Method for control of mercury

Abstract

A method and apparatus for reducing mercury in industrial gases such as the flue gas produced by the combustion of fossil fuels such as coal adds hydrogen sulfide to the flue gas in or just before a scrubber of the industrial process which contains the wet scrubber. The method and apparatus of the present invention is applicable to installations employing either wet or dry scrubber flue gas desulfurization systems. The present invention uses kraft green liquor as a source for hydrogen sulfide and/or the injection of mineral acids into the green liquor to release vaporous hydrogen sulfide in order to form mercury sulfide solids.

1 . In a method for receiving and scrubbing an industrial flue gas containing mercury with an aqueous alkali reagent in a scrubber, the improvement comprising: 
 generating hydrogen sulfide proximate to the scrubber by providing alkali to a solution comprising sodium sulfide or potassium sulfide; and    supplying the hydrogen sulfide to the scrubber to remove mercury from the industrial flue gas.    
     
     
         2 . The method according to  claim 1 , further comprising supplying air to the hydrogen sulfide to produce a mixture of air and hydrogen sulfide and wherein the step of supplying the hydrogen sulfide comprises providing the mixture of air and hydrogen sulfide to the industrial flue gas.  
     
     
         3 . The method according to  claim 1 , further comprising controlling the supplying the hydrogen sulfide step by adjusting at least one of the supply of acid and alkali to said solution to alter the pH of said solution and, correspondingly, a vapor pressure of the generated hydrogen sulfide.  
     
     
         4 . The method according to  claim 2 , wherein the mixture of air and hydrogen sulfide is supplied to the industrial flue gas at multiple locations by way of at least one of a plurality of pipes and a plurality of air foils, each having apertures therein, for discharging the mixture of hydrogen sulfide and air into a flue conveying the industrial flue gas to the scrubber.  
     
     
         5 . The method according to  claim 1 , wherein kraft green liquor is used to generate the hydrogen sulfide.  
     
     
         6 . The method according to  claim 5 , further comprising controlling the supplying the hydrogen sulfide step by adjusting the pH of the kraft green liquor and, correspondingly, a vapor pressure of the generated hydrogen sulfide.  
     
     
         7 . The method according to  claim 3 , wherein kraft green liquor is used to generate the hydrogen sulfide.  
     
     
         8 . The method according to  claim 1 , wherein the scrubber is a wet scrubber.  
     
     
         9 . The method according to  claim 1 , wherein the scrubber is a dry scrubber.  
     
     
         10 . The method according to  claim 1 , wherein the step of supplying the hydrogen sulfide to the industrial flue gas occurs at a rate sufficient to produce a concentration of hydrogen sulfide in the industrial flue gas of about 0.05 to 10 ppm.