Dust Control Handbook for Industrial Minerals Mining and Processing

Table 1.2. Emission factors for crushed stone processing operations (lb/ton)*SourceTotal PM-10**Tertiary crushing 0.0024Screening 0.0087Conveyor transfer point 0.0011Wet drilling—unfragmented stone 0.00008Truck unloading—fragmented stone 0.000016Truck loading—conveyor, crushed stone 0.0001* Uncontrolled emissions in lb/ton of material throughput.**PM-10 is particulate matter less than 10 micrometers (µm), in size.3The following formula can be used for converting lbs/min into grains/ft :7,000 grains(lbs/min)cfm3gr/ft(1.7)where lb/min = loading rate of the material, and cfm = airflow of the dust collector.The following expressions define various inlet loading relationships:low concentration = 10 gr/ft .3The air to cloth ratio is a measure of the volume of gas or air per minute per unit area of bag3 2(ft air per minute/ft of bag area), and can be expressed mathematically as follows:air to cloth ratio = Q/Awhere Q = quantity of gas (air) in cfm and, A = area of the filter cloth or total number of bags in2ft .The porosity of the filter media (cloth) will determine the amount of air that can be drawnthrough before the static pressure becomes too high for the collector housing or the fan capacity.By estimating the inlet loading, one can also determine the grains of dust striking each squarefoot of filter media per unit time.Air to cloth ratio is also a measure of the average velocity of the air moving towards the bags.Inlet loading directly affects the air to cloth ratio. The heavier the inlet loading the lower the airto cloth ratio should be. High inlet loading results in more dust being retained on the filter mediaand causing higher pressure drops. Air to cloth ratios below 4:1 are considered low, from 4:1 to7:1 are moderate, and above 7:1 are considered high. By lowering the air to cloth ratio, the filterFundamentals of Dust Collection Systems 33