JP3302770B2 - Steam pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam pipe used in a bleed air system through which steam containing moisture flows, for example, in a nuclear power plant.

[0002]

2. Description of the Related Art An example of application to a conventional moisture separator and a moisture separator heater of a bleed steam system in which steam containing moisture flows will be described.

In FIG. 4, main steam generated in a reactor 11 is saturated steam of about 68 kg / cm ² abs and flows into an inlet of a high-pressure turbine 13 through a main steam pipe 12.

[0004] The steam that has worked in the high-pressure turbine 13 becomes about 12 to 13% wet steam during rated operation, and flows into the cross-around pipe 14 from its outlet.
This flow containing a large amount of moisture exhibits a gas-liquid two-phase flow mode in the cross-around pipe 14, and the liquid film flows on the wall of the pipe,
In addition, a so-called annular spray flow in which liquid droplets flow in the center of the tube. Therefore, a moisture separator 15 is provided in the cross-around tube 14 to remove these moisture from the steam, and the moisture separator 1 passes through the cross-around tube 14.
The gas-liquid two-phase flow that has flowed into 5 is separated into vapor and drain, which is a collection of droplets. Here, the separated steam is
While being introduced into the inlets of the low-pressure turbines 17a and 17b, the drain is introduced into the high-pressure feedwater heater 23 via the moisture separator drain pipe 16, where heat is recovered.

On the other hand, the steam that has been expanded in the low-pressure turbines 17a and 17b to drive the generator 18 is supplied to the low-pressure turbine 1
The water flows out of the outlets 7a and 17b and flows into the condenser 19, where it is condensed and condensed. This condensate is extracted by the condensate pump 20, passed through low-pressure feed water heaters 21 a, 21 b, and 21 c, and boosted in pressure by the reactor feed pump 22.
Water is supplied to the reactor 11 via 3a and 23b as feed water. Further, steam is partially extracted from the high-pressure turbine 13 and the low-pressure turbine 17 to the high-pressure feed water heater 23 and the low-pressure heater 21 and extracted steams 24a, 24b, 24c, 24d,
24e, high pressure feed water heaters 23a, 23b, 23
c, to introduce into the low pressure heaters 21a, 21b, 21c respectively to heat the condensate water and the feed water. Each of these turbines 1
The extracted steam from 3 and 17 is wet steam, and the flow of the fluid in each of the extraction tubes 24a, 24b, 24c, 24d and 24e is a gas-liquid two-phase flow having a wetness of 4 to 40%. .

[0006] Each high pressure feed water heater 23a, 23b, 23c
The extracted steam to the low-pressure feedwater heaters 21a, 21b, and 21c is introduced from the upper portion of the heaters due to the arrangement of the equipment and the structure of the feedwater heater.
The route of 4c, 24d, 24e does not constitute a vertical tube that rises from below to above with a downward slope. On the other hand, the wet steam introduced from the high-pressure turbine 13 to the moisture separator 15 is often introduced from the lower part due to the structure of the moisture separator 15, and in this case, the route of the cross-around pipe 14 is The part to be introduced into the vessel 15 always constitutes a vertical tube which rises upward from below. FIG. 5 shows an example of a route of the cross-around pipe 14 that connects the high-pressure turbine 13 and the moisture separator 15. Cross-around pipe 14 connected to the lower part of high-pressure turbine 13
The vertical pipe is arranged at the bottom, and then a pipe with a gentle gradient is arranged below the moisture separator 15 through a curved pipe, and the vertical pipe rising from below is bent through the curved pipe to separate moisture. It is configured to be introduced from the lower part of the vessel 15. In addition, due to the arrangement of the devices, the cross-around pipe 14 may be provided with two or more vertical pipes that rise upward from below through a curved pipe from a gentle slope pipe.

[0007]

The above-described bleed tube 24 is described below.
The pipe diameters of the pipes a, 24b, 24c, 24d, 24e and the cross-around pipe 14 are determined so as to fall within the allowable pressure loss value limited by the plant efficiency. At this time, the average steam flow velocity in the pipe is about 40 m / s. However, when the allowable value of the pressure loss is severe, it is necessary to increase the pipe diameter to lower the average steam flow rate. Further, as described above, since the flow of the fluid in the bleed tubes 24a, 24b, 24c, 24d, 24e and the cross-around tube 14 is an annular spray flow, it is necessary to consider the flow state with respect to the decrease in the steam flow rate. There is.

FIG. 6A schematically shows a state of a gas-liquid two-phase flow in a pipe, in which a liquid film 31 flows on a wall 30 of the pipe.
A droplet 32 flows in the center of the tube. This flow pattern (flow pattern) depends on the operation output, wet steam flow rate, dryness,
It tends to change slightly as various state quantities (density, viscosity, surface tension, etc.) change with respect to the saturation pressure. As a method of determining these flow patterns, a flow pattern map is often used.

FIG. 7 shows an example of a flow pattern map.
Phase diagram of a horizontal tube Baker (o.Baker The Oil
and Gas Journal 1954-7 p185-195), the vertical axis is G / λ representing the gas flow rate, and the horizontal axis is (L / G) λΨ representing the flow ratio between liquid and gas, where λ and Ψ is the density (ρ
1, ρg), viscosity (μ), and surface tension (σ) are characteristic values for the working fluid.

G: Flow rate per unit area of gas L: Flow rate per unit area of liquid

Λ = [(ρg / 0.075) (ρ1 / 62.3)] ^1/2

２ = 73 / σ [μ (62.3 / ρ1) ² ] ^{1/3 In the} figure, the circles indicate points with respect to the flow pattern of the rated output, indicating that the flow is an annular spray flow. On the other hand, the triangles indicate points with respect to the flow pattern under a low load, and indicate a wavy flow. In this case, the wavy flow means that the liquid film 31 in the lower part 35 of the pipe becomes thicker than the top part 36 and the side wall part 37 as shown in FIG. 6B, and the amount of the droplets 32 in the pipe becomes smaller. Has become. This is because, when the load is reduced, the flow rate of the wet steam and the saturation pressure are each reduced, and therefore, particularly, the reduction amounts of the above-mentioned G and ρg are increased. From this, when the steam flow rate or the steam density decreases for the same pipe diameter, the flow pattern tends to change from the annular spray flow to a wavy flow.

In response to such a change in the flow pattern in the pipe, the bleed pipes 24a, 24b, 24c, 24d, and 24e are used.
As described above, since the gas is introduced from the heating unit due to the arrangement of the equipment and the structure of the feed water heater, the bleed tubes 24a,
The routes 4b, 24c, 24d, and 24e have a downward slope, and flow is stable in the direction of gravity even if the liquid film at the lower part of the pipe has a thick wavy flow. On the other hand, the route of the cross-around pipe 14 introduced from the high-pressure turbine 13 to the moisture separator 15 depends on the arrangement of the equipment and the structure of the model moisture separator 15 as described above. In the part introduced into the vessel 15, a vertical pipe which rises from the lower side to the upper side through a curved pipe from a pipe having a gentle slope is formed.

FIG. 8 (a) shows an example of a flow pattern of a vertical pipe which rises from a lower slope to a higher pipe via a curved pipe from a gentle slope pipe. In this case, the liquid film at the lower part of the pipe has a thick wavy flow in the gentle gradient pipe, and the annular spray flow is formed in the vertical pipe. In such a flow mode, when the vapor flow rate and the vapor density further decrease, the effect of gravity acting on the liquid film 31 in the vertical pipe becomes larger than the acting force on the liquid film by the vapor, and the vertical film faces the rising vapor. As a result, a state in which the liquid film flows downward is formed, and a liquid jumping portion 40 is generated at a portion where the gradient pipe changes to a vertical pipe, resulting in an unstable flow. FIGS. 8 (a) to 8 (c) schematically show this unstable flow mode. FIG. 8 (a) shows a state in which the liquid film 31 flows downward in the vertical pipe section, Portion 40 where the liquid film in the lower part of the pipe from the pipe is combined with the thick wavy flow
Indicates a state in which the liquid film becomes thicker. FIG.
In (b), further, this state progresses, and in the gradient tube, the liquid film of the joint 40 finally reaches the upper part of the gradient tube, so that a state is formed in which this liquid film blocks the flow of steam.
On the other hand, since the vapor flow is obstructed in the vertical tube, the liquid film 31 becomes thicker than the liquid film 31, and the volume ratio of the liquid in the tube becomes larger. FIG.
In (c), the upstream film 4
1 shows a flow pattern in which the pressure of 1 rises and pushes up the liquid mass 42 into a vertical tube. At this time, a slug flow in which the gas phase 44 and the liquid phase 43 rise alternately in the vertical tube. After the liquid mass 42 has been swept out, the state returns to the state of FIG. 8A, and the cycle is repeated. Therefore, such flow regimes result in unstable fluctuations in flow and pressure.

As described above, in the cross-around pipe 14 extending from the high-pressure turbine 13 to the moisture separator 15, due to the arrangement of the equipment and the structure of the horizontal moisture separator 15, a pipe having a gentle gradient must be provided via a curved pipe. The gas-liquid two-phase flow in the pipe constituting the vertical pipe rising upward from below becomes unstable flow when the low-load steam flow rate and pressure are low. In particular, when a liquid phase and a gas phase slug flows are generated, the liquid layer flows into the moisture separator 15 in a short time, so that the moisture separation performance is reduced. Also, if the drain water level rises sharply after moisture separation and reaches a high water level set for stable water level control, a plant trip may occur to protect the turbine. In order to avoid these problems, at the time of low load operation, a system and a control method for predicting the flow pattern in the cross-around pipe 14 in advance and preventing the generation of the liquid phase and gas phase slug flows are installed. There is a need to.

An object of the present invention is to provide a steam pipe capable of stably maintaining the flow of a gas-liquid two-phase flow in a pipe constituting a vertical pipe rising upward from below through a curved pipe from a pipe having a gentle slope. Is to do.

[0015]

Means for Solving the Problems In order to achieve the above object, the present invention provides a steam pipe for introducing steam containing moisture extracted from a steam turbine into a moisture separator. A first drain discharge means provided in the
Serial moisture connected to the separator has been set loose gradient tube followed vertical tube
A second drain discharging means, and first and second drain discharging means;
It characterized by having a a drain valve provided in each unit. The drain valve of this drain discharge means is
Wherein the open <br/> be closed controlled by the pressure signal of the turbine load signal or steam tubes.

[0016]

[Action] In the steam tube equipped with a draining means constructed as described above, the bottom of the path and, connected to the moisture separator
Since the liquid phase is discharged using the second drain discharge means provided on the gentle gradient pipe following the vertical pipe , the liquid film in the lower part of the pipe becomes thicker during low load operation, and the pipe is closed. It is possible to prevent the generation of a liquid phase and a gas phase slug flow, and to keep the flow stable. The first drain discharge means at the bottom of the path is used for discharging the drain since steam warming the pipes is condensed and a large amount of drain is generated at the initial start of the turbine. Even when the amount is small, the liquid film in the steam pipe can be made thin, so that a stable flow mode can be maintained. Ma
Further , since the flow state in the pipe is predicted based on the pressure in the steam pipe and the turbine load , and the drain valve is opened and closed, the steam flow rate is not discharged more than necessary outside the system, so that the plant efficiency is not affected.

[0017]

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, a cross-around pipe 14 connects a vertical pipe 3 downward from a high-pressure turbine 13 and a bent pipe 2.
The rising pipe 1 having a gentle gradient is disposed through the pipe, and then the rising pipe 1 is connected to the moisture separator 15 via the bent pipe 2 and the vertical pipe 3.
And a vertical pipe 3 rising upward from below through a curved pipe 2. First drain discharge means 4
Is connected to the condenser 19 (see FIG. 4) from the riser 1 at the lowermost part of the cross-around pipe 14 connecting the high-pressure turbine 13 and the moisture separator 15 via the drain pipe 4a.
A drain valve 4b is provided in this path. Further, the second drain discharge means 5 is connected to the rising pipe 1 having a gentle slope near the moisture separator 15 via the bent pipe 2 and from the rising pipe 1 immediately before the vertical pipe 3 which rises upward from below through the drain pipe 5a. To the condenser 19. A drain valve 5b is provided in this path. A controller 7 that opens and closes with a load signal or a bleed pressure signal is connected to the drain valves 4b and 5b.

In the cross-around pipe 14 provided with the first and second drain discharge means 4 and 5 having the above-described structure, first, when the turbine is initially started, steam containing moisture from the high-pressure turbine 13 is supplied to the cross-around pipe 14. However, this steam is used for warming the piping, so that a large amount of drain is generated. Then, the drain valve 4b of the first drain discharge means 4 installed at the lowermost part of the cross-around pipe 14 is opened, and this drain is discharged to the condenser 19 through the drain pipe 4a. Further, when the amount of steam further increases, the steam containing moisture from the high-pressure turbine 13 passes through the vertical pipe 3, the bent pipe 2, and the riser pipe 1 of the cross-around pipe 14 and flows into the moisture separator 15. I do. Even in this state, the vapor amount is still small, and the liquid phase portion flows back to the lowermost portion of the cross-around tube 14, so that almost the first
Is discharged from the drain discharge means 4. Furthermore, when the steam load increases and the turbine load begins to be taken, the flow in the pipe becomes a wavy flow in which the liquid film in the lower part of the pipe becomes thick in the riser 1, but the flow in the gentle riser 1 immediately adjacent to the moisture separator 15. The drain valve 5b of the second drain discharge means 5 is opened, and the liquid film is discharged to the condenser 19 through the drain pipe 5a. As a result, it is possible to prevent the liquid film in the lower part of the tube from being thickened and to block the inside of the tube to generate a slug flow of a liquid phase and a gaseous phase, and to stably maintain the flow. Further, when the steam amount further increases, the pressure increases, and the turbine load increases, the cross-around pipe 14
The flow inside becomes an annular spray flow and becomes a stable flow,
The drain valves 4a and 5a are fully closed. At this time, the controller 7 determines the conditions under which the gas phase carries over the liquid phase and the liquid phase does not flow backward. Various physical properties (density, kinematic viscosity) with respect to the steam flow rate, dryness, and pressure, the pipe diameter, and the length from the gradient pipe are determined. Turbine load or cross-around pipe 1
A control signal is output so as to output a close signal when the pressure becomes equal to or higher than 4, and to open the signal when the pressure is equal to or lower than the condition.

FIG. 2 is an example of a diagram used for the determination criterion. The liquid jL in the pipe shape shown in FIG.
FIG. 2B shows a limit diagram in the case where the gas and the gas jG face each other. The horizontal axis shows the dimensionless liquid velocity and the vertical axis shows the dimensionless gas velocity. In this figure, the conditions under which the gas phase carries over the liquid phase and the liquid phase does not flow backward are:
Obtained from obtaining the dimensionless gas velocity when the dimensionless liquid velocity becomes zero.

As described above, in this embodiment, a large amount of drain generated at the initial startup of the turbine is discharged by using the first drain discharge means 4 installed at the lowermost part of the cross-around pipe 14, and the amount of steam further increases. When the turbine load begins to be taken, the flow in the pipe becomes a wavy flow with a thick liquid film in the lower part of the pipe in the riser 1, but the second drain discharge means 5 of the riser 1 in the immediate vicinity of the moisture separator 15. Is used to discharge the liquid film to the condenser 19, so that it is possible to prevent the liquid film in the lower part of the tube from being thickened and to block the inside of the tube to generate a slug flow of the liquid phase and the gaseous phase, and to stabilize the flow. It is possible to keep. When the steam amount further increases, the pressure increases, and the turbine load increases, the flow in the crossflow pipe 14 becomes an annular spray flow and becomes a stable flow. The control signal is obtained from the turbine load or the pressure of the cross-around pipe 14 equal to the conditions, from the various physical properties (density, kinematic viscosity), the pipe diameter, and the length of the gradient pipe. , 5b to be opened and closed, so that unnecessary steam is not discharged to the condenser 19 to lower the plant efficiency.

Another embodiment of the present invention will be described with reference to FIG. This embodiment shows the configuration of the drain discharge means provided in the cross-around pipe 14 extending from the high-pressure turbine 13 to the moisture separator / heater 8. In addition to the above-described first and second drain discharge means 4, 5, The third drain discharge means 6 is disposed immediately before the vertical pipe 3 which rises from the lower part to the upper part via the curved pipe 2 from the middle riser pipe 1. This third
Drain discharge means 6 also includes a drain pipe 6a and a drain valve 6b.
Having.

In this embodiment as well, as in the above embodiment, the liquid film in the lower part of the tube generated under a low load becomes thicker and closes the inside of the tube, thereby generating a slug flow of a liquid phase and a gas phase. Can be prevented, and the flow can be kept stable. In particular, the performance of the moisture separator / heater 8 having a built-in heating unit can be maintained, and the soundness of the plant can be kept good.

[0023]

As described above, according to the present invention,
Drain discharge means is provided at the bottom of the steam pipe path, and drain discharge means is provided on a gentle gradient pipe following the vertical pipe connected to the moisture separator. , tube closes the lower portion of the liquid film becomes thicker tube prevents the liquid and gas phases slug flow occurs, becomes possible to maintain the flow stable, is always good health of the plant It has an excellent effect of being retained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment according to the present invention.

FIG. 2 is a schematic diagram showing a state in which a liquid jL and a gas jG flow in opposition, and a limit diagram in a case in which a liquid jL and a gas jG flow in opposition.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a system configuration diagram of a conventional nuclear power plant.

FIG. 5 is a diagram showing a route configuration of a cross-around pipe of a conventional nuclear power plant.

FIG. 6 is an explanatory diagram of a flow state of a gas-liquid two-phase flow caused by loads in a steam pipe and a cross-around pipe.

FIG. 7 is a state diagram of a baker for determining a flow mode in a horizontal pipe.

FIG. 8 is an explanatory diagram when an unstable flow of a gas-liquid two-phase flow composed of a gradient tube and a vertical tube occurs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ascending pipe 2 ... Bent pipe 3 ... Vertical pipe 4 ... 1st drain discharge means 4a, 5a, 6a ... Drain pipe 4b, 5b, 6b ... Drain valve 5 ... 2nd drain discharge means 6 ... 3rd drain Discharge means 13 ... High pressure turbine 14 ... Cross-around pipe 15 ... Moisture separator

Claims (2)

(57) [Claims] 1. A first drain discharge means provided at a lowermost portion of a steam pipe path in a steam pipe for introducing steam containing moisture extracted from a steam turbine to a moisture separator.
And a gentle gradient following a vertical tube connected to the moisture separator
A second drain discharge means provided in the pipe;
Steam pipe, characterized in that it comprises a and a drain valve provided in each drainage means. 2. A steam pipe as claimed in claim 1, wherein the drain valve, characterized in that the opened and closed controlled by the pressure signal of the turbine load signal or steam tubes.