Circulating fluid bed combustion with CO combustion promoter and reduced combustion air

• US 4,927,348 A
• Filed: 11/14/1988
• Issued: 05/22/1990
• Est. Priority Date: 11/14/1988
• Status: Expired due to Fees

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Avidan, Amos A.
• Primary Examiner(s): Dority, Carroll B.
• Application Number:
  US07/270,929
• Time in Patent Office: 554 Days
• Field of Search: 431/3, 431/4, 431/7, 110/342, 110/344, 110/345, 110/347
• US Class Current: 431/7
• CPC Class Codes: C10L 10/02 for reducing smoke development
• CPC Class Codes: F23C 10/10 the separation apparatus being located outside the combustion chamber
• CPC Class Codes: F23C 2206/101 Entrained or fast fluidised bed
• CPC Class Codes: F23J 2215/40 Carbon monoxide
• CPC Class Codes: F23J 7/00 Arrangement of devices for supplying chemicals to fire

Abstract

Addition of a CO combustion promoter to a circulating fluid bed (CFB) combustion unit and reduction of the air addition rate to 100-110% of stoichiometric improves the efficiency of CO burning, reduces emissions of CO and improves the efficiency of the unit. Stable, reduced temperature operation with air rates close to stoichiometric, reduces NO_x emissions. A circulating (100-400 micron particles) or fast settling (400-1200 micron particle) CO combustion promoter may be used.

Claims

1. In a circulating fluidized bed combustion zone wherein a carbon-containing fuel is burned at an elevated temperature by contact with oxygen-containing gas added in an amount equal to at least 110% of the amount needed for complete combustion of the fuel, said combustion occurring in a generally vertical combustor comprising a fast fluidized bed of patriculated including limestone or dolomite wherein at least a majority of the particulate matter in the fast fluidized bed has a particle diameter in excess of 100 microns, to generate a flue gas/particulate stream which is discharged from the top of the combustor, said flue gas comprising excess oxygen, fines having a particle diameter less than about 100 microns, and circulating particles having average particle size of about 100-400 microns, which flue gas passes through a separation means to recover from the flue gas at least a majority of the 100-400 micron particles which are recycled to the circulating fluidized bed combustion zone, the improvement comprising burning said fuel in the presence of about 0.001 to 100 wt. ppm CO combustion promoter selected from the group of Pt, Pd, Rh, Ir, OS, and mixtures and compounds thereof in the combustion zone and reducing the amount of oxygen containing gas added per amount of fuel burned so that a total of 100 to 110% of the oxygen required for complete combustion of said fuel is added.

2. The process of claim 1 further characterized in that the temperature in the combustion zone is decreased by at least 100°

F.

3. The process of claim 1 further characterized in that the oxygen containing gas is present in an amount equal to 100-105 percent of stoichiometric.

5. The process of claim 1 further characterized in that the CO combustion promoter circulates and is present as particles of 100-400 microns in diameter.

6. The process of claim 1 further characterized in that the CO combustion promoter is present on particles of 400-1200 microns diameter.

7. The process of claim 1 further characterized in that the oxygen-containing gas is air, and the air is added in at least two stages to the combustor.

8. The process of claim 1 further characterized in that the temperature and excess oxygen are reduced to the combined total of NO_x and CO emissions, expressed as ppm, to less than 100.

4. The process of claim further characterized in that 0.01-10 ppm platinum is present.

9. In a circulating fluidized bed combustion process for burning of a carbonaceous fuel comprising nitrogen and sulfur contaminants, wherein said combustion occurs in a combustion zone comprising fast fluidized bed in the presence of a circulating bed of limestone or dolomite operates at a combustion zone temperature of 1550°

-1650°

F. with at least 15 percent excess air in the flue gas to ensure complete combustion of carbon monoxide, and said combustion zone temperature and excess air produce flue gas containing more than about 200 ppm vol. NO_x, the improvement comprising adding 0.001-100 wt. ppm of a CO combustion promoter selected from the group of Pt, Pd, Rh, Ir, Os, and mixtures and compounds thereof, reducing the amount of air added to within the range of 100-110 percent of stoichiometric, and decreasing the temperature of the combustion zone by at least 100°

F., without increasing the emissions of carbon monoxide via the flue gas, as compared to operation prior to addition of the CO combustion promoter.

10. The process of claim 9 further characterized in that the oxygen containing gas is present in an amount equal to 100-105 percent of stoichiometric.

11. The process of claim 9 further characterized in that 0.01-10 ppm platinum is present.

12. The process of claim 9 further characterized in that the CO combustion promoter circulates and is present as particles of 100-400 microns in diameter.

13. The process of claim 9 further characterized in that the CO combustion promoter is present on particles of 400-1200 microns diameter.

14. The process of claim 9 further characterized in that the oxygen-containing gas is air, and the air is added in at least two stages to the combustor.

15. The process of claim 9 further characterized in that the temperature and excess oxygen are reduced to the combined total of NO_x and CO emissions, expressed as ppm, to less than 100.