JP6946124B2 - Pump number control device - Google Patents

Description

The present invention relates to a pump number control device and a pump number control method.

Patent Document 1 below discloses a method for controlling the number of operating pumps that controls the number of operating pumps for delivering low-temperature liquefied gas such as LNG. In this operation unit control method, an increase / decrease prediction pattern of the demand amount of low-temperature liquefied gas is set, and the stop of the payout pump in operation is delayed for a certain period of time according to the increase / decrease prediction pattern, or the payout pump in operation is stopped. By delaying the start-up for a certain period of time, a smooth and stable response to changes in demand is realized.

Japanese Patent Application Laid-Open No. 08-240185

By the way, the above-mentioned discharge pump is a pump that discharges low-temperature liquefied gas from a low-temperature tank such as an LNG tank, and in the above-mentioned operation number control, the discharge is performed according to a comparison between the demand amount and the rated capacity of the discharge pump, that is, the rated discharge amount. The number of pumps in operation is determined. This rated capacity (rated discharge amount) is a value indicating the performance of the discharge pump, and is a fixed value.

However, the liquid density of the low-temperature liquefied gas discharged from the low-temperature tank by the discharge pump changes depending on the production area of the low-temperature liquefied gas, the storage state in the low-temperature tank, and the like. Therefore, when the payout amount (discharge amount) of the payout pump is viewed as a mass flow rate, the payout amount fluctuates according to the liquid density even when the payout pump is operating at a constant rotation speed. It will be.
Further, the change in liquid density appears as a change in the calorific value of the gas at the consumption destination. Therefore, if the change in the calorific value of the gas exceeds the permissible range, abnormal combustion or misfire may occur in the combustor to be consumed.

The present invention has been made in view of the above circumstances, and provides a pump number control device and a pump number control method capable of suppressing fluctuations in the discharge amount (mass flow rate) due to changes in liquid density. The purpose.

In order to achieve the above object, in the present invention, as a first solution concerning the pump number control device, a pump number control device that controls the start and stop of a plurality of pumps, depending on the liquid density of the discharged fluid. A rated discharge amount calculation unit that calculates the rated discharge amount of the pump, an operation number calculation unit that calculates the required number of operating pumps based on the rated discharge amount obtained by the rated discharge amount calculation unit, and the operation. A means of providing a pump control unit that outputs a start or stop instruction to the pump according to the required number of operating units obtained by the number calculation unit is adopted.

In the present invention, as a second solution for controlling the number of pumps, in the first solution, the rated discharge amount calculation unit determines the rated discharge amount when the liquid density is equal to or higher than a predetermined threshold value. When the liquid density is lower than a predetermined threshold value, the rated discharge amount is calculated based on a predetermined function with the liquid density as a variable.

In the present invention, as a third solution for controlling the number of pumps, the first or second solution further includes an operation unit for inputting the liquid density, and the rated discharge amount calculation unit performs the operation. A means of calculating the rated discharge amount based on the liquid density input from the unit is adopted.

In the present invention, as a fourth solution for controlling the number of pumps, the third solution further includes an alarm, and the rated discharge amount calculation unit has the liquid density input from the operation unit. When the deviation from a predetermined upper limit value and / or lower limit value is deviated, a means of causing the alarm device to output an alarm is adopted.

In the present invention, as a fifth solution for controlling the number of pumps, the first or second solution further includes a density meter for measuring the liquid density, and the rated discharge amount calculation unit has the density. A means of calculating the rated discharge amount based on the liquid density measured by the meter is adopted.

In the present invention, as a sixth solution for controlling the number of pumps, any of the first to fifth solutions further includes a follow-up prevention timer that measures a first time when the pump is started. The pump operation control unit employs a means of reserving the re-start of the pump until the time-up of the re-start prevention timer.

In the present invention, as a seventh solution for controlling the number of pumps, in any of the first to sixth solutions, each power supply system for supplying electric power to the pump is provided, and when the pump is started. A rush prevention timer for timing the second time is further provided, and the pump operation control unit adopts a means of suspending the start of the pump of the same power supply system until the rush prevention timer times up. ..

In the present invention, as an eighth solution relating to the pump number control device, in any one of the first to seventh solutions, the pump is a payout pump that discharges a low temperature liquefied gas from a low temperature tank. Adopt the means.

In order to achieve the above object, in the present invention, as a solution for controlling the number of pumps, a method for controlling the number of pumps for controlling the start and stop of a plurality of pumps, the pumps according to the liquid density of the discharged fluid. The rated discharge amount calculation process for calculating the rated discharge amount of the pump, the operation number calculation process for calculating the required number of operating pumps based on the rated discharge amount obtained in the rated discharge amount calculation process, and the operation number calculation process. A means of having a pump control step for outputting a start or stop instruction to the pump according to the required number of required operations obtained in the above is adopted.

According to the present invention, it is possible to provide a pump number control device and a pump number control method capable of suppressing fluctuations in the discharge amount (mass flow rate) due to a change in liquid density.

It is a block diagram which shows the payout system of the pump number control device A and LNG (liquefied natural gas) which concerns on one Embodiment of this invention. It is a flowchart which shows the operation of the pump number control apparatus A which concerns on one Embodiment of this invention. It is a characteristic figure which shows the operation number change of the payout pump in the pump number control device A which concerns on one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pump number control device A and the pump number control method according to the present embodiment control the payout pumps P1 to P4 provided at the LNG terminal. In addition to the payout pumps P1 to P4, the LNG terminal is provided with LNG tanks T1 and T2, a shipping facility S, and the like, and the pump number control device A comprehensively controls such an LNG terminal. Among the control functions of the plant control device, it is a control function unit that exclusively controls the number of operating pumps P1 to P4.

First, the outline of the LNG terminal will be described. The LNG tanks T1 and T2 are low-temperature tanks having a predetermined capacity for storing LNG (liquefied natural gas) received from an LNG carrier. Although FIG. 1 shows two LNG tanks T1 and T2, the number of LNG tanks may be 1 or 3 or more. In the present embodiment, for convenience of explanation of the present invention, two LNG tanks T1 and T2 are used. LNG (liquefied natural gas) is a low-temperature liquefied gas in the present embodiment.

Of such LNG tanks T1 and T2, one of the LNG tanks T1 is provided with a densitometer M1 for measuring the liquid density of the internal LNG. The other LNG tank T2 is provided with a densitometer M2 for measuring the liquid density of the internal LNG. These two density meters M1 and M2 output the measurement result to the pump number control device A.

Here, the liquid density of LNG stored in the LNG tanks T1 and T2 changes depending on the LNG production area, the storage state of LNG in the LNG tanks T1 and T2, and the like. For example, the liquid density of LNG stored in the LNG tanks T1 and T2 can change in time series. Further, the liquid density of LNG stored in one LNG tank T1 and the liquid density of LNG stored in the other LNG tank T2 may be different values when viewed at a certain time.

Further, in the LNG tanks T1 and T2, new LNG from the LNG carrier may be received and internal LNG may be discharged by the payout pumps P1 to P4 at the same time. In such a case, since the old LNG and the new LNG are mixed in the LNG tanks T1 and T2, the liquid density of LNG in the LNG tanks T1 and T2 can fluctuate significantly.

The discharge pumps P1 to P4 are pumps that discharge LNG from such LNG tanks T1 and T2 and discharge it to the shipping equipment S as a discharge fluid. That is, the payout pumps P1 to P4 pay out LNG having a flow rate (discharge amount) corresponding to the required amount (load required amount) of the shipping equipment S corresponding to its own load from the LNG tanks T1 and T2 and supply the LNG to the shipping equipment S. do.

Although FIG. 1 shows four payout pumps P1 to P4, the number of payout pumps may be any number as long as it is two or more (plural). In the present embodiment, for convenience of explanation of the present invention, four payout pumps P1 to P4 are used. In this embodiment, all four payout pumps P1 to P4 have the same specifications.

More specifically, of the four payout pumps P1 to P4, two payout pumps P1 and P2 are provided in the LNG tank T1 or in the middle of the payout pipe communicating with the LNG tank T1. Pay out LNG in T1. Of the four payout pumps P1 to P4, the other two payout pumps P3 and P4 are provided in the LNG tank T2 or in the middle of the payout pipe communicating with the LNG tank T2, and are provided in the middle of the payout pipe. Pay out the LNG inside.

Further, of these four payout pumps P1 to P4, two payout pumps P1 and P3 receive power from the first power supply system, and the other two payout pumps P2 and P4 receive power. Power is supplied from the second power system. That is, the two LNG pumps that discharge LNG from the same LNG tank receive power from different power systems. Such a power supply method is for avoiding a complete stoppage of LNG discharge from the LNG tank due to a trouble in the power supply system.

That is, the flow rate (supply amount) of LNG supplied from the LNG tanks T1 and T2 to the shipping facility S is determined by the individual rotation speeds of the payout pumps in operation and the number of operating number of the payout pumps. The payout pumps P1 to P4 are mainly operated at a rated rotation speed at which the discharge efficiency of LNG is relatively high.

The shipping facility S includes a facility for LNG supplied by the payout pumps P1 to P4 as it is (LNG shipping facility) and a facility for vaporizing the LNG and shipping it as natural gas (natural gas shipping facility). The LNG shipping facility ships LNG (liquid) to tank trucks and the like, which are LNG transport vehicles. The natural gas shipping facility supplies natural gas to thermal power plants as fuel for generators.

Subsequently, the pump number control device A will be described. As shown in FIG. 1, the pump number control device A includes an operation unit 1, a rated discharge amount calculation unit 2, an operation number calculation unit 3, a pump capacity calculation unit 4, a pump control unit 5, and an alarm device 6.

The operation unit 1 is an input device operated by a monitor who monitors the operation of the LNG terminal, and is provided in a monitoring room where the monitor operates. By operating the operation unit 1, the operation unit monitor manually inputs the liquid density of LNG stored in each of the LNG tanks T1 and T2 to the pump number control device A. That is, in the pump number control device A according to the present embodiment, the observer can manually input the LNG liquid density for each of the LNG tanks T1 and T2 by operating the operation unit 1.

The rated discharge amount calculation unit 2 calculates the rated discharge amount of the discharge pumps P1 to P4 according to the liquid density based on the liquid density of LNG input from the operation unit 1 or the densitometers M1 and M2 described above. Calculate. Further, the rated discharge amount calculation unit 2 controls the alarm device 6 based on the evaluation result of the liquid density acquired from the operation unit 1. The method for calculating the rated discharge amount in the rated discharge amount calculation unit 2 will be described in detail later, but the rated discharge amount calculation unit 2 calculates the rated discharge amount in the discharge pumps P1 to P4.

The operating number calculation unit 3 calculates the required operating number of the payout pumps P1 to P4 based on the rated discharge amount obtained by the rated discharge amount calculation unit 2. That is, the operating number calculation unit 3 calculates the operating number of the payout pumps P1 to P4 for satisfying the LNG required amount of the shipping equipment S, which is the load of the payout pumps P1 to P4, as the required operating number. The details of such a calculation method for the required number of operating units will also be described later.

The pump capacity calculation unit 4 calculates the pump capacity total value and the pump load upper limit value based on the rated discharge amount obtained by the rated discharge amount calculation unit 2. This pump capacity aggregate value is the flow rate (discharge amount) of LNG that can be dispensed by the pump that is currently paying out LNG. The upper limit of the pump load is the flow rate of LNG that can be supplied to the shipping equipment S (load) by the pump that is currently delivering LNG. The details of the calculation method of the pump capacity total value and the pump load upper limit value in the pump capacity calculation unit 4 will also be described later.

The pump control unit 5 outputs a start or stop instruction to the payout pumps P1 to P4 based on the required number of operating units obtained by the operating number calculation unit 3 and the load upper limit value obtained by the pump capacity calculation unit 4. That is, when the calculation result (required number of operating units) of the operating number calculation unit 3 is larger than the number of operating units currently in operation, the pump control unit 5 outputs a start command to any of the stopped payout pumps. Then, when the calculation result (required number of operating units) of the operating number calculation unit 3 is smaller than the number of operating units currently in operation, a stop instruction is output to any of the payout pumps currently in operation.

Further, the pump control unit 5 includes a follow-up prevention timer 5a and a rush prevention timer 5b as shown in the figure. The follow-up prevention timer 5a clocks the first time when any of the payout pumps P1 to P4 is started. The rush prevention timer 5b is provided for each power supply system that supplies power to the payout pumps P1 to P4, and clocks a second time when any of the payout pumps P1 to P4 is activated.

The operation of the alarm device 6 is controlled by the operating number calculation unit 3, and an alarm sound is emitted based on the alarm signal input from the operating number calculation unit 3. Although the details will be described later, the alarm device 6 emits an alarm sound when the liquid density input from the operation unit 1 to the operating number calculation unit 3 is improper.

Here, among the pump number control devices A configured in this way, the rated discharge amount calculation unit 2, the operating number calculation unit 3, the pump capacity calculation unit 4, and the pump control unit 5 are dedicated pump number control programs (software). It is a software control device composed of (ware) and an electronic circuit (hardware) that executes the pump number control program (software).

The electronic circuit is a non-volatile storage device that stores a pump number control program (software), a CPU (Central Processing Unit) that executes a pump number control program, and a volatile storage device that temporarily stores the processing results of the CPU. , An interface circuit that receives the signals of the operation unit 1 and the densitometers M1 and M2, a bus line that interconnects these circuits, and the like.

Next, the operation of the pump number control device A according to the present embodiment, that is, the pump number control method using the pump number control device A will be described in detail with reference to FIGS. 2 and 3.

First, the rated discharge amount calculation unit 2 is input from the liquid densities m1 and m2 input from the operation unit 1 and the densities meters M1 and M2 based on the selection designation information previously specified by the operation unit 1. Any of the liquid densities n1 and n2 is taken in (step S1).

Then, when the liquid densities n1 and n2 of the densities meters M1 and M2 are selectively designated by the selection designation information, the rated discharge amount calculation unit 2 determines that the liquid densities m1 and m2 or the liquid densities n1 and n2 are preset. It is determined whether or not the threshold value Th is equal to or higher than the threshold value Th (step S2). The rated discharge amount calculation unit 2 presets the rated discharge amount when the determination result in step S2 is “Yes”, that is, when the liquid densities m1 and m2 or the liquid densities n1 and n2 are equal to or higher than the threshold value Th. Set to a predetermined value (step S3).

Subsequently, the operating number calculation unit 3 calculates the required operating number of the payout pumps P1 to P4 using the rated discharge amount set by the rated discharge amount calculation unit 2 in this way (step S4). This step S4 is an operation number calculation step in this embodiment. For example, the rated discharge amounts of all the payout pumps P1 to P4 are the same value C, the required amount (load required amount) of the shipping equipment S is the value Q, the LNG consumption amount in the LNG terminal is the value E, and the load margin is the value. If it is Y, the operating number calculation unit 3 obtains the required operating number D by the following equation (1).
D = (Q + E + Y) / C (1)

The above value Q is the sum of the LNG shipment amount in the LNG shipping facility of the shipping facility S and the value obtained by converting the natural gas shipment amount in the natural gas shipping facility into LNG. Further, the above-mentioned value E is the amount of LNG consumed required for cold insulation of various pipes and equipment at the LNG terminal. Further, the above-mentioned value Y is a margin amount with respect to the shipping amount, and is a value that changes depending on the number of payout pumps in operation (number of operating units), that is, a larger value (amount) as the number of operating units increases.

Further, the pump capacity calculation unit 4 calculates the pump capacity total value and the pump load upper limit value using the rated discharge amount set by the rated discharge amount calculation unit 2 in this way (step S5). For example, when the rated discharge amounts of all the payout pumps P1 to P4 are the same value C and the number of pumps currently being paid out is F, the pump capacity calculation unit 4 uses the following equation (2) to calculate the pump capacity total value Z. Ask for.
Z = CF (2)

Further, in the pump capacity calculation unit 4, the rated discharge amounts of all the payout pumps P1 to P4 are the same value C, the number of pumps currently being paid out is F, the LNG consumption amount in the LNG terminal is a value E, and the load margin is large. If the value is Y, the pump capacity calculation unit 4 obtains the pump load upper limit value U by the following equation (3).
U = CFEY (3)

When the calculation of the required operating number D by the operating number calculation unit 3 and the calculation of the pump capacity total value Z and the pump load upper limit value U by the pump capacity calculation unit 4 are completed in this way, the pump control unit 5 performs the required operating number. A start command or a stop command is output to the payout pumps P1 to P4 based on D, the pump capacity total value Z, the load upper limit value U, and the load request amount Q (step S6). This step S6 is a pump control step in this embodiment.

That is, the pump control unit 5 should compare the load request amount Q and the pump load upper limit value U, and when the load request amount Q is larger than the pump load upper limit value U, newly start the LNG pump. Judge (start request judgment). For example, when the two payout pumps P1 and P2 are currently in operation and the required number of operating units D is "3", and when the above start request determination is made, the pump control unit 5 sets the pump control unit 5. A start command is output to one (1 unit) of the payout pumps P3 and P4 when the operation is stopped. On the other hand, when the two payout pumps P1 and P2 are currently in operation and the required number of operating units D is "1", the pump control unit 5 outputs a stop command to the payout pump P2.

Here, some starting conditions are set in advance for the payout pumps P3 and P4 that are stopped. For example, since the number of LND pumps scheduled for maintenance cannot be controlled, it is set as a start condition that the number of pumps cannot be controlled. Further, the starting priority for the payout pumps P3 and P4 is also set as a starting condition. The pump control unit 5 selects an LNG pump that actually outputs a start command by referring to the above start conditions for the payout pumps P3 and P4 that are stopped.

The pump control unit 5 is provided with a follow-up prevention timer 5a, and the count state of the follow-up prevention timer 5a is also one of the above-mentioned start conditions. The follow-up prevention timer 5a clocks the first time when any of the payout pumps P1 to P4 is started, and the pump control unit 5 keeps the payout pump P3 until the follow-up prevention timer 5a is timed up. Reserve the output of the activation command to. That is, the pump control unit 5 outputs a start command to the payout pump P3 after the follow-up prevention timer 5a has timed up. This makes it possible to avoid restarting the LNG pump in a relatively short period of time.

Further, the pump control unit 5 is provided with a rush prevention timer 5b, and the count state of the rush prevention timer 5b is also one of the above-mentioned activation conditions. The rush prevention timer 5b clocks the second time when any of the payout pumps P1 to P4 is started, but the pump control unit 5 is the payout pump that is started earlier until the rush prevention timer 5b is timed up. The output of the start command to the payout pump P3 of the same power supply system as the above is reserved. That is, the pump control unit 5 outputs a start command to the payout pump P3 after the rush prevention timer 5b has timed up. Thereby, it is possible to suppress the rush current in one power supply system.

On the other hand, the rated discharge amount calculation unit 2 has a liquid density m1 when the determination result in step S2 is "No", that is, when the liquid densities m1 and m2 or the liquid densities n1 and n2 are lower than the threshold value Th. , M2 or the rated discharge amount is calculated based on a predetermined function K with the liquid densities n1 and n2 as variables (step S7). This predetermined function K is, for example, a linear expression with liquid densities m1 and m2 or liquid densities n1 and n2 as variables. In addition, this step S7 is a rated discharge amount calculation step in this embodiment.

For example, when the liquid density m1 or the liquid density n1 in one LNG tank T1 is equal to or higher than the threshold value Th, the rated discharge amount calculation unit 2 discharges the LNG from the LNG tank T1 in the rated discharge amounts P1 and P2. Is set to a predetermined value (step S3). On the other hand, when the liquid density m2 or the liquid density n2 in the other LNG tank T2 is lower than the threshold value Th, the rated discharge amount calculation unit 2 of the payout pumps P3 and P4 for discharging LNG from the LNG tank T2. The rated discharge amount is calculated based on the predetermined function K (step S7).

Further, when the liquid densities m1 and m2 or the liquid densities n1 and n2 at a certain time are equal to or higher than the threshold value Th, the rated discharge amount calculation unit 2 standardizes the rated discharge amount of the discharge pumps P1 to P4 based on step S3. However, when the liquid densities m1 and m2 or the liquid densities n1 and n2 at the next time are lower than the threshold value Th, the calculation is performed based on the predetermined function K based on step S7.

Then, the observer changes the rated discharge amount by using the operation unit 1 (step S8). Then, when the liquid densities m1 and m2 are selected by the selection designation information, the rated discharge amount calculation unit 2 keeps the liquid densities m1 and m2 within the control range defined by the predetermined upper limit value and lower limit value. It is determined whether there is a deviation from the measured liquid densities n1 and n2 within a predetermined deviation range (step S9).

The rated discharge amount calculation unit 2 determines that the determination result in step S9 is "Yes", that is, the liquid densities m1 and m2 are within the control range, and the deviation between the liquid densities m1 and m2 and the liquid densities n1 and n2 is predetermined. If it is within the deviation range of, the process of step S4 described above is performed. On the other hand, when the determination result in step S9 is "No", the rated discharge amount calculation unit 2 outputs an alarm signal to the alarm device 6 because there is a possibility that the observer erroneously inputs the liquid densities m1 and m2. And make the alarm sound sound (step S10). The observer can notice the erroneous input by this alarm sound, and correct the erroneous input.

As shown in FIG. 3, such a pump number control device A automatically changes the operating number of the payout pumps P1 to P4 according to the load request amount of the shipping equipment S for the payout pumps P1 to P4. That is, the pump number control device A increases the number of operating pumps P1 to P4 as the load requirement of the shipping equipment S increases.

According to this embodiment, the number of operating units of the payout pumps P1 to P4 is controlled based on the rated discharge amount of each of the payout pumps P1 to P4 set from the LNG liquid density of the LNG tanks T1 and T2. , It is possible to suppress fluctuations in the discharge amount (mass flow rate) of the discharge pumps P1 to P4 due to changes in the liquid density of LNG.

The present invention is not limited to the above embodiment, and for example, the following modifications can be considered.
(1) In the above embodiment, the case where the present invention is applied to the number control of the payout pumps P1 to P4 has been described, but the present invention can be applied to various pumps other than the payout pumps P1 to P4.

(2) In the above embodiment, when the liquid densities m1 and m2 or the liquid densities n1 and n2 are equal to or higher than the threshold value Th, the rated discharge amount of the discharge pumps P1 to P4 is set as a predetermined value, and the liquid densities m1 and m2 or the liquid density are set. When n1 and n2 are lower than the threshold value Th, the rated discharge amount of the payout pumps P1 to P4 is calculated based on the predetermined function K, but the present invention is not limited to this. For example, the rated discharge amount may be calculated by using a specific function in the entire area of the control range without setting the threshold value Th.

(3) In the above embodiment, the pump control unit 5 is provided with the follow-up prevention timer 4a and the rush prevention timer 4b, but the present invention is not limited to this. If necessary, the follow-up prevention timer 4a and the rush prevention timer 4b may be deleted.

A Pump number control device P1 to P4 Dispensing pumps T1, T2 LNG tanks (low temperature tanks)
S Shipping equipment 1 Operation unit 2 Rated discharge amount calculation unit 3 Number of operating units calculation unit 4 Pump capacity calculation unit 5 Pump control unit 5a Restart prevention timer 5b Rush prevention timer 6 Alarm

Claims (7)

A pump number control device that controls the start and stop of multiple pumps.
A rated discharge amount calculation unit that calculates the rated discharge amount of the pump according to the liquid density of the discharge fluid, and an operation that calculates the required number of pumps to operate based on the rated discharge amount obtained by the rated discharge amount calculation unit. Number calculation unit and
A pump control unit that outputs a start or stop instruction to the pump according to the required number of operating units obtained by the operating number calculation unit is provided .
The rated discharge amount calculation unit is
When the liquid density is equal to or higher than a predetermined threshold value, the rated discharge amount is set to a predetermined value.
A pump number control device, characterized in that, when the liquid density is lower than a predetermined threshold value, the rated discharge amount is calculated based on a predetermined function having the liquid density as a variable. Further provided with an operation unit for inputting the liquid density,
The pump number control device according to claim 1, wherein the rated discharge amount calculation unit calculates the rated discharge amount based on the liquid density input from the operation unit. With more alarms
Claim 2 wherein the nominal discharge amount calculation unit, the liquid density input from the operation unit in case of deviation the predetermined upper limit value or / and a lower limit value, characterized in that to output an alarm to the alarm device The number of pumps control device described in. Further equipped with a density meter for measuring the liquid density,
The pump number control device according to claim 1 , wherein the rated discharge amount calculation unit calculates the rated discharge amount based on the liquid density measured by the densitometer. Further equipped with a follow-up prevention timer that clocks the first time when the pump is started,
The pump number control device according to any one of claims 1 to 4, wherein the pump control unit reserves the re-start of the pump until the time-up of the re-start prevention timer. It is further provided with a rush prevention timer that is provided for each power supply system that supplies power to the pump and that clocks a second time when the pump is started.
The pump number control according to any one of claims 1 to 5, wherein the pump control unit reserves the start of the pump of the same power supply system until the rush prevention timer times out. Device. The pump number control device according to any one of claims 1 to 6, wherein the pump is a discharge pump that discharges low-temperature liquefied gas from a low-temperature tank.

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