Utilization of Discarded Fly Ash as a Raw Material in the Production of Portland Cement

Abstract This paper describes the high-volume use of fly ash as a raw material in the manufacture of Portland cement. This approach provides three critical benefits to cement manufacturing and the environment. First, being rich in silica, alumina, and iron, the fly ash can essentially replace raw materials in cement raw feed, such as shale and clay, which are otherwise mined or purchased. Second, the carbon content in fly ash can provide a fuel supplement for the energy-intensive cement manufacturing process. Finally, high-volume consumption of fly ash will reduce the annual volume of waste and improve the overall environment. This concept has been repeatedly demonstrated at commercial scale in which several hundred tons of dry fly ash with up to 20 % unburned carbon was used as a raw mix component in several cement plants in the Midwest. Prior to the demonstrations, the fly ash was evaluated for compatibility and fuel value to optimize its use (at rates up to 6 % of the raw mix). The demonstrations realized several material, operational, energy, and environmental benefits. The plant operations were efficient, stable, and predictable. The cement plants realized an approximate fuel savings of 4 % and a nearly 10 % increase in cement production. Cements produced from the demonstrations showed properties comparable to those of the normally produced cements. The demonstrations prove that using fly ash in this regard is beneficial to both cement plants and power plants, and the environment.