Low NO.sub.x burner

• US 5,257,927 A
• Filed: 11/01/1991
• Issued: 11/02/1993
• Est. Priority Date: 11/01/1991
• Status: Expired due to Term

• Current Assignee: Holman Boiler Works Incorporated (Cleaver-Brooks Incorporated)
• Original Assignee: Holman Boiler Works Incorporated (Cleaver-Brooks Incorporated)
• Inventors: Lang, Jerry M.
• Primary Examiner(s): Yeung, James C.
• Application Number:
  US07/786,869
• Time in Patent Office: 732 Days
• Field of Search: 431/184, 431/181, 431/182, 431/187, 431/183, 431/278, 431/189, 431/115, 431/285, 431/354, 431/173, 239/402.5, 239/403-406
• US Class Current: 431/184
• CPC Class Codes: F23C 7/006 adjustable
• CPC Class Codes: F23C 7/008 Flow control devices F23C7/006 takes precedence
• CPC Class Codes: F23D 14/24 at least one of the fluids being submitted to a swirling motion

Abstract

A low NO_x burner combustion system which may be adjusted for optimum burn rates, temperature and oxygen levels. The burner incorporates a plurality of gas nozzles which individually inspirate a portion of the combustion air and a spin vane diffuser to rotate and mix the gases within the primary combustion zone. The diffuser is axially adjustable in order to vary the distance between the vane and the first combustion zone while the blades of the diffuser can be angularly adjusted to optimize the rotation and mix of the gases. Air for combustion is supplied through primary, secondary and tertiary passages to create distinct combustion zones for complete combustion. The flow rate of the combustion air is controlled through a damper in accordance with the burn characteristics. The angular and axial position of the diffuser and the damper control of combustion air can be automatically adjusted throughout the firing range of the burner in response to demand levels. In order to convert existing burners to the efficient low NO_x burner of the present invention the primary air chamber may be retrofit into the main burner chamber. In a further embodiment, flue gas is recirculated and mixed directly with combustion fuel prior to combustion for reduced emission levels.

Claims

1. In a burner adapted to reduce emission of NO_x gases upon combustion of a fuel and air, the burner including a source of combustion air and a source of combustion fuel, at least a portion of the combustion air flowing through a central air passage into which the combustion gas is supplied for combustion in a primary combustion zone, the improvement comprising:

a plurality of eductor nozzles radially spaced about the central air passage for supplying combustion fuel to the central air passage, said eductor nozzles mixing secondary combustion air with combustion fuel prior to flow into said primary combustion zone;

a vane diffuser positioned within the central air passage for imparting a mix rotation on the combustion air flowing through the central air passage thereby optimizing mix of combustion gas and combustion air for combustion in the burner; and

means for controlling the volume of flow of combustion air into the central air passage for optimum combustion and reduction of NO_x emissions.

2. The improvement as defined in claim 1 wherein said vane diffuser includes a plurality of blades, the pitch angle of said blades being adjustable to optimize mix rotation of combustion air for combination with combustion gas.

3. The improvement as defined in claim 2 wherein said vane diffuser is axially adjustable within the central air passage to vary the distance between said vane diffuser and the primary combustion zone.

4. The improvement as defined in claim 3 wherein said secondary combustion air is mixed with combustion fuel through a force air system communicating with said eductor nozzles.

5. The improvement as defined in claim 3 wherein said eductor nozzles communicate with a flue gas recirculation chamber such that flue gas from combustion is recirculated to said eductor nozzles for mixing with combustion fuel within said eductor nozzles.

6. The improvement as defined in claim 3 wherein tertiary combustion air is supplied to a final combustion zone axially spaced from said primary combustion zone.

7. The improvement as defined in claim 6 wherein said means for controlling the volume of air flowing into the central air passage comprises a control damper whereby variance of air flow into the central air passage varies the volumes of secondary and tertiary air flow to vary the combustion mix within said primary and final combustion zones.

8. The improvement as defined in claim 7 wherein said burner includes a refractory throat formed of replaceable refractory materials, said refractory materials radiating heat to raise the temperature of said tertiary combustion air for improved combustion.

9. The improvement as defined in claim 2 wherein the central air passage is formed by a cylindrical housing, said housing being insertable into a conventional burner housing radially inwardly of the fuel spuds of the conventional burner thereby converting the conventional burner to a reduced NO_x emission burner.

10. The improvement as defined in claim 7 wherein the volume of combustion air into said central air passage, the position of said spin vane within said central air passage, the pitch angle of said blades of said vane diffuser, and the eduction mix through said nozzles are independently varied to optimize combustion while reducing NO_x emissions from the burner.

11. A burner adapted to reduce emission of NO_x gases upon combustion of a fuel and air, the burner including a source of combustion fuel, said burner comprising:

a central air passage communicating with the source of combustion air, the volume of primary combustion air flowing into said central air passage controlled by damper means;

a vane diffuser positioned within said central air passage for imparting a mix rotation on the primary air flowing through said central air passage, said vane diffuser axially adjustable within the central air passage;

a plurality of eductor nozzles radially spaced about said central air passage downstream of said vane diffuser, said eductor nozzles in fluid communication with said source of combustion fuel and a secondary flow of combustion air to direct a fuel/air mix into said central air passage for combustion within a primary combustion zone; and

a tertiary air passage directing a tertiary flow of combustion air past a refractory throat for combustion within a final combustion zone;

wherein said damper means for controlling the volume of primary air into said central air passage and the axial position of said vane diffuser within said central air passage relative to eductor nozzles are varied to optimize combustion within said burner while reducing NO_x emissions.

12. The burner as defined in claim 11 wherein said eductor nozzles comprise a central passageway through which combustion fuel flows and at least one lateral port for introduction of secondary combustion air into said central passageway for mixing with the combustion fuel, said fuel/air mix being directed into said primary combustion zone.

13. The burner as defined in claim 12 wherein the size of said at least one lateral port is altered to vary the fuel/air mix directed into said primary combustion zone thereby controlling the temperature of the combustion flame.

14. The burner as defined in claim 11 wherein said vane diffuser includes a plurality of angularly adjustable blades, the angle of said blades being adjustable to vary the mix rotation imparted on the primary air flowing through said central air passage.

15. The burner as defined in claim 11 wherein said damper means includes adjustable louvers for controlling the volume of flow into said central passage whereby adjustment of said primary air flow into said central passage correspondingly varies said secondary air flow to said eductor nozzles and said tertiary air flow to said refractory throat.

16. In a conventional burner having a burner chamber with a plurality of fuel spuds radially spaced within the burner chamber for supplying combustion gas to the burner chamber and a source of combustion air supplied to the burner chamber for mix with the combustion gas, the improvement comprising:

a retrofit insert for converting the conventional burner to a low NO_x burner, said insert received within the burner chamber radially inwardly of the fuel spud and including a housing forming a central air passage and an outer annulus, a duct for supplying combustion air to said central air passage, and means for directing combustion gas into said air passage, said central air passage having a vane diffuser positioned therein for imparting a mix rotation on the combustion air flowing through the central air passage, said vane diffuser axially adjustable within said central air passage to vary the distance between said diffuser and said means for directing combustion gas into said central air passage thereby optimizing mix of combustion gas and combustion air, said duct for supplying air to said central air passage having means for selectively varying the volume of combustion air flowing into said central air passage and said outer annulus whereby said mix rotation and said combustion air volume may be selectively varied to optimize combustion and reduce NO_x emissions.

17. The improvement as defined in claim 16 wherein said means for directing combustion gas to said central air passage includes a burner manifold comprising a corresponding plurality of inwardly extending fuel cells communicating with the fuel spuds, said fuel cells supplying combustion gas to said central air passage for mix with said combustion air and combustion within a primary combustion zone.

18. The improvement as defined in claim 17 wherein said vane diffuser includes a plurality of blades, the pitch angle of said blades being adjustable to optimize mix rotation of combustion air for combination with combustion gas, said central air passage having a greater diameter than said vane diffuser to form an annulus between said housing and said vane diffuser.

19. The improvement as defined in claim 18 wherein the volume of combustion air into said central air passage, the position of said vane diffuser within said central air passage, and the pitch angle of said blades of said diffuser are independently varied to optimize combustion within said converted burner while reducing NO_x emissions from the burner.

20. The improvement as defined in claim 16 wherein said means for selectively varying the volume of combustion air comprises a damper, said damper controlling the supply of primary combustion air flowing into said central air passage for mix with combustion gas and combustion in a primary combustion zone and the supply of secondary combustion air flowing through said outer annulus for combination in a secondary combustion zone.

21. In a conventional burner having a burner chamber with a plurality of fuel spuds for supplying combustion fuel to the burner chamber and a source of combustion air supplied to the burner chamber, the improvement comprising:

a retrofit assembly for converting the conventional burner to a low NO₂ burner, said assembly received within the burner chamber and including;

(a) a central housing coaxially positioned within the burner chamber radially inwardly of the fuel spuds, said central housing forming a central air passage and an outer annulus;

(b) means for directing primary combustion air into said central air passage and secondary combustion air into said outer annulus;

(c) a vane diffuser positioned within said central air passage and including a plurality of vane blades for imparting a mix rotation on the primary combustion air flowing through said central air passage; and

(d) means for directing combustion fuel from the fuel spuds in said outer annulus towards said central air passage downstream of said vane diffuser for mixing with the primary combustion air from said vane diffuser and combustion in a primary combustion zone;

said vane diffuser axially adjustable within said central housing to vary the distance between said vane diffuser and said means for directing combustion fuel into said central air passage thereby optimizing mix and combustion of combustion fuel and primary combustion air in the primary combustion zone.

22. The improvement as defined in claim 21 and further comprising damper means for controlling the volume of flow of primary combustion air into said central air passage and secondary combustion air into said outer annulus, said secondary combustion air circumventing said central housing for combustion within a secondary combustion zone downstream of said primary combustion zone.

23. The improvement as defined in claim 22 wherein said blades of said vane diffuser being angularly adjustable to optimize rotational mix of primary combustion air with combustion fuel.

24. A process for optimizing combustion within a burner while reducing NO_x emissions as a result of combustion, the burner including a central air passage and at least one outer annulus through which combustion air is supplied, the volume of combustion air flowing into the central air passage and the at least one outer annulus controlled by dampers, the central air passage having a vane diffuser disposed therein for imparting a mix rotation on the combustion air flowing therethrough, the vane diffuser axially adjustable within the central air passage and including a plurality of angularly adjustable blades, the processing comprising:

introducing combustion fuel into the central air passage through a plurality of nozzles radially spaced about the central air passage;

adjusting the dampers to vary the volume of combustion air flowing into the central air passage;

axially adjusting the position of the vane diffuser within the central air passage relative to a primary combustion zone to optimize the mix rotation imparted on the combustion air prior to engaging the primary combustion zone;

adjusting the angle of the diffuser blades to vary the mix rotation imparted on the combustion air;

wherein said adjustments are varied to optimize combustion within the burner while reducing NO_x emissions in accordance with the combustion demand levels of the burner.

25. The process as defined in claim 24 wherein said damper, said position of the vane diffuser and said angle of said diffuser blades are adjusted automatically in response to burner demand levels to optimize combustion within the burner while reducing NO_x emissions.

26. The process as defined in claim 25 wherein adjustment of the damper to vary the volume of combustion air flowing into the central air passage correspondingly varies the volume of combustion air flowing into said at least one outer annulus, the combustion air flowing into said at least one outer annulus circumventing the central air passage for combustion in subsequent combustion zones of the burner.

27. A method for converting a conventional burner to a low NO_x burner, the conventional burner having a burner chamber, a plurality of fuel spuds radially spaced within the burner chamber for supplying combustion fuel to the burner chamber, and a supply of combustion air, comprising the steps of:

inserting an inner housing within the burner chamber radially inwardly of the fuel spuds, said housing forming a central air passage and an outer annulus within which the fuel spuds are disposed;

directing primary combustion air into said central air passage and secondary combustion air into said outer annulus;

inserting a vane diffuser within said inner housing to impart a rotational mix upon primary combustion air flowing through said central air passage;

installing means for directing combustion fuel from the fuel spuds into said central air passage downstream of said vane diffuser for mixture of combustion fuel with primary combustion air and a combustion within a primary combustion zone;

adjusting the axial position of said vane diffuser relative to

said means for directing combustion fuel to impart an optimal rotational mix upon primary combustion air prior to combustion within the primary combustion zone.

28. The method as defined in claim 27 and further comprising the step of adjusting the angle of vane blades of said vane diffuser to vary the rotational mix imparted upon the primary combustion air.

29. The method as defined in claim 27 and further comprising the step of adjusting the ratio of primary combustion air flowing into said central air passage to secondary combustion air flowing into said outer annulus, said secondary combustion air circumventing the primary combustion zone for combustion in a subsequent combustion zone.