JPH0337084B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drain water level control device for a feed water heater of a turbine used in a power generation plant or the like.

A feedwater heater in a power generation plant is provided to preheat feedwater to a steam generator such as a boiler or a nuclear reactor using extracted steam from an intermediate stage of a turbine.

FIG. 1 is a block diagram showing a configuration in which a plurality of feed water heaters are generally used in a power generation plant. In addition, in the drawings, the same reference numerals indicate the same or corresponding parts.

A part of the steam that has done work in the turbines 2 and 3 is extracted as shown by the dotted line, and the feed water heater 5,
6, 8, and 9 heat the feed water from the condenser 4 to the steam generator 1 by exchanging heat with the feed water. Feed water heater 9, 8, 6, 5
The internal pressure increases in this order.

The steam used to heat the feed water is condensed in the feed water heater, and is sequentially sent to the feed water heater on the condenser side via the water level control valve due to the difference in internal pressure of each feed water heater. .

In FIG. 1, condensate condensed in the feedwater heater 5 is sent to the feedwater heater 6 via the water level control valve 13, and the condensate from the feedwater heater 5 and steam from the turbine 2 flow into the feedwater heater 6. , water level control valve 1
4, the drain is sent to a deaerator 7. If the internal pressure of the feed water heater 6 decreases and it becomes impossible to send condensate to the deaerator 7, the feed water heater 6
The drain bypasses the deaerator 7 and is sent to the feed water heater 8 via the water level control valve 15. Drain is sent from the feed water heater 8 to the feed water heater 9 through the water level control valve 17. The drain from the feed water heater 9 is pressurized by the drain pump 11 and sent to the condensate line through the water level control valve 16.

Here, the water level control valve 13 is operated by a signal from the water level controller so as to keep the drain water level of the feed water heater 5 constant. Similarly, the water level control valves 14, 15
is the drain water level of the feed water heater 6, and the water level control valve 17
is the drain water level of the feed water heater 8, and the water level control valve 16
operate to keep the drain water level of the feed water heater 9 constant.

By the way, FIG. 2 is a side sectional view showing the configuration of the feed water heater. Water supply (solid arrow) is water supply inlet 2
2 into the feed water heater 5 and passes through the heat transfer tube 24 to the drain cooling section 26, the condensing section 27, and the steam temperature reduction section 2.
5, the temperature is increased by heat transfer from the drain and bleed steam, and the water exits the feed water heater from the feed water outlet 21 and enters the next feed water heater. Bleed air from the turbine (dashed arrow) enters through the steam inlet 20 and transfers heat to the feed water via the heat transfer tubes 24. The steam is condensed by applying heat to the feed water in the condensing section 27, is supercooled from the saturated temperature state by applying heat to the feed water in the drain cooling section 24, and is then passed from the drain outlet 23 through the water level control valve to the condenser 4 side. into the feed water heater 6.

The condensate in the feed water heater must be kept below a certain level rise to prevent condensate from flowing back into the turbine through the bleed piping. In addition, in order to increase the effectiveness of heat exchange in the feed water heater, it is necessary to ensure that the amount does not fall below a certain level. For this reason, the drain water level in the feed water heater is controlled to a certain value.

The drain water level control of the feed water heater is performed as shown in FIG.

The drain water level of the feed water heater 5 is detected by the water level detector 32, and the water level controller 35 calculates the operation signal for the valve 13 to operate the water level control valve 13, thereby controlling the drain flowing from the feed water heater 5 to the feed water heater 6. This is done by varying the flow rate. The drain water levels of the feed water heater 6 and the next stage feed water heater 8 are also controlled by adjusting the flow rates through the water level control valves 15 and 17. The drain water level of each feed water heater becomes a constant value when the sum of the amount of steam entering the feed water heater and the amount of drain flowing in from the previous feed water heater is equal to the amount of drain flowing out from that feed water heater.

The amount of condensate flowing through the water level control valve 13 is influenced by the inlet pressure and outlet pressure of the water level control valve 13, the flow rate coefficient of the valve, and the temperature of the condensate fluid. If the degree of supercooling of the condensate in the feed water heater 5 is large, a flash phenomenon will occur at the outlet of the condensate valve 13 if the temperature of the condensate fluid is below the saturation temperature of the pressure on the outlet side of the water level control valve 13. Since there is no water level control valve 1
The amount of drain flowing through 3 is proportional to the product of the square root of the pressure difference across the valve and the flow coefficient of the valve. If the degree of supercooling of the condensate in the feed water heater 5 is small and the temperature of the condensate as a fluid is higher than the saturation temperature of the pressure on the outlet side of the water level control valve 13, a flashing phenomenon of the condensate occurs at the outlet of the valve 13. . In this case, water level control valve 1
The drain flow rate flowing through No. 3 must be corrected based on the drain temperature.

Therefore, the conventional water heater water level control has the following drawbacks.

○A Calculation is performed by the water level controller 36 from the value of the drain water level detected by the water level detector 33 and the water level setting value, and the opening degree of the water level control valve 15 is adjusted to keep the drain water level at a constant value. For,
Even if an imbalance occurs in the amount of inflow and outflow to the feed water heater 6, the control will not work until the water level changes due to the imbalance. For this reason, when a large disturbance occurs, such as when a power plant's load changes, the water level fluctuates greatly. In other words, there is a delay in control with respect to fluctuations in water level.

B. Each of the feed water heaters 5, 6, 8, and 9 is configured to drain drain to the feed water heater on the condenser 4 side. Therefore, when a water level fluctuation occurs in the feed water heater 5, the water level control valve 13 is operated to change the amount of drain flowing from the feed water heater 5 to the feed water heater 6, thereby making the water level equal to the water level setting value. At this time, when viewed from the feed water heater 6, the water level control valve 13
is operated and the amount of drain flowing in changes, causing an imbalance of inflow and outflow, and the water level changes. In this way, when a change occurs in the drain water level of a certain feed water heater, the change is sequentially propagated to the subsequent feed water heaters.

○C In the case of a power plant where a tank with a large water storage capacity, such as the deaerator 7, is installed in the condensate and water supply lines, when the plant load drops, the turbine extraction pressure will follow the load drop. However, since the feed water temperature has a large time delay due to the water storage capacity, the feed water temperature entering each feed water heater becomes transiently higher than the feed water temperature at the load balance point. This transiently reduces the degree of subcooling of the drain in the feedwater heater. As the degree of subcooling of the drain decreases, the flash of the drain on the outlet side of the water level control valve increases, the flow rate of the water level control valve decreases, and the drain water level rises.

In order to eliminate these drawbacks, the present invention estimates the amount of steam flowing into each feed water heater, the amount of condensate flowing in, and the amount of condensate flowing out from each feed water heater, and calculates the amount of inflow and outflow. It is an object of the present invention to provide a control device that includes a calculation unit that generates a signal according to the difference between and changes in the difference, and generates an operation signal to a water level control valve along with a signal calculated based on a water level signal from a water level detector. do.

FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 4 shows the water level control device for two feed water heaters 5 and 6, and shows the pressure and temperature of each feed water heater 5 and 6, the flow rate and temperature of the feed water, and the water level control valve 1.
Data such as opening degree of 3 and 15, turbine extraction pressure, etc. 4
2, 43, 45, 46, ... by the feed water heater 5
a bleed air flow rate calculation unit 49 that calculates the bleed air flow rate to 6;
54, . . . and drain flow rate calculation units 50, 55, . . . that calculate the drain flow rate flowing out from the feed water heater.
...and feed water heater drain water level detector 32, 3
3, the feed water heater drain water level from . . . and its water level set value 47, 52, .
54, . . . and drain flow rate calculation sections 50, 55, .
Control calculation units 48, 53, .
It consists of

That is, the present invention is configured by adding bleed air flow rate calculation sections 49, 54, ... and drain flow rate calculation sections 50, 55, ..., compared to the conventional device, so that pressure, temperature, valve opening degree, etc. Control calculations can be performed using the estimated changes in the amount of condensate flowing into the feedwater heater and the amount of condensate flowing out from the feedwater heater, together with the drain water level signal. By operating the water level control valve to maintain a constant balance between the amount of inflow and the amount of outflow from the feedwater heater, the cause of the water level change can be assisted in advance.

Next, a block diagram of another embodiment of the feed water heater water level control according to the present invention is shown in FIG.

The control section configured according to the present invention has 500,5
00',... and consists of the following parts.

() The differential pressure between the turbine and the feed water heater is detected by differential pressure detectors 57, 57,'... (42, 45,...
), and the square root calculators 49, 54,...
. . . A flow rate calculation unit for extracting air flowing from the turbine to the feed water heater;
58', ... are detected and the function generators 63, 6
3,'... compensate for the nonlinearity between the valve position and the flow coefficient, and the pressure on the outlet side of the valve is detected by the pressure detectors 60, 60',..., and the temperature detector 6
From the drain temperature detected at 1,61',...
The correction pressure on the valve outlet side when a drain flash occurs on the valve outlet side obtained by the function generators 64, 64', .
65', ..., the higher value is adopted as the valve outlet side pressure, and the pressure detectors 59, 59',
By taking the difference between the valve inlet pressure and the detected valve inlet pressure, and multiplying this value as the effective differential pressure of the valve by the signals of the function generators 63, 63', ..., from the feed water heater. Drain flow rate calculation units 50, 55, . . . for estimating the calculation of outflowing drain; The proportional differential calculators 69, 69', . . . calculate and generate a flow rate correction signal, and the drain water level detectors 32, 33, . . . and the water level setters 45, 49,
According to the signal of..., the proportional-integral calculators 70, 7
Control calculation units 48, 5 which generate a water level correction signal at 0' and sum these values to provide a control output.
3,... However, the adder/subtractor 68 is shown here for the case where drain flows from the feed water heater on the high pressure side.

A block diagram of yet another embodiment of the present invention is shown in FIG.

The values of the bleed air flow rate to each feed water heater, the opening degree of the water level control valve, the inlet pressure, the outlet pressure, the drain temperature, etc. when the load is constant are given as so-called heat balance data as a function of the load. When the load changes, the changes in these values each have a certain time delay. These delays can be approximately realized by certain delay elements.

FIG. 6 shows a bleed air flow rate calculation unit 49 that calculates the bleed air flow rate in steady state based on the load signal 73, a valve inlet pressure calculation unit 75 that calculates the valve inlet pressure, a valve outlet pressure calculation unit 76 that calculates the valve outlet pressure, and a valve outlet pressure calculation unit 76 that calculates the drain temperature. A process data estimator comprising a drain temperature calculation section 77, a valve opening degree calculation section 74, and delay elements 78 to 82 that calculate respective time delays at the time of excessive change is shown.

By using the estimator signal in Figure 6 as a substitute for the process data detector signal in Figure 5, it is possible to estimate the amount of bleed air flowing into the feed water heater and the amount of drain flowing in and out. .

Thus, in the present invention, the outflow and inflow amounts of steam and drain from the feedwater heater are utilized for control, so the following effects can be achieved.

○A It is possible to suppress fluctuations in water level due to changes in the flow rate of extracted air to the feed water heater and the amount of condensate flowing out from the feed water heater due to changes in the extraction pressure of the turbine, such as when the power plant load changes.

○B Fluctuations in water level caused by changes in the drain flow rate to the low-pressure side feedwater heater caused by water level fluctuations in the high-pressure side feedwater heater can be suppressed.

○C It is possible to suppress fluctuations in water level due to a decrease in flow rate gain at the water level control valve, which is caused by a difference in the ratio between the drop in the pressure inside the feed water heater and the drop in the temperature of the feed water, such as when the power plant load drops.

○ E. The amount of bleed air flowing into the feed water heater can be determined just from the load signal without installing a detector in the plant.
The inflow and outflow of drain can be estimated and calculated.

As described above, according to the present invention, estimated values of the inflow amount of extracted steam to the feedwater heater and the inflow and outflow amount of condensate are used together with the water level signal of the feedwater heater, and the By proactively correcting the imbalance in the inflow and outflow amounts that occurs due to water level fluctuations in the feed water heater, fluctuations in the drain water level can be reduced and the operation of the power plant can be more stabilized.

[Brief explanation of the drawing]

Fig. 1 is a schematic system diagram of a power generation plant, Fig. 2 is a sectional view of a feed water heater, Fig. 3 is a water level control system diagram of a condensate feed water heater, and Fig. 4 is an example of an embodiment of the present invention. FIG. 5 is a conceptual diagram of another embodiment of the present invention, and FIG. 6 is a conceptual diagram of a dynamic characteristic calculating section of a plant according to still another embodiment of the present invention. 1... Steam generator, 2, 3... Turbine, 4...
... Condenser, 5, 6, 8, 9 ... Feed water heater, 7...
... Deaerator, 10 ... Water supply pump, 11 ... Drain pump, 12 ... Condensate pump, 13, 14, 1
5, 16, 17...Water level control valve, 18...Water heater body, 19...Pre-stage drain inlet, 20...Bleed air inlet, 21...Water supply outlet, 22...Water supply inlet,
23...Drain outlet, 24...Heat transfer tube, 25...
Steam temperature reduction section, 26... Drain cooling section, 27... Condensing section, 28... Drain, 32, 33, 34... Water level detector, 35, 36, 37... Water level controller, 4
2, 43, 45, 46...plant data signal,
47, 52... Water level set value, 48, 53... Control calculation unit, 49, 54... Bleed air flow rate calculation unit, 50,
55... Drain flow rate calculation section, 57, 57'... Differential pressure detector, 58, 58'... Opening degree detector, 59,
59', 60, 60'...Pressure detector, 61, 6
1'... Temperature detector, 62, 62'... Square root calculator, 63, 63', 64, 64'... Function generator,
65, 65'... High value priority device, 66, 66'... Multiplier, 67, 68... Addition/subtraction device, 69, 69'...
...Proportional differential calculator, 70, 70'... Proportional integral calculator, 71, 72... Valve operation signal, 73... Load signal, 74... Valve opening calculation section, 75... Valve inlet pressure calculation section, 76... Valve outlet pressure calculation section, 77...
Drain temperature calculation section, 78, 79, 80, 81, 8
2...Delay element.

Claims (1)

[Claims] 1. A plurality of feed water heaters are connected in series from a condenser to supply water to a steam generator, and the feed water is heated by turbine extraction steam and the condensed drain is sequentially passed through a control valve. In a power plant feedwater heater water level control system, the feedwater heater water level control system controls the water level of the feedwater heater drain by controlling the drain water level from the high-pressure side to the low-pressure side feedwater heater by operating the water level control valve. A bleed air flow rate calculation unit that estimates and calculates the amount of bleed steam flowing into the feed water heater from data; a drain flow rate calculation unit that estimates a drain flow rate value from the amount of inflow from the high pressure side of the drain and the amount of outflow to the low pressure side; These extraction steam flow rate values, drain flow rate values,
The drain water level from the drain detector, the drain water level set value from the drain water level setting device, and the drain flow rate value given from the drain flow rate calculation section of the high pressure side feed water heater in the previous stage are respectively introduced and the water level control valve is adjusted. 1. A feedwater heater water level control device for a power generation plant, comprising: a control calculation unit that calculates and controls an operation output. 2. In the feedwater heater water level control device described in claim 1, the flow rate of extracted steam is estimated from the differential pressure between the turbine and the feedwater heater, and the drain amount flowing from the high-pressure side feedwater heater and the low pressure are calculated. From the amount of condensate flowing out to the feed water heater on the side, calculate the drain flow rate value of the deviation of the inflow and outflow amounts of condensate at the feed water heater, and calculate the difference between the previous extraction steam flow rate, drain flow rate value, and the previous high pressure side feed water heater. A power generation plant characterized in that an addition/subtraction operation is carried out with respect to a drain flow rate value given from a drain flow rate calculation section, and the added/subtracted signal and a control operation signal based on the drain water level are combined to form a control signal to a water level control valve. Feed water heater water level control device.