US3366163A - Industrial furnace cooling system - Google Patents

Description

Jan. 30, 1968 J. A. SCHARBROUGH 3,356,163

I INDUSTRIAL FURNACE CQOLING SYSTEM Original Filed May 19, 1964 2 Sheets-Sheet 1 INVENTOR. Y JAMES A.SCHARBROUGH Jan. 30, 1968 J. A. SCHARBROUGH 3,366,163

INDUSTRIAL FURNACE COOLING SYSTEM Original Filed May 19, 1964 2 Sheets-Sheet 2 Fig.6. 59 78 Fig.5.

INVENTOR. JAME S A. SCHARBR OUGH United States Patent 3,366,163 INDUSTRIAL FURNACE COOLING SYSTEM James A. Scharbrough, Lebanon Township, Allegheny County, Pa., assignor to Salem-Brosius, Inc., Carnegie, Pa., a corporation of Pennsylvania Original application May 19, 1964, Ser. No. 368,584, now Patent No. 3,302,939, dated Feb. 7, 1967. Divided and this application Dec. 21, 1966, Ser. No. 603,612

6 Claims. (Cl. 165-1) ABSTRACT OF THE DISCLOSURE A method for cooling the atmosphere of an industrial furnace is disclosed and relates to batch-type furnaces wherein stacks of metal coil or the like are heat treated and then cooled. The method primarily involves forcefully withdrawing and returning a portion of the cooled atmosphere through one or more cooling zones outside the furnace. The force applied in circulating and withdrawing the atmosphere portion is segregated and separately controlled from that applied in internally circulating the atmosphere within the furnace. In certain applications the amount of cooling imparted to the atmosphere portion in the one or more cooling zones is determined by controlling the outlet temperature or the temperature rise of a cooling fluid supplied to the zone or zones.

The present application is a division of my co-pending co-assigned application of the same title, filed May 19, 1964, Ser. No. 368,584, now Patent No. 3,302,939.

This invention relates to a cooling system for industrial furnaces such, for example, as batch annealing furnaces for a stack of metal coils, or other articles, to be heat treated and then cooled. More particularly, this invention pertains to methods for cooling work protecting atmosphere gas at least during the cooling phase of an operation cycle in such a furnace, preferably to reduce the cooling time to a length less than the heating period covering the heating, or heating and soaking phases.

Accelerated cooling has attracted much interest because of the long period usually required to cool down a stack of heat treated metal coils in a protective atmosphere, e.g., from a temperature in the neighborhood of 1200 F. or above, to a temperature below 300 F. in order to avoid undue oxidation and scaling of the heat treated work. Recently, means disclosed in British Patent No. 930,063 have effected a practical reduction in that country of the cooling period which, however, cannot achieve results demanded by the steel industry in this country in which heavier charges of work are common with greater equipment and labor costs.

On the other hand, with the atmosphere cooling methods of this invention, even under American practice conditions, it has been possible to reduce the cooling time by as much as 50% over conventional times, result which is a remarkable achievement and which yields marked economic and other advantages. Further, by reducing such cooling portion of the cycle to less than the heating and soaking time, if desired, a single heat treating furnace hood, the outer cover, can be used with each pair of stack stands, and, thereby increase the tons per hour output of heat-treated and cooled metal work. Moreover, with my novel methods, cooling can be flexibly regulated, in summer or in winter, as by setting the outlet temperature of the water at a preselected value and varying the quantity thereof used for cooling to maintain such value. Further, the amount of regulation obtainable in the atmosphere cooling process of the invention may utilize both control of the flow of liquid coolant therethrough and a separate fan. The heat exchanger utilized herein has a desired relatively low pressure drop even with the higher circulation velocity usually found in American practice. And, the instant process permits the cooling system to be embodied in a surface installation when there is no basement or available space below grade adjacent the furnace.

I accomplish these desirable results by providing a method for cooling atmosphere in an industrial furnace for the heat treatment of metal work, the steps comprising forcefully circulating atmosphere around said work in the furnace, forcefully withdrawing a predetermined portion of such atmosphere to a first cooling zone outside said furnace, -forcefully Withdrawing said atmospheric portion thence to a second cooling zone outside said furnace, passing a coolant fiuid in series through said cooling zones and in heat exchange relationship to said atmospheric portion, forcefully returning the cooled atmospheric portion to the inside of said furnace, segregating the application of force in the withdrawing and returning steps from the application of force in the circulating steps, and regualting the extent of cooling imparted to said portion in said zones by regulating the flow of said liquid coolant in response to the outlet temperature thereof.

Other objects, features and advantages of this invention will be apparent from the following description and the accompanying drawings, which are illustrative only, in which FIGURE 1 is a view in elevation end section of a batch annealing furnace utilizing one embodiment of the cooling method of this invention;

FIGURE 2 is a view taken generally along line IIII of FIGURE 1;

FIGURE 3 is a view in section taken generally along line III-III of FIGURE 1;

FIGURE 4 is a view in elevation showing a section of such cooling system taken generally along line IVIV of FIGURE 3;

FIGURE 5 is a perspective view, with a portion broken away, of the relatively low-pressure-drop, high thermal transfer heat exchanger used in such embodiment;

FIGURE 6 is a view in side elevation, with parts broken away, of such heat exchanger and adjoining parts of the atmosphere cooling circuit;

FIGURES 7 and 8 are respectively side elevation and plan views of a modified surface installation embodiment of a cooling process of this invention;

FIGURE 9 is a view in side elevation and section of a further modification of a cooling process of this invention; and

FIGURE 10 is a detail view in section taken along line XX of FIGURE 9.

Referring to FIGURES 1 to 6, inclusive, of the drawings, a circular batch annealing furnace 10 is shown therein on a refractory hearth stand 11 supported by the suitable frame members 12 which are in a basement 13 below a plant floor 14. Stand 11 may be a single stand as shown or may be one of a greater number on a multiple position stand. In operation, a superposed stack of metal coils 15, of strip or sheet metal, separated by connector plate coil separators 16 having gas passages therethrough between the inner and outer peripheries thereof, are supported at the bottom by a base 17 which in turn rests on stand 11. Such coils 15 when of ferrous and other metals are enclosed by a cylindrical inner cover 18 of steel or alloy metal having a cylindrical wall, either plain or corrugated. The foot 19 of inner cover 18 stands in a reasonably gas-tight sealing material, such as sand, in a circular trough around stand 11. An outer concentric trough having sand 21 therein is adapted to be engaged by a depending skirt 22 of an outer cover 23 during the heating and any soaking phase performed on coils 15 in furnace 10. Such heating may be accomplished by many means, one of them by the use of gas-fired radiant tubes (not shown) fastened to the inside of cover 23.

A gaseous protective or treatment atmosphere for the particular metal work in furnace may be introduced through a pipe until the entire space inside inner cover 18 and a cooling circuit 26 filled with such atmosphere, a vent pipe 27 being used until all of such interior space is so filled by such atmosphere whereupon a valve in pipe 27 is closed. Additional atmosphere may be supplied through pipe 25 during an operation to make up for any loss. The stack of coils 15 may be surmounted by a plate 28 which preferably has a central opening 29 therein, although it may be a solid disc. The opening 29 is in vertical alignment with the inner peripheral openings 30 of the coil separators 16 and the eyes 31 of the respective coils 15, all together forming a vertical central opening extending down to base 17 in coaxial relation therewith. Circulation of atmosphere inside inner cover 18 is laterally outwardly through base 17 during at least the heating phase of the heating and any soaking cycle, upwardly between the exterior of the coils 15 and the interior of inner cover 18, and downwardly through such central opening into the base 17 due to the influence of a centrifugal fan 3 positioned at the bottom to effect such atmosphere circulation in the space within the inner cover.

Base 17 comprises an annular support plate 33 having a central opening 34 coaxial with the vertical central opening of the stack. Support plate 33 in turn is directly supported on bars 34 which are radially and angularly spaced for circulation of atmosphere in an upper base chamber over the entire undersurface of support plate 33. Such bars 34 are affixed to an intermediate support plate 35 having an upstanding solid rim 36 extending to the outer edge of the upper plate 33. Intermediate plate 35 is also provided with a central opening 37 in alignment with the central opening 34 adjacent the rotor of fan 32. A bottom plate 38 on base 17 is pierced for the gas-tight passage of a rotary shaft 39 supporting the rotor 32 at its upper end, the lower end of shaft 39 being aflixed to a drive motor 40 mounted against the underside of stand 11. Bottom plate 38 may be provided with a series of generally radial, curved walls 41 which extend up to and support the underside of intermediate plate 35, the respective plates in base 17 being suitably affixed to one another. Deflecting plates 24 may be provided with an upward and outward slope from plate 38 between the outer ends of ribs 41, as an aid in directing circulation of atmosphere from the outer periphery of the lower chamber of base 17 upwardly around the outside of coils 15 and the inside of cover 18.

Bottom 38 and hearth 11 are pierced for the passage therethrough of an outflow duct 42 and a return duct 43, which are respectively gas-tight around the outsides thereof where they pass through the hearth 11. Outflow duct 42, at least during the cooling phase, receives atmosphere from the lower base chamber between plates 38 and 35. Return duct 43, on the other hand, by means of an extension 44, delivers such atmosphere after it is cooled to the upper base chamber between plates 35 and 33 through an opening 45, The returned atmosphere from the cooling circuit fills the interior of the upper base chamber within rim 36 and passes out through opening 37. Base 17 may be made with only one chamber, in which event the return duct 43 would discharge its cooled atmosphere during a cooling phase to the space between such inner cover 18 and the outer wrap of the lowermost coil 15 above the seal.

The cooling circuit in the embodiment being described comprises outflow duct 42, a substantial portion of the length of which is covered by a cooling jacket 42 constituting a cooling zone, a jacketed duct bend 47 at the bottom of the outflow duct constituting another cooling zone, an indirect heat transfer device 48 providing very extensive direct cooling for atmosphere gas passing through the cooling circuit and constituting still another cooling zone, return duct bend 49 and the return duct 43. Return duct 43 includes a motorized butterfly valve assembly 50 with a butterfly valve 50a therein to variably constrict the return duct, and an enlarged section 51 provided therein with an independent axial flow fan 52 driven by a motor 53, which may be a single speed variable mass flow motor for economys sake, supported in section 51 by brackets 54 or other suitable means to provide force circulation of the withdrawn atmosphere.

As shown more fully in FIGURES 1 and 4, a suitable cooling fluid, such as water from a water main 55, passes through an automatically controlled valve 56 around which a bypass 57 is provided in the inlet pipe line 58, in which there also may be a trap and a filter, if desired. Such cooling water passes through the aforementioned cooling zones in heat exchange relation with the withdrawn furnace atmosphere, i.e., into heat exchanger 48 through an inlet fitting 59 and exits therefrom through an outlet fitting 60 to pass by a pipe 61 into the jacket around the walls of duct bend 47 and from thence by pipe connection 62 into the jacket space 63 surrounding a substantial portion of duct 42 before the water exits from an outlet fitting 64. The outlet water or other coolant is discharged through a pipe 65 into a drain 66 connected to a drain manifold 67 which takes the discharged cooling water and returns it to a cooling tower, or a cooling pond, or into some waterway or other suitable place. As the cooling water is discharged into pipe 65, its temperature is sensed and the impulse passed by a tube 68 to a response device 69 which regulates the opening of valve 56 correspondingly to control the rate of water flow and to maintain the Water temperature leaving through outlet fitting 64 at a predetermined temperature. And if, as in a summer, the temperature of entering cooling water is warmer, the regulation affected by the response device 69 will increase the flow of cooling water through the control valve 56 and continue to obtain the desired amount of cooling for the portion of the atmosphere passing through the cooling circuit. Heretofore, it has been considered impracticable because of the poor heat transfer characteristics of gas-to-liquid through a separating metal wall, to drastically reduce the temperature of a hot furnace gas such as the atmosphere in an annealing furnace. However, in a cooling system of this invention, it has been discovered that such extensive surface area can be provided in a relatively short path with a relatively lower pressure drop therethrough so as to achieve markedly increased cooling efliciency suitable for industrial furnaces with which this invention is concerned. Butterfly valve 50a is opened in the cooling circuit at the start of such cooling, which usually immediately follows heating and any soaking of the work in the furnace to which such a cooling circuit is applied. And the fan 52 cooperates therein and, preferably, with fan 32 in obtaining the desired very fast cooling.

Jacket 46, as shown, is a concentrlc annular chamber around and along a selected length of outflow duct 42, the cooling water entering an inlet fitting 70 at the bottom of the jacket through pipe 62 and flowing in counterflow relation to atmosphere gas flowing through outflow duct 42 in the direction of arrow 71. Such countercurrent flow of cooling water relative to the flow of atmosphere gas being cooled, is preferred, although it is contemplated that concurrent flows can be used depending on the application of the invention. The upper and lower ends of jacket 46 are closed tight by annular plates 72. Bend 47 is also jacketed on the upper side, its front and back sides and on its bend side to provide a common chamber jacket, rods 73 being used to space the outer wall from the inner shell 74 at the bend. The inside of inner shell 74 communicates with the lower end of duct 42 and the atmosphere gas entry end of exchanger 48, the outer end of the exchanger gas passage being connected to the interior of return bend 49 which in turn communicates with the interior of the entry end of section 51 and return duct 43 for return of the cooled atmosphere gas, at the selected time or times, to the interior space, usually pressurized, within inner cover 18. Thereby, the pressuretight and the gas-tight integrity of the respective gas and coolant portions of the cooling circuit are preserved to the atmosphere space within cover 18.

The bend portion of the jacket in bend 47 desirably is bounded near the bottom by a cross wall 82 to form a transverse sump 83 at the lowest point in shell 74 and the cooling circuit. A drain outlet 84, which is normally closed by a petcock, is provided in the bottom of sump 83. In the heat treating of metal work, such as coils 15 when they are 'sheet coils, they may be coated with enough oil that there is a tendency for some of such oil to find its way down into the cooling circuit. When that happens, the sump 83 and drain 84 provide a collection place for such oil and a means for removing the same from the system.

Extraordinary cooling is obtainable in that cooling zone which includes exchanger 48 by virtue of the very extensive heat transfer area made available therein with the relatively low pressure drop desirable in the gas pass- 'age therethrough for the atmosphere. Exchanger 48 comprises partitioned upper panel cover 75 and a partitioned lowerpanel cover 76, the partitions in cover 76 being displaced one cross row of tubes 77 toward the entry end of the exchanger 48. The outsides of the upper and lower ends of tubes 77 are sealed tightly in tube sheets 78 and 79 to connect them with the respective transverse compartments formed by the respective partitions 80 and 81 whichextend across the entire interior of those respec tive covers. As shown in FIGURES 5 and 6, a tortuous path for the liquid coolant is provided in that beginning at the cross row nearest the gas exit from exchanger 48, the cooling water passes downwardly through all of the tubes in such cross row, upwardly through all of the tubes in the next cross row, downwardly in the next, and so on, until the cooling water exits from exchanger 48 through outlet fitting 60. Moreover, the tubes in any cross row are laterally staggered relative to the tubes in the next cross row with the result that atmosphere gas passing through the atmosphere passages in exchanger 48 is in markedly extensive contact with a plurality of heat transfer area surfaces to give up heat to the cooling water on the inside of those heat transfer tubes 77.

In addition, the provision of independent atmosphere flow promotion means in the outflow duct 43, as shown, where the enlarged section 51 permits fan 52 to be mounted in the flow stream or current of atmosphere gas without restricting the atmosphere gas passage cross section, which otherwise would increase the pressure drop through the cooling circuit, is a further regulation element. Thus, separate fan means 52 may be used in cooperation with the centrifugal fan 32 to select the proportion of atmosphere gas which is to circulate in the atmosphere space of furnace relative to the proportion of atmosphere which is to flow through the cooling circuit. Hence, a desired portion of the entire quantity of atmosphere in the whole furnace space including the space in the cooling circuit may be caused to pass through such cooling circuit for cooling to a desired temperature within the capacity range of the apparatus. At least during the cooling portion of the entire heating (including any soaking) and cooling cycle for a given stack of coils 15, at the inception of such cooling, valve 50a will be opened and centrifugal fan 32 will remain on to circulate and cool a portion of atmosphere gas which then will pass through the cooling circuit before it is returned. Motor 53 and fan 52 may not be turned on at the start of the cooling phase until there has been some drop in the temperature of the metal coils depending upon whatever metallurgical effect is being considered. At a predetermined time in the cooling phase,

fan 52 is turned on and a greater portion of atmosphere gas will pass through the cooling circuit to provide the selected quantity of atmosphere to be cooled and returned to the inside of cover 18. Greater flexibility may be obtained in some cases by the use of valve 56 as a modulating valve instead of using it as an off-on valve. Moreover, since prior to the inception of such a cooling phase the outer cover 23 is lifted off of stand 11 and taken away, additional cooling effect is obtained by radiation from the outside of inner cover 18 which, moreover, may have cooling air directed against the outside thereof, if desired. The remainder of the atmosphere gas at a given interval in the cooling phase which does not pass into outflow duct 42 admixes with discharged cooled atmosphere gas from outlet opening 45 and is circulated by fan 32 in the usual fashion to pass out, save for the quantity that enters duct 42, through the periphery of the lower chamber of base 17 into the space surrounding coils 15 inside cover 18.

Normally, during the heat and any soaking portion of the cycle on a given batch of coils 15, valve 50a is closed. In that situation, all of the atmosphere gas in the furnace portion of device 10 passes down through the central opening through the stack in the direction of the wavy arrows and through the central openings in base 17 for engagement by fan 32 and return laterally and outwardly through the lower base chamber, then upwardly in the annular space between the outside of the coils 15 and inner cover 18, and thence into the stack central opening completing the atmosphere circuit inside cover 18. In some cases, however, even during the heating and any soaking portion of an operation cycle, some tempering of the high temperature of the atmosphere gas may be desired. In that event, valve 50a may be partially opened and fan 52 turned on together with an appropriate flow of coolant through the cooling circuit, to draw some atmosphere into the cooling circuit and discharge it through opening 45 to mix with and effect the desired reduction in the temperature of the atmosphere gas inside cover 18. Further, if desired, an injection of materials which may be gas-borne may be provided in the cooling circuit for treatment of the metal work in the furnace in the course of the passage of gas through such cooling circuit. When the cooling circuit is opened up at the start of a cooling portion of a single operation cycle, normally closed valve r 50a usually is opened to its full extent and a predetermined portion of the atmosphere gas in the furnace and cooling system will thereupon circulate through the cooling circuit. At a predetermined point in the cooling phase, which may be measured, for example, by the temperature of the metal work being cooled, fan 52 will be turned on and a substantial and selected increased portion of atmosphere will circulate through the cooling system for discharge as cooled atmosphere through opening 45 to yield extraordinary cooling results of this invention. Moreover, the efliciency of heat transfer is advantageously held high both at the beginning of a cooling phase with valve 50a open and fan 52 off, when the thermal head of the atmosphere gas is higher, and, during the later operation of fan 52 in the cooling phase when, while the temperature head of the atmosphere gas from inside 'cover 18 has dropped, the mass flow of atmosphere gas through exchanger 48 will increase and maintain the exchangers high level of eflicient heat transfer. Consequently greater efliciency and flexibility are obtained in this invention.

In the modified surface installation embodying the process of this invention and illustrated in FIGURES 7 and 8, parts corresponding generally in construction and functioning are provided with the same reference numerals with the addition of prime accents thereto, respectively. Such modification utilizes a centrifugal fan 52' in lieu of an axial flow fan and is of interest in those places where a furnace installation may have insufficient or no room below the furnace stand, due to any of a variety of reasons such as the case of a furnace erected on the low bank of a river in which the water table is close to the ground surface supporting the furnace. Base 17', moreover, is conventional and has but a single chamber between upper annular support plate 33' and lower plate 35', the atmosphere being propelled laterally outwardly through the open outer periphery of base 17 between the ribs 41'. In such an installation, the return duct 43' also discharges its cooled atmosphere gas laterally outwardly substantially directly into the space between the inner cover 18 and the lowermost coil adjacent the outer edge of base 17'.

The further modification of FIGURES 9 and 10 illustrates anOther arrangement of a cooling circuit embodying the process of this invention and located in a space beneath the furnace proper. Those parts in the further modification of FIGURES 9 and 10 which correspond generally in construction and functioning to the parts of the above first-described embodiment are provided with the same reference numerals, respectively, with the addition of a double prime accent thereto. In such further modification, the second fan 52" again is a centrifugal fan, taking its suction directly off the delivery end of heat exchanger 48". Although the return duct 43 in such further modification has no cooling jacket thereon, such may also be provided if additional cooling regulation is desired, as such may also on the earlier described embodiments.

Various changes in details of the illustrated embodiments and in the specific processes utilized therewith may be made and other embodiments thereof provided, without departing from the spirit of this invention, or the scope of the appended claims.

I claim:

1. In a method for cooling atmosphere in an industrial furnace for the heat treatment of metal work, the steps comprising forcefully circulating atmosphere around said work in the furnace, forcefully withdrawing a predetermined portion of such atmosphere to a first cooling zone outside said furnace, forcefully withdrawing said atmospheric portion thence to a second cooling zone outside said furnace, passing a coolant fluid in series through said cooling zones and in heat exchange relationship to said atmospheric portion, forcefully returning the cooled atmospheric portion to the inside of said furnace, segragating the application of force in the withdrawing and returning steps from the application of force in the circulating step, and regulating the extent of cooling imparted to said portion in said zones by regulating the flow of said liquid coolant in response to the outlet temperature thereof.

2. The method according to claim 1 in combination with the additional steps of forcefully withdrawing said atmospheric portion to a third cooling zone outside said furnace, and circulating said coolant in series through said three cooling zones.

3. The method according to claim 2 in combination with the additional steps of variably constricting the fiow of said forcefully withdrawn atmospheric portion to aid in determining the quantity of withdrawn atmospheric portion and the degree of cooling imparted thereto, and passing said coolant in countercurrent series through said three zones relative to the flow direction of said atmospheric portion therethrough.

4. The method according to claim 1 in combination with the additional steps of variably constricting the flow of said forcefully withdrawn atmospheric portion to aid in determining the quantity of withdrawn atmospheric portion and the degree of cooling imparted thereto.

5. The method according to claim 1 in combination with the additional steps of forcefully circulating said atmospheric portion to a third cooling zone outside the said furnace, and circulating at least a portion of said liquid coolant to said third zone.

6. The method according to claim 5 in combination with the additional steps of circulating said liquid coolant in countercurrent series through said three cooling zones relative to the flow direction of said atmospheric portion, and regulating the flow rate of said coolant in accordance with the temperature rise thereof in the countercurrent series circuit.

References Cited UNITED STATES PATENTS 1,536,944 5/ 1925 Steenstrup 266-5 X 1,938,306 12/1933 Webb 266-5 X 1,979,732 11/1934 Carson -40 X 2,018,594 10/1935 Baer 165-40 X 2,228,564 1/1941 Guthrie 266-5 2,477,796 8/1949 Germany 266-5 2,479,814 8/1949 Cone 263-42 2,783,975 3/1957 Lans 165-40 3,097,836 7/1963 Beggs et al 266-5 X 3,140,743 7/1964 Cone 165-61 FOREIGN PATENTS 930,063 7/ 1963 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,366,163 January 30, 1968 James A. Scharbrough It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 2, line 21, for "regualting" read regulating column 3, line 25, for "fan 3" read fan 32 column 4, line 58, for "concentrlc" read concentric column 6, line 62, for "Consequently" read Consequently, column 7, line 43, for "segragating" read segregating line 46, for "step" read steps column 8, line 37, for "Carson" read Carson, Jr.

Signed and sealed this 3rd day of June 1969.

f/ Attest:

Edward M. Fletcher, J1". g l Attesting Officer comnlisioner of Patents

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