JP2003155508A - Instrument for measuring potential difference at bottom in blast furnace and method for estimating pig iron slag height in blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an instrument with which pig iron slag height in a blast furnace can accurately be estimated. SOLUTION: The instrument for measuring potential difference at the furnace bottom in the blast furnace has the peculiarity with which a plurality of measuring points 11 are arranged on a bottom brick 2 in the blast furnace with an interval in the vertical direction, and lead wires 12 extending from the potential measuring points 11 to the outer part of the blast furnace body are arranged, and the potential difference between the potential measuring points 11 by using the lead wires 12 is measured. The lead wire 12 is made to abut a sheath part 21 at the tip part of a metallic sheath thermocouple 20 inserted from the outer part of the blast furnace body to the potential measuring point 11 on the bottom brick 2 and extend the sheath part of the metallic sheath thermocouple 20 from the potential measuring point 11 to the outer part of the blast furnace body. The pig iron slag height is estimated based on the potential difference measured with the instrument for measuring the potential difference at the furnace bottom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blast furnace bottom potential difference measuring device for evaluating a pig slag level in a blast furnace, a pig slag level evaluation method, and a blast furnace bottom potential measuring contact.

[0002]

2. Description of the Related Art In a blast furnace, iron ore, which is a raw material, is supplied into the furnace body from the furnace top together with coke, and the temperature is raised by the hot air pressure-fed from the tuyere into the furnace body. Become. The hot metal is stored at the bottom of the furnace, and the molten slag (slag) is stored in contact with the hot metal. The position in the height direction of the part where the molten metal is present in the upper part of the molten metal stored in the blast furnace is called the molten metal level here.

With the passage of time, the amount of hot metal stored in the bottom of the furnace increases, and the level of pig iron rises. When the tap hole provided at the bottom of the furnace is opened, the hot metal and the slag are led out of the furnace through the tap hole, and the level of the slag inside the furnace is lowered.

In the operation of a blast furnace, it is important to understand the level of pig iron in the furnace in order to determine the tapping cycle and to carry out stable and economical operation. When the slag level rises and the slag level rises above a certain level, the blast pressure fluctuation increases and it becomes impossible to maintain a stable operating state.In particular, if the slag level rises to the blast tuyere level, the slag will be generated. The tuyere is blocked and it becomes impossible to operate. In order to stabilize the in-furnace condition that became unstable due to excessive rise of slag level, it is necessary to take measures such as increasing the amount of coke input and changing the amount of hot air, leading to an increase in operating costs. It will be.

In general, the level of pig iron in a furnace can be roughly estimated from the mass balance between the production and discharge of pig iron. For example, the amount of pig iron produced can be calculated from the amount of charge and its components charged into the blast furnace per unit time, and the amount of hot metal discharged can be determined by measuring the weight change of the torpedo car containing the hot metal, The amount of slag discharged can be estimated by measuring the weight of the slag produced from slag using a scale conveyor, etc. Therefore, the increase in the amount of slag in the furnace can be estimated from the difference between the amount of slag generated and the amount of discharged slag.

In Japanese Patent Laid-Open No. 7-150210, a tap computer acceleration is calculated using a process computer, and it is determined whether the present tapping situation belongs to an initial period, a stable period, a late period, or an ending period, Although a method of predicting the pig iron end time has been disclosed, this method is also a technique that basically uses the method for estimating the amount of residual iron in the furnace based on the above mass balance.

However, in the method for estimating the amount of residual slag in the furnace based on the mass balance, the amount of slag production is calculated on the assumption that the charged ores immediately melt, but it takes at least several hours before melting. In addition to the above, since the calculation is performed based on the component analysis value, an error occurs due to the accuracy, representativeness, variation, etc. of the analysis value.

Further, the amount of discharged pig iron is not measured by direct weighing of slag or the like, but the amount after slag turning is measured by a scale conveyor or the like, and the error is at least about 10%. It is said that. Therefore, when estimating the pig iron level from the material balance, it is essential to take measures with a large safety allowance, assuming a large error.

On the other hand, as a method of measuring the pig iron level using a pig iron detector without using the method for estimating the amount of pig iron residue in the furnace based on the mass balance, Japanese Patent Laid-Open No. 53-86242 discloses, for example. On the hearth wall of the blast furnace, a plurality of rod-shaped graphite electrodes consisting of an anode and a cathode are arranged in the height direction to electrically form a circuit and energize the molten iron to form a pair of rod-shaped graphite electrodes. A method of measuring the pig iron level by detecting the conduction upon contact with a pilot lamp or an ammeter is disclosed. This method requires at least a pair of electrodes to be inserted and placed in the furnace so as to be in contact with the slag in order to measure the energization of the slag, so the solidification formed by cooling the slag on the electrode surface. It is difficult to obtain reliable measurement data of the level of slag in the furnace because the energization state changes due to the fluctuation of the layer and its thickness. Further, in this method, since the electrode is installed at the bottom of the furnace by penetrating the furnace wall, when the electrode is melted, the hot metal may flow out from that part, which may cause a serious accident such as damage to the furnace bottom.

Further, in JP-A-59-140309, at least one pair of electrodes is provided on a brick forming a furnace wall near the furnace bottom of a blast furnace, and a resistance measuring system (double bridge system) by a four-terminal measuring method is used. A method of forming an electric circuit and measuring a pig iron level from a measured value of electric resistance is disclosed.
This method measures the electrical resistance of bricks and slag,
Changes in the conductivity of bricks due to the deterioration of bricks over time and the infiltration of pigs into the bricks, and the conductivity of pigs caused by the temperature of the pigs near the bricks and the solidification or flow state of the pigs Due to fluctuations, the measured electrical resistances of bricks and slag fluctuate, and it is difficult to obtain reliable measurement data of the slag level in the furnace.

It is known that a potential difference is detected between two positions in the height direction on the surface of the iron shell near the bottom of the blast furnace, and the potential difference is related to the level of slag in the blast furnace. Develo
pment & application of new techniques for blast fu
rnace process control at SSAB Tunnplant, Lulea wor
ks. 1995 Ironmaking conference Proceedings pp271-
According to 279, as a result of measuring the electric potential difference using the furnace surface of the furnace bottom and the tuyere upper part as the measurement point, there is a correlation between the start and end intervals of tapping and the temporal fluctuation of the measured electric potential difference. The points are listed. The detected potential difference is around 0.2 mV, and the potential difference increases by about 0.1 mV while the taphole is closed, and the potential difference is 0.1 mV while the taphole is opened and tapping is performed. It decreases and returns to the original.

[0012]

In the method for detecting the level of slag from the potential difference observed on the surface of the iron shell of the blast furnace, the potential difference detected is a weak value of 1 mV or less, so that the influence of noise is reduced. It is easy to receive. In addition, even if it was estimated that the slag level was the same, there was a difference in the value of the potential difference, and it was difficult to immediately estimate the slag level from the potential difference on the surface of the iron skin.

It is an object of the present invention to provide a method and an apparatus capable of accurately estimating a pig iron level in a blast furnace.

[0014]

Means for Solving the Problems A plurality of potential measuring points are provided at intervals in the height direction on a bottom brick inside a blast furnace body, and the potential difference between the potential measuring points is measured to be about 5 mV. It is clear that the potential difference significantly changes in the range of about 5 mV with the change of the pig iron level in the blast furnace. Compared with the potential difference detected on the surface of the iron shell of a conventionally known blast furnace body, both the value of the potential difference and the variation amount of the potential difference due to the variation of the pig iron level are higher by about one digit. Therefore, the error due to the influence of noise becomes very small, and it becomes possible to estimate the pig iron level with high accuracy compared with any conventionally known method.

The present invention was made on the basis of the above findings, and the gist thereof is as follows. (1) A plurality of potential measurement points 11 are provided on the bottom brick 2 of the blast furnace at intervals in the height direction, a conductor 12 extending from the potential measurement points 11 to the outside of the blast furnace body is provided, and the potential is measured using the conductor 12. A blast furnace bottom potential difference measuring device characterized by measuring a potential difference between points 11. (2) Among the plurality of potential measuring points 11, at least one mounting position is set to a level of taphole 3 or higher, and at least one mounting position is set to a level of taphole 3 or lower. The blast furnace bottom potential difference measuring device according to (1). (3) The blast furnace bottom potential difference measuring device according to (1) or (2) above, wherein the potential measurement point 11 is provided on the surface of the blast furnace bottom brick 2. (4) Metal sheath thermocouple 20 inserted from outside the furnace body of the blast furnace
The tip sheath part 21 of the
1. The blast furnace according to any one of the above (1) to (3), wherein the sheath portion of the metal sheath thermocouple 20 is in contact with the wire 1 and extends from the potential measuring point 11 to the outside of the blast furnace body. Bottom potential difference measuring device. (5) The blast furnace according to (4) above, wherein the distal sheath portion 21 of the sheath thermocouple is brought into contact with the potential measurement point 11 by the pressing force applied to the sheath thermocouple 20 using the pressing mechanism 22. Furnace bottom potential difference measuring device. (6) A slag level evaluation method, characterized in that the slag level in the blast furnace is evaluated based on the potential difference measured by the blast furnace bottom potential difference measuring device according to any one of (1) to (5) above. (7) The temperature of the electric potential measurement point 11 is measured using the sheath thermocouple 20, and the pig iron level evaluation is corrected based on the measured temperature, and the pig iron level described in (6) above is added. Evaluation methods. (8) Metal sheath thermocouple 20 inserted from outside the furnace body of the blast furnace
Connect the tip sheath portion 21 of the No. 1 to the potential measurement point 1 of the blast furnace bottom brick 2
The contact point 10 for measuring the bottom potential of the blast furnace, which is in contact with 1, is capable of measuring the potential at the potential measuring point 11 using the sheath portion of the metal sheath thermocouple 20 outside the furnace body of the blast furnace. A blast furnace bottom potential measuring contact characterized in that the temperature at the potential measuring point 11 can be measured by the thermocouple 20. (9) The blast furnace according to (8) above, characterized in that the distal sheath portion 21 of the sheath thermocouple is brought into contact with the potential measurement point 11 by the pressing force applied to the sheath thermocouple 20 using the pressing mechanism 22. Contact for measuring bottom potential.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, a furnace bottom brick 2 is built inside a steel shell 1 to form an inner structure near the furnace bottom of a blast furnace. A stave 5 is provided or a stamp material 6 is filled between them. In the present invention, the bottom brick 2 is provided with a plurality of potential measurement points 11. In order to measure the electric potential using the electric potential measuring point 11, a conducting wire 12 extending from the electric potential measuring point 11 to the outside of the blast furnace body is provided. Iron skin 1, stave 5, stamp material 6
An opening for passing the lead wire 12 is provided in the. The lead wire 12 contacts the hearth brick 2 at the potential measurement point 11,
It is guided to the outside so as not to establish conduction with the iron skin 1, the stave 5, the stamp material 6, etc., and another conductor 14 is connected to the conductor 12 outside the furnace body of the blast furnace, and a plurality of voltmeters 13 are used. The potential difference between the potential measurement points 11 is measured.

A plurality of potential measuring points 11 are provided at intervals in the height direction. This is because the potential difference effective for evaluating the pig iron level is generated in the height direction of the blast furnace. Since the potential difference is measured, it is necessary to have at least two. If three or more potential measurement points are provided over three locations in the height direction, it is possible to add the potential distribution in the blast furnace height direction to the evaluation. Is.

If the mounting positions of the plurality of potential measurement points in the height direction are arranged so as to sandwich the boundary surface between the hot metal and the slag, a preferable result can be obtained for evaluating the slag level from the potential difference measurement value. . Specifically, if at least one mounting position is set to be equal to or higher than the level of the taphole 3 and at least one mounting position is set to be less than the level of the taphole 3, the level of the pig iron residue is evaluated. It is preferable for measuring potential difference. In FIG. 1A, the potential measuring contacts 10 a and 10 b are arranged below the level of the tap hole 3, and the potential measuring contacts 10 c are arranged above the level of the tap hole 3.

The location of the potential measuring points 11 in the blast furnace radial direction on the hearth brick 2 may be provided on the surface of the hearth brick on the outermost side as shown in FIG. 3 (a).
As shown in (b), the non-through hole 30 is provided in the hearth brick 2, and the back end of the non-through hole 30 is set as the potential measurement point 11, that is, the potential measurement point is provided inside the bottom brick 2. May be. Providing the non-through hole 30 in the bottom brick 2
It is not preferable because the bottom of the brick tends to be damaged by leakage of hot metal when the erosion of the bottom of the brick progresses. Therefore, it is usually preferable to provide a potential measurement point on the surface of the bottom brick.

The potential measuring point 11 can be arranged at any position in the blast furnace circumferential direction of the bottom brick 2. The plurality of potential measuring points 11 for measuring the potential difference are
Normally, they are provided at the same position in the circumferential direction of the blast furnace at intervals in the height direction, but of course the potential between the potential measurement points 11 arranged at different positions in the circumferential direction may be measured. If the potential measurement point 11 is arranged by selecting a position near the taphole 3 in the circumferential direction of the blast furnace, the pigtail level near the taphole can be detected, and therefore the pigtail level is evaluated. Particularly favorable results can be obtained for use in management.

The potential difference measurement result according to the present invention in which the potential measurement point 11 was provided on the furnace bottom brick surface was compared with the conventional potential difference measurement result where the potential measurement point was provided on the blast furnace shell surface.
As the potential measurement position in the height direction of the blast furnace, the lower measurement point was at the furnace bottom carbon brick first stage level, and the upper measurement point was at the same level as the tuyere 4. The measurement results are shown in FIG. Figure 4
As is clear from the above, the potential difference measured on the surface of the iron shell is a small potential difference of around 0.5 mV, whereas the potential difference measured on the surface of the furnace bottom brick was a large potential difference of 4 to 8 mV.

As described in the above (4) and (8) of the present invention,
The sheath portion of the metal sheath thermocouple 20 can be used as the conducting wire 12 extending from the potential measurement point of the furnace bottom brick to the outside of the furnace body of the blast furnace. The metal sheath thermocouple 20 is a thermocouple enclosed in a cylindrical metal sheath, and the hot junction of the thermocouple is arranged near the distal sheath portion. As shown in FIG. 2, the metal sheath thermocouple 20 is inserted from the outside of the blast furnace body, and the tip sheath portion 21 of the metal sheath thermocouple 20 is brought into contact with the potential measurement point 11 of the blast furnace bottom brick 2. The metal sheath portion and the internal thermocouple are electrically insulated, and at the same time, the sheath portion also insulates the iron skin 1, the stave 5, and the stamp material 6. In FIG. 2, an insulating cylinder 27 formed of a magnetic tube or the like is arranged on the outer circumference of the metal sheath thermocouple 20 to insulate the sheath portion from the outer circumference thereof. The potential measuring contacts 10 thus configured are arranged at two or more positions in the height direction of the blast furnace, the conductors 14 are connected to the portions of the sheath portion of each metal sheath thermocouple 20 exposed from the iron shell 1, and a voltage not shown The potential difference can be measured by connecting a meter.

In a blast furnace, a thermocouple may be inserted from the iron shell to the inside of the blast furnace for the purpose of operation control and the temperature of the furnace bottom brick may be measured. When a sheath thermocouple is used for potential measurement as in the present invention, it is possible to use a thermocouple insertion port that has been conventionally used as a dual purpose without providing a new observation port on the iron skin for potential measurement. It will be possible.

Tip sheath portion 21 of metal sheath thermocouple 20
In order to abut the electric potential measuring point 11, the pressing mechanism 2
2, the sheath thermocouple 20 is applied with a pressing force so that its tip is pressed against the potential measurement point 11, and as a result, the tip sheath 21 can be brought into contact with the potential measurement point 11. As the pressing force applying mechanism 22, FIG.
As shown in FIG. 3, an elastic body such as a spring is arranged inside the thermocouple holding device 28 outside the blast furnace skin, and the reaction force of this elastic body is transmitted to the metal sheath thermocouple 20 by using the insulating stopper 25. The pair 20 can be pressed inside the furnace.

As a result of using the sheath thermocouple 20 for the potential measurement and bringing the tip of the thermocouple into contact with the potential measurement points, the potential difference between the potential measurement points can be measured and at the same time each potential measurement point 1
A temperature of 1 can also be measured. In FIG. 2, the thermocouple wire 24 exposed from the end portion of the metal sheath thermocouple 20 opposite to the tip sheath portion 21 can be guided to the temperature measuring device 23 to measure the temperature.

The furnace bottom potential difference measuring device of the present invention using the metal sheath thermocouple 20 was provided close to the taphole 3 in the circumferential direction of the blast furnace. The positions of potential measurement points in the height direction and the radial direction of the blast furnace were the same as in the case of FIG. At the same time as measuring the potential difference immediately before the tap hole 3 is closed, the bottom brick 3 at the potential measurement point 11 is measured using the thermocouple.
The surface temperature was measured. Immediately before the tap hole is closed, the pig iron level has dropped to almost the position of tap hole 3, and is at a substantially constant level at each block. Using the measurement results at this time, the temperature of the furnace bottom brick surface was plotted on the horizontal axis, and the potential difference measurement results were plotted on the vertical axis, and the results were plotted as x marks in FIG. As the temperature on the horizontal axis, the average temperature of the temperature measurement values at the two upper and lower positions is adopted. It can be seen that there is a correlation between the temperature and the potential difference, and the higher the temperature, the lower the potential difference. Based on this result, the measured potential difference was corrected by the temperature in order to cancel the influence of the temperature. The potential difference before correction is ΔE (m
V), the corrected potential difference is ΔE '(mV), the average value of the upper and lower two potential measurement point temperatures is Ta (° C.), and the correction is performed as ΔE' = ΔE + 0.0027 × Ta (1) formula , Marked with ● in FIG. Potential difference measurement results at the same slag level are within very small variations. That is, by using the metal sheath thermocouple 20 for potential measurement, the potential measurement point 11
It is clear that the level of slag in the blast furnace can be evaluated with higher accuracy by measuring the temperature of the sample and correcting the measured potential difference according to the measured temperature.

Furnace inner volume 3273 m ³ , hearth diameter 12.0 m
In this blast furnace, the level of pig iron was evaluated using the present invention. The potential measurement point was the furnace bottom brick surface, the lower measurement point was the furnace bottom carbon brick first level, and the upper measurement point was at the same level as the tuyere 3.8 m above the taphole.
As shown in FIG. 2, a potential measuring contact 10 using a metal sheath thermocouple 20 is used to measure the potential difference between the upper and lower two points and at the same time measure the temperature at each potential measuring point 11, using the above formula (1). The measured potential difference was corrected. In addition, the potential difference in the iron skin near the potential measurement point was measured.

The amount of residual slag in the furnace of the blast furnace was estimated by charging calculation and mass balance of generation and discharge of slag based on the measured value of the amount of slag discharge. In Fig. 6, the amount of residual slag thus calculated is plotted on the horizontal axis, the potential difference before temperature correction measured on the furnace bottom brick surface is indicated by x, and the potential difference on the furnace bottom brick surface after temperature correction is indicated by ●. ○, the potential difference measured on the surface of the iron skin
It is plotted with a mark. Here, the potential difference is the amount of residual slag =
The value at 0 is taken as a reference, and the increase width with respect to the reference value is taken as the vertical axis of FIG. The potential difference measured on the surface of the iron skin is extremely weak, whereas the potential difference measured on the surface of the furnace bottom brick has a large value, and as a result, the evaluation can be performed without being affected by noise. Regarding the potential difference measured on the surface of the brick at the bottom of the furnace, the correlation with the amount of residual slag in the furnace is high even in the case where the temperature is not corrected, and it can be seen that it has sufficient accuracy for use in the evaluation of the slag level. . The temperature-corrected data marked with ● has a significantly higher correlation with the amount of residual iron in the furnace, and it is clear that the level of iron residue can be evaluated with extremely high accuracy.

By evaluating the pig iron level by measuring the electric potential difference in the furnace bottom brick of the present invention, it becomes possible to measure the iron pig iron storage slag level in the furnace which is more reliable than before, and the electric potential difference is preset to a predetermined value. It is possible to avoid troubles due to the increase in the pig iron level in the reactor by controlling the operation so that the value is below the value.

When the measured value of the potential difference in the height direction of the furnace exceeds the preset value during the operation of the blast furnace, the operation of decreasing the pig iron production rate in order to lower the level of the pig iron stored in the furnace Either one or both of the action and the operation action for increasing the pig iron discharge rate may be performed.

The pig iron production rate is the production rate of the blast furnace itself, and can be changed by increasing or decreasing the amount of air blown per unit time. Therefore, as an operation action for reducing the pig iron slag generation rate, a method for reducing the tuyere air flow rate may be used.

Further, as an operation action for increasing the pig iron slag discharge speed, the diameter of the tapping hole in use in tapping is enlarged by digging with a large cone (promotion opening), or the tapping in use in tapping is expanded. A method to increase the amount of tapping metal per unit time by opening other closed tapping taps in addition to the tapping taps and tapping at multiple tapping taps at the same time (lap tapping) Can be used.

The preset value of the potential difference for determining whether or not to perform either one or both of the operation action for decreasing the pig iron slag generation rate and the operation action for increasing the pig iron slag discharge rate is The relationship between the operation results and the measured value of the potential difference, and without causing operational trouble,
It can be set in advance by the blast furnace operator based on the timing of the operation action that enables early recovery.

Specifically, the potential difference immediately before the blast pressure fluctuation increases due to the increase in the amount of residual iron in the furnace is obtained from past results, and the value or a set value in consideration of the safety factor is set. Can be determined, or can be determined based on the change over time in the potential difference that has increased after stopping the tapping for a certain period of time.

[0035]

According to the present invention, it is possible to accurately estimate the level of slag in the blast furnace by measuring the potential difference between a plurality of potential measurement points in the height direction of the blast furnace bottom brick. In addition, by using a metal sheath thermocouple inserted from the outside of the furnace body of the blast furnace to measure the potential, it is possible to use the thermocouple insertion port that has existed in the past as well, and the temperature measured by the thermocouple can be used. By correcting the measured potential difference based on this, it becomes possible to estimate the pig iron level with higher accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view showing a blast furnace bottom potential difference measuring device and a blast furnace bottom potential measuring contact of the present invention, (a) is a partial sectional view of the blast furnace bottom, and (b) is an enlarged view showing the vicinity of the potential difference measuring device. It is a figure.

FIG. 2 is a cross-sectional view showing a blast furnace bottom potential measuring contact of the present invention using a metal sheath thermocouple.

[Fig. 3] Fig. 3 is a cross-sectional view for explaining an arrangement position of a potential measurement point in a hearth brick, (a) shows the potential measurement point arranged on the surface of the bottom brick, and (b) shows the potential measurement point inside the bottom brick. It is a figure showing the case where it is arranged at.

FIG. 4 is a diagram comparing the electric potential differences measured on the surface of the iron shell and the bricks on the bottom of the furnace.

FIG. 5 is a diagram showing a relationship between a potential difference between potential measurement points provided on a bottom brick and a temperature at the potential measurement point, where x indicates no temperature correction, and ● indicates temperature correction.

FIG. 6 is a diagram showing the relationship between the amount of residual slag in the furnace and the range of increase in potential difference, where ○ is the potential difference measured on the surface of the iron shell, × is the potential difference measured on the brick at the bottom of the furnace (without temperature correction), and ● is the It is the potential difference (with temperature correction) measured on the bottom brick.

[Explanation of symbols]

1 iron skin 2 hearth bricks 3 taphole 4 tuyere 5 stave 6 stamp materials 7 castable 8 hot metal 9 slag 10 Contact for potential measurement 11 potential measurement points 12 conductors 13 Voltmeter 14 conductors 20 Metal sheath thermocouple 21 Tip sheath 22 Pressing mechanism 23 Temperature measuring device 24 thermocouple wires 25 Insulator stopper 26 Insulation cylinder 27 Insulation cylinder 28 Thermocouple holding device 30 non-through hole

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masato Sugiura             20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd.             Inside the surgical development headquarters (72) Inventor Hidetaka Konan             20-1 Shintomi, Futtsu City Nippon Steel Co., Ltd.             Inside the surgical development headquarters (72) Inventor Keiichiro Nakamura             1 Kimitsu, Kimitsu-shi Mr. Nippon Steel Corporation             Tsu Steel Works F-term (reference) 4K015 KA01

Claims (9)

[Claims] 1. A blast furnace bottom brick is provided with a plurality of potential measurement points at intervals in the height direction, a conductor wire extending from the potential measurement point to the outside of the blast furnace body is provided, and the potential measurement is performed using the conductor wires. A blast furnace bottom potential difference measuring device characterized by measuring a potential difference between points. 2. The at least one mounting position of the plurality of potential measuring points is higher than the tap hole level, and the at least one mounting position is lower than the tap hole level. 1. The blast furnace bottom potential difference measuring device according to 1. 3. The blast furnace bottom potential difference measuring device according to claim 1, wherein the potential measuring point is provided on a brick surface of a blast furnace bottom brick. 4. The tip sheath portion of a metal sheath thermocouple inserted from outside the blast furnace furnace body is brought into contact with a potential measurement point of a blast furnace bottom brick, and the sheath portion of the metal sheath thermocouple is moved from the potential measurement point to the blast furnace furnace body. The blast furnace bottom potential difference measuring device according to any one of claims 1 to 3, wherein the conductor wire extends to the outside. 5. The blast furnace bottom according to claim 4, wherein the tip sheath portion of the sheath thermocouple is brought into contact with the potential measurement point by the pressing force applied to the sheath thermocouple by using a pressing mechanism. Potentiometer. 6. A slag level evaluation method, characterized in that the slag level in the blast furnace is evaluated based on the potential difference measured by the blast furnace bottom potential difference measuring device according to any one of claims 1 to 5. 7. The pig slag according to claim 6, wherein the sheath thermocouple is used to measure the temperature at the potential measurement point, and the pig slag level evaluation is corrected based on the measured temperature. Level evaluation method. 8. A blast furnace bottom potential measuring contact in which a tip sheath portion of a metal sheath thermocouple inserted from the outside of the blast furnace furnace body is brought into contact with a potential measuring point of a blast furnace bottom brick, and the contact is provided outside the blast furnace furnace body. The potential of the potential measurement point can be measured using the sheath portion of the metal sheath thermocouple, and the temperature of the potential measurement point can be measured by the metal sheath thermocouple. Blast furnace bottom potential measurement contact. 9. The blast furnace bottom according to claim 8, wherein the tip sheath portion of the sheath thermocouple is brought into contact with the potential measurement point by the pressing force applied to the sheath thermocouple by using a pressing mechanism. Contact for potential measurement.