JP2003021305A - Boiler feed water supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent pump cavitation caused by self-evaporation at an inlet BEP 6, and prevent water hammering in a downcomer 5, in a boiler feed water supply system for a thermal power plant. SOLUTION: The boiler feed water supply system is provided with a cooling water injection system for downcomer, which is constituted of a cooling water injection valve 16 and piping, for directly injecting cooling water to a pipeline of the downcomer 5 by bypassing a portion of water to be returned to a deaerator 4. The valve 16 is opened and closed in accordance with the opening and closing conditions of a BFP outlet valve in order to control the rate of injecting cooling water to the downcomer 5, so that the feed water saturation pressure at the BFP outlet can be reduced about 30-100 kPa according to use. The pressure at the BFP inlet set so as to be constantly higher than the feed water saturation pressure, irrespective of the operational conditions. Thus pump cavitation caused by self-evaporation is prevented from occurring at the BFP inlet, and also water hammering is prevented from occurring in the downcomer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can prevent generation of pump cavitation due to a self-evaporation phenomenon at a boiler feed pump inlet of a thermal power plant, and can also prevent generation of water hammer in a downcomer pipe. Boiler water supply device.

[0002]

2. Description of the Related Art FIG. 5 is a system configuration diagram showing an example of a boiler water supply system used in a thermal power plant. The steam generated in the boiler 9 is condensed in the condenser 11 after rotating the steam turbine 10.

Condensed water from the condenser 11 is pumped out by the condensate pump 1, heated by the low-pressure feed water heaters 3a and 3b, and heated by the deaerator 4 by using steam from the turbine bleeder pipe 12. It is noticed and stored in the water storage section. After that, through the downcomer pipe 5, a boiler water supply pump (hereinafter abbreviated as BFP)
The pressure is increased by 6 and is heated by the high-pressure feed water heater 8 to supply water to the boiler 9.

When the plant load gradually decreases, such as when the plant is shut down, the pressure of the deaerator 4 decreases almost in proportion to the plant load, and the feed water temperature also follows the pressure of the deaerator 3. Therefore, it is unlikely that the feed water will cause a self-evaporation phenomenon at the inlet of the BFP 6.

On the other hand, if the auxiliary steam from the auxiliary steam pipe 14 cannot be sufficiently introduced when the plant load is sharply reduced, such as in the island operation or load runback, the amount of steam from the turbine extraction pipe 12 is reduced. Condensate having a small temperature and having a low temperature will flow into the deaerator 4, and the pressure of the deaerator 4 will suddenly decrease.

In this case, the water supply in the deaerator 4 and the downcomer pipe 5 remains at the temperature before the sudden load reduction until the entire amount is discharged, and B
Since the inlet pressure of FP6 is below the saturation pressure of the feed water,
There is a possibility that a transient self-evaporation phenomenon occurs at the pump inlet, causing pump cavitation and water hammer in the downcomer pipe 5.

In the conventional boiler water supply system adopting the downcomer cold water injection system, the cold water injection valve 16 is activated by these command signals when the plant load is suddenly reduced, such as in the island operation or load runback. By opening, bypassing a part of the condensate from the inlet side of the low-pressure feed water heater 3a, spraying in the spray chamber 19 installed in the downcomer pipe 5, and supercooling the feed water, the feed water saturation pressure at the BFP 6 inlet To prevent the occurrence of pump cavitation due to the self-evaporation phenomenon of the feed water at the inlet of the BFP 6 and the occurrence of water hammer in the downcomer pipe 5.

Such a downcomer cold water injection system is described in Japanese Patent Application Laid-Open No. 11-211007, "Deaerator and its operating method".

[0009]

However, in the conventional downfall cold water injection system, in order to interpose the spray chamber in the downfall pipe, an increase in pressure loss of the downfall pipe at the pipe confluence and a structural problem. There is.

Further, since the amount of cold water injected into the downcomer is unclear, if the amount of cold water injected into the downcomer is large, the heat on the wall surface of the downcomer due to the temperature difference between the feed water flowing through the downcomer and the cold water injected. May cause fatigue.

Further, in the conventional downcomer cold water injection system, the cold water injection valve is opened to inject cold water into the downfall pipe when the plant load sharply decreases. However, when the load suddenly decreases, the cold water injection valve starts to open. However, since the cold water cannot be sufficiently injected into the downcomer immediately after the sudden decrease, the saturation pressure of the feed water at the BFP inlet does not decrease, and the occurrence of pump cavitation due to the transient self-evaporation phenomenon at the pump inlet and the downcomer. May cause water hammer.

When the plant is restarted in a short time after being stopped due to an erroneous operation, etc., since the water stored in the deaerator remains at high temperature, the plant is started without injecting cold water into the downcomer pipe. Then, the inlet pressure of the BFP becomes equal to or lower than the saturation pressure of the feed water, which may cause pump cavitation due to a transient self-evaporation phenomenon at the pump inlet portion or water hammer at the downcomer pipe.

An object of the present invention is to enable a method of injecting cold water directly into a downcomer pipe line to prevent generation of pump cavitation due to a self-evaporation phenomenon of feed water at the inlet of a boiler feed pump regardless of operating conditions. In addition, it is to provide a boiler water supply device equipped with a downcomer cold water injection system that prevents the occurrence of water hammer in the downcomer.

[0014]

The boiler water supply apparatus of the present invention comprises a deaerator for heating and deaerating condensed water from a condenser, a boiler water supply pump for supplying water to the boiler, a deaerator and a boiler. It is equipped with a downcomer that connects the water supply pump and a downcomer cold water injection system that directly injects part of the condensate between the inlet side and the outlet side of the low-pressure water heater into the downcomer pipe line. By making the inlet pressure of the pump always higher than the saturation pressure of the feed water, it is possible to prevent the occurrence of pump cavitation due to the self-evaporation phenomenon at the inlet of the boiler feed water pump and to prevent the occurrence of water hammer in the downcomer pipe. Is.

The cold water may be any condensate between the inlet side and the outlet side of the low pressure feed water heater, such as the inlet side of the low pressure feed water heater,
Between the first stage and the second stage, it may be on the exit side.

In the above downfall cold water injection system,
It is desirable to control the injection amount of cold water into the downcomer pipe so as to reduce the saturation pressure of the feed water at the BFP inlet portion by about 30 kPa to 100 kPa according to the operation.

In the downfall cold water injection system,
It is desirable to open the cold water injection valve when the boiler feed water pump outlet valve is not closed and to close the cold water injection valve when the boiler feed water pump outlet valve is closed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of a boiler water supply apparatus equipped with a downcomer cold water injection system according to the present invention. In FIG. 1, the same applies when a condensate booster pump is installed between the condensate pump 1 and the control valve 2. Figure 5
Parts having the same reference numerals as in FIG.

As shown in FIG. 1, the boiler water supply system includes a deaerator 4 for performing deaerating by heating the condensate from the condenser 11 by using steam of the turbine extraction pipe 12, and a deaerator 4 to a BFP 6 It is composed of a downcomer pipe 5 for sending water to the boiler 9 and a BFP 6 for boosting pressure to send water to the boiler 9.

Further, the boiler water supply system in this embodiment is provided with a downcomer cold water injection system composed of a cold water injection valve 16 and piping, and partially bypasses the condensate on the inlet side of the low pressure feed water heater 3a. By directly injecting cold water into the downcomer pipe 5, the occurrence of pump cavitation due to the self-evaporation phenomenon at the inlet of the BFP 6 and the occurrence of water hammer in the downcomer pipe 5 are prevented and the cold water inlet 1
The pressure loss of the downcomer pipe 5 at 7 is reduced.

In FIG. 1, the downcomer pipe 5 and the BFP 6
Each downcomer pipe 5 by installing multiple BFP outlet valves 7
The same applies to the case where the cold water injection valve 16 and the cold water injection port 17 are installed, and the case where a plurality of the cold water injection ports 17 are installed for one downcomer pipe 5 is also the same.

The operation of the downcomer cold water injection system in this embodiment will be described below. Boiler feed pump (BF
When P) 6 is stopped, the BFP outlet valve 7 and the cold water injection valve 16 are fully closed, so that cold water is not injected into the downcomer pipe 5.

In the process of starting the plant, BFP6 is started to
When the FP outlet valve 7 is started to be opened, the cold water injection valve 16 is opened to start the cold water injection to the downcomer pipe 5, and the cold water injection to the downcomer pipe 5 is continued when the BFP outlet valve 7 is not closed. On the other hand, the cold water injection valve 16 starts to be closed at the stage where the BFP outlet valve 7 is fully closed due to the plant stop process, the BFP 6 emergency stop, etc., and the cold water injection to the downcomer pipe 5 is stopped.

By operating the downcomer cold water injection system by the above-mentioned method, when the plant which could not be performed by the conventional downcomer cold water injection system is stopped and then restarted in a short time, high temperature When the water stored in the deaerator 4 in this state flows into the downcomer pipe 5, cold water is injected to supercool the water supply, so that the saturation pressure of the water supply can be lowered.

As a result, it is possible to prevent the occurrence of pump cavitation due to the transient self-evaporation phenomenon at the inlet of the BFP 6 and the occurrence of water hammer in the downcomer pipe 5. In this embodiment, since the condensate on the inlet side of the feed water heater 3a is injected, a large difference in water temperature can be taken, so that the amount of cold water injected can be reduced.

FIG. 2 is a diagram for explaining the pressure characteristics when the load on the plant is rapidly reduced, and shows the changes over time of the feed water saturation pressure at the inlet of the BFP 6 and the inlet pressure of the BFP 6 when the load is rapidly reduced.

When the pressure in the deaerator 4 drops due to a sudden decrease in the plant load, the inlet pressure of the BFP 6 changes according to the pressure drop in the deaerator 4 with the characteristics shown in FIG. On the other hand, hot water stays in the deaerator 4 and the downcomer pipe 5 at the temperature before the sudden load decrease.

In the boiler water supply device having the conventional downfall pipe cold water injection system, the cold water injection valve 16 is opened in response to a command signal for a sudden decrease in plant load. The characteristics change as shown in b of FIG. 2 with a time delay d due to accumulated hot water between the BFPs 6 and a time delay e due to the opening / closing time of the cold water injection valve 16.

Therefore, when the time delay d and the time delay e shown in FIG. 2 become large, the inlet pressure of the BFP 6 exceeds the saturation pressure of the feed water, and the pump due to the self-evaporation phenomenon of the feed water at the BFP 6 inlet portion. Cavitation and water hammer in the downcomer 5 will occur.

On the other hand, in the boiler water supply system adopting the downcomer cold water injection system of the present invention, the cold water injection valve 1
Since there is no delay in the opening / closing time of 6, the feed water saturation pressure at the inlet of BFP6 can be lowered with the characteristic shown in FIG. 2c, and the occurrence of pump cavitation due to the self-evaporation phenomenon of the feed water at the inlet of BFP6. It is possible to prevent the water hammer from occurring in the downcomer pipe 5.

Next, a method of controlling the cold water injection amount in this embodiment will be described. Since the temperature of the water supply flowing through the downcomer pipe 5 and the cold water injected into the downcomer pipe (condensate on the inlet side of the low-pressure feed heater 3a) is usually 100 ° C. or higher, if the amount of cold water injected into the downcomer pipe 5 is large, 5 There is a problem of thermal fatigue on the wall surface.

As one method of controlling the chilled water injection amount, the valve type of the chilled water injection valve 16 is a throttle valve, and the saturated pressure of the feed water flowing through the downcomer pipe 5 at the rated output operation is 30 kPa to 30 kPa.
By determining the amount that can be reduced by about 100 kPa and controlling the cold water injection amount to be constant, the saturation pressure of the feed water flowing through the downcomer pipe 5 can be reduced from 30 kPa to 100 kP regardless of the operating state.
It can be reduced by about a.

As described above, the boiler water supply apparatus provided with the downcomer pipe cold water injection system of the present invention bypasses a part of the condensate to inject the cold water into the downcomer pipe and directly connects to the downcomer pipe line. By injecting cold water and supercooling the feed water, the inlet pressure of the BFP is always higher than the saturation pressure of the feed water, so it is possible to prevent the occurrence of pump cavitation due to the self-evaporation phenomenon of the feed water at the BFP inlet. , It is possible to prevent the occurrence of water hammer in the downcomer and reduce the pressure loss of the downcomer at the pipe confluence.

Further, the cold water injection valve is opened / closed according to the open / closed state of the BFP outlet valve, and the feed water saturation pressure at the BFP inlet is set to 30 kPa to 100 k depending on the amount of cold water injected into the downcomer pipe.
It is controlled so that it can be reduced by about Pa, and the inlet pressure of the BFP is always higher than the saturated pressure of the feed water regardless of the operating state. Therefore, the occurrence of pump cavitation due to the self-evaporation phenomenon of the feed water at the BFP inlet part is prevented. It is possible to prevent the occurrence of water hammer in the downcomer.

FIG. 3 shows a second embodiment of the boiler water supply device provided with the downfall cold water injection system according to the present invention. In FIG. 3, the cold water to be injected into the downcomer pipe 6 is directly injected into the downcomer pipe 5 by partially bypassing the condensate on the inlet side of the deaerator 4 in the first embodiment of FIG.

In this embodiment, since the condensate temperature on the inlet side of the deaerator 4 is higher than the condensate temperature on the inlet side of the low pressure feed water heater 3a, the saturation pressure of the feed water flowing through the downcomer pipe 5 is 30 kPa-1.
It is necessary to increase the injection amount of cold water in order to reduce it by about 00 kPa.

In this case, there is a concern that the pressure loss at the cold water inlet 19 will increase due to an increase in the amount of cold water injected into the downcomer pipe 5, but it is a negligible value when compared with the amount of decrease in the saturated pressure of the feed water. Therefore, even in this embodiment, the BFP
6 It is possible to prevent the occurrence of pump cavitation due to the self-evaporation phenomenon of the water supply at the 6 inlet portion and the occurrence of water hammer in the downcomer pipe 5.

FIG. 4 shows a third embodiment of the boiler water supply system equipped with the downfall cold water injection system according to the present invention. In FIG. 4, cold water to be injected into the downcomer pipe 6 is directly injected into the downcomer pipe 5 by partially bypassing condensate on the upstream side of the low-pressure feed water heater 3b as compared with the first embodiment of FIG.

In addition, three or more low-pressure feed water heaters are installed,
The same applies when the condensate on the upstream side of the low-pressure feed water heater is partially bypassed and directly injected into the downcomer pipe 5. Also in this embodiment, it is possible to prevent the occurrence of pump cavitation at the inlet of the BFP 6 due to the self-evaporation phenomenon of the water supply and the occurrence of water hammer at the downcomer pipe 5.

[0040]

According to the present invention, it is possible to prevent the occurrence of pump cavitation due to the self-evaporation phenomenon of the feed water at the BFP inlet, to prevent the occurrence of water hammer in the downcomer pipe, and to prevent the occurrence of the downcomer pipe at the pipe merging portion. The pressure loss can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a boiler water supply device provided with a downcomer cold water injection system according to the present invention.

FIG. 2 is a diagram showing a time change of a feed water saturation pressure at a BFP inlet and a BFP inlet pressure at the time of sudden load reduction.

FIG. 3 is a diagram showing a second embodiment of the boiler water supply device provided with the downcomer cold water injection system according to the present invention.

FIG. 4 is a view showing a third embodiment of the boiler water supply device provided with the downcomer cold water injection system according to the present invention.

FIG. 5 is a diagram showing an example of a boiler water supply device provided with a conventional downcomer cold water injection system.

[Explanation of symbols]

1 ... Condensate pump, 2 ... Control valve, 3a, 3b ... Low pressure feed heater, 4 ... Deaerator, 5 ... Downcomer pipe, 6 ... Boiler feed pump (BFP), 7 ... BFP outlet valve, 8 ... High pressure feed water Heater,
9 ... Boiler, 10 ... Steam turbine, 11 ... Condenser, 12
… Turbine extraction pipe, 13… Valve, 14… Auxiliary steam pipe, 15
… Control valve, 16… Cold water injection valve, 17… Cold water injection port, 18
… Cold water spray, 19… Spray chamber.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Sakuhana             3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Stock Association             Hitachi, Ltd., Thermal Power & Hydro Power Division F-term (reference) 3L021 AA03 BA02 CA02 CA10 DA07                       FA03 FA04

Claims (7)

[Claims] 1. In a boiler water supply system in which a deaerator in a thermal power plant and a boiler water supply pump located downstream thereof are connected by a downcomer pipe, condensate between the inlet side and the outlet side of a low-pressure feed water heater. Is equipped with a downcomer cold water injection system for directly injecting a part of the water into the downcomer pipe line, controlling the injection amount of cold water into the downcomer pipe, and setting the saturation pressure of the water supply at the inlet of the boiler water supply pump to about 30 kPa to 100 kPa A boiler water supply device characterized by being reduced. 2. In a boiler water supply system in which a deaerator in a thermal power plant and a boiler water supply pump located downstream thereof are connected by a downcomer pipe, condensate between the inlet side and the outlet side of a low-pressure feed water heater. A downfall chilled water injection system for directly injecting a part of the above into the downfall pipe line, wherein the downfall chilled water injection system includes a chilled water injection valve and a pipe, and the boiler feed pump outlet valve is not closed. The cold water injection valve is opened in the above, and when the boiler feed pump outlet valve is closed, the cold water injection valve is closed. 3. In a boiler water supply system in which a deaerator in a thermal power plant and a boiler water supply pump located downstream thereof are connected by a downcomer pipe, a part of condensed water is bypassed from the inlet side of a low-pressure water supply heater. A boiler water supply device comprising a downcomer cold water injection system for directly injecting into the downcomer pipe. 4. In a boiler water supply system in which a deaerator in a thermal power plant and a boiler water supply pump downstream thereof are connected by a downfall pipe, a part of the condensate is bypassed from the inlet side of the deaerator to cause the precipitation. A boiler water supply device comprising a downfall cold water injection system for directly injecting into a pipe line. 5. In a boiler water supply system in which a deaerator in a thermal power plant and a boiler water supply pump downstream thereof are connected by a downcomer pipe, a part of condensate is collected from the upstream side of a plurality of low-pressure water supply heaters installed. A boiler water supply device comprising a downcomer cold water injection system for bypassing and directly injecting into the downfall conduit. 6. The boiler water supply device according to any one of claims 3 to 5, wherein the amount of cold water injected into the downcomer pipe is controlled, and the saturation pressure of the water supply at the inlet of the boiler water supply pump is 30 kPa to 10 kPa.
Boiler water supply device that controls so that it can be reduced by about 0 kPa. 7. The boiler water supply device according to claim 3, wherein the downcomer cold water injection system includes a cold water injection valve and a pipe, and the cold water injection is performed when the boiler water supply pump outlet valve is not closed. A boiler water supply apparatus that closes the cold water injection valve when the valve is opened and the boiler water supply pump outlet valve is closed.