US2679979A

US2679979A - Boiler load control

Info

Publication number: US2679979A
Application number: US151650A
Authority: US
Inventors: Edward S Bristol
Original assignee: Leeds and Northrup Co
Current assignee: Leeds and Northrup Co
Priority date: 1950-03-24
Filing date: 1950-03-24
Publication date: 1954-06-01
Anticipated expiration: 1971-06-01

Description

BQILERLOAD- CNTROLA Filed March 2 4,- 1950 v --INVENTOR EVDWARDESBRISTIOL ATTORNEYS Filedl March 24, 195o 'I INVENTOR. v

Q SESE'. vom

"ATTORNEYS June 1, 1954 E S BRlSTOL 2,679,979

BOILER LOAD CONTROL v Filed March 24,- 1950 4 Sheets-Sheet 3 ATTORNEYS y I ,/QB INVENTOR. N EDWARD S. BRISTOL Patented `lune l., 1954 UNITED STATES PATENT OFFICE 13 Claims.

This invention relates generally to controlsystems for steam boilers and particularlyv 'to systems for controlling the flow of combustibles to the boiler furnaces. It is particular-ly useful in certain types of installations where, the absence of the invention, objectionable fluctuations inboiler output would result from variations in certain factors which,l for convenience, will be referred to asl fuel quality.

Steam boiler control apparatus has heretofore been devised for controlling the flow of. combustion air to the furnace for efficient combustionv o'f fuel. Control apparatus has been devised also for controlling the flow of fuel to the furnace to maintain substantially constant the steam pressure from the boiler. These systems are useful in single-'boiler installations Where the problem is` to maintain steam pressure under varying loads with good combustion efficiency. rEhe effect of varying fuel quality in a single-boiler ins-tallati'on merely is to' vary slightly the steam pressure, and the ow -of fuel then is corrected automatically in response to thisl slight change.

In certain important types of boiler control installations, however, it not feasible to rely upon variations in steam pressure alone to bring about compensation for varying fuel quality. r@ne exam-pleof such an installation is Where multiple boilers supply steam to a common load. In this case a change to poor fuel in only one boilerwould produce a cha-nge in the steam pressure of the whole system that would aifect all boilers alike causing a proportionate increase in fuel flow to all boilers. As are'sult the boiler receiving poor fuel would supply less than its intended share of the steam load. The principal object of the in'- vention is to so control the ow of fuel to the boilers of a multiple-boiler installation that each boiler supplies its predetermined share of the steam load regardless of ordinary variations in fuel quality at individual boilers.

Another example of a condition under which variations in steam pressure cannot be relied upon to control fuel flow is where it is desired to maintain constant the steam flow from an individual boiler. Suppose that one boiler in a inultiple-boiler installation has higher efficiency than others and that, therefore, it is desired to operate it continuously at its full-load capacity, fluctuatio'ns insystem load being met by other boilers. This boiler maybe disconnected from the steampressure control, as described more fully hereinafter, and connected to the equivalent of a constant-fuel-flow control thereby achieving constaat steam flow from the boiler if fuel quality does not vary.- To maintain constant the steam flow from sucha boiler despite varying fuel quality is another object of the invention.

To accomplish the 'aforesaid objects, in accordance with the invention, fuel fiow to a steamboiler .furnace is controlled in response to' two control quantities usually acting with different response times. The first control quantity, eX- empliiied by air-loading pressure as ameasure' of steam system load, by itself would cause the fuel flow to vary in response to slight variations in steam pressure,- such as are produced by changesin steam systei-n load, to maintain the steam pressure substantially constant by changing the rate of fuel feed in response to the changes in steam system load. The second control quanl tity, exempiied by the resistance of a rheostat,

automatically causes the' fuel flow to vary in response to any change in the relative value of this first control quantity andthe steam ilo-w from the boiler to maintain the proper relationship between steam system load and steam flow despite variations in fuel quality. Such a change in rela-- tive value' of the rst control quantity and steam now ordinarily would be clue to a change in' fuel quality, although it might be due to a change in other factors some of which are described vhereinafter.

Stated otherwise, the usual fuel control is provided for maintaining steam pressure having inherent therein a quantity that may be usedA as a measure of steam system load and an auxiliary fuel control is provided for maintaining a predetermined distribution of steam ow from the boilers. Steam flow is maintained constant despite variations in fuel quality when the air-loading pressure is constant;` the auxiliary fuel control operates only When steam flow fluctuates independently of air-loading pressure, as it would do when fuel quality varies. Such fiuctuation is measured by comparing the steam flow from the boiler, either directlyfor indirectly, with the first control quantity Whichmight be, in atypical case,-

air-'loading pressure. Any deviation from a predetermined relation b'etween these compared quantities due to varying fuel quality produces the second control quantity which adjusts the' fuel flow to compensate for the varying fuel quality.

Inasmuch as air i's a substantially constantheating-value component of combustion', it is supplied tothe boiler furnace' in proportion to the steam flow from the boiler in accordance with' invention. Since air flow is thus proportional 'to steam ow it may be substituted as a measure 3 of steam flow in the foregoing remarks without change of principle. Thus in accordance with another aspect of the invention, and as an object thereof, air flow, instead of steam new, is compared to the air-loading pressure to derive the above-mentioned second control quantity with resultant practical advantages to be described hereinafter.

Other objects and advantages of the invention will be apparent from the following more detailed description thereof with reference to the accompanying drawings, in which:

Fig. l is a diagrammatic view of a multipleboiler control system embodying the invention;

Fig. 2 is a more detailed diagrammatic view of a unit shown in Fig. l;

Fig. 3 is a fragmentary diagrammatic view of a modification of apparatus illustrated in Fig. l;

Fig. 4 is a fragmentary detail view taken substantially along the line 4-4 in Fig. 3, portions thereof being shown broken away;

Fig. 5 is a diagrammatic view of a modification of the unit shown in Fig. 2;

Fig. 6 is a vertical sectional detail view of a portion of the structure shown in Fig. 5;

Fig. 7 is a diagrammatic detail view of a portion of the apparatus shown in Fig. l

Fig. S is a fragmentary detail view taken along the line-B in Fig. 7;

Fig. 9'is a fragmentary diagrammatic detail view taken along the line 9-9 in Fig. 7; and

Figs. l0, 1l, and 12 are diagrammatic detail views of portions of the apparatus shown in Fig. 2.

Referring to Fig. l, boilers I0, II and I2 supply steam to turbine I3, or other suitable load, through a comm-on steam pipe or header I4. Master controller i6, described more fully hereinafter, regulates compressed air entering the system through pipe I5 from any suitable source, not shown, as a function of the steam pressure in header lil to produce a fluid pressure in pipe ita which is a measure of the steam demand or load on the multiple-boiler installation. The resultant compressed air, known as loading air in distinction from the combustion air mentioned hereinafter, controls the rate of feeding fuel to boilers I0, li, and i2 through loading valves 10a, Ila, and I2a, respectively; these loading valves are manually adjustable for apportionment of load as desired among the three boilers. Valves Ia, IIa, and 12a may be of any suitable well-known type, such as throttle-andbleed valves, adapted to produce individualboiler loading-air pressures of any desired mag- -nitude commensurate with the output loadingair pressure from master controller i6.

Fuel control units Ib, IIb, and IZb, described more fully hereinafter, normally supply fuel to boilers I0, H and i2, respectively, at a rate determined by the individual-boiler loading-air pressure from loading valves Illa, lia, and I2C. The relation between loading-air pressure and fuel flow at fuel control units Ib, IIb, and I2?) may be varied by auxiliary control units Ille, I ic, and I2C, described more fully hereinafter. The flow of combustion air through each of boilers I0, Il, and l2 is maintained proportional to steam flow from each boiler by dampers lcd, Hd, and I2d controlled by motors IIIe, IIe, and I2e, respectively, each of which is controlled by a steam-air unit if, Hf, or I2f, described hereinafter.

It will be understood that, as used herein, the expressions steam flow, air flow, and "fuel flow refer to the rate at which the respective substances pass toward or away from a boiler cr other point, and fuel flow is intended to apply to any form of fuel, whether solid or fluid, except where a specific form of fuel is indicated.

Referring to Figs. 7, 8, and 9 as exemplary of a suitable master controller, pipe Ita connects header Ed to Bourdon tube 1Gb which expands under steam pressure against spring 16o to actuate loading-air valve Id through push-rod Iie and lever 16j supported on pivot ig. Counterweight lh, Fig. 9, acting through lever I6f and push rod Ie opposes spring 16a so that extension under steam pressure of Bourdon tube liib is opposed by the net force of spring Ic and counterweight Ih and this net force may be adjusted by any suitable screw means ii by which spring Hic is anchored to frame member I6?" thereby adjusting as desired the midpoint of pressure about which controller IB operates.

l. Bourdon tube ib transmits force to push rod Ie through leaf spring Ik which yields under the contrastive force of Bourdon tube IBD when steam pressure is removed from pipe Ba without yielding, however, during the normal operation of controller i5.

Compressed air entering through pipe I5 is reduced in pressure, and thus converted to loading air, and applied to pipe Ic by valve Ib, Fig. 8, actuated by the cumulative effect of two forces applied to lever f. One force originating in Bourdon tube b tends to produce airloading pressure in pipe Ia having a pressure varying inversely with that in steam pipe Ilia.. As will be described more fully hereinafter the other force, originating in counterweight Ih, magnifies variations in loading-air pressure in pipe Ia according to the product of the duration and extent of deviations of steam pressure in pipe ita from a predetermined value, an effect known as reset action. As changes in system load produce changes in steam pressure, the loading-air pressure in pipe ita may be taken as a measure of system load.

When Bourdon tube ib expands in response to an increase in steam pressure in pipe Ilia, as would result from a decrease in system load, the right-hand end of lever IE, as viewed in Fig. 7, is tilted downward slightly to close by a slight amount Valve Ib thereby tending to reduce the air pressure in chamber |50 to which pipe I5a connects. Simultaneously cup I5d moving with valve i5?) permits air tc leak at a slightly increased rate through passageway E56 so that loading-air pressure in chamber 15e decreases in response to an increase in steam pressure 1n pipe Hic by the double effect of closing valve 65D- and increasing the leakage rate through passageway i5@ thus producing a substantial decrease in loading-air pressure with a very slightl increase in steam pressure.

Conversely, upon a decrease in steam pressure spring Ic predominates over the force from Bourdon tube ib slightly to open valve Ib and,

simultaneously to reduce the leakage rate through passageway 15e by moving cup 15d upward thereby increasing the loading-air pres-- sure. These changes in air-loading pressure effect changes in the fuel supply as mentioned above and more fully described hereinafter.

As thus far described the operation of master controller iii would provide a definite air-loading pressure and therefore a definite fuel flow for each value of steam pressure. The system normally would be so adjusted that this fuel flow would supply a normal demand for Ysteam at the desired 'steam pressure. Any `deviation from this demand, however, would require a corresponding change in fuel ow which might be brought about by 'an appropriate change, from that previously mentioned, in `the air-loading pressure for the particular steam pressure being maintained. IThis adjustment of fuel -iiow to maintain constant vsteam -pressure at varying boiler loads, as distinguished from the adjustment of fuel low -to meet varying fuel quality in accordance with the invention,is `known as reset action and may be produced bythe following-described reset means.

Referring to Fig. 9, loading air from pipe |5a is applied through valve |5f to storage tank |59 at --a VVrate depending upon the setting of valve |5f and -the diiference in pressure acrossit. The air pressure of storage tank |59 is applied to chamber 15h -of the master controller and 'to a mercury column |.5i therein to 'force the mercury col-umn downward thereby raising the opposite mercury column |57' to partially support, and therefore reduce the effective weight of, counter.- weight |6h. This reduction in the effective weight of counterweight |6h permits spring loc to further open valve |519. It is apparent that the pressure of air in storage tank |59, by reducing the 4eifective weight of counterweight |6h, will cause Bourdon tube |61) and spring |60 to be in equilibrium under a given steam pressure at a position 'of valve |51) and cup |5d which results in increased air-loading pressure in chamber |50 aldat pipe |501.

kAs mentioned., an increase in steam demand or load on the boiler results in a somewhat decreased steam pressure which increases the air-loading pressure in chamber |50. The further gradual increase in `air-loading pressure as air from chamber v|5c iiows through valve |5f into tank |59, and the consequent gradual increase in fuel flow -to the boiler, continues until the steam pressure returns to its proper constant value which actingthrough Bourdon tube |61) causes the pressure in chamber |5c to equal that in tank |59- whereupon reset action ceases, leaving fuel flow properly .adjusted for the increased demand as a result 'of increased air-loading pressure. On -a decrease in steam system load or demand this action is reversed. The final result of this reset action `is to adjust the air-loading pressure to compensate yfor variations in steam demand or total load on the steam boilers `or for `certain other Afactors that similarly change the fuel requirements for a predetermined steam pressure. It 4cannot, however, compensate for Varying vfuel quality at one particular boiler of a multipleboiler installation since it necessarily affects vall boilers alike, whereas, in accordance with the invention, individual `boiler steam flow also isv controlled.

Referring to Fig. 2, boiler l2 may be supplied with fuel from any suitable fuel supply means such "as, for example, coal pulverizer 'mill A portion of the combustion air for the furnaceof boiler |2, supplied by any suitable well-known source, such as blower lq, is blown through conduit lla to .pulve'rizer mill to carry the pulverized coal output thereof through conduit |.'b to boiler l2. The rate at which fuel is thus-supplied `to boiler |2 is determined by the speed at which feeder |lc is rotated by constant-speed motor ild through a variable-speed transmission such, forexample, as transmission 11e.

Variable-speed transmission fille comprises fa 6 cone -Ilf driven, directly or through any suitable reduction gearing, uby motor 11d, idler llg adapted to be moved along cone 1| 'lf by rotation vof worml 1h, and cone |11' arranged parallel to cone Il)c in contact with idler |'|g so that rotation Aof cone Hf rotates idler Ilg which in turn rotates cone Ilz' at a ratio determined by the vposition of idler Hg. Thus to vary the speedv of feeder |10 a :certain amount, it is yonly necessary to rotate worm I'h. a certain amount.

Rotation of worm Hh is accomplished by reversible motor lly controlled as described hereinafter. The speed fof feeder llc, and hence lthe rate .at which Vfuel flows to -boiler I2,-is measured by tachometer generator Ilk rotatably connected thereto and adapted to .generate an output'voltage proportional to its speed of rotation. Such generators are well `known and need not 'be described further herein.

Fuel feeder Vllc rotates within housing Ilm which is A'so .arranged that movement of each-of its lblades iin vpast fuel inlet conduit Hp preferably should feed a'predetermined volume of Vcoal to Vpulverizer mill In practicey this volume may Vary somewhat due to such things as wet coal sticking in the corners at the base vof the blades. It is apparent that the weight of coal in this predetermined volume will depend to `a certain extent on the size of the lumps of coal, and its "heating value will depend on its moisture content. Thus lump size and lmoisture content, in a coal feeder of the type described herein by way of example, constitute some of the abovementioned quality factors which, like fuel heating value, tend 'by their variation to cause the fluotuations in boiler output which are `corrected in accordance with the invention. As used vherein the expression fuel quality is intended to include anything that affects the amount of heat produced in the furnace at a `given speed of the fuel feeder or equivalent measure of fuel flow.

Referring to Figs. 2 and l'l, fuelefeed controller l, forming part of fuel control unit |212, controls f' a vquantity representative of steam flow, as descri-bedmore fully hereinafter.

Motor IIj may be of any suitable reversible type; for convenience it will be considered to be a two-phase inductionmotor operable from power line I9 in one direction when conductor i'Sb engages `conductor ISC, and in the other direction when conductor `|5319 engages conductor |8d, all in a well-known way. Movement of conductor Ib to cause .motor Iy' to rotate in one direction or the other is vbrought about bythe rotation of frame 13e, to which conductor i8?? is attached, about .pivot |8f under the net torque of solenoids |8g, |8`h, |82', and |876 opposed by torque from diaphragm |89' actuated by air-loading pressure from pipe |8m and acting through push rod HmV electrically that their magnetic fields are in opposition, all four solenoids being connected in series with each other and with tachometer generator I'Hc and rheostat 18a by suitably insulated conductors. Thus motor Il? will be operated whenever there is a departure from a predetermined relation between air-loading pressure and fuel flow as measured by tachometer generator I'i'lc, and it will be operated in the proper direction to restore that relation. The aforesaid predetermined relation may be varied, however, by adjustinent of rheostat I8a as described hereinafter.

For the purpose of maintaining the air iiow through each of boilers I0, II, and I2 proportional to its steam fiow, steam-air units If, IIf, and I2f are provided (Fig. 1).

Referring to Fig. 12 as exemplary of a suitable steam-air unit, it is desired to rotate fra-me 20 pivotally supported on stationary frame 23a by pivot 20h to cause conductor 20c to make contact with conductor 20d to cause motor I2e (Figs. 1, 2) to rotate in one direction or to make contact with conductor 20e to cause the motor to rotate in the opposite direction thereby to adjust damper I2d to control the flow of combustion air through boiler I2. Of course other suitable well-known means for controlling the flow of combustion air through the boiler may be employed, if desired. For example motor l2e may adjust a suitable speed control, not shown, for the corresponding one of blowers Illy, IIg, and 12g.

It will be understood that the followingdescribed means for measuring the now of combustion air may, in practice, be so positioned that they measure the ilow of all gaseous products of combustion instead of only air. The relation of these products of combustion to combustion air is well known and, therefore, measurement of one is equivalent for present purposes to a measurement of the other.

"As is well known, air flow through a furnace may be measured by a pair of properly positioned tubes, commonly known as draft taps, such as taps 29j and 26g, shown partly schematically in the drawings. Air under pressure from these taps is applied to opposite sides of diaphragm 20h, Fig. 12, to apply torque to frame 20 through push rods 201i and 209' and lever 20k pivotally mounted by pin 20m. When it is desired to change the ratio of air flow to steam ow because, for some reason such as the formation of boiler scale, the amount of heat produced in the furnace for a given steam flow from the boiler changes, this torque must be varied. For such purpose, motor 2G71. of any suitable wellknown type is mounted on frame 20 and operatively connected |by any suitable mechanical linkage to push rod 267' to move the upper end thereof toward or away from pivot 20D, thereby adjusting the distance from pivot point 20h to the point where pin 20p engages wall 20q of slot 20s which is the eifective lever arm whereby diaphragm 20h tends to rotate frame 20.

Motor 20u may be actuated by any suitable power supply and control apparatus such as a servo or push-button system, not shown. It will be understood that Fig. l2 is a diagrammatic view illustrating the principles of steam-air unit I2f and that, in a practical application, certain parts thereof preferably should be rearranged from the position in which they are shown for clearness: particularly motor 22u may be located near the center of gravity of frame 20 with suitable: counterbalancing of it and other parts; and

8 steam tubes 2Ilt and 28u, described hereinafter, may be coiled about the axis of pivot 20h to facilitate the free movement of frame 20 in response to slight unbalance torque.

As mentioned, the difference in pressure in taps 2Ilf and 20g is a measure of the air flow in boiler I2 (Figs, l, 2) so that the torque applied to frame 29 by diaphragm 28h is a function of the air flow. Steam flow from each of boilers I0, Il, and I2 may be measured in a well-known way by providing restrictions Iz', lli, and I2zl in steam pipes IDh, Iih, and I2h., respectively extending from the individual boilers to the header I4 (Fig. 1). Steam tubes 201i and 29u, connected to steam pipe I2h (Fig. 2) on opposite sides of restriction |21- are connected (Fig. l2) to pressure chambers 2010i and 20w, respectively, above mercury columns Zy and 202, respectively. Combustion-air ow through boiler I2 results in a clockwise torque on frame 29 while steam iiow from boiler I2 will displace mercury column 2oz toward column 20g to cause a counterclockwise torque on frame 20.

When these two torques are balanced, as a result of a predetermined relation between steam flow and air flow, conductor 29e occupies a position intermediate conductors 22e and 29d so that motor I2e (Figs. l, 2) is cle-energized and damper I2d remains stationary. A relative increase in steam flow over air flow will cause frame 20 to rotate counterclockwise so that conductor 20c' contacts conductor 20d to cause motor l2e to opendamper I2d sufficiently to re-establish the predetermined relation between steam flow and air flow thereby to rebalance steam-air controller I2f to disconnect conductor 20c from conductor 25d. Conversely, a relative decrease in steam flow compared to air flow will unbalance steamair unit I2f oppositely to cause motor I2e to close damper I2d suiiiciently to rebalance the unit.

Referring to Fig. 10 as exemplary of one of the auxiliary controllers Ic, lic, 2c (Figs. l, 2), loading air from valve I2c (Fig. 1) is applied to diaphragm 2Ia of auxiliary control unit i2c through pipe Im to apply a clockwise torque through push rod 2 Ib to frame 2 Ic pivotally supported on stationary frame 2Id by pivot 2 Ie. By itself this clockwise torque would cause conductor 2 I f attached to frame 2 lc continuously to engage conductor 2 I g thereby to energize motor 2 Ih, Fig. 2, to adjust contact 2|@l of rheostat Ia toward. its maximum-resistance position thereby requiring tachometer generator I'Hc to rotate at a high speed corresponding to fast fuel flow. However, counterbalancing the above-mentioned clockwise torque is a counterclockwise torque due to the unbalance of mercury columns 2 I7' and 2 Ik which, in magnitude and sense, depends on the air flow through boiler i2. Chamber 2m over mercury column Zik is connected to draft tap 20j and chamber Zim over mercury column 2li is connected to draft tap 20g which, being downstreamward of draft tap 201', has the lower pressure and consequently the greater height and weight of mercury. It will be understood that other liquids may be employed wherever mercury is referred to herein, if desired. i

When the aforesaid counterclockwise and clockwise torques are equal so that conductor 2 If assumes a position intermediate conductors 2Ig and 21p, contact 2li of rheostat 18a will remain' stationary and the fuel flow to boiler I2 will be controlled in the usual Way solely by master controller I6 and fuel-feed controller I8. Suppose now that the quality of fuel at boiler I2 becomes poorer than that at boilers I0 and Il resulting in a reduction in steam flow from boiler I2 and a slight reduction in the system steam pressure. Master controller I6 (Fig. l) will then cause the fuel` flow to al1 three boilers to increase slightly to maintain the system steam pressure by increasing slightly the loading-air pressure in pipe Ia` thereby increasing correspondingly the loading-air pressure in pipe |8171.. This increase in fuel flow for boilers I0, II, and l2 brought about by master controller I6 will maintain the system steam flow but it will not offset completely the assumed reduction in heating value of the fuel supplied to boiler I2 so that steam iiow from boiler I2 wil1 necessarily be reduced and that from boilers I and II correspondingly increased if only master controller I6 and fuelfeed controller I8 (Fig. 2) are relied upon for control.

However, in accordance with the invention, auxiliary control unit will be unbalanced to cause complete oifsetting of the assumed poor fuel quality at boiler i2 for two reasons. First, the air-loading pressure on diaphragm 2m (Fig. 10) will be increased slightly to increase the clockwise torque on frame EIC; and, second, the counterclockwise torque on frame EIC will be reduced due to the reduced air flow through boiler I2, the air flow in boiler I2 following the reduced steam flow therefrom as previously described.

This unbalancing of auxiliary controller 20 in response to the decrease in steam ilow from boiler I 2 relative to the air-loading pressure on diaphragm Zia causes conductor 2li to make contact with conductor 2Ig thereby energizing motor 2 Ih (Fig. 2) and causing it to rotate contact 2li of rheostat I 6a to the left, as viewed in Fig. 2, thereby increasing the fuel flow to boiler I2 by requiring a greater voltage from tachometer generator IIc to balance fuel-feed controller I8 as previously described.

This increase in fuel ow to boiler I2 over and above that brought about by master controller I6 continues until it is suiiicient to restore the steam output of the boiler and therefore the air flow therethrough to balance auxiliary controller l2c whereupon conductor Zlf (Fig. 10) resumes its position intermediate conductors 2 Ig and 2 Ip, and the auxiliary controller then remains inoperative until there occurs another change in quality of the fuel supplied to that particular boiler. As boiler I2 assumes its proper share of the load upon operation of auxiliary controller I2C, the eXtra load on boilers i e and i i disappears and the air-loading pressure resumes its normal value leaving as the sole result of the decrease in fuel quality at boilerv I2 the readjustment of rheostat I (Fig. 2) to oset the poor fuel quality.

Of course the operation of auxiliary controller I2C is reversible so that, if unsually good fuel is supplied to boiler i2, a counterclockwise torque is applied to frame Zic (Fig. 10) to cause motor 21h (Fig. 2) to reduce the resistance of rheostat I 8a so that a slower now of fuel and hence a lower voltage from tachometer generator I'Ilc will suiice to balance fuel-feed controller IS for that particular boiler. Motor 2Ih for adjusting rheostat |8a may be of the well-known two-phase type having its common phase-winding connection more or less permanently connected to conductor v2Iq of power line i9, the opposite ends of its two phase-windings being connected to conductors 2Igvand 2Ip with a suitable capacitor 2 I r in shunt relation thereto. As is well known, connectionA of. conductor 2'lf to conductor 2Ip will 10 cause rotation of motor ZIh in one direction, while connection of conductor 2If to conductor 21g will cause rotation in the opposite direction.

As will be readily understood by one skilled in the art, other well-known controllers may be employed instead of the specinc controller units |21), I2C, and I'Zf. Particularly, controllers depending for their operation on the relation of positions of elements, rather than upon forces or torques, are well-known substitutes and need not be described herein in detail.

In accordance with the invention it is contemplated that substantially independent adjustments of fuel ilow shall result from, rst, variations in steam pressure operating through the resultant variationv in air-loading pressure and, second, deviation from a predetermined, substantially permanent. relation between air-loading pressure, a measure of steam. demand, and steam flow or air ilow, a measure of steam supply. Ordinarilyv this rst adjustment of fuel flow in response to a change in air-loading pressure will be as rapid as possible, but acertain amount of delay in the completion of such adjustment may occur due to such factors as'the above-described reset action.

It may be desired` to delay completion of the aforesaid second adjustment in order that it may not objectionably aifect completion of the first adjustment. ln` other words, it may be desired to make the second adjustment in response to only sustained deviations in the relation of airloading pressure to steam flow rather than to transient deviations. To this end, make-andbreak element 2 Is (Fig. 2)v is interposed in conductor 2|)e oftransmission line I9 to interrupt the application of power to motor .'Ih periodically. Make-and-break element 2Is may be driven by motor 2 It of any suitable well-known type. Other delay means may be employed, if desired. l

In order that the aforesaid delay readily may be adjusted screw 2-Iu threaded in any suitable frame member 2 Iv is provided for adjusting the' position of conductor -2 Iw relative to the axis of rotation of cam or eccentric Zl. If conductor 2Iw is closer to camA ZI-, make-and-break element 2 Iswill remain closed longer at each revolution of the cam thereby operating motor 2Ih for a greater por-tionof the time, whereas if screw ZIu is adjusted to move conductor 2I-w farther from cam 2 I motor 2 I-h will operate only a small portion of the time auxiliary controller I 2c is unbalanced, and the correction of fuel now due to'operation of .controller I2c will proceed slowly.

As previously described, in accordance with the invention it is desired to balance some quantity representative of' steam flow from boiler i2 against air-loading pressure in pipe Him, a quantity representative of total steam system load, to adjust the fuel flow to boiler I2 tov compensate for variations in fuel quality. There has been described a system in which the quantity representative of steam now is the difference in pressure in draft taps Zf and 20g. This differential pressure, being a measure of air flow through boiler I2, is a satisfactory representation of steam ilow through boiler I2 because, as described, steam-air unit I2]c maintains a xed relation between steam flow and airv now. This air ow arrangement is advantageous since the draft taps supply a convenient" low pressure whereas steam pressure sometimes is too high for control purposes.`

i1 However, if desired, steam flow as measured by the differential steam pressure in steam tubes 2t and Zu connected on opposite sides of restriction I Iz' may be balanced against loading-air pressure in pipe ilm directly in auxiliary control unit 22, Fig. 3, corresponding exactly to auxiliary control unit l2c in principle and differing therefrom only in proportion and therefore not separately described herein. Preferably condensers 23a and 23h are interposed in steam tubes 26u and 2M, respectively, which are functionally interchangeable at control unit 22 with draft taps 20,1* and c', respectively, at control unit E2C. Preferably condensers 23a and 23h are positioned near steam pipe I Ih in order that pressure of water condensing therein and in tubes 201i and 20u will be substantially independent of temperature.

As hereinbefore mentioned, it may be desirable to isolate one of boilers I0, II, or I2 from master controller I6 in order that the isolated boiler may be operated at a substantially constant load as, for example, when it is desired to operate one of the boilers continuously at substantially its full rated load. To this end a transfer valve 24, Fig. 1, is interposed between valve I2a and pipe I5a whereby valve I2@ may be disconnected from the air-loading pressure in pipe iSd and connected to a suitable source of constant air pressure, not shown, through pipe 24a. This source of air pressure to which pipe 24a is connected preferably should be precisely regulated at a pressure comparable to the maximum pressure in pipe I5a in order that pressure-reducing valve I2a may be so adjusted that the constant air-loading pressure in pipe ISm will cause auxiliary control unit I 2c to balance at the desired steam flow from boiler I2. Any fluctuation in the air pressure in pipe 24a would result in uneven operation of boiler I2.

It should be noted that, in accordance with the invention, auxiliary control unit I2c functions to maintain constant the output from boiler I2 despite varying fuel quality supplied thereto when transfer valve 2li is set to connect pipe Im through valve 12a to pipe 24a. If poor fuel quality tends to reduce the steam flow from boiler I2,

control unit 52o will cause rheostat I8a to be adjusted to increase the fuel ow to boiler I2 suiioiently to increase the steam flow therefrom to rebalance auxiliary unit I2c against the airloading pressure in pipe I8m.

Referring to Fig. 5, in case the invention is applied to the burning of liquid or gaseous fuel the flow of which more appropriately may be measured by a pressure differential than by a tachometer generator voltage, a supplemental control unit may be substituted for fuel-feed controller I8. Supplemental control unit 25 may be like auxiliary control unit I2C structurally and therefore need not be described herein, It functions like the auxiliary control unit I2c of Fig. 5 except, first, the air-loading pressure supplied to it by pipe I8q is modified as described hereinafter; second, the motor 25e which it controls serves a different purpose; and, third, it balances against the modified air-loading pressure a differential pressure that is a measure of fuel ow instead of air ow.

By way of example, in the embodiment shown in Fig. 5, boiler I2 is supplied with gaseous fuel from any convenient source, not shown, through pipe 25a having a control valve 25h of any suitable well-known type interposed therein. When actuated, motor 25e positions valve 25o through l2 any suitable gearing to control the flow of fuel to boiler I2. Restriction 25d in fuel pipe 25a and

tubes

25e and 25f connected on opposite sides thereof serve to measure the flow of fuel to boiler l2 and to apply to supplemental control unit 25 a differential pressure representative thereof.

Tubes

25j and 25e may be connected to unit 25 in the same way that draft taps 25j and 20g, respectively, are connected to unit I2C. They function differently, however, being analogous to the tachometer generator I'Ik of Fig. 2 in that they both measure fuel flow. Thus unit 25 balances air-loading pressure against a quantity representative of fuel flow and, through motor 25o, adjusts fuel iiow in response to variations in air-loading pressure just as would be done by the equivalent apparatus shown in Fig. 2. As thus far described there is lacking in Fig. 5, however, a substitute for rheostat I8a whereby, in accordance with the invention, fuel flow is additionally controlled in response to the unbalance 0f auxiliary control unit I2C to control the output of boiler I2.

This additional control may be accomplished by modifying the air-loading pressure from pipe 48m by means of valve 25g which may be of the well-known throttle-and-bleed type like valve I 2a. It should have the characteristic of reducing the air pressure from pipe IBm to a lower but proportionate value in pipe I8q. In other words variations in air-loading pressure from master controller I6 will appear in pipe I8q, but they will be scaled down by manually adjusted loading valve I2a and by similar valve 25g adjusted by motor 2lb. Valve 25gmay be actuated by motor Zih through any suitable gearing.

When auxiliary control unit I2c is unbalanced due to a decrease in air flow, representing a decrease in steam flow, motor 2Ih will open valve 25g slightly to increase the loading-air pressure in pipe l8q thereby unbalancing supplemental control unit 25 to cause motor 25e to increase the fuel flow to boiler I2 to restore its steam now. Conversely, an increase in steam flow from boiler I2 without a corresponding increase in airloading pressure would unbalance unit I2c oppositely to cause motor 2Ih to close valve 25g slightly thereby unbalancing unit 25 in the direction to cause motor 25C to decrease the fuel flow to boiler I2 by adjustment of valve 25h. It will be apparent to one skilled in the art that valve 25g could be interposed in pipe I8m in the apparatus shown in Fig. 2, and that this valve when actuated by motor 2 Ih would serve the same purpose as rheostat Ida, namely, the adjustment of fuel flow in response to an unbalance of steam flow and steam pressure, this adjustment of fuel flow-being in addition to the usual control of fuel flow by master controller I6.

It is contemplated that valves 25g and I2a, Fig. 5, may be of the well-known throttle-andbleed type in which case operation of one would disturb the adjustment of the other by changing. the rate of bleeding air to the atmosphere, which would be an undesired result. To avoid this result pressure regulator 25h is connected between pipes I8m and l8r thus being connected between valves I2a and 25g. Regulator 25h includes a spring-loaded diaphragm 251' (Fig. 6) actuating a ball valve 257' to pass air from any suitable source, not shown, entering through pipe 25k to pipe l8r at a pressure proportionate to the air pressure in pipe I8m. Any other type of regulator that will pass to pipe l8r air pressure proportionate to that in pipe I8m without passing omero 13 objectionable quantities of air may be employed instead of valve 25h, if desired.

It will be understood that, as usedr herein, the Word steam is intended to include the vaporous or gaseous phases of Water and substances other than water such, forexample, as mercury.

While preferred embodiments of the invention have been described it will be understood that modifications thereof may be made within the spirit and the scope of the invention as set forth inthe-appended claims.

What is claimed is:

1. Control apparatus for maintaining substantially constant the steam pressure and relative 'steam outputs of a plurality of boilers adapted to supply a common variable steam load, said boilers utilizing fuel subject to independent variation in quality at each ofsaid boilers comprising, the combination of common pressure-responsive means for said boiiers for producing a control quantity varying in magnitude in response to variations in said common steam load, means associated with each of said boilers for measuring steam flow therefrom, means associated with each ofA said boilers and operatively connected tothe steam-flow measuring means associated therewith and to said common pressure-responsive means for comparing said measured steam flow and said control quantity, and an automatic fuel-feed controller for each of said boilers operatively connected to said comparing means associated therewith and to said common pressure-responsive means to adjust' the fuel flow to said boilers in response to said control quantity and inresponse to deviations from a predetermined relation between said compared quantities.

2. The method of maintaining Constant the rate of ow of steam from a boiler despite varying quality of fuel supplied to said boiler which comprises varying the fiow of combustion air to maintain the balance of effects respectively corresponding with the rate of flow of steam and the rate of iiow of combustion air, varying the rate of supply of fuel normally to maintain the balance of effects respectively corresponding With the rate of supply of fuel and a reference, and upon deviation from a predetermined magnitude of said air flow effect correspondingly changing the relationship of balance between said fuel effect and said reference effect in a compensating sense.

3. In the control of a group of steam generators supplying a common steam load, the method of compensating for variations in quality of fuel fed to the respective generators in avoidance of disturbing the sharing of said common load which comprises varying the rate of fuel supply to an individual generator of the group in accordance with variations in said common steam load, and effecting a supplemental control of the rate of fuel supply to said individual generator each in accordance with the unbalance of the relationship of the rate of generation of steam by said individual generator and said common steam load of the group.

4. A method as in claim 2 in which for effecting supplemental control of the rate of fuel supply, the combustionl air flow of said individual generator is balanced against its rate of generation of steam and the rate of fuel supply modied in accordance with the unbalance of combustion air of said individual generator and said common steam load of the group.

5. A method as in claim 2 in which for effecting the supplemental control of the rate of fuel supply; the rate ofv fuel supply to said individual generator is-'modied' in` accordance with the unbalance of steam flow from said individual generator and said common steam load of the group'.

`6L Apparatus for controlling the operation of a group of steam generators supplying a common steam load to compensate for variations in the qualityv of fuel supplied to the individual generators comprising means for varying the rate at which fuelv is supplied to a generator of the group in accordance with variations of said common steam load, and means for effecting a supplemental control of the rate at Which fuel is supplied to said generator in accordance with thev unbalance of the relationship of the steam supplied by` said' individual generator and the common steam load supplied by said group of steam generators.

7; An apparatus as in claim 6 in which the first-named means for varying the fuel includes pressure-responsive means for producing a rst control quantity varying in accordance with system load, in which a controller maintains balance between the combustion air to and the steamoutput of the individual generator and provides a second control quantity corresponding with deviation from a predetermined relation between said first control quantity and said combustion air, and in which the second-named means for varying the fuel includes a second controller responsive to unbalance of said first and second control quantities.

8. In the control of a plurality of steam generatorsl adapted to supply a common variable steam loa-d apparatus for compensating for variations in the quality of fuel fed to said generators to maintain the predetermined share of said common loa'd to be carried by each of said generators despite variations in fuel quality supplied to the individual generators comprising means responsive to said common steam load for producing a control quantity varying in magnitude and sense in accordance with variations in said common steam load, means for controlling the ow of fuel to each of said generators in accordance with the balance between said control quantity and rate at which fuel is supplied to each of said generators, and means for modifying the rate of supply of said fuel in accordance with the balance between said control quantity and a quantity representative of the steam ow supplied by each of said generators as its share of said common steam load.

9. The method of maintaining the rate of flow of steam from a boiler at a constant value despite varying quality of fuel supplied thereto which comprises upon departure of the rate of ow of steam from said constant value varying the rate of flow of combustion air in accordance with the sense and extent of such departure from said constant value of the rate of flow of steam, comparing the air ow so varied With respect to a reference, varying the rate of iiow of fuel in sense opposite to such departure of the rate of steam flow and depending upon the sense of the deviation of the air flow from said reference, and continuing such variation of the rate of flow of fuel in said opposite sense until such time that the steam flow is restored to said constant value and the air floW corresponds with said reference.

10. Apparatus for maintaining the rate of flow of steam from a boiler at a constant value despite varying quality of fuel supplied thereto comprising regulating means for varying the rate of ow of combustion air in the same sense as departure of the rate of flow of steam from said constant value, and a controller responsive to deviation of said air :dow from a predetermined value to vary the rate of ow of fuel in sense opposite to the departure in steam flow from said constant value and continuously to eiect Variation of fuel in such opposite sense until such time that the air flow is restored to said predetermined value.

ll. In control of a generator supplying steam to a system, the method of insuring said generator shall supply its share of the system load under varying system load conditions and despite varying quality of its fuel which comprises producing a first control quantity representative of the system load, varying the rate of fuel now to said generator in response to said first control quantity and in sense corresponding With the change in system load, comparing said rst control quantity with the steam now from said generator to produce a resultant second control quantity in sense corresponding with the deviation from a predetermined relation between said first control quantity and the steam flow from said generator, and further adjusting the rate of fuel flow to the generator continuously in sense corresponding with the aforesaid deviation of the second control quantity until such time that said predetermined relation is reestablished.

12. An arrangement for controlling the flow of fuel to a steam generator in a system to insure it shall supply its share of the varying system load despite varying quality of fuel supplied to that generator comprising pressure-responsive means for producing a control quantity varying in accordance with system load, a balanceable controller for comparing said control quantity with the steam-iiow from said generator, and automatic means operatively connected to said first-named means for varying the fuel now in accordance with said control quantity and in sense corresponding with the change in system load, and operatively connected to said balanceable controller to eiect further variation in the rate of now of fuel in sense compensatory of variation in fuel quality of the generator` and continuing until such time that a predetermined relation of the steam now of the generator to said control quantity is reestablished.

13. In the control of a group of steam generators supplying a common load, said group including a rst sub-group of one or more generators to supply a xed amount of steam and a second sub-group of one or more generators to supply the remainder of the common load demand, the method of compensating for variations in quality of fuel fed to the respective generators in avoidance of disturbing the sharing of said common load which comprises varying the rate of fuel supply to each generator of the second sub-group in accordance With variation of the load common to both sub-groups, effecting a supplemental control of the rate of fuel supply to each generator of the second subgroup in accordance with the unbalance of the relationship of its steam output to the load oommon to both sub-groups, and varying the rate of fuel supply of each generator of the rst subgroup in accordance with the unbalance of the relationship of its steam output to a constant reference.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,967,988 Dickey July 24, 1934 2,047,234: Smith July 14, 1936 2,652,375 Wunsch Aug, 25, 1936 2,218,454 Mdyette Oct. 15, 1940 2,259,417 Gorrie Oct. 14, 1941 2,328,499 Saathof Aug. 31, 1943