JPS59110810A - Water level control device for steam turbine degasifier - Google Patents

Abstract

PURPOSE:To prevent the water level of a condenser from being lowered by correcting a condensate flow rate command value, which is provided based on the water level of a degasifier and the feed-water flow rate, in accordance with the water level of said condenser. CONSTITUTION:In this device, the output signal of an adder-subtractor 13-a, which outputs a deviation between a water level signal from a degasifier water level gage 10 and a water level set value, is proportionately integrated 14-a before adding 15-a the feed water flow rate from a feedwater flow rate gage 8 as a feed forward signal to the above results, and the resultant output signal is made the command signal for the condensate flow rate. A deviation between this command signal and the condensate flow rate gage 9 is obtained by an adder- subtractor 13-b, and the opening of a degasifier water-level control valve 7 is controlled based on this deviation. In this case, further, a condenser water-level gage 17 is provided, its output is fed to an adder 15-b through a function generator 16-a, and added to the output which was proportionately integrated 14-a and the sum is fed to the adder 15-a.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a water level control device for a steam turbine deaerator used in a power generation plant.

(Background Art of the Invention) This type of water level control device is provided to maintain a constant water level in a deaerator, and has a system configuration as shown in FIG. The water level in the deaerator 1 is controlled by adjusting the flow rate of water in the condenser 2, which has been pressurized by the condensate pump 4, by operating the deaerator water level control valve 7. The operation signals to this control valve 7 are the water level of the deaerator 1, the water supply flow rate to the boiler, and the condenser 2.
It is formed by control calculation based on the flow rate of condensate from to the deaerator 1.

Here, there is a turbine bypass operation as an operating method of a power generation plant, and this is a method in which when the power generation output is small compared to the boiler output, surplus steam is bypassed to the turbine and flows directly from the boiler to the condenser. In this case, if high-temperature, high-pressure steam from the boiler flows directly into the condenser, there is a risk of damaging the condenser body, so in order to reduce the temperature of the steam, the condenser 2
A desuperheater 3 is provided at the inlet of the condensate pump 4, and cooling water is injected into the desuperheater 3 from the outlet of the condensate pump 4 through a cooling water spray valve 6.

The capacity of this turbine bypass needs to be such that, in a coal-fired boiler where the boiler output cannot be changed rapidly due to the combustion method, the capacity of the turbine bypass must be such that steam equivalent to 100% plant output can flow through the boiler. This is to allow the plant to switch to standalone operation or boiler standalone operation without shutting down the plant due to power system accidents, etc., and to cool such large amounts of steam.
Cooling water will be required accordingly.

On the other hand, in a turbine plant, the deaerator 1
Feed water heaters (not shown) are provided in the front and rear feed water and condensate lines to raise the temperature of the feed water and condensate that go from the condenser 2 to the boiler via the deaerator 1. The heating source for this feedwater heater is bleed steam from the intermediate stage of the turbine. The steam used to heat the feed water and condensate is condensed and becomes drain, which is recovered in the deaerator 1. Therefore, during normal operation, the feed water flow rate QB sent to the boiler, the drain flow rate Qd from the feed water heater flowing into the deaerator 1, the condensate water flowing out from the condenser 2 and the condensate pump 4,
The ratio to the condensate flow rate Qc passing through the deaerator water level control valve 7 is QB:Qd:Qc=1:0.4:0.
6, and the flow rate of condensate flowing through the condensate pump 4 and deaerator water level control valve 7 is about 60% of the flow rate of water supply. On the other hand, when the turbine is in bypass operation, such as when the plant is operating independently or when the boiler is operating independently, there is little or no steam flowing through the turbine, and in either case, the air extracted to the feedwater heater becomes zero and the boiler Almost all of the steam generated flows into the condenser 2. Therefore, in order to establish a flow balance between the flow in and out of the condenser 2 and deaerator 1, since the water equivalent to the amount of steam generated by the boiler flows from the deaerator 1 to the boiler, the same amount of water must be condensed. It is necessary to flow the water from the container 2 to the deaerator 1 through the condensate pump 4 and the deaerator water level control valve 2. Furthermore, since cooling water is extracted from the condensate pump outlet in order to reduce the temperature of the bypass steam, the flow rate j in the condensate pump 4 is the sum of this cooling water. Cooling water flow rate is approximately 50% of steam volume
Therefore, the ratio of each flow rate at the time of turbine bypass is (3 ) Qn:Qd:Qc':Qc'=1:O:
1.5: 1. Accordingly, in order to maintain a balance between inflow and outflow in the deaerator 1 and condenser 2, the ratio of flow rates flowing through the condensate pump 4 and deaerator water level control valve 7 during normal operation and during turbine bypass is determined. is: Condensate pump Qc: Qc' = 1: 2.5 Deaerator water level control valve Qc: Q(' = 1: 1,7. In this way, during turbine bypass, the flow rate through the condensate line is extremely low. need to be significantly increased.

In particular, in the case of coal-fired boilers, the rate of decrease in boiler output is small, so after the power plant is shifted to on-site isolated operation or boiler isolated operation due to an accident in the power system, remaining coal is used to reduce the amount of evaporation in the boiler. It takes a long time to burn.

Therefore, in order to establish the above-mentioned flow rate balance, it is necessary to flow a larger amount of condensate over a long period of time than during normal operation in order to establish the above ratios (5) and (4). The design of the condensate pump and condensate line is 10 (the flow rate and pressure at one power generation load plus a margin), so the maximum condensate flow rate is 100 even if the deaerator water level control valve 7 is fully opened. The condensate flow rate is approximately 110 to 130% of the condensate flow rate when the engine is loaded, and cannot be increased to the level required to establish flow balance during turbine bypass.

The water level in the condenser is controlled to be kept constant by releasing condensate to the outside of the system and supplying it from outside the system, but the maximum flow rate is generally about 10% to 20% of Qc, and the water supply flow rate and This is a small amount compared to the condensate flow rate.

Flow rate control in this condensate system is performed as deaerator water level control, as shown in Figures 1 and 2.
This is done by generating a command signal for the condensate flow rate from the water level controller 11 based on the water level signal from the deaerator water level gauge 10 and the water supply flow rate from the water supply flow meter 8, and adjusting the condensate flow rate using the flow rate controller 12. .

The water level controller 11 includes an adder/subtractor 13-a that compares the water level and the water level set value and outputs the deviation, a proportional integral calculator 14-a that generates a water level correction signal from the deviation, and a water supply from the water supply flow meter 8. It is constituted by an adder 15-a that adds the flow rate as a feedforward signal, and the output thereof becomes a command signal for the condensate flow rate.

The flow rate controller 12 adds and subtracts the deviation between the flow rate command value from the water level controller 11 and the condensate flow rate signal from the condensate flow meter 9.
b, and the proportional-integral calculator 14-b forms an operation signal to the control valve.

In such a control system, when there is a deviation between the deaerator water level and its set value, the command value of the condensate amount continues to increase or decrease by integral calculation until it reaches saturation or reaches the limit value of the output signal.

(Problems in background technology) The conventional device described above has the following problems.

If the plant is operating under high load, such as at 100% output, due to a system accident, etc., and the turbine is in standalone operation or in-plant standalone operation, resulting in turbine-by-vanu operation, the operation of the deaerator water level control device will be affected as described above. Regardless, it is not possible to flow the necessary amount of water from the condenser 2 to the deaerator 1 to achieve a flow rate balance. Therefore, as shown in FIG. 4, the deaerator water level 22 falls and the condenser water level 21 rises. Thereafter, as the boiler output decreases, the feed water flow rate 18 decreases, and when the relationship between the condensate flow rate 19 and the flow rate is reversed, the water level in the deaerator 1 rises and the water level in the condenser 2 falls. The control command value for the condensate flow rate is formed from the deaerator water level and the water supply flow rate, but since the water level has been falling for a long time, the dehydration type water level will recover to the set value by integral calculation for the water level deviation. The command value of condensate flow rate is maximum. During this time, since the flow rate regulator 12 cannot flow a flow rate corresponding to the command value, its output also becomes a value that causes the control valve 7 to be fully opened.

Even after the boiler output is reduced in this way, while the water level in the deaerator 1 recovers, the maximum amount of condensate that can flow in that system is allowed to flow through the deaerator 1, so the condenser water level 21 is maintained at the water supply level. , after the reversal of the condensate flow rate, the deaerator water level decreases until it recovers. During this period, condensate is released by controlling the condenser water level, and the water level of condenser 2 is kept constant by supply. However, since both the release amount and the supply amount are small compared to the condensate flow rate, It cannot contribute much to water level correction for changes in the condenser water level due to large fluctuations in flow rate.

The deaerator 1 has a tank that stores a large amount of water, and has a large tolerance for a drop in water level. Furthermore, the condenser 2 has a large tolerance against a rise in water level due to its structure. However, there is little margin for lower water levels. When the water level of the condenser drops below the limit value, the condensate pump 4 is stopped.
Leads to plant shutdown.

In this way, the conventional deaerator water level control device determines the condensate flow rate from the deaerator water level and the feed water flow rate, and increases the water level until the water level in the deaerator 1 recovers after the turbine bypass occurs. Since the flow rate of condensate is taken, the water level in the condenser 2 decreases, causing a situation in which the submerged water pump 4 and the plant are stopped.

(Object of the Invention) The present invention has been made in consideration of the above points, and provides a deaerator water level control device that does not cause condensate pump stoppage or plant stoppage due to a drop in condenser water level during turbine bypass. The purpose is to

(Summary of the Invention) In order to achieve this objective, the present invention reduces the command value to the condensate flow rate controller to reduce the condensate flow rate when the water level of the condenser drops. This is a deaerator water level control device designed to prevent this.

(Embodiments of the Invention) The present invention will be described below by way of embodiments with reference to FIGS. 3 to 5.

The present invention corrects the flow rate command value to the flow rate control section of the deaerator water level control device based on the water level of the condenser.

FIG. 3(a) shows an embodiment of the present invention, in which a water level gauge 17 is provided in the condenser 2 (FIG. 1), and the output of this water level gauge 17 is transmitted via a function generator 16-a. and the output of the proportional-integral calculator 14-a is added to the adder 15-a. The function generator 16-a is the third
It has the characteristics shown in Figure (b).

The other configurations are the same as in FIG. 2.

With such a configuration, when the water level of the condenser decreases and becomes below A in FIG. An action is taken to reduce the . As a result, the command value of the condensate flow rate decreases, and the condensate flow rate is reduced by the deaerator water level control valve 7, thereby preventing the water level of the condenser 2 from falling.

In order to prevent the function generator 16-a from outputting even if the water level of the condenser fluctuates during normal operation of the power generating plant, as shown in Fig. 3(b)
A dead zone between A and 8 is set.

Furthermore, when the condenser water level becomes equal to or higher than B, the function generator 16-a generates a positive output and further increases the output of the proportional-integral calculator 14a. Increase the water flow rate and suppress the rise in the water level of the condenser.

Due to such a control operation, the water level of the deaerator further decreases during turbine bypass, so that the proportional-integral calculator 14-a increases the signal up to its output limit value due to the deviation from the water level set value. Through integral calculation, this signal remains at the limit value until the water level becomes close to the set value.When the condenser water level decreases, a negative signal is output from the function generator 16-a, so the condensate The flow rate command value decreases.

Assuming that the condenser water level has now fallen to the lower limit of the detection range of the water level gauge 17, the output of the function generator 16-a is -D%.
becomes. The command value for the condensate flow rate is (water supply flow rate) + (
The output upper limit value of the arithmetic unit 14-a) is obtained. If D and the output upper limit value of the calculator 14-a are set equal, the condensate flow rate is controlled to follow the water supply flow rate. In this case, the water level does not change because the amount flowing out and flowing into the deaerator are equal. In addition, in the condenser, since the condensate flow rate - the amount of steam generated by the boiler = the condenser inflow rate (steam content), if the condensate flow rate - the feed water flow rate, a drop in the water level can be prevented. Furthermore, in this case, water is supplied from outside the line by controlling the water level of the condenser, so the water level of the condenser increases.

If the value of D in the characteristic of the function generator 16-a is set in consideration of the flow rate supplied to the condenser from outside the system, the condensate flow rate will respond as shown in characteristic 20 in Fig. 4, This corresponds to the water supply flow rate characteristic 18, and does not involve fluctuations like the characteristic 19 of the conventional device. In addition, the condenser water level characteristic 23 does not show a drop like the conventional characteristic 21, and the deaerator water level characteristic 24
Also, the characteristic 22 smoothly approaches the set value without showing any fluctuations as in the conventional characteristic 22.

Note that if the maximum output setting value of the function generator 16-a is set within the upper and lower limit values of the proportional-integral calculator 14-a, the water level of the deaerator can always be controlled.

5(a), (b), and (c) show the configuration and characteristics of another embodiment of the present invention, in which the output of the condenser water level gauge 17 is connected to two function generators 16-b, 16-
c, and these double numerical value generators 16-b, 16
- The upper and lower limit control values of the output of the proportional-integral calculator 14-a are set by the output of the proportional-integral calculator 14-a. The upper limit value is determined by the characteristics shown in FIG. 5(b), and the lower limit value is determined by the characteristics shown in FIG. 5 (cl).

With this configuration, when the water level in the condenser decreases to below A in Figure 5 (bl), the upper limit of the output limit value is reduced below 100 inches, and the amount added to the condensate flow rate command value to the feed water flow rate is limited. Prevent the water level from dropping by not taking too much water flow.On the other hand, if the water level rises and exceeds A in Figure 5 (C), increase the lower limit of the output limit value from -Zoo 9g and set the condensate flow rate command. By limiting the subtraction of the value from the water supply flow rate, the condensate flow rate is restricted and the water level is prevented from rising.

In this way, by correcting the flow rate restriction command value of the condensate flow rate according to the water level of the condenser, it is possible to control the condensate flow rate in a manner that coordinates the deaerator water level and the condenser water level.

In the present invention, instead of the function generator in each of the above embodiments, a means for switching the output stepwise depending on the condenser water level may be used.

As described above, the present invention corrects the condensate flow rate command value according to the water level of the condenser, so that the water supply and condensate flow rates may be temporarily uncontrollable as in the case of turbine bypass. When restoring a deaerator water level that has fallen due to loss of balance, it is possible to prevent the condenser water level from dropping because it is gradually restored to its set water level according to the respective water levels of the condenser and deaerator.

Additionally, if the condenser water level deviates significantly from the set value during normal operation, the condensate flow rate can be adjusted to quickly restore the water level to the set value.

[Brief explanation of drawings]

Figure 1 is a schematic system diagram of a steam turbine condensate system, Figure 2 is a diagram of its conventional deaerator water level control system, and Figures 3 (a), (
b> is a diagram showing the configuration of an embodiment of the present invention and the characteristics of its main elements, FIG. 4 is a characteristic diagram for explaining the operation of the embodiment of FIG. 3, and FIGS. 5(a), (b), ( c) is a diagram showing the structure of another embodiment of the present invention and the characteristics of its elements; 1... Deaerator 13-a, 13-
b...Addition/subtraction 2...Double water vessel 3...Desuperheater 14-8, 14-b...
Proportional term 4... Condensate pump Common unit 5...
・Turbine bypass 15-a, 15-b...
・Adder valves 16-a, 16-b
, 16-c6...Cooling water spray valve...Function generator 7...Deaerator water level control valve 17...Condenser water level gauge 8...Water supply flow meter 18...Water supply flow rate 9・
...Condensate flow meter 19...Condensate flow l・10...
・Deaerator water level gauge 20...Condensate flow rate (present invention 11
... (deaerator) water position controller
21... Condenser water level 12... Flow rate controller
22... Deaerator water level 23... Condenser water level (according to the present invention) 24... Deaerator water level (according to the present invention) Applicant's representative Kiyoshi Inomata Figure 1 / 47 No. 4 Figure 1'l:! 7] →Condenser water Ω □Condenser water Ω

Claims (1)

[Claims] A device that forms a command value for the flow rate of condensate flowing out from a condenser to the deaerator based on the water level of a steam turbine deaerator and the flow rate of water supply, and controls the flow rate of condensate according to this command value. A water level control device for a steam turbine deaerator, characterized in that the water level of the condenser is detected, and the condensate flow rate command value is corrected based on this detection signal.