Mercury removals by existing pollutants control devices of four coal-fired power plants in China.

The mercury removals by existing pollution control devices and the mass balances of mercury in four coal-fired power plants of China were carried out based on a measurement method with the aluminum matrix sorbent. All the plants are equipped with a cold-side electrostatic precipitator (ESP) and a wet flue gas desulfurization (FGD) in series. During the course of coal stream, the samples, such as coal, bottom ash, fly ash, gypsum and flue gas, were collected. The Hg concentrations in coals were measured by CVAAS after appropriate preparation and acid digestion. Other solid samples were measured by the RA-915+ Zeeman Mercury Spectrometer. The vapor phase Hg was collected by a sorbent trap from flue gas and then measured using CVAAS followed by acid leaching. The mercury mass balances were estimated in this study were 91.6%, 77.1%, 118% and 85.8% for the four power plants, respectively. The total Hg concentrations in the stack gas were ranged from 1.56-5.95 microg/m3. The relative distribution of Hg in bottom ash, ESP, WFGD and stack discharged were ranged between 0.110%-2.50%, 2.17%-23.4%, 2.21%-87.1%, and 21.8%-72.7%, respectively. The distribution profiles were varied with the coal type and the operation conditions. The Hg in flue gas could be removed by ESP and FGD systems with an average removal efficiency of 51.8%. The calculated average emission factor was 0.066 g/ton and much lower than the results obtained ten years ago.