JP2019049221A - Device and method for controlling the number of pumps - Google Patents

Abstract

To provide a device and method for controlling the number of pumps, capable of suppressing fluctuation of a discharge amount (mass flow rate) resulting from change of liquid density.SOLUTION: A device for controlling the number of pumps is configured to control activation/deactivation of a plurality of pumps, and comprises: a rated discharge amount calculation unit configured to calculate a rated discharge amount of a pump according to liquid density of discharge fluid; a unit for calculating the number of operating pumps, configured to calculate a necessary number of pumps based on the rated discharge amount obtained by the rated discharge amount calculation unit; and a pump control unit configured to output an activation or deactivation instruction to the pumps according to the necessary number obtained in the unit for calculating the number of operating pumps.SELECTED DRAWING: Figure 1

Description

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

  The following Patent Document 1 discloses a method of controlling the number of operating pumps to control the number of operating low-temperature liquefied gas discharge pumps such as LNG. This operation number control method sets an increase / decrease prediction pattern of the demand amount of low-temperature liquefied gas, delays the stop of the delivery pump in operation according to the increase / decrease prediction pattern for a certain period of time, or By delaying the start for a predetermined time, it is possible to realize a smooth and stable response to fluctuations in demand.

Japanese Patent Application Publication No. 08-240185

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

However, the liquid density of the low temperature liquefied gas discharged from the low temperature tank by the dispensing pump changes according to the production area of the low temperature liquefied gas, the storage condition in the low temperature tank, and the like. Therefore, when the discharge amount (discharge amount) of the discharge pump is viewed as the mass flow rate, the discharge amount fluctuates according to the liquid density even if the discharge pump is operating at a constant number of revolutions. It will be.
Further, the change in the liquid density appears as a change in the amount of heat of the gas at the consumption destination. Therefore, if the change in the calorific value of the gas exceeds an allowable range, it may lead to abnormal combustion or misfire in the combustor which is the consumption destination.

  The present invention has been made in view of the above-described circumstances, and provides a pump number control device and a pump number control method capable of suppressing the fluctuation of the discharge amount (mass flow rate) caused by the change in liquid density. To aim.

  In order to achieve the above object, according to the present invention, as a first solution according to a pump number control device, the pump number control device controls the start and stop of a plurality of pumps, and according to the liquid density of discharged fluid. A rated discharge amount calculation unit for calculating the rated discharge amount of the pump; an operating number calculation unit for calculating the required number of operating pumps based on the rated discharge amount obtained by the rated discharge amount calculation unit; A pump control unit is provided which outputs a start or stop instruction to the pump in accordance with the required number of operation obtained by the number calculation unit.

  In the present invention, as the second solution means according to the pump number control device, in the first solution means, the rated discharge amount calculation unit calculates the rated discharge amount when the liquid density is equal to or more than a predetermined threshold value. Is a predetermined value, and in the case where 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.

  In the present invention, as the third solution means according to the pump number control device, the first or second solution means further comprises an operation unit for inputting the liquid density, and the rated discharge amount calculation unit comprises the operation A means is employed to calculate the rated discharge amount based on the liquid density input from the unit.

  In the present invention, as the fourth solution according to the pump number control device, the third solution further includes an alarm, and the rated discharge amount calculation unit is configured to calculate the liquid density input from the operation unit. In the case of deviating from the predetermined upper limit value and / or the lower limit value, a means of outputting an alarm to the alarm device is adopted.

  In the present invention, as the fifth solution according to the pump number control device, the first or the second solution further includes a density meter for measuring the liquid density, and the rated discharge amount calculation unit calculates the density A means is employed to calculate the rated discharge amount based on the liquid density measured by a meter.

  In the present invention, as a sixth solution means relating to a pump number control device according to any one of the first to fifth solution means, an additional start prevention timer is further provided which measures a first time when the pump is activated. The pump operation control unit adopts a means of retaining the subsequent start of the pump until the subsequent start prevention timer is timed up.

  In the present invention, as the seventh solution according to the pump number control device, in any one of the first to the sixth solutions, it is provided for each power supply system for supplying electric power to the pump, and the pump is activated. The pump operation control unit adopts a means for keeping the start of the pump of the same power supply system until the time of the rush prevention timer is up, further comprising a rush prevention timer for clocking a second time. .

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

  In order to achieve the above object, the present invention is a pump number control method for controlling the start and stop of a plurality of pumps as a solution according to a pump number control method, wherein the pump according to the liquid density of discharged fluid Discharge amount calculating step for calculating the rated discharge amount of the pump, operating number calculating step for calculating the required number of operating pumps based on the rated discharge amount obtained in the rated discharge amount calculating step, and the operating number calculating step And a pump control step of outputting a start or stop instruction to the pump according to the required number of required operation units obtained in the above.

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

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the delivery system of pump number control apparatus A and LNG (liquefied natural gas) which concern on one Embodiment of this invention. It is a flow chart which shows operation of pump number control device A concerning one embodiment of the present invention. It is a characteristic view showing change in the number of operation of a delivery pump in pump number control device A concerning one embodiment of the present 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 this embodiment control the delivery pumps P1 to P4 provided in the LNG base. The LNG base is provided with LNG tanks T1 and T2 and a shipping facility S, etc. in addition to the delivery pumps P1 to P4. The pump number controller A controls the LNG base in an integrated manner. Among the control functions of the plant control apparatus, the control function unit exclusively controls the number of operating dispense pumps P1 to P4.

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

  Among such LNG tanks T1 and T2, one LNG tank T1 includes a density meter M1 that measures the liquid density of the internal LNG. The other LNG tank T2 is provided with a density meter M2 that measures the liquid density of the internal LNG. These two densitometers M1 and M2 output the measurement results to the pump number control device A.

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

  Furthermore, in the LNG tanks T1 and T2, there may be a case where the new LNG from the LNG vessel is received at the same time and the internal LNG is discharged by the discharge pumps P1 to P4. 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 the LNG in the LNG tanks T1 and T2 may fluctuate significantly.

  The delivery pumps P1 to P4 are pumps for discharging the LNG from the LNG tanks T1 and T2 and discharging the LNG to the shipping facility S as a discharge fluid. That is, the delivery pumps P1 to P4 deliver the LNG of the flow rate (discharge amount) corresponding to the required amount (load required amount) of the shipping facility S corresponding to the own load from the LNG tanks T1 and T2 and supply it to the shipping facility S. Do.

  Although four delivery pumps P1 to P4 are shown in FIG. 1, the number of delivery pumps may be any two or more (plural). In the present embodiment, four delivery pumps P1 to P4 are provided for the convenience of description of the present invention. In the present embodiment, all the four delivery pumps P1 to P4 have the same specifications.

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

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

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

  The shipping facility S is equipped with a facility (LNG shipping facility) for the LNG supplied by the dispensing pumps P1 to P4 as it is, and a facility (natural gas shipping facility) for vaporizing the LNG and shipping it as a natural gas. The LNG shipping facility ships LNG (liquid) to a tank truck or the like that is an LNG transportation vehicle. The natural gas shipping facility supplies natural gas to the thermal power plant as fuel for the generator.

  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 6.

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

  Based on the liquid density of the LNG input from the operation unit 1 or the density meter M1, M2 described above, the rated discharge amount calculation unit 2 calculates the rated discharge amounts of the dispensing pumps P1 to P4 according to the liquid density. Calculate Further, the rated discharge amount calculation unit 2 controls the alarm 6 based on the evaluation result of the liquid density obtained from the operation unit 1. In addition, although the calculation method of the rated discharge amount in the rated discharge amount calculating unit 2 will be described in detail later, the rated discharge amount calculating unit 2 calculates the rated discharge amount in the dispensing pumps P1 to P4.

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

  The pump capacity calculator 4 calculates the pump capacity tally value and the pump load upper limit value based on the rated discharge amount obtained by the rated discharge amount calculator 2. The pump capacity aggregation value is a flow rate (discharge amount) of LNG that can be dispensed by the dispensing pump that is currently dispensing the LNG. Further, the pump load upper limit value is the flow rate of the LNG that can be supplied to the shipping facility S (load) by the delivery pump that is currently delivering the LNG. The details of the calculation method of the pump capacity tally 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 dispensing pumps P1 to P4 based on the required number of operation obtained by the operation number calculation unit 3 and the load upper limit value obtained by the pump capacity calculation unit 4. That is, when the calculation result (the required number of operations) of the number-of-operations calculation unit 3 is larger than the number of operations currently in operation, the pump control unit 5 outputs a start command to any of the dispensing pumps in suspension. If the calculation result (required number of operations) of the operation number calculation unit 3 is smaller than the currently operated number of operations, a stop instruction is output to any of the currently operating payout pumps.

  Further, as shown in the figure, the pump control unit 5 includes an additional start prevention timer 5a and a rush prevention timer 5b. The additional activation preventing timer 5a counts a first time when any one of the dispensing pumps P1 to P4 is activated. The rush prevention timer 5b is provided for each power supply system that supplies power to the dispensing pumps P1 to P4, and counts a second time when one of the dispensing pumps P1 to P4 is activated.

  The operation of the alarm device 6 is controlled by the number-of-operations calculation unit 3, and an alarm sound is produced based on an alarm signal input from the number-of-operations calculation unit 3. Although the details will be described later, the alarm device 6 generates an alarm sound when the liquid density input from the operation unit 1 to the operation number calculation unit 3 is invalid.

  Here, among the pump number control device A configured as described above, the rated discharge amount calculation unit 2, the operation number calculation unit 3, the pump capacity calculation unit 4 and the pump control unit 5 have dedicated pump number control programs (software Software) and an electronic circuit (hardware) that executes the pump number control program (software).

  The electronic circuit is a non-volatile storage device storing a pump number control program (software) or the like, a central processing unit (CPU) executing the pump number control program, and a volatile storage device temporarily storing processing results of the CPU And an interface circuit for receiving signals from the operation unit 1 and the densitometers M1 and M2, and a bus line for interconnecting the circuits.

  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 inputs the liquid densities m1 and m2 input from the operation unit 1 and the density meters M1 and M2 based on the selection designation information specified in advance using the operation unit 1 One of the liquid densities n1 and n2 is taken in (step S1).

  Then, when the liquid densities n1 and n2 of the density meters M1 and M2 are selected and specified by the selection designation information, the rated discharge amount calculation unit 2 sets the liquid densities m1 and m2 or the liquid densities n1 and n2 to a predetermined value. It is determined whether or not it is equal to or greater than the threshold Th of (step S2). When the determination result in step S2 is "Yes", that is, when the liquid density m1, m2 or the liquid density n1, n2 is equal to or more than the threshold Th, the rated discharge amount calculation unit 2 sets the rated discharge amount in advance. It is set to a predetermined value (step S3).

Subsequently, the operating number calculating unit 3 calculates the required operating number of the dispensing pumps P1 to P4 using the rated discharge amount set by the rated discharge amount calculating unit 2 in this manner (step S4). This step S4 is an operation number calculation step in the present embodiment. For example, the rated discharge amount of all the delivery pumps P1 to P4 is the same value C, the required amount (load required amount) of the shipping facility S is the value Q, the LNG consumption amount in the LNG terminal is the value E, and the load margin is the value When it is Y, the number operation part 3 of operation | movement calculates | requires the required number of operation D by following Formula (1).
D = (Q + E + Y) / C (1)

  The above value Q is the sum of the shipment amount of LNG in the LNG shipping facility of the shipping facility S and the value obtained by converting the shipping amount of natural gas in the natural gas shipping facility into LNG. Further, the value E is the consumption of LNG required to cool various pipes and devices at the LNG terminal. Further, the value Y is a surplus amount with respect to the shipping amount, and is a value that changes according to the number of dispensing pumps in operation (the number of operating pumps), that is, a larger value (quantity) as the number of operating pumps increases.

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

In addition, the pump capacity calculation unit 4 is configured such that the rated discharge amount of all the dispensing pumps P1 to P4 is the same value C, the number of pumps currently dispensing is F, the LNG consumption amount in the LNG terminal is the value E, and the load margin is When it is the value Y, the pump capacity calculation unit 4 obtains the pump load upper limit value U by the following equation (3).
U = C · F−E−Y (3)

  When the calculation of the required number of operation D by the operation number calculation unit 3 and the calculation of the pump capacity tally value Z and the pump load upper limit value U by the pump capacity calculation unit 4 are thus completed, the pump control unit 5 The start command or the stop command is output to the delivery pumps P1 to P4 based on D, the pump capacity total value Z, the load upper limit value U, and the required load amount Q (step S6). This step S6 is a pump control process in the present embodiment.

  That is, the pump control unit 5 compares the load request amount Q with the pump load upper limit value U, and if the load request amount Q is larger than the pump load upper limit value U, the LNG pump should be newly started. Determine (start request judgment). For example, when the two delivery pumps P1 and P2 are currently in operation, and the required number of operations D is "3", and when the above start request determination is made, the pump control unit 5 A start command is output to one (one) of the dispensing pumps P3 and P4 during operation stoppage. On the other hand, when the two delivery pumps P1 and P2 are currently in operation, and the required number of operations D is "1", the pump control unit 5 outputs a stop command to the delivery pump P2.

  Here, several start conditions are preset to the delivery pumps P3 and P4 during operation stop. For example, since the LND pump scheduled for maintenance can not be subjected to the number control, it is set as the start condition that the number control can not be performed. Further, the activation priority order for the dispensing pumps P3 and P4 is also set as the activation condition. The pump control unit 5 selects an LNG pump that actually outputs a start command by referring to the above-described start conditions for the delivery pumps P3 and P4 during operation stoppage.

  The pump control unit 5 is provided with the additional activation prevention timer 5a, and the count state of the additional activation prevention timer 5a is also one of the activation conditions. The additional activation preventing timer 5a counts the first time when any of the dispensing pumps P1 to P4 is activated, but the pump control unit 5 continues the above-mentioned dispensing pump P3 until the additional activation preventing timer 5a times out. Reserve the output of the start command to That is, the pump control unit 5 outputs a start command to the dispensing pump P3 after the additional start prevention timer 5a has timed out. This makes it possible to avoid starting up the LNG pump in a relatively short and short period of time.

  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 start conditions. The rush prevention timer 5b counts the second time when any one of the dispensing pumps P1 to P4 is activated, but the pump control unit 5 dispenses the discharge pump that has been activated earlier until the rush prevention timer 5b is timed up. And the output of the start command to the discharge pump P3 of the same power supply system is reserved. That is, the pump control unit 5 outputs the start command to the dispensing pump P3 after the rush prevention timer 5b has timed up. This makes it possible to suppress the rush current in one of the power supply systems.

  On the other hand, when the determination result in step S2 is "No", that is, when the liquid density m1, m2 or the liquid density n1, n2 is a value lower than the threshold value Th, the rated discharge amount calculation unit 2 The nominal discharge amount is calculated on the basis of a predetermined function K having the liquid density n1 and n2 as variables (step S7). The predetermined function K is, for example, a linear expression having the liquid density m1, m2 or the liquid density n1, n2 as a variable. This step S7 is a rated discharge amount calculation step in the present 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 Th, the rated discharge amount calculation unit 2 calculates the rated discharge amount of the dispensing pumps P1, P2 that discharges LNG from the LNG tank T1. Is set as 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 outputs the LNG from the LNG tank T2 of the discharge pumps P3 and P4. The rated discharge amount is calculated based on the predetermined function K (step S7).

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

  Then, the monitor 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 sets the liquid densities m1 and m2 within the management range defined by the predetermined upper limit value and lower limit value. It is determined whether or not the deviation from the liquid density n1 or n2 which is the measured value is 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 management range, and the deviation between the liquid densities m1 and m2 and the liquid densities n1 and n2 is predetermined. When it is within the deviation range of the above, 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 6, since there is a possibility that the monitor erroneously inputs the liquid densities m1 and m2. The alarm sound is produced (step S10). The supervisor can notice the erroneous input by the alarm sound, and corrects the erroneous input.

  Such a pump number control device A automatically changes the number of operation of the dispensing pumps P1 to P4 according to the load required amount of the shipping facility S for the dispensing pumps P1 to P4 as shown in FIG. That is, the pump number control device A increases the number of operating the delivery pumps P1 to P4 as the load required amount of the shipping facility S increases.

  According to the present embodiment, the number of operating dispensing pumps P1 to P4 is controlled based on the rated discharge amounts of the dispensing pumps P1 to P4 set from the liquid densities of the LNG in the LNG tanks T1 and T2. It is possible to suppress the fluctuation of the discharge amount (mass flow rate) of the delivery pumps P1 to P4 caused by the change of the liquid density of the LNG.

In addition, this invention is not limited to the said embodiment, For example, the following modifications are considered.
(1) In the above embodiment, the present invention is applied to the control of the number of dispensing pumps P1 to P4. However, the present invention can be applied to various pumps other than the dispensing pumps P1 to P4.

(2) In the above embodiment, when the liquid density m1, m2 or the liquid density n1, n2 is equal to or more than the threshold value Th, the rated discharge amount of the dispensing pumps P1 to P4 is set to a predetermined value, and the liquid density m1, m2 or the liquid density When n1 and n2 are lower than the threshold value Th, the rated discharge amounts of the dispensing pumps P1 to P4 are 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 using a specific function in the entire management range without setting the threshold value Th.

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

A Pump quantity control device P1 to P4 Dispensing pump T1, T2 LNG tank (low temperature tank)
S Shipping Equipment 1 Operation Unit 2 Rated Discharge Calculation Unit 3 Operation Number Calculation Unit 4 Pump Capacity Calculation Unit 5 Pump Control Unit 5a Follow-up Prevention Timer 5b Rush Prevention Timer 6 Alarm

Claims (9)

A pump number controller for controlling the start and stop of a plurality of pumps, comprising:
A rated discharge amount calculation unit that calculates a rated discharge amount of the pump according to the liquid density of the discharge fluid;
An operating number calculating unit that calculates the required number of operating pumps based on the rated discharge amount obtained by the rated discharge amount calculating unit;
And a pump control unit for outputting a start or stop instruction to the pump according to the required number of operation obtained by the operation number calculation unit. The rated discharge amount calculation unit
If the liquid density is equal to or higher than a predetermined threshold value, the rated discharge amount is set to a predetermined value,
The pump number control device according to claim 1, wherein when the liquid density is lower than a predetermined threshold value, the rated discharge amount is calculated based on a predetermined function using the liquid density as a variable. It further comprises an operation unit for inputting the liquid density,
The pump number control device according to claim 1 or 2, wherein the rated discharge amount calculation unit calculates the rated discharge amount based on the liquid density input from the operation unit. Further equipped with an alarm,
The rated discharge amount calculation unit causes the alarm to output an alarm when the liquid density input from the operation unit deviates from a predetermined upper limit value and / or a lower limit value. The pump number control device according to. It further comprises a densitometer for measuring the liquid density,
The pump number control device according to claim 1 or 2, wherein the rated discharge amount calculation unit calculates the rated discharge amount based on the liquid density measured by the density meter. The system further comprises an additional start prevention timer that counts a first time when the pump starts.
The pump number control device according to any one of claims 1 to 5, wherein the pump control unit holds the further start of the pump until the second start prevention timer is up. The system further comprises an anti-lash timer provided for each power supply system that supplies power to the pump and clocking a second time when the pump is activated,
The pump control unit according to any one of claims 1 to 6, wherein start-up of the pump of the same power supply system is suspended until the time for preventing the rush timer expires. apparatus.   The pump number control device according to any one of claims 1 to 7, wherein the pump is a dispensing pump that dispenses the low temperature liquefied gas from the low temperature tank. A pump number control method for controlling start and stop of a plurality of pumps, comprising:
A rated discharge amount calculation step of calculating a rated discharge amount of the pump according to the liquid density of the discharge fluid;
An operation number calculating step of calculating the required number of operating pumps based on the rated discharge amount obtained in the rated discharge amount calculating step;
And a pump control step of outputting a start or stop instruction to the pump according to the required number of operation obtained in the operation number calculation step.

Images