Liquid lifting system and liquid lifting mechanism

Abstract

To provide a liquid lifting system capable of shortening the time required to open a tank.SOLUTION: A liquid lifting system has a tank which contains liquid and first and second liquid lifting mechanisms configured to lift and discharge the liquid from the tank, wherein the first liquid lifting mechanism is configured to lift and discharge the liquid from the tank by pushing up the liquid as a rotary body rotates, and the second liquid lifting mechanism comprises a suction port, a liquid lifting part, and a discharge port, and is configured to lift and discharge the liquid from the tank by sucking the liquid up through the suction port as the pressure in the liquid lifting part varies.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pumping system configured to pump liquid contained in a tank and discharge the liquid from the tank, and to a pumping mechanism capable of pumping the liquid. [Background technology]

[0002] Patent Document 1 discloses a method for opening a cryogenic tank that stores cryogenic liquid. In Patent Document 1, the cryogenic tank is opened by following the procedure of first discharging the cryogenic liquid from the cryogenic tank, raising the temperature inside the cryogenic tank to create an environment in which workers can enter the cryogenic tank, and then discharging (exhausting) the vaporized gas (e.g., methane gas) remaining in the cryogenic tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-133828 A Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the cryogenic liquid is discharged through the side of the cryogenic tank, but in a PC tank, the side of which is covered with a liquid retaining dike made of prestressed concrete, it is not possible to provide an opening on the side of the tank. For this reason, PC tanks are usually configured to pressurize the cryogenic liquid using a pressurized liquid pumping device installed inside the tank and discharge the cryogenic liquid from the top of the tank.

[0005] Incidentally, a pressurized liquid lifting device is usually configured to pressurize and lift liquid by rotating a rotor. In such devices, the depth of the liquid suction port is regulated as an operating condition, for example, to be 1 m or more, for reasons such as preventing the occurrence of cavitation. Therefore, even if liquid is discharged from a tank using a pressurized liquid lifting device, liquid to a depth of about 1 m remains in the tank.

[0006] There is a large amount of liquid remaining in the tank, and it takes a long time to vaporize and remove this liquid, which increases the time required to open the tank.

[0007] The present invention has been made in consideration of the above circumstances, and provides a liquid pumping system that can reduce the time required to open a tank. [Means for solving the problem]

[0008] According to the present invention, the following inventions are provided. [1] A pumping system having a tank for storing a liquid, and first and second pumping mechanisms configured to pump the liquid and discharge it from the tank, wherein the first pumping mechanism is configured to pump the liquid by pushing up the liquid as a rotating body rotates, and to discharge it from the tank, and the second pumping mechanism has a suction port, a pumping section, and a discharge port, and is configured to pump the liquid by sucking up the liquid through the suction port as pressure changes in the pumping section, and to discharge it from the tank. [2] A liquid pumping system as described in [1], wherein the liquid pumping section comprises first and second liquid pumping pipes, a connection section, first and second check valves, and a pressure adjustment mechanism, the first and second liquid pumping pipes are connected via the connection section, the first and second check valves are respectively configured to prevent backflow of the liquid stored in the first and second liquid pumping pipes, the first liquid pumping pipe is configured to be capable of storing liquid sucked in from the suction port, the second liquid pumping pipe is configured to be capable of storing the liquid sucked in through the connection section, and the pressure adjustment mechanism is configured to be capable of independently adjusting the pressure applied to each of the first and second liquid pumping pipes. [3] A method for opening a tank using the pumping system described in [1] or [2], comprising a pumping process, in which the liquid is pumped using first and second pumping mechanisms and discharged from the tank. [4] A method as described in [3] which cites [2], comprising a first step and a second step, in which the pumping of liquid using a second lifting mechanism comprises: in the first step, the pressure adjustment mechanism reduces the pressure in the first lifting pipe to suck in the liquid through the suction port and store it in the first lifting pipe; and in the second step, the pressure adjustment mechanism moves at least a portion of the liquid stored in the first lifting pipe to the second lifting pipe by making the pressure in the first lifting pipe higher than the pressure in the second lifting pipe. [5] A method according to [3] or [4], further comprising a vaporization process after the liquid pumping process, in which the vaporized gas produced by vaporizing the liquid is compressed to obtain a compressed gas, which is returned to the tank, thereby promoting the vaporization of the liquid remaining in the tank. [6] A lifting mechanism having an intake port, a lifting section, and an exhaust port, and configured to pump the liquid by sucking up the liquid through the intake port in response to pressure changes in the lifting section and discharge the liquid from the exhaust port, wherein the lifting section has first and second lifting pipes, a connection section, first and second check valves, and a pressure adjustment mechanism, the first and second lifting pipes are connected via the connection section, the first and second check valves are configured to prevent backflow of the liquid stored in the first and second lifting pipes, respectively, the first lifting pipe is configured to be capable of storing the liquid sucked in from the intake port, the second lifting pipe is configured to store the liquid sucked in through the connection section, and the pressure adjustment mechanism is configured to independently adjust the first and second pressures applied to the first and second lifting pipes, respectively. [7] [6] A method for pumping liquid using the pumping mechanism described in the above, comprising a first step and a second step, in which in the first step, the pressure adjustment mechanism reduces the pressure in a first lifting pipe to suck in the liquid through the suction port and store it in the first lifting pipe, and in the second step, the pressure adjustment mechanism moves at least a portion of the liquid stored in the first lifting pipe to the second lifting pipe by making the pressure in the first lifting pipe higher than the pressure in the second lifting pipe. Effect of the Invention

[0009] The liquid pumping system of the present invention includes a first liquid pumping mechanism configured to pump liquid with the rotation of a rotor, and a second liquid pumping mechanism configured to pump liquid by sucking up the liquid through a suction port with a pressure change in the liquid pumping section. The second liquid pumping mechanism is not a liquid pumping mechanism that operates with the rotation of a rotor, and therefore can operate stably even when the liquid suction port is shallower than the first liquid pumping mechanism. Therefore, according to the present invention, the amount of liquid remaining in the tank can be reduced, and the time required to open the tank can be reduced. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing a configuration of a pumping system 1 according to a first embodiment of the present invention. [Diagram 2]FIG. 1 shows the state after pumping liquid into the first liquid lifting pipe 21a in the second liquid lifting mechanism 20. [Diagram 3] This shows the state after pumping liquid into the second lift pipe 21b from the state in FIG. [Figure 4] This shows the state after pumping liquid into the third lift pipe 21c from the state in FIG. [Diagram 5] This shows a modified example in which the second liquid lifting mechanism 20 has two liquid lifting pipes. [Figure 6] FIG. 2 is a diagram showing a configuration of a pumping system 1 according to a second embodiment of the present invention. [Figure 7] 7 shows a state in which the second pumping mechanism 20 in FIG. 6 is pumping the liquid L. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0012] 1. First embodiment 1-1.Lifting system 1 A liquid pumping system 1 according to a first embodiment of the present invention will be described with reference to Figures 1 to 4. The liquid pumping system 1 of this embodiment has a tank 2 that stores liquid L, and first and second liquid pumping mechanisms 10, 20 that are configured to pump the liquid L and discharge it from the tank 2. The liquid pumping system 1 may also include a BOG compressor 3 and a re-liquefaction facility 4. Each component will be described in detail below.

[0013] <Liquid L and Tank 2> The liquid L contained in the tank 2 is preferably a low-temperature liquid having a temperature of -10°C or lower. The temperature of the liquid L in the tank 2 is, for example, -10°C or lower, preferably -20°C or lower, and more preferably -30°C or lower. This temperature is, for example, -250 to -10°C, and specifically, for example, -250, -200, -150, -100, -50, -40, -30, -20, -10°C, and may be in the range between any two of the numerical values ​​exemplified here or lower. Examples of the liquid L include liquefied natural gas (hereinafter, "LNG") and liquefied ammonia.

[0014] The tank 2 may have any configuration capable of storing the liquid L. However, from the viewpoint that the significance of applying the present invention is significant when the liquid L cannot be discharged from the side of the tank 2, the tank 2 is preferably configured such that the liquid L cannot be supplied or discharged through the side. An example of such a tank is a PC tank in which the side of the tank 2 is covered with a liquid retaining dike 2a made of prestressed concrete. In the tank 2, it is preferable that the liquid L and the vaporized gas generated by vaporizing the liquid L are supplied or discharged through an opening provided on the upper surface 2b of the tank 2. When the liquid L is LNG, the vaporized gas is a gas mainly composed of methane or ethane, and when the liquid L is liquefied ammonia, the vaporized gas is ammonia gas.

[0015] The height of the lowest part of the upper surface 2b of the tank 2 is, for example, 15 m or more, preferably 30 m or more, and preferably 40 m or more. This height is, for example, 15 to 100 m, specifically, for example, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100 m, and may be in the range between any two of the numerical values ​​exemplified here or any more. The outer diameter of the tank 2 is, for example, 20 m or more, preferably 40 m or more, and preferably 60 m or more. This outer diameter is, for example, 20 to 150 m, specifically, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 m, and may be in the range between any two of the numerical values ​​exemplified here.

[0016] <1st liquid pumping mechanism 10> The first liquid pumping mechanism 10 is configured to pump the liquid L by pushing up the liquid L with the rotation of the rotor, and discharge the liquid L from the tank 2. The pumped liquid L is discharged from the tank 2, and, if necessary, is vaporized and then sent to the demand destination 30. The first liquid pumping mechanism 10 includes, for example, a pipe 10a extending vertically in the tank 2, and a pump 10b disposed in the pipe 10a. The pump 10b includes a rotor (not shown), and is configured to be able to discharge the liquid L sucked from the suction port 10c with the rotation of the rotor to the outside of the tank 2 through the pipe 10a. In one example, the rotor is an impeller, and is configured to pressurize the liquid L by rotating the rotor to pump it. In one example, a centrifugal force (a force directed radially outward) is applied to the liquid L with the rotation of the rotor.

[0017] In such an apparatus, cavitation is likely to occur with the rotation of the rotor, and for reasons such as preventing the occurrence of cavitation, it is specified as an operating condition that the depth of the suction port 10c for the liquid L is a reference value (for example, 1 m) or more. Therefore, even if the liquid L is discharged from the tank using the pressurized liquid pumping device, a large amount of the liquid L remains in the tank 2. There is a problem that it takes a long time to vaporize and remove this large amount of liquid L. In particular, ammonia has a higher boiling point and a larger latent heat than LNG, so it is more difficult to vaporize it than LNG. Therefore, when the liquid in the tank is liquefied ammonia, the above problem is particularly serious. In this embodiment, the second liquid pumping mechanism 20 is provided, making it possible to reduce the amount of liquid L remaining in the tank 2.

[0018] The distance from the inner bottom surface 2c of the tank 2 to the suction port 10c is, for example, 100 cm or less, preferably 50 cm or less, and more preferably 30 cm or less. This distance is, for example, 5 to 100 cm, specifically, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 cm, and may be in the range between any two of the numerical values ​​exemplified here or less. The shorter this distance, the less the amount of liquid L remaining after the first liquid pumping mechanism 10 discharges the liquid L from the tank 2. On the other hand, the shorter this distance, the more likely the first liquid pumping mechanism 10 will collide with the inner bottom surface 2c when installing the first liquid pumping mechanism 10. In this embodiment, since the second liquid pumping mechanism 20 can pump the liquid, there is no need to forcibly bring the suction port 10c close to the inner bottom surface 2c. Therefore, according to the present invention, it is possible to reduce the risk of the first liquid lifting mechanism 10 colliding with the inner bottom surface 2c.

[0019] <Second liquid pumping mechanism 20> As shown in FIG. 2, the second lifting mechanism 20 includes an inlet 20a, a lifting section 20b, and an outlet 20c, and is configured to pump the liquid L by sucking it up through the inlet 20a in response to a pressure change in the lifting section 20b, and to discharge the liquid L from the tank 2 through the outlet 20c. The liquid L is sent to another tank 29, for example. The second lifting mechanism 20 is not a lifting mechanism that is associated with the rotation of a rotor, and therefore can operate stably even when the depth of the inlet 20a for the liquid L is shallower than that of the first lifting mechanism 10. Therefore, according to this embodiment, the amount of liquid L remaining in the tank 2 can be reduced, and the time required to open the tank 2 can be reduced.

[0020] The liquid lifting section 20b includes first to third liquid lifting pipes 21a to 21c, first and second connection parts 22a, 22b, first to third check valves 23a to 23c, and a pressure adjustment mechanism .

[0021] The first lift pipe 21a and the second lift pipe 21b are connected via a first connection part 22a. The second lift pipe 21b and the third lift pipe 21c are connected via a second connection part 22b. The first to third check valves 23a to 23c are configured to prevent backflow of the liquid L stored in the first to third lift pipes 21a to 21c, respectively. The first lift pipe 21a is configured to be able to store the liquid L sucked from the suction port 20a, the second lift pipe 21b is configured to be able to store the liquid L sucked through the first connection part 22a, and the third lift pipe 21c is configured to be able to store the liquid L sucked through the second connection part 22b. The pressure adjustment mechanism 24 is configured to be able to independently adjust the pressure applied to each of the first to third lift pipes 21a to 21c. The third lift pipe 21c is provided with a discharge port 20c for discharging the liquid L toward another tank 29 or the like.

[0022] The pressure adjustment mechanism 24 includes first to third pressure reducing valves 25a to 25c, first to third pressure adjustment valves 26a to 26c, The system includes a vacuum pipe 27 and a pressure adjustment pipe 28. The vacuum pipe 27 is connected to the first lift pipe 21a via a first pressure reducing valve 25a, to the second lift pipe 21b via a second pressure reducing valve 25b, and to the third lift pipe 21c via a third pressure reducing valve 25c. The pressure adjustment pipe 28 is connected to the first lift pipe 21a via a first pressure adjusting valve 26a, to the second lift pipe 21b via a second pressure adjusting valve 26b, and to the third lift pipe 21c via a third pressure adjusting valve 26c.

[0023] 2 to 4, a pumping method using the second pumping mechanism 20 will be described. In this method, pumping of the liquid L is performed in three steps as one cycle. The following description will be given assuming the state in FIG. 4 as the initial state.

[0024] (1) First step: Pumping liquid into the first lift pipe 21a In the first step, the pressure adjustment mechanism 24 reduces the pressure in the first lift pipe 21a to suck in the liquid L through the suction port 20a and store it in the first lift pipe 21a. More specifically, from the state of FIG. 4, the second pressure adjustment valve 26b and the third pressure reducing valve 25c are closed, and the first pressure reducing valve 25a is opened. As a result, the first lift pipe 21a is connected to the vacuum piping 27, and the pressure in the first lift pipe 21a is reduced. With this pressure change, the liquid L is sucked up into the first lift pipe 21a through the suction port 20a and the first check valve 23a, resulting in the state shown in FIG. 2. The liquid L in the first lift pipe 21a is prevented from moving toward the suction port 20a by the action of the first check valve 23a. In the state of FIG. 2, the liquid level in the first lift pipe 21a is higher than the first connection part 22a.

[0025] (2) Second step: Pumping liquid into the second lift pipe 21b In the second step, the pressure adjustment mechanism 24 makes the pressure in the first lift pipe 21a higher than the pressure in the second lift pipe 21b, thereby moving at least a part of the liquid L stored in the first lift pipe 21a to the second lift pipe 21b. More specifically, from the state shown in FIG. 2, the first pressure reducing valve 25a is closed, and the first pressure adjustment valve 26a and the second pressure reducing valve 25b are opened. As a result, the first lift pipe 21a is connected to the pressure adjustment pipe 28, so that the pressure in the first lift pipe 21a increases, and the second lift pipe 21b is connected to the vacuum pipe 27, so that the pressure in the second lift pipe 21b decreases. With this pressure change, the liquid L in the first lift pipe 21a moves to the second lift pipe 21b through the first connection part 22a and the second check valve 23b, resulting in the state shown in FIG. 3. The liquid L in the second lift pipe 21b is prevented from moving toward the first connecting part 22a by the action of the second check valve 23b. In the state shown in Fig. 3, the liquid level in the second lift pipe 21b is higher than the second connecting part 22b.

[0026] (3) Third step: Pumping liquid into the third lift pipe 21c In the second step, the pressure adjustment mechanism 24 makes the pressure in the second lift pipe 21b higher than the pressure in the third lift pipe 21c, thereby moving at least a part of the liquid L stored in the second lift pipe 21b to the third lift pipe 21c. More specifically, from the state shown in FIG. 3, the second pressure reducing valve 25b is closed, and the second pressure adjustment valve 26b and the third pressure reducing valve 25c are opened. As a result, the second lift pipe 21b is connected to the pressure adjustment pipe 28, so that the pressure in the second lift pipe 21b increases, and the third lift pipe 21c is connected to the vacuum pipe 27, so that the pressure in the third lift pipe 21c decreases. With this pressure change, the liquid L in the second lift pipe 21b moves to the third lift pipe 21c through the second connection part 22b and the third check valve 23c, resulting in the state shown in FIG. 4. The liquid L in the third lifting pipe 21c is prevented from moving toward the second connecting portion 22b by the action of the third check valve 23c.

[0027] When the liquid L that has moved to the third lift pipe 21c reaches the discharge port 20c, it is discharged from the tank 2 through the discharge port 20c and is transferred, for example, to another tank 29 or the like. Therefore, the liquid level in the third lift pipe 21c is at the same height as the discharge port 20c. Note that while the third pressure reducing valve 25c is open, the discharge port 20c may be closed, and after the movement of the liquid L from the second lift pipe 21b to the third lift pipe 21c is completed, the third pressure reducing valve 25c may be closed, and then the discharge port 20c may be opened. In this case, the liquid level in the third lift pipe 21c becomes higher than the discharge port 20c immediately before the discharge port 20c is opened.

[0028] (4) Summary As described above, the liquid L in the tank 2 is pumped up and discharged outside the tank 2 through the first to third steps. When one lifting pipe is used to pump up the liquid L, the height to which the liquid L can be pumped up is at most about 5 to 15 m, depending on the pressure in the tank 2 and the specific gravity of the liquid L, and when the height of the tank 2 is 20 m or more, the liquid L cannot be pumped up and discharged from the upper surface 2b of the tank 2. On the other hand, in the above configuration of this embodiment, two or more lifting pipes and check valves are used in combination, and the movement of the liquid L accompanying the pressure change in each lifting pipe is utilized, making it possible to pump up liquid above the height of the tank 2.

[0029] The pressures in the vacuum pipe 27 and the pressure adjustment pipe 28 are appropriately set so that the pumping of the liquid by the above method can be achieved. The pressure in the pressure adjustment pipe 28 only needs to be higher than the pressure in the vacuum pipe 27, and may be the same as atmospheric pressure or may be lower or higher than atmospheric pressure. The greater the difference between the pressure in the pressure adjustment pipe 28 and the pressure in the vacuum pipe 27, the faster the movement of the liquid L can be achieved, and therefore the more efficient the pumping of the liquid can be achieved.

[0030] In the above embodiment, three lifting pipes are used to perform pumping in one cycle of three steps, but the number of lifting pipes can be two and two steps can be performed in one cycle, or four or more lifting pipes can be used and four or more steps can be performed in one cycle. The more the number of lifting pipes, the easier it is to pump the liquid L to a higher position.

[0031] For example, when the number of lifting pipes is two and lifting is performed with two steps as one cycle, the lifting section 20b is configured to include first and second lifting pipes 21a, 21b, a connection section 22a, first and second check valves 23a, 23b, and a pressure adjustment mechanism 24, as shown in Fig. 5, and a discharge port 20c is provided in the second lifting pipe 21b. Then, by pumping the liquid to the first lifting pipe 21a and the second lifting pipe 21b in accordance with the above-mentioned first and second steps, the liquid L can be pumped and discharged from the tank 2.

[0032] More generally, when pumping liquid is performed in N or more steps as one cycle using N liquid pumping pipes, a suction port 20a is provided in the first liquid pumping pipe, and a discharge port 20c is provided in the Nth liquid pumping pipe. A check valve is provided in each liquid pumping pipe, and adjacent liquid pumping pipes are connected at a connection part. Then, in the first step, the liquid L is sucked up into the first liquid pumping pipe by reducing the pressure in the first liquid pumping pipe. In the second to Nth steps, the process of making the pressure in the (m - 1)th liquid pumping pipe higher than the pressure in the mth liquid pumping pipe is carried out by changing m in the order from 2 to N. By doing so, the liquid L in the first liquid pumping pipe is transferred to the second, third,..., Nth liquid pumping pipes in order, and can be discharged from the discharge port 20c provided in the Nth liquid pumping pipe. N is, for example, from 2 to 20, specifically, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and it may also be in the range between any two of the numerical values exemplified here.

[0033] <BOG Compressor 3 and Re - liquefaction Facility 4> In the tank 2, vaporized gas (boil - off gas, hereinafter referred to as "BOG") generated by the heat input from the outside of the liquid L is generated. In order to prevent the pressure in the tank 2 from becoming too high, it is preferable to discharge the BOG from the tank 2 through the BOG line 31. A BOG compressor 3 for compressing and boosting the BOG is provided in the BOG line 31. The compressed gas obtained by compressing with the BOG compressor 3 can be transferred to the demand destination 30, transferred to the re - liquefaction facility 4 for re - liquefaction and then returned to the tank 2, or returned to the tank 2 as it is for utilization. The transfer destination is configured to be switchable using a valve (not shown) and the like.

[0034] The BOG compressor 3 is at a high temperature due to the heat generated during operation. When the BOG is compressed by the BOG compressor 3, heat is transferred from the BOG compressor 3 to the BOG. Therefore, the compressed gas has an increased thermal energy compared to the BOG before compression.

[0035] When opening the tank 2, most of the liquid L in the tank 2 is discharged by the first liquid lifting mechanism 10 and the second liquid lifting mechanism 20, but it is difficult to completely discharge the liquid L, and some of the liquid L remains. This remaining liquid L can be removed by, for example, blowing a purge gas such as nitrogen into the tank 2 to vaporize it. In that case, the discharged gas becomes a mixed gas of vaporized gas and purge gas, and since this cannot be transported directly to the consumer 30, it is necessary to select either to purify it and use it or to treat it by combustion, both of which are undesirable from an economic and environmental standpoint. Therefore, in this embodiment, the compressed gas is returned to the tank 2 to promote the vaporization of the liquid L remaining in the tank 2. Since the compressed gas has the same components as the vaporized gas, the gas discharged from the tank 2 can be moved to the consumer 30. Therefore, the method of this embodiment is excellent in terms of economy and environment.

[0036] 1-2. How to open Tank 2 The method for opening the tank 2 according to one embodiment of the present invention includes a liquid pumping step. Also, a vaporization step may be included after the liquid pumping step.

[0037] In the pumping step, the first and second pumping mechanisms 10, 20 are used to pump the liquid L and discharge it from the tank 2. The first and second pumping mechanisms 10, 20 may be operated simultaneously, but if the first pumping mechanism 10 is capable of pumping liquid more efficiently than the second pumping mechanism 20, pumping may be performed using only the first pumping mechanism 10 and then using only the second pumping mechanism 20, or pumping may be performed using the first and second pumping mechanisms 10, 20, and when the remaining amount of liquid L becomes so low that the first pumping mechanism 10 cannot be operated, pumping may be switched to using only the second pumping mechanism 20.

[0038] In the vaporization step, the vaporized gas generated by vaporizing the liquid L is compressed, and the compressed gas obtained is returned to the tank 2, thereby accelerating the vaporization of the liquid L remaining in the tank 2. This makes it possible to efficiently remove the liquid L remaining in the tank 2.

[0039] When the amount of vaporized gas produced in the vaporization process becomes sufficiently small, a purging process may be performed in which a purge gas such as nitrogen gas is blown into the tank 2. This makes the inside of the tank 2 cleaner, making it possible to create an environment in which workers can work inside the tank 2. The gas discharged in the purging process can be treated by combustion or the like.

[0040] The tank 2 can be opened to inspect the inside of the tank 2. When the liquid L is liquefied ammonia, it is necessary to inspect it more frequently than LNG, taking into account the corrosiveness of ammonia. In addition, liquefied ammonia has a higher boiling point and a large latent heat than LNG, so it is not easy to vaporize it. Furthermore, since liquefied ammonia is more toxic than LNG, there is a stronger demand than for LNG to reduce the remaining amount of liquefied ammonia as much as possible before an operator enters the tank 2. According to this embodiment, the liquid L is pumped using the first and second pumping mechanisms 10, 20, so that the liquid L in the tank 2 can be discharged to a smaller remaining amount in a shorter period of time than when only the first pumping mechanism 10 is used. Therefore, the technical significance of the method of this embodiment is particularly remarkable when the liquid L is liquefied ammonia.

[0041] 2. Second embodiment A second embodiment of the present invention will be described with reference to Figures 6 to 7. This embodiment is similar to the first embodiment, and the contents described in the first embodiment can also be applied to this embodiment as long as they are not contrary to the spirit of the first embodiment. This embodiment differs from the first embodiment mainly in the configuration of the second liquid pumping mechanism 20. The following description will focus on the differences.

[0042] In this embodiment, the second liquid pumping mechanism 20 includes a liquid pumping section 20b having an inlet pipe 20d, an ejector 20e, and a liquid pumping pipe 20f. The inlet pipe 20d and the liquid pumping pipe 20f are connected via the ejector 20e, and the suction port 20a is provided in the ejector 20e. The discharge port 20c is provided in the liquid pumping pipe 20f. A liquefied gas pump 32 is connected to the inlet pipe 20d via a valve 20g.

[0043] When the valve 20g is opened and the liquefied gas L1 is injected from the liquefied gas pump 32 into the ejector 20e through the inlet pipe 20d, the space in the ejector 20e is depressurized by the flow of the liquefied gas L1, and the liquid L in the tank 2 is sucked into the ejector 20e through the suction port 20a, pumped through the lifting pipe 20f, discharged from the discharge port 20c provided outside the tank 2, and transferred to another tank 29, etc. In this manner, also in this embodiment, the liquid L is sucked up through the suction port 20a in accordance with the pressure change in the lifting section 20b.

[0044] By using liquefied gas L1 with the same composition as the liquid L in the tank 2, the liquid L in the tank 2 can be extracted without being mixed with a liquid of a different composition. This method has the advantage that if the liquid pumping section 20b is installed in the tank 2 in advance, preparations for operating the second liquid pumping mechanism 20 can be performed outside the tank 2, which places no burden on workers or the environment.

[0045] 3. Third embodiment The second pumping mechanism 20 described in the first embodiment can be used to pump liquid as a pumping mechanism with a new configuration, independent of the pumping system 1 of the first embodiment. By using this pumping mechanism, it becomes possible to pump liquid to a height that exceeds the height that can be achieved by suction, even in a situation where a pressurized pumping device such as the first pumping mechanism 10 cannot be installed. [Explanation of symbols]

[0046] 1: Lifting system 2:Tank 2a: Liquid dike 2b:Top surface 2c: Inner bottom surface 3: BOG compressor 4:Reliquefaction equipment 10: 1st pumping mechanism 10a: Pipe 10b: Pump 10c: Inlet 20:Second pumping mechanism 20a: Inlet 20b: Lifting section 20c: Outlet 20d:Introduction tube 20e : Ejector 20f: Lifting pipe 20g: Valve 21a: 1st liquid lift pipe 21b: 2nd lift pipe 21c: 3rd lift pipe 22a: First connection part 22b: Second connection part 23a: Third check valve 23b: Second check valve 23c: Third check valve 24: Pressure adjustment mechanism 25a: First pressure reducing valve 25b: Second pressure reducing valve 25c: Third pressure reducing valve 26a: First pressure regulating valve 26b: Second pressure regulating valve 26c: Third pressure regulating valve 27: Vacuum piping 28: Pressure adjustment pipe 29: Another tank 30: Demand destination 31:BOG Line 32: Liquefied gas pump L:Liquid L1: Liquefied gas

Claims

1. A liquid pumping system comprising a tank for storing a liquid, and first and second liquid pumping mechanisms configured to pump the liquid and discharge it from the tank, the first liquid lifting mechanism is configured to lift the liquid by pushing up the liquid in association with rotation of the rotor, and to discharge the liquid from the tank; A pumping system in which the second pumping mechanism has an inlet, a pumping section, and an outlet, and is configured to pump the liquid by sucking up the liquid through the inlet in response to pressure changes in the pumping section, and to discharge the liquid from the tank.

2. 2. The liquid pumping system according to claim 1, The liquid lifting section includes first and second liquid lifting pipes, a connection section, first and second check valves, and a pressure adjustment mechanism. The first and second lifting pipes are connected via the connection portion, the first and second check valves are configured to prevent backflow of the liquid stored in the first and second lift pipes, respectively; The first lifting pipe is configured to be capable of storing the liquid sucked from the suction port, The second lift pipe is configured to be capable of storing the liquid sucked through the connection portion, A liquid lifting system, wherein the pressure adjustment mechanism is configured to be able to independently adjust the pressure applied to each of the first and second liquid lifting pipes.

3. A method for opening a tank using the pumping system according to claim 1 or 2, comprising the steps of: Equipped with a liquid lifting process, The method includes, in the liquid pumping step, pumping the liquid using first and second liquid pumping mechanisms and discharging the liquid from the tank.

4. A method according to claim 3 which relies on claim 2, The pumping of liquid using the second pumping mechanism includes a first process and a second process, In a first step, the pressure adjustment mechanism reduces the pressure in a first lifting pipe to suck in the liquid through the suction port and store the liquid in the first lifting pipe, In a second step, the pressure adjustment mechanism moves at least a portion of the liquid stored in the first lift pipe to the second lift pipe by making the pressure in the first lift pipe higher than the pressure in the second lift pipe.

5. 4. The method of claim 3, A vaporization process is provided after the liquid pumping process, The vaporization step includes compressing the vaporized gas produced by vaporizing the liquid and returning the compressed gas to the tank, thereby promoting the vaporization of the liquid remaining in the tank.

6. A liquid lifting mechanism including a suction port, a liquid lifting section, and a discharge port, the liquid being pumped by sucking up the liquid through the suction port in response to a pressure change in the liquid lifting section, and being capable of discharging the liquid from the discharge port, The liquid lifting section includes first and second liquid lifting pipes, a connection section, first and second check valves, and a pressure adjustment mechanism. The first and second lifting pipes are connected via the connection portion, the first and second check valves are configured to prevent backflow of the liquid stored in the first and second lift pipes, respectively; The first lifting pipe is configured to be capable of storing the liquid sucked from the suction port, The second lift pipe is configured to be capable of storing the liquid sucked through the connection portion, The pressure adjustment mechanism is configured to be able to independently adjust the first and second pressures applied to the first and second lifting pipes, respectively.

7. A method for pumping liquid using the pumping mechanism according to claim 6, The method includes a first step and a second step, In a first step, the pressure adjustment mechanism reduces the pressure in a first lifting pipe to suck in the liquid through the suction port and store the liquid in the first lifting pipe, In a second step, the pressure adjustment mechanism moves at least a portion of the liquid stored in the first lift pipe to the second lift pipe by making the pressure in the first lift pipe higher than the pressure in the second lift pipe.

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