Coal dust is a fine
powder
A powder is a dry, bulk solid composed of many very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms ''powder'' and ''granular'' are sometimes used to distin ...
ed form of which is created by the crushing, grinding, or
pulverizing of
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when dea ...
. Because of the brittle nature of coal, coal dust can be created during
mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
, transportation, or by mechanically handling coal. It is a form of
fugitive dust
Fugitive dust is an environmental air quality term for very small particles suspended in the air, primarily mineral dust that is sourced from the soil of Earth's pedosphere. A significant volume of fugitive dust that is visible from a distance i ...
.
Grinding coal to dust before combusting it improves the speed and efficiency of burning and makes the coal easier to handle. However, coal dust is
hazardous
A hazard is a potential source of harm. Substances, events, or circumstances can constitute hazards when their nature would allow them, even just theoretically, to cause damage to health, life, property, or any other interest of value. The probabi ...
to workers if it is suspended in air outside the controlled environment of grinding and
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
equipment. It poses the acute hazard of forming an explosive mixture in air and the chronic hazard of causing pulmonary illness in people who inhale excessive quantities of it.
The distribution of the particle-size of coal dust is frequently measured in
mesh
A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands.
Types
* A plastic mesh may be extruded, oriented, ex ...
. The British slang term for cheap fuel consisting of coal dust (slack) containing small lumps of coal (nuts) is
nutty slack.
Risks
The
Occupational Safety and Health Administration
The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...
(OSHA) has set the legal limit (
Permissible exposure limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupational S ...
) for coal dust exposure in the workplace as 2.4 mg/m
3 (5% SiO
2) over an 8-hour workday. The
National Institute for Occupational Safety and Health
The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...
(NIOSH) has set a
Recommended exposure limit
A recommended exposure limit (REL) is an occupational exposure limit that has been recommended by the United States National Institute for Occupational Safety and Health. The REL is a level that NIOSH believes would be protective of worker safety ...
(REL) of 1 mg/m
3 (measured by MSHA) or 0.9 mg/m
3 (measured by ISO/CEN/ACGIH) over an 8-hour workday.
Explosions
Coal dust suspended in air is explosive—coal dust has far more
surface area
The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc ...
per unit weight than lumps of coal, and is more susceptible to
spontaneous combustion
Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high tem ...
. As a result, a nearly empty coal store is a greater explosion risk than a full one. The main attempts at prevention include using
safety lamp
A safety lamp is any of several types of lamp that provides illumination in coal mines and is designed to operate in air that may contain coal dust or gases, both of which are potentially flammable or explosive. Until the development of effectiv ...
s, adding stone dust coffers to mine galleries to dilute the coal dust, watering workings and ensuring efficient
ventilation
Ventilation may refer to:
* Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation
** Mechanical ventilation, in medicine, using artificial methods to assist breathing
*** Ventilator, a ma ...
of all the workings.
Another means of preventing coal dust explosions is by placing
rock dust
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
in the mine, which is usually pulverized
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
dust, which absorbs thermal energy from the heated gasses. Rock dusting has been used since the early 1900s, but there have been technological improvements since then.
The worst
mining accident
A mining accident is an accident that occurs during the process of mining minerals or metals. Thousands of miners die from mining accidents each year, especially from underground coal mining, although accidents also occur in hard rock mining. C ...
s in history have been caused by coal
dust explosion
A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or ...
s, such as the
disaster at Senghenydd in
South Wales
South Wales ( cy, De Cymru) is a loosely defined region of Wales bordered by England to the east and mid Wales to the north. Generally considered to include the historic counties of Glamorgan and Monmouthshire, south Wales extends westwards ...
in 1913 in which 439 miners died, the
Courrières mine disaster
The Courrières mine disaster, Europe's worst mining accident, caused the death of 1,099 miners in Northern France on 10 March 1906. This disaster was surpassed only by the Benxihu Colliery accident in China on 26 April 1942, which killed 1,5 ...
in Northern France which killed 1,099 miners in 1906, the
Luisenthal Mine
The Luisenthal Mine was a coal mine near Völklingen. The mine was known as the site of the largest mine accident in the history of the German Federal Republic, when 299 miners died on 7 February 1962.
1962 mine disaster
On 7 February 1962 a me ...
disaster in Germany, which claimed 299 lives in 1962, and the worst: the explosion at
Benxihu Colliery
Benxihu (Honkeiko) Colliery (), located in Benxi, Liaoning, Republic of China (1912–1949), China, was first mined in 1905. Originally an iron and coal mining project under joint Japanese and Chinese control, the mine came under predominantly Japa ...
, China, which killed 1,549 in 1942. Such accidents were usually initiated by
firedamp
Firedamp is any flammable gas found in coal mines, typically coalbed methane. It is particularly found in areas where the coal is bituminous. The gas accumulates in pockets in the coal and adjacent strata and when they are penetrated the releas ...
ignitions, the
shock wave
In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...
of which raised coal dust from the floor of the mine galleries to make an explosive mixture. The problem was investigated by
Michael Faraday
Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
and
Charles Lyell
Sir Charles Lyell, 1st Baronet, (14 November 1797 – 22 February 1875) was a Scottish geologist who demonstrated the power of known natural causes in explaining the earth's history. He is best known as the author of ''Principles of Geolo ...
at the colliery at
Haswell County Durham
Haswell is a village in County Durham, in England. It is situated east of the city of Durham, south of the city of Sunderland and north-west of the town of Peterlee.
Haswell was the birthplace of world champion road racing cyclist Tom Simps ...
of 1844, but their conclusions were ignored at the time.
Lung and skin problems
Coalworker's pneumoconiosis
Coal workers' pneumoconiosis (CWP), also known as black lung disease or black lung, is an occupational type of pneumoconiosis caused by long-term exposure to coal dust. It is common in coal miners and others who work with coal. It is similar to b ...
, or black lung disease, is caused by inhaling coal dust, typically dust produced in
coal mining
Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...
. Government agencies in the United States have set exposure limit guidelines for coal dust inhalation.
Energy generation
For use in thermal
power plant
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
Many pow ...
s, coal is ground into dust using a device called a powdered coal mill.
The resulting product, called powdered coal or pulverized coal, is then generally used in a
fossil fuel power plant
A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, wh ...
for
electricity generation
Electricity generation is the process of generating electric power from sources of primary energy. For electric utility, utilities in the electric power industry, it is the stage prior to its Electricity delivery, delivery (Electric power transmi ...
. Pulverised coal is a significant dust explosion hazard, as large quantities are suspended in air for transfer from the mill to the power plant. Explosions have occurred when the flow drops and flames in the burning chamber pass back along the ductwork delivering fuel.
See also
*
Coal burner
A coal burner (or pulverized coal burner) is a mechanical device that burns pulverized coal (also known as powdered coal or coal dust since it is as fine as face powder in cosmetic makeup) into a flame in a controlled manner.
Coal burner is mainly ...
*
Coal-water slurry fuel
Coal-water slurry fuel is a combustible mixture of fine coal particles suspended in water. It can be used to power boilers, gas turbines, diesel engines and heating and power stations.
Characteristics
A coal-water slurry fuel is defined by a num ...
*
Pulverized coal-fired boiler A pulverized coal-fired boiler is an industrial or utility boiler that generates thermal energy by burning pulverized coal (also known as powdered coal or coal dust since it is as fine as face powder in cosmetic makeup) that is blown into the firebo ...
Notes
References
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External links
Mining Topic: Explosion Prevention
{{Authority control
Coal
Mine safety
Occupational diseases
Dust
Powders