Mining Project: Improved Float Dust Controls in Underground Coal Mines

Research Summary

The accumulation of float coal dust (FCD) in underground mines is an explosion hazard that threatens all underground coal workers. This hazard is addressed by the application of rock dust to maintain an incombustible content of the total dust on mine surfaces at a minimum of 80%, but inadequate rock dusting practices can leave miners exposed to an explosion risk. Therefore, the development of controls aimed at reducing FCD accumulation in mine entries will provide another layer of protection in preventing mine explosions.

While dust controls and rock dusting are the main methods used to reduce this hazard, improved float dust source controls will reduce the accumulation of FCD, in turn improving the efficacy of current rock dusting practices. Since 2001, U.S. coal mine disasters have resulted in 59 fatalities, and 80% of these were attributed to explosions that were enhanced by the accumulation of float coal dust in the mine entries. While the occurrence of dust-fueled explosions is relatively low—three documented instances in 2001, 2006, and 2010—these incidents represented 31%, 36%, and 60% of the underground coal mining fatalities for their respective years. These explosions typically occur when methane gas ignites and the resulting pressure wave re-entrains coal dust that has settled out of the ventilating air onto the floor, roof, and ribs of the mine entries.

To address this problem, this project had three research aims, which were achieved as described below:

1. Evaluated the use of enclosures and/or chemical treatments for controlling emissions of FCD from non-cutting processes. This aim used both laboratory testing and in-mine testing to examine additional source controls of float dust that were not directly related to the cutting of coal. The aim built upon the research of a previous FCD project by using a transfer point water spray system in-mine that was modified to allow for chemical treatments.
2. Evaluated and optimized the full-scale water curtain, in the laboratory, to reduce FCD accumulations in longwall returns. A full-scale water curtain aimed at reducing the amount of airborne float coal dust that accumulates in a longwall return was developed through laboratory testing as part of this project’s predecessor. In the current project, the water curtain was further optimized on a simulated longwall section and evaluated using a continuous float dust monitor.
3. Evaluated the feasibility of a water-powered longwall shearer scrubber to capture FCD generated by cutting. Feasibility studies showed that water sprays were not able to induce sufficient air flow, under common operating parameters, to effectively capture FCD. Under this aim additional evaluations of air induction capacity and dust knockdown on water sprays, including venturi sprays, were completed.

This research evaluated and optimized, in the laboratory, three FCD controls that can be  used by the mining industry to reduce accumulations of combustible material or to improve the ratio of rock dust to combustible material on deposition surfaces, thereby increasing the efficacy of current rock dusting practices and reducing the likelihood of a dust-fueled mine explosion.  A reduction of combustible material along with non-caking rock dust may provide an opportunity for a business case for future rock dusting practices. There is also potential for controls developed in this project to have application in other industries that seek to control combustible dust.

Project Outcomes

2018—Comparison of the CAS POL and IOM samplers for determining the knockdown efficiencies of water sprays on float coal dust, Journal of Occupational and Environmental Hygiene 15(3):214–225.

2020—Dust control at a belt conveyor transfer point using water sprays and a wetting agent, SME Annual Meeting Preprints, Feb. 23–26, 2020, Phoenix, AZ.

2020—Design of a water curtain to reduce accumulations of float coal dust in longwall returns, International Journal of Mining Science and Technology 30(44):43–447.

2020—Laboratory testing of a water curtain designed to reduce float dust accumulations in longwall returns, SME Annual Meeting Preprints, Feb. 23–26, 2020, Phoenix, AZ.

Lab symposium poster—Use of the Cloud, Aerosol, and Precipitation Spectrometer (CAPS) for Studying Mining Dust Controls.