The Two-Phase Model Applied to Some US Coals - American

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Energy & Fuels 2000, 14, 364-372

The Two-Phase Model Applied to Some U.S. Coals Gavril Niac* and Ioana Muresan Universitatea Tehnicaˇ , Catedra de Chimie, 3400 Cluj-Napoca, Romania Received June 29, 1998. Revised Manuscript Received July 15, 1999

Carbon, hydrogen, sulfur, nitrogen, volatile matter content, and higher heating value of 6-21 samples for each of 11 U.S. coal sorts was checked for linearity versus ash content in order to learn how well they fit the two-phase model of coals. The linear relationship is very strong for carbon content and heating value within each seam, with correlation coefficients better than -0.998 in most cases, and with relative mean square errors (mse/mean) between 0.5% and 1.5%. The relationship is good for H, N, and VM content, with mse/mean of a few percent and poor for sulfur content, with mse/mean around 40%. Except for sulfur content, for which a pronounced inhomogeneity of samples is obvious, coal behaves as being formed of two “homogeneous phases”: the maceral phase and the mineral phase, each one containing wellmixed individual maceral and mineral particles of small size as compared to the mass of the sample. Within a certain area of a given seam, the only variable is the ratio between the two phases, which changes with the location in the seam, while the composition of each of the mineral phase and the maceral phase is unchanged, explaining the linearity with ash content. Extrapolation of any coal property to the ash content of pure mineral phase, i.e., to nil organic carbon content, results in the respective property of the pure mineral phase (mineral matter minus inorganic oxides of the maceral ions), which cannot be evaluated by any other means, without inducing compositional changes. For the studied coals the following properties of the mineral phase were calculated, using the linear relationships: ash, volatile matter, carbon, hydrogen, sulfur contents, and higher heating value, as well as carbon dioxide and water emerged by ashing. Mineral sulfur content relates linearly to heating value of the mineral phase, with a slope close to the heating value of pyrite.

Introduction Coal from a large area of a seam exhibits striking relationships among its analytical variables. Many authors found linear relationships between analytical properties such as elemental composition, volatile matter content, reciprocal density, calorific value, as well as ash oxide contents, versus ash content. Most related papers were summarized in earlier contributions.1,2 A theoretical model for the distribution of trace elements between inorganic and organic components, based on functions of ash content, was developed by Solari, Fiedler, and Schneider.3 A logical explanation of this behavior was the assumption that the two basic types of mineralogical constituents, macerals and minerals, exhibit constant composition each, over large areas of the seam. The only location-dependent variable is their mass ratio. Ash is formed from both the minerals and the macerals. Macerals contribute to ash content with as much as 8-12% for lignites and 2-4% for high rank coals. On the other hand, minerals have a not negligible contribution to any other analytical or technical property of the coal. For instance, moisture of the pure mineral part * Corresponding author. (1) Niac, G. Erdo¨ l, Erdgas, Kohle 1995, 111, 275-280. (2) Nascu, H. I.; Comsulea, D. I.; Niac, G. Fuel 1995, 74, 119-123. (3) Solari, J. A.; Fiedler H.; Schneider, C. L. Fuel 1989, 68, 536539.

has positive values, ranging to about 16% of the “asreceived” sample (the moisture of clay minerals), while it has a negative contribution to heating value, due to endothermic decomposition reactions. The higher the ash content of coal, the larger the contribution of minerals to any coal property. Therefore the properties of a coal sample are weighted averages of the properties of the two basic constituents. It follows that the individual maceral particles in the maceral part and the mineral particles in the mineral part of the coal are well mixed, maceral portion and mineral portion behaving as homogeneous phases each. Consequently, a coal sample can be considered being composed of two “phases”, the maceral phase and the mineral phase. Metal ions, bound by ionic or coordinative bonds to the organic matter, belong obviously to the “maceral phase” (carbonaceous matter), which differs from the conventional “organic matter content” (with no inorganic ions!) of the coal, while the “mineral phase” (noncarbonaceous matter) contains just the minerals, without these ions.1,4 Separation of a coal sample in density fractions by floating in liquids with different densities automatically yields fractions of different ash content. The linear relationships are valid again, as far as particles are a few millimeters large. For finer sizes (4) Niac, G. Mine, Petrol si Gaze 1977, 28, 267-274.

10.1021/ef980150j CCC: $19.00 © 2000 American Chemical Society Published on Web 01/12/2000

The Two-Phase Model Applied to Some U.S. Coals

Energy & Fuels, Vol. 14, No. 2, 2000 365

separation into individual maceral and mineral particles may occur, and the relationships become more complicated.5 The Two-Phase Model of Coals Any additive coal property, Y, can be regarded as the sum of the respective properties of the maceral phase (Basic carbonaceous matter), YB, and of the mineral phase (Terrous matter), YT, each multiplied with its mass fraction, B/100 and T/100 respectively, in the sample:

Y)

YB YT B+ T 100 100

(1)

or, since B ) 100 - T,

Y ) YB - (YB - YT)T/100

(2)

Interaction between the maceral phase and the mineral phase would give rise to an additional “excess term”, resulting in a deviation from linearity. The ash content of the coal is the sum of maceral ash (AB) and mineral ash (AT):

A ) AB + AT

a ) YB - 100fBb

AB ) fBB

(4)

AT ) fTB

(5)

Substituting these values in (3) and writing again B ) 100 - T, the ash content can be written as function of the mineral phase content, T:

W ) a + bAwet

(6)

(7)

(8)

(9)

YB - YT 100(fB - fT)

VT ) 3.664CT + 8.936HT

(14)

and rounding up the constant factors CO2/C and H2O/H (within errors less than 1%):

This equation yields the ash content of the mineral phase, AT, as a function of the straight-line parameters for volatile matter, carbon content, and hydrogen content versus ash content:

aV - 3.7aC - 9aH AT ) bV - 3.7bC - 9bH

with

b)

(13)

aV + bVAT ) 3.7aC + 3.7bCAT + 9aH + 9bHAT (15)

This is the equation of a straight line:

Y ) a + bA

VT ) (CO2)T + (H2O)T or

Property Y can now be written as function of the easily measurable ash content, A, instead of mineral phase content, T (in % of the bulk coal):

fB(YB - YT) YB - YT + (A/100) Y ) YB fB - fT fB - fT

(12)

Moisture content is sensitive to sampling procedure, transportation, and storing conditions; therefore, considerations below will focus on moisture-free coal properties. Often carbon content data refer to total carbon, including mineral carbon (from carbonates) as well. In such cases the ash content of the pure mineral phase, AT, can be estimated, assuming that volatiles emerging from the mineral phase are composed of carbon dioxide and water vapor only, (in a first approximation neglecting possible volatilization of SO3 from sulfates):

or vice versa:

100fB A T) fB - fT fB - fT

(11)

Given a property characterizing the maceral phase only (like organic carbon content, C), while YT () CT) equals zero, the conversion factor fT can be calculated as the ratio of the corresponding straight-line parameters: 100 fT ) -aC/bC. In the opposite case, YB equals zero, for instance the silicon (or silica) content of the maceral phase, and fB can be calculated as 100 fB ) -aSi/bSi. Once fB and fT are known, YB and YT can be computed from the respective straight-line parameters aY and bY, for any property Y. All properties which behave linearly with ash content are also linearly related to each other. Analytical data of carefully taken coal samples suggest that moisture content W is also additive from the moisture of the maceral phase, WB, and the moisture of the mineral phase, WT, thus the two-phase model applies both to wet and moisture-free coal. To get straight lines, the ash content of the wet coal for the former and that of the moisture-free coal for the latter have to be taken as abscissa. Moisture content is linearly related to ash content of the wet coal:

(3)

Assuming constant composition of each coal “phase”, the ash content of the two phases can be expressed as constant fraction (fB and fT) of the respective phase:

A ) 100fB - (fB - fT)T

and

(10)

(5) Niac, G.; Damian, L.; Horowitz O.; Nascu, H. Erdo¨ l, Erdgas, Kohle 1992, 108, 511-515.

(16)

In the absence of carbonates, the volatile matter content of the mineral phase equals 9 times its hydrogen content: VT ) 9HT. The “coke” of the mineral phase (i.e., the remainder of the mineral phase after heating

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Energy & Fuels, Vol. 14, No. 2, 2000

Niac and Muresan Table 1. Sample Sources

no.

location, county, state

seam name

1 Fruitland

San Juan basin, New Mexico Hanna, Wyoming Greene, Pa. Armstrong and Indiana, Pa. Washington, Pa.

2 Hanna No. 1 3 Waynesburg 4 Pittsburgh 5 Pittsburgh 6 Upper Freeport

9 Lower Kittanning Clearfield, Pa. 10 Mercer and Clearfield, Pa. Upper Mercer 11 Mercer Jefferson, Pa.

weathering

site numbers or names

distance ash range number between sites of samples (%) of samples

core

presumably fresh

Well GT-1a

one borehole

7-79

21

core channel channel

fresh Well #7b fresh 19-1 fresh to weathered 46-3, 46-8c

one borehole one site 5 km

8-43 12-28 8-39

10 6 12

channel

weathered to very weathered fresh

8 km

10-25

11

65-10,13, 66-2, up to 29 km 75-20, 76-7c 64-15, 65-10c 11 km 0.2 km 64-17, 64-39c

8-46

9

4-41 4-21

16 12

64-15,74-27c 64-15, 64-40, 74-27c 64-41c

9-45 9-47

7 16

25-66

6

Cambria, Clearfield channel and Indiana, Pa. Clearfield, Pa. core Jefferson, Pa. channel

7 Lower Freeport 8 Lower Freeport

a

sampling method

core core

fresh fresh-moderately weathered fresh fresh

core

fresh

7-9, 7-10c

4 km up to 2 km one borehole

See ref 6. b See ref 7. c See ref 8.

in the absence of air) calculates as KT ) 100 - VT, and in some cases exceeds the ash content of the mineral phase. On the other hand, the sum of carbon dioxide and water content of the mineral phase should equal the difference between pure mineral phase and its ash content 100 - AT, except there are other volatiles contained in the mineral phase (like free sulfur or SO3) or ash gains weight by oxygen uptake (as sulfate or iron(III) oxide). The moisture content (as-received), War T , as well as , of the wet mineral phase, can be the ash content, Aar T calculated from the moisture content vs ash content (both as-received) straight-line parameters, aW and bW, and the ash content, AT, of the moisture-free mineral phase: ar

WT )

100(aW + bWAar T)

ATar )

100 + bWAar T 100 - War T AT 100

(17)

(18)

To test the validity limits of the two-phase model of coals, it should suffice to verify the linearity of coal properties with ash content. In the present paper data available in the literature were used to check the linear relationships between analyzed properties of Fruitland coal from the San Juan basin, New Mexico,6 Hanna No. 1 coal from North Dakota,7 and Pittsburgh (with “D”and “D rider”), Upper Freeport (with “E” coal), Lower Freeport, Lower Kittanning, and Mercer coals from Pennsylvania.8 (6) Nuttal, H. E.; Walters E. A.; Niemczyk, M. Proceedings of the 5th Underground Coal Conversion Symposium, Alexandria, Virginia, June 18-21, 1979, 275-280. (7) Miknis, F. P.; Artuska V. J.; Maciel, G. E. Proceedings of the 5th Undergound Coal Gasification Symposium, Alexandria, Virginia, June 18-21, 1979, 429-435; Campbell, G. G.; Brandenburg C. F.; Boyd, R. M. BOM Coal Gasification Programm, Technical Progress Report 82, October 1974. (8) Skema, V. W.; Berg, Th. M.; Bragonier, W. A.; Edmunds, W. E.; Glass, G. B.; Glover, A. D.; Inners J. D.; Sholes, M. A. Analyses and Measured Sections of Pennsylvania Bituminous Coals, Part II, Mineral Resource Report 69, Commonwealth of Pennsylvania, Bureau of Topografic and Geologic Survey, 1975.

An attempt is made to evauate the analytical properties of the pure mineral phase of the coals, by extrapolating the straight lines to ash content of the mineral phase, using the theory developed above. Data Sources and Data Processing Samples taken from a San Juan basin well in New Mexico were analyzed by Nuttal, Walters, and Niemczik.6 Six-inch (15.24 cm) long samples were cut at 6 in. (15.24 cm) intervals and depths between 496 and 516.5 ft (151-157.5 m). Ash content varies irregularly with depth. The Fruitland formation coal was identified as a subbituminous A or B coal. The data were published on mf basis.6 Ten core samples were taken from well No. 7, that spanned the 10 m Hanna No.1 seam (Miknis et al.),7 while two other samples were taken from another bore hole (Campbell et al.).7 The original analytical data were converted from moisture- and ash-free, to moisture-free basis. The Bureau of Geological Survey of Pennsylvania published analytical data of coal samples from the main coalfield of Pennsylvania as well as sampling procedures.8 The sampling methods were channel or core, as mentioned in Table 1. Sizes of channel samples were about 2 pounds (1 kg) and the length of core samples varied from 0.1 to 2.7 ft (0.8 m) The most important analytical properties of concern were volatile matter (Var), carbon (Car), hydrogen (Har), nitrogen (Nar), sulfur (Sar), and moisture (War) contents as well as higher heating value (Qar), all on an “as-received” basis. The properties of the moisture-free coal were computed by multiplying the original data with 100/(100 - War), except for hydrogen content, H, for which the formula 100(Har - War/9)/(100 - War) was used. The regression parameters, along with the mean square errors and the regression coefficient were calculated for all available properties, in a conventional manner 1,2 as functions of ash content, referring to the moisture-free coal, except for moisture content, War, which is related linearly to the “as received” ash content, Aar. The following symbols were used:


• a, aY ) intercept of the ordinate • b, bY ) slope of the straight line • R ) regression coefficient • so ) mean square error of the data points related to the regression line • sa ) mean square error of the intercept • sb ) mean square error of the slope • n ) number of data points • Ym ) average value of the property Y • A ) ash content (%) • C ) carbon content (%) • H ) hydrogen content (%) • S ) sulfur content (%) • N ) nitrogen content (%) • V ) volatile matter content (%) • K ) coke yield (%) • HHV, Q ) higher heating value (MJ/kg) • W ) moisture content (%) • T ) mineral phase content (%) • B ) maceral phase content (%) • fB ) ash fraction of maceral origin • fT ) ash fraction of mineral origin • mf ) moisture free • ar ) as received Three points (two for sulfur content of Fruitland coals Table 2 and Figure 2sand one for volatile content of Hanna coalsTable 3), lying more than four times farther from the regression line than the mean square error so were regarded as accidental errors and were not considered in calculations. Seam names, sampling locations and methods, number of samples, site numbers, distance between sampling sites, ash range of samples (mf), as well as the degree of weathering are summarized in Table 1. Results and Discussion Some linear plots are exemplified in Figures 1-6, while the most important statistical data are summarized in Tables 2-12 for the 11 investigated sorts of coal. Carbon Content. The relationship between carbon content and ash content is linear and very strong. Correlation coefficients, R, for the investigated coals are between -0.9954 and -0.9993, except Pittsburgh coal


from Washington County (reported as weathered to very weathered) with R ) -0.988, while the mean square errors lie between 0.5% and 1.5% of the mean carbon content value. In all cases the intersection of the x-axis is less than 100% (roughly between 80% and 95% ash content), as does the mineral phase ash, AT. The intercept of the y-axis, a, which roughly estimates the maceral phase carbon content, makes between 80% and 90% for bituminous coals, and 75% for Hanna No. 1 coal. In fact, the true carbon content of the maceral phase is expected to be somewhat lower, since this phase contains small amounts of inorganic ions. Lack of ash composition data for the investigated samples (specifically silicon content or potassium content) did not allow a more precise evaluation of the maceral phase composition. Hydrogen Content. Hydrogen content shows a larger data scatter, with correlation coefficients between -0.976 and -0.995, except again Pittsburgh coal from Washington County, with R ) -0.84. Mean square errors make a few percent of the mean value of hydrogen content. The cut of the ash axis lies in all cases beyond 100% ash, while the intercept varies between 5.1% and 5.6%, except Fruitland coal from New Mexico with a value of about 5.9% hydrogen content of the maceral phase. Again, we can assume an overevaluation of the maceral phase hydrogen content, because of the extrapolation to zero ash content of the hydrogen content vs ash content straight line. Sulfur Content. Sulfur content is more evenly distributed between maceral and mineral phase and exhibits the largest scatter among the studied properties, due to larger inhomogeneities of sulfur distribution within the coal seam. The correlation coefficient is no longer a valuable measure of fitness to a straight line, since this line is in some cases more or less horizontal; instead, the mean square error so of data from the straight line is more meaningful. The relative mean square error so/Sav is in most cases about 30%, with a low of 19% and a high of 56%. Sulfur content correlates poorly to ash content, showing positive as well as negative slopes. Nitrogen Content. Although present in low concentrations, nitrogen content gives very good straight lines vs ash content, with correlation coefiicients ranging from -0.8 to -0.994, most values lying above -0.9. This behavior suggests a uniform distribution of nitrogencontaining molecules among macerals. Volatile Matter Content. The correlation between volatile matter and ash content is quite good, correlation coefficients ranging from -0.8 to -0.994, most of them better than -0.9. The cut of the x-axis lies beyound 100% ash, proving the evolution of volatile matter out of the mineral phase (mostly water and carbon dioxide). The mean square error is about 1% (between 0.13% and 2%). Higher Heating Value. Regression lines of HHV vs ash content of moisture-free coals are characterized by high values of the correlation coefficient, ranging from -0.993 to -0.9997, and consequently low mean square errors, between 0.12 and 0.75 MJ/kg. The intersection of the x-axis is at 89-92.5%, except for Lower Freeport coal from Jefferson County, with 80.5%.

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Niac and Muresan

Table 2. Fruitland Coal, San Juan Basin, New Mexico n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

21 -0.866 79.596 -0.868 -0.9991 0.704 0.008 0.247 59.391 1.18

21 -0.0586 5.9073 -0.0596 -0.9913 0.1512 0.0018 0.0531 4.5400 3.33

19 0.0060 0.5169 0.0138 0.66 0.1287 0.0017 0.0456 0.6432 20.01

21 -0.018 1.809 -0.025 -0.84 0.224 0.003 0.079 1.400 15.97

21 -0.439 46.993 -0.452 -0.986 1.460 0.017 0.513 36.741 3.97

21 -0.369 33.128 -0.370 -0.999 0.392 0.005 0.138 24.528 1.60

AT ) 91.3% VT ) 6.86% CT ) 0.50% HT ) 0.56% QT ) -0.54 MJ/kg ST ) 1.07% KT ) 93.1% (CO2)T ) 1.87% (H2O)T ) 5.0%

Table 3. Hanna No. 1 Coal, North Dakota C(mf), %

H(mf), %

V(mf), %

n) 12 12 11 b) -0.7942 -0.0494 -0.379 a) 75.489 5.616 45.121 by ) -0.7953 -0.0560 -0.404 R) -0.9993 -0.94 -0.97 so ) 0.58 0.36 2.0 sb ) 0.0093 0.0057 0.032 sa ) 0.31 0.19 1.10 Yav ) 53.66 4.26 34.24 1.08 8.41 5.79 so/Yav (%) )

Figure 1. Fruitland coal, San Juan basin, New Mexico. Carbon, hydrogen, and nitrogen content vs ash content of moisture-free coal.

Figure 2. Fruitland coal, San Juan basin, New Mexico. Higher heating value, volatile matter, and sulfur content vs ash content of moisture-free coal.

Variation of Coal Properties. Within the same seam at larger distances variations can be observed by comparing the straight-line parameters of Pittsburgh coal from sampling sites 46-3, 46-8 (Indiana & Armstrong Counties, Table 5), 7-9, 7-10 (Washington County, Table 6), the latter lying some 70 km west of the former, and from sampling sites 69-3, 69-5 (Georges Creek Field, Somerset County), and 98-5 (Broad Top Field, Bedford County), last three sites with equations for

wet (ar), % 12 -0.062 10.058 -0.124 -0.71 1.2 0.020 0.60 8.48 13.91

AT ) 94.8% VT ) 9.20% CT ) 0.21% HT ) 0.94% KT ) 90.8% (CO2)T ) 0.76% (H2O)T ) 8.4%

carbon content C ) 90.0 - 1.08 × Ash (R ) 0.99), hydrogen content H ) 4.7 - 0.0402 × Ash (R ) -0.95), higher heating value Q ) 36.0 - 0.43 × Ash (R ) -0.985), and volatile matter content V ) 22.5 - 0.15 × Ash (R ) )0.33), lying about 100 km east of sites 46-3 and 46-8. Increase of carbon content of the maceral phase, estimated by the intercept of the γ-axis, a, west to east, from 82.5% to 90%, and higher heating value from 34.5 to 36.0 MJ/kg can be observed, while hydrogen content and volatile matter content are decreasing significantly from west to east. The properties of the mineral phase are changing slightly, as can be seen from Tables 5 and 6. For Somerset and Bedfore sampling sites only a few data points were available, in a very narrow and low ash content range, therefore extrapolation to mineral phase was not possible. The two sample sets for Lower Freeport coal (Tables 8 and 9) were taken from sites 10 km apart in eastwest direction. Again, an increase in carbon content of the maceral phase from west to east is observed (from 86.6% to 87.7%). Sulfur content of the maceral phase is practically the same for the two sites, but there are important differences in mineral sulfur, changing from 12% to 1.2%, with the corresponding decrease in higher heating value of the mineral phase (from 1.9 to -0.15 MJ/kg) and of mineral-phase ash (from 85% to 81%). The other analytical parameters do not change significantly. Properties of the Mineral Phase Although the evaluation of mineral-phase properties implies sometimes extrapolation to large distances and consequently large errors, yet the results are plausible (Table 13). The water content of dry mineral phase lies between 3% and 12%, values close to the water content of clay minerals. Carbonate content of the mineral phase is very low.



Table 4. Waynesburg Coal, Greene County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

6 -0.940 84.674 -0.942 -0.9991 0.327 0.019 0.399 66.472 0.49

6 -0.0524 5.595 -0.0545 -0.98 0.0900 0.0053 0.1097 4.5817 1.96

6 0.0078 1.335 0.65 0.11 0.59 0.04 0.72 1.485 39.98

6 -0.0180 1.835 -0.02 -0.994 0.016 0.0010 0.0201 1.49 1.11

6 -0.361 39.307 -0.433 -0.91 1.362 0.081 1.660 32.325 4.21

6 -0.394 35.067 -0.394 -0.9992 0.135 0.008 0.165 27.443 0.49

AT ) 90.4% VT ) 6.7% CT ) -0.29% HT ) 0.86% QT ) -0.52 MJ/kg ST ) 2.04% KT ) 93.3% (CO2)T ) -1.06% (H2O)T ) 7.8%

Table 5. Pittsburgh Coal, Armstrong and Indiana Counties, Pennsylvania n) b) a) by ) R) so ) sb ) a) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

12 -0.946 85.216 -0.95 -0.998 0.64 0.019 0.38 67.73 0.94

12 -0.0453 5.389 -0.046 -0.994 0.057 0.0016 0.034 4.55 1.25

12 0.0757 0.668 0.13 0.77 0.72 0.020 0.46 2.21 32.52

12 -0.0130 1.676 -0.018 -0.85 0.090 0.0026 0.054 1.44 6.30

12 -0.257 36.43 -0.30 -0.93 1.10 0.032 0.66 31.68 3.49

12 -0.379 35.074 -0.38 -0.997 0.32 0.0090 0.19 28.07 1.13

AT ) 89.7% VT ) 13.4% CT ) 0.39% HT ) 1.33% QT ) 1.09 MJ/kg ST ) 7.45% KT ) 86.6% (CO2)T ) 1.42% (H2O)T ) 11.9%

Table 6. Pittsburgh Coal, Washington County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

11 -0.8953 82.497 -0.9174 -0.988 0.55 0.05 0.83 66.9 0.83

11 -0.0587 5.662 -0.0825 -0.84 0.15 0.012 0.22 4.64 3.16

11 0.0573 2.509 1.4597 0.198 1.11 0.09 1.68 3.51 31.78

11 -0.0117 1.633 -0.0179 -0.81 0.033 0.0028 0.05 1.43 2.34

11 -0.391 41.689 -0.6743 -0.76 1.34 0.11 1.95 34.99 3.83

11 -0.385 34.460 -0.3903 -0.994 0.17 0.015 0.26 27.75 0.62


Table 7. Upper Freeport Coal, Cambria, Clearfield, and Indiana Counties, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf.)

9 -0.938 87.065 -0.942 -0.998 0.83 0.074 1.324 73.972 1.13

9 -0.0499 5.200 -0.054 -0.964 0.18 0.0156 0.2800 4.503 3.92

9 0.0279 1.849 0.340 0.29 1.20 0.106 1.905 2.239 53.64

9 -0.0162 1.549 -0.018 -0.94 0.077 0.0068 0.12 1.322 5.85

9 -0.223 29.397 -0.323 -0.83 1.918 0.169 3.042 26.284 7.30

9 -0.391 35.786 -0.396 -0.994 0.570 0.050 0.905 30.328 1.88


Table 8. Lower Freeport Coal, Clearfield County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

16 -1.013 87.660 -1.021 -0.996 0.92 0.096 1.80 71.38 1.29

16 -0.052 5.331 -0.053 -0.985 0.09 0.010 0.18 4.50 2.09

16 0.135 0.825 0.322 0.65 1.62 0.170 3.17 3.00 54.02

16 -0.022 1.694 -0.024 -0.96 0.07 0.007 0.13 1.35 4.93

16 -0.199 31.026 -0.292 -0.83 1.38 0.145 2.71 27.83 4.97

16 -0.401 35.942 -0.402 -0.999 0.22 0.023 0.43 29.50 0.74


Heating value should be negative for the mineral phase, due to the vaporization heat of water, except for higher sulfur content, mostly as pyritic sulfur, when the heating value could be positive. In fact HHV depends linearly on sulfur content of the maceral phase, as shown in Figure 7. The scatter of higher heating values around the regression line is understandable, since no correction was made for hydrogen (water) content of the

mineral phase. Moreover, the slope of the regression line (about 200 kJ per % sulfur content) is close to the heating value of pyrite (about 140 kJ/% sulfur). The only large negative deviation from the regression line was found for Pittsburgh coal from Washington County, reported as very weathered (see Table 1), presumably containing sulfur in sulfate form. This point, as well as that of the Mercer coal from Jefferson County, with

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Niac and Muresan

Table 9. Lower Freeport Coal, Jefferson County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

12 -1.051 86.631 -1.06 -0.997 0.50 0.091 1.11 75.21 0.67

12 -0.0593 5.332 -0.06 -0.985 0.06 0.011 0.14 4.69 1.36

12 0.0046 0.780 0.15 0.18 0.16 0.028 0.34 0.83 18.74

12 -0.0228 1.730 -0.03 -0.91 0.06 0.011 0.14 1.48 4.25

12 -0.267 32.672 -0.35 -0.88 0.90 0.16 1.98 29.77 3.01

12 -0.441 35.493 -0.45 -0.995 0.28 0.050 0.61 30.70 0.90


Table 10. Lower Kittanning Coal, Clearfield County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

7 -0.934 87.054 -0.938 -0.998 0.88 0.074 1.59 70.22 1.25

7 -0.0483 5.320 -0.0487 -0.995 0.067 0.0056 0.12 4.45 1.50

7 -0.0318 3.314 -0.290 -0.33 1.27 0.11 2.31 2.74 46.46

7 -0.0138 1.420 -0.0158 -0.93 0.074 0.0062 0.13 1.17 6.28

7 -0.266 31.761 -0.267 -0.9994 0.134 0.011 0.243 26.96 0.50

7 -0.394 36.075 -0.395 -0.9994 0.189 0.016 0.344 28.97 0.65

AT ) 93.3% VT ) 6.89% CT ) -0.12% HT ) 0.81% QT ) -0.71 MJ/kg ST ) 0.35% KT ) 93.1% (CO2)T ) -0.44% (H2O)T ) 7.33%

Table 11. Mercer Coal, Clearfield County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H, %

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

16 -0.9573 87.14 -0.966 -0.995 0.99 0.025 0.63 64.44 1.54

16 -0.0485 5.28 -0.0538 -0.95 0.17 0.0043 0.11 4.13 4.20

16 -0.0138 3.80 -2.4353 -0.075 1.98 0.049 1.26 3.47 56.86

15 -0.0101 1.17 -0.0159 -0.80 0.0848 0.0021 0.054 0.94 9.04

16 -0.2445 32.77 -0.3246 -0.87 1.51 0.037 0.96 26.98 5.61

16 -0.3966 36.1 -0.3986 -0.9975 0.30 0.0075 0.19 26.69 1.13


Table 12. Mercer Coal, Jefferson County, Pennsylvania n) b) a) by ) R) so ) sb ) sa ) Yav ) so/Yav (%) )

C, %

H%

S, %

N, %

V, %

HHV, MJ/kg

(all mf)

6 -0.882 83.279 -0.883 -0.9991 0.45 0.019 0.76 48.73 0.93

6 -0.0424 5.13 -0.0437 -0.985 0.089 0.0037 0.15 3.47 2.57

6 -0.0882 6.907 -0.3187 -0.53 1.71 0.071 2.88 3.45 49.65

6 -0.0111 1.182 -0.0119 -0.968 0.035 0.0015 0.059 0.75 4.70

6 -0.297 37.856 -0.348 -0.924 1.48 0.061 2.48 26.21 5.64

6 -0.375 34.972 -0.376 -0.9997 0.12 0.0049 0.20 20.27 0.58

AT ) 94.5% VT ) 9.75% CT ) -0.09% HT ) 1.12% QT ) -0.50 MJ/kg ST ) -1.43% KT ) 90.3% (CO2)T ) -0.33% (H2O)T ) 10.1%

Table 13. Mineral Phase Properties of Some U.S. Coals no.

seam

AT %

KT %

VT %

CT %

HT%

(CO2)T %

(H2O)T %

ST %

HHVT, MJ/kg

1 2 3 4 5 6 7 8 9 10 11

Fruitland, San Juan Hanna No. 1, North Dakota Waynesburg, Greene Pittsburgh, Armstrong & Ind. Pittsburgh, Washington Upper Freeport Lower Freeport, Clearfield Lower Freeport, Jefferson Lower Kittanning, Clearfield Mercer, Clearfield Mercer, Jefferson

91.3 94.8 90.4 89.7 91.2 91.9 85.0 80.8 93.3 90.3 94.5

93.1 90.8 93.3 86.6 93.9 91.1 85.9 88.9 93.1 89.3 90.3

6.9 9.2 6.7 13.4 6.1 8.9 14.1 11.7 6.9 10.7 9.8

0.51 0.21 -0.29 0.39 0.9 0.91 1.6 1.7 -0.12 0.72 -0.09

0.56 0.94 0.86 1.33 0.31 0.62 0.93 0.54 0.81 0.89 1.12

1.9 0.76 -1.1 1.4 3.3 3.4 5.8 6.3 -0.4 2.7 -0.33

5.0 8.43 7.8 11.9 2.8 5.5 8.3 4.8 7.3 8.0 10.1

1.1

-0.53

2.0 7.5 7.8 4.4 12.3 1.2 0.35 2.6 -1.43

-0.52 1.1 -0.67 -0.13 1.9 -0.15 -0.71 0.3 -0.5

negative sulfur content due to a very large spread of data, were rejected. Conclusions Subbituminous and bituminous U.S. coals from 11 seams exhibit a linear relationship between analytical

properties and ash content. This behavior is consistent with the “two-phase model” of coals, stating the constant composition of each the maceral part (maceral phase) and the mineral part (mineral phase), over large areas of a given seam, the only location-dependent variable being the fraction of mineral phase, reflected in the ash


Figure 3. Pittsburgh coal, Armstrong and Indiana Counties, Pennsylvania. Carbon, hydrogen, and nitrogen content vs ash content of moisture-free coal.

Figure 4. Pittsburgh coal, Armstrong and Indiana Counties, Pennsylvania. Higher heating value, volatile matter, and sulfur content vs ash content of moisture-free coal.

Figure 5. Lower Freeport coal, Clearfield County, Pennsylvania. Carbon, hydrogen, and nitrogen content vs ash content of moisture-free coal.

content of the coal. As shown in Table 1, data of some samples taken from miles apart fit well the regression line.


Figure 6. Lower Freeport coal, Clearfield County, Pennsylvania. Higher heating value, volatile matter, and sulfur content vs ash content of moisture-free coal.

Figure 7. Dependence of mineral phase higher heating value on sulfur content. Points marked with x were not considered with regression (see text).

The extrapolation of any property to the ash content of the pure mineral phase, which can be calculated from proximate and ultimate analysis data, allows evaluation of the respective pure mineral phase property. This information is not accessible by any other means, since all known separation methods alter more or less the composition of the two “phases”. Unfortunately the available experimental data lay in the range of low ash content, therefore the extrapolation to high ash values is uncertain. Despite this uncertainty, interesting information can be gathered about the mineral phase of the coal. Results could be greatly improved if data would include samples with higher ash content. A correlation was found between heating value and sulfur content of the mineral phase in the case of the studied set of coals. The slope of the regression line is close to the heating value of pyrite. Extrapolation to pure maceral phase was not possible because ash composition data were not available to facilitate the evaluation of ash stemming from the macerals of the coal. The intersection of silicon content

372


regression line with ash content is suggested for evaluation of the ash content resulted from the maceral phase.2 The opprtunity to get data about the pure maceral and pure mineral phase, by extrapolation of coal sample data covering a large enough ash range, could be used

Niac and Muresan

in principal component analysis, to establish clusters not only for bulk properties, but also separately for maceral and mineral properties of coals. EF980150J

The Two-Phase Model Applied to Some US Coals - American

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