Partitioning of Mercury, Arsenic, Selenium, Boron, and Chloride in a Full-Scale Coal Combustion Process Equipped with Selective Catalytic Reduction, Electrostatic Precipitation, and Flue Gas Desulfurization Systems^†

Abstract

A full-scale field study was carried out at a 795 MWe coal-fired power plant equipped with selective catalytic reduction (SCR), an electrostatic precipitator (ESP), and wet flue gas desulfurization (FGD) systems to investigate the distribution of selected trace elements (i.e., mercury, arsenic, selenium, boron, and chloride) from coal, FGD reagent slurry, makeup water to flue gas, solid byproduct, and wastewater streams. Flue gases were collected from the SCR outlet, ESP inlet, FGD inlet, and stack. Concurrent with flue gas sampling, coal, bottom ash, economizer ash, and samples from the FGD process were also collected for elemental analysis. By combining plant operation parameters, the overall material balances of selected elements were established. The removal efficiencies of As, Se, Hg, and B by the ESP unit were 88, 56, 17, and 8%, respectively. Only about 2.5% of Cl was condensed and removed from flue gas by fly ash. The FGD process removed over 90% of Cl, 77% of B, 76% of Hg, 30% of Se, and 5% of As. About 90% and 99% of the FGD-removed Hg and Se were associated with gypsum. For B and Cl, over 99% were discharged from the coal combustion process with the wastewater. Mineral trona (trisodium hydrogendicarbonate dehydrate, Na 3 H(CO 3 ) 2 3 2H 2 O) was injected before the ESP unit to control the emission of sulfur trioxide (SO 3 ). By comparing the trace elements compositions in the fly ash samples collected from the locations before and after the trona injection, the injection of trona did not show an observable effect on the partitioning behaviors of selenium and arsenic, but it significantly increased the adsorption of mercury onto fly ash. The stack emissions of mercury, boron, selenium, and chloride were for the most part in the gas phase. † Progress in Coal-Based Energy and Fuel Production.

Temperature programmed desorption as a tool for the identification of mercury fate in wet-desulphurization systems

“…During the precipitation of the gypsum a part of the mercury contributes to the formation of the HgF 2 and the HgCl 2 species that are adsorbed onto the gypsum particles. It might be expected that at the pH of the scrubber liquor [4][5][6][7], the HgCl 2 would solubilise. However, as already demonstrated [11], in this particular plant the aqueous phase of the gypsum B slurry shows a higher concentration of Cl (3420 lg g À1 ) and there is a high concentration of HgCl 2 in the aqueous phase of this slurry which favours adsorption onto the solid.…”

“…These elements enter the WFGD in gaseous form or as particulate matter [2][3][4]. Oxidised mercury species (Hg 2+ ), which are soluble in water, are captured in scrubbers whose removal efficiencies range from 40 to 90% [2,5,6]. This variation in efficiency is a consequence of to the wide-ranging modifications in the operational parameters and the different pollution control devices (ESP and De-NOX), employed in each plant.…”

Emission characteristics of Cd, Pb and Mn from coal combustion: Field study at coal-fired power plants in China

“…The application of air pollution control devices (APCDs) in power plants can significantly affect the redistribution of trace metals in the combustion by-products and accordingly alter the route by which the elements reach the environment [7]. Research [7][8][9][10] shows that a certain proportion of the metals can be partitioned into solid by-product (gypsum) and water stream (gypsum slurry water) after passing through flue gas desulfurization systems (FGD). Particulate bound metals can be captured by particulate control facilities such as ESP and FF.…”

Partitioning behavior of Arsenic in circulating fluidized bed boilers co-firing petroleum coke and coal

“…In recent years, extensive field tests on the partitioning behavior of As across APCDs in coal-fired power plants have been conducted by many researchers [14,17,18]. Cheng et al [19] carried out a field test on a coal fired power plant to investigation the distribution of As for selective catalytic reduction (SCR), ESP, and WFGD. Swanson et al [20] determine the partitioning of As in combustion by products including bottom ash, economizer ash and fly ash from two US power plants.…”