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Respirable Dust Control 143

Figure 10.4 Continuous miner section with exhaust ventilation.

Fig. 10.4 shows a typical layout where a continuous miner section is ventilated by
the exhaust system and a scrubber is used to collect dust at the source.

10.3.1 Water Spray Systems
A typical continuous miner is equipped with a set of sprays above and below the cut-
ting drum as well as one spray behind some cutting bits. Each spray head delivers 0.5
to 1 gpm of water at 100 to 150 psi. Total water consumption ranges from 30 to
60 gpm. Besides suppressing dust, the sprays also wet the coal, keep the cutting bits
cool, and serve as a fire suppression system (in case the cutting bit ignites a methanee
air mixture). A well-designed spray system should have the right kind of sprays (a
solid cone spray works best) that operates at optimum pressures and consumes the least
amount of water. Such a system can reduce the dust concentration by 60%. Typical
reductions range from 30% to 50% mainly owing to poor selection of sprays, too
low pressures, and bad locations for sprays. Ideally, there should be a spray behind
each cutting bit delivering 0.5 to 1 gpm of water at 100 to 150 psi. Such machines
are known as wet-head continuous miners, and they achieve the best dust control.
Several attempts were made in the United Kingdom and Germany to equip mining
machines with very high pressure water jets that not only suppressed dust but also
assisted in cutting hard coals. Such machines are expensive and as such found limited
applications. However, they reduced the specific energy of cutting coal (kwh/ton)
considerably and also provided effective dust control.