Method of removing sulfur trioxide from a flue gas stream

• US 7,481,987 B2
• Filed: 09/15/2005
• Issued: 01/27/2009
• Est. Priority Date: 09/15/2005
• Status: Expired due to Fees

• Current Assignee: Solvay Chemicals Incorporated (Solvac SA)
• Original Assignee: Solvay Chemicals Incorporated (Solvac SA)
• Inventors: Maziuk, John Jr.
• Primary Examiner(s): Vanoy; Timothy C
• Application Number:
  US11/229,011
• Publication Number:
  US 20070081936A1
• Time in Patent Office: 1,230 Days
• Field of Search: 423/242.1, 423/244.07, 423/244.08, 423/235, 423/215.5, 423/551, 423/DIG.5, 423/DIG.8
• US Class Current: 423/215.5
• CPC Class Codes: B01D 2257/302 Sulfur oxides
• CPC Class Codes: B01D 2257/404 Nitrogen oxides other than dinitrogen oxide
• CPC Class Codes: B01D 53/505 in a spray drying process
• CPC Class Codes: B01D 53/508 by treating the gases with solids
• CPC Class Codes: Y10S 423/05 Automatic, including computer, control
• CPC Class Codes: Y10S 423/08 Corrosion or deposition inhibiting

Abstract

A method is provided for reducing the fouling during the removal of sulfur trioxide from a flue gas stream by maintaining the reagent (i. e. sodium sesquicarbonate) in contact with the flue gas for a sufficient time and temperature to react a portion of the reagent with a portion of the sulfur trioxide to substantially avoid formation of liquid phase NaHSO₄ reaction product that combines with the fly ash so as to not form a sticky ash residue that adheres to the flue gas duct, wherein the reaction product of the reagent and the sulfur trioxide is selected from the group consisting of Na₂SO₄, Na₂S₂O₇ and mixtures thereof.

Claims

1. A method for reducing fouling during the removal of SO₃ from a flue gas stream comprising SO₃ and fly ash, the method comprising:

providing a reagent, comprising sodium sesquicarbonate, wherein the mean particle size of the reagent is less than about 40 microns;

injecting the reagent into the flue gas stream in a flue gas duct, wherein the temperature of the flue gas is between about 500°

F. and about 850°

F.;

maintaining the reagent in contact with the flue gas for a time sufficient and at a sufficient temperature to react a portion of the reagent with a portion of the SO₃ to reduce the concentration of the SO₃ in the flue gas stream and to substantially avoid formation of a liquid phase NaHSO₄ reaction product that combines with the fly ash so as to not form a sticky ash residue that adheres to the flue gas duct, wherein the reaction product of the reagent and the SO₃ is selected from the group consisting of Na₂SO₄, Na₂S₂O₇, and mixtures thereof.

2. The method of claim 1 further comprising providing an NO_x removal system upstream of the location where the reagent is injected.

3. The method of claim 1 wherein the flue gas stream comprises at least about 3 ppm SO₃ upstream of the location where the reagent is injected.

4. The method of claim 3 wherein the flue gas stream comprises between about 10 ppm and about 200 ppm SO₃ upstream of the location where the reagent is injected.

5. The method of claim 1 wherein the mean particle size of the reagent is between about 10 micron and about 40 micron.

6. The method of claim 5 wherein the mean particle size of the reagent is between about 24 micron and about 28 micron.

7. The method of claim 1 wherein the temperature of the flue gas is greater than about 550°

F.

8. The method of claim 1 wherein the temperature of the flue gas is less than about 750°

F.

9. The method of claim 1 wherein the temperature of the flue gas is between about 500°

F. and about 750°

F.

10. The method of claim 1 wherein the reagent is injected at a rate with respect to the flow rate of the SO₃ to provide a normalized stoichiometric ratio of sodium to sulfur in the form of SO₃ of between about 1.0 and 1.5.

11. The method of claim 1 wherein the-reagent is injected as a dry material.

12. The method of claim 1 further comprising milling the reagent to a desired mean particle size at a location proximate the flue gas stream.

13. A method for reducing fouling during the removal of SO₃ from a flue gas stream comprising SO₃ and fly ash, the method comprising:

providing a source of trona, wherein the trona is provided in the form of particles with a mean particle size of between about 10 micron and about 40micron;

injecting the trona as a dry granular material into the flue gas stream in a flue gas duct, wherein the temperature of the flue gas is between about 500°

F. and about 850°

F. and wherein the flue gas stream comprises at least about 3ppm SO₃; and

maintaining the trona in contact with the flue gas for a time sufficient and at a sufficient temperature to react a portion of the trona with a portion of the SO₃ to reduce the concentration of the SO₃ in the flue gas stream, and to substantially avoid formation of a liquid phase NaHSO₄ reaction product that combines with the fly ash so as to not form a sticky ash residue that adheres to the flue gas duct.

14. The method of claim 13 wherein the flue gas stream comprises between about 10 ppm and about 200 ppm SO₃ upstream of the location where the trona is injected.

15. The method of claim 13 wherein the temperature of the flue gas is between about 500°

F. and about 750°

F.

16. The method of claim 13 wherein the reaction product of the reagent and the SO₃ is selected from the group consisting of Na₂SO₄, Na₂S₂O₇, and mixtures thereof.

17. The method of claim 13 further comprising adjusting the flue gas temperature upstream of the trona to obtain the desired flue gas temperature where the trona is injected.

18. The method of claim 17 wherein the adjusting further comprises introducing ambient air into the flue gas stream and monitoring the flue gas temperature where the trona is injected.

19. The method of claim 17 wherein the adjusting further comprises controlling the flow of a material through a heat exchanger in communication with the flue gas.

20. A method of reducing fouling during the removal of SO₃ from a flue gas stream comprising SO₃ and fly ash, the method comprising:

providing a reagent, comprising sodium sesquicarbonate;

injecting the reagent into the flue gas stream in a flue gas duct, wherein the temperature of the flue gas is at or above about 500°

F. and the reagent is maintained in contact with the flue gas at a sufficient temperature to avoid formation of a liquid phase NaHSO₄ reaction product that combines with the fly ash so as to not form a sticky ash residue that adheres to the flue gas duct;

maintaining the reagent in contact with the flue gas for a time sufficient to react a portion of the reagent with a portion of the SO₃ to reduce the concentration of the SO₃ in the flue gas stream; and

providing a NO_x removal system upstream of the location where the reagent is injected.

21. The method of claim 20 wherein the reagent is injected at a rate with respect to the flow rate of the SO₃ to provide a normalized stoichiometric ratio of sodium to sulfur in the form of SO₃ of between about 1.0 and 1.5.