JP3839121B2 - Cleaning and dismantling method for alkali metal contaminants - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of cleaning and disassembling prior to disposal of tanks, containers, and equipment in which alkali metal contaminants, particularly sodium, remain attached.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as the above-described alkali metal contamination container and equipment cleaning and dismantling methods, water vapor cleaning shown in FIG. 2 and alcohol cleaning shown in FIG. 3 are generally known.
[0003]
Alkali metal has high chemical activity, reacts with cleaning agents such as water and alcohol, and releases hydrogen gas to be chemically inactivated. That is, in the case of sodium, it reacts with water to form sodium hydroxide and reacts with alcohol to ethoxylate. In this case, if the container and the equipment to be treated are filled with air, there is a risk that the released hydrogen gas reacts with oxygen in the air in particular to cause an explosion.
[0004]
The steam cleaning method shown in FIG. 2 will be described. In FIG. 2, reference numeral 1 denotes a container in which sodium N remains attached. An inert gas such as nitrogen gas is fed into the container 1 from the gas tank 2 to fill and replace the inside, and by injecting water vapor from the water vapor generator 3, the sodium N is changed to sodium hydroxide N ′. It is intended to inactivate sodium N. In FIG. 2, 4 is a drainage tank, and 5 is an exhaust system in which a flame arrester (backfire prevention device) 6 is interposed.
[0005]
Also, FIG. 3 shows a cleaning method using alcohol, and parts common to those in FIG. In this case, an inert gas such as nitrogen gas is filled in the container 1 from the gas tank 2, and the alcohol 8 is injected from the alcohol tank 7 into the container 1 via the pump 8. The alcohol 8 is circulated by a circulation pump 9.
[0006]
In this way, after alkali metal (sodium N) is inactivated and hydrogen gas is no longer generated, the container 1 is disassembled and discarded by mechanical means such as a gas cutting method.
[0007]
[Problems to be solved by the invention]
However, according to the conventional method described above, it is necessary to always inject an inert gas in order to remove the danger of explosion caused by hydrogen gas, alcohol, or steam, a continuous inert gas injection device, water vapor Many additional devices such as a device for injecting a cleaning agent such as alcohol or the like are required, the operation becomes complicated, and the cost including the work execution cost increases.
[0008]
OBJECT OF THE INVENTION
Therefore, the present invention pays attention to the actual situation and problems of the related art, and solves such problems, thereby obtaining more reliable safety and reducing the cost required for equipment and work. An object of the present invention is to provide a method for cleaning and disassembling an alkali metal contaminant that is supposed to be sufficient.
[0009]
[Means for Solving the Problems]
In order to achieve this object, the method for cleaning and decomposing alkali metal contaminants according to the present invention covers at least the surface of the existing alkali metal with a sand layer, then introduces moist air to reduce the hydrogen concentration. The alkali metal is reacted to inactivate, and when the inactivation is completed and generation of hydrogen ceases, mechanical dismantling work is performed in an air atmosphere. In the case of a small amount, it is characterized by injecting a small amount of water as an auxiliary, and when the hydrogen concentration becomes a remarkable value, the introduction of the above-mentioned moist air is stopped and an inert gas such as argon gas or nitrogen gas is injected. It is characterized by reducing the hydrogen concentration while exhausting while stopping the introduction of humid air at the end of the working time and injecting inert gas such as argon gas and nitrogen gas to replace the air Air, is characterized in that inlet of the gas, and closes the discharge port keep prevent ingress of air.
[0010]
[Action]
Such a configuration eliminates the need for a continuous injecting apparatus for inert gas such as nitrogen gas and an injecting apparatus for cleaning agents such as water vapor and alcohol, which have been required in the past, and greatly reduces costs in terms of equipment and work. In addition, by providing a sand layer, more reliable safety can be obtained as described below.
[0011]
That is, by covering at least the surface of the alkali metal with a sand layer, it is anticipated due to the expected water retention in the target container, the internal local part of the equipment, or the inflow of water when a small amount of water is injected. Even if a large amount of hydrogen gas is generated at one time, the explosive hydrogen gas reacts with water to generate heat and sequester high-temperature alkali metals, and ignition It can be prevented from becoming a source.
[0012]
Moreover, even if the explosive hydrogen gas contained in the sand layer starts an explosion on the surface of the alkali metal where the temperature is high, the explosion flame is cooled and extinguished by passing through the sand layer, and the outside of the sand layer A large amount of explosive gas does not reach the flame and disappears only by a small explosion in the sand layer.
[0013]
Furthermore, when a large amount of water passes through the sand layer, the flow area is widened on the water outflow side due to the action of water retention and diffusion of sand, and in addition, the water flow peak is leveled and flattened. . Therefore, it is possible to prevent the passing water from concentrating and reacting with the alkali metal at a time, and it is possible to suppress the generation of a large amount of hydrogen gas and the high temperature of the reaction alkali metal serving as an ignition source.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a method for cleaning a sodium contaminated container embodying the present invention.
[0015]
In FIG. 1, reference numeral 10 denotes a container in which sodium N adheres and remains inside. In FIG. 1, at least the surface of the sodium 10 is covered with a sand layer 11, and a large amount of outside air including moisture is fed into the container 10 from the inlet horizontal piping of the container 1 by the blower 12. In this embodiment, air is supplied using the blower 12, but external air can be sucked using a fan or other means as necessary.
[0016]
In addition, in the figure, reference numeral 13 shown by an imaginary line is a water injection device for a very small amount of water, and water is injected into the container 10 by the pump 14, but the water injection device 13 is dry in the winter and the like and has low humidity. It will be used as a supplementary case. In the figure, reference numeral 15 denotes an exhaust system.
[0017]
Here, a specific example will be described with reference to FIG. 1. As the container 10, a cylindrical structure having a diameter of 3 m and a height of 8 m having a complicated structure not particularly shown inside is used. Some (sodium hydroxide) is present in about 2 t, and a plurality of (four locations) through holes are made in the lower body of the container 10, and dry sand is poured into the sand layer 11. The thickness of this sand layer 11 was about 30 cm.
[0018]
Next, a large amount of outside air is supplied by the blower 12 (more specifically, air supply amount is 50 m ³ / min, air temperature is 30 degrees Celsius, humidity is 80%, 1,169 Kgw / min water is injected, and air supply is performed for 5 hours a day. If it is performed for 4 days, 1403 Kgw of water will be injected). Moreover, in order to monitor the reaction state in the container 10, the hydrogen concentration in the container 10 was always measured with the measuring device.
[0019]
The reaction product adhering to the inner wall surface of the container 10 immediately after the start of air supply by the blower 12 begins to deliquesce, and the deliquescent solution and the reaction product flow down the inner wall surface of the container 10 to reach the surface of the sand layer 11. The deliquescent liquid was absorbed into the sand layer 11, and the reaction product further deliquescent on the surface of the sand layer 11. This process was extremely gentle.
[0020]
The sodium N in the lower end plate of the container 10 covered with the sand layer 11 reacted and became inactive due to the deliquescent liquid that passed through the sand layer 11 and the moisture diffused from the air on the surface of the sand layer 11. In this reaction process, a relatively intense reaction with a blunt explosion sound was occasionally observed in the sand layer 11, and it was found that the temperature slightly increased when the outer wall of the container 10 near the lower end plate was touched.
[0021]
When the hydrogen concentration in the container 10 becomes a significant value and exceeds the work continuation limit value for preventing explosions, air supply by the blower 12 is stopped and exhausted while injecting argon gas to calm the reaction. Waiting, when the hydrogen concentration decreased, air was blown again by the blower 12.
[0022]
When the working time of the day (the above-mentioned 5 hours) ends, the air supply is stopped, argon gas is injected into the container 10 to replace the air in the container 10, and the air supply and exhaust ports are blinded in that state. The plate was closed off with a plate to prevent outside air from entering the container 10 and left to stand.
[0023]
The above work process was repeated, and one week later, when no increase in the hydrogen concentration was observed even when air was supplied, it was judged that the inactivation was completed, and the operation was shifted to the dismantling work.
[0024]
The container 10 was disassembled by gas cutting. Cut the two parts of the body of the container 10 near the upper end plate and the lower end plate, water the upper and middle parts to wash away the remaining reaction products, and remove the sand from the bottom end plate part with a scoop. While dismantling, the attached reaction product was scraped off and washed with water.
[0025]
In the specific embodiment described above, the operation could be completed while being extremely economical and ensuring a large level of safety.
[0026]
【The invention's effect】
The alkali metal contaminant cleaning and disassembling method according to the present invention is configured as described above. Therefore, further safety is ensured, the cost required for equipment and work is greatly reduced, and the troublesomeness of the work itself is eliminated.
[Brief description of the drawings]
FIG. 1 shows a cleaning method embodying the present invention.
FIG. 2 is a diagram showing a conventional technique and a cleaning method using water vapor.
FIG. 3 is a diagram showing a conventional technique and a cleaning method using alcohol.
[Explanation of symbols]
10 Container 11 Sand layer 12 Blower 13 Small amount of water injection device 14 Pump 15 Exhaust system N Sodium

Claims (4)

Cover at least the surface of the existing alkali metal with a sand layer, then introduce humidified air to ventilate, reduce the hydrogen concentration and react with the alkali metal to inactivate it. A cleaning and dismantling method for alkali metal contaminants, characterized in that mechanical dismantling work is performed in an air atmosphere at the time when the generation disappears. 2. The method for cleaning and disassembling an alkali metal contaminant according to claim 1, wherein when the moisture content of the moisture-containing air is low, a small amount of water is injected as an auxiliary. When the hydrogen concentration becomes a significant value, the introduction of the moisture-containing air is stopped, the exhaust gas is exhausted while injecting an inert gas such as argon gas and nitrogen gas, and the hydrogen concentration is lowered. A method for cleaning and disassembling an alkali metal contaminant according to claim 1 or 2. At the end of the work time, the introduction of humid air is stopped, inert gas such as argon gas and nitrogen gas is injected to replace the air, and the air, gas inlet and outlet are closed, and the air The method for cleaning and disassembling an alkali metal contaminant according to claim 1, 2 or 3, wherein intrusion is prevented.

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