JPH0565763B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drain tank level control device for a boiler device, which controls the level of a drain tank in a boiler device such as a variable pressure once-through boiler.

[Conventional technology]

In recent years, in order to operate thermal power plants with high efficiency,
Boiler systems are now started and stopped quite frequently. by the way,
When the boiler is started in such an operation, a swelling phenomenon of the boiler furnace fluid occurs, especially in a variable pressure once-through boiler. In other words, in a variable pressure once-through boiler, the boiler pressure is low and the boiler furnace fluid temperature is close to the saturation temperature, so if the boiler is ignited under these conditions at startup to increase the amount of fuel, the amount of steam in the furnace fluid will rapidly increase. It increases and reaches a boiling state, causing the above-mentioned bulging phenomenon. This bulging phenomenon occurs particularly prominently when a burner with a large burner capacity is ignited. In addition, in a conventional constant pressure once-through boiler, even if the burners are ignited sequentially at startup, the boiler furnace is at full pressure (in a supercritical pressure boiler, the boiler pressure is 250 kg/
cm ² g) and the furnace fluid temperature is below the critical temperature, so no swelling phenomenon of the furnace fluid is observed.

In the startup system where the boiler circulation pump circulates the furnace fluid through the furnace, the steam separator, and the drain tank when the boiler is started, if the above-mentioned swelling phenomenon of the furnace fluid occurs, a large amount of steam is generated and the drain tank level (water level ), which causes the level control valve in the drain tank to open wide and release a large amount of furnace fluid in the drain tank to the condenser, which causes the level in the drain tank to drop abnormally, causing the above-mentioned There is not enough fluid to circulate.
In the case of boiler equipment, when such a fluid shortage occurs, the system is such that the boiler circulation pump is stopped and the boiler startup is also stopped. Therefore, when the above-mentioned swelling phenomenon of the furnace fluid occurs, a situation has arisen in which the boiler cannot be started.

[Problem to be solved by the invention]

In order to avoid this situation, conventional methods have been to reduce the boiler circulation flow rate and increase the amount of cold water from the boiler feed water pump accordingly, thereby lowering the furnace fluid temperature to below the saturation temperature prior to the boiler ignition operation and preventing the bulging phenomenon. Measures were taken to do so. However, such measures have the disadvantage of significantly increasing heat losses during start-up. Another method has been to gradually increase the amount of fuel to prevent the bulging phenomenon and reduce level fluctuations, but this method has the disadvantage of requiring an extremely long startup time. Ta.

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned conventional problems and prevent an abnormal drop in the drain tank level when starting a boiler. An object of the present invention is to provide a drain tank level control device for a boiler device that can smoothly start up the boiler.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a drain tank connected to a brackish water separator of a boiler device,
A drain tank level control device for a boiler apparatus comprising a level control valve that adjusts the level of the drain tank and a level control means that adjusts the level control valve according to the level of the drain tank. a bulge prediction means for predicting the bulge of the furnace fluid based on the furnace fluid temperature; and when the bulge prediction means predicts the bulge of the furnace fluid, the control by the level control means is stopped to adjust the level to the level. The present invention is characterized by providing a level drop prevention means for controlling the control valve at a predetermined constant value.

[Effect]

During normal operation of the boiler system, the level of the drain tank is controlled by the level control valve controlled by the level control means. When starting up the boiler equipment, the expansion of the furnace fluid is predicted based on the furnace tube wall temperature and the furnace fluid temperature, and when the expansion of the furnace fluid is predicted, the normal control by the level control means is stopped and the level is adjusted. The valve is controlled at a predetermined constant value.

〔Example〕

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a startup system diagram of a variable pressure once-through boiler according to an embodiment of the present invention. In the diagram, 1 is the boiler furnace, 2
3 is a brackish water separator that separates moisture from the furnace fluid from the furnace tubes constituting the boiler furnace; 3 is the brackish water separator 2;
4 is a turbine driven by the steam from the superheater 3, and 5 is a condenser that condenses the steam used in the turbine 4.

6 is a drain tank into which the water separated by the brackish water separator 2 flows; 7 is a level control valve that adjusts the level of the drain tank 6; 8 is a level control valve that controls the level of the drain tank 6; 6 is a boiler circulation pump for circulating the water, and 9 is a boiler circulation flow control valve. 10 is a water supply pump that supplies water to the boiler furnace 1, and 11 is a high-pressure water supply heater that heats the water supplied by the water supply pump 10. 12 is a furnace tube wall temperature detector for detecting the temperature of the boiler furnace 1; 13 is a furnace fluid temperature detector for detecting the temperature of the fluid from the boiler furnace 1; 14 is a drain tank 6
Drain tank level detector, which detects the level of
15 is a drain tank pressure detector that detects the pressure of the drain tank 6. 16 is a control device that controls the level control valve 7 and the boiler circulation flow rate control valve 9.

The water in the drain tank 6 is circulated by the boiler circulation pump 8 through the boiler circulation flow control valve 9, the boiler furnace 1, and the brackish water separator 2. During this period, the water supplied from the feed water pump 10 is also circulated through the high pressure feed water heater 11. After that, it is made to join the water in the drain tank 6. In the circulation mode in which the boiler circulation pump 8 is operated in this way, the level of the drain tank 6 is controlled by the control device 16.
Control is performed by adjusting the level control valve 7 and boiler circulation flow control valve 9, and when the level of the drain tank 6 rises, the opening degree of the level control valve 7 and the boiler circulation flow control valve 9 is increased to increase the opening of the drain tank. 6 is discharged to the condenser 5 and the water supply from the water supply pump 10 is suppressed. Conversely, if the level is decreasing, the level control valve 7 and the boiler circulation flow rate control valve 9 are throttled and the water is discharged from the water supply pump 10. increase water supply.

FIG. 2 is a system diagram of the control device shown in FIG. 1. In the figure, the same members as those shown in FIG. 2 are designated by the same reference numerals, and the explanation thereof will be omitted. 17 is a multiplier that multiplies the signal of the drain tank level detector 14 and the signal of the drain tank pressure detector 15; 18 is a PI regulator that proportionally and integrally integrates the signal of the multiplier 17; 19 is a signal switch; and 20 is a It is an automatic manual switch. 21
is an analog memory that stores the output signal of the automatic manual switch 20, that is, a signal instructing the opening degree of the level control valve 7. 22 is a subtractor that calculates the difference between the temperatures detected by the furnace tube wall temperature detector 12 and the furnace fluid temperature detector 13; 23 is a subtractor that determines whether the temperature deviation output from the subtractor 22 has reached a predetermined value; This is a signal detector that detects. When the temperature deviation reaches a predetermined value, the signal detector 23 outputs a switching command signal to the signal switch 19. Note that a description of the control system of the boiler circulation flow rate control valve 9 will be omitted.

Next, the operation of this embodiment will be explained with reference to the boiler temperature characteristic diagram shown in FIG. During normal operation of the boiler device, the level of the drain tank 6 detected by the drain tank level detector 14 is multiplied by the pressure detected by the drain tank pressure detector 15 in a multiplier 17, thereby correcting the pressure. This pressure-corrected level signal is sent to a PI controller 18,
The signal is transmitted to the level control valve 7 via the signal switch 19 and the automatic/manual switch 20, and the opening degree of the level control valve 7 is adjusted according to the level signal. In such control during normal operation, analog memory 2
1 always stores the signal transmitted to the level control valve 7. The signal stored in the analog memory 21 is input to the signal switch 19, but in this case, since the signal detector 23 does not output a switching command signal, the signal switch 19 switches between the PI controller 18 and the automatic/manual switch. The switching device 20 is connected, and the analog memory 21 and the automatic manual switching device 20 are released.
Therefore, the signal of the analog memory 21 is cut off by the signal switch 19.

When starting up the boiler system, the above-mentioned swelling phenomenon of the furnace fluid may occur. In response to this swelling phenomenon, the drain tank level detector 14
It is difficult to cope with the above-mentioned control system for the reasons mentioned above. Therefore, in this embodiment, the furnace tube wall temperature detector 12, the furnace fluid temperature detector 13,
A subtracter 22 and a signal detector 23 are provided to cope with the bulging phenomenon. Therefore, first, a means for determining the occurrence of a bulging phenomenon based on the temperature characteristics of the boiler shown in FIG. 3 will be described.

In Figure 3, the horizontal axis represents time, and the vertical axis represents temperature. In the figure, a solid line A indicates the furnace fluid temperature, and a broken line B indicates the furnace tube wall temperature. When the boiler is ignited at time t ₁ , the furnace fluid temperature and furnace tube wall temperature rise, but for a while (approximately 10 to 15 minutes) the furnace fluid temperature remains higher than the furnace tube wall temperature. It is in. At time t ₂ , the temperatures of both become equal,
After that, the furnace tube wall temperature becomes higher. The swelling phenomenon of the furnace fluid is observed just at the timing when the furnace tube wall temperature becomes higher. Therefore, by monitoring the furnace tube wall temperature and furnace fluid temperature, it is possible to determine whether a bulging phenomenon has occurred.

In FIG. 2, a furnace tube wall temperature detector 12 and a furnace fluid temperature detector 13 are provided to determine the occurrence of a bulging phenomenon. Both detectors 1
The detection signals 2 and 13 are input to a subtracter 22, and the deviation between the two is calculated. A signal corresponding to this deviation is input to the signal detector 23, where it is compared with a predetermined value. When the deviation reaches a predetermined value, that is, when it is determined that a bulge phenomenon has occurred, a switching command signal is output from the signal detector 23 to the signal switch 19. As a result, the signal switch 19 is switched, the PI controller 18 and the automatic/manual switch 20 are cut off, and the analog memory 2
1 and an automatic/manual switch 20 are connected. Therefore, regardless of the detected value of the drain tank level detector 14, the level control valve 7 uses the signal stored in the analog memory 21 immediately before switching, that is, the signal before the bulging phenomenon occurs, to determine its opening. controlled. As mentioned above, conventionally, when the bulging phenomenon occurs, the level of the drain tank 6 apparently rises rapidly, and for this reason, there is no control to open the level control valve 7 and discharge the water in the drain tank 6 to the condenser 5. However, in this embodiment, even if a bulging phenomenon occurs, the level control valve 7 is controlled by the pre-bulging signal stored in the analog memory 21. Therefore, the level control valve 7 does not open wide, and an abnormal drop in the drain tank level is prevented.

When the expansion of the furnace fluid is completed, the signal detector 23
The output of the switching command signal from
0, and connect the PI controller 18 and automatic manual switch 20. As a result, the level control of the drain tank becomes the control during normal operation. Note that the end of the expansion of the furnace fluid can be determined by, for example, incorporating a timer in the signal detector 23 and checking that a predetermined time has elapsed.

As described above, in this embodiment, when the deviation between the temperature detected by the furnace tube wall temperature detector and the temperature detected by the furnace fluid temperature detector reaches a predetermined value, the swelling phenomenon of the furnace fluid occurs. The system determines that a bulging phenomenon has occurred and controls the level control valve using the signal stored in the analog memory before the bulging phenomenon occurs, making it possible to prevent an abnormal drop in the drain tank level when starting the boiler. This allows the boiler to be started up smoothly.

[Effects of the Invention] As described above, the present invention predicts the occurrence of a swelling phenomenon of the furnace fluid when starting a boiler, and when it is determined that a swelling phenomenon will occur, stops normal level control. Since the level control valve of the drain tank is controlled at a predetermined value, it is possible to prevent the level of the drain tank from abnormally decreasing when the boiler is started, and thereby the boiler can be started smoothly.

[Brief explanation of the drawing]

FIG. 1 is a startup system diagram of a variable pressure once-through boiler according to an embodiment of the present invention, FIG. 2 is a system diagram of the control device shown in FIG. 1, and FIG. 3 is a temperature characteristic diagram of the boiler. 1...Boiler, 6...Drain tank, 7...Level control valve, 12...Furnace tube wall temperature detection device, 1
3...furnace fluid temperature detection device, 14...drain tank level detector, 15...drain tank pressure detector, 17...multiplier, 18...PI regulator, 1
9... Signal switch, 20... Automatic manual switch, 2
1...Analog memory, 22...Subtractor, 23...
...signal detector.

Claims (1)

[Claims] 1. A drain tank connected to a steam water separator of a boiler device, a level control valve that adjusts the level of the drain tank, and a level control means that adjusts the level control valve according to the level of the drain tank. A drain tank level control device for a boiler device includes a bulge prediction means for predicting the bulge of the furnace fluid based on the furnace tube wall temperature and the furnace fluid temperature, and a bulge prediction means for predicting the bulge of the furnace fluid. A drain tank level control device for a boiler apparatus, characterized in that a drain tank level control device for a boiler device is provided, comprising a level drop prevention device that stops control by the level control device and controls the level control valve at a predetermined constant value when the level control valve is controlled at a predetermined constant value.