US2273892A

US2273892A - Apparatus and method for preheating of air and the like

Info

Publication number: US2273892A
Application number: US338514A
Authority: US
Inventors: Herbert A Reece; Smalley Oliver
Original assignee: Meehanite Metal Corp
Current assignee: Meehanite Metal Corp
Priority date: 1940-06-03
Filing date: 1940-06-03
Publication date: 1942-02-24
Anticipated expiration: 1959-02-24

Description

Feb. 24, 1942.

APPARATUS AND METHO H. A. REI-:CE ET AL D FOR PREHEATING OF AIR AND` THE LIKE 2 Sheets-Shes?I l Filed June 3, 1940 and O/l Ver 5mm/ey W 71 7KATTRNEY5 Feb, 24, 1942. H. A. REECE ET A1. 2,273,392/

APPARATUS AND METHOD FOR PREHEATING OF AIR AND THE LIKE 2 Shets-Sheet 2 Filed June 3, 1940 Y INVENTORS and /zffa/A #fafa BY 0/1 ver `Smal/gy PatentedA Feb. 24, 1942 APPARATUS ANDMETIIOD FOR PREHEAT- ING OF AIR AND THE LIKEl Herbert A. Reece, Cleveland Heights, Ohio, and Oliver Smalley, Pittsburgh, Pa., assignors to Meehanite Metal C Tennessee rporatlon, a corporation of Application June 3, 1940, serial Nn. 338,514

(ci. zes-.14)

18 Claims.

Our invention relates to furnaces and more -particularly to metallurgical furnaces such as cupolas and the like, and to the operation of the same.

The invention disclosed herein is directed to the pre-heating of air supplied to a metallurgical furnace for the promotion of combustion therein. In the following discussion and description the operation and structure of a cupola for the remelting of metal will be. referred to but it is to be understood that our invention includes the structure and operation of 'other furnaces and similar devices wherein a blast of air or other gases is supplied through a plurality of tuyres or like openings to the interior of the furnace or similar device.

In the operation of metallurgical furnaces such as cupolas it is necessary to supply a blast o f air to the interior-of the furnace for supplying the air to the furnace contents to promote com- -bustion. Coke or similar combustible material is charged into the shaft of the cupola along with the `meta1 or other substance to be melted or otherwise processed, the coke and metal being usually disposed in alternate horizontal layers. The coke upon being ignited is in an-incandescent state and the oxygen of the air blown into` the furnace unites with the coke carbon and oxides of the carbon are formed. The heat generated by the oxidation melts the metal or otherwise processes the substances being processed by the furnace.

The location where'the oxidation takes place and where the greatest heat isliberated is referred to as the melting zone as it is here that the heat is `sucient to melt the metal which thereupon falls to the bottom of the cupola in a molten state. The importance of controlling the melting zone to obtain a proper melting of the metal by the control of the velocity of the air delivered to the furnace through the plurality of tuyres, has been pointed out in the Herbert A. Reece United States Letters Patent-No. 2,188,920 issued Eebruary 6, 1940; No. 2,197,947 issued April 23, 1940; No. 2,197,948 issued April 23, 1940; and N o. 2,197,949 issued April 23, 1940. 'I'he great advantage to" be derived by the equalization of the velocity oi the air flow through the plurality of tuyres was disclosed and demonstrated by those patent disclosures.

The use of pre-heated air for delivery through the tuyres -to the cupola has been practiced for some time prior to the present invention and the benets to be derived therefrom are well recognized in the industry. Cupolas or other furnaces in which the air is pre-heated at a distance from the cupola and is then supplied through a main blast pipe or blast main to the cupola wind box for distribution to theA several tuyres, are generally referred to as utilizing the hot-blast" principle.

It has beeny found that supplying pre-heated air to the cupola results in the productionv of hotter metal from the same amount of coke 'which would be used with uri-heated air, or conversely a, production of metal at an equal temperature with the use of less coke, Since it is possible to use less coke when the air is preheatedthere is a reduction in sulphur pickup by the metal in proportion to the reduction in the amount of coke used. Among other advantages which may be obtained by supplying pre-heated air to the furnace, .are the following: an increase in the melting rate per hour, areduction in the loss of metal and metalloids, capacity for a larger percentage of scrap metal in the charge by reason of the lower oxidation and lower sulphur pickup, improved conditions in the operation of the furnace, and a, more accurate metallurgical control over the metal produced.

There have been two general types of hotblast systems for pre-heatingv the air at a distance and conducting the pre-heated air through the blast main to the cupola wind box, In one of these types of systems an air heater or stove located to heat the air passingthrough the blast main is dependent upon the burning of coke or other fuel fed to the heater manually or by mechanical means. The heating is done at a distance from the cupola and is independent from the operation of the furnace. In the other of these two general types of systems, the heater or stove utilizes waste gases from the stacl; of the cupola as a fuel. In this type, the heater or stove is dependent for fuel supply upon the operation of the cupola to furnish the gases. The

heater or stove in this type of system is likewise positioned at a distance from the cupola andv heats the air flowing through the blast main.

Hot-blast systems in which the air is heated at a distance from the cupola and subsequently' delivered through the blast main to the cupola wind box are subject to many'limitations, defects v and operating disadvantages, of which the following examples may be cited: (l) There is a considerable heat loss incurred between the heater or stove and the cupola tuyres by reason of the distance the air must travel through the blast main and wind box in reaching the tuyres. (2) There is a lag\ or time loss between the heating requirement of the cupola and thearrival of the heated air to the cupola tuyres by reason of the time required for the air, after being brought to the' required temperature, to travel from the heater or stove to the tuyres. (3) There is a differential between the temperature oi' the air supplied to each of the several tuyres by reason of the different paths and distances the air travels through the wind box from the wind box inlet to the plurality of tuyres, r the air flowing freely through the wind box along different portions of the. walls of the wind box and cupola being subjected to different heat exchange conditions. (4) There is -a lack of uniformity of the temperature of the air supplied through the several tuyres by reason of the fact that there is not a uniform heating of all portions oi the total air blast nor is there a subjection to uniform heat exchange conditions after heating. (5) There is a lack of uniformity of the heat supplied through the several tuyres by reason of the inequality of the flow of heated air through the wind box to the tuyres. (6) Operating limitations and disadvantages apparent from the structure and arrangement of the hot blast systems in addition to the foregoing examples. l

'I'here is still another type of system in which the air is pre-heated before delivery to the cupola through the tuyres, in which system the heat is transferred to the air through the wall of the cupola, the wall being specially constructed to utilize the heat generated by the combustion within the cupola.' In this system there is no arrangement for a uniform heating of all portions of the air blast, the air passing next adjacent to the heat exchanging wall being heated more than other more distant portions of the air blast. There is no equalization of the flow of air and the currents of air are unequally heated and unequally supplied to the tuyres. 'I'his type of system fails to supply an equal flow of uniformly heated air to the several tuyres and falls short of meeting the requirements of an efllcient preheating system. Moreover, in addition to the many other limitations, defects and'disadvantages in this system there is the particular restriction upon its loperation of being dependent upon the operation of the cupola for heat. The heat may be obtained for the preheating of the air only after the cupola has been in operation suilciently long to generate the required heat. The pre-heating cannot be independently controlled nor can air be heated in accordance with requirements. Dependence upon heat exchange through a wall or partition on the side of the cupola does not afford the advantages nor render the results obtainable with the present invention.

It is an object of the present invention to obviate the limitations, defects and disadvantages of the prior systems.

Another object of the invention is the provision of an improved system of pre-heating the air supplied to a cupola affording results and presenting advantages not heretofore known nor obtainable.

Another object is the provision for the minimizing of the loss of heat from the pre-heated air.

Another object is the provision for substantially eliminating the time lag between the requlrement for heated air and the supplying of air at the required temperature.

Another object is the elimination of the differential in temperature of air delivered to a. plurality of tuyres.

Another object is the provision for equalization of heat exchange conditions affecting the temperature of air supplied to a plurality of tuyres.

Another object is the provision for uniformly pre-heating all portions of the air blast supplied to a furnace through a plurality of tuyres.

Another object is the provision for equalizing the ow of air being heated to supply heated air uniformly to a plurality of tuyres.

Another object is' the provision for spreading the flow of air over an area and uniformly heating all portions of the air in that area.

Another object is the provision of the combination of means for equalizing velocity of air and means for heating the air to supply air of uniform velocity and temperature to a plurality of tuyres.

Another object is the provision of an improved auxiliary pre-heater of air supplied to a furnace, that is not dependent upon the operation of the furnace.

Another object is the provision of an auxiliary heater having an improved construction and arrangement in a pre-heating system for producing an eilcient heating action and affording a proper control of the pre-heating.

Anoth er object is the provision of a pre-heating system for supplying heated air to a furnace in accordance with operating requirements and conditions.

Another object is 'the provision of an improved I method of pre-heating air and supplying the air to a furnace.

Other objects and a fuller understanding of our invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

Figure l is a cross-sectional view taken lengthwise of a cupola and `wind box embodying our invention and is a view looking in the direction of the arrows I-l of Figure 3;

Figure 2 is an elevational view of the wind box and cupola shown in Figure l;

Figure 3 is a transverse cross-sectional view taken through the line 3-3 of Figure 2;

Figure 4 is an enlarged view of a portion of the wind box and cupola showing the detail of the mounting of the heating units in the wind box of Figures 1, 2 and 3;

Figure 5 is a circuit diagram illustrating the electrical connection of one of the heating units illustrated in Figures l and 3;

Figure 6 is a transverse cross-sectional view of half of the cupola and wind box incorporating a modified form of heating units;

Figure 7 is a cross-sectional View taken length- Wise through the cupola and wind box shown in Figure 6 and further illustrates the mounting of the said modied form of heating units;

Figure 8 illustrates still another modified form of heater associated with a wind box and is a transverse cross-sectional view of the cupola and wind box in the direction of the arrows 8-8 of Figure 9; and

Figure 9 is a cross-sectional view taken lengthwise of the cupola and wind box shown in Figure 8 and further illustrates the said modied form of heating arrangement shown in Figure 8.

inasmuch as the invention disclosed herein is directed particularly to the Wind box, the portion of the cupola adjacent thereto and the heating arrangement associated therewith, it has not been considered necessary to show all parts ot parallel to 'a plane passing through the plurality the cupola in the several drawings and which therefore do not include the top portion and the"\` bottom portion of the cupola, which portions may. be considered as having the usual form. Also, for

.DurDOses of simplicity in illustration, the usual tap hole and slag hole are not shown. It has also been considered unnecessary to illustrate such other openings as a clean-outdoor, breast arch or drop-bottom door. The cupola to which the invention is associated and which is described herein may be considered, however, as having all of the parts necessary for the usual operation of the same.

As shown in the several views ofthe drawings, the cupola body or shell 2| is in the form of a cylindrical shaft, the inner ywalls of the cupola body 2| being lined by the fire brick lining 24. The body 2| and the lining 24are mounted upon the usual bottom plate, shown as plate 21 in Figure 9, andvthereby form the enclosed shaft or stack of the cupola. Suitable supports such as the support 26 of Figure 9 form a base for the support of the cupola. i

A wind box 22 of cylindrical shape is mounted upon the cupola body 2 by welding or other suitable means and in the embodiment shown, the outer wall of the cupola `body forms one of the enclosing walls of the wind box 22. It is therefore seen from the views of the drawings that they wind box 22 forms an enclosed jacket surrounding the cupola body 2| in such a way that air introduced into the wind box'may circulate entirely around the cupola body. i

An inlet conduit 23 is in communication with an air blower or other source of-an air blast (not shown) and the inlet conduit 23 is connected to the wind box 22 at the upper portion of the wind box 22 so as to afford communication between the air blower and the inlet opening 25 of the wind box 22.

In the cupola illustrated there are six tuyres extending through the wall and lining of the.

cupola body 2| to establish communication between the interior of the shaft'of the cupola and the wind box 22. All six tuyres 30, 3|, 32, 33, 34 and 35 are shown in dotted lines in the transverse cross-sectional views of the drawings and three of the tuyres 30, 3| and 32 as seen from the inside of the shaft of the cupola are illustrated in the cross-sectional views taken lengthwise of the cupola. These six tuyres are of substantially equal size and are uniformly spaced around the periphery of the cupola. It is to be noted that the tuyres enter the cupola body at a low level in the cupola and communicate with a low portion of the wind box. In order that the operator may look into the tuyres from the outside of the furnace, peep holes are provided in the wind box opposite each of the tuyres and mica or other suitable substance is sealed over these peep holes. Except when necessary, peep hole covers 28 hingedly connected to the wind box 22 are kept in position over the peep holes by means of the latch members 29 as illustrated in Figure 2.

The description of the first form of the invention is made in conjunction with the showing of Figures 1 to 5, inclusive. With reference to said figures there is shown positioned within the wind box below, and at a distance from, the inletopening 25 a series of electrical heating units denoted generally by the reference character 39. The

six units 39 are segmental portions of a complete circle and together extend around the annular extent of the wind .box 22. The assembled heating units 39 are disposed in a plane substantially of tuyres 30 to 35, inclusive. I'he plane in which the units 39 are disposed is intermediate of, and substantially parallel to, a plane passing through the said tuyres and a plane passing \through the inlet 25.

' CIOSS piece To facilitate the mountingof the units 39 in position with the wind box and also to permit access thereto for purposes of inspection and repair, removableside plates 31l are provided in the outer wall of the wind box 22. As there are sixheating units '39 six side plates 31 are provided around the outer wall of the wind box 22. Each lside plate 31 is secured to the wall of the wind box 22 by means of threaded bolts 38 and a hermetic seal is provided by the closure by the side plates 31 to prevent the escape of air through the side walls of the wind box.

Each of the electrical heater units 39 is comprised of a plurality of U-shaped frames 40 which are disposed vertically of the wind box. The several frames of each unit are assembled and retained inv position `by an outer annular 4|A and an inner annular cross piece 42 which are welded, riveted or otherwise secured The U-shaped frames are so positioned that the shoulders on both sides ofthe wall or sheet.

open space between the upper and lower arms are directed inwardly toward the cupola. The arrangementy of the frames 40 as connected together by the cross pieces 4| and 42 is such that the frames 40 extend radially of the wind box and cupola and the cross pieces 4I and 42 extend,u

in a circumferential direction. To provide an adequate support for the heating units ledges or 43 are secured by welding to the inner wall of the wind box to engageably support the frames 40,.

Suitable electrical resistance Wires 44 having the capacity to produce heat upon being energized by a source of electrical energy are mounted to the frames 40 by being strung upon suitable insulators 45 secured to the frames. The heating wires 44 extend substantially vertically in the wind box and heat air passingv adjacent thereto in its travel through the wind box. For

purposes of simplicity in illustration a relativelyn small number of turns of the heating wire 44 is shown upon each frame 40. In practice, a suiiicient number of heating wires is mountedeupon each frame to provide the required heating action and the plurality of turns of the heating wire 44 upon eachv frame 4|) presents, in effect, a wall or sheet of a heater adapted to heat air passing The portions of the air blast moving down thru the wind box between the spaced frames 4U are uniformly heated by the adjacent frames of the heating wire. i

Connected in .circuit relationship ywith each heating unit 39 is a temperature control device mounted upon the outside of the wind box and having a thermostatic element 49 extending inwardly of the wind box in the path of the ow of air from the heating units to the tuyres. Suitable connecting

wires

46 and 41 shown in the circuit` diagram of Figure 5 connect together the heating wires on the several frames in parallel relationship and in electrical connection with the temperature control device 5 0. Suitable leads 48 ext-end from the device 50 and connect with a source of electrical energy to pro-vide for the energization of the heating wires 44 as regu- 5I upon the control device 50 permits the manual regulation of the temperature desired by each heating unit and also sets the degree of responsiveness of the thermostatic element d@ connected to the control device 50. By adiustment of the handle 5I the required temperature may be set and the electrical energization of the heating units controlled in accordance with the required temperature.

In the event that greater energy is required to bring the air up to the.desired temperature on one side of the wind box the separate control for each of the units responsive to a separate thermostat permits this added heating energy to be applied in that locality. Air sweeping around through the interior of the wind box from the inlet is subjected to different degrees of heat exchange depending upon the distance the air travels through the Wind box and the amount or scope of the outer wall of the wind box encountered before the air enters the tuyres.. It may therefore be necessary to expend greater energy at one locality ,than another in order to bring all of the air up to an equal temperature before entering the plurality of tuyres. The flexible arrangement here provided of separate heating units controlled by.separate therrn'ostatic means facilitates this supplying of air at equal temperature to all of the tuyres.

It is to be noted that the arrangement of the frames 40 around the interior of the wind box is such that tangential ow of the air is resisted and currents of unequal velocity are broken up to flow at substantially equal Velocity down between the plurality of frames and heating wires at substantially equal velocity to the plurality of tuyres. The heating units therefore distribute the flow of air around the wind box and so modify the flow thereof as to pass equal amounts of air down through the wind box around its annular extent. The top surfaces of the frames 40 restrict the otherwise unrestricted flow of air which thereupon passes down through the open spaces between the frames. The arrangement aids in the equal distribution of the air and hence the uniforml heating of the air before being supplied to the furnace through the tuyres.

It is to be noted that the heating units are equidistant from the plane of the tuyres and therefore in the same general proximity thereto. Air passing from the heaters to the tuyres is subjected to the same heat exchange condition in all localities around the Wind box. The term heat exchange condition is to be considered as including heat losses through the outer wall of the wind box and also heat gain which may accrue from the heat generated within the cupola and radiated outwardly through the cupola wall or through the tuyre. In heating systems wherein the air is heated before it enters the wind box the air travels different distances and comes in contact with different amounts of inner and outer wall surface before reaching the tuyres. The air in such systems is subjected to different heat exchange conditions in reaching each of the plurality of tuyres. In systems embodying my invention the air after being uniformly heated throughout is subjected to the same heat exchange conditions throughout before being supplied to the furnace through the tuyres. By reason of the close proximity of the heaters to the tuyres the air is supplied to the tuyres almost instantaneously after being heated and time lag between the heating and the supplying of the air is practically eliminated. The

envases proximity of the heaters to the tuyres also greatly reduces the heat losses which are encountered in the heating of the air at a more distant point. Since the heating is done independently of the operation of the furnace and does not depend upon the combustion within the furnace for heat there is a more accurate and instantaneous control over the pre-heating of the air. By breaking up the ow of air and passing small portions down between closely spaced heating elements the air is uniformly heated throughout. The arrangement therefore -provides for the uniform heating of air and the supplying of the uniformly heated air at the same uniform temperature to all of the tuyres, the heating being done in accordance with the requirement and condition of the melting operation to afford complete and eincient metallurgical control.

In Figures 6 and 7 there is illustrated a modlfied form of heating unit in which a heating medium such as, for example, steam, hot water, other hot fluids and hot air, may be utilized. Six heat exchange units denoted generally by the reference character 53 are mounted within the wind box in a manner somewhat similar to that shown for the electrical heating unit previously described. The six heat exchange units 53 comprise segmental portions of a complete circle which extends around within the wind box 22 and between the walls thereof. As in the case of the electrical heating unit previously described, the heat exchange units 53 are disposed in a plane substantially parallel to a plane passing through the tuyres and are disposed in a plane intermediate the said :plane passing through the tuyres and a plane passing through the inlet 25.

Each heating unit 53 consists of a container having a suitable annular shape to fit within the wind box and is adapted to contain the heat-1 ing medium supplied thereto through the intake and outlet conduits 55 and 5B. A plurality of vertical passageways 54 extend through the heaters 53 to facilitate the flow of air from the upper portion of the wind box to the lower portion of the Wind box. The passageways 54 are so arranged` in the heaters 53 as to equalize the flow of air throughout the wind box in moving from the inlet 25 to the plurality of tuyres. Currents of the air blast of unequal velocity are resisted by the heating units andthe air flow is so distributed as to provide air at substantially equal velocity to all of the tuyres.

The air being uniformly distributed around the wind box and passing down through the evenly distributed passageways 54 is uniformly heated by the heatexchange through the walls of the heating unit by the heating medium circulating through the several heating units 53. A valve 51 upon the conduit 55 is operatively connected to the control device by means of a suitable connection 58 shown by the broken line and which may be a mechanical, electrical or other operating means to provide for the control of thevalve 51 by the device 5I). As in connection with the description of the electrical heaters the thermostatic elements 49 connected to the vplurality of control devices 50, respectively, regulate the respective heating units. The control devices 50 may be regulated by the handle 5| in accordance with requirement and need.

In the modification shown in Figures 6 and 7 the conduits and 56 connected to a suitable source of heating medium extend through openings provided in the side plates 31. To remove asvasoa a a heating unit 53 the side plates 31 may be removed and couplings on the

conduits

55 and 56 may be unfastened and the heating unit 53 and plate 31 removed from the wind box together.

Another modified form of a pre-heating system is illustrated in Figures 8 and 9 in which the heating is done by the burning of gas, oil vapors or other suitable fuel within heating chambers provided in the wind box. The heating chamber within the wind box is provided by an upper partition 66 and a lower partition 6| spaced apart and disposed horizontally within -the wind box. The partitions 60 and 6I divide the wind box into a portion adjacent the inlet 25, a lower .portion adjacent the tuyres, and an intermediate portion forming the heating chamber.v A plurality of tubular conduits 62 extend through and connect the partitions 60 and 6| to provide air pas-` sageways for the air flowing from the upper portion of the wind box tothe lower,A portion of the wind box. The tubular conduits 62 are spaced at regular intervals around the annular extent of the wind box and uniformly distribute the flow of air as it passes from the inlet conduit to the tuyres,

To provide for the heating of the heating chamber four tangentially disposed conduits or extensions 63 are provided to extend from the outer wall of the wind box at regular intervals around its peripherly. Extending into the end of each of these tangentially disposed conduits 63 is a burner 65 from which a flame of gas, oil vapor or other fuel is projected, the flame and combustion gases entering into the heating chamber to heat the air passing down through the conduits 53. Each tangential conduit 63 opens up into the heating chamber through'an inlet opening 64 in the side wall of the heating chamber. The

closed and the method of pre-heating air herein described we have provided asystem of preheating air delivered to a cupola and similar furnaces' to give results not heretofore obtainable and providing an improvement in cupola operation not heretofore known.

Although we have described ourinvention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in' the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope 'of the invention as hereinafter claimed.4

. We claim' as our invention:

1. In a metallurgical furnace having a wind box positioned around the body of the furnace for supplying blown air through a plurality of {tuyres to the interior of the furnace for the promotion of combustion therein, said wind box having an inlet adapted to communicate with a source of said blown air and having outlets in communication with' said tuyres, a heater mounted within said wind box intermediate. and at a distance from, the said inlet and said outlets in the path of the flow of air through the wind box, said heater having a plurality of passageways extending therethrough in a direction substantially longitudinal of the wind box for hot flamecirculates around through the heating chamber in contact with the tubular conduits 52 to heat the air therein. Inasmuch as the burners are distributed at intervals around the heating chamber the heating by the combustion of the gas is substantially uniform around the an` nular extent of the heating chamber.

Conduits delivering gas, oil vapor or other suitable fuel to the burners are denoted by the reference character 66; Valves 61 are located in the conduits 66 and control the flow of fuel there-- through. 'A suitable operating connection 68 connects each valve 61 with a control device 50 to provide for the operationv of the burners 65' the flow of air from the portion of the'wind box adjacent said inlet to the portion of the Wind box adjacent said outlets, said passageways being substantially uniformly distributed around the cross-sectional area of the wind box to equalize the iiow of air therethrough, said heater having heating surfaces substantially uniformly distributed around thev cross-sectional area of the wind box for uniformly heating the air flowing through the. cross-sectional area of the wind box to said outlets to supply the heated air through the tuyres to the interior of the furnace.

2.--In a furnace having a wind box positioned' around the body of the furnace for supplyingl blown air to the entrances of a plurality of tuyres communicating with the furnace, said wind box having an inlet adapted to communicate with a source of blown air, the location of the inlet in the wind box requiring the air to travel unequal distances, vand to travel adjacent to unequal portions of wall surfaces` of the wind box, in passing to said tuyre entrances. an auxiliary heater in said wind box for heating said air, said heater having air passages and heating surfaces distributed substantially unlformly around the cross-sectional area of the.

wind box for uniformly heating airl passing therethrough from the inlet to the tuyre entrances, said heater being in the same relative proximity to each of said tuyre entrances to provide for the maintenance of the same relative temperature of air supplied to each tuyre.

3. In a wind box for furnishing a blast of blown air from a common source to a plurality for tuyres, apparatus for supplying air from the y wind box to the tuyres at a raised and uniform temperature, said apparatus comprising equaliz-v ing means for substantially uniformly distributing the air flow through the cross-sectional area of the wind box and heating means for substantially uniformly heating said uniformly distributed air, said heating means being positioned in the wind box at substantially the same unobstructed distance from each ofthe tuyres to assure substantially uniformV heat exchange conditions encountered by the air in its travel from the heating means to the tuyres, the air being equally supplied to each of said tuyres at uniform temperatures.

4. In a wind box having an inlet and a plu-` fiets,` said equalizing means and said heating means being yuniformly distributed around the wind box to provide an air blast of uniform velocity and temperature to each of said outlets, and control means for regulating said heating means to provide for the desired heating of said air blast.

' 5. Ir. a wind box for furnishing a blast of blown air from a source of said blown air to a plurality of tuyres, said wind box having an inlet adapted to communicate with said source and having outlets in communication with said tuyres. a heater mounted in said wind box and disposed in a, plane intermediate of, and substantially parallel to, a plane passing through said outlets and a plane passing through said inlet, said heater having resisting surfaces and open spaces substantially uniformly distributed therein around the cross-sectional area of the wind box, said heater having heating surfaces disposed at an angle to the said plane of the heater and uniformly distributed throughout the heater in said cross-sectional area of the wind box to heat the air passing through said open spaces from the inlet to said outlets, the air passing through the heater in the Wind box being supplied equally to all of said outlets at uniform temperatures.

6. In a furnace having a wind box vpositioned around the body of the wind box for supplying blown air to the entrances Yof a plurality of tuyres communicating with said furnace, a heater positioned in the wind box at substantially the same proximity to a plane passing through said entrances for heating the air delivered to each of said tuyres, said heater cornprising a plurality of segmental portions arranged around the extent of the Wind box, and thermostatic means positioned adjacent tuyre entrances at dierent-'locations around the'wind box, said thermostatic means being responsive to the temperature of the heated air supplied to adjacent tuyre entrances for separately controlling said portions of the heater, respectively, to maintain uniform heating of air supplied to the plurality of tuyre entrances.

7. In a furnace having a wind box positioned around the body of the furnace for supplying blown air to the entrances of a plurality of tuyres communicating with said furnace, a plurality of heating units positioned in said Wind box around said furnace, said heater units having passageways for the passing of air through the wind box from the inlet to the said tuyre entrances and being adapted to heat the air around the extent f the wind box, thermostatic control devices positioned in the wind box adjacent different tuyre entrances and responsive to the temperature of the air heated by each of said units, respectively, for controlling the respective heater units in accordance with therequired temperature of air to be supplied to said tuyres. y

8. In a wind box for furnishing a blast of blown air at uniformly. high temperature to a plurality of tuyres of a furnace, the wind box having an inlet adapted to communicate with a source of blown air and outlets communicating with said tuyres, the arrangement of the wind box, inlet and outlets being such that unequal heat exchange conditions affect dierent portions of the blown air passing from the inlet to said plurality of outlets, a heater positioned within the Wind box in the path of the flow of air and at a substantially uniform unobstructed distance from said outlets to substantially equalize the heat exchange conditions affecting the air heated by said heater and passing directly to the closest outlets, said air being supplied through saidv outlets to the tuyres.

9. In a furnace having a Wind box for supplying a blast of air to a plurality of tuyres, said wind box having an inlet adapted to communicate with a source of an air blast and having outlets in communication with said tuyres, the out- Ilets being positioned in uniform relationship to each other and the inlet being positioned in different spaced relationship to the respective outlets whereby the flow of air from the inlet.

to the respective outlets is not uniform, a heater mounted within said Wind box in the path of the iiow of air therethrough, said heater having surfacesarranged to modify said flow of air to distribute the air substantially equally around the cross-sectional area of the wind box and being adapted to heat the said air substantially equally around the cross-sectional area of the wind box, said heater being positioned in substantially the same spaced relationship to all of said outlets to uniformly influence the flow of air to each.

10. In a furnace having a wind box for supplying a blast of air to a plurality of tuyres, said Wind box having an inlet adapted to communicate with a source of an air blast and having outlets in communication with said tuyres, a plurality of frames mounted in said wind box in the same relative proximity to said outlets, electrical heating elements mounted on said frames for uniformly heating the air passing through the wind box between said frames, thermostatic means responsive to the temperature of the air heated by said elements and supplied to said outlets, electrical connecting means connecting said heating elements and thermostatic means in circuit relationship to a source of electrical energy, and regulating means operative from the exterior of the wind box for regulating said thermostatic means.

1l. In a furnace having a wind box for supplying a blast of air to a plurality of tuyres, said Wind box having an inlet adapted to communicate with a source of an air blast and having outlets in communication with said tuyres. electrical heating means for heating said air mounted within the wind box in a plane substantially parallel to a plane passing through said outlets, a plurality of thermostatic members distributed around the wind box and responsive to the temperature'of the air heated by said heating means at different locations, and electrical connecting means connecting said heating means and said thermostatic members in circuit relationship to a source of electrical energy, said heating means and thermostatic members adapted to provide for the delivery of air to said outlets at uniform temperatures.

12. In a furnace having a wind box for supplyying a blast of air to a plurality lof tuyres, said the electrical energization of said heating means.

13. In a furnace having a wind box positioned i aroundl the body of the furnace for supplying air to a plurality of tuyres entering the furnace, said wind box having an inlet adapted to com municate with a source of an air` blast and having outlets in communication with said tuyres,

Aoutlets to heat the airr without unequal heat i 15. In a furnace having a wind box positioned around the body of the furnace for supplying air to a plurality of tuyres entering the furnace,

said wind box having an inlet adapted to communicate with a source of an air blast and having outlets in communication with said tuyres, a casing mounted in said wind box in the path of the flow of air from said inlet to said outlets and disposed around the cross-sectional area of the wind box, said casing having passageways extending therethrough for the said flow of air, said passageways being arranged to substantially uniformly distribute the flow of air around the extent of the wind box, said casing having a heating chamber therein for heating the air passing through said passageways. burner means for providing heat in said heating chamber, and

. regulating means for controlling the heating by heat exchange means mounted in said wind box in unobstructed communication with said lout-- lets and in the path of the air blast passing from said inlet to said outlets for heating the air supplied to said outlets, said heat exchange means having separately controllable portions, conduit means for delivering a heating medium to said heat exchange means, and thermostatic means responsive to the temperature of the heated air supplied at different locations around to a plurality of tuyres entering the furnace,4

said wind box having an inlet adapted to communicate with a source of an air blast and having outlets in communication with said tuyres', a plurality of heat exchange devices mounted in the. wind box and uniformly distributed around the extent of the wind box forheating the air supplied to the outlets, delivery means for delivering heating medium to each of said devices, and a plurality of thermostatic .members distributed around the wind box adjacent diiferent outlets and responsive to the temperature of the heated air supplied to the said adjacent outlets, each of said thermostatic members being in operative connection with the delivery means for each of said devices, respectively, for controlling and co-relating the heating by said each device to maintain a constant and uniform temperature of the air .supplied tosaid outlets, the arrangement of the heat exchange devices. delivery means, and thermostatic members providing for the delivery of air to the outlets at uniform and controlled temperatures.

said burner means.

16. In a furnace having a wind box for supplying a blast of air to a plurality of tuyres, said wind box having an inlet adapted to communicate with a source of an air blast and having outlets in communication with said tuyres, partitions dividing said wind box into a portion adjacent said inlet, a portion adjacent said outlets and an intermediate portion forming a heating chamber, said intermediate portion having conduits extending therethrough and being distributed ai'. intervals around the wind box, said conduits distributing the airow substantially equally to said outlets, a plurality of burners distributed around the Wind box for substantially uniformly heating said heating chamber, thermostatic means responsive to the temperature of the air supplied to the outlets for controlling the operation of said burners in accordance with the required temperature at diiferent localities around the extent of the wind box. and regulating means for adjustably regulating said thermostatic means, the air passing through the conduitsfrom the inlet to the outlets being heated to the required temperature by said heating chamber. l

17. In the operation of a furnace, the method of furnishing preheated air to the furnace through a plurality of tuyres, comprising: supplying an air blast to a wind box, distributing the air blast uniformly around the wind box,-

uniformly heating within the wind box said air blast, passing the heated air uniform distances to the entrances of said tuyres, and supplying the air equally to the plurality of tuyres at uniform temperatures.

HERBERT Ao Rance. OLIVER ssamm.