JP2010151055A - Steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam turbine capable of reducing moisture loss by reducing condensation loss. <P>SOLUTION: In the steam turbine, a stage pressure ratio (a stage inlet pressure (P3in)/a stage outlet pressure (P3out)) or an adiabatic heat drop (Δha3) in a third stage wherein a steam condition in a stage inlet is in a dry region and a steam condition in a stage outlet is in a moist region is set smaller than a stage pressure ratio or an adiabatic heat drop of a turbine stage in an upstream side than the third stage or a turbine stage in a downstream side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steam turbine capable of reducing wet loss, and more particularly to a steam turbine capable of reducing condensate loss of wet loss.

  In order to realize further improvement of the performance of the steam turbine, it is necessary to reduce the moisture loss peculiar to the steam turbine. This wet loss includes condensate loss (thermodynamic loss when micro water droplets are generated), braking loss (loss due to water droplets colliding with moving blades), acceleration loss (friction loss when steam accelerates water droplets) ) And can be classified into three losses.

Conventional methods for reducing wet loss are mainly aimed at removing moisture. Conventionally, for example, a drain catcher that effectively separates and removes water droplets blown to the outer peripheral wall surface by the centrifugal force of the moving blade, and sucks the water film formed on the nozzle blade surface and the wall surface by making the inside of the nozzle hollow Thus, the reduction of wet loss was suppressed using a slit, a drain separator, or the like that suppresses the generation of coarse water droplets (see, for example, Non-Patent Document 1).
Turbomachinery Association "Steam Turbine" pages 179-180

  However, in the conventional wet loss reduction method described above, moisture is separated and removed, which contributes to the reduction of braking loss and acceleration loss in the wet loss, but condensate loss that occurs when water droplets are generated. The effect of reducing was not obtained.

  Therefore, the present invention has been made to solve the above-described problem, and an object of the present invention is to provide a steam turbine that can reduce condensate loss and wet loss.

  In order to achieve the above object, according to one aspect of the present invention, in a steam turbine having a plurality of turbine stages composed of a cascade of stationary blades and moving blades, the steam condition at the stage inlet is in a dry region. In the turbine stage where the steam condition at the outlet of the stage is in a wet region, at least one of the stage heat drop and the stage pressure ratio is located upstream of the turbine stage and downstream of the turbine stage. A steam turbine is provided that is smaller than a paragraph heat drop or paragraph pressure ratio in the turbine stage.

  Further, according to one aspect of the present invention, in the steam turbine including a plurality of turbine stages composed of stationary blades and moving blade cascades, the steam condition at the paragraph inlet is in a dry region, and the steam condition at the paragraph outlet Is a turbine stage in which the steam condition is in a wet area, the steam condition at the inlet of the cascade of the stationary blade is in a dry area, the steam condition at the outlet of the cascade of the stationary blade is in a wet area, and the cascade in the cascade of the stationary blade A steam turbine having a pressure ratio of 1.5 or less is provided.

  Furthermore, according to one aspect of the present invention, in a steam turbine including a plurality of turbine stages composed of stationary blades and moving blade cascades, the steam condition at the paragraph inlet is in a dry region, and the steam condition at the paragraph outlet is Is a turbine stage in the wet region, the steam condition at the blade cascade inlet is in the dry region, the steam condition at the blade cascade outlet is in the wet region, and the blade row in the blade cascade A steam turbine having a pressure ratio of 1.5 or less is provided.

  According to the steam turbine of the present invention, it is possible to reduce the condensate loss and reduce the wet loss.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a relationship between a virus line and a pressure change on an enthalpy-entropy diagram (hereinafter referred to as hs diagram). FIG. 2 is a diagram showing expansion lines on the hs diagram for (a) when there is no supersaturation phenomenon, (b) when there is a small supersaturation phenomenon, and (c) when there is a large supersaturation phenomenon. FIG. 3 shows the relationship between the wetness and the loss of moisture shown in FIG. 2 for (a) when there is no supersaturation phenomenon, (b) when there is a small supersaturation phenomenon, and (c) when there is a large supersaturation phenomenon. FIG.

  First, condensate loss will be described.

  Generally, in a steam turbine, even when dry steam expands and reaches a wet region beyond the saturated steam line on the hs diagram, condensate of steam does not occur immediately. In FIG. 1, the dry region refers to a region above the saturated vapor line, and the wet region refers to a region below the saturated vapor line. The reason why steam condensate does not occur immediately after dry steam reaches the wet region is based on the effect of surface tension, and such steam is called supersaturated steam. The line connecting the points on the h-s diagram where the steam condensate starts from this supersaturated steam state is called the virus line, and is almost parallel to the isohumidity line.

  The virus line is affected by the magnitude of the pressure change of the steam. As shown in FIG. 1, the supersaturated state continues as the pressure change (ΔP) increases. Therefore, the larger the pressure change (ΔP), the more the viron line is located in a region where the wetness range is wider, that is, a region away from the saturated vapor line in the wet region. On the other hand, when the pressure change (ΔP) is small, the range of the supersaturated state is narrowed, and the virus ray is located in a region where the wetness range is narrow, that is, a region close to the saturated vapor line in the wet region. Here, the pressure change (ΔP) is expressed by the following equation (1).

                ΔP = −1 / P × (dP / dt) Equation (1)

  Here, dP / dt is the change in pressure per unit time, and P is the steam pressure in the turbine cascade.

  When condensate is generated from the supersaturated steam in the state on the virus line, heat transfer from the newly generated water droplet nucleus to the gas phase is performed. Therefore, the entropy of the gas phase is increased, resulting in a thermodynamic loss. This is called condensate loss.

  Further, as shown in FIG. 2, the entropy increases in the order of (c) large supersaturation phenomenon, (b) small supersaturation phenomenon, (a) no supersaturation phenomenon, It can be seen that the entropy increases with wider conditions. The expansion lines shown in FIG. 2 indicate the state quantities of steam in each stage of the turbine. From the pressure and temperature in the dry area above the saturated steam line, the pressure and wetness in the wet area below the saturated steam line. From the degree, the position of the expansion line can be specified.

  Moreover, as shown in FIG. 3, the wet loss increases in the order of (c) when there is a large supersaturation phenomenon, (b) when there is a small supersaturation phenomenon, and (a) when there is no supersaturation phenomenon. It can also be seen that the overall wet loss increases as the condensate loss generated when water droplets are generated, that is, as the wet loss increases under low wetness conditions. In FIG. 3, water droplets are rapidly generated under the condition that the wet loss is greatly increased and the wetness is small. From the results of FIG. 3, it can be seen that reducing the condensate loss leads to a reduction in the overall wetting loss and can improve the performance of the steam turbine.

  Here, the wet loss shown in FIG. 3 is obtained by measuring the turbine efficiency when the steam temperature is changed by adjusting the inlet temperature of the test steam turbine. The wet loss can be obtained based on the difference between the theoretical turbine efficiency that does not cause the wet loss and the actually measured turbine efficiency. Here, the turbine efficiency is defined by the ratio of the actual heat drop and the adiabatic heat drop in the hs diagram, and can be obtained from the pressure, temperature, and wetness at each point.

  Next, the steam turbine according to the first embodiment of the present invention will be described.

  The steam turbine according to the first embodiment of the present invention is configured in consideration of the above-described condensate loss generation factors. FIG. 4 is a diagram illustrating an example of an expansion line on the hs diagram in the steam turbine according to the first embodiment of the present invention. Here, a steam turbine having five stages of turbine stages is illustrated. Here, in the display of P1in to P5out shown in FIG. 4, P represents pressure, 1 to 5 represent the first to fifth paragraphs, in represents the paragraph inlet, and out represents the paragraph outlet. Further, the pressure at the paragraph outlet in the predetermined turbine stage is the same as the pressure at the paragraph inlet in the turbine stage immediately downstream thereof. Specifically, as shown in FIG. 4, for example, P1out and P2in have the same pressure.

  In the expansion line shown in FIG. 4, the region above the saturated vapor line is a dry region, and the region below the saturated vapor line is a wet region. As shown in FIG. 4, in the present steam turbine, the first and second paragraph inlets and outlets, the third paragraph inlet steam conditions are dry areas, the third paragraph outlet, The steam conditions at the paragraph inlet and paragraph outlet of the fourth and fifth paragraphs are in the wet zone. Therefore, condensate loss occurs in the third stage where the expansion line crosses the saturated vapor line. In addition, the expansion line is shown by the method similar to the method which shows the expansion line shown in FIG.

  In the steam turbine according to the first embodiment, the ratio of the paragraph inlet pressure to the paragraph outlet pressure (paragraph inlet pressure) in the third paragraph where the steam condition at the paragraph inlet is in the dry region and the steam condition at the paragraph outlet is in the wet region. The paragraph pressure ratio, which is (P3in) / paragraph outlet pressure (P3out)), is set to be smaller than the paragraph pressure ratio of the upstream turbine stage and the downstream turbine stage from the third stage.

  Specifically, the paragraph pressure ratio in the third paragraph is 50 to 95% of the paragraph pressure ratio of the turbine stage upstream and the turbine stage downstream of the third paragraph from the viewpoint of the continuity of the passage design. It is preferable to set in the range.

  Thus, by setting the paragraph pressure ratio in the third paragraph where the steam condition at the inlet of the turbine stage is in the dry region and the steam condition at the outlet of this -bin paragraph is in the wet region, the supersaturated state generated in the third paragraph The condensate loss becomes relatively small.

  Since P3in and P2out have the same pressure, and P3out and P4in have the same pressure, “(P3in) / (P4in)”, “(P2out) / (P3out)”, or “(P2out) / (P4in)”. May be set to be smaller than the paragraph pressure ratio of the upstream turbine stage and the downstream turbine stage from the third stage. The turbine stage in which the steam condition at the paragraph inlet is in the dry region and the steam condition at the paragraph outlet is in the wet region is not limited to the third paragraph, and may be another turbine stage.

  Further, in the above embodiment, attention is paid to the paragraph pressure ratio, but the same applies to the case where attention is paid to the adiabatic heat drop of each paragraph. That is, as shown in FIG. 4, when the difference between the enthalpy on the inlet side and the enthalpy on the outlet side of each turbine stage is defined as a paragraph heat drop Δha, the paragraph heat drop Δha in the first to fifth paragraphs is Δha1. ~ Δha5.

  That is, in the present embodiment, the adiabatic heat drop Δha3 in the third stage where the steam condition at the paragraph inlet is in the dry zone and the steam condition at the paragraph outlet is in the wet zone is the turbine paragraph upstream of the third paragraph. By setting it to be smaller than the adiabatic heat difference Δha2 and Δha4 of the (second paragraph) and the downstream turbine stage (fourth paragraph), the range of the supersaturated state occurring in the third paragraph is narrowed, and condensate loss Becomes relatively small.

  Note that the adiabatic heat drop Δha3 in the third stage of the turbine stage (second stage) upstream of the third stage and the downstream turbine stage (fourth stage) from the viewpoint of the continuity of the passage design. It is preferable to set in the range of 50 to 95% of the adiabatic heat difference Δha2 and Δha4.

  Thus, in the present embodiment, the paragraph heat drop or the paragraph pressure ratio in the turbine stage where the steam condition at the paragraph inlet is in the dry zone and the steam condition at the paragraph outlet is in the wet zone is higher than the turbine paragraph. It is set to be smaller than the paragraph heat drop or paragraph pressure ratio of the turbine stage on the side and the turbine stage on the downstream side.

  Here, whether the steam condition is in a dry region or a wet region is determined by whether the expansion line is shown on the hs diagram by the above-described method and is located above or below the saturated vapor line. It should be noted that the parameters for indicating the state of steam, such as pressure, temperature, enthalpy, entropy, etc. used for determining the steam conditions, in other words, indicating the expansion line, are distributed in the radial direction and the circumferential direction. Here, values obtained by averaging these parameters having distributions in the radial direction and the circumferential direction are used as representative values. Here, examples of the averaging method include a method of arithmetically averaging the parameters at a plurality of points in the radial direction and the circumferential direction, and a method of averaging by adding a weight to each parameter with a flow rate distribution.

  As described above, according to the steam turbine of the first embodiment, the stage pressure ratio or the adiabatic heat difference in the turbine stage where the steam condition at the paragraph inlet is in the dry region and the steam condition at the paragraph outlet is in the wet region is obtained. By setting the pressure ratio or the adiabatic heat drop between the turbine stage upstream and the turbine stage upstream of this turbine stage, a supersaturated state that occurs in the turbine stage that becomes a wet zone from this dry zone The condensate loss can be made relatively small by narrowing the range. Thereby, in the steam turbine, it is possible to reduce the condensate loss and reduce the wet loss.

(Second Embodiment)
5 and 6 are diagrams showing an example of an expansion line in the steam turbine according to the second embodiment of the present invention on the hs diagram.

  In the steam turbine according to the second embodiment of the present invention, the steam condition at the inlet of the paragraph is in the dry region, and the steam condition at the outlet of the paragraph is in the wet region, and the steam at the cascade inlet of the stationary blade When the condition is in the dry region and the steam condition at the cascade outlet of the stationary blade is in the wet region, the ratio of the cascade inlet pressure to the cascade outlet pressure in the stationary blade cascade (blade inlet pressure / blade The blade row pressure ratio (row outlet pressure) is set to be 1.5 or less.

  In the steam turbine according to the second embodiment of the present invention, the steam condition at the inlet of the paragraph is in a dry region and the steam condition at the outlet of the paragraph is in a wet region, and the blade row inlet of the moving blade When the steam condition in the blade is in the dry region and the steam condition in the blade row outlet of the moving blade is in the wet region, the ratio of the blade row inlet pressure to the blade row outlet pressure in the blade row (blade row inlet pressure) Blade cascade pressure ratio) is set to 1.5 or less.

  An example of the expansion line in the steam turbine according to the second embodiment of the present invention shown in FIGS. 5 and 6 will be described. Here, PNin shown in FIG. 5 is a stationary blade inlet pressure, PNout is a stationary blade outlet pressure, PBin is a moving blade inlet pressure, and PBout indicates a moving blade outlet pressure. Moreover, PNout and PBin are the same pressure.

  In the steam turbine shown in FIG. 5, the expansion line passes through the saturated steam line in the stationary blade flow path in a predetermined turbine stage. That is, the steam condition is in the dry region at the blade cascade inlet in the predetermined turbine stage and in the wet region at the blade cascade outlet.

  On the other hand, in the steam turbine shown in FIG. 6, the expansion line passes through the saturated steam line in the blade flow path in a predetermined turbine stage. That is, the steam condition is in the dry region at the blade row inlet of the moving blade and in the wet region at the blade blade outlet in the predetermined turbine stage.

  That is, the steam turbine shown in FIG. 5 and the steam turbine shown in FIG. 6 differ in the position of the steam condition of the working steam from the dry region to the wet region.

  Here, in the steam turbine shown in FIG. 5, the steam condition at the blade cascade inlet of the stationary blade is in the dry region, and the steam condition at the blade blade outlet of the stationary blade is in the wet region. The blade row pressure ratio, which is the ratio of the blade row inlet pressure to the blade row outlet pressure (blade row inlet pressure (PNin) / blade row outlet pressure (PNout)), is set to 1.5 or less. Since PNout is the same pressure as PBin, the ratio between the cascade inlet pressure in the cascade of the stationary blade and the cascade inlet pressure in the cascade of the moving blade immediately downstream of the stationary blade (the blade of the stationary blade) Row inlet pressure (PNin) / blade row inlet pressure (PBin)) may be set to 1.5 or less.

  In the steam turbine shown in FIG. 6, the steam condition at the blade row inlet of the moving blade is in the dry region, and the steam condition at the blade row outlet of the moving blade is in the wet region. The blade row pressure ratio, which is the ratio of the blade row inlet pressure to the blade row outlet pressure (blade row inlet pressure (PBin) / blade row outlet pressure (PBout)), is set to 1.5 or less. Since PNout is the same pressure as PBin, the ratio of the cascade outlet pressure in the cascade of the stationary blades immediately upstream of this rotor blade to the cascade outlet pressure in the cascade of this rotor blade (the stationary blade The blade row outlet pressure (PNout) / the blade row outlet pressure (PBout)) may be set to 1.5 or less.

  Here, the cascade pressure ratio, which is the ratio of the cascade inlet pressure and cascade outlet pressure (blade inlet pressure (PNin) / blade outlet pressure (PNout)) in the stationary blade cascade, is 1.5 or less. Alternatively, the cascade pressure ratio, which is the ratio of the cascade inlet pressure and the cascade outlet pressure (blade inlet pressure (PBin) / blade outlet pressure (PBout)) in the cascade of the moving blades, is set to 1.5 or less. The reason why this is preferable will be described.

  FIG. 7 is a diagram showing the relationship between the cascade pressure ratio and the condensate loss in the steam turbine according to the second embodiment.

  As shown in FIG. 7, the condensate loss increases as the cascade pressure ratio increases. The rate of increase in condensate loss increases especially when the cascade pressure ratio exceeds 1.5, and becomes monotonous when the cascade pressure ratio is 2 or more. From this relationship, it is understood that the condensate loss can be suppressed to a low level by setting the cascade pressure ratio to 1.5 or less. Therefore, in the steam turbine according to the present invention, the blade row pressure ratio is set to 1.5 or less.

  In order for the working fluid to flow smoothly in the blade row, the blade row inlet pressure needs to be higher than the blade row outlet pressure. Therefore, the lower limit value of the blade row pressure ratio is preferably set to 1.05.

  Here, the condensate loss shown in FIG. 7 is measured as follows.

  The cascade is composed of a two-dimensional cascade and the condensate loss for this 2-dimensional cascade can be measured by wind tunnel tests (eg, Akiba, Kawagishi, “Fluid characteristics and performance of gas-mixed geothermal turbines”, Japan (See JSME Proceedings (B), Vol. 51, No. 469, pp. 2991-2998, 1985).

  The steam wind tunnel used for the test can be operated continuously in supersonic flow and can be tested under conditions equivalent to the steam state in the turbine. The steam supplied from the boiler is led to the test section where the two-dimensional blade row is installed through the inlet pressure regulating valve and the temperature reducer, and flows out to the condenser through the outlet pressure regulating valve. For this reason, the steam conditions upstream and downstream of the test section can be arbitrarily set.

  As described above, according to the steam turbine of the second embodiment, the steam condition at the paragraph inlet is in the dry region, and the steam condition at the paragraph outlet is in the wet region, and the cascade of the stationary blades When the steam condition at the inlet is in the dry area and the steam condition at the cascade outlet of the stationary blade is in the wet area, the ratio of the cascade inlet pressure to the cascade outlet pressure in the cascade of the stationary blade (blade inlet pressure) By setting the blade row pressure ratio (pressure / blade row outlet pressure) to 1.5 or less, the condensate loss can be suppressed to a low level. Thereby, it is possible to reduce the wet loss.

  Further, according to the steam turbine of the second embodiment, the steam condition at the stage inlet is in the dry area, and the steam condition at the stage outlet is in the wet area, and the steam at the cascade inlet of the moving blade When the condition is in the dry region and the steam condition at the blade cascade outlet is in the wet region, the ratio of the cascade inlet pressure to the cascade outlet pressure in the blade cascade (blade inlet pressure / blade) By setting the blade row pressure ratio, which is the row outlet pressure, to 1.5 or less, the condensate loss can be suppressed to a low level. Thereby, it is possible to reduce the wet loss.

  Although the present invention has been specifically described above with reference to the embodiments, the present invention is not limited to these embodiments, and various modifications can be made without departing from the scope of the invention.

The figure which shows the relationship between a viral line and a pressure change on an enthalpy-entropy diagram (hs diagram). (A) When there is no supersaturation phenomenon, (b) When there is a small supersaturation phenomenon, (c) The figure which shows an expansion line on each case with a big supersaturation phenomenon on an hs diagram. FIG. 3 is a diagram illustrating the relationship between the wetness degree and the wet loss when (a) there is no supersaturation phenomenon, (b) there is a small supersaturation phenomenon, and (c) there is a large supersaturation phenomenon. The figure which shows an example of the expansion line in the steam turbine of 1st Embodiment which concerns on this invention on an hs diagram. The figure which shows an example of the expansion line in the steam turbine of 2nd Embodiment which concerns on this invention on an hs diagram. The figure which shows an example of the expansion line in the steam turbine of 2nd Embodiment which concerns on this invention on an hs diagram. The figure which shows the relationship between cascade pressure ratio and condensate loss in the steam turbine of 2nd Embodiment.

Claims (4)

In a steam turbine having a plurality of turbine stages composed of stationary blades and moving blade cascades,
A turbine stage in which at least one of a paragraph heat drop and a paragraph pressure ratio is upstream of the turbine stage in a turbine stage where the steam condition at the paragraph inlet is in a dry region and the steam condition at the paragraph outlet is in a wet region; A steam turbine characterized by being smaller than a stage heat drop or a stage pressure ratio in a turbine stage located downstream of the turbine stage. In a steam turbine having a plurality of turbine stages composed of stationary blades and moving blade cascades,
In the turbine stage where the steam condition at the paragraph inlet is in the dry zone and the steam condition at the paragraph outlet is in the wet zone, the steam condition at the cascade inlet of the stationary blade is in the dry zone, and the steam condition at the cascade outlet of the stationary blade Is a wet region, and the cascade pressure ratio in the cascade of the stationary blade is 1.5 or less. In a steam turbine having a plurality of turbine stages composed of stationary blades and moving blade cascades,
In the turbine stage where the steam condition at the paragraph inlet is in the dry zone and the steam condition at the paragraph outlet is in the wet zone, the steam condition at the blade cascade inlet is in the dry zone, and the steam condition at the cascade outlet of the bucket Is a wet region, and the cascade pressure ratio in the cascade of the moving blade is 1.5 or less.   4. The steam condition according to claim 1, wherein the steam condition is determined based on a representative value obtained by averaging various parameters for determining the steam condition, which have distributions in a radial direction and a circumferential direction. The steam turbine according to claim 1.

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