JPS63248904A - Control method for main steam bypass valve - Google Patents

Abstract

PURPOSE:To prevent shortening of service life of outlet pipes due to heat stress, by observing outlet temperature of a turbine bypass valve and that of a heater bypass valve respectively, and restricting the opening of each bypass valve when temperature of either of the outlets becomes over the preset value. CONSTITUTION:In controlling a main steam bypass valve set in a bypass pipe, which branches off from a heater or a main steam pipe and is connected to a condenser, at first, deviation if a main steam pressure signal 2 from a main steam pressure preset signal 1 is calculated by a subtracter 3. Next, the first opening of the main steam bypass valve is calculated according to the calculated deviation, and the second opening of the main steam by-pass valve is calculated by a function generator 5, according to the outlet temperature of the main steam bypass valve. The third opening of the main steam bypass valve is set, through calculating the preset opening of the main steam bypass valve under the abnormal condition of a plant. Then, under the abnormal operation, the smaller value of the first and the third opening values is selected by a low signal selector 17, for controlling the opening of the bypass valve.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling a main steam bypass valve of a turbine bypass valve or a superheater bypass valve in a thermal power plant or the like.

[Prior Art] Fig. 2 is a schematic system diagram of a transformer flow boiler for a thermal power photoelectric plant. In the figure, the turbine bypass valve (hereinafter TB
The valve 21 is branched from the main steam pipe 22 so that spray water from a turbine bypass spray control valve (hereinafter referred to as TBI valve) 23 is mixed and collected into a condenser 24 . In addition, a superheater bypass valve (hereinafter referred to as BE valve) 25 is branched at J3 at the inlet of the tertiary superheater 26, and is connected to the superheater bypass spray it! I Ill valve (BEI)
It is mixed with spray water from valve 36 and collected in condenser 24. The TB valve 21 or the 8E valve 25G is used to control the air pressure in the clay oven when starting the boiler.

In addition, 27 is a coal saver, 28 is a furnace, 29 is a steam separator,
30 is a steam cooling 111 box, 31 is a primary superheater, 32 is a primary superheater desuperheater, 33 is a secondary superheater, 34 is a secondary superheater desuperheater, 35 is a secondary superheater spray valve, 37 is a turbine bypass spray water pressure control valve (TBP valve), 38 is a desuperheater,
39 is a primary superheater spray valve.

(1) Figure 3 shows the conventional TB valve 21 or BE valve 25.
FIG. The main steam pressure control by the TB valve 21 or BE valve 25 is based on the main steam pressure set value (MSPD) 1.
and the main steam pressure value (MSP) are input to the subtracter 3, the deviation 7 is calculated here, and this deviation signal and the main steam pressure set value 2 are input.
Accordingly, the gain correction signal created by the function generator 5 is multiplied by the control device 4, and the signal corrected by the regulator 6 is output as the opening command for the TB valve 21 or the BE valve 25.
It will be done.

(2> TBI valve 23 outlet temperature 10 and signal generator (SG
) 12 with a deviation of 1 by the subtracter 11.
3 is corrected by the regulator 14 and output as the turbine bypass spray valve opening command 15. This also applies to the BE valve 25.

[Problems to be Solved by the Invention] In the conventional configuration as described above, if the spray control fails to reach the main steam pressure set value at the TB valve 21 or the BE valve 25, the TB valve 21 or the BE valve If the outlet piping temperature of No. 25 is manually adjusted, the piping design temperature may be exceeded and the life of the pipe may be reduced due to thermal stress. Furthermore, protection interlocks are not considered at all at present.

Therefore, the present invention prevents the outlet temperature of the TB valve or BE valve from exceeding the piping design temperature.
It is an object of the present invention to provide a control method for a main steam bypass valve that can extend the life of the piping after the E valve.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a main steam bypass valve which is provided in the middle of a bypass pipe that branches from the middle of a superheater or a main steam pipe and communicates with a condenser. In the method of controlling the opening degree, find the deviation between the main steam pressure and the set pressure,
The first opening degree of the bypass valve is determined from this deviation, the second opening degree of the bypass valve corresponding to this outlet temperature is determined from the outlet temperature of the bypass valve, and the plan! - Set a third opening degree of the bypass valve that determines a predetermined opening degree of the bypass valve in the event of an abnormality, and control the opening degree of the bypass valve during normal operation, and adjust it to the first opening degree in the event of an abnormality. Said third
The method of controlling the main steam bypass valve is characterized in that the opening degree of the bypass valve is controlled by selecting the smaller one of the opening degree and the opening degree of the bypass valve.

[Function] The present invention uses the output temperature of the TB valve or BE valve measured as described above, and if the monitoring setting temperature of the outlet of the TB valve or BE valve is exceeded, the temperature of the TB valve or BE valve is By limiting the opening degree, the piping can be protected from thermal stress.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. The above conventional example has the following points.

That is, the TB valve 21 or the BE valve 25 (both are the second
Measure the outlet temperature 10 of the figure), and compare it with the output of the regulator 6 using the low signal selector 17 with a signal generated by creating a program based on the outlet temperature of the TB valve 21 or BE valve 25 in the function generator 5. However, the signal is configured to be outputted as a signal TB valve 21 or BE valve opening command signal with a small output signal. Further, the switch A selects the function generator 9 side during normal operation, and selects the I= signal generator 8 side only in the case of PCB, runback, or abnormality. That is, when the spray control of the TB valve 21 or the BE valve 25 is malfunctioning, the opening degree of the BE valve 21 or the BE valve 25 is limited to protect the outlet line of the TB valve 21 or the BE valve 25 from piping thermal stress. Other than the points mentioned above, this is the same as the conventional technology described above.

As mentioned above, the bypass pipe (22 in Figure 2) branches off from the middle of the superheater or main steam pipe and communicates with the condenser.
In the method of controlling the opening degree of the main steam bypass valve 21 or 25 provided in the middle of 1, and from the outlet temperature 1o of the bypass valve 21 or 25, the second opening degree of the bypass valve corresponding to this outlet temperature is determined from the function generator 9. A third opening of the bypass valve 21 or 25 is set to determine a predetermined opening of the bypass valve 21 or 25, and during normal operation, the opening of the bypass valve 21 or 25 is controlled, and during an abnormality, the first opening and the opening of the bypass valve 25 are controlled. The opening degree of the bypass valve 21 or 25 is controlled by selecting the smaller one of the third opening degree by the low signal selector 17. TB valve or BE measured in this way
If the outlet temperature of the valve exceeds the monitoring set temperature of the outlet of the TB valve or BE valve,
By limiting the opening degree of the valve, the piping can be protected from thermal stress, and as a result, the outlet temperature of the TB valve 21 or BE valve 25 will not exceed the piping design temperature. It becomes possible to extend the life of the piping downstream of the valve 25.

[Effects of the Invention] According to the present invention described above, the outlet temperature of the TB valve or BE valve does not exceed the piping design temperature, and the TB
A method of controlling a main steam bypass valve can be provided that can extend the life of the valve or piping after the BE valve.

[Brief explanation of drawings]

FIG. 1 shows a main steam bypass for explaining the present invention. FIG. 2 is a schematic diagram of a conventional once-through boiler, and FIG. 3 is a diagram of a conventional main steam bypass valve control system. DESCRIPTION OF SYMBOLS 1... Main steam pressure setting signal, 2... Main steam pressure signal, 3... Subtractor, 4... Multiplier, 5... Function generator, 6... Regulator, 8... ...Signal generator, 9...Function generator, 10...TB valve or BE valve outlet temperature, 1
7...Low signal selector.

Claims (1)

[Claims] A method of controlling the opening degree of a main steam bypass valve installed in the middle of a bypass pipe that branches off from the middle of the superheater or the main steam pipe and communicates with the condenser, to detect the deviation between the main steam pressure and the set pressure. and from this deviation, the first
A second opening degree of the bypass valve corresponding to this outlet temperature is determined from the outlet temperature of the bypass valve, and a second opening degree of the bypass valve is determined to determine a predetermined opening degree of the bypass valve in the event of an abnormality in the plant. During normal operation, the opening degree of the bypass valve is controlled, and when an abnormality occurs, the opening degree of the first bypass valve is set.
A method for controlling a main steam bypass valve, characterized in that the opening degree of the bypass valve is controlled by selecting the smaller of the opening degree and the third opening degree.