US2218895A - Stoker control system - Google Patents

Description

Oct. 22, 1940. E, SEUG' R 2,218,895

STOKE-R CONTROL SYSTEME Filed Sept. 14, 1937 i I 3 Wu c MM Err/65L Jr 029% fizz/4f Ulla: mm

Patented Oct. 22, 1940 UNITED STATES PATENT OFFICE 6 Claim.

This invention relates to a control system for automatic stokers, and the main object of the invention is to devise a control system which will substantially reduce and/or eliminate the blowing of ash from the stoker.

In domestic heating systems using coal as a fuel and employing automatic means for intermittently supplying fuel to the burner, the fuel burns down during the shut-down periods, leaving a ring of ash around the burner or tuyere, and, upon starting up again, the blower supplying air to the burner blows the ash out of the burner, and this ash, passing through cracks in the combustion chamber and smoke pipe, passes out into the room and becomes a source of considerable annoyance. The fine ash that is carried out of the furnace in the manner described, is commonly known as "fly ash.

According to my invention, I substantially eliminate the dimculty of fly ash by arranging the control system so that upon starting up after each shut-down period, the full blast of air is not supplied immediately upon starting of the fuel feed device, but. means are provided to delay the application of the full blast of air for a time sufficient to allow the fuel feeding mechanism to feed enough coal to the burner to displace the ash from directly above the air nozzle or tuyere. In this manner, the fly-ash is removed from the direct path of the air blast supplied to the burner, and it drops down into the ashpit without being blown up into the combustion chamber.

In the forms of the invention disclosed herein, the delayed application of the full blast of air is controlled in accordance with temperature variations at a suitable point in or on the heating system.

A preferred embodiment of my invention, and several variations thereof, is illustrated in the accompanying drawing, in which:

Figure 1 is a diagrammatic view illustrating my invention applied to a coal-burning automatic stoker of a type commonly known;

Figure 2 illustrates a modified form of control in which the air is controlled by a damper in the blower outlet duct; and

Figure 3 illustrates a modified control system in which a heat-responsive expansible element controls a damper in the blower outlet by means of a Bowden wire.

Referring to Figure 1, a heating furnace of any suitable construction is indicated at l, the furnace being provided with an ash-pit la, a combustion chamber lb, and a flue It. A smoke pipe 2 connects the furnace with a chimney 3.

Arranged within the lower part of furnace I is a coal burner consisting of a tuyere 4 arranged within a casing 5 which constitutes an air chamber surrounding the tuyre l. The blower 6, driven by a motor I, supplies air to chamber 5 5 through a ductGa. The motor I is also arranged to drive suitable mechanism for transferring coal from a supply bin 8 to the tuyere 4 through a conveyor duct 8a. This mechanism usually involves a rotary screw conveyor located in the duct 10 8a,dalthough other types of conveyors may be use The motor I, which drives the fuel feed mechanism and the blower 6, is energized from a suitable electric supply circuit indicated at 9, and 15 the operation of the motor is controlled by a thermostatic switch It in accordance with the temperature or heat demands of the space in which the switch I0 is located. Thermostat I0 is usually but not necessarily located in one of 20 the first floor rooms. The motor 1 is preferably also energized at periodic intervals independently of the condition of the thermostat ill by means of known control mechanism indicated at II. This mechanism may assume various known forms. One suitable arrangement is shown in patent to Gray, et al. 1,667,001. It should be understood that the automatic control ll need not be employed, and the motor can be controlled directly by the thermostatic switch lll, if desired.

The blower 6 is provided with an adjustable damper 6b arrangedover the inlet port of the blower for controlling the amount of air supplied to the burner. The damper 6b is arranged to be operated by a time-delay device which becomes effective a predetermined time after the motor 1 begins to operate. This time-delay device may assume various forms, but the device as shown in Figure 1 comprises a temperature-responsive w switch arranged at a convenient point in the heating system and controlling a suitable motive device for varying the amount of blast supplied by the blower 6. In the arrangement shown in Figure 1, the temperature-responsive switch AI is located in the smoke pipe 2 and is responsive to the temperature of the gases passing through this pipe and is arranged to control the energizing circuit of an electromagnet l3, which in turn controls damper 6b through the rod [311. It will be understood that the switch A) is normally open for temperatures below a predetermined limit, and closes when the temperature rises above this limit.

In the operation of the arrangement shown in the fire from dyingout.

the flue I c and out the chimney 3.

Figure 1, the mechanism It willenergise the motor 1 at periodic intervals of short duration so long as the space to be heated does not require any additional heat. This intermittent operation of the stoker is for the purpose of preventing As soon as the temperature of the space being heated falls below a definite limit, the thermostat ll completes a circult and causes operation of the stoker until the temperature in the space to be-heated is brought back to normal. During the shut-down periods, the coal burns around the edge of the tuyere and leaves a ring of ash around the outer edge of the tuyere as indicated by the dotted area 4a in Figure 1, the hot spot of the fire 4b being located at the center of the tuyere. In the systems now commonly in use, the full best of air is supplied to the air chamber 5 surrounding the tuyere 4 as soon as the motor I begins operation, and the ring of ash la is violently blown upwardly into the combustion chamber lb, into Some of the fly ash filters through small cracks or openings around the doors of the furnace, or in the various joints, and is carried into other parts of the room. According to my invention, however, the damper 6b is normally set in a position such that the amount of air supplied to the air chamber 5 is insuflicient to cause any substantial blow- -ing of the fly-ash from around the rim of the burner. Accordingly, by arranging for sumclent time delay in the operation of electromagnet. is after motor 1 begins to operate, the fuel feeding mechanism will supp y enough coal to the tuyere to displace the ash from directly over the air openings in the tuyre by the time the damper 6b is fully open and the full blast becomes effective. As soon as the air openings in the tuyre become covered with unburned coal, the force of the air stream is thereby cut down andthere is no substantial blowing of the fly-ash.

In Figure 1, a small amount of air is supplied to the burner as soon as the fuel feeding arrangement begins to operate. This air is suflicient to raise the temperature of the heating system, but at a slow rate. Since it will require some time for the switch A) to operate, the full blast of air is delayed until after the fuel feed mechanism has supplied enough coal to the bumer to displace the ash.- The temperature-responsive device may be arranged in any number of difierent positions as shown in Fig. 1. For example, it may be arranged within the air chamber S'adjacent to the tuyere 4 as shown at All, where it will be a ermostatic switch and .will be responsive to 'the temperature of the tuyere or the temperature of the fuel bed. The switch may be arranged in the position Ab in Figure 1 where it will be responsive to the temperature within the combustion chamber, or at Ac where it will be responsive to the temperature of the walls of the combustion chamber. When located at Ad, the responsive element of the switch would extend into the water, steam or air space of the furnace or heating system and be responsive to temperature of the heating medium. In the position lie, the switch would be responsive to the temperature of the flue gases, while at As it would respond to the temperature of the smoke pipe, and at Ah, the temperature responsive element being located in the chimney would be responsive to the temperature of the chimney gases Instead of controlling side of the blower 0,

a damper on, the inlet he t perature-re p nsive switch may be arranged to control a damper located in the outlet duct of the blower O as shown in Figure 2. The thermostatic switch indicated at A may be located in any of the various positions indicated above for Figure 1. In this arrangement, the damper 6c is normally set to permit a predetermined reduced blast of air 1: 2!; siupplied to the burner when the motor 1 switch closes, the magnet i 3 is energized to operate the damper 6c and thereby increase the blast to full blast.

Instead of using a thermostatic switch responsive to the temperature of a selected point in the ,the temperature-responsive switch of Figure 1.

lily invention not only reduces and/or substantially prevents the blowing of fly-ash, but it also improves the efficiency of operation of the burner. This latter advantage is realized by reason of the fact that the full blast of air is not applied at the beginning of each period of operation but is delayed until unburned coal covers all of the air openings 'in the tuyre. In this manner, the air blast is rendered completely effective for promoting combustion of the coal and none of the air is lost by passing through openings in the tuyere which are uncovered by reason of the ash having been blown away. Since there is no substantial amount of air wasted by passing through uncovered tuyere openings, the operation of the burner is more efficient, the temperature of the furnace rises quicker and each operating period is correspondingly reduced.

solid fuel to said burner, means for supplying a blast of air to said burner, automatic means for intermittently operating said fuel and air supply means, and means responsive to an increase in temperature of the combustion gases for increasing the amount of air supplied to said burner.

2. In combination, a heating system including a furnace, a solid fuel burner for said furnace, means for supplying solid fuel to said burner, means for suppIying a blast of air to said burner, said air supply means being normally adjusted to supply less than thefull blast of air, means for intermittently operating said fuel and air supplymeans in accordance with the heat demands of a space to be heated, and means located in the path of the combustion gases and being responsive to increase in temperature of said gases full blast.

energized, and when the thermostatic 3. In combination, a furnace, a solid fuel burner for said furnace, means, for supplying solid fuel tosaid'jburner, means forsupplying a blast of air to-said burner, means for intermittently. operating said solid fuel and air supply means, a damper for normally restricting the Q ilt 01' air supplied to said burn'e electric means for operating said damper, and a thermal switch having a temperature responsive element located in the direct -path of the combustion gases and being responsive to increase in temperature of said gases to energize said electric means and increase the amount of air supplied to said burner.

4. In combination, a heating system including a furnace, a solid fuel burner for said furnace, means for supplying solid fuel to said burner, means for supplying a blast of air to said burner, said air supply means being normally adjusted to supply less than the full blast of air, means for intermittently operating said coal and air supply means in accordance with the heat demands of a space to be heated, means for periodically operating said coal and air supply means independently of the condition of said space to be heated, and a heat motor responsive to the temperature of the combustion gases in said furnace for increasing the air supplied to said burner.

5. In combination, a solid fuel burner comprising a tuyere provided with air openings therein,

means for supplying solid fuel to said burner to cover said openings, means for supplying a blast of air through said openings, means for intermittently operating said 'coal and air supply means, whereby during the shut-down periods the fuel burns out above certain of said openings, means operative upon each starting of said fuel and air supply means for restricting the amount of air supplied to said burner while said fuel feeding means supplies sufficient fuel to said burner to displace the ash from above the air openings in said burner, and means located in the direct path of the combustion gases in said furnace and being responsive to increase in the temperature of said gases for increasing the amount of the air supplied to said burner.

6. In combination, a heating system including a furnace, a solid fuel burner for said furnace, means for supplying solid fuel to said burner, means for supplying a blast of air to said burner, said air supply means being normally adjusted to supply less than the full blast of air, means for intermittently operating said coal and air supply means in accordance with the heat demands of a space to be heated, means for periodically operating said coal and air supply means independently of the condition of said space to be heated, means responsive to the temperature of a portion of said heating system heated by said burner, and being operative upon increase of temperature thereof for increasing the amount of air supplied to said burner.

ERNEST T. SELIG, J R.

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