JPH03265794A - Vapor liquid two-phase flow dividing pipe - Google Patents

Abstract

PURPOSE:To distribute steam and water to each equipment equally so as to prevent thickness reduction of the pipe resulting from erosion and corrosion by arranging the constitution of a dividing pipe which distributes vapor liquid two-phase flow to each equipment, in such a way that a branch pipe is extended from a mother pipe by the use of a curved pipe and that the mainstream is taken out from the rear of this curved pipe by means of a straight pipe. CONSTITUTION:The vapor liquid two-phase flow dividing pipe is the combination of two branch pipes. One branch pipe comprises a curved pipe 2a, which is connected to a mother pipe 1 and whose diameter is the same as this mother pipe, a reducer, which is connected to this curved pipe 2a and forms a diameter-reduced part, and a straight pipe 3a, which is extended from this reducer 4 and whose diameter is re duced. The other branch pipe comprises a straight pipe 3b, which is arranged separately on the outside of the curve of said curved pipe 2a so that the axis may deviate from the axis of the mother pipe to the center of the curve, and a curved pipe 2b and a straight pipe 3c, which range from it. This is so arranged that the latter branch pipe may be the mainstream side, and that the flows going straight on may be taken out of the branch pipes using the curved pipes 2a and 2b. For this reason, the liquid becomes easy to flow to the branch sides, and also it becomes possible to distribute both steam and liquid to each equipment by the dividing pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a branch pipe of a gas-liquid two-phase flow transport pipe used in chemical plants, nuclear power plants, etc.

(Prior Art) An example of application of a conventional gas-liquid two-phase flow branch pipe to a nuclear power plant will be described. For example, a boiling water reactor power plant has a system as shown in FIG. first,
The main steam generated in reactor 101 is approximately 68 kg/c
The saturated steam of the Tlabs flows into the high pressure turbine 103 via the main steam pipe 102 . The steam that has done work in this high-pressure turbine 103 is approximately 12% or more during rated operation.
The steam becomes 13% wet and flows into the cross-around pipe 104 from its outlet. Therefore, the flow of fluid inside this cross-around pipe 104 is a gas-liquid two-phase flow, with a liquid film flowing on the wall surface of the pipe and a so-called "annular spray flow" in which droplets flow inside the pipe. . Therefore, in order to remove this moisture from the steam, a cross-around pipe 1 is installed.
A moisture separator 105 is connected to the moisture separator 105, and the gas-liquid two-phase flow that flows into the moisture separator 105 through the cross-around pipe 104 is separated into liquid and vapor. Here, the separated steam is introduced into the low-pressure turbine 107a107b, and the liquid flows into the high-pressure heater 113 via the M/S drain pipe 106, where heat is recovered.

On the other hand, the steam that did work in the low pressure turbines 107a and 107b and drove the generator 108 is
It flows out from the outlet of 107b, enters the condenser 109, and condenses to become condensate. This condensate is supplied to a condensate pump 110 and a low pressure heater 1lla.

11 l b, 111 c, reactor feed water pump 11
2 and the high pressure heater 113 before returning to the nuclear reactor 101.

In addition, the steam is supplied to the high pressure turbine 103 and the low pressure turbine 1.
07a, 107b to bleed pipe 114a.

114b, 114c, 114d, 114e, high pressure heaters 113a, 113b and low pressure heater 1
1.1. a, 1llb, and 1llc, respectively,
Heating condensate and feed water. The steam extracted from these turbines is wet steam, and the steam extracted from the turbines 114a and 114b is
, 114c, 114d.

The fluid flow in 114e is a gas-liquid two-phase flow with a humidity of 4% to 40%.

Furthermore, in nuclear power plants, due to the arrangement of equipment,
Cross-around pipe 10 connected to moisture separator 105
4 and bleed pipes 114a, 114b entering each heater.
, 114c, 114d.

114e may be branched. FIG. 6 shows an example of a gas-liquid two-phase flow branch pipe. Here, in order to distribute wet steam from the high pressure turbine 103 to one moisture separator 105a, 105b, the cross-around pipe 104 is branched into two using a Y branch pipe 116. The steam from which the moisture has been separated is then transferred to a low pressure turbine 10.
7a.

While being supplied to 107b, the liquid is discharged from the M/S drain pipe.

(Problems to be Solved by the Invention) This conventional method of branching a gas-liquid two-phase flow using the Y branch pipe 116 uses the same method as the method of distributing a single-phase flow of only steam, so each moisture separation The piping is configured to account for losses after branching so that the same amount of steam flows into the vessel. However, recent T-junction pipes for gas-liquid two-phase flow
Steam-water distribution test result report (M, T
, Rubel +et a! , “Phase Dist.
r4bution during Steam-wat
er Flowin a l1orizontal T
-junction”, Int, J, Multjp
hase Flow, Vol. 14. No, 425-4
38.1.988), the steam distribution ratio and the water distribution ratio are not equal, and the steam and water distribution ratio after branching depends on the humidity and distribution ratio.
This suggests that the water distribution ratio changes. Figure 4 (,a
) shows the schematic configuration of a test device for measuring the distribution ratio between the amount of steam and the amount of water in a gas-liquid two-phase flow branch pipe. This test device has a T-joint configuration consisting of an upstream main pipe 10, a downstream main pipe 12, and a branch pipe 11 branched from these in a right angle direction. Then, based on the steam 1WGI and water amount WL1 flowing in the upstream main pipe 10 measured by this test device, and the steam NWG8 and water amount WL8 flowing in the branch pipe 11, the upstream main pipe 10 before branching is determined.
and the steam distribution ratio of branch pipe 11 after branching (WO2/WGI
) and the water volume distribution ratio (WL3/WLI) based on the test results are shown in FIG. 4(,b). In Figure 4(b), the horizontal axis represents the water distribution ratio (WL3/WLI).
However, the vapor distribution ratio (WO2/WGI) is also shown on the vertical axis. Here, WO2/WGI −WLl /W
The case of LI-1 represents the case where the full flow rate flows through the branch pipe 11. Moreover, the 45° diagonal line in FIG. 4(b) indicates the case where the amount of steam and the amount of water are divided at the same ratio.

The test results (Fig. 4(b)) show that the apparent average flow velocity of steam is G5-18. This is the case of 2tn/s. Here, if the wetness of the steam is small (data marked with a cross in Figure 4(b)), the apparent average flow velocity of water (droplets) is LS = 0.
．． 00544 m/s )), the distribution ratio of the amount of steam and the amount of water almost overlaps with the 45° diagonal line, and both are distributed at almost the same ratio. However, when the humidity increases (◇ mark shown in Figure 4 (b) (LS -0,0198 m/s)
and landmark data (LS-0,0342m/s))
, the amount of water flowing into the branch pipe 11 is smaller than the amount of steam flowing into the branch pipe 11. According to the landmark data (LS = 0.0198m/s),
When the steam distribution ratio is 0.5, the water distribution ratio is 0.22, which indicates that as the humidity increases, a considerable deviation occurs in the water distribution ratio.

In this way, the distribution of a gas-liquid two-phase flow using a branch pipe shows that unlike the distribution of a single-phase steam flow, even if the amount of steam distributed is the same, the distribution of moisture is not necessarily the same. These differences in the steam/water distribution ratio, especially when the steam is highly humid, result in a moisture level other than the design point of each device in the nuclear power plant, causing problems in its performance. In addition, the uneven distribution of water amount manifests as unevenness in the amount of separated drain (water amount) in the moisture separator, which may cause an imbalance in the drain system.

Furthermore, in gas-liquid two-phase flow piping, problems of thinning of the inner wall of the piping due to erosion and corrosion have conventionally occurred. This is because the rate of thinning of the inner wall of the pipe depends on the flow velocity, humidity, temperature, water quality, pipe shape, etc. in the pipe, and especially with regard to the humidity of steam, if other conditions are the same, the humidity will be higher. This is because the rate of thinning becomes large. In order to avoid these problems, distribution of gas-liquid two-phase flow using branch pipes is different from distribution of single-phase steam flow, in which the distribution ratio of steam and liquid (water) are made equal. It is necessary to have a suitable configuration.

The present invention has been made in view of the above points, and even if the branch pipe is branched into a T-shape due to the arrangement of the connected equipment, the flow of the fluid is changed so that the amount of steam and the amount of water can be distributed almost equally. The purpose of this invention is to provide a gas-liquid two-phase flow branch pipe.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a main pipe disposed on the upstream side, a bent pipe connected to the main pipe, and a tube axis of the main pipe located on the back side of the downstream side of the bent pipe. The present invention relates to a gas-liquid two-phase flow branch pipe characterized by comprising a straight pipe connected to a bent pipe biased towards the center of curvature.

(Function) In the gas-liquid two-phase flow branch pipe configured as described above, when the gas-liquid two-phase flow introduced from the main pipe passes through the region of the bent pipe,
Centrifugal force acts on the liquid film and droplets inside the pipe, and the flow direction of the mainstream is slightly shifted due to the deviation of the straight pipe, resulting in a large flow resistance. Therefore, the liquid film and droplets flow more easily to the straight pipe side than in the conventional case, and the amount of steam and water are distributed almost equally to each branch pipe.

(Example) An example of the gas-liquid two-phase flow branch pipe of the present invention will be described below with reference to FIG.

As shown in Fig. 1, the gas-liquid two-phase flow branch pipe that distributes the gas-liquid two-phase flow to two devices consists of a main pipe 1, a bent pipe 2a connected to the main pipe 1, and a bent pipe 2a of the same diameter. It consists of a reducer 4 connected to this bent pipe 2a to form a reduced diameter section, and a straight pipe 3a with a reduced diameter extending from this reducer 4, and this straight pipe 3a is used to connect equipment such as a moisture separator etc. 5a and 5b.

These bent pipe 2 a % reducer 4 and straight pipe 3 a constitute a branch pipe section (branch pipe). Furthermore, the bent pipe 2a
Another straight pipe 3b is arranged at the outer bent part (dorsal side) of the main pipe 1 so that its axis is shifted from the center of the bent part from the pipe axis of the main pipe 1, and the bent pipe 2b and the straight pipe 3C are connected. to configure another branch pipe. This branch pipe is then connected to the device 5b. Further, a guide vane 6 for guiding the flow of the gas-liquid two-phase flow to the device 5a is arranged inside the bent pipe 2a.

In the gas-liquid two-phase flow branch pipe configured in this way,
The fluid flow is as shown in FIG.

Figure 3 shows the flow of the gas-liquid two-phase flow (annular spray flow) in the branch pipe, and as shown in Figure 3(a), in the conventional gas-liquid two-phase flow branch pipe, the flow is The liquid film 20 and droplets 21 are in a state where it is difficult for the liquid film 20 and droplets 21 to flow in the branch pipe 11, which branches off from the flow in the downstream main pipe 12 that advances straight from the upstream main pipe 10.

On the other hand, in the gas-liquid two-phase flow branch pipe of the present invention, as shown in Fig. 3 (
As shown in b), since the bent pipe 2a is used in the branch pipe section, when the flow passes through the area of this bend N2a, centrifugal force acts on the liquid film 20 and droplets 21 in the pipe, causing the bent pipe to An excess liquid film is formed on the outer circumferential portion of tube 2a, particularly at the bent portion before branching into straight pipe 3b and at the reservoir portion in front of reducer 4. On the other hand, a thin liquid film 20 is formed on the inner circumference of the bent pipe 2. Furthermore, since the flow direction of the main pipe 1 is slightly shifted from the center of the bending part of the straight pipe 3b from the pipe axis of the main pipe 1, the flow resistance becomes large. In addition, the pressure loss on the branch pipe 3b side is reduced,
And the flow balance becomes equal. Therefore, the liquid film 20 and droplets easily flow toward the branched pipe 3a, and the amount of steam and water can be distributed to the branch pipes in substantially equal amounts. In particular, in the light branch pipe of the present invention, equipment 5a is removed from the branch pipe for steam distribution.

straight pipe 3 so that the pressure loss up to 5b is equal.
a, 3b, 3C% bent pipe 2a.

Since the apertures and lengths of the reducer 2b and the reducer 4 are set, the amount of steam and the amount of water are distributed almost equally.

Regarding the distribution of liquid (water), as shown in FIG. Since the flow can be changed to the pipe 3a, it becomes easier to accompany the flow of steam toward the branch pipe 3a, and the liquid (water) is distributed to the same extent as the steam.

In the gas-liquid two-phase flow branch pipe of this embodiment, the main stream (here, the flow is in the same direction as the upstream side) and the tributary stream (here, the flow is deflected with respect to the main stream) are bent into pipes 2a and 2b. This is done so that the straight pipe side becomes the main flow, and the straight flow is taken out from the bent pipe as a branch pipe. This makes it easier for liquid (water) to flow to the branch pipes, and the branch pipes make it possible to evenly distribute both steam and liquid to each device, ensuring the designed humidity level for each device.
In the end, the performance of each device is ensured. Additionally, the liquid is evenly distributed to the branch pipes, keeping the drain system well balanced. Furthermore, since the moisture level within each branch pipe after distribution is made uniform, thinning of the inner wall of the pipe due to erosion and corrosion is prevented as much as possible.

Further, an embodiment of the gas-liquid two-phase flow branch pipe of the present invention for distributing the gas-liquid two-phase flow to three devices will be described with reference to FIG. In the branch pipe of this embodiment, a bent first bent pipe 2a that branches to a first device 7 (for example, a moisture separator) is connected to the main pipe 1,
The diameter is reduced by a reducer 4a and connected to the first branch pipe 3a,
Connect to the first device 7. Then, a straight pipe 3b is arranged at the outer bent part (back side) of the bent pipe 2a so that its pipe axis is shifted from the pipe axis of the main pipe 1 from the center of the bent part, and the bent pipe 2b and the reducer 4b Connect the branch pipe 3c via
A second device 8, which is arranged in parallel with the first device 7, is disposed at this tip. Furthermore, in this embodiment, 1 is provided with another straight pipe 3 on the back side of the bent pipe 2b as described above.
d, and the second device 8 is connected via the bent pipe 2C and the branch pipe 3e.
The third device 9 is connected to the third device 9 installed in parallel.

Note that guide vanes may be provided within the bent pipes 2a and 2b as in the previous embodiment. In the branch pipe constructed in this way, the gas-liquid two-phase flow is evenly distributed as in the previous embodiment. In the gas-liquid two-phase flow branch pipe of this embodiment, the pressure loss in the tributaries flowing to each device with respect to the main stream is reduced, and the liquid can more easily flow into the tributaries. Therefore, it becomes possible to evenly distribute gas and liquid to each device. Furthermore, multiple branch pipes are installed in parallel in one direction (three in this example).
This makes it possible to save space for installing piping, making it possible to downsize nuclear power plants and the like as a whole.

〔Effect of the invention〕

According to the present invention, the branch pipe for distributing the gas-liquid two-phase flow to each device is extended from the main pipe using a bent pipe, and the main flow is taken out from the back side of the bent pipe using a straight pipe. As a result, pressure loss on the branch pipe side is reduced and liquid flows more easily into the branch pipe. Therefore, the amount of steam and water can be uniformly distributed to each device, and the designed humidity of each device can be ensured sufficiently. As a result, the performance of each device is guaranteed, and it is also possible to prevent thinning of the inner walls of the pipes due to erosion and corrosion caused by increased humidity due to uneven water flow between branch pipes. It has a great effect.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the gas-liquid two-phase flow branch pipe of the present invention, FIG. 2 is a schematic diagram of another embodiment of the present invention, and FIG. 3 is a schematic diagram of an embodiment of the gas-liquid two-phase flow branch pipe of the present invention. An explanatory diagram showing the flow state of a gas-liquid two-phase flow cut along the turbine axis in a branch pipe in order to compare the function of the pipe with a conventional one. Schematic diagram of the test device for measuring the distribution ratio of steam and water and the measured steam distribution ratio of branch pipes after branching (WG3
/WGl) and the water distribution ratio (WL3 /WLI>), Figure 5 is a schematic diagram of a nuclear power plant, and Figure 6 is an example of the use of a gas-liquid two-phase flow branch pipe in a nuclear power plant. It is a schematic diagram.]... Main pipe, 2... Bent pipe, 3a... Branch pipe, 3b
... Straight pipe, 4... Reducer, 5. 7. 8.
9... Equipment, 6... Guide vane, 101... Nuclear reactor, 103... High pressure turbine, 104... Cross-land pipe, 105... Moisture separator,] 07... Low pressure Turbine, 108... Generator, 109... Condenser, 114... Air extraction pipe.

Claims (1)

[Claims] A main pipe disposed on the upstream side, a bent pipe connected to the main pipe, and a bent pipe connected to the main pipe, and on the back side of the downstream side of the bent pipe, the pipe axis of the main pipe is biased toward the center of curvature of the bent pipe. A gas-liquid two-phase flow branch pipe characterized in that it consists of a connected straight pipe.