Oct.. 1922
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
919
The Classification of Coal’ By s. w.Parr UNIVERSITYOF IL&tNOIS, U R B A N A , ILLINOIS
B y use of the ordinary data of proximate analysis, a formula has been developed which gives the true value for the pure coal substance present in all types of coal. “Unit coal” is the term applied to this material to distinguish i f from the factors obtained by other formulas which are shown tobe in error. The calorific value for unit coal. because of the direct modification which i f undergoes as a result of the oxygen content, is shown to be aCgood index of rank or type. A diagram is proposed for indicating rank which makes use of the two characteristic factors, volatile matter and heat value of the unit coal. Data covering coals from widely separated regions and illustrations of practical application covering an extended period of time seem to establish the status of the method as of possible service to both the investigator and the technician.
CHEMES for the classification of coal have, in the main, been the outgrowth of technical activities in the countries where they originate, or they may be the formulation of investigational results which reflect the geological or botanical or chemical activities of their authors. A study of the development of methods of classification as an evolutionary process is exceedingly interesting and valuable, but would exceed the limit allowable for a paper of this sort. An accumulation of information, however, is now available which suggests the possibility of formulating a scheme which may serve the needs of both the investigator and technician to an extent which will justify its adoption as a general working proposition. This is a rather ambitious project, it must be admitted, but the end is worth the effort. Without any question, the most characteristic constituent of a coal is the volatile matter. But if we attempt to make use of that factor simply on a percentage basis, it is a t once obvious that it is subject to irregularities resulting from variations in the amount of extraneous matter, even though the coal substance itself remains the same. It becomes evident, therefore, that the use of a percentage value alone develops many inconsistencies.
S
HISTORICAL I n 1842-43, there was established a t the Washington Navy Yard a coal testing plant where more than one hundred and forty steaming tests were made on forty-four different American coals. The results were published in a volume of six hundred pages, but in a manner to be lost to public view. The bibliographic reference in this connection is interesting. It is Senate Document 386 of the 28th Congress, 1st Session, entitled “A Report to the Navy Department of the United States on American Coals Applicable to Steam Navigation and to Other Purposes,” by Walter R. Johnson12printed in 1844. This was a monumental piece of work, especially for its time, and while the results have now mainly historic interest, certain methods employed in summarizing the results have had a very pronounced influence on classification. Presented before the Division of Industrial and Engineering Chemistry a t the 63rd Meeting of the American Chemical Society, Birmingham, Ala., April 3 t o 7, 1922. Walter R . Johnson, Professor of Physics and Chemistry a t the University of Pennsylvania, 1839-43. 1
*
Professor Johnson had a propensity for reducing his results to relative values with reference to each significant item and tabulating the factors progressively for each item. At the present time, the plotting of a curve would doubtless be the method employed. It is interesting to note, however, that in one of his tables he devotes one column to the ratio of the fixed carbon to the volatile hydrocarbons,
,and V. h-c. these ratios are seen to have a certain agreement in their serial order with the “relative evaporation by equal weights of combustible matter.” No suggestion is made by Professor Johnson as to the possible use such ratios might serve in general coal classification. Persifor Frazer, according to a paper read before the WilkesBarre (1877) meeting of the American Institute of Mining Eng i n e e r ~ ,evidently ~ had been seeking for some method of improving upon the scheme of classification proposed by his predecessor, Professor R o g e r ~who , ~ made use of percentage values taken from Johnson’s report and elsewhere and referred to the total coal as received. I n seeking to eliminate the inconsistencies resulting from wide variation in the ash and moisture, Frazer brought into use the ratio idea of Johnson, arguing that if the fixed carbon and volatile matter were calculated to the ash- and moisture-free basis, the extraneous matter would be excluded. Then, by putting the two values into a ratio, a series of ranking index numbers would result which he proposed to group in a manner to indicate a system of classification. The odd thing about Frazer’s discussion is the fact that he seems to think it essential to calculate all values to the pure coal condition so that his two factors for C (fixed carbon) and V. h-c. (volatile hydrocarbons) will equal 100 per cent. Thus, C
+ W)
V. h-c.
+
~
= 100
-k 1-(ash W) He, therefore, calculated all the analytical data available t o the ash- and water-free condition in order to obtain his ratios free from the influence of extraneous or adventitious material. Now a very little inspection will show that this is all wasted energy, since these two values for C and V. h-c. will give the same ratio whether they are taken from the “pure coal” values totaling 100 per cent or from the “as received” values totaling, with the ash and moisture, 100 per cent. His zeal, however, has caused him to err in the right direction; for a ratio, to have any significance, must relate solely to the pure coal substance. Variations from this principle furnish ratios of little or no value. Note in this connection the ratio C proposed by Campbell5 of -, in which H includes all of the H hydrogen of the free moisture in the coal, though Strahan and Pollards use the same ratio referred to the dry ashless material.7 1-(ash
8
Trans. A m . I n s l . Mining Eng., 6 (1877), 430.
4
H.D. Rogers, “The Geology of Pennsylvania, a Government Report,”
2 (1858), 991. 6
U.S.Geol. Surv., Professional Paper 48, Part I, 156.
e “Coals of South Wales,” 1915. 7 Numerous errors are evident in Frazer’s paper; as, for example, his statement t h a t in the d a t a available at t h a t time, the factor for water was included in the volatile matter. All Johnson’s data give the moisture values as distinct from the volatile matter.
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
920
ANALYSIS OFLASTEW ANALYSIS 4LLlNOlS COALS COALS
AYALYSIS or
A
Sml-BiTumii.rous COAL
( R C A H O N T A 5 ) S d O W l N G CONSTITUENTS 11-
RELATIVE: PROFQRTIONS
Vol. 14, No. 10
. ANALYSIS OFLICFITIC
COALS
AVERAGE OF TEN lLLll'iOlS COALS SHOWING CONSTITUENTS IN RELATIVE PROPORTIOIYS
ANALysi5 OF LIGNIT'C OR 5R0\VN C O A L S C I O n h ' l N G C O N S T I T U C r iTS lm R E L A T I V E Pt7OPORTIONS
FIQ.1
In a former system of classification proposed by the author,* the ratio employed was
VC
X C
100, in which C represented
the total carbon and VC that part of the carbon which associates itself with hydrogen to form the volatile hydrocarbons. This ratio is free from inorganic variables and has the advantage with respect to the greater accuracy of obtaining one of the factors, the total carbon. It was recognized in that discussion that another significant element entered into the case which could not be covered conveniently by any ratio, This was the inert part of the volatile matter or oxygen compounds of the coal. I n that article, no satisfactory scheme was proposed for taking account of that constituent which we now recognize not only as a part of the true coal substance, but as a very significant factor which, to an equal extent with the volatile matter, determines the rank of a coal.
PROPOSED BASISOF CLASSIFICATION As illustrative of a method for taking account of the inert volatile matter, attention is called to the cross-hatched areas in each of the three diagrams in Fig. 1. These areas represent the oxygen compounds of the actual coal substance in each type: (1) a low volatile eastern coal, (2) a high volatile Illinois coal, and (3) a lignitic coal. It is now suggested that the most direct method of classification, and one which would give expression to this constituent, would be the calorific value of the pure coal substance. It should be recognized a t the outset, however, that the factors for ash and moisture must not only be very accurately determined, but one disturbing factor, the sulfur, should be eliminated altogether. While a small amount of sulfur is always present in organic form and is a true part of the coal material, the main part, as a rule, is in the form of FeSz. It is evidently of secondary formation and is so irregular in amount as t o indicate the desirability of eliminating it entirely from the actual coal substance. A glance a t Fig. 2, showing the organic and pyritic sulfur in different locations in the same mine, is sufficient evidence without further comment as to 8 S. W. Parr, "The Classification of Coals," J . A m . Chem. SOG.,28 (1906), 1425.
the desirability of counting the sulfur as part of the extraneous matter.9 One other ingredient should be taken account of. I n the case of Eastern coals where the ash is low, it has only minor significance, but in lower grade coals, where the ash will average 16 to 18 per cent and may sometimes reach 25 or 30 per cent, it is important. This is the volatile material, chiefly water of hydration, which is discharged a t a red heat from the shaley constituents of the ash. With this material assigned to its proper place, along with the sulfur as part of the ash, we are in a position to appreciate the significance of the heat value for the pure coal substance as unaffected by mineral impurities of any sort.
CORRECTION OF FACTORS This brings us to the method of correcting the factors as determined in the ordinary process of proximate analysis. Fortunately, it resolves itself into a very simple formula. It should be noted that the first description of this formula with a detailed account of its derivation-was published in 1909.'* Per Cent Su/ hur
00
/
2
Y4
/
2 \3 $4
5 6
7
G
-Pyr///CSu/phu/ ---(Tatad sff/Pnur
-.-.- urgm/c Su/phur
TOh/
FIQ.2 0 Yancey and Fraser, "The Distribution of the Forms of Sulfur in the Coal Bed," Univ. of Illinois Engineering Expt. Sta., Bulletin 125 (co6perative with U. S. Bureau of Mines and Illinois State Geological Survey); THIS JOURNAL, 18 (19211, 35. 10 Parr and Wheeler, "Unit Coal and the Composition of Coal Ash," Univ. of Illinois Engineering Expt. Sta., BuZEetin 87; THISJOURNAL, 1
(1909). 636.
Oct., 1922
.
T H E JOURNAL OF INDUSTRIAL AND ENGINEERING CHEXIXTRY
The application a t that time was solely in connection with the calculation of calorific values and had no reference to its use as a classification medium. After long-continued use with all types of coal, the marked accuracy of the formula as first proposed has led inevitably to its use as a classification factor. It is not necessary to repeat here in detail the derivation of the formula. Its fundamental principles may be readily shown as follows: Assuming the coal values as derived from analysis to be on the dry basis, then: Non-coal=Ash as weighed 6/8 S 0.08 (ash-*O/sS) (1) Combining and simplifying, we have Equation 2.
+
+ hTon-coal=1.08 ash +
2l/40
S
(2)
Hence, to derive the heat value for the unit coal, Equation 3 results. Indidted B. t. u. -5,000 S Heat value in (3) B. t. u. for unit coal = 1.00- (1.08 ash + 22/do S) I n Equation 1, it may be explained that the addition of b / s S corrects the ash, as weighed, back to the form in which the sulfur was weighed in the original sample, namely FeSz. The factor in Equation 2 which increases the ash as weighed by 8 per cent is really an arbitrary constant, though it was derived experimentally in the first place by taking the average loss (not including organic matter) on ignition of a number of shales from the Illinois coal measures. It is doubtless mainly water, but may have some carbon dioxide from carbonates, or even sodium chloride, but obviously it should not be applied to the iron pyrites which is shown to be subtracted as Fez03 from the ash as weighed, the 8 per cent being applied to the remainder only. Equation 3 is derived from Equation 2, by subtracting in the numerator the heat due to the burning of the sulfur and the formation of FezOs and in the denominator changing slightly the fraction 21/4~ to 2 2 / 4 ~ , as being in the direction of simplifying the calculation as well as promoting accuracy by compensating slightly for the sulfur not in the pyritic form. TESTSOF FORMULA Now while a certain basis in theory may thus be set forth in defense of the formula, it would still be of little value unless it could he proved out in actual use as correct. Several methods suggest themselves. Obviously a coal with high ash from the same mine, or from the same sampleby use of the “sink” and “float” method of separation, would respond unfavorably if the 8 per cent constant as applied to the ash were wrong. If this factor is correct, then so far as ash variations are concerned, the R. t. u. values for unit coal should calculate out to substantially the same number. Similarly, the sulfur corrections, when applied to wide variations in sulfur in the same sample or in samples from the same mine, should not produce a divergence in the thermal values when calculated to the unit basis. A great mass of data has accumulated from which only a limited number of illustrations can be given. However, they are typical and cover widely separated localities and practically all types of coal. Table I is an assembly of results from samples which have been subjected to the “sinlr” and “float” process. By this procedure, each sample is divided into two parts with widely different values for the ash and sulfur. Manifestly the calculation of the indicated heat value to the corresponding value for the unit coal substance furnishes a crucial test for the suitability of the factors chosen for correcting the ash with reference to water of hydration and for sulfur. If space permitted, very interesting evidence of an indirect character could be submitted in substantiation of the formula adopted. At least two other methods have been used to a greater or less extent for deriving the pure coal substance. If we compare the results obtained by use of these formulas
921
with the one here proposed, the discrepancies resulting in the case of sink and float samples of the same coal afford positive confirmation of 6he value of the new formula. A tabulated selection of a few cases only can be given in this connection. TABLEI-COMPARATIVE VALUES OF PUREOR “UNIT”COAL -B. t. U.--W a. t.e.. r Ash Sulfur Actual Unit Coal 1-Grundy Sink 0 . 0 0 21 99 5 . 0 0 10735 14262 Countv.111. Ploat 0.00 4:57 1 . 4 4 13:475 14:217 -. Sink 0 . 0 0 18 28 1 . 3 7 11 731 14667 2-Williamson County, 111. Float 0.00 4134 1 . 0 7 13:970 14:690 Untrtd. 0.00 16.84 7 62 11 790 14 698 3-Vigo County, Ind. Ploat 0.00 4 . 2 7 3:08 13:870 14:638 4-south Africa Sink 1 66 18 94 2 28 11 680 15093 Float 1:63 6106 1:38 13:703 15:065 &South Africa Sink 1 . 8 2 15 24 1 . 8 0 11 847 14 799 Float 2.07 S:S8 0.87 12:989 141779 6-South America Sink 3 . 5 9 49.25 2 . 5 8 5,922 14,162 5 . 9 7 17.24 0 . 6 8 10,602 14,127 (Brazil) Float ?--Walker County Ala. Sink 1 . 0 0 16.14 0 . 8 3 12,467 15,370 4 . 4 0 0 . 8 5 14,384 15,371 (Pratt ;earn) Ploat 1.20 8-Jefferson Sink 0 . 9 2 23 70 1 . 2 3 11 246 15 620 County, Ala. 9:78 0 . 9 9 13:683 15:576 (Mary-Leeseam) Float 1.04 9-Bituminous Sink 1.15 4 96 0 . 7 6 14 373 15443 from W. Va. Float 1.20 3:40 0 . 6 0 14:616 15:416 10-Cannel from Sink 1 . 2 0 39.04 2 . 8 7 8,908 16,179 Kentucky Float 0 . 9 7 13.40 1 . 7 4 13,560 16,205 Sink 0 . 7 0 16.76 1 . 0 7 12280 15,232 11-Anthracite from Pa. Float 0.86 7 . 2 0 0 . 7 2 13:795 15,166
Dif. +45 -23 +60 1-28
+20 +35 ’-
1
+44 +27 -26 +66
TABLE11-COMPARISONOF HEATVALUESFOR “PURECOALSUBSTANCE” AS CALCULATED BY THREE METHODS FROM ANALYTICAL DATA ON “DRY COAL” --Calculated B. t. u.-Ash Sulfur B. t. u. a b t Williamson Co.,111. Sink 17 75 1 15 11766 14306 14451 14,608 Float 4:08 0:99 13:924 14:535 141644 14,623 15 DIFFERENCE ; 229 193 Franklin Co., Ill. Sink 18 00 0 57 11639 14194 14236 14474 Float 4:64 0:54 13:765 14:436 14:492 14:512 DIFFERENCE 241 256 88 Perry Co Ill. Si2k 22 17 1 15 10922 14033 14183 14413 Float 4 : 2 2 0:86 13:763 14:369 14:464 14:452 DIFBERENCE 336 281 39 B . t . ~ . - 4 0 5 0S . B. t.u.-5000 S B. t . u. a’i 1.00-A’ b = 1.00-(A-S) ’ C=1.00-(1.08A--S~/toS)’
.................. .....
.......................
-.
.......................
The derivation of a, b, and c may be understood from the following: The expression B. t. u. is the indicated heat value, as obtained directly by means of the calorimeter. A is the ash as weighed, and 8 is the sulfur in per cent. The method under a is the usual one eniployed by the engineer for determining the heat values for “combustible.” Under b, the method employed by Lord and Haas for determining the value of H, i. e., the heat to be credited to the pure coal substance free from moisture, ash, and su1fur.l’ Under c, the formula is that for “unit coal” and has already been discussed. Note that the analytical values are on the “dry coal” or moisture-free basis. Hence W for water is not introduced into the formulas. For the reason that a zone of heat values may be indicated or prescribed for groups or types, a method of classification is therefore suggested as a result of the preceding discussion as t o the true heat value of the unit coal substance, as shown in Table 111. TABLE111-CLASSIFICATION OP FUELTYPESBY HEATVALUES FOR UNIT ACTUAL ORGANIC SUBSTANCE , 6 5 0 0 to 7 800 Cellulose and wood.. 7:800 to 11:500 Peat 1 1 5 0 0 t o 13 000 Lignite brown.. 13’000 to 14’000 Lignite’ black or sub-bituminous coal.. 14’000 to 15’000 Bitumihous cdal mid continental field). 15’000 to 16’000 , Bituminous coal leastern field). 15’500 to 16’000 Semianthracite and semibituminous . , 15:OOO t o 15:500 Anthracite..
OR
...................... ................................
..................... ... ... ... ........ ..... ............................. .
11 Trans. A m . Inst. Mining Eng., 27 (1898), 259; also Lord and Somermeier, “Report on Coal,” 4th Geoi. Surv., Ohio, 1008, 268.
T H E JOURNAL OF I N D UXTRIAL A N D EATGINEERING CHEMISTRY
922
The groups designated in Table I11 have been given the names as first proposed by Professor Rogers. These had become sufficiently established at the time of Frazer’s paper to make it seem advisable for him to continue their use.12 Campbell,l3 a t a still later date, follows the same general nomenclature and it does not seem wise now to introduce changes in these general and well-established names. One fundamental criticism has always arisen concerning the use of heat values for designating coal rank. This relates to the lower values for anthracites which bring them into the same class with certain coals of the bituminous type.
designating the rank than the physical characteristics which governed the designation a t the locality where the samples were taken. The cannels arrange themselves in a distinct group which reveals a t a glance their true characteristics. Similarly, the eastern bituminous of the high volatile type are sharply segregated from the western bituminous as a result of their difference in oxygen or inert volatile content. The names “eastern” and “western” bituminous, however, are not well chosen and should be replaced by names or letters which would be universally applicable. -4 word of explanation may be necessary concerning the method of deriving the percentage factor for the unit volatile matter. If we accept the factors as adopted for correcting the ash as weighed, it is seen that the chief constituents entering into those corrections are 8 per cent for the mater of hydration of the clayey matter and the addition of ”8 S to restore the ash to the condition as weighed out in the sample. Now these values are in fact the errors that should be assigned to the volatile matter in the ordinary process of determination, where the 8 per cent of water is driven off a t a red heat and approximately l / Z the sulfur is discharged from FeSz. The fixed carbon, therefore, has not been appreciably affected, since the errors of the volatile matter naturally appear in the ash as weighed, thus leaving the carbon by difference in substantially its true relationship to the original coal. Hence, to derive the fixed-carbon value on the unit coal basis, we would simply apply the standard formula for deriving the unit coal, thus: Unit fixed
/0000
=
Fixed carbon as determined 1.00- (1.08 A + 2 2 / 4 0 S )
and from this, by difference: Unit volatile = 1.00
FIG.3
This feature is really a virtue from the standpoint of the unit coal values as we have been discussing them. How therefore to incorporate this property in a classification scheme has been a problem. ‘It has been solved in a very satisfactory manner by use of a two-dimension diagram, as shown in Fig. 3.14 I n this chart, the percentage values for unit volatile matter have been located on the horizontal axis and the unit heat values on the vertical. By this means, the low volatile coals of the anthracitic type are segregated from the high volatile coals of the Illinois type even though their heat factors are closely related. The values in the diagram have been calculated mainly from analytical data published by the U. 8. Bureau of Mines.lb I n this way coal samples from widely separated regions are represented. The dividing lines have been chosen arbitrarily and a t even hundreds, but it is interesting to note that for most of the zones there is a marked thinning out of the group representatives at the lines of division. As would be expected, there is more of a blending between the lignites and their neighbors, but in those instances where a sample seems tobe out of place it is an even chance that the collector who named the sample was wrong in his diagnosis. At least, the author would hold that the unit B. t. u. is a safer criterion for See Frazer’s communication in defense of his classification, A m . Inst. Mining Eng., Bimonthly Bulletin, January 1906. 241. 18 U. S . Geol. Surv., Professional Paper 100-A. 14 From an unpublished thesis for the Master’s degree, by E. B. Vliet, University of Illinois, 1918. 1s Values obtained from analysis of coals found in Bur. Mines, Bulls. 16, 32, 86, 128, and U.S.Geol. Surv., Bull. 631.
VOl. 14, No. 10
- unit fixed carbon
TABLEI V (Calculated t o “as received” basis having normal variations of moisture, ash, and sulfur, as indicated, Unit coal: 14,300)
Sangamon south of Auburn
6
10 11
Perry
6
12 13 14 15 16 17 18 19 20
Randolph
6
Clinton
6
Madison
6
Montgomery
6
.
4 4 4 4
4
4 4 4 4 4 4
’
10,925 10,771 10,616 10,462 10,308 10,154 10,000 9,846 9,692 9,538 9,384
TABLEV-COAL INDEXNUMBERS
I-Anthracite, Scranton, Pa. 2--Bituminous, W. Va. 3-Walker Co., Ala. (Pratt seam) 4-South Africa 5-Brazi1,
So, America
6-Williamson 7-Grundy
Co., Ill.
Co., Ill.
12
8-Vermillion 9-Franklin
Co., Ill.
Co.,Ill.
10-Alberta, Canada C. P.R . Synd.
Sink Float Sink Float Sink Float Sink Float Sink Float Sink Float Sink Float Sink Float Sink Float Sink Float
Moisture Ash Sulfur 0 . 7 0 16.75 1.07 0.86 7 . 2 0 0.72 1.15 4.96 0.76 1.20 3.40 0.60 1.00 16.14 0 . 8 3 1.20 4 . 4 0 0.85 1 . 8 2 15.24 1 . 8 8 8.80 0 . 8 7 2.07 3.59 49.25 2 . 5 8 5 . 9 7 17.24 0 . 6 8 0.00 18.28 1.37 0.00 4.34 1.07 17.28 5.27 2 . 3 3 6.37 2.82 0.00 9 . 3 4 2.55 14.45 0.00 10.92 2.98 9 . 0 4 8 . 5 6 1.45 9.41 1.59 0.00 1 . 3 9 27.50 0 . 8 5 8.02 0 . 7 2 1.17
10,639 10,484 10,330 10,176 10,021 9,867 9,712 9,558 9,403 9,250 9,094
A Unit Coal 80.62 90.96 93.07 94.80 81.11 93.58 80.73 87.86 41.81 75.08 79.51 ’94.27 75.48 91.57 74.06 86.57 80.92 88.97 68.45 95.18
B Index No.
124.03 109 94 107.45 105.48 123.29 106.86 123.87 113.83 239.17 133.26 125.77 105.57 132.49 109.20 135.02 115.61 123.67 112.39 146.0% 105.06.
