Device for measuring electrode length of carbon electrode in electric resistance melting furnace, and method for operating electric resistance melting furnace

Abstract

The present invention more accurately measures the electrode length of a carbon electrode (10) in an electric resistance melting furnace. The present invention comprises a guide pipe (20) that is configured by connecting a plurality of metal guide pipe pieces (21) and that is inserted so as to reach the lower end of the carbon electrode (10), and a distance meter (30) that is installed on the upper end of the guide pipe (20) and that comprises a microwave or millimeter wave transceiving means and a waveguide, wherein: the inner diameter of the guide pipe (20) is greater than the inner diameter of the waveguide (35) of the distance meter (30); the guide pipe (20) and the distance meter (30) are coupled via a tapered structure (40), which has a hollow that widens in a tapered shape from the waveguide (35) toward the guide pipe (20); a microwave or millimeter wave is transmitted from the lower end of the guide pipe (20) toward a molten liquid surface (200) of a material to be melted; and the distance between the distance meter (30) and the molten liquid surface (200) is measured by receiving a microwave or millimeter wave reflected by the molten liquid surface (200).

Description

Device for measuring the electrode length of carbon electrodes in an electric resistance melting furnace and method for operating an electric resistance melting furnace

[0001] The present invention relates to a device for measuring the electrode length of carbon electrodes in an electric resistance melting furnace used to melt iron ore or other materials introduced into the furnace, and also to a method for operating the electric resistance melting furnace.

[0002] Electric resistance melting furnaces are used in which materials to be melted, such as iron ore, are introduced into a furnace, carbon electrodes are inserted into the piled materials, electricity is applied to melt the materials, and the molten material is recovered. Fig. 12 is a schematic diagram showing an example of an electric resistance melting furnace, illustrating the case of melting iron ore. As shown in the figure, in an electric resistance melting furnace 100, carbon electrodes 101 are inserted into iron ore 102 piled up in the furnace, and a current is passed through the carbon electrodes 101. The iron ore 102 present between the electrodes acts as a resistor, and the iron ore 102 is melted by Joule heat. Power is supplied to the carbon electrodes 101 from a power source 110 via an electrode holder 180 attached to the carbon electrodes 101. As the melting progresses, three layers are formed at the bottom of the furnace: unmelted iron ore 102, molten slag layer 103, and molten iron layer 104, from top to bottom. The molten slag is collected from the slag discharge port 105, and the molten iron is collected from the tapping port 106.

[0003] In this case, an electrode lifting device 120 is used to raise and lower the carbon electrode 101 in the vertical direction in the figure while passing current through the carbon electrode 101. Therefore, it is necessary to detect the molten liquid level of the molten iron layer 104 to determine the electrode length of the carbon electrode 101 and control the raised and lowered position of the carbon electrode 101.

[0004] Therefore, in Patent Document 1, the applicant inserts a metal guide pipe into at least one carbon electrode, reaching the lower end of the carbon electrode, attaches a microwave or millimeter wave transmitter / receiver to the upper end of the guide pipe, transmits microwaves or millimeter waves from the transmitter / receiver through the inside of the guide pipe, receives the microwaves or millimeter waves reflected by the lower end of the guide pipe, detects the molten iron layer's liquid level, and determines the electrode length of the carbon electrode from the distance from the transmitter / receiver to the molten iron level.

[0005] Japanese Patent No. 5671744

[0006] However, because the guide pipe is made of metal, if the material to be melted is a metal with a high melting point, such as iron ore, its lower end will melt away due to the high heat from the molten liquid surface. The inner wall of the carbon electrode is exposed where the guide pipe melts away, and this exposed carbon absorbs microwaves and millimeter waves, significantly attenuating the transmitted and received power. This raises concerns that the molten liquid surface may not be detected accurately, and the electrode length of the carbon electrode may not be measured accurately.

[0007] The present invention has been made in consideration of the above circumstances, and aims to more accurately detect the molten liquid level and more accurately measure the electrode length of the carbon electrode in an electric resistance melting furnace even if the metal guide pipe melts down.

[0008] In order to solve the above problems, the present invention provides the following (1) to (11) devices for measuring the electrode length of carbon electrodes in an electric resistance melting furnace.

[0009] (1) A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace in which a carbon electrode hanging down into the furnace is inserted into a material to be melted piled up in the furnace and an electric current is passed through the carbon electrode to melt the material, the device comprising: a guide pipe formed by connecting a plurality of metal guide pipe pieces and inserted so as to reach the lower end of the carbon electrode; and a range finder attached to the upper end of the guide pipe and comprising microwave or millimeter wave transmitting / receiving means and a waveguide, wherein the inner diameter of the guide pipe is larger than the inner diameter of the waveguide of the range finder, and the guide pipe and the range finder are connected via a tapered structure having a cavity that tapers from the waveguide toward the guide pipe, the device transmits the microwaves or millimeter waves from the lower end of the guide pipe toward the molten liquid surface of the material to be melted, receives the microwaves or millimeter waves reflected at the molten liquid surface, and measures the distance between the range finder and the molten liquid surface. (2) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), in which the guide pipe pieces are connected to each other with a threaded socket. (3) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), in which the guide pipe pieces are connected to each other with a taper union having an outer shape in which two tapered surfaces extending continuously from a central portion having a maximum diameter to both ends are formed. (4) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), in which the connection between the tapered structure and the guide pipe is closed with a member made of a material that is transparent to the microwaves or millimeter waves. (5) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), in which an inert gas is supplied to the guide pipe to increase the internal pressure, and when the internal pressure suddenly rises, it is determined that the guide pipe is in a blocked state and the amount of the inert gas supplied is increased to remove the blocked portion. (6) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), wherein a metal plate having holes with an opening diameter that does not allow microwaves or millimeter waves to penetrate, or a wire mesh with an opening size that does not allow microwaves or millimeter waves to penetrate, is attached to the inert gas supply port to the guide pipe.(7) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), which transmits the microwaves or millimeter waves as circularly polarized waves toward the molten liquid surface. (8) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), which has a measurement mode for measuring the electrode length of the carbon electrode multiple times and calculating the average value. (9) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), which has a measurement mode for measuring the electrode length of the carbon electrode multiple times and calculating the average value of either or both of the obtained received beat waveforms and a distance spectrum waveform obtained by FFT processing of the received beat waveforms. (10) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), which is made of stainless steel. (11) The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace according to (1), which observes reflected signals appearing at equal distances on the guide pipe.

[0010] In order to solve the above problems, the present invention also provides the following operating method (12).

[0011] (12) A method for operating an electric resistance melting furnace, in which a carbon electrode hanging down into the furnace is inserted into a material to be melted piled up in the furnace, and current is passed through the carbon electrode to melt the material to be melted, comprising the steps of: determining a distance (L1) from the range finder to the molten liquid surface using an electrode length measuring device for a carbon electrode described in any one of (1) to (11); placing a second range finder above the range finder and measuring a separation distance (L2) between the range finder and the second range finder; calculating a distance (L3) from the second range finder to the molten liquid surface by adding up the separation distance (L2) and the determined distance (L1); and controlling a hanging position of the carbon electrode based on the distance (L3).

[0012] In the following description, the "device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace" will also be simply referred to as the "measuring device."

[0013] According to the measuring device of the present invention, even if the metal guide pipe melts down, the molten liquid level can be detected and the electrode length of the carbon electrode can be measured more accurately.

[0014] Furthermore, according to the operating method of the present invention, even if the metal guide pipe melts, the electrode length of the carbon electrode can be measured more accurately, so that the raising and lowering of the carbon electrode can be controlled more accurately, enabling efficient and stable operation.

[0015] FIG. 1 is a cross-sectional view schematically illustrating the configuration of an embodiment of the measuring device of the present invention, taken along the axis of a carbon electrode. FIG. 2 is an enlarged view of a threaded socket. FIG. 3 is an enlarged view of a tapered structure and a plug member. FIG. 4(A) is a partial enlarged view of portion A in FIG. 1, FIG. 4(B) is a partial enlarged view of portion B in FIG. 1, and FIG. 4(C) is a partial enlarged view of portion C in FIG. 1. FIG. 5(A) is a cross-sectional view of a tapered union, and FIG. 5(B) is a plan view taken from the A-A direction of FIG. 5(A). FIG. 6(A) is a side view of a set screw, and FIG. 6(B) is a plan view taken from the B-B direction of FIG. 6(A). FIG. 7 is a schematic diagram illustrating the rotation direction of the electric field during transmission and reception when circularly polarized microwaves or millimeter waves are used. FIG. 8 is a chart illustrating the results of Verification Result 1. FIG. 9 is a chart illustrating the results of Verification Result 2. FIG. 10 is a chart illustrating the results of Verification Result 3. Fig. 11 is a diagram for explaining the method of operating the electric resistance melting furnace of the present invention, and Fig. 12 is a schematic diagram showing an example of an electric resistance melting furnace.

[0016] The present invention will now be described in detail with reference to the drawings.

[0017] As shown in Figure 12, in an electric resistance melting furnace, multiple carbon electrodes are inserted into the material to be melted, such as iron ore, and electricity is passed through the carbon electrodes to melt the material. In the present invention, at least one carbon electrode functions as a "device for measuring the electrode length of the carbon electrodes."

[0018] [Measurement Apparatus] Fig. 1 is a cross-sectional view showing the configuration of the measurement apparatus of the present invention, taken along the axis of a carbon electrode. As shown in the figure, the measurement apparatus 1 has a typical carbon electrode 10, a metal guide pipe 20 inserted therethrough, the metal guide pipe 20 reaching the lower end of the carbon electrode 10, and a rangefinder 30 attached to the upper end of the guide pipe 20.

[0019] The carbon electrode 10 comprises an electrode body 18 housed within a cylindrical metal electrode case (metal cover) 15. The electrode body 18 of the carbon electrode 10 is divided into an electrode baking section 18a, a coal tar melting section 18b, and an electrode material section 18c, in order from the side closest to the molten liquid surface 200 of the material to be melted. When the material to be melted is melted, the side of the electrode baking section 18a that contacts or faces the molten liquid surface 200 (hereinafter referred to as the "lower end") is consumed. To compensate for this consumption, a mixture of carbon blocks and coal tar pitch, which serves as the electrode material, is poured into the opening at the top of the electrode case 15. The electrode case 15 is made up of multiple electrode case pieces (metal cover pieces) 16 joined together to form a single piece. Because the lower end is consumed during melting, a new electrode case piece (metal cover piece) 16b is added on top of the lower electrode case piece (metal cover piece) 16a. Reference numeral 17 denotes the joints between the electrode case pieces 16.

[0020] The guide pipe 20 is made up of multiple guide pipe pieces 21 connected together using joints 22, and like the carbon electrode 10, the lower end is consumed when melted, so a new guide pipe piece 21b is connected above the lower guide pipe piece 21a using the joint 22. When connecting the guide pipe piece 21, a guide pipe clamp 25 is used to separate the tapered structure 40 (described later) and the guide pipe 20 and then reconnect them.

[0021] The joint 22 (see Figure 1) is preferably a threaded socket 70 as shown in Figure 2. The threaded socket 70 has a thread groove 71 formed on its inner peripheral surface, and accordingly, thread grooves 23 are formed on the outer peripheral surface of each end of the guide pipe piece 21 so as to engage with the thread groove 71 of the threaded socket 70. By using the threaded socket 70, the guide pipe piece 21 can be reliably connected and linearity can be achieved when multiple guide pipe pieces 21 are connected.

[0022] The electrode case piece 16 of the carbon electrode 10, the guide pipe piece 21 of the guide pipe 20, and the joint 22 are preferably made of a metal with a higher melting point. For example, SUS304 is suitable as such a metal because it is inexpensive, has excellent workability and environmental resistance, and does not rust. SUS304 prevents a decrease in propagation loss due to deterioration in the quality of the material, enabling stable measurements.

[0023] It is preferable that the waveguide 35 and tapered structure 40, which will be described later, are also made of SUS304.

[0024] The range finder 30 is equipped with a microwave or millimeter wave transmitting / receiving means (not shown) and is connected to the upper end of the guide pipe 20 via a tapered structure 40. As shown in Figures 1 and 3, the inner diameter of the guide pipe 20 is larger than the inner diameter of the waveguide 35 of the range finder 30, and the tapered structure 40 is a member having a tapered cavity 41 that widens from the tip of the waveguide 35 of the range finder 30 toward the upper end of the guide pipe 20. The tapered structure 40 is connected to the guide pipe 20 by, for example, a threaded socket 70.

[0025] The cross sections of the guide pipe 20, the waveguide 35 and the tapered structure 40 may also be square in addition to circular.

[0026] Microwaves and millimeter waves propagate well through the guide pipe 20 and even through the portion where the guide pipe 20 has melted (the exposed surface 12, described below), allowing for more accurate measurement of the electrode length of the carbon electrode 10. It is preferable that the inner diameter of the guide pipe 20 be larger than the inner diameter of the waveguide 35, but this may result in increased costs if the guide pipe 20 becomes too thick. Specifically, when using millimeter waves of 79 GHz and the inner diameter of the waveguide 35 is φ2.8 mm, the inner diameter of the guide pipe 20 is preferably φ35.0 to 38.0 mm, which is several dozen times larger. In the case of a carbon electrode that is not self-baking, the electrode length is measured using a circular hole drilled directly to the bottom end of the carbon electrode in place of the guide pipe 20.

[0027] 3, it is preferable to close the connection between the tapered structure 40 and the guide pipe 20 with a plug 50 made of a material that transmits the detection wave, such as a fluororesin. The plug 50 protects the internal components of the rangefinder 30, such as the transmitting and receiving means, because the internal components are exposed to high heat from the molten liquid surface 200 and dust from inside the furnace can enter through the guide pipe 20.

[0028] The detection wave is a microwave or a millimeter wave, but a higher frequency is preferable, and a millimeter wave is more preferable.

[0029] In the measuring device 1 configured as described above, the lower end of the carbon electrode 10 is worn away, and at the lower end of the guide pipe 20, a part of the guide pipe 20 and the joint 22 are melted down due to the high heat from the molten liquid surface 200, exposing the interface with the carbon electrode 10. For example, Fig. 4(A) is an enlarged view of part A in Fig. 1, Fig. 4(B) is an enlarged view of part B in Fig. 1, and Fig. 4(C) is an enlarged view of part C in Fig. 1, where Fig. 4(A) shows the part where the guide pipe 20 has begun to melt down and the interface with the carbon electrode 10 is beginning to appear, Fig. 4(B) shows the part where the joint 22 has melted down, and Fig. 4(C) shows the part where the guide pipe 20 has melted down.

[0030] As shown in Figure 4(A), the cross-sectional shape changes at the beginning of the burn-through of the guide pipe 20, but since the inner diameter of the guide pipe 20 is sufficiently larger than the wall thickness of the guide pipe 20, it can be said that this does not substantially affect the measurement. In Figure 4(A), the portion where the cross-sectional shape changes as the guide pipe 20 burns through is stepped, but the step does not have to be in the same horizontal position around the entire inner diameter, and may be different in the vertical direction in the figure. As shown in the figure, in the portion closer to the molten liquid level 200 than the lower half of portion A, the guide pipe 20 and the joint 22 burn through, and the interface with the carbon electrode 10 is exposed, as indicated by the reference numeral 12.

[0031] In the following description, the portion of the carbon electrode 10 exposed by the melting of the guide pipe 20 and the joint 22 will be referred to as the "exposed surface 12."

[0032] Normally, when microwaves or millimeter waves propagate through a carbon tube, the low electrical conductivity of the wall surface results in large propagation losses, resulting in the absorption of transmitted and received signals. Because the exposed surface 12 is made of carbon, the microwaves and millimeter waves are significantly attenuated while propagating through the exposed surface 12. However, as described above, by making the inner diameter of the guide pipe 20 larger than the inner diameter of the waveguide 35 and minimizing the excitation of unnecessary higher-order modes other than the circular TE11 mode that constitutes circularly polarized waves, propagation of the circular TE11 mode is primarily maintained, thereby reducing propagation losses and degradation of distance measurement accuracy.

[0033] Therefore, as shown by the symbol M in FIG. 1 , microwaves and millimeter waves from the transmitting / receiving means of the range finder 30 propagate through the waveguide 35, the cavity 41 of the tapered structure 40, and the guide pipe 20, and further propagate favorably through the exposed surface 12 without significant attenuation, before being transmitted from the lower end of the guide pipe 20 to the melt surface 200. The waves are then reflected by the melt surface 200, travel the reverse path, and are received by the transmitting / receiving means of the range finder 30, thereby detecting the melt surface 200. The distance from the range finder 30 to the melt surface 200, i.e., the electrode length of the carbon electrode 10, can be determined from the time difference between transmission and reception. Conventionally, microwaves and millimeter waves are significantly attenuated by the exposed surface 12. However, the measuring device 1 of the present invention suppresses attenuation by the exposed surface 12, making it possible to more accurately detect the melt surface 200 and determine the electrode length of the carbon electrode 10.

[0034] As described above, the detection wave propagates well through the exposed surface 12 with low attenuation. To further improve propagation, it is also preferable to use a tapered union 80 as the coupling 22, as shown in Figure 5. Figure 5(A) is a cross-sectional view of the tapered union 80, and Figure 5(B) is a plan view taken from the A-A direction in Figure 5(A). As shown in Figure 5(A), the tapered union 80 is formed in a cylindrical shape with a predetermined width and a central portion 81 having the maximum outer diameter. Two tapered surfaces 82 are formed extending continuously from the central portion 81 to both ends, giving the entire coupling a roughly barrel-shaped outer shape.

[0035] Furthermore, a stepped stopper 83 with the same width as the wall thickness of the guide pipe piece 21 protrudes in an annular shape from the inner peripheral surface of the center of the longitudinal direction of the taper union 80, and the guide pipe piece 21 is inserted so that its end abuts against the stopper 83. Here, because the stopper 83 has the same thickness as the guide pipe piece 21, it does not interfere with the propagation of microwaves or millimeter waves.

[0036] The longitudinal dimensions H1 and H2 of the central portion 81 and tapered surface 82 of the tapered union 80 are preferably equal to or greater than the wavelength of the microwave or millimeter wave. The length H2 of the two tapered surfaces 82 may be the same or different.

[0037] The maximum outer diameter D of the tapered union 80 is preferably set to a dimension that does not generate higher modes of microwaves or millimeter waves.

[0038] Furthermore, as shown in Fig. 5(B), a plurality of threaded holes 85 for attaching set screws 90 shown in Fig. 6 are formed at equal intervals along the circumferential direction in the central portion 81 of the taper union 80, penetrating all the way to the inner circumferential surface. Fig. 6(A) is a side view showing the set screw 90, and Fig. 6(B) is a plan view seen from the direction B-B in Fig. 6(A).

[0039] The set screw 90 has a longitudinal length L that is longer than the thickness of the central portion 81 of the taper union 80, and has a thread 91 formed on its outer circumferential surface that engages with the threads of the screw hole 85 of the taper union 80. A hexagonal hole 95 is formed on one end face. The set screw 90 is made of the same material as the taper union 80 and the guide pipe piece 21.

[0040] To connect the guide pipe piece 21 using such a tapered union 80 and set screw 90, the guide pipe piece 21 is inserted until it abuts against the stopper 83 of the tapered union 80, and then the set screw 90 is attached to the threaded hole 85 of the tapered union 80 and screwed in until the end face of the set screw 90 reaches the outer peripheral surface of the guide pipe piece 21, thereby fixing the guide pipe piece 21. Thereafter, the portion of the set screw 90 protruding from the threaded hole 85 of the tapered union 80 is cut off with a sander or the like, and the outer peripheral surface of the tapered union 80 is processed to eliminate any irregularities.

[0041] By using the tapered union 80 as the joint 22, the step portion 12a on the exposed surface 12 shown in FIG. 4B is eliminated, and the reflection of microwaves and millimeter waves by the step portion 12a is eliminated.

[0042] The measuring device 1 is configured as described above, but various modifications are possible. For example, as shown in FIG. 1, nitrogen gas (N ２ It is preferable to increase the internal pressure of the guide pipe 20 by supplying nitrogen gas or inert gas. Since the lower end of the guide pipe 20 is open, molten metal may flow in, and increasing the internal pressure of the guide pipe 20 prevents this. Also, the lower end of the guide pipe 20 may melt and block the guide pipe 20, causing a sudden rise in the internal pressure of the guide pipe 20. When a sudden rise in internal pressure is detected, the amount of nitrogen gas or inert gas supplied can be increased to remove any material (blockage) stuck in the guide pipe 20. The internal pressure is adjusted by a pressure regulator 60. Reference numeral 61 denotes a pressure gauge.

[0043] 3, a metal inert gas intake member 65 having a large number of fine holes 63 may be attached to the inlet 62 for nitrogen gas or an inert gas into the guide pipe 20. Although not shown, the inert gas intake member 65 may be a wire mesh. The opening diameter of the fine holes 63 is set to a diameter that prevents microwaves and millimeter waves from penetrating while facilitating the flow of the inert gas; for example, for millimeter waves of 79 GHz, the opening diameter is set to approximately 1.5 mm. The mesh size of the wire mesh is also set to a similar size. The inert gas intake member 65 can prevent microwaves and millimeter waves from leaking from the inlet 62.

[0044] It is also preferable to use circularly polarized microwaves or millimeter waves M'. As shown in Figure 7, the rangefinder 30 comprises a receiving circuit 31, a transmitting circuit 32, and a circular polarizer 33. The receiving circuit 31 receives linearly polarized waves with a different electric field orientation from the linearly polarized waves transmitted from the transmitting circuit 32. By utilizing this characteristic, the receiving circuit 31 and the transmitting circuit 32 can be separated and the circular polarizer 33 can be interposed between them and the waveguide 35, thereby improving the accuracy of signal processing.

[0045] 7, the arrows indicate the direction of the electric field of the detection wave M' in each part of the measurement device 1. The receiving circuit 31 and the transmitting circuit 32 both receive or transmit linearly polarized waves in which the electric field is oriented in one direction. When a received signal of circularly polarized waves in which the electric field direction is reversed passes through the circular polarization generator 33, the effect of the circular polarization generator 33 causes the signal to become linearly polarized waves in which the electric field direction is different from that of the transmitted wave.

[0046] Then, a circularly polarized wave generator 33 generates microwaves or millimeter waves M whose electric field direction is rotated in one direction (clockwise in the figure) from the transmission circuit 32. Ｏ ' is sent to the tapered structure 40 through the waveguide 35, and propagates through the guide pipe 20 and further through the exposed surface 12 of the carbon electrode 10 while remaining a right-handed electric field, and is transmitted toward the melt surface 200.

[0047] Microwaves and millimeter waves with circular polarization (right-handed circular polarization or positive circular polarization) in which the electric field rotates clockwise relative to the propagation direction. Ｏ' is a left-handed circularly polarized microwave or millimeter wave M, which, when reflected by the melt surface 200, has a left-handed electric field rotation direction with respect to the propagation direction of the microwave or millimeter wave. ｒ The left-handed circularly polarized wave is then sent to the range finder 30 via the exposed surface 12 of the carbon electrode 10, the guide pipe 20, the tapered structure 40, and the waveguide 35, and travels backward through the circular polarizer 33. At this time, the circular polarizer 33 converts the wave into a linearly polarized wave with a different electric field direction from the transmitted linearly polarized wave, and the wave is received by the receiving circuit 31.

[0048] In this way, by using circularly polarized microwaves or millimeter waves M', the receiving circuit 31 receives the microwaves or millimeter waves M from the transmitting circuit 32. Ｏ Microwaves and millimeter waves with different electric fields from ｒ Since only the transmitted wave and the received wave are received, the measurement accuracy can be improved significantly because the transmitted wave and the received wave can be almost completely separated.

[0049] Furthermore, in order to reduce the noise level and increase the S / N ratio, measurements are repeated multiple times (N times) and the average value is calculated, thereby reducing the floor noise power by 1 / N.

[0050] Alternatively, the floor noise power can be reduced by 1 / N by performing multiple measurements and averaging either or both of the received beat waveform and the distance spectrum waveform obtained by FFT processing of the received beat waveform.

[0051] (Verification Result 1) In imitation of the measuring device 1 in Figure 1, six SUS304 pipes with a total length of 2 m were connected as guide pipe pieces to create a SUS304 guide pipe with a total length of 12 m. An iron plate representing the molten iron surface was then used to cover the opening at one end of the SUS304 guide pipe, and millimeter waves were transmitted from the waveguide of a rangefinder attached to the other end to measure the signal strength at each distance. The results are shown in Figure 8.

[0052] In the chart shown, the peaks in signal strength are due to minute reflections at the joints of the SUS304 pipe. These peaks appear regularly every 2 m, and an equivalent peak appears at a distance of 12 m, indicating that the millimeter waves propagate throughout the entire length of the SUS304 guide pipe.

[0053] Furthermore, since peaks can be detected every 2 m, which correspond to the joints of the guide pipe pieces, by observing the peaks that appear at equal distances and the fixed reflections that appear further away, it is possible to estimate the locations of blockages within the guide pipe or locations where guide pipe pieces have come loose.

[0054] (Verification Result 2) A carbon pipe with the same diameter and total length of 2 m was connected to one end of a SUS304 guide pipe equivalent to that in Verification Result 1, and the opening of the carbon pipe was covered with an iron plate. The carbon pipe corresponds to the exposed surface 12 of the carbon electrode 10 in the measuring device 1 in Figure 1. Millimeter waves were then transmitted from the waveguide of a rangefinder attached to the other end of the SUS guide pipe, and the signal strength was measured at each distance. The results are shown in Figure 9.

[0055] In the chart shown, similar to Verification Result 1, peaks appear every 2 m, corresponding to the SUS304 guide pipe. A peak due to the joint also appears at a distance of 12 m, where the SUS304 guide pipe and the carbon pipe join. Furthermore, a peak also appears at a distance of 14 m, where the steel plate blocks the carbon pipe, indicating that the millimeter waves also propagate through the carbon pipe.

[0056] (Verification Result 3) As in Verification Result 2, a carbon pipe was connected to a SUS304 guide pipe, and an iron plate was placed 1 m away from the opening of the carbon pipe. Millimeter waves were then transmitted from the waveguide of a rangefinder attached to the other end of the SUS304 guide pipe, and the signal strength was measured at each distance. The results are shown in Figure 10.

[0057] In the chart shown, similar to Verification Result 2, peaks appear every 2 m, corresponding to the SUS304 guide pipe and the carbon pipe. A peak also appears at a distance of 15 m, 1 m from the carbon pipe, indicating that the millimeter waves propagate through the carbon pipe and even through the air. This indicates that stable measurements can be made even from the bottom end where the guide pipe 20 has melted away, propagating through the exposed surface 12.

[0058] In the above verification results, peaks due to the joints of the SUS304 guide pipe pieces are observed, so by counting the number of peaks in the measurement device 1, the number of guide pipe pieces 21 and the overall length of the guide pipe 20 can be determined. Furthermore, since peaks of the reflected wave appear every 2 m, the position of the joints can be measured without correction. This indicates that the signal velocity (group velocity) of the circular TE11 mode is approximately equal to the speed of light (plane wave velocity). This indicates that the inner diameter of the guide pipe 20 is sufficiently large compared to the inner diameter of the waveguide 35.

[0059] [Operation Method] The present invention also relates to a method for operating an electric resistance melting furnace using the above-mentioned measuring device 1. First, as shown in Fig. 11, the measuring device 1 is used to measure the distance (L1) of the guide pipe 20, i.e., the electrode length of the carbon electrode 10, from the distance meter 30.

[0060] Furthermore, a plate-shaped position measuring member 38, for example, is attached to the range finder 30, and a second range finder 210 is installed above the range finder 30 to measure the separation distance (L2) between the second range finder 210 and the range finder 30. A general microwave or millimeter wave range finder can be used as the second range finder 210, which transmits microwaves or millimeter waves from an antenna 220 toward the position measuring member 38, receives the microwaves or millimeter waves reflected by the position measuring member 38, and calculates the separation distance (L2) from the time difference.

[0061] Then, the distance (L1) and the separation distance (L2) are added together to determine the distance (L3), and the hanging position of the carbon electrode 10 is controlled based on the distance signal of the distance (L3).

[0062] Since the carbon electrode 10 is consumed by melting and gradually shortens, it is necessary to gradually lower the carbon electrode 10 accordingly. Therefore, as described above, the second distance meter 210 is fixed to a place where the height does not change, such as the ceiling of the furnace equipment, as a reference position, and the hanging position of the carbon electrode 10 can be controlled by knowing the distance (L3) from this reference position to the bottom end of the carbon electrode 10.

[0063] This will enable more stable operations.

[0064] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0065] This application is based on a Japanese patent application (Patent Application No. 2023-115847) filed on July 14, 2023, the contents of which are incorporated herein by reference.

[0066] 1 Measuring device 10 Carbon electrode 12 Exposed surface 12a Step portion 15 Electrode case (metal cover) 16, 16a, 16b Electrode case piece (metal cover piece) 18 Electrode body 18a Electrode baking portion 18b Coal tar molten portion 18c Electrode material portion 20 Guide pipe 21, 21a, 21b Guide pipe piece 22 Joint (joint) 23, 71 Thread groove 25 Guide pipe clamp 30 Rangefinder 31 Receiving circuit 32 Transmitting circuit 33 Circularly polarized wave generator 35 Waveguide 38 Position measuring member 40 Tapered structure 41 Cavity 50 Plug member 60 Pressure regulator 62 Inlet 63 Hole 65 Inert gas intake member 70 Threaded socket 80 Tapered union 81 Central portion 82 Tapered surface 83 Stopper 85 Screw hole 90 Set screw 91 Screw 95 Hexagonal hole 120 Electrode lifting device 200 Melt surface 210 Second range finder 220 Antenna

Claims

1. A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace in which a carbon electrode suspended within the furnace is inserted into a material to be melted accumulated in the furnace and an electric current is passed through the carbon electrode to melt the material, the device comprising: a guide pipe formed by connecting multiple metal guide pipe pieces and inserted so as to reach the lower end of the carbon electrode; and a range finder attached to the upper end of the guide pipe and comprising a microwave or millimeter wave transmitting and receiving means and a waveguide, wherein the inner diameter of the guide pipe is larger than the inner diameter of the waveguide of the range finder, and the guide pipe and the range finder are connected via a tapered structure having a cavity that tapers from the waveguide toward the guide pipe, the device transmits the microwaves or millimeter waves from the lower end of the guide pipe toward the molten liquid surface of the material to be melted, receives the microwaves or millimeter waves reflected at the molten liquid surface, and measures the distance between the range finder and the molten liquid surface.

2. The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, wherein the guide pipe pieces are connected to each other by a threaded socket.

3. A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, in which the guide pipe pieces are connected to each other by a taper union having an outer shape in which two tapered surfaces extending continuously from the central part, which is the maximum diameter, to both ends are formed.

4. A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, wherein the connection between the tapered structure and the guide pipe is closed with a member made of a material through which the microwaves or millimeter waves are transparent.

5. A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, which supplies an inert gas to the guide pipe to increase the internal pressure, and when the internal pressure suddenly rises, determines that the guide pipe is blocked, and increases the supply of the inert gas to remove the blocked portion.

6. A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, wherein a metal plate having holes with an opening diameter that does not allow microwaves or millimeter waves to penetrate, or a wire mesh with openings that does not allow microwaves or millimeter waves to penetrate, is attached to the inert gas supply port to the guide pipe.

7. An apparatus for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, wherein the microwaves or millimeter waves are circularly polarized and transmitted toward the molten liquid surface.

8. The device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, further comprising a measurement mode for measuring the electrode length of the carbon electrode multiple times and calculating the average value.

9. A device for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, comprising a measurement mode for measuring the electrode length of the carbon electrode multiple times and averaging either or both of the obtained received beat waveform and a distance spectrum waveform obtained by FFT processing of the received beat waveform.

10. The electrode length measuring device for a carbon electrode in an electric resistance melting furnace as described in claim 1, wherein the guide pipe is made of stainless steel.

11. An apparatus for measuring the electrode length of a carbon electrode in an electric resistance melting furnace as described in claim 1, which observes reflected signals appearing at equal distances on the guide pipe.

12. A method of operating an electric resistance melting furnace, in which a carbon electrode that hangs down into the furnace is inserted into a material to be melted that has piled up inside the furnace, and electricity is passed through the carbon electrode to melt the material, comprising the steps of: determining a distance (L1) from the distance meter to the molten liquid surface using an electrode length measuring device for a carbon electrode as described in any one of claims 1 to 11; locating a second distance meter above the distance meter and measuring a distance (L2) between the distance meter and the second distance meter; determining a distance (L3) from the second distance meter to the molten liquid surface by adding up the distance (L2) and the determined distance (L1); and controlling the hanging position of the carbon electrode based on the distance (L3).

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