JPH05340503A - Piping - Google Patents

Abstract

PURPOSE:To reduce the temperature of liquid in a falling water pipe to below the saturation temperature within a short distance from the cooling water injection point by a method wherein a cooling water injection pipe is attached to the falling water pipe at a specified tilting angle to the tangential line of the cross section perpendicular to the axis of the falling water pipe at the connection point. CONSTITUTION:A falling water pipe 6 is connected to a high pressure drain tank on the upstream side, and provided with a cooling water injection pipe 2. The cooling water injection pipe 2 is attached at an angle of 30-70 deg. to the tangential line of the cross section perpendicular to the axis of the falling water pipe 6 at the connection point of the injection pipe 2. Therefore, the injection water deflects the stream of the drain in the falling water pipe 6 and is easily mixed into the drain, so that the distance between the cooling water injection point and a point where the temperature of the drain drops below the saturation temperature is shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drain pump up system for returning a drain of a feed water heating pipe to a condensate pipe by a drain pump in a power plant, etc. The present invention relates to a piping device suitable for preventing the occurrence of cavitation in a suction section.

[0002]

2. Description of the Related Art In a high-pressure feed water heater drain pump up system of a power plant, drains of a high-pressure feed water heater, a moisture separator, and a steam heater are collected in a high-pressure drain tank and extracted from there by a high-pressure drain pump. After being mixed with the condensate flowing through the condensate pipe, the pressure is increased by the water supply pump and sent to the steam generator. That is, as shown in FIG. 7, the drain of the high-pressure feed water heater is sent to the drain tank 3 through the drain pipe 2 after being cooled by the built-in drain cooler. The drain of the upstream high-pressure feed water heater 4 is sent as it is to the drain tank 3 through the drain pipe 2, and the pressure of the drain tank 3 is kept equal to the pressure of the high-pressure feed water heater 4 by the pressure equalizing pipe 5. The drain thus collected is temporarily stored in the drain tank 3 and then extracted by the downcomer pipe 6, boosted by the high-pressure pump 7 and supplied to the condensate pipe 8 with sufficient pressure, and then the condensate flows there. It is supposed to be mixed with water. In the figure, reference numerals 9 and 10 indicate a low-pressure feed water heater, and 11 indicates a feed water pump.

The drain in the high-pressure drain tank 3 and the downcomer pipe 6 is saturated water, and the pressure in the high-pressure drain tank 3 drops during a transient operation such as a turbine load drop. Since the pushing pressure against the water decreases and the pressure at the pump inlet becomes the saturated pressure at the drain temperature, the saturated water in the downcomer pipe 6 is flushed and cavitation occurs, which adversely affects the function of the high-pressure drain pump 7. Further, when the cavitation is large, the high pressure drain pump 7 is damaged.

High pressure drain tank 3 during the above transient
Comparing the internal pressure drop and the pressure drop at the inlet of the high-pressure drain pump 7, the pressure drop at the inlet of the high-pressure drain pump 7 is due to the accumulation drain of the high-pressure drain tank 3 and the downcomer pipe 6. There is a time delay in switching to.

Since this time delay has a great influence on the occurrence of cavitation at the pump inlet, conventionally, the installation position of the high pressure drain tank 3 is raised to secure the effective suction head of the high pressure drain pump 7 and to reduce the amount of accumulated drain. The flow velocity in the downcomer pipe 6 is increased as much as possible to reduce the flow rate.

However, in this method, in order to cope with various transient changes of the plant, the installation position of the high pressure drain tank 3 becomes too high, or the high pressure drain pump 7 is installed.
It is not a realistic method because it has a large capacity.

Therefore, as a method for reducing the time delay of the pressure drop due to the accumulated drain against transient changes in these plants, there is a method of injecting cold water having a lower temperature than this drain into the drain of the suction pipe to cool the drain. ..

As shown in FIG. 7, this is a cold water injection pipe 1
2 is connected to the downcomer 6 to lower the temperature of the drain. As shown in FIG. 8, at this connection portion, the cold water injection pipe 12 joins the downfall pipe 6 through which drain flows from the side.
The shape of the joint is such that two fluids having different temperatures are mixed at the confluence of the T joint to lower the temperature of the drain.

[0009]

As described above, the drain in the drain tank 3 and the downcomer pipe 6 is saturated water, and the pressure in the drain tank 3 drops during transient operation such as when the turbine load drops. Therefore, the saturated water that is the drain in the downcomer pipe 6 is flushed, and cavitation is likely to occur. Therefore, cold water having a temperature lower than that of the drain in the downcomer pipe 6 is injected into the downcomer pipe 6 so that the drain in the downcomer pipe 6 has a temperature lower than the saturation temperature of the state at that time. In the configuration of (2), when the two fluids having different temperatures are merged, the cold water flowing from the side is pushed by the drain flowing from the upstream around the center of the downcomer pipe 6, and the drain in the downcomer pipe 6 is cooled on the cold water injection pipe 12 side. However, it is difficult to cool the opposite side. The drain temperature in the downfall pipe 6 on the opposite side of the cold water injecting pipe 12 decreases because the inner diameter of the pipe is D, and the straight pipe equivalent length L is about 20D to 30D downstream from the cold water injecting point. In such a structure, the cooling effect cannot be obtained. Therefore, it is an object of the present invention to provide a merging piping device that lowers the temperature of the liquid in the downcomer below the saturation temperature within a very short distance from the cold water injection point.

[0010]

In order to achieve the above-mentioned object, the present invention rains a cold water injection pipe for injecting cold water so as to lower the temperature of a liquid containing a two-phase flow in a downfall pipe connected with an upstream vessel. The pipe connected to the pipe is characterized in that the cold water injection pipe is attached at an angle of 30 to 70 degrees with respect to the tangent line at the attachment point of the cold water injection pipe with respect to a cross section perpendicular to the axis of the downfall pipe. In addition, the present invention is characterized in that at least two cold water injection pipes are attached to a downfall pipe in order to achieve the above object.

In order to achieve the above object, the present invention connects a cold water injection pipe for injecting cold water to the downcomer pipe so as to lower the temperature of the liquid containing the two-phase flow in the downcomer pipe connected to the upstream vessel. In this case, the cold water injection pipe is inclined 30 to 70 degrees downstream from the downcomer pipe axis, and is further inclined 30 to 70 degrees with respect to the tangent at the attachment point of the cold water injection pipe in a cross section perpendicular to the downfall pipe axis. It is what In addition, the present invention is characterized in that at least two cold water injection pipes are attached to a downfall pipe in order to achieve the above object.

[0012]

The principle of the present invention will be described with reference to FIG. Figure 6
(B) shows the temperature drop of the drain when the flow of the drain of the downcomer is eccentric and is changed into a vortex. The horizontal axis represents the straight pipe equivalent length L from the injection point of the cold water injection pipe, and the vertical axis represents the drain temperature T. The straight pipe equivalent length L until the drain temperature T changes from the temperature To to the temperature Te by cold water starts to drop at a length much shorter than 20D to 30D as compared with the conventional case shown in FIG. Further, FIG. 6C shows a graph regarding the mounting angles θ ₁ and θ ₂ of the cold water injection pipe.
θ ₁ is 0 degrees downstream and 18 degrees upstream with respect to the downcomer axis.
0 degree and θ ₂ represent the angle with respect to the tangent line of the attachment point of the cold water injection pipe in the cross section perpendicular to the downcomer pipe axis. The horizontal axis is the cooling water injection pipe installation angle θ ₁ , θ ₂ , one vertical axis (left)
Take the straight pipe equivalent length L until the temperature of the drain drops. The other vertical axis (right) shows the pressure loss ΔP with respect to the mounting angle θ ₁ of the cold water injection pipe. When the installation angles θ ₁ and θ ₂ of the cold water injection pipe are 0 degrees, the straight pipe equivalent length L until the temperature of the drain drops becomes long, and when the installation angles θ ₁ and θ _{2 of the} cold water injection pipe become large, The straight pipe equivalent length L until the temperature of the drain drops is improved, and the straight pipe equivalent length L until the temperature of the drain drops becomes 135 at 135 ° for the mounting angle θ ₁ of the cold water injection pipe. If it becomes larger than the degree, the straight pipe equivalent length L until the temperature of the drain drops becomes long. Further, for the installation angle θ ₂ of the cold water injection pipe, the straight pipe equivalent length L until the temperature of the drain decreases at 90 degrees becomes longer, and the straight pipe equivalent length L until the temperature of the drain decreases at 135 degrees becomes Becomes shorter,
When the temperature is larger than 135 degrees, the straight pipe equivalent length L until the temperature of the drain drops becomes long. However, the pressure loss ΔP increases as the mounting angle θ ₁ of the cold water injection pipe increases, and when the pressure loss increases, the flow rate required by the subsequent equipment cannot be obtained.

Considering the above two points, FIG.
From (c), the installation angles θ ₁ and θ ₂ of the cold water injection pipe are
The range in which the straight pipe equivalent length L until the temperature of the drain drops is improved, and the range in which the pressure loss ΔP is stable with respect to the change in the mounting angle θ ₁ of the cold water injection pipe 30 to
It turns out that a range of 70 degrees is desirable.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a cold water injection pipe 12 is attached to a downcomer pipe 6 connected to an upstream high-pressure drain tank (not shown). As shown in FIG. 1 (a), the cold water injection pipe 12 has a cold water injection pipe 12 in a cross section perpendicular to the downcomer pipe axis.
It is attached at an angle of 30 to 70 degrees with respect to the tangent line at the attachment point. For this reason, the cold water eccentrically causes the drain flow in the downcomer pipe 6 at the merging portion, and the cold water easily enters and mixes with the drain, and the distance from the cold water injection point until the drain temperature falls is set. Can be shortened. Further, four cold water injection pipes 12 of FIG. 2 are attached on the same cross section with the downcomer pipe 6 (FIG. 2A), and the drain flow of the downcomer pipe 6 is further eccentric at the confluence portion as compared with the above-mentioned embodiment. It is possible to make the cold water flow into the drain and mix easily, and it is possible to shorten the distance from the cold water injection point until the drain temperature drops. In addition, at least two cold water injection pipes 12 and 6 pipes as required.
You can attach up to a book.

Another embodiment of the present invention will be described. In FIG. 3, a cold water injection pipe 12 is attached to the downfall pipe 6. As shown in FIG. 3C, the cold water injection pipe 12 is inclined 30 to 70 degrees in the downstream direction with respect to the downcomer pipe axis,
Further, as shown in (a), the cold water injection pipe 12 is attached at an angle of 30 to 70 degrees with respect to the tangent line at the attachment point. For this reason, the drain flow in the downcomer pipe is eccentric at the confluence part, and the drain flow downstream from the confluence part changes into a vortex, so that cold water easily enters the drain and mixes easily. It is possible to shorten the distance from the cold water injection point until the water drops. Further, two cold water injecting pipes 12 of FIG. 4 are attached on the same cross section where the downfall pipe 6 is provided (FIG. 4A), and the drain flow of the downfall pipe 6 is further eccentric at the confluence portion as compared with the above embodiment, It is possible to make the flow of cold water that is easy to mix into the drain and mix, and it is possible to shorten the distance from the cold water injection point until the drain temperature drops. It should be noted that at least two cold water injecting pipes 12 can be attached, and up to six can be attached as required.

Further, another embodiment of the present invention will be described.
In FIG. 5, a cold water injection pipe 12 is attached to the downfall pipe 6. This cold water injection pipe 12 has an attachment angle with the downfall pipe 6 similar to the cold water injection pipe 12 of the embodiment of FIG. 4, and two cold water infusion pipes 12 are attached in a spiral shape in the axial direction of the downfall pipe 6. There is. Therefore, the flow of the drain of the downcomer pipe 6 can be changed in a vortex manner in the axial length to which the cold water injection pipe 12 is attached, so that the cooling effect of the cold water can be enhanced and the temperature of the drain from the cold water injection point can be increased. It is possible to shorten the distance until it descends.

[0017]

As described above, according to the present invention,
The cold water injection pipe for injecting cold water so as to lower the temperature of the liquid containing the two-phase flow in the downcomer pipe is connected with respect to the cross section perpendicular to the downcomer pipe axis.
30 to the tangent at the attachment point of the cold water injection pipe
Since it is attached at an angle of 70 degrees, the temperature of the liquid in the downcomer can be lowered to the saturation temperature or less within a very short distance from the cold water injection point. Therefore, according to the present invention, it is possible to prevent the occurrence of cavitation in the drain pump suction portion by flushing with saturated water.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a piping device according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the piping device according to the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the piping device according to the present invention.

FIG. 4 is a configuration diagram showing another embodiment of the piping device according to the present invention.

FIG. 5 is a configuration diagram showing another embodiment of the piping device according to the present invention.

FIG. 6 is a characteristic diagram showing changes in the drain temperature in the downcomer pipe and changes in the length from the cold water injection point.

FIG. 7 is a system diagram showing a conventional feed water heater drain pump amplifier system.

FIG. 8 is a configuration diagram showing a conventional cold water injection pipe.

[Explanation of symbols]

 1, 4 ... High-pressure feed water heater 2 ... Drain pipe 3 ... Drain tank 6 ... Precipitation pipe 7 ... High-pressure drain pump 8 ... Condensate pipe 9, 10 ... Low-pressure feed water heater 11 ... Water supply pump 12 ... Cold water injection pipe

Claims (4)

[Claims] 1. A cold water injection pipe for injecting cold water to lower the temperature of a liquid containing a two-phase flow in a downfall pipe connected to an upstream vessel is connected to the downfall pipe, wherein the cold water injection pipe is rained down. A piping device, which is mounted at an angle of 30 to 70 degrees with respect to a tangent line at a mounting point of a cold water injection pipe with respect to a cross section perpendicular to the pipe axis. 2. The piping device according to claim 1, wherein at least two cold water injection pipes are attached to the downcomer pipe. 3. A cold water injection pipe for injecting cold water to lower the temperature of a liquid containing a two-phase flow in a downfall pipe connected to an upstream vessel is connected to the downfall pipe, and the cold water injection pipe is rained down. A piping device, which is inclined 30 to 70 degrees in a downstream direction with respect to a pipe axis, and is further inclined 30 to 70 degrees with respect to a tangent line at a mounting point of a cold water injection pipe in a cross section perpendicular to the axis of the downfall pipe. 4. The piping device according to claim 3, wherein at least two cold water injecting pipes are attached to the downcomer pipe.