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By W. M. Merritts, Charles Findlay, Stephen Krickovic

Methane emission rates were studied in a Pittsburgh coalbed mine in northern West Virginia. A fullface boring-type continuous miner, equipped with a methane monitor, was used in the development of a set of eight main headings, one side of which was near old workings; the other side abutted virgin coal. Two air splits ventilated the section. Air volumes and methane percentages were recorded, and time studies of the miner were made during five consecutive operating days, during which a complete cycle of mining the headings and one line of related breakthroughs was accomplished. Methane emission rates increased significantly as mining progressed from the side near old mine workings toward the virgin area, and generally increased with coal extract ion. Mining in the heading immediately adjacent to virgin coal was interrupted quite frequently, owing to excessive methane concentrations at the face, despite adequate air volumes and acceptable methane concentrations in the immediate return airway.

Aug 1, 1970

By A. Wahab Khair

"Geologic materials emit transient noises when stressed /1/. The rate and pattern of these transient noises or acoustic emissions (A.E. hereafter) depend on the stages of deformation of the material /2/. It has been demonstrated that rock/coal fracture processes under stress consist of three distinctive stages--crack initiation, propagation and ultimate fracture--and that coalescence of numerous cracks leads to ultimate failure rather than the propagation of a single crack /2,3/. This paper presents an analysis of fracture formation in rock/coal specimens subjected to straight wedge indentors using A.E. technique.The effect of specimen geometry, wedge indentor angle, confining pressure, and material anisotropy on fracture type (tension, extension, and shear crack), fracture length, and fracture intensity were studied. Two types of material mainly Berea sandstone and Coal Berg No. 2 coal were used in this study. Prior to the experiment the mechanical properties of both sandstone and coal were determined using rectangular specimen (Figures 1 a) in standard compression tests and are given in Table 1. In this study cylindrical and rectangular specimens were first prepared to proper dimensions of 2 in. x 1.5 in. and 3 in. x 1.5 in. x 1.5 in. (5.08 cm x 3.81 cm and 7.62 cm x 3.81 cm x 3.81 cm), respectively and then instrumented with SR-4 strain gages as shown in Figure 1. The instrumented specimens were then tested under four distinct load boundary conditions as illustrated in Figure 2. During a typical experiment the instrumented specimen was placed in a specially designed loading jig (Figure 3) where a predetermined lateral pressure was applied mechanically to the specimen by adjusting the inner plate of the confining chamber via screw while monitoring strains in the specimen. Using rock/coal elastic constants and measured strains, a predeter¬mined lateral pressure was applied to the specimen. Then a vertical load was applied by the straight edge of a wedge indentor attached to the upper platen of the universal loading machine via ball and socket arrangement (Figure 4). The arrangement allowed uniform application of load in a straight line manner on the surface of the specimen. During the test a number of parameters namely strains, load and A.E. rates were recorded (Figures 5a-b)."

Jun 1, 1988

By Ronald D. Hill, Elmore C. Grim

Some of the terms defined here are not used in the text. However, the terms will be useful to those interested in this and other publications in the field of coal surface mining.

Jan 1, 1974

By D. J. Parker, D. Harrington, L. H. Harrison

The necessity for protection against the hazards of lightning manifests itself from time to time in the mining industry by reason of loss of life, damage to electrical equipment, fires in surface structures at mines, and accidents in the handling and use of explosives. This paper is intended to assemble, correlate, and present some of the salient. points embodied in the available literature on the subject and at the same time give some factual data concerning instances of such loss of, life and damage to property, with special application to the mining industry The annual loss of life and destruction of property by lightning is considerable; the former may be prevented to a limited extent, though use of common sense as to exposure is required and not always followed; the latter can be prevented to a considerable degree. The manufacturers of electrical equipment,, through improved types of lightning arresters,, have done much toward the protection of electrical equipment, with consequent safeguarding of life and of property. Education based on unfortunate experiences has gone far to discourage the handling of explosives and blasting accessories during thunder storms, especially in open pits and quarries, and to a much smaller extent in underground workings. The lowly lightning rod plays an important role in the protection of certain types of buildings (especially isolated buildings), stacks, monuments, and other structures. LIGHTNING PHENOMENA In 1751, Franklin proved that lightning was simply a visible display of electricity - an extended spark; and until a generation ago little had been added to his exposition, to define the various phases of the phenomenon. Matters pertaining to lightning are discussed in the following references:

By Paul Sands

Single- and two-stage tests were made with 6-inch, coal-cleaning hydrocyclones to determine the effect of hydrocyclone geometry, operating conditions, and feed composition on performance. Most of the testing was conducted in an open-circuit pilot plant that had a maximum capacity of about 9 tons per hour. The coals used in the investigation had top sizes of 1/4 inch and 28 mesh. Considerable latitude was found in the range of geometry variables that could be used without affecting performance adversely, although a certain minimum ratio of overflow to underflow openings had to be maintained for best operation. Two-stage cleaning proved distinctly better than operation with a single hydrocyclone, because clean coal lost in the refuse product of the primary unit can be partly recovered in the secondary. There is an unusually great difference in the specific gravities at which the individual sizes of the feed are separated in the hydrocyclone. This militates against high efficiency because maximum yield occurs when all sizes are cleaned at the same specific gravity. The size composition of the feed and, more particularly, the size composition of the impurity have a greater influence on the efficiency attainable in the hydrocyclone than in most other types of fine-coal cleaners.

Jan 1, 1968

By F. Garcia, J. Cervik

The cross-measure borehole technique has been shown by the Bureau of Mines to be an effective method of controlling methane liberated by fracturing the roof strata in longwall gobs where overburden is less than 750 ft (229 m). Boreholes are drilled into roof strata before mining operations affect the roof strata. Longwall mining fractures the roof strata and releases methane from source beds. Surface exhausters or vacuum pumps are used to draw the gas to the surface through an underground pipeline and vertical exhaust hole. The captured methane is thus prevented from entering the mine's ventilation system. About 71 pct of the methane produced by longwall mining in the Lower Kittanning Coalbed was captured by the cross-measure boreholes. Borehole spacing is an important factor affecting the performance of the technique. Interference tests and measurements of methane flows in return air indicate borehole spacing in the Lower Kittanning Coalbed should be limited to about 200 ft (61 m) except on the first 600 ft (183 m) of the longwall, where spacing should be reduced to about 100 ft (30 m) to capture the large quantities of methane released when the first large roof fall occurs. Comparisons between measured and calculated gas pressure differentials on boreholes indicate borehole length can be reduced from 280 to 140 ft (85 to 43 m), which reduces drilling costs significantly. Additional experimentation is necessary to verify the calculations.

Jan 1, 1985

The Bureau of Mines has been active in promoting the purchase of coal for Government use under specifications that define the requirements in terms of heating value of the coal, expressed in British thermal units, and the composition as shown by proximate analyses. To these, when required, are added the ash-softening temperature, the free-swelling index, and the Hardgrove, grindability index. Under most of these specification contracts the bidders guarantee the quality of the coal, and that guaranteed by the successful bidder becomes the standard of his contract. The deliveries are sampled in accordance with instructions 2 issued by the Bureau of Mines; the samples are analyzed in the Bureau laboratory to determine whether the coal is of the quality guaranteed by the contractor; if it is not, a price adjustment is made. Analyses of the delivered coal and tipple samples (samples collected at mine tipples as coal is being loaded into railroad cars or trucks) provide valuable data for use in evaluating future bids. In addition, the continuous sampling of coal as delivered is a check on the practical results obtained in burning the coal.

Jan 1, 1970

By G. A. Brady

Seven samples of Pennsylvania anthracite from the Bottom Ross bed were analyzed and tested to obtain data on cleaning characteristics, proximate and ultimate analyses, specific gravity, grindability, heating value, and ash softening temperature. Ash content of the samples varied irregularly from 9.0 to 34.4 percent, the range being narrowed to an upper limit of 14.8 percent ash by removing impurities dense enough to sink in a medium with a specific gravity of 1.90. Ash content of the sink material with specific gravity greater than 1.90 ranged from 56.4 to 80.4 percent; corresponding specific gravities were 2.095 to 2.534. Volatile matter contents were indicated to be higher for the ash-forming minerals than for the pure coal substance in the various specific gravity fractions of a given sample. Specific gravities of anthracites with compa¬rable ash contents but from different locations in the bed varied as much as 0.06. The grindability index increased significantly with increasing ash con¬tent of specific gravity fractions from all the samples.

Jan 1, 1968

By d&apos, Kathleen J. Amico

THIS summary appears in Minerals Yearbook volumes I and III, which cover mineral production in the United States, its island possessions, the Canal Zone, and the Commonwealth of Puerto Rico, as well as the principal minerals imported into and exported from the United States. The several commodity and area chapters contain further details on production. A summary table comparing world and U.S mineral production also is included.

Jan 1, 1964

By David P. Lindroth

The Bureau of Mines has developed and successfully tested a hangup clearance module for use in clearing hangups in underground mine chutes and ore passes. The Bureau's tests showed that the hangup clearance module can be effectively used to clear mine hangups. Furthermore, it is believed that clearance using this module is quicker, safer, and more efficient than the method currently used. The hangup clearance module uses a ballistic disk explosive charge that can clear hangups located as far as 50 feet (15.2 m) from the position where the charge is detonated. Mine personnel can therefore set up the module and the charge it contains without being exposed to dangerous areas. This report describes the principles of operation of the module, provides data and drawings for its construction, and gives instructions for its setup and use. The report also summarizes the development of the module, briefly discusses preliminary and underground tests, and lists the current and potential applications of the hangup clearance module to underground mining.

Jan 1, 1982

By Isaac A. Zlochower, Kenneth L. Cashdollar

The Pittsburgh Research Laboratory of the National Institute for Occupational Safety and Health conducted a study of the explosibility of various metals and other elemental dusts dispersed in air, with a focus on the experimental explosion temperatures. The data are useful for understanding the basics of dust cloud combustion, as well as for evaluating the explosion hazards in the minerals and metals processing industries. The dusts studied included boron, carbon, magnesium, aluminum, silicon, sulfur, titanium, chromium, iron, nickel, copper, zinc, niobium, molybdenum, tin, hafhium, tantalum, tungsten, and lead. The dusts were chosen to cover a wide range of physical properties - from the more volatile materials such as magnesium, aluminum, sulfur, and zinc to the highly "refractory" (very low volatility) elements such as carbon, niobium, molybdenum, tantalum, and tungsten. These flammability studies were conducted in a 20-L chamber, using strong pyrotechc ignitors. The experimental data obtained included the minimum explosible concentrations, maximum explosion pressures, and maximum explosion temperatures. A unique multiwavelength infrared pyrometer was used to measure the temperatures. For the elemental dusts studied, all ignited and burned as air-dispersed dust clouds except for nickel, copper, molybdenum, and lead. The measured maximum explosion temperatures ranged from -1 550 K for tin and tungsten powders to -2800 K for aluminum, magnesium, and titanium powders. The measured temperatures are compared to the calculated, adiabatic flame temperatures. In general, the dusts whose experimental temperatures were closer to the adiabatic values were those with the finer particle sizes, those that were more easily vaporized, and/or those that were intrinsically more reactive.

By Joseph W. Town

The Bureau of Mines conducted studies related to SO2 air pollution to determine attritioning rates, SO2 sorption rates, and sulfur loads that could be obtained on commercial alkalized alumina sorbent pellets. Fluidized-bed attritioning rates ranged from 0.025 pct/hr for alkalized alumina with a crushing strength of 4 kg to 0.075 pct/hr for 0.5 kg crushing strength mate¬rial. Airlift attritioning rates ranged from 0.50 pct/hr for 3 kg crushing strength alkalized alumina to about 3 pct/hr for 0.5 kg material. Attritioning rates for the commercial alkalized alumina were comparable to those obtained for sorbent pellets prepared in the Bureau of Mines laboratory. Sorption rates were related to S02 concentration in flue gas, temperature, and presence of nitrogen oxides in the gas stream. Sorption rates at 300° C were 0.35 X 10-6 gS/gp/sec (grams sulfur per gram pellet per second) in 0.045 pct so, gas, 5.1 x 10-5 gS/gp/sec in 0.34 pct SO2 gas, and 65 X 10-5 gS/gp/sec in 10 pct SO2 gas. For the 0.34 pct S02 gas, sulfur loads of 0.10 gS/gp (the projected load for regeneration) were obtained in 47 min at 130° C and in 116 min at 300° C. The presence of either NO or NO2 in the 0.34 pet S02 gas increased the SO2 sorption rates 2 to 3 times at 300° C, but had no effect at 130° C.

Jan 1, 1969

By T. R. Jolley

An investigation was begun by the Bureau of Mines in 1948 to determine the preparation characteristics of American coals. Results of the investigation were planned to be reported on a county basis and, from the data developed, to determine: I. Which coals either as mined or after beneficiation by conventional preparation are chemically suitable under present standards for producing metallurgical coke. 2. Which coals require special and more intensive treatment in preparation than is now practiced. 3. Which coals cannot be considered potential sources of metallurgical coke, regardless of preparation by present-day methods. This report is one in the county series that describes the preparation characteristics of the coals of Bell County, Ky.

Jan 1, 1957

By Clarence O. Babcock

This report describes the results of a Bureau of Mines investigation in which an elastic inclusion, orebody, or mining system is replaced for purposes of analysis with an imaginary effective inclusion of rectangular shape that encloses the region. This effective inclusion has averaged physical properties that are directly related to the average inclusion stresses. The results were in excellent agreement with those predicted by Donnell's theory (2)2 for an isotropic elliptical inclusion in a state of plane strain for all height-to-width ratios and for all degrees of inclusion hardness from very soft to very hard. The results are exact for an isotropic circular inclusion and provide an easy method of evaluating the stresses obtained by cylindrical inclusions in boreholes when the Poisson's ratio for both host and inclusion equals 0.25 for plane strain or 0.333 for plane stress. The theory was also used to predict the average stresses in 48 finite-element models of single transversely isotropic inclusions of ovaloid and rectangular shape. An interesting and useful observation from this work was that the forces on elliptical inclusions in the x and y directions, produced by applied uniaxial stresses in the y and x directions, respectively, were equal in magnitude but opposite in sign when the applied stresses were equal. This occurred when the plane strain condition was used with a Poisson's ratio of 0.25. The practical usefulness of the method is given by treating a variety of mining problems: (1) The average stresses in an orebody of irregular shape; (2) the average stresses in single-level room-and-pillar mining systems; (3) the average stresses in multiple-level room-and-pillar mining systems; (4) the effect of mining sequence on the average stresses produced during mining; (5) the stresses in cylindrical borehole plug related to host rock stresses as a function of plug hardness; and (6) methods for simplifying finite-element analysis of complex structures.

Jan 1, 1974

By J. E. Zeilinger

The technical feasibility of using energy from explosive ignitions of coal dust to pump water was .demonstrated in an exploratory investigation. Ignition of small amounts of pulverized coal that were dispersed in air over columns of water pumped up to 5.3 gallons of water per cycle when operated against a head of 30.75 feet. Water displacement was accomplished by either manual or automatic operation through a single cycle, and by automatic operation through a continuous series of cycles of I-minute duration. Operating through single cycles, slurries containing up to 3 pounds of coal and 4.6 gallons of water were also pumped. Possible uses of an efficient coal-fired pump would include pumping water for irrigation purposes, removing water from mines, transporting coal from mines in the form of a slurry, and pumping water to elevated reservoirs at electric powerplants so that it could be used to generate electricity during peak periods of demand.

Jan 1, 1966

By Richard J. Mainiero, Marcia L. Harris

The New York State Department of Transportation recently commenced highway widening and drainage improvement projects in Clarence and Amherst, NY. Drainage improvements including the installation of storm sewer lines required excavation to a depth of 2.5 m (8.2 ft). In September 2002, NYSDOT stopped further blasting when 800 ppm CO was detected in the basement of a house near the blasting site. At the insistence of NYSDOT, the general contractor developed a new blast plan with the assistance of an environmental consultant. The plan provided for the installation of multi-gas monitors in buildings of special concern and/or with basements and residential type CO monitors in all other buildings within 100m (330 ft) of the blast. The multi-gas monitors would be remotely monitored. The plan provided action levels which would ensure public safety. The blast design was also modified to allow for better venting of CO. Blasts were limited to 20 ft lengths. The overburden was to be removed from the rock and blasting mats put in place to prevent flyrock. Approximately twenty feet of trench adjacent to the blast was left open to allow ground movement and gas release. The use of CO monitors was effective to alert occupants of a building to the presence of CO. The most effective appeared to be the residential type CO alarms with digital readouts. They were simple and easy to use and allowed the public to participate in the process. False alarms were repeatedly received with the more sophisticated instrumentation. Residential type CO monitors are preferable to warn people near blast sites. More sophisticated instrumentation should be avoided unless personnel are experienced in its use. A general overview of the blasting and monitoring is presented and discussed. The use and effectiveness of residential type CO monitors and multi-gas monitors are discussed.

By Kelly C. Strebig

Laboratory tests were conducted by the Bureau of Mines to determine the effect of depth of cut and bit type on respirable coal dust generation. Apparatuses were constructed to contain the coal samples, measure the linear cutting forces, and analyze the dust generated. Single-bit tests were conducted in Illinois No. 5 and Pittsburgh seam coals with five bit types at four depths of cut. The results showed that bit type did not significantly influence dust production. On the other hand, deep-cutting bits were more efficient and generated substantially less respirable dust per pound of coal broke than shallow-cutting bits.

Jan 1, 1975

By James P. Ulery, Jon C. Volkwein

The U.S. Bureau of Mines investigated a method of using inert gas to prevent the formation of explosive gas mixtures in auger highwall mining of coal. A combination of gasoline and diesel engine exhaust gases was introduced into the auger drill hole using a short section of pipe located at the collar. Gas samples were taken and analyzed on-site with infrared detectors for oxygen, carbon dioxide, methane, and carbon monoxide. Evacuated bottle samples were also taken and analyzed by gas chromatography in the laboratory. These gas results were analyzed for explosibility. Coal samples from various depths were used to obtain the gas content of the coal using the modified direct method. Personal expo- sure to carbon monoxide was also monitored. The highest methane level observed was 9.55%. The levels of inert gas (carbon dioxide and nitrogen) were sufficiently high to prevent any ignition of the methane. Results showed that for all conditions during mining, gas concentrations were nonexplosive. The gas content of the coal was about 0.30 cm3/g. The maximum personal time-weighted average sample for carbon monoxide was 20 ppm. This system provides a safe, inexpensive, simple method for pre- venting explosions during auger mining.

Jan 1, 1993

By W. N. Marchant

The Bureau of Mines improved removal of selenium from zinc smelter acidic gas scrubber effluent by using zinc dust to precipitate soluble selenium prior to lime neutralization. Lime neutralization alone decreased selenium in the waste water from, typically, 6 parts per million to 2 parts per million, whereas the use of zinc dust precipitant gave an effluent containing less than 0.1 part per million of selenium. The waste treatment operation first was developed on a laboratory scale and later was successfully tested at a smelter site on a 1-gallon-per-minute basis. During the research a simple and rapid means was developed for determining selenium in waste water; the technique enabled visual semiquantitative selenium determinations that later were confirmed quantitatively by X-ray fluorescence.

Jan 1, 1978

By James P. Rider, Jeanne A. Zimmer, Andrew B. Cecala, Robert J. Timko, Earle H. Andrews

Many different types of structures and materials have been used to build mineral processing facilities over the past few decades. Although the structure type and building material were not viewed as significant factors affecting the health of employees in these facilities when they were built, the National Institute for Occupational Safety and Health performed an evaluation to determine to what extent building types could impact respirable dust and noise levels. This report discusses the evaluation of three different types of product sizing silica sand structures: a masonry design, a steel-sided design, and an open structure design. The data obtained in this study indicate that the open structure design (no walls) was superior from both a dust and noise (health) standpoint compared to the other two structures. The open structure design should also be beneficial from a cost standpoint because of lower material and construction costs. Companies and design engineers should consider this open design when building new mineral processing facilities in climates where it could be applicable. Some companies may also want to consider modifying existing structures with a more open design to further reduce dust and noise levels. As the trend continues in lowering allowable dust levels for federal health standards in the U.S. mining industry, the open structure design may be an approach for some companies to consider for their operations.

Jan 11, 2006