Process for removing mercury from flue gases

Abstract

Process for removing mercury from flue gases of high-temperature plants, in particular power stations and waste incineration plants in which a bromine compound is fed to the multistage furnace and/or the flue gas in a plant section downstream of the furnace, the temperature during contact of the bromine compound with the flue gas being at least 500° C., preferably at least 800° C. The combustion is carried out in the presence of a sulphur compound, in particular sulphur dioxide. Subsequently to the furnace, the flue gas is subjected to an optional multistage cleanup for removing mercury from the flue gas, which cleanup comprises a wet scrubber and/or a dry cleanup.

We claim: 
     
      
       1. Process for removing mercury from mercury-containing flue gases of a furnace within which a combustion or incineration is carried out, wherein 
       
         bromine, a bromine compound, a mixture of bromine compounds or a mixture of bromine and a bromine compound or compounds, is fed to the furnace or to the flue gas of the furnace in a plant section downstream of the furnace, or to both the furnace and the flue gas, the temperature during the first contact of the bromine or of said mixture with the flue gas being at least 500° C., 
         the combustion or incineration is carried out in the presence of a sulphur compound, 
         and then the flue gas is subjected to a cleanup for removing mercury from the flue gas. 
       
      
     
     
      
       2. Process according to  claim 1 , wherein the bromine compound is an aqueous solution of hydrogen bromide, an alkali metal bromide, or a mixture thereof. 
      
     
     
      
       3. The process according to  claim 2 , wherein said bromine compound is sodium bromide. 
      
     
     
      
       4. Process according to  claim 1 , wherein the bromine compound or said mixture or both are liquid or solid bromine-rich wastes. 
      
     
     
      
       5. Process according to  claim 1 , wherein the bromine, the bromine compound or the mixture is added to combustion air supplied to the furnace, to a recycled flue gas stream, a recycled fly ash or any combination thereof. 
      
     
     
      
       6. Process according to  claim 1 , wherein the mass ratio of bromine to mercury in the flue gas is in the range from 10 2  to 10 4 . 
      
     
     
      
       7. Process according to  claim 1 , wherein the combustion or incineration is carried out additionally in the presence of chlorine, a chlorine compound, a mixture of chlorine compounds, iodine, an iodine compound, a mixture of iodine compounds or combination thereof. 
      
     
     
      
       8. Process according to  claim 1 , wherein the furnace is provided with a flue gas emission control system comprising a multistage wet flue gas scrubber having at least one strongly acidic scrubbing, at least one weakly acidic scrubbing stage, at least one alkaline scrubbing stage, or a combination of said scrubbing stages. 
      
     
     
      
       9. Process according to  claim 8 , wherein the mercury content of the flue gas is measured continuously downstream of the flue gas emission control system and the amount of bromine, bromine compounds fed and any sulphur or sulphur compounds fed is controlled on the basis of the measured mercury content. 
      
     
     
      
       10. The process according to  claim 8 , wherein said emission control system comprises filtration, electrostatic separation or both. 
      
     
     
      
       11. The process according to  claim 10 , wherein fly ash loaded with mercury is recovered from said filtration or electrostatic separation and is subjected to a thermal secondary treatment to decrease mercury load in a rotary drum heated to temperatures of at least 200° C. 
      
     
     
      
       12. Process according to  claim 1 , wherein the furnace is provided with a flue gas emission control system comprising at least one dry or semi-dry absorption based emission control stage. 
      
     
     
      
       13. The process according to  claim 1 , wherein the temperature during the contact of the bromine compound or mixture with the flue gas is at least 800° C. 
      
     
     
      
       14. The process according to  claim 1 , wherein said sulphur compound is sulphur dioxide. 
      
     
     
       15. Process for removing mercury from mercury-containing flue gases of a furnace within which a combustion or incineration is carried out, wherein
 bromine, a bromine compound, a mixture of bromine compounds or a mixture of bromine and a bromine compound or compounds, is fed to the furnace or to the flue gas of the furnace in a plant section downstream of the furnace, or to both the furnace and the flue gas, the temperature during the first contact of the bromine, said bromine compound, said mixture of bromine compounds or of said mixture of bromine and a bromine compound or compounds with the flue gas being at least 500° C., 
 the combusion or incineration is carried out in the presence of a sulphur compound, and then the flue gas is subjected to a cleanup for removing mercury from the flue gas, 
 wherein the temperature during the contact of the bromine compound, said bromine compound, said mixture of bromine compounds or of said mixture of bromine and a bromine compound or compounds with mercury-containing flue gas is at least 800° C. and wherein the cleanup for removing mercury from the mercury-containing flue gas substantially removes mercury from the mercury-containing flue gas and includes atleast one of a wet scrubbing stage and a dry cleanup stage, the dry cleanup stage comprising at least one sorbent, and 
 wherein sulphur, a sulphur compound or a mixture of sulphur compounds is added to said furnace based on measuring a measured mercury content of the mercury-containing flue gas. 
 
     
     
      
       16. The process according to  claim 1 , wherein said furnace is a multistage furnace. 
      
     
     
       17. A process for removing mercury from mercury-containing flue gases of a furnace, comprising:
 carrying out a combustion or incineration process, within the furnace, in the presence of a sulphur compound;   feeding bromine, a bromine compound, a mixture of bromine compounds or a mixture of bromine and one or more bromine compounds to at least one of the furnace or a flue gas of the furnace in a plant section downstream from the furnace, a temperature at first contact of the bromine, bromine compound, mixture of bromine compounds, or mixture of bromine and one or more bromine compounds with the mercury-containing flue gas being at least 800° C.; and   subjecting the mercury-containing flue gas to a cleanup for substantially removing mercury from the mercury-containing flue gas, wherein the cleanup for substantially removing mercury from the mercury-containing flue gas includes a dry cleanup stage comprising at least one sorbent; and   the process further comprising adding sulphur, a sulphur compound or a mixture of sulphur compounds to said furnace based on a measured mercury content of the mercury-containing flue gas.   
     
     
       18. A process for removing mercury from mercury-containing flue gases of a furnace, comprising:
 carrying out a combustion or incineration process, within the furnace, in the presence of a sulphur compound;   feeding bromine, a bromine compound, a mixture of bromine compounds or a mixture of bromine and one or more bromine compounds to at least one of the furnace or a flue gas of the furnace in a plant section downstream from the furnace, a temperature at first contact of the bromine, bromine compound, mixture of bromine compounds, or mixture of bromine and one or more bromine compounds with the mercury-containing flue gas being at least 800° C.; and   subjecting the mercury-containing flue gas to a cleanup for substantially removing mercury from the mercury-containing flue gas, wherein the cleanup for substantially removing mercury from the mercury-containing flue gas includes a dry cleanup stage comprising at least one sorbent; and   wherein feeding the bromine, bromine compound, mixture of bromine compounds or mixture of bromine and one or more bromine compounds to the furnace comprises:   applying the bromine, bromine compound, mixture of bromine compounds or mixture of bromine and one or more bromine compounds in an aqueous solution of the bromine, bromine compound, mixture of bromine compounds or mixture of bromine and one or more bromine compounds to a waste feed for a waste incineration process; and   feeding the waste feed to the furnace,   the process further comprising adding sulphur, a sulphur compound or a mixture of sulphur compounds to said furnace based on measured mercury content of the mercury-containing flue gas.   
     
     
       19. Process for removing mercury from mercury-containing flue gas of a furnace within which a combustion or incineration of coal containing sulfur is carried out, comprising the steps of:
 feeding bromine to the mercury-containing flue gas, the temperature during the first contact of the bromine with the mercury-containing flue gas being at least 800° C., and the combustion or incineration being carried out in the presence of a sulphur compound such that a gas phase reaction takes place between the bromine and the mercury so as to produce a bromine-contacted mercury-containing flue gas wherein the mercury is essentially completely oxidized;   wherein said bromine is selected from the group consisting of bromine, a bromine compound, a mixture of bromine compounds and a mixture of bromine and a bromine compound or compounds, and wherein the feeding step feeds bromine to the furnace or to the flue gas of the furnace in a plant section downstream of the furnace, or to both the furnace and the flue gas; and   subjecting the bromine-contacted mercury-containing flue gas to a cleanup for removing oxidized mercury whereby mercury is substantially removed from the bromine-contacted mercury-containing flue gas, wherein the cleanup includes at least one of a wet scrubbing stage and a dry cleanup stage, the dry cleanup stage comprising at least one sorbent.   
     
     
       20. Process according to claim 19, wherein the feeding step comprises mixing the bromine with the coal to be combusted in the furnace, or upstream of the furnace. 
     
     
       21. Process according to claim 19, wherein the bromine compound is an aqueous solution of hydrogen bromide, an alkali metal bromide, or a mixture thereof. 
     
     
       22. Process according to claim 21, wherein the bromine compound is sodium bromide. 
     
     
       23. Process according to claim 19, wherein the bromine is liquid or solid bromine-rich wastes. 
     
     
       24. Process according to claim 19, wherein the bromine, is added to combustion air supplied to the furnace, to a recycled flue gas stream, a recycled fly ash or any combination thereof. 
     
     
       25. Process for removing mercury from mercury-containing flue gas of a furnace within which a combustion or incineration of coal containing sulfur is carried out, comprising the steps of:
 feeding bromine to the mercury-containing flue gas, the temperature during the first contact of the bromine with the mercury-containing flue gas being at least 800° C., and the combustion or incineration being carried out in the presence of a sulphur compound such that a gas phase reaction takes place between the bromine and the mercury so as to produce a bromine-contacted mercury-containing flue gas wherein the mercury is essentially completely oxidized;   wherein said bromine is selected from the group consisting of bromine, a bromine compound, a mixture of bromine compounds and a mixture of bromine and a bromine compound or compounds, and wherein the feeding step feeds bromine to the furnace or to the flue gas of the furnace in a plant section downstream of the furnace, or to both the furnace and the flue gas; and   subjecting the bromine-contacted mercury-containing flue gas to a cleanup for removing oxidized mercury whereby mercury is substantially removed from the bromine-contacted mercury-containing flue gas, wherein the cleanup includes at least one of a wet scrubbing stage and a dry cleanup stage, the dry cleanup stage comprising at least one sorbent, wherein the mass ratio of bromine to mercury in the flue gas is in the range from 10 2  to 10 4 .   
     
     
       26. Process according to claim 19, wherein the combustion or incineration is carried out additionally in the presence of chlorine, a chlorine compound, a mixture of chlorine compounds, iodine, an iodine compound, a mixture of iodine compounds or combination thereof. 
     
     
       27. Process according to claim 19, wherein the furnace is provided with a flue gas emission control system comprising a multistage wet flue gas scrubber having at least one strongly acidic scrubbing, at least one weakly acidic scrubbing stage, at least one alkaline scrubbing stage, or a combination of said scrubbing stages. 
     
     
       28. Process according to claim 27, wherein the mercury content of the mercury-containing flue gas is measured continuously downstream of the flue gas emission control system and the amount of bromine fed and any sulphur or sulphur compounds fed is controlled on the basis of the measured mercury content. 
     
     
       29. Process according to claim 27, wherein said emission control system comprises filtration, electrostatic separation or both. 
     
     
       30. Process according to claim 29, wherein fly ash loaded with mercury is recovered from said filtration or electrostatic separation and is subjected to a thermal secondary treatment to decrease mercury load in a rotary drum heated to temperatures of at least 200° C. 
     
     
       31. Process according to claim 19, wherein the furnace is provided with a flue gas emission control system comprising at least one dry or semi-dry absorption based emission control stage. 
     
     
       32. Process according to claim 19, wherein said sulphur compound is sulphur dioxide. 
     
     
       33. Process according to claim 19, wherein said furnace is a multistage furnace. 
     
     
       34. Process for removing mercury from mercury-containing flue gas of a furnace within which a combustion or incineration of coal containing sulfur is carried out, comprising the steps of:
 feeding bromine to the mercury-containing flue gas, the temperature during the first contact of the bromine with the mercury-containing flue gas being at least 800° C., and the combustion or incineration being carried out in the presence of a sulphur compound such that a gas phase reaction takes place between the bromine and the mercury so as to produce a bromine-contacted mercury-containing flue gas wherein the mercury is essentially completely oxidized;   wherein said bromine is selected from the group consisting of bromine, a bromine compound, a mixture of bromine compounds and a mixture of bromine and a bromine compound or compounds, and wherein the feeding step feeds bromine to the furnace or to the flue gas of the furnace in a plant section downstream of the furnace, or to both the furnace and the flue gas; and   subjecting the bromine-contacted mercury-containing flue gas to a cleanup for removing oxidized mercury whereby mercury is substantially removed from the bromine-contacted mercury-containing flue gas, wherein the cleanup includes at least one of a wet scrubbing stage and a dry cleanup stage, the dry cleanup stage comprising at least one sorbent, wherein the feeding step is carried out by adding bromine in an amount such that the gas phase reaction essentially completely oxidizes the mercury in the mercury-containing flue gas.