US3521872A - Apparatus for controlling the temperature of metal lances in molten baths - Google Patents

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y 23, 7 I N. J. THEMELIS I 3,521,872

APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL LANCES IN MOLTEN BATES Filed March 31. 1967 4 Sheets-Sheet l m N J l (D w u.

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APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL LANCES IN MOL'TEN BATHS Filed March 31, 1967 4 Sheets--Sheet 2 July 28, 1970 N. J. THEMELIS APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL Filed March 31, 1967 LANCES IN MOLTEN BATHS FIG.4

4 Sheets--Sheet 3 July 28, 1970 N. J. THEMELIS 3,521,872

APPARATUS FOR CONTROLLING THE TEMPERATURE OF METAL LANGES IN MOL-TEN BATHS Filed March 31, 1967 4 Sheets-Sheet 4 United States Patent 3,521,872 APPARATUS FOR CONTROLLING THE TEMPERA- TURE 0F METAL LAN CES IN MOLTEN BATHS Nickolas J. Themelis, Beaconsfield, Quebec, Canada, as-

siguor to Noranda Mines Limited, Toronto, Ontario, Canada Filed Mar. 31, 1967, Ser. No. 627,466 Claims priority, application Great Britain, Apr. 13, 1966, 16,232/ 66 Int. Cl. C21c 7/00 US. Cl. 26634 10 Claims ABSTRACT OF THE DISCLOSURE A water-cooled lance which may be used in the treatment of molten metal and which may be inserted beneath the surface of the metal. The lance structure provides a passage for gases and a passage for a coolant such as Water. The water vaporizes as it contacts the hot lance body and so acts as a cooling medium and the gas and water vapour are admixed as they pass through the lance body and enter the molten metal as a gaseous mixture.

This invention relates generally to a method and apparatus for controlling the temperature of metal lances in molten baths.

The major problem in introducing gases in molten metal baths for purposes of refining or converting has been that irrespective of the flow of gas through the lance, the heat transfer from the bath to the lance greatly exceeds the possible heat transfer from the lance to the gas stream within it. As an example, a steel lance exposed to a furnace atmosphere of 2400 F. may absorb a maximum heat input of 100,000 B.t.u./hr.ft. of exposed surface. The same lance, when submerged in a bath of molten copper at 2200 F., absorbs an estimated 400,000 to 800,000 B.t.u./hr.ft.

This enormous heat transfer rate in the molten bath is due to the fact that the conductivity of the liquid material is extremely high and also to the fact that the bath is usually superheated to at least 100 to 200 F. above its melting point and, therefore, constitutes a practically infinite source of heat due to the strong convection currents existing in the bath. On the other hand, for convection between the lance wall and the gas stream flowing through the lance at sonic, or even super-sonic gas velocities, the maximum heat transfer rates that can be achieved are in the order of 30,000 to 60,000 B.t.u./hr.ft. It can, therefore, be seen that it is almost impossible to prevent the lance wall from reaching the temperature of the bath even at the highest possible flow rate of gas through it, due to the limitation of the heat transfer coefficient by convection between the wall and the gas. Consequently, soon after the lance has been introduced into the bath, it reaches the temperature of the latter and because of the strong vibration caused by the gas injected in the bath, the lance is very soon broken up.

This problem has appeared to be insurmountable, since when used with a gas flow alone, even the best qualities of stainless steels and alloy lances available have very little strength in the temperature of molten copper baths and none at all in molten steel. The way in which this obstacle has been overcome in steel refining by the new oxygen lance technique for steel refining, is to avoid immersing the lance into the bath and also to provide the lance with a water-cooled jacket. However, in order for this method of injection to be effective, it is required that the oxygen emerges from the lance at very high velocities and also that the lance is kept at a safe distance above the bath; these factors have a pronounced effect on the efficiency utilization of oxygen gas.

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In the case of copper processing where the gas must be introduced below the surface, the use of lances has met with complete failure and has prevented the adoption of gas injection techniques into stationary furnaces not equipped with refractory tuyeres. In particular, failure of the lances has prevented their use in the deoxidation of anode copper.

The present invention relates to an eifective method for overcoming this problem and allowing the use of, for example, mild steel or other metal pipes for injecting gases in molten baths.

The lance of the present invention may be used generally for introducing gases into molten metal at-high tempertaures. In a process of deoxidizing copper by hydrocarbon gases, steam and hydrocarbon gases, such as propane and butane, may be mixed and reacted in the lance of the present invention. The steam may be replaced by water which is both vaporized and reacted in the same lance. The benefit of mixing water instead of steam is that the lance can be kept cooler making it possible to use ordinary mild steel pipes for introducing various gases into molten metals at high temperatures.

Advantages of the invention over previous water-cooled lances, such as water-cooled sheathed lances or the lance disclosed in US. Pat. No. 3,269,829 include the presence of a very advantageous safety aspect. Since the cooling water is atomized at a location outside the bath there can be no danger of structural failure of the lance or accidental discharge of a volume of water sufficient to cause an explosion in contact with the molten bath. Therefore, the tip of the present lance can be immersed in the liquid bath, since a failure of the tip will not afiect the formation of the fine water spray. All other types of water-cooled lances referred to above cannot be immersed in the liquid and must be kept at a safe distance above the bath.

In the drawings:

FIG. 1 is a side elevation of a rotary anode furnace with a cut-away section showing a lance of the present invention disposed therein.

FIG. 2 is a side view of a reverberatory anode furnace showing three lances in position in openings of the furnace.

FIG. 3 is a cross-section showing the atomizing nozzle of the lance of the present invention.

FIG. 4 is a section of a reverberatory furnace with a lance extending through a side port thereof into the melt.

FIG. 5 is a cut-away section of the lance showing the flow of water-gas mixture therein.

Broadly speaking the invention relates to a method and apparatus for controlling the temperature of pipes or other lancing devices, used for injecting a gas into a molten bath, by introducing a finely divided spray of water into the gas stream thereby greatly enhancing the heat transfer rate between the wall of the lancing device and the gas stream, and maintaining the lance at a temperature below the temperature of the bath, thus preventing fracture or dissolution of the lance material. This method and apparatus may be used in copper refining, either for the oxidation of blister copper or for reducing with gaseous reagents, converting of copper, refining of steel by oxidation or other means, and any other process or scheme where it is necessary to inject a gas stream into a molten bath of metal, matte, or slag.

The invention is based on the consideration that the heat transfer coefficient between the wall and the gas stream must be increased considerably in order to remove the heat received by the outside wall of the lance. This is achieved by introducing a very fine spray of water in the gas stream at the inlet of the lance located outside the furnace. The size of the spray droplets is preferably less than microns. A pneumatic nozzle is used which disperses a relatively low flow of water for example (30 gal/hr.) into the gas stream in the form of very fine droplets which, when they collide with the wall of the lance, absorb a large amount of heat by evaporation and then are reflected back into the main stream, much in the same way as a Water droplet falling on a hot plate and bouncing on it until it is completely evaporated. The water flow rate required will depend on the characteristics of heat transfer from the liquid bath to the lance (temperature of the bath, lance diameter, thermal conductivity, viscosity, specific heat and density of the liquid bath).

In this way, the heat transfer between the gas stream and the lance is increased enormously since the heat transfer coeflicient is not any more one between gas and wall, but between droplet and wall, which has practically infinite capacity as a heat sink.

FIG. 1 shows a typical rotary furnace A as used in copper refining. This type of furnace is supported on rollers 21 and may be rotated by a suitable motor connected to a ring gear 22. Steam is brought to the furnace via a pipe 1 and is controlled by a pressure regulator 2 which keeps the steam in a loader pipe 4 at a constant pressure. Steam feed to each lance is controlled by individual valves 3 and is connected to the lance with a flexible hose 5. A hydrocarbon, such as propane or butane, is brought to the furnace via pipe '7 and controlled by a main valve 8. The feed to each lance from a common loader pipe is also controlled by individual valves 9 and connected to the lance by flexible hose 11. The lance assembly consists of a mixing T 6 into which the steam and hydrocarbon is introduced, lance hanger 15, lance bushing 12 and lance 14. The lance slip-bushing 12 allows the lance to be manually or mechanically rotated periodically through. 180 about the lance axis in order to compensate for upward bending of the lance tip. The lance hanger is designed to suspend the lance at the proper angle for maximum depth of lance orifice 17 under the melt surface 19. The whole assembly is suspended to a suitable support by a hook 16 and cable or rope 24.

The lances in FIG. 1 are shown introduced through openings 18 in the end walls 13 of the furnace. However, it is also understood that the lance may be introduced through any openings in the furnace that are found suitable, such as openings around the cylindrical shell of the furnace 23.

FIG. 5 is a section of the lance of the present invention as it is introduced into a metal melt 20. Water or other liquid such as naphtha is delivered through an inlet tube 34 and end adapter 35 to a mixing and atomizing nozzle 36 and into the lance 14 through an orifice 37. The gas to be introduced into the molten metal is delivered to the lance 14 through an opening 33 in a mixing T 6 and passes through the atomizing and mixing nozzle 36 into the lance .14 through orifice 38. The orifices 38 are so shaped and dimensioned that water enters the lance 14 in the form of a fine spray. As the mixture of water droplets and gases pass through the lance 14, in the process of copper deoxidation, the Water is vaporized and reacts with the hydrocarbon gases in the lower hot section of the lance. It should be understood that gases other than hydrocarbons may be used when the purpose of adding water is solely to cool the lance. It should also be understood that the method used for the lance is only applicable when water is not detrimental to the particular process for which the lance is used. The resulting gases or gas-steam mixtures enter the molten metal through lance orifice 17 and rise through the melt 20 to the liquid metal surface 19 in the form of bubbles. Treatment of the melt 20 may consist of either a reaction between one, some, or all of the gases entering the melt and some impurity of the metal itself, such as in the removal of oxygen from molten copper, or the gases introduced may only act to remove other dissolved gases in the melt such as in common degassing processes.

The present lance has been tested in the gaseous atmosphere of an anode furnace at temperatures of about 2300 F., when a water flow rate of five gallons per hour was found sufficient to maintain the pipe below 1800 F. at its tip; the corresponding gas flow rate was 30 s.c.f.m. (standard cubic feet per minute) of propane. The lance was also tested under the extreme conditions prevailing when the lance is immersed to a distance of approximately four feet in a bath of molten copper when the required water flow rate was about 20 gal./ hr. for the same gas flow rate of 30 s.c.f.m. of propane.

It should be noted that the present method of cooling the lance by introducing a finely atomized spray of water affords great flexibility in controlling that part of the lance which in operation is submerged in the furnace melt since it is possible, by introducing more or less water, to increase or decrease the temperature at the tip of the lance as desired.

At the same time, since the metal of the lance can be kept at a relatively low and safe temperature, this invention dispenses with the necessity of using expensive or extremely strong stainless steels for lancing applications. In the example discussed previously herein, a mild steel pipe was introduced at an angle into the molten copper to a depth of two feet (corresponding length about four feet) and was subjected to intense conditions of vibration by introducing an overall gas rate of s.c.f.m. which resulted in very intense mixing conditions in the bath and vibration of the lance. Yet, two hours after the lance was introduced in the furnace, it was still operating at the same depth without showing any adverse effects of attack by the liquid bath or fatigue fracture.

It is clearly apparent from the foregoing that the lance of the present invention represents a significant advance in the art.

I claim:

1. A lance suitable for use under high temperature conditions in the treatment of molten material which comprises:

(a) a feed chamber adapted to allow the flow of a gaseous treating medium therethrough;

(b) a gas inlet in one wall of the feed chamber;

(c) a coolant liquid transmitting conduit extending axially through said chamber and terminating in a liquid outlet in a second wall of the feed chamber;

(d) at least one gas outlet in said second wall angled and positioned such that the flow of gaseous treating medium therethrough causes coolant liquid flowing through the liquid outlet of the transmitting conduit to disperse into liquid droplets; and

(e) an elongated body defining a flow passage extending axially through said body, said passage being adapted to receive the mixture of liquid droplets and gaseous treating medium and having one end terminating at the second wall of the said chamber and a second end terminating in a discharge outlet, said elongated body being adapted to be at least partially submerged in molten material and to be cooled internally by the impingement of liquid droplets on the walls of the flow passage.

2. A lance as claimed in claim 1 wherein the feed chamber is substantially T-shaped.

3. A lance as claimed in claim 2 wherein the gas inlet is situated in the base of the T-shaped chamber which is adapted for connection to a source of gaseous treating medium and the coolant liquid transmitting conduit traverses in the horizontal portion of the T-shaped chamber and is formed as a single unit with said second Wall.

4. A lance as claimed in claim 2, wherein said feed chamber is adapted for detachable connection to said body.

5. A lance as claimed in claim 1, wherein said feed chamber is adapted for detachable connection to said body.

6. A lance as claimed in claim 1 wherein said'coolant liquid transmitting conduit and said second wall are formed as a single unit, the end of said conduit remote from said second wall being adapted for connection to a supply source of coolant liquid, the other of said conduit terminating in the liquid outlet at said second wall.

7. Apparatus for use under high temperature conditions in the treatment of molten material which comprises a lance having:

(a) a feed chamber adapted to allow the flow of a gaseous treating medium therethrough;

(b) a gas inlet in one wall of the feed chamber;

() a coolant liquid transmitting conduit extending axially through said chamber and terminating in a liquid outlet in a second wall of the feed chamber;

(d) at least one gas Outlet in said second wall angled and positioned such that the flow of gaseous treating medium therethrough causes coolant liquid flowing through the liquid outlet of the transmitting conduit to disperse into liquid droplets;

(e) an elongated body defining a flow passage extending axially through said body, said passage being adapted to receive the mixture of liquid droplets and gaseous treating medium and having one end terminating at the second wall of the said chamber and a second end terminating in a discharge outlet, said elongated body being adapted to be at least partially submerged in molten material and to be cooled internally by the impingement of liquid droplets on the walls of the fiow passage; and

(f) a first source of supply of a gaseous treating medium, a second source of supply of a coolant liquid, a first conduit member connecting said first source of supply to said gas inlet into the feed chamber, a

second conduit member connecting said second source of supply to said coolant liquid transmitting conduit and adjustable valves adapted to control the flow of gaseous treating medium and coolant liquid from said first and second sources respectively.

8. The apparatus as claimed in claim 7 including supporting mechanism for suspending the lance body in operating position.

9. The apparatus as claimed in claim 7 including means connected to said lance permitting its rotation through an angle of about the lance axis.

10. The apparatus as claimed in claim 9 wherein said means on said lance is a slip bushing.

References Cited UNITED STATES PATENTS Re. 26,36 4 7/ 1965 Kurzinski. 2,937,864 5/ 1960 Kesterton. 3,093,157 6/1963 Aitken et al. 239-4245 X 3,093,314 6/19-63 Meyer 239425 X 3,291,471 12/1966 Heyer.

FOREIGN PATENTS 841,350 7/1960 Great Britain.

1. SPENCER OVERHOLSER, Primary Examiner I. S. BROWN, Assistant Examiner US. Cl. X.R. 239425

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