Using bromine gas to enhance mercury removal from flue gas of coal-fired power plants.
Bromine gas was evaluated for converting elemental mercury (Hg0) to oxidized mercury, a form that can readily be captured by the existing air pollution control device. The gas-phase oxidation rates of Hg0 by Br2 decreased with increasing temperatures. SO2, CO, HCl, and H2O had insignificant effect, while NO exhibited a reverse course of effect on the Hg0 oxidation: promotion at low NO concentrations and inhibition at high NO concentrations. A reaction mechanism involving the formation of van der Waals clusters is proposed to accountfor NO's reverse effect. The apparent gas-phase oxidation rate constant, obtained under conditions simulating a flue gas without flyash, was 3.61 x 10(-17) cm3 x molecule(-1) x s(-1) at 410 K corresponding to a 50% Hg0 oxidation using 52 ppm Br2 in a reaction time of 15 s. Flyash in flue gas significantly promoted the oxidation of Hg0 by Br2, and the unburned carbon component played a major role in the promotion primarily through the rapid adsorption of Br2 which effectively removed Hg0 from the gas phase. At a typical flue gas temperature, SO2 slightly inhibited the flyash-induced Hg0 removal. Conversely, NO slightly promoted the flyash induced Hg0 removal by Br2. Norit Darco-Hg-LH and Darco-Hg powder activated carbons, which have been demonstrated in field tests, were inferred for estimating the flyash induced Hg0 oxidation by Br2. Approximately 60% of Hg0 is estimated to be oxidized with the addition of 0.4 ppm of gaseous Br2 into full scale power plant flue gas.
Liu
Shou-Heng
SH
Environmental Energy Technology Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA.
Yan
Nai-Qiang
NQ
Liu
Zhao-Rong
ZR
Qu
Zan
Z
Wang
H Paul
HP
Chang
Shih-Ger
SG
Miller
Charles
C
D000327:Adsorption; D000393:Air Pollutants / Q000737:chemistry / Q000302:isolation & purification*; D000397:Air Pollution / Q000517:prevention & control*; D001966:Bromine / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D003031:Coal; D060729:Coal Ash; D008628:Mercury / Q000737:chemistry / Q000302:isolation & purification*; D009569:Nitric Oxide / Q000737:chemistry; D010084:Oxidation-Reduction; D052638:Particulate Matter / Q000737:chemistry; D011210:Power Plants
D000393:Air Pollutants; D003031:Coal; D060729:Coal Ash; D052638:Particulate Matter; D009569:Nitric Oxide; D002244:Carbon; D008628:Mercury; D001966:Bromine