Method and arrangement for removing gaseous elementary mercury from a stream of gas

1. A method for removing gaseous elementary mercury from a stream of gas, wherein the method comprises

(i) feeding the stream of gas into a first washing tower,

(ii) treating the stream of gas in the first washing tower with a first washing solution that circulates in a first closed system through the first washing tower and that contains mercury (II)-ions to form a stream of once processed gas of the stream of gas,

(iii) feeding the stream of once processed gas from the first washing tower into a second washing tower,

(iv) treating the stream of once processed gas in the second washing tower with a second washing solution circulating in a second closed system through the second washing tower and that contains a higher concentration of mercury (II)-ions than the first washing solution form a stream of twice processed gas of the stream of once processed gas,

(v) feeding the stream of twice processed gas from the second washing tower into a third washing tower,

(vi) treating the stream of twice processed gas in the third washing tower with a third washing solution circulating in a third closed system through the third washing tower and that contains a lower concentration of mercury (II)-ions than the first washing solution to form a stream of cleaned gas of the stream of twice processed gas, and

(vii) discharging the stream of cleaned gas from the third washing tower.

2. The method according to claim 1 , further comprising feeding additional washing solution containing mercury (II)-ions from a tank means into first washing solution circulating in the first closed system.

3. The method according to claim 1 , further comprising removing calomel from the first washing solution circulating in the first closed system.

4. The method according to claim 1 , further comprising feeding a part of the second washing solution circulating in the second closed system into first washing solution circulating in the first closed system to remove calomel from the second washing solution.

5. The method according to claim 1 , further comprising feeding additional washing solution containing mercury (II)-ions from a tank means into second washing solution circulating in the second closed system.

6. The method according to claim 1 , wherein the cleaned gas is brought to a filter for absorption of any remaining gaseous elementary mercury.

7. The method according to claim 1 , further comprising removing mercury from the third washing solution circulating in the third closed system by means of an active filter.

8. The method according to claim 1 , wherein the first washing solution has a mercury (II)-ion content that is between about 0.1 g/l and about 2 g/l.

9. The method according to claim 1 , wherein the first washing solution additionally contains an amount of ions selected from the group consisting of chlorine, bromine, iodine, cyanide and rhodanide ions, which said amount of ions is at least twice the amount of mercury (II)-ions.

10. The method according to claim 1 , wherein the second washing solution has a mercury (II)-ion content that is more than about 3.0 g/l.

11. The method according to claim 1 , wherein the second washing solution additionally contains an amount of ions selected from the group consisting of chlorine, bromine, iodine, cyanide and rhodanide ions, which said amount of ions is at least twice the amount of mercury (II)-ions.

12. The method according to claim 1 , wherein the third washing solution has a mercury (II)-ion content that is less than about 0.3 g/l.

13. The method according to claim 1 , wherein the third washing solution additionally contains an amount of ions selected from the group consisting of chlorine, bromine, iodine, cyanide and rhodanide ions, which said amount of ions is at least twice the amount of mercury (II)-ions.

14. An arrangement for removing gaseous elementary mercury from a stream of gas, wherein the arrangement comprises

a first washing tower for receiving a stream of gas containing gaseous elementary mercury, wherein the first washing tower is configured for treating the stream of gas with a first washing solution that circulates in a first closed system through the first washing tower and that contains mercury (II) ions to form a stream of once processed gas of the stream of gas,

a second washing tower for receiving a stream of once processed gas from the first washing tower, wherein the second washing tower is configured for treating the stream of once processed gas with a second washing solution circulating in a second closed system through the second washing tower and that contains a higher concentration of mercury (II)-ions than the first washing solution to form a stream of twice processed gas of the stream of once processed gas,

a third washing tower for receiving a stream of twice processed gas from the second washing tower, wherein the third washing tower is configured for treating the stream of twice processed gas with a third washing solution circulating in a third closed system through the third washing tower and that contains a lower concentration of mercury (II)-ions than the first washing solution to form a stream of cleaned gas of the stream of twice processed gas, and wherein the third washing tower is configured for discharging a stream of cleaned gas from the third washing tower, and

a filter for absorption of any remaining gaseous elementary mercury in the cleaned gas.

15. The arrangement according to claim 14 , further comprising first feeding means for feeding additional washing solution containing mercury (II)-ions from a tank means into first washing solution circulating in the first closed system.

16. The arrangement according to claim 14 , further comprising first removing means for removing calomel from the first washing solution circulating in the first closed system.

17. The arrangement according to claim 14 , further comprising second feeding means for feeding a part of the second washing solution circulating in the second closed system into first washing solution circulating in the first closed system.

18. The arrangement according to claim 14 , further comprising third feeding means for feeding additional washing solution containing mercury (II)-ions from a tank means into second washing solution circulating in the second closed system.

19. The arrangement according to claim 14 , wherein the third closed system is provided with an active filter for removing mercury from the third washing solution circulating in the third closed system.

20. The arrangement according to claim 14 , wherein the mercury (II)-ion content in the first washing solution is between about 0.1 g/l and about 2 g/l.

21. The arrangement according to claim 14 , wherein the first washing solution additionally contains an amount of ions selected from the group consisting of chlorine, bromine, iodine, cyanide and rhodanide ions, which said amount of ions is at least twice the amount of mercury (II)-ions.

22. The arrangement according to claim 14 , wherein the mercury (II)-ion content in the second washing solution is more than about 3.0 g/l.

23. The arrangement according to claim 14 , wherein the second washing solution additionally contains an amount of ions selected from the group consisting of chlorine, bromine, iodine, cyanide and rhodanide ions, which said amount of ions is at least twice the amount of mercury (II)-ions.

24. The arrangement according to claim 14 , wherein the mercury (II)-ion content in the third washing solution is less than about 0.3 g/l.

25. The arrangement according to claim 14 , wherein the third washing solution additionally contains an amount of ions selected from the group consisting of chlorine, bromine, iodine, cyanide and rhodanide ions, which said amount of ions is at least twice the amount of mercury (II)-ions.