Edward D. Thimons

Diffusion of methane through coal

Abstract Both methane and helium flow through solid coal by Knudsen diffusion, even at relatively high pressures. Knudsen permeabilities were determined for samples of Pittsburgh, Pocahontas No.3, and Oklahoma Hartshorne coals. The average permeability for dry methane was 1.3 × 10 −6 cm 2 /s for Pittsburgh coal, 20 × 10 −6 for Pocahontas No.3 coal, and 13.8 × 10 −6 for Oklahoma Hartshorne coal. A molecular-sieve effect exists for methane in all three coals examined and it is very strong in Pittsburgh coal. If the methane is saturated with water vapour the permeability decreases by a factor of 3 to 25, depending on the coal. The Knudsen permeability of solid coal discs seems to bear no relation to coalbed permeability. Lag-time measurements indicate systems of both larger and finer pores and the presence of blind pores. This effect is again more pronounced in the Pittsburgh coal.

An analysis of air volume-flowrate determinations for mines

Abstract The proper control and distribution of ventilation air is a key aspect in the productivity of an underground mining operation, and is crucial to the health and safety of mine workers. Accurate measurement of air velocity is an essential component in achieving effective ventilation planning and control. However, the measurement methodology and application is problematic, especially in the use of correction factors. This paper examines the accuracy of these factors as they are affected by measurement location, instrument, and flow characteristics. Definitive recommendations are presented to improve the accuracy of flowrate determinations.

Methods to Lower Dust Exposures at Mineral Processing Operations

Abstract The Bureau of Mines has been investigating techniques to reduce dust concentrations in mineral processing plants. This article discusses three projects that reduced the respirable dust exposures of plant workers. The first project involved designing and testing a total mill ventilation system for large surface structures. This total mill ventilation system uses clean outside air brought in at the base of the mill to sweep and clear contaminated areas, and then discharges this air out of the top of the structure, where it poses a minimal contamination hazard to employees working outside. Average respirable dust levels were reduced by 40 and 64 percent at two field sites using this technique. The second project involved a bag and belt cleaner device that uses a combination of brushes and air jets to clean the dust that collects on the outside of 50- to 100-lb. bags of product and the conveyor belt used to transport them. The system is totally enclosed and under negative pressure to contain all dust...

Moisture Application for Dust Control

Abstract The Bureau of Mines and several member companies of the National Industrial Sand Association have been working in many areas to reduce personal exposure to respirable dust. Areas investigated have included ventilation, improved hardware design, improved housekeeping practices, and addition of moisture to products. This article reviews information to date on various methods of using moisture to reduce respirable dust concentrations in mineral processing plants. Individual studies present an inconclusive case for additional work in this area. Together, however, these studies indicate a good potential for the development of an economical and practical plantwide dust control technique. Naturally, these techniques may only be applicable for certain mineral products. Methods used in the individual studies to evaluate dust reductions included observation, gravimetric filter analysis, and instantaneous light-scattering methods. Various methods of moisture addition included the use of foams, steam, and wa...

Monitoring Air Flow Through a Machine-Mounted Dust Scrubber

Abstract On mining sections using blowing ventilation, a machine-mounted scrubber is often required to maintain face dust levels below 2 mg/m3. The quantity of airborne dust entering a scrubber is directly related to the quantity of air drawn through the scrubber. Due to loading of the scrubber filter, scrubber air flow can decrease significantly during mining. Excessive loading can also cause the fan to be starved for air, resulting in a condition called aerodynamic stall. To restore scrubber flow, the scrubber filter must be removed and cleaned. During the mining operation, it is difficult to determine if scrubber air flow has decreased significantly until the fan stalls. Observation of scrubber performance is particularly difficult when the mining machine is operated by remote control. Periodically, scrubber flow readings can be taken. However, most air flow monitoring equipment will be damaged if left in the wet and dirty environment of the scrubber duct for long periods of time. Experiments were cond...

Reverse performance characteristics of main mine fans

Abstract During a mine fire or other emergency, it may be desirable to reverse the airflow in order to provide an escapeway or to isolate a fire. Also, in colder areas, the airflow may be reversed to prevent ice buildup. When reversing main mine fans, the mine operator usually does not know what operating characteristics of flow and pressure to expect. Laboratory and field tests of vane axial main mine fans were conducted to establish forward and reverse performance characteristics under controlled conditions and in typical mine installations. All fans tested were between 81 and 96 in. (2.1 and 2.4 m) in diameter. The data obtained suggest that reverse performance characteristics are dependent upon the blade angle and the hub to tip ratio. There is also evidence that reverse performance can be perdicted for a family of blade angles for a given hub to tip ratio. Generally fan quantity is 30–60% less in reverse than when operating in the normal forward mode, with static pressure equal to the square of the volume percentage change.