JP4815640B2 - Glass melting furnace - Google Patents

Description

  The present invention relates to a glass melting furnace for melting glass raw material in a melting tank using Joule heat by direct energization and vitrifying waste supplied into the melting tank together with the glass raw material. And inserting a hollow cooling rod with a tip swelled into a spindle shape into the center of the melting tank to ensure good flow of the molten glass and sufficient discharge. The present invention relates to a glass melting furnace that realizes a small amount of molten glass and suppresses deposition of conductive materials such as platinum group elements on the furnace bottom bath wall and prevents a reduction in processing capacity as much as possible. This melting furnace is useful for solidification treatment of various industrial wastes, in particular, vitrification treatment of high radioactive liquid wastes.

  Conventional electric melting furnaces for vitrification of waste glass are roughly classified into a refractory melting furnace and a metal melting furnace. The refractory melting furnace has a structure in which a furnace body and a melting tank are formed of refractory bricks, and one or a plurality of pairs of heat-resistant alloy heating electrodes are disposed on the side walls in the melting tank. On the other hand, a metal melting furnace has a structure in which one or a plurality of heating electrodes made of a heat-resistant alloy having the bath wall as a counter electrode are arranged in a melting bath having a bath wall made of a heat-resistant alloy. It is.

  In these electric melting furnaces, utilizing the fact that molten glass has conductivity, there is a direct energization method in which molten glass is heated by Joule heat generated by energizing molten glass in a melting tank via the heating electrode. It has been adopted. Here, when the radioactive liquid waste and the glass raw material are supplied onto the molten glass liquid surface from the upper part of the melting furnace, they are heated by the molten glass and become molten glass through the process of temperature rise, evaporation of moisture, and calcination. . Thereafter, the molten glass is discharged from the melting furnace and cooled to become a vitrified body.

  The soundness of the refractory bricks or metal materials constituting the melting furnace depends on the temperature of the molten glass in contact with them. Therefore, it is desirable that the temperature distribution of the molten glass in the melting tank is uniform. For this reason, various electrode arrangements have been attempted according to the shape of the melting furnace, the amount of waste disposal, and the like.

  By the way, when a high radioactive liquid waste is processed using such an electric melting furnace, the abnormal temperature rise of a furnace bottom bath wall arises, and the problem which a waste disposal capacity falls arises. This is because platinum group elements such as Ru, Pd, and Rh contained in highly radioactive liquid waste form a poorly soluble conductive material in glass and deposit on the furnace bottom. This is because the generated Joule heat is not sufficiently supplied to the upper molten glass liquid surface.

  For example, for refractory melting furnaces, Horst Wiese's “Industrial Vitrification of highly radioactive liquid waste in a Belgian Pamela plant” described on page 75 of Non-Patent Document 1 of High Level Liquid Waste with The PAMERA Plant in Belgium), the conductive properties of platinum group elements having a normal electrical resistance value of 1/3 were deposited on the bottom of the furnace. It has been reported that the glass production rate has dropped from 30 kg / hr to 20 kg / hr. In addition, Shinichiro Torada, described on page 82 of the same non-patent document 1, describes “Development of Glass Melter for PNC Tokai Vitrification Facility” (Development of Glass Melter for PNC Tokai Vitrification Facility) Several experiments using a laboratory-scale melting furnace with a bottom gradient showed that a 45 ° gradient was effective for discharging sediments composed of platinum group elements. It is reported that the effect was evaluated also from the test result of the melting furnace.

  Regarding the metal melting furnace, Non-Patent Document 2 contains a platinum group element in spite of good results regarding the extraction performance of the platinum group element in a metal melting furnace having a 45 ° furnace bottom gradient. It is described that the treatment capacity with the simulated waste liquid was confirmed to be 20% or more lower than the result of the test using the simulated waste liquid not containing platinum group elements. This is considered to be mainly due to the lowering of the heating current density distribution due to the fact that the concentration of the conductive platinum group element in the molten glass is higher at the upper and lower portions of the melting tank.

  As described above, in the conventional electric melting furnace, even though the furnace bottom has a gradient, sufficient discharge is not performed, and a small amount of conductive material is deposited on the bottom or slope surface of the glass melting furnace, It is expected that the concentration will increase, in which case the phenomenon of abnormal energization or a decrease in waste disposal capacity as described above will occur. In addition, when energization abnormality or reduction in processing capacity occurs, it is necessary to replace the melting furnace, and it is considered that processing of high radioactive liquid waste is delayed.

  Therefore, the present inventors, first, heat-resistant alloy cone furnace bottom bath wall, refractory brick vertical bath wall, the refractory brick vertical bath wall from the heat-resistant alloy cone furnace bottom bath wall The glass melting furnace which comprises a melting tank with the electrically insulated insulating vertical part bath wall was proposed (refer patent document 1). Although this glass melting furnace can suppress the occurrence of abnormal energization or a decrease in waste treatment capacity to some extent, it is not always sufficient. In addition, there is still room for improvement in terms of forming a flow near the bath wall when the molten glass flows and reducing the amount of molten glass in the melting tank.

JP 2008-37673 A

Proceedings of the International Topical Meeting on Nuclear and Hazardous Waste Management SPECTRUM'88 (Proceedings of the International Waste Management Conference Spectrum 88 held from 11 to 15 September 1988 in Pasco, Washington, USA) "Cylindrical electrode direct current melting furnace engineering test equipment 9th test (JCEM-E9 test)" (N8410 98-041)-Japan Atomic Energy Agency public research results report

  The problem to be solved by the present invention is to achieve a good flow formation in the vicinity of the bath wall when the molten glass flows down so that sufficient discharge is performed, and to realize a small amount of molten glass in the melting tank. Suppresses the deposition of conductive materials such as platinum group elements on the furnace bottom bath wall, thereby preventing a reduction in processing capacity as much as possible. And to keep the replacement part to a minimum and to allow smooth vitrification of the waste.

  In the present invention, the melting tank has a conical furnace bottom bath wall and a cylindrical vertical bath wall continuous above and serving as one heating electrode. The other heating electrode having the bath wall as a counter electrode is a cylindrical central electrode that includes cooling means and hangs down in the melting tank. Then, a cooling rod made of a heat-resistant alloy having a hollow structure in which a straight pipe portion and a tip portion bulging into a spindle shape are continuous, the straight pipe portion is located in the central electrode via an electrical insulator, and the tip portion is It installs in the said melting tank so that it may protrude from a center electrode lower end. As described above, in the present invention, the cooling rod made of a heat-resistant alloy having a hollow structure whose tip portion swells into a spindle shape is suspended in the center of the melting tank, and this is the most important feature.

  In the glass melting furnace according to the present invention, a cooling rod made of a heat-resistant alloy having a hollow structure in which the tip portion of the straight pipe portion swells into a spindle shape is suspended in the center of the melting tank. The flow formation in the vicinity of the wall is good, and coupled with the temperature control, the molten glass can be sufficiently discharged. Part of the heat generated by energization between the vertical bath wall (one heating electrode) and the central electrode heats the gas phase on the molten glass liquid surface through the vertical bath wall and central electrode made of heat-resistant alloy. Therefore, the melting rate of the raw material to be supplied can be accelerated, and the processing capacity is improved. As a result, it is possible to reduce the size of the melting furnace while maintaining the necessary processing capacity, so that the amount of glass held in the melting tank can be reduced, and in the case of high radioactive liquid waste processing, the platinum group in the melting tank Since the amount of elements held can be reduced, the amount of platinum group elements deposited on the bottom of the melting tank is reduced, and it is relatively easy to deposit due to the good flow formation by the bulging tip of the cooling rod. It becomes possible to discharge easily.

  In addition, the melting tank of the present invention is an integral structure made of a heat-resistant alloy consisting of a conical furnace bottom bath wall and a cylindrical vertical bath wall that continues above and serves as one heating electrode. The exchange is possible, and the central electrode can also be pulled out and exchanged, so that the exchange part can be kept to the minimum necessary, and the waste can be smoothly vitrified.

The longitudinal cross-sectional view which shows one Example of the glass fusing furnace which concerns on this invention. The top view of the glass melting furnace.

  The glass melting furnace comprises a vertical cylindrical melting tank, a glass material and waste supply port located at the top of the melting tank, a molten glass discharge port located at the bottom of the melting tank, and a heat-resistant alloy A melting furnace for waste glass solidification processing comprising a plurality of heating electrodes, and configured to heat and melt the glass raw material and waste supplied into the melting tank through the heating electrode and discharge the molten glass. It is. Here, the melting tank is a one-piece structure made of a heat-resistant alloy comprising a conical furnace bottom bath wall and a cylindrical vertical bath wall continuous above and serving as one heating electrode, and provided with cooling means. The other heating electrode having the bath wall as a counter electrode is a cylindrical central electrode that includes cooling means and hangs down in the melting tank. Then, a cooling rod made of a heat-resistant alloy having a hollow structure in which a straight pipe portion and a tip portion bulging into a spindle shape are continuous, the straight pipe portion is located in the central electrode via an electrical insulator, and the tip portion is It installs in the said melting tank so that it may protrude from a center electrode lower end.

  The center electrode is inserted from above to the position corresponding to the vertical bath wall along the center axis of the melting tank, and the tip portion of the cooling rod swelled into the spindle shape is surrounded by a conical furnace bottom bath wall. Installed to fit in the part. These central electrodes and cooling rods can be pulled out and replaced. Inside the vertical bath wall of the melting tank, a plurality of heating means are arranged in an upper stage and a lower stage, and these heating means can be drawn out and exchanged. A heating means is also provided around the furnace bottom bath wall of the melting tank.

  The entire outside of the melting tank is surrounded by an inner jacket provided with a cooling means, and the heating means around the melting tank and the furnace bottom bath wall is a unit from the inner jacket, or the melting tank is heated around the furnace bottom bath wall. It can be arbitrarily replaced as a unit together with the means or as a single melting tank.

  In the present invention, Joule heat is supplied by supplying glass raw material and highly radioactive liquid waste from the supply port of the melting tank and energizing between a vertical bath wall also serving as one heating electrode and a cylindrical electrode serving as the other heating electrode. And the surrounding glass is heated to form a molten glass containing waste. At that time, the temperature of the vertical bath wall and the central electrode, which are heating electrodes, is appropriately controlled by the cooling means. The molten glass flows along the conical bottom bath wall and is discharged from the outlet. At that time, a gradient of about 45 to 60 ° is provided at the bottom of the melting tank, and a spindle-type cooling rod is inserted at the tip, so that the molten glass flows smoothly and can be discharged sufficiently.

  Furthermore, in the present invention, a vertical bath wall made of a heat-resistant alloy is disposed above the surface of the molten glass, and heat of the high-temperature molten glass is efficiently transmitted to the upper space of the melting tank to increase the supply of heat to the raw material. . As a result, the waste treatment capacity is improved, the melting furnace can be downsized, and the glass holding amount in the melting tank can be reduced. In the case of treatment of highly radioactive liquid waste, the platinum group element holding amount in the melting tank also decreases. Accordingly, the amount of platinum group element deposited on the bottom of the melting tank is reduced, and in combination with the good flow formation by the bulging tip portion of the cooling rod, it can be discharged relatively easily even if deposited. A heating means is also provided around the discharge pipe continuous with the molten glass discharge port, and the heating means controls the outflow / stop of the molten glass containing waste from the discharge pipe.

  The drawings show an embodiment of a glass melting furnace for solidifying waste glass according to the present invention. FIG. 1 shows a longitudinal section thereof, and FIG. 2 shows an upper surface thereof.

  The glass melting furnace basically includes a vertical cylindrical melting tank 10, a glass material and waste supply port (not shown) located at the top of the melting tank, and a bottom of the melting tank 10. A glass having a molten glass outlet 12 and a plurality of heating electrodes made of a heat-resistant alloy, heated and melted by energizing the glass raw material and waste supplied in the melting tank through the heating electrode, and melted. Is discharged from the discharge port 12, and the waste is vitrified.

  The melting tank 10 is an integral structure made of a heat-resistant alloy, which includes a conical furnace bottom bath wall 14 and a cylindrical vertical bath wall 16 that continues upward and serves as one heating electrode. The furnace bottom bath wall 14 is provided with a 60 ° gradient slope toward the molten glass outlet 12 located in the center of the bottom. The vertical bath wall 16 is provided with an air cooling type cooling means 17. The entire outside of the melting tank 10 is surrounded by an inner jacket 20 provided with cooling means. The surrounding area is piled up with various refractory bricks and various heat insulating bricks 22, and the outside is covered with a metal casing 24 for maintaining the structure and maintaining the strength. As a result, the melting furnace is excellent in corrosion resistance, fire resistance and heat insulation, and has sufficient strength.

  The heating electrode is composed of a combination of the vertical bath wall 16 and a cylindrical central electrode 26 suspended in the melting tank 10. The central electrode 26 is also provided with an air cooling type cooling means 27. The central electrode 26 can be installed at an arbitrary height in the melting tank 10, and is inserted from above along the central axis of the melting tank 10 to a position corresponding to the vertical bath wall 16. In addition, the lifetime of these heating electrodes is extended by cooling the vertical bath wall 16 and the center electrode 26 which are heating electrodes by a cooling means.

  A cooling rod 30 made of a heat resistant alloy is installed in the cylindrical central electrode 26. The cooling rod 30 has a hollow structure in which a straight tube portion 30a and a tip portion 30b that swells into a spindle shape are continuous, and the straight tube portion 30a is located within the cylindrical central electrode 26, and the tip portion 30b. Protrudes downward from the lower end of the central electrode 26 and is installed so as to be within a portion surrounded by the conical furnace bottom bath wall 14. The tip portion 30b has a closed structure, and an air pipe 32 is inserted from the straight pipe portion 30a to the vicinity of the bottom of the tip portion 30b. Cooling air is supplied from the air pipe 32, is discharged from the lower end opening thereof, forms an air flow that rises inside the cooling rod 30, and is configured to cool the surrounding molten glass and control the temperature. . In order to electrically insulate the cooling rod 30 from the central electrode 26, an electrical insulator 34 is provided on the outer peripheral side of the straight pipe portion 30a of the cooling rod 30. The central electrode 26 and the cooling rod 30 can be pulled out and exchanged.

  In the vertical bath wall 16 of the melting tank 10, a plurality of heating means (such as resistance heating elements) 40 are incorporated in a dispersed state, divided into an upper stage and a lower stage. Thereby, the glass surrounded by the vertical bath wall 16 is heated to be meltable, and the starting operation of heating the glass in the melting tank 10 to a temperature at which direct energization can be performed is controlled. These heating means 40 can be pulled out and replaced. Further, a heating means (resistance heating element or the like) 42 is also installed around the furnace bottom bath wall 14 of the melting tank 10. Here, it is distributed in four locations. The heating means 42 heats the glass surrounded by the conical furnace bottom bath wall 14 so that the glass can be melted. Thereby, especially when discharging the molten glass containing waste, the glass accumulated at the bottom of the melting tank is easily discharged.

  As described above, the entire outside of the melting tank 10 is surrounded by the inner jacket 20 provided with cooling means, and the heating means 42 around the melting tank 10 and the bottom bath wall is used as a unit from the inner jacket 20 or melted. The tank 10 can be arbitrarily replaced as a unit together with the heating means 42 around the bottom bath wall or as a single melting tank 10. In addition, the peripheral structure outside the inner jacket (various refractory bricks, various heat insulating bricks 22, metal casing 24, etc.) is reused.

  Furthermore, the heating means 52 is also installed around the discharge pipe 50 extending downward from the molten glass discharge port 12 located in the center of the furnace bottom. For this, for example, an induction heating coil or a resistance heating element is used. This heating means 52 controls the start and stop of molten glass discharge. When the ambient temperature of the discharge pipe 50 is increased by the heating operation, the molten glass accumulated at the bottom of the melting tank can be discharged. When the temperature around the discharge pipe 50 is decreased by stopping the heating operation, The discharge can be stopped.

  In such a glass melting furnace, each cooling means is operated to cool the vertical bath wall 16 and the central electrode 26, while the glass is formed between the vertical bath wall 16 and the central electrode 26, which are heating electrodes for direct energization. Direct energization is performed, and the surrounding glass is heated by Joule heat generated thereby, and a molten glass containing waste is formed. Note that an AC power source that can be energized and controlled by constant power control, constant current control, constant voltage control, or the like is used for a power circuit for direct energization heating (not shown). Thereby, the molten glass is maintained at an appropriate temperature, and a uniform temperature distribution is realized.

  When high-radioactive liquid waste and glass raw material are supplied onto the molten glass liquid surface from the raw material supply port at the top of the melting furnace, they are heated by the molten glass, and then go through the process of temperature rise, evaporation of moisture, and calcination Molten glass containing waste is formed. By providing a 45-60 ° gradient slope at the bottom of the melting tank and inserting a spindle-type cooling rod at the tip, a good flow of molten glass is formed, and the flow down along with temperature control by the cooling rod Smooth and the molten glass is fully discharged. In addition, a part of the heat generated by energization between the vertical bath wall (one heating electrode) and the central electrode is transmitted through the vertical bath wall and the central electrode made of a heat-resistant alloy to the gas phase portion on the molten glass liquid surface. Is heated, the melting rate of the raw material to be supplied can be accelerated, and the processing capacity is improved. As a result, it is possible to reduce the size of the melting furnace while maintaining the necessary processing capacity, so that the amount of glass held in the melting tank can be reduced, and in the case of high radioactive liquid waste processing, the platinum group in the melting tank Since the amount of elements held can be reduced, the amount of platinum group elements deposited on the bottom of the melting tank is reduced, coupled with good flow formation by the bulging tip of the cooling rod, It becomes possible to discharge easily. The waste gas generated during the melting process is discharged from the waste gas outlet.

  Furthermore, in the present invention, since the vertical bath wall made of a heat-resistant alloy is disposed above the surface of the molten glass, the heat of the high-temperature molten glass is efficiently transmitted to the upper space of the melting tank to supply heat to the raw material. Can be increased, and waste disposal capacity is improved.

DESCRIPTION OF SYMBOLS 10 Melting tank 12 Glass discharge port 14 Furnace bottom bath wall 16 Vertical bath wall 17 Cooling means 20 Inner jacket 26 Central electrode 27 Cooling means 30 Cooling rod 30a Straight pipe part 30b Tip part 32 Air piping 34 Electrical insulator 50 Exhaust pipe 52 Heating means

Claims (6)

A vertical cylindrical melting tank, a glass raw material and radioactive liquid waste supply port located at the top of the melting tank, a molten glass discharge port located at the bottom of the melting tank, and a plurality of heat-resistant alloy heatings In the melting furnace for radioactive waste vitrification treatment, comprising an electrode, heated and melted by energizing the glass raw material and radioactive liquid waste supplied into the melting tank through the heating electrode, and discharging the molten glass,
The melting bath has a conical furnace bottom bath wall and a cylindrical vertical bath wall which is continuous above and serving as one heating electrode, and has an integral structure made of a heat-resistant alloy and provided with cooling means. The other heating electrode with the wall as a counter electrode is a cylindrical central electrode that has cooling means and hangs down in the melting tank, and has a hollow structure in which a straight tube portion and a tip portion that swells into a spindle shape are continuous. A heat-resistant alloy cooling rod in which an air pipe is inserted from the straight pipe portion to the vicinity of the bottom of the tip portion and cooling air can be supplied from the air pipe , and the straight pipe portion is an electric insulator in the central electrode. The glass melting furnace is placed in the melting tank so that the tip portion protrudes from the central electrode.
  The central electrode is inserted from the top to the position corresponding to the vertical bath wall along the central axis of the melting tank, and the tip of the cooling rod that swells into the spindle shape is surrounded by the conical furnace bottom bath wall The glass melting furnace of Claim 1 installed so that it may fit in.   The glass melting furnace according to claim 1 or 2, wherein the central electrode and the cooling rod are drawable and replaceable.   The glass according to any one of claims 1 to 3, wherein a plurality of heating means are distributed and arranged on the vertical bath wall of the melting tank in an upper stage and a lower stage, and the heating means can be drawn and replaced. Melting furnace.   The glass melting furnace according to claim 4, wherein heating means is disposed around the furnace bottom bath wall of the melting tank.   The entire outside of the melting tank is surrounded by an inner jacket provided with a cooling means, and the heating means around the melting tank and the bottom bath wall as a unit from the inner jacket, or the melting tank together with the heating means around the bottom bath wall 6. The glass melting furnace according to claim 5, wherein the glass melting furnace can be replaced as a unit or as a single melting tank.

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