Method for removal of mercury emissions from coal combustion

• US 7,514,052 B2
• Filed: 01/06/2004
• Issued: 04/07/2009
• Est. Priority Date: 01/06/2004
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Seeker, William Randall, Maly, Peter Martin, Lissianski, Vitali Victor, Zamansky, Vladimir M.
• Primary Examiner(s): Johnson; Edward M
• Application Number:
  US10/751,496
• Publication Number:
  US 20050147549A1
• Time in Patent Office: 1,918 Days
• Field of Search: 423/210, 423/99, 423/240.R, 423/240.S, 423/239, 423/239.1
• US Class Current: 423/210
• CPC Class Codes: B01D 2251/00 Reactants
• CPC Class Codes: B01D 2257/404 Nitrogen oxides other than dinitrogen oxide
• CPC Class Codes: B01D 2257/602 Mercury or mercury compounds
• CPC Class Codes: B01D 53/56 Nitrogen oxides B01D53/60 takes precedence
• CPC Class Codes: B01D 53/64 Heavy metals or compounds thereof, e.g. mercury

Abstract

A method to reduce emissions in flue gas due to combustion of coal in a combustion unit including the steps of: combusting coal in a primary combustion zone of the combustion unit; releasing elemental mercury from the combustion into the flue gas; injecting NH₄Cl, NH₄Br, or NH₄I into the flue gas; oxidizing the elemental mercury with halogen from the additive; adsorbing the oxidized mercury generated by the combustion of the coal with an adsorbent in the flue gas, and collecting the adsorbent with the oxidized mercury in a combustion waste treatment system.

Claims

1. A method to reduce emissions in flue gas due to combustion of coal in a combustion unit, said method comprising:

a. combusting coal in a primary combustion zone of the combustion unit;

b. releasing elemental mercury from the combustion into the flue gas;

c. injecting a halogen-containing additive into the flue gas, wherein the halogen-containing additive is selected from a group consisting of NH₄Br and NH₄I;

d. oxidizing the elemental mercury with a halogen from the halogen-containing additive;

e. adsorbing the oxidized mercury generated by the combustion of the coal with an adsorbent in the flue gas, and

f. collecting the adsorbent with the mercury in a combustion waste treatment system.

2. A method as in claim 1 wherein the coal comprises a coal having a low chlorine content.

3. A method as in claim 2 wherein the coal having the low chlorine content is a Powder River Basin coal or lignite coal.

4. A method as in claim 2 wherein the coal having the low chlorine content has less than 100 parts-per-million (ppm) of chlorine.

5. A method as in claim 1 wherein the combustion waste treatment system includes a particle control device.

6. A method as in claim 1 wherein the adsorbent is fly ash, and the oxidized mercury is adsorbed on the fly ash.

7. A method as in claim 1 wherein the adsorbent is activated carbon, and the oxidized mercury is adsorbed on the activated carbon.

8. A method as in claim 1 further comprising heating the halogen-containing additive with flue gas to generate HBr or HI and oxidizing the elemental mercury with the HBr or HI.

9. A method as in claim 1 further comprising injecting overfire air downstream of the primary combustion zone to generate excessive carbon fly ash and the adsorbent is the fly ash.

10. A method as in claim 9 wherein the stoichiometric ratio (SR1) in the primary combustion zone is less than 1.1, and the stoichiometric ratio (SR2) at an overfire air injection zone is above 1.0.

11. A method as in claim 10 wherein SRi is no greater than 0.8 and SR2 is no less than 1.16.

12. A method as in claim 1 further comprising coal reburning downstream of the primary combustion zone to form carbon in fly ash generated during combustion, and the fly ash is the adsorbent.

13. A method as in claim 1 further comprising injecting a nitrogenous reducing agent into the flue gas.

14. A method as in claim 13 further comprising a catalytic surface for NOx and mercury oxidation.

15. A method as in claim 1 wherein the halogen containing additive is injected where the flue gas is in a temperature range of 1600°

F. to 2300°

F.

16. A method as in claim 1 wherein the halogen containing additive is injected where the flue gas is in a temperature range of 1750°

F. to 1950°

F.

17. A method as in claim 1 wherein an amount of halogen injected into the flue gas by the halogen containing additive is in the range of 1 to 200 parts per million.

18. A method as in claim 1 wherein the halogen containing additive is injected in an aqueous solution into the flue gas.

19. A method as in claim 18 wherein the halogen containing additive is injected in the solution further comprises NH₄OH.

20. A method as in claim 18 wherein the halogen containing additive is injected in the solution further comprises urea.

21. A method as in claim 1 wherein the mercury released from combustion is mostly elemental mercury (Hg⁰) and further comprising oxidizing the elemental mercury as the flue gases cools.

22. A method as in claim 21 wherein the oxidized mercury is removed from flue gas in a scrubber.

23. A method as in claim 1 further comprising injecting an aqueous solution of the halogen containing additive with a carrier gas.

24. A method as in claim 23 wherein the carrier gas is at least one of air, recycled flue gas and nitrogen gas.

25. A method to reduce mercury in gas emissions from the combustion of coal in a combustion system, said method comprising:

a. combusting the coal in a primary combustion zone of the combustion system, wherein elemental mercury (Hg⁰) is released in the flue gas produced by the combustion;

b. staging combustion air supplied to the combustion system by adding a portion of the combustion air to the primary combustion zone and a second portion of the combustion air to an overfire air zone downstream of the combustion zone;

c. maintaining stoichiometric ratio in the primary combustion zone of no greater than 1.1 so as to form active carbon in the fly ash generated by the combustion of coal;

d. oxidizing the elemental mercury by injection of a halogen containing additive in the flue gas to generate oxidized mercury (Hg⁺²), wherein the halogen-containing additive is selected from a group consisting of NH₄Br and NH₄I;

e. adsorbing the oxidized mercury in the flue gas by the active carbon in the fly ash, and

f. collecting the fly ash with adsorbed mercury in a combustion waste treatment system.

26. A method as in claim 25 wherein the combustion waste treatment system comprises a particle control device capturing the fly ash with adsorbed mercury and discharging the captured fly ash to a fly ash collection unit.

27. A method as in claim 25 wherein the combustion waste treatment system comprises a particle control device capturing the fly ash after the fly ash cools to a temperature no greater than 400 degrees Fahrenheit.

28. A method as in claim 25 further comprising coal reburning in the combustion system to form carbon in the fly ash generated during combustion.

29. A method as in claim 28 wherein an amount of reburning fuel used during the coal reburning is in a range of about 10 to about 30 percent of a total heat input of fuel used for the combustion.

30. A method as in claim 28 wherein an amount of reburning fuel used during the coal reburning is in a range of about 15 to about 25 percent of a total heat input of fuel used for the combustion.

31. A method as in claim 25 wherein combustion occurs in a low nitrogen oxide (NOx) burner.

32. A method to reduce emissions in flue gas due to combustion of coal in a combustion unit, said method comprising:

a. combusting coal in a primary combustion zone of the combustion unit;

b. releasing elemental mercury from the combustion into the flue gas;

c. injecting a halogen-containing additive into the flue gas, wherein the halogen-containing additive includes NH₄I;

d. oxidizing the elemental mercury with a halogen from the halogen-containing additive;

e. adsorbing the oxidized mercury generated by the combustion of the coal with an adsorbent in the flue gas, and

f. collecting the adsorbent with the mercury in a combustion waste treatment system.