JPH02254206A - Minimum flow rate control device for water supply pump - Google Patents

Abstract

PURPOSE:To make it possible to close completely and automatically the minimum flow rate valve at a time when the rotational speed of a supply water pump driven by a turbine has an ample range of speed before it reaches the critical rotational speed by providing a minimum flow valve control device which outputs a signal of instruction for full opening of a pump minimum flow valve of a supply water pump driven by an electric motor. CONSTITUTION:A minimum flow valve control device 17 is provided which outputs the signal to open fully for a supply water pump minimum flow valve 15 driven by an electric motor when a supply water pump 11 driven by an electric motor is not operated and only one supply water pump 10 driven by a turbine is operated and, further, the flow rate of supply water is below a specified value. If M/T change-over is made, the operation of the supply water pump 11 is stopped, and at the same time if the supply water flow rate is below a specified flow rate when only one of the supply water pumps 10 driven by a turbine is operated, the minimum flow valve 15 of the supply water pump driven by an electric motor is fully open. With this arrangement the rotational speed of the turbine driving the supply water pump has an ample range of speed up to the critical speed of rotation and the supply water pump minimum flow valve 15 driven by the electric motor is automatically and fully open.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a minimum flow rate control device for a feed water pump of a steam turbine plant, and in particular, the present invention relates to a minimum flow rate control device for a feed water pump of a steam turbine plant. The present invention relates to a minimum flow rate control device for an electric motor-driven feed water pump for a steam turbine plant in which only one pump is installed.

(Prior Art) FIG. 4 is a schematic system diagram of a nuclear power plant equipped with one electric motor-driven water pump and two turbine-driven water pumps, in which steam generated in the reactor 1 is supplied to the turbine 2. , which performs work and rotates the generator 3 to generate electric power. The steam that has expanded and performed work in the turbine 2 is guided to the condenser 4, where it is cooled by cooling water supplied from the outside and becomes condensed water. This condensate is sequentially boosted in pressure by a low-pressure condensate pump 5 and a high-pressure condensate pump 6, and then sent to a low-pressure feed water heater 7, where it is sent to a turbine 2.
The temperature is raised by the oil vapor extracted from the tank. The condensate whose temperature has increased is further boosted in pressure by the feedwater pump 8, further heated to a predetermined temperature by the high-pressure feedwater heater 9, and then fed to the nuclear reactor 1.

The water supply pump 8 is composed of a turbine-driven water pump 10 driven by the extracted air of the turbine 2 and a motor-driven water pump 11 driven by an electric motor, and the water pumps 10 and 11 are connected in parallel to each other. The electric motor-driven water pump 11 is used as a backup water pump when the turbine-driven water pump 10 cannot be used when the plant is started or stopped, or when the turbine-driven water pump 10 is out of order.

By the way, in general, a required minimum flow rate is determined for a pump because it is necessary to continue stable operation to avoid heating due to shut-off operation, and if the required water supply amount is less than the required minimum flow rate, The practice is to run a minimum flow rate and allow excess water to escape into the condenser. That is, the turbine-driven water pump 10 and the motor-driven water pump 11 are provided with a water pump minimum flow system for circulating the water from the water pump to the condenser in order to maintain the minimum flow rate.

The water pump minimum flow system branches minimum flow pipes 12.13 from the discharge sides of the turbine-driven water pump 10 and motor-driven water pump 11, respectively, and connects the minimum flow pipes 12.13 to the condenser 4. Each minimum flow piping 12.1
3 are provided with minimum flow valves 14 and 15, respectively.

A turbine-driven water pump suction flow rate detector 16 is provided on the suction side of the turbine-driven water pump 1o, and each turbine-driven water pump suction flow rate detector]
The suction flow rate signal detected by 6 is input to the minimum flow valve control device 17, and the minimum flow valve 14 is opened when the suction flow rate of the turbine-driven water pump becomes equal to or less than a predetermined value. Similarly, a motor-driven water supply pump suction flow rate detector (not shown) is also provided on the suction side of the motor-driven water supply pump 11, and the minimum flow valve 15 is controlled to open and close via the minimum flow valve control device based on its detection signal. It is like that.

(Problems to be Solved by the Invention) By the way, when starting up the plant, the electric motor-driven water pump 11 is first used as the water pump, and then, after the plant load has increased to a predetermined level, the turbine-driven water pump 10 is started. Generally, the motor-driven water supply pump 11 is stopped, and the M/T
It's called switching. Furthermore, when the plant is stopped, T/M switching is performed to operate in the opposite direction to that when the plant is started.

However, in a plant with one electric motor-driven water pump,
In this case, the M/T switching needs to be carried out at a time when the plant load is lower than in a plant equipped with two electric m-drive water pumps for the following reason.

In other words, in a plant where two motor-driven water pumps are installed, while one motor-driven water pump is in operation, the other motor-driven water pump is in standby mode, and the motor-driven water pump in operation may stop due to failure. If you do,
The standby unit has started and water supply to the reactor can continue. However, in plants with one electric water feed pump, the electric water supply pump is in operation and there is no standby unit, so the electric If the drive water pump fails and stops, reactor water supply may be lost and the water level in the reactor etc. may be significantly affected.

Therefore, in a plant with only one electric motor-driven water supply pump 11, M/T switching is performed at a time when the water supply flow rate is small, that is, when the plant load is low, so that the influence on the water level of the reactor etc. is as small as possible. There is a need.

However, since the water supply pump driving turbine has its own critical rotation speed, it is necessary to operate at a rotation speed that avoids the vicinity of this critical rotation speed. Normally, the feed water pump driving turbine is operated at a rotation speed above this critical rotation speed with sufficient margin, but if the M/T switch is performed early at a low plant load, that is, at a low feed water flow rate. In this case, the water supply pump driving turbine is operated at a rotation speed with little margin relative to the critical rotation speed, resulting in problems such as poor controllability and problems with the integrity of the water supply pump driving turbine.

Furthermore, since the electric motor-driven water supply pump minimum flow valve 15 is a fully open-to-fully closed control valve, the electric motor-driven water supply pump 11 is operated so as to reduce disturbance to the water supply control system of a nuclear reactor, etc. when the valve is opened and closed. In order to avoid opening and closing, the system is forced to open fully manually, and is fully opened after the motor-driven water pump has stopped.

In this way, the electric motor-driven water supply pump minimum flow valve 15
If the pump is fully opened, the condensate flow rate increases and the water pump suction pressure decreases. As a result, the turbine-driven feed water pump 10 attempts to increase its rotational speed to ensure water supply to the reactor, so the margin for the critical rotational speed of the turbine for driving the turbine-driven water pump increases, and controllability is also improved to some extent.

However, by keeping the electric motor-driven feed water pump minimum flow valve fully open as described above, it is possible to increase the operating speed of the turbine-driven water feed pump and provide some margin from the critical speed, but in reality, The problem is the timing of full closure; if it is too early, the rotational speed of the turbine-driven water pump will drop, leaving no margin for the critical rotational speed, and if it is too late, the power loss of the water pump will increase.

In view of these points, the present invention keeps the electric motor-driven water pump minimum flow valve fully open even after switching from the electric motor-driven water pump to the turbine-driven water pump, so that the rotational speed of the turbine-driven water pump reaches the critical rotational speed. It is an object of the present invention to provide a minimum flow rate control device for a water supply pump that automatically fully closes the minimum flow valve when there is sufficient margin.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a minimum flow rate control device for a motor-driven water feed pump in a steam turbine plant having one motor-driven water pump in addition to a turbine-driven water pump. When the driven water supply pump is not operating and only one turbine-driven water supply pump is in operation, and the water supply flow rate is below the specified value, outputs a valve full open command signal to the motor-driven water supply pump minimum flow valve. It is characterized by having a minimum flow valve control device.

(Function) When M/T switching is performed and the operation of the motor-driven water supply pump is stopped, and only one turbine-driven water supply pump is in operation, if the water supply flow rate is below the specified value, The motor-driven water pump minimum flow valve is fully open. Therefore, during the above switching time, the flow rate of condensate flowing through the feed water pump becomes large, the operating speed of the turbine for driving the water feed pump has sufficient margin for the critical speed, and the feed water flow rate remains constant. Since the electric motor-driven water pump minimum flow valve is automatically fully closed when the specified value is reached, the power loss of the water pump is also kept to a minimum.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3. Note that the same parts in FIG. 1 as in FIG. 4 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 1, a suction flow rate detector 20 is provided on the suction side of the motor-driven water supply pump 11, and a water supply pump 8 is further provided with a suction flow rate detector 20.
A water supply flow rate detector 21 is provided on the discharge side of the flowchart, and the flow rate signals detected by each detector 20, 21 are input to the minimum flow valve control device 17. In addition, operation/stop state signals of the turbine-driven water pump 10 and motor-driven water pump 11 and position signals of the operation switch 22 are also input to the minimum flow valve control device 17, respectively.

FIG. 2 is a calculation block diagram of the minimum flow control section of the motor-driven water supply pump of the minimum flow valve control device 17, and the motor-driven water supply pump suction flow rate signal detected by the suction flow rate detector 2o is sent to the comparator 23. When the suction flow rate is above a predetermined set value, the output signal is input to the first AND circuit 24, and when the suction flow rate is below the predetermined value, the output signal is input to the second AND circuit 25. .

A signal indicating that the motor-driven water supply pump 11 is in operation is also input to the first and second AND circuits 24 and 25, respectively, indicating that the motor-driven water supply pump 11 is in operation and that the motor-driven water supply pump 11 is in operation. When the suction flow rate is less than the set value, a valve fully open signal is output from the second AND circuit 25 and input to the second OR circuit 27 via the first OR circuit 26. On the other hand, when the suction flow rate of the motor-driven water supply pump 11 is equal to or higher than the predetermined value, the first AND circuit 2
4, the self-holding circuit of the first OR circuit 26 is cut off, and the valve full-open signal to the second OR circuit 27 is erased.

Further, the water supply flow rate signal detected from the water supply flow rate detector 21 is input to the second comparator 28, and when the water supply flow rate is less than or equal to the set value, the signal is input to the third AND circuit 29. . This third AND circuit 29 also receives a signal indicating that the motor-driven water supply pump 11 is stopped and a signal indicating that only one turbine-driven water supply pump 10 is in operation. 11 is stopped, only one turbine-driven water supply pump lO is in operation, and the water supply flow rate is below a predetermined set value, the valve fully open signal is sent from the third AND circuit 29 to the second OR. added to circuit 27. Therefore, the third AND circuit 29
Alternatively, when a valve fully open signal is generated from either of the first OR circuits 26, a valve fully open signal is manually inputted from the second OR circuit 27 to the fourth AND circuit 30.

The automatic position signal of the operating switch 22 is also input to the fourth AND circuit 30, and when the operating switch 22 is in the automatic position and the valve fully open signal is output from the second OR circuit 27, the above-mentioned A valve fully open signal is output from the fourth AND circuit 30 and input to the third OR circuit 31.

The valve fully open position signal of the operation switch 22 is also input to this third OR circuit 31, and the operation switch 22 is in the valve fully open position or the valve fully open signal is output from the fourth AND circuit 30. In this case, from the third OR circuit 31, the motor-driven water supply pump minimum flow valve 15
A valve full-open signal is applied to the valve, and the valve is fully opened. Moreover, when the valve fully open signal is not output from the fourth AND circuit 30, the motor-driven water supply pump minimum flow valve 15 is fully closed.

By the way, FIG. 3 shows a pressure-flow rate characteristic curve when one turbine-driven water pump is in operation. In the past, the turbine-driven water supply pump was The drive water supply pump is in operation, and the rotational speed at this time is -NO.

However, this rotational speed NO is not close to the critical rotational speed N1 of the turbine for driving the water supply pump. However, when the electric motor-driven feedwater pump minimum flow valve is opened, the condensate flow rate increases by ΔQ, as shown on the condensate flow rate-turbine-driven feedwater pump suction pressure characteristic curve 33.
As a result, the suction pressure of the turbine-driven water pump decreases by ΔP.

Using a new system resistance curve 34 that takes this ΔP into consideration, the rotation speed when the flow rate remains unchanged is determined, and the rotation speed of the turbine for driving the turbine-driven water supply pump becomes N2, which is a sufficient margin ΔN for the critical rotation speed N1. have.

Therefore, the timing to close the motor-driven water supply pump minimum flow valve may be when the water supply flow mQ2 is reached such that the rotational speed does not become lower than N2 even after the motor-driven water supply pump is fully closed.

Similarly, when the timing is detected based on the rotational speed of the turbine-driven water supply pump, the rotational speed N3 is the timing at which the minimum flow valve is closed.

〔Effect of the invention〕

Since the present invention is configured as described above, even if the M/T switching timing is earlier in a plant with one electric motor-driven water supply pump, the electric motor-driven water supply bomb minimum flow valve remains in operation until the water supply flow rate reaches a predetermined value or higher. It is fully opened,
The turbine for driving the water supply pump is not operated in a range close to a critical rotational speed, and safe operation can be performed without impairing the integrity and controllability of the turbine.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of the minimum flow control section of the electric motor-driven water feed pump of the present invention, Fig. 2 is a calculation block diagram of the minimum flow control section, and Fig. 3 is a pressure-flow rate diagram when one turbine-driven water pump is in operation. The characteristic curve diagram, FIG. 4, is a schematic system diagram of a nuclear power plant equipped with one electric motor-driven water supply pump and two turbine-driven water supply pumps. DESCRIPTION OF SYMBOLS 10...Turbine-driven water supply pump, 11...Electric motor-driven water supply pump, 15...Electric motor-driven water supply pump minimum flow valve, 17...Minimum flow valve control device,
20... Suction flow rate detector, 21... Water supply flow rate detector. Applicant's agent: Maki Sa - male figure figure figure

Claims (1)

[Claims] In a turbine-driven feedwater pump minimum flow rate control device in a steam turbine plant that has one electric-driven water pump in addition to the turbine-driven feedwater pump, the electric-motor-driven feedwater pump is not in operation and only one turbine-driven feedwater pump is in operation. A water supply pump minimum flow rate control device, further comprising a minimum flow valve control device that outputs a valve fully open command signal to a motor-driven water supply pump minimum flow valve when the water supply flow rate is below a specified value. .