US2293550A - Method and apparatus for controlling heating furnaces - Google Patents

Description

Aug. 18, 1942. LE RoY KELLS METHOD AND APPARATUS FR CONTROLLING HEATING FURNACES Filed Sept. 9, 1939 h am L: Roy Keus Parental Aug. is, 1942 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOB CONTROL- LING HEATING FUBNACES Le Roy Kells, Salem, h10, B88131101' to Salem Engineering etorship Company, Salem, Ohio,v a promt Application September 9, 1939, Serial No. 294,123

ingots, billets and other articles from the fuel burner sources or sources and the hot gaseous products of combustion, after giving up some of their heat, pass to the cooler zones of the furnaces and thence in certain installations through recuperators employed to preheat primary ain for combustion and forl other purposes, such as the heating of particular zones of the furnace.

The control of the' operation of heating furp naces of the general type mentioned, irrespective of the character of the furnace and the use to which it is put, involves a nicety of balance between various operating factors, since care must be taken to insure the adequate and uniform heating of the articles placed in or moving through the furnace in order that they may reach a condition suitable for further Working as they leave the furnace without being overheated while insuring protection to the furnace parts, including the reeuperators-,against damaging high temperatures. The problem is particularly difficult in furnaces of the continuous type where interruption in the travel of the material being heated frequently occurs, since in this circumstance the total heat withdrawn fromv the furnace by the metalis erratic and the heat radiated by the articles standing in the furnace contributes to the absorption of heat by the walls and other elements of the furnaces.

In accordance with the present invention the control of the operation of the furnace is such that the material in the furnace will be uniformly heated to the accurate temperature required while the possibility of overheating the material is definitely eliminated. In addition, the control of the furnace is such that the maximum radiating or heat emitting capacity of, the furnace is fully utilized, while any probability of damage to the furnace parts because of over- 'heating is reduced to aminimum. It is, there- CII 7 Claims. (Cl. 236-15) perature zones of the furnace, as in the zone of highest temperature or the combustion zone and the zone of lowest temperature as in the flue. A

thermo-couple or other temperature responsive device in the hot zone of the furnace is employed primarily to determine thequality of the fuel consumed in the combustion chamber, thereby insuring the maintenance ofan efficient tem'- perature in such chamber at all times, while a thermo-couple or other temperature device positioned in the cooler zone of the furnace, as in the flue, controls primarily the quantity of the fuel consumed in the furnace, thereby insuring sufficient total heat input for eillcient operation of the furnace and adequate heating of the material placed therein. .To prevent overheating of the material and the furnace in certain circumstances, as when a particular batch .ofmaterial remains in the furnace for an abnormal length of time, the thermo-couple in the hotter zone is arranged to withdraw the control of the thermocouple in the coolerzone when the temperature in the hot zone rises above a predetermined maximum value. Thus the maximum temperature existent in the furnace is coxtrolled at all times, thereby preventing'damage to the material in the furnace because of overheating.

Another object of the invention is theprovision of an improved method for the control of the operation of an industrial heating furnace in which economical gaseous fuel, suchas blast furnace gas,`may be satisfactorily employed in such manner that substantial economies nfay be effected in the operation of the furnace. It is also an object of the invention to provide a fuel feedingv and control arrangement for such a furnace in which the economical blast furnace gas may be'used as a fuel, whilethe advantages of the control system outlined above may be retained.' These objects are accomplished, in accordance with the invention, by supplying both gases of high and low caloric values to the burners, the gas of low calorc value being preferably blast furnace gas and the rich gas being operation of an industrial heating furnace which will result in the more economical and accurate heating of the ingots, billets and the like, while the loss due to overheated material and damage to the furnace parts is kept to a Y The above object is accomplished by the present invention by controlling the operation of the furnace by'means of two or more temperature responsive devices positioned in different temmined by he temperature existing in the hot preferably either natural or coke oven gas.

The proportioning of the gases consumed is normally responsive to the relation existing between the temperature in the hot and cold zones of the furnace, the total quantity of the blast furnace gas supplied being determined by the temperature existing in the cold zone and the quantity of coke oven gas supplied being deterzone.- Due to the very low caloric value of the blast furnace gas, largequantities of such gas will be consumed While` a relatively small quantity of the coke oven gas will be supplied and therefore the thermo-couple in the hot zone of the furnace will normally control theJquality of the gas while the thermo-couple in the cold zoneu will-.normally control the general quantity of the These and other objects and advantages of the invention will become apparent from a consideration of the following detailed specification and the accompanying drawing disclosing a representative adaptation of 'the invention. By way of example, the invention is disclosed as applied to a circular ingot heating furnace commonlytermed a soaking pit and the single View of the drawing is a cross-sectional view of the furnace and a schematic representation of the fuel feedyto the principles of the invention.

Referring now to the drawing, reference numeral I indicates a circular ingotheating furnace having a circular hearth II to receive the ingots I2 and having a cover I2 removable by a cover crane I4. Immediately outward of the hearth II but spaced inwardly from the outer wall of' the furnace is a circular bridge wall 9 behind which is positioned a series of circumferentially spaced burners I5 positioned in the' outer wall of the furnace. `A fuel ring or manifold I6 encircles the furnace I0 adjacent to and preferably below. the Aburners I5, fuel conducting tubes I1 interconnecting the manifold ring I6 with the respectivev burners I5. Also encircling the furnace I0 and preferably vabove the burners I5 is the air ring or manifold I8 which is connected to the various burners by means of the conduits I9.

The fuel gas of low caloriflc value is supplied to the manifold I6 from a source 2l through valve 23 and tube 24. The fuel gas of high heat content or coke oven gas is supplied to the manifold I 3 from a source 25 through valve 26 and tube 21. Air for combustion is supplied under pressure from a blower` 29 which discharges into the header 30. A pair of parallel branches 3l and 32 communicates with the header 30 and discharges into an air distributor 33. The air thus provided is supplied to the manifold I8 through a conduit 34 from an air mixer 35. A portion of the air reaching the mixer 35 from the distributor 33 passes through a conduit 39, recuperator 3l and conduit 38 connecting with the mixer. A gate or valve 40 is positioned in the conduit 39 to determine the quantity of air passing through the recuperator. The remaining portion of air reaching the mixer 35 from the distributor 33 passes through a tube 36 leading directly from the distributor to the mixer. A valve or gate 4I in the tube 36 controls the quantity of air which so. passes directly into the mixer.

To maintain the proper ratio of air to gas, regardless of whether coke oven gas or blast furnace gasor any proportion of the two is being burnt in the furnace, a proportioning regulator is installedbetween each gaseous fuel supplying tube and one of the branches leading from the air supplying header 30. Thus a regulator, indicated generally. by the reference numeral 43, which is preferably an Askania ratio regulator, is so positioned that the forces tending to move one of its balancing diaphragms is responsive to the flow of gas through the tube 21, an orifice plate 44 being positioned in the tube 21 to enable the rate of flow therein to be sensed while the other balancing diaphragm of the regulator is responsive to the rate of flow of the air through the branch 32, an orifice plate 45 being positioned in the branch 32 and pressure lines leading from opposite sides of the orifice plate to opposite sides ofthe diaphragm. In a manner well understood in the art, the governing position of the nozzle '-ing and control system constructed according of the regulator proportioning the fluid pressure admitted above and below the piston in cylinder 46 is controlled by the position of the diaphragms above mentioned in such manner that variations in the relative rate of flow ofthe fluids in the conduits 21 and 32 will be reflected by changes in the pressures above and below the piston in cylinder 46 and, therefore, in the position of valve 41 controlled by the cylinder 46. The regulator operates in such manner that the quantity of air supplied through branch duct 32 is always proportional to the quantity of gas flowing through tube 21. If no gas flows through tubes 21, no air flows through branch duct 32 and, if a maximum quantity of fuel flows through tube 21, a maximum quantity of air is allowed to i'iow through duct 32. i

Likewise, a regulator 50, which is identical with the regulator 43, is positioned between the fuel supply tube 24 and the branch air duct 3| to control the flow of air through the duct 3l in response to the amount'of flow of the gas through ltube 24. An orifice plate 5I is positioned in the tube 24 and a similar plate 52 is positioned in the duct 3l. Air flow in the duct 3l is' controlled by a valve 54 operated by a balanced fluid pressure cylinder 53,Y the pressures of which are controlled by the diaphragms in the regulator 50. Thus the supply of air passing through the distributors 33 and mixer 35 into the manifold I8 is always correctly proportional to the amount of fuel supplied, regardless of the character of the fuel sup1 plied.

The quantity of the coke oven gas supplied to the manifold I6 is controlled by the valve 2B operated by a balancing valve drive mechanism 51, which in turn is energized through circuit 58 from a relay unit 6I. For a purpose to be later described, a switch 59 is incorporated in the circuit 58 to normally connect the valve drive mechanism 51 with the relay 6I and which is operative to connect the relay 5I with a circuit 61 controlling the operation of a second balanced valve drive mechanism 66, which in turn operates the i valve 23'controlling the flow of blast furnace gas to the manifold It. Relay 6I is controlled through circuit 60 by a controller 52 which is preferably a Micromax indicating and recording controller of the Leeds 8a Northrup Company.

its galvanometer in circuit with the thermocouple 64 positioned in the combustion zone of the furnace I0 adjacent the wall 9 and intermediate its adjacent burner I5. As is well understood in the art, the valve controlling system described is of the type which proportions the rate of ow of the gas through tube 21 in accordance with the extent of deviation from normal of the temperature existent at the location of the thermocouple 64.

A controller 1I.' similar to the controller 62, .is coupled through circuit 12 with a thermo-couple 13 positioned in the central flue of the furnace IIJ and through relay 10, circuit 69, switch S8 and circuit 61, normally controls the actuation of theV balanced valve drive mechanism 86, which actuates the valve 23. The controller 1I and its ancillary equipment is operative to proportion the flow of fuel through tube 24 in proportion to the extent of deviation from normal in the temperature existent at the location of thermo-couple 13. Y

` The operation of the fuel feeding and control arrangement thus far described should be readily v apparent. The thermo-couple 64 in the hot or combustion zone of the furnace normally controls the supply of coke oven gas or other gas of high caioriilc value through the controller I2 and valve drive mechanism I1. In operation, if

the hearth is cold or a quantity of cold steel has just been charged, the large deviation from normal in the temperature of the furnace adjacent the thermo-couple il will result in large quantities of the rich gas reaching the burners and the flame from the burners will be bright and intensely hot. As the gas passes .through tube 21, regulator ,I3 will automatically introduce the correct amount of airfor its combustion into the distributor 33. The hearth will therefore be rapidly brought up to the proper temperature required for the eillcient operation of the furnace and the rapid heating of the steel placed therein.

To insure the uniform and rapid heating throughout the extent of the furnace the thermocouple 13, normally controlling the ilow of the gas of low calorific value, such as blast furnace` gas, to the burners, is positioned in the cold zone of the furnace at a location substantially removed fromI the location of the thermo-couple Gt. Thermo-couple 13, through circuit 12, controller 1|, relay 10 and valve drive mechanism 66, controls the operation of valve 2t which regulates the amount of such gas furnished lto the .burner and, since such gas burns with a long low temperature flame, the burning of large quantities'of such gas inthe furnace results in large volumes of long relatively low temperature flames in the furnace which may propagate to substantially `the position of the thermo-couple 13, thereby insuring substantial heating of the furnace and the material placedthcrein throughout the extent of the furnace.

As stated above, although the invention is disclosed specically as applied to a circular ingot heating furnace, the invention is capable of many other adaptations as, for example, in large capacity pusher furnaces where the material entering end of the furnace is maintained at a relatively low temperature, for example 850, while at the cczitrol the supply of rich gas to the burners,

while a thermo-couple, corresponding to the thermo-couple 13, would be employed adjacent the material entering end of the furnace to control the supply of gas of low caloriic value to the burners. Likewise, in the adaptation of the lnvention to annealing furnaces where a baille wall is employed between the combustion chamber and the material being annealed, the thermo-couple normally controlling the supply of high quality gas is placed in the combustion chamber, while the thermo-couple normally controlling the supply of low quality gas' is placed in the compartment holding the material being annealed.

To prevent overheating of the furnace and the material placed therein and t enable the furnace to be satisfactorily operated while using the maximum amount of economical low quality gas andl the minimum amount of the high quality gas switches 59 and S8 are interposed inthe circuits 'leading from' the relay units Il and 1l, respectively, which in turn are controlled by the controuers sz and 1|. respectively. switches sa and tl are operated simultaneously from one limiting position to another limiting position by the solenoid 1I and when in one position connect the relays 6I and 10 with their respective valve drive mechanisms 51 and 66. When the switches are switch or contacts 18 -Switch 18 is built into the controller 60, being in the other of their limiting positions, switch Il interconnects relay unit 6l with the valve drive mechanism B6 while the switch il disconnects relay 'lll and controller 1| from any further control.

Solenoid is energized from a mutable line source of current 11 through circuit Vhaving a incorporated therein.

zone of high temperature, .the switch 59 by moving to the dotted position shown in the drawing connects controller 62 through relay 6l with the valve drive mechanism SB controlling the iiow of blast'furnace gas or other gas of low quality of the furnace. Simultaneously, switch Se is moved to open position, as indicated by the dotted lines of the drawing, thereby disconnecting controller 1l and consequently thermo-couple 13 from any further control.

The operating range of the valve drive mecha nism 51 and the valve 26 controlling the supply. of coke oven or other high quality gas to the furnace and the adjustment of the regulator 62 are so adjusted and correlated that the supply of such gas is entirely shutoff upon the attainment of the above mentioned predetermined temperature required for the closing of switch 1B, It should, therefore, beapparent that upon the attainment of the predetermined minimum temperature in the hot zone-.gf the furnace, as sensed by the thermo-couple 64, the furnace is then operated exclusively on the economical low quality fuel. Experience and trial determine the minimum temperature to be maintained in the combustion or high temperature zone of the furnace for eillcient operation of the furnace. So long as the temperature of such zone is above such minimum temperature, the low quality gas is used exclusivehr for the'maintenance of such temperature. If, however, cold steel is charged into the furnace or the load increased, as in the case of a continuous furnace, and the low quality gas is incapable of maintaining the pre-determined temperature in the high temperature zone of the furnace, controller -62 through switch 19 cie-energizes solenoid 15 thereby allowing switches E9 and 68 to return to their original positions and again allowing high quality gas to be supplied to the furnace. The intense heat of such gas rapidly ralses the temperature of the furnace to its preselected minimum value.

It should be observed that the employment of the control switching arrangement above described eliminates any possibility of the overheating of the furnace and itscontents. Due to the character and construction of the furnace itself and the quantity and condition of the steel contained therein as well as the location and nature of the surroundings of the low temperature thermo-couple in the furnace, it may happen,in the absence of such a switching arrangement. that the thermo-couple in the high temperature zone would be satisfied and the supply of high quality gas shut of! while the thermo-couple in the low temperature zone would not be up to temperature andwould be feeding large quantities of the low quality gas to the furnace, whereby the high temperature zone of the furnace and material adjacent thereto may become unduly overheated". By withdrawing the control by the thermo-couple in the low temperature zone when a predetermined temperature is reached in the high temperature zone, any possibility of the overheating of the furnace and its contents is eliminated.

ously connect said first mentioned temperature 'I'he above speciiicially described embodiment of the invention should be considered as illustrative only as obviously many changes may be made therein without departing from the spirit or scope of the invention. For example, it should be apparent that control instrumentalities other than the specific controlling apparatus disclosed may be employed for vthe perfomance of their respective functions.

What I claim is:

1. The method of operating a material heating furnace which' consists of normally supplying a gaseous fuel mixture to the burners of said furnace, said gaseous fuel mixture consisting of variable portions of high and low quality gases, controlling the quantity of `high quality gas in accordance with the temperature existing in a high temperature zone of said furnace, controlling-the quantity of low quality gas inaccordance withgas when the temperature in said rst mentioned zone reaches a predetermined degree and simultaneously shifting the control of the supply of low quality' gas to eifect the control in accordance with the temperature existing in said first mentioned zone.

2. The method of operating a material heating furnace having gaseous fuel burners which consist of supplying high quality gas to 'said burners in accordance withthe deviation from a predetermined value of the temperature of the combustion chamber of said furnace, controlling the supply of low quality gas to said burners in accordance with the temperature existing in a colder zone of said furnace, withdrawing the supply of high quality gas to said burners when said predetermined temperature is attained in said combustion zone and simultaneously shifting the control of the supply of low quality gas to effect such control in accordance .with the temperature of the combustion zone.

' 3. The method of heating material which con-2V sists of passing hot gaseous products of combustion over said material from a combustion area adjacent one end of said material, normally controlling the temperature in said area, normally controlling the volume of vsuch gases in accordance with the temperature existing at theother end of said material, and shifting the control'of the volume of such gases to thereafter effect the same in accordance with -the temperature existresponsive means with the means to control the quantity of low quality gas supplied tosaid burners. 5. Apparatus of the character described comprising a gaseous fuel burner, a combustion zone adjacent said burner, a low temperature zone associated with but spaced from' said ilrst menthermo-couple, a' second thermo-couple in said low temperature zone, a second regulator for controlling the opening of said second mentioned valve in accordance with the temperature sensed by the thermo-couple in said low temperature zone, and means associated with said rst mentioned regulator to render ineffectual the control by said second mentioned regulator and to interconnect said rst mentioned regulator with said second mentioned valve upon the attainment of a predetermined temperature at, the location of said iirst mentioned thermo-couple.

6. The method of operating a metal heating furnace having fuel burners and an adjacent zone normally maintained at a high temperature and ers in accordance with the. temperature existent,

in said adjacent zone, normally controlling the length of said flame in accordance with the telnperature existent in said second zone, withdraw- #ingsaid last mentioned control upon the teming in said area upon the attainment in said area of a predetermined temperature. l

4. Apparatus for controlling the operation of a material heating furnace having gaseous fuel burners and high land low temperature zones comprising means to supply high quality gas to "said burners, means to supply low quality gas to said burners, means responsive to the temperature of said high temperature zone normally in pera'ture in said first mentioned zone exceeding a predetermined maximum, and thereafter controlling the length of said flame in accordance with the temperature existent in said first mentioned zone.

7. The method of operating a material heating. furnace which consists of normally supplying a in accordance with the temperature existent in the rst mentioned zone.

' LE ROY vKEILLS.

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