WO2003023073A1

WO2003023073A1 - Oxygen blowing lance for the vacuum refining apparatus

Info

Publication number: WO2003023073A1
Application number: PCT/KR2002/001725
Authority: WO
Inventors: Hyeon-Soo Choi; Sang-Bok An; Chang-Hyun Lee; Wang-Yeol Seo; Frank Mucciardi
Original assignee: Posco; Mcgill University
Priority date: 2001-09-13
Filing date: 2002-09-13
Publication date: 2003-03-20
Also published as: CA2403081A1; KR20030023355A; KR100422186B1; BR0206031A

Abstract

The inventive oxygen-blowing lance for feeding oxygen includes a ladle for storing molten steel, a vacuum chamber arranged over the ladle and submerged conduits providing circulation channels for the flow of molten steel between the ladle and the vacuum chamber. The oxygen-blowing lance is mounted to penetrate the side wall of the vacuum chamber with an inclination angle and comprises: an oxygen feeding pipe for blowing oxygen into the vacuum chamber; a tubular body for surrounding the outer surface of the oxygen feeding pipe and extending from a leading end of the oxygen feeding pipe exposed within the vacuum chamber toward the outside of the vacuum chamber for a length, the tubular body being closed at both ends; and volatile liquid substance stored in a closed storage space defined between an inner surface of the tubular body and the outer surface of the oxygen feeding pipe.

Description

OXYGEN-BLOWING LANCE IN VACUUM REFINING APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oxygen-blowing lance in an RH vacuum refining apparatus for refining molten steel in an additional refining process of a steel making process for manufacturing very low carbon steel. More particularly, this invention relates to the oxygen-blowing lance for the vacuum refining apparatus which is installed in the side wall of a vacuum chamber of the RH vacuum refining apparatus with a predetermined inclination angle for blowing oxygen toward molten steel to decarburize molten steel within the RH vacuum refining apparatus, and which has cooling means for preventing fracture or erosion due to the temperature of molten steel without deteriorating the degree of vacuum in the vacuum chamber.

2. Description of the Related Art

In general, an RH vacuum refining apparatus 10 used for the manufacture of very low carbon steel containing carbon of 70ppm or less, as shown in Fig. 1, comprised a ladle 12 for storing molten steel tapped from a converter and was not deoxidized, a vacuum chamber 14 arranged above the ladle and submerged conduits 16 for defining a circulation path for the flow of molten steel between the ladle and the vacuum chamber. The submerged conduits 16 were constituted of an ascending conduit 16a through which molten steel ascends to the vacuum chamber 14 from the ladle 12 and a descending conduit 16b through which molten steel descends to the ladle 12 from the vacuum chamber 14 where molten steel was decarburized. A vacuum pump 18 was connected to the vacuum chamber 14.

When backflow gas was provided from backfiow gas feeding means 22 to the ascending conduit 16a and the internal pressure of the vacuum chamber 14 was lowered to several or tens of torr by the operation of the vacuum pump 18, molten steel stored in the ladle ascended to the vacuum chamber 14 through the ascending conduit 16a while carrying out decarburizing reaction that carbon in molten steel reacts with oxygen, and then flown into the ladle 12 through the descending pipe 16b. As a result, the carbon content in molten steel was lowered.

As well known in the art, an oxygen feeding apparatus forcibly feeds oxygen to molten steel introduced into the vacuum chamber 14 in order to accelerate the above decarburizing reaction. As shown in Fig. 2, the oxygen feeding apparatus had an oxygen-blowing lance 24 exposed within the vacuum chamber 14 for blowing oxygen.

Further, the oxygen feeding apparatus was provided with cooling means for preventing the fracture or erosion of the oxygen-blowing lance 24 due to the high temperature within the vacuum chamber 14. According to cooling means, the oxygen-blowing lance 24 was assorted into a water-cooled blowing lance and an air-cooled blowing lance, of which each outer surface was provided with coolant and cooling air, respectively.

This had a problem containing a risk that the explosion of the vacuum chamber was resulted from the leakage of cooling water to molten steel when the water-cooled blowing lance was locally fractured or eroded due to the internal heat of the vacuum chamber.

In the meantime, as shown in Fig. 3, the air-cooled blowing lance 30 was constituted of an inner pipe 32 for blowing oxygen and an outer pipe 34 for surrounding the outer surface of the inner pipe 32, and the inner and outer pipes 32 and 34 were coaxial. In this case, cooling gas composed of inert gas was sprayed into the vacuum chamber through a space between the outer surface of the inner pipe and the inner surface of the outer pipe, thereby the end of the blowing lance 30 exposed within the vacuum chamber was cooled. Then, the gas of Ar is sprayed through the inner pipe 32 while continuously blowing cooling gas through the space in order to prevent molten drops dispersed from molten steel within the vacuum chamber 14 from contacting with the end of the spray lance 30 after stopping oxygen-feeding through the inner pipe 32. However, when the air-cooled spray lance 30 is used, cooling gas is continually fed into the vacuum chamber 14 through the space even after stopping the oxygen-feeding process through the inner pipe 32 as described above.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the foregoing problems and it is an object of the present invention to provide an oxygen-blowing lance for forcibly feeding oxygen in an RH vacuum refining apparatus, in which the oxygen-blowing lance has cooling means capable of effectively cooling the oxygen-blowing lance without worsening the degree of vacuum in the vacuum chamber and having no leakage of cooling water in order to improve decarburizing efficient from molten steel in the RH vacuum refining apparatus.

In order to obtain the above object, the invention provides an oxygen-blowing lance for feeding oxygen installed in an RH vacuum refining apparatus which includes a ladle for storing molten steel, a vacuum chamber arranged over the ladle and a submerged conduits defining circulation channel for the flow of molten steel between the ladle and the vacuum chamber, and the oxygen-blowing lance penetrates through the side wall of the vacuum chamber with a certain inclination angle; it is characterized in that the oxygen-blowing lance comprises an oxygen feeding pipe for blowing oxygen into the vacuum chamber; a tubular body which surrounds the outer surface of the oxygen feeding pipe and extends from a leading end of the oxygen feeding pipe exposed within the vacuum chamber toward the side wall of the vacuum chamber for a certain length, the tubular body being closed at both ends; and volatile liquid substance stored in a closed storage space defined between an inner surface of the tubular body and the outer surface of the oxygen feeding pipe, wherein the volatile liquid substance is evaporated due to the internal temperature of the vacuum chamber, and the evaporated gas substance is condensed due to the temperature outside the vacuum chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a conceptual view illustrating a conventional RH vacuum refining apparatus:

Fig. 2 is a conceptual view illustrating the vacuum refining apparatus with an oxygen-blowing lance installed in a vacuum chamber according to an embodiment of the prior art:

Fig. 3 is a sectional view illustrating the leading end of a typical oxygen-blowing lance:

Fig. 4 is a conceptual view illustrating an RH vacuum refining apparatus with an oxygen-blowing lance installed in a vacuum chamber according to an embodiment of the invention:

Fig. 5 is a front elevation view illustrating the vacuum chamber having the oxygen-blowing lance installed in the sidewall according to the embodiment of the invention: Fig. 6 is a sectional view of the oxygen-blowing lance according to the embodiment of the invention:

Fig. 7 is a sectional view taken along a line A-A in Fig. 6:

Fig. 8 is an enlarged view illustrating regions of the oxygen-blowing lance in which a bellows-type coupling is installed according to the embodiment of the invention: and

Fig. 9 is a graph illustrating temperature variations measured from the oxygen-blowing lance installed in the sidewall of the vacuum chamber according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description will disclose a preferred embodiment of the present invention with reference to Figs. 4 to 9, in which the same reference numerals as in the conventional art is used to designate the same or similar components. An RH vacuum refining apparatus 10 for manufacturing very low carbon steel has a ladle 12 for storing molten steel, a vacuum chamber 14 arranged over the ladle 12 and a circulation conduits 16 constituted of an ascending conduit 16a through which molten steel within the ladle 12 ascends to the vacuum chamber 14 and a descending conduit 16b through which molten steel descends to the ladle 12 after being decarburized in the vacuum chamber 14. The vacuum chamber 14, as shown in Fig. 5, is divided into an upper vessel 14a maintained in vacuum by a vacuum pump 18 and a lower vessel 14b into which molten steel flows through the ascending pipe 16a from the ladle 12. The outside wall of the vacuum chamber 14 is made of a steel sheath, and refractory are constructed inside the steel sheath. According to the present invention, an oxygen-blowing lance 40 for forcibly feeding oxygen into the vacuum chamber 14 is installed in a lower section of the upper vessel 14a and penetrates the refractory of the vacuum chamber 14 with a predetermined inclination angle θ.

Further, the oxygen-blowing lance 40 of the invention, as shown in Fig. 6, has an oxygen feeding pipe 42 for guiding the flow of oxygen so that oxygen fed from an oxygen feeding tank (not shown) is blown into the vacuum chamber 14. The oxygen-blowing lance 40 is provided with a cylindrical tubular body 44 which is sealed at both ends by an upper plate 44a fixed to the outer surface of the oxygen feeding pipe 42 placed in a refractory layer of the vacuum chamber 14 and a lower plate 44b. Between the outer surface of the oxygen feeding pipe and the inner surface of the tubular body, a storage space of a proper size is formed, in which volatile liquid substance 50 is provided. In the meantime, the upper plate 44a is provided with a vent pipe 46 connected to a vacuum pump (not shown) for ventilating air within the storage space so as to maintain the storage space at the atmospheric pressure or below, in particular, in the vacuum state. The vent pipe 46 is provided with a first valve 46a. Further, the upper plate 44a is provided with a volatile material-feeding pipe 48 for feeding the volatile liquid substance 50 into the storage space. The volatile material-feeding pipe 48 is provided with a second valve 48a.

As described above, in the oxygen-feeding pipe 42 with the tubular body 44 being fixed by the upper plate 44a and the lower plate 44b, a portion of the oxygen-feeding pipe 42 located in the storage space maintains a separated structure in order to prevent any damage due to thermal stress that will be described later. The first oxygen feeding pipe 42a and the second oxygen feeding pipe 42b resulted from the separated structure are connected to each other by installing a bellows-type coupling 52 in separated region of the first and second oxygen feeding pipes 42a and 42b. In order to prevent the leakage of oxygen through a clearance C between the opposed separated regions of the first and second oxygen feeding pipes 42a and 42b, a pipe 54 is provided in the separated regions inside the bellows-type coupling 52 to close the clearance C.

Referring to Fig. 8, both ends of the bellows-type coupling 52 are supported by the first stoppers 56a and 56b each of which is provided on the first and second oxygen feeding pipe 42a and 42b, respectively in order to help the smooth expansion and contraction of the oxygen feeding pipe 42 due to the thermal stress and the like and to prevent the release of the first oxygen feeding pipe 42a from the second oxygen feeding pipe 42b. Further, a lower portion of the pipe 54 is supported by the second stopper 56c provided on the outer surface of the first oxygen feeding pipe 42a within the bellows-type coupling 52 in order to effectively prevent the leakage of oxygen through the cleavage C.

As set forth above, the oxygen-feeding pipe 42 is installed with the predetermined inclination angle in the refractory layer of the vacuum chamber 14 so that the volatile liquid substance 50 stored in the storage space between the outer surface of the oxygen feeding pipe 42 and the inner surface of the tubular body 44 is gravitationally placed within the lower portion of the oxygen feeding pipe 42, i.e. on the lower plate 44b which is exposed within the vacuum chamber 14. In this case, the volatile liquid substance 50 is vaporized by the absorption of heat within the vacuum chamber 14, in particular, around the lower end of the oxygen-feeding pipe 42, and resultant gas moves toward an upper portion of the storage space, i.e. the upper plate 44a. In this case, since the temperature of the upper plate 44a become lower due to its placement adjacent to the steel sheath outside the vacuum chamber 14 having a relatively lower temperature, the vaporized gas moved toward the upper plate 44a is condensed. Resultant liquid material moves toward the lower plate 44b along the outer surface of the oxygen feeding pipe 42 and/or the inner surface of the tubular body 44.

A volatile liquid substance, which volatilizes due to the absorption of external heat, is selected by considering physical properties such as specific gravity, surface tension, viscosity and latent heat of vaporization; price; available temperature; material of the tubular body and the oxygen feeding pipe and so on.

The following Table 1 indicates melting point, boiling point and available temperature range for volatile liquid substances. Table 1

In the meantime, relative values for the materials being capable of the heat transfer can be indicated with Merit Number (M) and expressed as in Equation 1 : pσλ M = - — ... Equation 1, μ herein, p is specific gravity of volatile liquid substance, σ is surface tension of volatile liquid substance, λ is latent heat of vaporization, and μ is viscosity of volatile liquid substance.

In order to select a volatile liquid substance as mentioned above, it should be considered about price, available temperature and materials of tubular body and oxygen feeding pipe in addition to the physical properties. So, although Li is higher in Merit Number than other materials shown in Table 1, to use Li requires an expensive alloy that can endure Li. On the contrary, to use Na or K as the volatile liquid substance can utilize a relatively cheap stainless steel.

Table 2 indicates materials for the volatile liquid substances. Table 2

Therefore, the material forming the storage space for storing the volatile liquid substance as above is selected by considering compatibility to the volatile liquid substance, thermal conductivity, convenience of processing, wettability and so on.

In the meantime, the volatile liquid substance stored in the storage space is charged to occupy about 15 to 20% of the entire volume of the storage space.

Hereinafter, it will be described about the operation of the oxygen-blowing lance 40 of the invention.

First, the oxygen-blowing lance 40 of the invention penetrates the wall of the vacuum chamber of the RH vacuum refining apparatus 10 to be installed. The vent pipe 46 is connected to the vacuum pump that is not shown; the volatile material-feeding pipe 48 is connected to a volatile material storage tank (not shown). In the open state of the first valve 46a, the storage space defined between the oxygen-feeding pipe 42 and the tubular body 44 is maintained in vacuum as air contained therein is vented by the operation of the vacuum pump. If the second valve 46b is opened while the first valve 46a is closed, the volatile liquid substance 50 is introduced into the storage space from the volatile material storage tank. The second valve 48a is closed when the volatile liquid substance 50 is introduced for a designated amount.

In this case, water, methanol, Na, K and so on can be utilized as the volatile liquid substance 50 depending on the available temperature as set forth above. According to the invention, Na liquid can be used as the volatile liquid substance 50 by the consideration of the internal temperature of the vacuum chamber 14 in the RH vacuum refining apparatus 10, that is about 800 to 1200 ^°C . In general, Na has a melting point of about 98 ^°C and a boiling point of 892 ^°C under the atmospheric pressure. Therefore, the boiling point of Na descends in the storage space maintaining its pressure at the atmospheric pressure or below as described hereinafter. In this case, the Na liquid 50 in use is charged into the storage space as much as to occupy about 10 to 25%) of the entire storage space in a completely condensed state. If the quantity of the Na liquid is under 10%, the liquid exists at sides of the storage space by a large amount in a repeating process of evaporation and condensation so that the Na liquid may not exist in the bottom. At the quantity exceeding 25%, the Na liquid evaporates thereby reducing a reserved space necessary for the Na liquid to evaporate and move therein.

Therefore, the Na liquid 50 introduced into the storage space is positioned adjacent to the inside of the vacuum chamber 14 due to its weight. The Na liquid is evaporated due to heat inside the vacuum chamber 14, and Na gas moves toward the upper portion of the storage space, i.e. the upper plate 44a. That is to say, the Na gas moves upward due to the difference between the gas pressure at the surface of the Na liquid 50 and the gas pressure at the upper portion of the storage space. The upper portion of the storage space is maintained at a relatively lower temperature compared to the lower portion thereof so that the Na gas is condensed into the Na liquid 50, and the condensed Na liquid moves toward the lower plate 44b along the side defining the storage space. By repeating the evaporation and condensation as mentioned above, the Na liquid under the vacuum state absorbs heat during the evaporation to cool the surroundings. The evaporated gas moves upward due to the difference of the internal pressures, the gas contacts with cold regions in the upper portion to condense again while releasing heat, and then the condensed liquid drops downward again due to the gravitation. The Na liquid repeats the above cycle to cool hot regions in the lower portion.

By blowing oxygen into the vacuum chamber from the oxygen storage tank through the oxygen-blowing lance 40 cooled as described, erosion of the oxygen-blowing lance 40 can be prevented.

In the meantime, an unexplained reference numeral 43 in the drawings indicates a screen made of stainless steel that is fixedly installed on the outer surface of the oxygen-feeding pipe 42. The screen guides the Na liquid 50 condensed in the upper portion of the storage space to uniformly flow down across the entire outer surface of the oxygen-feeding pipe 42. The screen 43 is preferably sized for 150 mesh or less since the installation of the screen 43 having an excessively fine mesh prevents the Na gas from contacting with the relatively cold outer surface of the oxygen feeding pipe 42 through the screen. Further, an unexplained reference numeral 45 indicates a spring installed adjacent to the inner side of the tubular body 45. The spring 45 is manufactured with a diameter capable of contacting a pipe having about 6mm diameter to the inner surface of the tubular body 44. The spring 45 guides the evaporated Na gas to move toward the upper portion of the storage space along a spiral route while acts to help the condensed Na liquid 50 uniformly exist across the inner face of the tubular body 44. Therefore, the evaporated Na gas condenses by contacting with the outer surface of the oxygen feeding pipe 42 and the inner surface of the tubular body 44, and the condensed Na liquid 50 uniformly exists across the outer surface of the oxygen feeding pipe 42 and the inner surface of the tubular body 44 via the screen 43 and the spring 45. In particular, the spring 45 causes the upper surface of the Na liquid 50 stored in the lower portion of the storage space to slightly move upward across the inner surface of the tubular body 44 resultantly preventing the tubular body 44 from the formation of hot spots.

The oxygen-feeding pipe 42, the tubular body 44 and the upper and lower plates 44a and 44b used in the oxygen-blowing lance 40 of the invention are made of stainless steel. Although those materials compatible with the Na liquid used as the volatile liquid substance include stainless steel, Ni or Inconel 800 as shown in Table 2, stainless steel is most adequate considering the workability and price of material. Further, the screen 43 fixedly installed in the outer surface of the oxygen-feeding pipe 42 is manufactured with stainless steel. An inert gas of about 60Nm³/hr such as Ar gas is sprayed in order to prevent clogging of a blowing end of the oxygen feeding pipe due to dispersion of slag or molten steel inside the vacuum chamber 14 as well as to cool the blowing end while oxygen-blowing through the oxygen feeding pipe 42 is stopped. When the inert gas is blown through the oxygen feeding pipe 42 as above, the temperatures of the oxygen feeding pipe 42 and the tubular body 44 are maintained at substantially 500 to 650 ^°C without substantially temperature difference although they have fluctuation according to the conditions inside the vacuum chamber of the RH vacuum refining apparatus 10. In particular, the temperature of the oxygen-feeding pipe 42 and the tubular body 44 is substantially uniformly maintained due to the Na liquid in the storage space.

However, in the process of the RH vacuum refining operation, if Al is added to an upper portion of molten steel while blowing oxygen in order to elevate temperature, the heat generated in the oxidation of Al intermittently elevates the temperature of molten steel. The inside B of the leading end of the oxygen feeding pipe 42 has a relatively narrow diameter so that oxygen can be blown at supersonic speed in a flow rate condition 1200Nm³/hr of oxygen by the following reason: Oxygen can be easily dissolved into molten steel when blown at supersonic speed. That is, oxygen dissolved into molten steel reacts with Al to generate heat or reacts with C in molten steel to raise decarburizing efficiency.

In general, when gas is blown exceeding supersonic speed through a nozzle Mach number and the temperature of blown gas can be expressed according to Equation 2: rri -I ι = 1 + -J-Mά - Equation 2. Wherein T₀ indicates the initial temperature of gas, T indicates the gas temperature at a nozzle exit, Ma indicates Mach number (multiple of sonic speed), and k is the ratio of specific heat (1.4).

From Equation 2, it shall be understood that the right term becomes 1 if Mach number exceeds 1 and accordingly the gas temperature T at the nozzle exit is lowered than the initial temperature of gas Tn. Equation 2 means that the gas temperature is abruptly lowered while rapidly cooling around the nozzle.

As set forth above, while oxygen is sprayed with a blowing quantity of about 20 times larger than that of Ar which is used when oxygen is not blown, the temperature of the oxygen feeding pipe 42 descends more rapidly than the tubular body 44 due to a gas temperature descending effect according to the adiabatic expansion of gas at the above supersonic speed nozzle and a cooling effect of a large quantity of oxygen itself. Accordingly, internal stress takes place due to the difference in linear expansion between the oxygen feeding pipe 42 and the tubular body 44, in which a fragile region such as a welded region would break. Therefore, according to the preferred embodiment of the invention, the oxygen-feeding pipe 42 is separated at a proper portion, and the separated region is connected with the bellows-type coupling 52. The pipe 54 is installed to prevent a twisting phenomenon that is resulted from its movement due to the difference in linear expansion of the oxygen-feeding pipe 42. This accordingly prevents any fracture that may be incurred due to formation of the internal stress based upon the difference in linear expansion of the oxygen-feeding pipe 42.

Fig. 9 is a graph illustrating temperature variation measurements of the oxygen-blowing lance 40 installed in the sidewall of the vacuum chamber 14 of the invention. The oxygen-blowing lance 40 is preheated for two days, and then the temperature thereof is measured from a terminal time point of preheating. When about 1 hour and 40 minutes have lapsed after the measurement began, RH .vacuum refining process is started. Numbers marked in Fig. 9 indicate positions of thermocouples distanced from the leading end of the oxygen-feeding pipe. That is, 1cm in the graph indicates variation of the outer temperature of the tubular body 44 according to time lapse at a 1cm distanced position from the leading end. This shows that although the inside temperature of the vacuum chamber generally indicates about 800 to 1200 ^°C, the temperature of the inside wall is maintained at about 600 ^°C or below while the temperature of the leading end of the RH vacuum refining apparatus continuously ascends up to about 1000^°C . Further, the temperature of a 1cm distanced region from the leading end of the oxygen feeding pipe 42 is lowered to 520 ^°C from about 570 ^°C at the terminal point of preheating process even if Ar gas is blown at 80Nm³/hr through the oxygen feeding pipe while oxygen-blowing is stopped as above. However, comparing to the oxygen-blowing lance of the prior art having a leading end temperature of 1000^°C or higher, the oxygen-blowing lance of the invention maintains the leading end temperature of 600 ^°C or below thereby effectively preventing oxidation or erosion of the lance.

As set forth above, the invention can effectively cool the leading end of the oxygen-blowing lance without worsening the degree of vacuum in the vacuum chamber or having any risk of explosion due to the leakage of cooling water thereby prolonging the life time of the blowing lance and enhancing the oxygen-blowing efficiency.

Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions can be made without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

What is claimed is:

1. An oxygen-blowing lance for feeding oxygen installed in RH vacuum refining apparatus which includes a ladle for storing molten steel, a vacuum chamber arranged over the ladle and a submerged conduits defining circulation channel for the flow of molten steel between the ladle and the vacuum chamber, and the oxygen-blowing lance penetrates through the side wall of the vacuum chamber with a certain inclination angle; characterized in that the oxygen-blowing lance comprises: an oxygen-feeding pipe for blowing oxygen into the vacuum chamber; a tubular body for surrounding the outer surface of the oxygen feeding pipe and extending from a leading end of the oxygen feeding pipe exposed within the vacuum chamber toward the outside of the vacuum chamber for a length, the tubular body being closed at its both ends; and volatile liquid substance stored in a closed storage space defined between an inner surface of the tubular body and the outer surface of the oxygen-feeding pipe; wherein the volatile liquid substance is evaporated due to the internal temperature within the vacuum chamber, and evaporated gas substance is condensed due to the temperature outside the vacuum chamber.

2. The oxygen-blowing lance according to claim 1, characterized in that the volatile liquid substance has a boiling point of 600 to 800 ^°C under the atmospheric pressure.

3. The oxygen-blowing lance according to claim 1, characterized in that the volatile liquid substance is Na.

4. The oxygen-blowing lance according to claim 3, characterized in that the tubular body is made of stainless steel.

5. The oxygen-blowing lance according to claim 4, characterized in that the lance further comprises a spring installed along the longitudinal direction of the tubular body adjacent to its inner surface.

6. The oxygen-blowing lance according to claim 1, characterized in that the volatile liquid substance is K.

7. The oxygen-blowing lance according to claim 6, characterized in that the tubular body is made of stainless steel.

8. The oxygen-blowing lance according to claim 7, characterized in that the lance further comprises a spring installed along the longitudinal direction of the tubular body adjacent to its inner surface.

9. The oxygen-blowing lance according to claim 1, characterized in that the oxygen feeding pipe is separated at a certain portion to define separated oxygen feeding pipes which are connected by a bellows-type coupling.

10. The oxygen-blowing lance according to claim 1, characterized in that the storage space is ventilated to maintain its pressure at the atmospheric pressure or below.