A new project proposed to start next year at NIOSH’s Pittsburgh Research Laboratory will look at coal charging characteristics and how they may influence the effectiveness of wetting agents used on coal for dust control.

The new project stems from research conducted in the early 1990’s. Coal and rock samples from different mines were bought back to the laboratory and were tested for their charge characteristics and dust generation. The coal and rock samples were fed through a crusher under controlled conditions with dust levels and charge characteristics measured downwind of the crusher.

“We found significantly different charge characteristics for coals from different seams and for the rock samples,” said NIOSH dust researcher Jay Colinet.

“In general, most coals were positively charged while the rock was negatively charged. Also, the magnitude of the charge on the rock was typically greater than that found with the coal samples.

“However, different coals did have different magnitudes of charge, depending on the coal rank. Most coals were positively charged although a few were negatively charged.”

“These differences in charge characteristics may provide some explanation into why water additives improve dust control in some operations but not in others. The surfactant that you are using to try and wet the coal could be either helping or hurting you.

“Previous research found that you could go to two coal mines in relatively similar working conditions and apply the same wetting agent. At one mine you might get a 30% dust reduction but at the other mine see no difference. There was never a good explanation as to why that was occurring.”

The current project will build on these findings by selecting specific coals, and looking at multiple wetting agents in trying to favourably match them up based on their charge characteristics.