JPH0134674B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for chemically cleaning the inner surface of a tank for storing chemical substances, particularly a spherical tank. [Prior Art] Generally, when a certain type of chemical substance is stored, iron oxide (so-called rust) generated from the steel materials that make up the spherical tank may act as a reaction catalyst for the substance. For example, ethylene oxide monomer undergoes a polymerization reaction due to this rust, becomes a polymer, and is mixed into the monomer. The contamination of this polymer is one of the major substances that cause quality deterioration, and the economic loss caused by this contamination is enormous, so to prevent this situation, rust removal methods are used during tank construction or periodically. Chemical cleaning is performed during inspection. [Problems to be solved by the invention] Conventionally, methods for chemically cleaning this type of tank include (a) full liquid cleaning, (b) foam cleaning, and (c) spray cleaning. It has some drawbacks. (b) Full liquid cleaning The volume of the target object is usually ^100m3 or more, and some large objects exceed ^1000m3 , so if a tank with such a capacity is to be filled with liquid, the amount of cleaning liquid will also be the same. This requires a large capacity and requires a large amount of cleaning costs. Furthermore, since the waste liquid needs to be treated, the necessary chemicals and treatment equipment must also be prepared, making it economically very expensive and impractical. (b) Foam cleaning This method adds a foam generating agent to the cleaning liquid, injects air or other gas to generate foam, and then fills the container with the foam for cleaning. Although it only takes a very small amount,
In the case of a spherical tank, the height inside the container is also 5m.
At this height, before the foam reaches the top, it is compressed by its own load,
impossible to reach the top easily;
Moreover, the inner wall area of the spherical tank is small compared to its volume, and the bubbles cannot effectively act on the wall surface, making it impossible to obtain a good cleaning effect and rust remaining on the wall surface, making it impossible to achieve the intended purpose. I'm worried that I can't do it. (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. It is. As the spray method used in this method, a rotating jetter or a sprinkler (a device that sprinkles water while rotating) is used. These devices are often used because they are simple and the construction method is simple. The biggest drawbacks of this method are (i)
The contact angle at which the sprayed liquid reaches the wall surface varies, and the liquid that reaches the wall surface is reflected and does not spread sufficiently, resulting in unstable action. (ii) 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 is 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. Ta. 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 the Problems] The present invention provides a method of cleaning by supplying a cleaning liquid to the inner wall surface of a spherical tank, in which the cleaning liquid is distributed over the entire upper circumferential area of the spherical tank without any gaps. The liquid is continuously sprayed radially at a pressure higher than the tank internal pressure in the range of 0.05 to 0.2 Kgf/cm ² to form an even, steady, and stable liquid film over the entire circumference of the tank's inner wall surface, and the liquid film is shaped into a sphere. This is a tank cleaning method in which water is allowed to flow evenly and naturally over the inner surface of the molded tank from the top to the bottom all around. In other words, when attempting to chemically clean the inner surface of a spherical tank without using the full liquid method, a falling film with a flow rate above a certain level is evenly formed to block gas and the wall surface, and the wall surface and It has been discovered that safe chemical cleaning can be performed by stabilizing the properties of the cleaning liquid that comes into contact with it. In practice, it is impossible to stably form a large liquid film from the north pole of the tank (the top point of the spherical tank), and according to the example, at a point 60° above the center of the tank, It was possible to achieve this. On the other hand, due to the usage conditions of the tank, it is only necessary to clean up to 90% of the capacity, so this point is calculated to be 47° above the center point, which is 60±
It has become clear from the examples that an even and stable falling film can be formed up to a point 47° upward from the center if the angle is within the range of 5°. In addition, when spraying cleaning liquid with a nozzle,
At 0.2Kgf/cm2 or ^more , when colliding with the tank wall,
There is a lot of scattering due to reflection, making it difficult to form a stable liquid film, and if it is less than 0.05 Kgf/cm ² , it is difficult to accurately adjust the liquid pressure and it is difficult to spray it evenly from a large number of nozzles. So, 0.05~
A pressure in the range of 0.2 Kgf/cm ² , preferably 0.1 Kgf/cm ² is suitable, and the amount of cleaning liquid is 1.8 to 1.8 kg at the tank equator.
Since 3.6 m ³ /m/h is appropriate, it was found that at a point 60° above the center, it would be 3.6 to 7.2 m ³ /m/h. [Example] To explain an example in which the present invention is applied to a spherical tank, as shown in FIG.
When chemically cleaning the inner surface of the tank, the cleaning liquid 2 is pumped by the pump 3 and sprayed into the tank 1 from the nozzle 7 located at 60°±5° above the center of the tank to form an even and stable falling film. It can be formed up to a point 47° upward from the center. In addition, when the cleaning liquid 2 is spouted from the nozzle 7, the amount is in the range of 0.05 to 0.2Kgf/ ^cm2 , preferably 0.1Kg
A pressure of f/cm ² is appropriate, and the amount of cleaning liquid is 3.6 to 7.2 m ³ /m/h at a point 60° above the center in order to achieve a pressure of 1.8 to 3.6 m ³ /m/h at the tank equator. This is necessary for proper cleaning treatment. A small amount of the cleaning liquid 2 is stored at the bottom of the spherical tank 1, and the pipe 6 containing the pump 3 is connected to the discharge port 1.
Set it so that it circulates from ₂ to manhole 1 ₁ ,
The liquid is sprayed through a nozzle 7 onto the inner wall surface of the tank. 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 valve adjustment,
Select and use pump adjustments and other adjustment methods. Further, 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. Comparative Experimental Example A spherical tank (inner volume 500 m ³ , diameter 9.84 m) storing ethylene oxide monomer was opened for periodic inspection. As shown in Fig. 3, the cleaning liquid is sent from the bottom of the tank (on the south pole side) through piping 6 by pump 3, heated, passes through flow meter 4, and is sent through piping 6 to a rotator installed in the tank. Jetstar (TOKO)
CLEAN JET) Spray toward the inner surface of the tank from 7'. The injection pressure at this time is monitored by a 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] The rotating jetter 7' rotates slowly (approximately 4 rpm) by the fluid pumped into the jetter body, and the injection nozzle attached to the body rotates due to the reaction force of the jet. . This rotating shaft is arranged perpendicular to the rotating shaft of the main body, and its rotation speed is 4 rpm, and one cycle of the rotating jetter takes about 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). Judging by measuring the concentration of iron ions (rust dissolves) dissolved in this cleaning solution, the elution of iron ions reached 3800 ppm after 5 hours, and after 7 hours.
It was determined that the iron ion elution had stopped and the rust had been dissolved and removed. After that, the acid cleaning solution is drained and water cleaning is performed for 30 minutes to finish the surface before applying rust prevention treatment.
Perform a 30 minute rinse using 0.1% ammonium citrate solution. Furthermore, ammonia water was added to the same solution to make the pH 9.5, and then the same solution was drained and the rust prevention treatment solution prepared in advance (with ammonia water, the pH was adjusted to 9.5).
9.7 and added 0.5% sodium nitrite),
Circulating injection treatment at 60°C for 4 hours was completed. After the cleaning process was completed, we inspected the inside of the tank and found that
Rust caused by reddish-brown iron oxide was observed all over the 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 soaked 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, we 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 (rotating jetter). . Embodiment of the present invention The spherical tank used in the implementation was a conventional example with rust, and was cleaned as shown in Figure 1.
The nozzle 7 is a rotating ring-shaped injection device and is installed so that the position where the jet stream reaches the inner wall of the tank is 60 degrees above the center of the tank. , so that it extends all the way around. The rotating ring-shaped injection device rotated at 1/3 to 1/5 rpm, and the distance from the injection nozzle to the inner wall of the tank was 150 to 200 mm. The cleaning specifications at this time are shown in Table 2.

〔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, and there is no need to increase the size of the cleaning device.Moreover, the nozzle can be operated without having to move it up, down, left or right inside the tank, and without changing the direction of the nozzle, making the device easy to operate. There are no restrictions on manufacturing, cheap and safe chemical cleaning is possible, and the economic burden can be greatly reduced.

[Brief explanation of drawings]

Figure 1 is the implementation flow of the present invention method, Figure 2 is its cleaning characteristic diagram, Figure 3 is the implementation flow of the conventional method, and Figure 4 is the implementation flow of the method of the present invention.
The figure shows its cleaning characteristics. 1... Spherical tank, 2... Cleaning liquid, 3... Pump, 4... Flow meter, 5... Pressure gauge, 6... Piping,
7... Nozzle.

Claims (1)

[Claims] 1. A method of cleaning by supplying and contacting the cleaning liquid with the inner wall surface of a spherical tank, in which the cleaning liquid is applied continuously over the entire upper circumferential area of the spherical tank without gaps, and at a pressure of 0.05% lower than the tank internal pressure. The liquid is sprayed radially at a high injection pressure in the range of ~0.2Kgf/ ^cm2 to form an even, steady, and stable liquid film over the entire circumference of the inner wall of the tank, and the liquid film is spread over the inner surface of the spherical tank. A tank cleaning method in which the water is treated evenly and naturally over the entire circumference from the top to the bottom. 2. In the method described in claim 1,
A cleaning method in which the starting point of forming a falling liquid film on the upper inner wall surface of a spherical tank when forming the above film is treated within a range of 60° ± 5° above the center of the tank with respect to the horizontal plane. 3. In the method according to claim 1 or 2, the flow rate of the cleaning liquid is 3.6 to 7.2 per unit circumferential length of the inner wall surface of the spherical tank at the starting point of the flow.
m ³ /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 (the position of the horizontal plane at the center of the spherical tank).