JP5843529B2 - Calorie measurement method and system for liquefied natural gas - Google Patents

Description

  The present invention relates to a calorimetric method for liquefied natural gas and a calorimetric system for liquefied natural gas. Is obtained in advance as reference density / calorific value relationship information, and the temperature and pressure of the liquefied natural gas to be measured are measured, and the liquid density of the liquefied natural gas to be measured is measured by a density measuring means using Coriolis force Measure the calorific value of liquefied natural gas to determine the calorific value of the liquefied natural gas to be measured based on the measured liquid density, temperature, pressure and the reference density vs. calorific value relationship information, and measure A temperature measuring means for measuring the temperature of the target liquefied natural gas, a pressure measuring means for measuring the pressure of the target liquefied natural gas, and the Coriolis force Density measurement means to be used, and the calorific value for storing the relationship between the liquid density and the calorific value of the liquefied natural gas in the reference state where the temperature and pressure are the reference temperature and the reference pressure, respectively, as the reference density / calorific value relation information Based on the calculation information storage means, the measurement information of the temperature measurement means, the pressure measurement means and the density measurement means, and the reference density vs. calorific value relationship information stored in the calorific value calculation information storage means The present invention also relates to a calorific value measurement system for liquefied natural gas provided with a calorific value calculation means for obtaining a gas calorific value of liquefied natural gas to be measured.

Such a calorific value measuring method and calorific value measuring system of liquefied natural gas measure the calorific value of liquefied natural gas, and are used to adjust the calorific value of city gas produced using this liquefied natural gas as a raw material. .
In other words, the relationship between the liquid density and the gas heating value in the liquefied natural gas in the reference state where the temperature and the pressure are the predetermined reference temperature and the reference pressure, respectively, is obtained in advance as the reference density / heating value relationship information.
Further, the temperature and pressure of the liquefied natural gas to be measured are measured, and the liquid density of the liquefied natural gas to be measured is measured by density measuring means using Coriolis force.
Then, for example, based on the measured temperature and pressure, the measured density of the liquefied natural gas is converted into the liquid density in the reference state, and based on the converted liquid density, the measurement object is obtained from the reference density vs. calorific value relationship information. The gas calorific value of the liquefied natural gas is obtained (for example, see Patent Document 1).

Although not described in the above-mentioned Patent Document 1, it is considered that the density measurement means using the Coriolis force measures the liquid density of the liquefied natural gas to be measured as follows.
That is, this density measuring means measures the density by using the Coriolis force generated when the liquefied natural gas to be measured flows through the flow tube that is vibrated by the vibration exciter. Is provided with a frequency related information detecting means for detecting natural frequency related information which is information related to the natural frequency of the flow tube. Incidentally, the natural frequency related information detected by the frequency related information detecting means may be the natural frequency itself of the flow tube or the natural period of the flow tube.

Advance, meet the first reference fluid having a predetermined reference temperature T _w liquid density D _w is known to the flow tube natural frequency associated which is information related to the natural frequency of the flow tube by the frequency-related information detecting means The information F _w is measured, the liquid density _Da is known, the second reference fluid having _a predetermined reference temperature Ta is filled in the flow tube, and the frequency related information detecting means relates to the natural frequency of the flow tube. previously measured natural frequencies related information F _a is information.
Further, the temperature measuring means and measures the temperature T _x of the liquefied natural gas to be measured, the liquefied natural gas to be measured by flow in the flow tube, the vibration frequency-related information detection unit, liquefied natural gas to be measured There measuring the natural frequency related information F _x which is information related to the natural frequency of the flow tube to flow.
Then, the liquid density D _w of the first reference fluid, the reference temperature T _w and the natural frequency related information F _w , the liquid density D _a of the second reference fluid, the reference temperature _Ta and the natural frequency related information F _a , the measurement target Based on the temperature T _x of the liquefied natural gas, the natural frequency related information F _x , and the coefficient α, the liquid density D _x of the liquefied natural gas to be measured is obtained by the following liquid density derivation function.

D _x = f [D _w , D _a , F _x ² × (1−α × T _x ), F _a ² × (1−α × T _a ), F _w ² × (1−α × T _w )]

  That is, in determining the liquid density of the liquefied natural gas to be measured, the liquid density of the first reference fluid, the reference temperature and the natural frequency related information, and the liquid density, the reference temperature and the natural frequency related information of the second reference fluid. It is intended to improve the measurement accuracy of the liquid density of the liquefied natural gas to be measured.

  In such a liquefied natural gas calorific value measuring method and calorific value measuring system, conventionally, although not described in Patent Document 1 above, the coefficient α is uniquely set to a constant value.

Japanese Patent No. 4393302

By the way, the vibration state of the flow tube when the fluid flows through the flow tube depends on the spring constant of the flow tube. On the other hand, the spring constant of the flow tube varies depending on the temperature of the fluid flowing through the flow tube. .
In the liquid density derivation function, the natural frequency related information F _w of the first reference fluid is a value when the temperature is the reference temperature T _w , and the natural frequency related information F of the second reference fluid. _{Since a is} also a value when the temperature is the reference temperature T _a , the natural frequency related information F _w and F _a may not correspond to the temperature T _x of the liquefied natural gas to be measured.

However, in the conventional calorific value measuring method and calorie measuring system of liquefied natural gas, the coefficient α multiplied by the natural frequency related information F _w , F _a is set to a constant value. In obtaining the liquid density of the liquefied natural gas to be measured, the temperature variation of the liquefied natural gas to be measured is not reflected. That is, the natural frequency related information F _{w of} the first reference fluid and the natural frequency related information F _{a of} the second reference fluid may deviate from the values at the temperature T _x of the liquefied natural gas to be measured. in measuring the liquid density D _x of liquefied natural gas by obtaining the liquid density D _x by the liquid density derivation function, the measurement accuracy was easy to decrease.

For example, as shown in white in FIG. 4, the temperature T of the liquefied natural gas to be measured (in this example, the liquefied mixed gas in which the liquefied natural gas for adjusting the calorific value of gas is mixed with the liquefied natural gas). _{As x} increases from about −145 ° C., the measurement error of the liquid density D _x of the liquefied natural gas increases, and when the temperature T _x is −135 ° C., the measurement error of the liquid density D _x is 2.3 kg / m. Increases to about ³ .
Therefore, conventionally, since the measurement accuracy of the liquid density of the liquefied natural gas is likely to be lowered, there is a problem that the measurement accuracy of the calorific value of the liquefied natural gas obtained using the liquid density of the liquefied natural gas is lowered. .

  The present invention has been made in view of such circumstances, and an object thereof is to provide a calorific value measurement method and a calorific value measurement system for liquefied natural gas that can improve the measurement accuracy of the calorific value of liquefied natural gas. There is to do.

The calorific value measurement method for liquefied natural gas according to the present invention is based on the relationship between the liquid density and the calorific value of the liquefied natural gas in the reference state in which the temperature and the pressure are the reference temperature and the reference pressure, respectively. In addition to measuring the temperature and pressure of the liquefied natural gas to be measured, the liquid density of the liquefied natural gas to be measured is measured by a density measuring means using Coriolis force, and the measured liquid density and temperature are measured. Based on the pressure and the reference density vs. calorific value relationship information, the calorific value of the liquefied natural gas to be measured is obtained,
Its characteristic configuration, in the measurement of liquid density of the liquefied natural gas to be measured temperature by the density measuring unit may change, the first reference fluid liquid density D _w is a predetermined reference temperature in a known T _w The natural frequency related information F _w , which is information related to the natural frequency of the flow tube when it is filled in the flow tube of the density measuring means, the liquid density _Da is known, and _a second reference of _a predetermined reference temperature Ta the flow is information relating to the natural frequency of the tube is measured in advance the natural frequency related information F _a, measuring the temperature T _x of the liquefied natural gas to be measured when filled with fluid to the flow tube At the same time, the natural frequency related information F _x , which is information related to the natural frequency of the flow tube through which the liquefied natural gas to be measured flows, is measured, and the liquid density D _w and the reference temperature T of the first reference fluid are measured. _w and And the natural frequency related information F _w , the liquid density D _a of the second reference fluid, the reference temperature T _a and the natural frequency related information F _a , the temperature T _x of the liquefied natural gas to be measured, and the natural frequency related information F _{Based on x} and the coefficient α, the coefficient α is a numerical value obtained by the following coefficient α derivation formula based on the temperature T _x of the liquefied natural gas to be measured. The point is to obtain the liquid density D _x of natural gas.
D _x = f [D _w , D _a , F _x ² × (1−α × T _x ), F _a ² × (1−α × T _a ), F _w ² × (1−α × T _w )]
α = a ₁ × T _x ³ + b ₁ × T _x ² + c ₁ × T _x + d ₁
Where a ₁ , b ₁ , c ₁ , d ₁ : constants

That is, the natural frequency related information F _w of the first reference fluid is obtained by filling the first reference fluid having a known liquid density D _w and a predetermined reference temperature T _w into the flow tube of the density measuring means in advance and performing natural vibration. In addition to the measurement, the second reference fluid having _a known liquid density D _a and a predetermined reference temperature Ta is filled in the flow tube of the density measuring means and caused to vibrate, and the natural frequency related information F _a of the second reference fluid is obtained. taking measurement. Further, while measuring the temperature T _x of the liquefied natural gas to be measured, by the natural vibration of the liquefied natural gas to be measured by flow in the flow tube density determination means, the natural frequency associated LNG to be measured Information _Fx is measured. The liquefied natural gas in the present application is a liquefied mixture in which liquefied natural gas is a main component and a calorific value adjusting liquefied gas (for example, liquefied petroleum gas) for adjusting the gas calorific value of the liquefied natural gas is mixed. Contains gas.
Then, the liquid density D _w of the first reference fluid, the reference temperature T _w and the natural frequency related information F _w , the liquid density D _a of the second reference fluid, the reference temperature _Ta and the natural frequency related information F _a , the measurement target Based on the liquid density derivation function based on the temperature T _x and natural frequency related information F _x of the liquefied natural gas and the coefficient α set to a numerical value corresponding to the temperature T _x of the liquefied natural gas to be measured, calculating a liquid density D _x liquefied natural gas to be measured.

Then, and natural frequencies related information F _w of the first reference fluid, the natural frequency related information F _a second reference fluid, even not corresponding to the temperature T _x of the liquefied natural gas to be measured, the coefficient Since α is set according to the temperature T _x of the liquefied natural gas to be measured, the natural frequency related information F of the first reference fluid can be obtained by multiplying “F _a ² ” and “F _w ² ” by a coefficient α. _w and the natural frequency related information F _a of the second reference fluid can be corrected to a value corresponding to the temperature T _x of the liquefied natural gas to be measured, and the liquid density of the liquefied natural gas to be measured can be measured. Accuracy can be improved.
Accordingly, it is possible to provide a calorific value measurement method for liquefied natural gas that can improve the measurement accuracy of the gas calorific value of liquefied natural gas.

Then , by setting the equation for deriving the coefficient α to a third-order approximation of the temperature of the liquefied natural gas to be measured, the liquid density of the liquefied natural gas to be measured can be obtained as accurately as possible regardless of the fluctuation of the temperature. The coefficient α can be appropriately set according to the temperature of the liquefied natural gas to be measured.
Therefore, the measurement accuracy of the gas calorific value of liquefied natural gas can be further improved.

The calorimetric system for liquefied natural gas according to the present invention is:
Temperature measuring means for measuring the temperature of the liquefied natural gas to be measured;
Pressure measuring means for measuring the pressure of the liquefied natural gas to be measured;
Density measuring means for measuring the liquid density of the liquefied natural gas to be measured using Coriolis force;
A calorific value calculation information storage means for storing the relationship between the liquid density and the gas calorific value in the liquefied natural gas in the reference state in which the temperature and the pressure are the reference temperature and the reference pressure, respectively, as reference density / calorific value relationship information;
Based on the measurement information of each of the temperature measurement means, the pressure measurement means, and the density measurement means, and the reference density vs. calorific value relationship information stored in the calorific value calculation information storage means, the liquefied natural to be measured is measured. A calorific value calculating means for obtaining a gas calorific value of the gas,
The characteristic configuration is that the density measurement means detects a flow tube for flowing the liquefied natural gas to be measured, and frequency related information detection for detecting natural frequency related information that is information related to the natural frequency of the flow tube. Density calculation means for calculating the liquid density of the natural gas to be measured based on the detection information of the frequency related information detection means, and density calculation for storing information for calculating the liquid density by the density calculation means Information storage means,
The density calculation information storage means, the natural frequency of the detected by frequency-related information detecting means when the liquid density D _w satisfies the first reference fluid having a predetermined reference temperature T _w known to the flow tube Related information F _w, liquid density D _a is the frequency-related information detecting means natural frequency related information detected by the F when the second reference fluid having a predetermined reference temperature T _a known filled in said flow tube _a , a liquid density D _w and a reference temperature T _w of the first reference fluid, a liquid density D _a and a reference temperature T _{a of} the second reference fluid, and a coefficient α are stored,
The density calculation means is stored in the density calculation information storage means, the measurement information in the temperature measurement means, and the frequency related information detection means when the liquefied natural gas to be measured flows through the flow tube. Based on the detection information, the liquid density D _w of the first reference fluid, the reference temperature T _w and the natural frequency related information F _w , the liquid density D _a of the second reference fluid, the reference temperature _Ta and the natural frequency related From the information F _a , the temperature T _x of the liquefied natural gas to be measured, the natural frequency related information F _x , and the coefficient α, the liquid density D _x of the liquefied natural gas to be measured is calculated by the following liquid density derivation function. Configured to ask for
Further, the density calculating means, the density calculation information storage means based on the coefficient α derivations based on the temperature T _x of the liquefied natural gas to be measured of the following stored, is configured to determine the coefficients α In the point.
D _x = f [D _w , D _a , F _x ² × (1−α × T _x ), F _a ² × (1−α × T _a ), F _w ² × (1−α × T _w )]
α = a ₁ × T _x ³ + b ₁ × T _x ² + c ₁ × T _x + d ₁
Where a ₁ , b ₁ , c ₁ , d ₁ : constants

That is, the natural vibration of the liquid density D _w is when brought into natural vibration meets the first reference fluid having a predetermined reference temperature T _w to the flow tube density determination means known, detected by the frequency-related information detecting means when the number-related information F _w, liquid density D _a is satisfied the second reference fluid having a predetermined reference temperature T _a to the flow tube density determination means known to the natural vibration, detected by the frequency-related information detecting means The natural frequency related information F _a , the liquid density D _w and the reference temperature T _w of the first reference fluid, the liquid density D _a and the reference temperature T _{a of} the second reference fluid, and the coefficient α are stored in the density calculation information. Stored in the means. This coefficient α is stored in the density calculation information storage means so as to be a numerical value corresponding to the temperature T _x of the liquefied natural gas to be measured.
The density calculation means includes the storage information of the density calculation information storage means, the measurement information of the temperature measurement means, and the detection information of the frequency related information detection means when the liquefied natural gas to be measured flows through the flow tube. Based on the liquid density D _w of the first reference fluid, the reference temperature T _w and the natural frequency related information F _w , the liquid density D _a of the second reference fluid, the reference temperature _Ta and the natural frequency related information F _a , and The liquid density derivation function from the temperature T _x and natural frequency related information F _x of the measurement target liquefied natural gas and the coefficient α set to a numerical value corresponding to the temperature T _x of the measurement target liquefied natural gas Thus, the liquid density D _x of the liquefied natural gas to be measured is obtained.

Then, and natural frequencies related information F _w of the first reference fluid, the natural frequency related information F _a second reference fluid, even not corresponding to the temperature T _x of the liquefied natural gas to be measured, the coefficient Since α is set according to the temperature T _x of the liquefied natural gas to be measured, by multiplying “F _a ² ” and “F _w ² ” by the coefficient α, the natural frequency related information of the first reference fluid is obtained. F _w and the natural frequency related information F _a of the second reference fluid can be corrected to values corresponding to the temperature T _x of the liquefied natural gas to be measured, and the liquid density of the liquefied natural gas to be measured can be corrected. Measurement accuracy can be improved.
Accordingly, it is possible to provide a liquefied natural gas calorific value measurement system capable of improving the measurement accuracy of the gas calorific value of liquefied natural gas.
Since the coefficient α derivation formula is set to a third-order approximation formula of the temperature of the liquefied natural gas to be measured, the liquid density of the liquefied natural gas to be measured can be obtained as accurately as possible regardless of the fluctuation of the temperature. The coefficient α can be appropriately set according to the temperature of the liquefied natural gas to be measured.
Therefore, the measurement accuracy of the gas calorific value of liquefied natural gas can be further improved .

A further feature of the calorific value measurement system for liquefied natural gas according to the present invention is that the liquefied natural gas flow path through which the liquefied natural gas is sent has a calorific value adjustment liquefaction for adjusting the gas calorific value of the liquefied natural gas. A liquefied gas flow path for adjusting the calorific value through which the gas is sent is connected,
Adjusting the mixing ratio of the calorific value adjustment liquefied gas to the liquefied natural gas flowing in the liquefied natural gas flow path, and provided with a mixing ratio adjusting means for adjusting the gas calorific value of the liquefied natural gas;
The liquefied natural gas after gas calorific value adjustment in which the mixing ratio of the calorific value adjusting liquefied gas is adjusted by the mixing ratio adjusting means is the liquefied natural gas to be measured.

That is, the calorific value of the liquefied natural gas after the gas calorific value adjustment in which the calorific value adjusting liquefied gas is mixed is measured by the liquefied natural gas calorific value measuring system of the present invention.
In other words, in order to adjust the calorific value of city gas supplied to consumers (factories, homes, etc.) to a predetermined range, the calorific value adjustment liquefied gas is mixed with liquefied natural gas and the calorific value thereof is adjusted. Adjust the mixing ratio of the adjustment liquefied gas. On the other hand, the temperature of liquefied natural gas and liquefied gas for adjusting the calorific value are different, so adjusting the gas calorific value by adjusting the mixing ratio of the liquefied natural gas to liquefied natural gas and adjusting the calorific value of that gas will adjust the calorific value of the gas. The temperature of the later liquefied natural gas tends to fluctuate.
Therefore, by measuring the liquid density of the liquefied natural gas after adjusting the calorific value of the gas, the liquid density can be accurately measured regardless of the fluctuation of the temperature of the liquefied natural gas by measuring the calorific value of the liquefied natural gas according to the present invention. In addition, by adjusting the mixing ratio of the calorific value adjusting liquefied gas using the measured value, the gas calorific value of the liquefied natural gas can be accurately adjusted within a predetermined range.
Therefore, it is possible to supply liquefied natural gas whose gas heat generation amount is accurately adjusted within a predetermined range.

According to a further feature of the calorific value measurement system for liquefied natural gas according to the present invention, the calorific value adjustment liquefied gas is liquefied petroleum gas,
The temperature T _x of the liquefied natural gas after adjusting the gas heating value fluctuates in the range of −160 to −120 ° C.,
In the fluctuation range of the temperature T _x of the liquefied natural gas, the constants a ₁ and b ₁ are set to 0, and the coefficient α derivation formula is as follows using the temperature T _x of the liquefied natural gas to be measured as a variable: The point is that it is set to a linear expression.
α = c ₁ × T _x + d ₁
Where c ₁ and d _{1 are} constants

That is, the temperature of liquefied natural gas is about −160 ° C., while the temperature of liquefied petroleum gas mainly composed of propane, for example, is about −42 ° C., and the temperature difference between liquefied natural gas and liquefied petroleum gas. Is relatively large.
That is, when liquefied petroleum gas is used as the calorific value adjustment liquefied gas, the temperature fluctuation range of the liquefied natural gas after the gas calorific value adjustment is relatively large.
In addition, the coefficient α derivation formula is set to the above-described linear expression using the temperature of the liquefied natural gas to be measured as a variable, so that the liquid density can be obtained accurately regardless of the variation in the temperature of the liquefied natural gas to be measured. The coefficient α can be set appropriately and easily according to the temperature of the liquefied natural gas to be measured.
Therefore, by using liquefied petroleum gas as the calorific value adjustment liquefied gas, the liquid density can be accurately measured even when the temperature fluctuation range of the liquefied natural gas to be measured is relatively large. The calorific value of the gas can be accurately measured.

Block diagram showing the overall configuration of a calorific value measurement system for liquefied natural gas Partial cutaway perspective view of the measuring unit of the density measuring device Vertical side view of the measuring unit of the density measuring device Diagram showing the relationship between the temperature of liquefied natural gas and measurement error of liquid density

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a calorific value measurement system S (hereinafter sometimes simply referred to as a calorific value measurement system) of liquefied natural gas (hereinafter sometimes referred to as LNG) is an LNG tank that stores liquefied natural gas. The liquefied natural gas that is sent from 1 to the LNG pump 2 and flows through the LNG delivery path 3 is measured, and the gas calorific value of the liquefied natural gas is measured.

In this embodiment, liquefied petroleum gas (hereinafter sometimes referred to as LPG) is used as a calorific value adjusting liquefied gas for adjusting the calorific value of liquefied natural gas, and LPG for storing the liquefied petroleum gas is used. An LPG delivery path 6 through which liquefied petroleum gas is delivered from the tank 4 by the LPG pump 5 is connected to the LNG delivery path 3.
The LNG delivery path 3 is provided with an LNG flow rate adjusting valve 14 for adjusting the flow rate of the liquefied natural gas flowing through the LNG delivery path 3, and the LPG delivery path 6 flows through the LPG delivery path 6. An LPG flow rate adjusting valve 15 for adjusting the flow rate of the liquefied petroleum gas is provided.
The LNG pump 2 and the LPG pump 5 are operated at a constant rotational speed set according to each, and the opening degree of each of the LNG flow rate adjustment valve 14 and the LPG flow rate adjustment valve 15 is adjusted individually. Thus, the mixing ratio of the liquefied petroleum gas to the liquefied natural gas flowing through the LNG delivery path 3 is adjusted. That is, the LNG flow rate adjusting valve 14 and the LPG flow rate adjusting valve 15 constitute a mixing ratio adjusting means M.

This calorific value measurement system S is a liquefied natural gas that flows downstream from the connection point of the LPG delivery path 6 in the LNG delivery path 3, that is, gas heat generation in which the mixing ratio of the liquefied petroleum gas is adjusted by the mixing ratio adjusting means M. It is provided to measure the gas calorific value of the liquefied natural gas after the amount adjustment.
Hereinafter, the heat quantity measurement system S will be described.
As shown in FIG. 1, the calorie measuring system S includes a temperature sensor 7 as a temperature measuring unit that measures the temperature of the liquefied natural gas to be measured, and a pressure as a pressure measuring unit that measures the pressure of the liquefied natural gas to be measured. Sensor 8, density measuring device E as a density measuring means for measuring the liquid density of the liquefied natural gas to be measured using Coriolis force, gas chromatography 9 for measuring the nitrogen content in the liquefied natural gas to be measured, and A control unit 10 for controlling the operation of the calorific value measurement system S is provided.

The control unit 10 includes a microcomputer, and includes a storage unit 11 including an HDD, and a program for executing various processes is installed.
The storage unit 11 stores the relationship between the liquid density and the gas heating value in the liquefied natural gas in the reference state in which the temperature and the pressure are the reference temperature and the reference pressure, respectively. Functions as a calorific value calculation information storage means.
Further, the program installed in the control unit 10 is based on the measurement information of the temperature sensor 7, the pressure sensor 8, and the density measuring device E, and the reference density vs. calorific value relationship information stored in the storage unit 11. The calorific value calculation means 12 for determining the gas calorific value of the liquefied natural gas to be measured is included.

The density measuring apparatus E includes a measuring unit 20 that obtains information for deriving density by flowing a fluid to be measured for density.
As shown in FIGS. 2 and 3, the measuring unit 20 is interposed in the middle of a conduit (in this embodiment, the LNG delivery path 3) through which the density measurement target fluid flows, and the density measurement target fluid. This is information related to the natural frequency of the flow tube 21, the vibrator 22 that vibrates the flow tube 21, and the U-shaped flow tube 21 that is returned to the pipe line again. It comprises a detector 23 as a frequency related information detecting means for detecting a natural vibration period (hereinafter may be referred to as a natural period) as the natural frequency related information.

The flow tube 21 is composed of a pair of flow tubes 21 and 21 arranged in parallel to each other. One end of each of the pair of flow tubes 21 and 21 is connected to the manifold 24 and the other end is also different. The manifold 24 is connected in communication, and the pair of flow tubes 21 and 21 are connected to each other at one end and the other end by a connecting plate 25.
A pair of flow tubes 21 and 21 are interposed in the middle of the LNG delivery path 3 via the pair of manifolds 24 and 24.

A pair of detectors 23 are arranged separately on both ends of the pair of flow tubes 21, 21, and the vibrator 22 is arranged at a position corresponding to the approximate center in the axial direction of each of the pair of flow tubes 21, 21. Has been.
As shown in FIG. 3, each detector 23 includes a coil 23 c fixed to one flow tube 21 and a permanent magnet 23 m fixed to the other flow tube 21.
As shown in FIG. 2, the vibrator 22 includes an electromagnetic drive coil 22 c fixed to one flow tube 21 and a permanent magnet 22 m fixed to the other flow tube 21.
And the control part 10 is comprised so that an alternating current may be sent through the coil 22c for electromagnetic drive in order to vibrate a pair of flow tubes 21 and 21 with a natural frequency.

  As shown in FIG. 1, the gas chromatography 9 includes a sampling unit 9s that samples the liquefied natural gas for measurement from the LNG delivery path 3, and contains nitrogen in the liquefied natural gas sampled by the sampling unit 9s. The rate (mol%) is measured.

  The program installed in the control unit 10 also includes density calculation means 13 that calculates the liquid density of the liquefied natural gas to be measured based on the detection information of the detector 23 of the detection unit 20. The storage unit 11 of the control unit 10 stores information for calculating the liquid density by the density calculation unit 13, and the storage unit 11 of the control unit 10 also functions as a density calculation information storage unit. .

The control unit 10 storage unit 11, the liquid density D _w is the natural period F detected by the detector 23 when filled with water as a first reference fluid given at a known reference temperature T _w to the flow tube 21 _w (natural frequency related information), the liquid density D _a specific period F detected by the detector 23 when filled with air as the second reference fluid having a predetermined reference temperature T _a known to the flow tube 21 _a (natural frequency related information), liquid density D _{w of} water and reference temperature T _w , liquid density D _{a of} air, reference temperature T _a , and coefficient α are stored.

In the present invention, the density calculation means 13 is stored in the storage unit 11 of the control unit 10, the measurement information of the temperature sensor 7, and the detector 23 when the liquefied natural gas to be measured flows through the flow tube 21. Based on the detection information, the liquid density D _{w of} water, the reference temperature T _w and the natural period F _w , the liquid density D _{a of} air, the reference temperature _Ta and the natural period F _a , and the temperature T _x of the liquefied natural gas to be measured And the natural period F _x and the coefficient α, the liquid density D _x of the liquefied natural gas to be measured is obtained by the following liquid density derivation function, and the coefficient α is the temperature of the liquefied natural gas to be measured. is a numerical value corresponding to T _x.

D _x = f [D _w , D _a , F _x ² × (1−α × T _x ), F _a ² × (1−α × T _a ), F _w ² × (1−α × T _w )]

The calorific value calculation means 12 of the control unit 10 includes reference density / calorific value relationship information stored in the storage unit 11, the liquid density D _x of the liquefied natural gas to be measured calculated by the density calculation means 13, and the temperature sensor 7. Based on the temperature T _x of the liquefied natural gas detected by the pressure sensor 8 and the pressure P _x of the liquefied natural gas measured by the pressure sensor 8, the gas calorific value of the liquefied natural gas measured It is comprised so that may be calculated.
Then, the control unit 10 controls the operation of each of the LNG flow rate adjustment valve 14 and the LPG flow rate adjustment valve 15 so that the gas heat generation amount calculated by the heat generation amount calculation means 12 falls within a predetermined set gas heat generation amount range. Thus, the mixing ratio of the liquefied petroleum gas to the liquefied natural gas flowing through the LNG delivery path 3 is adjusted.

Next, the heat generation amount calculation means 12 and the density calculation means 13 of the control unit 10 will be described.
As a specific example of the liquid density derivation function, the following expression 1 is set, and the following expression 2 is set as an expression for obtaining the coefficient α corresponding to the temperature T _x of the liquefied natural gas to be measured. The density calculating means 13 obtains a coefficient α according to the following equation 2 based on the temperature T _x of the liquefied natural gas to be measured detected by the temperature sensor 7, and uses the obtained coefficient α to According to Equation 1, the liquid density D _x of the liquefied natural gas to be measured is calculated.

D _x = (D _w −D _a ) × [[F _x ² (1−α × T _x ) −F _a ² (1−α × T _a )] ÷ [F _w ² (1−α × T _w ) −F _a ² (1−α × T _a )]] + D _a (Equation 1)
However,
D _x : Liquid density of the liquefied natural gas to be measured (g / ml)
D _w : Density of water (g / ml), storage information in the storage unit 11 D _a : Density of air (g / ml), storage information in the storage unit 11 F _x : Natural period of the liquefied natural gas to be measured (μs) ), Value detected by the detector 23 F _w : natural period of water (μs), storage information in the storage unit 11 F _a : natural period of air (μs), storage information in the storage unit 11 T _x : measurement object The temperature of the liquefied natural gas (° C.), the value detected by the temperature sensor 7 T _w : the temperature of the water (° C.), the stored information in the storage unit _Ta : the temperature of the air (° C.), the storage in the storage unit 11 information

α = a ₁ × T _x ³ + b ₁ × T _x ² + c ₁ × T _x + d ₁ (Equation 2)
Here, a ₁ , b ₁ , c ₁ , and d ₁ are constants obtained by experiments.
By the way, in this embodiment,
a ₁ = 0
b ₁ = 0
c ₁ = 0.0042
d ₁ = 4.24
Set to

The above expression 1 is a known arithmetic expression that is used as an arithmetic expression for calculating the density of the fluid to be measured in the density measuring device that measures the density of the fluid using the Coriolis force.
Expression 2 above is an approximate expression set based on data obtained through experiments.
That is, the density of a plurality of types of liquefied natural gas for test having different densities and temperatures is measured using a density measuring means different from that utilizing the Coriolis force. This another density measuring means can measure the density of the liquefied natural gas with high accuracy without being affected by the temperature of the liquefied natural gas. Then, when the same test liquefied natural gas was tested in the density measuring apparatus E according to the present invention and the liquid density D _x was calculated according to the above equation 1, the calculated value and the measured value of another density measuring means An approximate expression is set like the above expression so as to eliminate the difference or minimize the difference.

As described above, the coefficient α is set to a numerical value corresponding to the temperature T _x of the liquefied natural gas to be measured, and the liquid density D _x of the liquefied natural gas to be measured is calculated according to the above equation 1, thereby obtaining FIG. As shown in black in FIG. 2, even if the temperature T _x of the liquefied natural gas varies in the range of −150 to −135 ° C., the density measurement error can be reduced over the entire temperature variation range. For example, when the temperature T _x of the liquefied natural gas is in the range of −150 to −145 ° C., the density measurement error is reduced to the same level as when the coefficient α is measured to be constant (shown in white in FIG. 4). In the range where the temperature T _x of the liquefied natural gas is higher than −145 ° C., the density measurement error is significantly larger than that measured when the coefficient α is constant (shown in a white state in FIG. 4). Can be made smaller.
Although illustration is omitted, according to the present invention, even if the temperature T _x of the liquefied natural gas fluctuates in the range of −160 to −120 ° C., in the entire temperature fluctuation range, −150 to As shown in the temperature range of liquefied natural gas of −135 ° C., the density measurement error can be reduced.

The calorific value calculation means 12 of the controller 10 calculates the gas calorific value of the liquefied natural gas to be measured by the following four steps.
[Step 1]:
Heat generation amount computing means 12, a liquid density D _x liquefied natural gas to be measured, which is calculated by the density calculating means 13, by Equation 3 below, the pressure is a predetermined reference pressure P _0, the reference temperature is predetermined Converted to the liquid density D ₀ in the reference state at the temperature T ₀ .

D ₀ = D _x −a ₂ × (T ₀ −T _x ) −b ₂ × (P ₀ −P _x ) (Equation 3)
However,
D ₀ : Liquid density in the standard state (g / ml)
T ₀ : Reference temperature (° C)
T _x : Temperature of the liquefied natural gas to be measured detected by the temperature sensor 7 (° C.)
P ₀ : Reference pressure (MPa)
P _x : Pressure of the liquefied natural gas to be measured detected by the pressure sensor 8 (MPa)
a ₂ , b ₂ : Constants obtained by experiments.
Incidentally, in this embodiment, when the reference pressure P ₀ = 4.0 MPa and the reference temperature T ₀ = −160 ° C.,
a ₂ = −1.47
b ₂ = −0.87
Set to

The above Equation 3 is an approximate equation set based on data acquired through experiments.
That is, by experiment, the dependence of the density of the liquefied natural gas on the temperature and the pressure is investigated using a plurality of types of liquefied natural gas having different densities, temperatures, and pressures, and the dependence is approximated. Equation 3 above.

[Step 2]:
Heat generation amount computing means 12, a liquid density D ₀ of the reference state determined by the equation 3 above, by Equation 4 below, the standard state (0 ° C., 0.1013 MPa) in terms of the gas specific gravity D _G at.

D _G = a ₃ × D ₀ ³ + b ₃ × D ₀ ² + c ₃ × D ₀ + d ₃ (equation 4)
However,
D _G : Gas specific gravity in a standard state (0 ° C., 0.1013 MPa) a ₃ , b ₃ , c ₃ , d ₃ : Constants obtained by experiment Incidentally, in this embodiment, the reference pressure P ₀ = 4.0 MPa And the reference temperature T ₀ = −160 ° C.
a ₃ = 0
b ₃ = 0.0018
c ₃ = 0.26
d ₃ = 110
Set to

Expression 4 above is an approximate expression set based on data obtained through experiments.
That is, by experiments, the liquid density D ₀ of the reference state by using a plurality of liquefied natural gas that is different for various, examine the relationship between the gas density D _G of the liquid density D ₀ and the standard state in the reference state The above equation 4 is an approximation of the relationship.

[Step 3]:
Heat generation amount computing means 12, the gas specific gravity D _G under standard conditions as determined by equation 4 above, by Equation 5 below, is converted into the gas calorific value Q ₀ of the normal state.

Q ₀ = a ₄ × D _G ³ + b ₄ × D _G ² + c ₄ × D _G + d ₄ (Equation 5)
However,
Q ₀ : Gas calorific value in the standard state (MJ / m ³ (normal))
a ₄ , b ₄ , c ₄ , d ₄ : constants obtained by experiments Incidentally, in this embodiment,
a ₄ = 0
b ₄ = 0
c ₄ = 0.064
d ₄ = 4.64
Set to

The above equation 5 is an approximate equation set based on data acquired through experiments.
That is, by experiments, the gas specific gravity D _G plural kinds of liquefied natural gas that is different for different (liquefied natural gas in the standard state, liquefied petroleum gas for adjusting the gas heating value of the liquefied natural gas is liquefied mixture The relationship between the gas specific gravity _DG and the gas calorific value in the standard state is investigated using a mixed gas), and the relationship is approximated by Equation 4 above.

[Step 4]:
The calorific value calculation means 12 is based on the following formula based on the gas calorific value Q ₀ obtained by the above formula 5 and the nitrogen content (mol%) in the liquefied natural gas to be measured detected by the gas chromatography 9. 6 calculates the calorific value Q of the liquefied natural gas to be measured from which the influence of the nitrogen content has been removed.

Q = Q ₀ −e × N (Equation 6)
However,
Q: Gas calorific value of the liquefied natural gas to be measured without the influence of nitrogen content (MJ / m ³ (normal))
N: Nitrogen content (mol%) detected by gas chromatography 9
e: Constant obtained by experiment By the way, in this embodiment,
e = 0.79

Then, the control unit 10 displays the liquid density D _x and the gas calorific value Q (gas calorific value excluding the influence of the nitrogen content) of the liquefied natural gas obtained as described above, and the display unit 16 configured by an LCD. Display output.

That is, in this embodiment, in obtaining the gas calorific value of the liquefied natural gas in the reference state, the reference state is set to the standard state, and the reference temperature and the reference pressure are the standard temperature (0 ° C.) and the standard pressure ( 0.1013 MPa).
Moreover, Equation 4 above, shows the relationship between the gas density D _G of the liquid density D ₀ and the standard state in the reference state, Equation 5, the gas specific gravity D _G and the reference state (this embodiment in the normal state Shows the relationship between the gas calorific value Q _{0 in} the standard state, and the liquid density D ₀ in the reference state of the liquefied natural gas and the reference state (in this embodiment, The relationship with the gas calorific value Q ₀ in the standard state is shown, and the equations 4 and 5 correspond to the reference density / calorific value relationship information.

That is, in this embodiment, the storage unit 11 of the controller 10, as the reference density to the heating value related information, the liquid density D ₀ and gas specific gravity D information indicating the relationship between _G (wherein in the standard state in the reference state and 4), the gas specific gravity D _G and the reference state (this embodiment in its normal state, information indicating the relationship between the gas heating value Q ₀ of the normal state) (equation 5) is stored.
The calorific value calculation means 12 of the control unit 10 then measures the liquid density of the liquefied natural gas to be measured measured by the density measuring device E based on the reference density / calorific value relationship information stored in the storage unit 11. the D _x, the pressure is a predetermined reference pressure P _0, the temperature is converted to liquid density D ₀ of the reference state is a predetermined reference temperature T _0, further, standard liquid density D ₀ in the reference state in terms of the gas specific gravity D _G in the state (in this embodiment, the standard state) reference state of the liquefied natural gas to be measured from the gas density D _G at the standard state to seek gas calorific value Q ₀ in It will be configured.

[Another embodiment]
Next, another embodiment will be described.
(A) In the above embodiment, the liquid density D _x of the liquefied natural gas to be measured, which is measured by the density measuring device E, has a predetermined reference pressure P _{0 as} a pressure and a predetermined reference temperature T ₀ as a temperature. in terms of the liquid density D ₀ of the reference state, further, the liquid density D ₀ in the reference state in terms of the gas specific gravity D _G under standard conditions, from the gas density D _G to be measured in its standard state The case where the calorific value Q ₀ of the liquefied natural gas in the standard state (in this embodiment, the standard state) is obtained is illustrated.
Alternatively, the liquefied natural gas to be measured is measured at a density measuring device E liquid density D _x, the pressure is a predetermined reference pressure P _0, the temperature is in the reference state is a predetermined reference temperature T ₀ in terms of the liquid density D _0, the liquid density D ₀ in the reference state, directly it may be configured to determine the gas calorific value Q ₀ of the reference state of the liquefied natural gas to be measured.
In this case, the liquid density D ₀ of the reference state by using a plurality of liquefied natural gas that is different for various, examine the relationship between the liquid density D ₀ and the gas heating value Q ₀ of the reference state in the reference state Then, an approximate expression of the relationship is obtained, and the heat generation amount Q ₀ in the reference state is obtained from the liquid density D ₀ in the reference state using the approximate expression.

(B) In the above embodiment, the relationship between the coefficient α and the temperature T _x of the liquefied natural gas to be measured is stored in the storage unit 11 of the control unit 10 using an approximate expression. You may memorize | store in the memory | storage part 11 of ten.

(C) In the above-described embodiment, the liquid density of the liquefied natural gas to be measured according to the present invention is automatically executed by the density calculating means 13, but may be configured to be manually operated. .

(D) In the above embodiment, the density calculation means 13 is provided in the control unit 10, and information for calculating the liquid density from the density calculation means 13 is stored in the storage unit 11 of the control unit 10. In addition to the control unit 10, a density measurement control unit may be provided for the density measuring device E. Then, the density measurement control unit controls the operation of the measurement unit 20, the density measurement control unit is provided with the density calculation unit 13, and the density calculation unit 13 stores the liquid density in the storage unit of the density measurement control unit. It is also possible to store the information for calculating the value and to make the storage unit of the density measurement control unit function as a density calculation information storage unit.

(E) In the above embodiment, the natural frequency is the natural frequency related information, but the natural frequency may be the natural frequency related information.

(F) In the above embodiment, the calorific value measurement system S is provided so as to measure the gas calorific value of the liquefied natural gas flowing downstream from the connection point of the LPG delivery path 6 in the LNG delivery path 3. The calorific value measurement system S may be provided so as to measure the gas calorific value of the liquefied natural gas flowing upstream from the connection location of the LPG delivery path 6 in the LNG delivery path 3.

(G) The specific configuration of the density measuring apparatus E is not limited to the configuration exemplified in the above embodiment. For example, in the above embodiment, a pair of flow tubes 21 are provided, but only one flow tube 21 may be provided. Moreover, the shape of the flow tube 21 is not limited to the U shape illustrated in said embodiment, For example, circular arc shape may be sufficient.

  As described above, it is possible to provide a liquefied natural gas calorie measurement method and a liquefied natural gas calorie measurement system capable of improving the measurement accuracy of the gas calorific value of liquefied natural gas.

3 LNG delivery channel (liquefied natural gas channel)
6 LPG delivery path (liquefied gas flow path for calorific value adjustment)
7 Temperature sensor (temperature measurement means)
8 Pressure sensor (pressure measuring means)
11 Storage section (heat generation amount calculation information storage means, density calculation information storage means)
12 Calorific value calculation means 13 Density calculation means 21 Flow tube 23 Detector (frequency related information detection means)
E Density measuring device (Density measuring means)
M Mixing ratio adjusting means S Calorie measurement system of liquefied natural gas

Claims (4)

The relationship between the liquid density and the calorific value of the liquefied natural gas in the reference state where the temperature and the pressure are the reference temperature and the reference pressure, respectively, is obtained in advance as reference density / calorific value relationship information, and the temperature of the liquefied natural gas to be measured In addition to measuring the pressure, the liquid density of the liquefied natural gas to be measured is measured by a density measuring means using Coriolis force, and based on the measured liquid density, temperature, pressure, and the reference density / calorific value relationship information A calorific value measurement method for liquefied natural gas to obtain a gas calorific value of the liquefied natural gas to be measured,
In the measurement of the liquid density of the liquefied natural gas to be measured temperature by the density measuring unit may change, the liquid density D _w is the density measuring unit a first reference fluid having a predetermined reference temperature T _w known A natural frequency related information F _w that is information related to the natural frequency of the flow tube when the flow tube is filled, a liquid density Da, and _a second reference fluid having _a predetermined reference temperature Ta is used as the flow tube. is information related to the natural frequency of the flow tube when filled in advance measures the natural frequency related information F _a, as well as measuring the temperature T _x of the liquefied natural gas to be measured, the measurement target The natural frequency related information F _x , which is information related to the natural frequency of the flow tube through which the liquefied natural gas flows, is measured, and the liquid density D _w , the reference temperature T _w and the natural frequency of the first reference fluid are measured. Relation Information F _w , liquid density D _a of the second reference fluid, reference temperature T _a and natural frequency related information F _a , temperature T _x and natural frequency related information F _x of the liquefied natural gas to be measured, and coefficient Based on α, the coefficient α is a numerical value obtained by the following coefficient α derivation formula based on the temperature T _x of the liquefied natural gas to be measured, and the liquid density of the liquefied natural gas to be measured is calculated by the following liquid density derivation function. calorimetric method liquefied natural gas to obtain the D _x.
D _x = f [D _w , D _a , F _x ² × (1−α × T _x ), F _a ² × (1−α × T _a ), F _w ² × (1−α × T _w )]
α = a ₁ × T _x ³ + b ₁ × T _x ² + c ₁ × T _x + d ₁
Where a ₁ , b ₁ , c ₁ , d ₁ : constants Temperature measuring means for measuring the temperature of the liquefied natural gas to be measured;
Pressure measuring means for measuring the pressure of the liquefied natural gas to be measured;
Density measuring means for measuring the liquid density of the liquefied natural gas to be measured using Coriolis force;
A calorific value calculation information storage means for storing the relationship between the liquid density and the gas calorific value in the liquefied natural gas in the reference state in which the temperature and the pressure are the reference temperature and the reference pressure, respectively, as reference density / calorific value relationship information;
Based on the measurement information of each of the temperature measurement means, the pressure measurement means, and the density measurement means, and the reference density vs. calorific value relationship information stored in the calorific value calculation information storage means, the liquefied natural to be measured is measured. A calorific value measurement system for liquefied natural gas provided with a calorific value calculation means for obtaining a gas calorific value of gas,
The density measuring means includes a flow tube for flowing the liquefied natural gas to be measured, a frequency related information detecting means for detecting natural frequency related information that is information related to the natural frequency of the flow tube, and the vibration thereof. A density calculation means for calculating the liquid density of the natural gas to be measured based on the detection information of the number related information detection means, and a density calculation information storage means for storing information for calculating the liquid density by the density calculation means. Provided,
The density calculation information storage means, the natural frequency of the detected by frequency-related information detecting means when the liquid density D _w satisfies the first reference fluid having a predetermined reference temperature T _w known to the flow tube Related information F _w, liquid density D _a is the frequency-related information detecting means natural frequency related information detected by the F when the second reference fluid having a predetermined reference temperature T _a known filled in said flow tube _a , a liquid density D _w and a reference temperature T _w of the first reference fluid, a liquid density D _a and a reference temperature T _{a of} the second reference fluid, and a coefficient α are stored,
The density calculation means is stored in the density calculation information storage means, the measurement information in the temperature measurement means, and the frequency related information detection means when the liquefied natural gas to be measured flows through the flow tube. Based on the detection information, the liquid density D _w of the first reference fluid, the reference temperature T _w and the natural frequency related information F _w , the liquid density D _a of the second reference fluid, the reference temperature _Ta and the natural frequency related From the information F _a , the temperature T _x of the liquefied natural gas to be measured, the natural frequency related information F _x , and the coefficient α, the liquid density D _x of the liquefied natural gas to be measured is calculated by the following liquid density derivation function. Configured to ask for
Further, the density calculating means is configured to determine the coefficient α based on a coefficient α derivation formula based on the temperature T _x of the liquefied natural gas to be measured, which is stored in the density calculation information storing means. Calorie measurement system for liquefied natural gas.
D _x = f ^{_{[D w, D a, Fx 2}} × (1-α × T x), Fa 2 × (1-α × T a), Fw 2 × (1-α × T w) ]
α = a ₁ × T _x ³ + b ₁ × T _x ² + c ₁ × T _x + d ₁
Where a ₁ , b ₁ , c ₁ , d ₁ : constants A calorific value adjustment liquefied gas flow path for sending a calorific value adjustment liquefied gas for adjusting the gas calorific value of the liquefied natural gas is connected to the liquefied natural gas flow path for sending the liquefied natural gas,
Adjusting the mixing ratio of the calorific value adjustment liquefied gas to the liquefied natural gas flowing in the liquefied natural gas flow path, and provided with a mixing ratio adjusting means for adjusting the gas calorific value of the liquefied natural gas;
3. The liquefied natural gas according to claim 2 , wherein the liquefied natural gas after gas calorific value adjustment in which the mixing ratio of the calorific value adjusting liquefied gas is adjusted by the mixing ratio adjusting means is the liquefied natural gas to be measured. Calorimetry system. The calorific value adjustment liquefied gas is liquefied petroleum gas,
The temperature T _x of the liquefied natural gas after adjusting the gas heating value fluctuates in the range of −160 to −120 ° C.,
In the fluctuation range of the temperature T _x of the liquefied natural gas, the constants a ₁ and b ₁ are set to 0, and the coefficient α derivation formula is as follows using the temperature T _x of the liquefied natural gas to be measured as a variable: The calorimetric system for liquefied natural gas according to claim 2 or 3 , which is set to a primary expression.
α = c ₁ × T _x + d ₁
Where c ₁ and d _{1 are} constants

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