Process and apparatus for removing oxides of nitrogen and sulfur from combustion gases

• US 4,783,325 A
• Filed: 05/14/1985
• Issued: 11/08/1988
• Est. Priority Date: 05/14/1985
• Status: Expired due to Fees

• Current Assignee: Noell, Inc.
• Original Assignee: Dale G. Jones
• Inventors: Jones, Dale G.
• Primary Examiner(s): Doll, John
• Assistant Examiner(s): Langel, Wayne A.
• Application Number:
  US06/734,393
• Time in Patent Office: 1,274 Days
• Field of Search: 422/171, 422/172, 422/177, 423/235, 423/239 R, 423/239 A, 423/244 A, 423/400
• US Class Current: 423/235
• CPC Class Codes: B01D 53/56 Nitrogen oxides B01D53/60 takes precedence
• CPC Class Codes: B01D 53/60 Simultaneously removing sulfur oxides and nitrogen oxides
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

A process provided in accordance with practice of this invention for lowering the molar ratio of NO to NO₂ in flue gas by converting a portion of flue gas nitric oxide (NO) to nitrogen dioxide (NO₂), for removing the associated oxides of sulfur (SO_x) and nitrogen (NO_x) from the flue gas prior of discharge of the flue gas into the atmosphere and an apparatus for practicing the process.

Claims

1. A method for converting NO to NO₂ comprising the steps of contacting an NO containing gas stream with an injection gas, the injection gas comprising a peroxyl initiator other than hydrogen or hydrogen peroxide and sufficient oxygen to provide for conversion of NO to NO₂.

2. The method according to claim 1 wherein the NO containing gas stream is at a temperature of greater than about 800°

F. at the time of contact with the injection gas.

3. The method according to claim 1 wherein the injection gas comprises from about 5% to about 20% by volume oxygen.

4. The method according to claim 1 wherein the injection gas is at a temperature of less than about 800°

F. at the time of initial contact with the NO containing gas stream.

5. The method according to claim 1 wherein the NO containing gas stream has a velocity of from about 30 feet per second to about 70 feet per second and the injection gas is sprayed into the NO containing gas stream for contacting said NO containing gas stream at a velocity of at least about 10 times higher than the velocity of the NO containing gas stream.

6. The method according to claim 1 wherein the peroxyl initiator is selected from the group consisting of hydrocarbons, oxygen substituted hydrocarbons and mixtures thereof.

7. The method according to claim 1 wherein the oxygen content of the NO containing gas stream is less than 5% by volume prior to contact with the injection gas.

8. The method according to claim 1 wherein the oxygen content of the NO containing gas stream is less than 5% by volume prior to contact with the injection gas and the oxygen content of the NO containing gas stream is not increased by more than 1% from its initial percentage after it is mixed with the injection gas.

9. The method according to claim 1 wherein the peroxyl initiator contains carbon and the NO containing gas stream is at a temperature greater than about 1300°

F. at the time of contact with the injection gas.

10. The method according to claim 9 wherein the oxygen content of the NO containing gas stream is less than 5% by volume prior to contact with the injection gas.

11. The method according to claim 9 wherein the oxygen content of the NO containing gas stream is less than 5% by volume prior to contact with the injection gas and the oxygen content of the NO containing gas stream is not increased by more than 1% from its initial percentage after it is contacted with the injection gas.

12. The method according to claim 1 wherein the peroxyl initiator is selected from the group consisting of propane, benzene, ethane, ethylene, n-butane, n-octane, methane, methanol, isobutane, pentane, acetylene, methyl alcohol, ethyl alcohol, acetone, glacial acetic acid, ethyl ether, propyl alcohol, nitrobenzyl alcohol, methylethylketone, propylene, toluene, formaldehyde, camphor, ether and glycol and mixtures thereof.

13. A method for converting NO to NO₂ comprising:

(a) flowing a gas stream containing nitrogen oxides, including NO, through a conduit;

(b) introducing an injection gas into the conduit in a sufficient quantity and at a sufficient velocity to provide that such injection gas extends across essentially the entire conduit cross-section transverse to the direction of the flow of the NO containing gas stream, the NO containing gas stream thereby contacting injection gas as the NO containing gas stream flows through the conduit, wherein the injection gas comprises a peroxyl initiator and sufficient other than hydrogen or hydrogen peroxide oxygen to provide that NO, upon contact with the injection gas, is converted to NO₂.

14. The method according to claim 13 wherein the NO containing gas stream has a velocity of from about 30 feet per second to about 70 feet per second and the injection gas is sprayed into the conduit across the path of the NO containing gas stream at a velocity of at least about 10 times higher than the velocity of the NO containing gas stream.

15. The method according to claim 13 wherein the NO containing gas stream is at a temperature of from about 800°

F. to about 1400°

F. and the injection gas is at a temperature of less than about 800°

F. at the time said injection gas is introduced into the conduit.

16. The method according to claim 13 wherein the injection gas is introduced into the conduit through a plurality of nozzles wherein the exit velocity of the injection gas from each nozzle is at least about 10 times higher than the velocity of the NO containing gas stream.

17. The method according to claim 13 wherein the peroxyl initiator is selected from the group consisting of hydrocarbons, oxygen substituted hydrocarbons and mixtures thereof.

18. The method according to claim 13 wherein the nitrogen oxide containing gas stream is at a temperature greater than about 1300°

F. at the time of initial contact with the injection gas and the temperature of the nitrogen oxide containing gas stream remains greater than 1300°

F. for at least 40 milliseconds after initial contact.

19. The method according to claim 13 wherein the nitrogen oxide containing gas stream is preheated to a temperature of not more than about 800°

F. prior to introduction of the injection gas into the conduit.

20. The method according to claim 13 wherein the injection gas is introduced into the conduit through a plurality of nozzles wherein the exit velocity of the injection gas from each such nozzle is at least about 10 times greater than the velocity of the nitrogen oxide containing gas stream.

21. A method for converting NO to NO₂ comprising the steps of contacting a gas stream containing NO and NO₂ at an NO/NO₂ molar ratio of more than about 2 with an injection gas, the NO/NO₂ containing gas stream being at a temperature of from about 800°

F. to about 1400°

F. and the injection gas being at a temperature of less than about 800°

F. at the time the NO/NO₂ containing gas stream is initially contacted by the injection gas, said injection gas comprising a vaporized peroxyl initiator other than hydrogen or hydrogen peroxide and at least about 5% oxygen by volume.

22. The method according to claim 21 wherein the NO containing gas stream has a velocity of from about 30 feet per second to about 70 feet per second and the injection gas is sprayed into the NO containing gas stream for contacting said NO containing gas stream at a velocity of at least about 10 times higher than the velocity of the NO containing gas stream.

23. The method according to claim 21 wherein the peroxyl initiator is selected from the group consisting of hydrocarbons, oxygen substituted hydrocarbons and mixtures thereof.

24. The method according to claim 21 wherein the oxygen content of the NO/NO₂ containing gas stream is less than about 5% by volume prior to contact with the injection gas stream and the oxygen content of the NO/NO₂ containing gas stream is not increased by more than 1% from its initial percentage after it is contacted with the injection gas stream.

25. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO to NO₂ greater than about 4, and sulfur oxides with an injection gas comprising oxygen and a peroxyl initiator other than hydrogen or hydrogen peroxide present in an amount sufficient to convert NO to NO₂ in said conversion zone to thereby provide a resulting gas stream leaving the conversion zone having an NO to NO₂ molar ratio of less than about 2; and

(b) in an absorption zone contacting the resulting gas stream with a particulate absorbent for oxides of nitrogen and sulfur to thereby remove said oxides of nitrogen and sulfur from the gas stream.

26. The method according to claim 25 wherein the injection gas stream comprises from about 5% to about 20% by volume oxygen.

27. The method according to claim 25 wherein the injection gas is at a temperature of less than about 800°

F. at the time of its initial contact with the first gas stream.

28. The method according to claim 25 wherein the particulate absorbent comprises NaHCO₃, Na₂ CO₃, or mixtures thereof, including waters of hydration.

29. The method according to claim 25 wherein the particulate absorbent is injected into the first gas stream at a temperature of from about 200°

F. to about 450°

F.

30. The method according to claim 25 wherein the particulate absorbent is transported into the absorption zone by means of a carrier gas selected from the group consisting of air, recirculated flue gas, steam or mixtures thereof.

31. The method according to claim 25 wherein the particulate absorbent comprises a mixture of sodium and calcium compounds.

32. The method according to claim 31 wherein the particulate sorbent comprises a mixture of about 15% NaHCO₃ and 85% Ca(OH)₂ by weight.

33. The method according to claim 25 wherein the NO containing gas stream has a velocity of from about 30 feet per second to about 70 feet per second and the injection gas is sprayed into the NO containing gas stream for contacting said NO containing gas stream at a velocity of at least about 10 times higher than the velocity of the NO containing gas stream.

34. The method according to claim 25 wherein the peroxyl initiator is selected from the group consisting of hydrocarbons, oxygen substituted hydrocarbons and mixtures thereof.

35. The method according to claim 25 comprising the additional steps of removing the particulate absorbent from the gas stream to provide an absorbent-free flue gas stream and contacting the absorbent-free flue gas stream with a metal oxide sorbent for NO_x to thereby remove remaining NO_x from said absorbent-free flue gas stream.

36. The method according to claim 35 wherein a portion of the particulate absorbent removed from the gas stream is recycled into the inlet of absorption zone.

37. The method according to claim 25 wherein the particulate absorbant comprises a sodium based material.

38. The method according to claim 25 wherein the molar ratio of SO₂ to NO_x in the resulting gas stream is from about 1 to about 30.

39. The method according to claim 25 wherein the injection gas is preheated to a temperature of not more than about 800°

F. prior to contact with the first gas stream.

40. The method according to claim 35 wherein the injection gas stream comprises at least about 5% by volume oxygen.

41. The method according to claim 35 comprising the additional step of removing particulate matter including particulate absorbent and additional sulfur and nitrogen oxides from the gas stream exiting the absorption zone using a wet process to thereby provide a clean flue gas stream.

42. The method according to claim 25 comprising the additional step of removing particulate matter including particulate absorbent and additional sulfur and nitrogen oxides from the gas stream exiting the absorption zone using a dry process to provide a clean flue gas stream.

43. The method according to claim 42 comprising the additional step of contacting the clean flue gas stream in a flue gas contacting zone with a metal oxide sorbent for NO_x to thereby remove additional NO_x, including NO₂, from said clean flue gas stream.

44. The method according to claim 43 wherein a portion of the metal oxide sorbent is discharged from the flue gas contacting zone and regenerated for reuse by heating the metal oxide sorbent to at least 700°

F. to produce an off-gas containing NO.

45. The method according to claim 44 wherein the metal oxide is selected from the group consisting of aluminum, zirconium, titanium, iron, lithium, magnesium, nickel, copper, and alloys thereof.

46. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the method comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO/NO₂ of more than about 4, and sulfur oxides with an injection gas comprising a peroxyl initiator other than hydrogen or hydrogen peroxide and at least about 5% oxygen by volume, the first gas stream being at a temperature of greater than about 1300°

F. at the time said first gas stream is contacted with the injection gas, said contact resulting in NO being converted to NO₂ to provide a second gas stream wherein the molar ratio of NO/NO₂ in the second gas stream is less than about 2;

(b) passing the second gas stream into an absorption zone and contacting said second gas stream with a particulate sorbent comprising NaHCO₃ for removing sulfur and nitrogen oxides from the second gas stream; and

(c) removing particulate matter including the particulate sorbent from the second gas stream prior to discharging the resulting clean waste gas stream into the atmosphere.

47. The method according to claim 46 additionally comprising the step of contacting the clean waste gas stream with a metal oxide sorbent for NO_x to thereby remove remaining NO_x from said clean waste gas stream prior to discharging said gas stream into the atmosphere.

48. The method according to claim 47 wherein the metal oxide sorbent comprises Al₂ O₃.

49. The method according to claim 47 comprising the additional step of heating the metal oxide sorbent after said sorbent has contacted the clean waste gas stream to thereby drive any oxides of nitrogen sorbed thereon from the sorbent thereby regenerating the metal oxide for further use.

50. The method according to claim 46 wherein the injection gas stream comprises from about 5% to about 20% by volume oxygen.

51. The method according to claim 46 wherein the injection gas is at a temperature of less than about 800°

F. at the time of its initial contact with the first gas stream.

52. The method according to claim 46 wherein the particulate absorbent is injected into the second gas stream at a temperature of from about 200°

F. to about 450°

F.

53. The method according to claim 46 wherein the particulate absorbent is carried into the absorption zone by means of a carrier gas selected from the group consisting of air, recirculated flue gas, steam or mixtures thereof.

54. The method according to claim 46 wherein the particulate absorbent comprises a mixture of sodium and calcium compounds.

55. The method according to claim 54 wherein the particulate sorbent comprises a mixture of about 15% NaHCO₃ and 85% Ca(OH)₂ by weight.

56. The method according to claim 46 wherein a portion of the particulate sorbent removed from the second gas stream is recycled back to the inlet of the absorption zone and is introduced into the absorption zone for contacting the second gas stream.

57. The method according to claim 46 wherein the injection gas is introduced into the conversion zone through a plurality of nozzles wherein the exit velocity of the injection gas from each such nozzle is at least 10 times greater than the velocity of the first gas stream.

58. The method according to claim 46 wherein the particulate matter including particulate sorbent is removed from the second gas stream using a wet process.

59. The method according to claim 46 wherein the wet process uses a calcium based material.

60. The method according to claim 46 wherein the particulate matter including particulate sorbent is removed from the second gas stream using a dry process.

61. The method according to claim 60 wherein a portion of the particulate sorbent removed in the dry process is recycled back to the absorption zone and is re-introduced into the absorption zone for contacting the second gas stream.

62. The method according to claim 60 comprising the additional step of contacting the clean waste gas stream with a metal oxide sorbent for NO_x to thereby remove additional NO_x, including NO₂ from said clean waste gas stream.

63. The method according to claim 62 wherein a portion of the metal oxide sorbent is discharged from the zone in which it contacts the waste gas stream and is regenerated for reuse by heating the metal oxide sorbent to at least 700°

F. to produce an off-gas containing NO.

64. The method according to claim 62 wherein the metal oxide is selected from the group consisting of aluminum, zirconium, titanium, iron, lithium, magnesium, nickel, copper, and alloys thereof.

65. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the method comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides and sulfur oxides, including NO and NO₂ at a first NO/NO₂ molar ratio with an injection gas comprising a peroxyl initiator other than hydrogen or hydrogen peroxide and oxygen in an amount sufficient to convert NO to NO₂ to thereby provide a second gas stream exiting the conversion zone wherein the NO/NO₂ molar ratio of the second gas stream is less than the NO/NO₂ molar ratio of the first gas stream; and

(b) passing the second gas stream into an absorption zone and contacting the second gas stream with a liquid sorbent for NO₂ and sulfur oxides said liquid sorbent comprising an alkali containing at least 5% by weight sodium compounds.

66. The method according to claim 65 wherein the sodium based alkali is selected from the group consisting of NaOH and Na₂ CO₃ and mixtures thereof.

67. The method according to claim 65 wherein the liquid sorbent includes EDTA, ferrous sulfate or ferrous chelate.

68. The method according to claim 65 wherein the injection gas stream comprises from about5% to about 20% by volume oxygen.

69. The method according to claim 65 wherein the injection gas is at a temperature of less than about 800°

F. at the time of its initial contact with the first gas stream.

70. The method according to claim 65 wherein the NO containing gas stream has a velocity of from about 30 feet per second to about 70 feet per second and the injection gas is sprayed into the NO containing gas stream for contacting said NO containing gas stream at a velocity of at least about 10 times higher than the velocity of the NO containing gas stream.

71. The method according to claim 65 wherein the peroxyl initiator is selected from the group consisting of hydrocarbons, oxygen substituted hydrocarbons and mixtures thereof.

72. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides and sulfur oxides, including NO and NO₂ at a first NO/NO₂ molar ratio with an injection gas comprising a peroxyl initiator other than hydrogen or hydrogen peroxide and oxygen present in an amount sufficient to convert NO to NO₂ to thereby provide a second gas stream exiting the conversion zone wherein the NO/NO₂ molar ratio of the second gas stream is less than the NO/NO₂ molar ratio of the first gas stream; and

(b) in a first section of an absorption zone contacting the second gas stream with a particulate absorbent for oxides of nitrogen and sulfur to thereby remove oxides of nitrogen and sulfur from the gas stream to thereby form a third gas stream; and

(c) passing the third gas stream and particulate sorbent entrained in the third gas stream into a second section of the absorption zone wherein the third gas stream and particulate sorbent contact a liquid sorbent for NO₂ and sulfur oxides, so that said liquid sorbent removes NO₂ and sulfur oxides not removed by the particulate sorbent and also removes the particulate sorbent.

73. The method according to claim 72 wherein the liquid sorbent includes EDTA, ferrous sulfate or ferrous chelate.

74. The method according to claim 72 wherein the injection gas stream comprises from about 5% to about 20% by volume oxygen.

75. The method according to claim 72 wherein the injection gas is at a temperature of less than about 800°

F. at the time of its initial contact with the first gas stream.

76. The method according to claim 72 wherein the particulate absorbent comprises NaHCO₃, Na₂ CO₃, or mixtures thereof, including waters of hydration.

77. The method according to claim 72 wherein the particulate absorbent is injected into the first gas stream at a temperature of from about 200°

F. to about 450°

F.

78. The method according to claim 72 wherein the particulate absorbent is carried into the absorption zone by means of a carrier gas selected from the group consisting of air, recirculated flue gas, steam or mixtures thereof.

79. The method according to claim 72 wherein the particulate absorbent comprises a mixture of sodium and calcium salts.

80. The method according to claim 79 wherein the particulate sorbent comprises a mixture of about 15% NaHCO₃ and 85% Ca(OH)₂ by weight.

81. A method for removing nitrogen oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO to NO₂ greater than about 4, with an injection gas comprising oxygen and a vaporized peroxyl initiator other than hydrogen or hydrogen peroxide present in an amount sufficient to convert NO to NO₂ in said conversion zone to thereby provide a resulting gas stream leaving the conversion zone having an NO to NO₂ molar ratio of less than about 2; and

(b) in an absorption zone contacting the resulting gas stream with a metal oxide sorbent for nitrogen oxides to thereby remove said oxides of nitrogen from the gas stream.

82. The method according to claim 81 wherein the injection gas stream comprises from about 5% to about 20% by volume oxygen.

83. The method according to claim 81 wherein the injection gas is at a temperature of less than about 800°

F. at the time of its initial contact with the first gas stream.

84. The method according to claim 81 wherein the NO containing gas stream has a velocity from about 30 feet per second to about 70 feet per second and the injection gas is sprayed into the NO containing gas stream for contacting said NO containing gas stream at a velocity of at least 10 times higher than the velocity of the NO containing gas stream.

85. The method according to claim 81 wherein the peroxyl initiator is selected from the group consisting of hydrocarbons, oxygen substituted hydrocarbons and mixtures thereof.

86. The method according to claim 81 wherein the metal oxide is selected from the group consisting of aluminum, zirconium, titanium, iron, lithium, magnesium, nickel, copper, and alloys thereof.

87. The method according to claim 81 wherein the metal oxide is deposited on a suitable supporting substrate to provide a metal oxide specific surface area of greater than 10 square meters per gram of metal oxide sorbent material.

88. The method according to claim 81 wherein the metal oxide is introduced as a powder and removed from the absorption zone by means of a baghouse.

89. The method according to claim 81 wherein a portion of the metal oxide is discharged from the absorption zone and regenerated for reuse in the absorption zone by heating said metal oxide to at least 700°

F. to produce an off-gas containing NO.

90. The method according to claim 89 wherein the first gas stream is formed in the burner section of a boiler and said NO containing off-gas is recycled to the boiler burner section.

91. The method according to claim 81 wherein the first gas stream contains SO₂ as well as oxides of nitrogen.

92. A process for converting NO to NO₂ in combustion exhaust gas wherein a combustible peroxyl initiator is burned with an excess of oxygen and is then mixed with additional peroxyl initiator to provide a combustible, preheated injection gas mixture at a temperature of less than 800°

F., said injection gas then being used to contact an NO containing combustion exhaust gas stream having a temperature of between 800°

F. and 1400°

F., the preheated injection gas mixture containing peroxyl initiator and between 5% and 20% by volume of oxygen.

93. A process according to claim 92 wherein the combustible peroxyl initiator material is propane.

94. A process according to claim 92 wherein the combustible peroxyl initiator material is methanol.

95. A method for converting NO to NO₂ comprising the steps of contacting an NO containing gas stream with an injection gas, the injection gas comprising propane and sufficient oxygen to provide for conversion of NO to NO₂.

96. A method for converting NO to NO₂ comprising:

(a) flowing a gas stream comtaining nitrogen oxides, including NO, through a conduit; and

(b) introducing an injection gas into the conduit in a sufficient quantity and at a sufficient velocity to provide that such injection gas extends across essentially the entire conduit cross section transverse to the direction of the flow of the NO containing gas stream, the NO containing gas stream thereby contacting injection gas as the NO containing gas stream flows through the conduit, wherein the injection gas comprises propane and sufficient oxygen to provide that NO, upon contact with the injection gas, is converted to NO₂.

97. A method for converting NO to NO₂ comprising the steps of contacting a gas stream containing NO and NO₂ at an NO/NO₂ molar ratio of more than about 2 with an injection gas, the NO/NO₂ containing gas stream being at a temperature of from about 800°

F. to about 1400°

F., and the injection gas being at a temperature of less than about 800°

F. at the time the NO/NO₂ containing gas stream is initially contacted by the injection gas, said injection gas comprising vaporized propane and at least about 5% oxygen by volume.

98. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO to NO₂ greater than about 4, and sulfur oxides with an injection gas comprising oxygen and propane present in an amount sufficient to convert NO to NO₂ in said conversion zone to thereby provide a resulting gas stream leaving the conversion zone having an NO to NO₂ molar ratio of less than about 2; and

(b) in an absorption zone, contacting the resulting gas stream with a particulate absorbent for oxides of nitrogen and sulfur to thereby remove said oxides of nitrogen and sulfur from the gas stream.

99. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the method comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO/NO₂ of more than about 4, and sulfur oxides with an injection gas comprising propane and at least about 5% oxygen by volume, the first gas stream being at a temperature of greater than about 1300°

F. at the time said first gas stream is contacted with the injection gas, said contact resulting in NO being converted to NO₂ to provide a second gas steam wherein the molar ratio of NO/NO₂ in the second gas stream is less than about 2;

(b) passing the second gas stream into an absorption zone and contacting said second gas stream with a particulate sorbent comprising NaHCO₃ for removing sulfur and nitrogen oxides from the second gas stream; and

(c) removing particulate matter, including the particulate sorbent from the second gas stream prior to discharging the resulting clean waste gas stream into the atmosphere.

100. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the method comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides and sulfur oxides, including NO and NO₂ at a first NO/NO₂ molar ratio with an injection gas comprising propane and oxygen in an amount sufficient to convert NO to NO₂ to thereby provide a second gas stream exiting the conversion zone wherein the NO/NO₂ molar ratio of the second gas stream is less than the NO/NO₂ molar ratio of the first gas stream; and

(b) passing the second gas stream into an absorption zone and contacting the second gas stream with a liquid sorbent for NO₂ and sulfur oxides, said liquid sorbent comprising an alkali containing at least 5% by weight sodium compounds.

101. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides and sulfur oxides, including NO and NO₂ at a first NO/NO₂ molar ratio with an injection gas comprising propane and oxygen present in an amount sufficient to convert NO to NO₂ to thereby provide a second gas stream exiting the conversion zone wherein the NO/NO₂ molar ratio of the second gas stream is less than the NO/NO₂ molar ratio of the first gas stream;

(b) in a first section of an absorption zone, contacting the second gas stream with a particulate absorbent for oxides of nitrogen and sulfur to thereby remove oxides of nitrogen and sulfur from the gas stream to thereby form a third gas stream; and

(c) passing the third gas stream and particulate sorbent entrained in the third gas stream into a second section of the absorption zone wherein the third gas stream and particulate sorbent contact a liquid sorbent for NO₂ and sulfur oxides, so that said liquid sorbent removes NO₂ and sulfur oxides not removed by the particulate sorbent and also removes the particulate sorbent.

102. A method for removing nitrogen oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO to NO₂ greater than about 4, with an injection gas comprising oxygen and vaporized propane present in an amount sufficient to convert NO to NO₂ in said conversion zone to thereby provide a resulting gas stream leaving the conversion zone having an NO to NO₂ molar ratio of less than about 2; and

(b) in an absorption zone, contacting the resulting gas stream with metal oxide sorbent for nitrogen oxides to thereby remove said oxides of nitrogen from the gas stream.

103. A method for removing nitrogen oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO to NO₂ greater than about 4, with an injection gas comprising oxygen and vaporized methanol present in an amount sufficient to convert NO to NO₂ in said conversion zone to thereby provide a resulting gas stream leaving the conversion zone having an NO to NO₂ molar ratio of less than about 2; and

(b) in an absorption zone, contacting the resulting gas stream with a metal oxide sorbent for nitrogen oxides to thereby remove said oxides of nitrogen from the gas stream.

104. A method for converting NO to NO₂ comprising the steps of contacting an NO containing gas stream with an injection gas, the injection gas comprising propane and sufficient oxygen to provide for conversion of NO to NO₂, wherein the NO containing gas stream is at a temperature greater than about 1300°

F. at the time of contact with the injection gas.

105. A method for converting NO to NO₂ comprising:

(a) flowing a gas stream containing nitrogen oxides, including NO, through a conduit; and

(b) introducing an injection gas into the conduit in a sufficient quantity and at a sufficient velocity to provide that such injection gas extends across essentially the entire conduit cross section transverse to the direction of the flow of the NO containing gas stream, the NO containing gas stream thereby contacting injection gas as the NO containing gas stream flows through the conduit, wherein the injection gas comprises propane and at least about 5% by volume oxygen to thereby provide that NO, upon contact with the injection gas, is converted to NO₂.

106. A method for converting NO to NO₂ comprising the steps of contacting an NO containing gas stream with an injection gas, the injection gas comprising methanol and sufficient oxygen to provide for conversion of NO to NO₂.

107. A method for converting NO to NO₂ comprising:

(a) flowing a gas stream containing nitrogen oxides, including NO, through a conduit; and

(b) introducing an injection gas into the conduit in a sufficient quantity and at a sufficient velocity to provide that such injection gas extends across essentially the entire conduit cross section transverse to the direction of the flow of the NO containing gas stream, the NO containing gas stream thereby contacting the injection gas as the NO containing gas stream flows through the conduit, wherein the injection gas comprises methanol and sufficient oxygen to provide that NO, upon contact with the injection gas, is converted to NO₂.

108. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO to NO₂ greater than about 4, and sulfur oxides with an injection gas comprising oxygen and vaporized methanol present in an amount sufficient to convert NO to NO₂ in said conversion zone to thereby provide a resulting gas stream leaving the conversion zone having an NO to NO₂ molar ratio of less than about 2; and

(b) in an absorption zone, contacting the resulting gas stream with a particulate absorbent for oxides of nitrogen and sulfur to thereby remove said oxides of nitrogen and sulfur from the gas stream.

109. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the method comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides and sulfur oxides, including NO and NO₂ at a first NO/NO₂ molar ratio with an injection gas comprising methanol and oxygen in an amount sufficient to convert NO to NO₂ to thereby provide a second gas stream exiting the conversion zone wherein the NO/NO₂ molar ratio of the second gas stream is less than the NO/NO₂ molar ratio of the first gas stream; and

(b) passing the second gas stream into an absorption zone and contacting the second gas stream with a liquid sorbent for NO₂ and sulfur oxides, said liquid sorbent comprising an alkali containing at least 5% by weight sodium compounds.

110. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the process comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides and sulfur oxides, including NO and NO₂ at a first NO/NO₂ molar ratio with an injection gas comprising methanol and oxygen present in an amount sufficient to convert NO to NO₂ to thereby provide a second gas stream exiting the conversion zone wherein the NO/NO₂ molar ratio of the second gas stream is less than the NO/NO₂ molar ratio of the first gas stream;

(b) in a first section of an absorption zone, contacting the second gas stream with a particulate absorbent for oxides of nitrogen and sulfur to thereby remove oxides of nitrogen and sulfur from the gas stream to thereby form a third gas stream; and

(c) passing the third gas stream and particulate sorbent entrained in the third gas stream into a second section of the absorption zone wherein the third gas stream and particulate sorbent contact a liquid sorbent for NO₂ and sulfur oxides, so that said liquid sorbent removes NO₂ and sulfur oxides not removed by the particulate sorbent and also removes the particulate sorbent.

111. A method for converting NO to NO₂ comprising the steps of contacting a gas stream containing NO and NO₂ at an NO/NO₂ molar ratio of more than about 2 with an injection gas, the NO/NO₂ containing gas stream being at a temperature of from about 800°

F. to about 1400°

F. and the injection gas being at a temperature of less than about 800°

F. at the time the NO/NO₂ containing gas stream is initially contacted by the injection gas, said injection gas comprising vaporized methanol and at least about 5% oxygen by volume.

112. A method for removing nitrogen oxides and sulfur oxides from a gas stream, the method comprising the steps of:

(a) in a conversion zone, contacting a first gas stream containing nitrogen oxides, including NO and NO₂ at a molar ratio of NO/NO₂ of more than about 4, and sulfur oxides with an injection gas comprising methanol and at least about 5% oxygen by volume, the first gas stream being at a temperature of greater than about 1300°

F. at the time said first gas stream is contacted with the injection gas, said contact resulting in NO being converted to NO₂ to provide a second gas stream wherein the molar ratio of NO/NO₂ in the second gas stream is less than about 2;

(b) passing the second gas stream into an absorption zone and contacting said second gas stream with a particulate sorbent comprising NaHCO₃ for removing sulfur and nitrogen oxides from the second gas stream; and

(c) removing particulate matter including the particulate sorbent from the second gas stream prior to discharging the resulting clean waste gas stream into the atmosphere.