JPS6045322B2 - Boiler feed water heater water level control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a water level control device for a wheeler feed water heater, and more particularly to a water level control device that can stably control a drain level.

Boiler feed water heaters that heat boiler feed water using air steam from the turbine usually have multiple drain discharge systems and control level control valves according to the drain level and pressure in the heater. The condensate is then discharged to a deaerator or low-pressure water heater.

However, in such boiler feed water heaters, when the load suddenly drops, the pressure inside the boiler drops rapidly, but the temperature of the drain drops slowly. There is a risk of brushing (re-steaming) of the condensate on the inlet side of the drain. When this brushing begins, the drain expands its volume by about 106 times, so the capacity of the level control valve becomes insufficient, making it impossible to drain through it.Also, during this brushing, the drain flow is intermittent. Therefore, in normal feedback control, severe interference occurs between the brushing and the feedback signal, and the hunting phenomenon causes the drain level to fluctuate greatly between the upper and lower limits. The present invention has been made in order to eliminate the above-mentioned disadvantages in conventional devices, and detects and calculates j when the load decreases to predict the occurrence of brushing, and based on this predicted signal, controls the drain discharge system. The present invention aims to provide a water level control device for a boiler feed water heater that can stably control the drain level by switching the control gain of the controller.

H The present invention will be described in detail below with reference to embodiments shown in the drawings. In Fig. 1, high-temperature steam discharged from the turbine 1 is introduced into the feed water heater 2, where it is heated by indirect heat exchange with the boiler feed water sent by the boiler feed water pump 3, and the steam itself is cooled. The water is converted into drain and stored in the drain reservoir in the feed water heater 2.

This drain further performs heat exchange with the feed water, and the feed water heater 2
is overcooled to below the saturation temperature for the internal pressure. Further, the heated boiler feed water is sent toward the boiler 4. When the internal pressure of the feed water heater 2 is high, the condensate is discharged through the level control valve 5 to the deaerator 6 set at a high position, and when the internal pressure decreases, the condensate is discharged through the level control valve 7. It is discharged to the low pressure water heater 8.

In these cases, the drain level in the feed water heater 2 is detected by a drain level detector 9, and the drain level is detected by a level controller 10, 1 that selectively operates depending on the level of internal pressure.
The water is discharged to a deaerator 6 or a low-pressure water heater 8 through level control valves 5 and 7 whose opening and closing are controlled by 1, and the drain level in the container is controlled within a predetermined range. In the above, when the load decreases, the internal pressure of the heating water supply device 2 immediately decreases as the load decreases, but since the response of the drain temperature is slow, the saturation pressure and the internal pressure for a drain temperature of 1 are close to each other. shows a tendency to

In this case, especially since the level control valve 5 is installed at a higher position than the feed water heater 2, and the inlet pressure is lower by the head difference between them, there is a possibility that the drain may cause brushing at the inlet of the level control valve 5. There is sex. In the present invention, the brushing predictor 12 and the gain switch 13
If the possibility of brushing occurring increases due to the use of
is switched to reduce the control gain of the level control valve 5 to prevent brushing and to prevent extreme output fluctuations due to feedback interference.

FIG. 2 illustrates a specific circuit configuration of the brushing predictor 12, etc. After the load signal has a load drop rate calculated in the incomplete differentiator 14, it is guided to the load drop discriminator 15, and the load signal is guided to the load drop discriminator 15. It is determined whether brushing occurs under the load drop rate, drain temperature, and drain pressure.

In the normal state, that is, when the occurrence of brushing is not predicted, the control gain switch 13 is switched to the control gain setter 16 in the normal state, and the deviation value between the level setter 18 and the level signal is calculated by the control deviation calculator 19. After being output, it is calculated by the PI calculator 20 under the normal control gain, and the opening/closing control of the control valve 5 is performed via the A (automatic)/M (manual) switching operator 21. On the other hand, if the load drop discriminator 15 predicts that brushing will occur, the control gain switch 13 is switched to the control gain setter 17 in the brushing state, and a very small control gain is set to the PI calculator. Enter 20. As a result, the occurrence of brushing is suppressed, the fluctuation in the output of the PI calculator 20 is reduced, and the operation of the level control valve 5 is slowed down.
Severe interference between brushing and feedback is prevented. As described above, according to the present invention, the occurrence of brushing is predicted based on changes in load, and if necessary, the control gain of the level controller 20 is reduced to operate the level control valve. The occurrence of brushing is suppressed, and even if brushing occurs, interference with feedback is prevented, so the drain level in the feed water heater 2 does not fluctuate significantly between the upper and lower limits.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one embodiment of the apparatus of the present invention, and FIG. 2 is a block diagram illustrating the main parts of a control circuit used in the apparatus of the present invention. 2... Boiler feed water heater, 3... Boiler feed water pump, 5, 7... Lebel control valve, 9...
◆・Drain level detector, 10, 11... Lebel controller, 14... Imperfect differentiator, 15...
Load drop discriminator, 16, 17... Control gain setter, 18... Lebel setter, 19... Control deviation calculator, 20... PI calculator, 21・・
・A/M switching operation device.

Claims (1)

[Claims] 1. A water level control device that uses a level controller to control a level control valve provided in a drain drainage system of a boiler feed water heater that heats boiler feed water with extracted steam from a turbine,
A water level control device for a boiler feedwater heater, comprising: a brushing predictor that predicts the occurrence of brushing based on load fluctuation; and a gain switch that switches the level control valve gain based on the output of the predictor. . 2. The water level control device for a boiler feed water heater according to claim 1, wherein the brushing predictor comprises an incomplete differentiator and a load drop determination. 3 The level controller is a level setter, a control deviation calculator, etc.
A water level control device for a boiler feedwater heater according to claim 1 or 2, comprising a PI calculator and an A/H switching operation device. 4. Any one of claims 1 to 4, in which the brushing predictor and the gain switch are attached only to a level controller that controls higher-level level control valves of a plurality of drain discharge systems. A water level control device for a boiler feedwater heater described in .