JP2005207322A - Pump apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve pump efficiency of a pump apparatus which uses an ejector to raise a suction head. <P>SOLUTION: It is determined whether a cavitation is generated in a motor control portion based on a value of a current applied to an electric motor 22. If the cavitation is generated, the motor load is reduced to decrease the current value, and thus said determination can be made. When the determination is done, an opening and closing valve 32 is opened, and a part of handling liquid delivered from a centrifugal pump is returned to an ejector 18 through a flow back pipe arrangement 30. When it is determined that the cavitation is settled, the motor control portion closes the opening and closing valve 32 to stop the flow back to the ejector. When the ejector is not needed, the flow back to the ejector is inhibited to reduce a loss, thereby improving the pump efficiency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pump device in which an ejector or an eductor (hereinafter simply referred to as an ejector) is disposed in a suction pipe of a turbo pump, and the suction performance is enhanced by the ejector.

  When the suction head of the turbo pump is lowered, the pressure in the pump, such as the back surface of the impeller blades, becomes lower than the saturated vapor pressure of the handling liquid, and cavitation may occur. In order to prevent this, a technique is known in which an ejector is disposed in a suction pipe of a pump to increase a head in the intake pipe. The ejector is a device that ejects fluid from a nozzle at a high speed and sends a handling liquid to the suction pipe together with the ejected fluid. By converting the velocity head of the jetted fluid into a pressure head with a diffuser, the suction pressure is increased and cavitation in the pump is prevented. Further, the fluid ejected from the nozzle of the ejector is a part of the handling liquid discharged from the pump.

  As described above, when a part of the liquid discharged by the pump is circulated to the ejector, the discharge flow rate of the entire apparatus is reduced accordingly, and the efficiency of the pump is reduced. On the other hand, the operating conditions of the pump device are variously changed, and the above-described cavitation may or may not occur depending on the operating conditions. In order to suppress the cavitation, it is necessary to use an ejector. However, even if the cavitation does not occur, circulating the pump discharge flow to the ejector reduces the efficiency of the pump device. As a result, there is a problem that the overall efficiency of the pump device cannot be increased.

  The present invention has been made in consideration of the above-described problems, and aims to improve the efficiency of a pump device using an ejector.

  In order to solve the above-mentioned problems, the pump device of the present invention is provided with a control valve for controlling the flow of the circulation pipe that sends a part of the handling liquid discharged from the turbo pump to the ejector, and is based on the suction head of the turbo pump. Then, the control valve is controlled to control the return flow to the ejector. This is performed only when recirculation to the ejector is necessary, such as when cavitation occurs, so that the efficiency of the pump device can be improved when unnecessary.

  The suction head can be estimated based on the current supplied to the electric motor when the turbo pump is driven by the electric motor. When the suction head decreases, the load on the motor decreases and this is reflected in the current. Using this, the reduction of the suction head is estimated.

  Further, when the handling liquid is supplied from the supply tank, the suction head can be estimated based on the liquid level of the supply tank. If the height of the liquid level is lowered, the suction head is also lowered accordingly, so that the suction head can be estimated.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings. 1 and 2 are schematic configuration diagrams of the pump device of the present invention. FIG. 1 is a diagram illustrating the operation of the pump when the liquid level of the supply tank storing the handling liquid is high, and FIG. 2 is a diagram illustrating the operation when the liquid level is low.

  The centrifugal pump 10 belonging to the turbo pump sucks the handling liquid stored in the supply tank 12 through the suction pipe 14 and discharges it from the discharge pipe 16. An ejector 18 is disposed in the middle of the suction pipe 14. The centrifugal pump 10 is driven by an electric motor 22 that receives power supply from the motor control unit 20. The ejector 18 includes a nozzle 24 that ejects fluid, a liquid suction portion 26 that is supplied with the handling liquid from the supply tank 12, and a delivery pipe 28 that delivers the handling liquid together with the fluid ejected from the nozzle 24. The delivery pipe 28 has a diffuser part and converts the velocity head of the jetted fluid into a pressure head. The handling liquid discharged by the centrifugal pump 10 is sent to the nozzle 24 through the circulation pipe 30 branched from the discharge pipe 16. The recirculation pipe 30 is provided with an on-off valve 32 whose opening and closing is controlled according to the operation status of the pump device, and an orifice 34 that determines the flow rate of the handling liquid flowing through the recirculation pipe 30.

  As shown in FIG. 1, when the height h of the liquid level of the handling liquid in the supply tank 12 is high, the suction head of the centrifugal pump 10 is high because the position head is high. Therefore, a relatively high effective NPSH can be obtained. However, as shown in FIG. 2, when the liquid level height h of the handling liquid in the supply tank 12 decreases, the position head decreases and the effective NPSH becomes relatively low. Originally, in designing the pump device, even when the effective NPSH becomes low as described above, the pump device is made to be equal to or higher than the necessary NPSH. However, sufficient effective NPSH may not be obtained depending on the spatial conditions of the installation location and the characteristics of the handling liquid. The ejector 18 is used to raise the suction head under conditions where the effective NPSH is low.

  The handling liquid discharged from the centrifugal pump 10 is guided to the ejector 18 by the circulation pipe 30 and is ejected from the nozzle 24. This jet flows toward the delivery pipe 28 while entraining the handling liquid in the liquid absorption part 26. The delivery pipe 28 forms a diffuser whose cross-sectional area gradually increases along the flow direction, where the jet velocity head is converted into a pressure head and the suction head of the centrifugal pump 10 is raised.

  As described above, even in a single pump device, the effective NPSH varies depending on the operating conditions, and depending on the conditions, this may be less than the required NPSH. In the example described above, when the liquid level in the supply tank 12 is high, the amount of liquid to be handled is reduced and the liquid level is lowered even when sufficient effective NPSH is obtained. It is possible that the effective NPSH is not sufficient. The effective NPSH is not sufficient, and the ejector 18 is used in preparation for the suction head of the centrifugal pump 10 being lowered. However, when the recirculation to the ejector 18 is always performed, the effective NPSH is sufficiently obtained. Even if there is, the effective pump discharge flow rate is reduced by the amount of circulation. That is, even under conditions where the ejector 18 is not required, recirculation is performed and pump efficiency is reduced.

  In the pump device of this embodiment, when the effective NPSH is sufficiently obtained, the ejector 18 is not used, and the efficiency reduction due to the recirculation to the ejector 18 is avoided. Specifically, the open / close valve 32 is opened when an operating condition is determined such that the effective NPSH decreases and the suction head decreases. As a result, a part of the handling liquid discharged from the centrifugal pump 10 is sent to the ejector 18 through the circulation pipe 30, and the ejector 18 functions. On the other hand, under the condition that the effective NPSH is sufficiently obtained, the on-off valve 32 is closed to stop the recirculation to the ejector 28 and ensure the pump efficiency.

  Whether the ejector 18 is used is estimated based on the current value supplied to the motor 22. When the suction head of the centrifugal pump 10 decreases and cavitation starts to occur, the load on the motor 22 decreases and the supplied current decreases. A current value at the time of occurrence of cavitation is obtained in advance, and when the current value becomes this value, an opening signal S1 is sent from the motor control unit 20 to the on-off valve 32. The on-off valve 32 is opened according to this signal S 1, and a part of the handling liquid discharged from the centrifugal pump 10 is circulated to the ejector 18. Occurrence of cavitation is suppressed by the pressurizing action of the ejector 18. When the current value supplied to the motor 22 increases, the motor control unit 20 sends a closing signal S2 to the on-off valve 32, and the on-off valve 32 is closed. Thereby, the recirculation | reflux to the ejector 18 is blocked | prevented and it will be in the state without the loss by recirculation | reflux.

  Next, actual operation of the pump device will be described. Since the flow is not stable when the pump device is started, the current value of the motor also varies. For this reason, it is conceivable that the determination of cavitation cannot be performed properly. Therefore, the on-off valve 32 is closed and the engine is started. At this time, the ejector 18 is not used. Further, at the time of start-up, it is considered that the handling liquid in the supply tank 12 is sufficiently stored, so it is not necessary to use the ejector 18 from this aspect. After a certain period of time has elapsed from the start, cavitation generation determination based on the current value supplied to the motor 22 is started. When the occurrence of cavitation is estimated, the on-off valve 32 is opened, and when the occurrence of cavitation is stopped, the on-off valve 32 is closed.

  According to this embodiment, when the effective NPSH is sufficiently obtained and it is not necessary to raise the suction head, the ejector 18 is not used, and the decrease in efficiency due to the recirculation to the ejector 18 is prevented.

  The estimation of the occurrence of cavitation can also be performed based on the height of the liquid level in the supply tank 12. Once the equipment is installed, the change in the operating condition of the pump device is mainly the liquid level of the supply tank 12, and the effective NPSH, that is, the occurrence of cavitation can be estimated from the liquid level. For this purpose, a liquid level gauge is arranged in the supply tank 12, the cavitation occurrence and termination threshold values are measured for each installed pump device, and the on-off valve is controlled based on this.

It is a figure which shows schematic structure of the pump apparatus of this embodiment, and is a figure which shows the state at the time of not using an ejector especially. It is a figure which shows schematic structure of the pump apparatus of this embodiment, and is a figure which shows the state at the time of use of an ejector especially.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Centrifugal pump, 12 Supply tank, 14 Suction pipe, 16 Discharge pipe, 18 Ejector, 20 Motor control part, 22 Electric motor, 30 Recirculation piping, 32 On-off valve, 34 Orifice.

Claims (3)

A turbo pump that discharges the supplied handling liquid;
An ejector or an eductor disposed in the suction pipe of the turbo pump;
A recirculation pipe for sending a part of the handling liquid discharged by the turbo pump to the ejector or the nozzle of the eductor;
A regulating valve that opens and closes the reflux pipe and / or controls the flow rate;
A control unit for controlling the operation of the control valve based on the turbo pump suction head;
Having a pump device. The pump device according to claim 1,
The turbo pump is driven by an electric motor, and the control unit estimates a suction head based on a current supplied to the electric motor.
Pump device. The pump device according to claim 1,
The handling liquid is supplied from the supply tank to the ejector or eductor,
The control unit estimates a suction head based on a liquid level of the supply tank.
Pump device.

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