US3136353A

US3136353A - Burner means including flame rod detector with internal electric heating

Info

Publication number: US3136353A
Application number: US176620A
Authority: US
Inventors: Graham G Lloyd
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1962-03-01
Filing date: 1962-03-01
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09

Description

June 9, 1964 G. G. LLOYD 3,136,353

BURNER MEANS INCLUDING FLAME ROD DETECTOR WITH INTERNAL ELECTRIC HEATING Filed March 1, 1962 Ac SUPPLY 40 1 FURNACE /7 INVENTOR. FIG. I GRAHAM G. LLOYD .ATTOR Y United States Patent TO f 3 136 353 BURNER MEANS INLUlJING FLAME ROD DE- TECTOR WITH INTERNAL ELECTRIC HEATING Graham G. Lloyd, Hartford, Conn., assignor to Com- This invention relates to a flame detector for detecting the presence or absence of a flame, and in particular to means for preventing the build-up of deposits of combustible material on said flame detector, which deposits can prevent the detector from operating properly.

Wide useis made today of a flame detector comprising a pair of electrodes positioned near or adjacent to a burner, whereby the air gap between the electrode ends is ionized when a flame is present so that a current flows between said electrodes under such conditions. When no flame is present, the air gap is no longer ionized, and there is no current flow between the electrode ends. When no flame is present and current is thus not flowing between the electrodes, an electrical circuit is broken which normally actuates a light, alarm, or some control element, such as a valve in the fuel line for the burner.

Some fuels, for example oil or black liquor, when being sprayed into a combustion chamber, such as the furnace of a boiler, will be deposited on the surface of the adjacent walls, the burner housing, and the adjacent flame detector. The heat within the furnace will drive off the volatile constituents, leaving deposits of solid combustible material, such as carbon or sulphur, on such exposed surfaces. If a suflicient deposit of combustible material forms on the electrodes of the flame detecting means positioned adjacent the flame, it will prevent current from flowing therebetween, and thus the alarm or control device circuit will be de-energized, even though a flame may still be present in the furnace. The presently used method of removing the deposit from the flame detector is to remove such detector from the furnace, clean it, and then place it back into the furnace.

It is an object of my invention to provide means for eliminating deposits of combustible material, such as carbon or sulphur, from the flame detecting means, by placing a heater within the flame detecting rod, which heater has a capacity such that it maintains the detecting rod or electrode at a temperature above the ignition temperature of the combustible material.

The invention will be described with reference to the accompanying drawing wherein:

FIG. 1 is a cross sectional side view of a main burner and its associated pilot burner; and

FIG. 2 is an enlarged schematic view of the pilot burner shown in FIG. 1, incorporating my invention.

Looking now to FIG. 1, numeral depicts the wall of a furnace, for example the furnace wall of a steam generating unit. A main burner 13 extends through a refractory lined opening 12 in the furnace wall 10. A suitable fuel such as oil is supplied to the main burner by means of pipe 14. The air necessary to support combustion of the fuel is supplied by means of air duct 16.

Mounted within the same opening 12 is a pilot burner 17 which is used to initially light off or ignite the main burner 13. A suitable fuel, for example gas, is supplied to the pilot burner housing 18 by means of pipe 20. The air necessary to support combustion within the pilot burner is also supplied by means of duct 16. Numeral 22 designates a flame detecting electrode, and the pilot burner housing 18 forms a second electrode. These electrodes detect the presence or absence of a flame within the pilot burner, and can be utilized to actuate a light,

3,136,353 Patented June 9, 1964 alarm, ora suitable control element such as the valve 30, by means of solenoid 32. The electrode 22 is surrounded by suitable insulating sheath 21.

In normal operation, when it is desired to light off the main burner 13, air is allowed to flow through duct 16. Fuel is admitted to the pilot burner 18 through pipe 20, and a suitable igniting means, for example a spark plug 23 ignitesthe fuel issuing from the pilot burner 17. If ignition of the fuel does not take place within a predetermined short period of time, for example 10 or 15 seconds, the valve 30 is closed to stop the flow of fuel through pipe 20 to the pilot burner 17. If a flame is established at the pilot burner, this flame is detected by means of

electrodes

18 and 22, and thus the solenoid valve 30 will be held open. After combustion has been established in the pilot burner, a valve within pipe 14 is opened, thus supplying fuel to the main burner 13. This fuel is ignited by the flame issuing from the pilot burner 17. After the flame has been established at the main burner 13, the pilot burner can be shut off, since it will no longer be needed until it is again desired'to light off the main burner unit 13 at some later time. A suitable flame detecting means (not shown) can then be used to close a valve in the main fuel line 14 in the event that the flame goes out at the main burner.

Some of the oil issuing from main burner 13 will be deposited on the pilot burner housing 18 and the electrode 22. The heat within the furnace will drive off the volatile constitutents, thus leaving deposits of solid combustible material, such as carbon or sulphur. If a suflicient deposit of combustible material forms on electrode 22, it will prevent the electrode from operating properly.

Looking now to FIG. 2, the pilot burner and its associated flame detecting system embodying my invention is illustrated. As shown, the circuit for solenoid 32, which actuates valve 30, is completed by the closing of switch 35. Switch 35 is closed when relay 34 is energized. Relay 34 is tied in with the secondary winding of step down transformer 36. In the absence of a flame, the atmosphere between the

electrodes

22 and 18 forms a sufiicient insulation to prevent a spark or are discharge between the electrodes, and in these circumstances no secondary current exists which will energize relay 34. Timer contacts 37 are for the purpose of energizing solenoid 32 for 10 or 15 seconds, when the pilot burner is initially being fired. The timer can be one of any well-known types. For example, the initial energi zation of the system can energize a relay having an attached arm carrying a switch. This arm can also be connected to a pneumatic or hydraulic dashpot. When the relay is energized, it pushes against the diaphragm of the dashpot, with the bleed of the dashpot being so adjusted that after a predetermined length of time (for example, the 10 or 15 seconds referred to above) the switch carried by the arm has moved a suflicient distance to cause opening of the switch, thus de-energizing the circuit through timer 37. When a flame is emerging from the pilot burner 17, the air or atmosphere between the electrodes is ionized and thus there will be conduction between the electrodes, thereby energizing relay 34 and closing switch 35.

Normally, without my improved heating element, deposits of solid combustible material form on the pilot burner housing 18 and the electrode 22. When a sufficient deposit forms on electrode 22, conduction between the electrodes is no longer possible and the flame detector fails to perform its function. To prevent this problem from arising, a heating element 38 is placed within the electrode rod 22, which heating element or resistor is of such a capacity that it maintains the electrode at a temperature above the ignition temperature of the combustible material, thus preventing it from depositing on the electrode. means of electrical source 40 when switch 42 is closed.

The combustible material that normally deposits on the electrodes can be either sulphur or carbon, and thus electrode 22 should be maintained at a temperature above the ignition temperature of both of these elements. The ignition temperature of sulphur is approximately 500 F,, with the ignition temperature of carbon being in the neighborhood of 750 F. Thus electrode 22 should be maintained at a temperature of 750 F. or higher.

It is not necessary to prevent combustible material deposits from forming on the burner housing 18. Because of the large area of electrode 18, seldom if ever will the entire inner surface of this member be coated up to the point that it will prevent conduction between electrode 22 and itself. It should be readily apparent, however, that if two electrodes are used, both of which are in the form of rods, it would be desirable to place a heating element in both of these rods to thereby prevent deposits from forming.

While the preferred embodiment of the invention has been shown and described, it will be understood that such is merely illustrative and not restrictive.

What I claim is: 7 Ina furnace, main burner means for supplying fuel and air to said furnace, pilot burner means adjacent said main burner means for igniting said mainburner As shown, resistor 38 is energized by 7 means, flame detecting means comprising a pair of electrodes positioned in the vicinity of the pilot burner means, a source of electrical energy connected to one of the electrodes, the other electrode being electrically grounded, said electrodes being positioned such that when a flame is present between them the air therebetween is ionized and current flows between the electrodes, and when no flame exists between the electrodes the air between them is not ionized and there is no current flow between the electrodes, operable means electrically connected in series with the electrodes, said operable means being indicative of the presence or absence of flame when energized or de-energized, respectively, this operable means being energized or de-energized when a flame exists or is absent, respectively, between the electrodes, a heater positioned in oneof said electrodes, the capacity of said heater being such that it maintains the electrode at a temperature above the ignition temperature of the fuel, thus preventing the build-up of fuel deposits on said electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,637 Ballentine Mar. 23, 1937 2,374,610 MacLaren Apr. 24, 1945 2,396,146 Atwater Mar. 5, 1946 2,482,551 Korsgren Sept. 20, 1949 2,627,308 Clark Feb. 3, 1953 2,721,607 Damon et a] Oct. 25, 1955