JPS61226505A - Method for operating steam turbine - Google Patents

Abstract

PURPOSE:To prevent efficiency drop and generation of erosion by restraining generation of water drops through such processes of obtaining moisture degree of steam at low pressure stage inlet of a steam turbine and supplying overheat steam to the low pressure stage inlet when the degree is larger than the set value. CONSTITUTION:A duct for supplying main steam to the low pressure stage inlet of a steam turbine 4 from the lower course in relation to the main steam stop valve 2 of the main steam supplying system of a turbine through a mixed pressure steam regulating valve 8 and a reducing valve 9 is provided. And pressure and temperature of a calorie meter 10 provided at the final stage inlet are input in a computer 11 to obtain moisture degree of the steam at the low pressure stage inlet due to load fluctuation, and the mixed pressure steam regulating valve 8 is controlled by output corresponding to the difference thereof from the objective moisture degree so as to regulate the mixed pressure steam amount. When actual moisture degree is larger than the objective value, the valve 8 is opened to supply overheat steam so as to reduce moisture degree.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of operating a steam turbine, and particularly to a method of operating a steam turbine in which the humidity of the low pressure stage is high.

[Technical background of the invention and its problems] In general, industrial small and medium-sized turbines have a rotation speed of 5000
For high speed turbines, often above rpm, the humidity of the low pressure stage has a significant impact on turbine efficiency and reliability. Particularly recently, from the standpoint of energy conservation, there has been a trend to use exhaust steam from backpressure turbines used in factories to drive condensing turbines in order to recover its energy. In such condensing turbines, the thermal conditions of the main steam are low, resulting in high humidity in the low pressure stage.

Figure 6 shows an example of general small to medium sized high speed steam turbine equipment. In the figure, steam generated in a boiler 1 passes through a main steam stop valve 2 and a steam control valve 3, is led to a turbine 4, does work there, and is condensed in a condenser 5 to become water. turbine 4
The work generated by this is transmitted to the generator 7 via the reducer 6 to generate electricity. In some cases, the boiler 1 is not installed and the exhaust steam of an existing back pressure turbine (not shown) is used as the main steam. Further, a method is often adopted in which the turbine 4 and the generator 7 are directly coupled without using the reducer 6.

The i-8 diagram in FIG. 7 shows the expansion line of such small and medium-sized high-speed steam turbine equipment. In the figure, reference numeral 20 indicates a main steam pressure line, reference numeral 21 indicates an exhaust pressure line, and reference numeral 22 indicates an expansion line of the steam turbine. Expansion line 22 crosses saturated steam line 23, indicating that the low pressure stage is in the wet region.

Water droplets are generated within the steam that has become a humid region in the low-pressure stage. The water droplets impinge on the turbine blade rows, causing a braking effect that reduces turbine efficiency, as well as erosion of the turbine blades, known as drain erosion, reducing turbine reliability.

[Object of the Invention] The present invention has been made in view of the above circumstances, and provides a steam turbine that can effectively prevent a decrease in efficiency and the occurrence of drain erosion by reducing the humidity of the low-pressure stage. The purpose is to provide a driving method for .

[Summary of the Invention 1 That is, the present invention measures the pressure in the low-pressure stage of a steam turbine, determines the enthalpy of saturated steam and the enthalpy of saturated water at the pressure, and measures the pressure of a calorimeter connected to the low-pressure stage. The enthalpy of steam in the low-pressure stage population is determined based on the pressure and concentration, and then the wetness of steam in the low-pressure stage population is determined based on the respective enthalpy values, and this wetness value is set in advance. When the pressure is greater than 1flI, open the mixed pressure steam control valve inserted in the piping that leads superheated steam to the low pressure stage population, and when the pressure is smaller than 1flI,
The method of operating a steam turbine is characterized in that the mixed pressure steam control valve is closed.

[Embodiments of the Invention] Details of the method of the present invention will be explained below with reference to FIGS. 1 to 5. Note that in FIGS. 1 and 2, the same parts as in FIGS. 6 and 7 are given the same reference numerals.

FIG. 1 shows the steam turbine equipment used in the method of the present invention, in which most of the main steam that has passed through the main steam stop valve 2 is guided through the main steam control valve 3 to the first stage of the turbine.

On the other hand, some main steam passes through the mixed pressure steam control valve 8 and the pressure reducing valve 9.
into the low pressure stage of the turbine 4. Changes in humidity due to load fluctuations are determined by inputting the pressure and concentration of the calorimeter 10 installed in the final stage population into the computer 11, and the mixed pressure steam regulating valve 8 is controlled by an output according to the difference from the target humidity. and adjust the amount of mixed pressure steam.

The computer 11 must include an arithmetic unit as shown in FIG. That is, the final stage inlet pressure 1
2.Calculator 1 calculates the pressure 13 and concentration 14 in the calorimeter.
5 and the target humidity 17 are input to the subtractor 18, the obtained difference signal is input to the calculator 19, and the output signal obtained thereby is used to calculate the mixed pressure steam. Controls the regulating valve 8.

This control process is shown in a flowchart as shown in FIG. That is, first, the final stage inlet pressure is measured at the same time as the measurement starts, and the enthalpy of saturated steam h I+ and the enthal of saturated water and h' at that pressure are calculated from the amount of steam in the calculator.

At the same time, the pressure inside the calorimeter 10 was measured.
The enthalpy h in the calorimeter 10 is calculated from the concentration. Enthalpy h 1h ′, h calculated in this way
'', calculate the humidity at the final stage inlet using the following formula.

h -h' - h -h' Next, the target humidity setting value Yo is compared with Y, and if Y<YO, the direction is to close the mixed pressure steam control valve 8, and the process returns to the start. If Y≧Y, the direction is to open the mixed pressure steam control valve 8, and the process returns to the start. As a result, the wetness at the final stage inlet is improved due to the enthalpy increase due to main steam mixing, and erosion of the final stage blades is reduced.

According to such an operating method, the turbine expansion line is the fourth
The shape is as shown in the i-8 diagram in the figure, and an equal pressure enthalpy occurs on the mixed pressure line 24 in the mixed pressure stage, and the wetness of the stages below it is improved. In the figure, numeral 25 is an expansion line before mixing, and numeral 26 is an expansion line after mixing.

According to the above-mentioned turbine operating method, the humidity in the low pressure stage is reduced and the generation of water droplets is suppressed.
It is possible to effectively prevent a decrease in efficiency and the occurrence of drain erosion due to the braking action of water droplets.

FIG. 5 shows another embodiment of the invention. In this example,
A heat exchanger 27 is installed in the mixed pressure steam line branched from the main steam line, and the steam is heated by an external heat source, so it is possible to expect a larger increase in enthalpy in the mixed pressure stage, and the amount of mixed pressure steam is increased. It becomes possible to suppress the amount of This is a very effective means of reducing humidity when main steam conditions are extremely poor.

[Effects of the Invention] As described above, in the method of the present invention, a part of the main steam, which is superheated steam, is effectively mixed into the low pressure stage.
The wetness of subsequent paragraphs can be effectively reduced. Therefore, the generation of water droplets inside the turbine can be suppressed, a decrease in efficiency and the occurrence of drain erosion can be prevented, and highly reliable steam turbine equipment can be provided.

[Brief explanation of drawings]

Fig. 1 is a piping system diagram of a steam turbine used in an embodiment of the method of the present invention, Fig. 2 is a block diagram showing control of the mixed steam control valve, Fig. 3 is a flowchart showing the control process, and Fig. 4 is a A graph showing the action of the method of the present invention, FIG. 5 is a piping system diagram showing a steam turbine used in another embodiment of the method of the present invention, and FIG. 6 is a piping system diagram showing a conventional general small to medium-sized high-speed steam turbine. 7 are graphs showing the effect of the conventional method. 1...Boiler 2...Main steam stop valve 3...Main steam control valve 4...Turbine 5... Condenser 6... Speed reducer 7... Generator 8... Mixed pressure steam Regulating valve 9...Reducing valve 10...Calorimeter 11...
......Calculator 12...R final stage entry pressure 13...
...Calorimeter internal pressure 14...
Concentration in calorimeter 15.19... Calculator 16... Final stage inlet humidity 17...
...Target humidity 18...Subtractor 20...Main steam pressure line 21...Exhaust pressure line 22... ......Expansion line 23... Saturated steam line 24... Mixed pressure line 25... Mixed pressure forelimb tension line 26... Expansion line after mixed pressure 27... Heat exchanger applicant Toshiba Corporation Patent attorney Satoshi Suyama - Figure 1, Figure 2, D-C. Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] (1) Measure the pressure in the low-pressure stage of the steam turbine, determine the enthalpy of saturated steam and the enthalpy of saturated water at the pressure, and calculate the low pressure based on the pressure and concentration of the calorimeter connected to the low-pressure stage inlet. Find the enthalpy of steam at the paragraph entrance,
Thereafter, the wetness of the steam at the low pressure stage inlet is determined based on the enthalpy values, and this wetness value is
When the value is greater than a preset value, the mixed pressure steam regulator is opened, and when the value is smaller than the low pressure stage inlet, the mixed pressure steam regulator is closed. A method of operating a steam turbine characterized by: