US2738742A - Ignition system for stokers - Google Patents

Description

March 1956 D. T. CAMPBELL IGNITION SYSTEM FOR STOKERS 2 Sheets-Sheet 1 Filed Aug. 1, 1952 iinal INVENTOR. 1241/12) 73 GZMPW, BY:

March 20, 1956 D. T. CAMPBELL 2,738,742

IGNITION SYSTEM FOR STOKERS Filed Aug. 1, 1952 2 Sheets-Sheet 2 I 17 DA 1/10 7. BY;

United States Patent 2,738,742 IGNITION SYSTEM FOR STOKERS David T. Campbell, Indianapolis, Ind. Application August 1, 1952, Serial No. 302,103

' 6 Claims. (Cl. 110-4) This invention relates to Stoker-fed, solid-fuel burners and is concerned primarily with the provision of an automatic ignition system for. such burners.

It is the primary object of this invention to provide a relatively simple and dependable, automatic ignition system for solid-fuel burners which will automatically be put into operation upon ademand on the burner for heat fromthe room thermostat.

A further object is to so locate the igniter unit in the fire pot of the burner as to require a minimum amount of electrical energy to effect the ignition of the fuel.

Another object is to provide an automatic, cycling control system for the igniter unit which will energize the igniter unit upon a demand on the burner for heat, (and provided no combustion exists in the burner) for a time sufiicient to raise a portion of the fuel to its kindling ternperature, and then deenergize the igniter unit and simultaneously energize the draft producing means to force air over the fuel so heated to cause combustion thereof.

Further objects of the invention will appear as the description proceeds.

To the accomplishment of the above and related objects, my invention may be embodied in the form illustrated in the accompanying drawings, attention being i called to the fact, however, that the drawings are illus- .a portion of the stoker apparatus of Fig. 1;

Fig. 3 is a schematic wiring diagram of the electrical components constituting a part of my invention;

Fig. 4 is a longitudinal sectional view through the tire pot of the burner of Fig. 1 showing certain details thereof; and r Fig. 5 is a perspective view of the igniter unit of my invention.

Referring more particularly to the drawings, I have shown in Fig. 1, somewhat diagrammatically, a solidfuel burner and stoker. arrangement with which my invention is particularly adaptable. Such arrangement is fully illustrated and described in my patent No. 2,600,614, issued June 17,1952.

A burner (shown in phantom outline) defines a combustion chamber in which is located a tuyered fire pct 11. Surrounding the firepot 11, communicating with the tuyeres thereof, and extending outside the burner 10 is a duct or wind box 12. A fuel delivery conveyor in the form of a tube 13 having arranged therein a conveyor screw 14, passes through the duct 12 to communicate with the firepot 11, the other end thereof receiving fuel froma fuel reservoir 15 in accordance, for instance, with the disclosure of the above mentioned patent.

Patented Mar. 20, 1956 means, indicated generally by reference numeral 16 is connected to rotate screw 14 .(see Fig. 4) within said tube to feed fuel to the firepot under controlled conditions. A blower 17, driven by drive means 16, delivers air past a static damper 19 through a conduit 18 to duct 12 and thence into the burner combustion chamber. In similar systems, it is conventional practice to maintain the firepot and the proximal portion of the delivery tube tightly packed with fuel to prevent smoke from passing back through the tube. However, in the arrangement of my patent No. 2,600,614, I have deliberately eliminated this feature and, instead, have maintained the fuel in a shallow layer in the tube and only loosely packed in the throat of the firepot.

For the purposes of this invention, it is neceessary, if

not essential, that the delivery tube merge with the fire- Drive pot in a smooth curve, as at 20. I have found that by driving screw 14 according to the discloseur of Patent No. 2,600,614, and by extending the screw into the curved portion 20, the fuel will be relatively tightly packed about the outer wall 21 of portion 20 but only loosely packed along the inner wall 22 of the curved portion 20 as indicated in Fig. 4.

The conventional firepot 11 is formed with double walls 23 and 24, annular in shape, the inner wall 23 thereof having a plurality of induction ports 25 about the upper portion thereof communicating with the region between the two walls. The duct 12 also communicates with such region through suitable ports 26. Combustion supporting air is forced through ports 25 into firepot 11 and so into the combustion chamber. The primary combustion of the fuel takes place, therefore, immediately adjacent these ports 25, and it has been found that there is a definite plane 27, between the burning fuel and the raw fuel, including the lower extent of ports 25.

Beneath this plane 27 and on the inside wall 22 of the curved throat 20, I locate my igniter unit 28. So placed, the unit is out of the combustion zone of the firepot and in that region where the fuel is the most loosely packed. Therefore, by locating a by-pass scoop 17' in the blower 17, as disclosed in my Patent No. 2,600,614, and directing a part of the air from blower 17 into tube 13, a combustion supporting draft can be maintained past the igniter unit 28. This is only possible where the fuel is maintained in loosely packed condition in throat 20 and is not possible in the conventional burner because of the reasons stated above in regard to preventing smokeback through tube 13.

The igniter unit 28 is preferably in the form of a U with the curved end 29 thereof bent out of the plane of the legs 30 and 31. Only that portion 29 is placed within the firepot, and, as can be seen from an inspection of the drawings, presents a relatively small heating surface to the fuel within the firepot.

Preferably, a lip 32 is integrally formed in the wall 22 to deflect the flowing fuel away from direct frictional contact with the igniter unit.

Only a few bits of coal will bear directly against the igniter unit at any time. In spite of the small heating surface presented by the igniter unit, it has been found that a unit of 300 watts is suificient to raise these few pieces of fuel in contact therewith, to their kindling temperature in about four minutes. Because of the loosely packed condition of the fuel in the immediate vicinity of the unit 28, sufficient air may be forced through the fuel bed to cause the heated bits of fuel to ignite and the ignition of only these bits is suflicient then to ignite the entire fuel bed within a very few minutes.

The electrical control system for the igniter and draftproducing means comprises a room thermostat 33, which maybe referred to as a single throw switch, a stack switch 34, which may be referred to as a double throw switch, responsive to the temperature in the combustion chamber, a cycling device 35, and, since the above units usually operate on a voltage other than 110V, a transformer 36, and relays 37 and 38. Preferably a limit switch L is provided in the power lines leading to the entire control unit to disconnect the same in case the furnace should overheat.

The desired operation is as follows: upon closing of the room thermostat 33, a demand for heat is placed on the system. Assuming there is no combustion in the firepot 11, the armature 71 of the stack switch 34 will assume a position such that the cycling device 35 will be actuated. Actuation of device 35 energizes the relay 37, which in turn energizes igniter unit 28. Unit 28 will remain energized for approximately four minutes, or for a time sufficient to raise a particular fuel to its ignition temperature. Cycling device 35 will then deenergize relay 37, and thus igniter 28, and simultaneously therewith energize the motor 39 of drive means 16 which will drive the blower 17 forcing combustion-supporting air through the duct 12 into the combustion chamber. (This, I prefer to call a first draft.) The air picked up by scoop 17 is forced through tube 13, past igniter unit 28. (This I prefer to call a second draft.) Energization of drive means 16 also drives screw 14 to deliver fuel to the firepot.

The draft producing and fuel delivery means continue to operate through one cycle of the cycling device 35. At the end of the cycle (assuming ignition has taken place) the cycling device will be deenergized. The draft-producin g and fuel-delivery means will continue to function, however, until the demand for heat has been satisfied and the room thermostat opens.

To accomplish the desired operation, I provide a number of circuits. Motor 39 is connected to power lines 40 and 41 through line 42, line 43, motor 39, line 44, contact 45, armature 46 and contact 47 of relay 38, line 48 and line 49. Igniter unit 28 is similarly connected to lines 40 and 41 through lines 42, 50 and 51, igniter 28, line 52, contact 53, armature 54 and contact 55 of relay 37, line 56 and line 49. Transformer 36 has its primary coil 57 connected to the power source through lines 42 and d, coil 57, line 58 and line 49. As will be seen, transformer 36 is continuously energized so long as the limit switch L is closed.

The cycling device 35 comprises a motor 59 driving a pair of cams 60 and 61. Cam 60 is so shaped that it will hold the armature 62 in closed position with contact 63 throughout all but a small portion of the cycle. Cam 61 is so shaped that when the device 35 is stopped, the armature 64 will be held out of contact with both of contacts 65 and 66. Immediately upon energization of device 35 the armature 64 will move into engagement with contact 65. After a short period of time, armature 64 will move away from contact 65 and will engage with contact 66, where it will remain until it is returned to its illustrated position at the end of the cycle.

Cycling device 35 is energized by the closing of thermostat 33. Current flows from the secondary coil 67 of transformer 36, through wire 68, thermostat 33, wire 69, wire 70, armature 71 and contact 72 of stack switch 34, wire 73, wire 74, motor 59, wire 75 and wire 76. As motor 59 begins to turn earns 60 and 61, armature 62 is shifted and a holding circuit for motor 59 is established through wire 68, thermostat 33, wire 69, contact 63, armature 62, wire 74, motor 59, and wires 75 and 76. This is needed in case armature 71 should move away from contact 72 before device 35 completes its cycle.

At the same time, cam 61 shifts armature 64 into engagement with contact 65, whereby relay 37 will be energized through wire 68, thermostat 33, wire 69, wire 79, armature 64, contact 65, wire 80, relay 37 and wire 76. Energization of relay 37 moves the armature 54 into engagement with contacts 53 and 55 to close the energizing circuit for heater 28. After a predetermined time,

armature 64 will be moved out of engagement with contact and into engagement with contact 66. Thus relay 37 will be deenergized, permitting the armature 5.4 to move out of engagement with contacts 53 and 55 and into engagement with contacts 77 and 78 to energize the relay 38 through wire 68, thermostat 33, wires 69 and 79, armature 64, contact 66, wires 81 and 82, contact 77, armature 54 and contact 78, wire 83, relay 38, and wire 76.

When relay 38 is energized, armature 46 is moved into engagement with contacts 45 and 47 to complete the energization circuit for motor 39 as hereinbefore described. Draft and fuel are thus introduced through tube 13 into firepot 11. When the temperature of the combustion chamber is raised sufficiently to shift the armature of stack switch 34, the motor 39 will continue to run until thermostat 33 is opened to deenergize relay 38. Motor 39 is kept in operation by the continued energization of relay 38, after the movement of armature 71, through wire 68, thermostat 33, wire 69, wire 70, armature 71, contact 84, wire 85, wire 82, contact 77, armature 54, contact 78, wire 83, relay 38, and wire 76.

So long as combustion is maintained in the burner, to hold armature 71 of stack switch 34 in engagement with contact 84, a demand for heat will not set the cycling device in operation, but will energize only relay 38 to energize motor 39. Only when the fire dies completely, will the closing of thermostat 33 set the ignition system in operation. And the provision of the system so described permits a truly automatic operation of a solidfuel burner.

I claim as my invention:

1. A solid fuel burner comprising a combustion chamber, a firepot located in said combustion chamber and having an opening in the lower region thereof, means for delivering fuel to said firepot including a tube communieating with the opening therein, a first draft-producing means for delivering combustion-supporting air to said chamber, a second draft-producing means for delivering combustion-supporting air to said firepot through said tube, fuel igniter means located in said firepot directly below the normal zone of combustion therein, and electrical control means for said burner, such control means energizing said igniter means upon an initial demand on said burner for heat, maintaining said igniter in energized condition for a predetermined time, deenergizing said igniter means after the passage of such time, and thereafter, energizing said fuel-delivery means, said first draft-producing means, and said second draft-producing means.

2. The device of claim 1 in which said tube communicates with said firepot in a smooth curve and substantially at right angles to the vertical axis of said firepot, said fuel-delivery means comprising a conveyor screw disposed within said tube and with the end thereof extending into the region of said curve, and said fuel igniter means comprising an electrically energized heater arranged within said firepot and wholly on the inside of said curve.

3. The device of claim 2 in which said heater comprises two spaced, parallel legs, each having a portion turned substantially at right angles thereto and joined in a smooth curve, said portions so formed constituting that part of the heater exposed to fuel within said firepot, said parallel legs extending without said firepot.

4. The device of claim I in which said electrical control means comprises a single throw switch responsive to demands on said burner for heat, a double throw switch responsive to the temperature of said firepot, and a cycling device, the closing of said single throw switch, when said double throw switch is in the position it assumes when said firepot is cold, activating said cycling device, said cycling device then energizing said fuel igniter means for a predetermined time, and thereafter deenergizing such igniter means and simultaneously energizing said fuel delivery means, said first draft-producing means and said second draft-producing means, and the closing of said single throw switch when said double throw switch is in the position it assumes when said fire-pot is hot energizing only said fuel-delivery means, said first draftproducing means and said second draft-producing means.

5. An ignition system for a stoker-fed, solid-fuel burner comprising an igniter unit, fuel-delivery means, a first draft-producing means, a second draft-producing means, and an electrical control system for said unit and said means comprising a single throw switch responsive to demands upon said burner for heat, a double throw switch responsive to the temperature of the combustion chamber, said double throw switch assuming one position when combustion exists in said chamber and a second position when no combustion exists therein, a multiple contact cycling device, and conductor means establishing a plurality of circuits comprising a series circuit including a source of electrical energy, said single throw switch, said double throw switch when in said second position, and the motor of said cycling device, a series circuit including a source of electrical energy, the driving motor for said fuel-delivery means, said first draft-producing means and said second draft-producing means, and means including certain of the contacts of said cycling device which are closed after a predetermined time for controlling energization of said driving motor,

a series circuit including a source of electrical energy, said igniter unit, and means including other of the contacts of said cycling device which are closed upon initial energization of said cycling device and which are opened simultaneously with closing of said certain contacts for controlling energization of said igniter unit, and a series circuit including a source of electrical energy, said single throw switch, said double throw switch when in said first position, and said means which controls energization of said driving motor, for energizing said driving motor independently of the contacts of said cycling device.

6. The device of claim 5 including a holding circuit for the motor of said cycling device comprising a source of electrical energy, still other of the contacts of said cycling device which are closed upon initial energization of said motor and which are opened after the completion of one cycle of said device, and the motor of said cycling device.

References Cited in the file of this patent UNITED STATES PATENTS Hotchkiss Oct. 2, 1945

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