US2151906A - Control system fob fuel buhners - Google Patents

Description

' March 28, 1939. E. Q. ENGELS CONTROL SYSTEM FOR FUEL BURNERS Filed NOV. 1, 1955 III ll!IIIIIII'IIIIIIIIIIfll. I v I I T I I INVENTORZ.

i f i -1 T is r Patented'Mar 28, 1939 s PATENT orFlce};

' CONTROL SYSTEM FOR. FUEL BURNERS Eugene Oscar "Engels, Saginaw, Mich,

assignor to Baker Perkins Company," Inc., Saginaw, Mich., a corporation of New York Application November 1, 1935, Serial No. 41.804

1 timeinterval beforestartlng the fuelburner, then sembly comprises; a, motor-driven timing device, thermostatically or manually controlling, operas ir g, caused by intermittent. extinguishing. and

"closed to an open position.

any heat-absorbing system whichmay be inter-- posed between the point of combustion and the point of discharge of waste gases. V A burner -2 of known form for burning gas, oil, or powdered fuel, is mounted in the wall of the furnace Land thespent products of combustion are discharged through a flue 3 to the atmosphere after their usable heat has been absorbed. 7 Referring more particularly to Figs. 2. and 3, the apparatus embodying my invention isoperatively associatedwith a' draft control-damper 4 in the flue 3, and with the control circuit A of the fuel burner 2. Damper 4 is rotatably mount,- 1 ed in the walls of stack 3; topivot from a fully ated by a lever arm 5 connected at its outer end to aconnecting rod 6, which is journaled to a 'crankipin I. Crank pin 1 is; carried by and to. put the burner into operation. and flnally tomovethe.damperigraduallyto its full openposie tion, so thatthe burnerflame-is subjectedlto'full 'draftionly after the furnaceand burner. 9.

reached a temperature high enough tov sponse to each energizinggcurrent;impulsefrom the thermostatic or other control switch. A'ca'm .steadycomplete combustion of thefueL I By'partiallyrestricting the draft to the furnace when the burner is firstuignited the velocityrat the'freshly started relatively cool flame can not which gases leave the burner is reduced so that,

be blown out,ordrawn away from the burner nozzle. Thus theintermittent extinguishingof the. flame in a cold furnace,and consequent-exfuelsair mixture is prevented.

Further features and objects. of my invention,

accordance with the invention. Fig. 3 is a. topplanview of the burner control anddamper of Fig. 2. V T Fig. 1 shows diagrammatically a furnace l which may be utilized in any known way, for example, to heat a boiler, a dry kiln, or, more particularly to supply hot gases to a bake oven. 1

' burner flameso that it cannot be-ignited,:g,; when,

as shown in my United States Patent No. 1,857,-

tration, the'f'urnace includes,but does not-show plosive ignition ofthe-accumulated,

trol of Fig. 1. operatively connected thereto in control, or may be controlled by revolves-with power output: shaft 8 of an auto-v matic motor-driven control device 9, of known 2 form. v The motor control 9 may be connected in,con-. ventional manner to a high-low thermostatic a manuallyoperted switch in known manner. It is operable to 2 revolve shaft ,8 slowly one-half revolution re disk ill is also fixed to shaft}, and operativ'ely engages a cam follower H mounted onrthe trim ping arm of a switch l2. Switch 12 is connected to govern the burner control circuit. A, so that the burner operates in response. to the closing of.

the switch.

J; The operation ofZthecontroI system as followsz' f 1 I With the burner off and the furnace cold, damper .4 isin its closed position, as shown in broken lines in Fig. 2. The position of the oper ating linkage and the cam is also shown in broken 40 lines. In response to an i-mpulse from the thermostat or from a starting'push button, the timing motor 9 goes into operation to rotate the camdisk l0 clockwise through aone-hundred-eighty degree arc, or one-half a revolution, in a predetermined length 'of time, for example, thirty to sixty seconds... Asthe shaft revolves, damper 4, through lever 5, connecting rod 6 and crank pin 1, is gradually swung toward its open-position. During this time a slight draft of fresh air flows 5 through the furnace, scavengingany explosive amixtureor moving. it out of the range of the the dampercis approximatelyhalf way-' open'the leading edge of cam. engages the-:foliower -l The damper isactu- 15 i This closes the switch l2 and starts burner I, which is ignited by the usual automatic ignition system (not illustrated). cam, the damper, and the connecting linkage are in the position shown in dotted lines in Fig. 2,

and insolid lines in Fig. 3, and a period of fifteen seconds to half a minute has elapsed since the damper started to open. The timing motor 9 continues for anadditional fifteen to thirty secends. to rotate shaft 8 slowly through the remainder of its cycle of one-half revolution, gradually swinging the damper l to its full open posi- 'tion, indicated in Fig. l, and shown in solid lines in Fig. 3. The above described cycle of operation produces throughout the starting process the condition most favorable for successful ignition and warming up of the burner and furnace. It is a .common disadvantage of the ordinary oil or gas burning installations that when combustion is first started in a cold furnace, incomplete, unstable combustion occurs. An excessive air draft very easily extinguishes the flame by drawing it awayfrom the burner nozzle. The burner continues for an interval to inject a larger or smaller, amount of unburned combustible mixture into the furnace, so that when the ignition means again-lights the flame the accumulated mixture burns suddenly, producing pufiingfor at times damaging explosions.

Myinvention avoids the above disadvantage by assuring the following procedure in lighting a burner of-this type. First, the draft damper is opened part way to clear outany unburned gases that may haveaccumulated in the furnace and duct system through leakage; when the damper reaches a predetermined partially open position,

the burner is then lighted with only enough draft to prevent undue backpressure and smoky combustion, and finally, while the'furnace andcom.-' bustion chamber become hot enough to assure complete stable combustion, the damper or other draft control is swung gradually toits fully open position for maximum draft and normal combustion. Duringthe'first portion of the burner,

starting cycle of shaft 8, the damper is rotated to its partially open position. During this grad,

ual opening of the damper, the natural, induced, or forced draft 'of the heating system has a chance to scavenge out any accumulated explosivemixtures which may have leaked into the furnace and flue system during the shut-down period; Then, with the damper partly open, the burner is started with the minimum necessary draft, so that the cold combustible mixture will not be drawn away from the burner nozzle, ex

tinguishing the flame. As the burner and furnace warm up, damper 4 is progressively opened to its full extent gradually-enough so that, when it reaches its open position and the control motor 9 stops; the furnace will be suiiiciently hot for stable combustion.

When in response toithe action of a thermostatic or manual switchgmotor control 9 is again energized it rotates the shaft clockwise one hundred-eighty degrees farther,returning it and At this moment the,

the damper to their original positions. The hump on cam I0 is made long enough and is so positioned that as soon as rotation of shaft 8 commences, switch I2 is opened, turning off the burner 2. The damper 4 is gradually closed, requiring a time interval similar to that required for its opening position, say, thirty to sixty seconds. During this gradual closing of the damper the products of combustion and any unburned fuel and air which may have passed into the furnace after the burner was turned off are drawn into the stack 3 or moved out of the range of the burner flame when it is restarted on its next operating cycle. When motor 9 completes the halfrotation of shaft 8 and cam Hi, the damper 4 is restored to its closed position shown in broken lines in Fig. 3. During the period when the burner 2 is off the damper staysclosed, preventing the circulation of cold air in response to natural draft and the consequent cooling of the furnace or oven. Thus a maximum of the stored heat is retained in the furnace and associated heat transfer system.

Varlous modifications in the details of the control system described may bemade to adapt it to different heating systems and controls without departing from the spirit of the invention. While I have shown a stack damper for adjusting the draft, other means of varying the draft may be similarly governed and controlled. For example, a check-draft control dam'per,a draft damper at the combustion air inlet to the burner and furnace, or a power-driven fan or impeller for forced or induced draft, may be connected in .known ways to the motor-driven timing device to coordinate the adjustment of the furnace draftandthe starting of the fuel burner according to the operating cycle described above.

Having thus described my invention, .what I claim and desire to secure by Letters Patent is:

l. Ina heating (systemcomprising a furnace, an'automatic fuel burner, a stack leading from said furnace, and an adjustable draft damper in said stack, in combination, a motor-driven timing'device arrangedto control said burner and 4 'operatively connected to open and close said damper, said timingdevice operative to move said damper progressively from its closed to its open position and to' put the burner into operation when a portion only of the opening movement of I the damper has been completed.

'2. In a combustion control system for a heating system comprising a furnace and an automatic fuel burner, in combination adjustable means'forcontrollingv the draft through said furmace and a motor-driven timing device oper-.

atively connected with said draft control means and said burner, said timing device operative when energized to first actuate said draft control means to cause a moderate fiow of air through the furnace, next to put the burner into opera- .tion, and then to increase-the draft through said furnace gradually to a maximum as the burner and furnace become warm.

' EUGENE OSCAR ENGELS.

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