Role of clay minerals in UK coal combustion

Clay minerals are the dominant minerals in coals delivered to UK power stations and are therefore major ash contributors. Clay content carries an economic penalty in loss of calorific value of the coal and in costs associated with coal and ash handling and ash disposal, but clays also play a more direct role. A geographic distribution of clay minerals in UK Carboniferous coals is reflected in fly ash analyses and their properties. On a smaller scale, the distribution of clay minerals within individual coals, in conjunction with the fly ash analyses, may provide information on combustion mechanisms. In the fly ash, the mullite crystals are largely attributed to kaolinite, whereas illite contributes towards the glass and the cenospheres. Ash properties within the power plant may be predicted from the ash analyses, but improved predictions could result from the inclusion of mineralogical data. Although many of the elements of environmental concern in coal combustion are introduced into the coal swamp in solution and are incorporated into minerals other than the clays; nevertheless, the detrital clay input is responsible for significant concentration levels for some elements.