JP2008170292A - Measuring device of liquid density - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device of a liquid density capable of determining an accurate density without taking out liquid from a sealed container, and without performing air purge in the sealed container. <P>SOLUTION: This measuring device of the liquid density has a storage tank 10 having a heat insulating structure for storing volatile liquid L, two upper and lower connecting tubes 18A, 18B provided on each different height position of the storage tank, and pressure gages 22A, 22B or a differential pressure gage installed on each tip part of the connecting tubes 18A, 18B. The two connecting tubes 18A, 18B are provided with each horizontal part having a prescribed length, and gas acquired by vaporization of the liquid L stays on each horizontal part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid density measuring apparatus for measuring the density of a stored volatile liquid, for example.

Conventionally, when measuring the density of a volatile liquid, the following measurement method has been used.
(1) Remove the liquid from the sealed container, transfer the liquid to a container with a known volume, measure its weight, and divide by the volume to obtain the density.
In this method, since the liquid has to be transferred from the storage container to the measuring container, it is not only troublesome but also very difficult to handle in the case of a low-temperature liquid such as a liquefied gas.

(2) In the method described in Patent Document 1, two gas introduction pipes for pressure measurement are arranged in a sealed container containing a liquid while changing the immersion depth of each tip, and air is introduced into the introduction pipe. While purging, the liquid pressure at each position is measured. Thereby, the density was calculated | required by the formula of the density (density = pressure difference / (height of pressure difference * gravity acceleration)) from the difference of a pressure difference and immersion depth.
However, this method also requires an apparatus for air purge, which complicates the apparatus and work, and causes an increase in cost. Further, with respect to a liquid whose properties change when it comes into contact with the atmosphere, such as a cryogenic liquefied gas, the density cannot be accurately measured by these conventional methods.

JP 60-152934 A

  Therefore, an object of the present invention is to provide a liquid density measuring apparatus that can obtain an accurate density without taking out a liquid from a sealed container and without performing an air purge in the sealed container. .

  In order to achieve the above object, a liquid density measuring device according to claim 1 includes a storage tank having a heat insulating structure for storing volatile liquid, and two upper and lower guides provided at different height positions of the storage tank. A pressure tube and a pressure gauge or a differential pressure meter installed at the tip of the pressure guiding tube are provided. A horizontal portion having a predetermined length is provided in the two pressure guiding tubes, and the gas obtained by vaporizing the liquid stays in the horizontal portion. It is characterized by doing so.

  In the first aspect of the present invention, the volatile liquid is vaporized by heat input from the pressure gauge or the differential pressure gauge installed at the tip, and stays in the horizontal part. Therefore, the pressure of the liquid acting on the pressure gauge or the differential pressure gauge is constant regardless of the amount of vaporized gas, and an accurate liquid density can be measured with a simple configuration and an easy operation.

According to a second aspect of the present invention, there is provided the liquid density measuring device according to the first aspect, wherein a temperature adjusting means is provided in at least a part of each of the two pressure guiding tubes.
In the invention described in claim 2, since the temperature of the pressure guiding tube is adjusted by the temperature adjusting means, the amount of heat input from the pressure guiding tube to the liquid can be controlled, and the amount of gas staying in the horizontal portion can be stably increased. Can be maintained. In addition, it is possible to form a stable measurement environment around the pressure gauge or the differential pressure gauge to perform measurement with higher accuracy.

  According to the liquid density measuring apparatus according to claim 1 and claim 2, the liquid is not taken out from the sealed container or the air purge is not performed in the sealed container. Liquid density measurements can be made.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a liquid density measuring apparatus according to a first embodiment of the present invention, which is attached to, for example, a heat-insulating sealed container (storage tank) 10 that stores liquid L having volatility at room temperature. It is configured as something to do. The storage tank 10 is a pressure vessel formed in a cylindrical shape having a predetermined height from a material having a predetermined heat insulating property, and an inflow pipe 12 for the liquid L is provided near the bottom of the side surface, and an outflow pipe 14 is provided at the bottom. It is connected. These pipes 12 and 14 are covered with a heat insulating material 16 as necessary, and are kept warm. Since the well-known thing is employ | adopted about the raw material and heat insulation structure of a container, description is abbreviate | omitted.

  Two pressure guiding pipes 18 </ b> A and 18 </ b> B are provided on the side surface of the storage tank 10 apart from each other by a distance H. These pressure guiding pipes 18A and 18B are also covered with a heat insulating material 20 as necessary, and are kept warm. The inner diameters of the pressure guiding tubes 18A and 18B need to be small enough that the gas bubbles vaporized therein do not move easily, and are preferably 10 mm or less, for example. Pressure gauges 22A and 22B are provided at the tips of the pressure guiding tubes 18A and 18B, respectively. As the pressure gauges 22A and 22B, commercially available appropriate ones can be adopted. For example, one that detects a change in capacitance value due to ceramic deformation, or a change in resistance value due to deformation of a metal diaphragm. What to detect is mentioned. In this embodiment, the pressure gauges 22A and 22B themselves are not particularly kept warm, and thus operate at room temperature. When the liquid L is corrosive, the pressure detectors of the pressure gauges 22A and 22B need to have a corrosion resistant structure.

The outputs of these pressure gauges 22A and 22B are respectively input to the differential pressure measuring device 24, where, for example, the analog value is converted into a digital value, the difference is calculated, and converted into a differential pressure value. This differential pressure value output is further input to the density calculation device 26 and converted into the density of the liquid L stored by the following calculation formula.
ρ = (ΔP / (H × g))
Here, ΔP = P2−P1, H is the height difference between the pressure guiding tubes 18A and 18B, g is the gravitational acceleration, and P1 and P2 are the detected values of the pressure gauge. The pressures P1 and P2 measured by the pressure gauges 22A and 22B are the sum of the head pressure of the liquid L and the vaporization pressure at that temperature. If the temperatures in the two pressure gauges 22A and 22B are the same, vaporization occurs. Since the pressure cancels out, the above equation holds.

  In the liquid density measuring apparatus configured as described above, when a cryogenic volatile liquid L such as liquefied natural gas or liquefied propane gas is injected into the storage tank 10, the tips of the pressure guiding pipes 18A and 18B are supplied. Since the part is at a temperature close to room temperature, these gases are vaporized and become gas G, which fills the tip side of the pressure guiding tubes 18A and 18B. The amount of gas G generated here is determined by the amount of heat input from the tip side and the liquid pressure of the corresponding portion, but in a state where there is no excessive heat input, the amount of gas G is balanced so as to stay in the horizontal pressure guiding pipes 18A and 18B. To do. If the amount of heat input is excessive and the vaporization is intense due to the high outside air temperature or the large exposed part, a temperature adjusting means as described below is installed.

  Here, the detection outputs of the two pressure gauges 22A and 22B are automatically output to the differential pressure measurement device 24 and the density calculation device 26, and the density of the liquid L inside is constantly detected. At this time, the amount of heat input in the upper and lower pressure guiding pipes 18A and 18B is not necessarily the same, and therefore the amount of gas G in the upper and lower pressure guiding pipes 18A and 18B is not necessarily the same as shown in FIG. However, since the pressure guiding pipes 18A and 18B are horizontal, the liquid levels in the pressure guiding pipes 18A and 18B are also at the same position, and the pressure difference measured by the pressure gauges 22A and 22B is the pressure difference corresponding to the distance H. Become. On the other hand, when the pressure guiding pipes 18X and 18Y as shown in FIG. 1A are inclined, the position of the liquid level is changed according to the amount of the vaporized gas G, so that the measured pressure difference becomes the distance H. The corresponding pressure difference disappears and the accurate pressure difference cannot be measured.

  As described above, according to this apparatus, a volatile liquid such as a liquefied gas can be measured without performing an operation of sending air from the outside into the storage tank 10, and the apparatus configuration is simple. Work is also easy. Further, since it is not necessary to bring the external air into contact with the internal liquid L, the properties of the liquid L are not changed or contaminated.

  FIG. 3 shows a liquid density measuring apparatus according to a third embodiment of the present invention, which includes temperature adjusting means 28A and 28B for controlling the temperatures of the pressure guiding tubes 18A and 18B and the pressure gauges 22A and 22B. These parts are controlled to a predetermined temperature by an instruction from the temperature control device 30. Thereby, it is possible to appropriately control the amount of heat input to the liquid in the pressure guiding pipes 18A and 18B and adjust the vaporized gas so as to be contained in the pressure guiding pipes 18A and 18B. Of course, it is preferable to perform feedback control by arranging a temperature sensor in each part. The temperature control is not necessarily constant, and an appropriate temperature gradient may be formed.

  Also in the liquid density measuring device of this embodiment, the detection outputs of the two pressure gauges 22A and 22B are automatically output to the differential pressure measuring device 24 and the density calculating device 26, and the density of the liquid L inside is constant. Is detected. Since the temperature of the two pressure gauges 22A and 22B can be strictly controlled by the temperature adjusting means 28A and 28B, stable measurement can be performed. Further, it is possible to prevent an excessive increase in vaporization pressure in the pressure guiding pipes 18A and 18B, stabilize the measurement state, and prevent breakage and failure due to the pressure gauges 22A and 22B being exposed to an excessively low temperature. it can.

  FIG. 4 shows a liquid density measuring apparatus according to the fourth embodiment of the present invention. In this embodiment, the tip portions of the pressure guiding tubes 18A and 18B are bent upward, and the pressure gauges 22A and 22B are installed on the upper portions thereof. Similar to the previous embodiment, temperature adjusting means 28A, 28B and a temperature control device 30 for controlling the temperatures of the pressure guiding pipes 18A, 18B and the pressure gauges 22A, 22B are provided, and these portions are controlled to a predetermined temperature. I am doing so.

  In the liquid density measuring apparatus of this embodiment, gas reservoir spaces 34A and 34B for storing vaporized gas are formed at the tip portions of the pressure guiding tubes 18A and 18B. Therefore, the state where the low temperature storage liquid L and the pressure gauges 22A and 22B are in direct contact can be suppressed, and the pressure can be protected from low temperature and corrosion. Of course, also in this example, the amount of vaporized gas is controlled so that the boundary between the bubble and the liquid is in the horizontal portion of the pressure guiding pipes 18A and 18B.

It is sectional drawing which shows the measuring apparatus of the liquid density of 1st Embodiment of this invention. It is sectional drawing which shows the liquid density measuring apparatus of a comparative example. It is sectional drawing which shows the liquid density measuring apparatus of 2nd Embodiment of this invention. It is sectional drawing which shows the measuring apparatus of the liquid density of 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Storage tank 12 Inflow piping 14 Outflow piping 18A, 18B Pressure guiding pipe 20 Heat insulating material 22A, 22B Pressure gauge 24 Differential pressure measuring device 26 Density calculation device 28A, 28B Temperature adjustment means 30 Temperature control device 32A, 32B 1st temperature adjustment means 34A, 34B Gas reservoir space 36A, 36B Second temperature adjusting means

Claims (2)

A storage tank with a heat insulating structure for storing volatile liquid;
Two upper and lower pressure guiding pipes provided at different height positions of the storage tank;
A pressure gauge or a differential pressure gauge installed at the tip of the pressure guiding tube;
An apparatus for measuring a liquid density, wherein the two pressure guiding pipes are provided with a horizontal portion having a predetermined length, and a gas obtained by vaporizing the liquid is retained in the horizontal portion.   2. The liquid density measuring apparatus according to claim 1, wherein temperature adjusting means is provided in at least a part of each of the two pressure guiding tubes.

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