Circulating fluidized bed boiler and method of operation

1. A circulating fluidized bed boiler having improved reactant utilization, the boiler comprising:

a circulating fluidized bed including

a dense bed portion, and

a lower furnace portion above the dense bed portion;

a reactant to reduce the emission of at least one combustion product in the flue gas; and

a plurality of recirculated flue gas and secondary air injection devices positioned asymmetrically with respect to one another above the dense bed, wherein the devices are configured to mix the reactant and the flue gas in the furnace above the dense bed, thereby reducing the amount of reactant needed to reduce the emission of the at least one combustion product.

2. The apparatus according to claim 1 , further including a return system for returning carry over particles from the flue gas to the circulating fluidized bed.

3. The apparatus according to claim 2 , wherein the return system includes a separator for removing the carry over particles from the flue gas.

4. The apparatus according to claim 3 , wherein the separator is a cyclone separator.

5. The apparatus according to claim 3 , further including a fines collector downstream from the separator.

6. The apparatus according to claim 5 , wherein the fines collector is a bag house.

7. The apparatus according to claim 5 , wherein the fines collector is an electrostatic precipitator.

8. The apparatus according to claim 1 , wherein the reactant is selected from the group consisting of caustic, lime, limestone, fly ash, magnesium oxide, soda ash, sodium bicarbonate, sodium carbonate, double alkali, sodium alkali, and the calcite mineral group which includes calcite (CaCO 3 ), gaspeite ({Ni, Mg, Fe}CO 3 ), magnesite (MgCO 3 ), otavite (CdCO 3 ), rhodochrosite (MnCO 3 ), siderite (FeCO 3 ), smithsonite (ZnCO 3 ), sphaerocobaltite (CoCO 3 ), and mixtures thereof.

9. The apparatus according to claim 1 , wherein the reactant is limestone.

10. The apparatus according to claim 1 , wherein the dense bed portion of the circulating fluidized bed boiler is a fuel rich stage.

11. The apparatus according to claim 10 , wherein the dense bed portion of the circulating fluidized bed is maintained below the stoichiometric ratio.

12. The apparatus according to claim 1 , wherein the lower furnace portion is a fuel lean stage.

13. The apparatus according to claim 12 , wherein the lower furnace portion is maintained above the stoichiometric ratio.

14. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices are located in the lower furnace portion of the circulating fluidized bed boiler.

15. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices are arranged in a way selected from the group consisting of opposed inline, opposed staggered, and combinations thereof.

16. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices are positioned between about 10 feet and 30 feet above the dense bed.

17. The apparatus according to claim 1 , wherein the ratio of the exit column density to the column density of the dense bed top is greater than about 0.6, and wherein the secondary air and recirculated flue gas injection devices are positioned at a height in the furnace above the top of the dense bed.

18. The apparatus according to claim 1 , wherein an unopposed jet penetration of each secondary air and recirculated flue gas injection device is greater than about 50% of the furnace width.

19. The apparatus according to claim 1 , wherein the jet stagnation pressure is greater than about 15 inches of water above the furnace pressure.

20. The apparatus according to claim 19 , wherein the jet stagnation pressure is about 15 inches to about 70 inches of water above the furnace pressure.

21. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices are positioned at a height in the furnace wherein the column density is less than about 165% of the exit gas column density.

22. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices deliver about 10% to about 80% of the total air flow to the boiler.

23. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices deliver about 20% to about 70% of the total air flow to the boiler.

24. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices deliver an amount of air as a percentage of total air flow to the boiler selected from the group consisting of greater than about 20%, greater than about 25%, greater than about 30%, greater than about 35%, greater than about 40%, greater than about 45%, greater than about 50%, greater than about 55%, greater than about 60%, greater than about 65%, greater than about 70%, greater than about 75%, and greater than about 80%.

25. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices deliver an amount of air as a percentage of total air and flow to the boiler selected from the group consisting of: about 10% to about 80%, about 20% to about 80%, about 25% to about 80%, about 30% to about 80%, about 35% to about 80%, about 40% to about 80%, about 45% to about 80%, about 50% to about 80%, about 55% to about 80%, about 60% to about 80%, about 65% to about 80%, about 70% to about 80%, and about 75% to about 80%.

26. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices deliver an amount of secondary air as a percentage of total air flow selected from the group consisting of about 1% to about 40%, about 5% to about 40%, about 10% to about 40%, about 15% to about 40%, about 20% to about 40%, about 25% to about 40%, about 30% to about 40%, and about 35% to about 40%; and

wherein the secondary air and recirculated flue gas injection devices deliver an amount of recirculated flue gas as a percentage of total air flow selected from the group consisting of about 1% to about 40%, about 5% to about 40%, about 10% to about 40%, about 15% to about 40%, about 20% to about 40%, about 25% to about 40%, about 30% to about 40%, and about 35% to about 40%.

27. The apparatus according to claim 1 , wherein the secondary air and recirculated flue gas injection devices deliver about 20% to about 40% secondary air as a percentage of total air flow and about 20% to about 40% recirculated flue gas as a percentage of total air flow.

28. The apparatus according to claim 1 , wherein the plurality of secondary air and recirculated flue gas injection devices includes at least four injection devices positioned downstream of the dense bed for providing mixing of the reactant and the flue gas in the furnace above the dense bed.

29. The apparatus according to claim 1 , wherein at least one of the plurality of secondary air and recirculated flue gas injection devices is configured to provide cold FGR.

30. The apparatus according to claim 29 , wherein the cold FGR has a temperature of about 200° F. to about 350° F.

31. The apparatus according to claim 1 , wherein at least one of the plurality of secondary air and recirculated flue gas injection devices is configured to provide hot FGR.

32. The apparatus according to claim 31 , wherein the hot FGR has a temperature of about 550° F. to about 750° F.

33. The apparatus according to claim 1 , wherein at least one of the plurality of secondary air and recirculated flue gas injection devices is configured to provide cold SA.

34. The apparatus according to claim 33 , wherein the cold SA has a temperature of about 0° F. to about 100° F.

35. The apparatus according to claim 1 , wherein at least one of the plurality of secondary air and recirculated flue gas injection devices is configured to provide hot SA.

36. The apparatus according to claim 35 , wherein the hot SA has a temperature of about 350° F. to about 700° F.

37. The apparatus according to claim 1 , wherein the plurality of secondary air and recirculated flue gas injection devices is configured to provide at least cold or hot recirculated flue gas, and at least cold or hot secondary air.

38. A circulating fluidized bed boiler having improved reactant utilization, the boiler comprising:

a circulating fluidized bed including

a dense bed portion, and

a lower furnace portion above the dense bed portion;

a reactant to reduce the emission of at least one combustion product in the flue gas; and

at least one secondary air and recirculated flue gas injection device above the dense bed for providing mixing of the reactant and the flue gas in the furnace above the dense bed,

wherein the at least one device is configured to provide at least one of cold recirculated flue gas and hot secondary air,

wherein the at least one device is positioned at a height in the furnace wherein the column density is less than about 165% of the exit column density, and

wherein the at least one device is configured to deliver about 10% to about 80% of the total air flow to the boiler.

39. The apparatus according to claim 38 , wherein the at least one device is configured to have an unopposed jet penetration of greater than about 50% of the furnace width.

40. The apparatus according to claim 38 , wherein the at least one device is configured to have a jet stagnation pressure greater than about 15 inches of water above the furnace pressure.

41. The apparatus according to claim 40 , wherein the jet stagnation pressure is between about 15 inches and 70 inches of water above the furnace pressure.

42. The apparatus according to claim 38 , wherein the at least one device delivers an amount of air as a percentage of total air flow to the boiler selected from the group consisting of: about 10% to about 80%, about 20% to about 80%, about 25% to about 80%, about 30% to about 80%, about35% to about 80%, about 40% to about 80%, about 45% to about 80%, about 50% to about 80%, about 55% to about 80%, about 60% to about 80%, about 65% to about 80%, about 70% to about 80%, and about 75% to about 80%.

43. The apparatus according to claim 38 , wherein the at least one device delivers an amount of secondary air as a percentage of total air flow selected from the group consisting of: about 1% to about 40%, about 5% to about 40%, about 10% to about 40%, about 15% to about 40%, about 20% to about 40%, about 25% to about 40%, about 30% to about 40%, and about 35% to about 40%; and

wherein the at least one device delivers an amount of recirculated flue gas as a percentage of total air flow selected from the group consisting of: about 1% to about 40%, about 5% to about 40%, about 10% to about 40%, about 15% to about 40%, about 20% to about 40%, about 25% to about 40%, about 30% to about 40%, and about 35% to about 40 %.

44. The apparatus according to claim 38 , wherein the at least one device delivers about 20% to about 40% secondary air as a percentage of total air flow and about 20% to about 40% recirculated flue gas as a percentage of total air flow.

45. The apparatus according to claim 38 , wherein the at least two of the devices are positioned downstream of the dense bed for providing mixing of the reactant and the flue gas in the furnace above the dense bed.

46. The apparatus according to claim 38 , wherein the at least one device is configured to provide hot recirculated flue gas.

47. The apparatus according to claim 46 , wherein the hot recirculated flue gas has a temperature of about 550° F. to about 750° F.

48. The apparatus according to claim 38 , wherein the at least one device is configured to provide cold secondary air.

49. The apparatus according to claim 48 , wherein the cold secondary air has a temperature of about 0° F. to about 100° F.

50. The apparatus according to claim 38 , wherein the at least one device is configured to allow for the selective fluid delivery of at least two of cold recirculated flue gas, hot recirculated flue gas, cold secondary air, and hot secondary air.

51. The apparatus according to claim 38 , wherein the cold recirculated flue gas has a temperature of about 200° F. to about 350° F.

52. The apparatus according to claim 38 , wherein the hot secondary air has a temperature of about 350° F. to about 700° F.

53. A method of operating a furnace having a circulating fluidized bed, the method comprising:

combusting fuel in the fluidized bed, wherein the fluidized bed includes a dense bed portion and a lower furnace portion adjacent to the dense bed portion;

injecting a reactant into the furnace to reduce the emission of at least one combustion product in the flue gas;

injecting secondary air into the furnace; and

injecting recirculated flue gas into the furnace above the dense bed, wherein the secondary air and recirculated flue gas are injected through a plurality of injection devices positioned to create rotation in the furnace, thereby reducing the amount of reactant needed to reduce the emission of said at least one combustion product.

54. The method of claim 53 , wherein the secondary air is injected at a height in the furnace where column density is less than about 165% of the furnace exit column density.

55. The method of claim 53 , wherein the recirculated flue gas is injected at a height in the furnace where column density is less than about 165% of the furnace exit column density.

56. The method of claim 53 , wherein the secondary air is injected at a position between about 10 feet and 30 feet above the dense bed portion.

57. The method of claim 53 , wherein the recirculated flue gas is injected at a position between about 10 feet and 30 feet above the dense bed portion.

58. The method of claim 53 , wherein the ratio of the exit column density to the column density of the dense bed top is greater than about 0.6, and the secondary air is injected above the dense bed top.

59. The method of claim 53 , wherein the ratio of the exit column density to the column density of the dense bed top is greater than about 0.6, and the recirculated flue gas is injected above the dense bed top.

60. The method of claim 53 , wherein the dense bed portion has a column density greater than about twice the furnace exit column density.

61. The method of claim 53 , wherein at least one of the plurality of injection devices is operated to have an unopposed jet penetration of greater than about 50% of the furnace width.

62. The method of claim 53 , wherein at least one of the plurality of injection devices is operated with a jet stagnation pressure of greater than about 15 inches of water above the furnace pressure.

63. The method of claim 53 , wherein at least one of the plurality of injection devices is operated with a jet stagnation pressure about 15 inches to about 70 inches of water above the furnace pressure.

64. The method of claim 53 , wherein the secondary air and the recirculated flue gas provide about 10% to about 80% of the total air flow to the boiler.

65. The method of claim 53 , wherein the secondary air and recirculated flue gas are injected, as a percentage of total air flow, in an amount selected from the group consisting of: about 10% to about 80%, about 20% to about 80%, about 25% to about 80%, about 30% to about 80%, about 35% to about 80%, about 40% to about 80%, about 45% to about 80%, about 50% to about 80%, about 55% to about 80%, about 60% to about 80%, about 65% to about 80%, about 70% to about 80%, and about 75% to about 80%.

66. The method of claim 53 , wherein the secondary air is injected in an amount, as a percentage of total air flow, selected from the group consisting of: about 1% to about 40%, about 5% to about 40%, about 10% to about 40%, about 15% to about 40%, about 20% to about 40%, about 25% to about 40%, about 30% to about 40%, and about 35% to about 40%; and

wherein the recirculated flue gas is injected in an amount, as a percentage of total air flow, selected from the group consisting of: about 1% to about 40%, about 5% to about 40%, about 10% to about 40%, about 15% to about 40%, about 20% to about 40%, about 25% to about 40%, about 30% to about 40%, and about 35% to about 40%.

67. The method of claim 53 , wherein the secondary air is injected at about 20% to about 40% of total air flow, and the recirculated flue gas is injected at about 20% to about 40% of total air flow.

68. The method of claim 53 , wherein the secondary air includes cold secondary air having a temperature of about 0° F. to about 100° F.

69. The method of claim 53 , wherein the secondary air includes hot secondary air having a temperature of about 350° F. to about 700° F.

70. The method of claim 53 , wherein the recirculated flue gas includes cold recirculated flue gas having a temperature of about 200° F. to about 350° F.

71. The method of claim 53 , wherein the recirculated flue gas includes hot recirculated flue gas having a temperature of about 550° F. to about 750° F.

72. The method of claim 53 , wherein the dense bed portion is operated as a fuel rich stage maintained below the stoichiometric ratio.

73. The method of claim 53 , wherein the lower furnace portion is operated as a fuel lean stage maintained above the stoichiometric ratio.

74. The method of claim 53 , wherein said reactant is selected from the group consisting of caustic, lime, limestone, fly ash, magnesium oxide, soda ash, sodium bicarbonate, sodium carbonate, double alkali, sodium alkali, and the calcite mineral group which includes calcite (CaCO 3 ), gaspeite ({Ni, Mg, Fe}CO 3 ), magnesite (MgCO 3 ), otavite (CdCO 3 ), rhodochrosite (MnCO 3 ), siderite (FeCO 3 ), smithsonite (ZnCO 3 ), sphaerocobaltite (CoCO 3 ), and mixtures thereof.

75. A circulating fluidized bed boiler having improved reactant utilization, the boiler comprising:

a circulating fluidized bed including

a dense bed portion, and

a lower furnace portion above the dense bed portion;

a reactant to reduce the emission of at least one combustion product in the flue gas; and

a plurality of recirculated flue gas and secondary air injection devices above the dense bed,

wherein at least one of the plurality of secondary air and recirculated flue gas injection devices is configured to provide at least one of cold FGR and hot SA, and

wherein the devices are configured to mix the reactant and the flue gas in the furnace above the dense bed, thereby reducing the amount of reactant needed to reduce the emission of the at least one combustion product.