The Chemical and Mineralogical Characteristics of fly ash produced in the coal fired thermal plant is a function of nature of the coal, coal comminution system, boiler type & efficiency, fly ash collection ESP fields, as well as on the loading at which the thermal plant operates etc, as a result from the same thermal Plant source the fly ash characteristics could vary substantially in its Mineralogical and Morphological properties .
The Mineralogical make up of fly ash is of course governed by the Chemical composition of the Mineral matter of coal as well as the mineral matter Contents . The mineralogy of fly ash determines the reactivity of fly ash in its various applications, for e.g the pozzolanic reactivity of fly ash would depends on glassy/ amorphous silicate phase of fly ash and specific surface area available for reaction with lime .
Studies carried out by Joshi R.C and Rosauer E.A on synthetic fly ashes [2,3] produced at laboratory scale, indicated that prolonged heat treatment promotes sintering and devitrification which in turn influences other properties . Iron in an otherwise pure alumino-siliceous ash reduces pozzolanic strength, whereas calcium in an aluminosiliceous fly ash results in a very reactive ash.
The work by diamond concluded that fly ashes with CaO content upto 20% showed maximum indicative of siliceous glass whereas Haobostudied the influence of CaO addition on granulated cinders concluded that with increase in CaO content, the vitreous network of granulated cinders becomes disordered and is destroyed, the polymerization of network formed reduces and the hydraulic activity of granulated cinder improves.
Thus fly ash Mineralogy can be altered by Compositional as well as process parameters which alter the properties of fly ash, however this aspect necessitates better understanding of the influence of different minerals and minor constituents present in coal and processing conditions on the resultant fly ash properties so as to Tailor make a fly ash with enhanced reactivity in its applications.
Altering the Mineralogy of an available fly ash is another avenue available on hand to alter the Mineralogy of the fly ash for its desired applications and enhanced usage.
This Paper refers some of the reported work on Mineralogical alteration with the Fly ashes available and altering the Mineralogy of fly ashes during generation. The Paper also discusses some of the avenues studied at the author’s lab to alter Mineralogy of available fly ash as well as attempts on altering the fly ash Mineralogy at generation stage in a Coal Fired Power Plant.