US2414888A - Recuperative soaking pit furnace - Google Patents

Description

Jan. 28, 1947. v w. A. MORTON ETI'AL 2,414,888

RECUPERATIVE SQAKING PIT FURNACE 2 Sheets-Sheet 1 Filed July 3, 1941 Jan. 28, 1941.

W. A. MORTON ETAL REGUPEMTIVE SOAKING PI! FURNACE Filed July 3, 1941 2 Sheets-Sheet 2 INVEN M,

Jfi' ATTORNEY Patented Jan. 28, 1947 2,414Las RECUPERATIVE some rrr rpmmcs William A. Morton and Edwin G. Smith, Mount Lebanon Township, Allegheny County, Pa, as-

signors to The Amsler Morton Company, Pittsburgh, Pa., a corporation of Pennsylvania Application July 3, 1941, Serial No. 400,914

This invention relates generally to recuperative soaking pit furnaces for heating heavy ingots, billets and the like to rolling temperatures and more particularly to the construction and the method of operating the same.

Pit furnaces of the recuperative fired continuously or intermittently.

These furnaces may be equipped with automatic temperature control devices which constantly decrease the supply of fuel during the progress of the heating cycle of the ingots. The heat is thus proportioned for the batch of ingots constituting a single furnace heat and this type of furnace is frequently referred to as a full proportioning or batch type furnace.-

' If the furnace is fired intermittently the automatic temperature control turns the fuel on and off periodically. The full amount of fuel is applied until a predetermined furnace temperature is attained, then the fuel is automatically shut off until the furnace temperature drops to a predetermined degree, at which time the control again automatically functions to supply a full flow of fuel. These alternate on and off periods lengthen as the ingots approach the proper saturating temperature. These lengthened periods type may be 1 31 Claims. (Cl. 263-15) Again a burner flame projected in the free space above the ingots expands without imparting turbulence to the colder layers of gases adjacent the base of the standing ingots. It is desirable to create a maximum turbulence at the end adjacent the end of the first pass of the flame.

The principal object of this invention is the provision of a recuperative type soaking pit furnace which overcomes these difficulties for uniformly heating the ingots and the method of operating the same.

Another important object is the provision of a recuperative soaking pit furnace having burners in opposite walls and through which all or a major portion of the fuel is alternately introduced at any one time, to insure circulation of the gases about the ingots located remotely from the burners.

taken with the furnace temperature inform the operator that the ingots are properly saturated for rolling or other purposes.

A furnace of this character which is fired simultaneously with oppositely disposed burners in the end walls, produces a definite defect. in the heating characteristics whether the heating cycle is continuous or intermittent. The flames from both burners meet at a common point along the axis of the burners, causing a sudden increase in the rate of mixing the air and fuel, thereby liberatingan excessive amount of heatat the zone surrounding the impingement of the two streams of flames. Localization of heat produced in this manner is damaging to the steel being heated and is undesirable. The impingement of the flames from two opposed burners breaks the velocity head required to first carry the gases into the pit and consequently stops'the flames in the center there-' of. Proper and immediate circulation of the flames in the area of the burners is not obtained.

If the opposed burners are offset from one'another in a horizontal lane they must be raised above. the ingot tops to prevent direct flame impingement on the charge. However burner flames projecting acrossthe top of the furnace have the tendency to prematurely accelerate the rate of combustion, thereby liberating most of the heat overtop of the steel instead of surrounding itby the burning gaseous products.

Another object'is the provision of a recuperative soaking pit furnace having oppositely disposed burners in its end walls.

Another object is the provision of a recuperative soaking pit furnace having vertically spaced burners in opposite walls to selectively regulate the temperature of different vertical portions of the ingots.

Another object is the provision of a recuperative oaking pit furnace having the burners disposed in opposite walls and within the limit of the height of the charge in the furnace.

Another'object is. the provision of a recuperative soaking pit furnace having discharge ports in opposite walls and through which the flow of the'products of combustion is regulated.

Another object is the provision of a recuperative soaking pit furnace having discharge ports in opposite walls arranged to alternately convey the products of combustion from the pit.

Another object is the provision of a recuperative soaking pit furnace arranged to supply proportionate amounts of heated air to burners locatedin opposite walls of the pit.

Another object is the provision of a recuperative soaking pit furnace arranged to, alternately supply heated air to the burners on one side of the pit.

Another object is the provision of method and apparatus for regulating the alternate supply of fuel and heated air and the withdrawal of the products of combustion from the alternate end walls of a recuperative soaking pit furnace.

Another object is the provision of a. recuperative soaking furnace arranged to be fired at double capacity alternately from each end of the pit producing a stream of burning fuel in suf-,- ficient quantities to sustain a high velocity head to induce sumcient circulation of the gases to cause the gases to thoroughly envelop the ingots.

Another object is the provision of arecuperative soaking pit furnace having oppositely disposed .burner ports with the ingots arranged in rows on each side of the burner ports forming aisles into which the flames are propagated.

- Other objects and advantages appear in the following description'and claims.

In the accompanying drawings a practical embodiment illustrating the principles of this invention is shown wherein:

23 form the combustion chamber for the streams of flames issuing from the burner ports.

The fuel is delivered through the burner pipes 25 which extend through the preheated air passageways 28. The burning gases issuing from one end of the furnace project down the aisles to the opposite end wall I2 of the furnace. The expansion of the gases increases rapidly upon entering the pit.

The combustlbles enter the aisles between the ingots at relatively high velocities, preferably with all or 'lnost of the combustible entering first Fig. 1 is a vertical section of arecuperative soaking pit furnace charged with ingots.

Fig. 2 is a vertical section of a recuperative soaking-pit showing vertically spaced burners at a different location thanthat illustrated in Fig. 1. s Fig. 3 is a plan view of a recuperative furnace soaking pit showing the ingots placed in four rows from one end of the pit to the other with heating aisles therebetween.

Fig. 4 is an end view taken along the line 4-4 of Fig. 3. 1

Fig. 5 is a diagrammatic plan view of the-recuperative soaking pit furnace illustrated in Fig. 1 showing the apparatus for supplying fuel and air to the furnace pit and the discharge of the products of combustion therefrom together with the circuits for controlling the same.

Referring to the drawings: the soaking pit furnace chamber i0 is an individually constructed pit which would be located in rows of two on a rectangular plan making up a battery of similarly constructed furnaces. The heating units or recuperators I! are of the counterfiow type and are located between the consecutive rows of furnaces and are connected through the end walls I: of the pit. The top is of the furnace pit time on a recuperative pit. This method of firing is flush with the main deck level M of the furnace I battery. The latter is made in sections that are removable for purposes of inspection and maintenance. The mouth of the pit is closed in by the unitary cover i5 provided with an annular set of depending seal blades arranged to he stepped into the granular trough. The weight of the cover is supported on four adjustable pads at four points on the steel binding surrounding the cover.

Each cover is provided with four lugs i8 arranged to be engaged by the lifting Jaws I! depending from the carriage i8. The carriage I8 may span one or both of the furnace pits in rows of two and it is supported on a track secured to the main deck and extends longitudinally of the battery of furnaces. Each carriage is equipped with a hoist mechanism 20 for raising the furnace covers in each row and a traverse drive mechanism to carry them away from the mouth of the pit.

The pit iii of the furnace may be made rectangular or square in shape and has been constructed circular. The bottom of the pitis covered with approximately twelve inches of coke breeze and has an upwardly throated clean-out hole 2|. The ingots 22 stand in the coke breeze and are placed in spaced relation in rows extending from one end ofthe pit to the other, providing longitudinally disposed aisles. The central or main aisles 23, shown in Figs. 3, 4 and 5 are aligned with the induction type burner ports 24 located in the end walls iii. If the pit is sufficiently wide to accommodate two or more wide aisles between the rows of billets, as illustrated in Figs. 3 and 4, then additional burner ports '24 are placed in the end walls l2. The wide aisles from one side of an aisle and then from the opposite side by means of the reversing means hereinafter described and employed for the first the furnace permits the initial velocity head of the combustibles to carry the flames substantially across the furnace where the final available head will be-absorbed in creating circulation about the ingots on the side of the pit remote from the burners. The act of reversing the fiow of the flames in this furnace will insure uniform movement of the flames to all parts of the furnace and therefore, around all the ingots. The ingots will, therefore, be uniformly heated in every position in the furnace.

The confined aisle space produced by ingots increases the turbulence of the rapidly expanding gases, thereby increasing the outward fiow of the burning gases around the spaced ingots, which is essential for the proper circulation of the heat as well as for the recirculation of some of the earlier released and slightly cooler gases within the pit. The gases thus -fiow down the the side walls and return toward the end wall from which they were introduced. A portion of the gases swirls around each ingot and thus a constantly rotating envelope of the pit gases is maintained, providing a protective layer around the ingot keeping cooler gases from lying stagnant in the outer aisles or on the hearth, and resulting in uniform heating.

1 When all or a greater portion'of the gases are fired from one end of the pit all or a greater portion of the waste gases are removed through the outlet ports 21 positioned inthe same end wall l2 near the four corners of the side walls and slightly above the coke breeze. The gases pass from the outlets into the superimposed distributing header 28 and enter all of the hollow tile vertical fiues 30 simultaneously which results in cooling the entire waste gas flow by all of the air being preheated. The waste gases travel to the bottom of the recuperat'or and into the horizontal collecting passages M which direct them to the header 32 that is connected to the branch. passageway 33. The branch passageways 33 direct the products of combustion from the recuperators at each end of the pit to' theY connection 34 which leads them through the common passageway 35 to the stack.

Air is supplied by a fan or blower to the duct '36 which conveys it to the Y 31 where it may be directed to the recuperators at either or both ends of the pit through the ducts 38." These ducts terminate in the headers 40 which connect with the openings 4! of the first or lower pass of thecircuitous air circuit through the counterflow type recuperator where it is preheated and flows into the passageways 26 that lead to the burner ports 24.

In the furnace pit shown in Fig. -2 the burner ports fl in the end walls l2 are positioned above 7 type of fuel employed to fire the pit.

'aciqssa the outlets 121 and are below thecenter of the ingots, whereas in Fig; 1 they are positioned between the center and the tops of the ingots.

The relative position of these burner ports with .respect to the ingots depends largely upon the size and character of the steel ingots and the Againif the pit is to be loaded wit main firing aisles-23 as shown in Figs. 3, 4 and 5 the burner ports 24 in the opposite end walls l2 be aligned with the burner perm inthe opposite end wall as illustrated in Fig. 2.

Each burner shown in Figs. 1 and 2 may be fired alternately at double full volume or simultaneously and proportionately by alternating the greatest iuei volume from one end of the pit to the other with the total input volume of the burners being equal to the sum of the full volume of each burner.

When the burners are alternately fired they deliver a long flame extending across the pit and sweeping out the colder gases adjacent the walls as the velocity head is expended. This action is most efiective when theburners are alternately fired, at which time the volume of gases and therefore their weight to induce circulation is doubled.

When firing the burners at opposite ends of the pit simultaneously the turbulence is in the center of the pit where it isleast beneficial and the mass velocity of the gases is also halved and improperly expended at the center of the furnace.

The withdrawal of the products of combustion through the outlets 2i and the recuperators ii may be proportioned equally or unequally between the recuperators at both ends of the fur nace pit or the total discharge may be taken alternately from one end of the pit. When all or a greater portion of the products of combus= tion are being discharged through the recuperators at one end of the pit it is preferable to gradually change tothe recuperators at the other end of the furnace before the firing is trans' ferred, and all the air for combustion may be passed through those recuperators. Thus ample heat is provided in the recuperator before the air is forced therethrough for firing the furnace. Each recuperator is capable of receiving the total waste gas output of the pit. In this manner the discharge cycle of the products of combustion through the recuperators is out of phase with the firing cycle in that it leads the firing cycle and furnishes the alternate recuperator with heat so that it is amply supplied when the firing is transferred.

When the firing isfproportioned between the burners at either end of the pit it is also-advisof s fi that is ordinarily fired fromi one burner of a similar furnace which is fired from both ends 'simutaneously. A double. quantity of gas issuing from a single burner produces a stream a burning ,fuel having a high velocity head which proportionately increases the turbulence and provides good flame propagation. This increased turbulence aids in wiping the heat about the in-. gots, therebyuniformly distributing the heatto properly soak all of the ingots to the proper temperature. Loop flames may be produced in the aisles'and their magnitude varied from opposite sides by manuallyadjusting the nozzle and fuel at the burner port.

With two or more of the induction type burner ports 24 arranged in the same vertical planein each end wall, as shown in Fig. 4, selective firing may be carried-on at highefilciency by manually adjusting the firing, rate of each burner independently for any firing "condition. This arrangement of burners is desirable for a very deep pit furnace heating extremely tall ingots.

If the upper one of two or more induction type burners in subjacent relation/ were to be fired alone hot gases would be drawn into the passageways to? through the ports 24 of the burners in the same vertical plane and discharged through the port of the burner being fired. Thus hot gases from the furnace may be circulated and refired with the hot air from the recuperator, the fuel issuing from the burner 25. This is a very desirable condition not previously mployed in soaking pit furnace operation.

Again ii the middle burner of three'subjacent burners is idle the circulation of the hot gases from the pit may be proportioned between the upper arfd lower burners by regulating. the firing of these burners. It may also be desirable to draw the hot gases directly from the pit and mix them with the heated air from the recuperator as it travels upwardly to the two upper burners which are being fired. Once the burners have been adjusted for a given firing condition they may be readily reset to duplicate these conditions. Thus by providing a log for a plurality of conditions the furnace may be quickly changed for heating difierent kinds of steel. These furnace adjustments maybe made independently of the alternate end to end firing or alternate firing at both ends when the fuel is proportioned. The temperature of the furnace is registered by the pyrometers 4! located in the end walls it at one side of the burner ports 24 and preferably opposite from the location of an ingot as illustrated in Fig. 5. The pyrometers are electrically connected to the recording potentiometer temperature control 42 which in turn energizes the relay 43 for actuating the servomotor 44 which regulates the opening and 'closing of able to maintain this phase relation between the the reversing relay 5|.

the valve 45 in the fuel supply line 45, thereby controlling the temperature of the furnace. The fuel flowing through the supply line 46 passes through the orifice 41, the valve 45, and thence travels to the reversing valve 48. The reversing valve 48 may be employed to direct all or a greater portion of the fuel to one end of the furnace and none or a small proportionof the fuel to the other end of the furnace at the same time. In either event the'reversing valve 48 alternately switches the fuel from one end of the furnace pit to the other when it is actuated by the servomotor ill which in turn is energized by The air which is fed to the recuperators at both ends of the furnace is distributed or propcrtioned in the same furnace for a given manner as the fuel i? means of the reversing damper or valve '2 which is operated by the servomotor it energised from the relay 54.

The-air supply line 38 has an adjustable orifice '65 comparable to the adjustable fuel orifice 41 in the fuel line. Pressure linesconnected to the air and fuel lines .on opposite sides of the orifices "and 55 register theprcssure differential on op- V posite sides of the fuel and air diaphragms in the ratio controller 68. Since the temperature controller 42 determines the flow of fuel in accordance with the tem erature required in the furnace, the air supplied to'the burners must be proportioned to the amount of fuel consumed.

The ratio controller 56 thus energizes the servomotor 51 to regulate the valve 58 and thereby determines the proper amount of air that should be fed to the heat transfer units and thence to the furnace in proportion to the quantity of fuel and the valve 52 selects or proportions the flow between the burners at opposite ends of the pit.

The gases being discharged from the furnace pit are directed through the recuperators H, the

headers 32. the ducts 33 to the Y connection 34.

' The reversing valve 60 in this Y connection may be operated to permit the flow of gases from only one end of the furnace pit at a time. Dampers "1] may also be used for proportioning the relay 82. The three reversing relays ii, 54 and 82 which control the end or proportionate end supply of fuel, air and the discharge of the gases from the pit, respectively, are all energized at the proper time by. the cycle controller 83 which may be adjusted/to reverse each of the three relays in the propersequence at the proper time for alternating the on and of! end to and firing or proportional end to end firing from one end of the pit to the other. This controller may be adjusted to energize each of the three reversing relays simultaneously or at different timed intervals. In this manner the function controlled by the operation of any one of the reversingrelays may be kept in phase or out of phase with the function controlled by the operation oi the other relays. Thus the damper 80 may be reversed to discharge the products of combustion through the opposite recuperators before the air and the fuel is switched to. that end of the furnace.

Again it may be desirable to switch a'portion of the air supplied to the burners to the opposite side of the pit before the fuel is transferred. By properly timing the operating sequence of the reversing relays and by regulating the speed of the reversing valves the proper firing conditions may be continuously maintained within the soak-- ing pit during the switching operation.

The furnace pressure is maintained by regulating the stack damper s4, the operation of which is controlled by the servomotor 05. The servomotor is energized by the diaphragm actuated furnace pressure controller 66. One side of the diaphragm is. connected to the interior of the pit intermediate of its ends as shown at 61 while the other side is connected adjacent the exterior of the furnace as shown at 68. a

A pyrometer III is placed in a recess in the side to envelop each ingot as they meatless f i walls of the pit adiacenteach eornernear the bottom-of the furnace pit as-shown in 8' and 4. Each of these pyrometers is connected to a temperature recording instrument on the con= trol panel where they may be observed by the operator. The lower corners of the pit are the coolest positions of the'furnace and the last to reach the proper soakingtemperature. By observing the temperatures recorded by the pyrorneters as the operator is enabled to Judge the progress of the soaking operatlomand make any adjustments necessary to control the heating cycle. If these pyronieters indicate .an unbalance. in the firing conditions within the furnace the operator mal ---atiiust the fuel hand valves at each burner to rectify the unbalanced conditions. This gives the operator a quick and-accurate check on the operation of the furnace at all times. However the adjustment of the fuel hand valves is ordinarily necessary only during the first few times that the furnace is fired or after alterations have been made thereon.

The soaking pit commonly'uscd in present practice provides approximately 81% by. weight yield for each ingot which represents the weight of the steel in the ingot that is usable after the rolling operation. By the use of the furnace structure and the method of operating the same as disclosed herein, this yield may be raised to 84%. Thus 2% to 3% more metal per ingot is saved bythe use of this improved structure. This saving is principally due to the formation of a loose but monolithic scale of normal weight on each ingot. This scale is of remarkable uniformity and texture and clings as an unbroken sheath to the whole of the surface of the ingot until it is subiected to the mill operations. Thus no secondary .scale has a chance to form on the ingot from the time it is removed from the soaking pit until it is worked.

The low weight and uniformity of this scale is the result of not permitting the heating flames to directly play on the ingot during flame propagation but permitting the resultant waste gases swirl through the 1. A recuperative soaking 'pit furnace of the 1 character described comprising a furnace pit, recuperators positioned at each end of the pit, a

row of vertically aligned induction type burner openings in each of the end walls of the pit adjacent said recuperators and arranged to'project substantially continuous vertical sheets of heating flames across the pit, a common hot air conduit for each set of. vertically aligned burner openings, said conduits being connected to theadjacent recuperators to supply heated air to the burner openings, a fuel line for each burner opening. and means for independently regulating the flow of fuel through each line to control the 'recirculation of the products of combustion from the pit and the distribution of heated air from the recuperators through selected .burner openngs.

2. In a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings in the opposite end walls of the pit, re-

cuperators at, each end of the pit for supplying heated air to the burners at the corresponding end, discharge openings at each end of the pit for conductingthe products of combustion from the pit-to the recuperators to heat the air, and cycle controller means for alternately supplying fuel to the burner openings and air to the recuperators at opposite ends of the pit.

3. In a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings in the opposite end walls of the pit, re-

cupcrators at each end of the pit for supplying heated air to the burners at the corresponding end, discharge openings at each end of the pit for conducting the products of combustion from the pit to the recuperators to heat the air, and cycle controller means for alternately supplying fuel to the burner openings and'air to the recuperators and discharging products of combustion simultaneously at opposite ends of the pit.

d. In a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings in the dpposite end walls of the pit, recuperators at each end of the pit for supplying heated air to the burners at the corresponding end, discharge openings at each end of the pit for conducting the products of combustion from the pit to the recupcrators to heat the air, and

ture responsive means for controlling the flow of fuel, means for controlling the supply of air in' response to the supply oi fuel, furnace pressure 7 responsive means for controlling. the amount of the discharge of the products of combustion from v cycle controller means for alternately supplying proportionate amounts of fuel and air to the furnace and discharging proportionate amounts of the products of combustion at opposite ends of the pit simultaneously.

5. In a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings in the opposite end walls of the pit, recuperators at each end of the pit for supplying heated air to the burners at the corresponding end, discharge openings at each end of the pit for conducting the products of combustion from the pit to the recuperators to heat the air, means for supplying fuel to the burner openings, means for supplying air to the recuperators, temperature responsive means for controlling the flow of fuel, means for controlling the supply of air in response to the supply of fuel, and means for simultaneously controlling the proportionate amount of the discharge of the products of comloustlon from each end of thefurnace.

d. in a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings in the opposite end walls of the pit,

recuperators at each end of the pit for supplying heated air to the burners at the corresponding and, discharge openings at each end of the pit for conducting the products of combustion from the pit to the recuperators to heat the air, means for supplying fuel to the burner openings, means for supplying air to the recuperators, temperature responsive means for controlling the flow of fuel, means for controlling the supply of air in response to the supply of fuel, furnace pressure responsive means for controlling the amount of the discharge of the products of combustion from the furnace, and means for alternating the supply of fuel and air and discharging the products of combustion at opposite ends of the furnace pit.

7. In a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings in the opposite end walls of the pit, recuperators at each end of the pit for supplying heated air to the burners at the corresponding end, discharge openings at each end oi the pitfor conducting the products of combustion from the pit to the recuperators to heat the air. means for supplying fuel to the burner openings, means for supplying air to the recuperators, temperathe furnace,'and means for alternately supplying proportionate amounts of fuel and air and discharging proportionate amounts of the products of combustion at opposite ends of the fur? nace pit.

8. In a recuperative soaking furnace for heating ingots and the like comprising a pit, burner openings inthe opposite end walls of the pit. recuperators at each end of the pit for supplying heated air to the burners at the corresponding end, discharge openings at each end of the pit for conducting the products of combustion from the pit to the recuperators to heat the air, means for supplying fuel to the burner openings, means for supplying air ,to the recuperators, temperature responsive means for controlling the flow of fuel, means for controlling the supply of air in response to the supply of fuel, furnace pressure responsive means for controlling the amount of the discharge of the products of combustion from the furnace, and means foralternating the supply of fuel and air and discharging the products of combustion at opposite ends of the furnace pit, said last mentioned means alternating the fuel, air and the products of combustion at difierent phase relation with respect to one an other.

ii. The method of loading a horirontally fired recuperative soslringpit furnace having a plurality of horizontally disposed hurner openings at each end thereof fed by said recuperators which comprises setting the members making up the charge in rows forming an aisle on hath sides thereof, and aligning the aisles with the. burner openings in opposite walls of the pit to hathe both sides of the charge and prevent direct flame impingement.

ill. The method of loading a horizontally fired recuperatlve soaking pit face having a plurality of horiaontally disposed burner openings at each end thereof fed by said recuperators which comprises setting the members forming the charge in parallel rows attending between opposite walls which contain the burner openings of the pit, spacing the members from each other and from the wall surfaces of the pit, spacing the rows to produce aisles therebetween, and aligning the aisles with the burner openings in the opposite walls of the pit tobathe both sides of the intermediate rows of members and prevent direct dame impingement.

11. The method of operating a rccuperative I soaking pit furnace having fuel burner and diswaste gases, selectively through oppositely dis- I charge openings in opposite end walls which comprises supplying fuel alternately from the opposite ends, regulably controlling the duration of the fuel supply intervals, and exhausting the waste gases 'at the firing end through openings mitted.

12. The method of operating a recuperative soaking pit furnace having fuel burner and discharge openings in opposite end walls which comprises supplying fuel alternately from the opposite ends, regulably controlling the duration of the fuel supply intervals, and exhausting the posed openings other than those through which the fuel is admitted.

13.-'I'he method ofoperatinga recuperative soaking pit furnace having fuel burner and disr "atlases l2 1 bustibles to the burner openings at alternate ends charge openings in opposite end walls which comprises supplying proportionate amounts of fuel alternately from the opposite ends simultaneof the pit.

20. The method of operating a soaking pit furnace having an aisle between spaced ingotsand "fuelburner openings within the limits of the aisle in oppoflte end walls, which comprises supplying combustibles simultaneously from the opposed burners in spaced subjacent horizontal paths and exhausting the waste gases through 14. The method of increasing the magnitude of turbulence in a recuperative pit furnace having burners in opposite'ends of the furnace which comprises varying the quantity of fuel admitted simultaneously through the said burners in a timed sequence. I

15. In a recuperative furnace, a pit, burners in opposite vertical end walls. pyrometers in said walls arranged to regulate the supply of combustibles to the .burners, waste gas fines in said walls for exhausting the products of combustion from the furnace and communicating to a source of draft; means for alternating the supply of combustibles to the burners at each end of the pit independently of the discharge of waste gases from either end, and means for selectively controlling the alternating cycle of combustion. 16. In a recuperative furnace, a pit, burners in opposite vertical end walls, pyrometers in said walls arranged to regulate the supply of combustibles to the burners, waste gas fiues in said walls for exhausting the products of combustion from the furnace and communicating to a source of draft, means for supplying combustibles to the burners, means. for alternately directing the discharge of the products of combustion through the gas fiues at each end of the pit independently ofthe supply of combustibles to either end, and.

means forselectiveiy controlling the alternating cycle of combustion.

17. In a recuperative furnace, a pit. burners in opposite vertical end walls, pyrometers-in said walls arranged to regulate the supply of combustibles to the burners, waste gas fiues in said walls for exhausting the products of combustion from-the furnace and communicating to a source openings other than those through which the fuel is admitted.

21. The method of operating a soaking pit furnace having an aisle between spaced ingots and fuel burner openings within the limits of the aisle in opposite end walls, which comprises supplying combustibles simutaneously from the opposite ends, controllably interrupting the fuel supply at intervals to regulate the average temperature of the furnace, and exhausting thewaste gases selectively through oppositely dis-- posed openings other than those through which the fuel is admitted.

22. In a furnace having recuperators disposed all-opposite sides thereof, burner openings in opposite walls admitting preheated air from the recuperators into the furnace, waste gas openings in opposite walls for the delivery of waste gases to the waste gas passages of the recuperators, a pair of fiues leading from the spaced recuperators through a Y connection to a source of draft, unitary valve means in the Y connection of the waste gas fines for controlling the flow of gases whereby the gases may be alternatelyd'rawn through either 'recuperator and proportionately through both simultaneously. and valve means for selectively admitting air through a Y connection to either of the spaced recuperators in timed relation to the movements of the waste gases therethrough.

23. In a pair of spaced recuperators adapted for the passage of air to be preheated and waste gases therethrough simultaneously, the combination which includes a furnace positioned between of draft, means for alternately directing the discharge of the products of combustion through the gas fiues at each end of the pit, .means for alternating the supply of combustibles to the v burners at each end of the pit independently of the discharge of the products of combustion from either end. and means for selectively controlling the alternating cycle of combustion.

18. In a furnace of the recuperative type for heating ingots, a pit having burners in oppositely disposed walls positioned adjacent the top and bottom of the pit, said burners adapted for intermittent and continuous firing, a combustion space between the ingots formed by providing between the rows of ingots an aisle aligned with said burners, and discharge openings disposed in said end walls adjacent the bottom of the pit and offset from the burners for conducting products of combustion from the pit.

19. In a recuperative soaking furnace of the character described comprising a pit, a series of burner openings in spaced relation across the opposite end walls of the pit, the opposed and adjacent burner openings being at different levels, other openings in the pit for discharging the products of combustion therefrom, and means for supplying and regulating the flow 0! 90m the recuperators, means for delivering preheated I air to'the furnace and for removing waste gases from the furnace simultaneously through both recuperators. means for selectively varying the quantity of waste gases in motion simultaneously in each recuperator, and unitary means for reversing the adjusted variation from one recuperator to the other to regulate the desired fiow of gases in the furnace.

24. The method of operating a recuperative soaking pit furnace having fuel burner and discharge openings in' opposite end walls, which comprises applying heat during spaced periodic intervals of time alternately from opposite ends to the furnace to raise the temperature of the charge therein to the furnace temperature, controlling the heating periods by predetermined temperature limits of the furnace temperature until the heat supplied substantially balances the furnace loses, which condition indicates that the charge is properly soaked.

25. The method of claim 24 which also includes reducing the quantity of heat applied during successive firing intervals.

'26. The method of operating a soaking pit furnace' which comprises firing the furnace at 28. The method of operating a soaking pit fur- I 'to raise the temperature of the charge therein to the furnace temperature, controlling the heating periods by predetermined temperature limits of the furnace temperature until the heat supplied substantially balances the furnace losses, which condition indicates that the charge is properly soaked, the applied heat being obtained by firing at different levels from opposite ends of the furnace simultaneously and alternating the firing levels from one end of the pit to the other periodically. I

29. A soaking furnace for heating ingots and the like consisting of a pit having vertical walls and a hearth for supporting spaced upright ingots in aligned rows, a removable cover closing the top of the pit, burner means in the walls of the pit spaced from the hearth and from the cover and arranged to project substantially continuous vertical sheets of heating flames across the pit between the position of the rows of ingots thereby avoiding direct impingement on positioned ingots, and oppositely disposed means for exhausting the waste gases from the pit.

30. The structure of claim 29 characterized in that the exhaust means are positioned between the burner means and the hearth and are oifset from the burner means.

31. The structure of claim 29 which also includes oppositely disposed recuperators adjacent to the pit, one set of passageways connecting the exhaust means to the adjacent recuperator, means to supply air to the recuperators, and a second set of passageways connecting the air from the recuperators to the adjacent burner means.

' WILLIAM A. MORTON.

EDWIN G. SMITH.

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