JP2006057960A - Cooling water circulation supply system and control method of cooling water temperature in the system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling water circulation supply system capable of suppressing the occurrence of surface defects at the time of casting steel having high cracking sensitivity such as high-carbon special steel to be cooled and a method for controlling the cooling water temperature in the system.
A cooling water circulation supply system supplies cooling water W ₁ toward the cooling target A from the water supply tank 1, the cooling water W ₂ after feed was recovered in the recovery tank 18 toward the cooling target A, the recovery tank 18, the recovered cooling water W ₃ is sent to the cooling tower 23 to be cooled, and the cooling water W ₄ cooled by the cooling tower 23 is returned to the water supply tank 1. In addition to the system through which the cooling water W ₃ goes from the recovery tank 18 to the cooling tower 23, a system through which the bypass cooling water W ₅ goes from the recovery tank 18 to the water supply tank 1 is provided.
[Selection] Figure 1

Description

  The present invention relates to a cooling water circulation supply system and a method for controlling a cooling water temperature in the system.

  Conventionally, from the viewpoint of energy saving and process omission, in the metal industry, continuous cast slabs are sent to the hot rolling process as hot or hot pieces without lowering the temperature to room temperature, shortening the heating time or heating. A so-called direct feed rolling process, in which hot rolling is omitted, has been studied, and various methods such as those described in Patent Document 1 and Patent Document 2 have been proposed so far. At present, aluminum killed steel and the like, which are less prone to cracking on the surface of the slab, are produced at a considerable ratio by this direct feed rolling process.

  However, steel having a C concentration of 0.30% by mass or more, and steel having a C concentration of 0.10% by mass or more and containing one or more of Cr, Ni, and Mo (these steels are hereinafter referred to as “high charcoal special Steel casts) are often prone to surface cracks and are generally inspected before they are sent to the hot rolling process, and if there are defects, they are ground and removed. Taken. Due to the nature of this removal operation, the slab must be cooled to room temperature, and high-carbon special steel has been difficult to manufacture by a direct rolling process.

  For this reason, a vertical continuous casting machine that minimizes the distortion that occurs in the slab as one of the methods to suppress the occurrence of surface defects during casting of high cracking sensitive steel such as high-carbon special steel. There is a method of casting. However, this method is advantageous from the viewpoint of securing the internal quality of the slab, but disadvantageous from the viewpoint of productivity. Therefore, as a method to suppress the occurrence of surface defects during the casting of steel with high cracking sensitivity such as high-carbon special steel, a continuous casting machine (vertical bending die) that has a vertical part followed by a bending part and a straightening part. A method of casting with a continuous casting machine) is also employed.

  When this vertical bending type continuous casting machine is used, for example, as described in Patent Document 3 and Patent Document 4, the distribution of cooling water flow rate (secondary cooling water amount pattern) in the secondary cooling zone and a specific spray are used. By prescribing the method and reducing the cooling water flow rate at the site where the distortion generated in the slab should be reduced, measures may be taken to suppress the occurrence of surface defects during casting. The breakdown is as follows: (1) weak cooling by controlling the secondary cooling water volume pattern so that the slab passing through the bending part and straightening part does not enter the embrittlement region, and (2) easy to cool and tensile due to thermal stress There are two methods of locally increasing the surface temperature by restricting water injection to the slab corner where distortion is likely to occur. (1) is also referred to as “weakening of secondary cooling water” and (2) is also referred to as “width reduction of secondary cooling water”.

Here, in order to achieve the “weakening of the secondary cooling water” in (1), for example, the control device for the cooling tower fan in the water treatment facility described in Patent Document 5 and the cooling tower described in Patent Document 6 are used. As in the operation method, the cooling water may be circulated and used to increase the temperature and further reduce the cooling.
As shown in FIG. 5, the control device for the cooling tower fan in the water treatment facility described in Patent Document 5 is involved in cooling in the water treatment facility that cools the water A corresponding to the cooling water through the cooling tower 101. A wet bulb temperature detector 102 that detects a change in the wet bulb temperature of the air, and an air volume control mechanism 104 that controls the air volume of the cooling tower fan 103 using a detection signal from the wet bulb temperature detector 102 are provided. The cooling tower 101 is the principle of cooling by removing the latent heat of vaporization from the water droplets by bringing the cooling tower fan 103 into contact with the air flow generated by sucking outside air toward the water droplets falling from the sprinkling pipe 108, The cooled water A is temporarily stored in the cold water tank 109 and supplied to the object to be cooled (for example, slab) by the water supply pump 110. The temperature of the cooling water in the cold water tank 109 on the outlet side of the cooling tower 101 is controlled by controlling the air volume of the cooling tower fan 103 by the air volume control mechanism 104. In FIG. 5, reference numeral 105 denotes a signal converter, 106 denotes a variable speed controller, and 107 denotes a cooling tower fan motor.

In addition, as shown in FIG. 6, the operation method of the cooling tower described in Patent Document 6 is supplied to the upper water tank 203 from the water supply main pipe 201 through the distribution valve 202, and the cooling water sprayed from the upper water tank 203 is converted into the cooling water. A cooling tower operating method for cooling the corresponding treated water 206 by bringing it into contact with an air flow generated by sucking outside air with a variable speed blower 207, which includes a flow meter 208 in a water supply main pipe 201 and an upper water tank 203. A movable partition plate 209 and a water level meter 210 for adjusting the sprinkling area are disposed inside, and a water temperature meter 211 is disposed at the lower part of the cooling tower, and the position of the movable partition plate 209 is set based on the measured value of the flow meter 208. The rotational speed of the variable speed blower 207 is controlled based on the measured value of the total gauge 208 and the measured value of the water temperature gauge 211, and the opening degree of the distribution valve 202 can be adjusted based on the measured value of the water level gauge 210. It is intended to set the position correction of the partition plate 209. Then, the treated water 206 cooled by the variable speed blower 207 is temporarily stored in the lower water tank 205 and supplied toward the cooling target. Based on the measured value of the flow meter 208 and the measured value of the treated water temperature after cooling measured by the water temperature meter 211 at the bottom of the cooling tower, the rotational speed of the variable speed blower 207 is controlled, and the flow rate of the outside air passing through is controlled. Thereby, the temperature of the treated water in the lower water tank 205 on the exit side of the cooling tower is controlled. In FIG. 6, reference numeral 204 denotes a packing in the cooling tower body, 212 denotes a calculator, and 213 denotes a power control panel.
Japanese Examined Patent Publication No. 56-21330 Japanese Examined Patent Publication No. 56-24018 Japanese Patent Publication No. 2-18936 JP-A-1-95801 Japanese Utility Model Publication No. 56-140798 JP-A-4-273998

  However, in the cooling tower fan control device in the water treatment facility described in Patent Document 5 and the cooling tower operation method described in Patent Document 6, the cooling water in the cold water tank 109 and the lower water tank 205 on the outlet side of the cooling tower is used. Is controlled by controlling the number of revolutions of the cooling tower fan 103 or the variable speed blower 207. However, there are cases where the temperature cannot be controlled to a desired set temperature for the following reason.

  That is, theoretically, it should be possible to control from the set temperature when the rotation speed of the cooling tower fan 103 and the variable speed blower 207 is zero to the set temperature when the rotation speed is rated. 103 and the variable speed blower 207 are operated only within a range of, for example, 30 to 50% of the rated number of rotations due to the limitation on the specification of the supply / exhaust flow rate of the cooling tower. It was not possible to control to a set temperature that could not be realized without this.

  Specifically, in the example of the cooling tower performance curve represented by the relationship between the outlet side temperature of the cooling tower shown in FIG. 7 and the air flow rate involved in cooling, Case 1 has a wet bulb temperature in the vicinity of the packing of 5 ° C. In this case 1, the outlet side temperature is 46 ° C. (temperature at the cooling tower fan speed corresponding to the case where the air flow rate related to cooling is about 100 t / h) It was not possible to set a higher temperature. Further, in case 2, the performance curve is obtained when the wet bulb temperature in the vicinity of the filling is 10 ° C., and the outlet temperature cannot be set higher than 46 ° C. Similarly, Case 3 shows a performance curve when the wet bulb temperature near the packing is 20 ° C., and the outlet temperature could not be set higher than 47 ° C. Furthermore, in the case of Case 4, it is a performance curve when the wet bulb temperature in the vicinity of the filling is 30 ° C., and the outlet temperature cannot be set higher than 48 ° C.

  Moreover, since the temperature of the cooling water is lowered only by dropping inside the cooling tower, even if the number of rotations of the cooling tower fan 103 and the blower 207 is set to zero, the temperature of the cooling water always decreases somewhat. Therefore, only by controlling the number of revolutions of the cooling tower fan 103 and the variable speed blower 207, the set temperature of the cooling water in the cooling water tank 109 and the lower water tank 205 on the outlet side of the cooling tower can be set to a certain temperature or higher. was difficult. In particular, in winter, the temperature of the cooling water returning from the object to be cooled is low and the outside air temperature (wet bulb temperature) is low. Therefore, the set temperature is set only by controlling the rotation speed of the cooling tower fan 103 and the variable speed blower 207. It was finally difficult to set the temperature above a certain temperature.

  In addition, as the set temperature of the cooling water in the cooling water tank 109 or the lower water tank 205 on the outlet side of the cooling tower approaches the water temperature returning from the object to be cooled to the water treatment facility, the control range of the air flow rate related to the cooling is increased. It became narrow and hunting occurred, making control difficult. That is, the fact that the set temperature of the cooling water in the cold water tank 109 and the lower water tank 205 is close to the water temperature returning from the object to be cooled to the water treatment facility means that the set temperature is a higher temperature. As shown in FIG. 7, if the outlet temperature setting is suddenly increased, the air flow rate related to cooling needs to be further decreased suddenly even if it is slightly increased. Therefore, there is a problem that the reduction of the air flow rate cannot catch up and the control cannot be performed economically as set.

Further, depending on the type of steel to be cooled, it may be necessary to change the set temperature of the cooling water in the cooling water tank 109 or the lower water tank 205 on the outlet side of the cooling tower. For example, in the case of 1600 m ³ / h, which corresponds to the capacity of the water treatment facility, the volume of the water supply tank (the cold water tank 109 or the lower water tank 205) is almost 1000 m ³ or more, and it comes from such a huge volume Due to the large heat capacity of the cooling water, even if the outlet temperature setting is suddenly lowered, there is a problem that the temperature of the cooling water does not drop suddenly, and as a result it may not be controlled as set. .

Thus, if the temperature of the cooling water cannot be controlled to a desired set temperature, it is not possible to sufficiently suppress the occurrence of surface defects at the time of casting of steel with high cracking sensitivity such as high-carbon special steel to be cooled.
Accordingly, the present invention has been made in view of the above-mentioned problems, and the object thereof is to minimize the occurrence of surface defects during casting of high-susceptibility steels such as high-carbon special steels to be cooled. Another object of the present invention is to provide a cooling water circulation supply system and a method for controlling the cooling water temperature in the system.

  In order to solve the above problems, a cooling water circulation supply system according to claim 1 of the present invention supplies cooling water to a cooling target, collects the cooling water after supply to the cooling target, In the cooling water circulation supply system that sends the cooling water to the cooling tower and cools it, and supplies the cooling water cooled by the cooling tower again to the object to be cooled, in addition to the system through which the cooling water goes to the cooling tower, It is characterized by providing a system through which cooling water bypasses the cooling tower.

A cooling water circulation supply system according to claim 2 of the present invention is the cooling water circulation supply system according to claim 1, wherein the cooling water circulation supply system is measured by a thermometer that measures the temperature of the cooling water toward the cooling target, and the thermometer. And a control device for controlling the flow rate of the cooling water that bypasses the cooling tower based on the temperature of the cooling water.
Furthermore, the method for controlling the cooling water temperature in the cooling water circulation supply system according to claim 3 of the present invention uses the cooling water circulation supply system according to claim 2 to determine the temperature of the cooling water toward the cooling object as the thermometer. The flow rate of the cooling water that bypasses the cooling tower is controlled by the control device based on the temperature of the cooling water measured by the thermometer, thereby controlling the temperature of the cooling water toward the cooling target. It is characterized by doing.

  In addition, the cooling water temperature control method in the cooling water circulation supply system according to claim 4 of the present invention is the cooling water temperature control method in the cooling water circulation supply system according to claim 3, wherein the cooling tower bypasses the cooling tower. The time required for the temperature of the cooling water toward the cooling target to reach the target cooling water temperature on the cooling target side after the water flow rate is changed by the control device is predicted in advance, and the cooling is actually performed. The flow rate of the cooling water that bypasses the cooling tower is changed by the control device by the predicted time before the timing at which the target cooling water temperature on the target side should be changed.

  According to the cooling water circulation supply system according to claim 1 of the present invention, in addition to the system through which the cooling water goes to the cooling tower, a system through which the cooling water bypasses the cooling tower is provided. It is possible to bypass the warm cooling water without going to the cooling tower and supply it again toward the object to be cooled. For this reason, even in winter, the temperature of the cooling water toward the cooling target can be increased, and the temperature (set temperature) of the cooling water toward the cooling target can be adjusted to an appropriate value. Thereby, generation | occurrence | production of the surface defect at the time of casting of steel with high crack sensitivity, such as high-carbon special steel etc. which is cooling object can be suppressed to the minimum.

  Moreover, according to the cooling water circulation supply system according to claim 2 of the present invention, in the cooling water circulation supply system according to claim 1, a thermometer for measuring a temperature of the cooling water toward the cooling target, and the thermometer And a control device that controls the flow rate of the cooling water that bypasses the cooling tower based on the temperature of the cooling water measured in step 1. Therefore, the cooling water that bypasses the cooling tower based on the temperature of the cooling water toward the object to be cooled The flow rate can be controlled, whereby the temperature of the cooling water toward the cooling target can be controlled. Therefore, even when the control range of the air flow rate involved in cooling by controlling the rotation speed of the cooling tower fan or blower is narrow, the temperature of the cooling water (set temperature) toward the cooling target can be adjusted to an appropriate value.

  Furthermore, according to the control method of the cooling water temperature in the cooling water circulation supply system according to claim 3 of the present invention, the cooling water temperature toward the cooling target is set using the cooling water circulation supply system according to claim 2. The flow rate of the cooling water that is measured by the thermometer and that bypasses the cooling tower is controlled by the control device based on the temperature of the cooling water that is measured by the thermometer. Since the temperature is controlled, the temperature of the cooling water (set temperature) toward the cooling target can be adjusted to an appropriate value even in winter, and when casting steel with high cracking sensitivity such as high-carbon special steel that is the cooling target. The occurrence of surface defects in can be minimized. And even when the control range of the air flow rate involved in the cooling by controlling the rotation speed of the cooling tower fan or the blower is narrow, the temperature of the cooling water (set temperature) toward the cooling target can be controlled to an appropriate value.

  In addition, according to the cooling water temperature control method in the cooling water circulation supply system according to claim 4 of the present invention, in the cooling water temperature control method in the cooling water circulation supply system according to claim 3, the cooling tower is After the flow rate of the cooling water to be bypassed is changed by the control device, the time required for the temperature of the cooling water toward the cooling target to reach the target cooling water temperature on the cooling target side is predicted in advance. The flow rate of the cooling water that bypasses the cooling tower is changed by the control device in advance by the predicted time before the timing at which the target cooling water temperature on the cooling target side should be changed. When it is time to change the target cooling water temperature, it is possible to ensure that the cooling water temperature toward the cooling target reaches the target cooling water temperature on the cooling target side. . For this reason, the cooling water set temperature required at the required timing can be obtained.

Next, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a cooling water circulation supply system according to one embodiment of the present invention. FIG. 2 is an explanatory view showing details of the vertical bending type continuous casting machine. FIG. 3 is an explanatory diagram showing an overview of on / off control of the cooling tower fan and on / off control of the on / off valve.
In Figure 1, the cooling water circulation supply system, and supplied toward the cooling water W ₁ to cast a cooling water of the secondary cooling zone below pieces (cooling target) A by feed pump 2 from the water supply tank 1, the slab A The cooling water W ₂ after supply is recovered in the recovery tank 18, and the recovered cooling water W ₃ is sent to the cooling tank 23 by the cooling tower water pump 20 to be cooled by the cooling tower water pump 20, and is cooled by the cooling tower 23. The water W ₄ is returned to the water supply tank 1.

A water supply main pipe 3 is connected to the water supply tank 1, and a water supply pump 2 is installed in the middle of the water supply main pipe 3. As shown in FIG. 2, a plurality of nozzles 11 _{1 to} 11 ₁₀ arranged in each of a plurality of zones 10 ₁ to 10 ₁₀ of the vertical bending type continuous casting machine 4 are provided on the outlet side of the water supply main pipe 3. _{1 to} 12 ₁₀ are connected. The nozzles 11 _{6 to} 11 ₉ and the flow rate control valves 12 _{6 to} 12 ₉ are not shown. The vertical bending type continuous casting machine 4 includes a tundish 5 in which molten steel is stored, a mold 6 installed on the exit side of the tundish 5, and a slab guide device 7 installed on the exit side of the mold 6. ing. In the vertical bending type continuous casting machine 4, the molten steel stored in the tundish 5 flows into the mold 6 cooled by the water-cooling jacket, and in the process of passing through the mold 6, a solidified shell is formed on the outer periphery. The slab A coming out of the mold 6 is guided into the slab guide device 7 and passes through the slab guide device 7 while being cooled by the cooling water W ₁ from the plurality of nozzles 11 _{1 to} 11 _10. Yes. As shown in FIG. 2, the slab guide device 7 includes a vertical portion 8 and a plurality (19 in the present embodiment) of segments 9 _{1 to} 9 which are provided so as to be connected along the slab passage 13. _The vertical portion 8 and the segments 9 _{1 to} 9 ₁₉ are provided with a plurality of pairs of slab guide rolls 14 with the slab passage 13 interposed therebetween. The vertical portion 8 is constituted by _three zones 10 ₁ to 10 ₃ , the segment 9 ₁ constitutes the zone 10 ₄ , the segments 9 ₂ and 9 ₃ constitute the zone 10 ₅ , and the segments 9 ₄ and 9 ₅ constitute the zone 10. ₆ , segments 9 ₆ and 9 ₇ constitute zone 10 ₇ , segments 9 ₈ and 9 ₉ constitute zone 10 ₈ , segments 9 ₁₀ , 9 ₁₁ and 9 ₁₂ constitute zone 10 ₉ , The segments 9 ₁₃ , 9 ₁₄ , 9 ₁₅ , 9 ₁₆ , 9 ₁₇ , 9 ₁₈ and 9 ₁₉ constitute the zone 10 ₁₀ . Foregoing secondary cooling zone and include, but are not determined uniformly, the supply is directed to the cooling water in the slab, that the particularly large will likely site strain occurring in the cast piece, for example, zone ₁₀₆ and What is necessary is just to decide suitably like 10 < ₇ >.

Then, the cooling water W ₁ supplied from the water supply main pipe 3 from the water supply tank 1 by the feedwater pump 2 is a cooling object from each of the nozzles 11 ₁ to 11 ₁₀ through the respective flow control valves 12 ₁ to 12 ₁₀ slab A Supplied towards. Thereby, the slab A is cooled. At this time, the flow rate of the supplied cooling water W ₁ is controlled by the flow rate control valves 12 _{1 to} 12 _{10 for} each of the zones 10 ₁ to 10 ₁₀ .

Then, the cooling water W ₂ after being supplied to the slab A is recovered by a foreign substance removing device 16 such as a filter or a precipitation type through a recovery pipe 15, and then recovered in a recovery tank via another recovery pipe 17. 18 is recovered as cooling water W ′. The recovery tank 18 is provided with a recovery tank temperature detector 32 for measuring the temperature of the cooling water in the recovery tank 18 to be supplied to the cooling tower 23 from now on.

A water supply main pipe 19 is connected to the recovery tank 18, and a cooling tower water supply pump 20 is installed in the middle of the water supply main pipe 19. And the water supply main pipe 21 which goes to the cooling tower 23 is connected to the outgoing side rather than the cooling tower water pump 20 of the water supply main pipe 19. On the outlet side of the water supply main pipe 21, an on-off valve 22, a cooling tower 23, and an upper water tank 24 are sequentially arranged. The recovered cooling water W ′ is supplied to the recovery tank 18 as cooling water W ₃ by the cooling tower water pump 20 through the water supply main pipes 19 and 21 toward the upper water tank 24. The bottom of the upper water tank 24 is a perforated plate, the cooling water W ₃ is passed through the packing 25 inside the main body of the cooling tower 23, and the cooling water W _{3 that} has fallen through the packing 25 is cooled and cooled. The water W ₄ is collected, and the cooling water W ₄ is collected in the water supply tank 1. The cooling water in the water supply tank 1 is represented by the symbol W. A cooling tower fan 26 is installed in the upper part of the cooling tower 23, and this cooling tower fan 26 is connected to a control device 31 that performs on / off control of rotation thereof. The cooling water W _{3 that} is falling in the packing 25 is brought into contact with the air flow generated by sucking outside air by controlling the rotation of the cooling tower fan 26 by the control device 31 in the packing 25. Cooling is performed by removing the latent heat of vaporization from the water droplet-like cooling water W ₃ .

The “system through which the cooling water goes to the cooling tower” according to claim 1 is constituted by the water supply main pipes 19 and 21.
A bypass pipe 29 is provided on the outlet side of the water supply main pipe 19 from the cooling tower water supply pump 20 so as to branch from the water supply main pipe 21. An on-off valve 30 is provided in the middle of the bypass pipe 29, and the outlet side of the bypass pipe 29 is connected to the water supply tank 1. A bypass cooling water W ₅ from the recovery tank 18 toward the water supply tank 1 passes through the bypass pipe 29 by the pump pressure of the cooling tower water pump 20. The bypass pipe 29 constitutes the “system through which the cooling water bypassing the cooling tower passes” according to claim 1.

Then, the water supply tank 1, is installed thermometer 28 for measuring the temperature T _W of the cooling water of the slab to be supplied toward the A, the cooling water W in the water supply tank 1 is now cooled object, cooling the tower 23, wet-bulb temperature detector 27 for measuring the wet bulb temperature T _a around the packing 25 is installed. The thermometer 28 and the wet bulb temperature detector 27 are connected to the control device 31, and the measured value of the cooling water temperature T _W measured by the thermometer 28 and the wet bulb temperature T measured by the wet bulb temperature detector 27. The measurement value _A is sent to the control device 31. Controller 31 is configured to perform on-off control of the rotation of the switching controller and the cooling tower fan 26 of the on-off valve 30 based on the measured value of the temperature T _W of the cooling water.

Next, with reference to FIG. 1 and FIG. 3, an outline of on / off control of the cooling tower fan 26 and opening / closing control of the on-off valve 30 by the control device 31 will be described.
The on / off control of the cooling tower fan 26 and the on / off control of the on / off valve 30 are performed completely independently, and the on / off control result of the cooling tower fan 26 affects the on / off control of the on / off valve 30 or the on / off control of the on / off valve 30. The control result does not affect the on / off control of the cooling tower fan 26.

Therefore, first, on / off control of the cooling tower fan 26 will be described. As shown in FIG. 3, when the temperature T _W of the cooling water in the water supply tank 1 is within a range of ± 1.5 ° C. with respect to the set temperature (target cooling water temperature), the control device 31 The fan 26 is controlled to maintain the current state. For example, when the cooling tower fan 26 is controlled to turn on and is rotating, the cooling tower fan 26 is controlled to be turned on to maintain the state, and conversely, the cooling tower fan 26 is controlled to be turned off and is rotating. If not, the cooling tower fan 26 is controlled to be off so as to maintain the state.

When the temperature T _W of the cooling water in the water supply tank 1 becomes lower than 1.5 ° C. with respect to the set temperature, the control device 31 controls the cooling tower fan 26 to be turned off, and the cooling tower The rotation of the fan 26 is stopped, the air flow generated by sucking the outside air is stopped from contacting the cooling water in the filling 25, and the cooling of the cooling water is stopped. Accordingly, the temperature T _W of the cooling water in the water supply tank 1 rises.

On the other hand, when the temperature T _W of the cooling water in the water supply tank 1 exceeds 1.5 ° C. with respect to the set temperature, the control device 31 controls the cooling tower fan 26 to be turned on, and the cooling tower The fan 26 is rotated to bring the air flow generated by sucking outside air into contact with the cooling water in the filling 25 to cool the cooling water. Accordingly, the temperature T _W of the cooling water in the water supply tank 1 is lowered.

Next, opening / closing control of the opening / closing valve 30 will be described. As shown in FIG. 3, when the temperature T _W of the cooling water in the water supply tank 1 becomes lower than 0.5 ° C. with respect to the set temperature, the control device 31 controls to open the on-off valve 30. . Thereby, the warm bypass cooling water W ₅ in the recovery tank 18 is supplied into the water supply tank 1 through the water supply main pipes 19 and 29 by the pump pressure of the cooling tower water supply pump 20. For this reason, even in winter, the temperature T _W of the cooling water in the water supply tank 1 can be increased, and the temperature T _W (set temperature) of the cooling water in the water supply tank 1 can be adjusted to an appropriate value. . Thereby, the temperature of the cooling water supplied toward the slab (cooling target) A from the water supply tank 1 can be adjusted to an appropriate value even in winter, and cracking susceptibility of the high-carbon special steel that is the cooling target can be improved. The occurrence of surface defects during the casting of high steel can be minimized.

On the other hand, when the temperature T _W of the cooling water in the water supply tank 1 exceeds 0.5 ° C. with respect to the set temperature, the control device 31 controls to close the on-off valve 30. Thus, the supply of warm bypass coolant W ₅ from the recovery tank 18 toward the feed water tank 1 is stopped, the temperature T _W of the cooling water in the water supply tank 1 is lowered.
The control device 31 is configured to perform opening / closing control of the opening / closing valve 30, but the opening / closing valve 30 is configured by a flow control valve so as to control the flow rate of the bypass cooling water W ₅ to the water supply tank 1. Good. By doing so, based to T _W of the cooling water in the water supply tank 1 to control the flow rate of the bypass cooling water W ₅ toward the feed water tank 1, thereby the temperature T _W of the cooling water in the water supply tank 1 Can be controlled. Therefore, even when the control range of the air flow rate involved in cooling by controlling the rotation speed of the cooling tower fan 26 is narrow, the temperature (set temperature) of the cooling water in the water supply tank 1 can be appropriately controlled, and the water supply tank The temperature of the cooling water supplied from 1 to the slab A can be appropriately controlled.

Then, after the control device 31 changes the flow rate of the bypass cooling water W ₅ , the temperature T _W of the cooling water in the water supply tank 1 becomes the set temperature (target cooling water temperature) for the slab (cooling target) A. The time required to reach the target is predicted in advance, and the flow rate of the bypass cooling water W ₅ is changed in advance by the predicted time before the timing for actually changing the set temperature for the slab A comes. The time required for the temperature T _W of the cooling water in the water supply tank 1 to reach the set temperature for the slab A after changing the flow rate of the bypass cooling water W ₅ is estimated in the tundish 5 This is done by calculation and empirical results based on the remaining steel amount and molten steel processing speed (t / min). As a result, when it is time to actually change the set temperature for the slab A, the temperature T _W of the cooling water in the water supply tank 1 can reach the set temperature for the slab A. For this reason, even if the capacity | capacitance of the water supply tank 1 is large, the cooling water temperature required at a required timing can be obtained.

  As described above, the above-described embodiment is merely an example, and the embodiment of the present invention is not limited thereto. That is, various changes can be made. For example, the supply tank 1 and the recovery tank 18 and those not described in the claims may be omitted as appropriate. Further, the thermometers 28 and 32 do not have to be immersed in the cooling water in the tank, but may be in other embodiments, for example, immersed in the cooling water flowing through the piping.

When the temperature of the cooling water in the water supply tank is controlled to the set temperature in the cooling water circulation supply system shown in FIG. 1, and in the water supply tank without providing a bypass pipe for the cooling water circulation supply system shown in FIG. The case where the temperature of the cooling water was controlled to the set temperature was compared.
Here, a vertical bending type continuous casting machine having a vertical part length of 2.5 m is used, and the three cases where the set temperature of the cooling water temperature in the water supply tank is 35 ° C., 37 ° C., and 42 ° C. are compared. did.

The steel types, casting speed, slab thickness and width used for continuous casting are as follows.
Steel type: Low carbon steel with C concentration of 0.05 to 0.10% by mass, specific water amount of 2.0 to 2.50 / kg-steel
Medium carbon steel with C concentration of 1.00 to 1.50 mass%, specific water content of 0.6 to 2.0 / kg-steel
High carbon steel with C concentration of 1.50 to 2.00% by mass, specific water amount of 0.6 to 1.61 / kg-steel
Casting speed: 0.6 to 2.0 m / min
Cast slab thickness: 260 mm, slab width: 650-1650 mm

  4 shows the control results when the temperature of the cooling water in the water supply tank is controlled to the set temperature in the cooling water circulation supply system shown in FIG. 1 (in the case of the embodiment), and the cooling water circulation supply system shown in FIG. It is a graph which shows the comparison result with the control performance when the temperature of the cooling water in a water supply tank is controlled to preset temperature (in the case of a comparative example) without providing a bypass pipe, and (A) is in the case of winter (B) shows the comparison results of the control results in the spring season.

  As can be seen from FIG. 4A, in the case of the winter season (when the wet bulb temperature is 10 ° C.), in the embodiment, when the set temperature of the cooling water in the water supply tank is controlled to 37 ° C. Although the actual cooling water temperature was slightly higher than 37 ° C, the actual cooling water temperature was 35 ° C and 42 ° C when the set temperature was controlled at 35 ° C and 42 ° C. There was no problem. On the other hand, in the comparative example, when the set temperature of the temperature of the cooling water in the water supply tank was controlled to 42 ° C., the actual cooling water temperature was frequently lower than 42 ° C. It can be seen that when the set temperature is 42 ° C. in winter, the actual cooling water temperature cannot be controlled above a certain temperature only by controlling the rotation speed of the cooling tower fan. Moreover, the actual temperature of the cooling water when the set temperature of the temperature of the cooling water in the water supply tank is controlled to 37 ° C. is slightly higher than 37 ° C., and the variation is large. It can be seen that when the set temperature is 37 ° C. in winter, the actual cooling water temperature varies only by controlling the rotation speed of the cooling tower fan. In addition, when the preset temperature of the temperature of the cooling water in the water supply tank was controlled to 35 ° C., the actual cooling water temperature was frequently 35 ° C., and there was no problem.

  Further, as can be seen from FIG. 4B, in the case of spring (wet bulb temperature 20 ° C.), in the embodiment, the set temperature of the cooling water in the water supply tank is controlled to 37 ° C. Although the actual cooling water temperature was slightly higher than 37 ° C, the actual cooling water temperature was 35 ° C and 42 ° C when the set temperature was controlled to 35 ° C. The frequency of becoming 42 ° C. was high and there was no problem. On the other hand, even in the comparative example, when the set temperature of the temperature of the cooling water in the water supply tank was controlled to 37 ° C., the actual cooling water temperature was slightly higher than 37 ° C. However, when the set temperature was controlled to 35 ° C. and 42 ° C., the actual cooling water temperature was frequently 35 ° C. and 42 ° C., and there was no problem.

It is a schematic block diagram of the cooling water circulation supply system which concerns on one embodiment of this invention. It is explanatory drawing which shows the detail of a vertical bending type | mold continuous casting machine. It is explanatory drawing which shows the outline | summary of the on-off control of a cooling tower fan, and the on-off control of an on-off valve. The control results when the temperature of the cooling water in the water supply tank is controlled to the set temperature in the cooling water circulation supply system shown in FIG. 1 (in the case of the embodiment) and the bypass for the cooling water circulation supply system shown in FIG. It is a graph which shows the comparison result with the control performance when the temperature of the cooling water in a water supply tank is controlled to preset temperature without providing a pipe (in the case of a comparative example), and (A) is the control performance in the winter season. A comparison result and (B) show the comparison result of the control performance in the case of spring. It is a schematic block diagram of the control apparatus of the cooling tower fan of the water treatment facility of a prior art example. It is the whole apparatus arrangement | positioning schematic with the operating method of the cooling tower of a prior art example applied. It is a graph which shows an example of the relationship between the exit side temperature of a cooling tower, and the air flow rate in connection with cooling.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water supply tank 2 Water supply pump 3 Water supply main pipe 4 Vertical bending type continuous casting machine 5 Tundish 6 Mold 7 Slab guide device 8 Vertical part 9 _{1 to} 9 ₁₉ segment 10 ₁ to 10 ₁₀ zone 11 _{1 to} 11 ₁₀ Nozzle 12 ₁ to 12 ₁₀ Flow control valve 13 Slab passage 14 Slab guide roll 15 Recovery pipe 16 Foreign material removal device 17 Recovery pipe 18 Recovery tank 19 Water supply main pipe 20 Cooling tower water supply pump 21 Water supply main pipe 22 On-off valve 23 Cooling tower 24 Upper water tank 25 Filling 26 Cooling tower fan 27 Wet bulb temperature detector 28 Thermometer 29 Bypass pipe 30 On-off valve 31 Control device 32 Recovery tank temperature detector W, W ′, W ₁ , W ₂ , W ₃ , W ₄ Cooling water W ₅ Bypass cooling Water A slab

Claims (4)

Cooling water is supplied to the cooling target, the cooling water after being supplied to the cooling target is recovered, the recovered cooling water is sent to the cooling tower to be cooled, and the cooling water cooled by the cooling tower is cooled again. In the cooling water circulation supply system that supplies the target,
In addition to a system through which the cooling water goes to the cooling tower, a system through which the cooling water passes to bypass the cooling tower is provided.   A thermometer that measures the temperature of the cooling water toward the object to be cooled, and a control device that controls the flow rate of the cooling water that bypasses the cooling tower based on the temperature of the cooling water measured by the thermometer. The cooling water circulation supply system according to claim 1, wherein:   Using the cooling water circulation supply system according to claim 2, the temperature of the cooling water toward the cooling object is measured by the thermometer, and the cooling tower is bypassed based on the temperature of the cooling water measured by the thermometer. A control method of the cooling water temperature in the cooling water circulation supply system, wherein the flow rate of the cooling water to be controlled is controlled by the control device, thereby controlling the temperature of the cooling water toward the cooling target.   The time required for the temperature of the cooling water toward the cooling target to reach the target cooling water temperature on the cooling target side after changing the flow rate of the cooling water bypassing the cooling tower by the control device is predicted in advance. In addition, the flow rate of the cooling water that bypasses the cooling tower is changed by the control device in advance of the predicted time before the timing at which the target cooling water temperature on the cooling target side should actually be changed. The method for controlling the cooling water temperature in the cooling water circulation supply system according to claim 3.

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