During the field studies, the economic aspects of the stone crusher was discussed with several crusher owners in terms of fixed capital investment of setting up a stone crusher unit and typical annual operating costs and profit margins etc. Based on the information provided by the crusher owners (as reported), following tables are prepared which provide typical details on capital investment and annual operating costs of a small size stone crusher unit having production capacity of 20 Tons per hour.
Sources of Emissions
All quarrying and stone processing operations including surface mining , crushing, screening, material handling and transfer operations are potential sources of particulate emissions. These sources may be categorised as either process sources or fugitive dust sources. Process sources include those sources for which emissions are amenable to capture and subsequent control.
Fugitive dust sources generally involve the re-entrainment or settled dust by wind or machine movement. Factors effecting emissions from either source category include the type, quantity and the moisture content of the rock processed, the type of equipment and operating practices employed as well as topographical and climatic factors.
Emission During Mining Activity
Fugitive Emissions are generated during various mining activities such as drilling, blasting, excavation, breaking and loading etc. In some bigger mines the primary blasting emissions are quite substantial over a large area. The emissions during secondary blasting are also substantial but lesser compared to primary blasting. These emissions last only for a few minutes. There are hardly any controls adopted world over for controlling blasting emissions.
Emission During Transportation
During transportation of mined stones by heavy vehicles like trailors, trucks, dumpers, fugitive dust emission occur due to movement of heavy vehicles on earthern roads. The quantity of emissions depend on various aspects like climatic conditions, moisture in the soil, speed of the vehicle, frequency of the vehicles etc. Generally such emissions can be controlled to a great extent by spraying water on these roads intermittently.
Emission During Crushing Operation
During crushing operation, generation of particulate emissions is inherent and the emissions are most apparent at crusher feed and discharge points. The greater the reduction in size during subsequent crushing stages from primary, secondary to tertiary crushing, the higher the emissions.
Primary jaw crushers produce more dust than comparable gyratory crushers because of the bellows effect of jaw and because gyratory crushers are usually choke-fed, thus minimising the open spaces from which dust may be emitted. For subsequent reduction stages, cone or roller type crushers produce more fines as a result of attrition and consequently generate more dust.
Emissions During screening
In the screening section, the mixture of stones is classified and separated according to size. Generally the screening efficiency is considered to be in the range of 60 to 75%. The screening equipments commonly used include grizzlies, shaking screens, vibrating screens and revolving screens. Although screening may be performed wet or dry, dry screening is the most common. Dust is emitted from screening operations as a result of the agitation of dry stone. The screening of fines produces higher emissions than the screening of coarse sizes. Also screens agitated at large amplitudes and high frequency emit more dust than those operated at small amplitudes and low frequencies.
Emissions During material handling
In the material handling section, various handling devices like feeders, belt conveyors, bucket elevators and screw conveyors are used to transport crushed materials from one point to another. Particulates may be emitted from any of the material handling operations. Most of the emissions occur at transfer points. Since transport of material on the conveyor causes little disturbance of air and emissions that occur due to the wind are judged to be minimum. The transfer points include transfers from a conveyor on to another, into a hopper and on to a storage pile. The amount of uncontrolled emissions depends on the size distribution of the material handled, the belt speed and the free fall distance.
Nature and Spread of Emissions
The dust is generated primarily due to size reduction and handling of the stones at various stages. The major source of dust generation is during size reduction in the primary, secondary & tertiary crushers. The fines in the dust generated increases with subsequent stages of crushing i.e., more fines are generated in secondary crusher as compared to primary crusher. The dust is also generated during handling of stones, especially at the point where the stones fall through a height from places like one belt to another or from belt to hopper or stock piles etc. During vibratory screen large quantity of fine dust is emitted.
Nature and Spread of Emissions
Coarser part of the dust settles down within the premises but the finer particles get air borne and get carried away with wind to longer distances. The actual area of the source of the dust generation is quite small (about 0.5 to 1 square meter)at each source, but as the dust rises it spreads and typically the area in which it spreads is more than 10 –15 times larger than the area of actual emissions at about 3 to 4 metres height. This rising dust column shifts from left to right or north to south etc. depending on wind direction and current and eventually it gives an appearance that the dust is emitted from almost every inch of area in the stone crusher.
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Typical Economics of a Stone Crusher
During the field studies, the economic aspects of the stone crusher was discussed with several crusher owners in terms of fixed capital investment of setting up a stone crusher unit and typical annual operating costs and profit margins etc. Based on the information provided by the crusher owners (as reported), following tables are prepared which provide typical details on capital investment and annual operating costs of a small size stone crusher unit having production capacity of 20 Tons per hour.
Sources of Emissions
All quarrying and stone processing operations including surface mining , crushing, screening, material handling and transfer operations are potential sources of particulate emissions. These sources may be categorised as either process sources or fugitive dust sources. Process sources include those sources for which emissions are amenable to capture and subsequent control.
Fugitive dust sources generally involve the re-entrainment or settled dust by wind or machine movement. Factors effecting emissions from either source category include the type, quantity and the moisture content of the rock processed, the type of equipment and operating practices employed as well as topographical and climatic factors.
Emission During Mining Activity
Fugitive Emissions are generated during various mining activities such as drilling, blasting, excavation, breaking and loading etc. In some bigger mines the primary blasting emissions are quite substantial over a large area. The emissions during secondary blasting are also substantial but lesser compared to primary blasting. These emissions last only for a few minutes. There are hardly any controls adopted world over for controlling blasting emissions.
Emission During Transportation
During transportation of mined stones by heavy vehicles like trailors, trucks, dumpers, fugitive dust emission occur due to movement of heavy vehicles on earthern roads. The quantity of emissions depend on various aspects like climatic conditions, moisture in the soil, speed of the vehicle, frequency of the vehicles etc. Generally such emissions can be controlled to a great extent by spraying water on these roads intermittently.
Emission During Crushing Operation
During crushing operation, generation of particulate emissions is inherent and the emissions are most apparent at crusher feed and discharge points. The greater the reduction in size during subsequent crushing stages from primary, secondary to tertiary crushing, the higher the emissions.
Primary jaw crushers produce more dust than comparable gyratory crushers because of the bellows effect of jaw and because gyratory crushers are usually choke-fed, thus minimising the open spaces from which dust may be emitted. For subsequent reduction stages, cone or roller type crushers produce more fines as a result of attrition and consequently generate more dust.
Emissions During screening
In the screening section, the mixture of stones is classified and separated according to size. Generally the screening efficiency is considered to be in the range of 60 to 75%. The screening equipments commonly used include grizzlies, shaking screens, vibrating screens and revolving screens. Although screening may be performed wet or dry, dry screening is the most common. Dust is emitted from screening operations as a result of the agitation of dry stone. The screening of fines produces higher emissions than the screening of coarse sizes. Also screens agitated at large amplitudes and high frequency emit more dust than those operated at small amplitudes and low frequencies.
Emissions During material handling
In the material handling section, various handling devices like feeders, belt conveyors, bucket elevators and screw conveyors are used to transport crushed materials from one point to another. Particulates may be emitted from any of the material handling operations. Most of the emissions occur at transfer points. Since transport of material on the conveyor causes little disturbance of air and emissions that occur due to the wind are judged to be minimum. The transfer points include transfers from a conveyor on to another, into a hopper and on to a storage pile. The amount of uncontrolled emissions depends on the size distribution of the material handled, the belt speed and the free fall distance.
Nature and Spread of Emissions
The dust is generated primarily due to size reduction and handling of the stones at various stages. The major source of dust generation is during size reduction in the primary, secondary & tertiary crushers. The fines in the dust generated increases with subsequent stages of crushing i.e., more fines are generated in secondary crusher as compared to primary crusher. The dust is also generated during handling of stones, especially at the point where the stones fall through a height from places like one belt to another or from belt to hopper or stock piles etc. During vibratory screen large quantity of fine dust is emitted.
Nature and Spread of Emissions
Coarser part of the dust settles down within the premises but the finer particles get air borne and get carried away with wind to longer distances. The actual area of the source of the dust generation is quite small (about 0.5 to 1 square meter)at each source, but as the dust rises it spreads and typically the area in which it spreads is more than 10 –15 times larger than the area of actual emissions at about 3 to 4 metres height. This rising dust column shifts from left to right or north to south etc. depending on wind direction and current and eventually it gives an appearance that the dust is emitted from almost every inch of area in the stone crusher.