Alkaline sorbent injection for mercury control

• US 20020102189A1
• Filed: 11/16/2001
• Published: 08/01/2002
• Est. Priority Date: 12/07/1998
• Status: Active Grant

• Current Assignee: McDermott Technology, Inc.
• Original Assignee: McDermott Technology, Inc.
• Inventors: Holmes, Michael J., Madden, Deborah A.
• Granted Patent: US 6,528,030 B2
• Time in Patent Office: Days
• US Class Current: 422/168
• CPC Class Codes: B01D 53/508 by treating the gases with solids
• CPC Class Codes: B01D 53/64 Heavy metals or compounds thereof, e.g. mercury
• CPC Class Codes: B01D 53/80 Semi-solid phase processes, i.e. by using slurries
• CPC Class Codes: B01D 53/81 Solid phase processes

Abstract

A mercury removal system for removing mercury from combustion flue gases is provided in which alkaline sorbents at generally extremely low stoichiometric molar ratios of alkaline earth or an alkali metal to sulfur of less than 1.0 are injected into a power plant system at one or more locations to remove at least between about 40% and 60% of the mercury content from combustion flue gases. Small amounts of alkaline sorbents are injected into the flue gas stream at a relatively low rate. A particulate filter is used to remove mercury-containing particles downstream of each injection point used in the power plant system.

Claims

1. A mercury removal system for removing mercury from a flue gas generated in a combustion system having a boiler and a stack, comprising:

particulate removal means for separating and removing particulate matter containing mercury from the flue gas, the particulate removal means located between the boiler and the stack; and

sorbent injection means for providing an alkaline sorbent in one of powdered and slurried form to at least one location upstream of the stack, the alkaline sorbent containing at least one element selected from the alkaline earth elements, the sorbent further being provided in a stoichiometric molar ratio of alkaline earth to sulfur in a range of about 0.001 mole alkaline earth/mole sulfur to about 1.0 mole alkaline earth/mole sulfur.

2. The mercury removal system according to claim 1, wherein the stoichiometric molar ratio is in a range of about 0.001 mole alkaline earth/mole sulfur to about 0.5 mole alkaline earth/mole sulfur.

3. The mercury removal system according to claim 2, wherein the alkaline sorbent comprises one of limestone, lime, a calcium-based sorbent, and a combination thereof.

4. The mercury removal system according to claim 3, wherein the alkaline sorbent comprises limestone.

5. The mercury removal system according to claim 1, wherein the stoichiometric molar ratio is about 0.35 mole alkaline earth/mole sulfur.

6. The mercury removal system according to claim 5, wherein the alkaline sorbent comprises one of limestone, lime, a calcium-based sorbent, and a combination thereof.

7. The mercury removal system according to claim 1, comprising means for providing the alkaline sorbent to the boiler.

8. The mercury removal system according to claim 7, wherein the alkaline sorbent is provided to at least one of an upper furnace region and a convection pass of the boiler.

9. The mercury removal system according to claim 7, wherein the alkaline sorbent is one of limestone, lime, a calcium-based sorbent, and a combination thereof.

10. The mercury removal system according to claim 7, wherein the particulate removal means comprises an electrostatic precipitator.

11. The mercury removal system according to claim 1, wherein the particulate removal means comprises an electrostatic precipitator.

12. The mercury removal system according to claim 11, wherein the stoichiometric molar ratio is in a range of about 0.001 mole alkaline earth/mole sulfur to about 0.5 mole alkaline earth/mole sulfur.

13. The mercury removal system according to claim 11, comprising means for providing the alkaline sorbent to the boiler.

14. The mercury removal system according to claim 13, wherein the alkaline sorbent is provided to at least one of an upper furnace region and a convection pass of the boiler.

15. The mercury removal system according to claim 14, comprising means for providing the alkaline sorbent to at least one of upstream adjacent the electrostatic precipitator and upstream adjacent the stack, the stack further comprising separator means for separating and removing particulate containing mercury from the flue gas.

16. The mercury removal system according to claim 11, comprising means for providing the alkaline sorbent to at least one of upstream adjacent the electrostatic precipitator and upstream adjacent the stack, the stack further comprising separator means for separating and removing particulate containing mercury from the flue gas.

18. The mercury removal system according to claim 17, wherein the stoichiometric molar ratio is in a range of about 0.001 mole alkali metal/mole sulfur to about 0.5 mole alkali metal/mole sulfur.

19. The mercury removal system according to claim 18, wherein the alkaline sorbent comprises a sodium-based sorbent.

20. The mercury removal system according to claim 17, wherein the stoichiometric molar ratio is about 0.35 mole alkali metal/mole sulfur.

21. The mercury removal system according to claim 20, wherein the alkaline sorbent comprises a sodium-based sorbent.

22. The mercury removal system according to claim 17 comprising means for providing the alkaline sorbent to the boiler.

23. The mercury removal system according to claim 22, wherein the alkaline sorbent is provided to at least one of an upper furnace region and a convection pass of the boiler.

24. The mercury removal system according to claim 22, wherein the alkaline sorbent is a sodium-based sorbent.

25. The mercury removal system according to claim 22, wherein the particulate removal means comprises an electrostatic precipitator.

26. The mercury removal system according to claim 17, wherein the particulate removal means comprises an electrostatic precipitator.

27. The mercury removal system according to claim 26, wherein the stoichiometric molar ratio is in a range of about 0.001 mole alkali metal/mole sulfur to about 0.5 mole alkali metal/mole sulfur.

28. The mercury removal system according to claim 26, comprising means for providing the alkaline sorbent to the boiler.

29. The mercury removal system according to claim 28, wherein the alkaline sorbent is provided to at least one of an upper furnace region and a convection pass of the boiler.

30. The mercury removal system according to claim 29, comprising means for providing the alkaline sorbent to at least one of upstream adjacent the electrostatic precipitator and upstream adjacent the stack, the stack further comprising separator means for separating and removing particulate containing mercury from the flue gas.

31. The mercury removal system according to claim 26, comprising means for providing the alkaline sorbent to at least one of upstream adjacent the electrostatic precipitator and upstream adjacent the stack, the stack further comprising separator means for separating and removing particulate containing mercury from the flue gas.

17. A mercury removal system for removing mercury from a flue gas generated in a combustion system having a boiler and a stack, comprising:

particulate removal means for separating and removing particulate matter containing mercury from the flue gas, the particulate removal means located between the boiler and the stack; and

sorbent injection means for providing an alkaline sorbent in one of powdered and slurried form to at least one location upstream of the stack, the alkaline sorbent containing at least one element selected from the alkali metals, the sorbent further being provided in a stoichiometric molar ratio of alkali metal to sulfur in a range of about 0.001 mole alkali metal/mole sulfur to about 1.0 mole alkali metal/mole sulfur.

32. A mercury removal system for removing mercury from a flue gas generated in a combustion system having a boiler and a stack, comprising:

particulate removal means for separating and removing particulate matter containing mercury from the flue gas, the particulate removal means located between the boiler and the stack; and

sorbent injection means for providing an alkaline sorbent in one of powdered and slurried form to at least one location upstream of the stack, the alkaline sorbent containing a combination of at least one element selected from the alkaline earth elements and at least one element selected from the alkali metals, the sorbent further being provided in a stoichiometric molar ratio of alkaline earth and alkali metal to sulfur in a range of about 0.001 mole alkaline earth and alkali metal/mole sulfur to about 1.0 mole alkaline earth/mole sulfur.