Apparatus and method for removing mercury from a gas

Abstract

The present invention provides a method and apparatus for removing mercury from gases such as those discharged from roasters and other heat producing systems. In embodiments the method comprises reacting the mercury with dissolved molecular chlorine, and may also comprise reacting the mercury with mercuric chloride to yield mercurous chloride. The mercurous chloride may be removed by precipitation. There are also disclosed apparatuses for implementing the method.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A method for removing mercury from a gas, the method comprising reacting said mercury with chlorine gas to form mercuric chloride. 
     
     
         2 . The method according to  claim 1  wherein said chlorine gas and said formed mercuric chloride are in aqueous solution. 
     
     
         3 . The method according to  claim 2  wherein said solution and said gas form a gas/liquid interface and said reacting further comprises forming a 2-dimensional mercury vapour at said gas/liquid interface. 
     
     
         4 . The method according to  claim 1  wherein the reacting occurs at a temperature of less than about 65° C. 
     
     
         5 . The method according to  claim 2  further comprising the step of reacting any unreacted mercury with the mercuric chloride to form mercurous chloride. 
     
     
         6 . The method according to  claim 5  wherein said method further comprises the step of removing the mercurous chloride from the solution. 
     
     
         7 . The method according to  claim 2  wherein the chlorine solution is at a pH of between about 6.5 and about 7.5. 
     
     
         8 . The method according to  claim 1  wherein the gas is an off gas. 
     
     
         9 . An apparatus for removing mercury from a gas, wherein the improvement comprises a first mercury scrubber for reacting the mercury with a chlorine solution. 
     
     
         10 . The apparatus according to  claim 9  further comprising a chlorine feed system for regenerating the chlorine solution. 
     
     
         11 . The apparatus according to  claim 9  wherein the improvement further comprises a second mercury scrubber and a circulation system suitable to substantially continuously recirculate the chlorine solution between the two said scrubbers. 
     
     
         12 . The apparatus according to  claim 9  further comprising a harvester for harvesting precipitated mercurous chloride generated in the scrubber. 
     
     
         13 . A method for removing mercury from a gas wherein the improvement comprises reacting the mercury with a solution of chlorine gas to form mercuric chloride in solution. 
     
     
         14 . The method according to  claim 13  further comprising reacting the unreacted mercury with the mercuric chloride to form mercurous chloride. 
     
     
         15 . The method according to  claim 14  wherein said method further comprises the step of removing the mercurous chloride from the solution. 
     
     
         16 . The method according to  claim 13  wherein the solution and gas form a gas/liquid interface and said reacting further comprises forming a 2-dimensional mercury vapour at said gas/liquid interface. 
     
     
         17 . The method according to  claim 14  wherein said reaction of mercury with said solution of chlorine gas occurs in a first scrubber and said reaction of mercury with mercuric chloride occurs in a second scrubber. 
     
     
         18 . The method according to  claim 13  wherein said method is carried out at a temperature of less than about 65C. 
     
     
         19 . The method according to  claim 13  wherein said reaction between said chlorine and said mercury occurs under an ORP of between about 500 mV and about 2000 mV.