AMETEK Land - World Coal - Beat the Heat
Between the time a piece of coal is dug out of the ground and is burned in a power plant boiler, it has been through many stages of transportation and storage. One of the advantages of coal as a fuel for power generation is the ability to store substantial quantities on site. This provides a strategic buffer of at least one month's fuel supply, which can be valuable if there is a short- or long-term disruption in the supply chain. Stockpiles also allow producers and consumers to average out seasonal variations in electricity demand.
Transportation of coal from the mine to the plant includes many handling and storage steps. Typically, the coal is loaded onto a train, unloaded onto a storage pile, coarsely crushed, moved to a day silo and finally pulverised before being transported to the boiler. At each stage, it is important to ensure that the coal is in good condition and can be moved safely to the next.
Oxidation is a critically important problem. When coal is exposed to the air, the volatile components combine with oxygen in an exothermic reaction, leading to spontaneous heating. The Arrhenius equation tells us that the rate of oxidation approximately doubles with every 10°C increase in temperature, therefore a runaway condition can occur in which the coal self-ignites in a process of spontaneous combustion.
In addition to the obvious safety concerns, spontaneous heating and combustion can result in the loss of the purchased coal, which is then no longer available for use in the boiler. Lower rank coals are more susceptible to oxidation than hard coals. Paul Baruya of the IEA Clean Coal Centre has reported that sub-bituminous coals can lose as much as 1.5% of its mass between the mine and the power plant, and Brazilian coal stored for 10 months may lose over 5% of its heating value.
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