Liquid lifting system and liquid lifting mechanism

Abstract

Provided is a liquid lifting system with which it is possible to reduce the time required to open a tank.　The present invention provides a liquid lifting system including a tank for storing a liquid, and first and second liquid lifting mechanisms configured to be capable of lifting the liquid to discharge the liquid from the tank, wherein: the first liquid lifting mechanism is configured to be capable of lifting the liquid by pushing the liquid up in association with the rotation of a rotating body to discharge the liquid from the tank; and the second liquid lifting mechanism includes a suction port, a liquid lifting unit, and a discharge port, and is configured to be capable of lifting the liquid by sucking up the liquid through the suction port in association with a pressure change within the liquid lifting unit, to discharge the liquid from the tank.

Description

Liquid pumping system and liquid pumping mechanism

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

[0002] Patent Document 1 discloses a method for opening a cryogenic tank that stores a cryogenic liquid. In Patent Document 1, the cryogenic tank is opened by 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) any vaporized gas (e.g., methane gas) remaining in the cryogenic tank.

[0003] Japanese Patent Application Laid-Open No. 2020-133828

[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 barrier 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] A pressurized liquid pumping device is typically configured to pressurize and pump liquid by rotating a rotor. To prevent cavitation and other issues, the operating conditions for such devices require the liquid inlet to be at least 1 meter deep. Therefore, even if liquid is discharged from a tank using a pressurized liquid pumping device, a depth of about 1 meter remains in the tank.

[0006] The amount of liquid remaining in the tank is large, 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 view of the above circumstances, and provides a liquid pumping system that can reduce the time required to open a tank.

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

[0009] The liquid pumping system of the present invention includes a first liquid pumping mechanism configured to pump liquid in response to the rotation of the rotor, and a second liquid pumping mechanism configured to pump liquid by sucking up the liquid through a suction port in response to pressure changes in the liquid pumping section. Because the second liquid pumping mechanism does not rely on the rotation of the rotor, it 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 shortened.

[0010] FIG. 1 is a diagram showing the configuration of a liquid pumping system 1 according to a first embodiment of the present invention. FIG. 1 shows the state after liquid has been pumped to the first liquid pumping pipe 21a in the second liquid pumping mechanism 20. FIG. 2 shows the state after liquid has been pumped to the second liquid pumping pipe 21b from the state of FIG. 3 shows the state after liquid has been pumped to the third liquid pumping pipe 21c from the state of FIG. 3 shows a modified example in which the second liquid pumping mechanism 20 has two liquid pumping pipes. FIG. 6 shows the configuration of a liquid pumping system 1 according to a second embodiment of the present invention. FIG. 6 shows the state in which liquid L is being pumped by the second liquid pumping mechanism 20.

[0011] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an independent invention.

[0012] 1. First Embodiment 1-1. Liquid Pumping System 1 A liquid pumping system 1 according to a first embodiment of the present invention will be described using 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 re-liquefaction equipment 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, or -10°C, and may be in a range between any two of the numerical values ​​exemplified here or lower. Examples of the liquid L include liquefied natural gas (hereinafter referred to as "LNG") and liquefied ammonia.

[0014] The tank 2 may be of any configuration capable of containing the liquid L. However, from the viewpoint that the significance of applying the present invention becomes more pronounced when the liquid L cannot be discharged from the side of the tank 2, it is preferable that the tank 2 be configured so that the liquid L cannot be supplied or discharged through the side of the tank 2. An example of such a tank is a PC tank, the side of which is covered with a liquid barrier 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 top 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 portion 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, or 100 m, and may be in a range between any two of the values ​​exemplified here or greater than any two of them. 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, or 150 m, and may be in a range between any two of the values ​​exemplified here.

[0016] <First liquid pumping mechanism 10> The first liquid pumping mechanism 10 is configured to pump the liquid L by pushing up the liquid L as the rotor rotates, and discharge the liquid L from the tank 2. The pumped liquid L is discharged from the tank 2 and, if necessary, vaporized before being sent to the demand destination 30. The first liquid pumping mechanism 10 includes, for example, a pipe 10a extending vertically within the tank 2 and a pump 10b disposed within the pipe 10a. The pump 10b includes a rotor (not shown) and is configured to suck in the liquid L from an inlet 10c as the rotor rotates, and discharge the liquid L out of the tank 2 through the pipe 10a. In one example, the rotor is an impeller, and is configured to pressurize and pump the liquid L by rotating the rotor. In one example, centrifugal force (a force directed radially outward) is applied to the liquid L as the rotor rotates.

[0017] In such an apparatus, cavitation is likely to occur as the rotor rotates. To prevent cavitation, an operating condition is specified that the depth of the suction port 10c for the liquid L must be equal to or greater than a reference value (e.g., 1 m). Therefore, even if the liquid L is discharged from the tank using a pressurized liquid pumping device, a large amount of the liquid L remains in the tank 2. Vaporizing and removing this large amount of the liquid L requires a significant amount of time. In particular, ammonia has a higher boiling point and greater latent heat than LNG, making it more difficult to vaporize. Therefore, the above problem is particularly serious when the liquid in the tank is liquefied ammonia. In this embodiment, the provision of the second liquid pumping mechanism 20 makes it possible to reduce the amount of the 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, or 100 cm, and may be within a range between or less than any two of the values ​​exemplified here. The shorter this distance, the less likely 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 installed. 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, the risk of the first liquid lifting mechanism 10 colliding with the inner bottom surface 2c can be reduced.

[0019] <Second liquid pumping mechanism 20> As shown in Figure 2, the second liquid pumping mechanism 20 has an inlet 20a, a liquid pumping section 20b, and an outlet 20c. The second liquid pumping mechanism 20 is configured to pump the liquid L by sucking it up through the inlet 20a in response to pressure changes in the liquid pumping 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 liquid pumping mechanism 20 is not a pumping mechanism that relies on the rotation of a rotating body, and therefore can operate stably even when the depth of the liquid L inlet 20a is shallower than that of the first liquid pumping 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 shortened.

[0020] The liquid lifting section 20b includes first to third liquid lifting pipes 21a to 21c, first and second connecting sections 22a, 22b, first to third check valves 23a to 23c, and a pressure adjusting mechanism 24.

[0021] The first lift pipe 21a and the second lift pipe 21b are connected via a first connection 22a. The second lift pipe 21b and the third lift pipe 21c are connected via a second connection 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 in from the suction port 20a, the second lift pipe 21b is configured to be able to store the liquid L sucked in through the first connection 22a, and the third lift pipe 21c is configured to be able to store the liquid L sucked in through the second connection 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 liquid 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, a vacuum pipe 27, and a pressure adjustment pipe 28. The vacuum pipe 27 is connected to the first lifting pipe 21a via the first pressure reducing valve 25a, to the second lifting pipe 21b via the second pressure reducing valve 25b, and to the third lifting pipe 21c via the third pressure reducing valve 25c. The pressure adjustment pipe 28 is connected to the first lifting pipe 21a via the first pressure adjustment valve 26a, to the second lifting pipe 21b via the second pressure adjustment valve 26b, and to the third lifting pipe 21c via the third pressure adjustment 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 a cycle consisting of three steps. The following description will be given assuming the state in FIG. 4 as the initial state.

[0024] (1) First Step: Pumping Liquid into First Lift Pipe 21a In the first step, the pressure adjustment mechanism 24 reduces the pressure in the first lift pipe 21a, thereby sucking in liquid L through the suction port 20a and storing it in the first lift pipe 21a. More specifically, from the state shown in 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. This connects the first lift pipe 21a to the vacuum piping 27, reducing the pressure in the first lift pipe 21a. With this pressure change, 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 shown in FIG. 2, the liquid level in the first lifting pipe 21a is higher than the first connecting portion 22a.

[0025] (2) Second Step: Pumping Liquid to Second Lift Pipe 21b In the second step, the pressure adjustment mechanism 24 increases the pressure in the first lift pipe 21a to be higher than the pressure in the second lift pipe 21b, thereby moving at least a portion 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 adjusting valve 26a and the second pressure reducing valve 25b are opened. As a result, the first lift pipe 21a is connected to the pressure adjusting pipe 28, increasing the pressure in the first lift pipe 21a, and the second lift pipe 21b is connected to the vacuum pipe 27, decreasing the pressure in the second lift pipe 21b. With this pressure change, the liquid L in the first lift pipe 21a moves to the second lift pipe 21b through the first connecting portion 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 Figure 3, the liquid level in the second lift pipe 21b is higher than that of the second connecting part 22b.

[0026] (3) Third Step: Pumping Liquid to Third Lift Pipe 21c In the second step, the pressure adjustment mechanism 24 increases the pressure in the second lift pipe 21b to be higher than the pressure in the third lift pipe 21c, thereby moving at least a portion 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, increasing the pressure in the second lift pipe 21b, and the third lift pipe 21c is connected to the vacuum pipe 27, decreasing the pressure in the third lift pipe 21c. As a result of 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 lift 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 transferred, for example, to another tank 29. Therefore, the liquid level in the third lift pipe 21c is at the same height as the discharge port 20c. Note that the discharge port 20c may be closed while the third pressure reducing valve 25c is open, and the third pressure reducing valve 25c may be closed after the movement of the liquid L from the second lift pipe 21b to the third lift pipe 21c is complete, and then the discharge port 20c may be opened. In this case, the liquid level in the third lift pipe 21c will be 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 from the tank 2 through the first to third steps. When using a single lifting pipe to pump up the liquid L, the height to which the liquid L can be pumped is approximately 5 to 15 m at most, although this is affected by factors such as the pressure in the tank 2 and the specific gravity of the liquid L. If the height of the tank 2 is 20 m or more, the liquid L cannot be pumped up and discharged from the upper surface 2 b of the tank 2. On the other hand, the configuration of this embodiment uses a combination of two or more lifting pipes and check valves, and utilizes the movement of the liquid L caused by pressure changes in each lifting pipe, 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 set appropriately so that the liquid can be pumped by the above method. 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 liquid L can be moved, thereby enabling more efficient pumping.

[0030] In the above embodiment, three lifting pipes are used to pump the liquid L in one cycle of three steps, but it is also possible to use two lifting pipes to pump the liquid in one cycle of two steps, or to use four or more lifting pipes to pump the liquid in one cycle of four or more steps. The more lifting pipes there are, the easier it is to pump the liquid L to a higher position.

[0031] For example, when the number of lifting pipes is set to two and lifting is performed in one cycle consisting of two steps, the lifting section 20b is configured to include first and second lifting pipes 21a, 21b, a connection part 22a, first and second check valves 23a, 23b, and a pressure adjustment mechanism 24, as shown in Figure 5, and an outlet 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 first and second steps described above, the liquid L can be pumped and discharged from the tank 2.

[0032] More generally, when N pumping pipes are used to pump liquid in a cycle consisting of N or more steps, the first pumping pipe is provided with a suction port 20a, and the Nth pumping pipe is provided with a discharge port 20c. Each pumping pipe is provided with a check valve, and adjacent pumping pipes are connected at a connector. In the first step, the pressure in the first pumping pipe is reduced to suck liquid L into the first pumping pipe. In the second to Nth steps, the pressure in the (m-1)th pumping pipe is increased above the pressure in the mth pumping pipe. This process is repeated while changing m in the order of 2 to N. By this process, liquid L in the first pumping pipe can be transferred to the second, third, ..., Nth pumping pipes in order and discharged from the discharge port 20c provided in the Nth pumping pipe. N is, for example, 2 to 20, specifically, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, and may be in a range between any two of the numerical values ​​exemplified here.

[0033] <BOG Compressor 3 and Reliquefaction Equipment 4> In the tank 2, vaporized gas (boil-off gas, hereinafter referred to as "BOG") is generated when the liquid L is vaporized by heat input from the outside. To prevent the pressure inside the tank 2 from becoming too high, it is preferable to discharge the BOG from the tank 2 through the BOG line 31. The BOG line 31 is provided with a BOG compressor 3 for compressing and pressurizing the BOG. ​​The compressed gas obtained by compression in the BOG compressor 3 can be used by transferring it to a consumer 30, transferring it to the reliquefaction equipment 4 where it is reliquefied and then returned to the tank 2, or returning it directly to the tank 2. The transfer destination can be switched using a valve (not shown) or the like.

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

[0035] When opening the tank 2, the first and second pumping mechanisms 10 and 20 discharge most of the liquid L from the tank 2. However, complete discharge is difficult, and some liquid L remains. This remaining liquid L can be removed by vaporizing it by blowing a purge gas, such as nitrogen, into the tank 2. However, in this case, the discharged gas becomes a mixture of vaporized gas and purge gas, which cannot be transported directly to the consumer 30. Therefore, the user must choose between purifying the mixture or treating it by combustion, both of which are undesirable from an economic and environmental perspective. 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. Because the compressed gas has the same components as the vaporized gas, the gas discharged from the tank 2 can be transported to the consumer 30. Therefore, the method of this embodiment is advantageous from an economic and environmental perspective.

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

[0037] In the pumping process, 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 can pump the liquid more efficiently than the second pumping mechanism 20, it is possible to pump the liquid using only the first pumping mechanism 10 and then using only the second pumping mechanism 20, or to pump the liquid using both the first and second pumping mechanisms 10, 20, and then switch to using only the second pumping mechanism 20 when the remaining amount of liquid L becomes so low that the first pumping mechanism 10 cannot operate.

[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 allows the liquid L remaining in the tank 2 to be efficiently removed.

[0039] When the amount of vaporized gas produced in the vaporization step becomes sufficiently small, a purging step 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, creating an environment suitable for workers inspecting the inside of 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 interior of the tank 2. When the liquid L is liquefied ammonia, inspection is required more frequently than when the liquid L is LNG, taking into account the corrosive nature of ammonia. Furthermore, liquefied ammonia has a higher boiling point and greater latent heat than LNG, making it difficult to vaporize. Furthermore, liquefied ammonia is more toxic than LNG, so there is a stronger need than for LNG to reduce the amount of remaining liquefied ammonia as much as possible before workers enter the tank 2. According to this embodiment, the liquid L is pumped using the first and second liquid pumping mechanisms 10, 20. Therefore, the liquid L in the tank 2 can be discharged to a smaller amount in a shorter period of time than when only the first liquid pumping mechanism 10 is used. Therefore, the technical significance of the method of this embodiment is particularly significant when the liquid L is liquefied ammonia.

[0041] 2. Second Embodiment A second embodiment of the present invention will be described using Figures 6 and 7. This embodiment is similar to the first embodiment, and the details described in the first embodiment can also be applied to this embodiment as long as they do not contradict the spirit of the first embodiment. This embodiment differs mainly from the first embodiment in the configuration of the second liquid pumping mechanism 20. The following description will focus on these 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 inside the ejector 20e is decompressed by the flow of the liquefied gas L1, and the liquid L inside 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 way, also in this embodiment, the liquid L is sucked up through the suction port 20a in accordance with the change in pressure inside 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. With this method, 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 made outside the tank 2, which has the advantage of not burdening workers or the environment.

[0045] 3. Third Embodiment The second liquid pumping mechanism 20 described in the first embodiment can be used to pump liquid as a newly configured liquid pumping mechanism, independent of the liquid pumping system 1 of the first embodiment. By using this liquid pumping mechanism, it is possible to pump liquid to a height that exceeds the height achievable by suction, even in situations where it is not possible to install a pressurized liquid pumping device such as the first liquid pumping mechanism 10.

[0046] 1: pumping system, 2: tank, 2a: dike, 2b: top surface, 2c: inner bottom surface, 3: BOG compressor, 4: reliquefaction equipment, 10: first pumping mechanism, 10a: pipe, 10b: pump, 10c: suction port, 20: second pumping mechanism, 20a: suction port, 20b: pumping section, 20c: discharge port, 20d: introduction pipe, 20e: ejector, 20f: pumping pipe, 20g: valve, 21a: first pumping pipe, 21b: second pumping pipe, 21c: third pumping 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 adjustment valve, 26b: second pressure adjustment valve, 26c: third pressure adjustment valve, 27: vacuum piping, 28: pressure adjustment piping, 29: separate tank, 30: demand destination, 31: BOG line, 32: liquefied gas pump, L: liquid, L1: liquefied gas

Claims

1. A liquid pumping system having a tank for storing a liquid, and first and second lifting mechanisms configured to pump the liquid and discharge it from the tank, wherein the first lifting mechanism is configured to pump the liquid by pushing it up as a rotating body rotates, thereby enabling it to be discharged from the tank, and the second lifting mechanism has a suction port, a lifting section, and an outlet, and is configured to pump the liquid by sucking it up through the suction port as pressure changes in the lifting section, thereby enabling it to be discharged from the tank through the outlet.

2. A liquid lifting system as described in claim 1, wherein the liquid lifting section comprises first and second liquid lifting pipes, a connection section, first and second check valves, and a pressure adjustment mechanism, the first and second liquid lifting 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 lifting pipes, the first liquid lifting pipe is configured to be capable of storing liquid sucked in from the suction port, the second liquid lifting 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 lifting pipes.

3. A method for opening a tank using the liquid pumping system described in claim 1 or 2, comprising a liquid pumping process, in which the liquid is pumped and discharged from the tank using first and second liquid pumping mechanisms.

4. A method according to claim 3 which cites claim 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 claim 3, further comprising a vaporization step following the liquid pumping step, in which the vaporized gas produced by vaporizing the liquid is compressed and the compressed gas is returned to the tank, thereby accelerating the vaporization of the liquid remaining in the tank.

6. A lifting mechanism having an inlet, a lifting section, and an outlet, configured to lift the liquid by sucking up the liquid through the suction port in response to pressure changes in the lifting section and discharge the liquid from the outlet, 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 suction 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. A method for pumping liquid using the pumping mechanism described in claim 6, 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.

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