US3197184A - Apparatus for heating metals to high temperatures - Google Patents

Description

July 1965 E. NAVEZ ETAL APPARATUS FOR HEATING METALS TO HIGH TEMPERATURES 4 Sheets-Sheet 1 Filed July 25, 1962 y 27, 1955 NAVEZ ETAL 3,197,184

APPARATUS FOR HEATING METALS TO HIGH TEMPERATURES Filed July 25, 1962 4 Sheets-Sheet 2 Fig 2 Fig 3 Fig 5 4 Sheets-Sheet 5 E. NAVEZ ETAL APPARATUS FOR HEATING METALS TO HIGH TEMPERATURES July 27, 1965 Filed July 25, 1962 y 7, 1965 E. NAVEZ ETAL 3,197,184

APPARATUS FOR HEATING METALS TO HIGH TEMPERATURES Filed July 25, 1962 4 Sheets-Sheet 4 United States Patent 3,197,184 APPARATUS FQR Z EATWG METALS TO HIGH TEMPERATURES Emile Navez and (Camille Demoulin, Paris, France, as-

siguors to Stein & Roubaix, Paris, France, a company of France Filed July 25, 1962, der. No. 212,279 Claims prior-2W, application France, Nov. 13, 1% 878,797 6 Claims. (Cl. 2637) In many manufacturing processes involving large de formations of the treated metal, particularly in the case of steel, it is necessary to raise the metal to a high temperature, which may attain as much as 1250 to 1300" C.

Conventional heating methods using oxidizing combustion lead to oxidation of the metal, and the scale resulting from the oxidation causes large losses of metal due to the heating, along with rapid deterioration of the conversion tooling used on the heated metal.

From studies made on the subject, it is well known that to ensure oxidation-free heating of steel to high temperatures, the metal must evolve between 650/70() C. and 1250/ 1300 C. in an atmosphere the quality of which is defined by the following approximate ratios:

Such an atmosphere can only be obtained by the incomplete combustion (hereinafter termed primary combustion) of a gaseous fuel, using roughly 50% of the amount of air theoretically required for complete combustion.

Combustion with such a shortage of air will not give off all the latent heat of the fuel and will take place at temperatures that are low enough to prevent completion of the combustion and dissociation reactions. This results in the obtainment of oxidoreducing atmospheres, in conjunction with lampblack deposits on the products to be heated. This latter phenomenon is encountered particularly in the case of the incomplete combustion of rich gaseous fuels composed mainly of hydrocarbons which have escaped controlled cracking at some localized point.

in order to overcome these drawbacks of inadequate temperature for heating the product, of oxidoreducing combustion, and of lampblack deposits caused by disorderly cracking, a variety of solutions have been put forward.

It has been proposed that the combustion be effected in tWo stages, or even in three stages; industrial designs to conform with such proposals, however, are not applicable to conventional furnace designs, or raise extremely tricky technological problems in connection with the resistance to fire of the refractory materials employed. Moreover, the artifice of effecting combustion in two stages in the same heating chamber means certain pollution of the reducing atmosphere.

Another proposal calls for recourse to reversal processes for obtaining an adequate preheating of the air, so as to be able to attain high temperatures with reducing combustions. This heating method, however, has all the inherent drawbacks of the reversal system, namely inconsistency of the required atmosphere due to leaks of gas and air into the smoke during the reversals.

This invention has for its object to provide an industrial furnace of conventional design, capable of providing continuous oxidation-frce metal heating up to temperatures of 1250 to 1300 C., for example.

To this end, and in accordance with the present invention, the metal is heated to a high temperature by means of a direct flame resulting from the incomplete combus- 39 i 9 1 Patented July 27, 1965 tion of a gaseous fuel with combustive air, both the gas and the air being heated continuously in a recovery system utilizing the sensible heat of the neutral or oxidizing smoke issuing from. the furnace.

The zone providing heating in a constant reducing atmosphere basically comprises solid masonry-work made of the usual refractory materials and devoid of openings and absolutely lealrproot, evacuation of the combustible smoke resulting from the primary reducing combustion taking place transversely at one extremity of said zone, as in an ordinary furnace, instead of through apertures provided in the uprights, the hearth or the arch.

The primary combustion system is incorporated in the uprights and consists of burners designed to give rapid and energetic combustion of the hot air and gas supplied to them under pressure after being preheated in recuperators that are entirely external to the furnace, i.e. separate therefrom. It is to be noted that the device for heating this zone does not provide for contributory heat, through the uprights, the hearth and the arch, derived from a secondary combustion of the combustible products stemming from the primary combustion.

The distribution of hot air and gas to said furnace through a known arrangement of lagged piping of customary design, in conjunction with the burner design, enables high temperatures to be obtained which ensure rapid combustion and dissociation reactions and which produce a constant reducing atmosphere immediately upon exit from the burners and throughout the gaseous mass occupying the volume of the oxidation-free heating zone.

The sensible heat contributed by the fuel and the oxidant during the mixing at the burner nozzles compensates for the calorific loss due to the endothermic reaction which the dissociation of hydrocarbons, so that the desired physico-chemical balance is finally achieved without any fear of an oxidoreducing mixture.

On issuing from the oxidation-free heating zone, the combustible smoke is conveyed by natural draught to a metal-preheating zone which communicates with the oxidation-free heating zone.

Within said preheating zone, a portion of the combustible products originating from the oxidation-free heating zone is caused to sustain a secondary afterburning process, in order to heat the products disposed upon the furnace hearth. The secondary afterburner is so designed that air atmosphere which is still reducing be maintained in said preheating zone, to ensure that the products to be heated are in no case exposed to an oxidizing atmosphere right from the point where they are charged into the furnace up to their point of entry into the oxidation-free heating zone.

The smoke issuing from the heating zone still contains combustible constituents and is directed, by a natural draught process, into a flue incorporating a system for providing tertiary afterburning of the smoke still containing combustible constituents, as the result of which completely burnt-out combustion products can be discharged into suitable recuperators and thence out through the chimney.

Said tertiary afterburner provides the possibility of diluting the completely burnt-out smoke by injecting additional air, in order to avoid circulating unduly hot smoke through the fiue.

With a view to ensuring perfectly uniform secondary and tertiary afterburning (for instance when a secondary afterburning is used in order to avoid the products to be heated becoming oxidized because of imperfect mixing), it will be of advantage for the total secondary and tertiary combustive air to be preheated to a lower temperature than that of the primary combustible air.

Further particularities and advantages of the present "ice J) invention will become apparent from the description which follows of a specific embodiment of the invention, given with reference to the accompanying drawing, which is filed by way of example and not of limitation.

In the drawing filed herewith:

FIGURE 1 is a sectional view, taken through a plane parallel to the hearth, of a furnace executed in accordance with the invention;

FIGURE 2 is a sectional view of the same furnace, taken through the lines II-II of FIGURE 1;

FIGURES 3 and 4 are further sectional views of said furnace, taken through the lines III- 1H and IV-1V, respectively, in FIGURE 1;

FIGURE 5 is a vertical sectional view of a tertiary afterburning device;

FIGURE 6 is a longitudinal sectional view, on a larger scale, of a primary-combustion reducing burner; and

FIGURE 7 is a diagram showing the manner of regulation of the furnace in FIGURE 1.

Referring now to the accompanying drawing, the furnace described with reference thereto is a rotary hearth furnace of conventional design capable of ensuring, in continuous production, the oxidation-free heating of billets, ingots or other steel workpieces, up to temperatures of around l250 to 1300" C., for example.

Reference is now had to FIGURE 1 in particular, wherein it will be seen that the rotary hearth furnace illustrated comprises six zones A to F bounded by six radial barriers 1 to 6. The number of Zones is by no means critical and has here been given by way of example only and not of limitation.

The products are introduced into zone A through a charging door 7, are drawn along by the rotary hearth 9 in the direction of the arrow G and are evacuated from zone F through the discharging door 8.

The furnace is of the counter-streaming type, is. the smoke travels in the direction opposite to the direction of rotation of the products.

That part of the furnace in which the heavily reducing atmosphere is obtained by incomplete primary combustion and in which the metal is heated over the range which is dangerous from the oxidation standpoint, comprises four zones, of which only three are equipped with burners producing the reducing combustion. Starting from the discharging door 8, said four zones are the following:

One equalization zone F, comprised between barriers '6 and 5 and reducto-combustion-he-ated by burners If) such as those described hereinbefore with reference to FIG- URE 6.

Two heating zones E and D, respectively included between barriers 5 and 4 and 3, and likewise reducto-corn bustion-heated by burners 10, such as the burner shown in FIGURE 6.

One heating zone'C devoid of burners, comprised between barriers 3 and 2 and in wh ch the reducing combustion products from the preceding zones lose part of their sensible heat, thereby heating the metal while at the same time protecting it against oxidation.

Said four zones have the smallest possible transverse dimensions, as is clearly shown in FIGURE 2, the object of this being to obtain a very high calorific density per unit volume of internal zone-space.

Such a disposition makes it possible to achieve high temperatures and hightly efficient heat transfers due to the proximity of the products to be heated to the flames issuing from burners which have been specifically designed to give very bright flames.

Near the end of zone C (with reference to the direction of smoke circulation), part of the primary combustion products is sucked through orifices 11:: provided in the furnace uprights on a level with the hearth 9 and is led through fiues 11b to the first secondary afterburning burners 12 in preheating zone B, while the remaining part of the primary combustion products passes beneath barrier 2 and above the products being treated (see FIGURE 3).

of the masonry forming the uprights 11.

Thus the blanket of protective atmosphere which passes beneath barrier 2 provides protection for the metal products over the temperature range corresponding to incipient oxidation, while at the same time supplying heat to the metal.

Another part of the primary combustion products is drawn through orifices 13 provided in the uprights 11 level with hearth 9, and is led through flues 14 to other secondary afterburning burners 12 (see FIG. 4).

The rising motion of this part of the primary combustion products through the flues 14 is created by the induction of hot secondary combustion air delivered under pressure to the burners 12 through pipes 15 and tubes 16. Thus preheating zone B is used to burn the quantities of primary combustion product required to heat the metal to the temperature of entry into the oxidation-free heating zone C and compensate for the calorific losses.

The products resulting from this secondary afterburning are evacuated from the furnace through vertical lines I and led into the combustion chambers 18, in which tertiary afterburning is then effected with hot air (see FIGURE 5). This latter afterburning is performed with hot air delivered under pressure into rings 19 and introduced into chamber 18 via inclined passageways 19a.

Since this tertiary afterburning process can result in a large quantity of heat being given off in certain cases thereby leading to high smoke temperatures in the fines 17a connected to the main fine 41 provision is made for cold diluting air delivered through pipes 20 and tubes 21. Subsequent to the tertiary afterburning and to dilution of the smoke, the latter is conveyed into the chimney 45 through the flue 41, which flue incorporates recuperators such as those designated by reference numerals 4t 43 and 44.

The zones having a heavily reducing atmosphere, i.e. the equalization and heating zones F, E and D comprised between barriers 6 and 3, are preferably equipped with burners such as the burner illustrated in FIGURE 6.

Such a burner is supplied with hot air and gas at the temperatures required to ensure reductive combustion devoid of oxygen and lampblack, together with a high ambient temperature.

The hot gas is delivered under pressure through a lagged pipe 22 leading from recuperator 40. The pipe 22 is connected to a gas tube 23 by means of a flange 24. The flange 24 is welded to tube 23 and is rendered co-extensive with a certain length thereof by means of threaded sleeve 25. Sealing is provided by means of a stuffing-box 26 which is screwed to sleeve 25 and which clamps a packing seal against a socket 25a into which the sleeve 25 rigid with gas tube 23 is screwed.

The gas tube is free to rotate, advance or withdraw to permit adjustment and can be restrained in the desired position by a locknut 27. T o the extremity of the tube is welded a refractory nozzle 28, and the gas issues therefrom through holes 29 spaced regularly around the outer surface of the nozzle. In the specific embodiment illustrated, the nozzle 23 is provided with a convergent duct, followed by a cylindrical duct which is joined to the holes 2? through a divergent duct. The axes of the holes 29 are splayed about the longitudinal axis of tube 23 and the diameter of the holes 29 is chosen so that the gas velocity is very high.

The hot air from recuperator 43 is also delivered under pressure through a pipe 30, which pipe is connected to a T-tube 31 one of the branches of which surrounds tube 23 and is rigid with socket 25a. Sealing with respect to the furnace is achieved by means of a flange 32 which is rigid with tube 31 and with joints 33 affixed to the furnace enclosure 34. Lagging 32a surrounds all the piping outside the furnace.

Tube 31 debouches into a special part made of refractory concrete and comprised within the furnace masonrywork. The part 35 extends through the entire thickness Over nozzle 28 is fitted a moulded part 36 made of highly refractory material ports 37 which are so disposed that their axes be at right angles to those of the gas holes 29. Air under pressure delivered through tube 31 into the space comprised between parts 35 and 36 debouches at high velocity through ports 37 and impinges at right angles upon the gas fillets issuing from holes 29. The conical section 37a is extended by a conical part 33 which preferably embodies spiral grooves or spiral ribs.

An energetic combustion is thus initiated in the cone 37a of part 35, and this combustion takes place with a high degree of turbulence, extends through part 38 (the grooves or ribs of which further accentuate the turbulence), and terminates perpendicularly in line with the upright. This rapid and energetic combustion allows for dissociation reactions of short duration, thereby leading to physico-chemical equilibrium of exit from the burners, without any trace of oxygen and devoid of lampblack.

The cracking which the hydrocarbons undergo is endothermic, and the preheating of the gas compensates for the calorific losses due to the dissociation reactions of the fuel. Thus, by virtue of the turbulence, the heating of the gas, the heating of the air, the disposition of the air and gas orifices, and the high discharge velocities of the air and the gas, a very energetic combustion is ensured, which results in very high pyrometric efliciency. The eminently luminous flame obtained with this device is an excellent heat transmission factor.

Since all the combustion and dissociation reactions are completed in proximity to the burner, by reason of the high temperature and the turbulence, they ensure stable atmospheres within the furnace.

The method whereby hot gas and hot air are supplied to the furnace is illustrated diagrammatically in FIG- URE 7.

The oxidation-free heating zones D, E, F being the only ones to be supplied with gas, the gas distribution circuit comprises only one pipe leading to the furnace, which pipe terminates in the various branches supplying the burners.

The hot air distribution system may be divided into three circuits:

The first for supplying burners in oxidation free heating zones D, E and F.

The second for supplying burners 12 in the secondary afterburning zone B.

The third for supplying the burners in tertiary afterburning chamber 18.

Regulation of these supply circuits is so accomplished that with the gas as the pilot fluid and a regulating flowrneter measuring the same, a second flowmeter measures and regulates the total combustion air supplied to the furnace. The air flow regulator is slaved to the gas flow regulator through the medium of a ratio adjuster which enables the air to be metered in terms of the gas fiow and a complete neutral combustion to be invariably ensured after the tertiary afterburning process.

In addition, the proportionality existing between the gas and the air at each individual burner of each set of burners in the omdation-free heating zones is ensured by a ratio adjuster, which makes it possible to obtain reducing atmospheres of constant composition regardless of the flow rates.

The cold gas arriving from a distribution station through a duct 39 is heated in recuperator 4%, which is located in the smoke flue 41 extending between the furnace and chimney 45.

The total combustion air is supplied by a single blower 4-2; it is heated in the two recuperators 43 and 44, recuperator 43 serving for the primary combustion air and recuperator 44 for the secondary and tertiary afterburning air. The recuperators 53 and 44 are positioned upstream of gas-heating recuperator 4%}, the word upstream being 6 used with reference to the direction of evacuation of the smoke towards the chimney.

Inserted into the cold gas circuit is a diaphragm 46 connected to a regulating fiowmeter 47. Similarly inserted into the cold air circuit is a diaphragm 48 and a regulating flowmeter 49. The gas and air flowmeters 47 and 49 are interconnected by a ratio adjuster 50 which maintains the air-to-gas ratio constant at the figure corresponding to neutral or slightly oxidizing combustion, this being achieved by means of a power valve 51 which regulates the cold air flow. This provides a certainty of completely burnt smoke subsequent to the tertiary afterburning process.

The equalization zone F and the heating zones E and D are supplied with hot air through the pipes 30 (drawn in solid lines) connected to the pipes 53, which pipes are in turn connected to a pipe 53a leading from recuperator 43. They are supplied with hot gas through pipes 22 (shown in broken lines on the drawing) connected to pipes 52, which pipes 52 are in turn connected to a main duct 52a leading from recuperator 46 The gas flows are adjusted by power valves 54 and the air flows by similar valves 55. The gas valves 54- are controlled by regulating fiowmeters 56 and the air valves 55 by regulating flowmeters 57. The gas and air flowmeters 56 and 57 are interconnected by ratio adjusters 58 which maintain the air-to-gas ratios constant in the zones having highly reducing atmospheres, and this is achieved independently in each zone. The gas and air flowmeters 56 and 57 are connected to a temperature regulator 59 which is in turn connected to a temperature detector 60. When the temperature increases in the equalization zone for instance, regulator 59 of zone F reduces the gas and air flows by means of regulating flowmeters 56 and 57 and power valves 54 and 55, and 'at the same time maintains an invariable atmosphere in that zone by means of the associated ratio adjuster 58.

In preheating zone B, a temperature detector 61 is connected to a regulator 62 which controls a power valve 63. The power valve 63 regulates the flow of hot air through the duct 63a which extends between recuperator 44 and the pipes 15 of burners 12. If the temperature increases in the preheating zone for example, valve 23 closes and, since the air how is the same in recuperator 44, the air which no longer supplies preheating zone B feeds the tertiary combustion process through the duct 63b which leads up to rings 19 of combustion chambers 18. The flow of secondary air is regulated by a flowmeter 64 and the flow of tertiary air by a flowmeter 65.

The dilution air which cools the smoke subsequent to the tertiary combustion and which is introduced into flues 17:; through pipes 25 and tubes 21 is supplied by an independent blower 66. A temperature detector 67 is connected to a temperature regulator 68 which controls a fiowmeter 69, which fiowmeter in turn controls a power valve for regulating the flow of dilution air. Temperature detector 57 can .be positioned within the smoke, ahead of the first recuperator 44, or alternatively within the primary air exiting from its recuperator.

It will of course be understood that, without depart ing from the scope of the invention, many modifications and substitutions of parts may be made to the specific embodiment hereinbefore. described with reference to the accompanying drawings.

What we claim is:

1. A continuously operating furnace installation for heating metallic work on a hearth to high temperatures Without oxidation of the Work, comprising:

a hearth;

a first heating zone having an outlet opening for the discharge of work, and burner means directed toward the work;

means providing said burner means with preheated rich gaseous fuel and preheated primary air in such ratio as to produce incomplete com- 7 bustion products establishing a reducing atmosphere in the first heating zone;

at least one other heating zone separated from the first heating zone by barrier means located at such a distance above the hearth as to allow the passage of Work and of part of said incomplete combustion products, said other heating zone being provided with inlet means for the admission of Work,

afterburner means in the atmosphere thereof; means for feeding some of said incomplete combustion products to said afterburner means;

means for providing said afterburner means with preheated secondary air in such ratio with the incomplete combustion products supplied thereto as to produce partial afterburning of said incomplete combustion products, giving thereby reducing smoke in said other heating zone;

flue means leading from the other zone providing a draught of the incomplete combustion products from the first-named heating zone through the other heating zone and out of said other heating zone,

the first zone and said other heating zone thereby providing counter-current heating of the work Without oxidation thereof; and outside the furnace proper a tertiary afterburning chamber connected to said flue means and provided with teritary afterburner means;

means for providing said tertiary afterburner means with teritary preheated air in such a ratio as to cause a complete combustion of said reducing smoke into burnt smoke;

conduit means connecting said tertiary afterburning chamber to a chimney;

means for delivering cold diluting air into said conduit means;

a gas recuperator mounted on said conduit means in heat-exchange relationship with' said burnt smoke for preheating said gaseous fuel;

and at least one air recuperator arranged on said conduit means in heat-exchange relationship with said burnt smoke for preheating said primary combustion air and said secondary and teritary afterburning air.

2. The combination claimed in claim 1, the means for providing said burner means with preheated rich gaseous fuel and preheated primary air comprising pipe means for conducting said preheated air and preheated rich gaseous fuel to said burner means, said burner means having a mixing chamber opening into the interior of the first-named zone, and mixing means for discharging said preheated air and said preheated rich gaseous fuel separately into said mixing chamber.

3. A furnace according to claim 2 wherein said pipe means comprise fuel tubes and air passages, and said mixing means comprise ports connecting said air passages and said mixing chamber and holes connecting said fuel tubes and said mixing chamber, said holes inclined with respect to the axis of said fuel tubes, said ports being directed in a direction substantially perpendicular to the axes of said fuel tubes whereby said preheated air issues from said ports into said mixing chamber in a direction substantially perpendicular to said preheated fuel issuing from said holes.

4. A continuously operating counter-streaming furnace for heating metallic work to high temperatures without oxidation, comprising an equalization zone provided with burner means,

at least one primary combustion zone separated from said equalization zone by a barrier and provided with primary burner means,

at least one heating zone devoid of burners, separated from said primary zone by a barrier and receiving the combustion products therefrom,

at least one preheating zone separated from said heating zone by a barrier and provided with secondary burner means providing a flame in the atmosphere of said preheating zone,

duct means for feeding said secondary burner means with a portion of said combustion products from said primary zone,

at least one teritary combustion chamber provided with tertiary burner means,

fiues connecting said preheating zone to said tertiary combustion chamber,

feeding means to introduce combustion products from said preheating zone into said chamber,

a first recovery system fed with the smoke from said tertiary combustion chamber,

means to feed said first recovery system with primary combustion air and with gaseous fuel in heat-exchange relationship with said smoke in said system thereby to preheat said air and fuel,

pipe means for leading separately said preheated air and fuel to said primary burner means,

means for proportioning the ratio of air to fuel to said primary burner means in such ratio as to provide incomplete burning of the fuel,

mixing means to provide intimate mixture of said preheated air and fuel immediately beyond said primary burner means thereby to produce an incomplete, rapid and energetic primary combustion devoid of oxidation in said primary combustion zone,

a second recovery systemv in series with said first recovery system,

means for feeding said second recovery system with secondary and tertiary combustion air in heat-exchange relationship with said smoke in said second recovery system, and

leans for leading said preheated secondary and tertiary preheated air to said secondary and tertiary burner means respectively.

5. A continuously operating furnace installation for heating metallic work on a hearth to high temperatures without oxidation, said furnace installation having a work outlet and a work inlet and comprising:

a rotary hearth;

a first zone comprising first series of sub-zones starting with a first sub-zone having said work outlet; and another zone comprising a second series of sub-zones continuing from the last sub-zone of the first series and terminating in a last sub-zone having said work inlet;

all of said sub-zones, save for the last sub-zone of the second series and the next adjacent one being separated one from the other by barrier means located at such a distance above the hearth as to allow the passage there-beneath of work and incomplete combustion products;

said last sub-zone of said second series and said next adjacent sub-zone being separated from one another by a barrier located at such a distance above the hearth as to permit the passage therebeneath of work while substantially excluding the passage therebeneath of incomplete combustion products;

each of said sub-zones of said first series having therein burner means directed towards the work;

means providing the aforesaid burner means with preheated rich gaseous fuel and preheated primary air in such ratio as to produce incomplete combustion products establishing a reducing atmosphere in each of said first series of sub-zones;

afterburner means in the atmosphere of a certain one of the sub-zones of said second series other than said last one;

means for supplying to said afterburner means incomplete combustion products from a certain other sub-zone which is disposed on the side of said certain one of the sub-zones which is remote from said last sub-zone of said second series;

means for providing said afterburner means with preheated secondary air in such ratio with the incomplete combustion products supplied thereto as to produce partial afterburning of said incomplete combustion products, giving thereby reducing smoke in the sub-zone containing the afterburner means; and flue means leading from the sub-zone containing the afterburner means, said flue means providing a draught of the incomplete combustion products from the first sub-zone of the first series through the other sub-zones save for the last one of the second series, thereby providing counter-current heating of the work in a reducing atmosphere; there being a sub-zone of said second series which is disposed between the last sub-zone of the first series and said certain one sub-zone of the second series which is devoid of burner means and atterburner means. 6. A furnace according to claim 5, said atterburner means being disposed above the hearth level, the means 10 for feeding some of said incomplete combustion products to said afterbumer means comprising conduit means leading to said afterburner means from adjacent hearth level from the sub-zone which is devoid of burner means and afterburner means.

References Cited by the Examiner UNITED STATES PATENTS 2,233,474 6/38 Drefiein 263-15 2,639,910 11/49 Cone et al. 2665 2,622,863 5/50 Dauch 263-28 2,799,491 12/54 Rusciano 263-15 2,845,260 7/58 Rusciano 266-5 3,022,057 10/59 Schmidt et al. 26315 3,106,192 10/63 Hingst 1227 FOREIGN PATENTS 680,057 -8/ 39 Germany.

CHARLES SUKALO, Primary Examiner.

Claims (1)

1. A CONTINUOUSLY OPERATING FURNACE INSTALLATION FFOR HEATING METALLIC WORK ON A HEARTH TO HIGH TEMMPERATURES WITHOUT OXIDATION OF THE WORK, COMPRISING: A HEARTH; A FIRST HEATING ZONE HAVING AN OUTLET OPENING FOR THE DISCHARGE OF WORK, ANND BURNER MEANS DIRECTED TOWARD THE WORK; MEANS PROVIDING SAID BURNER MEANS WITH PREHEATED RICH GASEOUS FUEL AND PREHEATED PRIMARY AIR IN SUCH RATIO AS TO PRODUCE INCOMPLETE COMBUSTION PRODUCTS ESTABLISHING A REDUCING ATMOSPHERE IN THE FIRST HEATING ZONE; AT LEAST ONE OTHER HEATING ZONE SEPARATED FROM THE FIRST HEATING ZONE BY BARRIER MEANS LOCATED AT SUCH A DISTANCE ABOVE THE HEARTH AS TO ALLOW THE PASSAGE OF WORK AND OF PART OF SAID INCOMPLETE COMBUSTION PRODUCTS, SAID OTHER HEATING ZONE BEING PROVIDED WITH INLET MEANS FOR THE ADMISSION OF WORK, AFTERBURNER MEANS IN THE ATMOSPHERE THEREOF; MEANS FOR FEEDING SOME OF SAID INCOMPLETE COMBUSTION PRODUCTS TO SAID AFTERBURNER MEANS; MEANS FOR PROVIDING SAID AFTERBURNER MEANS; MEANS FOR PROVIDING SAID AFTERBURNER MEANS WITHH PREHEATED SECONDARY AIR IN SUCH RATIO WITH THE INCOMPLETE COMBUSION PRODUCTS SUPPLIED THERETO AS TO PRODUCE PARTIAL AFTERBURNING OF SAID INCOMPLETE COMBUSTION PRODUCTS, GIVING THEREBY REDUCING SMOKE IN SAID OTHER HEATING ZONE; FLUE MEANS LEADING FROM THE OTHER ZONE PROVIDING A DRAUGHT OF THE INCOMPLETE COMBUSTION PRODUCTS FROM THE FIRST-NAMED HEATING ZONE THROUGH THE OTHER HEATING ZONE AND OUT OF SAID OTHER HEATING ZONE, THE FIRST ZONE AND SAID OTHER HEATING ZONE THEREBY PROVIDING COUNTER-CURRENT HEATING OF THE WORK WITHOUT OXIDATIONN THEREOFF; AND OUTSIDE THE FURNACE PROPER A TERTIARY AFTERBURNING CHAMBER CONNECTED TO SAID FLUE MEANS AND PROVIDED WITH TERITARY AFTERBURNER MEANS; MEANS FOR PROVIDING SAID TERTTIARY AFTERBURNER MEANNS WITH TERITARY PREHEATED AIR IN SUCH A RATIO AS TO CAUSE A COMPLETE COMBUSTION OF SAID REDUCING SMOKE INTO BURNT SMOKE; CONDUIT MEANS CONNECTING SAID TERTIARY AFTERBURNING CHAMBER TO A CHIMNEY; MEANS FOR DELIVERING COLD DILUTING AIR INTO SAID CONDUIT MEANS; A GAS RECUPERATOR MOUNTED ON SAID CONDUIT MEANS IN HEAT-EXCHANGE RELATIONSHIP WITH SAID BURNT SMOKE FOR PREHEATING SAID GASEOUS FUEL; AND AT LEAST ONE AIR RECUPERATOR ARRANGED ON SAID CONDUIT MEANS IN HEAT-EXCHANGE RELATIONSHIP WITH SAID BURNT SMOKE FOR PREHEATING SAID PRIMARY COMBUSTION AIR AND SAID SECONDARY AND TERITARY AFTERBURNING AIR.

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