JPH09203500A - Delayering device for liquid in storage tank - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To effectively eliminate stratification of liquid in a storage tank while suppressing running cost with a circulation pump having a small capacity. SOLUTION: This is a device for destratifying a liquid in a storage tank provided in a storage tank that causes stratification of the liquid in the storage tank by changing a physical property of the received liquid, and the storage tank is provided at a position near a storage tank bottom portion 3 of a side wall 4. A lower mixing nozzle 22 for ejecting the liquid 11 toward the upper inside is disposed, and an intermediate mixing nozzle 23 for ejecting the liquid 11 toward the upper inside of the storage tank is disposed at an intermediate position in the vertical direction of the side wall. The liquid 11 is taken out of the storage tank and is circulated and supplied to the lower mixing nozzle 22 and the intermediate mixing nozzle 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents stratification of a liquid that occurs in a storage tank that receives and stores a liquid having different physical properties depending on the place of production such as LNG, and prevents the rollover phenomenon from occurring. The present invention relates to a destratification device for a liquid in a storage tank that is prevented.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventional storage tank that receives and stores LNG.
It has a double-shell structure composed of an inner tank 1 and an outer tank 2, and is composed of a storage tank bottom portion 3, a side wall 4, and a roof 5. A cold insulation layer 6 is provided between the inner tank 1 and the outer tank 2.

In the lower part of the storage tank, a receiving pipe 7 and a discharge pipe 8 are installed so as to penetrate the side wall 4, and the receiving pipe 7 and the discharge pipe 8 are further provided in the penetrating portions of the receiving pipe 7 and the discharge pipe 8. Expansion / contraction means (bellows or the like) 7 ', 8'for absorbing the thermal expansion / contraction of the above are provided. In the figure, 9 indicates a receiving valve and 10 indicates a discharge valve.

On the roof 5 of the storage tank, L stored in the storage tank
The vaporized gas (BOG) 12 obtained by vaporizing the NG liquid 11 is taken out and pressurized by the vaporized gas compressor 13, and the vaporized gas transport pipe 14 for supplying the pressurized vaporized gas 12 to a power plant or a natural gas supply facility is connected. ing. Reference numeral 15 is a vaporized gas control valve provided in the vaporized gas transport pipe 14, 16 is an extraction valve, and 17 is a tank safety valve.

Most of LNG is methane having a low density and a low boiling point (75% to 99%), and contains ethane, propane, butane, etc. having a high density and a high boiling point as a part. However, the content ratios of these gases (physical properties, especially the purity of methane) vary considerably depending on the country or place where LNG was produced.

Therefore, the LNG liquid 11 received and stored in the storage tank from the receiving pipe 7 has a large mass, that is, a liquid having a large content of ethane, propane, butane, etc., as shown by hatching in FIG. Layering is likely to occur so that a liquid having a small mass, that is, a liquid having a small content of ethane, propane, butane, etc. in B becomes the upper layer portion A.

When stratification occurs in this way, the upper layer A is vaporized to generate the vaporized gas 12 with respect to the heat input Q of the tank, so that the heat input Q of the tank is not accumulated, but the lower layer part Q is not accumulated. In B, since the generation of the vaporized gas 12 is suppressed by the upper layer portion A, the heat input Q of the tank is accumulated.

When the tank heat input Q is accumulated in the lower layer portion B as described above, the enthalpy of the lower layer portion B may be released all at once and the upper layer portion A and the lower layer portion B may be inverted. The inversion phenomenon of the upper and lower layers is called a rollover phenomenon, and when this rollover phenomenon occurs, a large amount of vaporized gas 12 is generated, and the internal pressure of the storage tank rises sharply, leading to the problem of opening the tank safety valve 17. Occurs.

In order to prevent this rollover phenomenon,
Conventionally, as shown in FIG. 4, one mixing nozzle 18 for ejecting the liquid 11 upward toward the inside of the storage tank is provided at a position near the peripheral wall of the storage tank bottom portion 3,
A part of the liquid 11 in the lower layer portion B close to the above is taken out by the liquid take-out pipe 19 and guided to the circulation pump 20, and further the liquid 11 from the circulation pump 20 is taken by the liquid supply pipe 21.
It is considered that the liquid 11 in the storage tank is forcibly circulated and mixed by being supplied to and jetted to the liquid No. 8 to prevent stratification of the liquid 11. Further, although FIG. 4 shows a case where the liquid take-out pipe 19 and the liquid supply pipe 21 are provided so as to penetrate the side wall 4 of the storage tank, the liquid take-out pipe 19 and the liquid supply pipe 21 penetrate the roof 5. Some are provided in.

[0010]

However, in the apparatus as shown in FIG. 4, the jet flow ejected from the mixing nozzle 18 entrains the surrounding liquid 11 and diffuses, which causes a rapid flow velocity. Will be reduced to. That is, while it is necessary to mix the liquid 11 which originally has a low specific gravity in the upper layer A for mixing, the heavy liquid 1 around the mixing nozzle 18 in the lower layer B before the light liquid 11 is involved.
When 1 is involved, the flow velocity of the jetted liquid 11 is remarkably reduced, so that there is a problem that sufficient mixing of the upper layer portion A and the lower layer portion B cannot be obtained, or that the mixing takes a long time. Particularly in recent years, LNG storage tanks have become larger, and it is not uncommon for the storage tank diameter to be 70 m or more and the liquid depth to be about 30 m. Mixing of the liquid 11 in such a large storage tank is even more difficult.

Further, the height of the boundary portion X between the upper layer portion A and the lower layer portion B changes due to the reception of the liquid 11 having different physical properties by the receiving pipe 7, but the height of the boundary portion X is changed in this way. Even if it changes, it is necessary to be able to perform sufficient mixing.

In order to enhance the mixing effect of the liquid 11 in such a storage tank, it is necessary to increase the jet velocity by increasing the pressure to increase the jet height, and to increase the flow rate. Since only one nozzle 18 is provided at the bottom, the height of the boundary portion X changes even at the maximum liquid depth of the liquid 11 and at the maximum density difference between the upper layer portion A and the lower layer portion B. In order to perform sufficient mixing, a circulation pump 20 having a very large capacity and a structure capable of withstanding a high pressure are required, resulting in high equipment cost and high running cost. Had.

The present invention has been made in view of the above circumstances, and is a circulation pump having a small capacity, which can effectively eliminate the stratification of the liquid in the storage tank while suppressing the running cost. Is intended to provide.

[0014]

The apparatus for destratifying a liquid in a storage tank according to the present invention is a layered solution for a liquid in a storage tank provided in a storage tank that causes stratification of the liquid in the storage tank by changing a physical property of the received liquid. In this device, a lower mixing nozzle that ejects the liquid upward toward the inside of the storage tank is provided on the side wall near the bottom of the storage tank, and the liquid is ejected toward the inside of the storage tank at an intermediate position in the vertical direction of the side wall. And a circulating pump for extracting the liquid in the storage tank to the outside of the storage tank and circulatingly supplying the liquid to the lower mixing nozzle and the intermediate mixing nozzle.

Further, the upward angle of the lower mixing nozzle is increased and the upward angle of the middle mixing nozzle is decreased.

In the present invention, the lower mixing nozzle and the intermediate mixing nozzle are provided inside the storage tank, and the liquid is ejected from the lower mixing nozzle and the intermediate mixing nozzle according to the level of the liquid in the storage tank and the height of the boundary. Since it is used by switching, the capacity of the circulation pump is reduced and the pressure is lowered to effectively mix the liquid in the storage tank and solve the problem of stratification of the liquid. You can

The mixing effect can be further enhanced by increasing the upward angle of the lower mixing nozzle and decreasing the upward angle of the middle mixing nozzle.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an embodiment for carrying out the present invention applied to the conventional storage tank of FIG. 4, in which the same symbols are used to represent the same items.

As shown in FIG. 1, a lower mixing nozzle 22 for ejecting the liquid 11 is provided near the side wall 4 of the storage tank and near the bottom 3 of the storage tank.
An intermediate mixing nozzle 23 that ejects the liquid 11 toward the upper inside of the storage tank is provided at an upper position of the lower mixing nozzle 22 at an intermediate position in the vertical direction of the side wall 4.

Further, the liquid 11 in the storage tank is guided from the vicinity of the storage tank bottom portion 3 through the side wall 4 through the liquid take-out pipe 25 having the take-out valve 24 to the outside of the storage tank and guided to the circulation pump 26. In addition, liquid supply pipes 27 and 28 for supplying the liquid 11 pressurized by the circulation pump 26 to the lower mixing nozzle 22 and the intermediate mixing nozzle 23 are provided on the side wall 4
Is provided so as to penetrate. The liquid supply pipes 27 and 28 are provided with liquid supply valves 29 and 30, respectively, and the liquid 11 by the lower mixing nozzle 22 and the intermediate mixing nozzle 23 is supplied.
It is possible to switch the squirt of.

Further, as shown in FIG. 2, the upward angle α of the lower mixing nozzle 22 is increased, and the upward angle β of the intermediate mixing nozzle 23 is decreased. The example of FIG. 2 shows the case where α = 60 ° and β = 35 °.

In the above-described structure, when the physical properties of the liquid 11 received from the receiving pipe 7 are changed to cause stratification in which the upper layer portion A and the lower layer portion B are formed in the storage tank, the circulation pump is used. 26 to drive the liquid 11 in the storage tank into the lower mixing nozzle 22 or the middle mixing nozzle 2
It is circulated to 3 and jetted into the storage tank.

At this time, since the density meter and the thermometer are arranged vertically in the normal LNG storage tank, the height position of the boundary portion X between the upper layer portion A and the lower layer portion B is determined from the density distribution and the temperature distribution. Can be estimated.

Therefore, when the height of the boundary X is low,
Alternatively, when the level of the liquid 11 in the storage tank is lower than that of the intermediate mixing nozzle 23, as shown in FIG. 1, the liquid supply valve 30 is closed, the liquid supply valve 29 is opened, and the liquid 11 is supplied only to the lower mixing nozzle 22. By supplying and squirting,
The upper layer portion A and the lower layer portion B are mixed to eliminate the stratification of the liquid 11. At this time, since the height of the boundary portion X is low or the level of the liquid 11 in the storage tank is lower than that of the intermediate mixing nozzle 23, the lower mixing nozzle 22 is effective for the liquid 11 in the storage tank even with a small ejection force. The problem of stratification of the liquid 11 can be solved by physically mixing. Therefore, good mixing can be performed even if the capacity of the circulation pump 26 is reduced (for example, about half the capacity of the conventional pump) or the pressure is relatively low.

If the upward angle α of the lower mixing nozzle 22 is increased, as shown in FIG.
The liquid 11 having a large specific gravity can be pushed up to further enhance the mixing effect.

Further, as shown in FIG. 3, the liquid 11 in the storage tank is
Is high and the height of the boundary portion X is higher than that of the intermediate mixing nozzle 23, the liquid supply valve 39 is closed and the liquid supply valve 30 is opened to open the intermediate mixing nozzle 2
By supplying and ejecting the liquid 11 only to No. 3, the upper layer portion A and the lower layer portion B are mixed and the stratification of the liquid 11 is eliminated. At this time, since the liquid 11 ejected from the intermediate mixing nozzle 23 comes to be ejected in the vicinity of the boundary X, the liquid 11 ejected from the intermediate mixing nozzle 23 effectively mixes even with a small ejection force. It is possible to solve the problem of layering of the liquid 11 by carrying out. Therefore, even if the capacity of the circulation pump 26 is reduced (for example, about half the capacity of the conventional pump), or even if the pressure is relatively low,
You will be able to perform good mixing.

Further, as shown in FIG. 3, when the upward angle α of the intermediate mixing nozzle 23 is set small, the liquid 11 close to the upper layer of the lower layer B and the liquid 11 having a small specific gravity of the upper layer A are formed. Let it act like a large movement in the lateral direction,
The effect of mixing can be further enhanced.

As described above, the lower mixing nozzle 22 and the intermediate mixing nozzle 23 are provided inside the storage tank, and the lower mixing nozzle 22 and the intermediate mixing nozzle are mixed in accordance with the level of the liquid 11 in the storage tank and the height of the boundary X. Nozzle 2
Since the jetting of the liquid 11 from 3 is switched and used, even if the capacity of the circulation pump 26 is made small or the pressure is made low, the mixing in the storage tank is effectively performed and the liquid is stratified. The problem can be solved, and thus the equipment cost and running cost can be reduced.

The present invention is not limited to the above embodiment, but the lower and middle mixing nozzles 2 are provided.
2 and 23 may each be provided with a circulation pump, the upward angles α and β may be arbitrarily selected, and various changes may be made within the scope not departing from the gist of the present invention. Of course.

[0031]

According to the apparatus for eliminating the stratification of the liquid in the storage tank according to the present invention, the lower mixing nozzle and the intermediate mixing nozzle are provided inside the storage tank to adjust the level of the liquid in the storage tank and the height of the boundary portion. Since the liquid ejection from the lower mixing nozzle and the middle mixing nozzle is switched and used, it is possible to effectively mix the liquid in the storage tank with a configuration in which the capacity of the circulation pump is reduced or the pressure is lowered. As a result, it is possible to solve the problem of stratification of the liquid, and thus it is possible to obtain an excellent effect that the equipment cost and the running cost can be reduced.

The mixing effect can be further enhanced by increasing the upward angle of the lower mixing nozzle and decreasing the upward angle of the middle mixing nozzle.

[Brief description of drawings]

FIG. 1 is a cut-away side view showing an example of an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a sectional side view showing the action of the present invention when the liquid level is high.

FIG. 4 is a cut side view showing an example of a storage tank provided with a conventional destratification device for liquid in the storage tank.

[Explanation of symbols]

 3 Bottom of storage tank 4 Side wall 11 Liquid 22 Lower mixing nozzle 23 Intermediate mixing nozzle 26 Circulation pump α Upward angle β Upward angle

Claims (2)

[Claims] 1. A destratification device for a liquid in a storage tank, which is provided in a storage tank for causing stratification of the liquid in the storage tank by changing a physical property of the received liquid, wherein the inside of the storage tank is located at a position near a bottom of the storage tank on a side wall. A lower mixing nozzle for ejecting the liquid upward is disposed, and an intermediate mixing nozzle for ejecting the liquid upward inside the storage tank is disposed at an intermediate position in the vertical direction of the side wall to store the liquid in the storage tank. A destratification device for a liquid in a storage tank, comprising a circulation pump which is taken out to the outside and circulates and circulates to the lower mixing nozzle and the intermediate mixing nozzle. 2. The destratification device for liquid in a storage tank according to claim 1, wherein the upward angle of the lower mixing nozzle is increased and the upward angle of the intermediate mixing nozzle is decreased.