JPS607168B2 - Turbine driven water pump recirculation flow control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recirculation flow rate control device for a turbine-driven water pump in a thermal power plant or a nuclear power plant.

Generally, in thermal power plants, etc., in order to prevent the pump from overheating when the water pump is operated at a low flow rate, a circulation system is installed that returns a constant flow rate from the discharge pipe of the water pump to the suction side. A recirculation flow control device is provided to ensure the minimum amount of cooling water necessary for safe operation of the feed water pump. That is, FIG. 1 shows an example of a secondary recirculation flow rate control device, in which a recirculation line 4 leading to a deaerator 3 is branched from a discharge pipe line 2 of a water supply pump 1. . The recirculation line 4 is provided with a flow rate control valve 5 and a pressure reduction orifice 6, and a portion of the feed water discharged from the water supply pump 1 passes through the flow rate control valve 5 and pressure reduction orifice 6 to the deaerator 3. It is circulated. On the other hand, a flow rate detection device 9 is provided on the discharge side of the booster pump 7 that supplies water from the deaerator 3 to the water supply pump 1, that is, on the suction pipe 8 of the water supply pump 1.
A flow rate signal is applied to a relay 11 from a flow rate transmitter 10 connected to the flow rate detection device 9.

A set flow rate (necessary recirculation flow rate) signal is also added to the relay 11, and when the suction flow rate of the water supply pump 1 reaches the set flow rate, the solenoid valve 12 is de-energized, and the suction flow rate reaches the set flow rate. When the number is doubled, the solenoid valve 12 is energized. By the way, the solenoid valve 12 has a supply valve 1.
A constant air pressure is supplied through the solenoid valve 12.
When the solenoid valve 12 is energized, the air pressure is supplied to the actuator 5a of the control valve 5, and the control valve 5 is fully closed.
The air pressure is released and the control valve 5 is fully opened. However,
When the suction flow rate (=discharge flow rate) of the water supply pump 1 decreases and reaches the set flow rate, the control valve 5 is fully opened and the discharge flow rate flows into the recirculation line 4 and then passes through the decompression orifice 6 to the deaerator 3.
This ensures the necessary recirculation flow rate of the water pump and prevents the water pump from overheating.

In addition, the suction flow rate of the water supply pump 1 recovers to 2 of the set flow rate.
When the amount is doubled, the control valve 5 is fully closed and the full discharge amount of the water pump is supplied to the boiler.

FIG. 2 shows yet another example of a conventional device, in which the suction flow rate of the water supply pump is detected by a flow rate detection device 9, and the flow rate signal is applied to a controller 14 via a flow rate transmitter 10, where it is set. It is constantly compared with the flow rate, and if a deviation occurs between the two, a control signal is immediately sent to the control valve 5.

In this way, in the past, ON-
Control called OFF control or continuous control as shown in FIG. 2 is performed, but in either example, the flow rate setting value is only at one predetermined point.

By the way, FIG. 3 is a diagram showing an example of a Q-day characteristic curve a, a system head curve b, and a minimum flow (required minimum circulating flow rate) curve C of a turbine-driven water supply pump.
As can be seen, the Q-day characteristic curve changes depending on the change in the rotational speed of the pump.

Therefore, the flow rate Q of the water pump at a certain rotation speed n
and the pump discharge pressure day is the Q daily curve a at that rotation speed.
It is determined by the intersection point A between n and the system head curve b.
On the other hand, the minimum recirculation flow rate at that time is determined by the intersection point B. Therefore, if the intersection point B is determined and plotted for each rotation speed, the result will be as shown in FIG. 5, and the optimum minimum recirculation flow rate will vary depending on the pump rotation speed at that time. However, as described above, the set flow rate in the conventional apparatus is selected as the maximum value of the minimum recirculation flow rate, that is, only the one point indicated by the intersection point ○ in FIG. 3 is selected as the set value.

Therefore, no matter what operating condition the water pump is in,
Once the control valve opens, a flow rate corresponding to intersection point D will flow. For example, in Figure 3, even though the required minimum recirculation flow rate when operating at point A may be the flow rate shown at point B, the set flow rate is the flow rate shown at point D, so the control valve is not opened. Then, an extra flow rate of ΔQ will flow through the recirculation line. If this recirculation flow rate becomes more than necessary, it may cause disturbance in the system from the boiler side. Therefore, it is preferable to suppress the recirculation flow rate to the necessary minimum.

In view of these points, the present invention changes the set value of the recirculation flow rate according to the operating status of the feed water pump, thereby ensuring the minimum required recirculation flow rate under the current conditions and minimizing disturbance to the boiler side. It is an object of the present invention to provide a recirculation flow rate control device for a turbine-driven water pump, which can efficiently control the operation of the entire plant.

FIG. 5 is a schematic system diagram showing an embodiment of the recirculation flow rate control device of the present invention.
5 is detected by the rotation speed detector 16, and the rotation speed signal is exchanged by the calculator 17 into a necessary minimum recirculation flow rate signal that matches the rotation speed at that time.
1' is applied as a set flow rate signal. Other points are the same as shown in FIG. Thus, the suction flow rate of the water supply pump is detected by the flow rate detection device 9, and the flow rate signal is applied to the relay 11 via the flow rate transmitter 10. compared to the recirculation flow signal.

When the suction flow rate of the water supply pump becomes less than the set flow rate, the solenoid valve 12 is de-energized by a signal from the relay 11, and the control valve 5 is activated by the actuator 5a.
is fully opened, and the discharge flow from the water supply pump is circulated to the recirculation line 4.

On the other hand, when the suction flow rate of the water supply pump 1 is equal to or higher than the set flow rate, the solenoid valve 12 is energized, compressed air is supplied to the actuator 5a, and the control valve 5 is fully closed. In addition, instead of determining the set flow rate according to the actual rotation speed of the turbine as in the above embodiment, the turbine rotation speed setting signal from the boiler control device is converted into the required minimum circulation flow rate and the set value of the flow rate control valve is changed. It is also possible to do this.

In this case, the set value of the recirculation flow rate is determined by directly using the set value of the rotational speed of the turbine, so that elements of advance control are taken into account, and there is no possibility of delays in operation. In addition, in the above embodiment, so-called ON-
Although OFF control has been described, it is of course applicable to continuous control.

As explained above, in the present invention, the set value of the recirculation flow rate in the feed water pump is changed in accordance with the actual rotation speed of the feed water pump driving turbine or its rotation speed setting signal. The required minimum amount of recirculation flow that is most suitable for the operating state of the turbine-driven water pump can be passed through the circulation line, and excess circulation flow can be reliably prevented from flowing, reducing disturbances to the boiler side. This has the effect of being able to keep the amount to a minimum.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic system diagrams of conventional recirculation flow rate control devices, and Figure 3 is a turbine-driven water pump Q
- Diagrams showing daily characteristic curves, system head curves and minimum flow curves; FIG. 4 is a diagram showing the required minimum recirculation flow rate versus feed pump rotation speed; FIG. It is a schematic system diagram of a circulation flow control device. 1...Water supply pump, 2...Discharge pipe line, 3...
・Deaerator, 4... Recirculation line, 5...
・Flow rate control valve, 8... Suction pipe line, 9...
・Flow rate detection device, 11... Relay, 12...
... Solenoid valve, 15 ... Turbine, 16 ... Rotation speed detector, 17 ... Arithmetic unit. Younger brother' figure 2 figure 3 figure 4 younger brother j figure

Claims (1)

[Claims] 1. Changing the set value of the recirculation flow rate in the feedwater pump in response to changes in the rotational speed of the turbine for driving the feedwater pump, and circulating the minimum flow rate most appropriate for the operating condition of the turbine-driven feedwater pump. A recirculation flow rate control device for a turbine-driven water pump, characterized in that: 2. Recirculation of a turbine-driven feedwater pump according to claim 1, characterized in that the set value of the recirculation flow rate is changed in accordance with a rotation speed setting signal of a turbine for driving the feedwater pump from a boiler control device. Flow control device.