System and process for controlling the flow of air and fuel to a burner

• US 4,645,450 A
• Filed: 08/29/1984
• Issued: 02/24/1987
• Est. Priority Date: 08/29/1984
• Status: Expired due to Fees

• Current Assignee: Control Techtronics Incorporated
• Original Assignee: Control Techtronics Incorporated
• Inventors: West, John S.
• Primary Examiner(s): Green, Randall L.
• Application Number:
  US06/645,337
• Time in Patent Office: 909 Days
• Field of Search: 431/12, 431/18, 431/76, 431/80, 431/90, 431/20, 431/89, 236/15 BB, 236/15 BD, 236/15 E
• US Class Current: 431/12
• CPC Class Codes: F23N 1/022 using electronic means
• CPC Class Codes: F23N 2223/08 Microprocessor; Microcomputer
• CPC Class Codes: F23N 2225/06 for determining flow
• CPC Class Codes: F23N 2235/06 at the air intake
• CPC Class Codes: F23N 2235/14 electromagnetically operated
• CPC Class Codes: F23N 2237/08 two or more different types of fuel simultaneously
• CPC Class Codes: F23N 5/006 the detector being sensitive to oxygen
• CPC Class Codes: F23N 5/02 using devices responsive to thermal changes or to thermal expansion of a medium
• CPC Class Codes: F23N 5/10 using thermocouples
• CPC Class Codes: F23N 5/18 using detectors sensitive to rate of flow of air or fuel

Abstract

A flow controller system for optimally controlling the flow of air and fuel to a burner in a plurality of operating modes throughout the firing range of the burner is disclosed herein. The system includes a pair of differential pressure sensors connected across the air conduit and the burner, and the fuel conduit and the burner, as well as a pair of electrically operated air and fuel valves for controlling the pressure of the air and fuel destined for the burner. The system further includes a microprocessor control means electrically connected to both the pressure sensors and the air and fuel pressure regulating valves. Optimal air-to-fuel pressure ratios are empirically derived at each point along the firing range of the burner by means of detachably connectable flowmeters, oxygen sensors and thermocouples, and this information is stored within the memory of the microprocessor control means. The use of a microprocessor control means, in combination with a detachably connectable flowmeter and thermocouple, allows the system to be easily retrofitted onto an existing burner system without the need for installation of orifice plate-type flowmeters.

Claims

1. A flow controller system capable of controlling the flow of air and fuel to a burner in a plurality of operating modes throughout the firing range of the burner, wherein said air and fuel are conducted to said burner by separate conduits fluidly connected to said burner, comprising:

(a) an air flow indicating means including a differential pressure sensing means fluidly connected across the air conduit and the burner for sensing the pressure drop of the air flow across the burner and generating a signal indicative of the rate of air flow into the burner;

(b) first and second valves for modulating the flow of air and fuel, respectively, to the burner which are fluidly connected upstream of the air flow indicating means;

(c) a fuel flow indicating means for generating a signal indicative of the rate of fuel flow into the burner, and

(d) a control means operatively and separately connected to both the first and second valves and the fuel and air flow indicating means for maintaining selected air and fuel flow rates throughout the firing range of the burner by comparison with precalibrated air and fuel flow ratios, wherein said control means is adjustable at all points throughout the firing range of the burner.

2. The flow controller system of claim 1, wherein the fuel flow indicating means includes a second differential pressure sensor fluidly connected across the fuel conduit and the burner.

3. The flow controller system of claim 1, wherein said control means is a combustion interface controller including a microprocessor having a memory, and wherein said first and second valves are electrically operated.

4. The flow controller system of claim 3, further including a flowmeter which is detachably connectable to the fuel conduit for providing a correlation between fuel flow rate and fuel flow differential pressure over a plurality of points throughout the firing range of the burner which may be entered into the memory of the microprocessor and used to compute optimal air-to-fuel pressure ratios.

5. The flow controller system of claim 4, wherein said flowmeter is a vortex-shedding, ultrasonic-type flowmeter.

6. The flow controller system of claim 4, wherein said flowmeter produces no more than a one pound pressure drop in the flow of fuel destined for the burner.

7. The flow controller system of claim 4, wherein said flowmeter is detachably connectable to the fuel conduit by means of a quick-disconnect type coupling.

8. The flow controller system of claim 3, wherein the burner is connected to a flue, and further including an oxygen probe which is detachably connectable with the flue for assisting the operator of the microprocessor in empirically determining the optimal air-to-fuel pressure ratios throughout the firing range of the burner.

9. The flow controller system of claim 3, further including a thermocouple thermally coupled to the output of the burner for assisting the operator of the microprocessor in empirically determining the optimal air-to-fuel pressure ratios throughout the firing range of the burner.

10. A flow controller system for a burner capable of controlling the flow of air and fuel cccthrough separate conduits to said burner in a plurality of operating modes throughout the firing range of the burner, comprising:

(a) an air flow and a fuel flow indicating means including a first pressure sensing means fluidly connected across the air conduit and the burner, and a second pressure sensing means fluidly connected across the fuel conduit and the burner for generating electrical signals indicative of the pressure differential between the air conduit and fuel conduit and the burner, respectively;

(b) first and second electrically operative valves for modulating the flow of air and fuel, respectively, to the burner, and

(c) a combustion interface controller including microprocessor control means electrically and separately connected to said air flow and fuel flow indicating means and said first and second valves for maintaining a plurality of preselected optimal ratios between the differential air pressure and the differential fuel pressure throughout the firing range of the burner by modulating said valves until the measured differential pressures equal the optimal differential pressures, wherein said first and second pressuring sensing means are fluidly connected downstream of said first and second air and fuel valves.

11. The flow controller system of claim 10, further including a flowmeter which is detachably connectable to the fuel conduit for providing a correlation between fuel flow rate and the differential pressure between the fuel flow in the fuel conduit and the burner over a plurality of points throughout the firing range of the burner which may be entered into the memory of the microprocessor and used to compute optimal air-to-fuel pressure ratios.

12. The flow controller system of claim 11, wherein said flowmeter produces no more than a one-pound pressure drop in the flow of fuel destined for the burner.

13. The flow controller system of claim 11, wherein said flowmeter is a vortex-shedding, ultrasonic-type flowmeter.

14. The flow controller system of claim 10, wherein the burner includes a flue, and further including an oxygen probe which is detachably connectable with the flue for assisting the operator of the microprocessor in empirically determining the optimal air-to-fuel pressure ratios throughout the firing range of the burner.

15. The flow controller system of claim 10, further including a thermocouple thermally coupled to the output of the burner for assisting the operator of the microprocessor in empirically determining the optimal air-to-fuel pressure ratios throughout the firing range of the burner.

16. A process for optimally operating and air and fuel regulating system for a burner having first and second pressure regulating valves for controlling the air and fuel flow to the burner, first and second pressure sensors for sensing the differential pressure of the air flow and the fuel flow, respectively, across the burner, wherein said sensors are fluidly connected downstream of said first and second valves, and a combustion interface controller including a microprocessor having an input which is electrically connected to the first and second differential pressure sensors and an output which is connected to first and second pressure regulating valves, comprising the steps of:

(a) deriving an optimal set of air and fuel flow rates by measuring the optimal differential pressures of the air flow and the fuel flow across the burner, respectively, for each point across the firing range of the burner;

(b) entering the optimal air and fuel differential pressures derived at step (a) into the microprocessor, and

(c) electrically adjusting the position of air flow and fuel flow valves by means of the microprocessor for any selected point on the firing range until the pressures sensed by the differential air and fuel flow sensors are equal to the optimal differential air and fuel flow pressures entered into the memory of the microprocessor for that particular point on the firing range.

17. The process of claim 16, wherein said burner is housed in a heaer, and further including the steps of:

(d) selecting a desired temperature for the heater;

(e) sensing the actual temperature of the heater, and

(f) electrically adjusting the positions of the air and fuel flow valves until the actual temperature of the heater equals the desired temperature of the heater.

18. The process of claim 17, wherein the rate of electrically adjusting the positions of the air and fuel flow valves is dependent upon the difference between the actual and desired temperature of the heater.

19. A process for optimally operating an air and fuel regulating system for a burner having first and second pressure regulating valves for controlling the air and fuel flow to the burner, first and second pressure differential sensors for sensing the differential pressure of the air flow and the fuel flow, respectively, across the burner, wherein said sensors are fluidly connected downstream of said first and second valves, and a combustion interface controller including a microprocessor having an input which is electrically connected to the first and second differential pressure sensors and an output which is connected to first and second pressure regulating valves, comprising the steps of:

(a) igniting the burner;

(b) recording the differential pressure of the air flow across the burner at a plurality of related points along the firing range of the burner;

(c) correlating the differential pressures obtained in step (b) with air flow rates;

(d) detachably connecting a flowmeter across the fuel flow of the system;

(e) recording the differential pressure of the fuel flow across the burner at a plurality of selected points along the firing range of the burner;

(f) recording the flow rate indicated by the flowmeter at each of the plurality of selected points in order to correlate a fuel flow rate with fuel flow differential pressure;

(g) interpolating both the recorded values of the air flow differential pressures and their corresponding air flow rates across the firing range of the burner;

(h) interpolating both the recorded values of the fuel flow differential pressures and their corresponding fuel flow rates across the firing range of the burner;

(i) computing the air and fuel differential pressures at each point along the firing range of the burner which corresponds to the stoichiometrically optimal air-to-fuel ratio;

(j) operating the burner across its entire firing range at the air and fuel differential pressure derived at step (i) while monitoring the resulting flue gases with an oxygen probe;

(k) adjusting the air and fuel differential pressures at all points in the firing range where the oxygen probe indicates a state of inefficient combustion;

(l) operating the burner across the lower half of its firing range in a plurality of excess air modes while recording the heat output of the burner;

(m) deriving an optimal set of air and fuel differential pressures across the firing range of the burner by splicing the air and fuel differential pressures corresponding to the most efficient excess air mode onto the adjusted air and fuel differential pressures derived at step (k);

(n) entering the air and fuel differential pressures derived at step (m) into the memory of the microprocessor, and

(o) electrically adjusting the position of air flow and fuel flow valves by means of the microprocessor for any selected point on the firing range until the pressures sensed by the differential air and fuel flow sensors are equal to the optimal differential air and fuel flow pressures entered into the memory of the microprocessor for that particular point on the firing range.