Method and system for controlling mercury emissions from coal-fired thermal processes

Abstract

The present disclosure is directed to the use of elemental or speciated iodine and bromine to control total mercury emissions.

What is claimed is: 
     
         1 . A method, comprising:
 selecting a mercury-containing feed material natively including mercury and halogen, the halogen comprising one or more of bromine and iodine;   contacting the mercury-containing feed material with a halogen-containing additive to form a treated feed material, the halogen-containing additive comprising one or more of bromine and iodine, wherein the one or more of bromine and iodine concentration of the treated feed material relative to a weight of the feed material is about 30 ppmw or less;   generating, from the treated feed material, a mercury-containing gas stream comprising vapor-phase mercury and vapor-phase halogen derived from the one or more of bromine and iodine; and   removing 50% or more of the mercury from the gas stream.   
     
     
         2 . The method of  claim 1 , wherein the one or more of bromine and iodine comprises bromine and wherein the mercury-containing feed material has from about 0.003 to about 100 ppmw mercury. 
     
     
         3 . The method of  claim 1 , wherein the one or more of bromine and iodine comprises iodine, wherein the halogen-containing additive facilitates the vapor-phase mercury to be removed from the mercury-containing gas stream, and wherein the mercury-containing feed material natively comprises no more than about 5 ppmw halogen. 
     
     
         4 . The method of  claim 1 , wherein the mercury-containing feed material natively has one of:
 (i) no more than about 5 ppmw iodine;   (ii) no more than about 4 ppmw iodine;   (iii) no more than about 3 ppmw iodine   (iv) no more than about 2 ppmw iodine; or   (v) no more than about 1 ppmw iodine.   
     
     
         5 . The method of  claim 1 , wherein the mercury-containing feed material comprises a high alkali, high iron, and/or high sulfur coal. 
     
     
         6 . The method of  claim 1 , wherein the halogen-containing additive comprises iodine and/or bromine. 
     
     
         7 . The method of  claim 1 , wherein the halogen-containing additive comprises at least one of an iodine containing coal, an alkali halide, an alkaline earth halide, and diatomic halide. 
     
     
         8 . The method of  claim 1 , wherein at least one of the following is true:
 (i) the mercury-containing gas stream comprises about 3.5 ppmw or less of the vapor-phase halogen derived from the treated feed material;   (ii) in the mercury-containing gas stream, a molar ratio of the vapor-phase halogen derived from the treated feed material to the vapor-phase mercury derived from the treated feed material is no more than about 600; and   (iii) at an air preheater outlet, a concentration of the vapor-phase halogen derived from the treated feed material ranges from about 0.1 to about 10 ppmw.   
     
     
         9 . The method of  claim 1 , wherein the mercury-containing feed material is combusted in a thermal unit to produce the mercury-containing gas stream. 
     
     
         10 . The method of  claim 1 , further comprising passing the mercury-containing gas stream through a particulate removal device to form a treated gas stream free of particulates and mercury. 
     
     
         11 . A method, comprising:
 contacting a mercury-containing feed material comprising a feed material iodine with a halogen-containing additive to from a treated feed material having an iodine content of about 30 ppmw or less, wherein the halogen-containing additive comprises one or more of bromine and iodine and wherein no more than about 2 ppmw of the treated feed material iodine comprises the feed material iodine;   generating, from the treated feed material, a gas stream comprising vapor-phase mercury and vapor-phase iodine derived from the treated feed material; and   removing 50% or more of the vapor-phase mercury from the gas stream.   
     
     
         12 . The method of  claim 11 , wherein the one or more of bromine and iodine comprises iodine and wherein the mercury-containing feed material has from about 0.003 to about 100 ppmw mercury. 
     
     
         13 . The method of  claim 11 , wherein the one or more of bromine and iodine comprises bromine, wherein the mercury containing feed material natively comprises bromine, and wherein the bromine concentration is:
 (i) no more than about 10 ppmw of bromine; or   (ii) no more than about 5 ppmw of bromine.   
     
     
         14 . The method of  claim 11 , wherein the halogen-containing additive comprises at least one of an iodine containing coal, an alkali iodide, an alkaline earth iodide, and diatomic iodine. 
     
     
         15 . The method of  claim 11 , wherein the halogen-containing additive comprises iodine and:
 (i) no more than about 25% of halogens other than iodine;   (ii) no more than about 10% of halogens other than iodine; or   (iii) no more than about 5% of halogens other than iodine.   
     
     
         16 . The method of  claim 11 , wherein the halogen-containing additive comprises iodine and bromine. 
     
     
         17 . The method of  claim 11 , wherein at least one of the following is true:
 (iv) the mercury-containing gas stream comprises about 3.5 ppmw or less of the vapor-phase halogen derived from the treated feed material;   (v) in the mercury-containing gas stream, a molar ratio of the vapor-phase halogen derived from the treated feed material to the vapor-phase mercury derived from the treated feed material is no more than about 600; and   (vi) at an air preheater outlet, a concentration of the vapor-phase halogen derived from the treated feed material ranges from about 0.1 to about 10 ppmw.   
     
     
         18 . A method, comprising:
 selecting a first mercury-containing feed material that natively includes mercury and less than about 2 ppmw iodine;   selecting a second mercury-containing feed material that natively includes mercury and greater than about 2 ppmw iodine;   mixing, in no particular order, the first mercury containing feed material, the second mercury containing feed material, and a halogen-containing additive to form a treated feed material, wherein the halogen-containing additive comprising one or more of iodine and bromine, and wherein the treated feed material has a halogen concentration relative to a weight of the treated feed material of about 30 ppmw or less;   generating, from the treated feed material, a mercury-containing gas stream comprising vapor-phase mercury and vapor-phase halogen derived from the treated feed material; and   removing 50% or more of the mercury from the gas stream.   
     
     
         19 . The method of  claim 18 , wherein the second mercury-containing feed material natively has one of:
 (i) greater than about 3 ppmw iodine;   (ii) greater than about 4 ppmw iodine; or   (iii) greater than about 5 ppmw iodine.   
     
     
         20 . The method of  claim 18 , wherein the halogen-containing additive comprises iodine and the treated feed material has a total iodine concentration relative to a weight of the treated feed material of about 30 ppmw or less. 
     
     
         21 . The method of  claim 18 , wherein the halogen-containing additive comprises bromine.