Page 400 - Advanced Mine Ventilation

Prevention of Frictional Ignitions 369

Figure 22.4 A typical antiignition back spray.

In the United States, an attempt was made by the author to modify a Joy continuous
miner to include a high-pressure pump and assist coal cutting with high-pressure (up to
5000 psi) water. The design failed for the following two reasons: (1) considerable
leakage through and frequent failure of seals and (2) blockage of pump and nozzles
because of impurities in water supply. Considering the fact that most frictional
ignitions take place on continuous miner faces, efforts to develop water-jet-assisted
coal cutting for continuous miners should be encouraged.
Benefits of water-jet-assisted cutting in conjunction with wet cutting can be
summarized as follows:
1. Minimized frictional ignitions,
2. Reduced respirable dust concentration,
3. Increased bit life,
4. Reduced machine vibration leading to increased equipment life, and
1
5. Improved product (raw coal) size ( / 4 inch size of coal is significantly reduced).
Fig. 22.5 shows a bit with a combination of a high-pressure jet in front of the bit to
assist cutting and a rear, bit-flushing spray to suppress ignitions. The system combines
the benefits of both wet cutting and water-jet-assisted cutting.