JPH03151504A - Reheating-type bleeder turbine - Google Patents

Abstract

PURPOSE:To protect a turbine blade from overload so as to improve safety by detecting the output of a generator connected directly to a bleeder turbine so as to determine the lower limit set value of reheat steam pressure, and controlling a high pressure turbine by-pass valve to be opened at the time of reheat steam pressure becomes lower than the lower limit set value. CONSTITUTION:Main steam pressure is detected by a pressure transmitter 21 so as to be inputted into a computing element 23, as well as turbine first stage exit pressure is detected by a pressure transmitter 24 so as to be inputted into the computing element 23 through a function generator 26 and the like, thus obtaining a deviation signal for making the main steam pressure lower than the ceiling value at the loaded time of a turbine part. The electric generating power of a generator is detected by a power transmitter 27, and the lower limit value of reheat steam pressure is obtained at a function generator 29 so as to be inputted into a computing element 30, where its deviation with reheat steam pressure detected by a pressure transmitter 31 is computed. A higher value signal out of the output of the computing elements 23, 30 is selected at a high value priority circuit 33 so as to generate an action signal to a high pressure turbine by-bass valve 12.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a reheat steam turbine device used in a thermal power plant, and in particular, to a reheating steam turbine device used in a thermal power plant, in particular, to supply process steam to a water production device, etc. in addition to power generation. related to extraction turbines.

(Prior Art) An example of the configuration of a conventional reheat extraction turbine will be explained with reference to FIG.

The main steam leaving the boiler 1 passes through the main steam pipe 2, enters the high-pressure turbine 3, performs work, passes through the low-temperature reheat steam pipe 4, is reheated in the reheater 5, and then passes through the high-temperature reheat steam pipe 6. Medium pressure turbine 7
, crossover tube8. Condenser IO via low pressure turbine 9
is exhausted. Each high pressure.

The work of the medium and low pressure turbines 3, 7.9 is extracted by the generator 11 as electrical output.

Turbine bypass valves are used to stabilize boiler operation when the turbine load is extremely low, such as when starting up a plant or shutting down the power system.

That is, steam from the boiler is transferred to the main steam pipe 2. High pressure turbine bypass valve 12. Low temperature reheat steam pipe 4. Boiler 1° high temperature reheat steam pipe 6. Condenser 1 via low pressure turbine bypass valve 13
The boiler operation is stabilized by also flowing to zero.

Process steam used in a freshwater generator or the like is extracted from, for example, a low-temperature reheat steam pipe 4, and is sent to the freshwater generator or the like via a process steam regulating valve 14.

In Figure 1, numerals 15 and 16 indicate steam control valves, and numeral 17 indicates a low temperature reheat check valve, respectively.

(Problems to be Solved by the Invention) Conventionally, such a reheat extraction turbine has the following problems.

The amount of process steam may be supplied in excess of the rated amount of steam due to requests from the process side, such as a fresh water generator.

In this case, conventionally, there are the following problems when the turbine is under high load.

If process steam is supplied in excess of the rated amount when the turbine is under high load, the flow rate to the intermediate pressure turbine 7 and the low pressure turbine 9 decreases by the amount of increase. As the flow to the intermediate and low pressure turbines 7.9 is reduced, the intermediate pressure turbine inlet, ie reheat steam pressure is reduced. The reason for this is as follows. That is,
The relationship between the steam amount and pressure of the turbine blade group can be expressed by the following equation (Studler's equation).

However, steam flow rate at G'2 planning point G: medium-pressure and low-pressure turbine steam flow rate after the flow rate decreases p1', p: flow rate G', medium-pressure and low-pressure turbine inlet pressure at G P2'lP2: same as above The intermediate pressure and low pressure turbine outlet pressure (approximately constant because it is the condenser internal pressure) Vyo' g 9 z: The intermediate pressure and low pressure turbine inlet specific volume Px7jhC or steam temperature at the same time does not change much depending on the load, and P2/ When the ratio of P is small like in a condensing turbine, the flow rate and the medium pressure and low pressure turbine inlet pressures are almost proportional, and it is expressed as follows.

Therefore, as the amount of steam to the intermediate and low pressure turbines 7.9 decreases, the intermediate and low pressure turbine inlet pressures decrease approximately proportionally. When the intermediate pressure and low pressure turbine inlet pressures decrease, the high pressure turbine outlet pressure also decreases, but this pressure decrease results in overloading of each stage of the high pressure turbine 3 as follows, and a force exceeding the design strength of each blade is applied. There is a risk. That is, in FIG. 4, explanation will be made using an expansion diagram of the turbine. In the expansion diagram, the horizontal axis shows entropy S (Kcag/
'kg°K), the vertical axis is enthalpy h (Kcal!/k
g) represents the expansion state of steam in the turbine, but 1
Normally, when the turbine inlet pressure is Pl, the turbine expands from state (2) to state (2) at the outlet. If there is no loss inside the turbine, there will be no increase in entropy, and the turbine output per unit steam amount will be AH1, that is, the adiabatic heat drop.However, since there is actually loss, entropy increases, and the outlet state becomes ■,
The output per unit flow rate is IJE, that is, the effective heat drop difference. Here, when the turbine outlet pressure decreases from P2 to P2', the state of the outlet becomes ■', the output per unit flow rate becomes UE', and the output of each blade in the turbine increases,
There is a risk of overloading and exceeding the blade's design strength.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reheat extraction turbine that can supply process steam without the risk of overloading the turbine blades.

[Ellipsis of invention]

(Means for Solving Problem a) In order to achieve the above object, the present invention has a high-pressure turbine bypass valve that connects the main steam pipe and the low-temperature reheat steam pipe, and In a reheat extraction turbine that extracts process steam from a turbine stage, the output of a generator directly connected to the extraction turbine is detected and the lower limit setting value of the reheat steam pressure at that generator output is determined. The present invention is characterized in that the high pressure turbine bypass valve is opened when the value falls below a lower limit set value.

(Operation) In the present invention, the output of the generator directly connected to the extraction turbine is detected, and the lower limit set value of the reheat steam pressure is determined from the output. At this time, the load on the turbine blades is determined not to exceed the load at rated output as a reference. FIG. 2 shows the limit value of the reheat steam pressure so that the load on the blades becomes the load at the rated output. The measured reheat steam pressure is compared with a set point based on this limit value, and
When the measured value is lower than this set point, the high pressure turbine bypass valve opens and the steam flows through the cold reheat steam pipe to the intermediate pressure and low pressure turbines, and as the turbine population pressure of both increases, the high pressure turbine outlet pressure increases. Rise. This pressure increase allows the blades of the high-pressure turbine to operate safely without being overloaded.

(Example) An embodiment of the present invention will be described below with reference to FIG.

The main steam pressure is detected by the pressure quadrature transmitter 21,
The signal is input to the arithmetic unit 23 via the converter 22 .

The turbine first stage pressure is detected by a pressure quadrature transmitter 24 and converted into a voltage signal by a converter 25. This signal is applied to the input end of a function generator 26 and a calculation is performed based on the input signal.
This electric power is converted into a voltage signal by a converter 28 and inputted to a function generator 29 . The function generator calculates the lower limit value of the reheat steam pressure based on this input signal.

The output is input to the calculator 30. The output from the pressure quadrature transmitter 31 that detects the reheat steam pressure is input to the calculator 30 via the converter 32, and the deviation between both input signals is calculated. They are respectively applied to the input end of the high value priority circuit 33 together with the deviation signal determined by the device 23 that makes the main steam pressure less than the upper limit value at the time of turbine partial load. The high value priority circuit 33 selects the signal with the higher value among both deviation signals, and its output is input to the electro-hydraulic converter 37 via the proportional integrator 34, manual automatic selection circuit 35, and positioner 36. The electro-hydraulic converter 37 converts the voltage signal into a hydraulic signal to generate an operating signal for the high-pressure turbine bypass valve 12 . In addition, the code 38
indicates a manual operation button.

Next, the effect of the above configuration will be explained.

In this embodiment, the electric output of the generator 11 is detected by the electric quadrature transmitter 27, and the function is generated. The lower limit value of the reheating pressure shown in FIG. 2 is calculated in the device 29. The set value based on this lower limit value is subtracted from the reheating steam pressure actually measured by the pressure quadrature transmitter 31, and if the actually measured value is lower, a positive deviation signal is output as the output of the calculator 30, The electro-hydraulic converter 37 receiving this signal outputs a signal for operating the high-pressure turbine bypass valve 12 in the opening direction. As a result, steam flows from the main steam pipe 2 through the high-pressure turbine bypass valve 12 into the low-temperature reheat steam pipe 5 and flows into the intermediate-pressure and low-pressure turbines 7.9, and the intermediate-pressure and low-pressure turbine inlet pressures and the high-pressure turbine outlet pressures are adjusted. The pressure rises and the pressure exceeds the lower limit value.

〔Effect of the invention〕

As explained above, the present invention detects the output of the generator, determines the lower limit set value of the reheat steam pressure at the generator output, and when the reheat steam pressure falls below the lower limit set value, the high pressure turbine bypass valve The turbine blades are opened to allow process steam to be delivered without overloading the turbine blades.

This has the excellent effect of improving the safety of reheat extraction turbines.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram showing a circuit for limiting the reheat steam pressure of the reheat extraction turbine according to the present invention, Fig. 2 is a diagram showing an example of the lower limit setting value of the reheat steam pressure, and Fig. 3 is a diagram showing an example of the lower limit set value of the reheat steam pressure. FIG. 4, a system diagram showing a conventional reheat extraction turbine, is an expansion diagram of a typical turbine. 3... High pressure turbine 4... Low temperature reheat steam pipe 7.
...Intermediate pressure turbine 9...Low pressure turbine 12...
high pressure turbine bypass valve

Claims (1)

[Claims] In a reheat extraction turbine that has a high-pressure turbine bypass valve provided in a path connecting a main steam pipe and a low-temperature reheat steam pipe, and extracts process steam from the reheat steam pipe or a turbine stage downstream thereof, the above-mentioned The output of the generator directly connected to the extraction turbine is detected to determine the lower limit set value of the reheat steam pressure at the output of the generator, and when the reheat steam pressure falls below the lower limit set value, the high pressure turbine bypass valve is activated. A reheat extraction turbine characterized by an opening.