US2728311A - Automatic ignition system for solid-fuel, stoker-fed burners - Google Patents

Description

Dec. 27, 1955 o. T. CAMPBELL AUTOMATIC IGNITION SYSTEM FOR SOLID-FUEL, STOKER- FED BURNERS 2 Sheets-Sheet 1 Filed Jan. 30, 1952 m m m W 06710 72' CL'QMPBELL) BY.

A1 7 OZP/VE Z Dec. 27, 1955 D. T. CAMPBELL AUTOMATIC IGNITION SYSTEM FOR SOLID-FUEL, STOKER-FED BURNERS Filed Jan. 30, 1952 2 Sheets-Sheet 2 I s'l'AcK L lT-\ERM06TAT E ATTORNEY United States Patent C AUTOMATIC IGNITION SYSTEM FOR SOLID- FUEL, STOKER-FED BURNERS David T. Campbell, Indianapolis, Ind.

Application January 30, 1952, Serial No. 268,989

10 Claims. (Cl. 110-1) This invention relates to stoker-fed, solid-fuel burners and is concerned primarily with the provision of an automatic ignition system for such burners.

Since the introduction of automatic stoker means for solid fuel burners, the problem of automatic ignition has presented a difficult and continuing challenge to those in the field. It is to the solution of this problem that my invention is directed.

Among the specific objects of my invention are:

To provide means whereby fuel in the fuel-delivery conduit, ahead of the firepot in the combustion chamber, may be heated to kindling temperature, upon a call for heat by the usual room thermostat at a time when the combustion chamber is cold, and whereby, thereafter, combustion-supporting air will be supplied to the heated fuel;

To arrange an electrically-energized heater unit in the fuel delivery conduit at a point where it will be reasonably protected against the heat of normal combustion, and where it will always be in contact with unburned fuel; and

To provide an automatic, cycling control system for such a heating unit including a timer, energized upon demand for heat at a time when the combustion chamber is cold, said timer being effective first to energize the heater, thereafter to energize a blower to supply combustion-supporting air to the region of the heater, and then, after a predetermined time, to deenergize the heater and, if the combustion chamber is still cold, to deenergize the blower.

To the accomplishment of the above and related objects, my invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that change may be made in the specific construction illustrated and described, so long as the scope of the appended claims is not violated.

Fig. 1 is a perspective view, more or less diagrammatic, showing the type of burner and stoker arrangement with which my invention is particularly useful;

Fig. 2 is a sectional view, more or less diagrammatic, through a blower and its discharge passages, forming a portion of the stoker apparatus shown in Fig. 1;

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

Fig. 4 is a transverse, sectional view through a detail of my invention taken substantially on line 4-4 of Fig. 3; and

Fig. 5 is a fragmentary perspective view of the ignition zone of the illustrated embodiment of my invention.

Referring more particularly to the drawings, it will be seen that I have shown a burner 10, in phantom outline, defining a combustion chamber in which is located a tuyered firepot 11. The burner is provided with the usual exhaust stack 12. Surrounding the firepot 11, communicating with the tuyeres thereof and extending outside the burner is a duct or wind box 13. A fuel delivery conveyor, generally in the form of a tube 14 having arranged therein a conveyor screw 15, is passed Patented Dec. 27, 1955 through the duct 13, to communicate with the firepot 11, the other end thereof receiving fuel from a fuel reservoir 16, for instance in accordance with the disclosure of my copending application Serial Number 78,193 filed February 24, 1949, for Non-Smoke-Back Solid Fuel Furnace, now Patent Number 2,600,614, issued July 17, 1952. Drive means, indicated generally by the reference numeral 17, is connected to rotate screw 15 within said tube to feed fuel to the firepot under controlled conditions. A blower unit 18, driven by drive means 17, delivers air through a conduit 19 to duct 13 and thence into the burner combustion chamber, said blower, conduit and duct comprising a first draft-producing means.

To this point, the structure is more or less similar to the conventional arrangement in this type of burner. My invention resides in the embodiment of a system, in such a burner, to provide for automatic ignition of the fuel in response to demands on the burner for heat. To this end, I provide an aperture 20 in the bottom of the conveyor tube 14 and into this opening, I place an electrically energizable heater unit 21. The positioning of unit 21 relative to the firepot 11 is an essential feature of my invention.

It is a characteristic of burners of the type illustrated, that, when the fire is allowed to burn out, a core or plug of ash 22 forms within the firepot 11. Prior attempts to provide automatic ignition for this type burner have failed, due, in part, to the fact that, in such conventional burners, combustion-supporting air can reach the fuel only at or beyond the tuyere region of the firepot 11. Thus, it has heretofore been presumed that kindling or ignition of the fuel must, of necessity, occur within the firepot which, under conditions demanding ignition, will be occupied by plug 22 of partially consumed fuel and ash. Such attempts have failed because, although means have been provided for attaining theoretically-effective high temperatures at that point, air supplied through the duct 13 simply escapes through the tuyeres of the firepot 11, being held out of combustion-supporting contact with fresh fuel heated by the igniter unit, by the ash plug 22. To overcome these difficulties I have removed the igniter unit from its heretofore supposedly essential position within the heart of plug 22 and have placed it in the tube 14 at a point removed from the normal combustion area and ahead of even the region of vestigial combustion within the firepot 11 which produces the plug 22 as the fire burns out.

Igniter unit 21 is positioned in tube 14 at a point closely ahead of the lowermost level of combustion in firepot 11, and preferably substantially at the near terminus of the horizontal run of said tube. This location is such that, normally, no combustion or burning of fuel occurs at the igniter unit. The optimum position of the igniter is such that normal combustion begins promptly after the fuel has passed the inactive unit 21. Thus, when the igniter is called into operation, it acts on the fuel in a region immediately ahead of the normal combustion region to initiate combustion.

Positioning of the igniter unit 21 out of the range of normal combustion materially adds to the length of the life of the igniter since it is not continually subjected to the extreme heat existing within the firepot.

Preferably, igniter unit 21 comprises a Calrod type heater coil. While the particular shape of the coil is not an essential feature of my invention, I have found (and so illustrated) that a coil in the shape of an S, elongated along the longitudinal dimension of the tube 14, performs most satisfactorily. The coil may be secured in place in tube 14 by any suitable means. As I have illustrated and described it, the aperture 20 is made just large enough to receive unit 21 and a retainer member 23 is secured to tube 14 to hold unit 21 in aperture 20.

The unit is curved to conform to the inner surface of tube 14 and is so positioned that its surface lies flush with, or just outside, the inner surface ofsaid tube, so that the unit is directly exposed to fuel in, or moving through, the said tube.

As screw 15 is rotated within the tube 14, fuel is forced along the bottom of the tube, over the igniter unit 21 and into chamber 11. For ignition purposes I have found that the optimum depth of fuel in tube 14 is approximately one-half the tube diameter. This can be easily regulated by the pitch and/or rotary velocity of screw 15 in relation to the rate of fuel feed to said screw.

Whenever ignition is called for and igniter unit 21 is energized, only loosely packed and unburned fuel is in contact with the unit 21 as a result of my particular positioning of said unit in tube 14 and, as a consequence, the introduction of combustion-supporting air to the heated fuel is a relatively simple matter. In the illustrated embodiment of my invention, I provide a scoop 24 in the outlet of blower 18; and by this means, I by-pass a portion of the air delivered by said blower into tube 14 through a conduit 25 or the like, said blower, scoop, conduit and tube comprising a second draft-producing means. Thereby, a suflicient supply of air is insured at the igniter unit 21. While I have used this expedient as a second draft-producing means to force air through tube 14, it is obvious that the end result could be accomplished by a separate blower unit independent from drive unit 17 and supplying air to flow through the tube 14. I have used this means, however, for obvious reasons of both economy and simplicity.

In operation, igniter unit 21 is energized before screw 15 begins to move fuel over unit 21 and also, before commencement of air being forced into tube 14. As a result, the loosely packed fuel lying on unit 21 is quickly raised to its kindling temperature. After this temperature is reached, air is forced into tube 14 and over unit 21 to cause the fuel, thus heated, to burn vigorously. At the same time, screw 15 commences to rotate and moves the burning fuel into chamber 11. This igniter unit 21 is subjected to the increased heat of the burning fuel for only a relatively short time, and is wiped clean, by the incoming fuel, for the next ignition cycle. After ignition, unit 21 is deenergized and is not thereafter in intimate contact with burning fuel until ignition is again required.

In order that operation of the igniter mechanism be entirely automatic, I provide a novel control system comprising a room thermostat 26, of single-pole construction, a double-pole, thermo-responsive switch 27 arranged (for instance, as a stack thermostat) so as to be responsive to the temperature of the combustion chamber, and a timing device or time delay switch 28. Such devices are usually designed for operation on low voltages thus necessitating the use of relays 29 and 30 in the circuits leading to unit 21 and the draft and screw propelling motor 31 of drive unit 17. A step-down transformer 32 is provided for operation of these relays and timing device 28.

The motor 31 is energized from a source of power 33 by means of a series circuit including wire 34, motor 31, wire 35, the contacts 36 and 37 of relay 29, and wire 38. A diagrammaticallydllustrated limit switch L will preferably be connected in this circuit and may be so located and designed as to deenergize motor 31 in case furnace temperatures exceed a predetermined maximum. Igniter unit 21 is energized from a source of power by means of a series circuit including wire 39, one set 40 of a pair of contacts in relay 30, wire 41, unit 21, wire 42, the other set 43 of said pair of contacts, and wire 44. Relays 29 and 30 are energized in response to demands of elements 26, 27 and 28.

A circuit including wire 34, wire 45, the primary winding 46 of transformer 32, Wire 47 and wire 38 provides the means for energizing the transformer 32.

From the secondary winding 48 of transformer 32, a

control circuit for relay 29 is established through wire 49, room thermostat 26, wire 50, wire 51, the armature 52 and pole 52a of switch 27, wire 53, wire 54, the coil of relay 29 and wires 55 and 56. The characteristic of switch 27 is such that when there is no combustion in burner 10, the armature 52 is in engagement with contact 52b but when combustion does exist, the armature is in contact with 52a. Preferably, switch 27 is of the snap type construction so that the intermediate position between contacts 52a and 52b is assumed by armature 52 only momentarily.

From transformer winding 48 a control circuit for relay 30 is established through wire 49, thermostat 26, wire 50, wire 51, armature 52, contact 52b, wire 57, wire 58, the coil of relay 30, and Wire 56.

A control circuit for the timing device 28 is established from transformer Winding 48 through wire 49, thermostat 26, wire 50, wire 51, armature 52, contact 52b, wire 57, timing motor 59, wire 60, and Wire 56.

An additional control circuit is provided for relay 29 from transformer coil 48 through wire 49, thermostat 26, wire 50, contact points 61 and 62 of time delay switch 28, wire 62, wire 54, relay 29, wires 55 and 56, thus bypassing the switch 27. A similar circuit is provided for relay 30 through wire 49, thermostat 26, wire 50, contact 61, contact 63, wire 64, wire 58, relay 30, and wire 56.

A holding circuit for timer motor 59 is established through wire 49, thermostat 26, wire 50, contacts 61 and 63, wires 64 and 58, wire 57, motor 59, and wires 60 and 56.

Operation Assuming. combustion has completely ceased in the burner and room thermostat 26 calls for heat, armature 52 of switch 27 will have assumed the position in which it is in engagement with contact 52b. In this position, when thermostat 26 calls for heat, relay 30 is immediately actuated thus energizing igniter unit 21. The timedelay switch 28 is also placed in operation. After a predetermined time (selected to accord with the known time required to raise the fuel in contact with unit 21 to its kindling temperature) timer 28 closes contacts 61, 62 and 63 whereupon relay 29 is actuated to energize motor 31. This, as explained, drives screw 15 and blower 18 to supply a flow of combustion-supporting air, and to move the fuel mass slowly, through tube 14.

After the lapse of another period of time, which is also preselected to accord with the known characteristics of the individual heating plant, timer 28 opens contacts 61, 62 and 63, thus deenergizing unit 21 and timer motor 59. If, at that time, the temperature of the combustion chamber is not sufiicient to have moved armature 52 out of engagement with contact 52b, timer 28 will complete another cycle as described. If, however, armature 52 has moved to engage contact 52a the timer will stop and the ignition process will have been completed. Motor 31 will continue to run until relay 29 is deenergized by the movement of thermostat 26.

Except by chance, armature 52 will not move from contact 52b to contact 520 at the exact moment timer 28 completes a cycle. In order to prevent the stopping of timer motor 59 in the middle of its cycle, thus leaving igniter unit 21 in energized condition, the holding circuit for timer motor 59 is provided, as previously described.

I claim as my invention:

l. A solid-fuel burner comprising a combustion chamber, means including a firepot located in said chamber and a tube communicating with said fire pot for delivering fuel to said chamber, a first draft-producing means for introducing combustion-supporting air into said chamber, a fuel igniter unit located in said tube, and a second draftproducing means for introducing air into said chamber through said tube and past said igniter unit.

2. The device of claim 1 in which said fuel igniter unit is directly exposed to fuel moving through said fuel dclivery tube at a point below the lowermost level of normal combustion in said combustion chamber.

3. In combination with a solid-fuel burner comprising a combustion chamber, a fuel conveyor tube connecting said chamber with a source of fuel, screw means arranged in said tube to convey fuel between said fuel source and said chamber, drive means cooperable with said screw means to rotate the same within said tube, and a first draft-producing means for forcing air into said combussion chamber, an igniter system comprising a fuel igniter unit exposed to the interior of said tube, and a second draft producing means associated with said tube to force air through said tube and over said igniter unit.

4. The device of claim 3 in which said igniter unit comprises an electrically-energized heater arranged in and exposed to the interior of said conveyor tube for direct contact with fuel flowing therethrough.

5. The device of claim 3 in which the igniter unit is positioned in said conveyor tube at a point slightly removed, in the direction opposite that of fuel flow, from the lowermost level of normal combustion in said combustion chamber.

6. The device of claim 3 including electrical control means for controlling the igniter system to energize the igniter unit for a predetermined period of time prior to the energization of the second draft producing means and the resultant flow of air over said igniter unit.

7. The device of claim 6 in which said control means comprises a first relay dominating the flow of electrical energy through said igniter unit, a second relay dominating the flow of electrical energy through said second draft-producing means, an energizing circuit for said second relay, and a timing device controlling energizing circuits for both said relays, a further energizing circuit for said first relay, and means for concurrently energizing said timing device and said first relay, said timing device being arranged to close the energizing circuit for said second relay after the lapse of a predetermined period of time.

8. The device of claim 7 including means for selectively placing said timing device into and out of opera tion comprising a single-pole switch responsive to demands upon the burner for heat, and a double-pole switch responsive to the temperature of said combustion chamber, said timing device being energized upon the closing of the single-pole switch and the movement of the armature in said double-pole switch to the position it assumes when no combustion exists in said combustion chamber.

9. An ignition system for stoker-fed, solid-fuel burners comprising an igniter unit, a draft-producing means, and an electrical control system for said unit and said means comprising a pair of relays, one of said pair dominating How of current through said igniter unit and the other of said pair dominating flow of current through said draft-producing means, a single-pole switch responsive to demands upon said burner for heat, a double-pole switch responsive to the temperature of the combustion chamber of said burner, said double-pole switch assuming one position when no combustion exists in said chamber and a second position when combustion exists therein, a multiple contact, time delay switch controlling actuation of said pair of relays, and conductor means establishing a plurality of circuits comprising a series circuit including a power source, said single-pole switch, said double-pole switch when said switch assumes said one position, and the actuating circuit of said time-delay switch, a series circuit including a power source, said singlepole switch, said double-pole switch when said switch assumes said one position, and the actuating circuit of said one relay, a series circuit including a power source, said single-pole switch, said double-pole switch when said switch is in said second position, and the actuating circuit of said other relay, a series circuit including a power source, said single-pole switch, a first set of contacts of said time-delay switch, and the actuating circuit of said one relay, and a series circuit including a power source, said single-pole switch, a second set of contacts of said time-delay switch, and the actuating circuit of said other relay.

10. The device of claim 9 including a holding circuit for said time-delay switch including a power source, said single-pole switch, the first set of contacts of said timedelay switch, and the control circuit of said time-delay switch.

References Cited in the file of this patent UNITED STATES PATENTS 2,176,009 Lange Oct. 10, 1939 2,210,720 Johnson et al. Aug. 6, 1940 2,234,959 Brice Mar. 18, 1941 2,237,237 Scoggin et a1. Apr. 1, 1941 2,242,580 Foulds May 20, 1941 2,375,900 De Lancey May 15, 1945 2,385,811 Hotchkiss Oct. 2, 1945

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