JPH0668361B2 - Water heater drain system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a feed water heater drain pump up system for a power plant, and is particularly suitable for preventing flushing and cavitation of a drain pump inlet at the time of a sudden load change. Regarding the system configuration and pump type.

[Conventional technology]

In the conventional system, when the drain of the feedwater heater is injected into the condensate water supply system, if the load on the plant suddenly decreases due to load, disconnection, etc. Since the decrease in temperature is delayed, the pressure at the inlet of the drain pump becomes insufficient, causing flushing and cavitation, and therefore the drain pump was tripped. On the other hand, the drain pump trip drastically reduces the amount of water supply to the steam generator, but the reactor bypasses the turbine bypass in order to protect the reactor by preventing a sudden change in reactor heat output even when the load suddenly decreases. Since excess steam is discharged to the condenser by the valve, it is necessary to ensure that the supply of water to the steam generator does not suddenly increase. Therefore, as for the amount of water supply to the steam generator, it is necessary to supply water by the condensate pump on the upstream side because the drain pump is stopped. At this time, the condensate flow rate of the condensate system rapidly increases, and the pressure loss also increases. Therefore, the inlet pressure of the downstream water supply pump becomes insufficient, causing cavitation. In order to prevent this, a bypass pipe and a stop valve are installed in the feed water heater, and when the load suddenly decreases, the stop valve is quickly and fully opened to secure the inlet pressure of the feed water pump.

Although this prior art is in a PWR plant,
Output load factor such as load and disconnection in WR plant is PW
Since it is not as fast as that of the R plant and is sharp, the problem in the characteristics of the BWR plant is not shown. That is, since the load change rate is large in the BWR plant,
There are the following problems.

First, since the rate of change in load is large, the pressure drop rate in the feedwater heater also increases, so the water rises due to the flushing of the drain in the feedwater heater. On the other hand, since the drain pump that discharges the drain trips, the water inside the feed water heater rises further. Here, the feed water heater has a line that discharges the drain directly to the condenser when the water level rises abnormally.The water level control valve on this line tries to discharge the drain, but the drain inside the feed water heater flashes. As a result, scavenging occurs in the pipe and the discharge capacity is significantly reduced. Yotsutte
There are problems such as an abnormal rise in the water level of the feed water heater and a reverse flow of flash steam to the main turbine, which causes significant disturbance to the water level control of the feed water heater and the main turbine speed control.

Next, since the drain pump of the feed water heater is tripped, the feed water supply capacity to the reactor is reduced. That is, the amount of drain injected into the feed water system by the drain pump is a large amount corresponding to about 25% of the rated feed water flow rate to the reactor, and conversely, the condensate pump and the condensate on the upstream side of the feed water pump. Boost pumps only have the capacity to transfer 75% of the rated feedwater flow rate. Similarly, the low-pressure feed water heater and the condensate purification device also have a treatment capacity of only 75%. On the other hand, even when the load is suddenly reduced, such as when the load is turned off or the like, the required supply water flow rate does not suddenly decrease and the 100% supply water flow rate is required in order to protect the reactor from a sudden heat output change. Therefore, since the condensate pump and the condensate booster pump operate at a flow rate higher than the specified point, the discharge pressure will drop and the pump drive motor will be overpowered. There is a possibility that the pump may trip due to a decrease in inlet pressure, and the condensate pump and the condensate booster pump may cause trips due to the excessive output of the electric motor, and the reactor will lose cooling water and scram. Even if a bypass pipe and a stop valve are placed in the low-pressure feed water heater and the load is suddenly reduced and the stop valve is fully opened rapidly, the operating flow rate of the condensate pump and condensate booster pump cannot be prevented from increasing. .

[Problems to be Solved by the Invention] The above-mentioned conventional technology is an application example in a PWR plant, and in the case of a BWR plant, consideration is not given to a large load change rate such as load or disconnection. Sometimes, if the drain pump is tripped to protect the drain pump, stable control cannot be maintained due to disturbance of the feedwater heater water level control and main turbine speed control.Reactor cooling by condensate feedwater pump tripping There was a problem of water loss and reactor scrum.

An object of the present invention is, in a plant having a large load change rate, such as a BWR plant, when the load is suddenly reduced, the drain pump is protected and the stability of the feed water heater water level control and the main turbine speed control is ensured, and the condensate feed water system is also provided. It is to prevent tripping of the pump, to secure a stable amount of reactor cooling water, and to prevent reactor scram.

[Means for solving problems]

The purpose of the above is to inject the condensate as the cooling water from the upstream side of the drain injection point to the condensate water supply system to the inlet pipe from the feed water heater to the drain pump, thereby making By keeping the temperature sufficiently lower than the saturation temperature of the pressure and adopting a vertical pump with a small amount of water in the pump for the feed water heater drain pump type, the temperature drop of the condensate of the pump can be increased rapidly and By preventing and protecting the drain pump from cavitation even when the load suddenly decreases, the drain pump can be operated stably and continuously, and by eliminating the need to trip the drain pump, the water level of the feed water heater can be reduced. It was achieved by eliminating disturbance to the control and main turbine speed control, and ensuring a stable feed water flow rate to the reactor without causing an excessive flow rate to the condensate feed water system pump. .

[Action]

Connect the condensate pipe taken from the upstream side of the injection point that injects the drain of the drain pump outlet into the condensate system to the inlet pipe from the feed water heater to the drain pump, and the temperature is always lower than that of the feed water heater drain. Fill with cooling water. In addition, the drain pump adopts a horizontal pump with a small amount of water retained so that the drain temperature in the pump quickly drops without a time delay when the pressure in the feed water pressurizer rapidly drops.
As a result, even if the pressure inside the feedwater heater drops sharply when the load on the plant suddenly decreases due to load or disconnection, the drain temperature from the feedwater heater to the inlet of the drain pump is saturated with the pressure inside the feedwater heater. The temperature is kept sufficiently lower than the temperature, and the drain temperature quickly drops with respect to the pressure drop in the feed water heater without a time delay.

Therefore, it is possible to prevent the flushing of the drain at the inlet of the drain pump and to prevent the occurrence of the cavitation, so that the drain pump does not need to be tripped and the operation can be stably continued.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

First, the overall configuration and the flow of fluid will be described. The steam generated in the reactor 1 is sent to the high-pressure turbine 2 and the low-pressure turbine 3, and the steam driving both turbines flows into the condenser 4. Cooling water (not shown) is supplied to the condenser 4,
The exhaust steam of the low-pressure turbine 3 is cooled and condensed to be condensed water. The condensate is temporarily stored in the condenser 4, extracted by the condensate pump 5, impurities are removed by the condensate purification device 6, and then sent to the condensate booster pump 7.

The condensate water booster pump 7 further boosts the condensate water, heats it up through the low-pressure feedwater heater 8, and then sends it to the reactor feedwater pump 9. After the condensate water is further pressurized by the reactor water supply pump 9 and further heated through the high pressure feed water heater 10,
Cooling water is supplied to the reactor 1.

The extracted steam from the low-pressure turbine 3 is sent to the low-pressure feed water heater 8, exchanges heat with the condensate, condenses to become drain, and the condenser 4
And is supplied to the reactor 1 together with the condensed water of the exhaust steam of the low-pressure turbine 3. The extracted steam of the high-pressure turbine 2 is sent to the high-pressure feed water heater 10, exchanges heat with the condensate, is condensed into drain, and is sent to the drain tank 11. The drain temporarily stored in the drain tank 11 is pressurized by the drain pump 13 and injected into the inlet condensate pipe 15 of the reactor feedwater pump 9 to be supplied to the reactor 1.

At the inlet of the drain pump 13, the cold water injection pipe 16 is taken out from the upstream of the injection point of the condensate pipe 15 for injecting the drain from the drain pump 13, and cold water is injected. As the drain pump 13, a horizontal pump having a small amount of water held in the pump is adopted.

In addition, when the load on the plant suddenly decreases due to load or disconnection, the reactor 1
A turbine bypass valve 17 that discharges the excess steam generated in 1 to the condenser 4 is provided.

Next, the main control in this figure will be described. Speed control of the high-pressure turbine 2 and the low-pressure turbine is controlled by a steam control valve (not shown).

The feed water flow rate control to the nuclear reactor 1 is controlled by adjusting the rotation speed of a steam turbine (not shown) that drives the nuclear reactor feed water pump 9 by the steam generated in the nuclear reactor 1.

The drain generated in the high-pressure feed water heater 10 enters the drain tank 11 and the water level detection device 1 provided in the drain tank 11
2 to detect the water level, adjust the opening of the water level control valve 14 provided on the discharge side of the drain pump 13,
It is controlled by adjusting the discharge flow rate of No. 3, that is, the amount of drain injected into the condensate pipe 15.

Here, since the high temperature drain of the high-pressure feed water heater 10 is not discharged to the condenser 4 but is injected into the condensate pipe 15 to recover heat, the plant efficiency is improved, and the condensate pump 5 and the condensate purification device are provided. 6, the condensate booster pump 7, the capacity of the low-pressure feed water heater 8,
Reduce the drain amount of the high-pressure feed water heater 10 by 25% to 75
It does not impair the advantages of the feedwater heater drain up system which can be reduced to%. This is because cold water is injected into the inlet of the drain pump 13, but the temperature of the inlet of the drain pump 13 is lowered and stabilized, and the heat energy of the high temperature drain of the high-pressure feed water heater 10 is recovered. This is because the entire amount was collected at the injection point of the condensate pipe 15 and was not released to the outside of the system.

Next, the form of the drain pump 13 will be described with reference to FIG.

Since the drain pump 13 handles a high-temperature saturated drain of about 200 ° C., conventionally, the NPSH during normal operation is used.
To ensure stable operation and ensure stable operation.
A vertical pump was used because it was relatively easy to secure SH. However, the pressure inside the high-pressure feed water heater 10 and the drain tank 11 sharply decreases not only in the steady state but also in a transient state when a sudden load change such as load or disconnection occurs. At this time, the temperature of the drain held in the drain tank 11 and the drain pump 13 is in a high state, and the temperature drops with a time delay with respect to the pressure change.
The high-temperature drain in 3 flushes, NPSH cannot be secured, and cavitation occurs, which makes it difficult to continue the operation of the drain pump 13, and if the operation continues, the pump will be damaged. Drain pump held water volume as shown in FIG. 2, with respect Vertical pumps about 6 m _3, when employing the horizontal pump, it can be reduced to about 0.3 m ₃ to about 5 percent held water volume, temperature in the pump There is no time delay in the descent speed, and it is possible to prevent flashing.

The feature of this embodiment is that the condensate taken out from the upstream side of the injection point where the condensed drain of the feed water heater 10 is injected into the condensate pipe 15 is injected into the inlet of the drain pump 13, and the drain pump is supplied. 13 Drain temperature at inlet to feed water heater 1
0 and the internal pressure of the drain tank 11 are kept sufficiently lower than the saturation temperature, and the type of the drain pump 13 is a horizontal pump to reduce the amount of water held and the internal pressures of the feed water heater 10 and the drain tank 11 are drastically reduced. Even in the transient state, the temperature drop rate in the drain pump 13 is increased to prevent the occurrence of flushing and cavitation at the inlet of the drain pump 13.

Changes in the drain pump inlet pressure and the like when the plant is loaded or disconnected in this embodiment will be described with reference to FIGS.

3 and 4 show the inlet pressure, temperature, and NPSH of the drain pump 13 when the load is suddenly reduced when the plant is loaded or disconnected.
It is obtained by dynamic characteristic analysis.

First, FIG. 3 shows the pressure and temperature changes at the inlet of the drain pump 13 when the plant is loaded or disconnected in the case of the prior art and the embodiment of the present invention.

As shown in FIG. 3, in the embodiment of the present invention, the pump inlet temperature can be kept low by about 20 ° C. even during normal operation, as compared with the prior art. Further, the pump inlet temperature at the time of load or disconnection drops with the drop of the inlet pressure, and there is no time delay, so that flashing can be prevented.

Next, FIG. 4 shows the required NPSH and effective NPSH of the Dorn pump 13 as in FIG.

As shown in FIG. 4, according to the embodiment of the present invention, as compared with the prior art, the effective N is effective for the required NPSH of the drain pump.
Since PSH can be kept sufficiently high, the occurrence of cavitation can be prevented, and the drain pump 13 can continue stable operation.

According to the embodiment of the present invention, even when the pressure in the feedwater heater is rapidly reduced when the load is suddenly reduced, such as when the plant is loaded or disconnected, flushing at the drain pump inlet and cavitation are effective. At the same time as the drain pump is protected, there is an effect that operation can be continued stably.

Furthermore, since the drain pump can continue stable operation,
As shown in the prior art, there is no need to trip to protect the drain pump, stable operation is possible without disturbance elements to the feed water heater water level control and main turbine speed control, and the condensate pump condensate booster pump Since it is possible to prevent overpower operation and to keep the inlet pressure of the reactor feed water pump and condensate booster pump high, the amount of cooling water to the reactor can be stably secured and the reactor scrum can be prevented. .

Another embodiment of the present invention will be described with reference to FIG.

The system configuration and fluid flow are almost the same as in Fig. 1,
The feature of the present embodiment is that the condensation drain of the low-pressure feed water heater 8 is not collected in the condenser 4 and the low-pressure drain tank 41 is used.
To the low pressure condensate pipe 45 upstream of the condensate pressure increasing pump 7
Water is supplied to the reactor 1 and is supplied to the inlet of the low-pressure drain pump as condensate upstream of the previous drain injection point as cooling water by the low-pressure cold water injection pipe 46. There is a horizontal pump with few

Also in this embodiment, the same effect as that of the embodiment of FIG. 1 can be obtained.

〔The invention's effect〕

According to the present invention, at the time of sudden load reduction of the plant such as load or disconnection, cooling water is injected into the drain pump inlet even when the drain pump inlet pressure sharply decreases together with the feedwater heater pressure decrease. In addition, by adopting a horizontal pump with a small amount of water as the drain pump, the inlet temperature drops without a time delay in the pressure drop rate at the drain pump inlet, so flushing at the drain pump inlet is prevented. There is an effect of preventing the drainage pump, and an effect of preventing the occurrence of the cavitation of the drain pump so that the operation can be stably continued.

Furthermore, since the drain pump can continue to operate stably, it is not necessary to trip the pump to protect the pump.Therefore, it is possible to continue operating stably without disturbing the drain water level control of the feed water heater and the main turbine speed control. In addition, since the condensate pump and the condensate booster pump are not overpowered, tripping of both pumps can be prevented and cooling water can be stably supplied to the reactor, so that there is an effect of preventing the reactor scrum.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a structural diagram of a drain pump, FIG. 3 is a diagram of a drain pump inlet pressure temperature at the time of loading or disconnection, and FIG. FIG. 5 is a system diagram of another embodiment of the present invention when the NPSH is disconnected. 1 ... Reactor, 2 ... High-pressure turbine, 3 ... Low-pressure turbine, 4 ... Condenser, 5 ... Condensate pump, 6 ... Condensate purification device, 7 ... Condensate booster pump, 8 ... … Low-pressure feed water heater,
9 ... Reactor feed pump, 10 ... High-pressure feed heater, 1
1 ... Drain tank, 12 ... Water level detector, 13 ...
Drain pump, 14 ... Water level adjusting valve, 15 ... Condensate piping, 16 ... Cold water injection pipe, 17 ... Turbine bypass valve, 41 ... Low pressure drain tank, 42 ... Water level detection device, 43 ... Low pressure drain Pump, 44 ... Water level control valve,
45: Low pressure condensate pipe, 46: Low pressure cold water injection pipe.

Claims (1)

[Claims] 1. A feed water heater drain system for supplying a feed water heater drain to a condensate water supply system, comprising a feed water heater, a feed water heater drain tank, and a drain pump in a power plant. Feed water heater A feed pipe connected to the drain pump inlet side is provided from the upstream side of the drain injection point to supply cooling water, and the drain pump type is a horizontal pump so that the feed water heater can be used when the load on the plant suddenly decreases. A drain water heater drain system that is capable of preventing drain flushing and drain pump cavitation at the drain pump inlet side when the internal pressure and drain pump inlet pressure are sudden.