US3663203A

US3663203A - Melting of fusible materials

Info

Publication number: US3663203A
Application number: US812062A
Authority: US
Inventors: James A Davis; Sherwood G Talbert; Herbert R Hazard; William A Gibeaut
Original assignee: Columbia Gas Syst
Current assignee: Columbia Gas System Service Corp
Priority date: 1969-04-01
Filing date: 1969-04-01
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: GB1286529A; DE2014043A1

Abstract

The melting of fusible materials wherein the materials are fed into the top of a shaft-type furnace and melted by a jet of gaseous combustion products introduced at the bottom of the furnace. The charge feeds countercurrent to the flow of the combustion products and the melted fusible materials are continuously removed before a pool of molten material forms within the furnace shaft.

Description

United States Patent Davis et al.

15] 3,663,203 1 May 16, 1972 [54] MELTING OF F USIBLE MATERIALS [72] Inventors: James A. Davis, Worthington; Sherwood G. Talbert; Herbert R. Hazard, both of Columbus; William A. Gibeaut, Worthington, all of Ohio [73] Assignee: Columbia Gas System Service Corporation, New York, NY.

[22] Filed: Apr. 1, 1969 [21] Appl. No.: 812,062

[52] US. Cl ..75/43, 75/65, 266/25 [51] Int. Cl ..C2lc 5/00 [58] Field of Search ..75/43, 65; 117/205, 207; 266/25 [56] References Cited UNITED STATES PATENTS 1,476,106 12/1923 Rochlitz ..75/43 X 1,578,648 3/1926 Dyer 75/43 1,948,695 2/1934 Brassert ..75/43 3,118,760 l/1964 Avery et a1 ..117/207 X 3,234,010 2/1966 Mahony ..75/43 3,424,573 1/1969 De Villiers ....75/43 3,499,637 3/1970 Grachev et al .266/25 Primary Examiner-L. Dewayne Rutledge Assistant E.\'aminer.l. Davis Attorney-Pennie, Edmonds, Morton, Taylor and Adams [57] ABSTRACT The melting of fusible materials wherein the materials are fed into the top of a shaft-type furnace and melted by a jet of gaseous combustion products introduced at the bottom of the furnace. The charge feeds countercurrent to the flow of the combustion products and the melted fusible materials are continuously removed before a pool of molten material forms within the furnace shaft.

12 Claims, 7 Drawing Figures PATEMH-Inm I6 I972 SHEET 2 [1F 3 INVENTORS JAMES A. DAVIS,

SHERWOOD G.TALBERT BY WELIZIIBESTAR. HAZARD "225 GIBEAUg -dw ATTORNEYS FIG.3

PATENTEDMAHBIHIZ 3.663.203

SHEEI 3 [IF 3 INVENTORS JAMES A. DAVlS SHERWOOD G.TAl' BERT BY HERBAZIRT RII-IBIEZeRD WL u;

ATTORNEY MELTING OF FUSIBLE MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the art of melting fusible materials with hot gas wherein the charge of material to be melted is passed countercurrently to the flow of combustion products.

2. Description of the Prior Art Present methods of melting fusible materials, particularly scrap metals such as scrap iron and steel are slow, require complex equipment, and are not efficient. Previously, most melting of this type has been done in electrical furnaces, blast furnaces, or cupolas. Electrical furnaces are too costly for most melting purposes and blast furnaces and cupolas require the addition of coke with the charge when melting certain metals. When certain hydrocarbon fuels, especially natural gas, are added to a cupola or blast furnace containing coke, the coke generally prevents complete combustion of the fuel which results in heat losses. The high cost of coke and extra labor involved, along with high cost of the necessarily complex melting equipment, led to the development of furnaces which can generate the required heat using only liquid or gaseous fuels such as natural gas, naphtha, and fuel oil. However, since the previously used coke layers provided support for the charge within the shaft, the new installations required other means of support such as inert materials, baffles, or retention grates, all of which added expense to the operation.

Also known in the art are the countercurrent flow-type furnaces in which the hot combustion gases are passed upwardly over the charge which passes downward through the furnace shaft as the lower portion of the charge is melted. Countercurrent flow furnaces using only gaseous fuels have been developed, most of them being reverberatory-type furnaces in which a molten pool of charge material is maintained at the bottom of the shaft or in an adjacent crucible. The reverberatory type furnaces have low melting rates and they are inefficient, often having overall thermal efficiencies as low as percent.

A common recurring problem associated with the countercurrent flow metal melting where no coke is used, especially where a molten charge pool is maintained in the shaft, is bridging or hang-up of the charge within the furnace shaft. Bridging or hang-up occurs when pieces of the charge material in the shaft above the melting zone melt prematurely and become welded or fused to adjacent pieces of the charge. When a number of pieces become joined together in this manner, the entire charge may become clogged in the shaft disrupting its continuous downward flow. In previous melting processes, the coke layers had prevented this welding or fusing together of the charge materials. In the processes where no coke is used and the height of the charge increased to any extent, the greater weight causes the charge pieces in the lower portion of the shaft to be compressed together with greater force. This, in turn, increases the chances of bridging. As a consequence of this effect, the height of the charge used in cokeless countercurrent flow furnaces has been limited, usually to 6 feet or less. Also, as heat input rates are increased, the tendency for bridging to occur is correspondingly increased. As a result, the capacities and efficiencies of previous cokeless countercurrent flow furnaces have been significantly limited.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention, fusible materials charged into a furnace shaft are melted by introducing hot gaseous products of substantially complete combustion into the bottom of the furnace shaft in the form of a high velocity stream or jet. The temperature, composition and velocity of the jet are controlled and its cross-sectional dimensions selected to effect a rapid heating and melting of the charge in a localized zone at the bottom of the shaft. The conditions of the gas jet are thus controlled so that the hot gas jet is cooled sufficiently within this small melting zone that it III does not cause melting higher in the shaft resulting in the disadvantages referred to above. As the charge is melted, the molten material is continuously led away from the charge and removed from the furnace. The direction of flow of the molten material during removal can advantageously be initially countercurrent to the flow of combustion products to cause superheating of the molten material and thus facilitate its flow through a suitable taphole.

The furnace for melting fusible materials as constructed according to this invention generally comprises a vertical or inclined shaft for retaining the charge to be melted. The lower portion of the bore of the shaft is constructed to facilitate downward flow of the charge, and the bottom of the bore is formed to direct the flow of melted charge toward at least one outlet at the side of the bore. A combustion chamber and an associated burner is provided to effect substantially complete combustion of a fuel and air mixture within the combustion chamber. A throat interconnects the combustion chamber and the shaft at the outlet, the throat being formed to provide a high velocity jet of combustion gases flowing from the combustion chamber into the shaft. Finally, a taphole is positioned to continuously remove substantially all of the molten material from the shaft immediately after melting.

The melting in a countercurrent flow furnace according to the present invention allows rapid melting at significantly higher thermal efficiencies than attainable with previous furnaces of comparable size. Also, the height of the charge may be increased without causing bridging within the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view through the center of a furnace constructed in accordance with the teachings of the present invention;

FIG. 2 is a sectional view of the empty furnace taken along lines 2-2 of FIG. 1; and

FIG. 3 is a partial sectional view of the empty furnace taken along line 3-3 of FIG. 1.

FIGS. 4, 5, 6, and 7 show alternate embodiments of the bottom of the furnace shaft wherein multiple burners are utilized.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1, 2, and 3 illustrate a vertical shaft-type furnace constructed according to this invention and used a melter for ferrous metals. Referring to FIGS. 1 and 2, the shaft of the furnace includes an outer shell, preferably of steel, consisting of an upper shell section 13, a lower shell section 15, and a base plate 17. The upper shell section 13 is cylindrical and defines that portion of the shaft into which the fusible material charge is loaded and through which waste gases escape. This upper portion of the shaft is disposed vertically although it may be inclined if desired. The inner surface of the shell is lined with a heat refractory material 19 such as tabular alumina castable refractory. Two or more layers of different refractory materials may be used where desirable. The refractory material 19 that lines the upper shell section 13 is formed to provide a uniform inside diameter over the entire length of the upper shaft section.

The lower shell section 15, also lined with the refractory material 19, is formed with a bore which is tapered outward toward the bottom to facilitate downward flow of the charge from the upper shaft section. The bottom of the bore advantageously is sufficiently slanted from the horizontal, as shown at 16, to direct the flow of melted charge toward a throat 20 as more fully discussed below. In the preferred embodiment of the invention shown in FIGS. 1 and 2, the bottom of the bore is formed in an arcuate or essentially hemispherical configuration to direct the flow of molten charge material through the throat and into a passage 21 located at the side of the furnace. The passage 21 has a lowermost point at which a taphole is located to effect continuous removal of the molten product. As seen from FIGS. 1 and 3, the taphole 23 includes a channel 24 in the bottom of the passage 21. The angle of incline of the shaft bottom should be sufficient to allow substantially all of the molten product to flow out through the throat 20, passage 21 and taphole 23 immediately after melting. In this manner no molten pool is allowed to form at the bottom of the shaft. This immediate removal of the molten material also advantageously reduces chemical interaction of gas and molten material, such as oxidation of carbon and silicon when melting cast iron.

Referring to FIG. 3, the passage 21 interconnects the bore of lower shell section to a pair of combustion chambers 25 (only one visible) of the burner assemblies 27. The burner assemblies 27 are mounted on the side of the lower shell section 15 at an angle to one another such that the axes of the burners converge at a point within the passage 21. The passage 21 flares out at the end opposite the shaft to funnel the converging combustion gases from the two combustion chambers 25 into the shaft. A sighting port 28, located between the burner assemblies, allows visual inspection of the melting process.

Each of the burner assemblies 27 consists of a fuel inlet 29, an air inlet 31, an air tube 33, a helical vaned mixer 35, a flameholder 37, a burner liner 39, and a burner casing 41 which is lined with the insulating material 19. One of the burner assemblies is provided with a lighting port 43 which extends through the burner casing 41 and the insulating material 19 to a point intermediate the vaned mixer 35 and the flame holder 37. Both the flameholder 37 and the burner liner 39 are constructed of a refractory material such as zircon.

The incoming air passes through the vaned mixer 35 which is positioned in the end of the air tube 33. The helical vanes of the mixer 35 impart a turbulence to the incoming air and cause the air to be thoroughly mixed with the incoming fuel which is introduced into the turbulent air stream through the end of the vaned mixer. In operation, the fuel and air mixture is ignited through the lighting port 43 and the resulting combustion flame is maintained in the combustion chamber 25 by the flameholder 37 of the type well known in the art. The burner assembly 27 is so dimensioned and constructed as to cause substantially complete combustion of the fuel and oxygen mixture within the combustion chamber 25. In this manner only the gaseous products of substantially complete combustion are allowed to pass over the exiting molten metal and into the shaft. 1

The fuel that is used is one having the required combustion temperature for a particular melting operation. Any of the hydrocarbon fuels may be used such as natural gas, naptha, and fuel oil. The most desirable fuel in terms of cost, availability, and versatility is natural gas. Particular success has been achieved using natural gas to melt various scrap iron mixtures in a furnace according to this invention. The fuel is preferably mixed with air or with air and oxygen to form the combustion mixture. In some instances the air may be preheated prior to mixing.

It is advantageous that substantially complete combustion of the fuel and air mixture, which is preferably a near stoichiometric mixture, occur before the combustion gases enter the furnace shaft and preferably before the combustion gases pass over the exiting molten material. This allows the maximum heat of combustion to be derived from the fuel and thereby increases the efficiency. Substantially complete cornbustion as used herein shall be construed to mean combustion of the fuel and air mixture which leaves no more than about 2 percent combustibles or 2 percent oxygen in the combustion gases. In the preferred embodiment, the combustion gases are controlled to give about 0.4 to 0.8 percent combustible and near 0.0 percent oxygen.

The passage 21 and throat through which the combustion products are directed are so dimensioned asto form a high velocity stream of combustion gases flowing from the combustion chambers into a localized region or zone 40 immediately adjacent the throat 20. For this purpose, the passage is formed with its smallest cross-sectional area being at or near the throat 20. The smallest cross-sectional area of the passage or throat is substantially smaller than the crosssectional area of the shaft. In the most advantageous embodiment, the ratio of the shaft cross-sectional area to the smallest passage cross-sectional area is about 8:] although ratios in the range of 4:1 to 20:] may be used depending on the type of charge material, burner size, and other operating considerations. The high velocity stream or jet of combustion gases produced at the throat 20 provides a high rate of heat transfer within the adjacent charge. This produces rapid melting of the charge in the localized or impingement zone generally indicated at 40. The balance of the'shaft acts as a preheater. Restricting the melting to a small localized zone near the bottom of the shaft minimizes bridging or hangup of the metal charge in the shaft and allows the height of the charge to be increased.

The passage 21 and jet of hot gas is also advantageously directed to the impingement or localized melting zone at an angle downwardly toward the bottom of the shaft and the charge to be melted. This not only prevents the accumulation of the charge or slag within the passage 21, but also inhibits the flow of the jet of gas upwardly through the shaft and aids in restricting the melting to the small localized zone near the bottom of the shaft.

The velocity of the stream or jet of combustion gases flowing into the shaft generally is greater than about feet per second and less than about 1,000 feet per second in order to melt the charge efficiently. Accordingly, the throat 20 and passage 21 are dimensioned to provide velocities within this range; and advantageously velocities of 200 to 300 feet per second are used. At velocities lower than about 100 feet per second the charge melts too slowly, the metal tends to oxidize, carbon and silicon losses are higher (when melting iron and steel) and'efiiciencies are significantly lower. At velocities in excess of about 1,000 feet per second excessive noise is generally experienced, droplets of molten charge material tend to be blown back up the shaft, and the flow of exiting metal is retarded. Gas flow velocities within the given range, however, provide rapid, efficient heat transfer within the shaft and allow higher melting rates in the localized melting Zone 40 than attainable with other furnaces of comparable size.

I The throat velocity of the combustion gases will depend upon the selected heat input rate and it will be necessary to consider the scope of all melting operations to be performed in the furnace before selecting the cross-sectional dimensions of the throat and passage. It is to be noted, however, that should a particular melting operation require a higher velocity than is possible using the original throat size, preformed refractory inserts may be used to decrease the throat size. These inserts can be removed and replaced whenever necessary with a minimum of effort. Other means may-be used to vary the cross-sectional area of the throat or passage, including mechanically variable devices.

For larger furnaces, such as are illustrated in FIGS. 4, 5, 6, and 7, more than one jet of combustion gases, spaced at intervals, may be introduced into the bottom of the shaft and the molten metal may be removed through one or more throats or tapholes. This will, however, require forming the bottom of the shaft to direct separate flows of melted charge toward the appropriate throats or tapholes. It is understood that one of the primary aspects of this invention is the melting of fusible materials with high velocity jets of combustion gases directed at localized melting zones or areas of the charge. The molten material can be removed from the melting zone or zones by way of separate tapholes or channels which do not necessarily communicate with one or more of the throats which produce the high velocity jets of combustion gases. When more than one jet of gases is employed, they should be positioned around the circumference of the shaft such that each jet performs an individual melting function, substantially independent of the other jets. If this is not done, bridging is more likely to occur and overall efficiency may decline.

FIG. 4 illustrates an alternate embodiment wherein two separate jets of gases enter the shaft through the passages 21 and throats 20 and produce localized melting in two separate,

spaced apart zones 40. The molten metal exits through the passages 21 and the converging taphole 45.

FIG. 5 illustrates an embodiment which also employs two separate jets of hot gases but the molten metal is removed through a taphole 47 which extends through the furnace wall and directly into the shaft bottom rather than communicating with the passage 21. The throats 20' are raised a short distance from the bottom of the shaft such that the melted material will flow downward toward the taphole 47 rather than out through the passage 21. The passages 21 may also be inclined downward toward the shaft bottom to further prevent molten material from flowing into them. As the material is melted in zones 40, it flows downward a short distance and exits through taphole 47.

FIGS. 6 and 7 illustrate other alternate embodiments wherein three separate hot gas jets are used. In FIG. 6 the taphole is located in one of the side passages and in FIG. 7 the taphole extends into the center passage. In both FIG. 6 and FIG. 7 the throats 20 communicate with the shaft a short distance above the bottom of the shaft and their respective passages 21 may be inclined downward to prevent molten material from flowing into the passages. The shaft bottom in each embodiment is formed to direct the flow of melted material toward the exit throat 20. The exit throat 20 and the slightly elevated throats 20' are spaced far enough apart to provide independent melting zones but close enough to prevent solidification of the molten material before it reaches the exit throat 20.

In a melting operation, the furnace is gradually preheated until the refractory linings are at a predetermined temperature, the air and gas to the burners is adjusted to provide the desired heat input rate and air-to-gas mixture, and the shaft is filled to the desired level with the charge. The throat size is selected prior to start-up to provide the desired high velocity jet of combustion gases. During melting, the molten charge material is continuously removed through the taphole in the passage 21. The hot combustion gases passing over the exiting molten material serve to superheat the material slightly and to keep it flowing. The slag that is normally produced in the melting of scrap iron is removed with the molten charge; and may thereafter be separated from the metal at the appropriate time and by conventional procedures. Also, the molten metal exiting from the furnace may be fed directly into separate furnaces for subsequent superheating and other treatments.

The heat input to the furnace is controlled by measuring the fuel rate with a flow meter. The air or oxygen is supplied by a positive-displacement blower. The air or oxygen flow is controlled automatically at the selected rate. Normally, the fuel flow is set at the desired rate in a hot but empty furnace and the air rate adjusted to produce about 0.4 to 0.8 percent of combustibles in the combustion products. Gas temperature may be increased when desired by preheating the combustion air.

EXAMPLE A charge consisting of 30 percent steel railroad spikes, 40 percent pig iron, and 30 percent scrap iron was loaded to a height of 9 feet within the furnace shaft. The upper shaft section of the furnace had a uniform inside diameter of 18 inches. The bore of the lower shaft section was 46 inches high and was tapered outwardly to a 24-inch diameter. The bottom of the bore was essentially hemispherical with a diameter of 24 inches. The cross-sectional area of the throat which communicated with the lower bore was 34 square inches. Two burners with a rated capacity of 1.5 million Btu per hour each were mounted with the axes of the burners converging at a point within the passage. A heat input rate of 2 million Btu per hour was used with no preheating of the air. Natural gas was the fuel. A melting rate of 2,430 pounds per hour was attained with an overall efficiency of 62.3 percent. The melting efficiency was calculated from the heat content of the metal tapped and the heat of combustion of the fuel fired. The

velocity of the combustion gases through the throat during the melting process was maintained at about 200 feet per second. A heat input rate of 3 million Btu per hour produced a melting rate of about 3,820 pounds per hour in the same furnace.

The advantages of the improved melting furnace of this invention from the standpoint of simplicity of initial construction and maintenance are numerous. The furnace can be of any convenient size and therefore can be used in a wide variety of applications. Smaller versions of the furnace can be used for melting of scrap metals in emerging industrial nations where the use of full scale blast furnaces or cupolas is impractical. The furnace, due to its simplified construction, may be installed more rapidly and at lower cost than presently available melting furnaces which generally have a high initial cost, high operating costs, and relatively low outputs.

The height of the charge that can be accommodated without causing bridging is considerably greater than in conventional countercurrent flow-type furnace. The increased height provides for greater efficiency in that the heat of combustion is more completely used in preheating the charge and not lost out the top of the furnace shaft. The height of the charge in any particular situation will depend on such things as the properties of the charge material and dimensional characteristics of the furnace itself.

The superheating, at least to some extent, of the molten materials leaving the furnace through the passage 21 as for example to F over the melting temperature, assures unimpeded flow through the taphole. A portion of the combustion gases passes through the taphole with the exiting molten materials and helps to maintain the material in a superheated state. This facilitates its subsequent handling. The amount of superheating may be varied depending on the particular charge material being melted and the subsequent treating operations contemplated.

The present furnace does not require retention grates, baffles, or inert filler materials to support the charge within the shaft. It may be used to melt any fusible materials including ores, metals, glass and minerals and is particularly effective in melting iron and steel scrap using natural gas as the fuel.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations and modifications may be made therefrom without departing from the scope of the invention as set forth in the following claims.

We claim:

1. The method of melting fusible materials comprising the steps of:

a. feeding comminuted fusible materials to form an elongated charge, the degree of compaction of said charge being sufficient to permit substantially free passage of hot gas therethrough;

b. impinging at least one jet of hot gas at at least one end of said charge at the outer surface thereof forming an impingement zone, said jet having a velocity and temperature sufficient to produce a localized melting of the charge in the impingement zone;

c. passing the hot gas through the charge to cause only a preheating of the remaining portion of the charge beyond the end, said preheating not exceeding the temperature beyond which the charge enters the molten or semi-molten state; and

d. continuously removing the melted materials from said charge at a rate sufficient to prevent the formation of a pool of melted materials at the end of the charge and at the same time, to substantially prevent exposure of the melted materials to the hot gases.

2. The method of claim 1 wherein the charge is substantially vertically disposed; and the jet of hot gas is directed at the bottom of the charge.

3. The method of claim 2 which includes a removal zone for the melted materials which is at a lower level than the bottom of the charge and the impingement zone.

4. The method of claim 1 in which the jet of hot gas is formed by burning a fuel and oxygen mixture in at least one combustion zone communicating with, but spaced from the bottom of the charge, and directing gaseous products of the combustion through a confined passage to cause impingement of the hot gas on an end of said charge.

5. The method of claim 1 wherein the cross-sectional area of said jet is substantially smaller than the cross-sectional area of said charge.

6. The method of claim 1 wherein the velocity of said jet is greater than about 100 feet per second and less than about 1000 feet per second.

7. The method of claim 4 in which the fuel is a hydrocarbon.

8. The method of claim 7 wherein the fuel is natural gas.

9. The method of claim 4 wherein the fuel and oxygen mixture are burned in said combustion zone to effect substantially complete combustion of the mixture before the gaseous products of combustion enter the impingement zone of the charge.

10. The method of claim 4 wherein the melted materials are removed from the confined passage along a path initially extending countercurrently to the flow of the products of combustion in said jet.

1]. The method of claim 10 wherein the fuel and oxygen mixture are burned in said combustion zone to effect substantially complete combustion of the mixture before the gaseous products of combustion pass countercurrently in heat exchange relationship with the exiting melted materials.

12. The method of claim 1 wherein a plurality of hot gas jets are impinged on at least one end of said charge in step (b), said plurality of jets being spaced to provide substantially independent melting zones.

Claims

2. The method of claim 1 wherein the charge is substantially vertically disposed; and the jet of hot gas is directed at the bottom of the charge.
3. The method of claim 2 which includes a removal zone for the melted materials which is at a lower level than the bottom of the charge and the impingement zone.
4. The method of claim 1 in which the jet of hot gas is formed by burning a fuel and oxygen mixture in at least one combustion zone communicating with, but spaced from the bottom of the charge, and directing gaseous products of the combustion through a confined passage to cause impingement of the hot gas on an end of said charge.
5. The method of claim 1 wherein the cross-sectional area of said jet is substantially smaller than the cross-sectional area of said charge.
6. The method of claim 1 wherein the velocity of said jet is greater than about 100 feet per second and less than about 1000 feet per second.
7. The method of claim 4 in which the fuel is a hydrocarbon.
8. The method of claim 7 wherein the fuel is natural gas.
9. The method of claim 4 wherein the fuel and oxygen mixture are burned in said combustion zone to effect substantially complete combustion of the mixture before the gaseous products of combustion enter the impingement zone of the charge.
10. The method of claim 4 wherein the melted materials are removed from the confined passage along a path initially extending countercurrently to the flow of the products of combustion in said jet.
11. The method of claim 10 wherein the fuel and oxygen mixture are burned in said combustion zone to effect substantially complete combustion of the mixture before the gaseous products of combustion pass countercurrently in heat exchange relationship with the exiting melted materials.
12. The method of claim 1 wherein a plurality of hot gas jets are impinged on at least one end of said charge in step (b), said plurality of jets being spaced to provide substantially independent melting zones.