JP2006046874A - Drum level control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control system that can appropriately control a drum level in case of sudden load change in a drum boiler. <P>SOLUTION: The control system comprises a drum level gauge for detecting a level in a steam separator drum of a boiler, a steam flowmeter for detecting a steam flow rate flowing out of the steam separator drum, a feedwater flowmeter for detecting a feedwater flow rate supplied to the drum, a feedwater flow control means for adding up a feedwater flow rate necessary to eliminate level deviation between a specified water level and the actual drum level and the steam flow rate detected by the steam flowmeter to produce a feedwater flow rate set point and outputting to a feedwater pump a control command to eliminate feedwater flow rate deviation between the feedwater flow rate set point and the actual feedwater flow rate, and a control means for setting the feedwater flow rate set point higher by a required amount for a required time in case of runback. The control system is further provided with a control means for calculating a drum holding water quantity from a boiler heat input under each load of the boiler and correcting the feedwater flow control command by a change in drum holding water across a load change. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drum level control device for a drum boiler, and more particularly to a drum level control device suitable for appropriately controlling a drum level when a load changes, particularly when a load is suddenly reduced.

  In general, a boiler such as a drum boiler for generating steam in a power plant or the like, as shown in FIG. 2, is pushed into a boiler body 1 in which a brackish water separating drum 2 is disposed at an upper portion, and combustion air is generated by a ventilator 3. Is supplied from the combustion air duct 4 through the wind box 5 and fuel is injected from the burner 6 to be combusted. The generated combustion gas heats the water in the heat transfer pipe of the boiler body 1 to generate steam. I am letting. This steam is taken out from the brackish water separation drum 2 through the superheater 7 and supplied to the turbine 8. On the other hand, the combustion gas deprived of heat is discharged from the chimney 10 to the atmosphere via the flue 9.

  The feed water supplied to the brackish water separation drum 2 in FIG. 2 is supplied by a boiler feed pump 11 via a feed water flow rate adjustment valve 12, and the drum level is kept constant by adjusting the amount of feed water to this drum. The

  This drum level control circuit is shown in FIG. The control circuit shown in FIG. 3 includes a subtractor 22 that calculates a difference between a specified water level 14 of the drum level inside the brackish water separation drum and an actual drum level detected by the drum level transmitter 21, and outputs a drum level deviation. A proportional-integral controller 23 that outputs a feed water flow rate required to eliminate the drum level deviation by proportionally integrating the drum level deviation output from the subtractor 22, and a water supply output from the proportional-integral controller 23 An adder 24 that adds the steam flow detected by the steam flow meter 26 to the flow rate and outputs it as a feed water flow set value, and a feed water flow set value output from the adder 24 and an actual feed water flow meter 25 A subtractor 27 for obtaining a difference between the feed water flow rate and outputting the feed water flow rate deviation, and proportionally integrating the feed water flow rate deviation output from the subtractor 27 to obtain the feed water flow rate deviation. The control command Sutame and a proportional integral controller 31 to be output to the feed water flow control valve 12.

  During the operation of the boiler, the drum level inside the brackish water separation drum is detected by the drum level meter 21, and the steam flow rate introduced into the steam header is detected by the steam flow meter 26, and further supplied to the brackish water separation drum. The actual feed water flow rate is detected by the feed water flow meter 25, and each detected value is input to the drum level controller. The subtractor 22 of the drum level controller defines the drum level inside the brackish water separation drum. The difference between the water level 14 and the actual drum level is obtained, and the drum level deviation is output to the proportional integration controller 23, and the drum level deviation output from the subtractor 22 is proportionally integrated in the proportional integration controller 23. The feed water flow rate for eliminating the drum level deviation is output to the adder 24, and the adder 24 outputs the proportional product. The steam flow rate detected by the steam flow meter 26 is added to the feed water flow rate output from the regulator 23 and is output to the subtractor 27 as a feed water flow rate set value. In the subtracter 27, the output from the adder 24 is output. The difference between the set value of the feed water flow rate and the actual feed water flow rate detected by the feed water flow meter 25 is obtained, and a feed water flow rate deviation is output to the proportional-plus-integral controller 31. The feed water flow rate deviation output from the vessel 27 is proportionally integrated and a control command for eliminating the feed water flow rate deviation is outputted to the feed water flow rate control valve 12 to adjust the amount of water supplied to the brackish water separation drum. The drum level of the brackish water separation drum is maintained at a specified water level.

  In the above control, since the drum level fluctuation is also affected by the balance between the feed water flow rate 25 and the main steam flow rate 26, the feed water flow rate 25 and the main steam flow rate 26 are added by the adder 24 and the subtractor 27 as a preceding signal. That is, if the feed water flow rate 25 increases, it will lead to an increase in the drum level, so the feed water amount will be reduced in advance, and conversely if the main steam flow rate 26 increases, the level will eventually drop, so the feed water will increase in advance. I am letting.

When runback (high-speed load narrowing) occurs, a constant amount of water generated by the signal generator 28 is added by the adder 29 for a certain period of time, and the water supply valve is increased by the proportional-plus-integral controller 31 so that the water amount increases temporarily. Issue the opening command.
JP 2002-39506 A

In the above-mentioned conventional technology, in the boiler high load zone where the boiler heat input is large, the actual amount of water retained in the drum is not considered depending on the boiler heat input, and load changes, runback (high-speed load narrowing), FCB (FAST CUT BACK ) When performing a rapid load reduction, etc., only a certain amount of correction was considered in order to prevent a decrease in drum level. Therefore, when the load at the start of load drop and the ultimate load are different, it is not possible to correct the water supply amount appropriately.
The subject of this invention is providing the drum level control apparatus which can control appropriately the drum level at the time of load change of a drum boiler, especially at the time of sudden load change.

  The present inventor has found that the above problems can be solved by automatically correcting the drum level fluctuation caused by the difference in the void ratio of the water retained in the drum at each boiler load, and has reached the present invention. Is.

The invention claimed in the present application is as follows.
(1) A feed water pump for supplying water to a brackish water separation drum of a boiler, a drum level meter for detecting a drum level of the brackish water separation drum, and a steam flow meter for detecting a steam flow rate flowing out of the brackish water separation drum A feed water flow meter that detects a feed water flow rate that is replenished to the brackish water separation drum, and a feed water flow rate that is necessary to eliminate the drum level deviation between the specified water level and the actual drum level detected by the drum level meter, Add the steam flow rate detected by the steam flow meter to obtain the feed water flow rate set value, and issue a control command to eliminate the feed water flow rate deviation between the feed water flow rate set value and the actual feed water flow rate detected by the feed water flow meter. A boiler comprising a feed water flow rate control means for outputting to the feed water pump and a control means for setting the feed water flow rate set value higher by a required time and a required amount when a runback occurs In the drum level control device, there is provided control means for calculating the amount of water retained in the drum from the boiler heat input at each load of the drum boiler, and correcting the control command for the amount of water supply based on the amount of change in the drum retained water before and after the load change. A drum level control device characterized by that.

(2) When the boiler load fluctuates, the drum level control system is provided with a circuit that compares the drum retained water corresponding to each load with the current retained water amount and corrects the retained water amount deviation (1). ) Drum level control device as described.
(3) The drum level control apparatus according to (1) or (2), in which a feed water lifting command at the time of sudden load change is added to a preceding signal of a feed valve opening command to improve response speed.

  According to the present invention, even if the amount of retained water varies depending on the boiler load, it is possible to always calculate the appropriate retained water and quickly supply the necessary water supply. There is nothing.

  Further, in the prior art, since the feed water flow rate set value was changed and the feed valve opening was corrected after the control deviation (output of the subtractor 27) occurred, the response was slow, but the retained water amount was corrected directly. The response speed of the water supply valve has been improved compared to the conventional method because it is added to the valve opening preceding signal.

  When the load change starts, the change speed of the retained water curve for each load is calculated, and the amount of retained water that is insufficient when the boiler load decreases is calculated. By loading the shortage of retained water into the water supply command, the drum level is controlled to be constant while compensating for the insufficient retained water by feedforward control when the boiler load decreases. Few.

The main body system of the drum boiler in the present invention is as shown in FIG. 2, and its drum level control circuit is shown in FIG.
The drum level is measured by the level transmitter 13 (FIG. 2), a deviation from the drum level set value 14 (FIG. 1) is created by the subtractor 22, and a feed water flow rate command corresponding to the deviation is generated by the proportional integral controller 22. To the water supply valve 12. Since the drum level fluctuation is also affected by the balance between the feed water flow rate 25 and the main steam flow rate 26, the adder 31 and the subtractor 27 add the feed water flow rate signal 25 and the main steam flow rate signal 26 as the preceding signals. In other words, if the feed water flow rate 25 increases, the drum level will eventually rise, so the feed water amount is reduced in advance. Conversely, if the main steam flow rate 26 increases, the level will eventually drop, so the water supply is increased in advance.

  The present invention pays attention to the fact that the amount of water retained in the boiler drum varies depending on the load because the void ratio of the can water varies depending on the boiler heat input, and follows the boiler heat input by the function generator 33 according to the fuel command (FRD) 32. In addition, the amount of retained water in the boiler is calculated, the retained water amount change rate is calculated based on this, and this is added to the water supply command as a water supply bias signal so that the drum level is controlled appropriately. That is, the difference from the conventional drum level control device of FIG. 3 is that a function generator 33 that calculates the amount of water retained in the boiler according to the boiler heat input, and a pulsation prevention LAG that converts the signal of the amount of water retained in the boiler into a stable signal ( Primary delay) and a change rate limiter 35, a differentiator 36 for converting the retained water amount signal into a retained water change rate signal, and a function generator for converting the retained water change rate signal into a valve opening command as a feed water bias signal. 37, and the valve opening command is added to the water supply command integral controller 31 via the switch 29 as a preceding signal. The retained water amount signal obtained by the function generator 33 is converted into a stable signal by the pulsation preventing LAG (first-order lag) 34 and the change rate limiter 35. Here, the LAG 34 also serves as a combustion and heat transfer delay. The change rate limiter 35 limits the signal in accordance with the feed pump capacity. This retained water amount signal is converted into a retained water change speed signal by the differentiator 36, converted into a valve opening command by the function generator 37 as a feed water bias signal, and switched as a preceding signal of the feed water command integral controller 31. It is added to the water supply command via the device 29. During normal operation, the switch 29 is switched to the b side, and 0 [t / h] is output from the switch 29 to the proportional-plus-integral controller 31 as an increase in the feed water flow rate set value. It is also effective to omit the switch 29 and use it as a water supply advance command even during normal operation.

  It is useful as a drum level control device for a drum boiler that generates steam in a thermal power plant or the like.

FIG. 3 is an explanatory diagram of a drum level control circuit according to the present invention. Explanatory drawing which shows the steam system of the boiler in this invention. Explanatory drawing of the control circuit of the drum level by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Boiler body, 2 ... Drum, 3 ... Push-in aerator, 4 ... Combustion air duct, 5 ... Wind box, 6 ... Fuel burner, 7 ... Superheater, 8 ... Turbine, 9 ... Flue, 10 ... Chimney , 11 ... Boiler feed pump, 12 ... Feed water flow control valve, 13 ... Drum level transmitter, 22 ... Subtractor, 23 ... Proportional integral controller, 24 ... Adder, 25 ... Feed water flow, 26 ... Main steam flow, 27 DESCRIPTION OF SYMBOLS ... Subtractor, 31 ... Water supply command integral controller, 33 ... Function generator, 34 ... Pag prevention LAG, 35 ... Change rate limiter, 36 ... Differentiator, 37 ... Function generator.

Claims (3)

A water supply pump for replenishing water to a brackish water separation drum of a boiler, a drum level meter for detecting a drum level of the brackish water separation drum, a steam flow meter for detecting a steam flow rate flowing out of the brackish water separation drum, and A feed water flow meter that detects the feed water flow rate supplied to the brackish water separation drum, a feed water flow rate that is necessary to eliminate the drum level deviation between the specified water level and the actual drum level detected by the drum level meter, and a steam flow meter The feed flow rate set value is obtained by adding the steam flow rate detected by the control flow, and a control command for eliminating the feed water flow rate deviation between the feed water flow rate set value and the actual feed water flow rate detected by the feed water flow meter is supplied to the feed pump. A boiler driver comprising: a feed water flow rate control means for outputting; and a control means for setting the feed water flow rate set value higher by a required time and a required amount when a runback occurs. In the level control device, there is provided control means for calculating the amount of water retained in the drum from the boiler heat input at each load of the drum boiler and correcting the control command for the amount of water supply based on the amount of change in the water retained in the drum before and after the load change. The drum level control apparatus characterized by the above-mentioned. The drum level control system according to claim 1, wherein when the boiler load fluctuates, the drum level control system is provided with a circuit that compares the drum retained water corresponding to each load with the current retained water amount and corrects the retained water amount deviation. Drum level control device. The drum level control apparatus according to claim 1 or 2, wherein a response speed is improved by adding a feed water lifting command at the time of sudden load change to a preceding signal of a feed valve opening command.

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