The mineral phase composition of fly ashes from coal fired Thermal Plants is a function of nature of the coal, coal fineness, efficiency of collection of fly ash. The mineral matter mineralogy & Chemistry , as well as , nature of coal , overboard temperatures and temperature of generation of fly ash , primarily determines the mineralogical composition of the generated fly ash , resultantly to a large extent influencing the pozzolanic reactivity of the fly ashes, as it would determine the type of crystallites formed as well as the chemistry of amorphous / glass content of fly ashes.
At the Quality & Product Development Division of ACC Ltd., India, considerable studies have been carried out on the fly ashes of different coal fired thermal plants in India, comprising of the pulverized fuel fired mega thermal plants as well as the crushed coal fired AFBC / CFBC type Captive Power Plants, with higher temperature (>1350oC) as well as lower (<900oC) overboard temperatures respectively. It has been observed that the temperatures at which the fly ashes are generated determines the morphological characteristics and mineralogical make up of the fly ash.
In order to understand the influence of different minerals present in coal on the resultant fly ash properties, synthetic coal ashes were produced under lab – simulated conditions, simulating lower as well as higher temperatures of fly ash generation. The changes in the composition of the mineral matter in coal being produced by external additions to coal of different additives at different levels.
The paper discusses the mineralogy of the fly ashes produced under the different simulated conditions of temperature, with the different additives attempting to evolve an interrelationship of the different additions to the resultant mineralogy of the fly ash produced, as well to its pozzolanic/cementitious property.
The authors conclude that the reactivity of the fly ashes can be altered with a suitable mineral additive. Such fly ashes with improved characteristics would help in its enhanced utilization.. The Paper was presented and published at 12th NCB Int Seminar