Dust suppression in Drilling, Blasting, and Crushers
The Dust Suppression system is very much required to control dust in large-entry stone mines, including both silica dust and Blue metal. Most stone mines are limestone mines, but substantial minorities are marble, sandstone, granite mines and Blue metal. These mines differ from most others in that entry widths are 30 ft or more and entry heights are 25 ft or more. Such mines, developed with room-and pillar methods, have large open areas that can make ventilation and dust control more difficult. Because of the difficulty of ventilating stone mines, improved ventilation is a major focal point. However, this also covers the control of dust from drills, blasting, and crushers. Another part of the chapter covers enclosed cabs, an effective dust control technique for some workers.
The major dust compliance problem in stone mines is caused by silica (quartz) in the rock. Mines in high-silica rock, 8% or more, are far more likely to have a dust problem than those where there is less silica. Pollution Control experts have analyzed Mine safety and health hazardousness from dust sampling results of the stone Crusher industry. They have concluded that, on average across the India, the workers exposed to the highest dust concentrations are rotary drill operators, front-end loader operators, truck drivers, and crusher operators. However, there are many regional differences. Also, occupations that work outside of cabins, such as blasters, roof bolters, and laborers, can be exposed to high dust levels.
CONTROL OF DUST FROM DRILLS, BLASTING, AND CRUSHERS
Drills, blasting, and crushers produce the most dust in stone mines. Drill dust can usually be controlled by proper maintenance of the water supply system. Blasting dust is controlled by firing off-shift. Crusher dust, a more difficult problem, is usually managed by high pressure Hydro Atomizing.
Control of drill dust Drill dust is suppressed by water injected through the drill steel, a common practice for many years .Usually, respirable dust is reduced by 95% or better However, this does not prevent dust from entering the air during the initial collaring period as the drill hole is started. Various means have been tried to prevent the escape of dust during collaring. These range from simple handheld sprays to elaborate types of suction traps around the end of the drill steel. None of these are very efficient.
Drills powered by compressed air are much less common than in the past, eliminating the dust problems associated with their use. For example, if some of the compressed air operating the drill leaks into the front head of the drill and escapes down the drill steel, it will cause dry drilling and carry dust out of the hole. Compressed air escaping through the front head release ports will atomize some of the water in the front head. This atomized water evaporates rapidly and, if the water is dirty, many dust particles will remain in the air, has listed the factors that can lead to high dust levels on drills. Many result from lack of proper maintenance. These are failure to use water, inadequate quantities of water, plugged water holes in the drill bit, dull drill bits, and dry collaring.
Control of blasting dust Control of blasting dust is described in more detail in the hard-rock mines. Water is used to spray the blast area beforehand. Ventilation is used to exhaust fumes and dust via an untraveled return and between shifts. In most cases, the faces are shot during an off-shift, so no workers are in the mine at the time of the blasts. Studies have shown, that in stone mines the retention time of the dust is usually less than 2 hr. If ambient levels of silica dust are high after this period or if workers are exposed to an excessive amount of dust from blasting when they reenter the mine, it usually indicates that the ventilation needs to be improved.
Control of dust from crushers Dust from crushers is controlled by water sprays and local exhaust ventilation from the crusher enclosure. The amount of water needed to do the job is hard to specify. It depends on the type of material crushed and the degree to which water will cause downstream handling problems. If the rock is dry, a starting point is to add a water quantity equivalent to 1% of the weight of the material being crushed. The nozzle pressure of sprays at the grizzly and crusher jaw should be below 1000 psi to avoid stirring the dust cloud and reducing the capture efficiency of the ventilation system, the dust control has a more comprehensive discussion on why high spray pressures should be used most of the time.
The amount of air required for dust control depends on how much the crusher can be enclosed. Enough air should be exhausted from a plenum under the crusher to produce a strong in draft at the jaw, grizzly, and any other openings around the crusher. The required airflow is usually large and how dust from a 5-ft cone crusher was reduced by using a 75,000-cfm. Large air quantities may be required because falling rock induces its own airflow. It was found that, the amount of air required to produce an in draft in surge bins at crusher installations. About 35,000 cfm was required at a large crusher installation. Exhaust ventilation system and a control booth for the operators. If large (80% or more) dust reductions are sought for workers near a crusher, the most practical way to achieve this is to provide an enclosed and pressurized control booth supplied with filtered air. has given a comprehensive set of design principles for dust control at crushing and screening operations. Crushers need lots of air and lots of water because they break lots of rock.
In stone mines, dust that escapes the crusher is hard to contain because of the large cross sectional area of the entries. Figure 4-1 shows a conceptual approach to controlling crusher dust in a limestone mine. The crusher is located in a crosscut that has been benched to facilitate dumping from trucks. The crusher operator is located in an enclosed booth that is pressurized with filtered air. The crosscut is divided by a stopping (or leak-tight curtain) that essentially puts the crusher and dump point in a stub heading. Air is exhausted from a plenum under the crusher to create an in draft at the crusher jaws. It is then directed through the stopping. Dust in this air can be removed with a bag house or directed into the return. Directing air through the stopping creates an inward air movement in the Passageway. Because of this inward air movement, dust that escapes the crusher is more likely to stay confined within the stub heading and not escape into the rest of the mine. If the air velocity in the Passageway is not high enough to confine the dust, a “half-curtain” approach might be helpful. Installing a half curtain in the passageway reduces the cross-sectional area and raises the air velocity. The higher air velocity provides better dust confinement. It first confines dust in the crusher, then in the passageway. Whether all of this is necessary will depend on the circumstances in each individual mine. An enclosed operator booth alone may be adequate. However, it is hard to reliably get better than a 90% dust reduction in such booths under real mining conditions, so additional measures to reduce dust may be required.