Page 213 - Advances In Productive, Safe, and Responsible Coal Mining

192 Advances in Productive, Safe, and Responsible Coal Mining

investigated other less-recognized ignition sources such as hot solids, thermite spar-
king from light metal alloys, adiabatic compression, static electricity, lightning
strikes, and sliding friction between blocks of rock or between rock and steel. In gen-
eral, technical instructions and regulations must be strictly followed during mining
operation to avoid unwanted disasters and to minimize the possibility of human error.
For instance, the surface temperature of permissible electrical and diesel engines
should not exceed 150°C (302°F). Also, in very gassy longwall panels, plows are less
likely to produce sparks than shearers, and the shallow cut made by a plow releases
less CMM per pass than that of shearer.
The spray fan system is an auxiliary ventilation system that makes use of the air-
moving ability of water sprays. Moving droplets in the spray with a suitable water
pressure and an appropriate spray location will drag the surrounding air forward to
create a considerable airflow.
According to Kissell [4], CMM ignitions at longwall faces may be controlled by:
installing methane detectors in critical locations to prevent CMM accumulations;
l
installing water sprays behind each cutter bit to quench the hot metal streak;
l
providing better ventilation around the shearer to control methane build up;
l
mounting arranged water sprays on the shearer to eliminate eddy zones;
l
replacing worn bits regularly;
l
l changing the attack and tip angles of conical bits; and
l using radial bits instead of conical bits.

10.4 CMM utilization

In underground coal mines, CMM has the potential to be extracted before, during, and
after mining as a valuable byproduct. Consequently, the mining industry’s interest in
recovering CMM for sale or for on-site utilization is increasing.
CMM is most often used for power generation, district heating, or boiler fuel; but it
can also be used as town gas or sold to natural gas pipelines. The production of gas
from coal has a long history and town gas, which is a potent mixture of methane,
hydrogen, and carbon monoxide, and was commonly used as a domestic fuel until nat-
ural gas became widely available. CMM can be injected into natural gas pipelines if
the infrastructure is available, since CMM is usually sweet (not sour like natural gas)
as it does not contain hydrogen sulfide (H 2 S). However, enrichment of the gas may be
required before CMM is considered pipeline quality.
CMM can also be used to generate power using a number of technologies, includ-
ing gas turbines, internal combustion engines, and boiler or steam turbines. This
on-site capability is valuable because the mining operation needs electrical power
to operate machinery and ventilation fans, coal cleaning plants, coal dryers to remove
moisture, and other surface facilities. Ventilation fans at an underground mine can
consume more than 70% of the total electricity used at the site.
There are a number of practical technologies for liquefying and compressing nat-
ural gas as LNG or CNG for vehicle fuel. In some countries, proper technologies that