JPS61291704A - Erossion monitoring method for nozzle blade - Google Patents

Abstract

PURPOSE:To monitor erosion with operation ongoing by detecting variation in condition of steam to estimate the condition of erosion generation for a nozzle blade. CONSTITUTION:A forward-pressure detector of a nozzle in a main steam lead pipe part is mounted in a rear main steam lead pipe of a regulation valve and detects pressure of said nozzle. A nozzle forward pressure P1 is compared with each of specified values and if the pressure is lower than a operation interrupting pressure PMIN, the nozzle blade is estimated to suffer from erosion generation, hence interrupting a turbine. Meanwhile, if the pressure is lower than a warning value PANN, a warning is generated. Erosion may thereby be monitored while the turbine operation is ongoing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for monitoring nozzle blade erosion of a steam turbine nozzle box, and relates to a monitoring method created to be suitable for a control valve opening method.

[Background of the invention]

Recent trends in new power generation plants are toward larger size and nuclear power. In particular, thermal power plants make full use of the latest technology to become highly efficient and have good operating characteristics, and systems that can be started and stopped every day or on weekends have become commonplace. Therefore, the existing plants, which were previously operated under base load,
Even in the MW class, intermediate load operation and beak load operation are carried out, such as lowering the load to the minimum at night or starting and stopping it every day.

The trend is toward adopting a system that starts and stops on weekends.

Therefore, in order to improve the efficiency of existing plants, changes to the control valve opening method are adopted in order to improve the efficiency not only in high load zones but also in low load zones.

Technical problems regarding damage sustained under such severe operating conditions apply not only to turbines but also to boilers. Here, the structure of a steam turbine will be explained, focusing on the flow of steam. FIG. 5 is a longitudinal sectional view of the turbine at the main steam inlet. Rotor 1. inner casing 2,
The main steam inlet 3° and the nozzle box 4, which is the object of the present invention, are the main structural parts.

FIG. 6 is an enlarged detailed view of the nozzle box 4, and arrows 5 indicate the flow of steam.

Four main steam inlets 3 shown in FIG. 5 are provided as shown at No. 7 rli, and working steam from a boiler (not shown) is introduced from these ports 3.

FIG. 8 is a sectional view of the central portion of the portion shown in FIG. 7 above. 1st control valve 6. Second regulating valve 7, third regulating valve 8. Fourth
The steam is controlled by the control valve 9.

The steam is introduced into the steam chamber 10 of the nozzle box 4, and as shown in FIG.
FIG. 9 shows the A--A new plane of FIG. 6. In a state accompanying this steam flow 5,
As the scale from the boiler flows into the turbine, there is an adverse effect on the turbine in the form of erosion of the nozzle vanes 13. Furthermore, the increase in pressure difference due to the aforementioned change in the control valve opening method increases the influence of this scale on the turbine.

The nozzle blades 13 arranged as shown in FIG.
Lol! It is adjusted to the appropriate start S shown in i, and serves to effectively supply steam to the rotor blades. However, the steam flow 5 supplied from the boiler also contains scale from the boiler, and as a result, a nozzle blade erosion part 14 (see Fig. 11) occurs and an unstable nozzle throat S1 is formed. As a result, the rotor blade outlet output shown in FIG. 12 increases. This FIG. 12 shows the relationship between the generator output and the high-pressure first stage pressure, and the rotor blade outlet pressure curve 15 and the rotor blade inlet pressure curve (design value) 16 are curves that indicate a normal pressure state. The pressure difference between the two at this time becomes the pressure difference that acts on the rotor blade. Here, when the nozzle blade erosion part 14 (Fig. 11) occurs due to the scale from the boiler mentioned above, the rotor blade inlet pressure at the time of nozzle blade erosion changes from curve 16 (normal characteristic) to curve 1.
7 (when erosion occurs). The pressure difference at this time will be explained. What is the pressure difference at &1 atomization when the adjustment valve is open at 4 atomizations?

With respect to the design value ΔP1, after nozzle blade erosion, ΔP
1', and the increase rate of nozzle throat S is 40
%, the ratio of the pressure difference will be 2 to 3 times higher, which may further accelerate nozzle blade erosion. As a result, not only the erosion of the puzzle blades increases, but also the amount of steam to the moving blades assembled on the rotor increases, and the worst case scenario is that the moving blades are blown off due to the shock. In the conventional nozzle box (publicly known example: Thermal Power Generation Technology Association's Turbine and Generator Course p. 63), there is no observation point for such pressure changes, and if I were to highlight it, No. 511I is the rotor blade exit rotor shown in Temperature detection seat 19. There is a rotor blade output pressure detection seat 20, but these are installed only for the purpose of operational control such as monitoring thermal stress, and the impact on the high pressure first stage due to nozzle blade erosion is .

Even if metal temperature changes or pressure changes occur, the reality is that they are only understood as changes in operational control. However, it is important for equipment safety to constantly monitor the pressure, etc., which changes due to nozzle blade erosion.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of monitoring the erosion occurrence state while continuing operation of a steam turbine without stopping the operation of the steam turbine or disassembling the turbine.

[Summary of the invention]

In order to achieve the above object, the monitoring method of the present invention is characterized in that, while operating a steam turbine, changes in the steam conditions are detected to determine the state of generation and growth of 20-john.

[Embodiments of the invention]

FIG. 1 is an explanatory diagram of the monitoring method of the present invention.

A main steam lead pipe section and a nozzle front pressure detection seat 20 are installed in the live steam lead pipe 18 after the control valve, and the pressure P4 in this section is monitored.

Figure 2 is a chart in which the horizontal axis shows the generator output and the vertical axis shows the pressure in front of the high-pressure beginner nozzle, and the solid line shows curve 21.
represents the design value of the nozzle front pressure. Curve 15 is shown for reference.

It represents the rotor blade outlet pressure.

When erosion occurs in the nozzle blade, the above curve 2
1 changes like a broken line curve 22.

Therefore, when the pressure in front of the first stage nozzle in the main steam reed section after the steam turbine control valve is detected, the detected value can be compared with this chart (FIG. 2) to determine the state of occurrence of erosion.

Here, the nozzle front pressure (design value) 21 and the nozzle front pressure 22 at the time of nozzle erosion will be explained. When the nozzle blades 13 arranged as shown in Fig. 9 are adjusted to the appropriate throat size S shown in Fig. 10, steam is effectively supplied to the rotor blades, and the nozzle front pressure (design value ) 21 (Fig. 2).However, as shown in Fig. 11, when the nozzle blade erosion part 14 occurs and an unstable nozzle throat S is formed, the steam flow 5 is not properly controlled. As a result, the nozzle front pressure (design value) 21 decreases and changes to the nozzle front pressure 22 at the time of nozzle erosion (Fig. 2).

Pressure curve 22 at the time of erosion shown in Fig. 2
shows one example, and the shape of this curve changes as the erosion grows.

Therefore, an alarm value curve P, □ indicating that the nozzle front pressure curve 21 in the normal state has changed and approaches the erosion occurrence curve 22, and a stop value p w x w at which the turbine should be stopped immediately are set.

When setting these values (P□□P□,), it is determined whether the stress on the rotor blades caused by the increase in steam power due to the large pressure difference falls within a dangerous range.

For the limit value determined in this way, the nozzle front pressure p
FIG. 3 shows a block diagram for comparing the magnitude of i (FIG. 1) and controlling the operation.

First, in step 31, the generator output KW is taken in. If nozzle two-losion occurs, the nozzle front pressure P1 with respect to the generator output is determined by the second ti! ! The value indicated by the nozzle front pressure 22 at the time of nozzle erosion of I is obtained. On the other hand, both the alarm value PAI11 and the stop value PII□ are given set values for the generator output, so the nozzle front pressure P2 and the alarm value pawn/stop value P□9 are compared ( Step 32. Step 33).

If the nozzle front pressure P1 is smaller than the stop value P□yo, the turbine will be stopped (step 34), and the turbine will be inspected for release (step 35).If the detected pressure is more than P m t w, the alarm value P,□ Comparatively, step 36), if it is smaller, an alarm value is generated (step 37), and
Check the rate of change of the nozzle front pressure Pi Step 38
), the system will provide back-up data for future countermeasure studies, select the change in opening of the adjustment valve to the side where the pressure difference ΔP1' shown in FIG. 12 becomes smaller, and continue operation.

The above describes the live steam lead pipe 1 after the control valve as shown in Figure 1.
8, the pressure curve 20 in front of the main steam lead pipe nozzle is installed directly on the main steam lead pipe nozzle.
As shown in the figure, it is also possible to detect steam conditions by installing a drain control nozzle front pressure curve 23 in the main steam lead pipe drain piping 19, and determine the occurrence of erosion based on this.

〔Effect of the invention〕

As explained above, according to the method of the present invention, the occurrence of erosion can be prevented while the operation of the steam turbine is continued without stopping the operation of the steam turbine or disassembling the turbine.
The state of growth can be monitored and appropriate measures can be taken. Therefore, it is possible to choose a safer driving method,
The worst case of rotor blades flying off can be prevented,
It greatly contributes to ensuring safety.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the position of the pressure detection seat for monitoring nozzle blade erosion in one embodiment of the present invention, and FIG.
A chart showing the relationship between load and high-pressure first-stage nozzle front pressure, and FIG. 3 is a block diagram showing the nozzle blade erosion monitoring system in the embodiment. FIG. 4 is an explanatory diagram of an embodiment different from the above. Fig. 5 is a longitudinal sectional view showing the vicinity of the main steam inlet of the steam turbine;
The figure is an enlarged sectional view of the vicinity of the nozzle box, Figure 7 is an explanatory diagram showing the position of the main steam inlet, Figure 8 is a sectional view of the center of the part shown in Figure 7, and Figure 9 is the same as that of Figure 6. A-A sectional view,
Figure 10 is an explanatory diagram showing the arrangement of the nozzle vanes in a normal state, Figure 11 is an explanatory diagram of the nozzle vane shown in Figure 10 in a state where 20-johns have occurred, and Figure 12 is an explanatory diagram showing the load and steam pressure. This is a chart showing the relationship between DESCRIPTION OF SYMBOLS 1... Rotor, 2... Internal casing, 3... Main steam inlet, 4... Nozzle box, 5... Steam flow, 6... First regulating valve, 7... No. 2 Adjustment valve, 8...
・Third well. 9... Fourth control valve, 10... Steam chamber, 11... Steam chamber partition, 12... Bridge, 13... Nozzle blade,
20.・Pressure detection seat in front of the main steam lead pipe nozzle, 21
...Pressure in front of nozzle (design value), 22...Pressure in front of nozzle during nozzle erosion, 23...Pressure detection seat in front of nozzle in drain piping section.

Claims (1)

[Scope of Claims] 1. A method for monitoring nozzle blade erosion, which comprises detecting changes in steam conditions of a steam turbine in operation and determining the state of erosion occurring in nozzle blades of a nozzle box. 2. The detection of the change in steam conditions is performed by detecting a change in the pressure in front of the first stage nozzle in the main steam lead after the steam turbine control valve. How to monitor nozzle blade erosion.