Method for removing mercury from flue gas after combustion
A method of removing mercury from flue gases from combustion plants, such as for example power plants or waste incineration plants, is achieved in which mercury-containing flue gases are brought into contact with an adsorption reagent either directly or indirectly by being contained in an absorption reagent, whereby mercury is substantially adsorbed by the adsorption reagent during this contact. After adsorption has occurred the adsorption reagent is separated from the flue gases and subsequently from the absorption reagent and added to an aqueous solution containing an oxidizing agent, whereby the adsorbed mercury dissolves as Hg 2+ . The Hg 2+ -containing solution is subsequently separated from the adsorption agent and the Hg 2+ then is removed from the solution. This method enables the mercury to be removed from flue gas in a simple and economical manner.
1. A method of removing mercury from a flue gas comprising:
a) bringing mercury present in the flue gas into contact with an absorption reagent comprising an adsorption reagent, whereby the mercury is substantially adsorbed onto the adsorption reagent,
b) separating the adsorption reagent comprising the adsorbed mercury from the absorption reagent,
c) bringing the adsorption reagent into contact with an oxidizing reagent, whereby the adsorbed mercury is desorbed and dissolves in the form of Hg 2+ in a solution,
d) separating the solution with Hg 2+ -enriched from the adsorption reagent, and
e) removing the Hg 2+ from the solution.
2. The method as claimed in claim 1 , wherein the Hg 2+ is removed from the solution by mixing the solution with Hg 2+ -present with a precipitating reagent, which forms with the Hg 2+ a low solubility precipitate and separating the latter from the solution.
3. The method as claimed in claim 2 , wherein an organosulfide is used as the precipitating reagent.
4. The method as claimed in claim 1 , wherein the Hg 2+ is removed from the solution by bringing the solution into contact with an ion exchanger.
5. The method as claimed in claim 1 , wherein the Hg 0 present in the flue gases is oxidized before bringing mercury present in the flue gases into contact with the absorption reagent comprising adsorption reagent.
6. The method as claimed in claim 1 , wherein the adsorption reagent is added to the flue gas before or in a flue gas desulfurization plant.
7. The method as claimed in claim 6 , wherein bringing mercury present in the flue gas into contact with an adsorption agent takes place in the liquid phase used in the flue gas desulfurization plant, to which the adsorption reagent is added.
8. The method as claimed in claim 6 , wherein solid materials produced in the flue gas desulfurization plant are separated from the adsorption agent by centrifugal separation.
9. The method as claimed in claim 1 , wherein hypochlorite, chlorine dioxide or chlorine gas or any other strong oxidizing reagent is used as the oxidizing reagent.
10. The method as claimed in claim 1 , wherein activated carbon is used as the adsorption reagent.
11. The method as claimed in claim 1 , wherein after bringing the adsorption reagent into contact with a solution containing an oxidizing reagent, the adsorption reagent is separated and recirculated.