US2122050A - Retard air control for stokers - Google Patents

Description

June 28, 1938. F. w. STUART RETARD AIR CONTROL FOR STOKERS Filed Oct. 13, 1936 2 Sheets-Sheet l INVENTOR. F760 #4 Szzmrf WW: 7 v

ATTORNEYS June 28, 1938. F. w. STUART RETARD AIR CONTROL FOR STOKERS Filed Oct. 13, 1936 2 Sheets-Sheet 2 INVENTOR. fiGQ 511107? BY W W ATTORNEY5 ill) Patented June 28, 1938 STTES The present invention relates to a means for automatically controlling the volume of air delivered from a fan driven by a constant speed motor and specifically to a device for restricting the amount of air delivery of a constant speed fan to a gore-determined minimum during the initial operation thereof and which gradually permits the delivery of air at the maximum fan volume.

My invention is particularly adapted for use in conjunction with automatic coal burning stoker equipment employing a fan for the delivery of air to the retort thereof. object of my invention is to provide a device which will materially reduce the amount of fly ash discharged by the heating machine thereby diminishing fly ash deposit on the heating surfaces of the furnace which is conducive to the eidcient operation of the unit, whilst also lessening the danger of the fly ash escaping into the air through the flue pipe and-chimney, thus in= creasing the personal health factor in stoker usage.

Another object of the invention is to provide a means whereby the maximum amount of air delivery from a stoker fan, during stoker activity, may be periodically decreased, thus allowing a greater-volume of air to be used-for combustion which permits a more intense fire without the consequent thinning of the fuel bed.

A further object of the invention is to provide lowing specification and drawings which disclose the preferred embodiment of my invention, and

in which:

Fig. 1 is a cross sectional view of my device positioned upon the air conduit of a stoker unit.

Fig. 2 is a front elevational view of the stoker unit with the device disposed thereon.

, Fig. 3 is a front elevational view of a stoker unit showing a modified form of my device.

v Fig. 4 is a wiring diagram used in conjunction with my device.

Generally, my device consists of a shutter interposed either in the air duct -of a stoker unit between the fan and the retort or over the air inlet of the fan thereof, and which is adapted to be moved to open or close said air conduit or inlet In this connection, an

by means of a heat responsive expansion element, connected thereto by suitable linkage. Associated with or adjacent this element is positioned an electrically operated heating coil which is wired in parallel with the stoker motor and fan motor circuits. The shutter is devised to be normally in a position to close the air conduit or fan inlet so that upon actuation of the motor, the heating coils will be energized to operate the expansion element, thus gradually moving the shutter to a position to open the air conduit or fan inlet.

The exhausted time of shutter'movement may be varied by means of an air escapement valve adapted to control the movement of air between the heating coil and the expansion element. A switch is placed in series in the heating coil circult which is adapted to break the circuit when the marlzimum movement of the expansion element has been reached and which closes the circuit at an intermediate position of the expansion element.

Specifically, my device ii as shown in Fig. 2, is positioned upon the air conduit i of a stoker unit 18 between the fan and the retort ill. The fan is driven in the conventional manner by a con= stant speed motor ii, the latter usually being employed to drive the coal feed screw oi the stoker. The device comprises a base casting i2 (Fig. 1) having a centrally disposed aperture iii and an ofiset portion i l. The opposite ends of the casting are provided with lateral grooves 25 adapted to receive straps it which are drawn over the casting and are fastened to the air conduit by bolts ii to permanently fasten the casting thereon. A sleeve casing it is positioned in a circular inset portion it of the base and encloses a porcelain coil mounting 2d. The coil mounting has a relatively large centrally disposed annular opening it, the vertical wall thereof being provided with a spiral groove 22 to receive an electric heating element or resistance 23. I

The terminals 24 and 25 of the coil are led through horizontal holes 26 in the mounting and are secured to circuit contacts 271. These con switch are closed. Thus.

flanges I! having holes. ll therein being adapted to receive elongated bolts 31 to permanently secure the cap and the casing to the base. An expansion element which conveniently takes the form of a metallic bellows 38 containing a volatile liquid or gas is disposed centrally of the coil mounting and adlacent the resistance coil. A threaded lug l8 integral with the bellows extends from the top central surface thereof and is received in a centrally disposed aperture 40 in the cap, a bolt ll being provided to engage the threaded portion of the lug and fasten the bellows permanently to the cap. The lower free end of the bellows has a projection l2 secured thereto by means of a screw ll, which extends through the central aperture II in the base and into the air conduit proper.

A valve or shutter 44 is interposed in the air conduit 1 and is substantially the same size as the transverse inside dimensions of said conduit there being provided a small air escapement 45 about the shutter and the conduit walls. The shutter is normally in vertical or closed-position and is pivoted on a transverse shaft 4! fastened to the vertical walls of the conduit. The expansion or contraction of the bellows is devised to open and close the shutter and to this end a lever 41 is provided which has for its fulcrum a pin 48 held in a bracket 49, the latter being fastened to the bottom surface of the base by bolt IO. One end of the lever has an elongated slot 8i therein to receive a pintle 52 secured in a circular arm ll fastened to the shutter adjacent the upper end thereof. Intermediate the fulcrum and the arm engaging end of the lever and ad- Jacent the fulcrum, the projection II is fastened to thelever by a pin ll. The free end of the lever has fastened thereon by means of spring clips II, a mercury tube switch 5!, which is normall held in a position to close its contacts II and I.

Thelead wires l9 and 60 are led to the contact plate 28 and are wired thereto in the following manner. Referring to Fig. 4, current is introduced to the constant speed motor Ii of the stoker unit by wires BI and If, the said circuit being controlled by the conventional thermostat. The heat producing resistance coil is wired in parallel to the motor circuit by wires 83 and N, the mercury tube switch contacts I! and ll being placed in series in the resistance coil circuit.

In operation therefore, (Figs. 1 and 4) when the constant speed motor for driving the fan and incidently, the feedscrew of the stoker unit is inoperative, the shutter 44 will remain in its normal or closed position. when the current is supplied to the fan actuating motor, its maximum volume of air will be forced through the air conduit to the retort in the direction of the arrow, the shutter serving to retard the air thus allowing a minimum amount of said air to reach the retort. A current will also be sent to the heat producing resistance coil II and because it is in normal lever position, the contacts of the mercury a minimum amount of air is delivered to the tuyere which is not of sufficient velocity to discharge the accumulation of ily ash therein, but allows the fire to reduce this ash to a .cinder formation.

As has been said, the resistance coil is energised when current is supplied to the motor. The coil therefore gradually raises the temperature of the air about the expansion element thus causing the movement of the free end thereof to move the lever and its associated parts, to bring them into a position indicated by the dotted lines 85, whereby the shutter is in open position thus permitting a maximum volume of air to be delivered to the tuyere.

To regulate the elapsed time of shutter movement which is dependent upon the rate of expansion of the expansion element it is necessary to permit the escape of heat set up by the resistance coils. To this end. I provide a sleeve 65 rotatably mounted inside the cap 33 which has a number of perforations 61 to register with a number of holes 88 formed in the cap. This construction results in an air escapement valve which may be regulated by rotating the sleeve to open or close the openings. Forced air from the conduitis therefore admitted through aperture l3 to be passed about the expansion element and discharged through these escapement valves. By adjustment of the valves, it will be seen that the effectiveness of the radiant heatof the coil upon the expansion of the expansion element may be varied to control the elapsed time of shutter movement.

when the lever has reached the maximum or open shutter position, the contact in the mercury switch is devised to be broken, thus interrupting the current flow to the heating coil. The subse quent cooling of the heating coil and the expansion element allows the latter to contract, and by action of the lever allows the shutter to decrease the conduit opening. When the shutter closes to 'a point intermediate its open or closed position, the mercury switch contacts are devised to-again close the heating coil circuit to again expand the expansion element and open the shutter. This cycle of operation continues so long as the fan driving motor is actuated. The last mentioned operation is devised to periodically decrease the maximum volume of fan delivery to allow a great:

er amount of air to be used for combustion which permits a more intense fire without the consequent thinning of the fuel bed as will readily be understood. The shutter will return to its normal closed position when the fan is inoperative.

A modification of the application of my device is shown in Fig. 3. The device 6 is constructed similar to the preferred form except that the lever 41 is pivoted to a substantially U-shaped arm ll which is fastened to the transverse shaft 48. The extended portion of the shaft is secured to an arm 69 which is rotatably fastened to a link 'Il,.the free end of the latter being pivoted to an arm H which regulates the rotary movement of a shutter 12. The shutter is mounted for rotation about the intake openings 13 of the fan II by means of a bolted flange 15. The shutter is provided with a number of openlugs-1' which register with the opening 12 when the expansion element is in maximum expanded condition.

In this way, the amount of air delivered through the air duct 1 may be regulated by my device 8 in a manner similar to that used in my preferred form.-

Whatisclaimed is: y

1. In a retard air control for stokers the combination of a constant speed motor, a fan driven by the motor, a circuit for said motor, a heat producing electrical resistance wired in parallel with the circuit,'a heat responsive, expansion element adjacent the resistance, means for varying the rate of movement of the expansion element, an air conduit for the fan, a shutter, pivotally interposed in the air conduit, means associated with the expansion element and the shutter to open and close said shutter and comprising a lever having a fulcrum disposed substantially centrally thereof, an arm positioned on the shutter and pivotally engaging an end of the lever, and means for connecting the expansion element to the lever intermediate the fulcrum and the arm connecting means, and a switch in series in the resistance circuit and associated with the lever, said switch being adapted to break the resistance circuit when the shutter is open and to energize said resistance circuit when the shutter is in an intermediate or closed position.

2. In a retard air control for stokers the combination of a constant speed motor, a fan driven by the motor, a circuit for said motor, an air conduit for the fan, a heat producing, electrical resistance wired in parallel with the circuit, a heat responsive expansion element adjacent the resistance, a casing for the resistance and the expansion element, a cap for the casing, means for introducing air from the air conduit to the interior of the casing, a plurality of adjustable openings in the cap to allow the escapement of air from the casing, a movable shutter interposed in the air conduit, means associated with the expansion element and the shutter to open and close said shutter, and a switch in series in the resistance circuit and adapted to break the resistance circuit when the shutter is open and to energize said resistance circuit when the shutter is in an.

intermediate or closed position. a I

-3. In a retard air control for stokers the combination of a constant speed motor, a fan driven by the motor, a circuit for said motor, an air conduit for the fan, a heat producing, electrical resistance wired in parallel with thecircuit, a heat responsive expansion element adjacent the resistance, a casing for the resistance and the expansion element, a cap for the casing, means for introducing air from the air conduit to the interior of the casing, a plurality of adjustable openings in the cap to allow the escapement of air from the casing, a shutter pivotally interposed in the air conduit, means associated with the expansion element and the shutter to open and close said shutter and comprising a lever having a fulcrum disposed substantially centrally thereof, an arm positioned on the shutter and pivotally engaging an end of the lever and means for connecting the expansion element to the lever in j termediate the fulcrum and the arm connecting -means, and a switch in series in the resistance circuit and associated with the lever, said switch being adapted to break the resistance circuit when the shutter is open and to energize said resistance circuit when the shutter is in an intermediate or closed position.

4. In a retard air control for stokers the combination of a constant speed motor, a fan driven by the motor, a circuit for said motor, an air inlet opening for the fan, a heat producing electrical resistance wired in parallel with the circuit, a heat responsive, expansion element adjacent the resistance, a casing for the resistance and the expansion element, a cap for the casing, means for introducing air from the air conduit to the interior of the casing, a plurality of adjustable openings in the cap to allow the escapement of air from the casing, a shutter movably positioned over the inlet opening of the fan, means associated with the expansion element and the shutter to open and close the inlet openings by the shutter and comprising a lever having a. fulcrum disposed substantially centrally thereof, a shaft, an

arm positioned on the shaft and pivotally engaging an end of the lever and linkage connecting the shaft to the shutter, and means for connecting the expansion element to the lever interme- 5. In a retard air control for stokers the combination of a retort, a constant speed motor, a circuit for the motor, a fan driven by the motor, an air conduit interposed between the fan and the retort, means actuated by the motor for supplying fuel to'the retort, a valve in the air conduit, and means wired in parallel with the motor circuit for gradually opening said valve when the motor is initially actuated.

6. In a retard air control for stokers, the combination of a constant speed motor, a retort, a fan driven by said motor, an air conduit interposed between the fan and the retort, means actuated by the motor for supplying fuel to the 7. In a retard air control for stokers, the combination of a constant speed motor, a retort, a fan driven by said motor,an air conduit interposed between the !an and the retort, means actuated by the motor for supplying fuel to the retort, a circuit for the motor, a heat producing electrical resistance wired in parallel with the circuit, a heat responsive expansion element adjacent the resistance, means for varying the rate of movement of the expansion element, a valve in the air conduit and means associating the movement of the expansion element with the valve for the gradual opening of said valve during initial actuation of the motor.

8. In a retard air control for stokers, the combination of a retort, a constant speed motor, a

i'an driven by said motor, an air conduit interfan driven by said motor, an air conduit interposedbetween the fan and the retort, means actuated by the motor for supplying fuel to the retort, a circuit for the motor, a. heat producing, electrical resistance wired in parallel with the circuit, a heat responsive expansion element adjacent the resistance, a. valvein the air conduit, means associating the movement of the expansion element with the valve to gradually open said valve and a switch wired in series in the resistance circuit and associated with the movement of the valve to break the resistance circuit when the valve is open and .to energize said circuit when the valve is in an intermediate or closed position.

FRED W. STUART.

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