JPH085538A - Measuring apparatus for liquid density for lng tank - Google Patents

Abstract

PURPOSE:To provide a safety solution to dropping of a probe wherein a structure is simple and small and cost is inexpensive. CONSTITUTION:A winding cable 4 is wound by a driver placed on a roof of an LNG tank, and a probe 3 attached to the cable 4 is driven in a predetermined vertical section at a predetermined position in the LNG tank to sense temperature and density in this section by a sensor 6. The winding cable 4 comprises a signal cable 8 and a cable wire longer than the signal cable 8 inserted into a flexible tube 7, while ends of the cable 8 and the wire are fixed to a console 3a and the sensor 6, respectively. When external force is applied to the probe 3, only the signal cable 8 is broken. Although the probe 3 is suspended from the cable wire 9, it does not reach a tank bottom causing no damage on the bottom. In addition, the change in a signal level is sensed due to the breakage of the signal cable, and an alarm is issued.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an LNG storage tank (tank).
Regarding the liquid density measuring device, more specifically, the density of LNG etc. is regularly measured on a fixed point vertical line in the tank so that the LNG stored in the LNG tank does not cause a rollover phenomenon. To a simple density measuring device.

[0002]

2. Description of the Related Art When LNG (liquefied natural gas), which has an extremely low boiling point, is stored in a tank, the density of LNG is not constant at all positions in the tank, and LNG varies depending on the origin. It is general that the components of (1) and (2) differ, and the density also varies depending on the components. In addition, the temperature distribution in the tank is not uniform, and the density changes depending on the temperature distribution even with the same component, so that layers having different densities may be formed in the tank.

When the density of the upper layer is lower than that of the lower layer, the layers are held stably, but in the opposite case, a rollover phenomenon occurs in which the upper and lower layers are inverted. At this time, thermal energy is generated due to fluid friction, and there is a danger that LNG having an extremely low boiling point will be rapidly vaporized and exploded.

In order to prevent such a rollover phenomenon, temperature and density in the vertical direction are measured at a fixed point of the LNG stored in the tank, and the measured values are examined and processed. Specifically, a probe containing a sensor for detecting the temperature and density of LNG is moved up and down from a fixed point on the bottom plate of the tank toward the liquid level, and the LNG in the tank is lifted.
We are observing the temperature and density distribution.

The probe is moved up and down in the tank, but a conventional probe for a small capacity tank, for example, is wound up from a reel driven by a stepping motor or the like via a drive cable attached to the probe. It was
The stepping motor is arranged in a sealed housing on the roof of the tank, and the stepping motor and the inside of the tank are communicated with each other via a stop valve having a drive cable inserted when the valve is opened.

To detect whether or not the probe has landed on the bottom plate of the tank, first, the length of the unwound drive cable is measured by the number of pulses for driving the stepping motor, and then,
This was done by detecting the change in tension acting on the drive cable.

Further, in order to prevent the probe from swinging when the probe is moved up and down, the anchor fixed to the two ribbon cables from the hermetically-sealed housing is wound down on the tank floor plate to tension the ribbon cable, resulting in a tensioned ribbon cable. By guiding the probe, the probe was prevented from rocking and safety was maintained. Further, when inspecting the probe, the probe is housed in a sealed housing and then the stop valve is closed to inspect the inside of the tank.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The liquid density measuring device in the G storage tank is attached with a ribbon cable that guides the probe while preventing swinging when the probe is moved up and down. Since the ribbon cable is fixed with an anchor for landing on the tank bottom plate. In some cases, depending on the lifting operation of the anchor, the anchor may collide with the tank bottom plate surface due to inertia and damage the expensive tank bottom plate surface.
Further, the force detection means for detecting the anchor landing, the length of the drive cable becomes long, and the detection accuracy of the probe landing decreases when the weight of the drive cable cannot be ignored with respect to the weight of the anchor, and The entire device was expensive because it required a compensator to compensate for the drive cable length varying with temperature.

It is an object of the present invention to provide a safety measure against dropping of a probe, to make it simple, compact and inexpensive.

[0010]

In order to solve the above problems, the present invention provides a probe containing a sensor for detecting a physical quantity such as the density of LNG stored in a tank, a signal cable of the sensor and one end of the probe. Is fixed to the sensor side, a cable wire that is longer than the signal cable is inserted, and one end of the winding cable is a flexible tube fixed to the probe, and at the other end side of the winding cable, A hoisting means for vertically driving the probe in a predetermined section on a vertical line of the tank bottom plate fixed point, an arithmetic means connected to the signal cable and arithmetically processing and outputting a signal such as density, and when the signal cable is disconnected, When a level change of a signal such as density is detected, an alarm is issued, and a portion of the cable wire longer than the signal cable is extended, and Buruwaiya in which is characterized by having a safety means which is suspended so as not to contact the probe to the tank bottom plate.

[0011]

Function: The probe and the hoisting device are connected by a hoisting cable. The hoisting cable is a signal cable,
A cable wire having a length longer than that of the signal cable and a tensile strength significantly larger than that of the signal cable is inserted into the flexible tube. The lowest position of the probe connected to the hoisting cable and moved up and down is slightly higher than the bottom surface of the tank. If the hoisting cable is overloaded, the flexible tube will stretch, and the cable wire between the flexible tubes will be longer than the signal cable, so it will stretch according to the extension of the flexible tube,
The probe is suspended by the cable wire and the flexible tube, while only the signal cable has a small amount of extension and is overloaded and cut. Further, since the signal transmitted from the probe is cut off, the level of the signal such as the density changes and the abnormality can be detected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a configuration diagram for explaining an embodiment of a liquid density measuring apparatus for LNG storage tank according to the present invention, in which 1 is an LNG tank, 2 is a drive unit main body, 3 is a probe, Reference numeral 4 is a hoisting cable, and 5 is an opening / closing valve.

The bottomed cylindrical LNG tank 1 having the roof 1a is almost buried in the ground with only the roof 1a projecting above the ground in order to prevent the temperature from being affected by the outside air. A cylindrical body 5a having an opening / closing valve 5 is vertically mounted on the roof 1a, and a sealed chamber drive body 2 is mounted in an upper space of the cylindrical body 5a.

The drive unit main body 2 is composed of a hoisting device 2a and a computing device 2b. A reel (not shown) driven to rotate is mounted on the hoisting device 2a, and a probe 3 is attached to the end of the reel. The attached hoisting cable 4 is wound. The probe 3 is on the vertical line L of the fixed point A of the bottom plate 1b in the LNG tank 1 as shown by the dotted line by the hoisting device 2a.
Driven up and down between sections.

The lower limit of the section L is a predetermined distance d from the bottom plate 1b, and the upper limit is the home position of the probe 3. The probe 3 is in the section L,
A detection signal having information about the density and temperature of LNG and air and the liquid level of LNG is transmitted to the arithmetic unit 2b through the winding cable 4 through the LNG and air phases.
When inspecting the probe 3, the probe 3 is wound up and moved into the sealed drive unit main body 2 through the on-off valve, and then the on-off valve 5 is closed to block the ventilation with the LNG tank 1.

FIG. 2 is a configuration diagram for explaining the probe according to the present embodiment. In the figure, 6 is a sensor, 7 is a flexible tube, 8 is a signal cable, and 9 is a cable wire. The same reference numerals as those in FIG. 1 are attached to the portions having the same functions as those in FIG.

The probe 3 comprises a casing 3a having a through hole through which LNG can flow, and a sensor 6 arranged in the casing 3a for detecting temperature and density. The temperature sensor in the sensor 6 is, for example, a resistance wire such as a platinum resistance wire, and the density sensor is, for example, a cylindrical resonator such as an elinvar of a constant expansion coefficient material. It is detected from the resonance frequency of the resonator.

A hoisting cable 4 connects between the probe 3 and the hoisting device 2a. The hoisting cable 4 includes a flexible tube 7, a signal cable 8 and a cable wire 9.
One end of a flexible tube 7 made of, for example, a braided stainless steel wire is fixed to the housing 3a, and a signal cable 8 connected to the sensor 6 is provided in the flexible tube 7. A cable wire 9 made of stainless steel or the like longer than the signal cable 8 is inserted.

The signal cable 8 is connected to the sensor 6 via a terminal (not shown), but a cable wire 9
Is welded to the housing of the sensor 6. A portion of the cable wire 9 that is longer than the signal cable 8 has, for example, a coil 9a wound in the housing 3a and has the same length as the signal cable 8 outside the housing 3a.

When some external force is applied to the probe 3 having the above structure and pulled downward, the hoisting cable 4
Tension acts on. At the same time, the flexible tube 7, the signal cable 8 and the cable wire 9 which constitute the hoisting cable 4 respectively expand according to the tension. At this time, the flexible tube 7 and the cable wire 9
Since the amount of extension of the signal cable 8 is extremely smaller than the amount of extension of the signal cable 8, when the external force is large, most of the external force is received by the signal cable 8 and only the signal cable 8 breaks.

However, when the flexible tube 7 and the cable wire 9 extend after the break and reach the length of the cable wire 9, the probe 3 is suspended by the cable wire 9 and does not collide with the bottom plate 1b of the tank 1. The predetermined length d shown in FIG. 1 is a length determined according to the length on which the probe 3 is suspended.

When the signal cable 8 is completely broken, the signal from the sensor 6 is not transmitted to the arithmetic unit 2b. In addition, a discontinuous signal is output even in the case of partial breakage, and an abnormality occurs in any case. These abnormal signals are discontinuous signals,
The discontinuous signal can be easily detected by a well-known technique, and an alarm for warning an abnormality can be issued based on the detected signal.

As described above, by selecting the cable configuration of the hoisting cable 4 for hoisting the probe 3, the signal cable 8 when an external force is applied to the probe 3 is selected.
Since a double safety measure is taken in which only the wire is broken and a warning is issued, and the probe 3 is suspended by using the cable wire 9 as a wire net, a compact and inexpensive density measuring device for an LNG storage tank can be provided.

[0024]

As is apparent from the above description, according to the present invention, the hoisting cable 4 for hoisting the probe 3 is
The flexible tube 7 and the signal cable 8 inserted through the flexible tube 7 and the cable wire 9 longer than the signal cable 8 are formed, and the signal cable 8 and the cable wire 9 are arranged in the probe 3 at a density. Etc. to the sensor 6. As a result, when a large external force is applied to the probe 3, only the signal cable 8 is disconnected and the probe 3 is suspended by the flexible tube 9, so that the probe 3 does not drop and damage the tank bottom plate. Further, since a signal abnormality occurs due to the breakage of the signal cable 8, this is detected and an alarm is given, so double safety measures are taken. Therefore, it is suitable for mounting on a small LNG tank, the safety cable of the probe 3 is not required, and it is possible to provide an inexpensive and compact density measuring device for an LNG storage tank.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a liquid density measuring device for LNG storage tank according to the present invention.

FIG. 2 is a configuration diagram for explaining a probe according to the present invention.

[Explanation of symbols]

1 ... LNG tank, 2 ... drive unit main body, 3 ... probe, 4
... winding cable, 5 ... open / close valve, 6 ... sensor, 7 ... flexible tube, 8 ... signal cable, 9 ... cable wire.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Shoji Sase 3-10-8 Kamiochiai, Shinjuku-ku, Tokyo Oval Co., Ltd. (72) Inventor Ken Ken Inagaki 3-10-8 Kamiochiai, Shinjuku-ku, Tokyo Oval Co., Ltd. Within

Claims (1)

[Claims] 1. A probe containing a sensor for detecting a physical quantity such as the density of LNG stored in a tank, a signal cable of the sensor, and one end of which is fixed to the sensor side and is longer than the signal cable. A hoisting cable consisting of a flexible tube having one end fixed to the probe and a wire inserted therethrough, and at the other end of the hoisting cable, the probe is vertically driven within a predetermined section on the vertical line of the tank bottom plate fixed point. A hoisting means, an arithmetic means which is connected to the signal cable and arithmetically processes and outputs a signal such as density, and when the signal cable is disconnected, detects a level change of the signal such as density and issues an alarm, and The cable wire extends longer than the signal cable, and the cable wire contacts the probe to the tank bottom plate. A liquid density measuring device for an LNG storage tank, which has a safety means suspended so as not to occur.