JPH0765860B2 - Control method for condenser cooling water - Google Patents

Description

Description: [Object of the Invention] (Field of Industrial Application) The present invention relates to a cooling water control method for a steam turbine condenser used in a thermal power plant, a nuclear power plant or the like.

(Prior art) When a steam turbine for thermal power or nuclear power generation is operated at a rated output or less, the amount of heat flowing into the condenser is smaller than that at the rated time, and accordingly, it is necessary for heat exchange. It is possible to maintain a predetermined condenser vacuum with a flow rate of cooling water that is smaller than that at the rated time. Even if the temperature of the cooling water is lower than the rated value, the temperature difference with the fluid flowing into the condenser will be larger than the rated value, so obtain the specified condenser vacuum with a smaller amount of cooling water than when rated. You can

If the amount of cooling water can be adjusted according to the output during operation and the cooling water temperature using such characteristics, the power of the pump can be saved and an economic gain can be obtained.

For this purpose, as a method of adjusting the amount of cooling water,
A variable blade circulating water pump (also called a movable blade circulating water pump) that can adjust the water amount by changing the blade opening of the impeller during operation is often installed.

Figure 1 shows an example of the cooling water system of a condenser.
Is a variable blade circulating water pump, and 2 is a condenser. Also, 3
Indicates a condenser inlet valve, and 4 indicates a condenser outlet valve.

The condenser inlet valve 3 is connected to the condenser front water chamber 5,
Further, the condenser outlet valve 4 is connected to the condenser rear water chamber 6. A seawater booster pump 7 and a seawater cooler 8 are connected between the upstream side of the condenser inlet valve 3 and the downstream side of the condenser outlet valve 4.

Each of the variable vane circulating water pumps 1 has a pump self-pressurizing water pipe 9
Is provided, and a pump outlet valve 10 is inserted on the discharge side of each variable blade circulating water pump 1. 11 is a water conduit and 12 is a drainage pipe.

In the condenser cooling water system configured as described above, in the conventional cooling water amount adjustment, the pump outlet valve 10, the condenser inlet valve 3, and the condenser outlet valve 4 are fully opened to open the blades of the variable blade circulating water pump 1. It was done by changing the degree.

In this case, the pump is operated at the intersection points a, b, c in FIG.
As shown in d and e, on the line where the condenser outlet valve opening degree is 100%, it changes corresponding to the blade opening degree of the variable blade circulating water pump 1, and as the cooling water amount decreases, the pump head also increases. Shows a declining property.

(Problems to be Solved by the Invention) As described above, in the conventional cooling water amount adjusting method, the pump head also decreases as the cooling water amount (pump discharge amount) decreases, so that the following problems occur. .

B) As the pump lift is lowered, the pressure in the condenser rear water chamber 6 is also reduced, so that gas stays in the condenser rear water chamber. Due to this stagnant gas, the cooling area may be reduced, and the condenser vacuum may not be maintained at a specified value.

Therefore, in order to avoid this problem, it is necessary to flow an excessive amount of flow to raise the head or to install a separate vacuum pump to extract the stagnant gas from the rear water chamber of the condenser.

B) As the pump head height decreases, the water pressure of the cooling self-pressurizing water pipes supplied to the pump bearings and pump variable vane device also decreases, making it impossible to secure the required amount of cooling water.

In order to solve this problem, it is necessary to separately install a booster pump to increase the water pressure of the pump self-pressurizing water pipe 9 to obtain the required amount of cooling water, which is uneconomical.

C) If the pump head is significantly reduced, there is a risk that the pressure will drop below the required NPSH of the seawater booster pump 7 that supplies cooling water to the seawater cooler 8.

[Structure of the Invention] (Means for Solving the Problem) A method for controlling condenser cooling water according to the present invention uses a circulating water pump driven by a variable blade or a variable speed motor as a cooling water pump for a condenser of a steam turbine. In the installed plant, the amount of cooling water in the condenser was adjusted by changing the blade opening or speed of the circulating water pump, and it was installed downstream from the condenser outlet according to the change in the blade opening or speed. It is characterized in that the lift of the circulating water pump is controlled within a predetermined range by changing the opening of the valve.

(Operation) According to the condenser cooling water control method of the present invention configured as described above, the pump operating point when only the blade opening or speed is changed in order to reduce the condenser cooling water amount A higher pump head is obtained as compared to.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a part of the cooling water (seawater) pumped up by the variable vane circulating water pump 1 is supplied to the pump self-pressurizing water pipe 9, and most of the cooling water (seawater) passes through a pump outlet valve 10 and a water conduit 11
Flow into. The cooling water exiting this water conduit enters the condenser front water chamber 5 via the condenser inlet valve 3 and exchanges heat with the steam side in the heat exchange pipe arranged in the condenser 2. After that, the water is discharged from the condenser rear water chamber 6 and returned to the sea through the condenser outlet valve 4 and the drain pipe 12.

In addition, a part of the cooling water that has exited the water conduit 11 is pressurized by the seawater booster pump 7, enters the seawater cooler 8, undergoes heat exchange, and is then drained through the drainage conduit 12.

In the condenser cooling water system configured as described above, when adjusting the amount of cooling water, a variable blade device (not shown) is used.
The blade opening of the variable blade of the variable blade circulating water pump 1 is adjusted,
In that case, in the present invention, the condenser water chamber outlet valve 4 is adjusted according to the blade opening of the variable blade of the variable blade circulating water pump 1.

By doing this, even if the amount of cooling water decreases,
It is possible to prevent the pump head from lowering.

That is, in FIG. 2, the pump operating point when the condenser outlet valve 4 is opened and closed according to the blade opening of the variable blade circulating water pump 1 moves on the line connecting a, f, g, h and i. To do. Therefore, a pump head higher than the line connecting the points a, b, c, d, and e (resistance curve at 100% condenser outlet valve opening), which is the pump operating point when only the blade opening is changed, is obtained. To be

Therefore, the gas does not stay in the rear water chamber 6 of the condenser to reduce the cooling area, and the self-pressurized water pipe 9 for cooling the pump is not used.
It is possible to prevent a decrease in water pressure.

Furthermore, the risk of the pressure falling below the required NPSH of the seawater booster pump 7 that supplies the cooling water to the seawater cooler 8 is also prevented.

In the above description, the example using the variable blade circulating water pump is described, but the present invention is not limited to this, and a variable speed motor-driven circulating water pump is used instead of the variable blade circulating water pump. The same effect can be obtained by using it and interlocking its rotation speed with the condenser outlet valve.

Further, instead of controlling the condenser outlet valve 4, a separate valve is installed on any drainage pipe 12 from the double condenser outlet to the drainage outlet, and this valve is used to adjust the blade opening of the variable blade circulating water pump or You may make it synchronize with the speed of the circulating water pump of a variable speed motor drive, and also in that case, the effect similar to the above can be acquired.

[Effects of the Invention] As described above, according to the method for controlling the condenser cooling water of the present invention, the following effects can be obtained.

B) Since it is possible to prevent the pressure in the rear water chamber 6 of the condenser from decreasing, it is possible to eliminate or minimize the gas retention there, and prevent the vacuum degree of the condenser from decreasing due to the gas retention. Is possible.

(B) It becomes possible to secure the required cooling pressure of the pump self-pressurized water pipe 9 which supplies the cooling water to the pump bearing, the pump variable vane device and the like.

C) The required NPSH of the seawater booster pump 7 for the seawater cooler 8 can be secured.

D) Since the adjustment of the amount of cooling water is adjusted by the blade opening or speed of the circulating water pump, the power of the pump can be saved and an economic gain can be obtained.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a cooling water system for a double water device,
The figure is a graph showing a performance curve of a variable blade circulating water pump. 1 …… Variable blade circulating water pump 2 …… Condenser 3 …… Condenser inlet valve 4 …… Condenser outlet valve 5 …… Condenser front water chamber 6 …… Condenser rear water chamber 7 …… Seawater booster pump 8 …… Seawater cooler 9 …… Pump self-pressure water pipe 10 …… Pump outlet valve 11 …… Water transfer conduit 12 …… Drainage conduit

Claims (1)

[Claims] 1. In a plant in which a variable blade or a circulating water pump driven by a variable speed motor is installed as a cooling water pump for a condenser of a steam turbine, the amount of cooling water for the condenser is set to the blade opening of the circulating water pump or Adjusting by changing the speed, the opening of the valve installed downstream from the outlet of the condenser is changed according to the change of the blade opening or the speed, and the lift of the circulating water pump is within a predetermined range. A method for controlling condenser cooling water, which is characterized in that: