Mercury emission and speciation of coal-fired power plants in China

Abstract

Abstract. Comprehensive field measurements are needed to understand the mercury emissions from Chinese power plants and to improve the accuracy of emission inventories. Characterization of mercury emissions and their behavior were measured in six typical coal-fired power plants in China. During the tests, the flue gas was sampled simultaneously at inlet and outlet of selective catalyst reduction (SCR), electrostatic precipitators (ESP), and flue gas desulfurization (FGD) using the Ontario Hydro Method (OHM). The pulverized coal, bottom ash, fly ash and gypsum were also sampled in the field. Mercury concentrations in coal burned in the measured power plants ranged from 17 to 385 μg/kg. The mercury mass balances for the six power plants varied from 87 to 116% of the input coal mercury for the whole system. The total mercury concentrations in the flue gas from boilers were at the range of 1.92–27.15 μg/m3, which were significantly related to the mercury contents in burned coal. The mercury speciation in flue gas right after the boiler is influenced by the contents of halogen, mercury, and ash in the burned coal. The average mercury removal efficiencies of ESP, ESP plus wet FGD, and ESP plus dry FGD-FF systems were 24%, 73% and 66%, respectively, which were similar to the average removal efficiencies of pollution control device systems in other countries such as US, Japan and South Korea. The SCR system oxidized 16% elemental mercury and reduced about 32% of total mercury. Elemental mercury, accounting for 66–94% of total mercury, was the dominant species emitted to the atmosphere. The mercury emission factor was also calculated for each power plant.

Synthesis of current data for Hg in areas of geologic resource extraction contamination and aquatic systems in China

“…Several emission tests on-site measurement of Hg in process streams and flue gases of coal-fired power plants equipped with various types of emission control devices have been conducted in China Tang et al, 2007;Zhang et al, 2008;Wang et al, 2010). In Guizhou province, statistical data for coal consumption suggested that large-scale coal-fired power plants, industrial boilers, and domestic users consumed about 30%, 48%, and 22% of the total, respectively .…”

Mercury in Bituminous Coal Used in Polish Power Plants

“…Speciation depends on chemical composition of combusted coal. In coals with higher chlorine, bromine or other halogen content share of oxidized mercury increases (Zhang et al, 2008;Wang et al, 2009;Wang et al, 2010;Buitrago, 2011). Salts containing these elements decompose during combustion to HCl, HBr and HI and further to Cl 2 , Br 2 and I 2 .…”

“…For 4 coal mines with highest Hg/Cl factor (from 0.00056 to 0.0008) the potential of mercury emission is significant. High mercury content and relatively low content of chlorine and bromine causes domination of reduced Hg 0 form, which will not be eliminated during dedusting and desulfurization processes (Galbreath & Zygarlicke, 2000;Wang et al, 2010;Chmielniak et al, 2010). …”

“…Content varies for specific power plants from 10 to 385 ppb (Zhang et al, 2008;Wang et al, 2010). Estimated yearly mercury emission originating from coal combustion in China varies from 161.6 to 219.5 Mg (Wang et al, 1999;Streets et al, 2005;Jiang et al, 2005).…”

“…Due to good solubility in aqueous solutions, oxidized mercury is also removed by Wet Flue Gases Desulfurization (WFGD). Practically all metallic mercury vapor is emitted to atmosphere (Galbreath & Zygarlicke, 2000;Wang et al, 2010;Chmielniak et al, 2010).…”