JP2024143121A - Cryogenic Liquid Supply System and Pump Control Device - Google Patents

Abstract

[Problem] Taking into account the operation of the flow rate control valve, the discharge capacity of the discharge pump is increased for operation. [Solution] A cryogenic liquid supply system comprising a storage tank for storing cryogenic liquid, a plurality of discharge pumps for supplying the cryogenic liquid stored in the storage tank to a vaporizer, a discharge line connected to the storage tank for supplying the cryogenic liquid to the vaporizer, a flow rate control valve provided on the discharge line and positioned upstream of the vaporizer for adjusting the flow rate of the cryogenic liquid flowing to the vaporizer, and a pump control device that acquires the liquid level of the cryogenic liquid in the storage tank and controls the flow rate of the cryogenic liquid dispensed by each of the plurality of discharge pumps based on the liquid level. [Selected drawing] Figure 2

Description

The present invention relates to a cryogenic liquid supply system and a pump control device.

For example, Patent Document 1 discloses a technology in which an LNG tank is prepared on the discharge side of a discharge pump, and in the event of an emergency stop of the pump, LNG is discharged from the LNG tank provided on the discharge side until the backup pump starts pumping.

Japanese Patent Application Publication No. 8-240185

At LNG terminals, which receive, store, and vaporize LNG (Liquefied Natural Gas), a type of low-temperature liquid, we are studying ways to increase the LNG discharge capacity per unit, thereby allowing other pumps to be stopped, thereby reducing electricity costs by reducing the annual operating hours and also extending the lifespan of pumps.
Here, when a plurality of discharge pumps are in operation, if one of the discharge pumps stops in an emergency, the discharge flow rate of the remaining discharge pump that is in operation is temporarily increased in order to maintain the discharge flow rate of the entire facility for several minutes until the replacement pump starts to follow up and start discharging. When the discharge capacity of each pump is increased, the discharge flow rate of the remaining discharge pump becomes excessively large compared to the conventional case, and the opening degree of the flow control valve on the discharge line also becomes larger than the conventional case. When the follow-up discharge pump starts discharging while this flow control valve is in a high opening state, the closing operation of the flow control valve is not in time, and an excessive amount of LNG temporarily passes through the flow control valve and flows into the vaporizer. Therefore, from the viewpoint of safety, there is a limit to the operation of increasing the discharge capacity of each discharge pump.
The present invention aims to increase the discharge capacity of the discharge pump by taking into account the operation of the flow rate regulating valve.

The cryogenic liquid supply system to which the present invention is applicable is a cryogenic liquid supply system comprising: a storage tank for storing cryogenic liquid; a plurality of discharge pumps for supplying the cryogenic liquid stored in the storage tank to an vaporizer; a discharge line connected to the storage tank for supplying the cryogenic liquid to the vaporizer; a flow control valve provided on the discharge line and positioned upstream of the vaporizer for adjusting the flow rate of the cryogenic liquid flowing to the vaporizer; and a pump control device that acquires the liquid level of the cryogenic liquid in the storage tank and controls the flow rate of the cryogenic liquid dispensed by each of the plurality of discharge pumps based on the liquid level.
Here, the pump control device can be characterized in that it sets a rated flow rate, which is the flow rate of low-temperature liquid that each of the multiple discharge pumps normally discharges per unit time, based on the height of the liquid level, and controls the discharge pump.
The pump control device may be characterized in that it increases the rated flow rate when the liquid level is higher than a predetermined value.
The pump control device may further include an acquisition unit that acquires a liquid density of the cryogenic liquid stored in the storage tank, and when the liquid level is higher than a predetermined value, the pump control device may set the mass flow rate to the rated flow rate in accordance with the acquired liquid density.

From another perspective, it is a pump control device that includes a liquid level acquisition means that acquires the liquid level of the cryogenic liquid stored in a storage tank that stores the cryogenic liquid, and a control unit that controls the flow rate of the cryogenic liquid dispensed per unit time by a dispense pump that dispenses the cryogenic liquid from the storage tank based on the acquired liquid level.

According to the present invention, the discharge capacity of the dispensing pump can be increased by taking into account the operation of the flow rate adjustment valve.

1 is a diagram showing an example of the overall configuration of an LNG supply system to which the present embodiment is applied. FIG. 2 is a diagram illustrating an example of a functional configuration of an overall control device according to the present embodiment. FIG. 2 is a diagram illustrating an example of processing performed by an overall control device. 11 is a diagram for explaining the relationship between the mass flow rate of LNG flowing to the vaporizer and the opening degree of the flow control valve when one of the pumps is stopped in an emergency. FIG. This is data for each piece of equipment when a pump is stopped in an emergency on the simulator and then restarted. This is data for each piece of equipment when a pump is stopped in an emergency on the simulator and then restarted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
<Overall configuration of LNG supply system 1>
FIG. 1 is a diagram showing an example of the overall configuration of an LNG supply system 1 to which this embodiment is applied.
The LNG supply system 1 to which this embodiment is applied comprises an LNG tank 10 for storing LNG as an example of a cryogenic liquid, an LNG receiving line 11 for supplying LNG to the LNG tank 10, a liquid level meter 12 for measuring the liquid level of the LNG stored in the LNG tank 10, a liquid density meter 13 for measuring the liquid density of the LNG stored in the LNG tank 10, and a plurality of pumps 20 (in the example of Figure 1, five pumps 20-1, 20-2, 20-3, 20-4, 20-5) which are an example of discharge pumps that discharge the LNG stored in the LNG tank 10. The LNG supply system 1 also includes a vaporizer 50 (two vaporizers 50-1 and 50-2 in the example of FIG. 1) that vaporizes LNG, a discharge line 40 that is a pipeline for discharging LNG discharged from the LNG tank 10 to the vaporizers 50-1 and 50-2, flow control valves 71-1 and 71-2 that adjust the flow rate of LNG flowing through the discharge line 40, mass flowmeters 72-1 and 72-2 that measure the flow rate of LNG flowing through the discharge line 40, and a trunk conduit 60 that sends NG (Natural Gas) vaporized by the vaporizer 50 to a demand destination. The LNG supply system 1 also includes an overall control device 30 that controls the entire LNG supply system 1.

The LNG tank 10 is, for example, an underground double-shell tank that includes an inner tank for storing LNG, an outer tank surrounding the inner tank, and a cold insulation layer that is filled with a cold insulation material (for example, perlite) and is provided between the inner and outer tanks.

The LNG receiving line 11 is a pipeline for receiving LNG unloaded from an LNG tanker into the LNG tank 10. For example, an unloading arm (not shown) of an LNG tanker (not shown) is connected to the LNG receiving line 11, and LNG is supplied from the LNG tanker.

The level gauge 12 measures the liquid level of the LNG stored in the LNG tank 10. Here, the liquid level is the height from the bottom of the inner tank of the LNG tank 10 to the liquid surface of the LNG stored in the LNG tank 10.

In this embodiment, two to four pumps 20 are normally operated, and at least one pump 20 is kept on standby to be restarted in the event of an emergency stop of any of the pumps 20. The number of pumps 20 included in the LNG supply system 1 is not limited to the example shown in FIG. 1. The pumps 20 are provided near the bottom of the inner tank of the LNG tank 10.

The vaporizer 50 is a device that vaporizes the LNG supplied to the vaporizer 50 with seawater or the like to produce NG, similar to known vaporizers.

The discharge line 40 is a pipeline for discharging the LNG discharged from the pump 20 to the vaporizer 50. The discharge line 40 includes a first discharge line 41 connected to the vaporizer 50-1, and a second discharge line 42 branching off from the first discharge line 41 and connecting to the vaporizer 50-2. The first discharge line 41 is provided with a flow control valve 71-1 for adjusting the flow rate of LNG flowing into the vaporizer 50-1, and a mass flowmeter 72-1 for measuring the mass flow rate flowing into the vaporizer 50-1. The second discharge line 42 is provided with a flow control valve 71-2 for adjusting the flow rate of LNG flowing into the vaporizer 50-2, and a mass flowmeter 72-2 for measuring the mass flow rate flowing into the vaporizer 50-2.

The overall control device 30 includes a CPU (Central Processing Unit) 31 that controls the entire LNG supply system 1, a RAM (Random Access Memory) 32 that is used as a working area during calculations, and a ROM (Read Only Memory) 33 that stores various programs executed by the CPU 31. The overall control device 30 also includes a storage device 34 that stores various information, and a communication interface (hereinafter referred to as "communication I/F") 35 that transmits and receives data. The overall control device 30 is connected to the devices controlled by the overall control device 30 via communication means, and is also connected to various detection means via communication means. Here, the devices controlled by the overall control device 30 are, for example, the pump 20 and flow rate control valves 71-1 and 71-2. The various detection means are, for example, the liquid level gauge 12, the liquid density meter 13, the mass flow meters 72-1 and 72-2, etc. The overall control device 30 is an example of a pump control device.

<Functional configuration of overall control device 30>
Next, the functional configuration of the overall control device 30 according to this embodiment will be described with reference to FIG.
FIG. 2 is a diagram showing an example of a functional configuration of the overall control device 30 according to the present embodiment.
The overall control device 30 includes a liquid level determination unit 310 and a pump control unit 320 .

The liquid level determination unit 310 includes a liquid level acquisition unit 311 and a liquid level comparison unit 312 .
The liquid level acquisition unit 311 acquires information on the liquid level of the LNG stored in the LNG tank 10 from the liquid level gauge 12. The liquid level may be acquired continuously (e.g., every minute), or may be acquired at regular intervals (e.g., every hour or every day) when the liquid level does not change much in a short period of time. The liquid level may also be acquired irregularly, for example, when LNG is supplied to the LNG tank 10 or according to the amount of LNG dispensed.

The liquid level comparison unit 312 determines whether the liquid level satisfies a predetermined condition. In this embodiment, it determines whether the liquid level is higher than a height determined for each liquid density. This condition is determined, for example, based on data obtained by simulating the LNG supply system 1. The liquid level height conditions determined for each liquid density will be described later with reference to Figures 5 and 6. Depending on this determination, the control of the pump 20 performed by the pump control unit 320 will differ.

The pump control unit 320 includes a liquid density acquisition unit 321 , a discharge mass determination unit 322 , a demand acquisition unit 323 , and a pump number determination unit 324 .
The liquid density acquisition unit 321 acquires the liquid density of the LNG in the LNG tank 10. In this embodiment, the liquid density is measured by the liquid density meter 13 (see FIG. 1 ) in the LNG tank 10. As a method for acquiring the liquid density, other than a method of constantly acquiring the liquid density from the liquid density meter 13 in the LNG tank 10, for example, a method of periodically measuring the LNG in the LNG tank 10 (for example, once a month) or a method of measuring the liquid density of the LNG in the LNG tank 10 when supplying LNG to the LNG tank 10 may be used. In addition, it is known that there is a correlation between the calorific value of LNG and the liquid density of LNG, and the calorific value of LNG may be acquired and converted into the liquid density of LNG.

The discharge mass determination unit 322 determines the discharge mass flow rate per pump. For example, the higher the liquid level, the higher the discharge mass flow rate per pump. The discharge mass determination unit 322 may also increase the discharge mass flow rate per pump as the liquid density of the LNG in the LNG tank 10 increases. Here, if the mass flow rate per pump is increased as the liquid density of the LNG increases so that the volumetric flow rate of LNG discharged by each pump 20 is constant, the discharge pressure of the LNG discharged by the pump 20 can be made almost constant. The discharge mass flow rate is expressed, for example, as the mass flow rate per hour (t/h).

The demand acquisition unit 323 acquires the demand amount of LNG to be delivered to the demand destination. The demand amount of LNG is constantly received from the demander.

The pump number determination unit 324 determines the number of pumps required to supply LNG to the vaporizer 50 at a flow rate corresponding to the demand, and controls the pumps 20. Here, the required number is the number of pumps that will result in a mass flow rate obtained by multiplying the discharge mass flow rate per pump 20 by the number of pumps, which is at least a value that exceeds the demand. Note that, in preparation for fluctuations in demand, the required number of pumps may be determined based on the demand amount plus a predetermined margin.

The flow of processing performed by the overall control device 30 will be described below.
<Processing of the Overall Control Device 30>
FIG. 3 is a diagram showing an example of processing performed by the overall control device 30. As shown in FIG.
First, the liquid level acquisition unit 311 acquires the height of the liquid level of the LNG stored in the LNG tank 10 (step 201). Next, the liquid density acquisition unit 321 acquires the liquid density in the LNG tank 10 (step 202). The liquid level comparison unit 312 judges whether the acquired liquid level is higher than the height determined for each liquid density (step 203). If the liquid level is higher than the height determined for each liquid density (YES in step 203), the discharge mass determination unit 322 determines the discharge mass flow rate according to the acquired liquid density (step 204). More specifically, when the liquid density is high, the discharge mass flow rate is increased to keep the discharge volumetric flow rate almost constant, and the discharge pressure of the pump 20 is controlled to be maintained at a constant level or higher.
Next, the demand acquisition unit 323 acquires the demand for LNG from the demand destination (step 205), and the pump number determination unit 324 determines the number of pumps 20 to be operated. Next, the pump number determination unit 324 issues an instruction to operate the determined number of pumps 20 (step 207), and the process ends.

Also, in step 203, if the height of the liquid level is lower than the height determined for each liquid density (NO in step 203), the discharge mass determination unit 322 sets the discharge mass flow rate of the pump 20 to a predetermined low discharge mass flow rate (step 208). This low discharge mass flow rate is set to a low discharge mass flow rate in order to provide the pump 20 with some spare capacity in case one of the pumps 20 is stopped in an emergency when the liquid level is low. Next, the demand for LNG is obtained (step 205), and the number of pumps 20 to be operated is determined (step 206). Next, the pump number determination unit 324 issues an instruction to operate the determined number of pumps 20 (step 207), and the process ends.

4 is a diagram for explaining the relationship between the mass flow rate of LNG flowing to vaporizer 50-1 and the aperture of flow control valve 71-1 when one of pumps 20 is stopped in an emergency. Note that, although the vaporizer 50-1 and flow control valve 71-1 are taken as examples for explanation here, the same applies to the relationship between the mass flow rate of vaporizer 50-2 and the aperture of flow control valve 71-2.
In FIG. 4, the horizontal axis represents the passage of time, a dashed line 401 represents the magnitude of the mass flow rate of LNG flowing into vaporizer 50-1, and a solid line 402 represents the opening degree of flow rate control valve 71-1.

In Figure 4, the tank flow rate is shown to be operating normally until time T1, when one of the pumps 20 is stopped in an emergency, and then at time T3, LNG is discharged from the pump 20 that is started again. Until time T1, the pumps 20 are operating normally, LNG flows to the vaporizer 50-1 at a mass flow rate of F1, and the opening of the flow control valve 71-1 is S1.

If one of the pumps 20 stops in an emergency, the discharge flow rate of the remaining pumps 20 is temporarily increased and the opening of the flow control valve 71-1 located between the LNG tank 10 and the vaporizer 50-1 is increased in order to maintain the overall discharge flow rate for several minutes until the pumps 20 start up again and begin discharging LNG.

At time T2, the opening degree of the flow rate adjustment valve 71-1 becomes S2.
Then, at time T3, LNG begins to be rapidly discharged from pump 20 that has been started up again, and at time T4, the mass flow rate of LNG flowing into vaporizer 50-1 becomes F1, which is the mass flow rate when pump 20 is operating normally, but the opening degree of flow control valve 71-1 at time T4 is larger than S1, which is the opening degree for normal operation, and flow control valve 71-1 is open up to S2. Therefore, excessive LNG flows into vaporizer 50-1 from flow control valve 71-1.
Then, at time T5, the mass flow rate flowing through vaporizer 50-1 reaches a maximum value F5, and as flow control valve 71-1 closes, the mass flow rate of LNG flowing through vaporizer 50-1 gradually decreases.

If the mass flow rate discharged by each of the pumps 20 during normal operation is large, if any of the pumps 20 is stopped in an emergency, the flow rate temporarily increased by each of the remaining pumps 20 is large, and the discharge pressure of the LNG discharged from the pumps 20 decreases. Therefore, if the mass flow rate discharged by each of the pumps 20 during normal operation is large, if any of the pumps 20 is stopped in an emergency, the opening degree of the flow control valve 71-1 becomes large, increasing the possibility that an excessive amount of LNG will flow into the vaporizer 50-1.

The opening of the flow control valve 71-1 cannot be changed instantly, but changes gradually, so a certain amount of time is required to achieve the desired opening. Therefore, the longer the time from when one of the pumps 20 is stopped in an emergency until the pump 20 starts to follow up and begin discharging LNG, the wider the opening of the flow control valve 71-1 will be. On the other hand, if the time until the follow-up pump 20 starts discharging LNG is short, LNG will be discharged from the follow-up pump 20 before the opening of the flow control valve 71-1 increases, so it is possible to prevent an excessive amount of LNG from flowing into the vaporizer 50-1.

It is known that the time until the pump 20 starts discharging LNG after being started is greatly affected by the height of the LNG liquid level in the LNG tank 10 in which the pump 20 is installed. Specifically, the higher the height of the LNG liquid level in the LNG tank 10, the more head pressure is applied to the pump 20 set near the bottom of the LNG tank 10, making it easier for the pump 20 to pump up LNG. This shortens the time until discharging starts.
Therefore, even if the discharge mass flow rate per pump 20 is increased, the higher the liquid level of LNG in the LNG tank 10, the more likely it is that an excessive amount of LNG can be prevented from flowing into the vaporizer 50-1.

Next, an example of a condition used by the liquid level comparator 312 (see FIG. 2) when determining whether the liquid level satisfies a predetermined condition will be described.
5 and 6 show data of each facility when one of the pumps 20 operating on the simulator is stopped in an emergency and the pump 20 is restarted.
5 and 6 show an operating vaporizer 511 indicating the vaporizer 50 in operation, an operating pump number 512 indicating the number of pumps 20 in operation, a discharge mass 513 of the pump 20 which is the mass flow rate discharged from the pump 20 under normal circumstances, a vaporizer flow rate before stop 514 which is the mass flow rate flowing to the vaporizer 50 before the emergency stop, a liquid level 515 of the LNG tank 10 which is the liquid level of the LNG in the LNG tank 10, a calorific value 516 of the LNG in the LNG tank 10, a liquid density 517 of the LNG in the LNG tank 10, and a maximum flow rate after stop 518 indicating the maximum value of the mass flow rate flowing to the vaporizer 50 after the emergency stop and the maximum value of the mass flow rate discharged by the pump 20. The vaporizer flow rate before stop 514 corresponds to F1 in FIG. 4, and the maximum flow rate after stop 518 corresponds to F5 in FIG. 4.

The first simulation data in FIG. 5 is an example in which the pump 20 is operated with a low discharge mass flow rate to allow for some margin, and the second to fourth simulation data are examples in which the pump 20 is operated with a large discharge mass flow rate in accordance with the liquid density 517 in the LNG tank 10. Note that the second to fourth simulation data differ in the liquid level height 515 of the LNG tank 10.

Here, when comparing the maximum flow rate 518 after stopping to the vaporizers 50-1 and 50-2 with the value of the first simulation as a reference, it increases in the second and third simulations and decreases in the fourth simulation. That is, when the liquid density of LNG is 464.5 (kg/m3), if the discharge mass 513 of the pump 20 is increased according to the liquid density of LNG, the maximum flow rate 518 after stopping increases when the liquid level is 15.0 (m) and 20.0 (m), and decreases when the liquid level is 25.0 (m). Therefore, it can be seen that when the liquid density 517 of LNG in the LNG tank 10 is 464.5 (kg/m3) and the liquid level in the LNG tank 10 is 25.0 (m) or higher, even if the discharge mass 513 of the pump 20 is increased according to the liquid density 517 of LNG, there is little effect on the vaporizer 50.

6, the magnitude of the liquid density 517 of the LNG in the LNG tank 10 is different from that in the example of FIG. 5, and the liquid density 517 is 450.8 (kg/m 3 ).
Here, when comparing the maximum flow rate 518 after stopping to the vaporizers 50-1 and 50-2 with the value of the fifth simulation as a reference, it increases in the sixth simulation, remains almost the same in the seventh simulation, and decreases in the eighth simulation. That is, when the liquid density 517 of the LNG is 450.8 (kg/m3), if the discharge mass 513 of the pump 20 is increased according to the liquid density 517 of the LNG, the maximum flow rate 518 after stopping increases when the liquid level height 515 is 15.0 (m), and remains almost the same or decreases when the liquid level height 515 is 20.0 (m) and 25.0 (m). Therefore, when the liquid density 517 of the LNG in the LNG tank 10 is 450.8 (kg/m3) and the liquid level height 515 in the LNG tank 10 is 20.0 (m) or more, it can be seen that even if the discharge mass 513 of the pump 20 is increased in accordance with the liquid density 517 of the LNG, there is little effect on the vaporizer 50.

In this manner, a simulation is performed to determine, for each LNG density, a condition for the liquid level at which the flow rate to the vaporizer 50 after an emergency stop of any of the pumps 20 falls within an allowable range. The determined condition is stored in the storage device 34 of the overall control device 30. The liquid level comparator 312 (see FIG. 2) uses the condition to determine whether the liquid level satisfies a predetermined height (see S203 in FIG. 3).
The conditions may be determined by simulation or based on measurement data at an actual LNG terminal.

In the simulation data of FIG. 5 and FIG. 6, the total discharge mass 513 of the pumps 20 (for example, 3 pumps x 135 t/h in the second simulation of FIG. 5) does not match the total vaporizer flow rate 514 before the shutdown (for example, 150 t/h + 225 t/h in the second simulation of FIG. 5). This is because, in order to simulate a state in which only the discharge mass 513 of the pumps 20 is changed without changing the total vaporizer flow rate 514 before the shutdown, a pipe branching from the upstream side of the flow control valves 71-1 and 71-2 of the discharge line 40 and connected to the LNG tank 10 is provided in the simulation, and the flow rate of the total discharge mass 513 of the pumps 20 that is greater than the total vaporizer flow rate 514 before the shutdown is returned to the LNG tank 10 for the simulation.

As described above, in this embodiment, when the liquid level in the LNG tank 10 is higher than the height determined for each liquid density of the LNG, the mass flow rate of LNG discharged from the pump 20 is increased. In this way, by increasing the mass flow rate discharged from the pump 20 when the liquid level in the LNG tank 10 is high, even if one of the pumps 20 in operation is stopped in an emergency, the time during which LNG is discharged from the pump 20 that is started again is shortened, and an excessive amount of LNG is prevented from flowing to the vaporizer 50.

In addition, in this embodiment, the determination is made based on the height determined for each liquid density in LNG tank 10, but the condition for the height of the liquid level that falls within the allowable range of the flow rate to vaporizer 50 may be determined regardless of the liquid density in LNG tank 10. For example, the highest liquid level condition among the height conditions determined for each liquid density may be adopted.
In addition, in this embodiment, the mass flow rate of LNG discharged from the pump 20 is changed according to the liquid density of LNG, but the mass flow rate of LNG discharged from the pump 20 may be changed regardless of the liquid density of LNG. For example, the mass flow rate of LNG discharged from the pump 20 may be increased as the liquid level increases.
In this embodiment, the pump 20 is provided near the bottom surface of the inner tank of the LNG tank 10. However, if the pump 20 is disposed at a position higher than the bottom surface of the inner tank of the LNG tank 10, the liquid level may be measured based on the position of the pump 20.

1...LNG supply system, 10...LNG tank, 12...liquid level gauge, 13...liquid density meter, 20...pump, 30...overall control device, 31...CPU, 40...discharge line, 50...vaporizer, 71-1...flow control valve, 71-2...flow control valve, 310...liquid level determination unit, 320...pump control unit

Claims (5)

A storage tank for storing a cryogenic liquid;
A plurality of pumps for supplying the cryogenic liquid stored in the storage tank to a vaporizer;
a delivery line connected to the storage tank for supplying cryogenic liquid to the vaporizer;
a flow rate control valve provided in the discharge line and located upstream of the vaporizer to adjust a flow rate of the cryogenic liquid flowing to the vaporizer;
a pump control device that acquires a liquid level of the cryogenic liquid in the storage tank and controls a flow rate of the cryogenic liquid discharged by each of the plurality of discharge pumps based on the liquid level;
A cryogenic liquid supply system comprising: The cryogenic liquid supply system according to claim 1, characterized in that the pump control device sets a rated flow rate, which is the flow rate of cryogenic liquid discharged per unit time by each of the multiple discharge pumps under normal conditions, based on the height of the liquid level, and controls the discharge pumps. The cryogenic liquid supply system of claim 2, characterized in that the pump control device increases the rated flow rate when the liquid level is higher than a predetermined value. an acquisition unit that acquires a liquid density of the cryogenic liquid stored in the storage tank;
Further equipped with
4. The cryogenic liquid supply system according to claim 3, wherein the pump control device sets the mass flow rate to the rated flow rate in accordance with the acquired liquid density when the liquid level is higher than a predetermined value. a liquid level acquiring means for acquiring a liquid level of a cryogenic liquid stored in a storage tank for storing the cryogenic liquid;
a control unit that controls a flow rate of the cryogenic liquid discharged per unit time by a discharge pump that discharges the cryogenic liquid from the storage tank based on the acquired liquid level;
A pump control device comprising:

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