JPH0476051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a measuring device for measuring the mass of liquid in a tank.

Prior Art When an extremely low boiling point liquid such as liquid natural gas (hereinafter referred to as LNG) is stored in a tank, phases may be formed due to differences in composition depending on the LNG production area, heat exchange, etc. In a multi-component system, a rollover phenomenon occurs in which layers are inverted when the upper layer density is greater than the lower layer density. When this rollover phenomenon occurs, phase mixing occurs, and the energy consumption thereof causes rapid generation of steam gas, which poses the risk of causing a major disaster.Therefore, it is necessary to prevent the rollover phenomenon. For this purpose, it is necessary to periodically measure the density of the liquid stored in the tank or a physical quantity such as a temperature related to the density, and to manage the measured quantity by considering its processing. The specific measurement method is to raise and lower a probe connected to one end of the signal cable, which examines physical quantities, from the bottom of the tank toward the ceiling using a guide cable fixed to an anchor lowered to a fixed point at the bottom of the tank as a guide. seeking by doing. The current position of the probe at this time is determined by the length of the signal cable rolled up with the bottom of the tank as a reference.

Conventionally, in density measurement using a probe, the rapid change in density that occurs when transitioning from the liquid phase to the gas phase and the drop in density measurement accuracy that occurs due to liquid or gas phase components entering the probe have been considered. To prevent this, the probe position is compared with the liquid level measured by a separately installed liquid level gauge to prevent the probe from protruding above the liquid surface, and the probe's elevation is controlled.

Purpose The present invention aims to reduce the maximum value of the density change due to the phase change without reducing the density measurement accuracy by lowering the lifting speed when moving the probe in the prior art as described above from the liquid phase to the gas phase. Taking advantage of the fact that the liquid level can be calculated from the position, the liquid level gauge is omitted, and the density is calculated from the average value from the bottom of the tank to the liquid level measured by the probe and the liquid level. This was done for the purpose of finding the mass of liquid in the tank from the product of the liquid volume.

Configuration FIG. 1 is a main part configuration diagram for explaining one embodiment of the present invention, which includes a tank 1 containing LNG at a liquid level LL, and a probe 4 containing a density meter. The probe 4 penetrates the ceiling of the tank 1 and is suspended via a guide cable 3, and is rotated by a drive source (not shown) with the guide cable 3 as a guide along the vertical line of an anchor 2 fixed to the bottom of the tank 1. It is connected to the signal cable 5 and moves. The signal cable 5 is sealed from the gas in the tank by a sealing mechanism 6, and wound up via a valve 7 and a sheave 8. The terminal is connected to the computing device 13 through a slip ring 15, and the signal cable 5 is wound up through a valve 7 and a sheave 8. The length of the probe, that is, the position of the probe, is determined by calculating the output signal of the detector 12 that detects the rotation of the sheave 8.
It is calculated as the distance from the bottom of the

Similarly to the signal cable 5, the guide cable 3 is moved up and down through a seal mechanism 6, a valve 7, and a sheave 9, with each end being fixed to a rotating drum 11 which is rotationally driven by a drive source (not shown).

FIG. 2 is a diagram showing an example of the density detector used in the probe 4, in which A is a plan view and B is a side view. A vibrating tube 41 is inserted. The vibration tube 41 is a thin cylinder 42 made of magnetic material, and the cylinder 42
The end face has a flange shape passing through a hole 43 through which fluid can flow. 44 is a drive coil;
Reference numeral 45 denotes receiving coils, which are arranged to face each other on the diameter of the cylinder. These coils are amplifier 4
6 and is configured to amplify the minute signal detected by the receiving coil 45 and drive the vibrating tube with the driving coil 44, and each coil and the amplifier constitute a closed circuit. The vibrating tube vibrates in an ellipse having major and minor axes on the drive shaft, as shown in Figure 2 C.
This vibration frequency is determined by the rigidity of the vibrating tube and the density of the fluid surrounding the vibrating tube, and ρ=ρ _p [(f _p /f) ² −1] ...(1) where ρ is the fluid to be measured. Density ρ _p : Constant f _p : Vibration frequency in vacuum f : Density is determined from the vibration frequency in the fluid to be measured. That is, as shown in equation (1), a vibration frequency that is an inverse function of density is obtained. This frequency is converted into density by a density calculator 47,
It is recorded by a recorder 48.

In addition, as mentioned above, in a detector whose resonant frequency changes depending on the density, the resonant frequency increases when the probe is in the liquid in the tank and when it comes out of the liquid, as shown in Figure 3. Therefore, the liquid level in the tank can be detected from the position where the change in resonance frequency, in other words, the rate of change in density is the largest.

Therefore, in a tank with a constant bottom area, when the liquid level is detected as described above, the detector 12
The liquid level from the bottom of the tank to the liquid level can be detected from the output signal of the output signal and the liquid level detected as described above, and therefore the volume of the liquid can be determined from this liquid level. The average density of the liquid can be determined from the liquid density determined as above, and the mass of the liquid can be determined from the volume and average density of the liquid.

Effects As is clear from the above description, according to the present invention, it is possible to accurately measure physical quantities in a tank, particularly density changes and liquid levels in the vertical direction of the liquid in the tank, and to accurately determine the mass of the liquid in the tank. You can ask for it.

[Brief explanation of drawings]

FIG. 1 is a side view of essential parts for explaining an embodiment of the present invention, FIG. 2 is a diagram showing an example of a density detector used in implementing the present invention, and A is a plan cross-sectional view; B is a side sectional view, C is a diagram showing the vibration state, 3rd
The figure is a diagram showing the relationship between liquid level and density. 1...Tank, 2...Anchor, 3...Guide cable, 4...Probe, 6...Seal mechanism, 7...
...Valve, 8,9...Sheave, 10,11...Drum.

Claims (1)

[Claims] 1. A probe that measures the density of the liquid stored in the tank is raised and lowered to the bottom and ceiling of the tank using a lifting device installed outside the tank, and the vertical density change of the liquid in the tank is measured. At the same time, the liquid level is detected from the maximum position of the density change rate, and the liquid mass is measured by multiplying the average value of the density measured by the probe from the bottom of the tank to the liquid level by the liquid volume determined from the liquid level. A device for measuring the mass of liquid in a tank, characterized by: