JPS6231243B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drain control device for a feedwater heater, and particularly to a drain control device for a feedwater heater that prevents drain from flowing back into a turbine in a feedwater heater that does not have a bleed check valve. Regarding equipment.

Generally, the feed water heater drain system of a thermal or nuclear power plant is constructed as shown in FIG.
That is, the exhaust gas from the turbine 1 is indirectly cooled and condensed in a condenser 2, and the condensate 3 is extracted and pressurized by a condensate pump 4, and then sent to feed water heaters 5, 6, 7.
The water is heated by a steam generator and supplied to a steam generator (not shown).

In the feed water heater 5, the feed water is heated by the air extracted from the heating steam line extracted from the middle stage of the turbine 1, that is, from the air extraction system 8.
In addition, the feed water heaters 6 and 7 are also connected to the extraction systems 9 and 1, respectively.
Heating of the feed water is done by bleed air from 0. On the other hand, the condensate heated and condensed in the feed water heater 7 passes through the drain pipe 11 to the control valve 12.
The drain condensed in the feed water heater 6 is controlled by the control valve 14 and supplied to the feed water heater 5 on the lowest pressure side through the drain pipe 13. . The drain condensed in the feed water heater 5 and the drain collected from other feed water heaters are collected into the condenser 2 via the drain pipe 15 and the control valve 16.

In addition, drain piping 1 connected to each feed water heater
1, 13, and 15, bypass pipes 20, 21, and 15 each have bypass control valves 17, 18, and 19, and communicate with the condenser 2 in order to cope with low plant output or drain water level control abnormalities. 22 is provided, and each feed water heater 5, 6, 7 is further provided with a water level transmitter 23, 24, 25, respectively.

On the other hand, the extraction systems 9 and 10 are provided with forced-closing check valves 27 and 28, respectively, which are operated via a solenoid valve 26 in response to a rapid stop signal S of the turbine.

By the way, recently, in order to significantly reduce the building cost and the amount of piping connecting the turbine and feedwater heater, and the amount of piping connecting the feedwater heaters, such equipment requires a large amount of plant construction space. It has been proposed to house a proportionate feedwater heater in the upper part of the condenser. However, installing multiple feedwater heaters in the limited space above the condenser may obstruct the high-speed turbine exhaust flow, so the feedwater heaters should be as small as possible, and all feedwater heaters should be It is desirable that the diameter be similar. In addition, from the point of view of thermal efficiency, the drain from the feedwater heater is sequentially collected and sent to the low-pressure feedwater heaters, so the flow rate at the last feedwater heater is extremely large, and the outer diameter of the feedwater heater is also large. Therefore, it is essential to place the drain cooling section separately.

That is, FIG. 2 is a diagram showing a device in which the feed water heaters are arranged in the upper part of the condenser 2 as described above, and the feed water heaters 5, 6, and 7 are respectively arranged in the upper part of the condenser 2. A feed water heater 31 which is disposed in
are arranged symmetrically to each other. However, the feed water heater 7
The heated feed water is further heated by the feed water heater 31 and supplied to the steam generator. On the other hand, the drain generated in the feed water heater 31 is supplied to the feed water heater 7 via the drain pipe 32 and the control valve 33, and then sequentially to the feed water heater on the low pressure side in the same way as shown in FIG. Can be collected.
In addition, the code|symbol 34 is a bypass pipe which has the bypass control valve 35. Also, the turbine rapid stop signal S
Forced closing check valve 27, 2 operated by
8 are provided in the extraction systems 10 and 30, respectively.

By the way, there is a drain tank 3 on the side of the condenser 2.
The drain collected in the feed water heater 6 is guided to the drain tank 36 through the drain pipe 37 and the control valve 38, and the drain from the feed water heater 5, which has the lowest pressure, is also connected to the drain pipe 39. It is guided to the drain tank 36. Further, the drain pipe 37 is connected to the condenser 2 by a bypass pipe 41 having a bypass control valve 40.

The drain collected in the drain tank 36 is
Drain cooling unit 4 installed separately from feed water heater 5
At 2, the water is subjected to heat exchange with the feed water supplied by the condensate pump 4, and is led to the condenser 2 via the drain pipe 43. Further, the upper part of the drain tank 36 and the feed water heater 5 are communicated with each other through a balance pipe 44.

In such a device, since the lowest pressure feed water heater 5 has no drain flowing into it, it can be made smaller like the other feed water heaters 6, 7, 31, and the condenser It can be installed together with other feed water heaters in the upper part of the interior, and has the advantage of being able to significantly reduce the size of the building and the number of piping connecting each feed water heater. Furthermore, by installing the drain tank 36 to collect the drain from the feed water heater, there is no need to store the drain in the feed water heater 5 and create a water level. Vessel 5
Even if the internal pressure changes, drain is guided to the condenser 2 by changing the water level in the drain tank 36. That is, since the pressure of the drain tank 36 is equalized with the feed water heater 5 by the balance pipe 44, the drain cooling is carried out from the drain tank 36 due to the difference between the pressure in the feed water heater 5 and the pressure in the condenser 2. Part 4
2 to the condenser via the drain pipe 43 is the value obtained by subtracting the friction loss of the flow path from the drain tank 3 to the condenser.
Since there is a difference between the water level in the drain tank 36 and the height at which the drain pipe 43 is connected to the condenser 2, the water level in the drain tank 36 moves up and down to create this balance, and the flow rate of the drain system is naturally controlled. It is done. Therefore, there is no need to install a complicated control valve that is difficult to adjust and maintain in the drain pipe 43, which is advantageous in terms of cost.

However, even such a device is not necessarily desirable in terms of preventing overspeed and water inflow when the turbine is tripped. That is, the heating steam extraction system 1 of the feed water heaters 7 and 31
0 and 30 are provided with forced closing check valves 27 and 28, which prevent the drain in the feedwater heaters 7 and 31 from evaporating and flowing back into the turbine, causing overspeed, when the turbine is tripped. Also, the extraction system 10, 3
Backflow of zero water is also prevented. However, condenser 2
In some cases, it may not be possible to install this forced-closing check valve in feed water heaters installed above the water heater. This is because the above-mentioned forced closing check valve must be installed outside the condenser for maintenance inspection and repair purposes, and in this case, the large-diameter extraction system piping must be returned to the condenser to supply water. Must be connected to a heater. Moreover, since the space above the condenser 2 is limited, the above method can usually only be applied to relatively small-diameter systems such as the high-pressure side bleed systems 10 and 30, as shown in Figure 2. . If we were forced to use this method for the bleed air system 9 on the low pressure side, we would need a lot of space above the condenser 2, and in order to take up the space above the condenser, we would have to rely on the restricted planar area. Because of this, it was necessary to extend the condenser in the height direction, and although we tried to reduce the volume of the plant building by installing multiple feed water heaters, the height of the building actually increased. Moreover, there are problems such as impeding the flow of exhaust gas from the turbine to the condenser at a high flow rate, causing a decrease in plant efficiency, and further causing damage to the condenser and extraction system due to erosion.

In view of these points, the present invention has been developed in which a feedwater heater is provided in the upper part of the condenser, and steam, etc. is discharged from the feedwater heater without a forced closing check valve when the turbine is tripped, etc. It is an object of the present invention to provide a highly reliable feedwater heater drain control device that reliably prevents backflow to a turbine.

An embodiment of the present invention will be described below with reference to FIG. Note that the same parts as in FIG. 2 are given the same reference numerals, and the explanation thereof will be omitted.

In FIG. 3, a conduit 45 connecting the drain tank 36 and the drain cooler 42 has one end connected to the condenser 2.
The other end of a bypass pipe 46 that opens to is connected to the bypass pipe 46, and a control valve 47 is interposed in the bypass pipe 46. The control valve 47 is fully opened by the turbine rapid stop signal S, and when the water level signal from the water level detector 48 provided in the drain tank 36 exceeds a predetermined level, the signal is transmitted via the solenoid valve 49. is applied to the control valve 47, and the control valve 47 is configured to be fully opened by the signal as well.

However, when the turbine suddenly stops due to the load on the generator directly connected to the turbine 1 being suddenly cut off, the pressure inside the feed water heater 5 also decreases rapidly, and the internal vacuum level of the condenser 2 decreases. The pressure decreases to approximately the same level as . On the other hand, at this time, the condensate accumulated in the drain tank 36 is high in temperature, so it evaporates in response to the pressure drop, and this evaporated condensate flows back into the extraction system 8 together with the steam in the feed water heater 5. It enters the turbine 1 and flows to the condenser 2 side. For this reason, the rotational speed of the turbine, which increases above the rated rotational speed due to load interruption, may further increase and exceed the specified value. However, the control valve 47 is fully opened by the rapid stop signal S of the turbine, and as a result, the drain in the drain tank 36 is quickly bypassed due to the positional difference between the drain tank 36 and the condenser 2 as described above. The amount of evaporated steam discharged into the condenser 2 through the pipe 46 and flowing back to the turbine 1 is significantly reduced, and overspeed of the turbine is suppressed within a limit value.

In addition, the feed water heater 5 and the drain cooler 42 are multi-tube heat exchangers, and the pressure of the condensate flowing inside the heat exchanger tubes is increased by the condensate pump 4, so that the pressure is higher than that outside the heat exchanger tubes. The pressure is extremely high.
Therefore, if damage occurs to this large number of heat exchanger tubes, condensate will flow from the damaged portion to the outside of the heat exchanger tubes. This results in the same result as an increase in the drain flow rate, and when the entire amount of drain is discharged to the condenser 2, the water level in the drain tank 36 rises rapidly in proportion to the square of the rate of increase in the flow rate. However, such damage to the heat transfer tubes cannot be directly monitored at all times, so the drain tank 36
The water level in the drain tank 36 suddenly rose, and the rise was rapid, so there was no hope that the operator would be able to handle it, and the drain tank 36 became full of water.
The feed water heater 5 may also become full of water, and the water may reach the turbine. Such inflow of water into the turbine may generate thermal stress in various parts of the turbine 1 and cause deformation, leading to a serious accident due to the rotor coming into contact with the casing.

However, in the present invention, the drain tank 3
If the water level in 6 rises abnormally, the water level detector 48
The rise in the water level is detected, and the water level rise signal is sent to the electromagnetic valve 49 to cause the control valve 47 to be fully opened. Therefore, the drain in the drain tank 36 is discharged into the condenser 2 through the bypass pipe 46,
The rising speed of the water level in the drain tank 36 can be significantly reduced. Therefore, during this time, the operator can have time to reduce the output of the plant or to normally stop the plant.

In this case, it would be even more effective to issue a signal at a water level slightly lower than the water level set by the control valve 47 or the water level detector 48 to notify the operator of the occurrence of an accident and prepare for the accident. .

As explained above, in the present invention, the drain from the feed water heater on the low pressure side is collected in a separately provided drain tank, and when the turbine suddenly stops or the rising speed in the drain tank is abnormal, By opening the bypass pipe that connects the drain tank and condenser, the drain in the drain tank is rapidly discharged to the condenser, so steam or water generated in the feed water heater is not transferred to the turbine. It is possible to reliably prevent backflow and the resulting accidents in the plant, and the reliability of the plant can be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a conventional drain control device for a feed water heater, Fig. 2 is a system diagram showing an improvement of the above drain control device, and Fig. 3 is a system diagram of a drain control device for a feed water heater of the present invention. be. 1... Turbine, 2... Condenser, 5, 6, 7,
31... Water heater, 36... Drain tank, 4
6...Bypass pipe, 47...Control valve, 48...Water level detector.

Claims (1)

[Claims] 1. In a feedwater heater drain control device in which a feedwater heater without a check valve is provided in the heating steam pipe is provided in the upper part of the condenser main body, and the drain in the feedwater heater is collected into the condenser. , a drain tank is connected to the feed water heater on the low pressure side and stores drain from the feed water heater, and a turbine trip signal or water level in the drain tank is provided between the drain tank and the condenser. A feed water heater drain control device, characterized in that it is provided with a bypass line that is opened in response to an over-rise signal.