Wet scrubber for removing sulfur dioxide from a process gas

1. A method of cleaning a process gas containing sulphur dioxide by a wet scrubber, said method comprising:

bringing the process gas into contact with an absorption liquid in an absorption vessel to absorb sulphur dioxide from the process gas,

mixing the absorption liquid with a carbon dioxide containing gas comprising at least 20% by volume carbon dioxide,

adding an absorbent material to at least a portion of the absorption liquid, and

returning at least a portion of the absorption liquid to the absorption vessel to absorb more sulphur dioxide from the process gas; and

mixing the absorption liquid with an oxygen containing gas containing at least 3% by volume oxygen (O 2 ) prior to mixing the absorption liquid with the carbon dioxide containing gas comprising at least 20% by volume carbon dioxide.

2. A method according to claim 1 , wherein the mixing the absorption liquid with a carbon dioxide containing gas comprising at least 20% by volume carbon dioxide is carried out simultaneously with the step of adding an absorbent material to at least a portion of the absorption liquid.

3. A method according to claim 1 , wherein the mixing the absorption liquid with an oxygen containing gas containing at least 3% by volume oxygen is performed in an oxidation tank from which the absorption liquid is transferred to an absorbent dissolution tank in which the step of mixing the absorption liquid with a carbon dioxide containing gas comprising at least 20% by volume carbon dioxide is carried out.

4. A method according to claim 3 , wherein a first portion of the absorbent material is added to the absorbent dissolution tank, and wherein a second portion of the absorbent material is added to the absorption liquid after the absorption liquid has left the absorbent dissolution tank.

5. A method according to claim 1 , wherein the carbon dioxide containing gas comprising at least 20% by volume carbon dioxide at least partly originates from process gas that is to be cleaned, or has already been cleaned, in the wet scrubber.

6. A method according to claim 1 , wherein at least a portion of the carbon dioxide containing gas comprising at least 20% by volume carbon dioxide is generated in an oxy-fuel boiler.

7. A wet scrubber for cleaning a process gas containing sulphur-dioxide, the wet scrubber comprising:

an absorption vessel operative for bringing the process gas into contact with an absorption liquid to absorb sulphur dioxide from the process gas,

an acidification system operative for mixing absorption liquid that has absorbed sulphur dioxide from the process gas with a carbon dioxide containing gas,

an absorbent dissolution tank operative for adding an absorbent material to at least a portion of the absorption liquid,

a return pipe operative for returning to the absorption vessel at least a portion of the absorption liquid that has been mixed with the carbon dioxide containing gas, and to which absorption liquid the absorbent material has been added, to absorb more sulphur dioxide from the process gas; and

an oxidation tank, which is operative for mixing absorption liquid that has absorbed sulphur dioxide from the process gas with an oxygen containing gas containing at least 3% by volume oxygen (O 2 ) the oxidation tank being located upstream of at least one vessel of the acidification system such that the oxidation tank is configured to mix the oxygen containing gas with the absorption liquid prior to the acidification system mixing that absorption liquid with the carbon dioxide containing gas.

8. A wet scrubber according to claim 7 , wherein the acidification system is arranged in the absorbent dissolution tank operative for adding an absorbent material to at least a portion of the absorption liquid, such that mixing the absorbent liquid with carbon dioxide containing gas may be performed simultaneously with adding absorbent material to the absorption liquid.

9. A wet scrubber according to claim 7 , further comprising a first absorbent supply pipe which is operative for supplying a first portion of the absorbent material to the absorbent dissolution tank, and a further absorbent supply pipe which is operative for supplying a second portion of the absorbent material to the absorption liquid in a position located downstream of the absorbent dissolution tank.

10. A wet scrubber according to claim 7 , further comprising a blower configured to direct the oxygen containing gas to the oxidation tank for mixing with the absorption liquid.

11. A wet scrubber according to claim 7 , further comprising a gas duct arranged upstream or downstream of the absorption vessel for transporting a portion of the process gas to the acidification system, such that said portion of the process gas will form the carbon dioxide containing gas.

12. A wet scrubber according to claim 11 , further comprising a blower arranged for transporting carbon dioxide containing gas via said duct to the acidification system.

13. A wet scrubber according to claim 7 , wherein the acidification system comprises at least one nozzle being operative for bubbling the carbon dioxide containing gas through the absorption liquid.

14. A wet scrubber according to claim 7 , further comprising a first gas transporting device which is operative for transporting the oxygen containing gas from a first source of gas to the oxidation tank and a second gas transporting device which is operative for transporting the carbon dioxide containing gas from a second source of gas to the acidification system, the first source of gas being different from the second source of gas.

15. A wet scrubber according to claim 7 , wherein the oxidation tank has at least one agitator.

16. A wet scrubber according to claim 7 , comprising:

an absorbent slurry preparation system being connected to the absorbent dissolution tank for feeding slurry containing the absorbent material to the absorbent dissolution tank.

17. A wet scrubber according to claim 16 , wherein the absorbent slurry preparation system comprises a silo configured to store the absorbent material in powder form and an absorbent slurry mixing tank being connected to the silo for receiving the absorbent material from the silo.

18. A wet scrubber according to claim 17 , wherein the absorbent slurry preparation system is connected to the absorbent dissolution tank by at least one pipe fluidly connecting the absorbent slurry mixing tank to the absorbent dissolution tank.

19. A wet scrubber according to claim 18 , comprising at least one first pH sensor connected to the absorbent dissolution tank.