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By Enguang Zhu, Kangning Zhang, Yang Li

"Due to the use of outdated mining technology or room and pillar mining process in small coal mines, the coal recovery ratio is only 10% - 25%. In many regions of China: the damage area caused by the small coal mines amounted to nearly one hundred square kilometers. Therefore, special mining techniques must be taken to reclaim the wasted resource in disturbed coal areas. This paper focuses on the different mining methods by analyzing the longwall panel layout and abandoned gateroad (AG) distribution in in the abandoned area of Cui Jiazhai Coal Mine in northwestern China. On the basis of three-dimensional geological model, FLAC- 3D numerical simulation was employed. The abutment pressure distribution was simulated when the panel face passed through the disturbed areas. The proper angle of the inclined face was analyzed when the panel face passed through the abandoned gateroads. The results show that the head end of the face should be 13-20m ahead of the tail end. The pillars on both sides of abandoned gateroads had not been damaged at the same time, and no large-area stress concentration occurred above the main roof. Therefore, the coal reserves of disturbed areas can be successfully recovered by using underground longwall mining. INTRODUCTIONDuring the 70-90's, there were a lot of small coal mines in China. Due to their disordered mining, most of the small coal mines left a great many abandoned gateroads (defined as AG in this paper) and a large area of damage coal seam. In these type of coalfields, there exist many mining risk issues, including nonuniform stress in the overburden, flooding and hazardous gases accumulated in the gob. So how to lay out a longwall panel and successfully mining under this type of abandoned small mines is a big issue nowadays in China.As mentioned above, longwall panel is being performed in the damaged coal seams in order to increase recovery of coal reserves (Wang, 2009). However, the abandoned geteroads intersect to each other all around the area. So a series of production issues arose while the panel face is passing through these AG. Gang and Gong (2015) analyzed the roof stability and abutment pressure distribution during the face was passing those AG that were parallel and inclined to the faceline. Xie, et al. (2015) proposed the ground control mechanism by passing the AG in top-coal caving longwall mining. He recommended to stop the face advance until the roof is over, using high strength bolts and cable bolts, and grouting consolidation. This paper studies the different mining methods by analyzing the longwall panel layout and AG distribution in damage coal seams. Theoretical analysis and field observation were conducted to determine the overburden movement when the face was advancing under the AG. The pillar between face and parallel AG changes from elastic to plastic and eventually to the residual supporting status. All these three status was combined with the roof structure to establish the theoretical model to calculate the shield support capacity. Numerical modeling was employed to simulate the pillar stability and determine the abutment pressure distribution as the face inclined to the AG during longwall mining."

Jan 1, 2016

By Mike Muchard

Augered cast-in-place piles are one of the most cost effective deep foundation options available to designers but have been largely underutilized due to skepticism associated with quality assurance and hence capacity. When installed correctly, unit friction values can rival any other competing foundation system. To this end, many means have been implemented to increase confidence in the competence of the foundation. One such method is load testing via the Statnamic test method. This paper presents an overview of the Statnamic test method, advantages and disadvantages of its use, and several case studies where Statnamic testing of augered cast-in-place piles confirmed quality construction, brought about design changes, or proof tested problematic installations.

Jan 1, 2000

By P. T. Bissert, L. Yan, M. D. Klein

"Federal regulations require the installation of refuge alternatives (RAs) in underground coal mines. Mobile RAs have a limited ability to dissipate heat, and heat buildup can lead to a life-threatening condition as the RA internal air temperature and relative humidity increase. The National Institute for Occupational Safety and Health Office of Mine Safety and Health Research performed heat testing on a 10-person tent-type training RA and contracted ThermoAnalytics, Inc. to develop a validated thermal simulation model (TSM) of the tested RA. The TSM was used to examine the effects of the constant mine strata temperature assumption, initial mine air temperature (MAT), initial mine strata surface temperature (MSST), initial mine strata temperature at depth (MSTD), and mine strata thermal behavior on RA internal air temperature using 117 W of sensible heat input per simulated miner. For the studied RA, when the mine strata temperature was treated as a constant, the final predicted RA internal air temperature was 12.8°F lower than it was when the mine strata thermal behavior was included in the model. A 10°F increase in the initial MSST resulted in a 7.1°F increase in the final RA internal air temperature, whereas a 10°F increase in the initial MSTD yielded a 2.5°F increase in the final RA internal air temperature. INTRODUCTION Since 2008, the Mine Safety and Health Administration (MSHA) has required the installation of refuge alternatives (RAs) in underground coal mines (1). MSHA requires that RAs provide an environment with breathable air for entrapped miners for a 96-hour period. Heat buildup inside an occupied RA is a serious concern. Without a means to dissipate the heat and humidity generated by the occupants and the carbon dioxide scrubbing system, the temperature and humidity inside RAs could lead to severe discomfort or heat stress depending on the mine ambient temperature before and during occupation of the RA. NIOSH recommended an apparent temperature limit of 95°F in its 2007 report to Congress (2). In 30 CFR 7.504, MSHA has specified a maximum apparent temperature of 95°F inside an occupied RA (3). The apparent temperature is calculated using both air temperature and relative humidity (4). Calculations could be used to determine if the air within an occupied RA will reach the apparent temperature limit. In these calculations, in order to simplify the problem, the mine temperature could be assumed to remain constant. With this assumption, the effects of the mine strata thermal mass and thermal conductivity on the heat buildup in an RA are ignored. OMSHR research has shown that the mine air and strata temperatures surrounding an RA increase when subjected to the heat of an occupied RA (5). Thus, calculations performed with the assumption that the mine temperature is constant would under-predict the resulting dry-bulb temperature and apparent temperature for a given RA occupancy. The mine air temperature has been used as the basis for RA temperature calculations. However, research has not been used to confirm that the mine air temperature is the appropriate basis."

Jan 1, 2016

By G. W. Jones

During the course of an investigation by the Bureau of Mines into the causes, behavior, and control of anthracite-mine fires, it was observed that the carbon monoxide disappeared from a sealed fire area much more rapidly than could be explained on the basis of leakage of gases. Two suggestions were offered for this high rate of disappearance: (1) That the carbon monoxide, was oxidized at temperatures below 150° C. by either the anthracite or its ash (tests on many anthracites have shown that at temperatures above 150° C. carbon monoxide is liberated in the oxidation products when air is passed through it); (2) that the carbon monoxide was oxidized by micro-organisms present in the sealed area.

Jan 1, 1939

By F. F. Aplan, J. A. Gutierrez-Rodriguez

"Contact-angle and flotation techniques were used to evaluate the influence of oxygen - both that inherent in the coal and that introduced by ambient temperature, aqueous oxidation - on a wide range of coal ranks. Oxidation was found to decrease the hydrophobicity and floatability of coal; with the effect being minor for coals of high rank but becoming increasingly important as the rank of coal is reduced. As an approximation, oxidation makes a coal behave as if it were one of lower rank. Frother only flotation' of coal· correlates with the captive-bubble contact angle whereas when oil is used as a collector, the flotation appears to follow the pattern shown by the water sessile drop on a fresh, un-reagentized coal surface. Coal recovery lost through oxidation may often be recovered by use of a variety of collectors, of which No. 2 foe! oil is among the best of those reagents tested. A simple alkali-extraction test may be used to estimate the influence of oxidation on coal preparation processes and use.INTRODUCTIONThe hydrophobicity of coal is not only a function of its rank but also of the extent of oxidation of the coal during and subsequent to its formation. Weathering and oxidation processes may proceed in-situ for coal deposits that outcrop near the earth's surface, or the oxidation of the coal particles may occur during mining, stockpiling or processing. Such oxidation, whether it affects the bulk-coal sample or on1y a thin outer layer on the coal surface, can dramatically influence the wettability of the particle and hence such processes as flotation, filtration, flocculation and dispersion.Many of the studies made on the oxidation of coals ·were designed to study its effect on flotation, coking or pyrolysis. The. present study 'is directed exclusively toward the effect of oxidation on the hydrophobicity and floatability of the coal. One of the first studies of the effect of oxidation on coal flotation was that of Sun [l] who found that as oxidation proceeds, coal becomes progressively more hydrophilic. Low-temperature oxidation (100-150°C for 250 h) generally lowered the coal floatability with an oily collector only slightly, but more extensive oxidation (200- 3500 C for 250 h) reduced coal floatability seriously. Sun also found that cationic amines were effective collectors for the oxidized coal which infers that oxidation makes the coal more negative in solution. He attributed the loss of floatability to be due to the accumulation of water-insoluble oxidation products at the coal surface. Gayle et al. [2] found that oxidation adversely affected coal flotation when an aliphatic-alcohol frother was used, though a small amount of oxidation appeared to improve the floatability of some coals using a kerosene-pine oil, collector-frother mixture in pilot-plant testing. Prolonged oxidation adversely affected the flotation recovery of the coals tested, the effect being more pronounced when an alcoholic-type frother only was used. They also noted that the reduction in floatability of lower rank bituminous coals was more affected by oxidation than was that of higher rank bituminous coals."

Jan 1, 1989

By G. W. Jones

During the course of an investigation by the Bureau of Mines into the causes, behavior, end control of anthracite-line fires, it was observed that the carbon monoxide disappeared from a scaled fire area much more rapidly than could be explained oil the basis of leakage of gases. Two suggestions were offered for this high rate of disappearance; (1) That the carbon monoxide was oxidized at temperatures below 150° C, by either the anthracite or its ash (tests on many anthracites have shown that at temperatures above 150° C carbon monoxide is liberated in the oxidation products when air is passed through it); (2) that the carbon monoxide was oxidized by micro-organisms present in the sealed area.

Jan 1, 1939

By Francis X. Cannaday

Equipment and techniques were developed with Bureau of Mines facilities for measurement in the laboratory of sonic shear wave velocity in variously shaped rock specimens in a wide range of sizes. A variety of rock types was tested. The shear wave front is produced by electronically excited, piezo-electric ceramic) disk-shaped transducers. Transmitter and receiver are interchangeable. Special equipment components were Bureau produced; other components were commercially available. The equipment permits quick measurement of shear wave velocity on variously shaped specimens with a minimum of specimen preparation. The technique, under favorable conditions, allows for determination of the moment of arrival of the shear wave when it is superimposed on a weak longitudinal wave.

Jan 1, 1968

"Tell us how you got involved in mining?I was first exposed to mining at a young age, as a consequence of my dad and his passion for the industry and rock collecting. Even though he graduated with a degree in mining engineering from Washington State University, my dad spent most of his career working as a structural engineer for the Boeing Company. At the time, Boeing supported a range of employee activities and clubs, including one devoted to mineral prospecting, small-scale dredging and rock hounding. My dad was extremely active in the Prospectors Club, where as a family, we spent a good part of my youth tramping around the Pacific Northwest digging for mineral specimens and panning for gemstones and gold. On my mother’s side of the family, I had relatives that mined in Dawson City and Fairbanks, AK which left a family legacy of sorts. I loved the stories that my dad and a close buddy of his, who was a geologist, would tell about various operations and towns, as well as the wild times at the annual Northwest Mining Association (NWMA) meeting in Spokane, WA. My first recollection of ever being at a commercial operation was during a tour of the Bunker Hill Mine with my dad when I was 7 or 8 years old; this had to have been shortly before the May 1972 fire at Sunshine. That visit of the mine and processing facilities made a permanent impression on me. While I always knew there was something special about the Silver Valley, I began to understand why. To this day, I still get the same feeling when I visit historic mining districts like Leadville, Morenci, Virginia City, Butte, Silverton and Barkerville. During our summer excursions to Helena, MT to dig sapphires, we would usually make visits to Butte and watch mine operations inside the Berkley Pit and surface activities at the Kelly and Mountain Con. In high school, I did well in math and science and began entertaining thoughts of pursuing a degree in engineering. Above all, I wanted to go to a college in the West that had a good academic reputation, where I could also play football. As a 6-ft, 190-lb nose guard, my options for a Division I scholarship were pretty slim, and there weren’t that many technical schools in the Northwest that were Division II that offered athletic scholarships. As fate would have it, I was unexpectedly contacted by Marv Kay, a legendary coach at the Colorado School of Mines (CSM), and was recruited to play ball. Fortunately, I had a couple of high school friends who were already attending CSM, and I had just secured a summer internship with Asamera Minerals in Wenatchee, WA. It was as if all the stars had aligned, and, with the support of my parents, I made the decision to attend Mines. Despite the stress of getting through CSM during a period when the mining industry was in freefall, it was a great decision to attend Mines, and I’m thankful for all the opportunities, friendships, and faculty mentoring I received as a student"

Mar 1, 2019

By Donald J. Ninteman

This Bureau of Mines publication is a literature study of the problem of spontaneous oxidation and combustion of sulfides in underground mines. It summarizes the present-day hazards, process mechanisms, and prevention and control techniques of this growing problem in underground mines. The iron sulfides generally have the greatest tendency to oxidize, particularly pyrrhotite. The presence of moisture and oxygen is essential for the oxidation reaction. Highly fractured sulfides, when found with timber or combustible refuse in slowly circulating air, pose the most serious fire hazard. Quenching with water is effective in quickly dealing with local hot spots, but ventilation at high flaw rates is the most effective and economical means for long-term prevention and control.

Jan 1, 1978

By S. J. Anderson

To deftne the capabilities of a nonexplosive excavation concept, the Bureau of Mines conducted reduced-scale laboratory tests of a mechanical excavation tool called a rock splitter. The splitter investigated was capable of applying combinations of radial and axial loads to rock when placed in a predrilled hole. Experiments conducted with the tool in concrete, limestone, and granite proved it capable of excavating all three materials. Break geometry in these three materials was the same, which encourages the prediction of performance in all rocks. The design of the radial-axial loading splitter's feather components significantly affected the tool's performance. It appears the design of this in-hole component should be tailored for the rock to be excavated.

Jan 1, 1987

By Walter D. Holland

This is one of a series of instruction guides developed to help instructors present health and safety training courses to workers in the metal and nonmetal mining industry. This course is intended for training those, usually the safety officers, who perform surveys for inhalation contaminants in above ground work areas. The handbook entitled ?Handbook for Surveys of Inhalation Contaminants in Above Ground Metal and Nonmetal Mining and Processing Work Areas? is used as a manual for the course and as a prime reference when performing the actual surveys or interpreting the sampling results. There are six experiments for the students to perform during the course to familiarize them with the sampling devices routinely used during the surveys.

Jan 1, 2011

By F. S. Kendorski

This report presents the results of a search for viable-self-drilling roof bolt concepts, detailed development, design, and manufacture of such bolts that drill their own holes, and testing in the laboratory and in the field in two different coal mines of three self-drilling roof bolts. Three new types of bolts were designed and tested, which drill their own holes and then anchor in continuous operation. These were a spring-actuated mechanical expansion shell, a slot and wedge, and a self-contained resin anchor bolt. Such bolts when fully developed for mine use would allow safer and remote installation of ground support and increase productivity. Recommendations are given for further work to improve drilling and anchorage performance.

Jan 1, 1979

By V. F. Parry, E. O. Wagner

This paper summarizes investigations during 1949 on three pilot plants for drying low-rank fine coal by entrapment in hot gases. Detailed operating results on processing seven coals having moisture ranging from 24 to 62 pet, formulas and data for calculating performance of large units, and general conclusions on the problem of drying fine coal are presented. THIS paper presents a summary of investigations by the Coal Branch of the Bureau of Mines during 1949 on the removal of internal moisture from low-rank coals by processing them in the entrained and fluidized state. A paper on this subject, giving a summary of the early work, was presented at the 1949 AIME annual meeting1 and gave a the- oretical discussion of the time and heat required to dry various sizes of low-rank coal. The investigations on two pilot plants were presented in the foregoing paper. During 1949, three additional pilot plants were built to study phases of the drying problem and to investigate different techniques of handling fine coal in the entrained and fluidized state. The present paper gives operating data on the new units and presents detailed data on the drying of seven coals having bed moisture ranging from 62 to 24 pct. The problem of removing surface moisture from fine coal is principally one of heat exchange and dispersion of the coal particles so that heat can reach the liquid moisture to permit evaporation, and it does not involve the factors of size and time of contact to any great extent. If enough heat can reach the surface of the particles at temperatures higher than 250°F, moisture evaporates almost instantly, and the factors of time and size are of secondary importance compared with the factors of heat balance and dispersion of the coal. Therefore, it does not appear to be necessary to employ a fluidized bed when removing surface moisture, and the most efficient process would be one in which the coal particles are entrained in a hot gas stream of optimum temperature traveling at a velocity that causes the particles to disperse into a low-density phase. When low-rank coals are dried, the fluidized bed is necessary to provide control of time of contact. This is done by adjusting the superficial velocity which controls the density or dispersion of the particles. The density of beds having fluidized properties suitable for drying low-rank coals appears to range from about 5 up to about 15 lb per cu ft. When the density is below 5 lb per cu ft, which represents a low-density phase, optimum conditions for removal of surface moisture should be found, and this requires superficial velocities of about 15 fps. The problem of removing bed moisture from low-rank coals involves consideration of size of coal, temperature, mass flow, heat balance, pressure, time of contact, and method of dispersing the coal in the heating mediums. The experimental work presented here gives data on these factors. Coal sizes up to 1/2 in. x 0 were dried with hot gases having initial temperatures ranging from 1900° to 2400°F. Coal

Jan 1, 1951

By E. A. Has, E. Mcl. Tittmann

Double roasting of sinter carrying a high percentage of lead concentrates, gave rise to the problem of removing the sheets of metallic lead formed in the wind boxes. The solution of the problem has been found in the water sealed wind boxes. The metallic lead is granulated and can be removed without seriously interfering with the operation of the machine and eliminates necessity of men going in wind boxes with air guns. THE practice of double sintering the charge for lead blast furnaces, which is now standard throughout the lead smelting industry, has introduced the rather difficult problem of cleaning the wind boxes on sintering machines used for the final pass. Two factors have more recently accentuated this problem: (1) the growing demand of workmen for better working conditions and less arduous labor, and (2) the growing dearth of crude lead ores and the improved grade of lead concentrates demand a charge carrying the maximum percentage of lead. One to 2 pct of such high lead charges (30 to 40) when processed on machines in reasonably good condition will pass through the grates and report in the wind boxes. One-half to three-quarters of this material will be metallic lead reduced by the coke breeze or other fuel mixed with the charge. This lead forms large cakes or chunks which are hard to remove and which substantially increase the time the machine is out of operation for cleaning the wind boxes. A high lead fall can reduce the operating time 30 pct. As a specific example, a 30 ft machine having 63 in. pallets, and equipped with three conventional wind boxes, requires 3 to 4 hr per day for removing the accumulation in the wind boxes when operated as a final pass machine. This same machine when operated on raw charge requires less than an hour per day for cleaning. To eliminate formation of large chunks of lead in the wind boxes of the final pass machines and time lost in cleaning the boxes, R. C. Rutherford of the Chihuahua smelter of the American Smelting and Refining Co., devised and patented* a wind box having a water bath to granulate the lead as it falls from the grate bars. Later, C. H. Harris of the San Luis plant made and patentedt an improvement on Rutherford's device in which the water bath seals the wind box in a manner permitting the latter to be readily cleaned without destroying the vacuum. The first machine to our knowledge to use the water bath box was at the Chihuahua plant along the lines of the Rutherford patent. In 1942, a machine was placed in operation at the El Paso plant which incorporated the features of both Rutherford and Harris. This machine is 40 ft long equipped with pallets 63 x 24 in., and having 4 wind boxes 10 ft 4 in. x 7 ft 2 in. x 51 ft 3 in. in size (fig. 1). The air from the fourth box is returned to the first three, and the gas from the first three discharged to a baghouse. The machine has conventional drive, discharge hopper,

Jan 1, 1951

By J. Allen Hennessy

INTRODUCTION The increasing price of gold and silver over the past 10 years has caused increasing activity in the exploration, evaluation and development of precious metals projects. Many of these deposits are relatively low grade and short lived which makes them economically sensitive to the major project variables such as metal price, capital cost, operating cost and of course, tonnage and grade. These deposits often have a high variability (a coefficient of variation -- o/u -- of 2 to 5) and an intermixing of ore and waste, making ac- curate ore reserve estimation difficult, especially when using traditional estimation techniques. Often, the estimation errors are not the 10-20% that we see in base metal deposits, but the errors in grade and tonnage can be as high as 50%, which can obviously have a very substantial impact on project Recent developments in geostatistics when coupled with a sound geologic under- standing of the deposit can significantly improve reserve estimates of these variable precious metals deposits. Examples will be given of actual deposits where the traditional estimates were significantly different from the mining reality. An attempt will be made to explain the applicable geostatistical tools with a minimum of geostatistical jargon and without complicated formulas. The key to improving the reserve estimates is a clear understanding of the deposit geology and especially the structural controls, the use of local estimation techniques that recognize the intermixing of ore and waste and the effect of selective mining on recoverable reserves, and the use of a global reserve estimation technique to check the results of local estimation. Geologic Controls The vast majority of gold and silver deposits being mined or developed in the western United States would be classified as epithermal deposits. These are formed by hydrothermal fluids (hot water) flowing upward through the rocks and depositing the precious metals as the fluids cool or reach areas of lower pressure or favorable chemical sites. These environments are similar to present day hot springs-type environments with some deposits being clearly associated with surface hot springs such as the Homestake McLaughlin deposit in northern California. These hydrothermal deposits can occur in sedimentary rocks resulting in deposits such as those of the Carlin district or the Jerritt Canyon deposit or the hydrothermal systems can occur in volcanic rocks forming deposits such as Round Mountain, Manhattan or Paradise Peak. The mechanisms of formation were similar in either case with the solution flow controlled by geologic structure and precious metals deposited when the conditions of temperataure, pressure and chemical environment were favorable. The gold and silver hearing solutions travel through permeable faults and fracture systems depositing the metals along these channels. The grades are often highest in the central parts of these conduits (veins) with lower grades in the surrounding rocks. An understanding of the nature, distribution and orientation of these plumbing systems is important to a realistic reserve estimate. The point to be emphasized here is that, good, sound geology in the form of geologic mapping, logging of rotary chip samples and a few carefully logged core holes can signifi- cantly improve an ore reserve estimate.

Jan 1, 1987

By E. O. Wagner, V. F. Parry

This paper summarizes investigations during 1949 on three pilot plants for drying low-rank fine coal by entrapment in hot gases. Detailed operating results on processing seven coals having moisture ranging from 24 to 62 pet, formulas and data for calculating performance of large units, and general conclusions on the problem of drying fine coal are presented. THIS paper presents a summary of investigations by the Coal Branch of the Bureau of Mines during 1949 on the removal of internal moisture from low-rank coals by processing them in the entrained and fluidized state. A paper on this subject, giving a summary of the early work, was presented at the 1949 AIME annual meeting1 and gave a the- oretical discussion of the time and heat required to dry various sizes of low-rank coal. The investigations on two pilot plants were presented in the foregoing paper. During 1949, three additional pilot plants were built to study phases of the drying problem and to investigate different techniques of handling fine coal in the entrained and fluidized state. The present paper gives operating data on the new units and presents detailed data on the drying of seven coals having bed moisture ranging from 62 to 24 pct. The problem of removing surface moisture from fine coal is principally one of heat exchange and dispersion of the coal particles so that heat can reach the liquid moisture to permit evaporation, and it does not involve the factors of size and time of contact to any great extent. If enough heat can reach the surface of the particles at temperatures higher than 250°F, moisture evaporates almost instantly, and the factors of time and size are of secondary importance compared with the factors of heat balance and dispersion of the coal. Therefore, it does not appear to be necessary to employ a fluidized bed when removing surface moisture, and the most efficient process would be one in which the coal particles are entrained in a hot gas stream of optimum temperature traveling at a velocity that causes the particles to disperse into a low-density phase. When low-rank coals are dried, the fluidized bed is necessary to provide control of time of contact. This is done by adjusting the superficial velocity which controls the density or dispersion of the particles. The density of beds having fluidized properties suitable for drying low-rank coals appears to range from about 5 up to about 15 lb per cu ft. When the density is below 5 lb per cu ft, which represents a low-density phase, optimum conditions for removal of surface moisture should be found, and this requires superficial velocities of about 15 fps. The problem of removing bed moisture from low-rank coals involves consideration of size of coal, temperature, mass flow, heat balance, pressure, time of contact, and method of dispersing the coal in the heating mediums. The experimental work presented here gives data on these factors. Coal sizes up to 1/2 in. x 0 were dried with hot gases having initial temperatures ranging from 1900° to 2400°F. Coal

Jan 1, 1951

By L. A. SCHOLL, J. K. CLEMENT

Among the problems investigated by the Bureau of Mines the coal- dust problem has received much attention. Several of the bureau's publications deal specifically with the subject. Bulletin 20° contains an account of preliminary experiments of the bureau to determine the explosibility of coal dusts as well as a review of pertinent literature. Bulletin 50 is a report of a laboratory study of the inflammability of coal dust. The first series of coal-dust explosion tests in the bureau's experimental mine at Bruceton, Pa., is described in Bulletin 56, and Technical Paper 56 presents notes on the prevention of dust and gas explosions in coal mines, and Technical Paper 84 discusses the causes of such explosions and describes methods and apparatus devised by engineers of the bureau for preventing and checking them. The present paper is a report of a detailed study of the bituminous dusts of Illinois mines, and is a part of the investigations conducted by the bureau in cooperation with the Illinois State Geological Survey and the department of mining engineering of the University of Illinois./ It is well known that bituminous coals like those found in Illinois yield dusts that may give rise to explosions of great violence. In order that proper methods might be devised for preventing dust explosions in Illinois mines it was considered desirable to obtain accu- rate information on the quantity and character of these dusts. Ex- periments and tests of dust explosions in an experimental mine as well as in a large steel gallery comparable in area of cross section to mine entries have been made by the Bureau of Mines. Similar experi- ments have been made in Austria, England, France, and Germany. Experiments under conditions similar to those of actual mining prac- tice are obviously more conclusive than tests made in a laboratory. On account, however, of the expense, time, and quantity of dust re- quired, it is not practicable to conduct large-scale tests in studying a large number of dusts and recourse must be had to laboratory apparatus and methods. Laboratory,devices for the study of coal-dust explosions have been devised by a number of investigators. Most of these were intended for qualitative tests only. Quantitative methods have been devised by investigators of the English and French mining-experiment stations." In the experiments described in this report, laboratory tests of inflam- mability were made with an apparatus devised by Dr. J. C. W. Frazer, formerly a chemist of the Bureau of Mines. Laboratory tests of inflammability have been made on more than 500 samples of dust from 100 representative Illinois mines. As a result of these tests it may be stated that: 1. The coals of Illinois when ground fine enough yield highly inflam- mable dusts which when suspended in air may give rise to violent explosions. 2. In the majority of the mines of the State the dusts adhering to the ribs are inflammable. In about one-fourth of the mines the quantity of rib dusts present in the entries is sufficient to form an explosive mixture with air. 3. Most of the road dusts are inflammable when ground to a suffi- cient degree of fineness.

Jan 1, 1916

By John T. Galey

Production of crude oil for 1940 in southwestern Pennsylvania was off nearly 70,000 bbl., largely as a result of the great number oi abandonments, together with the lack of extension of the Washington and Green County pools. Oil wells completed numbered 51, which is 26 more than last year, but the total initial production of 259 bbl. is only 18 bbl. greater than in 1939. There was an increase of 72 over last year for a total of 209f gas wells. However, 68 7 dry holes were drilled, which is 40 more than a year ago. Thus, 328f wells were drilled during the year, and rigs are erected or drilling is progressing on 59 t more. Shallow Development Oil.—Butler County led in number of oil wells completed, with a total of 27 for an initial production of only 69 bbl. Washington County, with 12 new oil wells, one of which made 40 bbl. from the Fifth sand in S. Franklin township, has 95 bbl., while in Allegheny County 9 wells gave an initial of 86 bbl. for the highest Per well average in the area. This initial was given a considerable boost by one 35-bbl and another 2;-bbl. well in West Deer township, where the Fourth sand produced at 1840 feet. Greene County had only one oil well completed during 1940, and Washington County had 12. The subnormal totals for these counties may be explained by the higher cost of completions and the declining price of crude. The first price change in crude during the year occurred on May 22, when a 25 cut was made. A second 25 cut was made July 12, and was followed by a 156 cut on .Aug. 28. This price held until Nov. 12, when there was a restoration of 156. On Dec. 17 a second 156 increase was put into effect, bringing the price to $I.So per barrel. Gas The large increase in the number of gas wells completed may be attributed to three factors; namely, the recently discovered production possibilities of moderately deep, hitherto little tested horizons, together with increased demand and price. The latter has been made possible by a recent decision of the court, which ruled restraining the public service Commision's prohibition of a raise in the minimum monthly charge to small consumers by one of the major gas companies. A portion of the revenue derived in this manner is being passed along to the producer in the form of higher prices in the field. This higher field rate will remain in effect until a new ruling is made, when it will be reduced in proportion to the reduction of the monthly minimum charge. In an effort to extend the chambers Dam Fifth sand oil pool southwest from Amwell township, Washington County, several wells have been drilled. One of these, in Morris township, washington County, had an initial of 3.2 million cu. ft. open flow from the Big Injun sand. This indicates an entirely new productive area for the latter horizon. Allegheny County had one spectacular well in South Fayette township-—at a depth of about 2500 ft. a 4-million-CU. ft.

Jan 1, 1941

By Orville R. Lyons, A. C. Richardson

THE Coal Division of Battelle Memorial Institute, during the course of an investigation conducted for a coal producer, carried out extensive sampling of the fine-coal section of a preparation plant. The information obtained during the testing period was used to evaluate the overall plant operation and provided the basis for. recommended changes in the plant flowsheet. Included in the information were data for the results obtained when using a Bird centrifuge to dewater the particular coal being treated. At the completion of the investigation, the coal producer gave Battelle permission to publish the operating data for the Bird centrifuge in order to make this information available to the coal industry. The authors wish to take this opportunity to express their appreciation to this company and its officials for their willing cooperation in the matter of publication. Description of Preparation Plant: The preparation plant on which the data were obtained is primarily a jig plant. The coal being washed is a low inherent moisture, friable, Pocahontus-type. The washed coal from the jig is dewatered and sized at 1/4 in. by a Parrish-type dewatering and sizing screen. The minus 1/4-in. coal and the underflow water from the shaker screen flow to a sludge tank where, after the coal settles, the coal is conveyed by a flight conveyor into a pump sump. The pump, a 300-gpm sand pump, delivers a mixture of fine coal and water to a Bird centrifuge which produces a dewatered cake and an effluent. At the time when the investigation was made, the centrifuge effluent was returned to the sludge tank and the cake product was mixed with a coarser size of coal prior to loading into railroad cars. The semiclarified water from the sludge tank overflowed into a pump sump from which it was pumped to the jig. As originally designed, the preparation plant was intended to operate with a closed water system but it was found, soon after operations started, that for various reasons this could not be done. In order to provide for removal of excess water from the system and to aid in maintaining the desired minimum percentage of solids in the circulating water, the plant was operated to provide from the sludge tank a continuous overflow of water and fine solids that was sent to waste. The centrifuge feed represents approximately 35 tons per hour of minus 1/4-in. coal in the form of a pulp averaging 38 pct solids. Sampling Procedure: In order to obtain basic data for determining the relationships existing in the fine-coal section of the preparation plant, samples were obtained for: (1) the centrifuge feed, (2) the centrifuge cake, (3) the centrifuge effluent, and (4) the circulating water. The sampling was arranged to start on a Monday, in order to begin operations with a sludge tank full of fresh water, and was continued long enough to allow sufficient time for fine solids to build up within the water system or for a two-day, four-shift operating period. All samples were taken at half-hour intervals except when plant stoppages occurred. After a stoppage the plant was

Jan 1, 1951

By R. Todd Swinderman

Variations in designs between belt cleaner systems are so wide that it is impractical to establish a dimensional stan- dard. The number of variables that affect the efficiency of belt cleaners is too great to assume a required number or style of cleaners for broad classifications of bulk solids or typical applications. The amount of carryback remaining on the belt is more dependent upon the characteristics of the bulk solid and the physical parameters of the conveyor system than it is on tonnage of material conveyed. Therefore, a performance-based standard is proposed. Three levels of cleaning performance are proposed: • Level I cleaning is general specified when concerns about carryback are not critical. Cleaning systems normally associated with achieving a Level I performance are single or double cleaner systems with one-piece blades undergoing poor to average maintenance. Frequent cleaning of the carryback that falls from the return run will likely be required. • Level II cleaning is generally specified when carry- back is of concern but does not create a safety or environmental problem. Cleaning systems normally associated with Level I1 performance are multiple cleaner systems with segmented blades undergoing the manufacturer's specified maintenance. Regular but infrequent cleaning of the carryback that falls from the return run will likely be required. • Level III cleaning is generally specified when con- cerns about carryback are critical. Concerns range from safety to environmental to product contamination. Cleaning systems normally associated with achieving a Level 111 performance are multiple cleaner systems in conjunction with at least one low- volume water spray. Scheduled inspection and the manufacturer's specified maintenance would have to be performed to maintain a high level of cleaning performance. Difficult-to-clean bulk materials may require the use of a washbox system with multiple cleaners using a combination of low-volume eater sprays to lubricate the cleaners and high-volume sprays to keep the washbox and discharge piping freely flowing. Further addition of a water and sludge recycling system reduces the amount of water that ends up in the product to a negligible amount. Very infrequent cleaning of the carryback that falls from the return run will be required. PURPOSE The purpose of this proposal is to propose a standard method for specifying belt cleaner systems based on user expectations and equipment performance over time. DEFINITION In bulk solids handling by conveyor belt, carryback is the material that adheres to the belt after the belt discharges its cargo. PROPOSED STANDARD Required Basic Good Practices There are a number of basic design and operating principles that are good practice for the selection, installation, and maintenance of belt cleaning systems on conveyors in order to achieve "standard belt cleaning performance over time. 1. The Belt Cleaning System shall be designed to meet the performance requirements based on the worst operating conditions and worst bulk solids proper- ties that are expected. 2. Each conveyor discharge point shall be designed to readily accept the manufacturer's recommended minimum number of belt cleaners. In addition, the discharge chute shall be designed to accept, with minor modifications, at least one additional cleaner if it is required.

Jan 1, 2004