US2394297A - Furnace air control system - Google Patents

Description

Feb. 5, 1946. R. R. FAYLES 2,394,297

FURNACE AIR CONTROL SYSTEM Filed Feb. 25, 1943 2 Sheets-Sheet 1 Feb. 5, 1946. R. R. FAYLES FURNACE AIR CONTROL SYSTEM Filed Feb. 25, 1943 2 Sheets-Sheet 2 Patented Feb..5, 1946 UNITED STATES PATENT OF ElCE FURNACE AIR CONTROL SYSTEM Robert Russell Fayles, Coatesville, Pm, assignor to Lukens Steel Company, Coatesville, Pa., a corporation of Pennsylvania Application February 25, 1943, Serial No. 477,153

3 Claims.

I have discovered that the amount of air theoretically required for complete combustion of gas-- 'eous fuels and fuel oil varies substantially according to the B. t. u. content of such gases or fuel oils.

on the other hand, it is known that for a given gaseous or oil fuel. the B. t. u. content thereof per unit is constant, and, therefore, the total B. t. u. content of each such fuel supplied to a furnace may be calculated by determining the quantity or amount of fuel supplied in a given period of time.

Based upon the foregoing discovery, the present invention provides a control system for regulating the delivery of air for fuel combustion in accordance with the total B. t. u. content of the one or more fuels employed.

Accordingly, the principal object of the present invention is to provide a control system of the stated character which is operable automatically to control the amount of air supplied to a furnace in accordance with the requirements for complete combustion of one or more gaseous or oil fuels.

Anothe object of the invention'is to provide a control system of the character set forth which is foolproof and efficient in operation, and which is comparatively inexpensive, involving no costly and complicated equipment and apparatus.

Another object of the invention is to provide a furnace air control system of the type described which is adaptable equally to the control of air supply in relation to one or more gaseous o oil fuels as desired.

A further object of the invention is to provide a novel air control system of the character stated which is quickly responsive to variations in the total B. t. u. content of the fuel or fuels supplied to a furnace so that there is no appreciable lag in effecting variations in the amount of air supplied in response to variations in the total B. t. u. content of the fuel or fuels.

These and other objects of the invention and the various features and details of the construction and operation thereof are hereinafter set forth and described, and shown in the accompanying drawings, in which:

Figure 1 is a diagrammatic illustration of a iii control system embodying the present invention for regulating the air-supplied to a furnace in accordance with variations in the B. t. 11. content of a fuel or fuels; 1 A

Figure 2 is a view illustrating the construction of several similar elements in the system shown in Figure 1;

Figure 3 is a graphic illustration of the operation of the control system to effect increases and decreases in the amount of air in accordance with like variations in the B. t. u. content of a fuel or fuels: and

Figure 4 is a fragmentary view of the control system showing a modification therein contemplated by the present invention.

Referring now to the drawings, and particularly to Figure 1 thereof, a control system embodying the invention is. for purposes of illustration. shown as applied to a furnace i, which may be a conventional open hearth furnace as used in the steel industry. In the illustrated embodiment of the invention, leading into the furnace i are two fuel lines 2 and 3, respectively, and an air duct 4, the two fuel lines 2 and I being entirely separate and independent from each other and from the air duct 4.

The fuels employed and supplied to the furnace I through the lines 2 and 3 may be both gaseous. or liquid, or may be a gas and a liquid fuel. In the system shown in the drawings the fuel supplied to the furnace I through the line 2 is a liqu d oil fuel such as, for example, bunker C oil, and the fuel supplied through the line 3 is a gas. for example, natural gas, coke oven gas, or the usual hydrocarbon fuels such as methane, propane, acetylene, benzene, etc.

The relationship between the B. t. u. OOIltGnt Der unit of such ga and oil fuels and the amount of air theoretically required for combustion there of, is approximately constant as exemplified in the following table:

and it will be observed that the ratio of air to the B. t. u. fired is substantially 1 cu. ft. air to B. t, u,

Now, as previously stated, the B. t. 11. content per unit of these'gaseous and oil fuels is constant and hence it is possible, by measuring the unit flow of such a fuel, or fuels, supplied to the furnace I, to determine and record the total B. t. u. input thereof. In the present control system, therefore, the unit rate of flow of each fuel is determined and interpolated and recorded in terms of the total B. t. u. content or input thereof.

In the present invention this may be accomplished by providing in each of the fuel lines 2 and 3 a flow metering orifice 5 and 6, respectively. Shunted across each of these orifices 5 and 6 and connected interiorly of the fuel lines 2 and 3 at opposite sides of said orifices are pipes 1 and 8 having in series with each thereof a suitable manometer device 9 or In which is responsive to the pressure differential at opposite sides of the asociated orifice. A similar orifice ll, pipe l2 and manometer l3 are provided in conjunction with the air duct 4.

These manometer devices 9, l0 and I3 are of substantially identical construction and a description of one thereof will suflice. Of course, the manometer may be of any suitable type and, for example, referring now to Figure 2 of the drawings, a suitable manometer is shown diagrammaticall and may comprise a U-shaped tube the opposite ends of which are connected, by means of the by-pass pipes 1 and 8, to the fuel line 2 at respectively opposite sides of the orifice 5 therein.

Within the U-tube l5 may be a predetermined quantity of mercury l6 which moves back and forth within said tube in accordance with fluctuations in the pressure difference across the orifice 5. Also within the tube I5 and arranged for contact by the mercury column It may be a suitable resistance l1 the current in which will be varied according to the rate of flow of oil through line 2 by movement of the mercury I8 within the tube l5 and relative to the resistance [1 in response to variations in the pressure difference across the orifice 5. Connected across the two current supply conductors l8 and I3 is the primary of a transformer 2| having the usual secondary winding 22. Leading from the secondary winding 22 are two conductors 23 and 24 and connected across these conductors are three generally similar branch circuits each of which includes the resistance of one of the manometer devices 9, In or l3, an indicating meter and a coil winding.

More particularly, and considering the branch circuit containing the oil fuel manometer 9, it will be observed that one end of the manometer resistance I1 is connected by a conductor 25 to the transformer secondary circuit conductor 23. The other end of the resistance i1 is connected by a conductor 26 to one terminal of a suitable current responsive flow meter 21, and the other terminal of said meter 21 is connected b a conductor 28 to one side of a coil 23, the other side of which is connected by conductor 30 to the other transformer secondary circuit conductor 24.

In like manner, the resistance of the manometer iii of the gas fuel line 3 is serially connected with a suitable current responsive flow meter 3! and a coil 32, across the transformer secondary circuit conductors 23 and 24 by means of suitable conductors 33, 34. and 35, while the resistance of the manometer ll of the air duct 4 is serially connected with a flow meter 31 and a coil 38, across said conductors 23 and 24, by means of conductors 33, 40, 4| and 42.

The current responsive or flow indicating meters 21, 3| and 31 may be in the nature of ammeters operable to measure the current passing through the particular branch circuit in which included, and this current will vary in response to variations in the resistance in the associated manometer occurring as the result of movement of the mercury column according to fluctuations in the pressure differential across the particular orifice.

The flow meters 21 and 3| are provided with indicating dials calibrated and marked to give readings showing the unit flow rate of the particular fuel passing through the fuel line associated therewith. The arrangement and operation of the flow meter 31 is substantially the same as the meters 21 and 3| except that said meter has its dial calibrated and marked to give readings in cubic feet of air, that is, the number of cubic feet of air flowing through the air duct 4.

In addition, and for the purpose of providing a visible indication of the total B. t. u. content of the fuels indicated by both of the flow meters 21 and 3|, there is provided a totalizing meter 43 which is connected across the meters 21 and 3| by conductors 44, 45, 48, 41, respectively, and has its dial calibrated and marked to indicate the total B. t. u. input supplied to the furnace l by both fuels.

The fuel air ratio is controlled by varying the quantity of air in relation to the quantity of fuel by means of a valve 48 operated by a reversible motor 49. The operation of the motor 48 is controlled by the electronic control apparatus 50 and the device 5|, of which the windings 23, 32 and 33 form a part.

Referring to the device 5 I, the above-mentioned windings are wound on a common magnetic core, along with a secondary winding 52, and the windings 29 and 32 are both wound in opposition to the winding 33. Moreover. these windings are so constructed that the ampere-turns in winding 38 will equal the total ampere-turns of windings 29 and 32 when the desired fuel-air ratio obtains. Therefore, the device 5| is balanced when the desired fuel-air ratio obtains and no voltage appears across the secondary winding, but any deviation from such ratio will cause unbalancing of the device, thus causing a voltage to appear across the secondary winding. This voltage effects operation of the electronic control apparatus 50 in the manner hereinafter described.

Referring to the apparatus 50. there are provided a pair of electronic tubes 53 and 54 of conventional trigger type, each of which may be fired by the application of a certain potential applied to its control grid. The voltages for heating the filaments or cathodes of the tubes and for supplying the necessary energy to the cathode-anode circuits of the tubes are supplied by a transformer 55 in conventional manner. The windings of relays 56 and 51 are included respectively in the cathode-anode circuits of the tubes and these relays serve to control the operation of the motor 49 in opposite directions through circuit connections 58 and 59. Thus, when either relay is energized, it operates the motor in one direction or another depending upon the particular relay which is energized. A manual switch 50 is provided in the common lead SI of the motor circuit and this switch is closed when the system is in operation. This switch 50 is particularly desirable in cases where the furnace l is of the regenerative type, wherein the flow of fuel to the furnace is interrupted at periodic intervals. In such instances the switch 30, in

the circuit of motor 49, is opened just before the fuel supply to the furnace is shut off so. that the air valve motor 49 cannot operate during the interval that fuel is not fed to the furnace, the switch 50 being closed again just after resumption of the flow of fuel to the furnace.

A transformer 62, whose primary winding may be connected in series with that of transformer 55, supplies voltage to a circuit which includes resistors 63 and 94 in series. Resistor 53 is connected between the cathode and grid of tube 53 by means of connections 65 and 96, while the resistor 54 is connected between the cathode and grid of tube 54 by the connections 61 and 59. The secondary winding 52 of device is connected across the resistor 64 by means of connections 69 and in series with the winding 52 is a high resistance 19. The voltages normally appearing across the resistors 53 and 94 are insuillcient to fire the tubes and, therefore, the tubes are normally non-conductive and the relays 56 and 51 are normally deenergized.

As previously stated, the coils 29, 32 and 39 are wound on the same core, with the coil 38 wound in the opposite direction to the windings of the coils 29 and 32, and the arrangement is such that at full scale deflection of the three meters 21, 3| and 31, respectively, the ampereturns in the coil 39 equal the total ampere-turns in the coils 29 and 32. In this connection it is pointed out that the dial scales or calibrations of the totalizing meter 43 and the air meter 31 are arranged so that at full scale deflection of both of these meters, the air meter 31 will give a reading approximately one one-hundredth that of the totalizing meter 43 (cf. Table). Thus, when the air meter 31 gives a reading approximately one one-hundredth of the total B. t. u. value indicated by the meter 43. the ampereturns in the coils 29, 32 and 38 will be zero. At this condition, no voltage will be induced in the winding 52 and the voltages normally appearing across the resistors 63 and 64 are, as previously stated, insufficient tov fire the tubes 53 and 54, with the result that they will be non-conductive and their associated relays 56 and 51 will be deenergized and in open circuit condition.

With the system in the condition recited above. should the B. t. u. input of either or both of the fuels passing through the lines 2 and 3, respectively, be increased (as measured by their rates of flow), the resulting increase in pressure differential across the orifices therein will actuate the mercury in the associated manometers thereby decreasing the resistance therein and causing a corresponding increase in the current flowing through the meters 21 and 3| and the coils 29 and 32, as the case may be. The total ampere-turns in the coils 29 and 32, therefore, will become greater than the ampere-turns in the coil 38, thereby inducing a voltage in the coil or winding 52 resulting in a decrease in the voltage across the resistor 64 and an increase in voltage across the resistor 63. This condition will cause the tube 53 to fire on every half-cycle thereby closing the relay 56 to complete a circuit through conductors 59 and BI to the reversible motor 49 which will be driven in the direction to open the air valve 48 and permit increase in the amount of air supplied through the duct 4 to the furnace I. x

As the amount of air passing through the duct 4 increases-in response to opening of the valve 49, the resultant increase in the pressure differential across the manometer i3 will cause a proportionate decrease in the resistance in the said manometer, thereby increasing the current flowing through the air meter 31 and coil 39. The ampere-turns in the coil 38'will thereupon increase while the ampere-turns in coils 29 and 32 remain constant, and the current in said coil 38 will continue to increase in response to increase 'in the amount of air supplied to the furnace I until the ampere-turns in the coil 39 equal the sum of the ampere-turns in the coils 29 and 32, whereupon voltage will no longer be induced in the winding 52. When voltage ceases to be induced in the coil 52, the voltage across the resistor 63 will 'drop to normal thereby causing the tube 53 to cease firing, the relay 56 to open and the motor 49 and the air valve 49 controlled thereby to stop. 1

Conversely, a decrease in the fuel supplied to the funace i results in the reverse operation of the electronic control device 50. Thus, a decrease in either or both fuels in the lines 2 and 3, respectively, will operate to induce in the coil 52 a voltage opposite that induced by. an increase in the fuel supply thereby increasing the voltage across resistor 64. This will cause the tube 54 to fire thereby closing relay 51 to complete a circuit through conductors 59 and SI to motor 49 which will then be driven in the opposite direction to close the air valve 49 in duct 4. Operation of the motor 49 and closing of valve 49 will continue until the induced voltage in coil 52 returns to zero at which time the proper fuel-air ratio will be established and the voltage across resistor 64 will return to normal thereby causing tube 54 to cease firing. relay 51 to open and the motor 49 and valve 49 to cease operating.

This operation of the system is graphically i1- lustrated in Figure 3 of the drawings wherein curve A indicates the normal voltage across the resistor 64 and curve B represents the voltage induced in the coil 52 by an increase in the B. t. u. input of the fuels producing a resultant decrease in voltage (indicated by curve C) across the resistor 64. Similarly, curve D represents the voltage induced in an opposite direction in coil 52 by a decrease in the B. t. u. value of the fuels thus producing a resultant voltage increase across the resistor 84 as represented by the curve E.

In order to permit of some variation in the .setting of the system both above or below the described ratio of 1 part air per B. t. u. of fuel I fired and thereby enable control by the operator of the leanness and richness of the.fuel-air mixture, there may be provided in the system, as illustrated in Figure 4 of the drawings, a suitable regulator for differentially varying the bias voltages for the tubes 53 and 54 to shift the balance point of the control network through a small adjustment range both above and below the described normal setting of the network for the 1 to 100 air-B. t. u. ratio.

It will be understood, of course, that while the invention has been illustrated and described with respect to a system employing a plurality of fuels, it may be employed, nevertheless, with like efficiency with but a single fuel. This may be accomplished, for example, merely by eliminat-- ing, say the fuel supply line 2 together with its manometer and associated circuit comprising meter 21 and coil 29 and modifying the other coil 32 so as to provide normally therein the same number of ampere-turns as in the air meter circuit coil 39 or, on the other hand, in the case of elimination of the fuel line 3 and circuit containing the coil 32, by providing'in the coil 29 normally the same number of ampere-turns as in coil 38. Of course, in such a single fuel arrangement, the totalizing meter 43 and its conductors 44, 45, 46 and 41 likewise may be eliminated, and it should be pointed out that in a single fuel arrangement oi the system, any fuel that is capable of being metered may be employed.

From the foregoing it will be seen that the present invention provides a control system for maintaining a proper fuel-air ratio which is operable automatically and which is foolproof, efficient and comparatively inexpensive. Too, the invention provides a control system which is quickly responsive to variations in the i'uel-air ratio and results in no appreciable lag in restoring that ratio to the desired value.

While a particular embodiment of the invention has been herein illustrated and described it is not intended that the invention be limited to such disclosure but that changes and modifications may be made and incorporated therein within the scope of the claims.

I claim:

1. A fluid control system comprising a plurality oi fluid ducts, a separate mercury-loaded manometer connected to each duct for detectingv variations of flow therein, a valve in one of said ducts for controlling flow therein, a reversible electric motor for opening and closing said valve, an electric circuit comprising two sections with an electric coupling device therebetween, one oi said sections including a separate resistance unit for and variably controlled by the mercury in each manometer and a primary coil in circuit therewith, said primary coil forming part of said coupling device, the second of said sections including a secondary winding forming part of said coupling device, a pair of switches for respectively controlling the directions 01' operation of said motor, and a pair of relay coils for respectively operating said switches, one of said primary coils being reversely wound with respect to the other primary coil of said coupling device, said coils being so constructed that their effect on the secondary winding will be balanced during normal predetermined flow in said ducts and adapted upon variation of flow in any one of said ducts to induce a corresponding reaction in said secondary winding and the second section of said circuit to operate a, corresponding one of said switches to rotate said motor in one direction and actuate said valve accordingly.

2. A fluid control system comprising a plurality of fluid ducts, a separate mercury-loaded manometer connected to each duct for detecting variations of flow therein, a valve in one of said ducts for controlling flow therein, a reversible electric motor for opening and closing said valve, an electric circuit comprising two sections with an electric coupling device therebetween, one 01 said sections including a separate resistance unit for and variably controlled by the mercury in each manometer and a primary coil in circuit therewith, said primary coil forming pa t of said coupling device, the second of said sections in cluding a secondary winding forming part of said coupling device, a pair of switches for respectively controlling the directions of operation of said motor, a pair of relay coils for respectively operating said switches, a pair 0! electronic tubes respectively associated with said relay coils, and a pair 01' resistors respectively associated with said tubes and effecting balancing oi said second section to normally retain said tubes and relay coils inactive, one of said primary coils being associated with the duct containing said valve andlreversely wound with respect to the other primary coil of said coupling device, said coils being so constructed that their effect on the secondary winding will be balanced during normal predetermined flow in said ducts and adapted upon variations of flow in any one of said ducts to induce a corresponding reaction in said secondary winding and the resistors of the second section of said circuit to fire a corresponding one 01 said tubes and excite its associated relay coil to operate the switch controlled thereby tor ei- Iecting rotation of said motor to actuate said valve correspondingly.

3. A fluid control system comprising a plurality of fluid ducts, a separate mercury-loaded manometer connected to each duct for detecting variations oi flow therein, a valve in one of said ducts for controlling flow therein, a reversible electric motor for opening and closing said valve, a motor circuit including an individual current supply for said motor and a pair of switches for respectively controlling the directions of rotation of said motor, an electric circuit comprising two sections with an electric coupling device therebetween, an individual current supply for each section, one of said sections including a separate resistance unit for and variably controlled by the mercury in each manometer and a primary coil in circuit therewith and with the individual current supply for said one section, said primary coil forming part of said coupling device, the second of said sections including in circuit with the individual current supply for said second section, a secondary winding forming part of said coupling device, a pair of relay coils for respectively operating said motor control switches, a pair of electronic tubes respectively associated with said relay coils, and a pair of resistors respectively associated with said tubes and eii'ecting balancing of said second section to normally retain said tubes and relay coils inactive, one of said primary coils being associated with the duct containing said valve and reversely wound with respect to the other primary coil of said coupling device, said coils being so constructed that their eil'ect on the secondary winding will be balanced during normal predetermined flow in said ducts and adapted upon variations of flow in any one of said ducts to induce a reaction in said secondary winding producing a corresponding unbalancing of the resistors of the second section of said electric circuit to fire a corresponding one of said tubes and excite its associated relay coil to operate the switch oontrolled thereby for eiiecting rotation of said motor to actuate said valve correspondingly.

ROBERT RUSSELL FAYLES.

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