Nox gas sensor method and device

• US 7,217,355 B2
• Filed: 05/25/2005
• Issued: 05/15/2007
• Est. Priority Date: 05/26/2004
• Status: Expired due to Fees

• Current Assignee: EmiSense Technologies, LLC (Trelleborg AB)
• Original Assignee: Ceramatec, Inc.
• Inventors: Nair, Balakrishnan G., Middlemas, Michael, Nachlas, Jesse A.
• Primary Examiner(s): Olsen; Kaj K.
• Application Number:
  US11/137,693
• Publication Number:
  US 20060027465A1
• Time in Patent Office: 720 Days
• Field of Search: 205/781, 205/785, 204/424, 204/426, 204/429, 73/233.1
• US Class Current: 205/781
• CPC Class Codes: G01N 27/4074 for detection of gases other than oxygen
• CPC Class Codes: G01N 33/0013 by a chemical reaction G01N33/0024 takes precedence
• CPC Class Codes: G01N 33/0037 for NOx
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

The present invention is a method and apparatus for measuring the total NO_x concentration in a gas stream utilizing the principles of a NO_x sensor, i.e., mixed potential sensor. The exhaust gas is first conditioned by a catalyst assembly that converts the various species of nitrogen oxide gases present to a fixed steady state concentration ratio of NO₂/NO, where NO₂ is approximately 0–10% of the total NO_x concentration present in the gas exhaust, thereby enabling the NO_x sensor to generate a meaningful and reproducible determination of the concentration of total NO_x present in the gas being measured. The catalyst assembly also functions to oxidize any unburned combustibles such as CH₄, CO, etc., and remove potential contaminants such as SO₂.

Claims

1. An apparatus for determining NO_x concentration of an exhaust gas, the apparatus comprising;

an input assembly capable of receiving the exhaust gas and producing a conditioned output gas, the input assembly including at least three of the following four stages;

a first stage including a first catalyst structure for converting NH₃ in the exhaust gas to N₂ and H₂O, the first catalyst structure comprising a catalyst material from the group consisting of Cu, Ag, NiAl₂O₄, MnO₂, V₂O₅, and any mixture thereof;

a second stage including a second catalyst structure having an absorbent material for absorbing SO₂ or H₂S from the exhaust gas;

a third stage including a third catalyst structure for oxidizing unburned hydrocarbons and gases to higher oxidation states; and

,

a fourth stage including a fourth catalyst structure for establishing a steady state equilibrium concentration ratio between NO and NO₂; and

,

a NO_x sensor operably connected to the input assembly and receiving the conditioned output gas of the input assembly wherein the concentration of the total NO_x present can be determined.

2. The apparatus of claim 1 wherein the NO_x sensor includes a mixed potential sensor for receiving the conditioned output gas and generating a voltage signal that is a function of the concentration of the total NO_x present.

3. The apparatus of claim 2 further comprising an oxygen sensor, wherein the oxygen sensor and the mixed potential sensor cooperate to determine the NO_x concentration in the exhaust gas.

4. The apparatus of claim 3 wherein the mixed potential sensor and the oxygen sensor are constructed of an electrolyte material.

5. The apparatus of claim 2 wherein the mixed potential sensor includes an electrolyte.

6. The apparatus of claim 5 wherein the electrolyte of the mixed potential sensor is tubular.

7. The apparatus of claim 5 wherein the electrolyte of the mixed potential sensor is planar.

8. The apparatus of claim 2 wherein the mixed potential sensor includes a sensing electrode.

9. The apparatus of claim 8 wherein the sensing electrode of the mixed potential sensor is a semi-conductive oxide material.

10. The apparatus of claim 9 wherein the semi-conductive oxide material includes at least one of the following:

WO₃, Cr₂O₃, Mn₂O₃, Fe₂O₃, TiO₂, CO₃O₄.

11. The apparatus of claim 8 wherein the sensing electrode of the mixed potential sensor is a multi-component oxide material.

12. The apparatus of claim 11 wherein the multi-component oxide material is a spinel or perovskite.

13. The apparatus of claim 12 wherein the multi-component oxide material includes at least one of the following:

NiCr₂O₄, ZnFe₂O₄, CrMn₂O₄, LaSrMnO₃, LaSrCrO₃, LaSrFeO₃.

14. The apparatus of claim 8 wherein the sensing electrode of the mixed potential sensor is a metallic material.

15. The apparatus of claim 14 wherein the metallic material includes at least one of the following:

Pt, Ag, Au, Rh.

16. The apparatus of claim 2 wherein the mixed potential sensor includes a metallic sensing electrode, the metallic sensing electrode includes an electrolyte material having a range of approximately 10–

40 vol. %.

17. The apparatus of claim 16 wherein the electrolyte material is approximately 15–

25 vol. %.

18. The apparatus of claim 16 wherein the electrolyte material comprises a doped zirconia material, or one of the following:

ceria, gadolinia, hafnia, thoria, bismuth oxide, or any mixture thereof.

19. The apparatus of claim 1 wherein the input assembly resides within an environment having a first temperature, the first temperature being above 300°

C.

20. The apparatus of claim 19 wherein the first temperature is between 650–

750°

C.

21. The apparatus of claim 1 further comprising:

a housing wherein the input assembly and the NO_x sensor are housed within the housing.

22. The apparatus of claim 21 wherein the housing is tubular.

23. The apparatus of claim 21 further comprising:

an oxygen sensor housed within the housing, the oxygen sensor residing within an environment having a second temperature.

24. The apparatus of claim 23 wherein the first temperature and the second temperature are different.

25. The apparatus of claim 23 further comprising:

a heating device affixed within the housing and including a first and second heating zone, wherein the first and second heating zones provide the environments having the first and second temperatures, respectively.

26. The apparatus of claim 25 wherein the heating device is a rod.

27. The apparatus of claim 23 further comprising:

a heating device affixed within the housing; and

,

an insulation assembly being positioned about the heating device so as to construct a first heating zone and a second heating zone.

28. The apparatus of claim 23 wherein the NO_x sensor resides within an environment having a temperature between 300–

700°

C. and the oxygen sensor and input assembly reside within an environment having a temperature of at least 500°

C.

29. The apparatus of claim 1 wherein the second catalyst structure comprises an absorbing material selected from the group consisting of:

CaO, MgO, a perovskite type material, or any mixture thereof.

30. The apparatus of claim 1 wherein the third catalyst structure comprises an oxidizing catalyst material capable of oxidizing CO to CO₂, H₂ to H₂O, and hydrocarbons to H₂O and CO₂.

31. The apparatus of claim 30 wherein the oxidizing catalyst material includes RuO₂, Pt, Ni, Ag, CoO₂, or any mixture thereof.

32. The apparatus of claim 1 wherein the fourth catalyst structure comprises Ag, Pt, Pd, Rh, RuO₂, or any mixture thereof.

33. The apparatus of claim 1 wherein each stage of the input assembly resides within an environment having a temperature, and wherein at least two stages of the input assembly reside within an environment wherein the temperatures are different.

34. The apparatus of claim 1 wherein the first stage of the input assembly resides within an environment having a temperature range of approximately 200–

500°

C.

35. The apparatus of claim 34 wherein the first stage of the input assembly resides within an environment having a temperature range of approximately 250–

400°

C.

36. The apparatus of claim 1 wherein the second stage of the input assembly resides within an environment having a temperature range of approximately 200–

900°

C.

37. The apparatus of claim 36 wherein the second stage of the input assembly resides within an environment having a temperature range of approximately 600–

800°

C.

38. The apparatus of claim 1 wherein the third stage of the input assembly resides within an environment having a temperature range of approximately 200–

900°

C.

39. The apparatus of claim 38 wherein the third stage of the input assembly resides within an environment having a temperature range of approximately 600–

800°

C.

40. The apparatus of claim 1 wherein the fourth stage of the input assembly resides within an environment having a temperature range of approximately 200–

900°

C.

41. The apparatus of claim 40 wherein the fourth stage of the input assembly resides within an environment having a temperature range of approximately 600–

800°

C.

42. The apparatus of claim 1 further comprising:

an oxygen ion conducting electrolyte including a conducting membrane having a first and a second side, wherein the first side includes a reference electrode capable of being controlled by a known gas concentration or a chemical potential, and the second side being exposed to the conditioned output gas of the input assembly.

43. The apparatus of claim 42, wherein the known gas concentration is atmospheric air.

44. The apparatus of claim 42 wherein the oxygen ion conducting electrolyte comprises a doped zirconia material, or one of the following:

ceria, gadolinia, hafnia, thoria, bismuth oxide, or any mixture thereof.

45. The apparatus of claim 1 further comprising:

an oxygen sensor; and

,

an electronic system utilizing a formula and capable of calculating the NO_x concentration of the exhaust gas based on a measured oxygen concentration and on output voltage signal from the NO_x sensor.

46. The apparatus of claim 1 further comprising:

an oxygen sensor; and

,

an electronic system and a database including a data table or a formula describing a mathematical relationship, wherein the electronic system, database, formula, or data table cooperate to determine the NO_x concentration of the exhaust gas as a function of oxygen concentration.

47. The apparatus of claim 46 wherein the oxygen sensor resides within an environment having a temperature of approximately 400–

900°

C.

48. The apparatus of claim 47 wherein the temperature range is approximately 600–

800°

C.

49. The apparatus of claim 1 wherein the input assembly is stable in H₂O containing gases.

50. A method for determining total NO_x concentration is a gas composition, the method comprising the steps of:

receiving an exhaust gas stream;

conditioning the exhaust gas stream through and input catalyst assembly, the input assembly comprising at least three of the following stages;

a first stage for converting NH₃ compounds to N₂ and H₂O, the first stage comprising a catalyst material from the group consisting of Cu, Ag, NiAl₂O₄, MnO₂, V₂O₅, any mixture thereof;

a second stage for absorbing SO₂ form the exhaust stream to improve the lifetime performance of the sensor by minimizing any long term poisoning effects associated with SO₂;

a third stage for oxidizing unburned hydrocarbons and oxidized gases to higher oxidation states; and

,

a fourth stage for establishing a steady state equilibrium concentration ratio between NO and NO₂; and

,

generating a voltage signal that is a function of the concentration of the total NO_x present in the exhaust gas stream.

51. The method of claim 50 further comprising the steps of:

providing an oxygen sensor; and

,

providing a first heating zone and a second heating zone, the first heating zone being positioned proximate the mixed potential sensor and the second heating zone being proximate the oxygen sensor.

52. The method of claim 51 further comprising the steps of;

heating the first heating zone; and

,

heating the second heating zone, wherein the first and second heating zones include different temperatures.

53. The method of claim 52 wherein the temperature of the first heating zone is at least 300°

C. and the temperature of the second heating zone is at least 500°

C.

54. An apparatus for determining NO_x concentration of an exhaust gas, the apparatus comprising;

an input assembly capable of receiving the exhaust gas and producing a conditioned output gas, the input assembly comprising,

a first stage including a first catalyst structure having an absorbent material for absorbing SO₂ or H₂S from the exhaust gas;

a second stage including a second catalyst structure for oxidizing unburned hydrocarbons and gases to higher oxidation states; and

,

a third stage including a third catalyst structure for establishing a steady state equilibrium concentration ratio between NO and NO₂; and

,

a NO_x sensor operably connected to the input assembly and receiving the conditioned output gas of the input assembly wherein the concentration of the total NO_x present can be determined.

55. The apparatus of claim 54, wherein the NO_x sensor includes a mixed potential sensor for receiving the conditioned output gas and generating a voltage signal that is a function of the concentration of the total NO_x present.

56. The apparatus of claim 54, further comprising:

a heating device affixed within the housing; and

,

an insulation assembly being positioned about the heating device so as to construct a first heating zone and a second heating zone.

57. The apparatus of claim 54, wherein the NO_x sensor resides within an environment having a temperature between 300–

700°

C. and the oxygen sensor and input assembly reside within an environment having a temperature of at least 500°

C.

58. The apparatus of claim 54, wherein the NO₂ concentration in the steady state equilibrium ratio is between about 0% an about 10% by volume.

59. An apparatus for determining NO_x concentration of an exhaust gas, the apparatus comprising;

an input assembly capable of receiving the exhaust gas and producing a conditioned output gas, the input assembly including at least three of the following four stages;

a first stage including a first catalyst structure for converting NH₃ in the exhaust gas to N₂ and H₂O;

a second stage including a second catalyst structure having an absorbent material for absorbing SO₂ or H₂S from the exhaust gas;

a third stage including a third catalyst structure for oxidizing unburned hydrocarbons and gases to higher oxidation states; and

,

a fourth stage including a fourth catalyst structure for establishing a steady state equilibrium concentration ratio between NO and NO₂, said NO₂ concentration between about 0% an about 10% by volume; and

,

a NO_x sensor operably connected to the input assembly and receiving the conditioned output gas of the input assembly wherein the concentration of the total NO_x present can be determined.

60. The apparatus of claim 59, wherein the NO_x sensor includes a mixed potential sensor for receiving the conditioned output gas and generating a voltage signal that is a function of the concentration of the total NO_x present.

61. The apparatus of claim 59, further comprising:

a heating device affixed within the housing; and

,

an insulation assembly being positioned about the heating device so as to construct a first heating zone and a second heating zone.

62. The apparatus of claim 59, wherein the NO_x sensor resides within an environment having a temperature between 300–

700°

C. and the oxygen sensor and input assembly reside within an environment having a temperature of at least 500°

C.

63. The apparatus of claim 59, wherein the first catalyst structure comprising a catalyst material from the group consisting of Cu, Ag, NiAl₂O₄, MnO₂, V₂O₅, WO₃ and any mixture thereof.

64. An apparatus for determining NO_x concentration of an exhaust gas, the apparatus comprising;

an input assembly capable of receiving the exhaust gas and producing a conditioned output gas, wherein said input assembly is not surrounded by or substantially enclosed by one or more oxygen ion conductors, the input assembly including at least three of the following four stages;

a first stage including a first catalyst structure for converting NH₃ in the exhaust gas to N₂ and H₂O, the first catalyst structure comprising a catalyst material from the group consisting of Cu, Ag, NiAl₂O₄, MnO₂, V₂O₅, WO₃, and any mixture thereof;

a second stage including a second catalyst structure having an absorbent material for absorbing SO₂ or H₂S from the exhaust gas;

a third stage including a third catalyst structure for oxidizing unburned hydrocarbons and gases to higher oxidation states; and

,

a fourth stage including a fourth catalyst structure for establishing a steady state equilibrium concentration ratio between NO and NO₂; and

a NO_x sensor operably connected to the input assembly and receiving the conditioned output gas of the input assembly wherein the concentration of the total NO_x present can be determined.

65. The apparatus of claim 64, wherein the NO_x sensor includes a mixed potential sensor for receiving the conditioned output gas and generating a voltage signal that is a function of the concentration of the total NO_x present.

66. The apparatus of claim 64, further comprising:

a heating device affixed within the housing; and

,

an insulation assembly being positioned about the heating device so as to construct a first heating zone and a second heating zone.

67. The apparatus of claim 64, wherein the NO_x sensor resides within an environment having a temperature between 300–

700°

C. and the oxygen sensor and input assembly reside within an environment having a temperature of at least 500°

C.