JP3383078B2 - Liquid density measuring device for LNG storage tank - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LNG storage tank (tank).
More specifically, for the liquid density measuring device for use, more specifically, the density of LNG is periodically measured on a fixed point vertical line in the tank so that a rollover phenomenon does not occur in the LNG stored in the LNG tank. And a simple density measuring device. 2. Description of the Related Art When LNG (liquefied natural gas) having a very low boiling point is stored in a tank, the density of LNG is not always constant at all positions in the tank. If different, the components of LNG are different, and the density is generally different depending on the components. Further, the temperature distribution in the tank is not uniform, and the density changes according to 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 the density of the lower layer, the layer is stably maintained, but when the density is opposite, a rollover phenomenon occurs in which the upper and lower layers are inverted. At this time, heat energy is generated due to fluid friction, and there is a risk that LNG having an extremely low boiling point may be rapidly vaporized and exploded. In order to prevent such a rollover phenomenon, it has been practiced to measure the temperature and density in a vertical direction at a fixed point of LNG stored in a tank and to examine the measured values. Specifically, a probe containing a sensor for detecting the temperature, density, etc. of LNG is moved up and down from a fixed point on the tank bottom plate toward the liquid level to move the LNG in the tank.
We observe the distribution of temperature and density. The probe is moved up and down in the tank. 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. Was.
The stepping motor is disposed in a sealed housing on the tank roof, and the stepping motor and the inside of the tank are communicated via a closing valve through which a drive cable is inserted when the valve is opened. [0006] To detect whether the probe has landed on the tank bottom plate, first, the length of the unwound drive cable is measured by the number of pulses for driving the stepping motor.
This is done by detecting a 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 ribbon cables are tensioned by rolling down the anchors fixed to the two ribbon cables from the sealed housing onto the tank floor plate. By guiding the probe, the swing of the probe was prevented and safety was maintained. Further, when checking the probe, the probe is housed in the sealed housing, and then the shut-off valve is closed, and the inspection is performed in the sealed housing in which the inside of the tank is shut off. [0008] As described above, the conventional LN
The liquid density measurement device in the G storage tank is equipped with a ribbon cable that guides the probe while preventing the probe from swinging up and down, and the ribbon cable has an anchor that is fixed on the tank bottom plate. Depending on the operation of raising and lowering the anchor, the anchor may collide with the tank bottom plate surface due to inertia and damage the expensive tank bottom plate surface.
In addition, the force detection means for detecting the anchor landing, the length of the drive cable becomes longer, and when the weight of the drive cable is not negligible with respect to the weight of the anchor, the detection accuracy of the probe landing is reduced, and The entire device was expensive because it required a compensator to compensate for the change in drive cable length with temperature. SUMMARY OF THE INVENTION It is an object of the present invention to take safety measures against dropping of a probe, and to make it simple, small, and inexpensive. [0010] In order to solve the above-mentioned 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, and a signal of the sensor. A wound cable having a cable and one end fixed to the sensor side, a longer cable wire than the signal cable being inserted, and a flexible tube having one end fixed to the probe, and the other end of the wound cable A hoisting means for driving the probe up and down within a predetermined section on a vertical line of the tank bottom plate fixed point, an arithmetic means connected to the signal cable for arithmetically processing and outputting a signal such as density, and the signal cable being cut off At this time, a level change of the signal such as the density is detected and an alarm is issued, and a longer portion of the cable wire than the signal cable is extended. And a safety means suspended so that the cable wire does not contact the probe with the tank bottom plate. The probe and the hoisting device are connected by a hoisting cable. The winding cable is a signal cable,
A cable wire whose length is longer than that of the signal cable and whose tensile strength is much 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 raised and lowered is located slightly higher than the tank bottom. If an overload is applied to the wound cable, the flexible tube extends, and the cable wires between the flexible tubes extend according to the extension of the flexible tube because they are longer than the signal cable.
The probe is suspended by the cable wire and the flexible tube, though only the signal cable has a small amount of extension and is overloaded and cut. In addition, since the signal transmitted from the probe is cut off, the level of the signal such as the density changes, and an abnormality can be detected. FIG. 1 is a block diagram for explaining an embodiment of a liquid density measuring device for an LNG storage tank according to the present invention. In FIG. 1, reference numeral 1 denotes an LNG tank, 2 denotes a driving unit main body, Is a probe, 4 is a raised cable, and 5 is an on-off valve. The bottomed cylindrical LNG tank 1 having the roof 1a is almost buried underground with only the roof 1a protruding above the ground in order to make it hard to be affected by the temperature of the outside air. A cylindrical body 5a provided with an on-off valve 5 is attached to the roof 1a in a vertical direction, and a sealed chamber driving unit main body 2 is mounted in an upper space of the cylindrical body 5a. The drive unit main body 2 comprises a hoisting device 2a and a calculating device 2b. A rotating reel (not shown) is mounted on the hoisting device 2a, and a probe 3 is provided on an end of the reel. The attached hoisting cable 4 is wound. As shown by the dotted line by the hoisting device 2a, the probe 3 is positioned on the vertical line of the fixed point A of the bottom plate 1b in the LNG tank 1.
Are driven up and down between the sections. The lower limit of the section L is defined by a predetermined distance d between itself and the bottom plate 1b, and the upper limit is the home position of the probe 3. Probe 3 is located between sections L,
After passing through the phase of LNG and air, a detection signal having information on the density and temperature of LNG and air and the liquid level of LNG is transmitted to the arithmetic unit 2b via the hoisting cable 4.
At the time of inspection of the probe 3, the probe 3 is moved into the sealed drive unit main body 2 through the open / close valve, and then the open / close valve 5 is closed to shut off the ventilation with the LNG tank 1. FIG. 2 is a configuration diagram for explaining the probe according to the present embodiment, in which 6 is a sensor, 7 is a flexible tube, 8 is a signal cable, and 9 is a cable wire. Parts having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. The probe 3 includes a housing 3a having a through hole through which LNG can flow, and a sensor 6 disposed in the housing 3a for detecting temperature and density. The temperature sensor in the sensor 6 is made of, for example, a resistance wire such as a platinum resistance wire, and the density sensor is made of, for example, a cylindrical resonator such as an elinvar made of a constant expansion coefficient material. It is detected from the resonance frequency of the resonator. The probe 3 and the hoisting device 2a are connected by a hoisting cable 4. 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).
Is welded to the housing of the sensor 6. For example, the cable wire 9 in a portion longer than the signal cable 8 is wound around a coil 9a inside the housing 3a, and has a length equal to that of the signal cable 8 outside the housing 3a. When a certain external force is applied to the probe 3 having the above-described structure and the probe 3 is pulled downward, the raised cable 4
Tension acts on At the same time, the flexible tube 7, the signal cable 8, and the cable wire 9 that constitute the hoisting cable 4 extend 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 small as compared with the amount of extension, when the external force is large, most of the external force is received by the signal cable 8 and only the signal cable 8 is broken. However, when the flexible tube 7 and the cable wire 9 extend after the breakage 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 of the probe 3 suspended. When the signal cable 8 is completely broken, the signal of the sensor 6 is not transmitted to the arithmetic unit 2b. Also, 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 transmitted based on the detected signal. As described above, by selecting the cable configuration of the hoisting cable 4 for winding up the probe 3, the signal cable 8 can be used when an external force is applied to the probe 3.
Only a safety measure is taken to break only the wire and to issue a warning and to suspend the probe 3 using the cable wire 9 as a wire mesh, so that a small and inexpensive density measuring device for an LNG storage tank can be provided. As is apparent from the above description, according to the present invention, the cable 3 for winding the probe 3 is
The flexible tube 7 includes a signal cable 8 inserted into the flexible tube 7 and a cable wire 9 longer than the signal cable 8, and the signal cable 8 and the cable wire 9 are arranged in the probe 3 at a density. And the like. 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 fall to the tank bottom plate and is not damaged. Further, since a signal abnormality occurs due to the breakage of the signal cable 8, this is detected and a warning of the abnormality is issued, so that a double safety measure is taken. For this reason, it is suitable to be mounted on a small-sized LNG tank, and a safety cable for the probe 3 is not required, so that an inexpensive and small-sized LNG storage tank density measuring device can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram for explaining an embodiment of a liquid density measuring device for an LNG storage tank according to the present invention. FIG. 2 is a configuration diagram for explaining a probe according to the present invention. [Description of Signs] 1 ... LNG tank, 2 ... Drive unit body, 3 ... Probe, 4
... Coiled cable, 5 ... Open / close valve, 6 ... Sensor, 7 ... Flexible tube, 8 ... Signal cable, 9 ... Cable wire.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoshi Inagaki 3-10-8, Kamiochiai, Shinjuku-ku, Tokyo Inside Oval Co., Ltd. JP-A-99838 (JP, A) JP-A-59-155719 (JP, A) JP-A-56-3270 (JP, A) JP-A-1-59849 (JP, U) JP-A-55-116227 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 9/00 G01F 23/00 JICST file (JOIS)

Claims (1)

(57) [Claim 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 thereof are fixed to the sensor side. A wound cable consisting of a flexible tube fixed to the probe at one end through a cable wire longer than the signal cable, and at the other end of the wound cable, the probe is connected to the tank bottom plate fixed point. Hoisting means for driving up and down within a predetermined section on a vertical line, calculating means connected to the signal cable for calculating and outputting a signal such as density, and when the signal cable is cut, a level change of the signal such as density. Detects and issues an alarm, and the cable wire, which is longer than the signal cable, extends, and the cable wire is in front of the probe. LNG storage tanks for liquid density measurement device, characterized in that it comprises a safety means which is suspended so as not to contact the tank bottom plate.