US2103913A - Stoker control and method of maintaining desired fuel bed resistance - Google Patents

Description

Dec. 28, 1937. H. s. MORTON I 2,103,913

STOKER CONTROL AND METHOD OF MAINTAINING DESIRED FUEL BED RESISTANCE Filed May 16, 1934 3 Sheets-Sheet 1 00 0000000 OOOOOOOOOOO OOOOOOOOOOO OOOOOOOOO OOOO ' Harald s. Morton 32% jyah Dec. 28, 1937. MORTON I 2,103,913

STOKER CONTROL AND METHOD OF MAINTAINING DESIRED FUEL BED RESISTANCE Filed May 16, 1954 s Sheets-Sheet 2 Harold .S. Jitorian/ Dec. 28, 1937. H. s. MORTON 2,103,913

STOKER CONTROL AND METHOD OF MAINTAINING DESIRED FUEL BED RESISTANCE Filed May 16, 1934 3 Sheets-Sheet 3 AIR DUCT FAN INLET OVER FIRE m DUCT FAN INLET OVER FIRE Elma/whoa,

Harald 5'. Mar

Patented Dec. 28, 1937 STOKER CONTROL AND METHOD OF MAIN- TAININ G DESIRED ANCE FUEL BED RESIST- HaroldS. Morton, St. Paul,'Minn.

Application May 16, 1934, Serial No. {725,930

4 Claim;

This is a device adapted to provide automatic control of fuel feed and operates by'changes in the resistance of the fuel bed to the air flow, whereby it is possible to maintain constantly the desired fuel bed resistance in astoker.

My invention relates to an improvement in stoker control comprising a method of regulating the feeding of fuel ina stoker so that the fuel is replenished as fast as it is consumed in order to maintain the fuel bed resistance at the most efiicient point. 6 v

A further feature of the invention is in means of effecting such control in accordance with the changes of resistance of the fuel bed to theair flow. Thus when the flow of air through the tuyeres or grate of the stoker changes, my automatic control regulates the feeding of fuel so as to automatically maintain the fuel bed sufficiently' built up to provide the resistance most desirable for the fire for which the controller is .set.

By this means of automatically controlling the fuel feeding in a stoker, I am able to continually maintain higher eiilciency in burning fuel than 5 is possible with hand regulation. Further, by eliminating the human operation in the feeding control of a stoker, prevents unskilled operators from wasting fuel or possibly actually damaging the stoker.

My automatic control of the fuel feeding means provides automatic correction of manual adjustments, reduces cost of stoker construction by permitting the use of a single feeding rate intermittently instead of using a gearset or other means of providing a multiplicity of feeding rates, and further, has the advantage of restoring the 'fuel bed to'normal after hours of idleness after. which the fire has burned down low, by feeding at the maximum rate until resistance reaches normal. Further, my automatic control may operate in the maintenance of normal fire during periods when the stoker fan is not running by causing the stoker feed to operate intermittently when the fire is burned down by natural draft.

In the drawings forming part of this specification: I Figure l diagrammaticaliy illustrates my stoker fuel feed control associated with 'a" stoker and furnace.

method of effecting the control and is for the purpose of illustrating themanner in; which my method is carried out.

Figure 3 is a plan view of my controller.

' Figure 4 is a section elevation of the same.

Figure 2 diagrammatically illustrates the resistance. A change in the ratio of pressure Figure 5 diagrammatically illustrates the measurement of pressure differentials by inverted bells floating in liquid as an alternative construction of my controller in one form.

Figure 6 diagrammatically illustrates another 5 form of the use of the inverted bells similar to the principle of Figure 5, to be used to measure the pressure differentials instead of the other form of my controller.

The method of effecting this control is based on the fact that the flow of air through ducts or orifices or through fuel beds causes a drop in pressure which, ingeneral, is approximately proportional to the square of the rate of flow. A If two sections of the air travel have equal re- 15 sistance, the drop in pressure in one will be the same as the other regardless of the rate of flow. I

If one section has a resistance several times as great as another, the drop in pressure will be the same number of times greater whether rate 29 of fiow be large or small.

The fuel bed constitutes one portion of air travel in a stoker; but the same air that passes through the fire also enters the inlet of the forced draft fan and passes through the fan and 5 air duct and the windbox before it reaches the fire. Thus suppose that the air entering the fan passes a large orifice whose resistance is a small fraction of the resistance of a normal fuel bed, then the drop in pressure through this orifice will 3 be a small fraction of the drop through the fire.

This method of effecting this control is diagrammatically illustrated in Figure 2, wherein the furnace A is provided with the stoker B,

the windbox i0 and the air inlet duct l.l leading from the air fan l2. A motor l3 drives the airfan ii. The air inlet chamber to the fan I5 has air inlet openings i6. An indicator U-tube I'I is connected to the chamber l5. Further, an indicator tube 19 connected between theduct II and 40 the fire chamber 20 of the furnace A indicates the pressure differentials between the duct and the fire chamber.

The diagrammatic illustration of Figure 2 is for the purpose 01 indicating the pressure diiierentials to show the principles by'which mymeth- 0d is carried out. Thus, in my method it will be apparent that the ratio will remain constant regardless of the rate of airflow unless the condition of the fuel bed changes so as .to alter its drops is an immediate indication that the fuel bed resistance has changed, and this change in the ratio is made to operate the stoker feeding control in carrying out my method.

My controller C is constructed as illustrated in Figures 3 and 4, with the floating discs or pistons 2| and 22 which are connected to the shaft 23 and adapted to be arranged in a manner to measure pressure differentials. The larger disc 22 is subjected to atmospheric pressure on one side through the openings 24 under the hood 25. The other side of the larger disc connects with the windbox D through the opening 26 with the reduced pressure inside the chamber l5 which has an inlet orifice I 6 so as to feed air through the chamber l5 to the fan I. Thus the larger disc 22 is subjected over its entire area to a net difference in pressure equal to the drop in pressure caused by the inlet orifice.

The smaller disc 2| is connected on one side through the chamber 28 and through the flexible tube 21 with the air inlet tube leading from the fan H to the windbox l0, so that one side of the disc 2| is subjected to the air pres sure in the windbox l0 and the tube ll of the stoker. The other side of the disc 2| is connected through the chamber 29 and the flexible tube 30 to the pressure of the combustion chamber 20 of the furnace A. Thus the net difference in the pressure acting on the disc 2| is equal to the pressure drop through the fuel bed 3| because these two pressures. are the pressure below and above the fire, respectively.

Thus the connection of the discs 2| and 22 by total force acting on each disc will be the same and there will be no tendency to move either way. The controller C is constructed with a ratio of disc areas equal to the ratio of a normal fire resistance to an average size inlet orifice, such as IS. The inlet orifice l6 may be adjusted larger or smaller by the valve blades 32 than its average value or size, and if the ratio of resistance is maintained it will then be possible to have a fire lighter or heaviergthan normal as well as to maintain a normal average fire. The inlet orifice l6 forms the standard of comparison by which the fuel bed resistance isregulated and controlled, and to which it maintains a constant ratio of resistance, which ratio is established by the ratio of disc areas in the controller.

The control instrument C is most' conveniently located on or near the fan inlet box D and as hereinbefore set forth the larger disc 22 is subjected on the top to atmospheric pressure, and

on the bottom to the pressure inside the chamber 5. The lower side of the small disc connects through 'the flexible tube 21 to the windbox |IJ under the fire of the stoker B while the flexible tube 30 connects the upper side of the disc 2| to the chamber 20 above the fire of the stoker B. The shaft 23 is connected by the link 33 to the lever 34 which is pivotally mounted at 35. The weight of the two-discs 2| and 22 and the shaft 23 with the link 33 is balanced-by an adjustable counterweight 36 on one end of the lever 34. The lever carries a mercury electrical switch 31 which closes an electric circuit when the free end of the lever drops toward the rubber bumper 38 and opens the circuit when the lever moves up into normal or neutral position between the bumpers 38 and 39 in the position illustrated in Figure 4. The mercury switch 31 is adapted to control the fuel feeding screw or plunger 40 of the stoker B, the electric motor for operating the fuel feeder '40, not being illustrated in the drawings, so that when the switch 31 closes the circuit which controls the motor which operates the feeder 40, fuel is fed to the fire bed 3| on the tuyeres and grate of the stoker B and as soon as the circuit is opened the feeder 40 ceases to feed fuel.

My stoker control and method of maintaining desired fuel bed resistance is simple and effec tive in operation and provides a means of economically operating a stoker to secure the best efiiciency from the fuel fed to the furnace. In operation, when the fire resistance bears the correct ratio to the inlet orifice resistance, the upper force on the small disc 2| exactly balances the downward force on the large area of the disc 22. As fuel is consumed the fire resistance decreases so that the pressure drop through the fire exerting an upward force on the small disc 2| becomes proportionally less than the pressure drop through the inlet orifice l6 which exerts a downward force on the large disc 22. The re suit is a downward movement of both discs 2| and 22 whichtilts themercury switch 31, closing the circuit which operates the coal feeding member 40 or any other suitable mechanism for feeding fuel to the stoker B.

When coal has been fed to the fire faster than it is burned, the thickness and'resistance of the fire increases until it equals and finally exceeds the established ratio to the inlet resistance and the controller C is operated by upward force on the small disc 2| to a point exceeding the downward force on the large disc 22 which moves both of --the discs to bring the lever 34 back into the normal position illustrated in Figure 4, which immediately breaks the circuit in the switch 31 and stops thefuel feeding operation.

As the fuel burns away the fuel bed resistance is decreased and the cycle of operation is again repeated being automatically controlled in the starting and stopping of the fuel feeding means by the controller C. The controller C may be very accurately constructed with light moving parts so that very small changes in pressure are suflicientto move the discs 2| and 22 operating the lever 34 so that the fuel feeding means starts and stops at short intervals with such small variation in fire condition in the furnace A that they can scarcely be noticed. Thus I provide a controller C which is far more accurate and by which a greater efliciency can be attained than the most skillful operator, even though the operator constantly watched the fire and endeavored tokeep it uniform by manual control.

When the stoker is installed with my controller C the erector adjusts the size of the inlet orifice until the control produces a fire thickness and resistance which gives the greatest efliciency and the best results from all standpoints, after which no further adjustments are necessary as the controller automatically regulates the stoker fuel feeding means. Should it ever be desired to maintain a heavier average bed this can be done by reducing the area of the inlet l6 by the valve blades 32. If a lighter fire is desired at any time the inlet can be increased by opening the valve.

With my controller it is possible that instead of,

resistance maintained at a higher value when burning fuel at the maximum rate than when burning fuel at slower rates. If this is the case, instead of exactlybalancing the weight of the discs and connecting members with the counterweight, the counterweight is adjusted to make it a little heavier than the discs and connections so that it takes a definite excess of downward pressure to swing the control to the feeding position. The result will be that'the fire has to be thinner at low burning rates and low rates of airflow in order to produce a sufiicient force'to overcome the excess counterweight and start the stoker, than at high burning rates when airflow and air pressures are greater.

Should the opposite condition be desired, viz., maintaining a lower average resistance at high burning rates than at lower, this can be accomplished by adjusting the counterweight at a position to be a little lighter than the combined weight of the discs and connections. It will then be obvious that at low burning ratesit takes a thicker fire to develop enough excess pressure to stop the fuel feeding means than it does at high burning rates. The burning rates lierein discussed are controlled by an adjustable damper E at the inlet of the fan ll which limits the total flow of air through the system without in any way effecting the relationship between the pressure drops through the inlet orifice and through'the fire which are used to control the fuel bed.

Thus it is apparent from the foregoing that a particular form of controller is provided to carry out my method of controlling fuel feed in a stoker as herein specified to maintain constantly the desired fuel bed resistance. It is also apparent that the same principle of operation would apply if the drop in pressure between the fan and the windbox were used instead of the drop at the inlet orifice, or if an orifice were introduced into the pressure duct and the difference in pressure between its two sides applied to the larger disc 22.

To decrease the sensitiveness the lever counterweight 36 may be raised by the adjusting screw 42. The adjusting screw operates to raise or lower the yoke 43 which supports the adjustable counterweight 36 on the screw 44. The lever 34 is delicately balanced on the adjustable pivoting points 35 so that the instrument C may be adjusted to be very sensitive tothe operation of the disc pistons 2| and 22.

' I have illustrated in Figures 5 and 6 a means whereby the differentials may be measured by inverted bells F and G or H and I, floating in liquid instead of the discs 25 and 22. The discs in the controller C serve as pistons without friction due to the fact that there is a slight clearance around the same so that the discs do not touch the walls of the cylinders in which they move. While I have not shown the same, it is apparent that the ratio of pressures might be established by balancing with the lever or adjustable lever arm means or by having discs or bells of different areas and the standard of fuel bed resistance might be altered by varying the ratio 'ing on the area of the plate creates a pressure tending to move it in the direction of flow. The balancing of this force against the force of air pressure which acts on the fire constitutes another variation in the application of this method of fire control. It is also apparent that the use of any or all of these various ways of balancing the two pressure drops against one another at any given ratio, may be used with electrical control, such as the switch 31 and other electrical controls of common knowledge, not shown, or may engage directly with a mechanical pneumatic or hydraulic form or relay device for operating the fuel feed.

Further, my method clearly discloses that by employing a connection from the controller C to the combustion chamber above the fire, the use of the controller is not confined to the time when the forced draft fan I4 is running. It is possible also to use it when fuel is being burned by natural draft. The chimney draft which acts on the fire, acts also on the control, and theinstrument or controller C issensitive enough to start and stop periodically under very small pressure differences which prevail when natural draft is used. When so employed the control will keep a banked fire up to normal indefinitely. If the control is shut off when the fire is banked so that the fire burns down badly, the control nevertheless, acts to restore the fire to normal in the shortest possible time when the stoker is started; and thereafter will maintain it at normal as long as operation continues.

The method consists in providing a controller extremely sensitive to the change of pressure differentials over and under the fire bed as well as the change of pressure differentials of the atmosphere and the draft inlet to a furnace to automatically operate the fuel feeding means to maintain constantly the desired fuel bed resist- .ance to secure as near as possible the most perfect controlling means for a stoker fora furnace without manual control.

While the apparatus and method described sets forth certain structure and principles to be carried out, the same should be defined within the scope of the following claims:

I claim:

1., In a fuel feed control for stokers and the like comprising, a large disc subjected to atmospheric pressure on one side and to. reduced pressure inside the air inlet orifice of thestoker fan or draft on the other side, a shaft for fioatingly supporting said disc, a smaller disc mounted on said shaft subjected to the pressure in the windbox of the stoker on one side, and to the pressure of the combustion chamber on the other side, and an electric switch connected to said shaft controlling the operation of the fuel feeding mechanism operable by the movement of said discs and shaft; whereby the change in pressure differentials acting on said discs will control the feeding of fuel to a furnace.

2. A stoker control for regulating the feeding of fuel to a furnace to maintain the desired fuel bed resistance including, a pair of 'fioating discs, one of which is connected on one side to the pressure of the outer atmosphere and on the other side to the draft inlet passageway or chamber of the furnace, the other of said discs being connected on one side to the windbox of the stoker of the furnace while the other side of said disc is connected to the chamber above the fire in the furnace, means supporting said discs in spaced 'relation, and operating means connected to said supporting means which is adapted to start and stop the fuel feeding means of the stoker carried by said floating disc means to cause the fuel feeding means to be started and stopped in accordance with the change in pressurediflerentials on said discs by any change in the fuel bed resistance of the furnace.

4. An electric stoker control adapted to maintain a predetermined fuel bed resistance in a furnace, having an electric switch to operate the fuel feeding device, counterbalanced floating air pressure sensitive means adapted to operate said switch into open and closed position, said means including a pair of elements adapted to be influenced by the air pressure under and above the fire to operate in one direction, and an element sensitive to atmospheric and air pressure at the orifice of the draft urging said counterbalanced element in the other direction, said counterbalanced element being adjusted to a neutral position when the fuel bed resistance is at normal and adapted to move into position to operate said switch when caused to move out of neutral position by a change in the fuel bed resistance.

- HAROLD S. MORTON.

Images