Method and apparatus for mitigating mercury emissions in exhaust gases

Abstract

The illustrated embodiment of the invention is a method for mitigating mercury emissions in an exhaust gas. The method includes the steps of noncatalytically forming a chemically deposited compound of mercury on a surface from a substantial portion of the total amount of mercury in the exhaust gas. The deposited compound of mercury is sublimed back into the exhaust gas as volatile mercury dichloride from the surface without any substantial production of elemental mercury. The sublimed mercury dichloride is removed from the exhaust gas by scrubbing.

1 . A method for mitigating mercury emissions in an exhaust gas, the method comprising: 
 noncatalytically forming a chemically deposited compound of mercury on a surface from a substantial portion of the total amount of mercury in the exhaust gas;    subliming the deposited compound of mercury back into the exhaust gas as volatile mercury dichloride from the surface without any substantial production of elemental mercury, and    removing the sublimed mercury dichloride from the exhaust gas by scrubbing.    
     
     
         2 . A method for mitigating mercury emissions in an exhaust gas, the method comprising: 
 providing a surface which is in contact with the exhaust gas;    noncatalytically depositing chemically a substantial portion of the total amount of mercury in the exhaust gas upon the surface to form a stable compound of mercury;    subliming the deposited compound of mercury back into the exhaust gas as volatile mercury dichloride without any substantial production of elemental mercury; and    scrubbing the sublimed compound of mercury from the exhaust gas.    
     
     
         3 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises providing an exhaust gas prior to mitigation which includes elemental mercury.  
     
     
         4 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises providing an exhaust gas prior to mitigation which includes at least one sulfur compound.  
     
     
         5 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises providing an exhaust gas prior to mitigation which includes a form of chlorine selected from the group consisting of: hydrogen chloride; atomic chlorine; and molecular chlorine.  
     
     
         6 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises providing a flow modifying spoiler configured to enhance gas-surface collisions.  
     
     
         7 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises a flow modifying spoiler disposed at a location within the flow of exhaust gases which enhances deposition of mercury thereon.  
     
     
         8 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises a flow modifying spoiler disposed at a location within the flow of exhaust gases where the exhaust gases maintain the surface at a temperature of between approximately 150° C. and 300° C.  
     
     
         9 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises a flow modifying spoiler disposed within the flow of exhaust gases; and further comprising heating the surface if necessary to a temperature between approximately 150° C. and 300° C.  
     
     
         10 . The method as recited in  claim 2 , wherein providing a surface which is in contact with the exhaust gas comprises at least one of a base-metal and a ceramic material.  
     
     
         11 . The method as recited in  claim 2 , wherein noncatalytically depositing chemically a substantial portion of the total amount of mercury in the exhaust gas upon the surface to form a stable compound of mercury comprises mercury oxide deposited on the surface, which is subsequently converted into mercury dichloride.  
     
     
         12 . The method as recited in  claim 2 , wherein noncatalytically depositing chemically a substantial portion of the total amount of mercury in the exhaust gas upon the surface to form a stable compound of mercury comprises mercury sulfate deposited on the surface, which is subsequently converted into mercury dichloride.  
     
     
         13 . The method as recited in  claim 2 , further comprising adding sulfur dioxide to the exhaust gas, if necessary to a sulfur poor exhaust gas, prior to the exhaust gas contacting the surface, so that it is in excess of the mercury concentration and to enhance a formation of mercury sulfate and hence dichloride upon the surface.  
     
     
         14 . The method as recited in  claim 2 , further comprising adding, if necessary in a chlorine poor exhaust gas, at least one of atomic chlorine, molecular chlorine and hydrogen chloride to the exhaust gas prior to the exhaust gas contacting the surface, so as to ensure and enhance a formation of mercury dichloride upon the surface.  
     
     
         15 . The method as recited in  claim 2 , wherein scrubbing the sublimed compound of mercury from the exhaust gas comprises water scrubbing or chemical dry scrubbing.  
     
     
         16 . A method for mitigating mercury emissions in an exhaust gas which prior to mitigation comprises at least one sulfur compound or a form of chlorine selected from the group consisting of hydrogen chloride, atomic chlorine and molecular chlorine, the method comprising: 
 providing a flow modifying spoiler disposed at a location within the flow of exhaust gases which enhances deposition of mercury thereon at a location within the flow of exhaust gases where the exhaust gases will maintain its temperature between approximately 150° C. and 300° C., so that mercury deposited upon the surface forms mercury oxide or mercury sulfate, which is subsequently converted into mercury dichloride;    noncatalytically depositing chemically a substantial portion of the total amount of mercury in the exhaust gas upon the spoiler to form a stable compound of mercury;    subliming the deposited compound of mercury as mercury dichloride back into the exhaust gas without substantial production of elemental mercury; and water scrubbing or chemical dry scrubbing the sublimed mercury dichloride from the exhaust gas without substantial production of elemental mercury; and    adding sulfur dioxide or a form of chlorine to the exhaust gas prior to the exhaust gas contacting the spoiler, so as to enhance a formation of mercury sulfate and hence dichloride upon the spoiler.