JP6565802B2 - How to clean the tank - Google Patents

Description

  The present invention relates to a tank cleaning method when a liquid leak occurs from a storage tank that stores a corrosive liquid.

  Conventionally, a sulfuric acid leaching method such as an HPAL (High Pressure Acid Leaching) method has been performed as a hydrometallurgical method for recovering valuable metals such as nickel and cobalt from nickel oxide ore. In the smelting of low grade Ni ore using HPAL technology, 98% concentrated sulfuric acid is used, and the process liquid after adding concentrated sulfuric acid becomes an acidic liquid having a pH of 2 to 4.

  In order to store such process liquids, the tank is usually made of carbon steel with a corrosion resistant lining such as rubber lining and solventless epoxy resin lining so that an acidic liquid can be used.

  A rubber lining in a tank, a solventless epoxy resin lining, or the like may cause pinholes due to deterioration due to aging, collision with foreign matters contained in slurry or solution, and the like. Corrosion also occurs on the outer surface of the tank starting from this pinhole, and the process liquid may leak from the tank.

  Regarding leakage of the process liquid from the tank, for example, Patent Document 1 discloses that a Zn coating is thermally sprayed to a thickness of 100 μm or more and 400 μm or less on the surface of a thick steel plate, and further 5% or more and 55% or less of Al It is described that corrosion of the bottom plate of an oil storage tank such as crude oil or petroleum is prevented by spraying a Zn coating containing 10 to 40 μm.

  Patent Document 2 discloses a tank for storing crude oil, oil, etc. in an oil storage tank installed on foundation soil such as mountain sand by mixing a non-electrolyte water-absorbing material into the foundation soil at the bottom of the tank. A method for preventing the bottom plate back surface from corroding is described.

JP-A-5-339696 JP-A-8-13174

  In case of leakage from the tank side wall, the process liquid leaking to the outer surface can be removed by washing, but the liquid leaking from the tank bottom accumulates between the outer surface of the tank bottom plate and the tank foundation, It will cause corrosion of the outer surface and tank foundation. Therefore, in order to prevent corrosion of the outer surface of the tank bottom plate and the tank foundation, it is necessary to wash the tank bottom plate and the tank foundation after draining the liquid in the tank.

  Although Cited Document 1 and Cited Document 2 describe a method for preventing corrosion of the bottom plate, they do not describe a method for cleaning a tank when a liquid leak occurs.

  In general, as a method of cleaning the liquid between the outer surface of the tank bottom plate and the tank base, there is a method of inserting a hose from the outer periphery of the tank between the outer surface of the tank bottom plate and the tank base and washing with water or chemicals. However, in this method, cleaning is performed from the outer periphery of the tank bottom plate toward the center, and sufficient cleaning is performed because the pressure is weakened until the cleaning water or chemical liquid (hereinafter also referred to as cleaning liquid collectively) reaches the vicinity of the tank center. There is a problem that the tank bottom plate may corrode due to an event that the process liquid cannot be completely discharged.

  The present invention has been proposed in view of such circumstances, and a tank cleaning method that can more reliably perform cleaning between a tank bottom plate and a tank foundation when a liquid leak of corrosive liquid occurs. I will provide a.

  In order to solve this problem, the present inventor has studied in detail and washed the corrosive liquid accumulated between the tank bottom plate and the tank foundation from the perforated part during repair in order to prevent the tank from being corroded due to the above-described liquid leakage. Invented a method to do.

That is, one aspect of the present invention is a tank cleaning method when a liquid leak has occurred from a bottom plate of a storage tank that stores corrosive liquid, and detects that a liquid leak has occurred at the bottom plate of the storage tank. The liquid leakage detection process, and when the liquid leakage is detected, the contents of the storage tank are removed, and the cleaning liquid is sent through the nozzle by installing the cleaning nozzle on the inner surface of the bottom plate of the storage tank. and a confirmation step of confirming that a cleaning step of cleaning the occurrence location of a leak, the cleaning of the occurrence point of leakage in the cleaning process being carried out sufficiently.

  According to one aspect of the present invention, since the cleaning nozzle is installed on the inner surface of the bottom plate of the storage tank, the cleaning can be performed radially from the tank bottom plate toward the outer periphery of the tank. Cleaning between foundations can be performed.

  At this time, in one aspect of the present invention, in the nozzle installation step, the plate with the nozzle may be installed by welding to the inner surface of the bottom plate of the storage tank.

  In this way, by firmly installing the nozzle, the nozzle is prevented from being detached by water pressure or the like during cleaning.

  In one embodiment of the present invention, in the nozzle installation step, a hole may be provided in the bottom plate of the storage tank, and the nozzle may be installed so as to face the hole.

  Thus, by providing a hole in the bottom plate of the storage tank, it becomes easier to send the cleaning liquid, so that the cleaning can be performed more efficiently.

  At this time, in one embodiment of the present invention, the storage tank may be provided with a recess or a crack on the inner surface of the bottom plate, and the recess or the crack may be processed to obtain a hole.

  Thus, if a hole is provided in a place where a dent or crack is generated, the bottom plate of the storage tank can be prevented from being damaged excessively.

In one embodiment of the present invention, in the confirmation step, it is determined that the cleaning is sufficiently performed when the absolute value of the difference between the pH of the cleaning liquid and the pH of the discharged liquid after cleaning is within 0.1. May be.

  Thus, if the pH of the cleaning liquid is substantially the same before and after cleaning, it can be said that the corrosive liquid has been sufficiently cleaned.

  In one embodiment of the present invention, the cleaning liquid may be water or an aqueous solution.

  The corrosive liquid can be sufficiently washed by using water or an aqueous solution.

  According to the present invention, when a corrosive liquid leaks, cleaning between the tank bottom plate and the tank foundation can be performed more reliably.

It is process drawing which shows the outline of the process of the cleaning method of the tank which concerns on one Embodiment of this invention. (A) is schematic sectional drawing of the storage tank at the time of liquid leak generation | occurrence | production, (B) is schematic sectional drawing when the tank cleaning method which concerns on one Embodiment of this invention is applied. is there.

Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and all the configurations described in the present embodiment are essential as means for solving the present invention. Not necessarily.
1. 1. Tank cleaning method 1-1. Liquid leak detection process 1-2. Nozzle installation process 1-3. Washing process 1-4. Confirmation process

<1. Tank cleaning method>
FIG. 1 shows an outline of a process of a tank cleaning method according to an embodiment of the present invention. One embodiment of the present invention is a tank cleaning method when a liquid leak occurs from a storage tank that stores corrosive liquid, and a liquid leak detection step that detects that a liquid leak has occurred in the storage tank When the liquid leakage is detected in S1, the contents of the storage tank are removed, and the nozzle installation step S2 in which the nozzle for cleaning is installed on the inner surface of the bottom plate of the storage tank, and the cleaning liquid is sent through the nozzle to prevent the liquid leakage. A cleaning step S3 for cleaning and a confirmation step S4 for confirming that the liquid leakage is sufficiently cleaned in the cleaning step.

  By doing so, the cleaning liquid is directly supplied to a narrow area sandwiched (enclosed) between the outer surface of the tank bottom plate and the tank base, so that the pressure of the cleaning liquid can be applied. As a result, the process liquid does not stay and can be discharged in the outer circumferential direction. Further, by reliably mounting the nozzle, there is no leakage from the supply port of the cleaning liquid, and cleaning between the outer surface of the tank bottom plate and the tank base can be performed without impairing the supply pressure. Thereby, it can wash | clean more effectively than the method of applying a hose from a tank outer periphery between a tank baseplate and a tank foundation, and can prevent corrosion.

  An example of a storage tank to which a tank cleaning method according to an embodiment of the present invention is applied will be described with reference to the drawings. FIG. 2A is a schematic cross-sectional view of a storage tank when a liquid leak occurs, and FIG. 2B is a schematic view when a tank cleaning method according to an embodiment of the present invention is applied. FIG.

  The storage tank 10 has a lining 12 process applied to the inner surface of the tank body 11 and stores a corrosive liquid 13. The storage tank 10 is installed on the tank foundation 20. The tank body 11 is made of, for example, a material such as carbon steel, and examples of the lining 12 include rubber lining and solventless epoxy resin lining. Examples of the corrosive liquid 13 include sulfuric acid and slurries caused by ore sulfuric acid leaching.

  Such a lining 12 in the storage tank 10 may have pinholes due to deterioration due to aging, collisions due to foreign substances contained in the above-described slurry or solution, and the like. Corrosion also occurs in the tank body 11 starting from this pinhole, and eventually a crack 14 is generated, so that the corrosive liquid leaks from the storage tank 10 and may become a liquid leak 15. The tank cleaning method according to the embodiment of the present invention is applied to such a case. Hereafter, each process is demonstrated in order, respectively.

(1-1. Liquid leak detection process)
In the liquid leak detection step S1, it is detected that a liquid leak has occurred in the storage tank 10.

  As described above, the lining 12 such as the rubber lining or the solvent-free epoxy resin lining in the storage tank 10 may cause pinholes due to deterioration due to aging, collision by foreign matters contained in the slurry or solution, and the like. Cracks 14 also occur in the tank body 11 starting from the pinhole, and the corrosive liquid 13 leaks from the storage tank and leaks 15 (in addition to the corrosive liquid 13 itself, the corrosive liquid 13 is dried or corrosive. The liquid 13 is a product produced by a chemical reaction with air, the tank foundation 20 or the like.

  Therefore, it is necessary to quickly detect these liquid leaks 15 and perform cleaning and repair. As a method for detecting the liquid leak 15 in the storage tank 10, it may be detected by a change in the water level or pressure of the solution in the tank by a sensor or the like. A method of confirming whether there is a liquid leak 15 of the corrosive liquid 13 from the bottom 11A of the tank 10 may be used.

(1-2. Nozzle installation process)
In the nozzle installation step S <b> 2, when the liquid leak 15 is detected, the contents (corrosive liquid) 13 of the storage tank 10 are removed, and the cleaning nozzle 16 is installed on the inner surface of the bottom plate 11 </ b> A of the storage tank 10.

  In the nozzle installation step S2, first, the contents 13 of the storage tank 10 are removed. This is because the tank cleaning method according to the embodiment of the present invention needs to work inside the storage tank 10. Therefore, it is desirable not only to remove all the corrosive liquid 13 but also to confirm that no harmful gas or the like is generated in the storage tank 10.

  If the corrosive liquid 13 is removed from the storage tank 10 and the work can be performed in the storage tank 10, then the inner surface of the bottom plate 11A of the storage tank 10 is directed from the inner surface to the outer surface (from the inner side to the outer side of the storage tank 10). (Toward) A nozzle 16 for cleaning is installed. When installing the nozzle 16, it is preferable to remove the lining 12 at the installation location. This is because if the nozzle 16 is installed on the lining 12, the nozzle 16 becomes unstable and the nozzle 16 may come off when the cleaning water is fed. For example, a hose 18 is connected to the cleaning nozzle 16, and the cleaning water 21 is sent from the outside of the storage tank 10.

  In one aspect of the present invention, the plate 17 with the nozzle 16 may be installed by welding to the inner surface of the bottom plate 11A of the storage tank 10. By welding the plate 17 with the nozzle 16, the nozzle 16 can be firmly installed on the inner surface of the bottom plate 11 </ b> A of the storage tank 10, so that the nozzle 16 does not come off due to water pressure or the like during cleaning.

  In one embodiment of the present invention, the hole 19 may be provided in the bottom plate 11A of the storage tank 10 in which the nozzle 16 is installed. By disposing the nozzle 16 so as to face the hole 19, it becomes easy to send the cleaning liquid, so that the cleaning can be performed more efficiently. By setting the size of the hole 19 to be equal to or larger than the diameter of the nozzle 16, the nozzle 16 can be inserted to prevent the cleaning liquid from escaping. In addition, when the size of the hole 19 is not more than twice the diameter of the nozzle 16, the temporal change in the position of the nozzle 16 can also be suppressed.

  If the hole 19 is installed at a location where a depression or crack 14 is generated, the bottom plate 11A can be prevented from being damaged. When it is difficult to find the location where the dent or crack 14 is generated, providing the hole 19 in any location of the bottom plate 11A of the storage tank 10 can save time and effort for discovery. May be. It is preferable that the hole 19 is provided at the center of the bottom plate 11A of the storage tank 10 because the cleaning liquid can be fed radially from the tank bottom plate toward the outer periphery of the tank.

(1-3. Cleaning step)
In the cleaning step S <b> 3, the liquid leakage 15 is cleaned by sending a cleaning liquid through the nozzle 16.

  Water can be used as the cleaning liquid. The temperature of the water is preferably 20 to 40 ° C. because it can be easily obtained, but 40 to 100 ° C. water is used to increase the solubility, and 0 to 20 ° C. water is used to cool the heat of dilution. You can also. By using such a cleaning liquid, the liquid leakage 15 between the tank bottom plate 11A and the tank base 20, the deposits around the crack 14 of the tank bottom plate 11A, etc. are dissolved and diluted to be washed away as the discharged liquid 21. If the liquid leak 15 contains valuable materials such as heavy metals and harmful substances such as acids and alkalis, the discharged liquid 21 is collected.

  Various aqueous solutions can be used as the cleaning liquid. In particular, by using the drainage liquid 21 again as a cleaning liquid, water can be saved and at the same time the storage cost of the collected drainage liquid 21 can be reduced. When using the discharge liquid 21 as the cleaning liquid, the concentration of the discharge liquid 21 (the concentration of the solute common to the corrosive liquid) is periodically checked, and the cleaning effect is obtained when the concentration remains high (when it becomes constant). Therefore, it is desirable to switch the cleaning liquid to new water.

  The cleaning liquid can be selected according to the nature of the corrosive liquid. For example, if the corrosive liquid is an acid, neutralize it using an alkaline aqueous solution, and if it is basic, use an acidic aqueous solution as a cleaning liquid, or if the corrosive liquid is harmful, make it chemically harmless. It is conceivable to use such a solution as a cleaning liquid. When the corrosive liquid is an organic substance, an organic solvent (alcohol, acetone, cyclohexane, etc.) can be used as a cleaning liquid, or a surfactant can be used in combination.

(1-4. Confirmation process)
In the confirmation step S4, it is confirmed that the liquid leakage is sufficiently cleaned in the cleaning step S3.

  The confirmation method is not particularly limited, but it is necessary to confirm that the corrosive liquid accumulated between the tank bottom plate 11A and the tank base 20 has been sufficiently washed away and that there is no risk of corrosion.

  As a confirmation method, it may be confirmed that the cleaning is completed when the pH of the cleaning liquid and the pH of the cleaning liquid after the cleaning are substantially the same. If the pH of the cleaning liquid is substantially the same before and after cleaning, it can be said that the corrosive liquid has been sufficiently cleaned. “Substantially the same” means, for example, a case where the absolute value of the difference between the pH of the cleaning liquid and the pH of the cleaning liquid after cleaning is within 0.1.

  When using this confirmation method, use water (aqueous solution) other than the drained liquid 21 as the cleaning liquid, and then reduce the flow rate of the cleaning liquid or temporarily stop the supply in consideration of the speed at which the corrosive liquid spreads, and start measuring pH. Is desirable.

  It is preferable that the pH is measured not at one place but at a plurality of places so as to surround the storage tank (at a position lower than the storage tank so as to surround a vertically extending region of the storage tank). Specifically, it is preferable to measure in all directions of the tank as much as possible, with points in four directions, front, rear, left and right with respect to the tank, more preferably points in eight directions, more preferably points in sixteen directions. By checking the pH from various directions, it can be determined with high accuracy whether or not the cleaning is sufficient. If it is determined in the confirmation step S4 that the cleaning is insufficient, the cleaning in the cleaning step S3 is continued.

  Although the tank cleaning method according to the embodiment of the present invention has been described above, the storage tank 10 after cleaning is repaired. That is, the periphery of the nozzle 16 installation portion of the tank bottom plate 11A is cut out, and a plate having the same shape, the same material, and the same thickness is welded to the cut out portion, and then the lining process is performed. If there are other cracks 14, the crack 14 is also repaired.

  The present invention can also be applied to the side surface of the tank in the same manner as applied to the tank bottom plate. When applied to the side surface of the tank, cleaning can be easily performed when the tank side surface has a double structure (multiple structure) such as a cooling jacket or when the tank is close to the wall surface.

  EXAMPLES The present invention will be described in further detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1
In Example 1, the contents (sulfuric acid in which various sulfates such as nickel sulfate were dissolved) were removed from the storage tank in which the liquid leakage was visually confirmed, and after marking on the inner surface of the tank bottom plate, The lining of the part was removed. A hole having the same size as the nozzle diameter of 25 mm was formed in the tank bottom plate, and the nozzle was attached to the inner surface of the tank bottom plate by welding. A hose was connected to the nozzle, and washing was performed with water at a flow rate of 20 L / min for 2 hours. After the cleaning was completed, the tank bottom plate around the nozzle mounting portion was cut out at about 100 mm square, and a new plate having the same material and thickness as the bottom plate was welded to the cut out portion. Thereafter, a lining process was performed. The pH of the liquid before and after washing was measured. The results are shown in Table 1.

(Comparative Example 1)
In Comparative Example 1, the contents were removed from the storage tank in which liquid leakage was visually confirmed, and a hose was applied from the outer periphery of the tank between the tank bottom plate and the tank base, and washing with water was performed. The pH of the liquid before and after washing was measured. The results are shown in Table 1.

  In Example 1, the pH of the solution was 4 before washing, but the pH was 7 after washing. That is, it can be seen that the corrosive liquid can be sufficiently washed away because the pH is substantially the same as that of water as the cleaning liquid. On the other hand, in Comparative Example 1, the pH of the solution was 4 before washing and 5 after washing. That is, it can be seen that the corrosive liquid is not sufficiently washed away, and the corrosive liquid remains.

  From these results, it can be seen that the tank bottom plate and the tank foundation can be reliably cleaned by applying the tank cleaning method according to the embodiment of the present invention.

10 storage tank, 11 tank body, 11A tank bottom plate, 12 lining, 13 corrosive liquid, 14 crack, 15 liquid leak, 16 nozzle, 17 plate, 18 hose, 19 holes, 20 tank foundation, 21 drainage liquid

Claims (6)

A method of cleaning a tank when a liquid leak occurs from the bottom plate of a storage tank that stores corrosive liquid,
A liquid leak detection step for detecting that the liquid leak has occurred at the bottom plate of the storage tank;
When the liquid leak is detected, the content of the storage tank is removed, and a nozzle installation step of installing a cleaning nozzle on the inner surface of the bottom plate of the storage tank;
A cleaning step of cleaning the occurrence site of the liquid leakage by sending the cleaning liquid through the nozzle;
And a confirmation step for confirming that the portion where the liquid leakage has occurred is sufficiently washed in the washing step.   2. The tank cleaning method according to claim 1, wherein in the nozzle installation step, the plate with the nozzle is installed by welding to an inner surface of a bottom plate of the storage tank.   3. The tank cleaning method according to claim 1, wherein in the nozzle installation step, a hole is provided in a bottom plate of the storage tank, and the nozzle is installed so as to face the hole.   The said storage tank equips the inner surface of a baseplate with the hollow or a crack, The tank cleaning method of Claim 3 which processes this hollow or this crack and obtains the said hole. 5. In the confirmation step, it is determined that the cleaning is sufficiently performed when the absolute value of the difference between the pH of the cleaning liquid and the pH of the discharged liquid after cleaning is within 0.1. The tank cleaning method according to any one of the above.   The tank cleaning method according to any one of claims 1 to 5, wherein the cleaning liquid is water or an aqueous solution.