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By Martin Hertzberg

The concept of limit burning velocities is being used to formulate a quantitative theory of flammability limits. Competing and complicating processes dissipate power from a combustion wave and quench propagation at some characteristically low limit velocity. Two earlier reports dealt with process (a), natural convection (RI 8127); and with process (b), conductive-convective wall losses (RI 8469). This report considers process (c), radiative losses, and process (d), selective diffusional demixing. The limit burning velocity for radiative losses is [(SU)c ~ e cp] It is normally not a significant process for premixed gas flames; however, for laminar flame propagation in a gravity-free environment, it is the only loss process present. Accordingly, limit velocities at zero gravity should be much lower than on earth, and premixed gases should be flammable over wider composition ranges. For highly emissive dusts, soot, or ash-forming flames, radiative losses are significant even under normal gravity conditions. Selective diffusional demixing is a complication that manifests itself in the form of cellular flame structures and wide gaps in composition between upward and downward propagation limits. It induces a burning velocity shift (?Su)d, causing the flame to behave as though it were richer or leaner than its initial composition, depending on whether the fuel or the oxidizer mole¬cule has the higher diffusivity. A simple pertubation analysis shows that the process generates stable cellular flames whenever [dsu] > 0, where ci is the concentration of the reactant with the higher diffusivity. The same analysis indicates that at the opposite stoichiometry, where [dcu] < 0, laminar structures are stabilized. A simple formula for the diameter of cellular flames is derived, which predicts that dcell should vary inversely with the product of the diffusivity difference Di -DJ, and the burning velocity slope [dc ]. Those predictions are in good agreement with the available data. Buoyancy forces for upward propagation induce flame front curvature, and hence buoyancy and selective diffusion are mutually supportive in upward propagation. Thus large gaps in composition between upward and downward limits are present in those composition domains where cellular flames are stable.

Jan 1, 1981

By K. K. Kershner

Sulfide ore concentrates containing cobalt, nickel, copper, lead, and iron were salt roasted and leached on a laboratory scale. More than 95 percent of the cobalt, nickel, and copper was recovered. Heating patterns for salt roasting different concentrates were established. More cobalt, nickel, and copper were recovered from a bulk concentrate composed of a mixture of copper concentrate and iron concentrate. This mixture corresponded roughly with the mixture of these materials in stockpiles in southeastern Missouri. A temperature range of 375° to 400° C. was best for salt roasting. Metal chlorides were leached at a pH of 1 from chloridized charges of concentrates, Although the amounts of cobalt, nickel, and copper extracted were high, the amount of iron dissolved simultaneously interfered with subsequent separation and recovery of these metals. The amount of dissolved iron was reduced substantially by steam treating chloridized charges of bulk concentrate at 300° C. In this way, the ratios of cobalt, nickel, and copper to iron in leach liquors permitted satisfactory separation and recovery of these metals. INTRODUCTION The Federal Bureau of Mines is experimenting with chloridizing reactions.4 5 6 7/ Salt roasting of sulfide ores and concentrates, or their calcines, to form metal chlorides has certain advantages. Chlorides of

Jan 1, 1961

By Robert J. Willard

This chapter includes tables from 1983 that were not available in time for publication of the 1983 Minerals Yearbook, but does not include corresponding tables for 1984. The value of raw nonfuel minerals produced in the United States during 1984 was estimated at $23.2 billion, an increase of $2.1 billion over the value for 1983. This is the second consecutive year that the value has increased, and except for a decrease in 1982, the value for each year has increased since 1971, or 12 out of 13 years. In 1984, 16 out of 21 metal commodities increased in output while 5 metals decreased; 14 metals increased in value and 7 decreased. Of 46 nonmetal commodities. 37 increased in output while 7 decreased and 2 remained unchanged; 35 nonmetals increased in value and 11 decreased. These statistics are grounds for continuing the cautious economic optimism expressed in 1983. Despite the note of optimism, however, numerous problems plague the mining industry, weakening its stability and inhibiting its growth potential. The problems are a complex mix of international and domestic factors that have been building in the recent past, but have become even more troublesome in 1984.

Jan 1, 1985

By A. Sainato, S. J. Kravits, G. L. Finfinger

This Bureau of Mines report describes and compares the procedures, capital investments, and operating costs of rotary and in-hole motor drilling techniques used to drain methane gas from the Pittsburgh Coal- bed in an underground mine located in southwestern Pennsylvania. A timestudy was conducted during the drilling of each of two boreholes, and the data were collated to serve as a base for comparing drilling procedures and operating costs. Findings indicate that drilling with an in-hole motor offers four advantages over rotary drilling; namely, an increase in drilling productivity, fewer worker-hours required, ease of maintaining vertical and horizontal bit trajectory, and less expensive drilling cost per foot of borehole.

Jan 1, 1985

By E. G. Davis

The flash reduction of fine iron ore in a dilute-phase system was investigated at 500° to 900° C within a heated stainless steel tubular coil. Alabama brown iron ore and Mesabi semitaconite ore were fed into the coil concurrently with reducing gases of hydrogen and reformed natural gas, so that the velocity of the gas at the reaction temperature was sufficient to entrain and pneumatically transport the solids through the coil. Reduction is very rapid with retention time of the ore in the coil varying from 4 to 15 seconds. Variables affecting reduction are temperature, ore feed rate, and gas flow or velocity. Results of the studies show that a partially reduced product (10-to 25-percent reduction) can be made which, on subsequent magnetic concentration, yields a concentrate containing 64 to 70 percent iron with a 90-to 94-percent iron recovery. Maximum reduction of 77 percent was obtained when hydrogen was used in a four-stage reduction test to yield a product containing 61 percent metallic iron.

Jan 1, 1972

By T. E. Purcell

(a) Moisture. - Moisture, "as fired," is specifically significant in pulverized-coal firing because of its effect upon the continuity of raw-coal feed to the pulverizer, pulverizer capacity, flame stability, and speed of ignition. The extraneous moisture content is a rough index of potential difficulties in unloading and maintaining the flow of raw coal to the pulverizer and of pulverized coal to the furnace, with the troubles increasing geometrically as the percentage increases. Sticking or other stoppage of coal flow at any point between the bunker and the furnace is especially serious with pulverized-coal firing because there is danger of immediate loss of output. Where moisture is a problem, the designer must exercise great care in the design of coal-handling and preparation apparatus.

Jan 1, 1951

By Kenneth L. Cashddollar, Terry G. Montgomery, Eric S. Weiss, John E. Going

The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) conducted joint research on dust explosions by studying post-explosion dust samples. The samples were collected after full-scale explosions at the PRI, Lake Lynn Experimental Mine and after laboratory explosions in the PRL 20-L chamber and the Fike 1-m3 chamber. The dusts studied included both high and low volatile bituminous coals. Low temperature ashing for 24 hr at 515°C was used to measure the incombustible content of the dust before and after the explosions. The data showed that the post-explosion incombustible content was always as high as or higher than the initial incombustible content. The MSHA alcohol coking test -was used to determine the amount of coked dust in the post-explosion samples. The results showed that almost all coal dust that was suspended within the explosion flame produced significant amounts of coke. Measurements of floor dust concentrations after LLEM explosions were compared to the initial dust loadings to determine the transport distance of dust during an explosion. All of these data will be useful in future forensic investigations of accidental dust explosions in coal mines or elsewhere.

By Ralph L. Brown

"IntroductionThe accumulation of gummy and resinous deposits in consumers' gas meters began to assume serious proportions about 1917. As the trouble developed and spread in the years following, it manifested itself in several ways, which ultimately began to the expressible in distinctly economic terms, more specifically in terms of costs; in 1922 an organized and fundamentally based investigation of this trouble was begun. In an earlier paper*** a short statement of the occurrence and costs of the deposition was given and at the same time an analysis of the problem, as well as well as a general plan of attack, was presented. That plan included two general phases, first, a chemical study of typical was 1 quarry or 2 cosinous content , mauformly consituents, rmln and selected subjects; and secondly, a comparative survey of plants affected and sufficient therewith, attention being paid to construction, operation, meter conditions and related data. In reporting progress in the axtual investigation, it was definitely set down that the basis of the gummy deposits was the unsaturated hydro consulting from the carburxtion of the water-gas with oil. That the presence of oily-gas condensate was closely associated with and largely"

Jul 1, 1923

By David C. Peters, Robert S. Crosson

A method of error analysis has been applied to the location technique of non-linear least squares iterative inversion in order to evaluate the resolving power of several seismic array configurations with various assumed earth models and errors and inaccuracies in arrival times. The results obtained demonstrate that lateral accuracies of location are improved significantly when the depth of the miner is known. Lateral location to within 100 feet appears achievable in many instances. If it is possible to refine earth models significantly beyond what has normally been assumed in this work by the use of on-site data, or if the mine is shallow (300 feet or less), accuracies of-about 30 feet or so may be attainable. Inaccuracies in earth models of about 5% are found to contribute much more heavily to these location inaccuracies than errors of a few milliseconds in picking arrival times; however, arrival time errors of 15-20 ms or above will dominate these model inaccuracies. The expected accuracy of location is found to fall off very rapidly as the miner moves outside the array. The strength of this effect depends markedly upon the geometry of the array configuration and can be reduced by careful design. Also, as the size of the array is increased, expected location errors within the array are not altered much, but continue to match the error associated with the smaller array over a larger area (assuming that all stations can still pick up the miner&apos;s signals). Better location accuracy, especially with respect to depth control is achievable in an earth where the velocity is depth-dependent (increasing with depth) than in one which is homogeneous. This is an advantage since the

Jan 1, 1974

By Syd S. Peng

The design of retort interchamber pillars is important in determining surface stability over in situ retort mines and to the health and safety of miners, particularly with respect to possible escape of heat and toxic gases from retort chambers. Stress distribution in retort interchamber pillars, roof, and floor was examined with the aid of linear, finite-element analysis using data from experimentally determined mechanical properties. Properties determined included elastic moduli, strength, and creep constants in laboratory tests on core covering a 100-foot depth interval in the oil shale from the Piceance Basin in Colorado. The most critical stress concentration was found in the rib side of the interchamber pillar at a height above the floor line of 1.25 times the width. Guidelines for pillar design that consider pillar strength, creep, and retorting temperature effects are proposed.

Jan 1, 1981

By R. H. Sprute

This report describes Bureau of Mines laboratory test results in electro-kinetic dewatering and consolidation of metal-mine mill tailings from five mines in the Coeur d&apos;Alene, Idaho, district. Classified (coarse) tailings, slimes, and unclassified material were separately tested. Tailings were placed in 0.3 ft3 plexiglass models, and dc potential was applied until dewatering ceased. Time-oriented measurements of water removal, changes in resistivity, and power consumption were recorded during the dewatering process. Moisture content and density of the dewatered material at test end indicated the method to be generally effective for all materials examined, but best results were achieved with well-mixed unclassified tailings.

Jan 1, 1974

By M. Kanda, J. W. Adams

A system for measuring amplitude probability distributions (APD’s) of electromagnetic noise in coal mines is described and typical APD’s from an underground coal mine are presented. The APD is a basic statistic required for the design and analysis of communication systems, especially those intended for use in noisy environments, and where neither overdesign nor underdesign is acceptable. The rms and average field strengths are obtained by integration of the APD, and examples are shown at several frequencies. All field strength levels are given in absolute units. Selected frequencies cover the range from 10 kHz to 32 MHz.

Jan 1, 1973

By J. M. Kuchta

The chemical and thermal criteria used for predicting the spontaneous combustion hazard are briefly reviewed and data are presented to characterize the gas desorptions and self-heating tendencies of 29 U.S. coals. Closed vessel desorption experiments showed that CO, CO2, and CH4 are the main gases evolved and that the CO, CO/?O2 index, and 02 absorption rate increase with decreasing rank and increasing oxygen content of the coal. In this Bureau of Mines report, the effects of temperature, moisture, and other variables are discussed together with the application of the data to the complex conditions encountered in a mining environment. An important finding is that the presence of CO alone in a mine is not necessarily an indication of a self-heating reaction of the coal. Based upon experiments conducted in an adiabatic-type calorimeter, the self-heating temperatures of lignite and subbituminous coals can be as low as 30° C, whereas the bituminous coals require a temperature of about 60° C or more. The self-heating hazard is greatest when the coals are dried and exposed to a high humidity condition, apparently as a result of the "heat-of-wetting." Generally, the hazard is greatest with the western coals of the United States.

Jan 1, 1980

By James H. Russell

The Bureau of Mines, U.S. Department of the Interior, in cooperation with the Department of Energy, has attempted to increase the activity of nickel catalysts for converting synthesis gas, derived from coal, to a substitute natural gas. This report describes the effects of low-level additions of B, Ca, Ce, Co, Mn, Mo, Pd, Re, Ti, Y, Zn, and Zr on the methanation activity of Raney nickel. The methanation rate at 320° C and the resistance to poisoning by 2 ppm H2S were used to compare catalysts. The effects of the additions were small, and the experimental variances were large, necessitating the use of statistical methods to identify significant effects. Co, Ti, Y, and Zn improved the resistance to H2S poisoning, but only Co improved the methanation rate In some individual catalysts containing Ca, Mo, or Mn, both the methanation rate and resistance to H2S poisoning were improved.

Jan 1, 1980

By S. Gallagher

If we consider ergonomics to be an exercise in matching job demands to worker capabilities, one of the principal capabilities we must be concerned with is that of human strength. Our ability to evaluate different characteristics of muscular strength has increased dramatically over the past couple of decades with the development of new and increasingly sophisticated instrumentation. One would think that armed with such advanced techniques, we might be able to develop methods to conclusively identify workers at risk of injury in physically demanding jobs. Unfortunately, this has not yet proven to be the case. Instead, what these instruments have continued to point out is how intricate a function muscular strength really is, and how complicated and ambiguous its relationship is to musculoskeletal injury. While we cannot just use isolated tests of strength to specify precisely who may be at risk of injury, studies have indicated that strength testing can be a useful tool for job design and, under certain circumstances, selection of workers for demanding jobs. However, because strength is such a complex phenomenon, there has often been some confusion regarding the proper application and interpretation of strength tests in ergonomics, especially among persons not thoroughly familiar with the limitations and caveats associated with the available procedures. The purpose of this chapter is to discuss some of the fundamental principles of strength assessment in ergonomics, so that these procedures can be better applied to control the risk of musculoskeletal disorders in the workplace 1.1. What is Strength? (And what are we Measuring?) Many of the complications associated with strength assessment arise from the simple fact that even our most sophisticated machinery does not directly measure the force or tension developed by a muscle in a living person. Instead, we can only observe the consequences of force development by a contracting muscle, or more likely, by a combination of muscles There are many ways in which we can measure the effects of muscular contraction, and the techniques we use can have a dramatic impact on the strength readings we will obtain. Consider the situation illustrated in Figure 1. In this example, the muscle exerts a constant force of 1000 Newtons (N). However, the forces we measure can vary quite dramatically depending on where we place the force cuff - from 167 N if we place it near the wrist to 500 N if we place it near the elbow. Which value should we select as properly representing the muscular strength for this elbow flexion exertion? The preceding example illustrates some important points with regard to strength assessment. Perhaps the most important is that "muscular strength is what is measured by an instrument" (Kroemer et al. 1999). It should also be clear from this example [ ] that two researchers could perform an elbow flexion strength experiqent on the same group of subjects, but if each selected different force cuff positions, they might end up with wildly differing estimates of strength. Differences in the strengths of various muscle groups in the published literature may be the results of differences in the procedures and measurement methods used by the experimenters Thus, it is critical that any strength data presented be accompanied by a detailed account of the manner in which the data were obtained. A few additional points need to be made with regard to the testing of human strength. We must be clear that what we are obtaining in such tests are not a person&apos;s maximal strength capability, but their maximal voluntary strength. The voluntary nature of the exertion introduces an unknown, but surely substantial, amount of variability in our measurements of strength. One can imagine two subjects with identical muscular strength capabilities, but with varying levels of motivation or discomfort tolerance, for example. We are likely to observe considerable differences in the voluntary force exerted by the two, but it should be understood that such results may be largely the result of psychological factors, and not differences m muscular strength per se. The important point to be made here is that not only are we unable to directly measure muscular force, what we are able to measure is modified by an invisible filter - a filter subject to a wide variety of influences and which will differ considerably for every person we test To make matters worse, this filter would be expected to change even within a given individual on a given day. From the foregoing discussion, one can perhaps better appreciate some of the difficulties with establishing a definitive relationship between an individual&apos;s measured strength and that individual&apos;s risk of injury.

By A. M. Stubbs

The Bureau of Mines has devised a procedure to selectively extract and recover chromic oxide (Cr203) from waste high-temperature shift catalysts that contain approximately 6 pct Cr and 62 pct Fe, both in oxide form. The Bureau&apos;s procedure consists of roasting the waste catalyst with sodium hydroxide (NaOH) or sodium carbonate (Na2C03) followed by water leaching. The chromium from the leach liquor was recovered utilizing an oxidation-reduction reaction with pH adjustment to form a hydrous chromic oxide (Crp3oXHp) precipitate. The roast-leach procedure produced chromium extractions greater than 89.7 pct, with product recovery in excess of 99 pct from the leach liquor. The costs of the NaOH and Na2C03 roast processes, including sizing and equipment-related recommendations, were determined by the Bureau&apos;s Office of Process Evaluation. The economic evaluation indicates that producing a Crp3 product, at the present time, is not competitive with the present-day cost of imported chromites. The estimated average operating cost for both processes was $5.44/1b of recovered Cr203 concentrate. However, this procedure offers a potential alternative to the disposal of this waste through landfiIl.

Jan 1, 1988

By R. Stefanko

The industrial hygiene and safety aspects with internal combustion engine in mining systems is truly interdisciplinary and encompasses many fields such as mine ventilation, exhaust gas and particulate analyses, mine atmospheric environment monitoring, mathematical modeling of generation, dilution and dispersion of pollutants in ventilation systems, and engine testing and approval. Mathematical models of the dilution and dispersion of diesel exhaust contaminants can be useful only if these models can be validated. In this research report, experiments that were specially designed for the above purpose are described. These experiments were conducted in the U.S. Bureau of Mines, Safety Research Coal Mine, in Bruceton, Pa. On the basis of this study, the data collected, and further review of available literature, it is concluded that mathematical models of dilution and dispersion are useful tools for mine ventilation planning. Additional objectives of this study about which conclusions and recommendations are reported here include: (a) evaluation of mine atmosphere contaminant monitoring systems; (b) optimum sampling site locations; (c) model sensitivity and error analyses; (d) computer coding of mathematical models; and (e) development of a diesel bibliography. While an extensive bibliography on diesels is provided in this report, Volume II of this final report has 511 references.

Jan 1, 1977

By W. W. Adams

Reports received by the Bureau of Mines, Department of Commerce, from State mine inspectors, for November, 1930, showed that 219 men were killed in the coal mines of the United States during the month, an increase of 25 over the previous month and 33 over November, 1929. On the other hand the production of coal decreased, the output of 43,329,000 tons in November being 8,397,000 tons less than in October and 9,005,000 tone less than in November a year ago. The larger number of fatalities accompanied by a smaller output of coal resulted in a higher death rate4 per million tons in November than in the same month last year or in October, 1930. The November rate was 5.05, as compared with 3.55 for November, 1929 and 3.75 for October, 1930. The increase in the rate for the industry as a whole was chargeable entirely to bituminous mines, as the anthracite mines had fewer fatalities in November than in either of the previous months to which reference has been made. Reports for bituminous mines alone showed that accidents at this class of mines resulted in a death rate of 5.12, based on 195 fatalities and a production of 38,122,000 tons. This rate indicated an increase of 55 per cent over the rate for October, of the same year, and 72 per cent over the rate for November, 1929. The October record was 146 fatalities and 44,150,000 tons, and that for November a year ago was 138 deaths and a production of 46,514,000 tons.

Jan 1, 1930

By Robert E. Wood

[The temperature dependency of the low-density thermal conductivity coefficients, ?°T, of nitrogen, 100° to 1,200° K, is correlated with the Keyes&apos; equation, ?T ½ -1 -12/T) WT = aT+ bT 10 The equation ?T,P = ?°T +a[ ]ß represented 509 experimental higher V pressure thermal conductivities in the temperature range 131.2° to 973.15° K for pressures to 500 atmospheres, with a mean absolute deviation of 2.35 percent. This equation was used to compute thermal conductivities of gaseous nitrogen for 47 pressures, 1 to 240 atmospheres, and 110 temperatures, 133° to 740° K, which are common to conditions encountered in Bureau of Mines helium purification processes. Isobaric heat capacities, CP, and viscosities, ?T,P, from previous work were combined with the present thermal conductivities, ?T,P, to compute Prandl1 numbers, C?T P / ?T ,P, of nitrogen. Tabular values of Prandtl num¬bers are presented for 49 pressures, 1 to 240 atmospheres, and 75 temperatures, 133° to 740° K. Estimated uncertainties are ±5 percent in the tabulated thermal conductivities and ±15 percent for the computed Prandtl numbers. However, the uncertainty may rise to ±10 percent for thermal conductivities and to ±30 percent for Prandtl numbers as the critical conditions of nitrogen are approached.]

Jan 1, 1971

By W. C. Smith

This Bureau of Mines report discusses how pull-test data can help establish polyester resin column length criteria for roof bolts in evaporite minerals. The study evaluates the effectiveness of partial to full columns of resin in anchoring 4-ft, No.6, grade 40 rebar roof bolts in potash, salt, trona, gypsum, and borate mine roofs. Pull tests were performed on over 600 roof bolts in 11 evaporite mines. Column lengths ranging from 6 to 48 in (fully grouted) were evaluated for each test site. In general, comparative results among all test sites indicate that pull-out loads in excess of 10 tons (force) were attained with resin-grouted bolts having 13 to 75 pet less than a full column of polyester resin. Ten tons (force) of load-carrying capability compared favorably, in terms of strength, with the calculated yield strength of the rebar used in the tests, which was 8.8 tons (force). The site-specific nature of each test site, due to the unique combinations of geology, mine-induced stresses, and other unknown parameters, prevented the establishment of valid generic column-length criteria. For these reasons, data to evaluate resin-column-length effectiveness are best obtained on a mine-specific basis.

Jan 1, 1987