Method for preparing calcium carbonate for scrubbing sulfur oxides from combustion effluents

• US 5,575,984 A
• Filed: 12/06/1994
• Issued: 11/19/1996
• Est. Priority Date: 06/09/1994
• Status: Expired due to Fees

• Current Assignee: ALSTOM Power Inc. (General Electric Company)
• Original Assignee: ABB Environmental Systems DIV of ABB Flakt Incorporated
• Inventors: Bresowar, Gerald E.
• Primary Examiner(s): LANGEL, WAYNE A
• Application Number:
  US08/349,796
• Time in Patent Office: 714 Days
• Field of Search: 423/244.08
• US Class Current: 423/244.08
• CPC Class Codes: B01D 53/501 by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
• CPC Class Codes: B01D 53/502 characterised by a specific solution or suspension
• CPC Class Codes: B01D 53/504 characterised by a specific device
• CPC Class Codes: B01D 53/73 After-treatment of removed components
• CPC Class Codes: C01F 11/185 After-treatment, e.g. grinding, purification, conversion of crystal morphology
• CPC Class Codes: C01P 2004/61 Micrometer sized, i.e. from 1-100 micrometer
• CPC Class Codes: F23J 15/006 Layout of treatment plant
• CPC Class Codes: F23J 15/04 using washing fluids scrubbers for removing solids only F23J15/022
• CPC Class Codes: F23J 2215/20 Sulfur; Compounds thereof
• CPC Class Codes: F23J 2217/102 electrostatic
• CPC Class Codes: F23J 2219/30 Sorption devices using carbon, e.g. coke
• CPC Class Codes: F23J 2219/40 Sorption with wet devices, e.g. scrubbers
• CPC Class Codes: Y02P 20/129 Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Abstract

Limestone is dried for grinding to very fine particles e.g., about 8μ or less with more than 99% of the particle by weight less than 44μ, by utilizing waste heat from the flue gas from a large combustor. The finely-divided calcium carbonate is then introduced dry into a scrubbing tower where it mixes with and renews the slurry employed therein for scrubbing SO_x -laden effluent.

Claims

1. A process for preparing finely-ground calcium carbonate in dry form to remove sulfur oxides from flue gases by wet scrubbing, comprising:

(a) dividing a flow of hot flue gas containing SO.sub. x from a combustor into at least a first flue gas stream and a second flue gas stream;

(b) introducing the first flue gas stream into a scrubbing tower wherein it flows upwardly, countercurrent to a spray of an aqueous slurry of fine particles of calcium carbonate within a vertical scrubbing section, the slurry falling through the vertical scrubbing section and being collected in a reaction tank at the bottom of the tower;

(c) directing the second flue gas stream into contact with coarse calcium carbonate to dry the calcium carbonate to a moisture content suitable for dry-grinding;

(d) dry-grinding the coarse calcium carbonate; and

(g) introducing the resulting dry, ground calcium carbonate into the scrubbing tower.

2. A process according to claim 1 wherein the calcium carbonate is ground to a weight median diameter of 10μ

or less with at least about 99% by weight being less than 44μ

.

3. A process according to claim 1 wherein the second flue gas stream is contacted with the coarse calcium carbonate in a dry-grinding device and, following grinding and separation of the ground calcium carbonate from the second flue gas stream, a portion of the separated second flue gas stream, still having some drying capacity, is returned to the dry-grinding device.

4. A process according to claim 1 wherein, following division of the flue gas from the combustor into the first and second flue gas streams and contact of the first stream with the calcium carbonate, at least the first flue gas stream is brought into contact with a heat exchanger to transfer heat to effluent from the scrubbing tower.

5. A process according to claim 1 wherein the median size of the calcium carbonate particles is in the range of from 5 to 8μ

, with at least 99.5% by weight of the particles being less than 44μ

.

6. A process according to claim 1 wherein the finely-divided calcium carbonate is dried sufficiently to achieve a moisture content of less than 1% following grinding.

7. A process for preparing finely-ground calcium carbonate in dry form for use in a process to remove sulfur oxides from flue gases by wet scrubbing, comprising:

(a) dividing a flow of hot flue gas containing SO_x from a combustor into at least a first flue gas stream and a second flue gas stream;

(b) introducing the first flue gas stream into a scrubbing tower wherein it flows upwardly, countercurrent to a spray of an aqueous slurry of fine particles of calcium carbonate within a vertical scrubbing section, the slurry falling through the vertical scrubbing section and being collected in a reaction tank at the bottom of the tower;

(c) directing the second flue gas stream into contact with coarse calcium carbonate in a dry-grinding device to dry the calcium carbonate to a moisture content less than 1%;

(d) dry-grinding the coarse calcium carbonate to a weight median diameter of about 10μ

or less with at least about 99% by weight being less than 44μ

;

(e) following grinding, separating the ground calcium carbonate from the second flue gas stream;

(f) returning a portion of the separated second flue gas stream, still having some drying capacity, to the dry-grinding device; and

(g) introducing the resulting dry, ground calcium carbonate into the scrubbing tower.

8. A process according to claim 7 wherein, following division of the flue gas from the combustor into the first and second flue gas streams, the first flue gas stream is brought into contact with a heat exchanger to transfer heat to effluent from the scrubbing tower.

9. A process according to claim 7 wherein the median size of the calcium carbonate particles is less than about 8μ

, with at least 99.5% by weight of the particles being less than 44μ

.