US3528802A - Deoxidation process - Google Patents

Description

' Sept. l5, 1970 A, P. MORRIS E'rAL 3,528,802

DEoxIDATIoN PROCESS Filed Oct. 5, 1966 United States Patent O U.S. Cl. 75-76 4 Claims ABSTRACT OF THE DISCLOSURE This application relates to a process for reiining oxygen-bearing molten copper in a furnace that is equipped with tuyeres, to reduce its oxygen content, that comprises providing heat to a liquid hydrocarbon material that is gaseous under standard conditions of temperature and pressure, and that predominantly is a material that is selected from the group consisting of propane, butane, and mixtures thereof to form a pressurized vapor, and injecting said vapor into the molten copper, beneath its surface, through the tuyeres utilizing the pressure of said vapor created in forming said vapor from the liquid hydrocarbon material for said injecting and apparatus to accomplish the same.

This invention relates to the deoxidation of molten copper. More particularly, the invention relates to processes and apparatus for refining oxygen-bearing molten copper, to reduce its oxygen content.

In the production of copper anodes for an electrolytic refinery, converter or blister copper is iire refined before casting, to decrease the content of gases and of impurities. The fire refining process involves oxidation, skimming off such slag as may have inadvertently been permitted to escape from the converters into the rening furnace, and reduction to the desired low oxygen content.

One conventional way of oxidizing is by introducing compressed air under the molten metal surface through lances, which are simply iron pipes. This causes a bubbling that exposes the molten copper to the furnace atmosphere, and copper oxide is formed. This dissolves in the molten metal and reacts with copper sulfide present, forming sulfur dioxide, that escapes to the atmosphere. The copper oxide also gives up its oxygen to certain impurities, so that metal oxides may be formed that can be combined with an added silica flux to form a slag. The slag is removed mechanically. The oxygen is removed by reduction.

It has been conventional practice to reduce the molten copper by covering the molten metal with coke and inserting wood poles through the furnace door, forcing one end beneath the surface of the molten metal. The reducing gases formed by the poles are effective to deoxidize the copper. However, a more recent practice is to use a reformed natural gas.

Aside from cost, the use of poles for deoxidation is hazardous, involving the danger of splashing and pole slippage. In addition, the pole inventory takes up space and involves a housekeeping problem. Moreover, when poles are employed for deoxidation, it is not practical to use tuyeres for oxidation because they must be plugged rice with clay While the furnace is being poled. The use of reformed gas avoids these difliculties but requires a substantial capital investment for a reformer.

One object of the present invention is to provide new and practical processes and apparatus for the deoxidation of oxygen-bearing molten copper.

Another object of the invention is to provide processes and apparatus for the refining of oxygen-bearing molten copper, to reduce its oxygen content, that are much more attractive than previous processes, by reason of greater safety, less expense, greater convenience, and less labor.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

The single ligure of drawing is a schematic diagram that shows one way in which apparatus can be disposed and connected for the deoxidation of oxygen-bearing molten copper, in accordance with one preferred embodiment of the present invention.

Referring now in detail to the drawing by numerals of reference, the numerals 10` and 10' denote respectively, a pair of storage tanks for liquified hydrocarbon material, such as, for example, propane, butane, or mixtures thereof, under pressure. The outlet port of the tank 10` is connected through a line 11, a valve 12, and a line 14 to a manifold 15. The outlet port of the second tank 10 is similarly connected to the manifold 15 through a line 11', a valve 12 and a line 14. The manifold 15 is connected through a valve 16 and a line 18 to one end of a heat exchanger 19. The discharge port of the heat exchanger is connected through a line 20, a valve 21, and a line 22, to a T-junction 24.

One side of this T-junction 24 connects with a manifold 25. The manifold 25 is connected to the tank 10` through a line 26, a valve 28, and a line 29. Similarly, the manifold 25 is connected to the second tank 10 through a line 26', a valve 28 and a line 29.

The T-junction 24 is connected at its other side through a line 30, a valve 31, and a line 352, to one side of a T- junction 34.

The opposite side of the T-junction 34 is connected through a line 35, a valve 36, and a line 38, to a source of compressed air (not shown).

The third port of the T-junction 34 is connected through a line 40, a valve 41, and a line 42, to the tuyere manifold 44 of an anode furnace 45.

To operate the heat exchanger, it is connected to a steam supply line 48 and a condensate return line 42. A steam supply of up to about 250 p.s.i. is adequate, since operating steam pressures of from about p.s.i. to about 215 p.s.i. are adequate to permit operations over a wide range of ambient temperatures.

To practice the process of the present invention, utilizing apparatus such as that which has been described briefly above in connection with the schematic drawing, a batch of molten copper from a converter is transferred into the anode furnace 45. Air is then blown into the anode furnace through tuyeres, utilizing the piping illustrated in the drawing, by having open the valves 36 and `41, and by having the valve 31 closed. When the copper approaches saturation with CuzO, a condition sometimes called the peahole stage, the surface is skimmed free of slag. When this has been completed, the furnace is rotated so the tuyeres are above the copper. The tuyeres are then reamed, and the copper is ready for deoxidizing.

To commnce deoxidization, the valve 36 is closed, and the valve 31 is opened. The tank 10 is then made ready for use by opening the valves 12, 16, 21, and 31. Steam is supplied to the heat exchanger 19 through the line 48, and con-densate is drained off, as required, through the drain line 49. Liquid hydrocarbon material such as, for example, liquified propane, flows from the tank into the heat exchanger, where it absorbs suicient energy to pass into the vapor phase.

Since the liquitied propane is maintained under substantial pressure in the tank 10, the valves preceding the heat exchanger are adjusted, as necessary, to attain the desired flow of material into the heat exchanger. As the propane is heated and therefore vaporized, it develops substantial pressure, and the pressure at which it is permitted to enter the tuyere manifold 44 is controlled by adjusting one or more of the valves on the discharge side of the heat exchanger. In a typical operation, liquid propane under a pressure in excess of 200k p.s.i. in the storage tank is converted to propane vapor 4at 20 to 25 p.s.i. at the discharge side of the heat exchanger.

Preferably, the vaporizing system is maintained under pressure continuously, so that it is simply necessary to open the line between the heat exchanger and the tuyere manifold, in order to direct propane vapor into the tuyere manifold.

When smoke from the furnace indicates that there is a good ow of propane, the furnace is rotated until the tuyeres are below the surface of the copper. For many operations, injection of the propane at about 18 inches below the surface of the molten copper has been found to give good results.

Injection of the propane into the copper is continued until a sample shows a flat set, which indicates that the copper is sufficiently reduced for casting. Occasionally, the tuyeres may require reaming during the reducing cycle. This takes only a few minutes. Ordinarily, the entire refining cycle, including oxidizing, skimming, and reducing, can be completed in about four hours.

As is shown in the drawing, it is preferred to provide a return line directly from the heat exchanger to the supply tanks for the propane or other hydrocarbon material. This permits the circulation of heated vapors back to the storage tanks during periods of very cold weather. With this arrangement shown, for example, when the temperature goes to F. or lower, it is still possible to maintain the system under pressure simply by having a partly opened circuit from the tanks to the heat exchanger and back again.

When propane is employed as the hydrocarbon material, average usage observed is about 1.5 to 3 gallons of liquified propane per ton of copper. Several variables affect the efficiency of deoxidation by propane. These include the rate of injection and the depth below the surface at which the propane is injected. When the propane is injected into an anode furnace .equipped .with only two tuyeres, a blowing rate of about 100 standard cubic feet per minute of gaseous propane has been found to be satisfactory. The use of propane permits completion of deoxidation within a period of about 11/2 hours, as compared to about 3 hours required for a 200 ton batch of copper, when poles are employed in the conventional manner. When using propane or other hydrocarbon material in accordance with the invention, we prefer to follow the customary practice of keeping the surface of the molten copper, in the furnace, protected by a blanket of coke or some similar material.

Instead of using propane, it is possible to employ butane, or mixtures of propane and butane, with equally satisfactory results. Such materials are readily available on a commercial basis. As commercially available, either propane or butane is a highly purified material. However, less purified materials can be employed. Generally speaking, the invention contemplates the use of the vapor of a hydrocarbon material that is gaseous under standard conditions of temperature and pressure and that is free from undesirable contaminants. Also, it appears that the hydrocarbon material must have a sufficiently high molecular weight so that the Volume of gas, that must be injected into the molten copper, for deoxidation, is sufficiently small so that the reaction takes place within a reasonable time. In practice, this means that the hydrocarbon material should have a calculated molecular weight of at least about 44.

Unfortunately, natural gas is ineffective, and it must be reformed in order to be effective. A possible theoretical explanation is that methane, the chief component of natural gas, is relatively stable thermodynamically, whereas its higher homologs tend to become less stable as the molecular weight increases.

Practice of the present invention eliminates the need for handling heavy poles and thus eliminates heavy labor and increases the safety of the deoxidation process. Also, the cost of maintaining tuyeres and associated piping is less than that of maintaining poling equipment in operating condition. There is also less dirt and dust, which are always associated with logs, and there is no need for storing the logs themselves. These factors lead to better housekeeping.

In addition to all of these advantages, there is the important additional advantage that hydrocarbon materials used for deoxidation in accordance with the present invention result in important and substantial economies. The most important economy is derived from the decreased cost of the hydrocarbon material as compared to the cost of poles. Another source of operating economies lies in the fact that the hydrocarbon material cools the molten copper less than is the case when poles are used. This results in important savings in the cost requirements for heating the anode furnace during refining operations.

While the invention has been disclosed herein by reference to the details of preferred embodiments thereof, it is to be understood that such disclosure is intended in an illustrative sense, and it is contemplated that various modifications in the mode and apparatus for practicing the invention will readily occur to those skilled in the art, Within the spirit of the invention and the scope of the appended claims. For example, while reference has been made to the use of the invention in the fire refining of copper, the invention has general applicability in any process for the deoxidation of a molten copper bath. When the invention is used in the production of wirebars, billets, cakes and ingots, ordinarily, the oxygen content will be reduced to a lower level, such as, for example, 0.03% to about 0.04%, than is the case when the invention is used in connection with the production of anodes.

What is claimed is:

1. A process for refining oxygen-bearing molten copper in a furnace that is equipped with tuyeres, to reduce its oxygen content, that comprises providing heat to a liquid hydrocarbon material that is gaseous under standard conditions of temperature and pressure. and that predominantly is a material that is selected from the group consisting of propane, butane, and mixtures thereof to form a pressurized vapor, and injecting said vapor into the molten copper, beneath its surface, through the tuyeres utilizing the pressure of said vapor created in forming said vapor from the liquid hydrocarbon material for said injecting.

2. A process in accordance with claim 1 comprising maintaining reducing conditions at the surface of the molten copper throughout and following said treat-ment.

3. A process for refining oxygen-bearing molten copper in a furnace, in accordance With claim 1, wherein the injection of the vapor of the hydrocarbon material is accomplished through tuyeres, with the pressure and volume of injected vapor being such that the molten bath is substantially quiescent during injection.

4., The process in accordance with claim 1 wherein the hydrocarbon matter has an average molecular weight of OTHER REFERENCES at least 44' De-Oxidation of Blister Co pper, Metal Industry, pp. References Cited SL88 Jan. 17, 1963 UNITED STATES PATENTS 57 969 9/1866 Reese 266 25 5 L. DEWAYNE RUTLEDGE, Primary Examiner 2,989,397 6/ 1961 Kuzell 75-76 J. E. LEGRU, Assistant Examiner 3,258,330 6/1966 Ito 75-76X FOREIGN PATENTS U'S' C1' X'R' 75-93 10,014 6/1963 Japan. 10

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