JP3272116B2 - Method for monitoring first stage nozzle erosion in steam turbine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring the amount of erosion of a first stage nozzle in a steam turbine during operation.

[0002]

2. Description of the Related Art FIG. 8 is a partial view showing a general first stage structure of a steam turbine in a thermal power plant. The steam is supplied to the first-stage nozzle box 4 through the steam control valve 3, and is supplied from the first-stage nozzle 5 to the first-stage blade 6.
And a rotational force is applied to the rotor 7.

However, since the steam generated by the boiler 1 generally contains solid matter such as scale, the solid matter causes the erosion a at the outlet end of the first stage nozzle 5 as shown in FIG. May occur, and as a result, the steam flow area at the outlet of the first stage nozzle 5 may increase. When the area of the steam flow path increases in this way, the state such as the amount and direction of the ejected steam from the first-stage nozzle changes from the design value. This causes a trouble that the blade 6 and the cover 8 are damaged.

Conventionally, such erosion of the first stage nozzle is
There was no method other than direct inspection such as visual inspection to stop the turbine and disassemble it.

[0005] However, in a situation where the reserve ratio of the power equipment with respect to the power demand is small recently, it is difficult to stop and inspect the turbine in order to check the erosion amount of the first stage nozzle. In addition, the method of restoring the nozzle erosion is relatively short, such as replacing the nozzle box 4. However, if the first stage blade 6 or the cover 8 is damaged, it takes a long time to restore the damage. For this reason, if the erosion of the first-stage nozzle is left until the blades and the cover are damaged, there is a problem that the recovery period is extended and the stable supply of electric power is hindered.

In view of the foregoing, the present invention has been made to monitor the erosion amount of the first stage nozzle based on the state value of each part during operation, and to prevent erosion of the nozzle before damage to the blades or the like occurs. It is an object of the present invention to obtain a first-stage nozzle erosion monitoring method capable of taking measures.

[0007]

According to a first aspect of the present invention, the control valve is measured by measuring a large number of first stage shell pressures with respect to the control valve opening at the time of operation immediately after the repair of the first stage nozzle is completed. The relationship between the opening and the first-stage shell pressure is prepared as an approximate expression to be an initial reference value, and the adjustable valve opening and the first-stage shell pressure after aging are measured. The first-stage shell pressure is obtained from the approximate expression serving as the initial reference value, and the increase amount is relatively determined from the measured first-stage shell pressure and the first-stage shell pressure obtained from the approximate expression. Detecting the amount of erosion of the first-stage nozzle from the relationship between changes in the first-stage shell pressure before and after erosion of the first-stage nozzle with respect to the same opening of the control valve determined from the operation results of the first stage. And

[0008] In a second aspect based on the first aspect, the first aspect is the first aspect.
The stage shell pressure is corrected by the main steam pressure and the main steam temperature.

In a third aspect based on the first aspect, a large number of data measured in a certain period after the lapse of time are used to calculate
The average value of the first stage shell pressure with respect to the opening / closing valve opening is obtained as an approximate expression, and the average value of the first stage shell pressure in the vicinity of the maximum point of the opening / closing valve opening of the measured data is obtained from the above approximate expression serving as the initial reference value. It is characterized in that it is compared with a value.

In a fourth aspect of the present invention, a plurality of points are determined by using the frequently used control valve opening as an observation point, and the increase in the first-stage nozzle outlet area based on the first-stage shell pressure for each of the openings is determined. It is characterized in that the change with time is represented by an approximate expression, the current nozzle area increase rate is obtained by the approximate expression, and the erosion amount of the first stage nozzle is detected.

[0011]

In general, the amount of erosion of the nozzle plate can be evaluated by the area of the steam flow path formed by the nozzle plate outlet end.

That is, when the nozzle outlet area increases, the amount of steam passing through the nozzle increases even if the opening degree of the control valve is constant, so that the steam pressure immediately after passing through the first stage blade 6 The first-stage shell pressure P increases by an amount corresponding to the increase in the amount of steam. Then, the control valve opening CV, the first-stage shell pressure P, and the first-stage nozzle exit area NA before erosion.
0, the first-stage nozzle outlet areas NA1 and NA2 after erosion have the relationship shown in FIG. There is a relationship shown in FIG. 11 with the increase amount ΔP.

Therefore, utilizing the characteristics of the control valve opening CV and the first stage shell pressure P, the control valve opening CV is used.
By monitoring the increase ΔPa in the first-stage shell pressure with respect to the pressure, it is possible to monitor the increase in the nozzle exit area, that is, the amount of erosion of the nozzle plate.

[0014]

FIG. 1 is a flow chart of a method for monitoring a nozzle plate according to the present invention, which mainly includes two parts, that is, preparation of an initial reference value and monitoring during operation of a turbine.

First, regarding the creation of the initial reference value, in the operation immediately after the steam turbine is stopped and the maintenance of the first stage nozzle is completed, the control valve opening degree C is used as the initial value data.
V and the first stage shell pressure P are measured. Since the measured values vary due to measurement problems, FIG.
, An approximate expression indicating an average value of these measured values is created, and this is set as an initial reference value Pb.

On the other hand, for monitoring during operation of the turbine,
During the operation after the creation of the initial reference value, the control valve opening CVa and the first stage shell pressure Pa are measured. Then, the initial reference value Pb ₁ of the first stage shell pressure on the measured acceleration valve opening CVa obtained from the approximate expression.

That is, Pb ₁ = f (CVa) Therefore, the rate of increase ΔPa of the measured first stage shell pressure Pa with respect to the initial reference value Pb ₁ is determined.

That is, ΔPa = (Pa−Pb ₁ ) / P
b become ₁ - 100%.

Then, the first-stage nozzle area increase ratio △ NA ₁ is obtained from FIG. 1 from the measured control valve opening CVa and the first-stage shell pressure increase ratio △ Pa, and is displayed.

On the other hand, a range in which the blades and the cover of the first stage are not damaged is considered in advance with respect to the increase ratio ΔNA1 of the first-stage nozzle, and a limit value ΔNAL as shown in FIG.
Is prepared, and the increase rate ΔNA1 of the nozzle area calculated from the above measured value is evaluated in FIG. 3. If the limit value is exceeded, an instruction to repair the first stage nozzle plate as soon as possible is given. Is given.

In this way, the amount of erosion of the first-stage nozzle plate, which could not be confirmed without disassembling after stopping the turbine in the past, can be known during the operation of the turbine. That is, the present invention displays the nozzle plate erosion amount as an increase rate of the nozzle outlet area, and if the increase rate of the nozzle outlet area exceeds a limit value determined from the possibility of causing damage to the blades and the cover, the turbine is turned off. Since it is instructed to stop and repair the nozzle plate which can be restored in a relatively short period of time, it is possible to prevent the blades and the cover, which require a long period of time for restoration, from being damaged.

FIG. 4 is a flow chart showing another embodiment of the present invention, in which the first stage shell pressure P is equal to the main steam pressure PM.
Since the influence of S, the main steam temperature TMS, and the like is given, a value obtained by correcting the measured first stage shell pressure P with the state value at the time of measurement is used. That is, when creating the initial reference value,
During the monitoring during operation, the first-stage shell pressure is corrected by the main steam pressure or the like, and at the time of monitoring, the corrected first-stage shell pressure Pa ′ is compared with the reference value Pb1.

FIG. 5 is a flowchart showing still another embodiment of the present invention. As shown in FIG. 4, the first stage shell pressure P is corrected by the main steam pressure PMS, the main steam temperature TMS, etc. An average value of the first stage shell pressure with respect to the control valve opening CV is obtained as an approximate expression from a number of measurement points during a certain period later, and then the shell pressure near the maximum point of the control valve opening CV in the measurement data is obtained. Is used as the representative value Pa 'of the first stage shell pressure, and the increase ratio ΔPa of the first stage shell pressure is obtained from the difference between this and the initial reference value, thereby obtaining the increase ratio ΔNA1 of the nozzle outlet area.

FIG. 6 is a flow chart showing still another embodiment of the present invention. The frequently used control valve opening CV is determined as an observation point at several points, and the exit area of the first-stage nozzle is changed over time. , The change over time is approximated by a plurality of mathematical expressions, and the current value on the approximate expression is defined as the increase rate of the nozzle area.

FIG. 7 shows an example of a graph of the change with time of the increase amount of the nozzle outlet area.

[0026]

As described above, according to the present invention, the rate of increase in the nozzle exit area is determined by the change in the first-stage shell pressure, and the erosion amount of the first-stage nozzle is detected. The amount of erosion of the nozzle plate can be known during the operation of the turbine, and effects such as prevention of damage to the first stage blade and its cover can be achieved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of a first stage nozzle erosion amount monitoring method of the present invention.

FIG. 2 is a diagram showing an example of an initial measurement value and an initial reference value of a first-stage shell pressure measurement value with respect to a control valve opening degree.

FIG. 3 is a diagram showing an example of a relationship between a control valve opening and a first-stage nozzle outlet area increase limit value;

FIG. 4 is a flowchart showing another embodiment of the present invention.

FIG. 5 is a flowchart showing still another embodiment of the present invention.

FIG. 6 is a flowchart showing another embodiment of the present invention.

FIG. 7 is a graph showing an example of a change with time of a nozzle outlet area.

FIG. 8 is a sectional view showing a schematic configuration of a first stage section of a general steam turbine.

FIG. 9 is a diagram showing an example of erosion of the first stage nozzle plate.

FIG. 10 is a diagram showing a relationship between a control valve opening, a first-stage shell pressure, and a first-stage nozzle outlet area.

FIG. 11 is a diagram showing a relationship between a control valve opening, a first-stage shell pressure increase ratio, and a first-stage nozzle outlet area increase ratio.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01D 21/14 F01D 9/02 101 F01D 25/00

Claims (4)

(57) [Claims] A large number of first-stage shell pressures are measured with respect to the opening / closing valve opening at the time of operation immediately after completion of repair of the first-stage nozzle.
By doing so, the relationship between the control valve opening and the first stage shell pressure is prepared as an approximate expression to be an initial reference value, and after a lapse of time, the control valve opening and the first stage shell pressure are measured.
First-stage shell for opening and closing valve measured after the lapse of time
Obtain the pressure from the approximation formula used as the initial reference value,
1st stage shell pressure and the 1st stage
Calculated relative the increment from the stage shell pressure, advance over
In response to the same opening of the control valve
First stage shell before and after erosion of the first stage nozzle
A method for monitoring the erosion amount of a first-stage nozzle in a steam turbine, comprising detecting an erosion amount of a first-stage nozzle from a relationship of a change in pressure . 2. The first stage shell pressure is set to a main steam pressure and a main steam temperature.
Characterized in that it further modified whenever, the first stage nozzle erosion amount monitoring method in a steam turbine according to claim 1, wherein. 3. An average value of the first-stage shell pressure with respect to the opening / closing valve opening is obtained as an approximate expression from a large number of data measured over a certain period of time after lapse of time. The method for monitoring the erosion amount of a first-stage nozzle in a steam turbine according to claim 1, wherein a comparison is made between a first-stage shell pressure in the vicinity and a value obtained from the approximate expression as an initial reference value. A plurality of points are determined using the frequently used control valve opening as an observation point, and the change with time of the increase amount of the first-stage nozzle outlet area based on the first-stage shell pressure for each of the openings is approximated. And a method for monitoring the erosion amount of the first stage nozzle in the steam turbine, wherein the erosion amount of the first stage nozzle is detected by calculating the current nozzle area increase rate by the approximate expression.