1so
INDUSTRIAL AND ENGINEERING CHEMISTRY
The foundry coke produced from the established coal mixt.ure has been maintained with little variation and has found wide acceptance by the foundry trade. While the Pocahontas coal has had an advantage in reaching set standards for foundry coke, its substitution by Mary Lee would yield a coke of good physical standards but slightly higher in ash and sulfur contents. An average analysis of the 3-inch and higher foundry coke as now produced is as follows: 0.93 Shatter ( f 2 in.) Volatile, % Tumbler test, 70 Fixed carbon, % 89.97 Stahilitr Ash, 7% 9.10 0.70 Hardness Suliur, % True gravity 1.89 Apparent gravity 1.04 Porosity 45 Ash softening temp., F. 2646
83 36.5 62.9
OKE point mentioned in the above discussion of blending to produce foundry coke is the economic side which is most essential for continued, successful oven operation. Although
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the production of good foundry coke is the principal consideration, the other by-products must meet certain requirements for their disposal. The total, as well as the foundry coke yield from the coal charged, should be as high as possible. From this established blending operation, the total coke yield is 75 per cent, with 60 per cent of thia amount screening out into the 3-inch and higher foundry size, and the remaining 40 per cent going into the various sizes of domestic grades. This is considered good for a 16-inch width oven and 24-hour coking time. These domestic grades require a coke of high B. t . u., combustibility, and ash fusion. The latter was one point considered in the selection of the coals now used. The yield of by-products is of secondary importance, and the operator must be satisfied if the coke meets the market demands. It may be of interest, however, to state that the yield of by-products from these coals is somewhat higher than the lower volatile coking coals of other sections of this country.
Influence of Storage on Caking and Coking Properties of Coal L. D. SCHMIDT, 1. L. ELDER, AND J. D. DAVIS U. S. Bureau of Mines Experiment Sfation, Pittsburgh, Penna.
Samples (400 pounds) representative of fifteen different coal beds were oxidized progressively in an accelerated weathering apparatus and then subjected to a series of tests to follow the changes in various aspects of their coking and caking behavior. The length of time each coal could withstand standard oxidizing conditions before losing its coking power (termed "durability of coking power") showed a sixteen fold range among the coals tested. The durability of coking power of most coals can b e predicted with fair accuracy from their analysis b y the method developed. Loss in caking tendency (leading to
improved performance in underfeed stokers) was followed b y several different tests. Comparisons showed: (a) D e crease in agglutinating value predicts decreased strength of coke; (6) the amount of unfused char remaining in the retort after carbonization can b e correlated with strength of coke and also with the agglomerating index that is based upon classification of coke buttons made in the standard volatile matter test. The caking tendency of coals can b e reduced greatly b y storage or oxidation long before the true loss in heating value exceeds 1 or 2 per cent.
TORAGE of coal near the point of consumption assures S regularity of supply and evens out seasonal demands on railroads and coal mines. An important factor determining
years without serious loss in coking power, while others should not remain in storage more than a few weeks before being carbonized. The changes that take place in coal on storage are not always disadvantageous. Some coals show somewhat greater coking power after some time in storage (9). Furthermore, complete loss of coking power may even be considered advantageous in special instances, such as that of coal to be used in domestic underfeed stokers.
the amount and kind of coal to be stored is the extent of deterioration and loss to be expected on storage. Previous work by the Bureau of Mines has shown that if spontaneous heating does not occur, the loss in heating value on storage is so small as to have little commercial importance (6). The loss of coking power is, however, of vital interest in the operation of coke plants where large quantities of coal must be stored to assure absolute dependability of supply. Use of coal that has suffered too much deterioration in storage results in decreased production of usable coke and causes operating difficulties, such as trouble in removing coke from ovens. I n severe cases damage to the coke ovens may result. Changes in the properties of coke brought about by use of oxidized coal often result in decreased production of iron in the blast furnace and decreased efficiency of operation. Experience has shown that some coals can be stored for
Accelerated Storage Tests
To investigate the effects of storage on representative coking coals, an accelerated weathering or storage test was developed by the Bureau of Mines. Coal samples (400 pounds) that are representative of the coal bed are stagecrushed to pass a 1/4-inch screen and then exposed to air a t 100" C. in a steam-jacketed drum that rotates slowly. Periodically 90-pound samples are taken for carbonization in steel retorts a t 800" C. (Bureau of Mines-American Gas
February, 1943
Figure 1.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Sections of Coke from Pond Creek Coal Carbonized at 800' Oxidation
C.,
151
Showing Effect of
Association Carbonization Procedure, 2). I n this way enough surface exposed to air). I n general, other conditions being coke is made so that standard methods of coke testing can be equal, a coal of high characteristic rate of oxidation tends used to determine the quality of coke. to heat spontaneouslyin storage, and a coal whose coking The rates a t which various coals consume oxygen in the power is very sensitive to oxygen deteriorates rapidly in accelerated weathering drum (8) as well as studies on the storage, even though no serious heating occurs. effect of various storage conditions on rate of oxidation (7) Results previously reported (7) showed that the effect of were reported previously. oxidation and storage on coking power can be represented Previous studies (IO) showed that major changes in carvery well by the changes in the coke-strength index : bonizing properties brought about by oxidation or storage Coke-strength index = 0.225 (11/2-inchshatter) + 0.293 are: decreased strength of coke, decreased yield of tar, ininch tumbler) 0.352 (1-inch tumbler) 0.202 (per cent creased yield of coke breeze or unfused char, decreased pore fusion) 0.408 (100 - friability) size in the coke, in general, increase in the apparent specific gravity of the coke. This index is obtained from the results of the various standFigure 1 illustrates the changes in the appearance of coke ard tests on coke by averaging five test values, weighted so as produced when Pond Creek coal No. 53 is preoxidized. Coke to give approximately equal weight t o each value. A cokeA was made from fresh coal, whereas B and C were made from strength index of 100 corresponds to the average coke-strength coal oxidized 6.4 and 10.3 days, respectively, in air at 100" C., index of nine representative coking coals ( 7 ) . consuming 1.4 and 2.0 per cent of its weight of oxygen, reFigure 2 shows that the coke-strength index of fifteen cokspectively. The cell structure of coke B was finer, as can ing coals (unoxidized) ranges from 68 to 115. The cokebe seen from the photograph, and the strength was somewhat higher than that of coke A . Additional oxiTable 1. Sources, Rank, Volatile-Matter Contsnt, O x y g e n Content, and Durability of Coking Power dation resulted in the Doorlv of Coals Tested fused, weak, pebbly cokk Durability of seen in coke C. Coking Power Volatile Ratio t o Under a given set of storMatter OxygenG PittsCoal age conditions, the length County Contentb, Content , Tu, burgh NO. Bed (VI0 (010 days bed coal and,State Rank' of time a coal can be stored 57 Pocahontas No. 4 Raleigh W Va Low-volatile 17.3 2.6 3.4 0.25 without serious impairment 56 Pocahontas No. 3 WyomiAg W.+a. Same 2.4 18.3 6.5 0.48 Wyoming: W. Va. Mediumof its coking properties de55 Sewell volatile 22.5 2.8 10.4 0.77 pends on several specific 64 Bakerstown Tucker W. Va. Same 23.1 3.2 9.7 0.72 58 Lower Banner Buchadan Va Same 23.1 2.9 11.1 0.82 properties of the coal, in60 Lower Freeport Indiana $en&. Same >15 >1.1 26.4 3.9 eluding characteristic rate 69 Upper Freeport Monong'alia, W. Va. Highvolatile A 32.0 12.6 5.7 0.93 of oxidation, sensitivity of 53 Pond Creek Pike K y 6.1 Same 34.3 10.9 0.81 Same Hadan. Kv. 37.3 67 Tag art 6.5 13.5 coking power to oxygen 72 T h i s Freeport Allegheny -Penna. Same 38.3 6.3 12.6 0.93 73 McAlester Pittsburg 'Okla Same 39.2 8.6 2.4 0.18 (that is, the amount of 52 Pittsbur h Alle henf, Pen;.. Same 39.3 7.1 13.5 1 oxygen required to give a 54 HighSpfint Harfan Ky Same 39 6 8.8 2.4 0.18 71 Bevier Cherokke Kans Same 42.8 6.5 20.8 1.54 certain decrease in coke 68 Henryetta Okmulpe;, Okli. Highvolatile B 38.0 7.2 1.3 .10 strength). and the friabilitv 'All &re bituminous coals, and the samples are representative of the beds at the points taken. of &e ioal (that is, thk b Fresh coal, moisture- and mineral-matter-free basis. property that sometimes C Fresh coal, moisture- and ash-free basis. determines the amount of
+
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Figure 2.
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Effects of Storage (Accelerated) of Coal on Strength Index of Coke Produced on Carbonization
strength index is plotted against the time (days) of oxidation of 1/4-inch slack in air (20.93 per cent oxygen) a t 100" C. It will be noted that some coals withstand the effect of oxidation much longer than do others. For many coals the cokestrength index even rises somewhat for a time. However, in all instances the end result is the same, loss of coking power. The figures on each of the curves indicate the quantity of oxygen consumed by the coal, in per cent b y weight of moisture and mineral-matter-free coal. The distance between these figures on each curve is a measure of the characteristic rate of oxidation of the coal and, hence, is a measure of its propensity to heat spontaneously in storage. The sources and partial analysis of the coals tested are given in Table I. In all tables the coals are listed in the order of decreasing rank. The testing procedure calls for oxidizing each coal sufficiently to reduce its coking power below that required for use in commercial coke ovens. KO standards are available, but this result probably was achieved for each coal tested by the time the coke-strength index had been reduced by 15 per cent. Hence, using Figure 1 as a master chart, we find the time of oxidation under standard conditions (l/,-inch slack in air at 100" C.) required for each coal to reduce its coke-strength index by 15 per cent. The time of oxidation ( T I 5 required ) to give this standard decrease in coke-strength index will be used as a measure and definition of "durability of coking power". Thus, durability of coking power is a specific property or characteristic of each coal and differs from coal to coal. Table I shows that the values of the durability of coking pov-er for the various coals tested range from 20.8 days for Bcvier coal to only 1.3 dags for Henryetta coal. This means that if storage conditions, such as screen size, temperature, oxygen concentration, etc., are maintained exactly equal, Bevier coal can be stored sixteen times longer than Henryetta without serious impairment of coking power. The basis chosen for calculating durability of coking
power-that is, the point at which the coke-strength index had decreased by 15 per cent-is entirely arbitrary. The allowable time of storage of any coal, in piles outdoors, is difficult to predict because of the great effect of small variations in storage conditions (7). One day in the accelerated TTTeathering drum is, however, roughly equivalent t o about 100-day storage outdoors (with no serious spontaneous heating). Regardless of the basis of comparison chosen, the relative durability of coking pon-er (Table I) should remain about the same. I n this table the ratios of durability of coking power are based on that of Pittsburgh bed coal taken as unity. Figure 3 shows a n empirical correlation of durability of coking power with the proximate and ultimate analyses of the fresh coals and leads to an equation for predicting durability of coking power from analysis. The accuracy of this prediction for the coals tested is shown in Table 11. It indicates that durability of coking power could have been predicted accurately enough for many purposes, for all coals except GO and 68. The reason for the abnormal behavior of these two coals is not known with certainty. Figure 4 shows the effects of oxidation on the agglutinating value. The agglutinating value is obtained from a laboratory
w 0 , VOLATILE MATTER CCNTENT OF FRESH COAL PERCENT(MOISTURE-AND MINERAL-MATTER-FREE BASIS)
Figure 3. Estimation of Durability of Coking Power from Proximate and Ultimate Analysis of Fresh Coal
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1943
test and indicates the crushing strength of pellets made by carbonizing a small charge containing 15 parts of sand or silicon carbide to 1part of powdered coal (1).
Table 11. Coal
I
Comparison of Observed and Calculated Value of Durability of Coking Power TI^)
NO.
Observed
57 56 55 64 58 60 59 53 67 72 73 52 54 71 68
3.4 6.5 10.4 9.7 11.1 >15 12.6 10.9 13.5 12.6 2.4 13.5 2.4 20.8 1.3
Durability of Coking Power Calculated 5.3 6.8 10.7 10.1 11.1 10.7 9.8 10.8 12.3 14.6 1.7 11.3 0.85 19.0 9.1
2’16,
Dam Deviation +1.9 +0.3 +0.3 +0.4 0 >4.3 -2.8 -0.1
-1.2 f2.0 -0.7 -2.2 -1.55 -1.8 +7.8
Agglutinating value decreases with oxidation of the coals in much the same way that the coke-strength index does. Consequently, agglutinating value can be used as a measure of the extent of oxidation of a stored coal where the agglutinating value of the original fresh coal is known. So far we have considered only the coking power of coalthat is, the strength of the coke obtained when the charge is carbonized in containers with exclusion of air. The behavior of coking coals while burning in the fuel bed brings up other aspects of the same general phenomenon. Caking in Fuel
Beds
The term “caking” is often associated with the melting and coalescence of coal particles in the fuel bed. The agglomerates so formed have more or less strength, but strength usually has secondary importance; the main feature is increased difficulty of getting combustion air to all points partly because of the decreased surface area of the fuel charge. I n domestic underfeed stokers, use of highly caking coals often causes formation of coke trees, especially under light heating load. Ostborg, Limbacher, and Sherman (6) reported
153
that “in residential stokers excessive coke formations cause deep fuel beds which give trouble in removal of clinker. They result in a slow rate of pick up which, in extreme cases, results in extinction of the fire.” Trouble is also experienced in industrial stokers because of formation of excessive amounts of coke. Oxidized doking coals give less trouble from excessive coke formation in the fuel bed. For this reason it may often prove advisable to burn stored coals, outcrop coal, or deliberately preoxidized coal. Domestic stokers with special arrangements for preoxidizing the coal have been developed for use with highly coking slacks. I n these stokers introduction of a portion of the combustion air into the agitated coal about 7 inches below the active burning zone gives enough preoxidation to eliminate coke-tree formation and to improve operation (4). The coke-strength index, as one measure of caking tendency, has already been discussed in connection with the tests on fifteen representative coking coals a t various stages of oxidation. Serving as measures of different aspects of the fusing or caking tendency, several other tests were carried out on these coals: PERCENTFUSION.A screen analysis was made on each coke as it was removed from the carbonization retorts. The amount of the charge retained upon a 1-inch square-hole screen is termed the “per cent fusion”. All the coals tested when fresh showed less than 2.5 per cent of the charge smaller than 1 inch, and the average per cent fusion for these fresh coals was 99.2. Progressive oxidation caused a continued increase in the quantity of unfused particles or loose char that would pass through a 1-inch hole. This corresponds to an increase in the quantity of coke breeze formed in commercial ovens. Figure 5 and Table I11 (column 4) show the decrease in per cent fusion with oxidation of each coal. If the coals were oxidized long enough, the caking tendency would be destroyed and the per cent fusion would approach zero. AGGLUTINATING VALUE. Comparison of the agglutinating values of fresh coals (column 5, Table 111) with the corresponding coke-strength index (column 3) shows that the agglutinating-value test does not predict directly the strength of coke made from fresh coal in a carbonization retort. For example, coal 54, with an agglutinating value of 2.6 kg., gave almost as strong a coke as coal 52, with an agglutinating
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 35, No. 2
100
80
I-
5
60
P Y
i 0 Lo
2 40
20
0
2
4
Figure 5.
6
8 10 12 DAYS OXIDATION IN AIR AT l @ C
Coal NO.
16
Effect of Storage (Accelerated) of Coal on Fusion
value of 8.4 kg. Nevertheless, as discussed above and shown in Figure 4, the decrease in agglutinating value with oxidation does prove to be a good measure of the decrease (with oxidation) in coke-strength index. This is brought out more clearly in Table IV. Column 2 shows the agglutinating value after the standard amount of weathering-that is, after each coal has been oxidized sufficiently to reduce its coke-strength index by 15 per cent. The average agglutinating value of all the coals a t this point is 3.9 kg., with some variation between coals. This corresponds to an average decrease in agglutinating value of 38 per cent of the value for fresh coal. This large decrease shows that the agglutinating-value test is a valuable labora-
Table Ill.
14
tory test for measuring the extent of oxidation of a stored coking coal. Carbonizing conditions in the agglutinating-value test simulate caking in the fuel bed in two respects-that is, in high rate of temperature rise and in essentially free expansion conditions. Column 4, Table IV, shows for all coals the per cent fusion in the carbonization retort after oxidation has decreased the coke-strength index of each coal by 15 per cent. The average per cent fusion a t this point is 87.5; that is, 12.5 per cent of the carbonized charge remained as essentially unfused char. Study of these data shows that, in general, progressive oxidation results in a general decrease in strength of coke for the
Effect of Storage (Accelerated) of Coal on the Coke-Strength Index, Fusion, Agglutinating Value, and Agglomerating Index Days of Day8 of Storage in CokeFusion, AgglutiAgglomStorage i n CokeFusion, AgglutiAgglomAir a t Strength Per nating Value, erating Coal Air a t Strength Per nating Value, erating 1000 C. Index Cent Kg. Index No. 1000 c. Index Cent Kg* Index 67 97.9 7.1 89.2 98.6 5.6 CG 0 103.1 CG 62.5 3.4 90.5 98.6 4.54 76.5 5.4 1.9 CF 26.1 87.6 97.4 7.79 4.6 CF 76.5 96.0 3.5 CF 93.2 65.5 2.6 5.1 0 103.5 98.6 5.0 3.29 101.5 96.4 72 91.4 98.7 CG 7.1 43.7 3.0 9.85 64.4 99.4 CG 93.3 6.7 CG 90.0 98.4 4.8 100.0 6.8 0 97.9 CF 79.8 4.4 6.7 3.97 100.0 CP 2.8 ' 62.5 89.4 53.5 2.0 12.95 73 0 68.7 99.4 CF 7.5 0 CF 1.41 65.5 98.6 7.6 3.95 CP 83.1 2.85 52.7 5.5 8.01 50.4 CF 4.79 34.0 2.8 11.82 2.1 16.11 52 0 79.6 97.5 8.4 CF 7.96 79.8 98.0 CF+ 6.9 11.67 5.3 CF 0 113.4 99.5 72.3 97.8 6.0 98.9 4.3 5.09 115.8 99.5 CF 3.2 13.68 54 0 76.7 60.0 2.6 77.0 CF 50.5 63.3 1.6 4.04 CF 38.8 34.2 1.8 6.64 0 100.0 CG 7.0 CG 7.0 6.65 99.0 100.0 CG 71 0 81.2 8.7 5.9 CG 15.18 87.9 CG 76.9 99.1 1.61 8.9 CG 4.06 76.9 99.6 7.7 0 7.9 CG CG 99.9 8.46 82.8 6.9 CG 5.7 9.12 CF 76.2 4.5 98.6 16.65 3.7 CG 13.79 68 0 75.4 99.8 4.5 CF 0 99.9 99.1 8.2 CG 1.27 63.7 85.2 3.9 CF 100.1 98.6 6.8 CF 2.57 39.8 1.3 6.40 CP 10.33 87.8 97.2 5.4 CF 4.18 ... 25.6 0.4 CP
...
...
58
60
59 53
+
...
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1943
Table IV. Comparison OF Agglutinatin Value Per Cent Fusion, and Per Cent Decrease in Heating Vayue OF eoals at the Point Where Oxidation H a s Decreased the Coke-Strength Index of Each Coal by 15 Per Cent
Yo Fusion
Agglutinating Value Coal No. 57 56 55 64 58 60 59 53 67 72 73 52 64 71 68 Av. 4
Kg. 4.4 4.2 3.1 4.8 3.5 Go
47 37 39 44 44 35 27 62 16
3.9 38 Not included in averages.
Value 74 74 79 85 .~
81 I70 5 3 4 3
Deoreaee in Heating Value, % 0.55 0.68 1.54 1.24 1.23
...
15
1.80 1.69 1.80 2.09 1.05 2.46 8.78 4.23 0.72
12
1.78
10
-0.5 19 3
high-volatile coals (of not too high oxygen content), but the caking tendency as measured by the per cent fusion remains relatively strong. Conversely, with low-volatile coals the caking tendency decreases rapidly, but the coke produced tends to remain relatively strong. Column 6 shows the per cent decrease in heating value of the coal at the point where the coke-strength index has been reduced by 15 per cent. At this point, where the coking power has been essentially destroyed as far as use in commercial ovens is con120 cerned, the average decrease in heating value caused by oxidation is only 1.78 per 110 cent. This decrease has no commercial importance, es100 pecially when it is realized that the true loss in heat on storage is probably only 90 about one third this apparent loss in heating value. Study of the changes in 80 analysis of these coals on oxidation leads to the rouah e s t i m a t e t h a t , o n tGe average, about two thirds of the observed loss in heating value shown in column 6 due to the gain in weight of the coal caused by addition of oxygen. AGGLOMERATING INDEX. The agglomerating index ( 3 , I l ) of a coal is obtained by examination and classification of the button reo maining in the crucible after the standard volatile-matter determination. The buttons are made under free swelling conditions and at a high rate of heating. Thus, the carbonizing conditions in these tests simulate in these respects the conditions in a fuel bed; consequently, Figure 6. Comparison the agglomerating index of As lomeratin Index may serve as a measure of and Co\e-StrangtI Index the caking tendency. of Various Coals
1
I I
155
Comparison of columns 2 and 6 in Table I11 and reference to the system of classification show that with oxidation most coals passed from buttons showing strong swelling, pronounced cell structure, and metallic luster to buttons showmg slight swelling, small cells, and slight gray luster. I n the case of each coal tested, the swelling and amount of cell structure decreased with oxidation of the coal. Figure 6 compares the agglomerating index with the cokestrength index for fifteen coals, both fresh and a t various stages of oxidation. As would be expected, the points are very scattered; but in general, buttons classified as good caking (CG) correspond to coke-strength indices above 75, and buttons classified as poor' caking (CP) correspond to a cokestrength index below about 65. There is considerable overlapping of the buttons classified as fair caking (CF). Table V compares agglomerating index and per cent fusion in the carbonization retort for fifty-five coals, both fresh and a t various stages of oxidation. The results are scattered; however, the average per cent fusion decreases from 96.4 for coals in the good-caking classification to 83.8 for faircaking coals, with the still lower value of 51 for coals classified as poor caking. Thus, a rough correlation exists between these two different tests of the caking tendency. Table
V. Comparison OF A glomerstin Index and Per Cent Fusion in Car%onization lotort CG CF 27 21
Agglomerating index Number of tests Range of per cent fusion Average per cent fusion
53.4-100 96.4
34.2-99.8 83.8
CP 7 25.6-89.4 51
Conclusions
I n conclusion, the work has shown that there is a wide range (more than sixteen fold) in durability of coking powerthat is, in the allowable time of storage (under exactly equal condition as to screen size, temperature, etc.) for coal to be used in coke ovens. Durability of coking power can be predicted for most coals from the standard coal analysis ordinarily available before a coal is selected for storage. The effects of storage can be assayed by either the agglutinatingvalue test or by examination of coke buttons made in the standard volatile-matter determination. Acknowledgment
The authors wish to thank W. A. Selvig and W. H. Ode for the determinations of agglutinating value and H. M. Cooper for the chemical analyses and determinations of agglomerating index. Literature Cited (1) Am. SOC.for Testing Materials, A. S. T. M. Standards on Coal
and Coke, pp. 77-82 (1940). (2) Fieldner, A. C., and Davis, J. D., U. S. Bur. Mines, Monograph 5 (1934). (3) Gilmore, R. E.,Connell, G. P., and Nicolls, J. H. H., Trans. Am. Inst. Mining Met. Engrs., 108,255-65(1934). (4) Guthrie, S. W.,Am. SOC.Mech. Engrs., preprint of paper at Cleveland Meeting, 1942. (5) Ostborg, H. N., Limbacher, H. R., and Sherman, R. A., Am. SOC.Testing Materials, preprint of paper a t 45th meeting, 1942. (6) Porter, H. C., and Ovitz, F. K., U. S. Bur. Mines, Bull. 136 (1917). (7) Schmidt, L. D., Iron Steel Engr., 18,No. 3, 67-70 (1941). (8) Schmidt, L. D.,and Elder, J. L., IND.ENO.CHBM.,32, 249-56 (1940). (9) Schmidt, L. D., Elder, J. L., and Davis, J. D., Ibid., 28, 134653 (1936). (10)Ibid., 32,548-55 (1940). (11) Stanton, F. M.,Fieldner, A. C., and Selvig, W. A., U. 8 . Bur. Mines, Tech. Paper 8,36-7 (rev. 1938). PUBLISXXD by permission of the Director, U. S. Bureau of Mines.
