Mercury control using moderate-temperature dissociation of halogen compounds

Abstract

A system and method is provided for the removal of mercury from flue gas. Effective removal of mercury is obtained by oxidation of elemental mercury, with highly reactive halogen species derived from dissociation of halogen compounds at moderate temperatures brought into contact with the flue gas with or without the addition of carbon.

1 . (canceled) 
     
     
         2 . A method of removing mercury from a flue gas of a coal combustion system, the method comprising:
 generating a reactive halogen from a precursor within the flue gas at about 500° C. or less;   reacting the reactive halogen with mercury in the flue gas; and   removing the reacted mercury from the flue gas using a pollution control device.   
     
     
         3 . The method of  claim 2 , wherein the reactive halogen comprises a molecular halogen, a halogen radical, an organohalide radical, a radical comprising a halogen atom bonded to a heteroatom, or a combination thereof. 
     
     
         4 . The method of  claim 2 , wherein removing the reacted mercury from the flue gas comprises removing particulates comprising the reacted mercury from the flue gas using a particulate collector device. 
     
     
         5 . The method of  claim 2 , wherein the pollution control device comprises an electrostatic precipitator, a fabric filter, a scrubber, or a combination thereof. 
     
     
         6 . The method of  claim 4 , wherein the particulates comprise ash generated by combustion of coal in the coal combustion system. 
     
     
         7 . The method of  claim 4 , wherein the particulates comprise ash, a sorbent material, or a combination thereof. 
     
     
         8 . The method of  claim 7 , wherein the sorbent material comprises activated carbon, carbon black, char, soot, an alkaline sorbent, lime, calcium silicate, or a combination thereof. 
     
     
         9 . The method of  claim 4 , further comprising injecting at least some of the particulates into the flue gas upstream of the pollution control device. 
     
     
         10 . The method of  claim 9 , wherein the reaction of the reactive halogen with the mercury in the flue gas occurs upstream of an injection location of the injected particles. 
     
     
         11 . The method of  claim 9 , wherein the reaction of the reactive halogen with the mercury in the flue gas occurs downstream of an injection location of the injected particles. 
     
     
         12 . The method of  claim 2 , wherein the reaction of the reactive halogen with the mercury in the flue gas is a gas-phase reaction. 
     
     
         13 . The method of  claim 4 , wherein the reaction of the reactive halogen with the mercury in the flue gas is a heterogeneous reaction occurring on the surface of the particulates. 
     
     
         14 . The method of  claim 4 , wherein the particulates comprise at least some of the reactive halogen. 
     
     
         15 . The method of  claim 2 , comprising generating the reactive halogen within the flue gas at about 60° C. to about 400° C. 
     
     
         16 . The method of  claim 2 , comprising generating the reactive halogen within the flue gas at about 320° C. to about 420° C. 
     
     
         17 . The method of  claim 2 , comprising generating the reactive halogen within the flue gas at about 125° C. to about 200° C. 
     
     
         18 . The method of  claim 2 , comprising reacting the reactive gas with the mercury in the flue gas at about 60° C. to about 400° C. 
     
     
         19 . The method of  claim 2 , wherein the precursor comprises an inorganic halide, an inorganic nonmetallic halide, a halide salt, an organic halide, or a combination thereof. 
     
     
         20 . The method of  claim 2 , wherein the precursor is bromomethane, bromoethane, 1-bromopropane, allyl bromide, 1-bromo-2-methylpropane, 1-bromo-2-chloroethane, 1.2-dibromoethane, t-butylhypobromite, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,2-dichloroethene, trichloroethane, tetrachloroethane, a dihalide, a polyhalide, an allyl halide, allyl chloride, oxalyl chloride, t-butyl peroxychloroformate, methyl chlorosulfite, an alkyl hypochlorite, phosgene, chlorodifluoromethane, hexafluoroacetone, acetone, trifluoroacetic acid, a halide of phosphorus, a halide of selenium, a halide of sulfur, a halide of silicon, a halide of nitrogen, Se 2 Br 2 , SeOBr 2 , SO 2 Cl 2 , PBr 3 , PBr 3 , POBr 3 , SiBr 4 , or a combination thereof. 
     
     
         21 . The method of  claim 2 , wherein at the time of formation into the reactive halogen the precursor is a solid, liquid, gas, or combination thereof.