Influence of Coal-Fired Power Plant Emissions Regulations and Consequent Engineering Controls and Coal-Supply Modifications on Fly Ash Chemistry and Petrology

The chemistry and petrology of fly ash are controlled by a number of factors: (1) chemistry of the feed coal (and added fuels, such as petroleum coke, tires, biomass, etc.), (2) particle size of the fuel feed (controlled by pulverized fuel vs. cyclone combustion, maintenance of pulverizers, etc.), (3) design of the boiler and pollution-control system, and (4) temperature of the flue gas at the collection point. In general, for any electrostatic precipitator or baghouse system, the concentrations of volatile trace elements in fly ash will increase with a drop in the flue gas temperature and a decrease in the particle size. Mercury is an exception, requiring carbon to be present in the fly ash for any appreciable amount of Hg to be captured. From the 1970s to the present, several air-quality regulations have forced coal-fired power plants to switch coal supplies, add new emission-control equipment, reconfigure boilers, or all of the above. As a consequence, the nature of fly ash has changed. In this study, several Kentucky power plants were followed by sampling at 5-year or lesser intervals. Changes in the fly ash chemistry and petrology were documented.