JPH08159826A - Back flow measuring preventive type turbine flow meter - Google Patents

Abstract

PURPOSE: To provide a back flow measurement preventive type turbine flow meter in which mismeasuring is prevented when a fluid flows in the reverse direction. CONSTITUTION: In the turbine flow meter 1 which is equipped with a vane wheel 3, which is set in a guide cylinder 6 and rotates by the flow of a fluid, and measures flow rate based on the rotation amount thereof, a reverse flow preventive lid 8 is provided on the downstream side from the vane wheel 3 so that the lid 8 is pushed so as to be folded along the flow when the fluid flows in the regular direction and so that the lid 8 is pushed and spread by the fluid so as to block the flow and to close the guide cylinder 6 when the fluid flows in the reverse direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbine type flow meter for measuring a flow rate from the amount of rotation of an impeller, and more particularly to a reverse flow measurement prevention type turbine type flow meter which prevents erroneous measurement when a fluid flows in a reverse direction. It is about.

[0002]

2. Description of the Related Art A turbine type flow meter is known as a device for measuring the flow rate of a fluid. The turbine type flow meter is configured such that an impeller having a plurality of blades arranged radially around a rotating shaft is placed in a fluid and a pulse is generated for each predetermined rotation amount of the impeller. When the fluid is pushed by the fluid and rotates, the pulse generated is counted to obtain the rotation amount of the impeller, and the flow rate of the fluid is measured from this rotation amount.

Turbine flow meters are, for example, LNG, LP
BOG (boil-off gas) of a low temperature liquefied gas tank such as G
It is installed in a pipe, and is used for the purpose of detecting the amount of BOG generated in the tank from the flow rate of BOG flowing in the pipe and measuring the heat insulation performance of the tank from the amount of BOG generated. L
In the NG tank, the amount of BOG generated is slightly different depending on the liquid level and the time elapsed after charging, but it is a level where a slight pressure is constantly generated in the LNG tank, and the amount of BOG generated during LNG storage is constant. The smaller the amount, the better the heat retention of the LNG tank. Therefore, the amount of BOG generated is used as the guaranteed value of the performance of the LNG tank.

For the purpose of detecting the flow rate of BOG flowing in the pipe as described above, the turbine type flow meter is advantageous for measuring with a low resistance because the flow velocity is a slow flow of several m / sec at most. is there. Also, the amount of BOG generated can be found by detecting the change in the liquid level in the LNG tank. This is suitable for long-term measurement, and for short-time measurement, the flow rate of BOG flowing in the pipes. Is better to detect.

[0005]

By the way, the conventional turbine type flow meter is constructed so that the impeller can rotate either left or right, and the rotation amount is obtained by counting the pulses generated by the rotation of the impeller. , It cannot be detected whether it is rotating left or right. For this reason, even if the fluid flows in the forward direction (which is originally the direction in which the flow rate is desired to be measured) or in the reverse direction, there is a characteristic that both are counted regardless of the direction.

In the LNG tank to which the BOG generation amount detection method described above is applied, usually, a plurality of LNG tanks are connected to each other by piping of a BOG line. In this case, the amount of BOG generated may vary depending on the LNG tank. For this reason, the pressure balance between the LNG tanks may change, and the BOG flow in the BOG pipe may flow in and out. Even in a single LNG tank, depending on the operating condition, for example, when the negative pressure is obtained by paying out, B
The flow of OG goes in and out. In the conventional turbine type flow meter, the impeller rotates both left and right, and counts both the inflow and outflow of the BOG flow. In this way, since the direction of the flow cannot be detected, the measurement is made as if it is actually coming in, but in that case, an error equivalent to twice the measured value is generated, and the reliability of the measurement is increased. Sex is impaired.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a reverse flow measurement prevention type turbine type flow meter which prevents erroneous measurement when a fluid flows in the reverse direction.

[0008]

In order to achieve the above object, the present invention has a turbine type flow meter which has an impeller provided in a guide cylinder and which is rotated by the flow of fluid, and which measures the flow rate from the amount of rotation thereof. In the downstream of the impeller, when the fluid flows in the forward direction, it is pushed by the fluid and folded along the flow, and when the fluid flows in the reverse direction, it is pushed by the fluid and expanded so as to interrupt the flow. A backflow prevention lid for closing the guide cylinder is provided.

The backflow prevention lid is a hinge in which two semicircular plates are attached to one shaft to form a hinge. These semicircular plates are substantially inclined at a folding position and a flow inclined at a predetermined angle toward the downstream side. Movement may be allowed between orthogonal expansion positions.

[0010]

With the above structure, when the fluid flows in the forward direction, the impeller upstream of the backflow prevention cover rotates, and the backflow prevention cover is folded and follows the flow, so that the flow that rotates the impeller can be prevented. Absent. When the fluid flows in the opposite direction, the backflow prevention lid is opened to block the fluid. Since the impeller is located downstream of the backflow prevention lid (downstream of the reverse flow), it does not rotate.

When the two semi-circular plates are in the folded position inclined by a predetermined angle toward the downstream side, an acute angle is formed toward the impeller and does not hinder the flow in the positive direction from the impeller. When viewed from the opposite direction, the two semi-circular plates are in a shape that is susceptible to flow. Then, in the opposite direction, 2
The half-discs are pushed by the flow in the opposite direction and are expanded to the expanded position which is almost orthogonal to the flow. The flow is impeded when the two semi-circular plates are approximately perpendicular to the flow. When the flow in the forward direction again occurs, the two semi-circular plates are pushed by the flow in the forward direction and closed to the folding position.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, a reverse flow measurement prevention type turbine type flow meter 1 of the present invention is placed in a horizontal pipe 2 through which a fluid flows. The impeller 3 is provided with a plurality of blades 5 radially around a rotating shaft 4 placed along the flow. The impeller 3 is housed in a bottomless cylindrical guide tube 6 having a predetermined length in the axial direction. A proximity sensor 7 (FIG. 2) using magnetism is provided on the body of the guide cylinder 6 radially outward of the impeller 3. This proximity sensor 7
Is connected to a pulse generator (not shown), and a pulse is generated when the approach of the blade 5 is detected. This pulse is generated each time the rotating shaft 4 rotates by the pitch angle of the blade 5, so that the amount of rotation of the impeller 3 can be known by counting. From this rotation amount, horizontal piping 2
The flow rate of the fluid flowing through can be measured.

In FIG. 1, the flow from right to left (solid line arrow) is the flow in the forward direction in which the flow rate is to be measured.
The flow from the left to the right (broken line arrow) is the flow in the opposite direction.
A backflow prevention lid 8 is provided downstream of the impeller 3 when viewed from the normal direction.

As shown in FIGS. 2 (a), 2 (b) and 2 (c), the backflow prevention lid 8 is provided with shaft supports 9 above and below the end portion of the guide cylinder 6, and the upper and lower shaft supports 9 are provided. , 9 is provided with a shaft 10 along the diameter of the guide cylinder 6, and two semi-circular plates 11 having substantially the same diameter as the guide cylinder 6 are attached to the shaft 10. The semicircular plate 11 has a chord portion on the shaft 10 side and an arc portion on the outside of the shaft 10. The semi-circular plates 11 are attached while being allowed to move in opposite directions about their respective axes. That is, the backflow prevention lid 8 is a butterfly-shaped lid 1 in which two semi-circular plates 11 are attached to one shaft 9 to form a hinge.
It is composed of two. These semi-circular plates 11 are allowed to move from an expanded position (broken line) almost orthogonal to the flow to a folded position (solid line) inclined by a predetermined angle toward the downstream side. However, this angle is an angle at which the cross-sectional area of the fluid at the folded position is secured as necessary, and the impeller 3
In order to deploy the backflow prevention lid 8 before the reverse rotation of the backflow, the backflow prevention lid 8 can receive a necessary force from the fluid.

As shown in FIG. 3, the backflow measurement prevention type turbine type flowmeter 1 is placed at a position 20% off from the center on the vertical diameter of the horizontal pipe 2. This is separated from the center in order to avoid the influence of turbulence, and is based on the finding that the average flow velocity of the fluid can be obtained at a position of 20% of the pipe diameter.

Also, as shown in FIG.
When the G tanks 41 are connected to each other by the BOG pipe 42, the backflow measurement prevention turbine type flowmeter 1 is provided for each LNG tank 41. However, although the backflow measurement prevention turbine type flow meter 1 is shown in the BOG pipe 42 for convenience in FIG.
A horizontal pipe is provided for each NG tank 41, and the reverse flow measurement prevention turbine type flow meter 1 is placed in the horizontal pipe with the direction in which BOG flows out from the LNG tank 41 as the forward direction.
Further, the horizontal pipe is placed at a position separated from the rising portion from the LNG tank 41 by a straight pipe length longer than a predetermined length. This is to ensure a sufficient length to stabilize the turbulent flow in order to avoid the influence of the turbulent flow.

Next, the operation of the embodiment will be described.

It is assumed that the two semi-circular plates 11 of the backflow prevention lid 8 are in indefinite positions within the movable range.

When the fluid starts to flow in the forward direction, the impeller 3 upstream of the backflow prevention lid 8 is pushed by the fluid and rotates.
This flow hits the two semi-circular plates 11 downstream. The two semi-circular plates 8 are pushed by the fluid and come to the folding position which is inclined at a predetermined angle toward the downstream side. In this way, the backflow prevention lid 8 formed by the two semi-circular plates 11 is folded to form a V-shape with the apex facing the impeller 3. The backflow prevention lid 8 does not prevent the flow from the impeller 3 in the forward direction. Therefore, the impeller 3 rotates properly, and a pulse is generated each time the proximity sensor 7 detects the approach of the blade 5. By counting this pulse, the rotation amount of the impeller 3 is obtained, and the flow rate of the fluid flowing through the horizontal pipe 2 is measured from this rotation amount.

At this time, when viewed from the opposite direction, the two semi-circular plates 11 are on the inner corner side of the V-shape, and are shaped so as to easily receive the flow. The angle is an angle at which the cross-sectional area of the fluid is sufficient to deploy the backflow prevention lid 8 before the impeller 3 rotates in the reverse direction.

Next, when the fluid begins to flow in the opposite direction, the two semi-circular plates 11 are pushed by the fluid in the opposite direction and expanded to the expanded position which is substantially orthogonal to the flow. Thus two half-disks 1
The backflow prevention lid 8 by 1 is expanded to block the fluid. Also,
One end of the guide cylinder 6 is almost closed. Impeller 3
Does not rotate because it is located downstream of the backflow prevention lid 8 (downstream of the flow in the opposite direction) and within the guide tube 6. Therefore, the measured flow rate becomes zero.

According to the present invention, the flow rate is measured only when the fluid flows in the forward direction, and the flow rate becomes zero when the fluid flows in the reverse direction, so that erroneous measurement is prevented. LN using the present invention
When measuring the BOG generation amount of the G tank 41, since only the flow rate of the discharged BOG is measured, the correct BOG generation amount is known, and the measurement reliability is improved.

For the purpose of blocking the fluid flowing in the opposite direction,
Configure the impeller blades to move according to the direction of flow,
When the fluid flows in the opposite direction, the blade may move to a position where the impeller does not rotate, but the structure of the movable part becomes complicated. Compared with this, the backflow prevention lid of the present invention has a simple structure.

The present invention can be applied to the BOG generation amount measurement of the LNG tank described in the embodiment, the BOG generation amount measurement of the LPG tank, and the flow meter of the interchange pipe for gas trading.

[0026]

The present invention exhibits the following excellent effects.

(1) The flow rate is measured only when the fluid flows in the forward direction, erroneous measurement when the fluid flows in the reverse direction is prevented, and the reliability of the measurement is improved.

(2) The backflow prevention lid can be simply constructed by attaching two semi-circular plates to one shaft to form a hinge.

[Brief description of drawings]

FIG. 1 is a side view in a horizontal pipe of a reverse flow measurement prevention type turbine type flow meter showing an embodiment of the present invention.

2 (a) is a plan view, FIG. 2 (b) is a side view, and FIG. 2 (c) is a front view of the reverse flow measurement prevention turbine type flow meter of FIG.

FIG. 3 is an internal side view of horizontal piping on which the reverse flow measurement prevention type turbine type flow meter of the present invention is placed.

FIG. 4 is a schematic view of an LNG tank using the present invention.

[Explanation of symbols]

 1 Turbine type flow meter 3 Impeller 8 Backflow prevention lid

Claims (2)

[Claims] 1. A turbine type flow meter having an impeller, which is provided in a guide cylinder and rotated by the flow of fluid, and measures the flow rate from the amount of rotation of the impeller, when the fluid flows in the forward direction downstream of the impeller. A backflow prevention lid that is pushed by the fluid and folds along the flow, and is expanded by the fluid to block the flow when the fluid flows in the opposite direction and closes the guide tube is provided. Backflow measurement prevention type turbine type flow meter. 2. The backflow prevention lid is a hinge in which two semi-circular plates are attached to one shaft to form a hinge, and these semi-circular plates have a folding position and a flow that are inclined at a predetermined angle toward the downstream side. 2. The backflow measurement prevention type turbine type flow meter according to claim 1, wherein movement is allowed between the expanded position and the position substantially orthogonal to.