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Evaluating longwall dust sources and controls.

Rider-JP; Colinet-JF; Listak-JM; Chekan-GJ
World Coal 2001 Oct; 10(10):71-76
NIOSH is conducting full-scale laboratory studies to evaluate dust liberation and control for dust generated by shearer cutting. Varying face air velocities had the greatest impact on dust levels at the sampling locations along the face. Gravimetric sampling results showed dust levels were reduced for all test conditions when the air velocity was increased to 2.29 ml s across the face. Dust levels were reduced by 55% when compared to tests conducted with the air velocity at 1.3 m/s. Results also show increases in drum spray pressure had minimal but adverse effects on dust levels when the shearer was cutting in the head-to-tail direction, for both the shearer clearer and basic external spray systems. Lower drum spray pressure impacted respirable dust levels when the shearer clearer spray system was tested and the cutting sequence was in the tail-to-head direction. Dust levels at the tailgate position were reduced while levels downwind of the shearer increased when compared to higher drum spray pressures. Gravimetric sampling results at the tailgate and jacksetter operator positions increased substantially when the external spray pressure was increased, while the shearer was cutting head to tail and the shearer clearer spray system was operational. Dust profiles along the longwall face for tests conducted with the shearer cutting in .the tail-to-head direction showed the dust cloud was contained against the face a distance of 3.1 - 4.6 m further downwind when the shearer clearer external sprays were used. Also, the dilution of the dust cloud occurred faster and peak dust concentrations in the walkway were not as severe with the shearer clearer external 7 sprays. The type of external spray configuration had minimal impact on dust levels downwind of shearer. When the dust cloud mixed with the ventilating air it seemed to stabilise and remained reasonably constant. Once again, variations in air velocities had a significant impact on the dust levels along the face. To better understand the effects of shield dust entrairnent at air velocities being observed on today's longwall faces, research was conducted in a wind tunnel at test velocities of 2.0, 4.1, 6.1 and 8.1 m/s. Higher air velocities result in higher air quantities, which can serve to dilute dust and should therefore lower concentrations in the wind tunnel. However, both total and respirable dust concentrations rose at each successive higher air velocity indicating that particle entrainment was greater than dilution effects for these tests. Statistical analysis of the concentrations measured at each velocity resulted in significant differences at a 95% confidence interval. Size distribution of the sampled dust shows that as velocities increased, a higher percentage of the dust particles in the air stream were finer (<10 microns) than those collected at the lowest test velocity (2.0 ml s). The mass median diameter was found to be 10.8 microns at 2.0 m/s and decreased to 7.7 microns at 8.1 m/s. Higher concentrations and finer particle size distributions suggest that at a moisture content of approximately 1%, a portion of the dust particles were loosely agglomerated and remained agglomerated at the 2.0 m/s velocity. As the velocity increased, the adhesion forces were overcome by the increased energy supplied to the system resulting in higher concentrations and smaller particle sizes in the air stream.
Dust-control; Dust-analysis; Airborne-dusts; Gravimetric-analysis; Statistical-analysis; Coal-dust; Coal-mining; Underground-mining
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Journal Article
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NIOSH Division
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World Coal