The amount of airborne respirable dust generated from breakage of different coals varies widely.This research was conducted to identify the facets of airborne respirable dust liberation from the coal product.Laboratory crushing experiments were conducted ona range of low to high volatile bituminous coals to investigate the various factors influencing airborne respirable dust generation.Bituminous coal samples from 8 mines(5 U.S.and 3 Polish) were uniformly prepared and processed through a double roll crusher located in a low air velocity wind tunnel.Experimental factors studied included inherent coalseam constituents,specific energy of crushing,product size characteristics,dust cloud electrostatic field,and specific quantity of airborne respirable dust generated.The results of this investigation build upon previously published results,which indicated that a combination of several factors are associated with the generation of airborne respirable dust.One factor involved is the effect of coal rank,described by the inherent moist fuel ratio,on the product size characteristics,defined by Schuhmann size function parameters.However,sincecoals of high moist fuel ratio(high rank) are generally more extensively cleated,it is suggested in the present work that the degree of cleating is directly respon sible for the quantity of respirable-sized particles produced in the crushed product material for eastern U.S.coals.This is implied by the relation ship of ash contentand at least one mineral constituent (pyrite,determined from pyritic sulfur anlaysis) to the percentage of airborne respirable dust.To validate this hypothesis,a description is offered that is based on known coal petrography.Another key factor is the effect of air dry loss moisture in the coal seam on the breakage-induced electrostatic field of airborne dust.The air dry loss moisture factor appears to control the amount of airborne respirable dust that is liberated from the product.The resultant effect of these factors is that different percentages of coalparticles smaller than 10 mum aredispersed as airborne respirable dust,with a welldefined peak in the normalized airborne respirable dust for a narrow range of air dry loss moisture/ash ratos.A clear delineation of coals,based on well-known proximate analysis characteristics,that generate the most respirable dust appears to be possible.It was also shown that the dust-generating characteristics of coals could be reasonably described by both the moist fuel ratio and the Hardgrove Grindability Index (HGI).These results show a clear distinction between eastern and western U.S.caols.however,no consistent distinction for Polish coal was observed.
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