US1522877A - Furnace regulation - Google Patents

Description

Jan. 13, 19257 G. H. GIBSON FURNACE REGULATION Original Filed Nov. 9, 1915 4 Sheets-Sheet 1 INVENTR Lwa' ATTORNEY Fig.2.

1,522,877 G. H. GIBSON FURNACE REGULATION Original Filed Nov. 9,1915 4 Sheets-Sheet 2 -INVENTOR ea 7Q 4W l/wd' ATTORNEY Jan. 13, 9 Q 1,522,877

G. H. GIBSON FURNACE REGULATI ON Original Filed Ndv. ea, 1915 4 sheets sheet 3 INVENTOR G. H. GIBSON FURNACE REGULATI 0N Original Filed Nov. 9, 1915 4 Sheets-Sheet 4 stokers the traveling fuel bed is, in efi'ect,-

Patented as. is, was.

summon nneura'rron.

Original application filed November 9, 1915, Serial No. 60,623. Divided and this April 22, 1920. Serial No. 375,728.

To all whom it may concern:

Be it known that I, GEORGE H. GII 5SON, a citizen of the United States, and resident of Montclair, in the county of Essex and The primary object of my present inven-.

tion is to provide an improved method of, and means for regulating the supply of air for combustion to the combustion chambers of boiler and other furnaces. An important specific'object of my invention is to provide satisfactory means for supplying primary and secondary air in definite-relative proportions to the combustion space of a furnace when the character of the furnace or its mode of use make it necessaryor desirable to provide the two proportioned air supplies to the combustion space-of the furnace for its most satisfactory or eflicient use; and my invention comprises novel means effective to automatically maintain a predetermined ratio between the rates of flow of the two streams of air.'

The need for accurately proportioned supplies of primary and secondary air to the combustion space of a furnace is experienced in connection with many different kinds of furnaces. For instance, where air is passed through a sufficiently deep bed of fuel on an ordinary grate, the gaseous product rising from the fuel bed is substantially" a producer gas. For the complete and eilicient combustion of this producer as, a definite quantity of secondary air sho d be supplied to the-combustion space of-the furnace above the fuel bed.

In fuel beds fed by ordinary automatic divided into two sectionsin one of which the coal is subjected to a coking operation whereby the volatile matter is distilled out of the coal, and in ,the other of which the coke residue of the coal from which the excess of air for the complete combustion in application filed the space above the fuel bed, of the combustible gas rising from the first section of the fuel bed. The eflicient operation of a furnace equipped with a stoker of this type reijiluires the two supplies of air to be carefu y as to the quantity of coal consumed.

IIn burning oil or pulverized coal it is commonly found desirable to provide pri-. mary air to facilitate the introduction of the fuel into the combustion space and its proportioned to one another as well initial combustion, andto provide a secondary supply of air to complete combustion, and for the most eflicient operation the two supplies of air should be proportioned to one another. I

' The provision of two'proportioned supplies of air is also of prime importance in cases where solid fuel is burned initially with an insufficient supply of airin order to get a reducing flame and is subsequentlyburned 'witlrmore air to supply heat in another portion of the apparatus.

The various, features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, and the advantages possessed by it, reference should be had tothe accompanying drawings and descriptive matter in whichI have illustrated and described the preferred embodiments of my invention.

Of the drawings:

Fig. 1 is a diagrammatic elevation partly in section, of a steam generating plant haviiig provisions for passing regulated and proportioned .streams of air through two zones or sections of a fuel bed maintained by an automatic stoker;

Fig. -21is a diagrammatic representation of a portion of a steam generating plant provided with means for supplying proportioned amounts of air to the furnace chamber above and below the fuel bed;

Fig.- 3 is a view taken similarly to Fig. 2 of apparatus accomplishing the same general purpose butin a' somewhat different manner;

Fig.4 is a diagrammatic elevation partly in section illustrating the use of my invention in aplant'in which powdered coal is burned with a restricted amount ofair to supply a reducing flame to a reverberatory furnace, and the combustion of the reducing flame gases is thereafter completed and the heat of these gases utilized in supplying heat to a boiler;

Fig. 5 is a diagrammatic elevation partly in section illustrating the application of my invention to a furnace in. which liquid or gaseous fuel is burnt;

Fig. 6 is a view taken similarlyto Fig. 3, illustrating a modified form of mechanism for obtaimng the same general kind of furnace regulation;

Fig. 7 is a view taken similarly to Fig. 2 and illustrating a modified form of apparatus for obtaining the same kind of furnace regulation; and

Fig. 8 is a sectional view of a detail empkiyed in Fig. 7.

n the construction shown in Fig. 1, I have illustrated the application of my invention to a steam generating plant of the kind in which an automatic stoker is employed to continuously feed fuel on to the inclined grate A of a furnace A. The ashes and cini ders fall off the lower edge of the grate A into an ash pit A. As shown, the grate A is perforated to permit the passage through the fuel bed of primary and a. secondary air from the air chambers A and A respectively beneath the grate. The air supplied to the'chamber A does not com pletely burn the fuel on the portion of the grate A adjacent to the chamber A The air is supplied to the chamber A in excess of that required to burn to ashes the coke ing from the upper section' as the commingled products pass into and through the spaces beneath the tubes of the water tube boilers B shown as heated by the fuel burnt on the grate A.

. In the conventional form illustrated, the stoker comprises a reciprocating plunger C which withdraws coal from the hopper D supplied to the latter through a chute D and forces it into the upper head of the fuel bed in successive relatively small charges.

As shown the plunger C is reciprocatedthrough the crankv C, suitable intermediate gearing C and a belt C by the engine E which is shown as directly conected to, and

. driving the forced draft blower H. vAs

plied the engine E and hence the speed of i the latter is I regulated by the. pressure generated in the boiler. The regulating means comprising a regulating valve F and a diaphragm device F subject to the steam pressure and tending to open and close the valve J F 2 accordingly as the steam pressure falls and rises. .The outlet pipe I from the blower H is connected to the chambers A and A by branch conduits IA and 1B which are'shown as comprising each a Venturi section. With this arrangement it will be apparent that the difference between the pressures at the small cross section portions of the conduits IA and IE will be a function of the ratio betweenj'the rates of flow through the two conduits. By maintaining a predetermined ratio between these pressures it is therefore possible to maintain a predetermined ratio between the rates of flow through the two branch conduits. This with one chamber connected by the pipe Ix to thesmall-diameter portion of the conduit IA, and the other chamber connected by the pipe K to the small diameter portion of the conduit IB. The diaphragm is connected by a stem j and'link 7' to a lever L on which the damper M which is vertically movable rests. A .weight L adjustably mounted on the lower L forms a means for bringing the damper lever and connected diaphragms into balance. A dash pot piston working in the dash pot chamber 7" prevents the damper regulating means from hunting. An adjustment of the ratio of the rates of flow in the conduits IA and IB may be had by the manually adjusted damper N.

Advantageously the flow controlling provisions already referred to are combined with means for proportioning the total amount of air supplied to the furance to the fuel supplied to the furnace. As shown, the means for accomplishing this result comprise a small blower O which is driven by the engine E and therefore is driven at a speed proportional to the rate at which coal is fed into the combustion space of the furnace by the stoker plunger C. The blower O is formed with a central inlet connected by the pipe 0' to the chamber 7' of a fluid pressure damper regulating device JA. As shown, the blower O is formed with a radial slot 0 and is provided with an adjustable damper P formed with an inclined slot P. By adjusting the. damper F, the outlet from the blower 0 formed by the intersection of the slots and P can be moved toward or away from the axis of the blower with the effect of decreasing or increasing the suction of the pump. The fluid pressure device JA 7 comprises three chambers J, 7' and j. The chamber j is separated from the chamber j by the flexible diaphragm 7' The chambers j and are separated by a flexible diaphragm 9' substantially larger in area than the diaphragm j. The outer wall of the'chamber j is formed with a central opening closed by a diaphragm j of the same area as the diaphragm 3' A central stern j connected to the diaphragm j", j and j, is connected to a lever LA on which rests the vertically movable'damper MA projecting into the conduit I at a point between the blower and the division of the conduit into its branches IA and I13. The chamber 7' is connected by a pipe K to the small diameter portion of the conduit IA and the chamber 7' is connected by the pipe KB to the conduit I and thus serves to transmit the static pressure of the conduit I to the chamber lVith the arrangement described it will be apparent that the damper MA will auto- 'ing device JB is employed.

matically be adjusted to preserve a constant ratio between the differential of the static pressures in the body of the pipe I and at the small cross section portion of the conduit IA on the one hand, and the pressure in the chamber i on the other hand. The latter pressure is a function of the stoker speed of operation, and the differential pressure referred to is a function of the-rate at which air is supplied to the furnace. The device JA operates therefore to proportion the total amount of air supplied to the furnace to the amount of coal supplied. The device J operates. as will be readily apparent to those skilled in the art, to maintain a predetermined ratio between the amounts of air supplied to the furnace through'the conduits IA and IB. 'lhis ration may be adjusted by the adj ustment of the manually controlled damper I.

In the modification illustrated in Fig. 2, a fire tube boiler BB is shown in'a hand fed furnace AA with a stack outlet A, and a fuel supporting grate A and.- with an air inlet A for primary air opening to the ash pit underneath the grate, and with an inlet or channel A in the furnace bridge wall for supplying secondary air to the combustion space above the grate. To automatically proportion the amounts of primary and secondary air, a damper-regulat- The device JB is essentially the same as the-device JA with the exception that it comprises an extra chamber 7' separated from the chamber j by the diaphragm 7' The chamber 7' is formed with a port communicating with the secondary air conduit IB at the inlet side of a damper NA therein which 'may be manually adjusted to vary the ratio of primary and secondary air to be maintained. The chamber 1' is connected to the conduit IB at the outlet side of the damper NA. The chamber j of the device JB isconnected to a Pitot tube KC in the primary air supply conduit IA, and a plpe KD transmits the static pressure of the conduits IA to the chamber j. In the diagrammatic illustration of Fig. 2, the stem 7' connecting the three diaphragms of the device JB passes through, but does not fill the opening between the chamber j and the conduit IB into the latter where it operates a. damper MB. As shown, the damper MB is of the pivoted or'butterfly type. It is to be observed, however, that in practice the damper of flow regulating valve operated in this manner should, in general, be of a more perfectly balanced type than is abutterfly valve.

In the modification illustrated in Fig.

3, the boiler BC and .its furnace A are shown as substantially the same as the boiler BB and furnace AA of Fig. 2 with the exception that in Fig. 3 no air passage A isformed in the bridge wall. As conventionally illustrated in Fig. 3, the secondary air is'supplied to the combustion chamber above the fuel bed through an air inlet A in the front of the boiler. In practice it will be understood that in a boiler of this type the air admitted to the combustion chamber above the fuel bed may not. v

only pass through inlet ports formed in the boiler housing for the purpose, but also through leaky .joints and cracks in the masonry and iron work of the boiler housing. In'the arrangement shown in Fig. 3, the primary air is forced into the ash pitth'rough the conduit 10 and inlet A y the forced draft fan H driven by the engine E and the rate of combustion may be con,- trolled by varying the "speed of the blower which may be accomplished by the manual adjustment of the throttle valve F in the steam supply pipe FA ofthe engine E. A manuall adjustable damper NE in the conduit I is-employed to regulate or adjust the ratio of the primar and secondary air. 'A device JC and a amper MC operated thereby and located in the stack outlet A are employed to directly maintain a predetermined ratio between the amounts of primary air supplied to the furnace and. the total products of combustion'issu'ing from the furnace and thereby, since the volume of the total products of combustion is a definite function of the amounts of sistance to'fiOw of those tubes and a presjusts the damper MC as required to provide the increased suction or drop 1n pressure above the furnace grate necessary to cause the increased influx of secondary air required to maintain the predetermined ratio between the amount of primary air and products of combustion. When the amount of prlmary air decreases the pressure above the furnace grate is correspond in 'l raised. The )ressure in the combustio-n chamber above the furnace grate thus varies inversely with the rate at which primary air is supplied, with the rate at which secondary air is supplied and consequently, with the rate of combustion.

For this purpose the chamber 1' is connected to the combustion space of the boiler immediately above the fuel bed by the pipe K while the chamber 7' is connected by the conduit K to the stack outlet A below the damper MC. The differential of the pressures in the chambers 7' and j is a function of the loss of head due to the passageof the entire body .of heating gases through the boiler tubes and hence is a function of the volumetric rate of flow of these gases. The chamber 9' is connected by a pipe K to the conduit IO at the outlet'side of the damper NB. The chamber 1' is connected by the pipe K to the conduit IC at the inlet side of the damper NB. The difference between the pressures in the chambers j and 1' due to the frictional resistance to the flow of air to correspondingly open or close the damper MC and thus to correspondingly increase 0I' decrease the amount of secondary air which Wlll be drawn mto the furnace and out through the stack. Similarly, a momentary increase in the amount of secondary air ad-' m itted such as may occur when a firing door is left open, 0 erates to effect a closure of the damper M and thus restores the normal ratio between the two rates of flow. It will.

be observed that the valve N of Fig.1, the valve NA of Fig. 2 and the hinged valve controlling the port A of Fig. 3 each serves as a regulating damper on adjustable constriction in'apassageway through which air is passed into the combustion chamber of the furnace, and that the differential of the pressures at the opposite sides of each of thesedampers depends upon and is controlled by the setting of a corresponding control valve, namely the' valve )1 of Fi 1, the valve lVIB of Fig. 2 and the valve M6 of Fig. 3. Each of these control valves is automatically a'ctuated by a mechanism responsive to a pressure differential to thereby automatically maintain a differential between the pressures at the opposite side of the corresponding regulating damper, which varies in predetermined relation with the load carried by the boiler.

In the modification illustrated in Fig. 4, the boiler ED is a waste heat boiler receiving the partially cooled heating gases from a reverberatory metallurgical furnace Q through the air inlet A opening to the supplementary combustion space A below the boiler BD. The gaseous products for heating the reverberatory furnace are formed byv the combustion of powdered coal blown into the furnace with primary air in amount sufficient for the combustion of the coal to a reducing flame, HA representing the blower and RR the powdered fuel feeding device. The latter is driven by the same engine which drives the blower HA and serves to feed the pulverized fuel at the proper rate from the hopper B into the conduit ID lead ing from the bloweroutlet to the fninacef (.2. Secondary air to complete the combustion of the gaseous products from we reverberatory furnace is supplied to the compxustion chamber A throughthe air inlet The quantity of primary air and the rate of combustion in this case is controlled by the manually actuated steam supply valve F in the-steam supply line F for the engine E driving the blower HA. A damper MD in the secondary air supply line ID is automatically actuated to proportion the secondary air to the primary air. The proportioning mechanism employed. for this purpose might be generally like the proportioning mechanism shown in Fig. 1 Or Fig. 3, but as actually shown in Fig. 4 it comprises a pair of pressure chambers S and S having opposed flexible diaphragms acting in opposite directions on one end of a lever S pivoted on a fulcrum block S. A pipe K connects a Pitot tube facing the direction of flow in the conduit ID tothe chamber S. A pipe K transmits the static pressure of the conduit IDto the chamber. S At the opposite side of'the fulcrum S the lever S is acted upon inopposite directions by the opposed flexible wall portions of two pressure chambers S and S. The chamber S is connected by a pipe K to a Pitot tube located in and facing the direction of flow in the conduit ID, while a conconduit ID' to the chamber S.

du-it K transmitsthe static pressure in the The damper MD is operated by a fluid ressure dam-v per operating device FA wiich receives pressure fluid through the pipe T and the restricted orifice T in the latter from a suitable source. The pressure in the device FA, and consequently the position of the damper MD is a function of the leakage through the orifice T which is throttled more or less depending on the osition of the lSBVGI' S by avalve S carrie by the lever With the apparatus shown in Fig. .4 the differential of the pressures in the chambers S and S is a function of the rate of flow through the conduit ID, and the differential of the pressures in the chambers S and S is a function of the rate of flow through the conduit ID. The device S operates to vary the pressure to which the operating device "FA is' subjected and consequently to vary the opening of the damper MD as required to maintain the predetermined ratio between the primary and secondary supplies-of air. The apparatus shown in Fig. 4 may be made more sensitive than the apparatus shown in the other figures for the reason that the diaphragmsor flexible wall portions of the pressure chambers S, S S and S need have but very little movements, for the extent of movement of the damper MD is not dependent upon the mere extent of movement of the diaphragm or flexible wall portions of the pressure chambers.

In Fig. 5 I have illustrated the use of my invention in maintaining a predetermined ratio between two fluid streams, one of fuel and one of primary air, so as to secure and maintain a definite mixture composition and also in dividing a stream of air into definitely proportioned branch streams of primary and secondary air. In the arrangement shown in Fig. 5, AE represents the combustion chamber of a steam generating plant. Gaseousor liquid fuel is supplied to the burner W through the conduit U, and primary air is also supplied to the burner W through the branch 1A of the main air supply conduit'IE. A. second branch IB of the air supply conduit IE supplies secondary air to the combustion amount of primary air supplied to the burnerW is fixed by the adjustment of a damper ME and the latter is automatically adjusted to preserve the desired ratio between the quantity of gaseous or liquid fuel and the primary *air by the difl'erential pressure device JE. The device .JE com- -prises a casing divided into chambers j Y and j by a diaphragm j which is connected to the damper MEQThe chamher 7' is open to the conduit U and the 'chamberj is open to the conduit IA.

With gas or liquid fuel the rate of dischamber AE. The.

charge of both the fuel and theair through the burner V will ordinarily be a function of the corresponding supply pressure, and with the apparatus shown in Fig. 5, the damper ME-will be adjusted to maintain a predetermined ration between the pressure in the primary air supply conduit IA at the outlet side of the damper ME, and'the pressure in the fuel supply conduit U.. The

proper ratio of secondary to primar air is obtained by means of the damper M 4 in the conduit IE and its differential pressure controlling device J F which is essentially the same as the device JE. The two chambers 7' and j of the device J F are open to the conduits 1A and IE at the outlet sides respectively of the dampers ME and MF. It

will be understood, of course, that the modes of draft regulationsimflar or analogous to I those already described may be carried by different means from those already dedescribed, and Figs. 6 and 7 are examples of modifications which may thus be made.

In Fig. 6 I have illustrated apparatus- 'differing from that shown in Fig. 3, but

adapted to give the same kind of regulation.

In 'Fig. 6, the total rate of combustion is controlled by the flue damper MD which as shown, is adapted for manual actuation.-

The ratio of primary and secondary airis regulated by the balanced valv'e F in the steam supply pipe F for the engine E driving the blower H. The controlling means for the valve F comprises four bellows chambers K, K K and K. The chambers X and X have opposed ends Walls X rigidly connected to the stationary frame X, and a common floating end wall X",

mechanically connected to the movable frame X by which the valve F is operated. Similarly the bellows chambers X and K have opposed end walls X rigidly connected to the stationary frame X and a movable intermediate wall X connected to the mov- I 'the chambers X and X subject the frame X to an opposing differential force which is a function of the flow of air through the conduit IC- to the under side of the grate.

It will be obvious, of course, that more positive of powerful means for setting up the air flow or operating the dampers than those already referred to in detail may be employed if and when this seems desirable. This is illustrated for example in Figs. 7

and 8 which show a modified form of apparatus for accomplishing the same regulation as is intended to be secured with the a paratus of Fig. 2. In Fig. 7 the blower I- B employed is of the positive rotating piston type. The discharge conduit 1 leading from the blower outlet to the primary and secondary air admission passages A" and A" reslxictively. of the furnace is divided adjacent its discharge end by the partition I into branches 1A and 1B. A pivoted damper N controls the division of the air discharged by the blower between the branches IA and 1B. This damper is shown as operated by the reversible electric motor Y having a worm Y on its shaft in mesh with the gear segment N secured to the arbor of the damper N. The means shown in Fig. 7 for starting, stopping or reversing the motor Y in response to changes in the distribution of flow through the channelsIA and IA comprises a switch YA. for opening, closing and reversing the armature connections ot'the motor Y, and an o crating device Z for operating this switc 1. The device Z comprises an axle Z pivoted in the wall between the channels IA and IA and provided with arms Z projecting into each of these channels and each carrying an adjustable v'ane Z Preferably provisions are made to restrict racing or undesirable oscillation of the vanes Z and this is accomplished in the form shownby turning the two arms backwards so that the vanes make an angle a little less than 180 with one another. The device Z also comprises a portion formed with a. race-way Z for a rolling weight in theform of a ball Z. In

the neutral condition of the apparatus, the ball Z rests in a central cavity Z, in the raceway Z and the arms of the switch YA do not contact with any of the cooperating switch contacts 1, 2 or 3. An excess flow through the channel IA, and a consequent tilting of the member Z in a clockwise direction causes the switch arms of the switch YA to be moved into engagement with the contacts 1 and 2 which has the effect of starting the motor Y with such direction of rotation that the damper N is turned clockwise to cut down the flow through the channel IAP. When the desired ratio of flow is restored, the member Z assumes a neutral position and-Ache motor stops. Similarly when the flow through the channel 113 becomes excessive, the member Z is tilted'to move the arms of the switch A into the position in which they engage the contacts 2 and 3 and thus causes the m0- tor to be operated in the direction to adjust the damper N so as to restrict the flow through the channel IB -When the member Z isturned from any position previously occupied by it sufiiciently to displace the weight Z from its previous position, the

shifting of the weight insures an extent and rapidity of turning movement of the member minimizing sparking at the switch contacts. The particular construction shown in Fig. 1 and .claimed generically but not specifically herein. is claimed specifically in my Patent No. 1,360,285, granted November 30, 1920, of which this application is a division.

While in accordance with the provisions of the statutes I have illustrated and described the best forms of my invention now known to me, it will be apparent to those skilled in the art that changes can be made in the form of my invention without departing from its spirit, and that some features of my invention can be used without a corresponding use of other features of the invention.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a furnace having primary and secondary air supplies, the combination of means jointly responsive to the amounts of primary and secondary air supplied, and flow controlling means actuated by the first mentioned means to regulate the ratio of primary air to secondary air.

2. In a furnace having primary and secondary air supplies, the combination of fluid pressure means 'ointly responsive to the rates of flow of t e primary and secondary air, and flow controlling means actuated by the first mentioned means to regulate the ratio of air. g

3. In a furnace having primary and sec ondary air supplies, the combination of fluid pressure means for creating a differential pressure .Which is a function of the ratio of the volumes of flow of the primary and secondary air and flow controlling means actuated thereby on a variation from said ratio from a predetermined standard to afl'ect a compensating'adjustment in said ratio. V

4. The mechanism for maintaining a predetermined ratio between the amounts of primary and secondary air supplied to a combustion furnace which comprises means for creating a pressure differential which is a measure of the rate of flow of primary air, means for creating a pressure difi'erential whichis a measure of the rate of flow of secondary air and flow adjusting means controlled by said pressure differentials.

5. Mechanism for-maintaining a predei te'rmined ratio between the amounts of primary and secondary air supplied; to a combustion furnace comprising means responsiveto the amount of primary air and secondary air. supplied and flow adjusting apparatus controlled by said means and regupressure controlled mechanism regulatin the relative amounts of primary 'air an secondary air supplied to the furnace, and

means for subjecting said mechanism to a lating furnaces operating under controlling pressure which is a function of the amount of primary air sup lied, and to a controlling pressure which 15 a function of'the amount of secondary air supplied. y

7. In a' furnace having a fuel bed and having rovisions for supplying primary air to the urnace chamber at one side of the fuel bed, and for supplying secondary air to the furnace chamber at the opposite side of the fuel bed, the combination therewith, of means responsive to the volume of flow of the primary air supplied for regulating the relative amounts of primary and sec ondary air supplied.

8. In a furnace having a fuel bed and a primary air supply connection opening to the furnace chamber at one sideof the fuel bed and a secondary air supply connection supplying air to the opposite side of the fuel bed to burn the combustible'gases issuing from the bed on that side,'the combination therewith, of means responsive to the volume of flow of primary air supplied to the furnace chamber, and means controlled by the last mentioned means for regulating the relative amounts of primary and secondar air supplied. t

9. The met 0d herein described of regulating furnaces operating under forced draft which consists in varying the pressure in the furnace chamber inversely with the varying rates of combustion.

10. The method herein described of regulating furnaces of a vapor generat or-ioperating under forced draft which consists in varying the pressure in thefurnace chamber inversely with the varying demand on the generator.

- 11. The method herein described of reguforced draft which consists in maintaining in the furnace chamber a pressure less than atmospheric pressure and varying inversely with the varying rates of combustion.

12. The method herein described of regulating furnaces of a vapor generator operating under forced draft which consists in maintaining in the furnace chamber a pressure less than atmospheric pressure and varying inversely with the demand on the generator.

13. The method herein described of regulating furnaces which consists in discharging gases from the furnace in quantities proportional to varying rates of combustion and supplying air to the furnace at such rates that the pressure in the furnace will vary inversely with the rates of combustion but at such a rate as to maintain under such varying rates of combustion pressure below atmospheric pressure.

14. The method herein described of regulating furnaces of a vapor generator operating under forced draft which consists in discharging gases from the furnace in quantities proportionalto varying demands on the generator and supplying air to the furnace at such rates that the pressure in the furnace will vary inversely with the demands on the generator but at such a rate as to maintain under such varying demands on the generator a pressure below atmospheric pressure.

15. The combination with a combustion chamber, means for supplying air thereto and means for maintaining therein a pres-- sure below atmospheric pressure and for ,automatically varying such pressure inversely with varying rates of combustion.

i 16. The combination with the combustion chamber of a vapor generator operating under forced draft, means for supplying air thereto and means for maintaining therein a pressure below atmospheric pressure and for automatically varying such pressure in versely with varying demands on the generator.

17. The combination with chamber, of a blower for supplying air thereto, means for establishing therein a pressure below atmospheric pressure and me a'ns for varying such pressure inversely proportional to varying rates of combustion.

18. The combination with acombustion chamber, of a blower for supplying air to said chamber, means for establishing therein a pressure below atmospheric pressure and for varying such pressure inversely to varying rates of combustion, said means comprising appartus for varying the exhaust of gases from the furnace and substantially simultaneously so varying the supply of air to the furnace that the pressure in the furnace will-not exceed a minus pressure.

19. In combination with a furnace, means for varying the escape of gases from the furnace in quantities graduated between the extremes, a blower, and means for varying the supply of air to the furnace from the blower in such quantities so graduated between the extremes as to maintain a pressure in the furnace inversely proportional to the graduated quantities of gases disa combustlon charged from the furnace, the parts being the combustion chamber, and means for controlling the differential in pressure at the damper whereby the quantity of air flowing past the damper is controlled. p

- 21. A combustion controlling system comprising a combustion chamber, a passageway for the air and gases through and including said chambcrfa damper in said passageway regulating the flow of air to the combustion chamber, and means for controlling the relation between the differential in pressure at the damper and the area of the damper opening.

22. The method of regulating furnaces which consists in controlling a constriction in the passageway for the air and gases through the furnace and in controlling'the differential in pressure at the point of constriction.

23. The method of controlling furnaces which consists in regulating the flow of air to the furnace by varying a constriction in the passageway for the air and gases through the furnace and in controlling the differential in pressure at the point of constriction.

24. The method of regulating the flow of gas under pressure through a passageway which consists in controlling a constriction in the passageway for the gas and in controlling the differential in pressure at the point of constriction.

25. The method of regulating the. flow of gas under pressure through a passageway which consists in regulating the flow of gas by varying a constriction in the passageway and in controlling thedifferential in pressure at the point of constriction.

26. An apparatus of the class described comprising a conduit, a damper in the conduit, means to adjust the position of the damper to vary the areaof the conduit at the damper, and means for controlling the differential in pressure at the damper whereby the quantity ofgas flowing past the damper is controlled.

27. An apparatus of the class described comprising a conduit, a damper in said conduit regulating the flow of gas therethrough, and means for controlling the relation between the differential in pressure at the damper and the area of the damper opening.

28. An apparatus of the class described comprising a conduit, a pair of dampers located at different points in the conduit, means for varying the position of one of said dampers to vary the damper opening,

and means controlled by the differential in.

pressure effecting the flow through said damper opening, acting to vary the position of the other damper to maintain constant the said differential in pressure.

29. The combination with a furnace having separate primary and secondary air supplies of means automatically responsive to variations in the ratio of primary air to secondary air supplied for adjusting one of said supplies in a direction tending tomaintain said ratio constant.

30. The combination with a furnace burning fuel on a grate and having separate

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