JP2008174396A - Method and apparatus for discharging molten glass from glass melting furnace - Google Patents

Abstract

An object of the present invention is to prevent the discharge efficiency of a platinum group element in the molten glass from decreasing even if the platinum group element concentration in the vicinity of the wall increases due to the precipitation of the platinum group element mixed in the molten glass in the melting tank. .
The viscosity of the molten glass in the melting tank is controlled by controlling the temperature of the molten glass in the portion to be discharged when discharging the molten glass in the melting tank to be higher in the vicinity of the wall than in the central portion. Is made lower in the vicinity of the wall than in the central portion, so that the molten glass having a high platinum group element concentration in the vicinity of the wall can be made easy to flow down.
[Selection] Figure 1

Description

  The present invention relates to a discharge method and apparatus for discharging molten glass melted in a glass melting furnace.

  In various types of industrial waste treatment, a technique has been proposed in which waste glass and glass are melted in a melting furnace, and then molten glass containing the waste is discharged from the melting furnace and solidified.

  Such an industrial waste disposal method is convenient as a means for vitrifying and processing a highly radioactive liquid waste.

  In such an electric melting furnace for solidifying waste used for industrial waste treatment, in a refractory melting furnace, a furnace body and a melting tank are formed by refractory bricks, and one or more pairs are formed on the side walls of the melting tank. It is a structure that maintains the molten glass at a high temperature by heat generated by disposing an electrode made of a heat-resistant alloy and passing it through the molten glass.

  The molten glass is discharged (extracted) from the melting tank so as to flow down from an outlet provided at the center of the bottom of the furnace. In order to increase the discharging efficiency, the wall surface of the bottom of the melting tank Is formed in the shape of a filter funnel having a slope inclined toward the discharge port.

JP-A-7-155728 Proceedings of the International Topical Meeting on Nuclear and Hazardous Waste Management SPECTRUM'88 American Nuclear Society, Inc. Cylindrical Electrode Direct Current Melting Furnace Engineering Test Unit 9th Test (JCEM-E9 Test)-High Radioactive Waste Liquid Solidification Research Report-February 1998 Tokai Works

As shown in FIG. 2, in the process of vitrifying highly radioactive liquid waste by a conventional electric solidification furnace for solidifying waste, as shown in FIG. 2, Ru (ruthenium), Pd (palladium), Rh (rhodium) contained in the waste Such as platinum group elements or their oxides (hereinafter referred to as platinum group elements) exist as particles in the molten glass, settle toward the bottom of the melting tank, and close to the bottom of the platinum group elements There is a phenomenon in which the concentration is increased and the viscosity of the molten glass is increased so that the molten glass in the portion is hardly discharged. For example, in a molten glass having a density of 2.5 g / cm ³ , a platinum group element that is hardly soluble in glass, such as RuO ₂ having a density of 7.05 g / cm ³ , accumulates at the bottom of the melting tank by coagulation sedimentation, flow, etc. There is a tendency to accumulate.

  In such a conventional electric solidification furnace for solidifying waste, in the electric heating type melting furnace, during the electric heating operation for melting the glass in the melting tank, the maximum temperature of the molten glass is 1200 ° C. in the upper region of the melting tank. Thus, control is performed such that a voltage is applied between any of the electrodes and the current is heated. Then, as shown in FIG. 3, when the molten glass is discharged, by applying a current between the main electrode and the bottom electrode and conducting heating by a predetermined time before the discharge start, the inside of the melting tank to be discharged The temperature of the lower molten glass is about 1000 ° C. in the central portion and about 850 ° C. in the vicinity of the wall.

At the time of discharging the molten glass, the concentration of the platinum group element in the molten glass of the discharge target portion is already higher in the vicinity of the wall than in the central portion due to the precipitation of the platinum group element. Incidentally, the concentration of the platinum group element in the molten glass in the central portion is, for example, about 0.7 wt% for RuO ₂ , and the concentration of the platinum group element in the molten glass in the portion near the wall is about 5 wt%.

  Molten glass has the property that when the concentration of the platinum group element increases, the viscosity rises even at the same temperature and it becomes difficult to flow, and the molten glass in the central portion and the portion near the wall caused by the temperature difference and platinum group element concentration difference described above. As shown in FIG. 4, the difference in the viscosity of the molten glass is about 80 Pa · s for the molten glass in the central portion (1), and about 800 Pa · s for the molten glass in the vicinity of the wall (2). Is about 10 times. Therefore, when the molten glass in the melting tank is naturally allowed to flow down and discharged from the outlet in a state where there is such a viscosity difference, only the molten glass having a low viscosity in the central portion (1) flows out from the outlet, and the wall A phenomenon occurs in which the molten glass having a high viscosity in the vicinity (2) does not flow out and remains along the inclined bottom wall surface in the melting tank.

  If such a phenomenon is repeated, this phenomenon increases, and the deposition of platinum group elements occurs and proceeds on the bottom wall portion in the melting tank, and the discharge efficiency of the platinum group elements in the molten glass decreases. .

  In addition, since the platinum group element is a conductive substance, when it is deposited on the wall portion of the melting tank, the current flow path by the electrode is changed and desired current heating is inhibited.

  One object of the present invention is to provide a molten glass discharging method and apparatus capable of preventing or reducing a decrease in the efficiency of discharging molten glass from the melting tank even if the waste to be solidified contains a platinum group element. Is to propose.

  Specifically, platinum group elements contained in the waste to be vitrified accumulate on the bottom and side walls of the melting tank to increase the viscosity of the molten glass in the molten part and discharge the platinum group elements in the molten glass. Is to prevent the inhibition.

  The present invention controls the temperature distribution of the molten glass in the melting tank so that the viscosity of the molten glass in each part of the melting tank can be adjusted, thereby facilitating the flow of the molten glass. Even if a platinum group element is mixed, the discharge efficiency of the molten glass is reduced or prevented.

Specifically, for example, the glass raw material introduced into the melting tank by Joule heat due to the current flowing in the molten glass by supplying power to the electrode provided on the wall of the melting tank and the electrode provided in the center of the melting tank In a molten glass discharging method and apparatus from a glass melting furnace for melting and heating waste and discharging the molten glass by flowing down from a discharge port provided at the bottom of the melting tank,
When discharging the molten glass in the melting tank, the temperature distribution of the molten glass in the melting tank is controlled by cooling the electrode provided in the center of the melting tank, etc. Viscosity can be adjusted.

  Further, in order to control the temperature distribution of the molten glass in the melting tank in order to adjust the viscosity of the molten glass in the melting tank, a heating device is provided on the wall of the melting tank, and the heating control by this heating device is provided. Is configured to be performed.

  According to the present invention, when the molten glass in the melting tank is discharged, the viscosity of the molten glass in the melting tank can be adjusted so that the waste to be vitrified contains a platinum group element. It is possible to prevent or reduce a decrease in the discharge efficiency of the platinum group elements in the molten glass from the melting tank.

In the best embodiment of the present invention, the method for discharging molten glass includes a glass raw material charged into a melting tank by Joule heat generated by a current flowing in the molten glass by supplying power to a pair or a plurality of electrodes provided in the melting tank. In a method for discharging molten glass from a glass melting furnace, in which waste is heated and melted, and the molten glass is discharged from a discharge port provided at the bottom of the melting tank.
When discharging the molten glass in the melting tank, the heating by the heating device provided on the wall of the melting tank is intensified and the electrode provided in the central part of the melting tank is cooled, so that the molten glass in the melting tank is cooled. The temperature distribution is controlled so that the viscosity of the molten glass in the melting tank is lower in the vicinity of the wall than in the central portion.

In addition, the glass melting furnace device is heated by a heating device provided on the wall of the melting tank, and Joule heat is generated by an electric current flowing in the molten glass by supplying power to the electrode provided on the wall of the melting tank and the electrode provided in the central portion. In the glass melting furnace apparatus that heats and melts the glass raw material and waste charged into the melting tank by the above and discharges the molten glass from the discharge port provided at the bottom of the melting tank,
When discharging the molten glass in the melting tank, means for lowering the temperature of the electrode provided at the center of the melting tank to lower the temperature of the molten glass near the electrode, and heating provided on the side wall of the melting tank It is set as the structure which provided the means to raise the temperature of the molten glass of the wall vicinity part of the said melting tank by an apparatus.

  In the first embodiment of the present invention, the temperature of the molten glass in the portion to be discharged when discharging the molten glass in the melting tank is controlled so that the portion near the wall is higher than the central portion. Near the wall due to sedimentation of platinum group elements mixed in the molten glass in the melting tank by making the viscosity of the glass lower in the vicinity of the wall than in the central part and facilitating the flow of the molten glass in the vicinity of the wall. Even if the concentration of the platinum group element is increased, the discharge efficiency of the molten glass is not lowered.

  FIG. 1 is a schematic view illustrating a longitudinal side surface of a melting furnace in the first embodiment.

  In FIG. 1, a melting tank 1 has a cylindrical portion 1 a in an upper region, a conical portion 1 b in a lower region, and a lower end of the conical portion 1 that opens to the outside via a discharge nozzle 2. The cylindrical part 1a of the melting tank 1 is provided with a cylindrical electrode 3 so as to be exposed in the tank, and an induction heating coil constituting auxiliary heating means is provided in the wall or the back surface of the conical part 1b. A pair of direct energizing electrodes or resistance heating elements 4 are provided, and a columnar electrode 5 that is paired with the cylindrical electrode 3 is provided at the center of the cylindrical portion 1a so as to hang down, and a lower end of the conical portion 1b. The part is provided with an annular bottom electrode 6 that allows the flow of molten glass.

  The columnar electrode 5 is a hollow body whose lower end is closed, and the columnar electrode 1 can be cooled by circulating the refrigerant in the columnar electrode 1 by installing the refrigerant supply cylinder 5a at the center thereof. Configure.

  Further, on the outer periphery of the discharge nozzle 2, a discharge control heating coil 7 that controls the flow in the discharge nozzle 2 by controlling the temperature of the molten glass in the discharge nozzle 2 to adjust the viscosity is installed. The discharge control heating coil 7 is constituted by an induction heating coil or a resistance heating element.

  A control device for arbitrarily applying a voltage between the cylindrical electrode 3 and the cylindrical electrode 5 and the bottom electrode 6 or generating a voltage for energizing the heating device 4 such as an induction heating coil is provided by a microcomputer or the like. Although it is configured and realized so as to be controlled, a description thereof is omitted.

  In such a melting furnace, melting of the raw material glass charged into the melting tank 1 is performed by applying a voltage between the cylindrical electrode 3, the column electrode 5, and the bottom electrode 6 to electrically heat the molten glass. In such heating, energization control is performed so that the maximum temperature of the molten glass is about 1200 ° C. Incidentally, the temperature of the molten glass of the lower area | region of the melting tank 1 at this time is about 700-900 degreeC.

  When the glass is melted, the coolant is supplied to the cylindrical electrode 3 and the column electrode 5 as necessary so that the cylindrical electrode 3 and the column electrode 5 are not overheated.

  Next, when the molten glass in the melting tank 1 is discharged, a heating device such as an induction heating coil and an induction heating coil by controlling voltage application between the cylindrical electrode 3 and the column electrode 5 before a predetermined time before the discharge starts. 4 to control the heating of the conical portion 1b of the melting tank 1 to selectively increase the temperature of the molten glass in the vicinity of the wall surface (4) of the conical shape portion 1b to about 1000 ° C. The temperature of the molten glass located in the central part (3) of 1 is maintained at about 850 ° C. Further, by cooling the cylindrical electrode 5 by increasing the supply amount of the refrigerant to the refrigerant supply cylinder 5 a of the cylindrical electrode 5, the temperature of the molten glass located in the vicinity of the cylindrical electrode 5 is lowered, and the lower side of the cylindrical electrode 5 It is possible to control the temperature of the molten glass located in the central portion (3) of the melting tank 1 to a low temperature state of about 850 ° C.

  When the temperature distribution of the molten glass in the melting tank 1 is in such a state, for example, the platinum group element concentration of the molten glass in the central portion (3) at the bottom of the conical portion 1b of the melting tank 1 is about 0.7 wt%. When the platinum group element concentration of the molten glass in the vicinity of the wall surface (4) is about 5 wt%, the molten glass of the central portion having a platinum group element concentration of about 0.7 wt% has a viscosity of about 300 Pa · s at about 850 ° C. The molten glass in the vicinity of the wall surface with a platinum group element concentration of about 5 wt% has a viscosity of about 100 Pa · s at about 1000 ° C. The viscosity of the molten glass in the melting tank 1 Therefore, it is easy to flow down.

  In such a state, when the molten glass in the discharge nozzle 2 is heated to a state where it can flow out by heating by the discharge control heating coil 7, the molten glass in the melting tank 1 flows out of the discharge nozzle 2 from the discharge nozzle 2 by natural flow due to its own weight. However, the viscosity of the molten glass in the conical portion 1b of the melting tank 1 is in a state where the wall vicinity portion (4) is reduced to about 約 with respect to the central portion (3) and is likely to flow down. The molten glass having a high platinum group element concentration in the vicinity of the wall flows down preferentially and is discharged.

  Thus, when discharging the molten glass in the melting tank 1, the viscosity of the molten glass in the cone-shaped portion 1 b is made lower by making the portion near the wall lower than the central portion, so that the platinum group element concentration is reduced. The molten glass in the vicinity of the high wall is preferentially flowed down and discharged, and accordingly, a decrease in the discharge efficiency of the platinum group elements in the molten glass in the melting tank 1 can be prevented or reduced.

  This Example 2 is melted by Joule heat due to the current flowing in the molten glass by heating by the heating device provided on the wall of the melting tank and supplying power to the electrode provided on the wall of the melting tank and the electrode provided in the central part. In a glass melting furnace apparatus that heats and melts the glass raw material and waste charged in the tank and flows the molten glass down through a discharge nozzle provided at the bottom of the melting tank, the molten glass in the melting tank is discharged. Sometimes, a cooling means is provided to lower the temperature of the molten glass in the vicinity of the electrode by lowering the temperature of the electrode provided at the center of the melting tank.

  FIGS. 5A and 5B are longitudinal front views of the melting tank portion of the glass melting furnace in the second embodiment. FIG. 5A shows an example of the temperature distribution when the glass is melted, and FIG. 5B shows an example of the temperature distribution when the molten glass is discharged.

  In FIG. 5, the melting tank 1 is configured to be surrounded by a conical heat-resistant furnace bottom wall 1c, an annular refractory brick vertical wall 1d, and a cylindrical heat-resistant alloy vertical wall 1e to form a melting space. The conical heat-resistant furnace bottom wall 1c forms an inclined wall surface narrowed by a 60 ° gradient toward the molten glass discharge nozzle 2 located below the center portion thereof. And various refractory bricks which have heat insulation are arrange | positioned on the outer side of these said part walls 1c, 1d, and 1e, Furthermore, the outer periphery is covered with a metal casing, and the whole furnace is comprised.

  The inclined wall surface in the conical heat-resistant furnace bottom wall 1c is formed by depositing the confined heat-resistant furnace bottom wall 1c on the wall surface of the conical heat-resistant furnace bottom wall by forming a platinum group element contained in the waste, forming a hardly soluble conductive material in molten glass. This is to make it possible to easily discharge the conductive deposit that causes an electrical problem from the molten glass discharge nozzle 2 together with the molten glass.

  Below the molten glass discharge nozzle 2, a glass solidified body container (not shown) is installed so that it can be taken in and out.

  Then, the molten glass discharge nozzle 2 is led out of the conical heat-resistant furnace bottom wall 1c to the outside of the furnace, and the molten glass discharge nozzle 2 is controlled by heating to control (outflow / shut off) the molten glass. A coil (not shown) is arranged to control whether the molten glass flows out of the molten glass discharge nozzle 2.

  A cylindrical electrode 5 made of a heat-resistant alloy is suspended from the center of a disc-shaped refractory brick (not shown) located on the ceiling of the furnace body. The heat-resistant alloy cylindrical electrode 5 hangs down from the center of the melting tank 1 so that the heat-resistant alloy vertical wall 1e is positioned as a counter electrode. The heat-resistant alloy cylindrical electrode 5 has an air-core structure and forms a cooling passage inside. The cooling passage is formed around the cooling air supply cylinder 5a by inserting a cooling air supply cylinder 5a having an open end concentrically into the air core portion of the cylindrical electrode 5 made of heat-resistant alloy. The cooling air supplied from the cooling air inlet provided at the upper end portion of the cylinder 5a is jetted from the tip opening to the air core portion to be circulated and discharged from the cooling air outlet provided at the upper end portion of the heat resistant alloy cylindrical electrode 5. Constitute. In addition, a cooling air jacket (not shown) is also provided in the heat resistant alloy vertical wall 1e to form a cooling passage. In addition, the means of Embodiment 1 can be combined as necessary.

  In the electric melting furnace configured as described above, the melting and heating of the glass charged in the melting tank 1 is caused by alternating current between the heat-resistant alloy vertical wall 1e and the heat-resistant alloy cylinder 5 as shown in FIG. This is performed by Joule heat generated by applying voltage to energize the molten glass. At this time, cooling of the heat-resistant alloy cylindrical electrode 5 by supplying cooling air to the heat-resistant alloy cylindrical electrode 5 is performed to such an extent that the heat-resistant alloy cylindrical electrode 5 is not overheated as necessary.

  When the current heating is controlled so that the maximum temperature of the molten glass in the melting tank 1 at this time is about 1150 ° C., the temperature distribution of the molten glass in the melting tank 1 is as shown in FIG. The temperature of the molten glass decreases in a substantially horizontal state from the upper layer portion to the bottom portion, and the temperature of the bottom portion is about 950 ° C.

  When the molten glass is to be discharged, as shown in FIG. 5 (b), the supply of cooling air to the cooling air supply cylinder 5a in the cylindrical electrode 5 made of heat-resistant alloy is increased for a predetermined time before the discharge starts. While the cooling of the cylindrical electrode 5 made of heat-resistant alloy is enhanced, the melting is caused by Joule heat generated by applying an AC voltage between the vertical wall 1e made of the heat-resistant alloy and the cylindrical electrode 5 made of the heat-resistant alloy and energizing the molten glass. Control is switched to heat the glass so that the maximum temperature is about 1150 ° C.

  Thus, if it switches to the energization heating while cooling the heat-resistant alloy cylindrical electrode 5, the temperature of the molten glass located in the vicinity of this heat-resistant alloy circular cylindrical electrode 5 will fall because the temperature of the heat-resistant alloy cylindrical electrode 5 will fall. As shown in FIG. 5B, the temperature distribution of the molten glass in the melting tank 1 is particularly about 900 ° C. at the bottom of the molten glass located immediately below the heat-resistant alloy cylindrical electrode 5. To fall. However, the molten glass located far from the heat-resistant alloy cylindrical electrode 5 and in the vicinity of the wall surface of the melting tank 1 has a high temperature of about 950 ° C. even at the bottom of the melting tank 1.

  In such a state, when the molten glass discharge nozzle 2 is heated to allow the molten glass to flow out, the molten glass in the melting tank 1 flows down from the molten glass discharge nozzle 2 by its own weight. At this time, the molten glass in the melting tank 1 has a relatively high temperature at a portion located in the vicinity of the conical heat-resistant furnace bottom wall 1c and a lower viscosity than the central portion. The molten glass in the vicinity of the high wall flows down preferentially and is discharged, so that the molten glass in the portion having a high platinum group element concentration does not remain in the melting tank 1.

  Thus, the structure which controls the temperature distribution of the molten glass in the melting tank 1 by switching the temperature of the heat-resistant alloy-made heated cylindrical electrode 5 when the glass is melted and when the molten glass is discharged is the melting efficiency and melting of the glass. This is advantageous for improving the discharge efficiency of platinum group elements in the glass together.

  Example 2 was configured to control the temperature distribution of the molten glass in the melting tank 1 by cooling the cylindrical electrode 5 made of heat-resistant alloy when discharging the molten glass in the melting tank 1, but from the time of melting the glass. While supplying cooling air to the cooling passage in the heat-resistant alloy cylindrical electrode 5 to cool the heat-resistant alloy cylindrical electrode 5, an AC voltage is applied between the heat-resistant alloy vertical wall 1 e and the heat-resistant alloy cylindrical electrode 5. A glass melting furnace with good discharge efficiency of platinum group elements in the molten glass even when the molten glass is deformed to be heated so that the maximum temperature is about 1150 ° C. by Joule heat generated by energizing the molten glass Can be realized.

It is a vertical front view of the glass melting furnace in Example 1 of this invention. It is a schematic diagram which shows the mechanism of platinum group element deposition in a melting tank. It is a schematic diagram which shows the molten glass discharge mode in the conventional melting furnace. It is a characteristic view which shows the relationship between the temperature of a molten glass containing a platinum group element, and a viscosity. It is a vertical front view of the melting tank part of the glass melting furnace in Example 2, (a) shows an example of temperature distribution at the time of glass melting, (b) at the time of discharge of molten glass.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Melting tank, 1a ... Ring-shaped refractory brick vertical part wall, 1b ... Conical heat-resistant furnace bottom wall, 2 ... Discharge nozzle, 3 ... Cylindrical electrode, 4 ... Cylindrical heat-resistant alloy vertical part wall, 5 ... Cylindrical electrode , 6 ... bottom electrode.

Claims (4)

In a method for discharging molten glass from a glass melting furnace, in which a glass raw material and waste charged in a melting tank are heated and melted and discharged from a discharge port provided at the bottom of the melting tank,
The molten glass from the glass melting furnace is characterized by controlling the temperature distribution of the molten glass in the melting tank so that the viscosity of the molten glass in each part in the melting tank can be adjusted when discharging the molten glass in the melting tank. Discharge method. By supplying electricity to a pair or a plurality of pairs of electrodes provided in the melting tank, the glass raw material and waste put into the melting tank are heated and melted by Joule heat due to the current flowing in the molten glass, and provided at the bottom of the melting tank. In a glass melting furnace apparatus that discharges molten glass by flowing down from an outlet,
When a heating device arranged on the gradient wall at the lower part of the melting tank is provided and the molten glass in the melting tank is discharged, the vicinity of the gradient wall in the melting tank is heated by the heating device provided on the gradient wall at the lower part of the melting tank. A glass melting furnace apparatus provided with means for raising the temperature of molten glass. By supplying electricity to a pair or a plurality of pairs of electrodes provided in the melting tank, the glass raw material and waste put into the melting tank are heated and melted by Joule heat due to the current flowing in the molten glass, and provided at the bottom of the melting tank. In a glass melting furnace apparatus that discharges molten glass by flowing down from an outlet,
A heating device disposed on the gradient wall at the bottom of the melting tank and a cooling member disposed at the center of the melting tank are provided, and when the molten glass in the melting tank is discharged, the heating provided on the gradient wall at the bottom of the melting tank There is provided means for increasing the temperature of the molten glass near the gradient wall in the melting tank by heating by the apparatus, and means for decreasing the temperature of the molten glass near the cooling member by cooling by the cooling member. Glass melting furnace equipment. Heated by a heating device provided on the wall of the melting tank and fed into the melting tank by Joule heat due to the current flowing in the molten glass by supplying power to the electrode provided on the wall of the melting tank and the electrode provided in the center part In a glass melting furnace apparatus that heats and melts glass raw materials and waste, and discharges molten glass by flowing down from a discharge port provided at the bottom of the melting tank,
A glass provided with cooling means for lowering the temperature of an electrode provided in the center of the melting tank to lower the temperature of the molten glass in the vicinity of the electrode when discharging the molten glass in the melting tank Melting furnace equipment.

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