US2226923A

US2226923A - Control for fuel feeding apparatus

Info

Publication number: US2226923A
Application number: US225119A
Authority: US
Inventors: Bertram J Cross
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1938-08-16
Filing date: 1938-08-16
Publication date: 1940-12-31
Anticipated expiration: 1957-12-31

Description

Dec. 31, 1940. B. J. CROSS 2,226,923

A CONTROL FOR FUEL FEEDING APPARATUS Filed Aug. 16, 1938 FURNHCE 15 FH N @1. EX HHUSTER d 67 T0 MOTOR23 58 Q J T0 MOTOR 24 H? 0!? OIL PUMP Q .4 1 I Z 7 I CONTROL LINE (FLUID PRESSURE) v 52 18 INVENTOR ATTORNEY lie e 219% CQNTROL FORFUEL FEEDING APPARATUS Bertram .ll. Cross, Grand View, N. Y., asaignor to Combustion Engineering Company, llnc., New

York, N. Y.

Application August 16, 1938, Serial No. 225,119

' 3 Claims.

This invention relates to fuel feeding apparatus and particularly to apparatus for controlling the feeding of pulverized fuel to a furnace wherein it is burned.

In carrying out the present invention, as shown in the illustrative embodiments disclosed herein, raw coal is withdrawn from a storage bin by a feeding means and suppliedto a pulverizing mill from which a part of the pulverized coal is carried on a stream of air directly to the burners in the furnace of a steam generating boiler. The

' remainder of the pulverized coal passes to a cyclone separator and the separated coal is discharged into a reservoir from which varying quantities are withdrawn by a feeder, as from time to time required, and fed into the stream of coal and air supplied to the burners in order to provide the amount of coal required to maintain the boiler load. The coal is withdrawn from the reservoir at the same rate that it is delivered into the separator, excepting during sudden changes in the furnace demand for coal, whereupon the rate of coal withdrawal from the feeder temporarily exceeds or recedes from the rate at which coal is then being delivered to the separator to meet, respectively, the increased or decreased furnace demands;

A feature of the present. invention resides in automatically regulating the rate of fuel withdrawal from the reservoir by means responsive to the furnace demand for coal and in turn automatically regulating the rate of coal supply to the pulverizing mill by means responsive to the weight of coal present in the reservoir.

The invention will best be understood upon consideration of the following detailed description when read in conjunction with the accompanying drawing in which;

Figure 1 is a diagrammatic elevational view of a coal feeding system embodying the invention and supplying coal to the furnace of a steam generating boiler;

Figure 2 is a detail view showing another form of control apparatus which is applicable to the coal feeding system of Figure 1.

In the drawing the numeral l0 designates a coal storage bin from which raw coal is wit drawn by a suitable feeder H and supplied to the pulverizing mill l2. From the mill I 2 the pulverized coal is carried on a current of air b means of an exhauster device driven either with the mill H2, or by a separately driven exhaust r 9 as indicated in Figure 1. The coal laden air discharged from the exhauster is in part passed through the conduit l3 directly to the burner or .time to time required and fed into conduit l3 burners ll of the furnace l5 while the remainder passes through the branch by It to a separator ii. In the separator I! the pulverized coal is separated from the carrier air and discharged into a. reservoir iii, the air from the separator together with any fine coal'dust being fed into the furnace through the pipe 20. -As the load upon the boiler fluctuates, varying quantities of coal are withdrawn from the reservoir l8 as from by a feeder 2i via a pipe 22, thus instantaneously regulating the amount of coal in the mixture supplied to the burners.

Many types of variable speed mechanism may be interposed between a driving engine or motor and the feeders I! and 2| for operating them at varying rates. However, for simplicity of illustration these feeders are shown as driven by

electric motors

23 and 24, the speed of which may be varied by regulating the amount of elec- 20 trical resistance in the motor circuits.

The variations in the speed of motor 24 driving thefeeder 2| which withdraws coal from reservoir [8 may be affected by various types of mechanism responsive to fluctuations in the load on the boiler.

As an example, the control apparatus of Figure 1 embodies a bellows 25 responsive to pressure in the steam main 26. The bellows is connected to a pivoted lever 21 so that as the steam pressure rises and falls the amount of resistance 28 included in the circuit of motor 24 may be varied to regulate its speed and hence to cause withdrawal of more or less coal from the receiver [8 to add to the amount supplied by mill l2 to the burners as required by the load fluctuations on the boiler.

Receiver I8 is shown as resiliently mounted on a support 30 by means of springs 3i so that the reservoir may rise and fall in accordance with variations in the amount of coal stored therein. Where the feeder 2| and separator I! are attached to the receiver l8 it is desirable to provide flexible conduit parts 32 in the conduit I3 and between the separator l1 and reservoir l8 to permit the movements of the reservoir and feeder which result from changes in the weight of coal within the reservoir. As the quantityof coal in the reservoir varies it rises and falls and this movement is communicated to a lever 33 which regulates the amount of resistance 34 that is included in the circuit of the motor 23 driving the feeder H with the result that the feeder ll is driven at varying speeds to supply the mill H2 in accordance withthe weight of coal in the reser- 55 voir l8. Initially the feeder ll may be set by a control 35 for motor 23 to operate at a speed corresponding to the amount of coal required for average boiler load, in which case the variations 5 need only be adjusted for by the control 33 and 34 responding to changes in Weight of coal in the reservoir I8. If the coal in the reservoir reaches a predetermined high limit, the feeder may be stopped entirely.

The operation is as follows: An increase in the demand upon the furnace causes an-increase in the speed of feeder 2|, immediately resulting in an increase in the amount of coal supplied to the furnace. The increased withdrawal of coal from reservoir l8 causes its weight to decrease and thus cause the mill feeder H to increase its speed.

The increased rate of supply to mill |-2 by feeder (after an interval depending upon the lag characteristic of the mill),, will in .time result in an increase in coal density (i. e. in the amount of coal in the mixture of coal and air) delivered to the branch l3 and thence to the burners M. This increase in coal density in branch I3 will cause a temporary overfeed of coal to the furnace and a corresponding load increase to an overload, which overload, however, will be compensated for by a reduction in speed of the feeder 2| actuated by the

automatic control

25, 21, 28 responding again to fluctuation of the furnace load. The 30 coal reservoir 3 being still low in coal weight maintains an increased coal supply from the mill I through conduits l3, IE, but as reservoir l8 fills due to the decreased withdrawal of coal by the feeder 2| the coal supplied to the mill by feeder Hand the delivery from the mill slows up, and upon refilling the reservoir a .new balance is established. A corresponding inverse cycle occurs when the load demand decreases.

When the primary control is on feeder 2| this 40 control 'should be more sensitive than that of the mill feeder so that when the load fluctuates rapidly the mill speed need not be changed but it will operate at a speed corresponding to the average load. a One feature of this combination of apparatus is that it greatlywidens the range of loads that may be carried on the furnace. High loads of short duration, that is, loads requirin amounts of coal in excess of the capacity of mill |2, may be carried by reason of the storage of fuel in the reservoir I8. Also very low loads may be car- 1 ried which would be impossible to maintain in the event that the mill |2 were directly connected to the furnace without the intervening reservoir and feeder. At times of low load the mill may be shut down entirely for considerable periods and the burners supplied with fuel from the coal stored in reservoir 8. The primary air may then be supplied from the mill exhauster if the latter is separately driven, as shown in Fig. 1.

In accordance with the invention the speed of both mill feeder l and the feeder 2| may be changed simultaneously by controls responsive to the furnace load and a secondary control appa- 6 ratus responding to the weight of the coal in the This pressure differential is transmitted by means of bellows 3|, 42 to a lever 43 associated I witha section 44 of the rheostat resistance 28 for motor 24. The arrangement is such that as the steam flow increases part of the resistance 5 44 is cut out of the motor circuit. If then, the steam pressure falls, the

pressure control

25, 21 supplements the flow control 4| 42 and causes a further increase in the speed of the motor 24 for feeder} An increased rate of coal withdrawal 10 corresponding to the increased steam flow is maintained by the reduction in resistance 44 caused by-the control 4|, 42 actuated by the steam flow. When the steam pressure is reestablishedlever 21 returns to normal and the 15 control 4|, 42 actuated by the steam flow holds "the motor 24 at the new speed so that the rate of coal supplied to the burners corresponds to the increased load on the boiler.

The pressure differential between points H and 0 h is' simultaneously communicated to another pair of

bellows

45, 46 acting on a lever 41 associated with a section 48 of the rheostat 44 for motor 23. Consequently, as soon as a change in the rate of steam flow occurs motor 23 also speeds up 25.

and the supply of coal to the mill I2 is increased instead of awaiting a substantial decrease in the weight. of coal in the reservoir I8 to act through lever 33 to increase the coal supply to the mill.

Inasmuch as the action of the coal feeding ap- 0 paratus is similar when the control apparatus of Figure 2 is employed, only a diagrammatic illustration of the control apparatus and the directly related parts of the system appears in this figure. In this form of control apparatus any suitable 35 fluid such as oil or air is maintained under pressure in a pressure line 50. Included in this line are needle valves 5|, 52 regulating the supply of pressure fluid to the cylinders of pistons 53, 54. Between these valves and the piston cylinders 40 are ports 49 open to the atmosphere so that there is a constant leak of pressure from the system at these points. Accordingly, as the opening of valves 5| and 52 permit the pump to force fluid through the lines 50 at a rate greater than the 45 venting capacity of the ports 49, pressure will be built up in the piston cylinders in proportion to the amount of opening of the valves. The piston 53 is connected to the regulating

members

55, 56 forboth resistances 51, 58 provided for motors 50 23 and 24 respectively. As needle valve 5| is operated inresponse to fluctuations of the load on the boiler the motor 23 for feeder speeds up increasing the rate of supply of coal to mill l2 simultaneously with increase in the rate of with- 55 drawal of coal from the reservoir l8 by feeder 2| as motor 24 speeds up. The needle valve 52 connected by alever 6| to the coal reservoir and piston 54 is connected to the mounting 62 for resistance 51 so that as needle valve 52 is opened 60 or closed upon change in the weight of coal in the reservoir l8 the resistance 51 is moved bodily about pivot 63 with respect to member 55. As a result, the speed of motor 23 for the mill feeder is again augmented to still further increase the 65 rate of supply to the mill, or decreased to lessen the rate of supply of coal t6 the mill all in accordance with the weight of coal in the reservoir With both the arrangements shown in Figures 1 and 2 where the rate of coal supply to the mill and the rate of withdrawal from the reservoir respond simultaneously to changes in load on the boiler an increased milling demand is anticipated rather than waiting for such a demand to be evidenced by a lower weight of coal in the reservoir l8. The secondary adjustment of mill speed re= sponding to the weight of coal in the reservoir then operates to prevent an oversupply of coal to the reservoir or compensate for an undersupply to the mill.

It should be noted that inasmuch as the additional coal required upon rises in the boiler load is drawn from the reservoir 88 the response to a change in load is prompt. The increased amount of coal reaches the furnace quickly and therefore avoids a further substantial drop in steam pressure or delay in meeting the load demand after initiation of the control such as would be, occasioned due to a lag between feeding of an increased amount of coal to the mill l2 and its delivery to the burners id as would be the case tween a change in the rate of the raw coal fed to the pulverizing mill and the delivery of powdered coal at a corresponding rate to the furnace; In all coal pulverizers there is a certain circulating load of partly ground coal in the mill which varies in amount with the rate of grinding. When the rate of feed of raw coal to the mill is changed, the circulating load of partly ground coal in the mill must reach an equilibrium corresponding to the new rateof feed before the mill discharges pulverized coal at a uniform rate. This lag due to the variable circulating load varies for mills of different design. It is' more pronounced when the coals are moist and must be dried in the mill as it is being pulverized. In some mills this time lag is as much as fifteen minutes; In the invention herein described this time lag which temporarily causes insufficient deliv-- ery of fuel is eliminated. Conversely, upon a fall in load the amount of coal supplied to the burners is promptly decreased and thereby avoids a further substantial rise in steam pressure beforethe control is effective to correct for the change'in load conditions. At the same time the control of the rate of feeding of raw coal to the mill in response to variations in the quantity of pulverized coal in the reservoir assures maintenance in the latter of a quantity adequate to meet rises in load as they occur, the reservoir holding aquantity of coal alone sufficient for operation over a short period as, say, for thirty minutes. This also prevents loss of the fire in the furnace due to temporary discontinuance of the supply of the mill as a result of the plugging of the conduit through which coal passes from the latter to the storage bin.

What I claim is:

1. In a coal feeding apparatus for the furnace of a boiler having a storage bin for raw coal, a pulverizing mill, means for feeding raw coal to said mill, a conduit for conveying pulverized coal from said mill to said furnace, a coal reservoir, a branch pipe leading from said conduit to said reservoir for storing therein part of the coal pulverized by said mill, and a coal feeder for withdrawing pulverized coal from said reservoir and supplying it to said furnace; means for regulating the operation of said coal feeding means; means for regulating the operation of said coal feeder; and means responsive to the load demand on said boiler arranged to control both regulating means so as to simultaneously vary the amount of coal supplied to said mill and the amount Withdrawn from said reservoir.

2. In coal feeding apparatus for the furnace of a boiler having a storage bin for raw coal, a pul-= verizing'mill, means for feeding raw coal to said mill, a conduit for conveying pulverized coal from said mill to said furnace, a coal reservoir, a

drawing pulverized coal from said reservoir and supplying it to said furnace; means for regulating the operation of said coal feeding means; means for regulating the operation of said coal feeder; and means responsive to the load demand on said boiler arranged to control both regulating means so as to simultaneously vary the amount of coal supplied to said mill and the amountwithdrawn from said reservoir; and means responsive to the quantity of pulverized coal in said reservoir arranged to control said coal feeding means to vary the amount supplied to said mill.

3. In coal feeding apparatus for the furnace of a boiler having a storage bin for raw coal, a pulverizing mill, means for feeding raw coal to said mill, a conduit for conveying pulverized coal from said mill to said furnace, a coal reservoir, a branch pipe leading from said conduit to said reservoir for storing therein part of the coal pulverized by said mill, and a coal feeder for withdrawing pulverized coal from said reservoir and supplying it to said furnace; means for regulating the operation ofv said coal feeding means; means for regulating the operation of said coal feeder; and means responsive to the load demand on said boiler arranged to control both regulating meansso as to simultaneously and correspondingly vary the amount'of coal supplied to said mill and the amount withdrawn from said reservoir; and means responsive to the quantity of pulverized coal in said reservoir arranged to control said coal feeding means tovary the amount supplied.