JP3922623B2 - Crucible abnormality detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for detecting an abnormality in a heating and heating process of a crucible used for melting incombustible materials such as metal and concrete, or burning inflammable ash as it is after burning combustible materials. is there.
[0002]
[Prior art]
In order to melt metals and incombustible materials at a high temperature for waste disposal, or to burn incinerated ash as it is after burning combustible waste, alumina, silicon carbide, for example, is used inside a high-frequency melting furnace. A method is adopted in which a ceramic crucible made of, for example, is set and induction heating is performed by a surrounding induction coil. Crucibles are, of course, inspected before use, and only those that are not defective in appearance are used. However, in the process of heating and raising the crucible to a high temperature of 1500 ° C. or higher, a large tensile stress due to thermal expansion may occur in the lower part of the cylinder, causing local cracks or peeling on the outer surface of the lower part of the cylinder. There is.
[0003]
Such an abnormality is very slight in the initial stage, but if it is ignored and heating and heating is continued as it is, the crucible may be damaged in the worst case. Therefore, the present inventors examined a method of monitoring a change in the appearance of the crucible by arranging a television camera inside the melting furnace. However, since this method has the following problems, it has been found difficult to put it into practical use.
(1) Since the gap between the crucible and the refractory surrounding the outer periphery is as narrow as several centimeters, in order to monitor the entire circumference of the crucible from this gap, a large number of TV cameras of 10 or more are required.
(2) It is difficult to obtain a heat-resistant camera that operates stably in a high temperature environment of 1500 ° C. or higher.
(3) Since the surface of the crucible is in a red hot state, it is difficult to grasp the change in the appearance image with a television camera, and even if a temperature camera is used, the initial minute cracks and peeling cannot be detected.
[0004]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems and can detect crucible abnormality immediately and accurately when a crack or peeling occurs on the outer surface of the crucible in the heating and heating step. It was made to provide a method.
[0005]
[Means for Solving the Problems]
The present invention has been made in order to solve the aforementioned problem, see contains carbon or carbon compound, in the step of heating heating a ceramic crucible having a glaze layer for preventing oxidation on the surface, purge flow around the crucible It is characterized by measuring the concentration of CO ₂ or CO in the air and detecting abnormalities in which fine cracks or peeling occurs on the surface of the crucible due to the change. In this case, it is preferable to sample the purge air from a location below the height of the crucible. The present invention is particularly suitable for use when a crucible is heated by a high-frequency melting furnace.
[0006]
According to the crucible abnormality detection method of the present invention, when fine cracks or peeling occurs on the surface of the ceramic crucible in the heating temperature raising step, the carbon or carbon compound contained in the crucible reacts with oxygen in the air. Thus, CO ₂ or CO is utilized. Since this chemical change proceeds instantaneously in a high temperature state, it is possible to detect the abnormality of the crucible with very high accuracy by measuring the concentration of CO ₂ or CO in the purge air.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention are shown below.
FIG. 1 is a cross-sectional view showing a state in which a crucible 1 is set inside a high-frequency melting furnace. The crucible 1 is made of ceramic that can withstand high temperatures, and is placed on a lifting platform 2, and its outer periphery is surrounded by a cylindrical refractory wall 3 at intervals of several centimeters. A coil (not shown) for induction heating is installed on the outer periphery of the refractory wall 3 to heat the crucible 1 in which the object to be melted is charged.
[0008]
Although the objects to be melted are various as described above, the heating temperature is preferably 1500 ° C. or higher because the melting point of the most iron in the metal waste is about 1500 ° C. However, from the relationship between the strength of the crucible 1 and the generated thermal stress, it is not preferable to set the heating temperature to 2000 ° C. or higher. In practical operation, the maximum temperature is preferably 1600 ° C. or lower. The induction heating furnace is roughly classified into a low-frequency induction furnace having a frequency of 50 to 200 Hz and a high-frequency induction furnace having a frequency of 500 to 10 kHz, and a region of 500 to 1000 Hz is preferable in terms of electric efficiency and melting rate.
[0009]
In order to perform induction heating, a conductive heating element is required. Considering the case where the content to be melted is a nonconductive material such as ceramics or concrete, black smoke powder or tar pitch is contained in the ceramic. A conductive crucible containing carbon such as is generally used. In this case, the carbon content is preferably 30 to 40%. If it is less than 30%, heat generation is difficult and the melting performance is lowered, and if it exceeds 40%, the strength is lowered.
[0010]
In addition, when the content to be melted is limited to a conductive material containing a metal, it is not necessary to make the crucible 1 itself conductive, and therefore a carbide ceramic containing a carbon compound such as SiC should be used. There are many. The present invention is applicable to both ceramic crucibles containing these carbons and ceramic crucibles containing carbon compounds. Note that a glaze for preventing oxidation at a high temperature is usually applied to the surface of both the conductive and non-conductive crucibles 1.
[0011]
As shown in FIG. 1, a purge air supply port 4 is provided at the lower part of the refractory wall 3, and an upward purge air flow as shown in the figure is formed around the crucible 1. This purge air has a role of preventing the combustion gas when the contents are heated and combusted from flowing in the direction of the lifting platform 2.
[0012]
In the present invention, the purge air is sucked from the sampling nozzle 5 and the concentration of CO ₂ or CO is measured by the analyzer 6. If the surface of the crucible 1 is healthy, the CO ₂ concentration is stable at about 350 ppm as in the atmosphere, and the CO concentration is almost zero. However, if cracking or peeling occurs on the surface of the crucible 1 in the heating and heating process, the anti-oxidation glaze layer is broken, and oxygen in the purge air reacts instantaneously with carbon or carbon compounds contained in the crucible 1 to produce CO _2. Or it becomes CO. Therefore, by measuring the concentration of CO ₂ or CO with the analyzer 6, it is possible to instantaneously detect an abnormality in the surface of the crucible 1.
[0013]
Note was confirmed by experiments, CO concentration in the heating temperature of 600 ° C. is extremely higher than the CO ₂ concentration, it was confirmed that the better of 1000 ° C. In the CO ₂ concentration becomes extremely high. The temperature at which the CO concentration and the CO ₂ concentration are reversed is around 800 ° C. For this reason, it is preferable to use a CO ₂ concentration meter and a CO concentration meter as the analyzer 6 in order to cover the entire temperature range. If only the high temperature range of 800 ° C. or higher is required, only the CO ₂ concentration meter is used. Use it.
[0014]
In the present invention, it is possible to detect only the abnormality of the surface of the crucible 1 generated below the position where the sampling nozzle 5 is installed. For this reason, it is preferable to raise the installation position of the sampling nozzle 5 in order to cover as wide a range as possible. However, if the sampling nozzle 5 is brought close to the mouth of the crucible 1, it malfunctions due to the influence of CO ₂ generated from the melted material inside the crucible 1, so that the total height of the crucible 1 is about 70% or less. It is preferable to do. As described above, cracks and peeling of the crucible 1 are highly likely to occur in the lower part of the body, so there is no actual harm even if the surface near the mouth of the crucible 1 is removed from the detection target.
[0015]
【Example】
Examples of the present invention are shown below.
A ceramic conductive crucible containing carbon was prepared by applying a glaze to the surface, filled with metal, a heat insulating material, and concrete, set in a high frequency induction furnace, and heated to raise the temperature. After the start of temperature increase, the CO ₂ concentration in the purge air of the crucible was continuously measured.
When the temperature of the crucible reached about 1650 ° C. about 65 minutes after the start of temperature increase, the concentration of CO ₂ in the purge air rapidly increased from about 500 ppm to 4200 ppm. Therefore, the melting operation was stopped by lowering the temperature of the crucible. After the stop, the external appearance of the crucible was examined, and fine cracks were formed on the surface. The crack was only on the surface and there was no leakage of the melt.
[0016]
The temperature of the crucible and the behavior of the crucible temperature and CO ₂ concentration after the temperature reached 800 ° C. or higher are shown in the graph of FIG. It is combustion of carbon on the crucible surface that the CO ₂ concentration begins to rise at about 800 ° C., and a gradual decrease at about 1100 ° C. is an antioxidant effect due to the burning of the glaze applied to the crucible surface. The reason why the CO ₂ concentration suddenly increased after about 65 minutes was that the surface on which no glaze was applied was exposed due to the occurrence of cracks, and the carbon in that portion burned rapidly.
Thus, the change in the CO ₂ concentration due to the occurrence of cracks was remarkable, and could be easily detected.
[0017]
【The invention's effect】
As described above, the crucible abnormality detection method according to the present invention measures the concentration of CO ₂ or CO in the purge air flowing around the crucible and detects the abnormality of the surface of the crucible based on the change. If the height is equal to or less than the nozzle, it is possible to quickly and reliably detect an abnormality occurring in any part of the crucible surface. Moreover, since the method of the present invention is not an appearance inspection, it is possible to accurately grasp abnormalities on the surface of the crucible in a red hot state, and it is not necessary to arrange a large number of sensors around the crucible, so the equipment cost is also low. There are also benefits. When an abnormality is detected by the method of the present invention, it is possible to immediately take measures such as stopping the temperature rise, so that a crucible breakage accident can be prevented in advance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of the present invention.
FIG. 2 is a graph showing changes in crucible temperature and CO ₂ concentration in Examples.
[Explanation of symbols]
1 crucible, 2 lift, 3 refractory wall, 4 purge air supply port, 5 sampling nozzle, 6 analyzer

Claims (3)

Look containing carbon or carbon compound, in the step of heating heating a ceramic crucible having a glaze layer for preventing oxidation on the surface, to measure the CO ₂ or CO concentration in the purge air flowing around the crucible, the A crucible abnormality detection method characterized by detecting an abnormality in which fine cracks or peeling occurs on the surface of a crucible due to a change.   The crucible abnormality detection method according to claim 1, wherein the crucible is heated by a high-frequency melting furnace.   The crucible abnormality detection method according to claim 1, wherein the purge air is sampled from a location below the height of the crucible. "

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