Modulating Burner With Venturi Damper

• US 20150354809A1
• Filed: 06/04/2014
• Published: 12/10/2015
• Est. Priority Date: 06/04/2014
• Status: Active Grant

• Current Assignee: Lochinvar, LLC (A O Smith Corporation)
• Original Assignee: Lochinvar, LLC (A O Smith Corporation)
• Inventors: Putnam, Benjamin P., Doura, Mohamed Mehdi, Baese, Dave C., Wiseman, Robert Wesley
• Granted Patent: US 9,746,176 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F23C 3/004 the chamber being arranged for submerged combustion F23C3/002 takes precedence
• CPC Class Codes: F23C 9/00 Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber fluidised bed combustion apparatus with means for recirculation of particles entrained from the bed F23C10/02; fluidised bed combustion apparatus with devices for removal and partial reintroduction of material from the bed F23C10/26
• CPC Class Codes: F23D 14/04 induction type, e.g. Bunsen burner
• CPC Class Codes: F23D 14/60 Devices for simultaneous control of gas and combustion air
• CPC Class Codes: F23D 2208/00 Control devices associated with burners
• CPC Class Codes: F23D 2900/00014 Pilot burners specially adapted for ignition of main burners in furnaces or gas turbines
• CPC Class Codes: F23D 2900/21003 for heating or re-burning air or gas in a duct
• CPC Class Codes: F23L 13/04 with axis perpendicular to face
• CPC Class Codes: F23N 1/025 using electrical or electromechanical means
• CPC Class Codes: F23N 2227/22 Pilot burners
• CPC Class Codes: F23N 2233/04 with variable speed
• CPC Class Codes: F23N 2235/10 power assisted, e.g. using electric motors
• CPC Class Codes: F23N 2235/18 Groups of two or more valves
• CPC Class Codes: F23N 2237/10 High or low fire
• CPC Class Codes: F23Q 9/00 Pilot flame igniters
• CPC Class Codes: F24H 1/0027 using fluid fuel

Abstract

A modulating burner apparatus includes a burner and a blower placed upstream of the burner. A venturi is placed upstream of the blower. A damper valve is placed upstream of the venturi. The damper valve has an open position and a restricted position. A smaller gas valve and a larger gas valve are communicated with the venturi. A controller is operably associated with the system to select a position of the damper valve and to select the appropriate one of the gas valves so as to provide a low output operation mode and a high output operation mode, which in combination provide an overall turndown ratio of at least 25:1.

Claims

1. A burner assembly, comprising:

a burner;

a blower configured to supply pre-mixed air and fuel gas mixture to the burner, the blower including a blower inlet;

a venturi including a venturi inlet, a venturi outlet, and a reduced pressure zone intermediate of the venturi inlet and the venturi outlet, the blower inlet being communicated with the venturi outlet such that the blower pulls air through the venturi;

at least one gas valve communicated with the reduced pressure zone such that the at least one gas valve supplies fuel gas to the reduced pressure zone at a fuel gas flow rate corresponding to a pressure in the reduced pressure zone; and

an air flow restrictor located upstream of the reduced pressure zone and movable between an open position and a restricted position, such that in the restricted position air flow through the venturi is restricted.

2. The burner assembly of claim 1, wherein:

the air flow restrictor comprises a disc-shaped valve element, the restrictor defining an annular flow path around the disc-shaped valve element when the air flow restrictor is in the restricted position.

3. The burner assembly of claim 2, wherein:

the annular flow path has an annular thickness in a range of from 0.010 inch to 0.150 inch.

4. The burner assembly of claim 1, wherein:

the at least one gas valve includes a larger gas valve and a smaller gas valve, both gas valves being communicated with the reduced pressure zone of the venturi.

5. The burner assembly of claim 4, wherein:

the smaller gas valve includes a reference pressure line communicated upstream of the air flow restrictor.

6. The burner assembly of claim 4, further comprising:

a controller operably associated with the flow restrictor, the larger gas valve and the smaller gas valve, the controller being configured to operate the larger gas valve when the flow restrictor is in the open position, and the controller being configured to operate the smaller gas valve when the flow restrictor is in the restricted position.

7. The burner assembly of claim 6, wherein:

the blower is a variable speed blower having a blower speed variable within a blower speed range; and

the controller is operably associated with the blower and configured such that the burner is modulatable within a higher burner output range by varying the blower speed within the blower speed range when the larger gas valve is operable and the flow restrictor is in the open opposition, and such that the burner is modulatable within a lower burner output range by varying the blower speed within the blower speed range when the smaller gas valve is operable and the flow restrictor is in the restricted position.

8. The burner assembly of claim 7, wherein the higher burner output range overlaps the lower burner output range.

9. The burner assembly of claim 7, wherein the burner assembly has a turndown ratio from a high end of the higher burner output range to a low end of the lower burner output range of at least 25 to 1.

10. The burner assembly of claim 7, wherein the burner higher output range has a high end of at least 750,000 BTU/hr.

11. The burner assembly of claim 6, further comprising:

a pilot located adjacent the burner such that a pilot flame from the pilot can ignite the burner;

a pilot valve communicating a gas source with the pilot; and

wherein the controller is configured to open the pilot valve so as to initiate the pilot flame prior to transitioning between operation of the smaller gas valve and operation of the larger gas valve.

12. The burner assembly of claim 11, wherein:

the controller is configured to close the pilot valve after transitioning between operation of the smaller gas valve and operation of the larger gas valve.

13. The burner assembly of claim 1, wherein:

the venturi includes a venturi body, including a venturi passage from the venturi inlet to the venturi outlet; and

the flow restrictor is located within the venturi passage.

14. The burner assembly of claim 1, wherein:

the venturi includes a reduced diameter throat, and the reduced pressure zone includes an annular zone surrounding and communicated with the reduced diameter throat.

15. The burner assembly of claim 1, in combination with a water heater, the water heater being in heat exchange relationship with the burner.

16. A burner assembly, comprising:

a burner;

a blower upstream of the burner;

a venturi upstream of the blower;

a damper valve upstream of the venturi, the damper valve having an open position and a restricted position;

a smaller gas valve communicated with the venturi;

a larger gas valve communicated with the venturi; and

a controller operatively associated with the blower, the damper valve, and the smaller and larger gas valves.

17. The burner assembly of claim 16, wherein:

the controller defines a low range operation mode of the burner assembly and a high range operation mode of the burner assembly.

18. The burner assembly of claim 17, wherein:

in the low range operation mode the damper valve is in the restricted position, the smaller gas valve is operably communicated with the venturi, and the blower is modulated to provide fuel and air mixture to the burner within a low output range.

19. The burner assembly of claim 18, wherein:

in the high range operation mode the damper valve is in the open position, the larger gas valve is operably communicated with the venturi, and the blower is modulated to provide fuel and air mixture to the burner within a high output range, the high output range extending higher than the low output range and overlapping with the low output range.

20. The burner assembly of claim 17, further comprising:

a pilot located adjacent the burner;

a pilot valve communicating a gas source with the pilot; and

wherein the controller opens the pilot valve to initiate a pilot flame prior to transitioning between the low range operation mode and the high range operation mode.

21. The burner assembly of claim 16, wherein:

the damper valve includes a valve body having a circular cross-section passage therethrough, the passage having a longitudinal axis, the damper valve further including a disc-shaped valve element disposed concentrically within the circular cross-section passage when the damper valve is in its restricted position, the disc-shaped valve element being dimension such that an annular spacing in a range of from 0.010 inch to 0.150 inch is defined between the disc-shaped valve element and the passage when the damper valve is in its restricted position, the disc-shaped valve element being rotatable to a position parallel to the longitudinal axis when the damper valve is in its open position.

22. The burner assembly of claim 21, wherein the annular spacing is in a range of from 0.050 inch to 0.120 inch.

23. The burner assembly of claim 21, wherein:

the disc-shaped valve element has a diameter in a range of from 3.0 inches to 6.0 inches.

24. The burner assembly of claim 16, wherein the damper valve comprises:

a damper valve body having a circular cross-section passage therethrough and having a passage diameter;

a valve shaft extending diametrically across the passage;

a valve disc attached to the valve shaft and having a diameter less than the passage diameter; and

a valve motor attached to the valve shaft and constructed to rotate the valve shaft approximately 90°

between the open position and the restricted position.

25. The burner assembly of claim 24, wherein:

the valve motor always rotates in the same direction as it moves the damper valve between its open and restricted positions.

26. The burner assembly of claim 24, wherein the damper valve further comprises:

a spring disposed around the valve shaft and biasing the valve shaft relative to the damper valve body so as to eliminate slack in the diametrical positioning of the valve disc within the circular cross-section passage.

27. The burner assembly of claim 16, in combination with a water heater.

28. A method of operating a premix burner, the method comprising:

(a) modulating the burner within a low output range by modulating a speed of a variable speed blower while drawing air to a venturi through a damper valve in a restricted position, and while drawing fuel gas to the venturi through a smaller gas valve; and

(b) modulating the burner within a high output range by modulating the speed of the variable speed blower while drawing air to the venturi through the damper valve in an open position, and while drawing fuel gas to the venturi through a larger gas valve.

29. The method of claim 28, wherein:

a low end of the high output range is at least 50,000 BTU/hr less than a high end of the low output range.

30. The method of claim 28, wherein:

in step (a) air flows to the venturi through an annular passage of the damper valve adjacent an inner wall of the venturi so that the air flows primarily in a boundary layer adjacent the inner wall.

31. The method of claim 28, further comprising:

controlling a transition from the low output range to the high output range with an automatic controller which modulates the blower speed, activates the larger gas valve, de-activates the smaller gas valve, and opens the damper valve.

32. The method of claim 31, further comprising:

opening a pilot valve to light a pilot adjacent the burner before transitioning from the low output range to the high output range.

33. The method of claim 28, further comprising:

controlling a transition from the high output range to the low output range with an automatic controller which modulates the blower speed, activates the smaller gas valve, de-activates the larger gas valve, and moves the damper valve to the restricted position.

34. The method of claim 33, further comprising:

opening a pilot valve to light a pilot adjacent the burner before transitioning from the high output range to the low output range.