high volatile bituminous range.

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229

BACKGROUND

Hardgrove grindability and mechanical coal properties

Hardgrove grindability has been indirectly correlated with parameters important in mining and beneficiation (Burstlein, 1954; Schapiro et al., 1961; Peters et al., 1962 ). Knowledge of the HGI, as well as the other coal parameters which influence HGI, can be of assistance in planning coal mining and coal utilization operations.

The Hardgrove method of determining grindability evolved as a constant- work test, simpler and faster than the ball-mill test which required grinding to constant fineness (Yancey, 1936; Black, 1936; Yancey and Geer, 1945). The ball-mill test, requiring about 9 hours per sample, was compared to Hardgrove grindability by Fitton and others (1957). (The Hardgrove test, as described in ASTM standard D-409, requires less than 20 minutes once the coal is pre- pared for the test) . They found a near-linear correlation between the two tests up to HGI 90. HGI 50 is equivalent to a ball mill index of about 34 and HGI 70 is equivalent to a ball mill index of about 50.

The impact strength index (ISI), determined by sizing the product of the dropping of a 4-lb. (1.39 kg) weight on 100 g of 3/8" × 1/8" (0.95×0.32 cm) coal, has a minimum at about 19% volatile matter, within the range in which HGI passes through a maximum (easiest grindability) (Lawrence, 1978). Tests by Evans and Pomeroy (1966) on British high-volatile coals showed that for ISI values in the 50-70 range, compressive strength perpendicular to bedding fell in the 2000-7000 lb/in 2 (13.8-48.3 MPa) range, an increase of about 222 lb/in 2 (1.5 MPa) per one impact strength unit. Hardgrove grindability is related to ISI according to the formula (after Lawrence, 1978):

ISI = 0.015 HGI 2 - 2.62 HGI + 159 (1)

Power requirements in continuous miner operations are proportional to coal compressive strength, the impact strength index, and the Hardgrove grindability index. Plowing forces are at a minimum in the 15-20% volatile matter range (Dumbleton et al., 1958; Evans and Pomeroy, 1966). Schapiro et al. (1961) and Peters et al. (1962) demonstrated the influence of variations in lithotype hardness on power requirements for the D seam in Harlan County, Kentucky. Differences in lithotype grindability of 25 HGI units, not uncom- mon for Appalachian coals, imply compressive strength differences exceeding 4000 lb/in 2 (27.6 MPa) (after formula 1 from Lawrence, 1978).

The Bond test, similar to the ball-mill test, is tedious but can be scaled to estimate comminution energy. The Bond work index (Wi), in Kwh/t , is the energy required to reduce a short ton of theoretical infinite particle size to 80% passing 100 mesh (150 microns). McIntyre and Plit t (1980) performed Bond and volumetric ( 36 cm 3 ) Hardgrove tests on 11 materials, including two coals.

230

For the coals 36 cm 3 was slightly more than the 50 g called for in a standard Hardgrove test according to ASTM D409-71. The correlation between the two tests is expressed by:

Wi = 1622/HGI l°s ( 2 )

Bond indices for 50 and 100 HGI coals would be 23.7 and 11.2, respectively. Scieszka (1985) developed an equation from which the work (W) required to produce a product of size P (80% passing) could be estimated from the Bond index and the size of the feed, F (80% passing):

W:Wi~ F ] \ P ] (3)

HGI can be substituted for Wi after the McIntyre and Plitt (1980) formula, allowing a practical estimation of comminution energy.

Differences in grindability due to variations in lithotype petrography are important in determining the size of coal passing through preparation plants. The HGI differences can be exploited in the development ofbeneficiation flow- sheets designed to produce a variety of products from one feed coal. Burstlein (1954, 1971 ) discussed the applications of designing beneficiation around differences in lithotype hardness and the technique is well established in the preparation of metallurgical coals.

Hardgrove grindability and coal composition

Rank Coal rank exhibits a strong influence on grindability. Hsieh (1976) modeled

grindability as a function of rank, mineral matter, and organic petrography for a set of 101 high-volatile to anthracite coals. For coals with low mineral matter and greater than 90% vitrinite, rank alone was a good predictor of HGI. Gomez and Hazen (1970) constructed a predictive model using data from 735 coals analyzed by the U.S. Bureau of Mines. Ash and sulfur were included in the non-linear, 25-term equation along with five rank-related parameters: calorific value (mmmf), moisture (as-received), volatile matter (dry), and fixed car- bon (dry and dmmf). The equation with an r 2 = 0.93 and a standard error = 5.58 was tested with 1029 other samples, with 95% of the coals falling within _+ 2 standard errors. For high-volatile coals, as considered in this study, an increase in rank would be accompanied by an increase in the Hardgrove grindability index (easier grinding with an increase in rank ).

Microlithotypes Among the coals and lithotypes studied by Hsieh (1976), a grindability dif-

ference of 50 HGI was noted between a fusain and a durain of similar hvA

231

volatile mat ter contents. Among lithotypes from the same coal, durains would be expected to have the lowest HGI and fusains the highest HGI (see also Temeeva, 1979). In a study of float/sink products of coals of similar rank, Chandra and Maitra (1976) noted that for a given mineral content there is a minimum HGI corresponding to the lowest vitrinite content. Hsieh's (1976) model for petrographic variation, given constant rank and mineral matter, showed that increases in fusinite and semifusinite increased HGI while an increase in micrinite decreased HGI. Using data from the study by Terchick et al. (1963), Leonard (1964, 1965) developed equations from 20 hvA Pittsburgh seam and Harlan County, Kentucky, coals:

HGI = 76.04 - 0.99 ( SFI ) - 0.27 ( F ) - 1.22 ( M ) - 0.32 ( MM ) ( 4 )

HGI=23.95+0.133 ( S F R ) - 1 . 3 7 ( E ) - 0 . 5 3 1 (R)+0 .613 (V) (5)

where: V = vitrinite; R = resinite; E = exinite; SFR = reactive semifusinite (1/3 of total); S F I = i n e r t semifusinite (2/3 of total); F=fusini te ; M = micrinite; MM = volumetric mineral matter.

Both equations had an r 2 = 0.88. Using the same 20 coals, Terchick et al. (1963) correlated HGI with micrinite, exinite, and resinite, obtaining an r 2 = 0.86. In general, the presence of vitrinite in a hvA coal increases grindability while micrinite and the liptinite macerals decrease grindability.

Mineral matter In terms of its influence on grindability, Hsieh (1976) classed mineral mat-

ter into four groups: (1) clays and sulfates; (2) quartz, oxides, and silicates; (3) pyrite and other sulfides; and (4) carbonates. Group 2 minerals are the hardest and the group 1 minerals are the softest. The other two groups are generally softer than the hvA coals of eastern Kentucky included in this study. Shales have a wide, 50-250 HGI, range of grindability but are generally softer than the associated coal (Agus and Waters, 1971). The influence of free shale is largely dependent upon its grindability while intergrown shale will generally lower the HGI (Kanjilal et al., 1979 ).

PROCEDURE

Samples were collected according to lithotype divisions in most cases. Sam- ples were collected from the Leatherwood ( BD- 1-3 ), the Upper Coalburg ( MC- 1-3 ), and the No. 5 Block (MC-4) seams. The MC-4 site was the lone surface mine in the study. Limitations brought about by the need to have sufficient thicknesses for sampling and to limit the number of intervals per seam section to 10-12 served to force some modifications of the sampling procedure. Litho- type descriptions were made with modifications of the clarain range into bright clarain ( > 70% vitrain bands) , clarain (40-70% vitrain bands) , and dull clarain (10-40% vitrain bands) . Lithotypes thicker than 3 mm are described with

232

T A B L E 1

M i c r o l i t h o t y p e s (a f t e r S t a c h et al., 1982) . For t h e d i s c u s s i o n o f Figs. 2 a n d 4: t h e b imace ra l m i c r o l i t h o t y p e s a re clar i te , v i t r ine r t i t e , a n d dur i te ; a n d t h e t r imace ra l m i c r o l i t h o t y p e s are duro- clari te , c la rodur i te , a n d v i t r ine r to l ip t i t e

Mic ro l i t ho type Mace ra l group c o m p o s i t i o n

Vi t r i te Vi t r in i t e (V) > 95%

Lip t i t e L ip t in i t e ( L ) > 95% Ine r t i t e I ne r t i n i t e ( I ) > 95% Clar i te V + L > 95 % Vi t r ine r t i t e V + I > 95 % Dur i t e L + I > 95 % Duroc la r i t e V > L,I *

C la rodur i t e I > V,L * Vi t r ine r to l ip t i t e L > V,I * C a r b o m i n e r i t e 20 -60% quar tz , clays,

or c a r b o n a t e s by vol. or

5 - 2 0 % sul f ides by vol.

*Each group > 5%

TABLE2

Litholo$cdescriptionsofrepresenmtive~amsections

BD-2 - Leatherwood seam MC-3 - Upper Coalburg seam MC-4 - No. 5 Block seam

KCER# Lithotype Lithotype KCER# Lithotype Lithotype KCER# Lithotype Lithotype thickness thickness thickness

4489 Clarain 3397 3408 Durain Bright Clarain Pyrite 3409 Bright Clarain

4490 Fusain 3398 3410 Bright Clarain 3411 Clarain Dull Clarain Vitrain Durain 3412

4491

4492

4493

4494

4495

Siltstone Clarain Bright Clarain Clarain Bright Clarain Clarain Bright Clarain Fusain Bright Clarain Clarain Bright Clarain

1.4 cm 2.4 2.3 0.1 4.0 0.2 0.8 5.3 2.5 0.4 1.1

13.0 1.5 1.5 7.1 2.8 6.1 1.0 0.1 4.4

22.0 9.0

Clarain Fusain Clarain Fusain Bright Clarain Fusain Bright Clarain Fusain Bright Clarain Fusain Vitrain Clarain Fusain Dull Clarain Bright Clarain Fusain Bright Clarain Fusain Bright Clarain Fusain Bright Clarain Dull Clarain

5.0 cm 0.1 6.9 0.1 4.0 0.1 1.8 0.1 0.8 0.1 0.3 0.7 0.05 0.6 1.4 0.05 1.5 0.05 1.7 0.2 3.5 2.0

3413

3414 3415

Bright Clarain Clay Bright Clarain Fusain Dull Clarain Bright Clarain Durain Sandstone Bone (Splint) Durain Dull Clarain Clarain Dull Clarain Bright Clarain Durain Bright Clarain Dull Clarain Bright Clarain Dull Clarain Pyrite Dull Clarain Clarain

6.0 cm 0.1 5.4 1.0 6.0 6.9 9.1 0.2 9.3

15.0 4.5

12.5 4.5 4.0 4.2

12.8 2.6 7.9 7.0 0.5 0.3

25.7

TABLE 2 (continued)

233

BD-2 - L e a t h e r w o o d s e a m MC-3 - Upper Coalburg s e a m MC-4 - No. 5 Block s e a m

K C E R # Lithotype Lithotype K C E R # Lithotype Lithotype K C E R # Lithotype Lithotype thickness thickness thickness

4496 Fusain 1.0 3399 Part ing 3416 Bright Clarain 8.0 Bright Clarain 21.0 Dull Clarain Fusain 0.1

4497 Durain 8.0 Bright Clarain Bright Clarain 4.4 4498 Bright Clarain 4.0 Fusain Fusain 0.4

Dull Clarain 3.5 Bright Clarain Bright Clarain 6.8 Bright Clarain 5.5 3400 Part ing Fusain 0.1

4499 Durain 2.0 Clarain 3417 Bright Clarain 2.7 Bright Clarain 162 3401 Part in Dull Clarain 4.5

Vitram Bright Clarain 2.5 total 150 cm Fusain Bone 9.0

Clarain 3418 Vitrain 0.5 Durain Clarain 15.5 Clarain Durain Clarain Vitrain Clarain Par t in

3403 Dull Clarain Clarain

3404 Clarain Dull Clarain Clarain Pyri te Clarain Vitrain Clarain

3405 Clarain Fusain Bright Clarain Clarain

3406 Clarain 3407 Clarain

3402 3402

1.0 1.0 2.3 0.05 4.2 0.9 5.9 3.5 0.1 1.8 3.0 0.5 4.0 1.8 1.6 0.4

12.5 3.5

10.0 5.0 4.0 1.8 4.4 1.0 1.3 0.5 2.0 9.5 0.1 1.6 3.8

15.0 15.0

total 154 c m

total 200 c m

fusains and partings thinner than 3 mm also being noted in seam descriptions. Combined maceral/microlithotype analysis was performed on one of the two polished pellets with just the maceral analysis being done on the second pellet. Microlithotypes (see Table 1) were defined on the basis of maceral associa- tions within a 50-micron circle (see also Stach and others, 1982). Hardgrove grindability was performed on the samples according to procedures in ASTM standard D409-71.

DISCUSSION

Typical seam descriptions from each of the seams are given in Table 2. Each seam has a variety of bright and dull lithotypes, providing the opportunity for

234

comparisons of grindability versus lithotype petrography without the variations in grindability imposed by rank changes.

All three seams are high volatile A bituminous. The Upper Coalburg and No. 5 Block sets both have vitrinite maximum reflectances of 0.78% Rm,x and the Leatherwood coal has a vitrinite maximum reflectance of 0.87% Rmax. The microlithotype percentages and modified maceral group (micrinite listed sep- arated from other inerts ) percentages are given in Table 3. Complete combined maceral/microlithotype data is given in Lineberry et al. (1984) and Hower et al. (1985).

The advantage of the combined maceral/microlithotype analysis over either maceral or microlithotype analysis is the large amount of information gener- ated. With eight macerals and ten microlithotypes counted, 80 possible combinations exist. Not all combinations are equally likely but, as even the "monomaceral" microlithotypes could have minor (less than 5%) quantities of other maceral groups, all combinations are possible. The lithotypes of channel BD-2 of the Leatherwood seam (Fig. 2) serve as an example of the petrographic complexity of many eastern Kentucky coals. Only bi- and tri-maceral

B D 2

M i c r o l i t h o t y D e

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J

composrtion

, brnaceral x t r i m a c e r a l

F%2 /' /

// /' //

c/

J /

a

Ko~ G

,;\ J\

\ \

Fig. 2. Composition of bimaceral and trimaceral microlithotypes (greater than 1% abundance) in channel BD-2, Leatherwood coal. Letters refer to lithotypes in Table 3. Note that for each lithotype, the microlithotype compositions can be plotted in each of the bimaceral (clarite, durite, vitrinertite) or trimaceral (clarodurite, duroclarite, vitrinertoliptite) fields, such as with the microlithotypes of lithotype B.

235

microlithotypes present in quantities greater than 1% were plotted, therefore not all lithotypes (designated by letters) appear in all fields. It is evident that problems with the counting statistics with low numbers can lead to microlithotypes appearing in the wrong field. For example, the clarite of lithotype J is plotted on the 100% vitrinite corner and the clarodurite of lithotype A (italic letter A) appears in the durite field. All bi- and tri-maceral microlithotypes are represented in BD-2 and some microlithotypes, particularly duroclarite, vi~rinertoliptite, durite, and clarite, exhibit wide ranges in composition. BD- 2-K and BD-2-H are examples of lithotypes with similar maceral composition but different microlithotype compositions. Both lithotypes are relatively high in vitrinite (dmmf) but their duroclarite and vitrinertoliptite compositions are significantly different. BD-2-H has significantly more of those two lithotypes while BD-2-K has more carbominerite. The varied composition of the microlithotypes is one reason why physical characteristics of lithotypes do not necessarily bear a simple relationship to the maceral composition.

The bulk maceral composition, with and without mineral matter, is plotted for the BD-2 lithotypes on Fig. 3. Hardgrove grindability is plotted in terms of the mineral-inclusive maceral group composition. For the Leatherwood BD-2 lithotypes as well as the other eastern Kentucky coals, the plot of grindability on the ternary maceral group diagram shows the decrease in grindability towards the midpoint of the vitrinite-inertinite axis and particularly towards

/

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4489-4499

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Fig. 3. Maceral group composition and Hardgrove grindability by maceral group for channel BD- 2, Leatherwood coal. Letters refer to lithotypes in Table 3.

236

T A B L E 3

Microli thotypes, macerals, and Hardgrove grindabil i ty for Leatherwood (BD-1 -3 ) , Upper Coal- burg (MC-1-3 ), and No. 5 Block (MC-4) lithotypes. Macerals and microl i thotypes reported on volume basis

Li thotype KCER # Microli thotypes

VT LP IN CL DU VI DC CD VL CM

B D - 1 - A 4477 B 4478 C 4479 D 4480

par t ing 4481 E 4482 F 4483 G 4484 H 4485 I 4486 J 4487 K 4488

BD-2- A 4489 B 4490 C 4491 D 4492 E 4493 F 4494 G 4495 H 4496 I 4497 J 4498 K 4499

B D - 3 - A 45OO B 4501 C 4502 D 4503 E 4504 F 4505 G 4506 H 4507 I 4508 J 4509 K 4510 L 4511

MC-1 - A 3375 B 3376 C 3377 D 3378 E 3379

19.1 0.0 6.4 2.7 16.1 7.6 31.4 4.2 1.3 11.2 16.0 0.4 8.5 1.5 7.0 5.9 29.0 4.6 2.6 24.6 18.3 0.0 6.6 1.0 2.3 12.3 42.0 7.5 3.3 6.7 14.1 0.2 12.9 2.0 8.4 17.6 33.9 6.3 0.6 4.1 6.6 0.8 9.3 1.5 1.9 14.4 39.6 6.1 2.7 17.1

14.6 0.2 6.5 1.6 1.2 12.4 52.5 7.3 1.6 2.2 10.3 0.2 8.3 2.4 4.0 12.7 46.3 12.1 1.8 2.0 26.8 0.2 1.0 2.6 0.0 21.5 43.9 0.6 0.8 2.6 29.2 0.0 4.6 5.4 1.8 13.7 35.7 1.6 0.0 8.1

9.4 0.6 14.2 1.4 15.4 6.6 25.0 12.9 2.1 12.5 12.2 0.2 7.9 3.9 7.0 6.4 32.4 4.5 2.9 22.7 20.3 0.2 2.5 2.3 2.5 1.8 8.5 1.0 0.5 60.3

15.4 0.2 8.7 4.0 11.1 6.9 43.7 5.3 1.0 3.8 13.9 0.2 13.1 1.1 9.7 3.4 26.6 6.2 2.4 23.4 18.8 0.0 11.5 2.0 3.1 15.2 33.6 9.6 0.8 5.5 15.2 0.0 10.0 1.8 4.0 14.4 45.9 6.8 0.2 1.8 14.6 0.2 6.0 1.2 1.8 14.2 48.7 11.6 1.0 0.8

8.4 0.0 8.6 2.0 5.6 10.4 48.1 11.0 2.2 3.8 25.9 0.0 6.4 5.2 0.0 19.2 39.7 0.8 0.0 2.8 33.2 0.0 2.6 5.1 0.4 14.9 35.8 1.2 1.6 5.3

5.9 0.4 16.3 1.8 18.9 6.1 20.8 14.9 2.9 12.0 13.6 0.2 9.2 2.6 13.6 8.4 34.2 4.6 3.0 10.6 21.8 0.0 2.8 1.4 1.4 3.9 5.3 0.5 1.6 61.4

18.6 0.0 11.5 4.0 5.5 6.6 23.1 0.7 0.4 29.7 19.3 0.0 2.2 1.1 0.0 0.6 0.5 0.0 0.1 76.2 15.9 0.0 23.5 3.1 8.0 6.6 33.2 3.5 1.0 5.2 6.6 0.7 17.0 1.8 13.0 2.8 10.4 3.3 4.3 40.1

15.3 0.0 13.8 0.2 2.8 10.2 37.5 14.7 1.0 4.5 11.6 0.4 10.0 1.6 1.6 13.7 46.2 12.2 1.8 1.0 6.2 0.4 8.6 0.8 9.7 11.1 43.0 15.2 1.9 3.1

24.1 0.0 2.4 4.6 0.4 18.1 45.2 0.8 0.2 4.2 30.2 0.2 1.4 6.7 0.4 13.3 40.5 0.6 0.2 6.5 11.1 0.4 12.8 1.3 19.2 5.3 17.7 11.9 1.7 18.5 13.2 0.2 6.5 3.6 12.4 8.9 34.3 3.9 3.0 14.0 18.4 0.2 6.9 2.4 1.4 5.5 11.5 1.7 1.9 50.1

23.9 1.0 6.6 2.9 3.3 6.2 35.5 6.0 3.1 11.6 22.9 0.6 6.9 8.0 1.4 4.9 44.9 2.9 2.4 5.1 28.8 0.4 3.5 12.1 0.2 2.7 24.4 0.0 0.2 27.8 23.3 0.2 2.5 11.4 4.3 2.7 28.6 1.4 2.8 22.8 33.3 1.0 3.0 11.0 5.9 2.9 21.0 2.7 3.0 16.2

237

Macerals

VIT INT MIC

M M ( P A R R )

LIP

MOIS Ash $1, HGI

52.3 24.1 10,7 12.9 12.9 49.6 30.4 5,5 14.6 21.3 57.5 21.2 10,7 10.6 11.5 52.7 28.0 9.6 9.6 7.2 47.4 30.3 10,5 11.8 18.7 48.1 24.8 16,8 10.4 5.5 53.8 20.0 11,7 16.5 5.0 79.7 2.9 12.3 5.1 3.4 74.9 9.0 10.6 6.6 4.1 37.5 42.2 6.3 13.9 12.3 56.0 24.1 5.4 14.5 9.8 77.5 10.9 2.8 8.8 26.5

49.7 25.3 12.8 12.9 8.3 47.1 35.1 2.6 15.2 24.6 56.5 25.6 6.6 10.3 6.5 59.8 26.8 6.1 7.3 4.5 53.8 25.3 10.1 10.8 8.3 45.5 27.8 13.4 13.3 5.1 72.8 9.7 12.7 4.8 3.2 76.1 4.8 13.2 6.0 4.6 34.1 42.5 6.2 17.2 13.6 53.8 26.6 5.7 13.9 9.1 78.6 9.5 4.0 7.9 18.0

67.2 21.0 4.0 7.8 14.1 93.8 4.9 0.5 0.8 68.1 46.1 45.1 8.6 9.8 9.2 28.6 50.6 1.5 19.3 52.2 44.5 30.9 12.5 12.1 9.7 53,0 26.3 8.7 12.3 4.1 36.8 38.1 12.5 12.7 7.7 69.6 9.4 15.1 5.9 3.0 79.9 3.7 9.8 6.6 4.1 35.7 40.3 5.3 18.7 15.4 49.0 22.8 9.7 18.5 8.7 71.8 15.3 4.2 8.7 28.0

60.8 20.6 3.0 15.6 8.4 70.2 15.3 4.7 9.8 9.3 84.4 6.2 3.5 3.9 19.2 76.0 7.2 4.9 11.9 29.0 85.3 12.5 3.8 8.4 19.4

2.23 2.40 2.48 2.72 1.92 2.54 2.20 2.49 2.81 2.22 2.26 2.58

2.26 2.30 2.79 2.73 2.69 2.11 2.55 2.55 2.14 2.13 2.69

2.55 1.91 2.80 1.88 2.78 2.54 2.01 2.70 2.60 2.12 2.32 2.77

3.10 3.11 3.03 2.79 3.25

11.26 18.99 10.08

6.24 16.47

4.70 4.26 2.78 3.42

10.88 8.57

23.49

7.21 22.06

5.60 3.79 3.63 4.38 2.57 3.80

12.04 7.93

15.83

11.46 60.57

7.94 47.29

8.48 3.43 6.75 2.42 3.43

13.71 7.58

24.83

7.14 7.95

14.91 25.48 16.65

0,80 0,46 0,52 0,51 1.05 0.49 0.49 0.55 0.54 0.50 0.60 0.74

0.65 0.45 0.54 0.51 0.49 0.50 0.62 0.63 0.49 0.63 0.84

2.50 2.56 0.61 0.32 0.51 0.53 0.51 0.57 0.62 0.52 0.66 0.73

0.74 0.72 4.56 1.20 1.50

39 43 43 46 n /a 41 39 48 51 45 42 48

40 41 42 46 41 38 5O 49 39 40 5O

44 58 42 44 41 41 35 48 49 39 38 47

4O 4O 45 41 46

(cont inued)

238

TABLE 3 (continued)

Lithotype KCER # Microlithotypes


M C - 1 - F 3380 G 3381 H 3382 I 3383 J 3384 K 3385

MC-2- A 3386 B 3387 C 3388 D 3389 E 339O F 3391 G 3392 H 3393 I 3394 J 3395 K 3396

MC-3- A 3397 B 3398 C 3399 D 3400 E 3401 F 3402 G 34O3 H 34O4 I 3405 J 3406 K 3407

MC-4- A 3408 B 34O9 C 3410 D 3411 E 3412 F 3413 G 3414 H 3415 I 3416 J 3417 K 3418

45.2 0.0 4.8 7.3 0.6 4.8 30.2 0.6 1.6 5.0 9.9 0.4 8.9 0.5 16.5 2.5 19.7 6.1 2.7 32.7

22.1 0.6 8.5 2.2 2.0 12.1 41.3 4,5 2.2 4.5 23.0 0.0 6.8 3.0 0.4 13.6 42.1 5.4 3.8 2.0 16.5 1.0 13.4 3.6 3.1 2.7 25.5 3.3 3.6 27.3 22.7 0.2 7.9 3.8 1.5 5.5 21.7 3,0 2.1 31.6

28.5 1.0 9.4 3.1 2.7 5.5 33.9 5.8 3.1 7.0 28.0 0.4 6.5 8.1 2.2 6.3 35.9 3.9 2.6 6.1 27.6 0.0 1.7 9.6 0.2 4.8 37.4 0,4 0.0 18.3 34.3 0.0 0.9 13.9 0.4 1.9 27.5 0.2 1.3 19.5 26.4 0.2 4.9 11.7 8.3 3.8 15.6 0.8 1.9 26.6 30.5 0.4 2.1 6.9 0.8 6.2 41.5 0.8 2.9 7.9 17.7 0.2 9.8 1.5 10.0 3.7 11.6 4.4 3.3 37.8 17.2 0.2 9.5 2.7 3.7 8.5 31.5 7.9 4.6 14.3 19.1 0.0 10.3 2.2 3.6 5.5 38.1 8.7 4.3 8.3 24.9 0.2 8.3 3.4 0.0 12.3 39.7 6.5 1.2 3.6 24.6 0.0 11.1 3.2

28.8 0.4 3.7 7.5 33.1 0.6 14.7 4.2 30.5 0.2 5.0 12.5 28.2 0.2 1.7 15.3 28.1 0.2 7.5 7.5

3.2 6.7 41.4 4.8 1.8 3.4

0.0 8.2 37.3 0.6 1.0 12.5 1.0 7.5 27.5 4.6 4.6 2.4 0.4 2.9 21.5 0.6 1.5 25.0 2.6 1.9 21.7 0.2 4.3 23.9 7.1 1.9 12.9 0.8 1.7 32.2

41.5 0.2 1.4 7.6 0.0 4.9 30.8 0.6 1.4 11.7 17.0 0.7 10.0 2.4 14.4 3.0 18.1 8.1 2.4 23.7 21.7 0.0 8.8 1.0 2.3 10.2 35.5 6.3 2.3 11.9 24.7 0.8 8.4 3.9 2.3 8.2 30.2 2.3 3.7 15.6 23.2 0.2 12.8 5.4 2.9 5.8 13.3 1.5 1.5 33.3 23.9 0.2 0.9 5.0 0.2 3.9 22.9 0.5 0.4 42.1

32.0 0.0 14.1 2.1 0.8 7.3 26.1 7.9 0.8 8.9 12.6 0.4 8.1 0.6 23.7 4.5 25.8 11.4 4.3 8.5 21.7 0.0 8.2 3.9 2.3 8.6 39.1 2.3 0.4 13.5

4.9 0.2 9.2 0.6 13.2 12.4 11.7 9.2 1.1 37.5 9.3 0.6 14.1 2.8 15.5 12.9 26.8 7.6 4.2 6.2

12.0 0.6 8.1 3.4 5.5 13.8 36.7 5.5 4.7 9.7 29.2 0.0 6.6 4.0 0.4 21.7 30.4 1.8 0.0 6.0 15.2 0.2 9.9 1.9 8.0 15.4 32.7 7.0 1.9 7.8 28.3 0.2 6.6 6.6 0.0 18.9 35.3 2.6 0.6 1.0 20.5 0.4 7.1 2.6 10.7 14.2 23.7 3.9 2.6 14.4 39.9 0.1 4.8 3.5 1.5 10.7 17.1 0.7 0.2 21.7

VT - vitrite LP - liptite IN - inertite CL - clarite

DU - durite V! - vitrinertite DC - duroclarite

CD - clarodurite VL - vitrinertoliptite CM - carbominerite

239

M a c e r a l s

VIT INT MIC LIP

M M M O I S

( P A R R )

Ash ST HGI

81.3 8.1 3.8 42.6 34,3 3.6 61.4 14,2 10.1 66.8 16,9 7.7 51.1 30,6 4.6 57.8 21.7 6.8 62.8 21,2 3.5 68.3 14.9 5.8 87.2 4.5 2.4 86.4 4.0 1.9 71.7 13.6 2.7 75.8 7.1 8.6 55.1 29.5 1.9 63.3 20.2 5.1 55.9 21.2 7.1 67.7 15.4 9.3 61.0 25.5 3.7

81.5 7.2 4.6 66.8 19.2 4.7 79.4 11.2 1.9 78.7 6.3 5.1 69.8 20.1 1.5 85.8 4.2 3,6 44.5 32.7 3,6 62.3 21.2 7,1 66.0 20.5 4,6 64.0 23.5 3,2 88.3 4.5 2.6

63.1 27.6 3.8 39.0 34.1 5.4 64.8 22.2 4.2 28.3 55.1 3.4 45.3 35.3 4.5 56.6 25.6 4.7 76.3 14.7 4.5 53.2 26.4 10.1 74.2 13.6 6.1 58.3 26.0 4.7 79.5 13.6 2.3

6.8 9.2 3.52 7.62 19.5 21.8 2.61 18.05 10.8 7.5 2.80 6.22

8.6 10.7 2.82 9.20 13.7 27.2 2.39 24.29 14.7 24.4 2.54 21.60 12.5 11.5 3.01 9.92 11.1 5.8 2.99 4.82

6.0 14.1 3.22 12.07 8.0 18.7 3.24 15.98

12.0 27.0 2.87 23.23 8.5 13.9 3.11 11.89

13.5 29.2 2.37 23.79 11.4 9.8 2.29 7.76 15.8 12.0 2.63 10.33

7.6 22.4 2.79 19.77 8.8 16.4 2.84 14.22

6.6 7.4 3.14 6.17 9.4 7.1 2.93 6.00 7.6 21.6 2.81 18.84

10.0 20.8 2.83 17.54 8.6 25.8 2.60 22.49 6.4 9.1 3.03 7.62

19.2 20.9 2.41 16.89 9.4 10.4 2.58 7.75 8.9 14.3 2.44 12.44 9.3 24.8 2.31 22.07 5.6 26.5 2.43 23.30

5.5 13.9 3.34 11.99 21.5 6.9 3.29 5.88

8.9 12.2 3.16 10.69 13.2 45.5 2.20 40.97 15.0 15.3 2.91 13.47 13.1 8.8 3.22 7.58 4.5 7.1 3.34 6.11

10.3 11.1 3.32 9.59 6.1 5.8 3.42 4.78

11.0 13.9 3.08 12.10 4.8 24.6 3.14 21.75

1 . 0 9

3.12 1.06 0.87 0.63 0.92 0.80 0.77 1.10 1.57 2.14 1.13 5.19 2.22 0.96 0.71 0.98

0.88 0.77 1.13 2.39 1.46 1.14 3.86 3.17 0.88 0.75 1.18

0.86 0.60 0.56 0.47 0.49 0.54 0.53 0.68 0.85 0.68 0.62

47 39 41 42 41 41 43 42 47 46 45 43 43 38 40 43 43

42 38 46 42 43 42 38 41 40 39 42

48 37 42 56 38 37 44 38 43 42 47

VIT - vi t r ini te INT - iner t ini te MIC - micrini te LIP - l ipt ini te

M M - m i n e r a l m a t t e r MOIS - moisture S T - total sulfur HGI - Hardgrove grindabili ty index

240

the liptinite corner. Not evident on Fig. 3 is the increase in grindability with an increase in mineral matter which is seen in some lithotypes. Grindability of whole seam channels is not available in any of the cases discussed here but data from current research in our laboratory supports the additive nature of grindability. Even in a case where the range of lithotype grindabilities was 43-72, the whole channel and the weighted average of the lithotypes had grindabilities within 2 HGI units.

These trends are less evident in the vitrinite-rich western Kentucky coals which were part of the original study (Lineberry et al., 1984). For comparison, Figs. 4 and 5 illustrate the microlithotype composition and maceral group- Hardgrove grindability trends for a high-volatile-C bituminous Herrin (No. 11) coal from Union County in western Kentucky (note the change in scale from the BD-2 plots). Lithotypes from eastern Kentucky coals typically exhibit a greater variety and greater range of composition than the lithotype assem- blages in western Kentucky coals.

The difference in lithotype composition between the two coal fields compli- cates grindability comparisons between coals of apparent similar rank. Based solely on rank, certain Upper Coalburg and No. 5 Block lithotypes should have a grindability similar to the lower-vitrinite lithotypes of the hvA Springfield ( No. 9 ) coal from Webster County, western Kentucky ( compare lithotypes D-

vi1 RINITE /"\

PC-3 Microlithotype J~"B I \

composition #/ ~ I G ~\

. . . . . . . . . . / ' ' c ~ F FE"~ D x trlmaceral w / \e H ~

\ a

LIPTINITE 50 INERTINITE 50 "vITRINITE 5O VITRIN]TE 5O

Fig. 4. Composition of bimaceral and trimaceral microlithotypes in channel PC-3, Herrin coal, Union County, Kentucky (from Lineberry et al., 1984. Note change of scale from Fig. 2).

241

VITRINITE v l t r j n j tE v l t r l n [ t l

\ \ \ \

PC-3 \\ ~ \\ ~o

7 9 3 9 - 7 9 5 1 ~ \ \

/ (dmmD \ (dry) \ o r l n D a B I u t ¥

I w t l n l t e so In~r TJNIT~ so ([nEr t ln lT [ + { INI:RTIN[ [ [ + min l ra l mattErb5l ~ MInEral m a l t l r , 5 0

VI3 RINITF 50 VI3RINII LS0 VI] R]NITE50 v]TRINItl 50

Fig. 5. Maceral group composition and Hardgrove grindability by maceral group for channel PC- 3, Herrin coal, Union County, Kentucky (from Lineberry et al., 1984. Note change of scale from Fig. 3 ).

l-B, -C, and -D on Table 4 with MC-3-A, -C, and -E and MC-4-G, -I, and -K on Table 3). Instead, the Springfield (D- l ) grindabilities are consistently higher. While the Springfield lithotypes do contain durite and clarodurite, both rare in western Kentucky coals, the equivalent microlithotypes in the Upper

TABLE4

Microlithotypes, macerals, and Hardgrove grindability of selected lithotypes of the Springfield coal, Webster County, Kentucky. Macerals and microlithotypes reported on volume basis

Sample Microlithotypes


D-1 - B 7988 32.0 0.0 5.0 2.6 ~.2 10.6 17.3 1.5 0.0 30.7 C 7989 23.7 0.0 12.2 3.4 4.4 14.9 32.5 3.6 0.4 5.0 D 7990 31.9 0.4 5.0 8.3 1.8 10.3 23.2 3.6 0.6 15.0

Sample Macerals MM MOIS Ash ST HGI ( PARR )

VIT IN MIC LIP

D-1 - B 7988 78.9 13.8 4.5 2.8 20.0 1.72 14.81 6.66 54 C 7989 65.2 26.0 3.0 5.8 6.6 1.80 4.79 2.41 55 D 7990 80.8 13.5 1.4 3.4 6.3 2.04 4.26 2.84 55

242

Coalburg and No. 5 Block coals contain more liptinite. Vitrinertoliptite is also present in the eastern Kentucky coals.

Due to the difference in rank, as indicated by vitrinite maximum reflectance, between the Leatherwood (BD-1-3) and Upper Coalburg (MC-1-3)/No. 5 Block (MC-4) sets, regression analyses of petrographic components versus grindability were performed on each of the data sets rather than both sets together. Future reports from our laboratory will deal with a much larger data base of high-volatile coals. The approximation of a continuum of rank in the larger set of coals should allow better consideration of rank as a variable in the analysis of grindability.

Regression analysis on all the macerals plus dry ash and sulfur could be performed. The advantage in using maceral groups (splitting micrinite from the other inertinite macerals) rather than individual macerals lies in the dis- crepancies in recognition and identification of individual macerals between petrographers and laboratories. For example, the recognition of pseudovitrin- ite is far from universal and even among laboratories recognizing it, the criteria for identification are not applied uniformly. Similarly, the distinction between fusinite and semifusinite is difficult to standardize.

Consideration of the petrography of the Leatherwood lithotypes led to the stepwise-regression equation:

HGIBD = 124.79 + 0.69 vitrinite - 28.79 In ( vitrinite )

- 2.32 In ( liptinite ) ( 6 )

with a multiple r 2 of 0.82. Regression of the microlithotype percentages against grindability led to the equation:

H G IBD = 49.29 -- 0.25 durite + 0.40 - vitrinertite - 0.18 duroclarite

- 0.28 ctarodurite - 1.09 vitrinertoliptite + 0.11 ash (7)

with a multiple r 2 of 0.84. The two equations, despite the different y-intercepts and levels of maceral organization, are similar in illustrating the contrasting role of vitrinite and liptinite in their contributions to grindability. The contribution of vitrinite alone is complex but in eqn. (7) it can be seen that vitrinertite, generally dominated by vitrinite in the Leatherwood lithotypes, has a positive contribution to grindability (indicating easier grinding). As observed graphically on Fig. 3, an increase in liptinite will decrease grindability (more difficult grinding). Durite and the complex, liptinite-rich trimacerites all serve to decrease grindability.

The Upper Coalburg and No. 5 Block lithotypes did not yield equations with as much predictive power as the Leatherwood lithotypes:

HGIMc =50.25+0.25 ash-5 .08 in (liptinite) (8)

and

243

HGIMc = 37.80 + 0.15 vitrite + 2.40 liptite - 1.21 vitrinertoliptite

-0 .12 carbominerite+0.32 ash (9)

with multiple r 2 of 0.50 and 0.67, respectively. Perhaps due to the small amount of variation explained by the two equations the contribution of liptinite and liptite is uncertain. In the maceral eqn. (8) an increased liptinite content decreases grindability ( as in eqn. ( 6 ) for the Leatherwood seam ), while in the microlithotype eqn. (9) liptite and liptinite-rich vitrinertoliptite have oppo- site signs. Liptite occurs in smaller quantities than vitrinertoliptite and was the last term added to the equation. While liptite's addition represents a sig- nificant improvement, and after it no microlithotype is close to entering the equation, its positive contribution to grindability may not represent a trend to be expected in other coals. As in the Leatherwood coal, an increase in ash leads to an increase in the Hardgrove grindability index.

SUMMARY

In general for the two equations; monomaceral microlithotypes and ash increased grindability, complex trimaceral microlithotypes - - including carbominerite - - decreased grindability, and the bimaceral microlithotypes exhibited a varied influence depending upon their composition. Microlithotype composition can vary widely such that microlithotypes in different lithotypes can be considerably different in their mechanical behavior. Neither macerals nor microlithotypes alone fully explain the iso-rank differences in grindability observed within lithotypes of the same rank. The next level of statistical analysis would involve the use of the combined maceral/microlithotype values, not possible with this study as it would have involved more variables than samples.

ACKNOWLEDGEMENTS

Carla Pryor of the Kentucky Energy Cabinet Laboratory assisted in the grindability analysis. The work was supported by grants from the Kentucky Energy Cabinet to the Kentucky Energy Cabinet Laboratory.

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Documents

Influence of microlithotype composition on hardgrove grindability for selected eastern Kentucky coals