JPS6064106A - Method and device for preventing rise of water level of feedwater heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention is directed to preventing an abnormal rise in the water level that occurs in a feed water heater that heats condensate supplied to a deaerator or feed water supplied to a boiler (by turbine bleed air). , relates to a method and device for preventing water level rise in a feed water heater, which is prevented by adjusting the amount of bleed air.

[Background of the Invention] In recent years, power generation plants have been increasingly automated in order to save labor during startup and shutdown. The bleed valve installed in the turbine bleed system that heats the feed water heater is also automated as an electric valve, and is automatically opened at 10 to 20% of the turbine bleed air when the plant is started, and 20 to 10% when the plant is stopped.
It is designed to automatically close at % load.

In this case, with the conventional method of opening the bleed valve, when the bleed valve is opened, the pressure in the feed water heater rises rapidly, and the pressure response in the water level detection piping installed in the feed water heater is delayed, causing the pressure in the water level detector to rise rapidly. There is a drawback that the water level temporarily rises abnormally and a high water level alarm is issued even though the actual water level in the feed water heater has not risen. In addition, there is an interlock that closes the bleed valve to prevent backflow to the turbine when the water level in the feedwater heater reaches an extra-high water level, but due to the above abnormal rise, this was activated and began to open. This has the disadvantage of re-closing the bleed valve.

That is, FIG. 1 shows a system around a conventional general feed water heater that heats the feed water to a steam boiler using turbine oil air.

The feed water from the water supply tank/pull is heated by the feed water heater 5 and supplied to the boiler. On the other hand, the heated steam of the feed water heater 5 is
It is supplied to the feedwater heater 5 through the turbine 1, the bleed pipe 2, the electric bleed valve 3, and the air-operated bleed check valve 4. The heated steam exchanges heat with the feed water, passes through a drain pipe 6 and a water level control valve 7, and is discharged to the next low-pressure stage feed water heater. The feed water heater 5 includes a water level regulator 8 that controls the water level control valve 7 to keep the water level in the feed water heater constant, a water level gauge 9 for monitoring the water level, an alarm for abnormal water level rise, and air via a solenoid valve 12. High level switch 10% for forcibly closing the actuated check valve A high level switch 11 is installed to close the electrically operated bleed valve in order to prevent drain from flowing back into the turbine due to an abnormal rise in the water level.

Also provided are air pipes 13 and orifices 14 for discharging the air extracted when the heated steam condenses and becomes drain to a deaerator or condenser. Incidentally, at the time of startup when the turbine load is low at the time of blunt startup, the turbine bleed pressure is also low, so it is difficult to discharge the drain from the feed water heater 5, so the electric bleed valve 3 is closed and the turbine load is between IO and 20. It is designed to open when the bleed pressure of the pipe increases.

In this system, until the electric bleed valve 3 is opened at the time of plant startup, the pressure in the feed water heater 5 is the same low pressure as the deaerator or condenser to which the air pipe 13 is connected. Turbine load 10 to 20 with increased bleed pressure
Since the electric bleed valve 3 is opened at step 1, the internal pressure of the feed water heater 5 rises rapidly, causing a phenomenon in which the water level in the water level detectors 8, 9, 10, and 11 temporarily rises abnormally. This phenomenon of abnormal water level rise will be explained with reference to FIGS. 2 to 4.

The horizontal axis in FIG. 3 shows the elapsed time of the electric bleed valve 3 (hereinafter referred to as the bleed valve 3), and the vertical axis shows the opening degree (%) of the bleed valve 3. Also, the horizontal axis in FIG. 4 similarly shows the elapsed time, and the vertical axis shows the water level in the water level detectors 8 to 11.

When the bleed valve 3 is opened at the time of plant startup, the pressure inside the feed water heater 5 rises rapidly. A response difference occurs in pressure transmission. In other words, the pressure response on the drain side of the water level detectors 8 to 11 is fast because it is a liquid, and the pressure response on the steam side is slow because it is a gas, and inside the water level detectors 8 to 11, the gas side pressure is temporarily higher than the liquid side pressure. The water level in the low water level detectors 8 to 11 temporarily rises abnormally as shown in FIG. 4 at the same time as the bleed valve 3 opens.

Conventional bleed valves open linearly from fully closed to fully open as shown by the solid line a in Figure 3 at an opening/closing speed determined by the electric motor and the valve drive speed reducer, or by opening the valve at a speed approximately equal to 1 for warming the feed water heater 5 and the bleed pipe 2. 10 - After opening to the opening degree, holding it for a certain period of time and then opening it to the full opening position is adopted.
With this method, immediately after opening the bleed valve 3 or when the opening is further increased from the warming opening, the pressure in the feed water heater will rise rapidly and the water level in the water level detectors 8 to 11 will rise to the solid line A in Figure 4.
Or, it has been confirmed by oscilloscope measurement using an actual machine that there is a temporary abnormal rise as shown by the dotted line B.

Note that the above drawback is due to a temporary abnormal water level rise in the water level detector 8 etc. when the bleed valve 3 is open, and is not due to an abnormal water level rise in the feed water heater 5 itself. Although it is possible to avoid closing the stop valve 4 and re-closing the bleed valve 3 by providing an interlock exclusion circuit using a timer, this method is an essential method for preventing an abnormal rise in the water level in the water level detector 8, etc. Alternatively, a method of increasing the diameter of the water level detection piping and making it extremely short can be considered, but this is difficult to implement due to layout restrictions.

[Purpose of the invention]

The present invention was devised in order to solve the above-mentioned drawbacks, etc., and its purpose is to temporarily raise the abnormal water level in the water level detector that engages the feed water heater by opening the bleed valve at the time of plant startup. It is an object of the present invention to provide a feedwater heater water level rise prevention method and apparatus that effectively eliminates blockage and eliminates the need for turbine bleed air.

[Summary of the invention]

In order to achieve the above object, the present invention provides a method for preventing a water level rise in a feed water heater, which adjusts the amount of turbine bleed air sent from a turbine into the feed water heater in order to prevent a sudden rise in pressure within the feed water heater. Feedwater heater water level, characterized by: a water level control means for controlling the amount of extracted air that maintains a change over time in the amount of turbine extracted air passing through an extraction valve interposed between the turbine and the feedwater heater to a predetermined value or less. It features a lift prevention device.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a water level rise prevention device suitable for carrying out the method of the present invention will be described based on the drawings.

First, the outline of this embodiment will be explained with reference to FIG. 8 and FIG. 5(b).

In FIG. 8, the same reference numerals as in FIG. 1 indicate the same components or components with the same function. A small bypass valve 17 is arranged in parallel with the bleed air valve 3 as a bleed air amount control means. The bleed air from the turbine 1 is sent to the feed water heater 5 side from both the bleed air valve 3 and the small bypass valve 17. The small bypass valve 17 is formed to be smaller than the bleed valve 3, and the amount of bleed air passing through it is set to be several times smaller than the full opening of the bleed valve 3 even when the valve is fully open. Now, as shown in FIG. 5(b), at the beginning of turbine extraction, only the bypass valve 17 is opened, and after a certain period of time, when the bypass small valve 17 is fully open, the extraction valve 3 is opened.
is fully opened. As a result of the above operation, the temporal change in the amount of bleed air passing through the bleed air valve 3 and the small bypass valve 17 becomes a gentle straight line as shown in C in the figure.

Now, if we assume that the 40% opening of the bleed valve 3 is the full opening of the small bypass valve 17, then the bleed valve 3 will open as if the bleed valve 3 was opened slowly until it reached its 40% opening. Since the amount of extracted air is below a certain value, an abnormal increase in the pressure inside the feed water heater 5 is prevented.

Next, this embodiment will be explained in more detail.

In the embodiment shown in FIG. 5(a), as the oil amount control means, the opening degree of the bleed valve 3 per hour is adjusted to the valve intermediate opening degree (approximately 3
A control means is adopted which changes the degree stepwise from 0 to 40 (full valve opening degree), and this control means is engaged with the bleed valve 3 of the electric chute.

That is, after the bleed valve 3 starts opening, for example, after rotating the bleed valve 3 by 2% opening of the valve fully open, approximately 25
Hold this state for 2 seconds, then open the opening 2 degrees in the same way, and then hold for 25 seconds. This is repeated to open the bleed valve 3 in a stepwise manner. When the valve opening reaches 30 to 40 degrees, the bleed valve 3 is fully opened. By controlling the valve opening as described above,
When the valve intermediate opening is 30 to 40%, the turbine bleed air amount changes very slowly over time, and the feed water heater 5
A sudden rise in pressure within is prevented. That is, the pressure difference between the drain side and the steam side in the water level detectors 8 to 11 is small, and the water level in the water level detectors 8 and the like does not temporarily rise abnormally. No. 60 shows the results of the confirmation test using a solid line, with time on the horizontal axis and the water level in the water level detector on the vertical axis. As shown by curve d, it was confirmed that the rise in the water level inside the water level detector 8 etc. became extremely small.

The reason why the bleed valve 3 is changed stepwise from 30 to 40% opening is because the bleed valve is a gate valve, and at 30 to 40% opening, the turbine side bleed pressure and the feed water heater side pressure become almost close to each other. This is also because the opening time of the bleed valve 3 is too long if it is opened stepwise to the opening degree of 100 inches. By the above method, the water level in the water level detectors 8 to 11 never reaches the high water level (iWL) or the extra high water level (Hf1WL), and the high water level warning when the bleed valve 3 is open and the air-operated bleed back check It is possible to prevent a problem in which the valve 4 or the bleed valve 3 is closed.

Next, referring to FIG. 7, a control means for automatically opening the bleed valve 3 as shown in FIG. 5(a) will be explained using a block diagram.

The feedwater heaters 5 of the πL-producing plant are generally installed in five to seven stages, and the plant start-up bleed valves 3 are sequentially closed from the low-pressure stage feedwater heater to the high-pressure stage feedwater heater. I'll go. FIG. 7 shows a block diagram of an embodiment of the present invention in which feed water heaters are installed before and after the feed water heater 5, and the opening/closing speed of the bleed valve is 50 seconds. AND circuit 52 of the master start command 50 and the electric bleed valve opening degree 51 of the pre-stage (low-pressure stage) feed water heater or more
The opening operation is started. The bleed valve starts to open in response to the open signal, but the timer 53 activates it. After 1 second, the open signal is wiped out 54, and at the opening degree after 1 second (1150 x 100 = 2 inch opening degree), the timer 55 activates it for 925 seconds. Retained. 26 seconds after the start of the open signal, the timer 53 opens for 91 seconds ((t+
1) 150 x 100 = 4 degrees of opening) The timer 55 holds the opening at 4% for 25 seconds. Opening due to this staircase shape,
When the holding and opening operations are repeated and 520 seconds have elapsed by the timer 56 after the start of the open signal, the bleed valve is opened in a straight line until it is fully open without being held in a stepped manner. Further, when the opening degree of the bleed valve is equal to or greater than the specified opening degree, a command to open the bleed valve of the rear stage (high pressure stage) feed water heater is issued.

Therefore, as shown in Fig. 5, after opening for 1 second (2-inch opening), holding the constant opening for 25 seconds 20 times (520 seconds ÷ 26 seconds - 20 times), opening to 40% (2% opening × 20 times = 40%) to 100 degrees are opened in a straight line. In addition, in the above explanation, the timers 53, 55, and 56 are set to 1 second, 25 seconds, and 5 seconds, respectively.
An example is shown in which the timer is set to 20 seconds, and by changing the set value of the timer, it is possible to change the stepwise opening degree, the holding time, and the degree of opening at which the stepwise opening operation ends. In order to prevent an abnormal rise in the water level in the water level detectors 8 to 11 of the feed water heater 5, the timer 53 is set to 1. to 2 seconds, timer 55 is 20 to 30
It is effective to set the timer 56 to about 400 to 600 seconds.

FIG. 8 shows another embodiment of the present invention, in which, as described above, the bypass small valve 17 is used as the bleed air amount control means.
They are arranged side by side. The small bypass valve 17 has a diameter cross-sectional area of 20 to 40% of that of the bleed valve 3;
If the opening/closing speed of the bleed valve 3 is set to 50 seconds as described above, the opening/closing speed of the small bypass valve 17 is as slow as 200 to 300 seconds.

Therefore, the amount of bleed air passing through the bypass small valve F when fully opened is extremely small, 115 to 215 of the bleed air valve 3. At the beginning of turbine extraction, as shown in Fig. 5(b),
The bleed valve 3 is closed and only the small bypass valve 17 is opened. The small bypass valve 17 is opened little by little and is fully opened after a predetermined period of time has elapsed.

The opening degree converted to the bleed valve 3 when fully open is approximately 40 inches. At this time, the bleed valve 3 is fully opened. As a result of the above, the bleed valve 3
The same effect can be obtained if the curve changes as if it were a straight line C. Incidentally, the slope of 1g1c is almost the same as the step-like change in the embodiment described above, and as in the embodiment described above, it is possible to prevent an abnormal rise in the water level in the water level detector 8 and the like.

FIG. 9 shows yet another embodiment of the invention.

In the figures, the same reference numerals as in FIG. 1 indicate the same parts or the same functions. In this embodiment, the bleed air amount control means is formed by a pressure detector 18, a Lang function unit 19, and a pressure regulator 20.

The pressure detector 18 engages the feed water heater 5 and
detects the pressure inside and sends this signal to the pressure regulator 20.

The ramp function operator 9 calculates the change dp/dt of the pressure P in the feed water heater 5 per unit time, and sends this information to the pressure regulator 20. The pressure regulator 20 engages with a bleed valve 3 having a variable rotation speed transmitter, and according to the value of dp/di,
Adjust the amount of air extracted from the air bleed valve 3. With the bleed air amount control means having the above configuration, the pressure in the feed water heater 5 does not rise suddenly, and an abnormal rise in the water level in the water level detector 8 and the like is prevented, as in the previous embodiment.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, abnormal water level rise in the water level detector of the feed water heater can be reliably prevented,
This effectively prevents the closure of the bleed valve and the formation of a high water level pipe layer.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a conventional general feed water heater system, Figure 2 is an explanatory diagram explaining the abnormal water level rise phenomenon in the water level detector, and Figure 3 is a line showing the conventional bleed valve opening operation. 4 is a diagram showing the water level change in the water level detector based on the opening operation shown in FIG. 3, and FIG. FIG. 5(b) is a diagram showing a method of opening the bleed valve according to another embodiment of the present invention, and FIG.
), FIG. 7 is a block diagram showing a control method for implementing the embodiment shown in FIG. 5(a), and FIG. $Z diagram of the example in case (b)

Claims (1)

[Claims] 1. A feedwater heater water level rise prevention method that prevents an abnormal rise in the water level that occurs in a feedwater heater that heats condensate water supplied to a deaerator or feedwater supplied to a boiler by turbine extraction air. The method is characterized in that a change over time in the amount of extracted air passing through an extraction valve interposed between the feed water heater and the turbine is maintained at a predetermined value or less to prevent an abnormal increase in pressure within the feed water heater. Method for preventing water level rise in feed water heaters. 2. A feedwater heater that heats the condensate supplied to the deaerator or the feedwater supplied to the boiler by turbine bleed air, a bleed valve provided between the feed water heater and the turbine, and a water level in the feed water heater. Changes in a feedwater heater water level rise prevention device that prevents abnormal rises and falls in the water level that occur in the feedwater heater in the feedwater heater system of the turbine, which is comprised of a water level detector that detects and controls the bleed valve. 1. A water level rise prevention device for a feed water heater, characterized in that the water level rise prevention device is provided with a bleed air amount control means for maintaining the amount of bleed air below a predetermined value. 3. The bleed air amount control means rotates and temporarily stops the electric bleed valve so as to change the opening degree of the electric bleed valve in a stepwise manner until the valve reaches an intermediate opening degree. With,
The feed water heater water level rise prevention device according to claim 2, characterized in that the device is a control means that fully opens the bleed valve after the valve is opened halfway. 4. Set the intermediate valve opening to 30 to 40 degrees of the full valve opening, and rotate the bleed valve by 'pL of the full opening per hour until the intermediate valve opening is reached. 4. The feed water heater water level rise prevention device according to claim 3, wherein said state is maintained for a certain period of time each time said rotation is made, and said bleed valve changes stepwise. 5. The bleed air amount control means is formed from a small bypass valve installed in parallel with the bleed valve, and the amount of the bleed air corresponds to a fraction of the amount of bleed air that passes when the bleed valve is fully opened. The small bypass valve is formed so as to be sequentially rotated and fully opened until the bleed valve reaches an intermediate valve opening when the bleed valve is fully opened. A feed water heater water level rise prevention device according to claim 2. 6. The bleed air amount control means includes a pressure detector that detects the steam side pressure in the feed water heater, detects a change in the steam side pressure per unit time, and controls the opening degree of the electrically operated bleed valve. The feed water heater water level rise prevention device according to claim 2, characterized in that it is comprised of a pressure regulator that adjusts the water level of the feed water heater.