Experimental study on foam coverage on simulated longwall roof

Abstract

Testing was conducted to determine the ability of foam to maintain roof coverage in a simulated longwall mining environment. Approximately 27 percent of respirable coal mine dust can be attributed to longwall shield movement, and developing controls for this dust source has been difficult. The application of foam is a possible dust control method for this source. Laboratory testing of two foam agents was conducted to determine the ability of the foam to adhere to a simulated longwall face roof surface. Two different foam generation methods were used: compressed air and blower air. Using a new imaging technology, image processing and analysis utilizing ImageJ software produced quantifiable results of foam roof coverage. For compressed air foam in 3.3 m/s (650 fpm) ventilation, 98 percent of agent A was intact while 95 percent of agent B was intact on the roof at three minutes after application. At 30 minutes after application, 94 percent of agent A was intact while only 20 percent of agent B remained. For blower air in 3.3 m/s (650 fpm) ventilation, the results were dependent upon nozzle type. Three different nozzles were tested. At 30 min after application, 74 to 92 percent of foam agent A remained, while 3 to 50 percent of foam agent B remained. Compressed air foam seems to remain intact for longer durations and is easier to apply than blower air foam. However, more water drained from the foam when using compressed air foam, which demonstrates that blower air foam retains more water at the roof surface. Agent A seemed to be the better performer as far as roof application is concerned. This testing demonstrates that roof application of foam is feasible and is able to withstand a typical face ventilation velocity, establishing this technique’s potential for longwall shield dust control.

Laboratory results of foam application testing for longwall shield dust control in a simulated environment

“…These reductions are lower than the reductions at the lower velocity reductions. During previous roof application testing, foam coverage at high-velocity ventilation was not as good as that provided at low-velocity ventilation (Reed et al 2017). The reduction in coverage at high-velocity ventilation would explain the high-velocity ventilation's lower dust reductions.…”

“…Possible explanations are most likely lack of foam coverage on the top surface plate. During previous roof application testing, foam coverage with agent B at high-velocity ventilation was not good (Reed et al 2017). Therefore, the reduction in coverage at high-velocity ventilation would explain the lack of dust control in highvelocity ventilation resulting in increases at several of the locations.…”

“…5. It was used as it provided better coverage over the roof than other nozzles that were previously tested for roof application (Reed et al 2017).…”

“…The 3-min time frame is significant as this represents the approximate time between the shearer passing a shield and the shield movement, which is based upon observations of longwall shield movement. The compressed-air-generated foam has demonstrated potential for effective shield dust control through its application to the mine roof (Reed et al 2017).…”

“…The high expansion ratios of these foams also reduces the amount of time that is available for dust control as high ventilation airflow tends to cause rapid decay of the foam. The blower-generated foams are generally stable for the 3-min time frame for shield movement (Reed et al 2017).…”