JP2009057253A - Glass melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass melting furnace where, during driving, the presence and position of deposits in the vicinity of the bottom part of a melting tank thereof are specified, and the vicinity of the deposition part thereof can be locally heated, thus the viscosity of the deposits is reduced and the deposits can be selectively extracted, and which can be continuously driven with high efficiency. <P>SOLUTION: The glass melting furnace comprises: a melting tank 14 with a structure whose bottom part is tilted downward toward a downflow nozzle 12; and a plurality of main electrodes 16 arranged at the side walls thereof, and wherein a glass raw material and a radioactive effluent charged to the inside of the melting tank are directly energized by the main electrodes, and are heated and melted by the generated Joule heat, and a molten glass is extracted from the downflow nozzle. The vicinity of the bottom part of the melting tank is installed with: a deposition part detection device specifying the presence and position of deposits; and a local heating device heating the vicinity of the deposition part specified thereby, and, by reducing the viscosity of the deposits by the local heating, the extraction of the deposits by the selective flow-down thereof is made possible. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a glass melting furnace for vitrifying radioactive waste liquid. More specifically, the presence and position of deposits are identified by a deposition location detector, and the vicinity of the identified deposition location is identified by a local heating device. The present invention relates to a glass melting furnace in which deposits can be selectively flowed down and extracted by local heating.

  A radioactive liquid waste generated from a nuclear facility such as a reprocessing plant is concentrated, supplied to a glass melting furnace together with a glass raw material, melted and vitrified. As a glass melting furnace, a main electrode is usually installed so as to face the side wall of the melting tank, and glass is heated and melted by using Joule heat generated by directly energizing the glass (direct energization method). This type of glass melting furnace is conventionally known, and its detailed structure is described in, for example, Patent Document 1. The molten glass is extracted by gravity from a falling nozzle provided at the bottom of the melting tank and injected into a glass solidified container. The obtained vitrified body is stored in a radioactive waste storage facility.

  By the way, the highly radioactive waste liquid generated from a reprocessing plant or the like contains metals (chromium, ruthenium, palladium, etc.) having low solubility in glass, and when they exceed the solubility, they precipitate as oxides. Some of these precipitates having a specific gravity greater than that of glass settle to the bottom of the melting tank and gradually accumulate at the bottom without being discharged from the flow nozzle. Glass with a high precipitate concentration has a lower electrical resistance and a higher viscosity than ordinary molten glass. For this reason, since the current for melting the glass is concentrated on the deposit, the current distribution is biased and the glass is hardly heated. In addition, the deposits obstruct the flow nozzle, obstruct the glass flow path flowing into the flow nozzle, and make it difficult to extract the glass from the flow nozzle.

In order to prevent the occurrence of such a situation, in the conventional method, when the deposit concentration is high and deposition is predicted, the supply of the glass raw material and radioactive waste liquid is stopped, and all the glass in the melting tank is discharged. It was necessary to take measures such as lowering the temperature of the glass melting furnace and removing the remaining deposits by physical or chemical methods. Thus, after removing the deposit, the operation of the glass melting furnace is resumed. Therefore, the operation of the glass melting furnace is interrupted, and not only the operation efficiency is lowered, but also a troublesome sediment removal operation is required, and the cost required for the furnace maintenance is increased.
Japanese Utility Model Publication 3-48183

  The problem to be solved by the present invention is to determine the presence and position of deposits in the vicinity of the bottom of the melting tank during operation of the glass melting furnace so that the vicinity of the deposit can be heated locally. The object is to reduce the viscosity of the product, to selectively extract deposits, and to allow the glass melting furnace to operate efficiently and continuously.

  In the melting and solidifying treatment of radioactive liquid waste in a glass melting furnace, metal oxides such as chromium, ruthenium, and palladium that are deposited at the start of operation gradually settle and accumulate at the bottom of the melting tank because of their high specific gravity. These deposits have a low electrical resistance and the viscosity decreases with increasing temperature. The present invention pays attention to such physical properties, specifies the presence and position of the deposit, and locally heats the vicinity of the deposit so that the viscosity of the deposit can be lowered and selectively extracted. It is a thing.

  The present invention includes a melting tank having a structure in which a bottom portion is inclined downward toward a flow nozzle, and a plurality of main electrodes disposed on a side wall of the melting tank. In a glass melting furnace in which waste liquid is heated and melted by Joule heat generated by energizing directly with the main electrode and the molten glass is extracted from the flow nozzle, the presence and position of deposits are specified in the vicinity of the bottom of the melting tank. By installing a deposition location detection device and a local heating device that heats the vicinity of the deposition location identified by the deposition location detection device, and by reducing the viscosity of the deposition by local heating, the selective flow of the deposition It is a glass melting furnace characterized by enabling extraction.

  For example, a plurality of bottom electrodes are dispersedly embedded at the bottom of the melting tank, the deposition point detection device detects deposits by a resistance measurement method between the bottom electrodes, and the local heating device directly connects between the bottom electrodes. It is configured to perform local heating by an energization method. Alternatively, a plurality of bottom electrodes are dispersedly embedded at the bottom of the melting tank, and a rod-shaped electrode can be inserted so as to reach the vicinity of the bottom of the melting tank, and the deposition point detection device is disposed between the bottom electrode and the rod-shaped electrode. The deposit may be detected by the resistance measurement method, and the local heating device may be configured to perform the local heating by the direct current method between the bottom electrode and the rod-shaped electrode.

  The deposition location detection device may be a probe that can be inserted so as to reach the vicinity of the bottom of the melting tank, and may be configured to detect deposits by a contact detection method. In addition, the local heating device can be configured to include a plurality of heat generating resistors dispersedly embedded in the bottom of the melting tank, and to perform local heating by energization heat generation to the heat generating resistors.

  In addition, the present invention uses these glass melting furnaces, and continues the glass melting operation by the main electrode, while locally heating the specified deposition position, so that the deposit is selectively flowed down and extracted. This is a method of operating a glass melting furnace.

  In the glass melting furnace according to the present invention, a deposition location detection device that identifies the presence and position of deposits and a local heating device that heats the vicinity of the deposition location identified thereby are installed near the bottom of the melting tank. By configuring, during the glass melting furnace operation, the presence and location of deposits are specified, and the vicinity of the deposit position is locally heated, thereby lowering the viscosity of the deposit and selectively flowing down the deposit. Can be extracted. Therefore, it becomes possible to carry out efficiently and continuously without interrupting the operation of the glass melting furnace, and the operation cost can be reduced.

  Here, a plurality of bottom electrodes are dispersedly embedded at the bottom of the melting tank, the deposition spot detection device is embedded in the resistance measurement method between the bottom electrodes, and the local heating device is directly energized between the bottom electrodes. The bottom electrode can be shared by both devices. A plurality of bottom electrodes and rod-shaped electrodes are used, the deposition point detection device is a resistance measurement method between the bottom electrode and the rod-shaped electrode, and the local heating device is a direct current method between the bottom electrode and the rod-shaped electrode. The electrode can be shared by the device.

  FIG. 1 is an explanatory view showing an embodiment of a glass melting furnace according to the present invention. A shows the entire configuration, B shows a deposition site detection device, and C shows a local heating device. The glass melting furnace 10 includes a melting tank 14 having a corrosion-resistant and fire-resistant structure with a bottom inclined downward toward the flow-down nozzle 12, and a plurality of main electrodes 16 arranged to face the side walls of the melting tank 14. It has. The highly radioactive waste liquid is sent to the glass supply system 18 and supplied into the melting tank 14 in a state where the glass raw material 20 is preliminarily soaked. The glass raw material and the highly radioactive liquid waste introduced into the melting tank 14 are directly energized by the main electrode 16 and heated and melted using the generated Joule heat, and the molten glass 22 is flowed down from the flow-down nozzle 12 and extracted. The gas generated at that time is discharged through the off-gas treatment system 24.

  As described above, the highly radioactive waste liquid contains a metal having low solubility in glass such as chromium, ruthenium, and palladium, and precipitates as an oxide or the like when the solubility is exceeded. Some of these precipitates 26 have a higher specific gravity than the molten glass 22. Therefore, in the glass melting furnace 10, metal oxides such as chromium, ruthenium, and palladium are deposited in the melting tank 14 at the start of operation, and settle to the bottom of the melting tank 14 as time passes. They are not discharged from the flow-down nozzle 12 but gradually accumulate and become deposits 28. By the way, since the electrical resistance of the molten glass 22 changes depending on the concentration of precipitates, the deposition state can be predicted by measuring the electrical resistance of the molten glass 22 sequentially during operation. The deposit accumulation status in the furnace can be monitored. Glass with a high precipitate concentration has a lower electrical resistance and a higher viscosity than ordinary molten glass. For this reason, the current that melts the glass is concentrated on the deposit, the current distribution is biased, and the glass is hardly heated. Since these deposits 28 have the property that the viscosity decreases as the temperature increases, the viscosity decreases when the periphery of the deposits is heated, and the deposits can be selectively flowed down.

  Therefore, in the present invention, a deposition location detection device that identifies the presence and position of deposits and a local heating device that heats the vicinity of the deposition location identified thereby are installed near the bottom of the melting tank 14. In this embodiment, a plurality of bottom electrodes 30 dispersedly embedded in the bottom of the melting tank 14 are used, which is a so-called “bottom fixed type”. As shown in FIG. 1B, the deposition location detection device is a resistance measurement method in which the electrical resistance between any adjacent bottom electrodes 30 is measured by an ohmmeter 32, and the local heating device is shown in FIG. 1C. As described above, a direct energization method is employed in which electricity is supplied from the power source 34 between the bottom electrodes 30 and heated. By measuring the electrical resistance between the adjacent bottom electrodes 30 by changing the bottom electrode 30, the presence and position of the deposit 28 can be specified from the distribution of the parts having low resistance values. Therefore, by electrifying between the bottom electrodes 30 corresponding to the position, the deposit 28 can be locally heated using the generated Joule heat, the viscosity can be lowered, the fluidity can be increased, and the flow can be lowered. . In this embodiment, the plurality of bottom electrodes 30 can be shared by the deposition point detection device and the local heating device, and there is an advantage that the configuration is simplified. Due to the local heating by the local heating device, the viscosity of the deposit is lowered, whereby the deposit 28 can be selectively extracted. As a result, an increase in the concentration of precipitates in the glass is suppressed, and the glass is easily heated.

  FIG. 2 is an explanatory view showing another embodiment of the glass melting furnace according to the present invention. Here too, A shows the overall configuration, B shows the deposition site detection device, and C shows the local heating device. Since the structure of the glass melting furnace main body may be basically the same as that shown in FIG. 1, the same reference numerals are given to corresponding parts, and description thereof will be omitted.

  In this embodiment, a plurality of bottom electrodes 30 distributed and embedded at the bottom of the melting tank 14 and a rod-shaped electrode 36 inserted from above so as to reach the vicinity of the bottom of the melting tank 14 are used. Formula ". As shown in FIG. 2B, the deposition location detection device is a resistance measurement method in which the electrical resistance between the bottom electrode 30 and the rod-shaped electrode 36 is measured with an ohmmeter 32, and the local heating device is shown in FIG. As shown in the figure, a direct energization method is employed in which a power source 34 energizes and heats between the bottom electrode 30 and the rod electrode 36. Therefore, also in this embodiment, the plurality of bottom electrodes 30 and the rod-shaped electrodes 36 can be shared by the deposition site detection device and the local heating device, and the configuration is simplified. By the local heating by the local heating device, the viscosity of the deposit 28 is lowered and fluidized, thereby realizing the selective extraction of the deposit 28.

  In the present invention, the deposition site detection device is not limited to the configuration as in the above embodiment. FIG. 3 shows an example in which a contact probe 40 is used. A vibration / impact sensor is attached to the probe 40 and inserted from above the melting tank 14, and the tip of the probe 40 is moved along the bottom surface while maintaining a slight distance from the inclined bottom surface of the melting tank 14. To identify the presence and location of deposits. This is because if there is a deposit, the tip of the probe contacts and can be detected by vibration / impact at that time.

  In the present invention, the local heating device is not limited to the configuration as in the above embodiment. FIG. 4 shows an example of the bottom fixed type, and FIG. 5 shows an example of the probe type.

  In the case of the bottom fixed type in FIG. 4, there is a heating resistor type as shown in A, an induction heating type as shown in B, or the like. In the heating resistor system, the heating resistors 42 are dispersedly arranged at the bottom of the melting tank 14, and the heating resistors 42 are energized to generate heat, thereby reducing the viscosity of the deposit 28. In the induction heating method, the coils 44 are dispersedly arranged at the bottom of the melting tank 14, and a high frequency current is supplied to the coils 44 to cause the deposit 28 to generate heat locally. In these cases, a separate electrode can be disposed near the heating resistor 42 and the coil 44, and the deposition site detection device can be configured using these electrodes. Of course, a system using a contact type probe may be used.

  Also in the case of the probe type of FIG. 5, there are a heating resistor type as shown in A, an induction heating type as shown in B, and the like. In the heating resistor method, a heating resistor 48 is incorporated at the tip of the probe 46, and the heating resistor 48 is energized to generate local heat, thereby reducing the viscosity of the deposit 28. In the induction heating method, a coil 52 is incorporated at the tip of the probe 50 and a high frequency current is supplied to the coil 52 to cause the deposit 28 to generate heat locally. In these cases, a plurality of electrodes 30 can be dispersedly arranged at the bottom of the melting tank 14, and the deposition site detection device can be configured using these electrodes 30. Of course, a system using a contact type probe may be used.

An example of a melting furnace operation method for treating radioactive waste liquid using the glass melting furnace according to the present invention is shown in FIG. The feature of this operation method is that it is not necessary to interrupt the operation of the melting furnace in order to remove deposits. The operation procedure is as follows, for example.
(A) The glass raw material and the radioactive liquid waste are charged into the melting tank (continuously charged throughout the operation period).
(B) The glass is heated and melted by energizing the main electrode.
(C) Since electric resistance changes according to the density | concentration of the precipitate in glass, deposition can be estimated by resistance measurement. In addition, the deposit detection is performed by the deposition point detection device in parallel with the electric heating. Note that the deposition location detector is calibrated in advance by utilizing the fact that there is no deposit in the melting tank at the beginning of the operation of the melting furnace.
(D) The above steps (a) to (c) are repeated until the glass holding amount in the melting tank reaches a specified value.
(E) When the glass holding amount in the melting tank reaches a specified value, heating of the falling nozzle is started to flow down the molten glass.
(F) When deposits are detected in the step (c), local heating is performed in the vicinity of the deposition position simultaneously with the falling nozzle heating. The deposit decreases in viscosity with heating and can be selectively flowed down. The local heating device causes the deposit to flow down from the flow nozzle while adjusting the heating output so that the deposit can flow down.
(G) The heating of the flow nozzle is continued until the flow rate of the molten glass reaches a specified value, and the flow of the molten glass is continued.
(H) When the flow-down amount of the molten glass reaches a specified value, the flow-down nozzle is stopped from heating and cooled to finish the glass solidification operation.

  In this way, even if deposits are accumulated at the bottom of the melting tank, the deposits can be selectively flowed down and extracted while continuing operation, and it is not necessary to stop the melting furnace. Efficiency will be greatly improved.

Finally, the characteristics of the glass that is the physical basis of the present invention will be described. In the glass melting furnace, metal oxides such as chromium, ruthenium, and palladium are deposited in the melting furnace as the operation starts, and deposit on the furnace bottom as time passes. Since the specific resistance of molten glass changes in accordance with the physical properties shown in FIG. 7 according to the concentration of precipitates, the deposition status can be predicted by measuring the specific resistance of the molten glass sequentially during operation. Thereby, the deposit accumulation situation in the melting furnace is monitored. As shown in FIG. 8, the viscosity of the deposit decreases as the temperature increases. Therefore, by heating the deposit and the surroundings by local heating, the viscosity can be lowered and the deposit can be selectively flowed down. Note that the glass measured in FIG. 8 is prepared so that the concentration ratio of Ru, Rh, and Pd contained in the high-level radioactive liquid waste is constant. Therefore, the concentration of RuO ₂ is shown as a representative on the x-axis in FIG. 8, but actually Rh and Pd also increase and decrease in proportion to RuO ₂ .

Explanatory drawing which shows one Example of the glass melting furnace which concerns on this invention. Explanatory drawing which shows the other Example of the glass melting furnace which concerns on this invention. Explanatory drawing which shows the other example of a deposition location detection apparatus. Explanatory drawing which shows the other example of a local heating apparatus. Explanatory drawing which shows the further another example of a local heating apparatus. The flowchart which shows an example of the operating method of a glass melting furnace. The graph which shows the relationship between a ruthenium oxide density | concentration of molten glass, temperature, and a specific resistance. The graph which shows the relationship between a ruthenium oxide density | concentration of molten glass, temperature, and a viscosity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Glass melting furnace 12 Flowing nozzle 14 Melting tank 16 Main electrode 18 Glass raw material supply system 20 Glass raw material 22 Molten glass 24 Off-gas treatment system 26 Precipitate 28 Deposit 30 Bottom electrode 32 Resistance meter 34 Power supply

Claims (6)

A melting tank having a structure in which a bottom portion is inclined downward toward the flow-down nozzle and a plurality of main electrodes arranged on a side wall of the melting tank, and the main material is added to the glass raw material and radioactive waste liquid charged in the melting tank. In a glass melting furnace that is heated and melted by Joule heat that is generated by energizing the electrode directly, and the molten glass is extracted from the flow nozzle.
In the vicinity of the bottom of the melting tank, a deposition location detection device that identifies the presence and position of deposits and a local heating device that heats the vicinity of the deposition location identified by the deposition location detection device are installed, and by local heating A glass melting furnace characterized in that the deposit can be extracted by selective flow down by reducing the viscosity of the deposit.   A plurality of bottom electrodes are dispersedly embedded at the bottom of the melting tank, the deposition location detection device detects deposits by a resistance measurement method between the bottom electrodes, and the local heating device is a direct energization method between the bottom electrodes The glass melting furnace according to claim 1, wherein local heating is performed.   A plurality of bottom electrodes are dispersedly embedded at the bottom of the melting tank, and a rod-shaped electrode can be inserted so as to reach the vicinity of the bottom of the melting tank, and the deposition point detection device has a resistance between the bottom electrode and the rod-shaped electrode. The glass melting furnace according to claim 1, wherein deposits are detected by a measurement method, and the local heating device performs local heating by a direct energization method between the bottom electrode and the rod-shaped electrode.   The glass melting furnace according to claim 1, wherein the deposition site detection device is a probe that can be inserted so as to reach the vicinity of the bottom of the melting tank, and detects deposits by a contact detection method.   5. The glass melting furnace according to claim 1, wherein the local heating device includes a plurality of heat generating resistors dispersedly embedded at the bottom of the melting tank, and locally heats the energized heat generated by the heat generating resistors.   Using the glass melting furnace according to any one of claims 1 to 5, the deposit is selectively flowed down by locally heating the specified deposition position while continuing the glass melting operation by the main electrode. A method of operating a glass melting furnace that operates to be extracted.

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