As production levels on longwalls increase, the goal of controlling dust exposures also becomes more of a challenge. Many of the more productive longwalls in the United States are operating in higher coal seams. Currently the highest seams in the US being mined are approximately 3 to 3.5 metres high.

Much of the water spray technology for dust control was originally developed for lower seam conditions and has been adapted to higher seam operations.

“When directional sprays were originally developed it was for seam heights of two meters. Now many mines in the US, particularly in the west, are mining higher seams and we need to ask whether the external spray systems are being implemented in an efficient manner,” said NIOSH dust researcher Jay Colinet.

“We have to ask which types of sprays need to be implemented to optimise dust control,” he said.

The project, to be carried out in NIOSH’s dust gallery, will look at optimising external sprays for higher coal conditions. Different external spray systems will be tested on a simulated shearer in a full-scale dust gallery under varying conditions.

Tests will be conducted to evaluate different spray configurations, each of which will be operated at different operating pressures and spray orientations. Instantaneous and gravimetric dust sampling will be conducted in the walkway around the shearer to document the effectiveness of each spray system.

Presently, US mines usually employ some form of directional spray system to take advantage of the air moving capabilities of water sprays. This consists of a splitter arm that extends from the headgate side of the machine parallel to headgate drum and as far past the drum as possible. Six to 12 sprays are mounted on top of the splitter arm, depending on the spray type and water quantities available. All sprays are angled (as measured from perpendicular to the face) at approximately 30 degrees toward to the tailgate side. Also, conveyor belting is typically hung down from the splitter arm towards the face conveyor to provide a physical barrier to seal the area under the splitter arm near the spill plate.

When air comes down the longwall face, the splitter arm sprays and belting separate the air into two distinct air streams. The clean air in the walkway continues to flow past the shearer down the walkway. The air over the face conveyor is directed towards the shearer drum and coal face. Any dust that is generated by the headgate drum is forced toward the face by the splitter arm sprays.

A series of spray manifolds located on the face side the shearer help to hold this dust-laden air near the face and move it along the body of the shearer toward the tailgate drum. Sprays on the tailgate side of the shearer then direct the dust laden air past the tailgate drum for some distance downwind of the shearer.

“What we have seen recently on the tailgate end of the shearer at a few mines is manifolds mounted directly over the face conveyor with six to 12 sprays directed down the face conveyor towards the tailgate and spraying past that tailgate drum,” Colinet said.

“Dust around the tail gate drum that may come out into the walkway is pushed down the face conveyor before reaching the tailgate shearer operator location.”

The NIOSH research team will evaluate the various sprays system designs under controlled conditions in their full-scale longwall gallery to determine which are the most effective for mines operating in higher seam heights.