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The propensity of colliery wastes to combust spontaneously, is related to the specific ability of seams or splits of seams to self heat during or after mining. The instances of burning coal wastes are increasing with the increase in the percentage of coal mined by open cut methods. Wastes created in open cut mining often contain coal from seams and splits that for either reasons of quality and/or thickness are not reclaimed. This coal is often blended with the overburden by the heavy machinery used in mining, and if liable to spontaneous combustion results in numerous pockets of heating across and through the wastes. This process of spreading the source of heatings through the overburden makes reclamation of mined out areas very awkward and in two cases known to authors reclamation has failed over large areas due to spontaneous combustion.
Spontaneous combustion in washery rejects has also been a problem in with coal from certain seams. Washery rejects can be seen burning after many years in a number of locations in New South Wales. The extent of environmental impact of such reject fires however is less in potential than that from burning overburden, in that the rejects are normally more concentrated and not as extensive(and therefore more easily disposed of by deep burial) as overburden. Colliery rejects are also often able to be re-washed to obtain otherwise lost coal values, while at the same time reducing the propensity for spontaneous combustion.
Other sources of environmental damage from coal spontaneous combustion are burning coal stockpiles and insitu coal seams. These sources of pollution are normally short lived due to the economic cost of losing mined or minable coal.
If a major source of pollution is from burning spot fires in overburden and reclaimed mined areas, a means of reducing this environmental hazard is to identify coal that is liable to spontaneous combustion but not to be taken in the mining process(but is to be disposed of with the overburden). If this coal was identified during the exploration or mine planning it could be selectively removed during mining and safely disposed of.
M.E.T.T.S. by using techniques developed during this study, will be able to assist mining operators predict the likelihood of spontaneous combustion in their coal and overburden. Such a prediction will assist operators in designing their mining techniques (so as to avoid spontaneous), better manage their stockpiles, and improve their land reclamation practices. By monitoring the spontaneous combustion potentials of coal in stockpiles, users of coal will have fewer problems with stockpile fires, and will have a better environmental scorecard.
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