JPH0358649B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for detecting the glass level of a melter, which can accurately detect the glass level regardless of the glass composition or temperature, and particularly relates to a method for detecting the glass level of a melter, which is capable of accurately detecting the glass level regardless of the glass composition or temperature. It is suitable for ceramic melters for dry treatment.

(Prior Art) For example, as a method for treating highly radioactive waste liquid generated at a reprocessing plant, a technology has been developed in which the waste liquid and glass raw materials are made into molten glass at high temperature, and the molten glass is filled into a canister serving as a container for solidification.

That is, the highly radioactive waste liquid is subjected to appropriate pretreatment and is first supplied to the melter together with glass raw materials. In this way, the highly radioactive waste liquid becomes molten glass together with the glass raw materials in the melter. This molten glass is periodically filled into a canister. The glass is sealed in a filled canister and temporarily stored in a solidification facility.

In these processes, the glass melting furnace is tasked with the function of the primary barrier for the confinement of radioactive materials. Therefore, from the viewpoint of preventing the spread of contamination due to radioactive substances, it is necessary to detect the glass level in the melting furnace in order to prevent the release of radioactive substances from the melting furnace due to excessive supply of raw materials. Furthermore, from the viewpoint of protecting the direct current-carrying electrodes of the glass melting furnace, it is also necessary to detect the glass level to prevent excessive glass extraction.

However, no effective technology for detecting the melter glass level has yet been established. The reason is,
This is because the changes in the glass composition and temperature are larger than in a general glass melting furnace, making it impossible to fully compensate for them, resulting in errors in level detection.

A well-known type of level meter is an electric level meter, which applies a voltage between a probe electrode installed at the level of the glass to be detected and an electrode installed inside the molten glass. The level is detected by using the fact that an electric circuit opens and closes depending on the contact state of the sensor. In addition, there are bubble level meters that detect gas pressure, reflective level meters that irradiate ultrasonic waves to the liquid surface, and hot junction level meters that use thermocouples, but these are complicated, expensive, and have poor durability. .

Electric level meters can be said to be an extremely simple means of detecting the glass level by a sudden change in the electrical resistance value, but the electrical resistance value of glass changes depending on the glass composition and temperature, and the level It is necessary to correct for factors other than fluctuations. For example, in Japanese Patent Publication No. 52-24524, in addition to the first and second electrodes for detecting the level, a third electrode for detecting changes in temperature and material is provided, and the It is said that the detected value is corrected by the detected value by the second electrode and the third electrode, and changes in the temperature and material of the molten glass are canceled out to obtain a true level change.

In cases where the temperature distribution and material of the molten glass change uniformly within the furnace, correction using the third electrode is considered to be effective. Unlike general glass melting furnaces, which continuously draw out molten glass in a small amount compared to the amount of glass in the furnace, ceramic melters for vitrification, which have an extremely small internal volume, are able to handle changes in temperature. varies depending on the location in the furnace, that is, changes in temperature distribution are important, and to correct all of these, a large number of correction electrodes are required.

The ceramic melter for vitrification is housed in a small room called a cell that has taken strict measures to prevent radioactive contamination, and the internal capacity of the furnace is reduced to a minimum in order to ensure heat generation when the molten glass for one canister is drawn out. Since the capacity is so small that only the necessary amount of molten glass remains, there is no room for installing multiple electrodes, and in any case, the method of detecting the glass level of the melter is limited by operating conditions and design conditions, and is not safe. Further improvements were desired.

(Objective of the Invention) The technical object of the present invention is to be able to accurately detect the glass level using only the first electrode and the second electrode, regardless of changes in glass composition or temperature. Technical means to provide a level detection method particularly suitable for ceramic melters for treating highly radioactive waste liquid by vitrification, and to prevent excessive supply of waste liquid and excessive withdrawal of molten glass. The goal is to take the following steps.

(Structure of the Invention) In order to achieve the above-mentioned object, as shown in the claims, the rate of change in electrical resistance value is detected via a differential calculation circuit, preferably a ratio change rate. This is how it was done.

The electrical resistance value changes both due to changes in the glass level of the molten glass and changes in the specific resistance of the glass, which is controlled by composition and temperature, but changes when the glass level passes near the probe electrode. Note that the rate of change in resistivity is significantly larger and steeper than the rate of change in resistivity due to composition and temperature, and the moment when the rate of change shows the maximum value is the moment when the glass level matches the reference level to be detected. It is characterized by the fact that

The ratio change rate is the rate of change in resistance divided by the previous original value, and it is less affected by glass composition and temperature than simply the rate of change, and the detection method using the ratio change rate is more preferable. It can be said.

(Embodiment) FIG. 1 shows a block diagram for explaining the method of the present invention. The ceramic melter 10 has a plurality of sets of melting electrodes, and has basically the same structure as a general glass melting furnace in which glass raw materials are introduced from the upper part and molten glass is taken out from the lower part, and only the main parts are illustrated. .

A first electrode 13 for level detection is provided on the reference level surface 11 of the molten glass.
A second electrode 14 is provided inside. A high frequency power supply device 20 is connected between these two electrodes via a resistor 21, and constantly applies a high frequency voltage of 3KHz.
A differential calculation circuit 30 is connected to both terminals of the resistor 21 via a DC conversion circuit 31, and the calculation results are indicated by a meter 32. What is indicated by the symbol Rg is the equivalent resistance between the electrodes 13 and 14.

In such a configuration, when the glass surface is at a (-) level 11a lower than the reference level surface 11,
The equivalent resistance Rg is an extremely high resistance value. and in the (−) level range, the change in level and
Since Rg is irrelevant, Rg
remains flat. However, it is clear that when the glass level rises and reaches the reference level (0), at that moment Rg changes to a low resistance value and shows a curve as shown in Figure 2A.

Next, if we look at the case where the glass level continues to rise, after it exceeds the reference level surface 11, Rg does not change and remains flat.

However, as mentioned above, the resistance value of glass varies depending on changes in temperature and composition, so Rg may change as shown in (1), (2), or (3). However, these changes are generally slow.

The above-mentioned change in Rg is expressed as a change in the 3KHz high frequency current, and is taken out by the resistor 21 as a voltage value. Then, when the high frequency voltage is converted to a DC value via the DC converter 31 and differentiated, the time (t) is calculated.
It is shown as a curve of the rate of change as shown in Fig. 2 (b) over the course of . In other words, the glass level changes from a (-) level to a (+) level as time passes, and at the moment when the glass level reaches the reference level (0) during this period, the meter 32 displays the maximum rate of change and returns to the reference level (0).
When the value exceeds 0, the rate of change is displayed as 0 again. Even if the electrical resistance value Rg changes slightly as shown in (1), (2), or (3), it is a gradual change, so it is not output as a rate of change and therefore does not generate noise.

(Effects of the Invention) As described above, the present invention detects the rate of change by calculating the change in the electrical resistance value of molten glass using a differential calculation circuit, and detects the glass level at the maximum value of the rate of change. This is the moment when the resistance value matches the desired reference level surface, and there is no need to compensate for changes in resistance due to temperature or composition.Therefore, no compensation electrodes are required, so the configuration is simple and the ceramic melter is compact. It is suitable for

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining the method of the present invention, FIG. 10 is a ceramic melter, 11 is a reference level surface, 12 is molten glass, 13 and 14 are level detection electrodes, 20 is a high frequency power supply device, 21 is a resistor, 30 is a differential operation circuit, 31 is a DC conversion circuit 3
2 is a meter.

Claims (1)

[Claims] 1. Attach the first
A second electrode is disposed within the molten glass, and the electrical resistance value between the two electrodes is detected, and the speed of change in the electrical resistance value is detected via a differential calculation circuit. A glass level detection method characterized in that the time point at which the rate of change shows the maximum value is the moment when the glass level coincides with the reference level surface.