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A large compost pile can spontaneously combust if improperly managed. 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 temperatures) and finally, autoignition. [1]
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. However, five elements are needed for an explosion to occur: oxygen, an ignition source, coal dust, dispersion of the coal dust, and confinement of the dust. [4]
Spontaneous combustion is caused when coal oxidizes and airflow is insufficient to dissipate heat; this more commonly occurs in stockpiles and waste piles, rarely in bedded coal underground. Where coal fires occur, there is attendant air pollution from emission of smoke and noxious fumes into the atmosphere.
The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. [1]
The burning of a solid material may appear to lose weight if the mass of combustion gases (such as carbon dioxide and water vapor) are not taken into account. The original mass of flammable material and the mass of the oxygen consumed (typically from the surrounding air) equals the mass of the flame products (ash, water, carbon dioxide, and ...
Larger coal stockpiles have a reduced rate of heat loss, leading to a higher risk of spontaneous combustion. Travelling, luffing boom stackers that straddle a feed conveyor are commonly used to create coal stockpiles. Tunnel conveyors can be fed by a continuous slot hopper or bunker beneath the stockpile to reclaim material.
Photomicrograph made with a scanning electron microscope and back-scatter detector: cross section of fly ash particles. Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK)—plurale tantum: coal combustion residuals (CCRs)—is a coal combustion product that is composed of the particulates that are driven out of coal-fired boilers together with the flue gases.
The combustion of coal releases diverse chemicals into the air. The main products are water and carbon dioxide, just like the combustion of petroleum. Also released are sulfur dioxide and nitrogen oxides, as well as some mercury. The residue remaining after combustion, coal ash often contains arsenic, mercury