US2003985A - Fuel control system - Google Patents

Description

June 4, 1935. F. o. WALLENE 2,003,935

FUEL CONTROL SYSTEM Filed Feb. 19, 1.931

ATTORNEY Patented June 4, 1935 c v I UNITED STATES PATENT OlFiFlCEv FUEL CONTROL SYSTEM Frank O. Wallene, Lakewood, )hio Application February 19, 1931, Serial No. 516,937 g 4 Claims. (01. 110-103)- This invention relates to the-control of the fed to the crusherlll from a' hopper l2 by a fuel supplies of both fuel and air to a furnace operated feeding motor I3, which can operate any sort of with pulverized coal or other similar fuel. In. feeding device lid of such character that the such furnaces the raw coal, in theform of slack rate of inflow of coal from the hopper I to the or larger sizes, is often pulverized just before it crusher It! depends upon the speed of operation enters the furnace and it has been customary, to of motor l3. As shown, the motor shaft I3, control both the air supply and the fuel supply in through worm gearing, operates a drive shaft l3b accordance with variations in steam pressure, connected to operate the feeder l3a. Coal is fed for the purpose of maintaining uniform steam to hopper l2 from bunker H in any' suitable in pressure. manner. v

The object of the present invention is to pro- It is customary, in the operation of systems of vide an improved control system in which, upon a this kind, to utilize some device subject'to presvariation in some factor of boiler operation de-' sure of st am in t boi r. f controlling ot sirably maintained uniform, such as steam presthe device, s h as damper which regulates h g sure, a correcting influence is imparted to the pp and the dev tsuch a o 3, 15 control system and the effect thereof is transwhich regulates the fe d of coal from the hop mitted to the devices for governing the delivery I! o the Crusher, but h Systems r 1 1 l y of both-air and coal to the furnace, so that the f t ry. The reason is that upon an insupplies thereof are varied more nearly in strict crease in the steam pressure, Such nd proportionality in such manner as to maintain reduction in fuel a d 8 supplies, both the 20 proper and efilcient combustion conditions under a p d motel e immediately l all circumstancesthereby avoiding, particularly Simultaneously adjusted to Produce a n w 1 during a change in feeding conditions, either dition. Adjustment of the damper Sdoes actualover-supplyof coal as compared with air and the 1? immediately vary the upp y- A justment consequent production of smoke and CO and loss, 01 r to decrease its p however. does of efliciency on the one hand, or, oppositely, an n imm y reduce the inflow pulverized under-supply of coal as compared with air and fu l o the furnace, ue to the f hat the the consequent loss of efficiency, as well as the cr already contains n only the fuel possibility of blowing out the fire on the other already pulverized, but pp in the PIOOeSS hand. of being pulverized and ready for such action, 30

Further objects of the invention are in part 80 that even er Spe d of motor I3 is actually.

obvious and in part will appear m r i d t il reduced the responseis not felt in the furnace hereinafter. chamber until some time later, due to the neces- In the drawing, the view represents somewhat' sity for first consuming the excess of fuel on hand diagrammatically one embodiment of appar tus in the crusher. As a result, for some time there 35 embodying the invention. is an excess of fuel over air, with a consequent A portion of the wall. of the combustion cham- Prqduetieh, 01 C0 and black Smoke and the 1068 her of the furnace is conventionally indicated 01 emeiehey- Likewise, 119011 a duction in at l. Through it extend one or more burners 2 steam pressure, which should be met with an in- 40 communicating both with the air supply conduit crease in the amounts of both air and fuel, the 40 I and with a conduit 4 through which is conair supply is actually changed immediately, but ducted the pulverized fuel, which is usually 9.0- the coal supply entering the furnace chamber complished by the blowing effect of what is called does not experience an increase until some time the primary air. Any number of burners may later, because increasing the speed of the motor be employed, but the drawing shows one for siml3 does not immediately increase theamount of 45 plicity of illustration. The air supply through fuel passingfromthe pulverizer to the furnace. the conduit 3 is governed in any suitable manner, As a result, under these conditions there is an such as by a damper 5 having an arm 6 actuated excess of air over fuel, with the usual loss of through-a link connection 1 by an arm 8 on a efficiency and the possibility of actually blowing 5o reversible electric motor 9. The fuel supply, in. out the fire.

pulverized form, comes through the conduit I" My invention aims toovercome the, objections from a suitable crushing device conventionally to these prior control'systems by subjecting the indicated at Hi, the crushing mechanism therein devices forcontrolling the supplies of bothair (not shown) being operated by a motor II. Raw and fuel to the influence of a device sensitive to i 56 coal, in the form of slack or even larger sizes, is that: factor of furnace operation which it is ,de-'

sired to maintain uniform, such as steam pressure, but at the same time to correlate the two sets of feed controlling devices, to wit, the air supply controlling device on the one hand and the fuel supply controlling device on the other hand, so that the quantities of air and fuel are always in proper proportion to each other. That is to say, upon either an increase or a decrease in steam pressure the quantities of both air and fuel are decreased, but always in step with each other, so that the relative proportions of the two do not vary even while conditions are changing. This I accomplish by making the control system sensitive to a factor which is more nearly, or indeed,

may be said to be almost exactly proportional to the actual rate of flow of fuel from the crusher to the furnace chamber. The factor chosen for this purpose is the load on the motor or driver for the crushing mechanism. As a consequence, when the quantity g fuel being crushed in the pulverizer is large, the load on the crusher motor is heavy, and when the crusher contains a smaller amount of fuel the load on said motor'is reduced, and in all 'cases, whatever be the conditions existing or demanded, the rate of air supply is maintained at a value in step with the load on the crusher motor.

The drawing shows conventionally one control system for this purpose. As before, some means is provided by which a change in a factor of boiler operation desirably maintained uniform, such as steam pressure, for example, varies the speed of the fuel feeding motor l3; Many commercial control devices are obtainablein the open market to produce this effect. The drawing shows conventionally for the purpose an expansible bellows l5 which expands or contracts according to variations in boiler pressure conveyed to it throughthe conduit Hi. The movable portion of the bellows is connected to actuate a lever |l pivoted at l8 and biased toward the bellows 'by a tension spring IS, the movable end of said lever being suitably connected, as by a link 20, to the arm 2| of a rheostat 23 in the circuit from the supply leads to motor l3. Upon an increase in steam pressure lever rises andshifts the position of rheostat arm 2| and decreases the speed of motor l3, thereby reducing the rate of supply of coal from hopper |2 to crusher i0. Ultimately, when the influence of the change is felt at the boiler,

the steam pressure falls and a reverse influenceis reflected back through the control system. The parts act like a governor, with the lever ll always tending to return to a neutral position.

It will be observed that so far the only effect of rising steam pressure is to decrease the speed of the feeder motor |3. No immediate effect is produced upon the supplies .of either air or fuel entering the furnace, but these are adjusted or changed in step with each other later on, as will appear. a

Motor 9 is a reversible motor which is operated by the reversing switch mechanism generally indicated at 24. is operated in one direction or the otherto adjust the damper 5 toward open or closed position.

The new position of the damper produces a change in pressure at the bellows 34, with a consequent opening of the appropriate pair of contacts 42 and 43 on the one hand, or 42 and 44 on the other hand, as the case may be, thus ultimately stopping motor 9 and damper 5 in a new position. The switch mechanism 24 is made sensitive to the flows of both air and fuel by a suitable relay mechanism for the purpose. This resimilar to a D. C. watt meter.

Motor 9 is normally stationary andv As to the first of said instruments,-that responsive to the crusher or crusher driver,-said instrument will of course be of a character depending upon the type ofdriver used for the crusher. steam turbine, the first instrument of the relay mechanism would be made responsive to steam flow to the turbine, as will be readily understood. In the drawing, however, the crusher driver is an electric motor so that the first instrument of the relay mechanism is of electrical character. The relay mechanism includes a suitable support (notshown) on which are mounted the said electrical instrument A sensitive or responsive to the power taken by the motor II from the electric supply leads 25. This electrical instrument of course will be of a character suitable to the kind of current required for motor II. For an A. C.

system it will be similar to a polyphase or single For a D. C. system it may be In the arrangement shown, which is A. C. as regards motor H, the electrical instrument A includes a disc 26 carrying an arm 21 and influenced by coils 28, 29 supplied by current transformers, 3| associated with leads from the main line to motor M,

phase watt meter.

For example, if the crusher driver is a a and also two potential coils 32, 33 suitably connected to the line. The torque developed by the disc 26 is proportional to the amount of power taken from the supply. leads 25 by the motor H, and is balanced against the usualadjustable loading spring 26a.

The instrument B includes an expansible bellows 34 made to expand and contract according to the pressure conducted to it by the pipe 135 communicating with the air supply pipe 3 on the furnace side of the damper 5. The movable part of the bellows actuates a rack 36 connected to a pinion 31 with which rotates an oscillating arm 38, the bellows pressure being balanced against the usual adjustable loading spring 34a.

Arm 21 of instrument A is connected by a link 39 to arm 40 pivoted at 4| and carrying a double ended contact member 42 cooperating with two adjustable contacts 43, 44 on the arms of a yoke carried by a lever 45 also pivoted at 4| and working between the usual limit stops 45a and connected by link 46 to be operated by arm 38.

The center contact ,42 is. connected by a wire 41 to the center one of the supply leads, while the contacts 43, 44 are connected through coils 48, 43 of the reversing switch 24 to the other two wires of the system. These two coils 48, 49 separately actuate the switch parts 24a, 24b which connect the motor 9 up to the main leads 25, so as to cause rotation of the motor 9 in one direction or the other according to which switch part is closed.

The drawing in full lines shows all parts of the apparatus in neutral position, with the boiler operating at normal pressure. Assuming an increase of boiler pressure, the first effect is at the bellows l5, which expands and elevates lever arm I! pivoted at 3 to increase the resistance of rheostat 23, thereby decreasing the speed of motorl3. As before stated, motor I3, through a shaft l3b, operates a conventional type of feeder so constructed as to vary the amount of coal fed from hopper |2 into the crusher In in proportion to the rate of speed of motor l3. Therefore, reducvaried in step with variations inspeed of motor l3, with the result that when the speed of motor 13 is reduced too little air isadmitted to the combustion space for efllcient combustion, because it requires the elapse of a material length of. time for a'decrease in the quantity of coal supplied to the crusher to produce a decrease in the rate ofv flow of coalthrough duct 4 to the combustion.

space. vIn the present system, when the speed of motor 13 is reducedv in the manner stated, no immediate change is produced in the rate of air supplied to the combustion space. Such air supply is not reduced in quantity until the load on the driving motor H is reduced, Theload on the driving motor II is utilized as a controlling factor for the air supply becauseit' has been found from experience that thepowertaken by motor H is very nearly proportional to .the flow of fuel and carrier air through duct 4 to the combustion space. In the example now being described, steam.

pressure has risen beyond the desired normal and the speed of motor l3 has beenreduced. As soon as motor ll feels the effect of the reduced quantity of coal being supplied to the crusher and feeder l0, and therefore takes lesspower from the feed lines 25, the watt-meter element A with its disc 26 exerts reduced torque upon arm 21 about the center of disc 26, allowing spring 34a to pull lever 40 to the right, closing contacts 42, 44, and energizing coil 49 of the reversing magnetic switch 24. The consequenceis the closing of the switch parts 24b, connecting motor 9 tothe line in such manner that it slowly rotates lever 8 to the left in the drawing, moving damper 5 toward closed position, thus reducing the air pressure in the duct 3 and the communicating pipe 35 and bellows 34. Bellows 34 therefore partially collapses and, through rack 39 and pinion 31, moves arm 38 to the right, causing arm 45 and the contact 44 mounted thereon also to move to the right, thus opening contacts 42, 44 and de-energizing coil 49 of magnetic switch 24, opening the switch parts 24b and stopping further rotation of motor 9. Thus it will be observed that the element B, sensitive or responsive to the air supplied to the combustion chamber, acts as a restoring device or, more accurately, to terminate the regulating'or control operation with contacts 42, 44 open and the motor 9 stopped.

If steam pressure again rises, or rises further, the same cycle is repeated or continued until finally the parts come to rest in a position in which the rate of supply of fuel has been reduced at the feeder 13a and the damper 5 has been moved toward closed position, both to an amount sufficient to off-set the rise in boiler pressure. In the case of a decrease in boiler pressure opposite effects are produced in the sense that the first effect is a reduction in pressure at the bellows l5 with a lowering by spring l9 of the lever 11, areduction in the resistance of rheostat l3 and a consequent increase in the speed of motor l3. This immediately increases the rate of supply of fuel by the feeding device l3a. to the crusher and feeder Ill, but the effect of this increased rate of fuel supply is not felt at the motor II for a material period of time. Consequently, at first, there is no immediate adjustment of damper 5. However, when the load on motor ll increases, due to the increased duty of said motor in coping with the heavier load on the crusher and feeder,

the wattmeter element A responds'with an increased torque effect upon arm 21, moving it to the left in the drawing, and also moving arm 40 to the left, ultimately closing switch contacts 42,

'43. Closing of these contacts energizes coil 48,

closes switch 'elements 24a and again connects the motor 9 to the line, but in amanner to rotate it in the opposite direction from before, or in such manner as to rotate arm} to the right and moving damper 5 toward open position. This inlcreases theair pressure in the duct 3, in conduit 35 and in bellows 34, resulting in arms 38 and being .movedito the left, thus opening contacts 42 and 43 against the tension of spring 26a. This terminates the control operation which in the meantime, has adjusted both the fuel supply and the air supply sufficiently to meet the assumed decrease in boiler pressure;

Thus, the system is automatically accommo-' dating or self-adjusting to either increases or decreases in boilerpressure, in each case first adjusting the fuel supply and then, after the passage of a material period of time, also-adjusting the air supply to meet the new condition.

- Preferably,the electrical circuits to the motor 9 include travel limit switch devices which automatically open the circuits to saidmotor whenthe limit positions, open or closed, of the damper 5 are reached. As illustrated, a wire coming from one of the supply leads 25, is connected to the stationary contacts 5| of the two limit switches, each of which includes a spring contact 52, one of which is connected by a wire 53 to the coil 43 and the other by a wire 54 to the coil 49. The spring contacts are operated by an extension 8a of the motor arm 3. The arrangement is such that when the arm 9 approaches either limit of its motion the extension 9a engages one or the other of the spring contacts 52 and. thereby opens the motor circuit. This arrangement is a simple expedient to automatically open the motor circuit and limit its operation under any circumstances, particularly under unusual conditions, as when the circuit to the motor I I is opened for any reason, thereby deenergizing all of the coils 28, 29, 33 and 32, so that no influence of motor II can be effective in the control of motor 9. I

As a result of all of the foregoing, the several control devices conjointly function as a governor, each change of steam pressure producing an operation of the rheostat23 which controls motor I3, so as to change its speed and consequently to change the rate of supply of coal to the crusher Ill, and the air damper or controlling device is later adjusted in step with the change of power required for crushing and hence with the change in the rate of feed of coal to the'furnace, so that ultimately the rates of supply of both air and fuel to the furnace are adjusted proportionately in such manner as to restore the steam pressure to the original value at which it should be maintalned. This avoids any lack of proportionality between air and fuel and maintains eilicient combustion conditions at all times.

While the drawing shows the damper 5 ar-' ranged to control the flow of air to the furnace through a conduit 3 which is separate from that communicating with the crusher, it should be and should not be considered in any sense of limitation, because any arrangement which controls the supply of air to the furnace is satisfactory.

In these furnaces, the air supply is taken care understood that such illustration is conventional of in various ways.

arrangements are possible, but'in any event, the

system herein described will include a'motor 9 whose function it is to properly control the quantity of air supplied to'the furnace, wherever or whatever the air regulating device may be.

What I claim is: 1., In combination, a boiler furnace, fuel crushing and feeding means communicating therewith,

fuel supply means for said fuel crushing and feed-- ing means, air supply means for the, furnace, means responsive tovariations in a factor of boiler operation desirably maintained uniform for controlling said fuel supply means, and means re-V sponsive to the operating load of the fuel crushing means for controlling the air supply means.

2. In combination, a boiler furnace, fuel crushing andfeedingmeans communicating therewith, fuel supply means for said fuel crushing and feeding means, air supply means for-the furnace,

means responsive to variations in a factor of boiler operation desirably maintained uniform for controlling said fuel supply means, and means responsive both to the operating load of the fuel crushing means and to said air supply for controlling the air supply means.

3. In combination, a boiler furnace, fuel crushing and feeding means communicating therewith, variably operating fuel supply means for said fuel crushing and feeding means, a regulator therefor, air supply means for the furnace, a regulator therefor, means responsive to variations in a factor of boiler operation desirably maintained uniform for controlling the regulator for said fuel supplymeans, and means responsive to the operating load of the fuel crushing means for controlling the regulator for the air supply means.

4. In combination, a boiler furnace; fuel crush ing and feeding means communicating therewith,

variably operating fuel supply means for said fuel crushing and feeding means, a regulator therefor, air supply means for the furnace, a regulator therefor, means responsive to variations in a factor of boiler operation desirably maintained uniform for controlling the regulator for said fuel supply means, and means responsive both to the operating load of the fuel crushing means and to said air supply for controlling the regulator for the air supply means. I

FRANKO. WALLENE.

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