Mercury behaviour in a modern coal power plant: Mass balance and mercury attachment on particles

The study consists of mass balance studies of mercury, measurements of total mercury and mercury species in flue gases, measurement of gaseous flue gas compounds (CO, CO2, NOx, SO2, N2O, HCl, CH4), utilision studies of fly ash and modelling of mercury behaviour before an electrostatic precipitator (ESP) in a modern coal power plant. The measurements were done with two different air ratios. Gaseous mercury species are not likely to reach super saturation state in flue gases. In measurements at power plants it has been observed that a significant fraction of the mercury may be in the particulate phase, however. Here we present a constrained equilibrium - collision theory model approach, in which the distribution of elemental mercury and oxidized mercury species in the gas phase are determined by thermodynamic equilibrium at high temperatures (>800 K), whereas the oxidation is frozen at lower temperatures. The uptake of elemental gaseous mercury and oxidized gaseous mercury species on already existing particles in the flue gas is described by collision theory. The model application is difficult due to the lack of the actual particle concentration and particle size distribution in flue gases.