JPS6356701A - Boiler steam temperature advance control device - Google Patents

Abstract

PURPOSE:To improve steam temperature control characteristics of a boiler by generating an advance signal only in the beginning of load variation based on an output command when the load on a control system varies. CONSTITUTION:A command signal with a waveform in a figure (a) is differentiated by a differentiator 18 to have a waveform in a figure (b), and further differentiated by a differentiator 19 to have a signal waveform in a figure (c). This signal is applied to a limiter 19 which limits the upper and lower limits; and the upper limit is limited to a +alpha value and the lower limit is limited above zero. This limited signal is supplied to a variation rate limiter 20 and the variation rate is limited to obtain a signal waveform shown in a figure (d). This signal waveform is applied as an advance signal 16 to an adder 15. Consequently, the advance signal 16 is generated only in the beginning of the load variation, so a control valve 9 is not opened too much and the steam temperature on the entrance side of a turbine 4 is controlled to proper temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steam temperature advance control device for a boiler that can give a advance signal only at the beginning of a load change.

[Prior Art] Conventionally, advance control signals have been used to improve controllability for control systems with large time constants.

As an example of a control system with a large time constant, the control system of a transformer boiler is explained using Fig. 5. In the figure, 1 is a boiler, 2 and 3 are superheaters that superheat the steam generated in boiler 1, and 4 is a superheater that is rotated by steam. 6 is a water supply pump that supplies water between the boiler 1 and the superheaters 2 and 3; 7 is a control valve for controlling the flow rate of fuel supplied to the burner 8; 9 is the superheater 2; .3 A control valve that controls the water supply flow rate between
10 is an adder that adds the control signal 11 and the preceding signal 12 and outputs a command signal to the control valve 7; 13 is the steam downstream of the superheater 3; a temperature detector that detects 3 degrees; and 14; detects 8 degrees. a gain setting device 15 that multiplies the signal from the device 13 by gain C;
is an adder that adds the signal from the gain setter 14 and the preceding signal (6) and supplies it to the control valve 9.

In the above-mentioned transformer pressure boiler, a preceding signal 12.18 is given to an adder 10.15 which gives a command to the control valves 7 and 9, and the flow rate of fuel to the burner 8 and the flow rate of water supplied between the superheaters 2 and 3 are controlled. ing.

The circuit that generates the preceding signal 12.18 mentioned above will be explained with reference to FIG. 3. In the figure, 17 is an output command, 18 is a differentiator,
Reference numeral 19 denotes a limiter 120 which is a rate-of-change limiter, in which the output command 17 is differentiated by a differentiator 18, and the signal obtained by the differentiation has its upper limit limited by the limiter 19 and is then applied to the rate-of-change limiter 20. , the signal whose rate of change is limited by the rate of change limiter 20 is output as the preceding signal 12 or 16 while the load is changing. In this case, the output command 17 is given to the differentiator 18 with a waveform as shown in FIG.
The preceding signal 12 or 16 is outputted from the rate of change limiter 20 with a waveform as shown in FIG. 4(b).

[Problems to be Solved by the Invention] However, especially in the steam temperature control system of a variable pressure boiler, if a preceding signal is applied while the load is changing, the steam temperature at the turbine inlet will drop too much, and the steam temperature of the variable pressure boiler will decrease too much. Depending on the characteristics of the process other than the control system, various troubles may occur if a preceding signal is applied while the load is changing.

The present invention has been made in view of the above-mentioned circumstances, and is aimed at solving the above-mentioned problems by generating a preceding signal only at the beginning of a load change.

[Means for Solving the Problems] The present invention provides an advance control device that performs control by giving a advance signal to the control system when the load of the control system changes, which includes a differentiator that differentiates the output command twice, and a differentiator that differentiates the output command twice. The control system includes a limiter that extracts a signal of a predetermined magnitude from a signal given by the limiter, and a rate-of-change limiter that limits the rate of change of the signal given from the limiter and outputs it to the control system.

[Function] When the load of the control system changes, a preceding signal is generated only at the beginning of the load change based on the output command and is given to the control system.
Boiler steam temperature controllability is improved.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention, which includes a differentiator 18 and a limiter.
Another differentiator 21 is inserted between the differentiator 19 and the other differentiator 21, which is otherwise the same as that shown in FIG.

The output command 17 applied to the differentiator 18 with a waveform as shown in FIG. 2(A) is differentiated into a waveform as shown in FIG. Jin 1>
The waveform becomes as shown in , and the upper limit is + with limiter -19.
α or less, and the lower limit value is limited to 0 or more, which is applied to the rate of change limiter 20.The rate of change is limited by the rate of change limiter 20, and the leading signal IB of the waveform shown in FIG. It is output and added to adder 15 in FIG.

The preceding signal 16 with the waveform shown in Figure 2) does not occur continuously throughout the load change, but occurs only at the beginning of the load change. The advance signal 16 is applied so that the control valve 9 does not open too much, so that the steam temperature on the inlet side of the turbine 4 is easily controlled to the appropriate temperature.

In the embodiments of the present invention, the case where the advance control device is applied to a variable voltage boiler has been described, but the present invention can be applied not only to variable voltage boilers but also to control systems with large time constants, and does not depart from the gist of the present invention. Of course, various changes can be made within the scope.

[Effects of the Invention] According to the boiler steam temperature advance control device of the present invention, the advance signal is required to be Z only at the beginning of a load change, and control can be performed easily and reliably when the advance signal is not required thereafter.
The effect of improving controllability of boiler steam temperature can be achieved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of an embodiment of the boiler steam; , Figure 2 (b) is an explanatory diagram of the waveform of the signal when the output command in Figure 2 (a) is differentiated, and Figure 2 Q\) is the signal when the signal in Figure 2 < D) is differentiated. Figure 2) is an explanatory diagram of the waveform of 0
) is an explanatory diagram of the waveform of the signal obtained by passing the signal through a rate-of-change limiter, Fig. 3 is an explanatory diagram of an example of a conventional boiler steam temperature advance control device, and Fig. 4 (a) is an explanatory diagram of the waveform of the signal obtained by passing the signal of An explanatory diagram of the waveform of the output command applied to the leading side gJ device, Fig. 4 (b)
is an explanatory diagram of the waveform of a signal obtained by differentiating the output command in FIG. 4(a) and passing through a rate-of-change limiter, and FIG. 5 is a general explanatory diagram of a control system for a transformer boiler. In the figure, 1 is a boiler, 4 is a turbine, 10 is an adder, 11 is a control signal, 12 is a preceding signal, 13 is a temperature detector, 15 is an adder, 16 is a preceding signal, 17 is an output command, 18 is a differentiator , 19 is a limiter, 120 is a rate of change limiter, and 21 is a differentiator.

Claims (1)

[Claims] 1) In the advance control device that performs control by giving a advance signal to the control system when the load of the control system changes, there is a differentiator that differentiates the output command twice, and a signal of a predetermined magnitude from the differentiated signal. 1. A steam temperature advance control device for a boiler, comprising: a limiter for extracting a signal; and a rate-of-change limiter for limiting a rate of change of a signal given from the limiter and outputting the same to the control system.