JPH07158812A - Controlling method for boiler and control device for boiler - Google Patents

Abstract

PURPOSE:To enable a low pressure steam drum to keep its stable level even if a high pressure steam drum of a boiler shows a reduced level. CONSTITUTION:There are provided a high pressure steam drum and a low pressure steam drum, wherein boiler water in the low pressure drum is removed and fed to the high pressure drum and then water is supplied to the low pressure drum through a low pressure feedwater adjusting valve 2. A signal of a boiler water level transmitter 11 of the low pressure drum and a signal of a level setting device 12 are compared with each other by a comparator 13 so as to get a first signal. A signal of a steam flow rate transmitter 16 taken out of the low pressure drum and a signal from a feedwater flow rate transmitter 17 outputted through both high and low pressure drums are added by an adding device 18, this value and a signal of the feedwater flow rate transmitter 15 for the low pressure drum are compared to each other by a subtractor 13 so as to get a second signal. The low pressure feedwater adjusting valve 2 is controlled in response to a signal in which this signal and the first signal are added by an adder 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a high-pressure boiler having a high-pressure steam drum and a low-pressure drum having a low-pressure steam drum. With regard to the boiler type of supply type, especially when the water level of the high pressure steam drum drops sharply,
The present invention relates to a boiler control method and a control device for preventing the level of the low-pressure steam drum from dropping sharply and falling below a specified value when the amount of canned water discharged from the low-pressure steam drum to the high-pressure boiler suddenly increases.

[0002]

2. Description of the Related Art FIG. 4 shows a water supply system and a steam system of a boiler apparatus provided with a high and low pressure boiler for supplying water to a high pressure boiler by extracting canned water from a low pressure steam drum of a low pressure boiler. The control system diagram is shown in FIG. In FIG. 4, the condensate from the turbine condenser is supplied by the condensate pump 1 to the low-pressure boiler.
The flow rate is adjusted by the low pressure steam drum 4 through the low pressure economizer 3.
Is supplied to the low pressure steam turbine through the low pressure main steam pipe 9. On the other hand, the canned water in the low-pressure steam drum 4 is supplied to the high-pressure steam drum 8 through the high-pressure feed pump 5, the flow rate of which is adjusted by the high-pressure feed water control valve 6, the high-pressure economizer 7, and the steam generated here is the high-pressure main steam. Tube 10
Through the high pressure steam turbine.

The control of the boiler device will be described with reference to FIG. The low-pressure feed water flow rate is controlled by each of the single element and the three elements. Single-element control is performed until low-pressure steam is generated at plant startup, and then three-element control is performed when low-pressure steam is generated, and the switching of each control is performed by the signal switcher 19. First, in the single element control, the actual level signal from the low pressure drum level transmitter 11 and the level setter 12
The level setting value given in step 2 is compared by the subtractor 13, and the proportional-integrator 14 performs a proportional-integral operation signal. The low-pressure feed water control valve 2 is controlled by this signal value. Next, in the case of the three-element control, the respective flow rate signals from the low pressure main steam flow rate transmitter 16 and the high pressure feed water flow rate transmitter 17 are added by an adder 18 to obtain a feed water flow rate signal extracted from the low pressure steam drum. This signal and the low pressure feed water flow rate signal from the low pressure feed water flow transmitter 15, that is, the feed water flow rate supplied to the low pressure steam drum are compared by the subtractor 13, and this signal and the output signal of the proportional integrator 14 described above are added. Then, the low-pressure feed water control valve 2 is controlled by the signal proportionally integrated by the proportional integrator 21.

[0004]

In the above-mentioned prior art, when the high-pressure steam drum level is drastically lowered, a large amount of tap water of the low-pressure steam drum is discharged to the high-pressure steam drum side by the high-pressure feed water control valve, so that the low-pressure steam drum is discharged. Although the level drops sharply and the low-pressure feed water flow rate increases to compensate for it, there was an unavoidable problem that the low-pressure steam drum level fell below the specified value in time. An object of the present invention is to solve the above-mentioned problems of the prior art, and to control a boiler capable of ensuring a stable level without being affected by the low-pressure steam drum level even if the high-pressure steam drum level is lowered. It is to provide a control device.

[0005]

In order to achieve the above object, the invention claimed in the present application is as follows. (1) Having a high-pressure steam drum (hereinafter referred to as a high-pressure drum) and a low-pressure steam drum (hereinafter referred to as a low-pressure drum), extracting can water from the low-pressure drum to supply the high-pressure drum with water, and through a low-pressure water supply control valve. In the method of controlling the boiler that supplies water to the low-pressure drum, the first signal is calculated by comparing the measured value of the can water level of the low-pressure drum with the set value, and this signal is used until steam is generated in the low-pressure drum at startup. After controlling the low-pressure feed water control valve and generating steam in the low-pressure drum,
A second signal is calculated by comparing the added value of the steam flow rate signal taken out from the low pressure drum and the feed water flow rate signal extracted from the low pressure drum to the high pressure drum with the feed water flow rate signal to the low pressure drum. The low-pressure feed water control valve is controlled by a control signal based on the first signal, and when the feed water flow rate signal extracted from the low-pressure drum to the high-pressure drum is equal to or less than a predetermined value, the signal for controlling the low-pressure feed water control valve is A boiler control method, characterized in that adjustment is made so as not to fall below a predetermined minimum flow opening signal. (2) A high-pressure drum, a low-pressure drum, a means for supplying canned water from the low-pressure drum to the high-pressure drum, and a low-pressure water supply control valve for controlling the amount of water supplied to the low-pressure drum. The means for generating the first signal by comparing the measured value with the set value is compared with the sum of the flow rate of steam taken out from the low pressure drum and the amount of water supplied from the low pressure drum to the high pressure drum and the amount of water supplied to the low pressure drum. In the controller of the boiler provided with means for generating a second signal, and means for controlling the low-pressure feed water control valve based on the first signal and the second signal, in the low-pressure drum to the high-pressure drum, Means for generating a minimum flow opening signal of the low pressure feed water control valve when the feed water flow rate is below a predetermined value, and a low signal limiter for preventing the control signal of the low pressure feed water control valve from falling below this minimum flow opening signal. And Controller of the boiler, characterized in that digit.

[0006]

[Operation] Even when the flow rate of the high-pressure feed water is low, the low-pressure feed water control valve is not narrowed down to the fully closed position and is limited by the minimum flow opening, and the low-pressure steam drum is supplied with the feed water above the specified amount. Therefore, the high-pressure drum level drops sharply, and even if the high-pressure feed water flow rate supplied from the low-pressure steam drum to the high-pressure steam drum transiently increases rapidly, the low-pressure steam drum level does not drop below the specified value.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Since the same reference numerals as those in FIG. 2 perform the same operations, the description thereof will be omitted. A high-pressure feed water flow rate signal from the high-pressure feed water flow rate transmitter 17 is input to generate a minimum flow opening signal 24 given to the low-pressure feed water control valve 2 by a function generator 22, and this signal is sent to a low signal via a signal switch 23. Input to the limiter 20. On the other hand, the valve opening signals from the proportional integrators 21 and 14 are respectively input to the low signal limiter 20, and the output signal of 20 is restricted so as not to be less than the minimum flow opening signal. Therefore, even if the high-pressure feed water flow rate is low, the low-pressure feed water control valve 2 supplies the low-pressure steam drum with feed water of a specified value or more. The signal switch 23 selects the minimum flow opening signal side only when the high-pressure feed water flow rate is low, and does not limit it when the high-flow rate is high. This is because when the flow rate is high, the opening degree of the low-pressure feed water control valve is high and is equal to or larger than the minimum flow opening degree, so that it is not necessary to limit it. Also, no limitation is imposed when the low-pressure steam drum level is higher than the specified value. This is to prevent the low-pressure steam drum from having sufficient water in that state and to prevent the low-pressure steam drum level from rising too high to reach a dangerous water level.

FIG. 3 shows the result when the present invention is applied.
Shown in. When the steam is rapidly taken out from the high-pressure steam drum when the plant is started, and the steam pressure in the drum sharply decreases, steam is rapidly generated from the saturated water in the can water in the drum,
When the apparent water level in the drum rises, the high-pressure feed water flow rate is narrowed down to a low flow rate, and the low-pressure feed water flow rate also becomes a low flow rate. When the pressure drops sharply, the high-pressure feed water flow rate transiently increases rapidly, and as a result, the low-pressure steam drum level also drops sharply. However, according to the present invention, since the low-pressure feed water control valve has the minimum flow opening degree, it is possible to prevent excessive narrowing of the low-pressure feed water flow rate as shown by the dotted line.
It is possible to prevent the low-pressure steam drum level from falling below the specified value.

[0009]

According to the present invention, it is possible to prevent a decrease in the water level of the low-pressure steam drum beyond the specified value due to a rapid change in the high-pressure feed water flow rate to the high-pressure steam drum, and to ensure safe operation of the boiler.

[Brief description of drawings]

FIG. 1 is a control system diagram showing an embodiment of the present invention.

FIG. 2 is a control system diagram of a conventional technique.

FIG. 3 is a diagram showing an effect of the present invention.

FIG. 4 is a water supply and steam system diagram of a boiler to which the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Condensate pump, 2 ... Low pressure water supply control valve, 3 ... Low pressure economizer, 4 ... Low pressure steam drum, 5 ... High pressure water supply pump, 6 ... High pressure water supply control valve, 7 ... High pressure economizer, 8 ... High pressure steam drum,
9 ... Low pressure main steam pipe, 10 ... High pressure main steam pipe, 11 ... Low pressure drum level transmitter, 12 ... Low pressure drum level setting device, 1
3 ... Subtractor, 14 ... Proportional integrator, 15 ... Low pressure feed water flow transmitter, 16 ... Low pressure main steam flow transmitter, 17 ... High pressure feed water flow transmitter, 18 ... Adder, 19 ... Signal switcher, 20 ... Low Signal limiter, 21 ... Proportional integrator, 22 ... Function generator, 2
3 ... Signal switch, 24 ... Minimum flow opening signal.

Claims (2)

[Claims] 1. A method for controlling a boiler having a high-pressure steam drum and a low-pressure steam drum, extracting canned water from the low-pressure steam drum to supply the high-pressure steam drum with water, and supplying water to the low-pressure steam drum via a low-pressure water supply control valve. In the above, the first signal is calculated by comparing the measured value of the can water level of the low-pressure steam drum with the set value, and the low-pressure feed water control valve is controlled by this signal until steam is generated in the low-pressure steam drum at startup. After the steam is generated in the low-pressure steam drum, the sum of the steam flow rate signal taken out from the low-pressure steam drum and the feed water flow rate signal taken out from the low-pressure steam drum to the high-pressure steam drum, and the feed water flow rate signal to the low-pressure steam drum And a second signal is calculated, the low-pressure feed water control valve is controlled by a control signal based on this signal and the first signal, and the high-pressure steam is discharged from the low-pressure steam drum. When the feed water flow rate signal withdrawn to the air drum is below a predetermined value, the signal for controlling the low-pressure feed water control valve is adjusted so as not to fall below a predetermined minimum flow opening signal, and a boiler control method is characterized. . 2. A high-pressure steam drum, a low-pressure steam drum,
The low-pressure steam drum has means for supplying can water to the high-pressure steam drum and a low-pressure water supply control valve for controlling the amount of water supplied to the low-pressure steam drum, and the can water level measurement value and set value of the low-pressure steam drum are set. In comparison, the means for generating the first signal is compared with the sum of the flow rate of steam extracted from the low-pressure steam drum and the amount of water supplied from the low-pressure steam drum to the high-pressure steam drum, and the amount of water supplied to the low-pressure steam drum. In a boiler control device comprising means for generating a second signal and means for controlling the low-pressure feed water control valve based on the first signal and the second signal, from the low-pressure steam drum to the high-pressure steam drum. A means for generating a minimum flow opening signal of the low pressure feed water control valve when the water supply flow rate to be extracted is equal to or less than a predetermined value, and a control signal of the low pressure water feed control valve should not fall below this minimum flow opening signal. By providing a low signal limiter controller of the boiler, characterized in that.