JPH01203804A - Feed water heater drain system - Google Patents

Abstract

PURPOSE:To protect a drain pump, by a method wherein, during rapid decrease of an output, a part of feed water passing a feed water heater is caused to bypass, a pressure lowering velocity in the feed water heater or a drain tank during the rapid decrease of a load is relaxed, and cavitation due to pressure reduction at the inlet of a drain pump is prevented from occurring. CONSTITUTION:Condensate is heated by means of bleed air from a turbine by a high pressure feed water heater 11, and high temperature high drain enters a high pressure drain tank 14. The drain is boosted with the aid of a high pressure drain pump 15 and is injected in the inlet part of a water feed pump 10. During transition, e.g., shut off of the load of a plant, a part of feed water passing a high pressure feed water heater 11 is forced to bypass a heater bypass pipe 18 through control of a feed water bypass valve by means of an output control device 17. By the passage of a small amount of condensate through the high pressure feed water heater 11 by means of a flow rate limit orifice, an inner pressure in the high pressure feed water heater 11 and the high pressure drain tank 14 is gradually decreased. This constitution enables prevention of the occurrence of flush of drain in the high pressure drain tank 14 and at the inlet part of the high pressure drain pump 15, and damage of the high pressure drain pump due to cavitation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a feed water heater drain system, and in particular, Plan 1 - A three-way valve installed in the water supply piping is used to drain the feed water heater during a transient period such as a load cutoff. This invention relates to a feed water heater drain system that bypasses and prevents cavitation at the drain pump inlet.

[Conventional technology]

FIG. 3 shows a system diagram of a turbine cycle of a boiling water nuclear power plant as an example of a conventional power plant.

Steam generated in the steam generator 1 is passed through a high pressure turbine 2, a moisture separation heater 3, and a low pressure turbine 4 to a condenser 5.
supplied to The steam supplied to the condenser 5 is cooled in the condenser 5 and condensed to form condensate. The condensate condensed in the condenser is extracted by a low-pressure condensate pump 6 and then sent to a high-pressure condensate pump 8 via a condensate purifier 7. The condensate sent to the high-pressure condensate pump 8 is heated by the low-pressure feed water heaters 9a, b, and then sent to the water feed pump 10. Water pump 1
The condensate water sent to the steam generator 1 is heated by the high pressure feed water heater 11 and then returned to the steam generator 1.

On the other hand, the steam for heating the feedwater extracted from the high-pressure turbine 2 heats condensate in the high-pressure feedwater heater 11 and then condenses to become drain, which enters the high-pressure drain tank 14 . Drain that has entered the high-pressure drain tank 14 is extracted by a high-pressure drain pump 15 and supplied to the inlet side of the water supply pump 10. Further, the steam for heating the feedwater extracted from the low-pressure turbine 4 heats condensate water in the low-pressure feedwater heaters 9a and 9b, and then condenses to become drain and enters the low-pressure drain tank 12. Drain that has entered the low-pressure drain tank is extracted by the low-pressure drain pump 13 and supplied to the inlet pipe of the high-pressure condensate pump 8.

Note that related devices of this type include, for example,
JP-A-56-48596 is mentioned.

[Problem to be solved by the invention]

The above conventional technology does not take into account the fact that cavitation occurs at the pump inlet due to a pressure drop in the drain tank and at the drain pump inlet during a transient period such as sudden load reduction or load shedding. There was a risk of damage.

An object of the present invention is to protect the drain pump by preventing flash and cavitation in the drain tank and the drain pump inlet pipe during transient times such as load interruption.

[Means to solve the problem]

The above objective is achieved by installing piping in the main water supply pipe that bypasses the feedwater heater, and by lowering the flow rate to cool the feedwater heater, the pressure drop in the feedwater heater and drain tank is made gentler. Ru.

[Effect]

Valves installed in water supply piping and bypass lines.

During a transient event such as a load cutoff, a signal issued from the output control device switches the water supply destination from the high-pressure feed water heater to the bypass line, and a small amount of water is supplied to the high-pressure feed water heater via a flow rate restriction orifice using other piping. be done. As a result, the pressure inside the high-pressure feed water heater gradually decreases, and the pressure inside the drain tank also gradually decreases, making it possible to prevent flash and cavitation from occurring inside the drain tank and at the drain pump inlet pipe. .

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

This embodiment shows a case of a pump-up system in which feed water heater drain is injected into condensate system piping using a drain pump.

The high-pressure feedwater heater 11 heats condensate using oil from the turbine. High-temperature drain generated by the high-pressure feed water heater 11 enters the high-pressure drain tank 14, is further pressurized by the high-pressure drain pump 15, and is injected into the inlet of the water feed pump 10. The high pressure drain tank 14 has the same pressure as the high pressure water heater 11 through a pressure equalizing pipe 20.

During transient times such as plant load shedding, the extraction pressure suddenly decreases, so if the normal amount of condensate is passed through the high pressure feed water heater 11, the pressure of the high pressure feed water heater 11 will also drop rapidly. etc., the output control device 17
The feed water bypass valves 21a and 21b are operated to bypass the high pressure feed water heater 11 with the heater bypass pipe 18, and a small amount of condensate is passed through the flow rate restriction orifice 19 to the high pressure feed water heater 11.
The internal pressure of the high-pressure water heater 11 and the high-pressure drain tank 14 can be gradually reduced by passing water to the high-pressure drain tank 14, and a flash of drain occurs inside the high-pressure drain tank 14 and at the inlet of the high-pressure drain pump 15. Damage to the high pressure drain pump due to cavitation can be prevented.

Moreover, as another example, a water supply bypass valve 21a.

FIG. 2 shows an embodiment in which three-way valves 16a and 16b are used in place of valves b. This system requires fewer valves than the first embodiment. The effect of preventing damage to the drain pump is the same as in the first embodiment.

〔Effect of the invention〕

According to the present invention, flashing and cavitation inside the drain tank and at the drain pump inlet pipe can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a system diagram of an applied example of the present invention, and FIG. 3 is an overall system diagram of the prior art. 1... Steam generator, 5... Condenser, 6... Low pressure condensate pump, 8... High pressure condensate pump, 9a, b... Low pressure feed water heater, 10... Water supply Pump, 11... High pressure water heater, 12... Low pressure drain tank, 13...
Low pressure drain pump, 14... High pressure drain tank, 15
...High pressure drain Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A condensate water supply system consisting of a feedwater pump, a feedwater heater, and a piping system connected to a steam generator of a power plant, and a condensate drain of the feedwater heater injected into the condensate water supply system. In a feed water heater drain system consisting of a drain tank and a drain pump, the feed water heater drain system is configured to bypass a portion of the feed water passing through the feed water heater when the output suddenly decreases.
Or, reducing the rate of pressure drop in the drain tank,
A feed water heater drain system characterized in that cavitation due to reduced pressure at the inlet of the drain pump is prevented. 2. In claim 1, a bypass line of the feed water heater is installed in the water supply line of the feed water heater, and a flow of the bypass line and a flow of the water supply line are arranged between the bypass line and the water supply line. A feed water heater drain system characterized by being provided with a flow restricting valve. 3. The feedwater heater drain system according to claim 2, further comprising a third pipe that bypasses a valve that limits the flow rate of the feedwater heater side of the water supply line.