NIOSH logo and tagline

Engineering Controls Database

Engineering control title: Guidelines for the Control and Monitoring of Methane Gas on Continuous Mining Operations – Effects of Scrubber Operations – Effect of Scrubber Flow on Intake Flow

The introduction of conventional mining methods, which increased the rate of mining, was an important step in the mechanization of mining. The intermittent nature of the conventional mining process halted the extraction process for ore-loading and usually allowed time for methane gas to be dispersed. However, the introduction of continuous mining machines in the 1940s produced a constant flow of ore from the working face of the mine and resulted in an increase in methane levels.

The number of face ignitions increased as more continuous mining machines were placed underground. Methane levels were found to be dangerously high. In some cases, methane concentrations measured 20 ft from the mining face exceeded the lower explosive limit (5% by volume) [USBM 1958]. The need for better face area ventilation was recognized to reduce the potential for explosions.
Excessive levels of methane gas can affect the safety of the underground work force. Available methane control systems have been challenged in recent years by mining developments which include the use of continuous mining machines.

In the past 10 years, explosions have led to 65 fatalities and 18 injuries with major explosions occurring at the Sago Mine in West Virginia in 2006 (12 fatalities and 1 injury), the Darby No. 1 Mine in Kentucky in 2006 (5 fatalities and 1 injury) and, most recently, at the Upper Big Branch Mine in West Virginia in 2010 (29 fatalities) [NIOSH 2011]. The occurrence of a methane gas explosion puts the lives of the entire underground workforce at risk.
The U.S. Bureau of Mines (USBM) was formed in 1910 following a series of underground explosions that resulted in many fatalities and injuries [Kirk 1996]. The agency was responsible for conducting scientific research and disseminating information on the extraction, processing, use, and conservation of mineral resources. The USBM research program for mining health and safety was transferred to NIOSH in 1996. Since that time, NIOSH has established a ventilation test gallery where techniques for methane control and monitoring are evaluated under a variety of conditions that simulate airflow near the working face of a continuous mining section. Airflow patterns and methane concentrations are studied in a detailed manner that is not possible in a working underground mine.

Effect of Scrubber Operation on Face Airflow

Scrubbers are used to remove dust from the air in the environment of the mining face. Dusty air from the face passes through and captured on a wetted filter and the cleaner air is exhausted at the rear of the mining machine. The scrubber moves a large quantity of air in the face area. Earlier work had shown that this air movement can improve the dilution and removal of methane gas from the face area.

Effect of Scrubber Flow on Intake Flow

For each of the scrubber tests shown in Figure 1, intake airflow velocities were measured at the end of the blowing curtain, with and without the scrubber operating. Intake flows were always higher when the scrubber was operating, and intake flow increased as scrubber flow increased.
Figure - 1 - Effect of scrubber flow on intake air quantity.

Figure - 1 - Effect of scrubber flow on intake air quantity.

Further tests were conducted to determine the source of the additional intake flow that resulted from scrubber operation [Taylor et al. 2006]. For these tests, one of the three regulator doors was opened completely (Figure 2) and the other two were closed completely. With the scrubber off, an outside door was opened enough to adjust intake flows behind the blowing curtain to either 4,000 or 6,000 ft3/min. Intake and scrubber flow quantities were set at either (4,000 or 6,000 ft3/min), while flow quantities were measured at the open regulator door and at the mouth of the blowing curtain.
Figure - 2 - Test conditions while measuring flow at the regulator door and behind curtain.

Figure - 2 - Test conditions while measuring flow at the regulator door and behind curtain.

Figure 3 shows changes in flow in the intake and at the regulator door for two test conditions:

• 4,000 intake [4K(I)] and 6,000 scrubber [6K(S)]
• 6,000 intake [6K(I)] and 4,000 scrubber [4K(S)]
Figure - 3 - Changes in intake flow measured at curtain and regulator due to operation of the scrubber.

Figure - 3 - Changes in intake flow measured at curtain and regulator due to operation of the scrubber.

During scrubber operation, intake flow increased and flow through the regulator decreased.

• Intake flow increased more when scrubber flow was greater than the intake flow.
• The increase in intake flow was slightly greater than the decrease in flow through the regulator door.
o Increased curtain flow was primarily due to air removed from the regulator.
o Additional flow behind the curtain was due to leakage of air around the curtain.
o Although scrubber use increased flow of uncontaminated air at the mouth of the blowing curtain, leakage around the curtain added contaminated air to the intake air. Too much leakage could result in higher face methane levels. Maintaining intake flows higher than scrubber flows will reduce methane leakage around the curtain.

NOTE: The above control information is taken directly from the following publication:
NIOSH [2010]. Information circular 9523. Guidelines for the control and monitoring of methane gas in continuous mining operations. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2010-141.
Kirk WS [1996]. The history of the Bureau of Mines. In: U.S. Bureau of Mines Minerals Yearbook, 1994. Washington, DC: U.S. Bureau of Mines.

NIOSH [2011]. Ventilation and explosion prevention highlights.

Taylor CD, Chilton JE, Hall E, Timko RJ [2006]. Effect of scrubber operation on airflow and methane patterns at the mining face. In: Mutmansky JM, Ramani RV, eds. 11th U.S./North American Mine Ventilation Symposium. Leiden, The Netherlands: Taylor & Francis/Balkema, pp. 393–399.

USBM [1958]. Auxiliary ventilation of continuous miner places. By Stahl RW. Washington, DC: U.S. Bureau of Mines, Report of Investigations, No. 5414.
coal mining
continuous mining operations
deep-cut mining
Operation of machine-mounted dust scrubbers increases the volume of air reaching the face, improves airflow across the face, and maintains higher air velocities.