JPS62152586A - Method for washing tank - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for chemically cleaning the inner surface of a tank for storing chemical substances, particularly a spherical tank.

[Conventional technology]

Generally, when storing certain types of chemical substances, iron oxide (so-called rust) generated from the steel materials that make up the spherical tank is
It may act as a reaction catalyst for the substance. For example, the ethylene oxide monomer undergoes a polymerization reaction due to this rust, becomes a polymer, and becomes a monomer.

The contamination of this polymer is one of the major substances that cause quality deterioration, and the economic loss of tM due to this contamination is enormous, so in order to prevent this situation, it is used as a rust removal method when constructing the tank. or chemical cleaning is performed during periodic inspections.

[Problem that the invention seeks to solve]

Conventionally, the method of chemically cleaning this type of tank is a) (
There are three methods: 1) IR liquid cleaning, 1) foam cleaning, and 3) spray cleaning, but each method has the following drawbacks.

b) The volume of the object to be cleaned with liquid is often 100 m' or more,
Some large tanks exceed 1000m', and if a tank with such a volume is to be filled with liquid, the same volume of cleaning liquid will be required, and the cleaning cost will be significant, and the waste liquid must be disposed of. However, the necessary chemicals and processing equipment must also be prepared, which is economically very expensive and impractical.

Mouth) Foam cleaning: Add a foam generating agent to the cleaning solution, inject gas such as air,
This is a method of cleaning by generating foam and filling the container with this foam, but what is the feature of this method? Although only a very small amount of f1.51 is required, in the case of a spherical tank, the height inside the container will exceed 5 m, and at this height, before the foam reaches the top, it will be overwhelmed by its own load. compressed,
It is impossible to reach the top easily, and the inner wall area of the spherical tank is small compared to its volume, so the bubbles cannot effectively act on the wall surface, making it difficult to obtain a good cleaning effect. There is a fear that rust will remain on the wall and the intended purpose will not be achieved.

C) Spray cleaning The advantage of spray cleaning is that the cleaning liquid is sprayed in a tank using a pump to clean the walls.In this case, the cleaning liquid can be circulated and the amount of cleaning liquid can be small, making it economical. be. The spray method used in this method is a rotating jetter or a sprinkler.
(a device that sprinkles water while rotating) etc. are used.

These devices are often used because they are simple and their construction methods are economical.

The biggest drawback of this method is that the contact angle at the time the spray liquid reaches the wall surface varies;
The liquid that reaches the wall is reflected and does not spread sufficiently (
, the action is unstable. (11) The cleaning liquid acts intermittently, and the flow of the cleaning liquid on the wall surface is not constant. Due to these two points, the cleaning action on the inner wall surface of the tank becomes unstable, and rust may remain on the wall surface or new rust may occur. Therefore, it is difficult to completely remove the rust by spray cleaning, and there has been a long-awaited method for cleaning the inner wall surfaces of storage tanks, where the presence of iron rust such as ethylene oxide monomer is inconvenient. .

In any case, conventional cleaning methods have had problems with cleaning results.

It is an object of the present invention to eliminate these conventional drawbacks, to provide a chemical cleaning method that can more accurately clean the inner wall surface of a storage tank, is easy to handle, and is economical.

[Means for solving problems]

The present invention is a method for cleaning while flowing a cleaning liquid from the top of a spherical tank over the entire circumference of the tank's inner wall surface so as to form an even, steady, and stable liquid film.

That is, a? & When attempting to chemically clean the inner surface of a spherical tank without relying on the law, a falling film with a flow rate above a certain level is evenly formed, the gas is cut off from the wall surface, and the cleaning liquid comes into contact with the wall surface. We have discovered that safe chemical cleaning can be performed by stabilizing the properties of .

During implementation, from the north pole of the tank (the highest point of the spherical tank) to the large? It is impossible to stably form a liquid film of 100 ft, but according to the example, it was possible to achieve this at a point 60° above the center point of the tank.

On the other hand, since it is only necessary to clean up to 90% of the capacity due to the usage conditions of the tank, this point should be 47 points above the center point.
It is clear from the example that the point at 60° corresponds to the calculated position, and if the range is 60±5°, it is possible to form an even and stable falling film up to a point 47° upward from the center. became.

In addition, when spraying the cleaning liquid from a nozzle, 0.2k
g f / ci or more, there will be a lot of scattering due to reflection when colliding with the tank wall, making it difficult to form a stable liquid film, and below 0.05 kgf / c + d, it will be difficult to accurately adjust the liquid pressure; and 0.05 to 0.2 kg, since it becomes difficult to distribute the jet evenly from a large number of nozzles.
f/- range, preferably 0.1 kg f/c
The pressure of d is appropriate and the amount of cleaning liquid is 1.8 at the tank equator point.
~3.6 m'/m/h is appropriate, so 6 from the center
It was found that at the point above 0', it was 3.6 to 7.2 m''/ya/h.

〔Example〕

To explain an example in which the present invention is applied to a spherical tank, as shown in FIG. It is possible to form an even and stable falling film from the center to a point 47@ above by ejecting it into the tank l from the nozzle 7 located at a position of 60°±5'' upward.

In addition, when the cleaning liquid 2 is spouted from the nozzle 7, 0, 0
Range from 5 to 0.2 kg f/ct, preferably 0
．． A pressure of 1 kgf/cj is appropriate, and the amount of cleaning fluid is 3.6 to 7.2 at a point 60" above the center to make it 1.8 to 3.6 m'/m/h at the tank equator.
m ff/m/h is necessary for proper cleaning treatment.

A small amount of the cleaning 82 is stored at the bottom of the spherical tank l, and the pipe 6 including the pump 3 is set to circulate from the discharge port 1z to the manhole 11, and is sprayed onto the tank inner wall surface through the nozzle 7. That's what I do.

Further, it is preferable to arrange a flow meter 4 and a pressure gauge 5 in this pipe 6 and use it as a detection section that can adjust the flow rate and pressure range as described above. As the adjustment means, known means such as pulp adjustment, pump adjustment, and other adjustment means are selected and used. The nozzle 7 may be either a fixed nozzle or a rotating nozzle, as long as it forms a steady and stable falling liquid film of the cleaning liquid. It is preferable to use a closely spaced ring-shaped pipe with a number of nozzles on the outside of the pipe to spray the cleaning liquid so that the cleaning liquid constantly flows down onto the inner wall of the tank, i.e., so that there are no cuts in the liquid film.

Furthermore, in order to promote the cleaning effect, the cleaning liquid is heated. This heating method is performed by an electric heating method or a method such as injection of superheated steam, but a method using steam is generally often used.

Next, for comparison, an experimental comparative example based on the prior art and an example of the present invention will be shown.

Experimental Comparative Example A spherical tank (inner volume 500 m', diameter 9.84 m) storing ethylene oxide monomer was opened for periodic inspection.

As shown in Figure 3, the pipe 6 is connected from the bottom of the tank (South Pole side).
The cleaning liquid sent through the tank by a pump 3 is heated, passes through a flow meter 4, and is injected toward the inner surface of the tank from a rotary jetter (TOKOCLEAN JET) 7' installed inside the tank through a pipe 6. The injection pressure at this time is
Monitor with pressure gauge 5. The sprayed cleaning liquid flowed on the inner surface of the tank, returned to the bottom 2, and was circulated again through the same route.

First, ethylene oxide residue (polymer) adhering to the inner surface of the tank was removed by water washing, followed by chemical cleaning.

The specifications of the cleaning liquid at this time are shown in Table 1 below.

Table-1 Ammonium citrate 21% solution has approximately 2.800 iron ions
Ability to understand ppm i8.

The rotating jetter 7' rotates slowly (approximately 4
The injection nozzle attached to the main body rotates due to the reaction force of the injection.

This rotating shaft is disposed perpendicular to the rotating shaft of the main body, and its rotational speed is approximately 4 rpm, and one cycle of the rotary juicer is approximately 13 minutes.

The inner surface of the tank was chemically cleaned in this way, and the cleaning effect during this process was as shown in FIG. 4 (relationship diagram between time and iron ion concentration).

Iron ions that dissolve in this cleaning solution (rust dissolves)
Judging from four measurements, the elution of iron ions reached 3.800 pp+w after 5 hours, and 3.850 pp+w after 7 hours.
pp+*, the elution of iron ions had stopped, and it was determined that the rust had been dissolved and removed.

Thereafter, the acid cleaning solution is discharged, water cleaning is performed for 30 minutes, and rinsing is performed for 30 minutes using 0.1% ammonium citrate solution to finish the surface before performing rust prevention treatment. Furthermore, ammonia water was added to the same solution to adjust the pH to 9.5, and then the same solution was drained and a previously prepared rust prevention treatment solution (adjusted to pH 9.7 with ammonia water, 0.5% sodium nitrite) was added. was added), and the cyclic injection process was completed at 60°C for 4 hours.

After the cleaning process was completed, the inside of the tank was inspected and rust caused by reddish-brown iron oxide was found on the entire wall.

It has been found that prior art methods do not achieve the objective of removing rust when chemically cleaning large capacity spherical tanks.

In this case, when some of the remaining rust was removed from the tank and crushed in the same cleaning solution, it was found that it was dissolved in 30 minutes at 60'C. Therefore, although the rust was dissolved by washing with ammonium citrate, it was thought that new rust was generated in the subsequent treatment steps.

As a result of investigating the cause of this problem, it was found that rust occurs during the rinsing and neutralization process, and the conditions for this occurrence are when the liquid flows intermittently on the wall surface (rotating generator). .

The spherical tank used in the embodiment of the present invention was a conventional model with rust, and was cleaned as shown in Figure 1.The nozzle 7 was a rotating ring-shaped injection device, and the jet stream reached the inner wall of the tank. The position is 60'' above the center of the tank, and when the jet reaches the wall, the distance from the tank to the inner wall is 150 ~
It was set to 200 mW.

The cleaning specifications at this time are shown in Table 2.

Table 2 The reason why the ammonium citrate concentration was set to 2% is because the amount of adhered liquid was smaller than in the experimental comparative example.

The cleaning effect of the present invention example was evaluated using the same method as the experimental comparative example, and the relationship between the elapsed time and the eluted iron ion concentration is shown in FIG. That is, the iron ion concentration reached 1.900 ppm 2 hours after the start of cleaning, and 1.950 ppm after 4 hours.
There was a slight increase in ppm, and from this result it was judged that the rust had been completely dissolved and removed. Subsequent water washing, rinsing,
Neutralization and antirust treatment were performed in the same manner as in the experimental comparative example.

When the inside of the tank was inspected after cleaning, no red rust was found on the walls, but since the cleaning solution had not reached a position above 60@ above the center, only this area exhibited reddish-brown rust.

As shown in the examples of the present invention, it can be seen that the cleaning effect on the inner wall of the tank is sufficient.

The amount of rust removed at this time can be determined by the following formula.

20m3XI, 950 g/m' (1,950pp
m)=39. If OOOg = 39 kg of iron and the form of rust is Fe201, then the amount of rust removed is Fe, and the rust per unit area of the wall of the spherical tank is:
If calculated as the entire inner wall surface, it would be 55.8 kg.
55.8 kg 55.8 kgπD”
3.14X9.84” 304 g=0.1
8 becomes +r/n(.

The results of comparative experiments using conventional technology show that new rust can be reduced to 0.
18 kg/n (this means that it was generated.

This comparison also shows that the effects of the present invention are safe and sufficient.

〔Effect of the invention〕

The present invention allows the cleaning liquid to flow down from the top of the spherical tank so as to form an even, steady, and stable liquid film over the entire circumference of the inner wall of the tank, so that the flow of the cleaning liquid becomes a continuous flow on the inner wall of the tank, allowing the outside air to flow. Since the water is cut off from the flow, rust will be less likely to occur, and if the specific flow rate is selected, no rust will occur at all.This flow can be easily achieved by forming a stable water film, and the specific flow rate can also be The cleaning effect can be significantly improved without increasing the size of the cleaning device, safe chemical cleaning can be performed without the need to increase the size of the cleaning device, and the economic burden can be greatly reduced.

[Brief explanation of drawings]

FIG. 1 is an implementation flow of the method of the present invention, FIG. 2 is a diagram of its cleaning characteristics, FIG. 3 is an implementation flow of the conventional method, and FIG. 4 is a diagram of its cleaning characteristics. 1... Spherical tank, 2... Cleaning liquid, 3... Pump, 4... Flow meter, 5... Pressure gauge, 6... Piping, 7
···nozzle.

Claims (4)

[Claims] (1) In a method of cleaning by supplying cleaning liquid into contact with the inner wall of the tank, the cleaning liquid flows down from the top of the spherical tank to form an even, steady, and stable liquid film over the entire circumference of the inner wall of the tank. How to clean a tank while processing. (2) In the method according to claim 1, when forming the film, the starting point for forming the falling liquid film at the upper part of the inner wall surface of the tank is set 60°± above the horizontal plane from the center point of the tank.
A cleaning method that processes within a 5° position range. (3) In the method according to claim 1 or 2, the flow rate of the cleaning liquid is 3.6 to 7.2 m^3/per unit circumferential length of the inner wall surface of the tank at the starting point of the flow. m/h, and a cleaning method in which liquid is supplied so that it is in the range of 1.8 to 3.6 m^3/m/h at the equator point (position of the horizontal plane at the center of the tank). (4) In the method according to claim 2 or 3, the cleaning liquid is injected from a nozzle onto the inner wall surface of the tank to form a liquid film, and the injection pressure is 0.0% relative to the tank internal pressure. 0.05 to 0.2 kgf/cm^2, preferably 0.1 kgf/cm^2.