Calculations of the Chemistry of Coal Combustion Effluents

Unique computer programs and solution models have been developed to perform calculations of the chemistry of coal combustion involving hundreds of chemical species in gaseous, solid and liquid phases, as well as the complex solution chemistry inherent in liquid silicates. In addition, we have shown that kinetic constraints on the equilibria can alter the chemistry in significant ways. For Illinois #6 coal at high temperatures (2::1400 K), the condensed phases are liquid and solid silicates, silica, and iron oxides (magnetite and hematite). At lower temperatures, liquid and solid sulfates, silica, and solid silicates are present. Because of the relative volatility of alkalis (as N aCI(g)) and the relatively slow kinetics expected for the reaction of S03 and NaCI with solid silicates, liquid alkali sulfates can form on particulate surfaces, enhancing agglomeration and fouling. In addition, corrosion by both liquid silicates and sulfates can be significant. The computer calculations provide detailed information on the total chemistry of coal combustion, some of which may be difficult to measure. When coupled with an experimental program that permits the deduction of kinetic constraints for a particular mode of combustion, the computer program will permit one to make reliable predictions, and, thus, greatly reduce the number of measurements needed to deduce the chemistry for any particular coal. Our methods provide a promising tool for formulating strategies to reduce fouling and corrosion.