Process for reducing sulfur emissions with calcium-containing sorbents

• US 5,368,617 A
• Filed: 04/30/1992
• Issued: 11/29/1994
• Est. Priority Date: 11/30/1987
• Status: Expired due to Fees

• Current Assignee: General Research Corporation
• Original Assignee: General Research Corporation
• Inventors: Kindig, James K.
• Primary Examiner(s): MEDLEY, MARGARET B
• Application Number:
  US07/876,496
• Time in Patent Office: 943 Days
• Field of Search: 423/235, 423/244 R, 423/244 A, 423/242, 44/604, 44/620, 44/622, 44/580, 431/3, 110/342, 110/343, 110/345
• US Class Current: 44/622
• CPC Class Codes: B03B 13/005 Methods or arrangements for controlling the physical properties of heavy media, e.g. density, concentration or viscosity
• CPC Class Codes: B03B 5/30 using heavy liquids or suspensions
• CPC Class Codes: B03B 5/34 Applications of hydrocyclones
• CPC Class Codes: B03B 5/442 composition of heavy media
• CPC Class Codes: B03B 5/447 recovery of heavy media
• CPC Class Codes: B03B 9/005 specially adapted for coal
• CPC Class Codes: C01G 49/06 Ferric oxide [Fe2O3]
• CPC Class Codes: C01G 49/08 Ferroso-ferric oxide [Fe3O4]
• CPC Class Codes: C01P 2004/52 highly monodisperse size distribution
• CPC Class Codes: C01P 2004/61 Micrometer sized, i.e. from 1-100 micrometer
• CPC Class Codes: C01P 2006/10 Solid density
• CPC Class Codes: Y02P 20/129 Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Abstract

An improved process for reducing sulfur oxide emissions from the combustion of coal is disclosed wherein a fuel mixture comprising calcium-containing sorbent and coal is fed to the burners and sulfur oxides react with calcium from the sorbent in a high temperature sulfur capture region, followed by additional sulfur capture in a lower temperature, high humidity sulfur capture region prior to separation of particulates from the flue gas. Sulfur capture using calcium-containing sorbents can be combined with aggressive coal beneficiation techniques to further enhance reduction of sulfur oxide emissions. The process of the invention provides a process for reducing sulfur oxides that efficiently uses calcium-containing sorbents to enhance sulfur capture while reducing the need for expensive equipment or process modifications.

Claims

1. A process for reducing the emission of sulfur oxides from the combustion of coal, comprising:

(a) combusting a fuel mixture of sulfur-containing coal and calcium-containing sulfur sorbent, said coal comprising coal particles resulting from aggressively beneficiating raw coal, wherein said aggressive beneficiation comprises (i) separating the raw coal into a coarse size fraction and a fine size fraction (ii) density separating the coarse fraction into a clean coal fraction, a refuse fraction and a middling fraction, (iii) comminuting said middling fraction, and (iv) combining said comminuted middling fraction with said fine fraction and further beneficiating the combined fraction, said calcium-containing sulfur sorbent comprising a calcium-containing compound selected from the group consisting of lime, limestone, hydrated lime, calcium oxide, dolomite, burnt dolomite, hydrated dolomite and combinations thereof, at least a portion of calcium in said sulfur sorbent reacts with sulfur oxides emitted during the combustion of coal, said combusting producing a flue gas comprising sulfur and calcium derived from said sulfur sorbent;

(b) following said combusting, allowing a first portion of said calcium in the flue gas to react with a first portion of said sulfur in the flue gas in a first stage of sulfur capture in a high temperature region following combustion;

(c) following said reaction of said first portion of said calcium in the flue gas, cooling said flue gas to a temperature within about 100°

F. above the condensation temperature using heat exchange or adding water to the flue gas said condensation temperature is the temperature at which aqueous liquid condenses from said flue gas; and

(d) following said cooling, allowing a second portion of said calcium in the flue gas to react with a second mortion of said sulfur in the flue gas at a temperature within about 100°

F. above the condensation temperature of the flue gas stream in a second stage of sulfur capture prior to particulate separation from said flue gas, said second stage of sulfur capture having a residence time of greater than about 0.1 second.

2. The process of claim 1, wherein said second stage of sulfur capture comprises reacting said second portion of calcium with said second portion of sulfur in the flue gas at a temperature within 50°

F. above the condensation temperature at the flue gas stream.

3. The process of claim 1, wherein said second stage of sulfur capture comprises reacting said second portion of calcium with said second portion of sulfur in the flue gas at a temperature within 30°

F. above the condensation temperature at the flue gas stream.

4. The process of claim 1, wherein said second stage of sulfur capture comprises reacting said second portion of calcium with said second portion of sulfur in the flue gas at a temperature within 15°

F. above the condensation temperature of the flue gas stream.

5. The process of claim 1, wherein said second stage of sulfur capture further comprises a residence time of greater than 1 second.

6. The process of claim 1, wherein said second stage of sulfur capture further comprises a residence time of greater than 3 seconds.

7. The process of claim 1, further comprising separating particulates from the flue gas stream after said second stage of sulfur capture by electrostatic precipitation.

8. The process of claim 1, wherein said raw coal comprises pyrite that is difficult to separate in that aggressive beneficiation of said raw coal would result in rejecting less than 85% of the pyrite in the raw coal while recovering about 85% of the BTU value in the aggressively beneficiated coal relative to the raw coal.

9. The process of claim 3, wherein said raw coal comprises organic sulfur in an amount greater than about 1.5% by weight on an ash-free basis.

10. The process of claim 1, wherein said sulfur sorbent comprises a pelletized intimate mixture of ultrafine coal particles and limestone.

11. The process of claim 10, wherein said pelletized mixture comprises coal particles of a size from about 0.015 mm to about 0.105 mm.

12. The process of claim 1, further comprising releasing sulfur dioxide emissions to the atmosphere in an amount below about 1.2 pounds per million BTU of coal in the fuel mixture.

13. The process of claim 1, wherein said mixture of coal and sulfur sorbent comprises ash-forming materials in an amount less than about 20% by weight.

14. The process of claim 1, wherein said mixture of coal and sulfur sorbent comprises ash-forming materials in an amount less than about 15% by weight.

15. The process of claim 1, wherein said mixture of coal and sulfur sorbent comprises ash-forming materials in an amount less than about 12% by weight.

16. The process of claim 1, wherein said cooling is an air preheater heat exchange after said first stage of sulfur capture and before said second stage of sulfur capture.

17. The process of claim 1, wherein said calcium-containing sorbent is selected from the group consisting of limestone, lime, dolomite, and combinations thereof.

18. The process of claim 1, further comprising separating particulates, including unreacted sulfur sorbent, from said flue gas after said second stage of sulfur capture and injecting at least a portion of said separated particulates into the flue gas before said second stage of sulfur capture.

19. The process of claim 1, wherein said first stage of sulfur capture further comprises reacting said first portion of sulfur sorbent with said first portion of sulfur in the flue gas at a temperature above 1500°

F.