Coal dust explosions in underground coal mines are prevented by generous application of rock dust (usually limestone). If an explosion should occur, the rock dust disperses, mixes with the coal dust and prevents flame propagation by acting as a thermal inhibitor or heat sink.
Why is limestone powder scattered around a coal mine?
Limestone powder, known as rock dust, is spread throughout the mine workings on a regular basis. … When explosions do occur, the dispersed limestone powder absorbs the heat generated from the explosion and will either stop the chain reaction or reduce the intensity of the explosion.
What is rock dusting in coal mines?
Rock dust (generally pulverized limestone dust) serves as a heat sink material that prevents or suppresses a propagating coal dust explosion through the absorption of thermal energy from the heated gases and absorption of radiant energy, which reduces the preheating of unburned coal particles ahead of the flame front.
Why do coal mines explode?
Coal mine explosions are generally caused by either methane or coal dust. Methane gas is a byproduct of coal. It can build up over time in coal mines when there are not enough other types of gases to dilute it to prevent an explosion. … Explosions happen when the methane comes in contact with a heat source.
What are the two types of coal mines?
There are two types of room and pillar mining–conventional mining and continuous mining. Conventional mining is the oldest method and accounts for only about 12% of underground coal output. In conventional mining, the coal seam is cut, drilled, blasted and then loaded into cars.
Which factor explains why coal dust is explosive?
Coal dust suspended in air is explosive—coal dust has far more surface area per unit weight than lumps of coal, and is more susceptible to spontaneous combustion. As a result, a nearly empty coal store is a greater explosion risk than a full one.
What caused the Westray mine disaster?
Early in the morning beneath the small town of Plymouth, Nova Scotia, a methane gas leak into the Westray mine shaft from the Foord coal seam mixed with coal dust and caused in an explosion. … The nearby Allan mine, which closed in 1951, experienced eight methane explosions in its 40-years of operations.
What are slurry ponds?
Any natural or artificial pond or lagoon for settling and draining the solids from washery slurry.
How does removing the overburden during coal extraction affect the environment?
Strip mining eliminates existing vegetation and alters the soil profile, or the natural soil layers. Mining disturbs and may even destroy the beneficial micro-organisms in the topsoil. Soil also may be damaged if reclamation operations mix the topsoil with subsoils, diluting matter in the surface soil.
Are coal mines dangerous?
Open cut hazards are principally mine wall failures and vehicle collisions; underground mining hazards include suffocation, gas poisoning, roof collapse, rock burst, outbursts, and gas explosions. Firedamp explosions can trigger the much-more-dangerous coal dust explosions, which can engulf an entire pit.
How explosive is methane?
While any methane concentration within the flammability range has the potential to explode in the presence of an ignition source, a methane concentration of ~9.5% in air can produce the most damaging explosion.
What gas is responsible for most of the explosion in coal mines?
What are the 4 types of coal?
Coal is classified into four main types, or ranks: anthracite, bituminous, subbituminous, and lignite.
Which is the best quality of coal?
Anthracite: The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter.
Which country has the best quality coal?
Experts told Fact Check that Australia’s coal is on average high quality as a result of its low moisture and ash content, and high carbon content, compared with other countries, particularly Indonesia, the largest coal exporter in the world.