ABSTRACT

The “pulverized fuel ash” (PFA) or the so-called “¤y ash” (FA), used as a mineral admixture in cement and concrete, is a product of the pulverized coal ring system, through conventional boilers, mostly used in the thermal power plants. While carbon burns in oxidizing surroundings, the inorganic mineral matter gets sintered and liqueed at high temperature. The melt ¤ows down the walls of the furnace and about 25% gets collected as “bottom ash” (BA). It is crushed before disposal. The rest, PFA or FA, gets entrained in the up-¤owing hot gas in the form of ne particles, which get trapped in the economizer, air-preheater, mechanical separator, and, nally, battery of electrostatic precipitators (ESP). As a general practice in many countries, PFA and BA are mixed with water and transported to ash ponds/lagoons. The ash thus deposited in lagoons is called “lagoon ash” (LA) or “pond ash. It causes problems besides occupying huge stretches of agricultural land. Notwithstanding the greater utilization of PFA (and BA) in recent times in cement and concrete, in bricks, and for land lling, a large quantity of ash still lies unutilized. In order to get a measure of the enormity of the problem, the estimate on coal ash production in 2020, in the major producing countries or regions, is given in Table 1.1 [1]. The data in Table 1.1 should be viewed along with the estimated cement demand and carbon dioxide (green house gas) generation by cement industry for that period. The principal sources of green house gas generation in the cement industry are the manufacturing process, fossil fuels, transport, and power. Table 1.1 gives an estimate of possible reduction in CO2 emission using the mineral admixtures, namely, the PFA and the blast furnace slag. As per several estimates, the cement industry contributes about 5% of the global generation of carbon dioxide. The cement industry’s sustainable program developed by the World Business Council for Sustainable Development (WBCSD) prepared an “Agenda for Action” for a 5 year period from 2002 to 2007 [2], endorsed by the leading cement manufacturers of the world.