Fine bituminous coal dust is highly explosive when suspended in air. In a typical coal dust explosion, the dust is scoured by a small methane gas explosion, which also provides the initiating flame. If the initiating explosion is strong enough, even wet coal dust can explode.
Can coal explode if present as a dust in air?
Sources of dust Many common materials which are known to burn can generate a dust explosion, such as coal and sawdust. Powdered metals (such as aluminum, magnesium, and titanium) can form explosive suspensions in air, if finely divided.
What is the chemical reaction in coal mines that causes explosions?
Methane explosions occur when a buildup of methane gas contacts a heat source and there is not enough air to dilute the gas level below its explosion point. Likewise, fine particles of coal dust in the right concentration that contact a source of heat can also be explosive.
Why does dust explode so violently if ignited?
If a concentration of dust is too low, there is not enough of it present to fuel an explosion. If the concentration is too high, there is not enough oxygen to support combustion. The ignition causes the dust to combust quickly—a process called deflagration that creates a wave of high air pressure.
How do you stop coal dust explosion?
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.
Is coal dust hazardous?
Exposure to coal mine dust causes various pulmonary diseases, including coal workers’ pneumoconiosis (CWP) and chronic obstructive pulmonary disease (COPD). 2. Coal miners are also exposed to crystalline silica dust, which causes silicosis, COPD, and other diseases.
What coal dust is explosive?
The resulting product, called powdered coal or pulverized coal, is then generally used in a fossil fuel power plant for electricity generation. Pulverised coal is a significant dust explosion hazard, as large quantities are suspended in air for transfer from the mill to the power plant.
Does coal dust burn?
Preventive procedures, however, must rely on fundamental knowledge concerning the behavior of coal dust combustion. In addition, it is known that coal particles do not always burn simply as shrinking spheres, but can burn internally and form cenospheres (hollow spheres) as well.
Is coal dust 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.
Why is grain dust explosive?
Moving grain generates dry dust and that grain dust is highly combustible. The primary explosion is frequently the result of ignition sources such as welding sparks or overheated bearings causing fuel sources such as corn or wheat dust to combust.
How can dust explosion be prevented?
To prevent a dust explosion, OSHA recommends employers:
- Implement a hazardous dust inspection, testing, housekeeping and control program.
- Use proper dust collection systems.
- Regularly inspect for dust residues in open and hidden areas.
Is coal highly flammable?
Coal is a readily combustible rock consisting more than 70% by volume and 50% by weight of carbonaceous material [20]. The inorganic non-combustible compounds which produce sulphur compounds and ash is the non-carbonaceous matter and mineral matter in coal.
What causes dust explosions in coal mines?
In most cases, dust explosions are first initiated by methane explosions. The pressure wave or wind forces created by a small methane explosion can scour the mine entry, blowing coal dust up into the air.
What are the different types of coalmine explosions?
There are two main types of coalmine explosions: methane and coal dust. Methane explosions occur when a buildup of methane gas contacts a heat source and there is not enough air to dilute the gas level below its explosion point.
How does rock dusting prevent explosions?
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. It is critical that this inertization practice of rock dusting be consistent with the mining process.
What is produced in underground coal mining?
Underground coal mining produces finely divided coal dust that deposits throughout the mine and serves as a source of combustible material for coal dust explosions. Limestone powder, known as rock dust, is spread throughout the mine workings on a regular basis.
