JP2016183610A - Pump system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pump system capable of surely detecting occurrence of cavitation, and capable of eliminating such situations in which cavitation occurs.SOLUTION: A pump system 50 includes a pump 51, a driving motor 52 which transmits driving force to the pump 51 and of which rotation speed is adjusted in accordance with a frequency, a primary side pressure sensor 55 for detecting a primary side pressure of the pump 51, and a control section 91 which can control the driving motor 52 by a prescribed set frequency. The control section 91 monitors a measurement value of the primary side pressure sensor 55, and controls the driving motor 52 by a frequency lower than the set frequency when a pressure lower than a threshold set on the basis of a pressure in a steady state in which cavitation does not occur is detected. The control section 91 notifies the occurrence of the cavitation via a display section 93 when the frequency is lowered to a lower limit frequency.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pump system in which a pump is driven by a drive motor controlled by a frequency.

  In a pump system for supplying water to equipment, cavitation may occur inside the pump due to fluctuations in flow rate or pressure loss, and the amount of water supplied to the supply destination may become unstable. For example, Patent Literature 1 discloses a method for preventing water supply failure due to cavitation. Patent Document 1 discloses a pump system that adjusts the pump discharge amount in accordance with changes in the internal pressure of the boiler and suppresses the occurrence of cavitation.

JP 2014-105880 A

  By the way, the strainer provided on the upstream side of the pump may be clogged, the pump inlet pressure may be reduced, and cavitation may occur. In this regard, the method disclosed in Patent Document 1 can cope with the change in the internal pressure of the boiler body that is the water supply destination, but the occurrence of cavitation caused by the fluctuation of the pressure loss that occurs upstream of the pump. It was difficult to prevent. Further, if the pump continues to be driven in a state where cavitation has occurred, it will lead to damage to the pump, and it is preferable to quickly eliminate the state in which cavitation occurs.

  An object of the present invention is to provide a pump system that can reliably detect the occurrence of cavitation and eliminate the state in which cavitation occurs.

  The present invention relates to a pump, a drive motor that transmits a driving force to the pump and whose rotation speed is adjusted by a frequency, a primary pressure sensor that detects a pressure on the primary side of the pump, and the drive motor. A control unit capable of controlling at a set frequency, and the control unit monitors a measurement value of the primary side pressure sensor and reduces a pressure below a threshold set based on a steady-state pressure in which cavitation does not occur. When detected, the present invention relates to a pump system that controls the drive motor at a frequency lower than the set frequency.

  The pump system includes a notification unit that notifies maintenance information, and the control unit operates the notification unit when a measured value of the primary pressure sensor falls below a predicted pressure value that is set to be higher than the threshold value. It is preferable to notify the necessity of maintenance.

  When the control unit detects a pressure lower than the threshold, the frequency of the drive motor is gradually decreased from the set frequency until the pressure of the primary pressure sensor exceeds a predetermined value set to be equal to or higher than the threshold. It is preferable to perform control.

  When the control unit detects a pressure lower than the threshold value, the control unit preferably decreases the frequency so as not to fall below a preset lower limit frequency.

  The pump system includes a notifying unit for notifying cavitation information, and the control unit activates the notifying unit when the pressure falls to a preset warning pressure value when detecting a pressure below the threshold. It is preferable to notify the occurrence of cavitation.

  According to the pump system of the present invention, it is possible to reliably detect the occurrence of cavitation and eliminate the state where cavitation occurs.

It is the schematic of the boiler system with which the pump system of this embodiment is applied. It is a flowchart which shows the flow of control which detects a cavitation and reduces a setting frequency.

  Hereinafter, a preferred embodiment of the pump system of the present invention will be described with reference to the drawings. The pump system 50 of the present embodiment is applied to the boiler system 1 and is used for supplying water to the boiler 10. The “line” in the present specification is a general term for lines capable of flowing a fluid such as a flow path, a path, and a pipeline. In addition, the configuration of a valve or the like that is arranged in each line and opens and closes the path may be omitted.

  FIG. 1 is a schematic diagram of a boiler system 1 to which the pump system 50 of the present embodiment is applied. The boiler system 1 according to the present embodiment is a closed system that supplies steam to the load device 100, collects drain generated by using the steam in the load device 100, and supplies water to the boiler 10 without opening it to the atmosphere. First, the overall configuration of the boiler system 1 will be described.

  As shown in FIG. 1, the boiler system 1 includes a plurality of boilers 10, a steam header 11, a drain tank 12, a control unit 90, and a pump system 50 as main components. Further, the boiler system 1 includes a drain supply line L10, a plurality of boiler steam lines L11, a collective steam line L12, a first steam supply line L13, a drain recovery line L14, and a second steam supply line L15. Prepare as the main line.

  Each structure and each line of the boiler system 1 will be described. The plurality of boilers 10 generates steam by heating water supplied therein with combustion gas. A boiler steam line L11 is connected to each of the boilers 10. The plurality of boiler steam lines L11 are respectively connected to the collective steam line L12.

  The steam generated in each boiler 10 is collected in the steam header 11 through the boiler steam line L11 and the collect steam line L12. The steam collected in the steam header 11 is supplied to the load device 100 in response to a request from the load device 100.

  The load device 100 uses the steam generated in the boiler 10 as a heat source, and performs direct heating or indirect heating of the heating object. I do. The steam generated by the boiler 10 is condensed in the load device 100 to generate drain (condensed water). The drain generated in the load device 100 is recovered to the drain tank 12 through the drain recovery line L14.

  The drain tank 12 is composed of a pressure vessel that has pressure resistance and can be sealed. Drain generated by condensation of a part of the steam used for heat exchange in the load device 100 is collected in the drain tank 12 in a high temperature and high pressure state without being released to the atmosphere.

  Further, the drain tank 12 is connected to the steam header 11 through the second steam supply line L15. A pressure regulating valve 21 is provided in the second steam supply line L15. The pressure inside the drain tank 12 is adjusted by the steam supplied through the second steam supply line L15.

  The drain tank 12 is connected to the upstream end of the drain supply line L10. The drain supply line L10 is branched according to the number of boilers 10 at the downstream branching section 30, and is connected to each boiler 10 respectively. Moreover, the boiler system 1 of this embodiment can supply makeup water to the drain tank 12 by an open tank (not shown).

  A Y-type strainer 22 is disposed in the drain supply line L10. The strainer 22 is disposed on the primary side of the pump 51 in the drain supply line L10. The strainer 22 removes impurities in the drain.

  The control unit 90 is a computer that performs various controls of the boiler system 1. The control unit 90 of the present embodiment includes a control unit 91 that controls a pump system 50 described later, a storage unit 92 that stores various programs and data, and a display unit 93 as a notification unit.

  The pump system 50 of the present embodiment includes a pump 51, a drive motor 52, an inverter 53, a primary pressure sensor 55, a control unit 91, a storage unit 92, and a display unit 93 as main components. Drain is supplied to the boiler 10. Hereinafter, each component of the pump system 50 will be described.

  The pump 51 is a pressure feeding unit that creates a pressure difference by rotation of an impeller (not shown) provided therein and feeds fluid. In the present embodiment, the pump 51 is disposed between the strainer 22 and the branch part 30 in the drain supply line L10.

  The drive motor 52 is a drive means for rotationally driving the impeller of the pump 51. An inverter 53 is electrically connected to the drive motor 52.

  The inverter 53 adjusts the rotational speed of the drive motor 52 by frequency control. Thereby, the discharge amount of the pump 51 is adjusted. The inverter 53 is electrically connected to the control unit 90 and controls the drive motor 52 based on a control signal from the control unit 90.

  The primary pressure sensor 55 is disposed between the strainer 22 and the pump 51 in the drain supply line L10. The primary pressure sensor 55 measures the pressure on the primary side (upstream side) of the pump 51 inside the drain supply line L10. The primary pressure sensor 55 is electrically connected to the control unit 90 and transmits measurement information to the control unit 90. The pressure value detected by the primary pressure sensor 55 is the inlet pressure of the pump 51, and becomes a substantially constant value when the set frequency is fixed in the steady state. The steady state here is a state where no cavitation occurs.

  The controller 91 controls the drive motor 52 based on the water supply request from the boiler 10 and performs control to supply drain to the boiler 10. In the present embodiment, in order to reduce the number of times the pump 51 is started and stopped, a continuous operation in which the operation of the pump 51 is continued for a predetermined time is performed at a predetermined frequency set in advance (set frequency at normal time). When water supply is unnecessary, the drain is returned to the drain tank 12 by a return line (not shown) connecting the secondary side of the pump 51 and the drain tank 12. Moreover, adjustment of the amount of water supply to the boiler 10 is performed by a flow rate adjustment valve (not shown) on the boiler side.

  In the present embodiment, the control unit 91 predicts the cavitation of the pump 51 and performs control for detecting the occurrence of cavitation and eliminating the cavitation. The cavitation prediction and detection by the control unit 91 will be described. In the case of the boiler system 1 of the present embodiment, the strainer 22 disposed on the upstream side of the pump 51 may be clogged. When the strainer 22 is clogged, the inlet pressure of the pump 51 is lowered and the boiling point is lowered. As a result, the high-temperature drain enters a boiling state and cavitation occurs.

  Therefore, in the present embodiment, the pressure (inlet pressure) on the primary side of the pump 51 that also causes cavitation is monitored and cavitation is predicted and detected. That is, the primary pressure sensor indicates whether there is no cavitation, a state in which a decrease in the inlet pressure starts and cavitation is likely to occur, or a state in which cavitation occurs. It is grasped through 55 measured values (inlet pressure). When the inlet pressure starts to decrease due to clogging of the strainer 22 or the like, the control unit 91 predicts the occurrence of cavitation. When the inlet pressure further decreases to a level that satisfies the conditions for cavitation generation, it is determined that cavitation has occurred.

  The control unit 91 performs control to lower the set frequency of the inverter 53 after detecting cavitation. Since the frequency and the rotational speed are in a proportional relationship, the flow rate of the pump 51 becomes smaller as the rotational speed decreases. If the flow rate decreases in the same piping system, the pressure loss decreases, and the effective NPSH (Net Positive Suction Head) of the system system determined by the fluid pressure, vapor pressure, flow rate, etc. can be increased. In general, it is known that cavitation occurs when the effective NPSH of the system system falls below the required NPSH determined by the design of the pump 51 or the like (effective NPSH <required NPSH). In the present embodiment, by reducing the pressure loss by frequency control of the control unit 91, the effective NPSH is made higher than the required NPSH to eliminate cavitation (effective NPSH> required NPSH). In the present embodiment, the control for detecting the cavitation is not performed during the idling control, but the cavitation may be detected even during the idling control.

  The storage unit 92 stores various programs and data. The storage unit 92 stores various types of information for executing the above-described control for suppressing the influence of cavitation of the pump 51. The storage unit 92 of the present embodiment stores a determination threshold (threshold value), a predicted pressure value, a detected value (predetermined value), a lower limit frequency, a warning pressure value, and the like as information for suppressing the detection of cavitation and its influence. .

  The determination threshold is information for determining whether or not cavitation has occurred in the pump 51. The determination threshold is a value that is set based on the pressure value on the primary side of the pump 51 in a state in which cavitation is not generated in the pump 51 while being controlled at a certain set frequency (for example, 60 Hz or 50 Hz). It is. In this embodiment, it is set based on the boundary between a state where no cavitation occurs and a state where cavitation occurs. The controller 91 determines that cavitation has occurred when the pressure value on the primary side of the pump 51 falls below the determination threshold.

  The controller 91 determines that cavitation is occurring when the primary pressure falls below the determination threshold. The determination as to whether or not the determination threshold value is below can be changed as appropriate depending on the equipment to which the pump system 50 is applied. For example, the determination condition can be set so that it is determined that cavitation has occurred when the measurement value of the primary pressure sensor 55 continuously falls below the determination threshold for a predetermined time. Further, when the measured value of the primary pressure sensor 55 falls below the determination threshold value a plurality of times within a predetermined time, it may be determined that cavitation has occurred, or the determination threshold value has fallen even once. In some cases, it may be determined that cavitation has occurred. As described above, the condition for determining that cavitation has occurred can be set as appropriate according to the circumstances, based on the viewpoint of detecting a decrease in the pressure value of the primary pressure sensor 55.

  The predicted pressure value is a pressure value that serves as a trigger for detecting an abnormality on the primary side of the pump 51 and predicting the occurrence of cavitation. The predicted pressure value is a pressure value that is higher than the determination threshold value and lower than the average pressure value in the steady state. When the measured value of the primary pressure sensor 55 falls below the predicted pressure value, the control unit 91 notifies the user that the strainer 22 needs to be maintained by the display unit 93 described later. In the present embodiment, the predicted pressure value is set based on the saturated steam pressure at the water temperature obtained by adding a predetermined temperature (for example, 5 ° C.) to the water temperature on the primary side of the pump 51.

  The detected value is information for determining whether or not the pressure drop that causes cavitation has been eliminated after cavitation detection, and is stored in the storage unit 92 according to the frequency of the set frequency. When the measured value of the primary pressure sensor 55 exceeds the detected value, the control unit 91 determines that the cause of causing cavitation (for example, clogging of the strainer 22) has been eliminated. In the present embodiment, the detection value is set higher than the determination threshold value according to the set frequency. The determination condition as to whether or not the detected value is below is set so that it is determined that cavitation has been eliminated when the detected value is continuously exceeded for a predetermined time. As for the determination condition of the detection value, the condition can be set as appropriate according to the equipment to which the pump system 50 is applied, similarly to the determination threshold value. For example, the detection value may be the same value as the determination threshold value, or a value calculated based on the changed set frequency may be applied.

  The lower limit frequency is a minimum frequency required to feed the drain into the boiler 10. The control unit 91 performs control to gradually lower the set frequency so as not to fall below the lower limit frequency. The lower limit frequency is set based on the apparatus configuration of the boiler system 1. The lower limit frequency is appropriately set based on the model and capacity of the pump to be used. For example, when the normal set frequency is set to 60 Hz, the lower limit frequency is set to 50 Hz. In this example, the lower limit frequency is set to 50 Hz, but the value of the lower limit frequency can be made lower than 50 Hz. Thus, the frequency adjustment range between the set frequency and the lower limit frequency can be set narrower or wider depending on the situation where the pump 51 is used. That is, the set frequency and the lower limit frequency can be changed as appropriate.

  The warning pressure value is a pressure value that serves as a trigger for notifying the user of the boiler system 1 that cavitation has occurred in the control for eliminating cavitation. When the measured value of the primary pressure sensor 55 falls below the warning pressure value in the control of gradually lowering the set frequency described above, the control unit 91 informs the user that cavitation has occurred by the display unit 93 described later. Inform. In the present embodiment, the warning pressure value is set based on an inlet pressure in a range where water can be appropriately supplied to the boiler 10. If the measured value of the primary pressure sensor 55 falls below the warning pressure value, the water supply to the boiler 10 may be affected. Therefore, the occurrence of cavitation is notified to the user when the warning pressure value is reached. It has become. In the present embodiment, the warning pressure value is set lower than the determination threshold value.

  The display unit 93 will be described. The display unit 93 is configured by a display panel or the like that displays an image of the operating status of the boiler 10 or the like. The display unit 93 of the present embodiment functions as a notification unit that transmits information about cavitation generated by the pump 51 to the user. The notification of the occurrence of cavitation by the display unit 93 may employ an appropriate method such as image display, sound by a speaker function, a combination of image display and sound.

  The main configuration of the boiler system 1 is as described above. Next, the flow of control for changing the set frequency after detecting cavitation will be described. FIG. 2 is a flowchart showing the flow of control for detecting cavitation and lowering the set frequency.

  When water supply control is started in response to a request from the boiler 10, a cavitation detection process is started. As shown in FIG. 2, the control unit 91 monitors the measured value of the primary pressure sensor 55, and determines whether or not the primary pressure of the pump 51 has fallen below the predicted pressure value (S101). If it is determined in S101 that the primary pressure has fallen below the predicted pressure value, the display unit 93 is activated to notify the user that maintenance is necessary (S102), and the process proceeds to S103. . If it is determined in S101 that the pressure is not below the predicted pressure value, the process returns to S101.

  In the process of S103, the control unit 91 acquires the measurement value of the primary pressure sensor 55 in real time (or a predetermined interval), and determines whether or not the determination value is below the determination threshold value. In the process of S103, as described above, when it is detected that the pressure value is continuously lower than the determination threshold for a predetermined time, or when the determination threshold is lower than the determination threshold a plurality of times, the determination threshold is set based on a preset condition. It is determined whether or not the value has fallen below. If it is determined in S103 that the value is not below the determination threshold, the process returns to S101.

  When it determines with having fallen below the determination threshold value by the process of S103, the control part 91 changes a setting frequency to a frequency lower than the present condition (S104). In the present embodiment, the frequency is decreased at a predetermined rate. Next, the control unit 91 determines whether or not the set frequency that has been changed to a low frequency in the process of S104 has fallen below the lower limit frequency, or the measurement value of the primary pressure sensor 55 has fallen below the warning pressure value. (S105).

  When the set frequency is not lower than the lower limit frequency and the measured value of the primary pressure sensor 55 is not lower than the warning pressure value in the process of S105, the control unit 91 is changed to a frequency with a lower set frequency (S104). ) State, it is determined whether or not the measured value of the primary pressure sensor 55 exceeds the detected value (predetermined value) (S106). As described above, the detected value is a criterion for determining whether or not the cause of cavitation has been eliminated. If it is determined that the measured value of the primary pressure sensor 55 has exceeded the detected value, the control for lowering the frequency is terminated. In the process of S106, when it is determined that the measured value of the primary pressure sensor 55 does not exceed the detected value, the process returns to the process of S104 in order to further lower the set frequency. In the process of S106, whether or not the measured value of the primary pressure sensor 55 exceeds the detected value is determined based on a preset condition as described above.

  When it is determined in the process of S105 that the set frequency is lower than the lower limit frequency or the measured value of the primary pressure sensor 55 is lower than the warning pressure value, the control unit 91 changes the set frequency to the lower limit frequency (S107). . Along with the change to the lower limit frequency, the occurrence of cavitation is notified by the display unit 93 (S108).

  The pump system 50 of this embodiment monitors the measured value of the primary side pressure sensor 55, and until the primary side pressure (inlet pressure) returns to a state where cavitation does not occur, or reaches a lower limit frequency, or the primary side pressure. Control is performed to gradually lower the set frequency until the measured value of the sensor 55 falls below the warning pressure value. As a result, the cavitation of the pump 51 due to clogging of the strainer 22 and the like is reliably detected, and the state in which the cavitation occurs is automatically eliminated. As described above, by applying the pump system 50 of the present embodiment to the boiler system 1, it is possible to reliably prevent a situation in which the pump 51 breaks down or a water supply failure occurs due to cavitation, and the boiler 10 is stably operated. In addition, the maintenance cost can be reduced by preventing the failure.

The pump system 50 according to the present embodiment described above has the following effects.
The pump system 50 of the present embodiment includes a pump 51, a drive motor 52 that transmits a driving force to the pump 51, and the number of rotations is adjusted according to a frequency, and a primary pressure sensor 55 that detects a primary pressure of the pump 51. And a control unit 91 capable of controlling the drive motor 52 at a predetermined set frequency. When the control unit 91 monitors the measurement value of the primary pressure sensor 55 and detects a pressure lower than a threshold value set based on the steady-state pressure in which cavitation does not occur, the drive unit 52 has a frequency lower than the set frequency. Control.

  As a result, the occurrence of cavitation can be accurately detected using the decrease in pressure on the primary side of the pump 51 that causes cavitation. In addition, after detecting the cavitation, the pressure loss is reduced by the frequency control of the control unit 91 to eliminate the cavitation. Accordingly, it is possible to reliably prevent the drive failure of the pump 51 due to the occurrence of cavitation.

  The pump system 50 further includes a display unit 93 that notifies maintenance information and cavitation information. When the measured value of the primary pressure sensor 55 falls below the preset predicted pressure value, the control unit 91 activates the display unit 93 to notify the necessity of maintenance.

  Accordingly, the measurement of the pressure on the primary side of the pump 51 can notify the user of the necessity of maintenance before cavitation occurs, and the malfunction of the pump system 50 caused by cavitation can be more effectively prevented. be able to.

  When the control unit 91 detects a pressure lower than the determination threshold, the control unit 91 gradually decreases the frequency of the drive motor 52 from the set frequency until the pressure value of the primary pressure sensor 55 exceeds the detection value set to be equal to or higher than the determination threshold. The control to let you do.

  As a result, the control for decreasing the frequency is continued until the decrease in the inlet pressure is eliminated, so that cavitation is unlikely to occur, and the pump system 50 can be operated more stably.

  When detecting a pressure below the determination threshold, the control unit 91 reduces the frequency so as not to fall below a preset lower limit frequency.

  Thereby, by setting the lower limit frequency as a frequency that guarantees the operation of the equipment (boiler system 1) to which the pump system 50 is applied, the control unit 91 lowers the set frequency, thereby causing problems such as poor water supply. Can be prevented reliably.

  When the pressure below the determination threshold is detected, the control unit 91 activates the display unit 93 to notify the occurrence of cavitation when the measured value of the primary pressure sensor 55 decreases to a preset warning pressure value.

  Accordingly, since the occurrence of cavitation is notified, the user can quickly resolve the cause of the occurrence of cavitation. For example, in the boiler system 1 of the present embodiment, a user who knows the occurrence of cavitation removes the foreign matter from the strainer 22, thereby removing the cause of cavitation and realizing stable operation of the boiler system 1.

  The preferred embodiment of the pump system of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and can be modified as appropriate. In the above embodiment, the determination threshold value and the detection value are stored in the storage unit 92 as different information, but are not limited to this configuration. For example, the determination threshold value and the detection value can be handled as the same data. More specifically, each time the set frequency is changed after cavitation detection, the data table is referred (or calculated by a predetermined mathematical formula), and a determination threshold value based on the currently set frequency can be used as a detection value. .

  In the above-described embodiment, control is performed so that the set frequency is gradually decreased after cavitation detection, but the present invention is not limited to this configuration. When cavitation is detected, the set frequency may be lowered at a stretch to the lower limit frequency.

  In the embodiment described above, the cavitation information is notified by the display unit configured by a display panel or the like, but the cavitation information may be notified by a buzzer or the like. Moreover, you may perform the timing which alert | reports a cavitation to a user just before a setting frequency falls. Thus, the configuration and timing for notifying the user of the cavitation information can be changed as appropriate according to the circumstances.

  In the said embodiment, although the closed boiler system 1 was demonstrated as an example to which the pump system of this invention is applied, it is not necessarily limited to this structure. Moreover, although the example which applies this invention to a boiler system provided with a plurality of boilers was demonstrated in the said embodiment, this invention is applicable also to a boiler system with the number of boilers. The pump system of the present invention can be applied to various systems that need to deliver fluid.

DESCRIPTION OF SYMBOLS 50 Pump system 51 Drive motor 55 Primary side pressure sensor 91 Control part 93 Display part (notification part)

Claims (5)

A pump,
A driving motor that transmits a driving force to the pump and whose rotation speed is adjusted by a frequency;
A primary pressure sensor for detecting the pressure on the primary side of the pump;
A control unit capable of controlling the drive motor at a predetermined set frequency;
With
The controller is
The measured value of the primary side pressure sensor is monitored, and when the pressure lower than the threshold value set based on the steady state pressure where cavitation does not occur is detected, the drive motor is controlled at a frequency lower than the set frequency. Pump system. A notification unit for notifying maintenance information;
The controller is
2. The pump system according to claim 1, wherein when the measured value of the primary pressure sensor falls below a predicted pressure value set higher than the threshold, the notification unit is operated to notify the necessity of maintenance. The controller is
When a pressure lower than the threshold is detected, control is performed to gradually decrease the frequency of the drive motor from the set frequency until the pressure of the primary pressure sensor exceeds a predetermined value set to be equal to or higher than the threshold. The pump system of Claim 1 or 2 to perform. The controller is
The pump system according to any one of claims 1 to 3, wherein when a pressure lower than the threshold is detected, the frequency is lowered so as not to fall below a preset lower limit frequency. An informing unit for informing cavitation information is provided,
The controller is
5. The pump system according to claim 1, wherein when a pressure lower than the threshold value is detected, when the pressure drops to a preset warning pressure value, the notification unit is operated to notify the occurrence of cavitation. .

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