JPH0472471A - Feedwater heater drain pump up system - Google Patents

Abstract

PURPOSE:To prevent the damage of drain pumps by connecting a drain tank to plural drain pumps by drain tank downcast pipes, and providing condensate filling pipes for filling low temperature condensate from a condensate pipe into the drain tank downcast pipes. CONSTITUTION:Drain from a drain tank 12 is extracted by drain tank downcast pipes 17A 17B connected to drain pumps 15A, 15B in operation, and condensate is filled into the drain by condensate filling pipes 18A, 18B branched from the exit of a low pressure feedwater heater 6. Since the drain of constantly reduced temperature flows in the drain downcast pipes on the upstream side of the drain pumps 15A, 15B in operation and there is no drain holdup part, the generation of drain flash is prevented even at the time of transient operation when the pressure in the drain tank is suddenly lowered. Also, since a drain tank downcast pipe 17C on the upstream side of a drain pump 15C in the stop state is completely separated from the other drain downcast pipes 17A, 17B, even if drain flash is generated, generated bubbles escape going up to the drain tank 12.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention relates to a water supply system for a nuclear power plant, and in particular, the present invention relates to a water supply system for a nuclear power plant, and in particular to a method for increasing the pressure of condensate condensed in a feed water heater with a drain pump and sending it to a condensate pipe. Regarding the feed water heater drain pump up system.

(Prior Art) Generally, in a nuclear power plant, condensate or feed water is heated by turbine bleed air in a feed water heater and then sent to a steam generator.

The turbine oil condensed in the feedwater heater becomes drain and is sequentially cascaded and sent to the feedwater heater on the low pressure side, and finally recovered to the condenser.

However, as a means to further improve the thermal efficiency of nuclear power plants, a system in which the drain from the feedwater heater is not cascaded and collected in the condenser, but is instead supplied to the condensate pipe that supplies condensate via a drain pump. In other words, feed water heater drain pump-up systems are increasingly being adopted. In this feedwater heater drain pump-up system, the condensate condensed in the feedwater heater is directly mixed with condensate, which greatly contributes to increasing the condensate temperature and feedwater temperature, improving the efficiency of the power plant by approximately 0.5%. I can do it. For this reason, the latest nuclear power plants tend to adopt the feed water heater drain pump-up system.

An example of a feed water heater drain pump-up system that has already been proposed is shown in Figure 3. The prior art will be described below with reference to this drawing.

The exhaust gas from the turbine 1 is condensed in the condenser 2, becomes condensate and temporarily stagnates, and is then boosted by the condensate pump 3.
After passing through the condensate purification device 4 , it is heated in a low-pressure feedwater heater 5 , 6 and led through a condensate pipe 7 to a feedwater pump 8 . This condensate is further pressurized as feed water by a feed water pump 8, further heated by a high pressure feed water heater 9, 10, and then sent through a water feed pipe 11 to a steam generator (not shown).

, low-pressure feedwater heater 5.6 and high-pressure feedwater heater 9.1
The bleed air from the turbine 1 is connected to the bleed air pipe (not shown).
5.6.9.10 of each of the above feed water heaters.
It exchanges heat and condenses to produce condensate. The drain of the low pressure feed water heater 5 is cascaded to the low pressure feed water heater 6.
and finally recovered as condensate 'JSi6. on the other hand,
After the drain of the high-pressure feed water heater 10 is cooled down by a built-in drain cooler, it passes through a drain pipe 7 to a drain tank 1.
Sent to 2. The drain from the high-pressure feed water heater 9 is directly sent to the drain tank 12 through a drain pipe, and the pressure in the drain tank 12 is kept equal to the pressure in the high-pressure feed water heater 9 by a pressure equalizing pipe 13. The drain collected in this manner is temporarily stored in the drain tank 12 and then extracted by the drain tank downcomer pipe 14. The drain tank downpipe 14 branches into three pipes in the middle, and three drain pumps 15 are connected.
It is configured to lead the drain to A115B and 15C. Drain pumps 15A, 15B, and 15C each have a capacity of 50%, and normally two are in operation and the remaining one is on standby. In this way, if the drain pump in operation stops due to some kind of failure, the system is configured so that operation of the system can be continued using the backup pump. Drain pump 15A, 15B.

15C increases the pressure of drain from the drain tank 12 and supplies it to the condensate pipe 7 with sufficient pressure, so that the drain is mixed with condensate.

In this way, the above-mentioned feedwater heater drain pump-up system mixes the drain of the high-pressure feedwater heater 9.10 with condensate, increases the condensate temperature and the feedwater temperature, and improves the thermal efficiency of the power plant. There is.

(Problem to be Solved by the Invention) However, in the feed water heater drain pump system described above, the drain in the drain tank 12 is saturated drain, so when the load of the turbine 1 changes, that is, during plant transient operation. At times, there is a problem in that a flash phenomenon of the drain in the downcomer pipe of the drain tank occurs in the container.

That is, when the load on the turbine 1 decreases rapidly, the turbine bleed pressure also decreases almost proportionally.

Accordingly, the pressure in the high-pressure feed water heater 9,10 also drops rapidly, causing a rapid flash of condensate in the drain tank 12. Since this flash steam is sent to the high-pressure feed water heater 9 through the pressure equalization pipe 13, it causes a pressure drop in the drain tank 12, and furthermore, a flash phenomenon occurs in the drain tank downcomer pipe 14.
Since the generated air bubbles are brought into the drain pumps 15A, 15B, and 15C, there is a problem that in the worst case, the drain pumps may be damaged due to cavitation.

Several methods have already been proposed as a countermeasure to this problem.
As shown in FIG. 4, part of the condensate at a temperature lower than the drain temperature in the drain tank 12 is guided to the drain tank downpipe 14 through the condensate injection pipe 16, and cold water (condensate ) has been attempted to suppress the above flash phenomenon. However, even with this method, sufficient effects cannot be obtained in a feed water heater drain pump-up system using a plurality of drain pumps including a backup pump, as described below.

FIG. 5 is a diagram showing the state inside the drain tank downcomer pipe 14. Drone from the drain tank 12 passes through the drain tank downpipe 14 and joins with condensate from the condensate injection pipe 16 which branches off from the condensate pipe 7. The drain, whose temperature has decreased slightly due to its confluence with condensate, is then branched into three drain tank downcomer pipe branch pipes 14A, 14B, and 14C.
It is led to drain pumps 15A, 15B, and 15C.

As mentioned above, there are two drain pumps, for example, drain pump 1.
5A and 15B are in operation, and one drain pump, for example, drain pump 15C, is on standby (stopped), so all the drain flows into drain downcomer pipe branch pipes 14A and 14B, and the inside of drain downcomer pipe branch pipe 14C is It has become a stagnant drain. Therefore, during a transient operation in which the pressure of the drain tank 12 rapidly decreases, condensate whose temperature has been reduced by condensate does not flow into the drain tank downcomer branch pipe 14C, so that a flash phenomenon of accumulated condensate occurs. Air bubbles generated in the drain tank downcomer pipe branch pipe 14C are sucked into the drain tank downcomer pipe branch pipe 14B or 14A, which communicates with the drain tank downcomer pipe branch pipe 14C, so they are mixed into the drain pumps 15A and 15B that are in operation, and the drain pump is not activated during transient operation. Cavitation may occur and damage the drain pump.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable feedwater heater drain pump-up system that prevents a flash phenomenon in a drain tank downcomer pipe even during transient operation of a plant.

[Structure of the Invention] (Means for Solving the Problems) The feed water heater drain pump up system according to the present invention collects drain condensed in a feed water heater into a drain tank, and pumps this feed water heater drain through a plurality of drain pumps. In a feed water heater drain pump-up system in which the pressure is increased and injected into the condensate flowing in the condensate pipe, the drain tank and multiple drain pumps are connected by independent drain tank downpipe pipes, and The present invention is characterized in that condensate injection pipes are provided for injecting condensate at a temperature lower than the temperature of the feed water heater drain to be extracted into each drain tank downcomer pipe.

(Function) In the present invention, all the drain tank downcomer pipes from the drain tank to the plurality of drain pumps are connected independently, and branching at the drain downcomer pipes is eliminated. Furthermore, since condensate at a temperature lower than the drain temperature of the feedwater heater is injected into each of the drain tank downcomer pipes, in so-called transient operating conditions where the pressure inside the drain tank rapidly decreases, the temperature upstream of the drain pump during operation is By eliminating stagnation, it is possible to suppress the occurrence of drain flash in the drain tank downcomer pipe, and to prevent the occurrence of cavitation in the drain pump.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. In addition, the same reference numerals are given to the same constituent members as those in the above-described specific example in the present invention.

In FIG. 1, three drain tank downcomer pipes 17A, 17B, and 17C are each independently pulled out from the drain tank 12, and three drain pumps 15A, 15B, and 15C are pulled out from the drain tank 12.
This eliminates the need for a separate drain tank downcomer pipe. Further, it branches from the condensate pipe 7 and supplies a portion of the condensate at a temperature lower than the drain temperature in the drain tank 12 to the respective drain tank downcomers 17A, 17B, and 17C through condensate injection pipes 18A, 18B, and 18C. is configured to do so.

In the embodiment of the present invention configured as described above, the drain from the drain tank 12 is drained by the drain pump 15A in operation;
Drain tank downcomer pipes 17A and 1 connected to 15B respectively
Extracted by 7B. The drain is fed to a condensate pipe 7 whose temperature is lower than the drain temperature in the drain tank 12, that is, in this embodiment, a condensate injection pipe 18 branched from the outlet of the low pressure feed water heater 6.
Condensate is injected by A and 18B into redrain tank 1.
It joins the drain from 2. For this reason, cooled condensate always flows through the drain downcomer pipes upstream of the drain pumps 15A and 15B during operation, and since there is no condensate stagnation section, even during transient operation when the pressure inside the drain tank 12 suddenly decreases. No drain flash occurs. In addition, since the drain tank downcomer pipe 17C upstream of the stopped drain pump 15C is completely separated from the other drain downcomer pipes 17A and 17B, even if a drain flash occurs in the drain downcomer pipe 17C, Since the generated air bubbles rise to the drain tank 12 and escape, the air bubbles do not mix into the drain pumps 15A and 15B that are in operation.

As mentioned above, according to this embodiment, the drain pump 1 in operation
The drain tank downcomer pipes upstream of the drain tanks 5A and 15B can always prevent flash from occurring, and cavitation in the drain pumps 15A and 15B can be prevented by reliable and easy means.

In this embodiment, a part of the condensate in the condensate pipe 7 is always supplied to the three drain tank downcomers 17A, 17B, and 17C through the condensate injection pipes 18A, 18B, and 18C, but the present invention For this reason, it is not necessary to inject the condensate into the drain tank downpipe upstream of the drain pump, which is not necessarily in operation. For this reason, for example, as shown in FIG.
119B and 19C are installed, and each drain pump 15A
, 15B, 15C may open the corresponding condensate injection valve. That is, for example, if the drain pumps 15A and 15B are in operation and the drain pump 15B is stopped, the condensate injection valves 19A and 19B are open, and the condensate valve 1 is closed.
9C is closed, the condensate from the condensate pipe 7 is supplied only to the drain downcomer pipes 17A and 17B, and the injection of condensate to the drain tank downpipe 17C upstream of the stopped drain pump 15C can be blocked. .

[Effects of the Invention] As described above, according to the present invention, condensate condensed in a feed water heater is collected in a drain tank, and the pressure of this feed water heater condensate is increased by a drain pump, and the condensate flowing in a condensate pipe is In the feedwater heater drain pump-up system, the drain from the drain tank is sent to each drain pump through an independent drain tank downpipe, and a portion of the condensate at a temperature lower than the feedwater heater drain temperature is sent to the drain tank. Since it is injected into each of the downcomer pipes, it is possible to suppress the flash phenomenon in the drain tank downcomer pipes even when the turbine load suddenly changes, and this has the excellent effect of preventing damage to the drain pump.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the feed water heater drain pump-up system according to the present invention, Fig. 2 is a system diagram showing another embodiment according to the invention, and Figs. FIG. 5 is a system diagram showing a feed water heater drain pump up system, which is currently proposed. 1... Turbine 2... Condensate pipe 3... Condensate pump 4... Condensate purification device 5.6...Low pressure feed water heater 7...Condensate pipe 8...Water pump 9.10...High pressure feed water heater 11... ... Water supply pipe 12 ... Drain tank 13 ...... Pressure equalization pipe 14 ... Drain tank downpipe 14A, 1
4B, 14C...Drain tank downcomer pipe branch pipe 15A, 15B, 15C...Drain pump 16...
・・・・・・Condensate injection pipe

Claims (2)

[Claims] (1) Condensate condensed in the feed water heater is collected into a drain tank, and this feed water heater drain is pressurized using multiple drain pumps and then injected into the condensate flowing in the condensate pipe. In the system, the drain tank and the plurality of drain pumps are connected to each other by independent drain tank down pipes, and condensate extracted from the condensate pipe and having a temperature lower than the feed water heater drain temperature is transferred to the drain tank down pipes. A feedwater heater drain pump-up system characterized by each having a condensate injection pipe for injecting water into the water heater. (2) Feed water heating according to claim 1, characterized in that each of the condensate injection pipes is provided with a condensate injection valve, and the corresponding condensate injection valve is fully opened by a start signal of the drain pump. Drain pump up system.