US1518924A - Combustion control - Google Patents

Description

L. J. HESS ET AL COMBUSTION CONTROL Filed April 22,v 1921 3 Sheets-Sheet J IHVENTOI.

Dec. 9, 1924. 1,518,924

L. J. HESS ET AL COMBUSTION CONTROL Filed April 22, 1921 3 Sheets-Sheet 2 PERCENT BOILER EFFICIENCY FUEL IN POUNDS PER HOUR l 1 Al I l I I00 200 300 400 I00 200 300 400 PERCENT BOILER RATING PERCENT BOILER RATING.

a 5 4. 5. i E 3 5 Q m 3? a a m m u "4 h x E E a u. l l J l I I00 200 300 400 I00 200 300 400 PERCENT BOILER RAT/Iva PERCENT BOILER RAT/Na 1 l I00 200 300 400 I00 200 300 400 All? T0 BESI/PPLIED IN POUNDS PER HOUR PERCENT BOILER RATING PERCENT BOILER mar/Iva ZQZ M447 L. J. HESS ET AL COMBUSTION CONTROL Filed April 22,. 1921 3 Shees-Sheet 5 l /00 200 PER CE/VT BOILER RAT/N6 l J /00 200 300 PERCENT BOILER flflT/NG PERCENT BOILER RATING PERCENT BO/L ER R/lT/NG M m w M 4 T a -w 3 mm K6 N U A 0 m D F 0 I n 2 M 0. mm 0 61 m R0 mm PERCENT BOILER RflT/NG Patented Dec. 9, 1924.

UNITED STATES.

PATENT OFFICE,

LAWRENCE J. HESS, OF COI'ISV'ILLE TOWNSHIP, MAHONING COUNTY, AND MmILL G. BENJAMIN, OF LAKEWOOD,'OHIO, ASSIGNORS TO THE BENJAMIN ENGINEERING COMPANY, OF CLEVELAND, OHIO, A. CORPORATION OF OHIO.

COMBUSTION CONTROL.

Application filed April 22, 1921. Serial No. 463,675.

To all whom it may concern:

Be it known that we, LAWRENCE J. Hess, residing in the township of Coitsville, county of Mahoning, and State of Ohio, and MERRILL G. BENJAM'fiFI, residing at Lakewood, county of Cuyahoga, and State of Ohio, have invented a new and useful Improvement in Combustion Control, of which the following is a full, clear,'and exact description.

This application is a continuation in part of our copendingapplication for furnace control, Serial No. 292,954, filed April 26, 1919.

The present invention relates to combustion control and more particularly to means for correlating the air and fuel supplies for furnaces to maintain the proper furnace regulation, together with the most economical combustion at varying rates of combustion.

The present invention may be applied to the combustion control in various types of furnaces, such, for example, as steam boiler furnaces, gas producers or the like, in which it is desired to have an automatic regulation combined wit-hautomatic correlation of the air and fuel supplies. .Th term furnace is intended to define broadly any device which is su pliedwith fuel and air and in. which combustion takes place. The fuel may be solid fuel, for example coal or coke either in lump, pulverized or powdered form, or may be liquid or gaseous fuel; The combustion is controlled in accordance with some function of the furnace or furnaces. For example, in the case of steam boiler furnaces the combustion will be controlled in accordance with theload carried by the boiler, or the total load on the station or battery of boilers, the object being to regulate the combustion to meet the boiler load requirements. In the case of. steam boilers, the function which'corresponds to the load may be the pressure variation in the boilers or in the steam supply header, or may be the flow 'of steam through the header. In the case of gas producers it may be the pressure of the gas in the main or-the flow of gas throughthe main. In other words, the expression function of a furnace or function of a battery of furnaces as used in this application is intended to include any of the indicia of variations in the performance of a furnace or battery of furnaces.

The present invention will be described with particular reference to its embodiment in the control of steam boiler furnaces. It is to be understood, however, that it may be embodied in other types of furnaces. I

Forthe best automatic control of steam boiler furnaces certain objects should be attained. The airand fuel supply should be properly correlated for the most advantageous combustion at the various rates of combustionover which the boiler furnace is to beeperated. In the case of a battery of boilers the load should be equalized among all of the units operating, each furnace being supplied with the same or the properly correlated amount of fuel and air so that each boiler carries its proportion of the total load. The proper regulation of the combustion will result in the maintaining of substantially uniform steam pressure over the various boiler ratings.

The following considerations show the necessity of meeting the above requirements if a proper automatic control is to be obtained. For every rating of a boiler there exists a certain relation between the fuel bed thickness, the fuel feed and the quantity of air supplied, which results in the highest efficiency. Knowing this and the character istics of the boiler furnace being used, we are able-to approximate these vconditions automatically throughout the entire range of operation from the minimum to the maximum boiler rating. In a modern underfeed stoker, for instance, the grate area is fixed imposed upon the boiler; It is possible to maintain a constant fuel bed thickness and carry the same variableload. The method which results in the most efiicient operation of the particular furnace is employed.

For efiicient operation the load must be equalized among all of the boilers in operation. If all of the boilers operating can be. depended upon to carry their proper share of the load, especially during peak loads on the station, fewer boilers are-necessary than under common practice which requires that sufficient boilers be carried on the line so that there will be at all times boiler capacity enough connected to carry peak loads even when some boilers are oper ating at a much lower capacity due to urnace conditions beyond the momentary control of the fireman. The first cost of the station installation may be reduced if the regulation insures an equalization of the load over all of the boilers. It is well known that boilers operated continuously at moderate ratings show better efiiciency than boilers operating-with varying load from low to very hi h. V The life of the furnace brick work an parts is greater under the conditions of constant load than other wise. By automatically equalizing the load on all of the boilers, the variations in rat ings at which the individual boilers are operated is reduced to the actual variation in the station load. By the s stem of combustion control herein descri ed, we are enabled to equalize the load among all of'the units operating, to secure the most advantageous combustion. at the various boiler ratings and to maintain a substantially uniform steam pressure.

In the drawings which illustrate the preferred embodiment of the invention as applied. to the control of a battery of steam oilers;

Fi ure 1 is a diagrammatic view ofthe ating system; and igures 2 to 13, inclusive, are curves illustrating certain conditions and calculations employed in correlating and proportioning the various parts of the system. I

In the illustrated embodiment of the invention, two units'of a battery of steam boilers are indicated enerally by reference numerals 1 and 2. rdinarily aconsiderable larger number of units are employed in a battery but twounits only are shown for the purpose of illustration. Each unit comprises a steam boiler 3 and its furnace 4.

; The boilers are shown as provided with ec onomizers 5. The furnaces are fed by power operated stokers 6 driven b electric stoker motors 7. The stokers may of any suitable form such, for'example, as underfeed or chain gate stokers.

The air sup ly or'draft'is controlled by forced andin uced draft fans 8. and 9, respectively." The forced and induced draft fans are driven by electric fan motors 10p and 11, respectively. While it is preferred, and particularly in cases where an economizer is used, to employ induced draft fans as well as forced draft fans, a chimney draft may be employed, if desired, in I which case the induced draft will be controlled by individual dampers inthe uptake flues of the several furnaces, such dampers being preferably controlled inaccordance with the pressure of the gases in the combustion chamber or asses of the boiler so that the dampers wil open in accordance with the air supplied by the forced draft fans, while maintalning the desired pressure of the gases'over the. fire or-in the boiler passes. In such cases the regulation of the ,air supply in accordance with the load will be controlled by the forced draft fans.

The armatures 12 of the stoker motors 7, the armatures 13 of the forceddraft fan motors 10 and the armatures 14 of the. induced draft fan motors 11 are supplied with current from constant volta e direct current feeder main 15. The spee s of the several motors 7, 10 and 11 are regulated by the current supplied to their res ective shunt fields 16, 17 and 18. The fiel currents for such shunt fields are supplied by the variable speed, variable voltage generators 19, 20

and 21 of a variable s eed motor generatorset indicated general y by reference numeral 22. The motor generator set is driven by a motor 23, the speed of which is controlled in accordance with the steam pressure in the main steam header 24 of the battery The armature 25 of the motor 23 is supplied with a constant voltage current from the constant voltage direct current feeder mains 15. The shunt field26 of the motor also receives its current from the feeder mains 15. The current in the shunt field 26 of this motor is varied to vary the speed of the motor by means of a rheostat 2 having a movable contact 28 controlled it is therefore not illustrated in detail. The 7 well known Mason regulator is preferably employed although other makes of regulatorsmay be used. The regulator 29 has an arm 31 which assumes various positions in accordance with the steam pressure. The regulator is socompensated that the arm 31 has a step-by-step movement, assuming a definite position for any particular steam pressure throughout its range of operation. As illustrated inthe drawin s, the arm 31 is shownas vertically movab e, falling with a decrease in steam pressure and rising with an increase in steam pressure. When the stem ressure decreases, the arm 31 and the mova le rheostat contact 28 descend cutting out resistance in the rheostat 27, T thereby increasing the stren h of the motor field 26 and decreasing t e speed of the motor the rheostat 27, the speed of the motor generator is regulated in accordance with the steam pressure. The exact relation of the motor generator speed to the steam pressure will hereinafter be described in greater detail. A hand operated rheostat 32 is interposed in the leads on the motor field 26 so that the speed can be adjusted manually in accordance with particular furnace-operating conditions. The hand operated rheostat 32 is not depended upon for regulation in accordance with the variations in the load, but is rather in the nature of a permanent adjustment, which may be set once for allor may be readjusted occasionally upon variation in the character of the fuel, etc. I

The armature 40 of the generator 19 is connected to leads 41 from which is taken the exciting current for the fields 16 of the stoker motors7 of the several furnaces. The shunt field 42 of the generator 19 is connected across. the constant voltage supply mains 15. A manually adjustable rheostat 43 is inserted in the field circuit. The voltage of the current supplied by the generator 19 varies in accordancewith the speed of the motor generator set 22 which is varied in accordance with the demandv for steam as is shown by the steam pressure regulator 29. When the steam ressure decreases, indicating increased loa the motor generator set decreases in speed, thereby decreasing the voltage supplied by the generator 19 to the fields of the stoker motors and thereby weakening the stoker motor fields and increasingthe motor speeds to supply more fuel. The rheostat 43 is not depended upon for adjustment of the stoker motor speeds in accordance with the variations in steam pressure, but is in the nature of a permanent adjustment which may be set once for all or readjusted occasionally when it is necessary to adjust the stoker motors with respect to the draft appliances. Each stoker motor has a manually adjustable rheostat 44 in series with its field. This rheostat allows hand regulation of each stoker motor. This hand regulation is in the nature of a permanent adjustment of the hand rheostat 44 and may be adjusted occasionally to correct any inequalities or differences in conditions between the individual stokers.

The generator 19 has a series field 45 of such strength that the voltage at any given s eed will be maintained constant for variations in the load imposed upon the generator such, for example, as throwing on a different number of stoker motor fields. This renders the relation independent of the load thrown upon the regulating device by a reater or smaller number of-units.

he generator 20 has its armature 50 connected to the leads 51 from which is taken' the exciting current for the fields 17 of the forced draft motors 10 of the severalfurnaces. The field 52 of the generator 20 is connected across the constant voltage feeder mains 15. A manually adjustable rheostat 53 is interposed in the field circuit. This rheostat is in the nature of a permanent adjustment or may be adjusted occasionally when it is desiredto adjust the speeds of the forced draft fans as a whole with relation to the other devices. An automatically adjustable rheostat 54 is also included in the circuit of the field 52. The rheostat 54 has a movable contact 55 which is carried on the arm 31 of the steam pressure regulator 29. The action of the rheostat 54 is to modify the variations in voltage of the generator 20 due to the variations in speed of the motor generator set. When the arm 31 of the steam pressure regulator 29 rises, and thereby increases the resistance in the rheostat 27 of the motor generator motor 23 to increase its speed, the same movement throws resistance into the circuit of the field 52 of the generator 50. The effect of increasing the speed of the motor generator set is to increase the voltage of the generator 20, but such tendency to increase the voltage is counteracted in part by the increase inthe resistance of the circuit of the generator field 52. In consequence of this,-the variations in voltage of the generator 20 uponvariations in speed of the motorgenerator set are not as great as the variation in the voltage of the generator 19-, whose variations in voltage are due entirely to the variation in speed of. the motor generator set.

Each forced draft fan motor 10 has a manually adjustable rheostat 56 in series with its field whereby an individual manual adjustment of the speeds of the individual forced draft fans is permitted. Such adjustments are in the nature of permanent or semi-permanent adjustments. The adjustment of one of the rheostats 56 changes the relative speed.- of the particular fan with relation to the other forced draft fans. Such adjustment does not effect the automatic variations of the speeds of all of the forced draft fans as a system in accordance with the variation in steam pressure through the variable speed of the motor generator set.

The generator 20 has a series field 57 of such strength that the voltage at any given speed will be maintained constant for variations in the load thrown on such generator, such for example as throwing on the fields of a different number of forced draft fan motors when different numbers of boilers are put into or out of commission.

The generator 21 has its armature 60 connected with leads 61 from which is taken the current for the shunt fields 18 of the motors 11 for the induced draft fans. The

1 on the arm 31 of the steam pressure regulator 29. The operation of this rheostat is similar to that of the rheostat 54 of the generator 20. It serves to modify the voltage of the generator 21 so that its voltage does not exactly follow the variations in speed of the motor generator set. The rheostats '54 and 64 have their resistance values so selected that the voltages of the generators and 21 will have the proper variations for the difierent speeds of the motor generator set. The computation of such voltage variations is hereinafter described in detail. a

Each. of the induced fan motors 11 has a manually adjustable rheostat 66 in series with its field. These manually adjustable rheostats provide a means for manually adjusting the speeds of the induced draft fans relative to each other to meet inequalities in the conditions encountered in the individual 'furnaces. These manual adjustments are in the nature of permanent or semi-permanent adjustments. The regulation "of the induced draft fans taken as a system is automatic and responds to various loads on the boilers through the motor generator set 'which serves as a master regulator-for the entire "1 battery.

The generator 21 has a seriesfield 67 of such strength that the voltage at any given f speed will be'maintained constant irrespective of the number of induced draft fan .motors whose fields are thrown upon the generator 21.

The battery of boilers willordinarily be operated to meet permanent or semi-permanent variations in load by putting the requisite number of units into commission. The units which are out of commission will ordinarily havetheir fires banked and the draft'and stoker motors will be disconnected. As above pointed out, the generators-J19,- 20 and 21 of the motor generator set. are so designed as to excite the fieldsof a variable number of fan or stoker motors whiIe jmaintaining a predetermined voltage I onysuch fields for any particular speed of the motor generator set. The regulation of the furnace in accordance with the steam pressure is thereby rendered independent of the number of units bein operated and control apparatus will 'regu ate the steam pressure with the same accuracy independently ofthe number of units being operated, pro- 'quired for a full stroke. of the vided, of course, a suflicient number of units are being operatedto carry the load.

The operation of the apparatus'will first be described enerally and then the computations for etermining the various constants of the systems will be explained.

The steam pressure regulator 29 responds to the variations in the steam pressure. The arm 31 illustrated as rising with an increase in steam pressure andfalling with a decrease in steam pressure. The'arm 31 will: take diflerent positions "for different steam pressures. The-regulator is setto travel througha complete stroke for a predetermined pressure variation. For example, if this pressure variation is taken as ten pounds, the arm 31 will be at its bottom position, when the pressure is five pounds below normal, and will be in its top position when the pressure is five pounds above normal. Since the flow of steam out of a boiler can be anything from zero to maximum at practically the same steam pressure at the outlet, and since there is a definite loss orldrop of steam pressure in flowing through a pipe, the connection, to the-regulator 29 is preferably taken from the'main steam header 24 at a point where, at; the maximum load on the station, the pressure drop to that point from the boilers is approximately that at which the regulator is set'to make a full stroke. Under these conditions, with no load on the station the pressure at the boilers and at this point will be the same, and slightly above normal,

whereas, at a maximumdoad, the pressure at the point where the connection 30 is taken ofi, will be lower than that at'th e boilers by approximately the number of-pounds reressure regulator 29, for example, ten poun s in the above assumed example. By. tapping the connection to the steam pressure regulator as above'described, the action ofthe regulator will follow closely the load on the station.

As the load on the station decreases, the arm 31 of the steam pressure regulator rises thereby increasing the resistance of the rheostat 27 and weakening the field of the motor 23 of the motor generator set. This in- In I creases the speed of the motor generator thereby increasing the voltages of the generators 19, 20 and 21. These voltage inr creases in turn increase the field strengths of the stoker'and the forced draft fan and the induced draft fan motors, thereby decreasing such motor speeds. Less fuel and air is supplied to the furnaces to compensate for the decreased load on the station. Conversely, if the load on the station increases, the arm 31 of the steam pressure regulator descends cutting. resistance out of the rheostat 27-and decreasing the speed of the motor generator set. ThlS in turn decreases the voltage T supplied to the fields of the stoker motors and the fan motors, thereby increasin their speeds and supplying more fuel an more air to the furnaces to carry the increased load on the boilers.

The speeds of all of-the individual stoker and fan motors of the units of the battery are controlled through the motor generator electrical system from the single master steam pressure regulator 29 which is in turn controlled by the pressure in the main ste'am header 24. The rate of combustion over the entire battery will therefore be varied in accordance with the load carried by the entire battery. The variations in speed of the motor generator set causes properly responsive variations in speeds of the motors of all of the units so that the variations in fuel and air supplies for the different rates of combustion are properly correlated overthe entire battery. The motors of each unit have their own adjustable hand rheostats so that any motor may be adjusted relatively to the other motors of its system. By means of such adjustment the load can be very accurately equalized over the several boilers of the entire battery.

The change in the speed of the motor generator due to the variations in the load does not effect the equal distribution of the load between the several units, as changes in the speed of the motor generator cause proportionate changes in speed of the motors of all of the units. H y p When the manually adjustable rheostats for the different units are set, the operation of the system is entirely automatic and the hand rheost'ats will not need to be touched until there is some permanent or seml-permanent change inthe operating conditions. For example, when one boiler is dirty and another. freshly cleaned, it may be necessary to adjust the rheostats so as to give somewhat greater speed to the draft fans of the dirtyboiler to overcome the gre'ater resistance through its passes. After such adjustment is made, the regulation is thereafter .automaticand no further hand adjustment will be necessary until condit ons are changed, for example cleaning the dirty boiler and the gradual fouling of the clean boiler. 1

The system not only equalizes the load over the several units of the battery, but also supplies properly correlated amounts of fuel and air at different rates of combustion, whereby the most efficient burning of the fuel is maintained over the entire boiler ratings from the minimum rating to maximum overlo'ad. The constantsof the system for such regulation are determined as follows: For the purposes of explanations a number of curves, Figures 2 to 13, inclusive, are presented. It is to be understood that thesecurves are merely diagrammatic and are used for the purpose of more graphic explanation. They are not intended to be accurately drawn to scale.

. A curve ofthe efliciency of the boiler or boilers to be controlled is obtained. This is ordinarily obtainable from actual tests of the boilers previously installed. A typical curve ofthis kind isshown in Figure 2 in which the percentage of boiler ratings are indicated by the 'abscissae and the percentage of boiler efiiciency at. the various ratin is indicated by the ordinates. With thls curve as a basis, the actual quantity of a coal of known analysis which will be required for the different ratings of the boiler may be com uted. Such a curve. representing the relation between the quantity of fuel in pounds per hour and the percentage of boiler rating is shown in Figure 3.

From the knowledge of the quantity of fuel which mustbe supplied per hour at the different boiler ratings, the stoker speeds at the different boiler ratings may be computed. The curve showing the relation of the stoker speeds in revolutions per minute at the different boiler ratings is shown in Figure 4. This curve furnishes the basis upon which the speeds and the speed variationsof the stoker motors at different rates of combustion are computed. v

Fromithe tests. conducted for obtaining the data necessary to plot' the curve of Fig ure 2, the percentage of excess air re uired to burn, the fuel most efficiently at di erent boiler ratings is determined. The relationship of the excess air to the present boiler ratings is 'indicated'in the curve shown in Figure 5. V

The curve shown in Figure 6 is then plotted-with the curves 3 and 5 as'a basis. This curve shows the quantity of air in .pounds perKhour which must be delivered to the furnace atdifi'erent boiler ratin The fuel bed thicknesses for the iflerent percentages of boiler ratings are determined for the most efficient combustion and the static pressures under which the forced draft fan must operate at-the different percentage boiler ratings is then'determined. A curve showing the pressure in inches of water to be maintained under the fire by the forced draft fan at the different boiler ratings is shown in Figure 7. The curve in Figure 8 which shows the speed of the forced draft fan at the different boiler ratings is then calculated on the basis of the curves of Figuresfi and 7. This curve furnishes the basis for computin the electrical constants of the forced draft an motors and their regulating system.

The quantity of burned gases to be removed by the induced draft fan at the different rates of combustion or boiler ratings is then computed. Since the exact quantities of air and fuel supplied to the furnaces tee hour of t have been fixed, the quantity of the gases of combustion is known. In plotting the curve of Figure 9, allowance must be made for the infiltration of air through the boiler setting and economizer. Such infiltration increaseslwith the boiler rating and may run from about ten" per cht at one hundred per cent rating to about twenty per cent at four hundred per cent rating. The curve of Figure 9 is lotted showing the pounds per l ie gases of combustion to be removed by the induced draft fan at the different boiler ratings.

The curve shown in Figure 10 is plotted from data obtained by'tests with the boiler.

' Thiscurve shows the negative stack pressures in inches ,of water under which the induced draft fan will operate at the different boiler ratings.

i The curve of Figure 11 is next plotted on the basis of Figures 9 and '10. This curve shows the induced draft fan speed in revolutions per minute at the different boiler ratwhich data the speeds of the fans, both ofthe forced and induced drafts, may be accurately'computed atfthe different boiler ratings. The speedsrequiredat the'difien.

cut boiler ratings by the stokers, the forced draft fansand the induced draft fans, together withthe loads tobe carried at such speeds, being known, electric motors of'the' rope'r size and range 'of speed'may be seected. Motors are also selected having thedesirable shunt field characteristics to give the pro er speed re ation b varyin the field v0 tage applieg to the nl otors. Since the speeds of the stoker, the forced draft fan and the induced draft fan motors at different boiler. ratings is known, and since their shunt field characteristics are known, curves may be plotted showing the voltage" which must be applied to the shunt field windings ,of the motors at the different boiler ratings to obtain'the proper speed ofthe stoker, theinduced draft an and the, forced draft motors. Typical curves showing this relationship are shown in Figure 12. In the example selected, the stoker motor'has the greatest variation in speed over the different boiler ratings, the induced.

gs. In plotting this curve thev tempera-- per cent boiler rating to 600degres Fahren j ince the field currents for the induced dra motors may be computed, so that the proper forced draft fan the least variation. These speed variationsaredetermined very largely by the charactertistics of the fan and for fans of some charactertistics these relative relationships of the s eeds of the'stoker and the fans may be di erent.

Since the voltages which may be applied 'to the fields of the various motors are known, suitable generators 19,20 and 21 are selected. The to supply e voltages required by the curves of-Flg. 12 may be'then computed. Since the voltage'curves for the shunt-fields of the Stoker; the forced draft fan and the induced draft fan motors have" different slopes, andsince the generators 19,- 20 and V speeds of the generators necessary t.

21 are mounted on the same shaft,.the neces- .sary voltage regulation cannot in general be attained for all generators by the speed variation of the motor generator set alone.- Therefore, the voltage'for one set of the motors, say the stoker motors, is obtained by: the speedcontrol of the stoker motors generator 19 and voltage for the fields of the forced draft fans and induced draft fans is regulated by the speed of the motor generator set as modified by the rheostats 54 and 64.

" On the basis of the curve of the stoker motor shunt field voltage shown in Figure ferent b0iler ratings. This fixes the speed of the motor generator set 22. From the characteristics of the motor 23 of the motor elements of the rhe'ostat27 may be comput- 1 ed. The steam pressure regulator 29 by means of the movable contact 28 will therefore impa rt to the motor generator set the correct speeds for the different boiler rat- 1n i the speed of the motor generator set is fixed by the stoker motors and their generator 19, thevolt age of the generators supplyin the fields of the fan motor must he modi edtoive the proper variations in-Jthe shunt fiel ;voltage as shown in Figure 12. Q Witl'r Figure 12 as a basis, the ,values of the resistance'elements of the rheostat 64. of the generator 21 which supplies t an voltages, will be supplied at. the. various boiler ratings. F

Similarly, on "the this a h s 12, thevaluesof the resistance'el'ementsof the rheostat 54 for the generator 20, which supplies the field .current for'the forced draft fan motors is computed. While, for -"the accurate proportioning of the air and fuel supplies at different rates of combustion a is f necessary in most cases to employ the voltage modifying rheost-ats, 54 and 64, these might be dispensed with in case the stoker, or fans and their motors had such characteristics that the curves as shown in Figure 12 were substantially parallel.

From the foregoing'description it will be apparent that we have provided for an accurate equalization of the load among the several units of the battery and atall rates of combustion we have also provided for an accurate proportioning of the air and fuel supplies at all rates of combustion. This regulation results in the maximum efiiciency of the boilers being operated and the maintenance of a substantially uniform steam pressure at diiferent'loads.

While the invention has been particularly described as applied to a battery of steam boilers, it will be understood that it may be readily applied to boiler furnaces employin a liquid; other than water as, for examp e, the recently developed mercury boiler.

While the invention has been described in considerable detail 'withreference to its illustrated embodiment, it is to be understood that the invention is not limited to such embodiment but may be otherwise embodied both in the regulation of .steam boiler furnaces and in the regulation of other types of furnaces. I

We claim: 1. The method of operating a-battery of furnaces having independent means for each furnace for supplying an element of combustion to the furnace and'having an electric motor for operating each of such supply means, which includes supplying current to a winding of each motor and varying such .current in accordance with a function of the.

3. 'The method of. operating a furnace,- which includes supplying fuel and air in a definite ratio at a given furnace load,'and

V varying such ratio with changes in the furgiven load, and automatically varying'such 1 regulate the speeds of the motors in accord nace load, substantially as described.

4. The method of operating a battery of furnaces, which includes supplying fuel and air to each furnace in a definite ratio at a ratio with variations in the load of the battery, substantially as described.

5. The method of operating a battery of furnaces, which includes supplying fuel and air to each furnace in definite proportions at a given load, automatically varying such proportions with variations in the load of the battery, and supplementally varying the fuelair'ratio -of a furnace in the'battery to compensate for its individual characteristics while leaving it susceptible to said automatic variation, substantially as described.

6. The combination with a battery of fur naces, of at least one draft fan for each furnace, electric motors for driving the fans, and; means for automatically controlling the speeds of the motors comprising means for supplying to a winding of each motor electric current having its voltage controlledin accordance with a function of the battery, substantially as described.

7. The combination with a battery of furnaces, of fuel'supply means for each furnace, electricmotors for driving the same, and means for automatically controlling the speeds ofthe motors comprising means for supplying to a winding of each motor electric current having its voltage controlled in accordance with a function of the battery, substantially as described.

8. The combination with a batter of fur naces, of fuel supply means and at east one draft/fan for each furnace,-electric motors for driving the fuel supply means and fans, and means for automatica ly controlling the speeds of the motors comprising means for supplying to a winding of each motor electric current having its voltage controlled'in' accordance with a function of the battery, substantially as described. I

9. The combination witha battery of furnaces, of air-and fuel supplying means, electric driving motors therefor and a common controlling means therefor, comprising gen.- erators having their output varied, accordance with a function of the battery, said enerators being connected with the air and uel supplying motors to correspondingly var their speeds, and means for independent y regulating the speed of the individual motors, substantially as described.

I 10. The combination with a battery .of furnaces, of air and fuel supplying means, electric driving motors therefor and a .common controlling means comprising a plurality of generators having their output varied in accordance with a function of the battery,.

nerators being connected withythe a r said and uel supplying motors to control their speeds, substantially as described.

11. The combination with a furnace, of

air and fuel supplying means therefor and .motors therefor, and controlling means comprisingv generators connected with the air and .fuel supplyingmotors and adapted to ance with afunction of the furnace to supply proportionate amounts of fuel and air varied in accordance with-a function of the battery, one of the .generators being connected with the air supply means so as to vary the speed of said motors in accordance with said function of the furnace, another generator being connected with the fuel control means andadapted to vary t supply motors and adapted to vary the speeds of said motors in accordance with said, function 'of the furnace, substantially as described.

13. Control apparatus for a battery of furnaces, including fuel supplying means, air supplying means, fuel-supplying control meansadapted to control the fuel supplying means for all the furances inthe battery, air-supplying control means adapted to control the air supplying means for allthe furnaces in the battery, means responsive to a function of the battery operatively connected with both the air and fuel supplying I e same to increase or, decrease the rate of fueland air supply. with varying demands on the battery, and means for varying the effect of variations ofthe meansresponsive to the battery function on the fuel and air supplying control means whereby the'fuel-air ratio forv the entire battery may be varied by such adjustment, substantially as described.

14. Control apparatus for a battery of furnaces, including fuel supplying means,

air supplying means, fuel-supplying control means adapted to control the fuel supplying means for allthe furnaces inthe battery, air-supplying control means adapted to con trol the air supplying means for all thefurnaces in the battery, means responsive to a function of the battery operatively connected with both the air and fuel supplying control means and adapted to vary the same to increase or decrease the rate of fuel and air supply with varying demands on the battery, means for varying the effect of variations of the means responsive to the battery.

function on the fuel and air supplying control means whereby the fuel-air ratio for the entire battery may bevaried by such adjustment, and means for individually" adjusting the air and fuel supplying means for any furnace inthe battery while leaving .such means susceptible to the common battery control, substantially as described.

15. Control. apparatus for a battery of furnaces, including fuel supplying means, forced draft means and forced draft regulating means and induced draft means and induced draft regulating means, fuel-supplying control means adapted to control the fuel supplying means for all the furnaces in the battery, forced draft control means adapted to control all the forced draft regulators, induced draft control means adapted to control all the induced draft regulators, means responsive to a function of the battery operatively connected with all of'said con trol means and adapted to vary the same to increase or decreasethe rate of fuel and air supply with varying demands on the battery, and means for varying the effect of variat'ionsof the means responsive to the battery function on-any of said control means, sub-o stantially as described. I e

a 16. The combination with a battery of furnaces, of air and fuel supplying means, electric driving motors therefor and a common controlling means comprising a motor generator set having its output varied in accordance with a function of'the battery, the generators of such set being connected with the air and fuel supplying motors to correspondingly vary their speeds, and meansfor independently regulating the speed of the individual motors, substantially as described.

17. The combination with a battery of furnaces, of air and fuel supplying means, electric driving motors therefor, and a com-; mon controlling means comprising a motor generator set having its output varied in accordance with a function of the battery, the generators of. such set being connected with the air and fuel supplying motors to control their speeds, substantially as described. V

18. The combination with a battery of furnaces, of air and fuel supplying means, 105

electric drivingmotors therefor,';and a common controlling means therefor comprising a motor generator set having its speed varied in accordance with a function of the battery,l the generators of such set being connected with the air and fuel supplying motors to correspondin ly vary their speeds, and meansfor indepen speed of the individual as described.

19. The combination withra battery of furnaces, of air and fuel supplying means,

electric driving motors therefor, and acommon controlling means comprising a motor generator set having its speed varied in accordance with a function 'of'the battery, the generators ofsuch set being connected with ently regulating the f motors, substantially the air and fuel supplying motors to control their speeds, substantially as described,

so constructed and arranged as to regulate the speeds of the motors in accordance with the said function of the furnace to supply the correct proportionate amounts of air and fuel at the varying rates of combustion, substantially as described.

21. The combination with a furnace, of air and fuel supplying means, and controlling means therefor acting automatically to supply air and fuel in suitable ratio to carry a given load upon the furnace, said means being adapted to varythe fuel-air ratio. as the rate of combustion is varied, substantially as described. U

22. The combination with a battery of furnaces, of air and ,fueLsupplying means for each furnace, electric driving motors therefor, and a controllin vmeans comprising a motor generator set aving its output varied in accordance with a function of the furnace, and having generators connected with the air and fuel supplying motors so as to vary. the motor speeds in accordance with the output of the motor generator set, and means connected with one of the generators for modifying the voltage impressed by said generator upon its controlled motors, substantially as described.

23. The combination with a battery of furnaces, of air and fuel supplying means for each furnace, electric driving motors therefor, and a controlling means comprising generators having their output .varied in accordance with a function of the furnace andhaving such generators connected with theair and fuel supplying motors so as to vary the motor speeds in accordance with the output of the enerators, and means connected with one of the generators for modifying the voltage impressed by said generator upon its controlled motors, substantially as described.

24. The combination with a battery of furnaces, of independently driven air supplying and fuel supplying means for each furnace adapted to supply air and fuel to such furnace in definite proportions for a given load, controlling means therefor acting automatically to suppl approximately equal amounts of fuel an air to each of the individual furnaces in predetermined proportions, means for su plementally controlling the proportions 0 air and fuel supplied to any furnace while leaving its air and fuel supplying means susceptible to the centralized controlling means and means for modifying the effect of said control means on the supplying means for one .of the elements of combustion for all of the furnaces, substantially as described.

25. Control apparatus for a battery. of furnaces, including fuel-supplying means and a stack damper for each of the furnaces, fuel-supplying control means adapted to control the fuel-supplying means for all the furnaces in the battery, damper control means and adapted to vary the same to in crease ordecrease the rate of fuel and air supply with varying demands on the battery, substantially as described.

26. Control apparatus for a battery of furnaces, including fuel-sup lying means and a stack damper for each of the furnaces, fuel-supplying control means adapted to control the fuel supplying means for all the furnaces in the battery, damper control meansadapted to control the stack dampers for all the furnaces in the battery, means responsive to a function of the battery operatively connected with both the control means and adapted to vary the same to increaseor decrease the rate of'fuel and air supply with varying demands on the battery, and means for varying the effect of variations of the function-responsive means on at least one of said control means, substa'ntially as described.

27. Control apparatus for a battery of furnaces, including fuel-supplyin means and an induced draft fan for eac of the furnaces, fuel-supplying control means adapted to control the fuel-supplying means for all the furnaces in the battery, induced draft fan control means adapted to control the induced draft fans for all the furnaces in the battery, and means responsive to a function of the battery operatively connected with both the control means and adapted to vary the same to increase or decrease the rate of fuel and air supply with varying demands on the battery, substantially as .described.

28. Control apparatus 'for a battery of furnaces, including fuel supplying means and an induced draft fan for each of the furnaces, fuel-supplying control means adapted to control the fuel-supplying means for all the furnaces in the battery, induced draft fan control means ada ted to control the induced draft fans for a l the furnaces in the battery,means responsive to a function of the battery operatively connected with both the control means and adapted to vary the same to increase or decrease the rate of fuel and air supply with varying demlands on the battery, and means for varying the effect of variations of the func tion responsive means on at least one of said. control means, substantially as described.

29. The combination with a battery of furnaces, of independently driven fuel and air supplying means for the individual furnaces in the battery, control means aotuated in accordance with a function of the battery and effective for controlling tery effective for controlling all of the supply means and tending toward the supply of fuel and air to all of the furnaces in a predetermined ratio, means associated with an individual furnace to modify the fuel-air ratio imposed by said control means onsuch furnace and means for modifying the effect of said control means on the supplying means of'one of the elements of combustion for all of the furnaces, substantially as described; I v

31. The method 'of operating a battery of furnaces which includes controlling the rate ofsupply of the elements of combustion to the furnaces in the battery in accordance with a function of the battery and supplementally controlling at least one furnace in the battery to cause a departure from such rate of supply of an element of combustion to such furnace to compensate for its individual characteristics and divide the load uniformly over the furnaces constituting the battery, substantially as described.

32. The method of operating a battery of furnaces each having at least one motor for supplying an" element of combustion thereto, which includes varying the speeds v of the motors in accordance with a function of the battery and supplementally regulating the speed of at least one motor to compensate for the individual character: istics of its furnace, substantially as do scribed. Y

33. The combination with a battery of furnaces, of a draft fan for each furnace, an individual driving means for each fan, all of said driving means forming a set, a fuelsupplying device for each furnace, an individual driving means for the fuel. supplying device of each furnace, all of said driving means forming another set, a control means operating in accordance with a function of the entire'battery, and sep-' arate connections between said control means and the said several sets of driving means, substantially as described.

34. The combination with a battery of furnaces, of a draft fan for each furnace, an individual driving means for such fan. all ofisaid driving means forming a set, a fuel supplying device for each furnace, an

4 motors, substantially as described.

individual driving means for the fuel supplying deviceiof each furnace, all of said driving means forming'another set,a control means operating in accordance with a function of the entire battery, separate connections between said control means and the said several sets of driving means, and supplemental control means for adjusting the fuel-air ratio of each individual furnace while leaving its air and fuel supplying means susceptible to; said control means, substantially as described. I

35.'The combination with a battery of furnaces, of independently driven air-supplying means for each furnace in the bat tery, an electrio driving' motor therefor, a common control means actuated in accordance with a function of the battery and effective for controlling all of such motors, and means for modifying the effect of the control means onflat least one of the motors, substantially as described. 36. The combinationwith a battery of furnaces, of independently driven fuel-supplyingmeans for each furnace in the battery, an electric driving motor therefor, a. common control means actuated in accord-' ance with a function'of the battery and ef-' fective for controlling all of such motors, and means for modifying the effect of the common control means on at least one of said motors, substantially as described.

37. The combination with a battery of furnaces, of independently driven fuel and air supplying means for each furnace in the battery, an electric driving motor for each of said supplying means, a common control actuated in accordance with a function of the battery and effective for corn trolling all of the driving motors, and means for modifying the effect of said control means on at least'onc of the driving 38. The method Ofoperating a battery of furnaces, which includes -an element of combustion-"to'the several furnaces of the battery at a rate for one furnace differing from the rate for another furnace in accordance with the individual characteristics of such furnaces, and varying the rate of supply of such element of combustion for each of the furnaces in the battery in accordance with a function of the battery, substantially as described.

39. The method of oper'a'tinga battery of furnaces, which includes supplying fuel and air to the several furnaces of the battery at rates for one furnace varying from the rates for another furnace in accordance with the individual characteristics of such furnaces, and varying the rate of supply of fuel and air for each of the furnaces 1n the battery in accordance with'a function of the battery, substantially as described. 40. The method of operating a battery of furnaces, which includes supplying fuel and air to the several furnaces o the battery at rates for one furnace varying from the rates for another furnace in accordance with the individual characteristics of such furnaces, varying the relative rate of fuel and air supply for an individual furnace in the battery, and var ing the rate of supply of fuel and air or'each furnace in the battery in accordance with a function of the battery, substantially as described.

41. The method of operating a battery of furnaces each having an air supply means and each having a fuel sup 1y means, which includes operating the fuel and air supply means for the several furnaces to supply fuel and air thereto, operating the fuel supplying means for one furnace at a speed differing from that of another furnace, and

controlling the operation of allof the fuel and air supply means in accordance with a function of the battery, substantially as described.

42. The method of operatin abattery of boiler furnaces, which inclu es supplying an element of combustion to the several furnaces of the battery at a rate for one furnace differing from the rate for another furnace in accordance with the individual charbustion for each of the furnaces in the battery in accordance with variations in ressure in the battery header, substantial y as described.

44. The method of operatin a battery of furnaces each having air supp ymeansand each having fuel supply means, which in cludes operating the fuel and air supply means for the several furnaces to supply fuel and air thereto, controlling a supply means for one of the furnaces to effect the supply of fuel and air thereto in a ratio differing from the fuel-air ratio forjanother furnace in the battery, and controlling all of the fuel and air supply means in accordance with a function of the battery,'substantially as described.

45. The method of controlling a battery of furnaces having individual supply means for supplying the elements of combustion thereto, which includes substantially simultaneously adjusting a plurality of control means constituting a centralized battery control in accordance with a function of the battery, utilizing the Various control means to automatically regulate thesupply of the different elements of combustion to all of the furnaces in accordance with such function, and su plementally regulating at least one of the urnaces to compensate for its individual characteristics while leaving it susceptible to the centralized battery control, substantially as described.

46; The method of controlling a battery of furnaces having individual supply means for supplying the elements of combustion thereto, which includes substantially simultaneously adjusting a pluralit of control means in accordance with a unction of the battery, utilizing the various control means each to automatically regulate the individual supply means for the various elements of combustion to the several furnaces in the battery and relatively adjusting the several control means, sub stantially as described.

47. The method of controlling a battery of furnaces having individual supply means for 'supplyin the elements of combustion thereto, whic includes substantially simultaneously adjusting a plurality of control means in accordance with a function of the batter utilizing the various control means eac to automatically regulate the individual supply means for the various elements of combustion to the several furnaces in the battery, relatively adjusting the several control. means, and supplementally regulating the individual supply means to compensate for the characteristics of the furnaces while leaving such supply means susceptible to the centralized battery control, substantially as described.

In testimony whereof, we have hereunto set our hands.

LAWRENCE J. HESS.

MERRILL G. BENJAMN.

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