JP5578112B2 - Induction heating device cooling method - Google Patents

Description

The present invention relates to a cooling method for a channel type induction heating device installed in an induction furnace.

Molten metal discharged from the blast furnace is supplied to a converter (smelting furnace) through a topped car (mixing car), a hot metal ladle, or the like. At that time, the molten metal supply conditions to the converter vary depending on the amount of molten metal discharged from the blast furnace (hereinafter sometimes referred to as “molten metal”) and the amount of molten steel produced in the converter. The molten metal is temporarily stored in the induction furnace. This induction furnace is provided with an induction heating device that performs heat retention and heating of the stored molten metal.

A loop-shaped molten metal flow path is formed in the induction heating device. An iron core around which an induction heating coil is wound is disposed at the center of a region surrounded by a loop-shaped molten metal flow path (hereinafter also referred to as “runner”). The molten metal is heated by configuring the transformer circuit with the induction heating coil as the primary circuit and the molten metal flowing through the runner as the secondary circuit.

In a channel type (groove type) induction heating device in which a channel type (groove type) runway is formed, in order to increase power efficiency, the thickness of the refractory facing the runway is made the minimum necessary thickness, and the induction heating coil And the runway as close as possible. As a result, when molten metal leaks due to melting or cracking of the refractory facing the runner, the outer case or induction heating coil covering the induction heating device is damaged, and cracks grow and are attached to the induction heating device. When reaching the water-cooled pipe, there is a risk that the cooling water and the molten metal react to induce a steam explosion.
Therefore, a leak detector antenna is embedded in the refractory facing the runway, a voltage is applied between the leak detector antenna and the molten metal, and the molten metal and the leak detector antenna are connected via the refractory. By monitoring the current flowing between them, detection of hot water leakage (leakage of molten metal) is performed (see, for example, Patent Documents 1 to 3).

In the case of an electric circuit of a hot water leak detection system, since electric resistance is large in normal times, almost no current flows. However, when a hot water leak occurs, the electric current is caused by the short circuit between the hot water leak detection antenna and the runway and the circuit closing. Flows and a leak is detected. For this reason, for example, when a lead abnormality extending from the hot water leak detection antenna breaks and cuts and a facility abnormality occurs in the hot water leak detection system, there is a high risk of not being aware of this. Therefore, in Patent Document 4, by drawing out two or more lead wires for one molten metal leak detection antenna, current is conducted between these lead wires to determine whether or not the lead wires are disconnected. Yes.

Japanese Utility Model Publication No. 53-48231 JP-A-9-133601 JP 2008-267758 A JP 2008-170062 A

As described above, the molten metal detection system flows between the molten metal and the molten metal detection antenna via the refractory by applying a voltage between the molten metal detection antenna embedded in the refractory and the molten metal. The current is monitored, and a leak is determined by the behavior of the current value. That is, when the electric resistance value between the molten metal in the induction furnace and the molten metal leak detection antenna falls below a certain reference value, it is determined that the molten metal leak has occurred.
However, the cause of the decrease in the electrical resistance value is not only the leakage of hot water, but the electrical resistance value may be decreased due to other factors, and it may be mistakenly recognized that a leakage of molten metal has occurred (water leakage error detection). Specifically, the applied electric power of the channel type induction heating device is in a low output state (heat insulation operation), that is, only the minimum electric power for maintaining the molten metal without melting the cold iron source such as scraps and molds. When a transition is made from the applied state to the high output state (heating operation), that is, the state where the maximum cold iron source is melted using the rated output of the induction heating device, erroneous detection of hot water leakage will occur temporarily. There is.

As will be described later, the present inventors have found that the cause of the erroneous detection of hot water leakage is caused by dew condensation occurring in the channel type induction heating apparatus. Accordingly, an object of the present invention is to prevent erroneous detection of hot water leakage that temporarily occurs when shifting from a heat retaining operation to a heating operation by improving the cooling method of the channel type induction heating device.

The inventors of the present invention have discovered that the erroneous detection of hot water leakage that temporarily occurs when shifting from the heat retaining operation to the heating operation is caused by moisture present in the induction heating apparatus.
In the induction heating apparatus, in order to increase power efficiency, a refractory having a minimum thickness is arranged facing the runner, and the induction heating coil and the runner are as close as possible. For this reason, as a refractory constituting the runner, a powdery amorphous refractory called a dry stamp material (also referred to as a dry ramming material) to which water is not added is often applied. When the dry stamp material is applied, the vicinity of the running surface of the runner exposed to high temperature is baked and solidified to become a sintered body, and the runner wall surface is formed. On the other hand, the back surface is maintained in a dry and unsintered powder compact. As a result, even if a crack occurs in the sintered body and the molten metal enters the crack (start of leakage), the powder compact on the back surface is sintered by the heat of the molten metal, and further leakage of molten metal is caused. Be blocked. As a result, hot water leakage that reaches the outer case is avoided.
However, even when a dry stamp material is applied, the refractory constituting the induction heating device contains a small amount of free water or crystal water. Moreover, the moisture contained in the atmosphere at the time of construction of the induction heating device is confined in the induction heating device. The present inventors evaporate these moisture at a high temperature portion in the vicinity of the runner and have a water-cooled outer case or bushing (a partition wall provided between the refractory forming the runner and the induction heating coil). It has been discovered that by forming condensation in the vicinity of the refractory and forming a wet portion in the refractory nearby, the electrical resistance value decreases via the refractory wet portion between the outer case and the leak detector antenna.

Since the channel type induction heating device has a large output (applied power), the outer case and the bushing are often water-cooled to protect the outer case and the bushing from induction heat generation. On the other hand, the hot water leak detection antenna is often embedded in the vicinity of the back surface of the refractory, that is, in the vicinity of the exterior case and the bushing. In order to prevent abnormal heat generation of the bushing and / or the outer case due to the induction current flowing through the bushing and / or the outer case, the bushing is often electrically insulated from the outer case. In some cases, the bushing itself also has the function of a hot water leak detection antenna as described in (1).

Therefore, even when the channel type induction heating device is in operation, the vicinity of the hot water leak detection antenna is maintained at a relatively low temperature, and water vapor desorbed from the vicinity of the operating surface of the refractory constituting the runway of the channel type induction heating device. Condensation occurs in the vicinity of the hot water leak detection antenna, and the electrical resistance value between the outer case and the hot water leak detection antenna is reduced. In addition, when the function of the hot water leak detection antenna is also used for the bushing itself, it is equivalent to powerful cooling of the hot water leak detection antenna itself to cause a large amount of dew condensation. The contact resistance of the part tends to decrease. As a result, the insulation resistance value between the hot water leak detection antenna (that is, the bushing) and the outer case is likely to decrease, and there is a strong tendency for erroneous detection of hot water leak.

In general, there is a bare metal that adheres to bridge from the refractory operating surface of the molten metal outlet to the furnace core, and there is electrical continuity between the molten metal in the furnace and the furnace core Often to do. In addition, since the outer case is firmly fastened to the furnace body skin using bolts and nuts, there is often electrical continuity between the outer case and the furnace body skin. That is, there is often an electrical continuity between the outer case and the molten metal in the induction furnace. Therefore, a decrease in electrical resistance value between the outer case and the molten metal detection antenna cannot be distinguished from a decrease in electrical resistance value between the molten metal and the molten metal detection antenna, and erroneous detection of molten metal occurs.
In particular, in the transition period in which the induction furnace shifts from the standby state (heat retention operation state) to the scrap melting state (heating operation state), the applied power of the channel type induction heating device shifts from the low output state to the high output state, The temperature in the vicinity of the working surface of the refractory constituting the runner of the channel type induction heating device is greatly increased. Along with this, water vapor generated from a high-temperature portion near the runner is condensed in the vicinity of the hot water leak detection antenna, thereby causing false detection of hot water leak. However, when the channel type induction heating device is in a high output state, the temperature of the outer case and bushing also rises due to heat generated by the applied power, etc., so that condensation does not occur after about 1 to 6 hours, and erroneous detection of hot water leakage is eliminated. .

In short, the cause of hot water leak detection that occurs temporarily when shifting from heat insulation operation to heating operation is that the channel temperature rises as the channel type induction heating device shifts from the low output state to the high output state. Accordingly, moisture evaporated from the vicinity of the running surface of the runner is condensed on the inner surface of the outer case and the bushing where the temperature has not risen yet. In addition, when the high output state continues, the temperature of the outer case and the bushing gradually increases, so that moisture condensed on the inner surfaces of the outer case and the bushing is evaporated again, thereby eliminating erroneous detection of hot water leakage.

The cooling equipment attached to the channel type induction heating device is designed to exhibit a cooling capacity commensurate with the rated output of the channel type induction heating device, and thus is overcooled in a low output state. Therefore, in the present invention, by improving the cooling method of the channel type induction heating device, erroneous detection of hot water leakage that temporarily occurs when the heat-holding operation is shifted to the heating operation is prevented.
That is, the present invention provides a refractory that forms a loop-shaped flow path through which molten metal flows , an exterior case that covers the refractory, a bushing that is lined on the inner peripheral surface of the refractory, the exterior case, A channel-type induction heating apparatus comprising: a water-cooled tube attached to the bushing; an induction heating coil disposed in the center of a cavity defined by the bushing; and a hot water leak detection antenna embedded in the refractory. The method of cooling
The temperature of the cooling water flowing through the cooling water pipe is, wherein the coolant is a position where the respective starts heat exchange of the outer casing and the bushing, 40 ° C. or higher in the inlet of the outer casing and the bushing, and wherein The cooling water and each of the outer case and the bushing are at positions where heat exchange is finished, and each outlet of the outer case and the bushing is less than 100 ° C.

In general, in a cooling facility for cooling an outer case and a bushing of a channel type induction heating device, the setting of a chiller (cooling device) and the flow rate of cooling water are constant regardless of the magnitude of applied power. For this reason, the cooling is excessive in the low output state. On the other hand, when shifting from the low output state to the high output state, the dew point increases in the vicinity of the outer case and the bushing, and therefore the temperature near the outer case and the bushing becomes lower than the dew point. As a result, when shifting from the low output state to the high output state, condensation is likely to occur in the vicinity of the outer case and the bushing.
With respect to the above phenomenon, in the present invention, the temperature of the cooling water supplied to the outer case and the bushing is controlled so that the cooling water temperature becomes 40 ° C. or higher even in a low output state. Thereby, also when changing from a low output state to a high output state, the vicinity temperature of an exterior case and a bushing is maintained at a temperature higher than a dew point, and generation | occurrence | production of dew condensation is suppressed. Note that the upper limit value of the temperature of the cooling water is less than the boiling point (100 ° C.).

In the cooling method of the induction heating device according to the present invention, the temperature of the cooling water supplied to the outer case and the bushing is controlled to be 40 ° C. or higher even in a low output state, so that condensation in the vicinity of the outer case and the bushing is prevented. Generation | occurrence | production is suppressed and the hot water leak erroneous detection which generate | occur | produces temporarily when it transfers to heat operation from heat insulation operation can be prevented.

It is a schematic diagram of an induction furnace. (A) is a plane sectional view of a channel type induction heating device, and (B) is a sectional view taken along line AA. It is the graph which showed the temperature distribution of the refractory material temperature and dew point in the exterior case vicinity when the cooling method of the conventional induction heating apparatus was used for every operating state. It is the graph which showed the temperature distribution of the refractory material temperature and the dew point in the exterior case vicinity when the cooling method of the induction heating apparatus which concerns on one embodiment of this invention was used.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.

As shown in FIG. 1, the induction furnace 10 for storing molten metal (molten metal) has a cylindrical shape with both end faces sealed, and is installed on a support base 26 so that the center axis of the furnace body is horizontal. ing. The induction furnace 10 is covered with an iron skin, and a refractory layer is formed inside the iron skin.
A plurality of channel-type induction heating devices 11 (hereinafter simply referred to as “induction heating devices”) are provided at lower portions on both sides of the induction furnace 10 at intervals in the central axis direction of the induction furnace 10 (this is simply referred to as “induction heating device” hereinafter). In the embodiment, three on one side, a total of six are installed.) In addition, a scrap charging port 12 for charging scrap is provided on one side surface of the induction furnace 10, and a receiving port (not shown) for charging molten metal and a molten metal are discharged on the other side surface. Is provided with an outlet (not shown).

Each induction heating device 11 has a flat prismatic shape (see FIG. 2B), and is installed so as to protrude outward from the side surface of the induction furnace 10. The induction heating device 11 includes a flow path 13 through which the molten metal flows, refractories 18 and 19 disposed facing the flow path 13, an iron outer case 17 that covers the induction heating apparatus 11, and heating the molten metal. An induction heating means (see FIG. 2A), and heat retention and heating of the molten metal stored in the induction furnace 10 is performed.

The channel 13 has a substantially “mountain” shape in plan view, and is formed on both sides of the central channel 14 formed along the central axis of the induction heating device 11 and the central channel 14. A pair of side flow paths 15 and an end flow path 16 formed at the distal end portion of the induction heating device 11 that communicate with the central flow path 14 and the pair of side flow paths 15 are configured. The molten metal stored in the induction furnace 10 flows into the induction heating device 11 from the central flow path 14, branches left and right in the end flow path 16, and then flows from the pair of side flow paths 15 toward the induction furnace 10. It is said to be a looped runner that flows out.

The refractory 19 disposed between the central flow path 14 and the side flow path 15 has a “B” shape in plan view, and a copper bushing 20 is lined on the inner peripheral surface of the refractory 19. (See FIG. 2A). In addition, an iron core 23 around which an induction heating coil 22 that is induction heating means for heating the molten metal is wound is disposed in the center of the hollow portion 21 defined by the bushing 20. The iron cores 23 arranged in the respective hollow portions 21 are connected by a horizontal member 24 to constitute a “B” -shaped yoke as viewed from above (see FIG. 2B).
By passing an alternating current through the induction heating coil 22, magnetic flux is generated in the iron core 23. When this magnetic flux is linked to a molten metal circuit made of molten metal flowing in the flow path 13, an induced current is generated in the molten metal circuit, and the molten metal is heated by Joule heat generated by the induced current. Generally, the induced current generated in the one-turn molten metal circuit is a large current.

In order to detect molten metal leakage (melted metal leakage) due to melting or cracking of the refractories 18, 19, the refractory 18 in contact with the outer case 17 is placed along the outer case 17 and the refractory 19 in contact with the bushing 20. A hot water leak detection antenna 25 is embedded along each bushing 20. The distance between the flow path 13 and the outer case 17 and the bushing 20, that is, the thickness of the refractories 18 and 19 is about 100 mm to 400 mm, respectively.
The exterior case 17 and the bushing 20 are provided with water cooling tubes (not shown) for cooling each. The exterior case 17 and the bushing 20 are often water-cooled jackets. Since the water cooling facility attached to the induction heating device 11 is designed to exhibit a cooling capacity corresponding to the rated output of the induction heating device 11, it is overcooled in a low output state.

Next, a cooling method for the induction heating apparatus according to an embodiment of the present invention will be described.
The refractories 18 and 19 are made of a powdered and irregular refractory material called dry stamp material or dry ramming material, and the refractories 18 and 19 contain a small amount of free water or crystal water. Further, since the stamp material is driven in by a rammer, the moisture contained in the atmosphere is confined in the induction heating device 11 as the induction heating device 11 is installed. Since the moisture contained in the atmosphere varies depending on the season of construction, the amount of moisture trapped in the induction heating device 11 also varies depending on the season of construction. It may be considered as the amount of water contained in the atmosphere at 35 ° C. and humidity 40-70%.

As described above, moisture is always present in the induction heating device 11, and this inevitably present moisture induces erroneous detection of hot water leakage. In other words, when shifting from the heat retention operation to the heating operation, moisture evaporated from the vicinity of the flow path 13 is condensed in the vicinity of the exterior case 17 and the bushing 20 where the temperature has not risen yet, and in the nearby refractory. Form a wet part. As a result, the electrical resistance value decreases via the refractory wetted portion between the outer case 17 and the hot water leak detection antenna 25, and erroneous hot water leak detection occurs.

This will be described in more detail. In the induction heating device 11, the molten metal in the flow path 13 is treated as a secondary coil, and the molten metal is heated by Joule heat generated by the current flowing through the secondary coil. The temperature distribution is such that the side that comes into contact with the exterior case 17 and the bushing 20 that are high-temperature and water-cooled is the lowest.
When the output of the induction heating device 11 is shifted from the low output state to the high output state, the temperature of the flow path 13 is increased by the applied power. Along with this, the temperature distribution of the refractories 18 and 19 shifts to the high temperature side, so that the region where moisture can exist as a liquid in the induction heating device 11 decreases and is expelled from the high temperature side in the refractories 18 and 19. The collected moisture accumulates in the vicinity of the inner surfaces of the outer case 17 and the bushing 20 to form a wet portion in the nearby refractory. As a result, the electrical resistance value decreases via the refractory wetted portion between the outer case 17 and the hot water leak detection antenna 25, and erroneous hot water leak detection occurs.

Therefore, in the cooling method of the induction heating apparatus according to the present embodiment, the temperature of the cooling water flowing through the water cooling pipe is 40 ° C. or more at each inlet of the outer case 17 and the bushing 20 (inlet of each water cooling jacket), and the outer case. 17 and the outlets of the bushing 20 (exit of each water-cooled jacket) are set to be less than 100 ° C.

FIG. 3 is a graph showing the temperature distribution of the refractory temperature and the dew point in the vicinity of the outer case when the cooling method of the conventional induction heating apparatus is used for each operating state. The thickness of the refractory was 100 to 400 mm, the molten metal temperature was 1300 to 1500 ° C., and the actual range was used. The amount of heat dissipated in the furnace body was constant regardless of the temperature.
In the figure, the line A1 represents the refractory temperature during the heat insulation operation, and the line B represents the refractory temperature during the heating operation. The line C1 represents the temperature of the refractory during the transition period from the heat retention operation to the heating operation, and represents the case where the output increase rate is fast (over 0.1 MW / min). On the other hand, the A0 line represents the dew point during the heat retention operation, and B0 represents the dew point during the heating operation. Further, C0 represents a dew point in a transition period in which the heat retaining operation is shifted to the heating operation.

The following can be seen from FIG.
(A) Since the outer case 17 is cooled, the temperature of the refractory becomes lower as it gets closer to the outer case 17, and the temperature of the outer case 17 (refractory thickness 0 mm) during the heat insulation operation is 30 ° C., heating operation The temperature of the outer case 17 at that time is 40 ° C. When shifting from the heat retaining operation to the heating operation, the temperature of the molten metal in the flow path 13 that is induction-heated increases, and the temperature of the outer case 17 also starts increasing with a time lag.
(B) In the region where the refractory temperature is 100 ° C. or higher, the adsorbed water in the refractory evaporates and the amount of water decreases. Conversely, the region where the refractory temperature is less than 100 ° C. has a large amount of moisture (high dew point). However, since the refractory has air permeability, it is considered that there is no large deviation in the moisture content.
(C) At the time of heating operation, since the area below 100 ° C. is reduced as compared with that at the time of heat insulation operation, the amount of water (dew point) in the area below 100 ° C. increases. In other words, the dew point increases in the vicinity of the outer case 17 with the transition from the heat retaining operation to the heating operation.

(D) If the refractory temperature is lower than the dew point, there is a high possibility of condensation. When condensation occurs, a wet portion is formed in the refractory material between the hot water leak detection antenna 25 and the outer case 17, and the electric resistance value between the hot water leak detection antenna 25 and the outer case 17 is interposed therethrough. Lowers and causes false detection of hot water leaks. If the heat transfer operation rapidly shifts to the heating operation, the dew point of the part increases before the refractory temperature of the part close to the outer case 17 rises to 40 ° C. For this reason, C1 <C0 at a portion close to the outer case 17, and condensation is temporarily generated, causing erroneous detection of hot water leakage.

On the other hand, FIG. 4 is a graph showing the temperature distribution of the refractory temperature and the dew point in the vicinity of the outer case when the cooling method for the induction heating device according to the present embodiment is used. In the figure, the A2 line is the refractory temperature during the heat insulation operation, and the C2 line is the refractory temperature during the transition period from the heat insulation operation to the heating operation, and the output increase rate is fast (0. 1 MW / min). The other lines are the same as in FIG. The test conditions are the same as in FIG.

The following can be seen from FIG.
(E) Even in the case of a rapid transition from the heat retaining operation to the heating operation, the temperature of the refractory in the vicinity of the exterior case 17 is always 40 ° C. or higher, so C2> C0 and no condensation occurs.

Note that the same phenomenon as in FIGS. 3 and 4 also occurs in the vicinity of the bushing 20.

Here, two specific hardware configurations for realizing the cooling method for the induction heating apparatus according to the present embodiment will be described.
(1) Use a thermostat or other temperature controller to turn off the chiller so that the chiller turns off when the cooling water temperature reaches 40 ° C and the chiller turns on when the cooling water temperature reaches 100 ° C. ON / OFF control.
(2) A bypass path in which a part of the cooling water bypasses the chiller is provided. When the temperature of the cooling water is less than 40 ° C., the temperature of the cooling water is set to 40 ° C. or more by allowing a part of the cooling water to flow through the bypass path.

If the flow rate of the cooling water is suppressed, the water temperature at each outlet of the outer case 17 and the bushing 20 increases, but the water temperature at each inlet of the outer case 17 and the bushing 20 does not increase. That is, there is a risk that condensation occurs near the entrances of the outer case 17 and the bushing 20. However, since the outer case 17 has a thickness of 30 to 40 mm and the bushing 20 has a thickness of about 10 mm, the refractory temperature in the vicinity of the hot water detection antenna 25 is maintained at 40 ° C. or higher only by controlling the flow rate of the cooling water. This may be possible depending on the conditions.

Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of matters described in the claims. Other possible embodiments and modifications are also included.

10: induction furnace, 11: channel type induction heating device (induction heating device), 12: scrap charging inlet, 13: flow channel, 14: central flow channel, 15: side flow channel, 16: end flow channel, 17 : Outer case, 18, 19: Refractory material, 20: Bushing, 21: Cavity, 22: Induction heating coil, 23: Iron core, 24: Horizontal member, 25: Hot water leak detection antenna, 26: Support base

Claims (1)

A refractory that forms a loop-shaped flow path through which molten metal flows , an outer case that covers the refractory, a bushing that is lined on the inner peripheral surface of the refractory, and an attachment to the outer case and the bushing A cooling method for a channel-type induction heating apparatus comprising a water-cooled tube , an induction heating coil disposed in the center of a cavity defined by the bushing, and a hot water leak detection antenna embedded in the refractory. ,
The temperature of the cooling water flowing through the cooling water pipe is, wherein the coolant is a position where the respective starts heat exchange of the outer casing and the bushing, 40 ° C. or higher in the inlet of the outer casing and the bushing, and wherein A cooling method for an induction heating apparatus, wherein the cooling water and each of the outer case and the bushing are at a position where heat exchange is finished, and each outlet of the outer case and the bushing is less than 100 ° C.

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