JP2014112045A - Composition analysis method of cryogenic liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition analysis method of a cryogenic liquid capable of improving accuracy of the composition analysis of the cryogenic liquid.SOLUTION: A part of a cryogenic liquid is collected as a sample; the state of the sample keeps in a liquid state; the sample is pressurized so that the pressure of the liquefied sample becomes a critical pressure or more; the sample pressurized to the critical pressure or more is heated, and thereby the sample becomes a supercritical fluid; the pressure of the sample decreases to a pressure in which composition analysis can be performed, and thereby the sample becomes gas; and then, the composition analysis of the sample is performed.

Description

  The present invention relates to a composition analysis method for a cryogenic liquid.

Conventionally, as a method for accurately measuring the composition and impurity concentration of low-temperature liquids (also called “cryogenic liquids”) such as liquid air, liquid oxygen, liquid nitrogen, liquid argon, and LNG, all collected samples are vaporized and analyzed. There is a way to do it.
However, when such an analysis method is used, it takes a long time to obtain an analysis value after taking a sample.

As conventional techniques capable of solving such problems, there are Patent Documents 1 to 3.
Patent Document 1 discloses a method of measuring a cryogenic liquid as it is without vaporizing by infrared spectroscopic analysis.
Specifically, in Patent Document 1, the absorption spectrum of a cryogenic liquid sample is measured while the cryogenic liquid sample is present in the cell, and the absorption spectrum of the cryogenic liquid sample, the cryogenic liquid and impurities are measured. A method for the identification of impurities in cryogenic liquids is disclosed that compares the spectra of and confirms the presence of absorption spectra of samples associated with impurities.

Patent Document 2 discloses a method of measuring after vaporizing a low temperature liquid.
Specifically, in Patent Document 2, in order to measure impurities such as nitrous oxide, carbon dioxide, or hydrocarbon in a cryogenic liquid such as liquid oxygen or liquid nitrogen, the cryogenic liquid to be measured is sampled. A method is disclosed in which after passing through a vaporizer from a line and heating the vaporizer wall to vaporize the entire amount, a part of the gas phase is introduced into an analyzer and analyzed.

Patent Document 3 discloses a low-temperature liquefied gas sampling device capable of generating evaporative gas having the same composition as the liquid composition and continuously extracting it when analyzing low-temperature liquefied gas having various compositions in pipes and storage tanks. It is disclosed.
Patent Document 3 discloses that a porous body is used for sampling for analysis, and that a low-temperature liquid is allowed to pass through the porous body by capillary action or pressure difference, and then the sample is evaporated and vaporized. Yes.

  In order to perform an accurate composition analysis of a cryogenic liquid using the method disclosed in Patent Documents 1 and 2 or the sampling device disclosed in Patent Document 3, the temperature and pressure conditions of the location to be measured are maintained. Therefore, it is necessary to take a measurement or a sample for measurement.

JP-T-2002-543419 JP 2004-69676 A Japanese Patent Laid-Open No. 7-20012

  By the way, when the method disclosed in Patent Document 1 is used, the measurement of the absorption spectrum in the liquid state is less sensitive than the measurement in the gas state, so it is difficult to accurately measure a very small amount of impurities. It was.

  Further, when the method disclosed in Patent Document 2 is used, in the process of continuously vaporizing the collected liquid, the low boiling point component tends to be gasified first, so that the composition may be changed.

  Further, when the analysis is performed using the sampling device disclosed in Patent Document 3, the vaporization becomes unstable because there is a local pressure rise when the liquid measurement object vaporizes. As a result, the pressure easily fluctuates, making it difficult to obtain an accurate composition.

  That is, when analysis of a cryogenic liquid (also referred to as “cryogenic liquid”) is performed using the method disclosed in Patent Documents 1 and 2 and the sampling device disclosed in Patent Document 3, the analysis is performed in a relatively short time. However, there is a problem that the accuracy of the composition analysis of the low temperature liquid is lowered.

  In order to solve the above-described problem, according to the invention according to claim 1, a collecting step of collecting a part of a cryogenic liquid as a sample, and the pressure of the sample that is made into the liquid while holding the state of the sample in the liquid A pressurizing step of pressurizing the sample so as to be equal to or higher than the critical pressure, a supercritical fluid generating step of making the sample a supercritical fluid by heating the sample having a pressure equal to or higher than the critical pressure, and the supercritical fluid After the fluid is generated, the pressure of the sample is reduced to a pressure at which composition analysis is possible, whereby a pressure reduction step using the sample as a gas, and a composition analysis step for analyzing the composition of the sample after the pressure reduction step, A method for analyzing a composition of a cryogenic liquid is provided.

  Moreover, according to the invention which concerns on Claim 2, in the said collection process, a part of said cryogenic liquid is extract | collected as said sample in the micro syringe of a micro syringe pump, and in the said pressurization process, in the said micro syringe. 2. The cryogenic liquid composition analysis method according to claim 1, wherein the sample is pressurized by pushing out the collected sample with a piston of the microsyringe pump.

  Moreover, according to the invention which concerns on Claim 3, the said micro syringe pump is cooled before the said collection process, The composition analysis method of the cryogenic liquid of Claim 1 or 2 characterized by the above-mentioned is provided.

  According to the composition analysis method of a cryogenic liquid of the present invention, the state of the sample that is a part of the cryogenic liquid is maintained in the liquid, and the pressure of the sample that has been made liquid is pressurized so as to be equal to or higher than the critical pressure. By heating a sample having a pressure equal to or higher than the pressure to make the sample a supercritical fluid, it is possible to suppress vaporization of low-volatile components contained in the sample before performing composition analysis.

  Therefore, the composition of the cryogenic liquid is analyzed by reducing the pressure of the sample, which is a supercritical fluid, to a pressure at which composition analysis can be performed before the analyzer, and using the sample gas as a gas, and then analyzing the composition of the sample. The accuracy of analysis can be improved.

It is a figure which shows schematic structure of the cryogenic liquid collection | recovery and composition analyzer used when implementing the cryogenic liquid composition analysis method of embodiment of this invention. It is the figure which expanded the cryogenic liquid collection | recovery part shown in FIG.

  Embodiments to which the present invention is applied will be described below in detail with reference to the drawings. The drawings used in the following description are for explaining the configuration of the embodiment of the present invention, and the size, thickness, dimensions, etc. of each part shown are the dimensions of the actual cryogenic liquid sampling and composition analyzer. The relationship may be different.

(Embodiment)
FIG. 1 is a diagram showing a schematic configuration of a cryogenic liquid collection and composition analysis apparatus used when performing a cryogenic liquid composition analysis method according to an embodiment of the present invention. In FIG. 1, for convenience of explanation, a heat insulating member 11 and a pipe 12 that are not components of the cryogenic liquid collection and composition analyzer 10 are illustrated. Moreover, in FIG. 1, only the heat insulation member 11 is shown as sectional drawing.
In addition, A shown in FIG. 1 indicates a cryogenic liquid collecting part (hereinafter referred to as “cold liquid collecting part A”).

First, with reference to FIG. 1, a cryogenic liquid collection and composition analysis apparatus 10 used when implementing a cryogenic liquid composition analysis method according to an embodiment of the present invention will be described.
The cryogenic liquid sampling and composition analyzing apparatus 10 is an apparatus that is arranged in a heat insulating space 11A formed in the heat insulating member 11 and extracts a sample that is a cryogenic liquid from a pipe 12 that transports the cryogenic liquid, and performs composition analysis of the sample. It is.

The “cold liquid” in this embodiment means a liquid that becomes vapor at room temperature and standard atmospheric pressure, more specifically, a liquid that becomes vapor at 15 to 25 ° C. at 1 atmosphere (1013 hPa). say.
Examples of the low-temperature liquid include liquid oxygen, liquid nitrogen, liquid argon, liquid methane, liquid helium, liquid neon, liquid hydrogen, and liquid fluorinated hydrocarbon.

  The cryogenic liquid collection and composition analysis apparatus 10 includes a sample collection line 15, a microsyringe pump 16 that is a sample collection and pressurization unit, a first check valve 18, an analysis sample supply line 21, and a heating unit. 22, a second check valve 23, a first valve 24, an analyzer 26, an exhaust line 28, and a second valve 29.

The sample collection line 15 is disposed in the heat insulating member 11 (heat insulating space 11A). The sample collection line 15 branches from the pipe 12 and is a line for extracting a low temperature liquid flowing in the pipe 12 as a sample.
The tip 15A of the sample collection line 15 is connected to a first tube tip 51 (see FIG. 2 described later) of the microsyringe 38.

The length of the sample collection line 15 (in other words, the distance between the inner wall surface of the pipe 12 and the first tube tip 51) is preferably as short as possible (for example, 10 cm or less).
This makes it possible to suppress a part of the collected sample from being vaporized via the sample collection line 15, so that all the collected low-temperature liquid can be used as the sample.
The sample collection line 15 can be made of the same material as the pipe 12, for example.

  Here, the heat insulating member 11 will be described. The heat insulating member 11 accommodates a pipe 12 through which a low-temperature liquid flows and a microsyringe pump 16. The heat insulating space 11A in the heat insulating member 11 can be set to a vacuum, for example. Moreover, as a material of the heat insulating member 11, for example, a vacuum heat insulating material using silica-based pearlite powder as a core material can be used.

  Referring to FIG. 1, the micro syringe pump 16 is accommodated in the heat insulating member 11. Thereby, the cryogenic liquid (sample) collected by the microsyringe pump 16 is kept cold by the cold air of the cryogenic liquid flowing through the pipe 12.

FIG. 2 is an enlarged view of the cryogenic liquid collecting part shown in FIG. 2, the same components as those in the structure shown in FIG.
Referring to FIGS. 1 and 2, the microsyringe pump 16 includes a fixing base 34, a moving body driving unit (not shown), a microsyringe fixing member 35, a moving body 37, and a microsyringe 38. Have.

  The fixing table 34 is a table on which the microsyringe 38 is fixed. A moving body drive unit (not shown) is built in the fixed base 34. The moving body driving unit (not shown) is a driving unit for moving the plunger 47 in the same direction as the moving body 37 by moving the moving body 37 in the extending direction of the outer cylinder 42 of the microsyringe 38. is there. As the moving body drive unit (not shown), for example, an electromagnetic drive unit can be used.

  The microsyringe fixing member 35 is provided on the fixing base 34. The microsyringe fixing member 35 is a member for fixing the microsyringe 38 to the fixing base 34. Thereby, the position of the micro syringe 38 with respect to the fixed base 34 is regulated.

The moving body 37 is provided on the fixed base 34 and connected to the other end of the plunger 47 of the microsyringe 38. The moving body 37 is moved in the extending direction of the outer cylinder 42 of the microsyringe 38 by driving of a moving body driving unit (not shown). At this time, the plunger 47 is moved in the same direction as the moving body 37.
By moving the moving body 37 so that the tip 42A of the outer cylinder 42 and the piston 45 of the microsyringe 38 are in contact with each other in a state where a cryogenic liquid (sample) is collected in the outer cylinder 42 of the microsyringe 38, The cryogenic liquid (sample) is pressurized at a pressure above the critical pressure.
Then, the sample having a pressure equal to or higher than the critical pressure is transported to the heating unit 22.

  Further, after the tip 42A of the outer cylinder 42 and the piston 45 are brought into contact with each other, the moving body 37 is moved so that the piston 45 is separated from the tip 42A of the outer cylinder 42. The sample which is a part of the cryogenic liquid is introduced into the outer cylinder 42 (specifically, a space defined by the inner wall of the outer cylinder 42 and the piston 45) through the check valve 18.

The microsyringe 38 includes an outer cylinder 42, a flange 43, a piston 45, a plunger 47, a first cylinder tip 51, and a second cylinder tip 52.
The outer cylinder 42 is fixed to the fixing base 34 by a microsyringe fixing member 35. The outer cylinder 42 has an open end at the rear end. The flange 43 is provided at the rear end of the outer cylinder 42.

  The piston 45 is disposed in the outer cylinder 42. The piston 45 is in contact with the inner wall of the outer cylinder 42 in the circumferential direction of the outer cylinder 42. The piston 45 is provided at one end of the plunger 47. The piston 45 is moved in the extending direction of the outer cylinder 42 of the microsyringe 38 via the plunger 47 when the moving body drive unit (not shown) moves the moving body 37.

The plunger 47 has one end connected to the piston 45 and the other end connected to the moving body 37.
The first tube tip 51 is provided at the tip 42 </ b> A of the outer tube 42. The first cylinder tip 51 is an introduction part for introducing a sample, which is a part of the cryogenic liquid extracted from the pipe 12, into the outer cylinder 42. The first tube tip 51 is connected to the tip 15 </ b> A of the sample collection line 15.

The second cylinder tip 52 is provided at the tip 42 </ b> A of the outer cylinder 42. The second tube tip 52 is connected to one end of the analytical sample supply line 21.
The second tube tip 52 is a derivation unit for deriving a sample (low temperature liquid) that has been brought to a pressure equal to or higher than the critical pressure by the microsyringe pump 16 to the sample supply line 21 for analysis.

As the microsyringe pump 16 having the above-described configuration, for example, a pump that can be controlled at about 1 cm ³ / min can be used as the sample extraction speed derived from the outer cylinder 42 of the microsyringe 38.
By using such a microsyringe pump 16, the outer diameter and inner diameter of the analytical sample supply line 21 can be reduced.

The micro syringe pump 16 is a device that can easily increase the pressure up to a pressure of 10 MPa or more. Thus, as shown in Table 1, various samples (substances) can be set to a pressure higher than the critical pressure by using the microsyringe pump 16 as a device for increasing the pressure of the sample higher than the critical pressure. .
Table 1 is a table showing the relationship between substances that can be analyzed by the cryogenic liquid sampling and composition analyzer 10 of the present embodiment and the critical pressure.

The first check valve 18 is provided in the sample collection line 15. As described above, by providing the first check valve 18 in the sample collection line 15, the sample in the microsyringe 38 does not flow back to the pipe 12, and the pressure of the sample is set to a pressure higher than the critical pressure. be able to.
The first check valve 18 is housed in the heat insulating member 11. For this reason, the first check valve 18 is kept cold by the cold air of the low-temperature liquid flowing through the pipe 12.

One end of the analysis sample supply line 21 is connected to the second tube tip 52, and the other end is connected to the analyzer 26. As the analytical sample supply line 21, for example, a microtube can be used.
Thus, by using a microtube as the analysis sample supply line 21, the thickness of the analysis sample supply line 21 can be reduced, and the cryogenic liquid collection part A can be downsized.
As the microtube used as the analytical sample supply line 21, for example, a microtube having a thickness of 1 mm or less and a withstand pressure of 50 MPa can be used.

  Although not shown, the analysis sample supply line 21 arranged in the heating unit 22 is spiral from the viewpoint of efficiently heating the sample moving in the analysis sample supply line 21.

Referring to FIG. 1, the heating unit 22 is provided in an analysis sample supply line 21 located outside the heat insulating member 11. The heating unit 22 heats the sample having a pressure equal to or higher than the critical pressure to make the sample a supercritical fluid. The sample that has been made a supercritical fluid is supplied to the first valve 24 side.
When the liquid fluid serving as the sample is nitrogen, the heating unit 22 heats the sample so that the temperature of the sample at a pressure equal to or higher than the critical pressure is 126.2K.

The second check valve 23 is provided in the analysis sample supply line 21 located in the heat insulating member 11. The second check valve 23 prevents the sample led out from the microsyringe pump 16 and having a pressure equal to or higher than the critical pressure from flowing back into the microsyringe pump 16.
The second check valve 23 is accommodated in the heat insulating member 11. For this reason, the second check valve 23 is kept cold by the cold air of the low-temperature liquid flowing through the pipe 12.

The first valve 24 is a pressure adjusting valve for adjusting the pressure of a sample that is a supercritical fluid. For example, the first valve 24 adjusts the pressure of the sample that is a supercritical fluid to a pressure close to atmospheric pressure.
The first valve 24 is provided in the analysis sample supply line 21 located between the heating unit 22 and the analyzer 26.

  The analyzer 26 is connected to the other end of the analysis sample supply line 21. As the analyzer 26, for example, gas chromatography can be used.

The exhaust line 28 branches off from the analysis sample supply line 21 located between the first valve 24 and the analyzer 26. The second valve 29 is provided in the exhaust line 28.
In this way, by providing the second valve 29 in the exhaust line 28 branched from the analysis sample supply line 21, the opening degree of the second valve 29 is adjusted, so that the supercritical fluid flowing into the analyzer 26. The amount of sample taken can be adjusted.

  The cryogenic liquid sampling and composition analyzing apparatus 10 having the above-described configuration is suitable for accurately analyzing trace impurities in the cryogenic liquid in the air liquefaction separation process.

Next, the cryogenic liquid composition analysis method of the present embodiment using the cryogenic liquid sampling and composition analysis apparatus 10 will be described with reference to FIGS. 1 and 2.
First, the plunger 47 is moved several times in the direction in which the piston 45 is separated from the tip 42A from the state in which the piston 45 and the tip 42A of the outer cylinder 42 are in contact with each other. A part of the cryogenic liquid flowing in the pipe 12 in the outer cylinder 42 is collected as a sample via the check valve 18.

At this time, since the amount of the sample collected in the outer cylinder 42 is small, the sample can be easily kept cool by the cold air of the low-temperature liquid flowing through the pipe 12 accommodated in the heat insulating member 11. This makes it possible to suppress the vaporization of the sample, so that the state of the sample can be easily maintained in a liquid state.
In particular, when the composition analysis of nitrogen (low temperature liquid) is performed using the analyzer 26, the amount of collected low temperature liquid can be, for example, 2 to 10 cm ³ .

  Next, by moving the plunger 47 in the direction in which the piston 45 approaches the tip 42A, the sample collected in the outer cylinder 42 is pressurized, and the pressure of the liquid sample is increased above the critical pressure, A sample having a critical pressure or higher is supplied to the heating unit 22.

At this time, the flow rate of the sample set to be equal to or higher than the critical pressure derived from the outer cylinder 42 of the microsyringe pump 16 can be set to 1 cm ³ / min, for example.
Although it is desirable that the pressure of all components of the sample to be analyzed (cold fluid) is equal to or higher than the critical pressure, the pressure of only the main component may be simply set to the critical pressure or higher.

  Next, the heating unit 22 heats the sample whose pressure is equal to or higher than the critical pressure, thereby making the sample a supercritical fluid, and supplying the sample made the supercritical fluid to the first valve 24 (pressure regulating valve). To do.

Specifically, when nitrogen is used as the low temperature liquid (sample), the heating unit 22 heats the sample so that the temperature of the sample is in the range of 0 to 20 ° C. (near the atmospheric temperature). As a heating method at this time, for example, an air temperature method can be used.
Moreover, the sample flowing through the analysis sample supply line 21 located between the heating unit 22 and the first valve 24 is made a supercritical fluid by making the sample into a supercritical fluid by the heating unit 22.

Next, in the first valve 24, the pressure of the sample whose pressure is equal to or higher than the critical pressure is reduced to a pressure at which the composition analysis of the sample can be performed by the analyzer 26, so that the sample is gasified.
Specifically, for example, when nitrogen is used as the cryogenic liquid (sample) and gas chromatography is used as the analyzer 26 to analyze the composition of the sample, the second valve 29 is opened to open the pressure of the sample. Is reduced to atmospheric pressure (pressure at which the composition of the sample can be analyzed).

  Thereafter, the gas sample is supplied to the analyzer 26 via the analysis sample supply line 21. At this time, by adjusting the opening degree of the second valve 29, the flow rate of the sample that is gas supplied to the analyzer 26 is adjusted. Thereafter, the analysis device 26 performs composition analysis of the gas sample.

  The state of the sample that is a part of the cryogenic liquid of the present embodiment is held in the liquid, and the pressure of the sample that is made liquid is pressurized so as to be equal to or higher than the critical pressure, and then the sample that is set to a pressure higher than the critical pressure. Is heated to make the sample a supercritical fluid, so that low-volatile components contained in the sample can be suppressed from vaporizing before performing composition analysis.

  Therefore, reducing the pressure of the sample that has been made a supercritical fluid to a pressure at which composition analysis is possible, gassing the sample gas, and then analyzing the composition of the sample, thereby improving the accuracy of the composition analysis of the cryogenic liquid Can do.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and within the scope of the present invention described in the claims, Various modifications and changes are possible.

  The present invention can be applied to a low-temperature liquid composition analysis method capable of improving the accuracy of low-temperature liquid composition analysis.

  DESCRIPTION OF SYMBOLS 10 ... Low temperature liquid collection and composition analyzer, 11 ... Thermal insulation member, 11A ... Thermal insulation space, 12 ... Piping, 15 ... Sample collection line, 15A, 42A ... Tip, 16 ... Micro syringe pump, 18 ... First check Valve, 21 ... Analytical sample supply line, 22 ... Heating unit, 23 ... Second check valve, 24 ... First valve, 26 ... Analyzer, 28 ... Exhaust line, 29 ... Second valve, 34 ... Fixing base, 35 ... Micro syringe fixing member, 37 ... Moving body, 38 ... Micro syringe, 42 ... Outer cylinder, 43 ... Flange, 45 ... Piston, 47 ... Plunger, 51 ... First tube tip, 52 ... Second Tube tip, A ... Cryogenic liquid sampling part

Claims (3)

A collecting step of collecting a part of the cryogenic liquid as a sample;
A pressurizing step of holding the state of the sample in a liquid and pressurizing the liquid so that the pressure of the sample is equal to or higher than a critical pressure;
A supercritical fluid generating step in which the sample having a pressure equal to or higher than the critical pressure is heated to make the sample a supercritical fluid;
After generating the supercritical fluid, the pressure of the sample is reduced to a pressure at which composition analysis is possible, thereby reducing the pressure of the sample to gas,
A composition analysis step of analyzing the composition of the sample after the pressure reduction step;
A method for analyzing the composition of a cryogenic liquid, comprising: In the collecting step, a part of the cryogenic liquid is collected as the sample in a microsyringe of a microsyringe pump,
2. The cryogenic liquid composition analysis method according to claim 1, wherein in the pressurizing step, the sample is pressurized by pushing out the sample collected in the microsyringe by a piston of the microsyringe pump.   3. The cryogenic liquid composition analysis method according to claim 1, wherein the microsyringe pump is cooled before the collection step.

Images