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By J. D. Price, W. M. Bertholf

W. J. PARTON*—I have not had the opportunity to read this paper, and I do not have a written discussion. However, I thought it might be interesting for me to relate some of the experiences we had with equipment similar to the vibrating filter as described by the' authors. At the Tamaqua flotation plant of the Lebigh Navigation Coal Co. approximately 40 tons per hour of froth concentrate carrying 60 pct by weight moisture are produced. The major problem encountered at this plant is the dewatering of this coal froth so that a satisfactory product can be sent to market. In the original design of the plant a centrifuge of solid bowl type was included for de-watering this material. The centrifuge did not work out as well as we had hoped. High maintenance costs and moisture content in the cake were obtained. A Robbins dewatering screen was installed at a later date with the idea of using it in conjunction with the centrifuge. The froth concentrate from the flotation cells was fed directly to the Robbins dewatering screen. The cake from the screen carried approximately 55 pct of the feed solids. Moisture in the cake was approximately 24 pct by weight. The underflow from the screen carried 45 pct of the feed tonnage at about 80 pct moisture by weight. The underflow product was then pumped into the centrifuge with the idea of using the cen-trifuge for recovering the tonnage lost through the screen. This circuit did not operate as satisfactorily as we expected. The only benefit derived was in the reduction in the power consumed by the centrifuge. The maintenance on the centrifuge was approximately the same as previously. The next step in our experiments was to pump the underflow from the screen into a cyclone thickener which was mounted directly over the vibrating screen. This thickener increased the concentration of the solids to approximately 60 pct by weight and dropped the mate- rial back 011 the filter cake which had formed toward the discharge end of the screen. Unfortunately, the screen was not capable of handling this additional tonnage, and our experiments stopped at that point. We have been considering installing a second screen to make possible the complete mechanical dewatering of this product by the use of the dewatering screen and the cyclone thickener. Another possibility under study is to pump the underflow from this screen to a thickener which is available in the flotation plant, and to combine this thickeued underflow with the original feed going to the screen. Again, however, a second dewatering screen will be required to handle the total tonnage. 0. R. LYONS*—I had an opportunity to read this paper ahead of the meeting, and I did a little pencil engineering on it. As Mr. Bertholf said, it is very difficult to make a comparison and to carry the results of work at one plant over to what might be expected at another. What I did was to find information on filtering operations more or less comparable to the type of operation that Mr. Bertholf has with his vibrating filter. The only information that I was able to find was for drum type filters, and I found the operating characteristics of the vibrating filter and the drum type filters were very similar. The moisture contents of the cakes were almost identical. The output per square foot was about the only way that I could compare their capacities— using square foot of screen area against square foot of filter area—and I found the capacity of the vibrating filter to be slightly greater per unit area than the capacity of the drum-type filters. W. H. NEWTON†—Do I understand that the only escape for the solids is by overflowing the thickener? That is, does the filter have a chance to recover all the solids except that lost in the thickener overflow ? W. M. BERTHOLF (authors' reply)— Actually, the only escapc from that part of the circuit is over the top of the thickener. There are other places the fines could be lost in the washery. but once they get into that part of the circuit, they must go over the top to escape. W. H. NEWTON—I would like to ask Mr. Lyons if, in the study of rotary filters, he has any basis for comparison of operating costs? 0. R. LYONS—No, I had no information on costs. The only information I was able to find was on screen size, moisture content, and tonnage output per unit area. W. L. McMORRIS*—Are you wasting that overflow water or re-using it? W. M. BERTHOLF—Right now, we are not re-using it. D. R. MITCHELL† —What is the approximate per capita cost of one of these units? W. M. BERTHOLF—It appears to be somewhere in the neighborhood of $200, for the screen. W. H. NEWTON—The cost would be about $2500 for the complete unit including the vibrating power unit. G. A. VISSAC‡—I do not like to come on the floor after I have been talking so long, but I thought you might be interested in our experience in dewatering, as well as drying our very fine coals. We have used both centrifuge and vibrating screens. The type of vibrating screens we have used in Canada are called the Zimmer. That is a screen of German construction, and I guess it is along the same lines as the dewatering screens you are using now. We use wedge wires, and the minimum size opening is a quarter of a millimeter. In our experience, the cheapest way is still a dewatering bin. A dewatering bin takes 48 hr to do work that takes 20 min in a dewatering screen. We use old wedge wire from our driers which we cover with brattice cloth, and

Jan 1, 1950

By H. L. Washburn, G. L. Judy

DURING recent years thermal drying of fine coal has increased at a tremendous rate, but very little discussion of the several excellent units has found its way into print. This is particularly true for operating and maintenance costs, and the operator who is faced with his first fine coal drying installation must depend chiefly on hearsay when trying to determine what his drying costs will be. This article presents the maintenance and operating costs for the seven drying units now installed in preparation plants of Pittsburgh Consolidation Coal Co. and lists other cost information that should be obtained before any particular drying unit is selected. Plant Description: The fine coal drying section of Plant A consists of four Flash driers operating on two furnaces equipped with spreader stokers. Plant B has one Flash drier operating (together with a screen-type coarse coal drier) on one furnace equipped with a spreader stoker. Plant C has two Cascade-type driers operating on a single furnace with a spreader stoker. Plant Costs: Tables I, 11, and III present the cost of operating these units as reported by the individ- ual plants. As can be seen, the labor rates vary, depending on the amount of overtime paid and the time interval the cost figures cover. There is considerable variation in thermal units used and in the value given to the thermal units at the particular mine. There is some difference in power costs at a given location and, finally, the power costs of conveyors leading to the drying plants were included in some cases. Maintenance supply costs are simply a tabulation of the cost of all supplies used on the driers, furnaces, and stokers. Depreciation is not included, and the tables omit items such as supervision, plant cleanup, oiling, general maintenance, taxes, and insurance. These tables in themselves do not offer a true comparison of costs. This information must be reduced to some common basis. But what is this common basis to be? A mine operator must calculate his overall mine and preparation plant costs in terms of tons of clean coal sold. Unit costs on pieces of equipment within a given plant are correctly calculated on the same basis. However, when unit costs are compared between one plant and another, some thought must be given to unit design. This reasoning is similar to the old argument concerning i solid bowl vs basket-type centrifuges—the units themselves are not directly comparable without their supporting equipment. So it is with thermal driers. Except in rare cases of low entering moisture i content, driers are sized on the basis of water that must be evaporated, while the wear each unit gets de-

Jan 1, 1958

By H. F. McCullough

The success of a coal-mining venture as relates to operations at the gob or break-line, such as the drawing of pillars or the working of long-faces, depends upon the control of face conditions. The measures required to control the latter are dependent upon the action of the coal seam, roof and floor at and in the vicinity of the faces, but the manner in which these will act is dependent upon the rate of face movement as well as upon the facc characteristics and upon the forces exerted. Yet the merits of a method of working—the practicability of controlling face conditions and the means required for such control when applied to any particular case—are usually judged only upon a consideration of the characteristics of coal seam, roof and floor, and the manner in which they have been observed to act. Practically every coal-mining man knows that face conditions are influenced by the rate of face movement, but few have appreciated that this is as much of a factor in the control of face conditions as are the face characteristics and the forces exerted. Fewer yet have recognized or taken advantage of faster rates of face movement as one of the principal means of establishing control of face conditions or of securing more favorable face conditions. Seemingly inherent difficulties, particularly in the control of roof conditions, but also in the control of conditions of the coal seam and floor, are frequently mitigated or disappear when the rate of movement of the faces is sufficiently increased. The characteristics of the coal seam, roof and floor and the forces exerted upon them do determine the general trend or tendency of face action, but the manner in which the coal seam, roof and floor will act and be aeted upon and the magnitude of the action during the time the site of mining operations remains at any particular point are very largely determined by the rate of movement of the faces. Progressive Nature of Forces Exerted Coal seam, roof and floor are composed of materials having definite properties or characteristics. The potential or ultimate values of the

Jan 1, 1927

By Carroll F. Hardy

The day by day loss of industrial plants to gas and oil is chiefly by default. The coal industry is not selling its superior economy, safety, and other advantages to its customers. THE position of the coal industry has been affected by a wide variety of developments in the production and use of energy. The tempo of development and change has been increasing and the end is not in sight. Legislation is currently being proposed for commercial use of atomic power, and the employment of atomic energy in significant quantity will probably occur about the same time as the decline in production of petroleum and natural gas. But these developments are in the future and have little immediate effect on utilization and marketing of coal. While no one should try to suppress or retard the development of a new and economical source of energy, both the coal and private utility industry should be allowed to question how the nuclear power is to be used, who is to use it, and who is going to pay for it. The taxpayers have a monopoly on fissionable material and the knowledge to employ it. Any commercial use must stem from this source. It is not hard to visualize either taxpayer-subsidized private utility atomic power plants on one hand and super TVA's on the other. In view of the gains of gas and oil in the home heating field, it is interesting to compare the 1940 and 1950 census reports on the kind of fuel used for heating in occupied dwelling units. Table I shows that whereas coal provided 77 pct of the fuel for central heating (furnaces and boilers) in 1940, it was down to 45.4 pct in 1950. However, only about 1 1½ million units were lost in this 10-year period. In the non-central heating category, which principally includes stoves, the percentage declined from 39.2 to 25.6, but the units declined about 2½ million in number. The big increase was in heating units designed to burn gas and oil. Use of wood for central heating declined about one-third. Data on amount of fuels used for residential heating are not available, but information is on hand for residential and comnlercial space heating, see Table 11. Commercial space heating includes office buildings, churches, schools. and similar structures. The annual use of bituminous coal in these two categories declined about 1 million tons in the 10-year period. Other forms of solid fuel showed greater losses, except wood, which remained the same. Domestic stokers reached their high point in 1948 with about 1,200,000 in use. At the end of 1951 there were approximately 1,116,790 stokers in use. Conversions to gas and oil have been from hand-fired heating plants in the ratio of about 7 to 1 compared to stokers. In other words, for every one stoker which has been converted to gas or oil, seven hand-fired units have been converted to gas or oil. A bare recital of these data would indicate that the coal industry is holding its own reasonably well. However, 93.4 pct of the new homes built in 1951 were heated by gas or oil. Oil-burning equipment was installed in 37.8 pct and gas equipment in 55.6 pct of the new homes. This indicates that the public prefers gas when it is available, and that oil is second choice, with all forms of solid fuel apparently used when it is unavoidable. It must be pointed out, however, that during the period of rapid expansion of gas pipelines gas has been sold for house heating at prices that are in some cases actually lower than coal prices, or very nearly on a par. Gas has been sold at wells at far below the comparable price for oil produced from the same wells, and far below its actual worth. This situation is being remedied at the present time by increases in gas prices at the wells. For example, the wellhead price of gas in Texas averaged 7.494 per Mcf in 1952. In 1949 it was 4.59c per Mcf. This increase in price is being reflected in pipeline gas prices, and in most of the markets served by the pipelines the tendency is to get it out of the bargain basement type of sales. The American Gas Association estimates that at the end of 1952 there were in the United States about 11 million customers for gas house-heating, and the Association expects additional gains each year until around 18 million homes will be heated by gas in 1975. By 1975 there should be 60 million dwelling units to be heated in the United States, if dwelling units increase at the same rate as the population. If the gas industry heats 18 million dwelling units by that time, this still leaves 42 million units to be heated by some other fuel. If oil is used to heat 18 million dwelling units in that same year, 24 million would of necessity be heated by coal, coke, wood, electricity, or another fuel. The total number of dwelling units using coal listed in the 1950 Census was 18,776,000, so it would appear that coal has a chance at least to stand still in the tonnage sold for domestic use. In the first quarter of 1953, 2044 domestic stokers

Jan 1, 1955

By G. E. Keller, G. D. Coe

Several methods have been devised for rapid determination of sulfur in coal using a high-temperature combustion furnace. The fundamental principles of the various methods are similar but the techniques vary widely. The method described herein is no different in principle from some of its predecessors but varies considerably in technique. Originally devised to overcome the low-accuracy criticism leveled against the others, the tube-furnace method has proved successful for limited applications. Work is being done to widen the applicability of the technique. Subsequent to the work of A. Vita1 in 1920, a number of investigators have published data dealing with the rapid determination of sulfur in coal using a high-temperature combustion furnace.2-5 These, together with several unpublished methods, involve wide differences in technique although they are all similar in principle. Investigation of typical details of procedure showed that poor precision or accuracy could be attributed to one or more of the following: 1) inadequate quantity of sample to be representative, 2) a delivery tube temperature too low to confine condensation to a washable area of the tube, 3) no provision for back washing the delivery tube, 4) incomplete absorption of the sulfur compounds due to inadequate bubbler, and 5) the false assumption that all of the sulfur is evolved as sulfur dixoide. The method herein discussed is no different in principle from some of its predecessors; the differences are in technique. Although the method is rapid—a determination can be completed in 5 min— accuracy has riot been sacrificed in order to achieve speed. MATERIALS AND EXPERIMENTAL WORK Fig. 1 shows the arrangement of the equipment. A metered volume of oxygen is passed through calcium chloride for removal of moisture, then through Ascarite for removal of carbon dioxide, and thence through a glass tee to the feed end of the combustion tube. Connected to the side arm of the glass tee is a rubber tube that is closed with a pinch clamp during combustion of a sample. The products of combustion are expelled through a Vycor bubbler, the end of which is submerged 3 cm below the surface of a 1 pct hydrogen peroxide solution contained in a 300 ml high-form beaker. At the completion of the 4-min combustion period the contents of the beaker are titrated to a yellow end point, using a methyl red indicator, with 0.05 N sodium hydroxide (or sodium tetraborate). The pinch clamp on the tube leading from the tee in the oxygen line is then opened and mouth suction applied to draw the hydrogen peroxide up into the bubbler past the ell, almost to the rubber tube connecting the bubbler to the combustion tube. This washing of the bubbler is repeated until no further acid reaction with the indicator is obtained. The hydrogen peroxide-sul-furic acid solution is then titrated to the final yellow end point. Test work conducted at the Robena Laboratory disclosed the following critical conditions that had important bearing on the precision of the method: Weight of Sample: Several series of tests wherein the sample weight ranged from 0.1 to 0.5 g of -60 mesh coal showed that the lowest variance (standard deviation squared) resulted from the use of 0.5-g samples; the variance was slightly greater when 0.3-g samples were used, and with less than a 0.3-g sample weight the variance increased rapidly with decrease in weight. Although the use of a 0.5-g sample invariably resulted in a very slight explosion as soon as the sample entered the hot zone of the combustion tube, this did not detract from the precision of the method. Temperatures: Mott and Wilkinson5 found that a combination of low temperature (1250°C) and low oxygen flow rate (less than 700 ml per min) tended to give high results due to formation of oxides of nitrogen. Although the method herein employs a much higher oxygen rate than 700 ml per min, as an additional precaution to assure accurate results, 1315°C (2400° F) is recommended as the most desirable furnace temperature. The temperature of the elbow of the bubbler should be at least 75°C to minimize condensation

Jan 1, 1961

By C. W. Thompson

Paul D. Suloff (Goodyear Tire and Rubber Co., Inc., Akron, Ohio)—I would like first to comment on problems of the conveyor belt discussed in Mr. Thompson's excellent paper, since that is what we hope we know most about. Twists in relatively wide conveyor belt unavoidably produce a lateral maldistribution of tension, raising tension at belt edges and reducing it at the center. They also produce a lateral collapsing force on the belt at the center of the twist owing to the inherent tendency of all the longitudinal elements of the belt to try to pass through a point at the twist center. Calculation of the twist geometry by the methods shown in Mr. Thompson's paper keeps these extraordinary forces within limits which the belt designer can tolerate. No reduction in belt life due to twisting need be contemplated when this geometry is maintained. There is a minor exception that belts of extreme lateral flexibility will tend to curl laterally at the center of the twist. However, any ordinary fabric construction will perform satisfactorily in this respect. These twists are always made in regions of low tension in the conveyor so that even in the edges of the twist, belt tension does not exceed the average tension found in highly stressed regions of the conveyor. Offsetting these out-of-ordinary belt stresses is the advantage that Mr. Thompson has brought out of getting the return run up out of the dirt where it can be seen. This not only makes it easier to train, but also, in the event that it is not properly trained, frees it of the normal return run edge wear hazard. It is well known that return run edge wear is a prominent cause of belt mortality underground. An interesting aspect of this two-way conveyor is that the belt may be made what is known as a Mobius Strip. A Mobius Strip is obtained by splicing a belt after turning one end of it 180" about its longitudinal axis. In other words, one end is turned upside down before splicing. A belt spliced in this fashion turns itself upside down every time it comes around, but the twist which has been put in the splicing, of course, stays at one location on the conveyor, in this case one of the twist sections at the end. Turning the belt over every revolution might have advantages in some cases. Belts could be made with equal covers and the two sides worn equally and simultaneously. In this case there would be no problem of getting belts on upside down by mistake. However, the two-way conveyor does not have to be a Mobius Strip. It can be twisted in such fashion that the same side is up on both runs. It is simply a question of which way the final 90" twist is made before joining the ends. Another interesting aspect of the two-way conveyor is the problem of operating two-way conveyors in series. Here the sequencing of starting brings up some new problems. It will be recognized, although not always at first glance, that if the starting sequence is planned for one run of the conveyor the reverse will result on the other run. With the two runs carrying bulk material in both directions a reverse sequence on one run would be intolerable. In this situation the only solution appears to be a simultaneous starting of all conveyors in the series. However, with the coal in one direction and intermittent supplies in the other it would be entirely practical to sequence the conveyors for the coal run and accept a reverse sequence on the supply run. The two-way conveyor also lends itself to new driving possibilities. First, it is quite possible to drive at the head end of each run, which of course, means a drive at each end of the two-way conveyor. Driving in this way a given belt can be extended to substantially greater lengths than a conventional conveyor with drive at one end only. In addition to this, under certain conditions the conveyor can be extended to extreme length by driving at one end and at some intermediate point on the most heavily loaded run. As a particular case, a belt carrying coal downgrade and supplies back upgrade could be extended to extreme lengths by driving at the head of the coal run and at an intermediate point of the supply run. Mr. Thompson has been a pioneer in belt conveyor transportation underground and his accomplishment here with the first two-way conveyor of any consequence is another notable addition to the art.

Jan 1, 1954

By W. A. White

UNDERCLAY squeeze is the plastic flowing of underclay below coal pillars into mined-out entries and rooms. Squeezes may be caused either by wet mine conditions where the moisture is taken up by the clay—making it more plastic—or by the presence of certain clay minerals, such as mont-morillonite, which are plastic when there is enough natural moisture. Under either condition, sufficient stress will cause the underclay to flow. Squeezes may fill an entry or room within several hours, or it may be several months before movement stops. Squeeze areas commonly cover hundreds or thousands of square yards. The Coal Div. of the Illinois State Geological Survey has collected samples of underclays from various mines and from cores drilled by coal companies in the state. From these samples natural moisture content, particle size and particle size distribution, and clay mineralogy are determined. Data from samples collected from the underclay below Herrin (No. 6) coal in the Lumaghi Coal Co. mine near Collinsville, Ill., are used in this report to clarify points in the discussion. Data from samples taken from other mines lead to the same conclusions. A generalized geological section for the area is given in Table I. The underclay below coal No. 6 ranges from a few inches to 3 or 4 ft thick. The upper 6 to 18 in. are noncalcareous; the lower part becomes more calcareous with depth. Limestone nodules become larger with depth, almost grading into the limestone below. In areas where the clay is nearly absent the limestone may thicken to take its place; thus they may complement each other in thickness. There are two types of squeeze areas in a mine. In one type up to 3 or 4 ft of underclay lie in what appears to be a depression in the limestone underneath. This is suggested by a rim surrounding the squeeze area where the underclay is thin and the limestone lies within a few inches of the coal. In the second type the underclay of the squeeze area is surrounded by underclay of similar thicknesses which does not squeeze. Test Methods: Natural moisture content, particle size and particle size distribution, and clay mineralogy were determined by the following methods: Natural moisture is the moisture content a clay contains in its natural environment, expressed in percentage of the weight of ovendried clay (110°C or 230°F). To obtain the natural moisture content, given in Table 11, the clay samples were sealed in containers as soon as the samples were taken in the mines. Particle size and particle size distribution were determined by the pipette method,' and the data were plotted as cumulative curves, Fig. 1, on semi-logarithmic paper. Particle size was plotted on the logarithmic scale and percentage on the arithmetic scale. The quartiles (diameters that correspond to frequencies of 25 and 75 pct) and medians (diameters that correspond to the frequency of 50 pct) of the samples were determined from these curves. The clay minerals were identified from the data obtained by differential thermal' and X-ray powder" techniques. The differential thermal analyses were made on the whole samples, whereas the X-ray analyses were made on fractions of less than 2p. Data and Discussion Moisture Content: After the sealed jars had stood for 24 hr, those that contained squeeze samples had perspired, so that droplets of water had accumulated on the insides of the jars. Table II shows the moisture in the clay after it had perspired for 24 hr. (This perspiring was not noted in samples from nonsqueeze areas.) After perspiration one of the squeeze samples still had a higher moisture content than the samples that did not squeeze. Clay Mineralogy: The thermal analysis, Figs. 2 and 3, indicates that the clay minerals are chiefly micaceous in type; the low-temperature endothermal

Jan 1, 1957

By Cloyd M. Smith

A few years ago, the Ventilation Committee established the practice of resenting one topic each year for discussion at the annual meeting. The practice has met good response on the part of committee members and I suggest that it be continued. The topic chosen for this year, "Underground Anemometry," is a topic which has bothered me for more than 20 years. It seems to me that the coal industry is content to rely on slipshod methods for measuring the rate of flow of air underground, so I prefaced my discussional charge to committee members with the statement that I regard air measnrements made in the usual way, with hand held anemometer, as no good. Agreements and disagreements came in from more than a dozen engineers, some of whom are with operating companies, coal and metal; some with manufacturers; others with government agencies. The statement was accompanied by a questionnaire on the use of the rotating vane anemometer and by one describing two methods of using a mechanically held anemometer. The questionnaire will be considered first. The questionnaire and statement are as shown on pages 5 and 6, the committee members and respondents are given on page 4, and the general comments of the latter on page 5. Questionnaire 1. Has your company or agency issued written instructions for care and use of anemometers? If so, please enclose a copy with reply. Only one answer, McElroy's, was affirmative. It gave reference to Bureau of Mines publications1'5 which recom- mend the hand held anemometer for rough measurements and indicate that am accuracy of 5 pct can be had if calibration and method factors are used. Mathews said that instructions are principally oral while Maize reported that state inspectors of his department are well trained in use and care of anemometers. 2. Are your anemometers calibrated periodically? If so, by their manufacturer? or by? Are calibralion corrections applied to all observed mean velocity readings? Only one respondent, Lee, answered negatively as to calibration. This means that anemometers are generally calibrated but the questionnaire failed to ask how often this is done. As no one volunteered the information, we have no data on this point. In six cases the instruments are sent to their manufacturers for calibration. but Krickovic reports that his company limits manu-facturers' calibrations to anemometers which are used by operating personnel; those used by the engineering department being calibrated by U. S. Bureau of Standards. The Anaconda Copper Mining Co. has its ventilation engineers calibrate its anemometers. Most of the respondents say that a calibration correction is applied to each mean velocity reading, but Krickovic limits this to surveys made by the engineering department. Since Lee does not calibrate, he has no correction to apply. Maize reports that his department has its anemometers calibrated but does not apply corrections. 3. Do your men hold the anemometer by hand in measuring air flow? for 1 min? or traverse the section? for 1 min? or at? points for 5 sec each? Of 10 replies, 6 were "yes," 3 were "no," and one was "seldom" with respect to holding by hand. Among the six hand holders, four hold in a central position in the measuring section for a minute, except that two of them, Krickovic and Matthews, traverse the section by hand for survey or fan test. Their operating personnel hold by hand, centrally, for routine measurements. McElroy sometimes traverses with hand-held anemometer in rapid survey work. 4. If the anemometer is not held by hand, how is it supported? Augustadt supports the anemometer on an adjustable rod, Condon on "a rod of sufficient length to reach all points with observer standing in one position throughout traverse and at arm's length from plane of traverse." I presume that arm's length must be interpreted liberally enough to allow for arm movement, otherwise it would be impossible to manipulate the anemometer throughout the traverse section. Mancha upholds Condon in this method of traversing. Glanville hangs the anemometer on the end of a 4-ft staff by the hasp at the top of the anemometer frame. McElroy mounts it on the end of a rigid square shaft, 12 in. long, the staff being at right angles to the axis of the instrument. He traverses the section in two halves, holding the anemometer 3 feet from his body.

Jan 1, 1950

By E. Swartzman, G. C. Behnke

THE free-swelling index, a numerical value for the free-swelling properties of coal, is being used to an increasing extent in specifying coal for burning in various types of equipment. The empirical standard ASTM method for determining this index uses, as a source of heat, a gas burner which requires frequent calibration because gas pressures are not constant, relatively small changes in gas pressure resulting in rather wide variations in the temperature attained in a crucible and thus in the resultant size of the coke button. Furthermore, the quartz crucibles specified for the test are not standard equipment, and relatively small variations in dimension and wall thickness from those specified often result in rather wide variations in the resultant size of the button. A method of analysis to be satisfactory not only for a scientific laboratory but also for use in industrial control laboratories under varying conditions should employ equipment which is rugged, easily calibrated, and readily replaceable by standard materials. Gas is not universally available as is electricity, and it is generally easier to calibrate and control a simple electric furnace or heater than a gas burner, the voltage not usually fluctuating to the degree that gas pressure does. Quartz crucibles are fragile, and the size specified in the test is not normally used for any other purpose in the laboratory. Although more expensive, the 15-cc platinum crucible, available in all laboratories where volatile matter in coal is determined by the standard ASTM method, is sturdy and standard and easily replaced. Because of these considerations, a modification of the standard method has been developed which employs a standard laboratory 350-w cone heater and standard 15-cc platinum crucibles. The results of numerous tests conducted with such apparatus show conclusively that the free-swelling index values as judged by the buttons produced with this equipment are exactly the same as those obtained by the standard gas burner method. Thus it is suggested that this electric cone heater method employing standard 15-cc platinum crucibles be considered as an alternative to the ASTM method, Designation: D720-46. The free-swelling index of coal is determined by means of the ASTM method, D720-46. This method, which is an adaptation of the crucible swelling test for coal of the British Standards Institution, consists of heating 1 g of coal in a special covered quartz crucible in a regulated gas flame for a period of not less than 2.5 min in which time the temperature of the inner surface of the bottom of the crucible reaches a temperature of 82025°C. The residual coke button is then compared in size and shape with a series of standard profiles shown in Fig. 1 and designated by number from 1 to 9 in increasing order of size. As the method is empirical, it requires rigid standardization of the apparatus and repeated calibration of the gas burner. The dimensions of the low form quartz crucible recommended must be rigidly adhered to as small variations in diameter or wall thickness result in variations in the rate of heat transmission and thus in the resultant size and shape of the coke button. The gas burner must be calibrated almost every time a new set of determina-

Jan 1, 1952

By T. Gleason

Problems involved in applying wet scrubbers to gas cleaning coal dust from thermal dryers are reviewed. Careful consideration of all the elements going into a modem coal preparation plant is required in view of the increasing difficulty of applying suitable gas cleaning equipment. This problem arises not only from the presence of finer coals to be handled, but also from the pressures applied by both the general population and the plant operators to improve the standard of gas cleaning performance. The Peabody scrubber is presented by the author as a machine designed to help improve this cleaning operation. Wet scrubbing of fine coal from thermal dryers poses a number of problems in adapting the gas cleaning equipment to the fine particulate matter. Among them are: 1) Dust in gases leaving the thermal dryer cyclones is often extremely fine with high percentages of total dust loading less than 1p in size. 2) Flue gas entering the scrubber is corrosive since the coal fired in the thermal dryer furnace is in the range of 0.7% by weight sulfur or higher. Therefore, comparatively high cost stainless steel alloys or corrosion resistant linings are required for a satisfactory service life. 3) Requirements for residual coal loadings leaving the gas scrubber are continually being lowered, while modern coal preparation operation is imposing heavier burdens on the collection system through introduction into the thermal dryer system of very fine coal previously not recovered. The advent of flotation systems in increasing numbers is typical of this trend. 4) Installation of a scrubbing system on thermal dryers is made primarily to reduce air pollution and product recovery value is of little or no value. Therefore, the operating costs of gas pressure drop and water requirements must be held to a minimum. We have, then, the basic situation which calls for comparatively high cost stainless steel alloy wet scrubbers, which must be highly effective in removing coal fines particularly in the 0 to 5-p size range. Further, the standards of scrubber performance are continually being raised towards the level where gas discharged from the scrubbers must be essentially free of any coloration due to residual dust. In view of the highly refractive nature of fine coal dust, residual loadings of 0.01 grains per cu ft or less are required to provide a color free discharge gas. In the present specifications under consideration a residual coal loading of 0.05 grains per cu ft would be considered color free, since the discharge gases are saturated in the range of 150°F. The steam plume acts as a masking agent at the point of discharge, and upon dissipation of the 150° saturated vapor stream, the effluent gas stream could be essentially color free. The specification under consideration calls for residual solids loading of 0.05 or less grains per cu ft, given a coal size distribution shown in the basic data in Table I. It is noted that the dust laden coal stream has a size distribution by weight of 33% in the 2 to 5-p size range and 55% in the 0 to 2-p size range. The particle size distribution given in the specifications does not detail the percent by weight less than 1-p in size, and more important, the size distri-

Jan 1, 1963

By A. G. Gilbert

Paradoxical is the word. The coal industry, despite reach- ing a 22-year high in production (590 million tons), has been tagged as having its back to the wall vis-a-vis its valiant attempts to quench the nation's still unabated craving for coal. What must be even more reassuring to the industry, infected once with rumors of a uranium takeover, is a nation's almost insatiable appetite for electricity. Between 1967 and the summer of 1970, utility stockpiles were being gobbled up, diminishing to 79% of the January 1968 level.

Jan 1, 1971

By Paul Averitt

require both time and money. Any attempt to secure a quick answer will yield a figure that very likely cannot be substantiated, and certainly will not yield information in the detailed form now desired. It will be about 10 years before a completely new estimate can be prepared for the coal reserves of the United States at our present rate of progress, though of course, much information will be available in the interim. We would like to present such information as we obtain in the form most acceptable to the industry, and to that end we are working closely with coal resource committees of the AIME, the National Bituminous Coal Advisory Council, and the Bureau of Mines. DISCUSSION G. H. Cady*—Mr. Averitt's description of the nature of the coal resources investigations of the United States Geological Survey and the progress of this work is very timely in view of the general interest in the subject of coal resources. The Federal Survey is obviously taking the "long view" with respect to the appraisal of the coal resources as part of the preparation of the general geological map of the country and the attendant determination of the quantity of all mineral and fuel resources. It is apparently for regional surveys of the conventional type that the detailed procedures employed by the Federal Survey are applicable. Even if so it is somewhat unexpected to find the same criteria for evaluation will be applied to the country as a whole. The work on coal resources appraisal has been proceeding at various rates in a number of coal producing states for various periods. Undoubtedly since there has been no common practice in the method of appraisal the states each have worked independently and independently of the Federal Survey, and each has adopted certain practices to meet local conditions. I do not know how much consideration has been given by the U. S. Geological Survey to these practices. It seems probable that such consideration might result in important modifications of the standards which apparently have been set up by the Federal group in line with local requirements. It is the practice in some state surveys to present the facts in regard to the occurrence and distribution of coal beds and their variations in thickness down to thicknesses of 1 to 1 1/2 ft in relatively narrow stages up to maximum thickness. It is then possible for any one using such figures to compile quantitative estimates of workable coal at various minimum thickness limits. This is a desirable objective where surveys are detailed and information correspondingIy good. However, vast quantities of coal lie in beds that are relatively thin about which little information is available and the quantity of such coal might affect the final appraisal to the extent of several thousand million, depending upon the minimum limitation observed. Thus in the case of Illinois a difference of 1 ft in average thickness of coal in the coal field would make a difference of approximately 35 billion tons in the estimated quantity present. One is dealing with a very large area and small differences in thicknesses are very irnportant in the overall picture. The estimate of 10 years to accomplish the sort of detailed appraisal outlined by Mr. Averitt is viewed somewhat skeptically and certainly would require many more trained geologists than seem to be available. The requisite detailed mapping and study are very time consuming not only because of the geological field work required, which is difficult in certain seasons, but also in order to assemble data from company and personal files, and to study drill records and cores, and to sample and analyze the coal. Unless the staff of geologists could be increased in the order of several hundred per cent the prospects are that the appraisal of the type suggested will require many decades not just one. The permanent value of such appraisal, however, is not questioned and it should be expedited as rapidly as means allow. Satisfactory appraisal is not easily achieved and will vary from time to time. The main function of a geological survey is to collect and present the facts that will make possible appraisal in terms of existing conditions by individuals, particularly engineers, qualified by training and expcrience for making such estimates. Thickness and character of the coal bed, nature of the overlying and underlying strata, position, thickness, and character of "partings," relationship to other coal beds, and a variety of other factors must be assembled by the geologist in order to present a complete picture of the geological setting. The economic and engineering factors are in general outside the field of geological experience. The geologist should see to it that the pertinent geological facts are available; much more information than simply thickness and depth of the coal beds is essential to meet all the requirements of appraisal in the future as well as at present. With respect to the present demand by engineers and coal mine operators and others for a rapid re-appraisal of the available coal resources, in the light of existing practices and those in immediate prospect, the Federal procedure of systematic mapping and appraisal is scarcely in line. It will be necessary for those particularly interested in having such an estimate made to establish standards with respect to the various factors involved so that the scope of the geological work can be definitely restricted for the various coal fields. There is little use in setting up general standards since no such standards will be applicable to all fields. Thus it is folly to establish a standard minimum thickness to be generally applicable which is one-half to one-third the minimum minable thickness in some fields. The greatest difficulty in appraisal of the presently actually workable coal bed lies in the variation in the importance placed on roof, floor, structural conditions, bedded impurities. sulphur content and other factors that affect judgment relative to the value of a coal bed. It is doubtful whether any appraisal will have universal approval in view of the variable factors involved. For this reason if none other, the facts should be carefully and painstakingly assembled after the manner of a systematic geological survey such as that advocated by Mr. Averitt. Only upon the basis of sucb information can reliable estimates be made in line with selected conditions. Paul AveRitt (author's repty)— In this paper I discussed, but did not define as such, two major phases of our activities on coal, which are closely related, and which normally we in the U. S. Geological Survey see as an integrated whole. It is understandable, therefore, that Dr. Cady should assume that my remarks applied only to the current work on coal reserves with which I am directly concerned. In view of Dr. Cady's discussion, however, I think a brief summary of the two phases of U. S. Geological Survey activities on coal will be appropriate. The long-term function of the U. S. Geological Survey on coal investigations is to make detailed geologic studies, involving the preparation of detailed geologic maps showing the outcrops and correlations of coal beds, direction and dip of coal-bearing rocks, nature and thickness of overburden, location of faults and fold axes, and similar features. Such studies also yield many measured sections of coal and associated strata, which show variations in the thickness of the beds, and the intervals between coal beds. Taken as a whole, detailed geologic studies provide much useful information for mine operators and engineers. As Dr. Cady points out, this type of geologic work is arduous and time consuming, but it provides the basic data that are necessary both in the development of our coal fields, and also in the preparation of coal-reserve estimates, which are discussed in the next paragraph. The U. S.

Jan 1, 1950

By Ancel St. John

During a session on coal and coke at the February, 1926, meeting of the American Institute of Mining and Metallurgical Engineers, the writer called attention to the important work on the X-ray analysis of coal1,2 being carried on in England by C. Norman Kemp and his associates. This aroused so much interest that a paper on the subject was requested for the October meeting. It has seemed advisable to make this paper a preliminary survey of the present status in the application of X-ray methods to coal problems and to follow it from time to time with further articles as the art develops. A survey of this sort naturally divides itself into two parts, radio-scopic analysis of the distribution of constituents through the body of the coal, and diffraction analysis of the state of association of the elementary components. In this article the subject matter concerning radioscopic analysis has been drawn almost entirely from the writings of Kemp and his associates and the illustrations have been sptcially furnished by him. It is a pleasure to record here a great indebtedness for this courtesy and cooperation. The subject matter and illustrations concerning diffraction analysis are taken from the author's unpublished researches. Nature and Properties of X-rays Before proceeding it is well to recall the nature and some of the properties of X-rays, as well as our present conception of atomic structure According to the accepted theory atoms are composed of electrically-charged particles. A positively-charged center, called the nucleus,

Jan 1, 1927

By C. Heath

US coal consumption reached new heights in 1985, but production was constrained by excess consumer inventories. Domestic consumption of coal reached a record 742 Mt (818 million st) during the year. This is a 3.4% gain over the previous consumption high 718 Mt (791 million st) in 1984. An additional 84 Mt (92.7 million st) of US coal were shipped abroad in 1985, up 13.7% from exports a year earlier. Coal production in 1985 totaled 804 Mt (886 million st), 1.1% below the record 813 Mt (896 million st) produced in 1984. The slight decline in coal output is attributed primarily to a 13% drawdown of large consumer stockpiles built up in 1984 in anticipation of a miners strike that never occurred. Coal demand, and hence production, were also restrained by slower economic growth in 1985 and additional gains in nuclear generation of electricity. Domestic market requirements for coal in 1985 were mixed. Electric utility consumption rose 4.4%; coke plants consumed 6.7% less coal; coal requirements in the other industrial sector expanded by 2.1% and consumption in the residential and commercial sector fell 14.8%. The 2.2% increase in electric power generation in 1985 resulted in a 4.4% rise in utility coal consumption, totaling 630 Mt (694 million st) for the year. Twenty-nine of 45 states where coal-fired electric power plants were operating shared in the 26.7 Mt (29.5 million st) increase in 1985. Coal receipts at utilities fell by 16 Mt (18 million st) as these facilities worked off 21 Mt (23.4 million st) from stockpiles during the year. Electricity generation at coal-fired power plants similarly climbed 4.4% to 1.4 trillion kWh in 1985. This gave coal a 56.8% share of electricity generated from all energy sources compared with 55.5% in 1984. The average price of coal delivered to these facilities remained essentially unchanged during the year. It declined on 1.5% from $38.26/t ($34.71 per st) during the fourth quarter of 1984 to $37.70/t ($34.20 per st) in the fourth quarter of 1985. Coal consumption at coke plants continue to reflect a depressed steel industry. After rebounding 18.9% in 1984 for the first time in five years, coal consumption at coke plants again declined 6.7% to 37 Mt (41.1 million st) in 1985. Coke consumption 26.5 Mt (29.3 million st) exceeded production, 26 Mt (28.7 million st), in 1985. This resulted in a 1-Mt (1.2-million st) decline in coke stocks at producer and distributor levels during the year. The average price of coal delivered to coke plants decreased 7.6% from $64.30/t ($58.34 per st) during the final quarter of 1984 to $59.42/t (53.91 per st) in the last quarter of 1985. Coal consumption in other industries, including all manufacturing and industrial consumers except coke plants, totaled 68.3 Mt (75.3 million st) in 1985. This was the highest level attained in more than a decade. But the lower percentage rise last year (2.1% compared to 11.8% in 1984) reflected slower growth in the nation's economy in 1985. The average price of coal delivered to industrial firms declined 4.5% from $42.32/t ($38.39 per st) in the fourth quarter of 1984 to $40.39/t ($36.65 per st) in the last quarter of 1985. Coal-producing states in Appalachia mined 9.8 Mt (10.8 million st) tons less in 1985 than in 1984 for a 2.4% loss. The largest contributors to the region's production decrease to 393 Mt (433 million st) were Pennsylvania, down 14.7% to 60 Mt (66 million st); Ohio, down 8.3% to 32.6 Mt (36 million st); and West Virginia, down 2.9% to 115 Mt (127 million st). Conversely, eastern Kentucky production was up 4.8% to 111 Mt (122.8 million st) in 1985, while production in Tennessee climbed 9.7% to 40 Mt (44 million st). No coal was mined in Georgia last year. Coal production in the interior region in 1985 declined 3.9% to 173 Mt (190.4 million st). Substantial production losses occurred in Indiana, down 8% to 31 Mt (34.5 million st); and in western Kentucky, down 7.9% to 36 Mt (40 million st). Coal production in Texas rose 5.7% to 39 Mt (43.5 million st) in 1985. Louisiana began mining lignite 140 kt (151,000 st) during the year. Production in the western region increased 3.4% to 238 Mt (262.5 million st) in 1985. Wyoming, up 5.3% to 125 Mt (140 million st); and North Dakota, up 16.5% to 23.5 Mt (26 million st) contributing the largest amounts. Production gains were also shown in Washington, Utah and, notably, in Alaska where coal output climbed 72.9% to 1.3 Mt (1.5 million st) in 1985. Most of the additional coal produced in Alaska last year was shipped abroad. Coal stocks held by consumers totaled 154 Mt (170 million st) at the end of the year. This was 27 Mt (30 million st), or 13.7% below the inventory level at the end of 1984. Stocks held by producers and distributors declined by 868 kt (957,000 st), or 2.8% in 1985 to 30 Mt (33 million st). A drawdown in stockpiles occurred in each consumer sector during 1985. Stocks held by electric utilities totaled 142 Mt (156 million st) at the year's end, 13% lower than stock levels at the end of 1984.

Jan 5, 1986

Continued market pressure on the US coal industry was the overriding factor affecting developments in underground mining in 1986. An oversupply of coal in the spot market kept prices low throughout the year and caused a number of operations to close their doors. Operators stepped up their efforts to improve productivity at existing operations. They made technology advances and improved their relations with employees. A continuing market-related development during 1986 was the divesting of coal properties and operations by major oil companies, which were faced with economic pressures in both the oil and coal industries. Further increases in contract mining production resulted as some larger operators were unable to compete in a tough economic environment. Longwall mining is still seen by many as the technology that will provide the necessary productivity to remain cost-effective. But the number of active faces in the US declined in 1986, as reserves were depleted and economics forced some closures. At the first Longwall USA meeting in June, much attention was placed on improved technology, as electro-hydraulic controls for roof supports gained acceptance. Other recent developments include shearer initiation of roof supports, automatic horizon control for shearer drums, and collection and storage of machine data for predicting maintenance requirements. The government and academic communities continued their research on dust control at longwall faces. Jankowski, Kissel, and Daniel, (October 1986, Mining Engineering), gave an overview of progress in longwall dust control. And Mukherjee, Singh and Jayarman (November 1986, Mining Engineering), recommended design guidelines for improving water spray systems for dust control. Surface subsidence Increasing attention is being given to surface subsidence. This is primarily because of longwall mining and the Surface Mining Control and Reclamation Act. Improved methods of prediction of surface subsidence, especially computerized methods, are being continually developed. Mining engineering faculty at major universities such as Virginia are helping develop public policy and regulations concerning subsidence. As part of this effort, Unrug and Johnson identified major subsidence areas of Western Kentucky. Peng and Chen (February 1986, Mining Engineering), gave an overview of history and research of surface subsidence. And Elifrits and Aughenbaugh, (February 1986, Mining Engineering), discussed effects of moisture variations and overburden on subsidence. This research culminated in a Symposium on Surface Subsi¬dence at the SME 1986 Fall Meeting in St. Louis and the 2nd Workshop on Surface Subsidence at West Virginia University. Ground control in coal mining continued to be an item of major research interest. Some 30 papers were presented at the 5th International Conference on Ground Control in Mining at West Virginia University. And six sessions were related to coal mining at the 27th US Symposium on Rock Mechanics at the University of Alabama. At the 4th Annual Workshop, Generic Mineral Technology Center, Mine Systems Design and Ground Control emphasized efforts of the participating universities to improve ground control. Peng and Chiang summarized results of studying support capacity and roof behavior with longwall shield supports. And Unrug, Johnson, and Nandy analyzed the process of deterioration of shale roof in a case study of a room-and-pillar coal mine. The importance of geologic conditions in determining mining productivity is receiving increased attention in coal mine design in the US. Mullenex related, through case studies, the benefits to be derived through analyzing the depositional system of coalbeds as an integral part of mine design. Improved technology in this area was related by Lloyd, Semborski, and Stolarczyk. They discussed a case study of using radio imaging to indicate coal-seam discontinuities in advance of mining. Improved coal mining technology in general is being researched more heavily, to help improve US coal competitiveness. However, much of this research and development process has yet to be widely implemented. Equipment manufacturers are devoting more resources to development of continuous-haulage systems, mobile roof-supports, mine-monitoring systems, and predictive-maintenance systems using computers to extract machine data.

Jan 5, 1987

By E. R. Pantos

US coal production increased 3% to a record 832 Mt (917 million st) in 1987, according to preliminary Energy Information Administration (EIA) data. Most of the increase was due to the unusually warm summer and the increased coal-fired electricity demand for air conditioning. Drought conditions in the Northwest lowered hydroelectric generation, contributing to the higher use of coal by electric utilities. However, excess production capacity and increased competition from natural gas added further downward pressure on delivered coal prices, continuing the declining price trend of the last several years. Coal production by region Appalachian coal production reached 402 Mt (443 million st) in 1987. This is about 3% more than in 1986 and just short of its 1984 peak. Virginia produced 7% more than its 1986 level, due to increased coal-based electricity demand. Smaller percentage increases were attained in eastern Kentucky, Pennsylvania, and West Virginia. Ohio and Alabama were the only major coal-producing states in Appalachia that produced less coal in 1987 than in the previous year. In the Interior region, 1987 coal production reached a record 182 Mt (201 million st), about 2% above 1986. Illinois is the largest coal-producing state in that region. Production there fell about 3.7%, primarily because of lowered demand at electric utility plants in Alabama and Tennessee. However, this was more than offset by production increases in western Kentucky, Texas, and Indiana. After falling slightly in 1986, coal production in the West resumed its upward trend to a record 248 Mt (273 million st). Wyoming is that region's dominant coal producer. It mined 7% more coal than in 1986. Wyoming's increase offset the 11% decline in New Mexico production and smaller declines in other Western states. Coal consumption and prices Domestic coal consumption reached a record 759 Mt (837 million st) in 1987. Most of the increase resulted from the unusually warm summer that led to higher than normal peak demands for electricity in the third quarter. Electric utility coal consumption was also boosted by the below-normal hydroelectric generation that resulted from low water levels in the Northwest. These factors more than offset the effects of increased nuclear power generation and competition from natural gas. As a result, coal provided 56.9% of electric utility generation in 1987, compared with 55.7% in 1986. Electric utilities consumed a record 651 Mt (718 million st) of coal. While electric utility coal consumption increased, the average cost of coal to utilities was down, from $1.58 per million Btu in 1986 to $1.52 in 1987. The average price of coal delivered to utilities in 1987 was $35.09/t ($31.84 per st), the lowest since 1981. Coal prices were held down by a glut of coal supplies and by a decline in the average price of natural gas to electric utilities. Coal consumption at coke plants in 1987 was 2.6% above the 1986's 32.5 Mt (36 million st). This increase reflects steel's recent resurgence. Coking coal demand, though, was reduced by the increased use of continuous casting and electric furnace technologies. The average price of coal delivered to coke plants fell from $56.02 to $51.35/t ($50.83 to $46.59 per st). Coal consumption in the industries other than coke plants amounted to 68.2 Mt (75.2 million st) in 1987, slightly less than in 1986. Coal lost part of its market share to natural gas, which was priced favorably relative to coal. The average price of coal delivered to manufacturing plants was at its lowest level of the current decade. It fell from $39.50/t in 1986 to $37.27/t ($35.84 to $33.81 per st). Residential and commercial coal consumption fell to 6.2 Mt (6.9 million st) that is 9.8% below 1986 and the lowest since 1980. This decline is also attributed to the relatively low price of natural gas in 1987. Coal stocks Coal consumers held 169 Mt (186 million st) of coal stocks at the end of 1987, 5.9% above the 1986 year-end level. Most of this increase was due to stockpiling by electric utilities in anticipation of a possible strike by the United Mine Workers of America early in 1988. Stocks at electric utilities increased to an estimated 154 Mt (171 million st) at the end of 1987, 5.6% higher than the previous year. This was much lower than 1984's stock buildup. Coke plants increased their coal stocks by 30% in 1987 to 3.5 Mt (3.9 million st), rebounding from the unusually low inventories of 1985 and 1986. Other industries increased their stocks slightly in 1987. Coal producers and distributors ended 1987 with 25 Mt (28 million

Jan 5, 1988

By M. L. Mellish

The year 1988 unexpectedly turned out to be a good year for the US coal industry. In fact, it was a third consecutive year of record coal production. Accord¬ing to preliminary Energy Information Administration data for 1988, domestic coal consumption went up 5%, or 41 Mt (45 million st), from 1987. Coal exports were up by a surprising 13.6 Mt (15 million st). In 1988, 22.7 Mt (25 million st) of coal were drawn from stockpiles for consumption. Even so, US coal production increased to 862 Mt (950 million st). That was up 28 Mt (31 million st) from 1987. While coal consumption, exports, and production were up, delivered prices for steam coal continued to slide during the year. Metallurgical coal prices, however, firmed up and showed a moderate increase. This reflected tight metallurgical coal markets at home and abroad. Coal consumption US coal consumption reached 800 Mt (882 million st), compared with 759 Mt (837 million st) in 1987. Increased metallurgical coal consumption was one factor. Most of the rise in coal consumption, however, was due to unexpectedly high electricity demand. Unseasonably hot summer weather al lowed added coal-fired electric generation to supplement the drought-related reduction in hydro-electric power supply. Electric utilities consumed 687 Mt (757 million st) of coal in 1988, 35.4 Mt (39 million st) more than in 1987. Coal-fired power plants remained the primary source of US electricity generation, providing 57% of the total in 1988. Coal consumption at coke plants increased 13%, to 38 Mt (42 million st), from the level consumed in 1987. This increase reflects the recent recovery in the iron and steel industry. Metallurgical coal consumption in 1988 could have been greater. But US coke plants reportedly reached their maximum practical production capacity. As a result, net US coke imports amounted to 1.45 Mt (1.6 million st). Despite increased industrial activities, steam coal consumption by industrial plants was up only slightly from the 1987 level, amounting to 69 Mt (76 million st) in 1988. Residential and commercial coal consumption remained virtually unchanged at 6.4 Mt (7 million st). Coal exports and imports US coal exports rebounded in 1988, reaching 86 Mt (95 million st). It was the highest level of annual US coal exports since 1982, when they reached 96 Mt (106 million st). An unusual set of factors led to an opening for US coal exporters in 1988: • a high level of industrial production in Japan and the European Economic Community, • supply disruptions due to labor problems at coal mines in Poland and Australia, • a drought-related reduction in hydro-electric power generation in Canada, requiring increased coal-fired generation, • China's problems in meeting its export commitments, and • a fall in the value of the US dollar. US metallurgical coal exports in 1988 amounted to 56 Mt (62 million st), 9.1 Mt (10 million st) more than the 1987 level. Europe, Japan, and Canada were the principal importers of US metallurgical coal in 1988. European countries, in particu¬lar, increased their take by one-third of US metallurgical coal. The labor problems in Poland and Australia contributed to these higher levels of imports. So did increases in pig iron production of 8% in Japan and 9% in the European Economic Community. US steam coal exports - including bituminous, anthracite, and lignite-increase to 30 Mt (33 million st). This was up from 25.4 Mt (28 million st) in 1987 Contributing to this overall rise were 1.8-Mt (2-million st) increase in shipments to Canada and a 2.7-Mt (3-million st) increase to Europe. Unaffected by the somewhat tighter world coal market, US coal imports showed a slight increase to 1.8 Mt (million st) in 1988. Colombia continue to be the leading exporter to the United States, followed by Canada and Venezuela. Venezuela's entry into the US market is a relatively recent one, having made its first significant shipment in the fourth quarter of 1987.

Jan 1, 1989

By M. L. Mellish

In 1989, for the third consecutive year, both the production and consumption of coal in the United States reached record levels. Domestic coal consumption totaled 806.5 Mt (889 million st) in 1989, a 5.4 Mt (6 million st) increase from the year before (Table 1). US coal exporters also had a banner year. For the first time since 1982, exports ex¬ceeded 91 Mt (100 million st). US coal production in 1989 rose by a surprising 27.3 Mt (30 million st), reaching 889 Mt (980 million st) for the year. To a certain extent, the sizable difference between production and demand growth was due to smaller consumer stock withdrawals. Coal consumers withdrew only 12.7 Mt (14 million st) of coal from their stocks in 1989, com¬pared to 22.7 Mt (25 million st) in 1988. Despite strengthening coal consumption, exports, and production, coal prices to all domestic sectors declined slightly during the year. That essentially continued the trend of the past several years. On the labor front, the United Mine Workers of America struck the Pittston Coal Group in 1989. It was a bitter work stoppage that was not settled until February of 1990. This was the first major coal strike since 1985. The strike also precipitated a series of wildcat outages by UMWA members in June and July. At their peak, more than 40,000 UMWA members participated in the wildcat strikes. Except at Pittston, however, most miners were back to work by August. It is estimated that perhaps 4.5 to 9.1 Mt (5 to 10 million st) of coal production was lost due to the Pittston and associated wildcat strikes. However, some of this production may have been recouped by other coal companies not affected by the wildcat strikes, and by the affected companies after the strikes ended.

Jan 1, 1990

By M. M. Williams

WESTERN CAN ADA'S coal industry has experienced a serious set-back since 1949, following a pattern well known to its counterpart in the United States. The loss in coal markets in Western Canada has been particularly severe as the discovery of large reserves of oil and natural gas and the subsequent construction of re-fineries and pipelines roughly coincided with the dieselization of both main railways. While the coal industry will have to face a further decline in markets of long standing, others with a large growth potential can be se-cured if present marketing methods are changed where needed and if fundamental and applied research programmes are actively pursued. The energy and chemical potential of Western Canada's coals will eventually find their place in the ever-growing needs of industry and electric power producers. Electric power generation would appear to offer the largest and most immediate market for coal. If the coal industry is to serve this market adequately and gain as much of it as possible, coal operators ? must have a good knowledge of certain characteristics -of the electric utility industry and its fuel requirements. This paper is prepared primarily to set out some of these characteristics, but also discusses other probable markets for coal.

Jan 1, 1958

By John J. Laffin

"Nova Scotia Department of Mines and Energy Throughout the history of Nova Scotia, trends in the production and use of its coal resources have resulted in major impacts on the economy and society of the province. Current trends in coal demand locally, nationally and internationally are having and will have an increasing positive effect on Nova Scotia over the next twenty years-in terms of energy supply, job creation and general economic development. Coal for electrical generation is an immediate and key objective of Nova Scotia's energy plan; and, in the long term, coal-derived fuels will meet the province's needs for transportation fuels. Demand for metallurgical coal is also expected to increase, especially if the merchant coke plant currently under investigation becomes a reality.Meeting these coal supply and utilization objectives in the face of increasing environmental, social and economic constraints poses a tremendous technical challenge. Work has begun on projects to expand coal production capacity and to adapt new technologies for coal preparation and utilization to the specific needs of Nova Scotia; much more work will be required in the coming decade in order to succesfully tap this resource.IntroductionThe energy problem facing Atlantic Canada has a few unique features not found in the rest of the country. Canada, as a whole, has access to a diverse mix of energy resources, including crude oil, natural gas, coal, hydro and uranium, with the result that crude oil supplies only about 40 per cent of Canada's primary demand. In contrast, foreign crude oil dominates Atlantic Canada's energy mix, supplying over 70 per cent of the primary energy demand.This results in important differences in various sectors. Nationally, about 5 per cent of the electricity is generated from oil whereas last year in Nova Scotia approximately 40 per cent of the electricity generated was from imported oil. Residential, commercial and industrial space heating, and industrial process heating in Atlantic Canada was almost 100 percent dependent on foreign oil. This is in sharp contrast to the situation in central and western Canada, which have access to secure domestic natural gas, oil and hydro electricity."

Jan 1, 1982