US3237929A - Process and apparatus for heating molten materials by injection of flames into the bath - Google Patents

Description

March 1, 1966 E. PLUMAT ETAL 3,237,929

PROCESS AND APPARATUS FOR HEATING MOLTEN MATERIALS BY INJECTION 0F FLAMES INTO THE BATH Filed Dec. 5, 1961 M1 1o v ZqL/l. 181 514 United States Patent 3,237,929 PRCESS AND APPARATUS FOR HEATING ML'IEN MATERIALS BY INlEtCTlUN 0F FLAMES INTO THE BATH Emile Plumat, Gilly, Pierre Eloy, Lodelinsart, and Alfred `lacobs, Montigny-sur-Sambre, Belgium, assignors to S. A. Glaverbel, Brussels, Belgium, a company of Belgium Filed Dec. 5, 1961, Ser. No. 157,063 Claims priority, application Belgium, Dec. 9, 1960, 475,592, Patent 598,022 1t) Claims. (Cl. 2056-33) The present invention relates to a process and an apparatus for heating molten material by injecting flames or hot combustion gases into the bath of molten products contained in the furnace.

In a large number of furnaces for melting materials, the flames are in direct Contact with the materials to be melted. These furnaces are, for example, those commonly called reverberatory furnaces. Regardless of the constructional forms of these furnaces, or the type of materials contained therein, the mode of transmission of the heat of the flames and fumes to the bath of molten materials in such furnaces is not essentially different from one another. In such furnaces, the flames are produced by burners on the surface of the bath contained in the furnace. Consequently, the transfer of heat takes place exclusively on the surface of separation between the liquid and gas phases. This mode of transmission is not satisfactory because the hottest products are on the surface and therefore in contact with the flames, while the convection currents in the bath are impeded.

Any reactions between the fumes and the molten products are inhibited for similar reasons. The surface layer of the bath becomes enriched in reaction products, which tends to block the desired reactions.

lt has already been proposed to inject the combustible mixture into the bath of molten products, but in doing this many difliculties are encountered. The mixture of fuel and combustion-assisting agent burns badly in the bath. As soon as it is introduced into the bath, the mixture becomes broken up into a large number of bubbles within which the combustion takes place. These bubbles rise to the surface more rapidly as the bath is denser and more fluid, so that in general the time during which the bubbles remain in the bath is short. In practice, the combustion is not complete in the bath and is completed on the surface of the bath, which is disadvantageous, as has been shown above. Since the mixing is not effected in an exact proportion of fuel and combustion-assisting agent in each bubble, there is an excess of one reactant or the other in each bubble.

The effect of this excess is that, on the one hand, some of the reactants do not react in the bath, and on the other hand, the speed of reaction of the fuel and the combustion-assisting agent is reduced.

In the process according to the invention all these disadvantages are obviated.

In accordance with the invention, the combustible mixture is completely gasied and intimately mixed in a chamber, and a con-siderable proportion of the combustible mixture is burnt before being injected into the bath of molten materials.

The constituents of the mixture may be gasified by various methods. The gasification may consist either in a vaporisation of the non-gaseous constituent or constituents of the mixture, or in a reaction of one or more of the constituents ysupplying gaseous reaction products, or in a combination of the aforesaid methods. The reactions giving rise to a conversion of the constitutents into gas are of at least two types. For example, the

3,237,929 Patented Mar. 1, 1966 fuel is dissociated into lighter fractions which are gaseous, or a combustion is effected giving gases as combustion products.

Although a partial combustion in the mixing chamber is suicient to produce a turbulence contributing to the mixing of the gases, the intimate mixing of the fuel, of the combustion-assisting agent and of the combustion products is effected by intentionally imparting whirling movements thereto, either by imparting to the jets of gas and/or of liquid, directions of movement which are chosen for this purpose, or giving the walls of the chamber curvatures which produce the same result.

In addition, the degree of combustion of the combustible mixture is adjusted before it is introduced into the bath of molten materials by modifying the time for which the constituents of the mixture are in contact before being injected into the bath.

In one embodiment of the process, the supply of constituents is divided into two partial flows which are in contact with the other constituent for unequal periods of time. The mean period of contact, and therefore the degree of combustion, is then adjusted by varying the ratio of the partial liows.

In accordance with the present invention, there are added to the mixture of fuel and combustion-assisting agent substances which are intended to be added to the molten materials. These substances are uniformly dispersed in the mixture like the constituents of the mixture themselves. The oxidising or reducing character of the gases flowing through the bath of molten materials is adjusted by varying the ratio of fuel to combustionassisting agent in the mixture. The introduction of substances by this means is especially advantageous because the substances are thus very uniformly dispersed in the bath owing to the turbulence of the latter and the renewal of the surfaces of contact between the gases and the bath. Likewise, by modifying the oxidising or reducing character of the gases, a very vigorous and rapid oxidising or reducing action exerted on the bath of molten materials.

The constituents of the combustible mixture are therefore intimately mixed and partially burnt before being introduced into the bath of materials to be heated. Preferably, the degree of combusion is so adjusted that the submerged combustion is completed before the gaseous mixture leaves the bath of molten materials. The highest temperature of the gases is therefore developed in the bath. The surface of Contact between the gases and the molten materials in the bath is therefore very extensive because the gases are occluded in numerous bubbles. The transfer of heat takes place rapidly owing to the high temperature of the gases and the considerable surface of contact. In addition, the gases leaving the bath are already at a substantially reduced temperature, so that they heat to a less extent the walls and the roof of the furnace. In the process according to the invention, the heat losses and the wear on the refractory materials of the furnace are reduced.

In accordance with the process, there are introduced into the mixing chamber additives intended to prevent the formation of carbon deposits or to remove these deposits, which generally form with liquid fuels, more especially with heavy fuels, such as fuel oil. These additives may consist of steam or of combustible materials rich in hydrogen, which form by combustion an appreciable quantity of steam, such as methane, town gas, propane or butane. At the temperature obtaining in the mixing chamber, the steam is partially dissociated and oxidises the carbon liberated by the partial combustion of the combustible mixture. Since this carbon is preferably evolved in a particular region of the chamber, it is advantageous to arrange the conduit carrying the additives so that it opens into this region.

A burner according to the invention comprises essentially a precombustion chamber provided with conduits for the supply of fuel and combustiomassisting agent, and also an outlet orice for the mixture of fuel, combustionassisting agent and combustion products.

In some constructions, the precombustion chamber consists of a tube of refractory material and two cheeks or walls fitted on to the said tube. In other constructions, the chamber is a closed receptacle of refractory material. The walls of the chamber are formed with orifices for Athe introduction of fuel and combustionassisting agent into the chamber and for discharge of the mixture. In one embodiment, the outlet orifice for the mixture formed in the precombustion chamber is extended by a nozzle integrally formed with the burner, the said nozzle serving to introduce the mixture into the bath of molten materials and extending through the wall of the furnace. In a preferred embodiment, the precombustion chamber is surrounded by a cooling jacket in which a uid, for example water, is c-irculated. The burner preferably comprises a layer of refractory materials between the precombustion chamber and the cooling jacket. The degree of cooling of the chamber is adjusted by choosing as the refractory material a material of higher or lower thermal conductivity.

A precombustion chamber according to the invention is advantageously designed to increase further the turbulence of the gas currents circulating therein. This design consists in well-chosen curvatures applied to the walls of the chamber. Preferably, the various parts of the chamber have walls of different curvatures. In a preferred embodiment, the conduits carrying fuels and combustion-assisting agent lead into parts of the chamber which have different curvatures.

For example, the fuel conduit and a conduit carrying combustion-assisting agent lead into a part of the chamber which is of smaller curvature, while another conduit supplying the combustionassisting agent leads into a part of greater curvature, preferably on the axis of the conduit or of an outlet conduit for the mixture formed in the chamber.

In a precombustion chamber according to the invention, the conduits for the fuel and the combustion-assisting agent are so oriented as to induce whirling movements. The direction of the conduits is chosen more especially as a function of the curvatures of the walls of the chamber. In addition, the distance between the mouths of these conduits and the outlet conduit for the mixture is variable by displacement of the conduits within the precombustion chamber. By this means, the duration of contact of the constituents of the mixture within the chamber, and therefore also the degree of combustion, is varied.

The degree of combustion is also varied by choosing the dimensions of the chamber in accordance with the type of fuel employed and more especially of the rate of fuel flow. In addition, the degree of combustion is adjusted by varying the point of introduction of the fuel into the chamber.

In some constructions, the burners according to the invention are combined with a supply conduit for substances intended to be introduced into the bath of molten materials. These substances are advantageously introduced into the chamber close to the point of introduction of the constituents of the combustible mixture. Thus, the uniform-ity of their dispersion in this mixture is generally improved. It is obvious that it is also possible to introduce them at any other point of the chamber, for example close to or in the nozzle for the ejection of the gases from the chamber.

The burners may also be provided with a conduit for the injection of steam or materials rich in hydrogen which form on combustion steam which is intended to prevent the formation of carbon by the partial combustion of the combustible mixture. This conduit advantageously leads Cil into that region of the mixing chamber in which the carbon tends to be deposited.

The accompanying drawings illustrate by way of example a number of constructional forms of burners according to the invention.

FIGURE 1 illustrates one type of burner consisting of a tube,

FIGURE 2 illustrates a type of burner of integral form,

FIGURE 3 illustrates a burner whose chamber has been specially shaped with a View to producing whirling currents in the mixture, and

FIGURE 4 is a section along the line IV-IV of FIG- URE 3.

In FIGURE l, the burner, which -is denoted as a whole by 1, is shown in combination with a furnace, of which a fragmentary section is shown. The burner comprises a chamber 2 bounded by a wall 3 of refractory material and cheeks or side walls 4 and 5 also consisting of refractory material. The wall 3 consists, for example, of a tube which is advantageously of circular section. A conduit 6 supplies the combustion-assisting agent, which is normally air, and if desired, preheated. A conduit 7 serves for the injection of the fuel into the chamber 2. Preferably, the fuel employed is a fluid, either a liquid or a gas. If a liquid fuel is employed, it is advantageously atomised when injected into the chamber 2. An atomiser 8 is then secured on the fuel supply conduit 7. Preferably, the air supply conduit 6 is concentric with the fuel supply conduit 7. The conduits extend into `the chamber 2 by way of an orifice 9 in the cheek or outer wall 4 of the burner 1. The cheek or inner wall 5 positioned against the wall 10 of the furnace Iis formed with an orifice 11 through which the mixture formed in the chamber 2 is discharged. The wall 10 is in turn formed with an orifice 12 through which the mixture is injected into the bath 13 contained in the furnace.

The burner 1 is fixed to the wall of the furnace by a plate 14, for example of metal, which is connected to the wall 10 of the furnace. The said plate is formed with a hole aligned with the orifices 11 and 12, the said hole preferably being of larger diameter then the said orifices. On the other side of the burner, a plate 16 is positioned against the cheek 4 and formed with an oritice 17 for the passage of the conduits 6 and 7. The plates 14 and 16 are connected by tie rods 18 and bolts 19. By tightening the said bolts, the cheeks 4 and 5 are secured against the tube 3 and the burner 1 is made fast with the wall 1() of the furnace.

In an advantageous constructional form, the combustion chamber 2 is surrounded by a cooling jacket 20, preferably consisting of sheet metal, in which there flows a cooling fluid, for ex-ample water, the conduit-s for which are shown at 21. Banked between the wall 3 of 4the precombustion chamber and the cooling jacket 20 is a bed or layer 22 of a refractory material chosen from materials of higher or lower thermal conductivity, for example powdered magnesia or fibers of a very refractory glass. In this way, the behaviour of the refractory walls 3 of the chamber is improved by reduction of their operating temperature, which is readily adjusted by variation of the thickness and the nature of the material of the bed or layer 22.

In some cases, the burner also comprises a conduit 23 for the supply of substances intended to be added to the bath of molten materials. The conduit 23 leads either into the combustion chamber 2 or into one of the conduits for the constituents of the mixture, for example the combustion air conduit, as illustrated in FIGURE 1. These substances are, for example, oxidising agents or reducing agents employed in the metallurgical industry, or colouring agents employed in the glass industry.

The conduit 23 also serves for introducing into the chamber 2 steam or combustible materials rich in hydrogen which produce steam by combustion, unless there is provided for this purpose a special conduit, which then preferably leads into that region of the chamber in which the carbon evolved by the combustion of the combustible mixture tends to be deposited. At the high temperature obtaining in the chamber 2, the steam readily oxidises this carbon and thus prevents the formation of carbon deposits.

The burner operates as follows: the fuel and the combusion air are introduced under pressure into the chamber 2 at 8 and 9 respectively. As soon as the fuel comes into contact with the combustion air, the combustion commences under the effect of the temperature obtaining in the chamber 2. At least a part of the fuel is burnt, and the evolution of heat vaporises the remainder of the fuel and may produce fractionation of the fuel into additional vaporised lighter bodies. In addition, the various gases present in the chamber are intimately mixed by the turbulence produced by the combustion. The mixture thus created is injected into the bath 13 of molten materials, in which it completes its combustion. The supply pressure is sufficient to compensate for the hydrostatic pressure of the bath at the level of the orifice 12. The degree of combustion in the chamber 2 is so adjusted that the combustion is absolutely complete at the instant when the products of combustion leave the bath 13, By adjusting the combustion in this way, the gases are brought to their maximum temperature in the bath 13 itself, that is to say, while they are in intimate contact with the bath of molten materials and while the surface of Contact between the gases and the bath is very large.

The degree of combustion in the chamber 2 is adjusted by the choice of the length and the volume of the chamber as a function of the rate of flow and the nature of the fuel employed. The latter adjustment of the degree of combustion is advantageously effected by modifying the penetration of the conduit 7 and therefore the position of the atomiser 8. In this Way, the period of contact between the constituents of the mixture in the combustion chamber is modified.

FIGURE 2 illustrates another type of burner suitable for the application of the process. It consists of a receptacle 24 consisting of refractory material which bounds the chamber 2. The Said receptacle is advantageously integrally moulded from a fused refractory material or a refractory concrete. Alternatively, it may be formed of a number of parts joined together by means of refractory cement. The receptacle 24 is extended by a nozzle 25 which injects the gases into the furnace. The said nozzle is introduced into the orifice 12 in the pillar or wall of the furnace. The receptacle 24 is advantageously surrounded by a cooling jacket and a refractory layer 22 as stated above. In FIGURE 2, the outer face 26 is not enclosed in the jacket 20, but it is obvious that the chamber 2 may be entirely surrounded by the said jacket.

The degree of combustion is adjusted by varying the position of the atomiser 8 in the chamber 2 as described above.

FIGURES 3 and 4 illustrate a burner consisting of a member 27 of refractory material in which the combustion chamber 2 is formed. The chamber is divided into two communicating zones 28 and 29, of which the zone 28 comprises walls having a smaller curvature and the zone 29 comprises walls having a greater curvature. In the lower part 28, the fuel and all or part of the combustion air are tangentially introduced at 31, the air preferably surrounding the jet of fuel. Owing to the tangential introduction, the mixture is whirled in the lower part 28. The fuel partially burns.

The secondary air, if any, is introduced into the combustion chamber 2 through a conduit 30 which is coaxial with the orifice 12 and leads into the second zone 29 of hemispherical form.

The mixing of the fuel, combustion-assisting agent and combustion gases is improved by creating currents in the 6 combustion chamber 2 by an appropriate arrangement of the conduits for the fuel and combustion-assisting agent and by giving the chamber a profile which promotes the movements of the gases and of the atomised liquids. The currents of gas and/or liquid are thus given a whirling movement in the chamber 2.

The secondary air blown through the conduit 30 into the zone 29 is injected with the mixture contained in the lower zone 28 into the bath through the orifice 12 in the pillar on wall 10 of the furnace. The degree of combustion in the chamber 2, and therefore the temperature of the chamber 2, is readily adjusted by varying the proportion of primary air and secondary air while maintaining the chosen ratio of air to fuel. The primary air reacts, at least to an appreciable extent, with the fuel in the combustion chamber 2, while the secondary air reacts mainly with the fuel in the bath 13, the time for which the secondary air stays in the chamber 2 being shorter.

Of course, the invention is not limited to the embodiments which have been described and illustrated by way of example, and modifications may be made thereto without departing from its scope.

We claim:

'1. The method of blowing heating gases through molten material in a furnace having a chamber for containing a bath of the molten material, comprising providing a bath of molten material in the furnace chamber, introducing separate supplies of fuel and a combustion assisting agent into the closed combustion chamber of an adjoining auxiliary furnace so as to produce Within such combustion chamber from such constituents an intimate mixture of partially burnt, completely gaseous, combustible material, and injecting such partially burnt gaseous mixture into the bath of molten material in the furnace chamber at a place located below the upper surface of said bath to enable complete combustion of such mixture within the bath as it rises towards the upper surface of the latter and before the gases escape through the upper surface of such bath, whereby the combustion within the bath imparts heat to said bath.

2. The method of blowing heating gases through molten material in a furnace having a chamber for containing a `bath of the molten material, comprising providing a bath of molten material in the furnace chamber, introducing separate supplies of fuel and a combustion assisting agent into the closed combustion chamber of an adjoining auxiliary furnace so as to produce within such combustion chamber from such constituents an intimate mixture of partially burnt, completely gaseous, combustible material, and injecting such partially burnt gaseous mixture into the bath of molten material in the furnace chamber at a place located below the upper surface of said bath to enable the combustion of such mixture to continue within the ybath during its rise towards the upper surface of the latter, whereby the combustion within the bath imparts heat to said bath.

3. The method defined in claim 2 in which at least one of said constituents upon its entry into the closed combustion chamber is caused to travel therein with such whirling movements as will cause the said constituents to become intimately intermixed.

4. The method defined in claim 2 in which the period of contact between the constituents in the combustion chamber is controlled to give the resulting gaseous combustible material produced therefrom a given preburnt condition before injection thereof into the bath of molten material.

S. The method defined in claim 4, in which the period of contact between the constituents is effected by dividing the flow of one of the constituents into a number of partial flows and bringing such partial flows of such one constituent into contact with the other constituent for different lengths of time.

6. The method defined in claim 2 including introducing into the closed combustion cham-ber with the constituents d an ingredient capable of inhibiting the formation of substantial carbon deposits upon the walls of such chamber.

7. Apparatus for heating molten materials, comprising a furnace having a chamber for containing a bath of molten material, an auxiliary furnace adjacent to one wall of said furnace chamber and having a closed combustion chamber, means for introducing into said combustion chamber separate supplies of fuel and a combustion assisting agent so as to produce within such chamber lfrom such constituents an intimate mixture of partially burnt, completely gaseous, combusti-ble material, means for in jecting the partially burnt gaseous mixture of combustible material produced in said combustion chamber into the bath of molten material in said furnace chamber at a place located below the upper surface of said bath to enable the combustion of such mixture to continue within the bath during its rise towards the upper surface of the latter to impart heat to the bath, theV means for supplying one of the constituents into said combustion chamber being selectively movable relative to the means for supplying the other of the constituents therein to control the preburnt condition of the gaseous combustible material discharged from such chamber into the bath of molten material.

8. Apparatus such as defined in claim 7, in which the means for supplying the constituents are constructed and arranged to introduce such constituents into the combustion chamber so that one of such constituents is discharged into the path of flow of the other constituent at a place spaced from the place of entry of such other constituent.

9. Apparatus such as defined in claim 7, in which the walls of said combustion chamber are configured to impart O 0 to at least one of such constituents a whirling movement such as will cause an intimate mixture of such constituents. 10. Apparatus such as defined in claim 7 in which said means for injecting the partially burnt gaseous mixture of combustible material into the bath of molten material extends through said one side wall of said furnace at a place in which the supply pressure of such combustible material is sufficient to compensate for the hydrostatic pressure of the bath at the level of the discharge orifice of such injecting means, and in which said constituent introducing means includes at least one constituent supply means capable of discharging such one constituent into said combustion chamber so that the entry liow thereof is substantially aligned with the axis of the discharge orice of such injecting means.

References Cited by the Examiner UNITED STATES PATENTS 1,656,723 1/1928 Call 266-41 2,333,654 11/1943 Lellep 266-35 2,526,472 10/1950 Gilliland 266-34 2,833,643 5/1958 Newman 266-29 2,878,644 3/1959 Fenn 126-360 X 2,906,616 9/1959 Alland et al. 75-52 3,034,887 5/1962 Henne 266-35 3,060,015 10/1962 Spolders et al 75-60 WHITMORE A. WILTZ, Primary Examiner.

RAY K. WINDHAM, Examiner.

F. R. LAWSON, J. C. HOLMAN, P. M. COHEN,

Assistant Examiners.

Claims (1)

1. THE METHOD OF BLOWING HEATING GASES THROUGH MOLTEN MATERIAL IN A FURNACE HAVING A CHAMBER FOR CONTAINING A BATH OF THE MOLTEN MATERIAL, COMPRISING PROVIDING A BATH OF MOLTEN MATERIAL IN THE FURNACE CHAMBER, INTRODUCING SEPARATE SUPPLIES OF FUEL AND A COMBUSTION ASSISTING AGENT INTO THE CLOSED COMBUSTION CHAMBER OF AN ADJOINING AUXILIARY FURNACE SO AS TO PRODUCE WITHIN SUCH COMBUSTION CHAMBER FROM SUCH CONSTITUENTS AND INTIMATE MIXTURE OF PARTIALLY BURNT, COMPLETELY GASEOUS, COMBUSTIBLE MATERIAL,

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