US2497879A

US2497879A - Overfire air blower control for

Info

Publication number: US2497879A
Authority: US
Publication date: 1950-02-21
Anticipated expiration: 1967-02-21

Description

Patented Feb. 21, 195G OFFICE OVERFIRE AIR BLOWER CONTROL FOR STOKER SUPPLIED FURNACES Paul G. Frerer, Milwaukee, Wis., assignor to Perfex Corporation. Milwaukee, Wis, a corporation of Wisconsin Application August 12, 1944, Serial No. 549,225

Claims. 1

This invention relates to automatic controls for stoker fired furnaces. It has become common to control the output of small or medium sized stoker fired furnaces by starting and stopping the stoker in accordance with demand for heat. In most cases, when the stoker is stopped the fire begins to smoke, dueto thefact that there is still green coal in the retort and insufficient air is being supplied for proper combustion. In the larger sizes of stoker fired furnaces this smoking has been substantially "reduced by pro viding a small auxiliary blower which supplies air over the fire. This over-fire air completes the combustion and thus smoking. is avoided. The present invention relates to a control system for controlling stokers having over-fire or auxiliary blowers.

The primary object of the present invention is to provide a control system for a stoker fired furnace which serves to operate an over-fire blower for a period of time after the stoker is stopped.

Other objects of the invention will appear from the following description and the appended claims.

For a full disclosure of the invention, reference is made to the following detailed description and to the accompanying drawings, in which,

' Fig. 1 is a schematic illustration of one form of the invention; and

Fig. 2 schematically illustrates a modification.

Referring to Fig. 1, reference character I indicates a furnace which is fired by astoker 2 having a motor 3 which drives both the fan and coal feeding mechanism (not shown). The furnace is also provided with an over-fire blower 4 which is driven by a motor 5 and which serves to deliverair into the combustion chamber above the fire.

The stoker and over-fire blower are controlled by means of a relay generally indicated as B. This relay includes a coil 1 which is connected across line wires 8' and Sin series with a control device ||J which may be a thermostat responding to the temperature of the space heated by turnace The relay coil 1 also maybe controlled by means of a holdfire timer II which is wired in parallel with the thermostat. This timer functions in the usual manner to operate the stoker at fixed intervals independently of the thermostat so as to prevent the fire from going out. The relay 6 includes a switch arm l2 which is adapted to engage an in contact I3 when coil 1 is en-- ergized, and which engages an out" contact |4 when the coil 1 isdeenerzized.

The over-fire blower 5 is controlled by a timing mechanism, generally indicated as I5, preferably through a relay it. This relay I6 is of usual form, consisting of a coil I! and a switch arm It which engages a fixed contact l9 when coil I7 is energized.

The timing mechanism I5 is preferably of the thermo-electric type and is diagrammatically illustrated as including a bimetallic element 2| which is heated by means of an electric heater 22. The element 2| actuates a movable contact 23 which cooperates with a stationary contact 24. This mechanism is arranged so that when the element 2| is cool it tends to warp downwardly for engaging contacts 23 and 24. However, when element 2| becomes heated under the influence of heater 22, it warps upwardly for disengaging contact 23 from contact 2'4. Preferably contacts 23 and 2t engage and disengage with snap action. This may be obtained by a permanent magnet 25 which cooperates with an armature 26 carried by element 2|.

The bimetal element 2| is latched in its upper or hot position by a latching means which is illustrated diagrammatically as including a spring latch member 28. The spring 28 is fixed at its lower end, and at its upper end bears against an abutment member 29 attached to the bimetal element. The spring 28 is shown in its normal position. This spring is adapted to be fiexed to the left so as to disengage member 29 when the relay coil 1 is energized. This result is obtained by means of an arm 30 actuated by the relay armature with the switch arm l2.

Operation-Fig. 1

With the parts in the positions shown, the thermostat has been satisfied .for a prolonged period of time and the relays 6 and 16 are deenergized. This causes both the stoker and overfire blower to be at rest.

When the thermostat calls for heat it completes a circuit from line wire 8, through the relay coil 2' to line wire 9, and thus energizes the relay 5'. This causes the relay switch arm l2 to disengage contact l4 and to engage contact l3. This completes a circuit to the stoker motor 3 as follows: From line wire 8, wire 32, switch arm I2, contact l3, wire 33, limit control 34, and stoker motor 3 to line wire 9. Simultaneously with movement of switch arm l2 into engagement with contact l3 the relay arm 3|] engages the latch spring 28 and deflects it to the left so as to disengage it from the latch member 29. The bimetal element 2| at this time is cold so that it snaps contact 23 into engagement with contact 24. This has no immediate result inasmuch as the circuit to contact 24 is broken at the relay contact M. The stoker will normally operate until the thermostat |6 becomes satisfied. When this occurs, the relay coil 1 will be deenergized, thus causing the switch arm l2 to disengage contact l3 and engage contact l4. The switch arm |2 in disengaging contact |3 breaks the circuit to the stoker motor and thus stops the stoker. It will be recalled that the contact 23 of the timer is now in engagement with the contact 24. Thus when the switch arm l2 of the relay engages contact hi it completes a circuit to the relay coil I! as follows: From line wire 8, wire 32, switch arm l2, contact I4, timer contacts 24 and 23, element 2|, wire 31, and relay coil I! to line wire 9. This also completes a circuit from the bimetal element 2| through heater 22 and wire 38 to line wire 9. Energization of the relay coil l1 causes the switch arm |8 to engage fixed contact l9 which energizes the over-fire blower through the following circuit: From line wire 8, wire 40, contacts l9 and I8, wire 4|, blower motor 5, and wire 42 to line wire 9.

From the foregoing it will be apparent that when the thermostat l8 becomes satisfied it deenergizes the relay coil 1 which through its out contact energizes the blower motor relay |6 for starting the over-fire blower. At the same time the heater 22 of the thermo-electric timer is energized for causing the timer to begin heating.

After a period of time, usually between five and ten minutes, the temperature of bimetal element 2| will rise to a point at which it overcomes the holding force of magnet 25 and disengages contact 23 from contact 24 with snap action. This breaks the circuit to the relay coil l'l, thereby stopping the over-fire blower 4. It also breaks the circuit for the heater 22. The bimetal element 2| thus begins to cool. However, on cooling, the element 2| is prevented from re-engaging contacts 23 and 24 by the latch member 28 which has taken a position under the latch member 29. This prevents contacts 23 and 24 from closing until the next time that the relay 6 is energized. When the thermostat again calls for heat the cycle of operation above described will be repeated.

Figure 2 In Fig. 1 the timer is permitted to be deenergized during the balance of the off periods by means of the mechanical interlock with the relay 6. In Fig. 2 the same result is obtained electrically. In this figure the stoker motor is controlled by a relay 52 having a coil 53 and a switch arm 54 which engages a stationary contact 55 when coil 53 is energized.

The over-fire blower 56 is controlled by a relay 5'! having a coil 58 and switch arms 59 and 66 which engage contacts 6| and 62 respectively, when the coil 58 is energized. The relay 5'! is controlled by a relay 64 having a coil 65 and a switch arm 66 which engages a contact 61 when coil 65 is energized, and which engages a contact 68 when coil 65 is deenergized. The relay 51 is further controlled by means of a timer 18 con-- sisting of a bimetallic element H and an electric heater 12. The element H when cold causes its contact 13 to engage a stationary contact 14. When the timer element H is hot, it disengages contact 13 from contact 14.

Operation of Fig. 2

With the parts in the positions shown, the thermostat I5 is satisfied and the thermal timer 10 is in its cold position. The

relays

52, 51, and 64 are all deenergized and thus the stoker and overfire blower are out of operation. When the thermostat 15 calls for heat it completes a circuit from the line wire 16, through relay coil 53 to line wire Tl. This causes relay switch arm 54 to engage contact 55, which completes a circuit to the stoker motor 5| as follows: From the line wire 16, wire 18, switch arm 54, contact 55, wire 19, limit control 89, wire 8|, and stoker motor 5| to line wire 71. The relay 52 thus places the stoker into operation. Engagement of the relay switch arm 54 with contact 55 also completes a circuit through the relay coil 65 and wire 82 to line wire Tl. This causes the relay switch arm 66 to disengage contact 68 and engage contact 61, which establishes a circuit for relay coil 58 as follows: From line wire 16, wire 85, timer element 1|, contact 13, wire 86, wire 81, switch arm 66, contact 61, wire 88, relay coil 58, and wire 82 to line wire 11. This causes energizetion of relay coil 58, thereby causing relay switch arms 59 and 69 to engage contacts 6| and 62. At this time engagement of relay switch arm 69 with contact 62 has no result, inasmuch as contact 62 is connected by wire 90 to the relay contact 68 of relay 64, which contact is now open. Engagement of the relay switch arm 59 with the contact 6| establishes a holding circuit for the relay coil 58 as follows: From line wire 16, wire 85, timer element H, contact 14, wire 86, wire 9|, contact 6|, switch arm 59, wire 92, relay coil 58. and wire 82 to line wire 11. It will be noted that this holding circuit is independent of the initial energizing circuit established by the switch arm 66 engaging contact 61.

From the foregoing it will be apparent that when the thermostat calls for heat all three of the relays are energized, the stoker motor 5| now being operated through relay 52, and the over-fire blower remaining at rest due to relays 51 and 64- being simultaneously energized.

When the thermostat 15 becomes satisfied it I breaks the circuit through the coil 53 of relay 52, thereby causing the switch arm 54 of this relay to disengage contact 55. This breaks the circuit to the stoker motor 5| and thus stops the stoker. This also breaks the energizing circuit for the coil 65 of relay 64, which causes the switch arm 66 to disengage contact 67 and engage contact 68. Disengagement of contact 66 from contact 61 has no effect, dueto the relay coil 58 now being energized independently through its holding contacts 59 and 6|. Engagement of the switch arm 66 with contact 68 however will establish a circuit for the over-fire blower 56 as follows: From line wire 16, wire 85, timer element 1|, contact 14, wire 86, wire 81, switch arm 66, contact 68, wire 90, contact 62, switch arm 66, wire 93, blower motor 56, and wire 94, to line wire 11. This will also establish a circuit through the heater 12 of the timer, this circuit extending from wire 93, through wire 95, heater 12,'wire 96, and wire 92, to line wire Tl.

From the foregoing it will be seen that when the operating control becomes satisfied it deenergizes the relay 52 which stops the stoker motor, and also deenergizes the relay 64, while the relay 51 remains energized due to its holding circuit through the timer contacts. This operates the overfire blower and also energizes the heater of the timer.

After a period of time,'such as five or ten minutes, the bimetal element 1| heats up to a point at which it disengages contactsli and '14. This breaks the holding circuit for the coil 58 of'relay 51 and consequently the switch arms 59 and E- disengage contacts BI and 62. Disengagement of switch arm 5!! from contact 62 opens the circuit to the over-fire blower and also opens the circuit to the timer heater l2. Disengagement of switch arm 59 from contact 6! opens the holding circuit for the relay coil 58. The bimetal element H of timer ill will eventually cool down for reclosing contacts 13 and 14. This will have no effect due to switch arms 59 and 6B now being disengaged from contacts 5'! and 62. The over-fire blower and stoker will now remainoutof operation until the relay :52 is again energized, at which time the cycle of operation will be repeated.

From the foregoing it will be apparent that the present invention provides .a simple and dependable control system which functions to cause the over-fire blower to operate for a period of time after each operating period of the stoker. "While I have shown and described only two formsthe invention may take, it is apparent that many modifications may be made without departing from the invention. It is therefore desired to be limited only by the scope of the appended claims.

What is claimed is:

1. In a control system for a stoker fired furnace having an over-fire blower, means for starting and stopping the stoker, means for starting and stopping the blower, said last mentioned means including time controlled means energized by the stopping of the stoker to operate the overfire blower for a predetermined period after cessation of stoker operation and to stop the overfire blower at the expiration of said period.

2. In a control system for a stoker fired furnace having an over-fire blower, means for starting and stopping the stoker, means for starting and stopping the blower, said last mentioned means including time controlled means comprising thermal time delay means energized by the stopping of the stoker to operate the over-fire blower for a predetermined period after cessation of stoker operation and to stop the over-fire blower at the expiration of said period.

3. In a control system for a stoker fired furnace having an over-fire blower, a first switch for controlling the stoker, a second switch for controlling the blower, means for actuating said switches so as to open one switch and close the other and vice versa, a timer having a switch for selectively preventing or permitting operation of the blower under the control of said second switch, said timer being constructed and arranged so that it has an initial position in which it permits operation of the blower and an actuated position in which it prevents operation of the blower, and means for causing said timer to move from its initial position to its actuated position after actuation of said first switch to stop the stoker.

4. In a control system for a stoker fired furnace having an over-fire blower, a first switch for controlling the stoker, a second switch for controlling the blower, means for actuating said switches so as to open one switch and close the other and vice versa, a thermo-electric timer constructed and arranged to move between hot and cold positions, connnections between said timer and blower arranged to permit operation of the blower under the control of said second switch when the timer is in its cold position and to stop operation of the blower when the timer is in its hot position, and means for energizing said timer when the stoker is stopped by said first switch to cause movement of the timer to its hot position.

5 .'-In a control system vfor a stoker fired furnace having an overfire blower, a first switch for controlling the stoker, a second switch for controlling the blower, means for actuating said switches so as to open one switch and close the other and vice versa, a thermoaelectric timer constructed and ar-:

the control of said .second switch when the timer is inv its. cold position and to stop operation of the blower when the timer is in its hot position, means: for .energizin-gsaid timer when the stoker is stopped by said first switch to cause movement of the-timer to its hot position, means for deenergizing the timer when it reaches its hot position. and means for preventing the timer from restarting the blower or reenergizing itself until the stoker is restarted.

.6. a control system for a stoker fired furnace having an over-fire blower, a first switch for controlling the stoker, a second switch for controlling the blower, means for actuating said switches so as to open one switch and close the other and vice versa, a thermo-electric timer constructed and arranged to move between hot and cold positions, connections between said timer and blower arranged to permit operation of the blower under the control of said second switch When the timer is in its cold position and to stop operation of the blower when the timer is in its hot position, means for energizing said timer when the stoker is stopped by said first switch to cause movement of the timer to its hot position, means for deenergizing the timer when it reaches its hot position, mechanical means for retaining the timer in its hot position, and means for releasing said mechanical means when the stoker is restarted.

7. In a control system for a stoker fired furnace having an over-fire blower, a first switch for controlling the stoker, a second switch for controlling the blower, means for actuating said switches so as to open one switch and close the other and vice versa, a thermo-electric timer constructed and arranged to move between hot and cold positions, connections between said timer and blower arranged to permit operation of the blower under the control of said second switch when the timer is in its cold position and to stop operation of the blower when the timer is in its hot position, means for energizing said timer when the stoker is stopped by said first switch to cause movement of the timer to its hot position, means for deenergizing the timer when it reaches its hot position, mechanical means for retaining the timer in its hot position, and means actuated by the actuating means for the first switch upon energization of said actuating means for releasing said mechanical means.

8. In a control for a stoker fired furnace having an over-fire blower, a relay for controlling the stoker, a thermo-electric timer for controlling the blower, said timer having a cold position in which it permits operation of the blower and having a. hot position in which it prevents blower operation, means for energizing the timer when the relay stops the stoker to cause the timer to move to its hot position a period of time thereafter, means controlled by the timer on reaching its hot position for deenergizing the same, a latch for preventing return movement of the timer to its cold position, and means actuated by the relay upon energization thereof for releasing said latch.

9. In a control for a stoker fired furnace having an over-fire blower, a relay having an in" contact for operating the stoker and an out contact for operating the blower, a thermo-electric timer having a switch in series with said out contact, said timer being constructed and arranged to close said switch when cold and to open said switch when hot, means for energizing said timer when the stoker is placed out of operation, means actuated by the timer for deenergizing the same, a latch for preventing said timer from reclosing said switch, and means actuated by the relay upon energization thereof for releasing the latch.

10. Ina control for a stoker fired furnace having an over-fire blower, a switch for controlling the stoker, a relay for controlling the blower, means controlled by said switch for causing the relay to be energized for operating the blower when the stoker stops, a holding circuit for the relay which is adapted to maintain the relay energized independently of said last mentionedmeans, said holding circuit being incapable of initially energizing the relay, a switch in said holding circuit, and a timer for opening said last mentioned switch a period of time after the stoker is stopped.

PAUL G. FRERER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS