Title of Invention

LANCE SYSTEM, METALLURGICAL FURNACE USING THE SAME, AND LANCE POSITIONING METHOD

Technical Field

[0001] The present invention relates to a lance system to be used in a metallurgical furnace, such as an electric furnace or a converter, and also relates to a metallurgical furnace using the same, and a lance positioning method.

[0002] A metallurgical furnace, such as an electric furnace, which is used to melt or refine metal material, such as steel, is provided with a lance for blowing reactant gas, such as oxygen gas, onto the surface of molten metal in the furnace. Such a lance is designed to be moved up and down by an up/down drive mechanism so as to be positioned at an adequate height depending on the surface level of the molten metal (Japanese Patent Application Publication No. 8-176639 (JP 8-176639 A)). In the field of converters, a method of determining the distance between a lance and the surface of molten metal has been proposed, in which microwaves are used (Japanese Patent Application Publication No. 2009-97035 (JP 2009-97035 A)).

Summary of Invention

Problems to be Solved by the Invention

[0003] While the electric furnace is in operation, however, it is often difficult to determine the surface level of the molten metal because a large amount of slag is present on the surface of the molten metal, for example. For this reason, in a case where a large amount of slag is present, a method has been used, in which the surface level of the molten metal is determined from the amount of fed solid metal material to determine the position of the tip of the lance based on the surface level, for example. However, the accuracy in determining the surface level of the molten metal is not always so high and therefore, the tip of the lance cannot be positioned to an adequate position in some cases. Moreover, the adequate distance between the surface of the molten metal and the tip of the lance itself has been empirically determined by repeating operations and may therefore be inadequate from the viewpoint of chemical reactions. It has therefore been difficult to maintain the reaction state, in which the molten metal and the reactant gas react with each other, within a certain range even when the surface level of the molten metal, that is, the distance between the lance and the surface of the molten metal is accurately determined, because whether the position of the lance relative to the surface of the molten metal is optimal or not from the viewpoint of chemical reactions depends on the properties of the molten metal and the reactant gas, the blowing conditions, etc. In particular, in the case of an electric furnace that continuously melts solid metal material, it is further difficult to keep the tip of the lance at the adequate position because the surface level of the molten metal varies with time.

. . .. Means for Solving the Problems ^{.. ... ...}

[0004] The present invention has been made in view of the above circumstances and an object of the present invention is to provide a lance system capable of positioning a lance for blowing reactant gas to an adequate position independently of the absolute position of the surface of the molten metal in a metallurgical furnace, and provide a metallurgical furnace using the lance system and a lance positioning method.

[0005] A first aspect of the present invention is a lance system for blowing reactant gas onto molten metal in a metallurgical furnace, the lance system including: a lance configured to blow the reactant gas; a driving mechanism configured to move the lance toward and away from a surface of the molten metal; and a detector configured to detect a parameter indicating a reaction state, in which the reactant gas and the molten metal react with each other in a striking region, in which the reactant gas blown toward the surface of the molten metal strikes the surface of the molten metal, wherein the lance system is configured so as to position the lance to an adequate position based on a value of the parameter indicating the reaction state, which value is supplied from the detector.

[0006] It is preferable that the lance system according to the above first aspect further include: a controller configured to control the driving mechanism to position the lance to the adequate position, based on the value of the parameter. It is preferable that the controller be configured to determine a transition position of the lance, at which the reaction state suddenly changes, from a variation curve of the value of the parameter with respect to the position of the lance, and to position the lance to the adequate position based on information on the transition position.

[0007] It is preferable that, in the lance system according to the above first aspect, the detector be configured to detect the parameter optically. It is preferable that the detector include an optical fiber for detecting light from the striking region, and a measurement unit for measuring the parameter based on information obtained through the optical fiber. It is preferable that the optical fiber be inserted in a passage hole for the reactant gas provided in the lance. It is preferable that the measurement unit be provided at a proximal end portion of the lance.

[0008] It is preferable that, in the lance system according to the first aspect, the detector include a camera that shoots the striking region. It is preferable that the camera be provided at a proximal end portion of the lance.

[0009] It is preferable that, in the lance system according to the above first aspect, the detector be provided at a location away from the lance. It is preferable that the parameter in the striking region be selected from a group consisting of a temperature of the molten metal, an intensity of light, a spectrum of light, and an intensity of a particular wavelength of light. It is preferable that the reactant gas be oxygen gas.

[0010] A second aspect of the present invention is a metallurgical furnace that includes: a melting chamber for storing the molten metal; and the lance system according to the above first aspect that blows the reactant gas onto the molten metal in the melting chamber.

[001 1] It is preferable that the metallurgical furnace according to the above second aspect be an electric furnace for melting solid metal material with the use of an electric arc. It is preferable that the electric furnace be configured so that the solid metal material is continuously fed into the melting chamber and the solid metal material is continuously melted.

[0012] A third aspect of the present invention is a lance positioning method of positioning a lance for blowing reactant gas onto molten metal in a metallurgical furnace, the method including: bringing the lance closer to a surface of the molten metal while blowing the reactant gas; detecting a parameter indicating a reaction state, in which the reactant gas arid the molten metal react with each other in a striking region, in which the reactant gas strikes the surface of the molten metal; and positioning the lance to an adequate position based on a value of the parameter indicating the reaction state.

[0013] It is preferable that the lance positioning method according to the above third aspect further include: determining a transition position of the lance, at which the reaction state suddenly changes, from a variation curve of the value of the parameter with respect to the position of the lance; and positioning the lance to the adequate position based on information on the transition position. It is preferable that the parameter be detected optically.

Advantageous Effects of Invention

[0014] In the present invention, reactant gas is blown onto a molten metal surface through the lance, the parameter indicating the reaction state of the reactant gas and the molten metal in the striking region on the molten metal surface is detected, and the adequate position of the lance in blowing reactant gas is determined using the fact that the value of this parameter greatly varies at or near the adequate position for the lance to blow the reactant gas. Consequently, it is possible to consistently position the lance to the adequate position independently of the absolute position (height) of the molten metal surface. Moreover, since the parameter indicating the reaction state of the reactant gas and the molten metal is used, the position of the lance, at which it is possible to blow reactant gas so as to actually cause the reactant gas and the molten metal to efficiently react with each other, is determined from the value of this parameter, so that it is possible to improve the reactivity between the reactant gas and the molten metal.

Brief Description of Drawin S

[0015]

FIG. 1 is a sectional view showing an electric furnace (electric arc furnace) that functions as a metallurgical furnace, to which a lance system according to an embodiment of the present invention is applied.

FIG. 2 is a sectional view showing a structure of a lance of the lance system according to the embodiment of the present invention.

FIG. 3 A is a schematic diagram showing an operating situation of the lance, in which blowing of oxygen is started when the lance is at a retracted position (Situation 1).

FIG. 3B is a schematic diagram showing an operating situation of the lance, in which the lance is being lowered while blowing oxygen (Situation 2).

FIG. 3C is a schematic diagram showing an operating situation of the lance, in which the temperature in a striking region on a surface of molten steel reaches the hot-spot temperature (Situation 3).

FIG. 4 is a diagram showing a relation between the temperature in the striking region and the position of the lance in the Situations 1 to 3 shown in FIGS.

3A to 3C.

FIG. 5 is a sectional view showing a lance system according to another embodiment of the present invention.

FIG. 6 is a sectional view showing a lance system according to still another embodiment of the present invention.

Description of Embodiments [0016] An embodiment of the present invention will now be described with reference to the accompanying drawings. This embodiment shows a case where the present invention is applied to an electric furnace (electric arc furnace), in which cold iron source such as iron scrap, used as solid metal material, is continuously fed into a melting furnace and heated and melted by arc electrodes.

[0017] FIG. 1 is a sectional view showing the electric furnace (electric arc furnace) that functions as a metallurgical furnace, to which a lance system according to the embodiment of the present invention is applied. The electric furnace 1 includes a melting chamber 2 for melting the cold iron source such as iron scrap by electric arcs, and a shaft-type preheating chamber 3 for preheating the cold iron source that is directly connected to part of an upper portion of the melting chamber 2. The inside of an iron shell of the melting chamber 2 is lined with a refractory material. The iron shell of the preheating chamber 3 is water-cooled.

[0018] A furnace roof 4 designed to be opened and closed is provided on part of the upper portion of the melting chamber 2, which part is the other than the region of the preheating chamber 3. Three electrodes 5 are vertically inserted in the melting chamber 2, passing through the furnace roof 4 from above the melting chamber 2. The electric arcs generated by applying alternating voltage from a power source (not shown) to the electrodes 5 heat molten steel 8;, and preheat and melt the cold iron source 7 in the melting chamber 2, which is turned into the molten steel 8. Slag 9 is formed on the molten steel 8 and the electric arcs are formed in the slag 9. A tap hole (not shown) is provided in a bottom portion of the melting chamber 2.

[0019] A feed port 10 for feeding the cold iron source 7 is provided at a top end portion of the preheating chamber 3. An open/close gate 1 1 is provided inside the feed port 10. The cold iron source 7 is fed from a cold iron source feeder (not shown) into the preheating chamber 3 through the feed port 10. An exhaust portion 12 connected to an exhaust gas suction system (not shown) is provided at an upper portion of the preheating chamber 3.

[0020] The electric furnace 1 of this embodiment has a lance system 20 that is used to, for example, perform a refining process, such as decarhonization, or help melt the cold iron source by blowing oxygen gas as reactant gas from above the molten steel 8 in the melting chamber 2. The lance system 20 includes: a lance 21 that blows oxygen gas in the form of a jet of oxygen; a detector 22 for detecting a parameter indicating a reaction state, in which the oxygen and the molten steel react with each other in a striking region, in which the oxygen jet blown from the lance 21 toward the molten steel surface strikes the molten steel surface; a position sensor 23 for detecting the position of the tip of the lance 21 relative to a fixed point in the electric furnace 1 ; a cylinder mechanism 24 that functions as a driving mechanism for driving the lance 21 ; and a controller 25 that determines an adequate position of the lance 21 and controls the position of the lance 21, based on the information obtained through the detector 22 and the position sensor 23.

[0021] The parameter indicating the reaction state of the oxygen and the molten steel in the striking region is such that the value of the parameter varies depending on the reaction state when oxygen is blown onto the molten steel and reacts with a component in the molten steel, such as carbon. As the parameter, one of a temperature in the striking region, an intensity of light from the striking region, a spectrum of light from the striking region, and an intensity of a particular wavelength of light from the striking region, for example, or a combination thereof may be used.

[0022] Note that another lance system for blowing carbon material as an auxiliary heat source may be provided in addition to the lance system 20. A stroke sensor, an optical position sensor, etc. may be used as the position sensor 23. The driving mechanism for driving the lance 21 is not limited to the cylinder mechanism 24. Another mechanism, such as a gear motor, may be used as the driving mechanism.

[0023] The lance 21 is obliquely disposed with respect to the molten steel surface and supported by a cylinder portion of the cylinder mechanism 24 via a supporting portion 26. The lance 21 is configured to be able to be moved toward and away from the molten steel surface along a guide member (not shown) by driving the cylinder mechanism 24.

[0024] As shown in FIG. 2, the lance 21 has an oxygen gas passage hole 31 therein and is designed to blow a jet of oxygen from a nozzle 32 at a tip portion of the lance 21 to the molten steel surface. The detector 22 has an optical fiber 27 for detecting the light from the striking region, at which the oxygen jet strikes the molten steel surface, and a measurement unit 28, connected with the optical fiber 27, for measuring the parameter indicating the reaction state of the oxygen and the molten steel in the striking region, based on the information obtained through the optical fiber 27. The optical fiber 27 is inserted in the oxygen gas passage hole 31 of the lance 21 and extended so that the tip of the optical fiber 27 is positioned near the nozzle 32, that is, near the molten steel surface. The measurement unit 28 is attached at a proximal end portion of the lance 21.

[0025] The detector 22 is an optical fiber radiation thermometer, for example. In this case, the parameter indicating the reaction state of the oxygen gas and the molten steel in the striking region of the oxygen jet is the temperature in the striking region. Specifically, the light emitted from the striking region of the oxygen jet is detected via the optical fiber 27 to measure the temperature in the striking region in the measurement unit 28 based on the radiant intensity of the light.

[0026] The reaction state of the oxygen gas and the molten steel varies with the distance between the nozzle 32 of the lance 21 and the striking region on the molten steel surface. As shown in FIG. 3 A, the lance 21 is first at a retracted position above the molten steel surface, at which blowing of oxygen is started (Situation 1). As the nozzle 32 of the lance 21 approaches the molten steel surface while blowing oxygen as shown in FIG. 3B (Situation 2), the value of the parameter indicating the reaction state in the striking region 33 increases. When the distance between the nozzle 32 and the striking region is further reduced as shown in FIG. 3C (Situation 3), the temperature in the striking region 33 reaches hot-spot temperature (2,200°C, for example). It is considered that, when the position of the lance 21 is near the position, at which the Situation 3 is reached, the lance 21 is at an adequate position, at which it is possible to blow oxygen so that oxygen efficiently reacts with the molten steel 8.

[0027] The parameter indicating the reaction state in the striking region 33, such as the temperature in the striking region 33, varies with the position of the lance 21 as shown in FIG. 4, for example. Specifically, when the lance is brought closer to the molten steel surface while blowing oxygen, the temperature in the striking region 33 suddenly rises at a point in time and then, the temperature levels off when the hot spot appears. Accordingly, the adequate position of the lance 21 is determined, at which it is possible to blow oxygen under favorable conditions in terms of reaction efficiency, based on this variation in temperature. The temperature variation curve shown in FIG. 4 shifts left or right depending on the amount of oxygen blown. However, the mode of variation, or the form of the curve, does not change depending on the amount of oxygen blown.

[0028] Accordingly, when oxygen is blown onto the molten steel surface to cause reaction, it is possible to determine the adequate position of the lance 21 independently of the amount of oxygen blown, based on the variation in temperature as shown in FIG. 4.

[0029] In the case where the intensity of light, the spectrum of light, or the intensity of a particular wavelength of light is used, for example, as the parameter indicating the reaction state of the oxygen and the molten steel in the striking region, at which the oxygen jet strikes the molten steel surface, a device suitable to detect such a parameter may be used as the measurement unit 28 of the detector 22.

[0030] Operation of the electric furnace 1 thus configured will next be described. The cold iron source 7, such as iron scrap, is charged into the melting chamber 2 and the preheating chamber 3 to make a situation, in which the cold iron source 7 is continuously present both in the melting chamber 2 and in the preheating chamber 3.

[0031] Electric arcs are formed by applying voltage between the cold iron source 7 in the melting chamber 2 and the electrodes 5 in this situation to melt the cold iron source 7. When the cold iron source 7 in the melting chamber 2 melts and a certain amount of molten steel is formed in the melting chamber 2, oxygen is blown onto the surface of the molten steel 8 via the lance 21 in order to perform a refining process, such as decarbonization, or help melt the cold iron source. During this process, the oxygen and the carbon in the molten steel react with each other to produce CO, C0 ₂ , etc. The gas thus produced is discharged through the preheating chamber 3 and the exhaust portion 12 and the heat of this exhaust gas preheats the cold iron source 7 in the preheating chamber 3. When the cold iron source 7 melts in the melting chamber 2, the cold iron source 7 in the preheating chamber 3 is fed into the melting chamber 2, so that it is possible to continuously melt the cold iron source 7 in the melting chamber 2.

[0032] As the cold iron source 7 in the preheating chamber 3 is fed into the melting chamber 2, the upper end level of the cold iron source 7 in the preheating chamber 3 descends. For this reason, in order to maintain the situation, in which the cold iron source 7 is continuously present both in the melting chamber 2 and in the preheating chamber 3, the cold iron source 7 is continuously or intermittently fed into the preheating chamber 3 through the feed port 10.

[0033] It is necessary to position the lance 21 to an adequate height in accordance with the level of the molten steel surface. However, it is in some cases difficult to determine the absolute level (height) of the molten steel surface while the electric furnace 1 is in operation because there is a large amount of slag on the molten steel surface. In such a case, for example, a method of determining the position of the tip of the lance based on the height of the molten steel surface estimated from the amount of cold iron source that has already been fed, has been adopted. This method, however, cannot maintain the position of the tip of the lance at an adequate position in some cases. Moreover, the height of the molten steel surface (molten steel level) varies with time and it is further difficult to keep the tip of the lance at the adequate position in such a type of electric furnace 1 that continuously melts the cold iron source as in the case of this embodiment.

[0034] In this embodiment, an adequate position of the lance 21 is determined by detecting the parameter indicating the reaction state of the oxygen and the molten steel in the striking region, in which the oxygen jet strikes the molten steel surface, when the oxygen is blown through the lance 21 and the molten steel surface is exposed. Specifically, blowing of oxygen is started when the lance 21 is at a retracted position above the molten steel surface as shown in FIG. 3 A (Situation 1). The lance 21 is lowered and brought closer to the molten steel surface while blowing oxygen as shown in FIG. 3B (Situation 2). As a result, the parameter indicating the reaction state of the oxygen and the molten steel in the striking region 33, such as the temperature in the striking region 33, suddenly rises at a point in time as shown FIG. 4. When the distance between the nozzle 32 and the striking region 33 is then further reduced as shown in FIG. 3C and the position (hereinafter referred to as "hot-spot position"; Situation 3) is reached, at which the temperature in the striking region 33 reaches the hot-spot temperature (2,200°C, for example), the temperature in the striking region 33 levels off as shown in FIG. 4. It is considered that, when the position of the lance 21 is near the hot-spot position, the lance 21 is at an adequate position, at which it is possible to blow oxygen so that oxygen efficiently reacts with the molten steel 8. For this reason, the transition position of the present invention is determined based on the variation curve of the value of the parameter with respect to the position of the lance as shown in FIG. 4, the transition position being the position of the lance when it is determined that the temperature in the striking region 33 reaches or becomes close to the hot-spot temperature, or when the temperature variation to be exhibited near the hot-spot temperature is detected. The lance 21 is positioned to an adequate position based on the information on this transition position. Note that it is possible to determine, in a similar way, an adequate position of the lance 21 with the use of another parameter than the temperature, such as the intensity of light from the striking region, the spectrum of light from the striking region, or the intensity of a particular wavelength of light from the striking region.

[0035] The electric furnace 1 continuously melts the cold iron source, so that the level of the molten steel surface rises with time. However, since it is possible to calculate the speed of rise of the molten steel surface based on the operating conditions, such variation in level of the molten steel surface can be handled by raising the lance 21 at a predetermined speed of rise determined from the operating conditions in accordance with the command sent from the controller 25. In this way, even when the level of the molten steel surface rises during blowing of oxygen, it is possible to maintain the distance between the tip of the lance 21 and the striking region on the molten steel surface to blow oxygen under favorable conditions in terms of reaction efficiency.

[0036] Alternatively, after the position of the lance 21 is determined by detecting the value of the parameter, such as the temperature in the striking region, or the variation thereof as described above, detection of the value of the parameter or the variation thereof may be continued to feed-back control the position of the lance 21 so that the detected value is consistently maintained within an appropriate range. This also makes it possible to maintain the distance between the tip of the lance 21 and the striking region on the molten steel surface to blow oxygen under favorable conditions in terms of reaction efficiency when the level of the molten steel surface rises during blowing of oxygen.

[0037] In this embodiment, the cold iron source 7 is continuously melted as described above and, when a certain amount of molten steel (the amount ' corresponding to one charge, for example) accumulates in the melting chamber 2, the melting chamber 2 is tilted to tap the molten steel to a ladle or the like through a tap hole (not shown).

[0038] Since the level of the surface of the remaining molten steel is different between before and after tapping, it is preferable that positioning of the lance 21 using the parameter indicating the reaction state as described above be performed again after tapping.

[0039] In this embodiment, as described above, oxygen is blown onto the molten steel surface through the lance 21 , the parameter indicating the reaction state of the oxygen and the molten steel in the striking region on the molten steel surface is detected, and the adequate position of the lance 21 in blowing oxygen is determined using the fact that the value of this parameter greatly varies at or near the adequate position for the lance to blow oxygen. Consequently, it is possible to consistently position the lance 21 to the adequate position independently of the absolute position (height) of the molten steel surface. Moreover, since the parameter indicating the reaction state of the oxygen and the molten steel is used, the position of the lance, at which it is possible to blow oxygen under actually favorable conditions in terms of reaction efficiency, is determined from the value of this parameter, so that it is possible to improve the reactivity between the oxygen and the molten metal.

[0040] Moreover, in this embodiment, the efficiency in preheating the cold iron source with the use of exhaust gas is high because the cold iron source 7 is fed into the preheating chamber 3 so as to maintain the situation, in which the cold iron source 7 is continuously present both in the melting chamber 2 and in the preheating chamber 3, and the cold iron source 7 is continuously present both in the melting chamber 2 and in the preheating chamber 3 also when a certain amount of molten steel is formed in the melting chamber 2 and the molten steel is tapped.

[0041] The present invention is not limited to the above embodiment and various modifications can be made. For example, while the detector that has an optical fiber extended so that the tip of the optical fiber is positioned near the nozzle, that is, near the molten steel surface, and a measurement unit for measuring the parameter indicating the reaction state, is used in the above embodiment, the present invention is not limited to this configuration. A configuration as shown in

FIG. 5 may be adopted, in which a camera 34 capable of shooting the striking region of the oxygen jet is provided as the detector at a proximal end portion of the lance 21 to shoot the striking region of the oxygen jet through the oxygen gas passage hole 31. The optical fiber and the camera may be used in combination.

[0042] While the detector is attached to the lance 21 in the above embodiment, the present invention is not limited to this configuration. As shown in FIG. 6, a detector 36 for detecting the parameter in the striking region 33, in which the oxygen jet strikes the molten steel surface, may be provided at a position other than the lance 21.

[0043] While the above embodiment shows an example embodiment, in which steel is used as solid metal material and oxygen gas is used as reactant gas, the solid metal material and the reactant gas are not limited to them. While the above embodiment illustrates, as an example of a metallurgical furnace, an electric furnace that continuously melts the cold iron source, which is solid metal material, the present invention may be applied to a conventional electric furnace. Moreover, the present invention is not limited to electric furnaces as long as the furnace refines metal material by blowing reactant gas onto the molten metal. The present invention can be applied to various applications, such as converters, vacuum oxygen decarburization (VOD) furnaces, or RH (Ruhrstahl-Heraeus) vacuum degassing furnaces for performing the Ruhrstahl-Heraeus oxygen blowing (RH- OB) process. .

[0044] The timing to perform the operation to determine the adequate position of the lance by detecting the parameter indicating the reaction state, such as the temperature in the striking region, is not limited to that of the above embodiment. The operation may be performed as needed.

Reference Signs List

[0045]

1 ; electric furnace (metallurgical furnace)

2; melting furnace

3 ; preheating chamber

4; furnace roof

5; electrode

7; cold iron source

8; molten steel

9; slag

10; feed port

20; lance system

21 ; lance 22, 36; detector

23; position sensor

24; cylinder mechanism

25; controller

27; optical fiber

28; measurement unit 31 ; oxygen gas passage hole 32; nozzle

33; striking region

34; camera