Method and system for metering calorific value of LNG gasified natural gas in real time

Abstract

The invention relates to the field of LNG (Liquefied Natural Gas) gaseous output metering and operation, and discloses a method and a system for metering the calorific value of LNG gasified natural gas in real time, and the method comprises the following steps: establishing a corresponding mathematical fitting relational expression based on a pre-established rho-T preset relation table of a built-in database; according to the actually-measured density of the LNG mass flow meter and the actually-measured values of the thermometer and the pressure meter at the nearest position, the temperature in the built-in database is inquired so as to find the density value closest to the current actually-measured density at the corresponding actually-measured temperature, and then typical LNG corresponding to the density value in the built-in database is determined; calculating the density value of the natural gas after the current typical LNG is gasified at the temperature of 20 DEG C; calculating an LNG density value at 20 DEG C and under one atmospheric pressure according to the actually measured pressure and the actually measured density through a density-pressure relational expression; and calculating the high calorific value HHV20 DEG C under the reference / combustion temperature condition of 20 / 20 DEG C and the pressure of 101.325 kpa based on the density value, and further calculating to obtain the WI20 DEG C at the temperature of 20 DEG C, thereby completing the real-time metering of the calorific value of the LNG gasified natural gas.

Description

Technical Field

[0001] The present invention relates to the technical field of LNG gaseous outflow measurement and operation, and in particular to a method and system for real-time measurement of LNG gasified natural gas calorific value. Background Art

[0002] At LNG receiving stations, LNG liquefaction plants, and LNG storage stations, the only practical engineering technology for measuring the calorific value of natural gas after LNG gasification is a technical method based on traditional gas chromatography analysis and calculation. However, due to the high price of gas chromatography equipment of nearly one million RMB and the low efficiency of the chromatography analysis, which takes 4 to 5 minutes to complete at the fastest, it cannot be applied to the actual situation where the quality of LNG changes rapidly in the LNG export gasification process and the quality of natural gas gasified by exported LNG changes continuously. It is impossible to achieve real-time measurement in seconds and accurate measurement. Summary of the invention

[0003] In view of the above problems, the purpose of the present invention is to provide a method and system for real-time metering of the calorific value of natural gas after LNG gasification, which can realize real-time online metering of the calorific value of natural gas after LNG gasification in seconds at LNG receiving stations, LNG liquefaction plants, and LNG storage stations, and simultaneous online metering of the calorific value of natural gas after LNG gasification in multiple pipelines, so as to meet the calorific value balance, trade handover, and process control within the station and plant.

[0004] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for real-time measurement of calorific value of LNG gasified natural gas, comprising: establishing a corresponding mathematical fitting relationship based on a ρ-T preset relationship table of a pre-established built-in database; querying the temperature in the built-in database according to the measured density of the LNG mass flowmeter and the measured values ​​of the nearest thermometer and pressure gauge to find the density value closest to the current measured density at the corresponding measured temperature, and then determining the typical LNG corresponding to the density value in the built-in database to calculate the density value of the current typical LNG gasified natural gas at a temperature of 20°C; calculating the LNG density value at 20°C and one atmosphere according to the measured pressure and the measured density through the density-pressure relationship; calculating the high heating value HHV under the reference / combustion temperature conditions of 20 / 20°C and a pressure of 101.325kpa based on the density value. 20℃ , and then calculate the Wobbe number WI at 20℃ 20℃ , complete the real-time measurement of the calorific value of LNG gasified natural gas.

[0005] Furthermore, based on the ρ-T preset relationship table of the pre-established built-in database, the corresponding mathematical fitting relationship is established as follows:

[0006] ρ real =b1+b2×(T real+160)+b3×(T real +160) 2

[0007] In the formula, ρ real Indicates the measured density value, T real represents the measured temperature value, b1~b3 are the first calculation coefficients.

[0008] Furthermore, the temperature in the built-in database is queried to find the density value closest to the current measured density at the corresponding measured temperature, which is: real ∣} formula calculation, find the density value closest to the current measured density at the corresponding measured temperature; where ρ is the density closest to the current measured density ρ real The closest density value, ρ real ∣ is the measured density value.

[0009] Furthermore, the density of LNG at 20°C and 1 atmosphere is calculated based on the density-pressure relationship and the measured pressure and density:

[0010] ρ 20 / 101.325kpa =ρ 20 ×[1+β×(P real -101.325) / 10]

[0011] In the formula, ρ 20 / 101.325kpa is the density of LNG at 20°C and 1 atmosphere; β = 0.19235 / 100; ρ 20 is the density value of the current typical LNG at a temperature of 20°C; P real The actual measured pressure.

[0012] Furthermore, the HHV at reference / combustion temperature conditions of 20 / 20°C and pressure of 101.325 kPa is calculated based on the density value. 20℃ ,include:

[0013] Based on the density of LNG at 20℃ and 1 atmosphere and the HHV at reference / combustion temperature conditions of 20 / 20℃ and pressure of 101.325kpa 20℃ According to the relationship between the molar content of nitrogen, Mol N2 Divide into three groups of intervals;

[0014] By estimating and manually setting the molar content of nitrogen Mol N2 value, select one of the interval formulas to calculate the high heating value HHV 20℃ .

[0015] Further, according to the molar content of nitrogen Mol N2Divide into three groups of intervals: 0≤N2<0.3%; 0.3%≤N2<0.6%; N2≥0.6%.

[0016] Furthermore, the interval formula for 0≤N2<0.3% is:

[0017]

[0018] The formula for the interval 0.3%≤N2<0.6% is:

[0019]

[0020] The formula for the interval N2≥0.6% is:

[0021]

[0022] Further, the Wobbe number WI at 20°C was calculated. 20℃ for:

[0023] WI 20℃ =HHV 20℃ / (ρ 20℃ / 1.205) 0.5

[0024] Among them, HHV 20℃ It is the high calorific value under reference / combustion temperature conditions of 20 / 20℃ and pressure of 101.325kpa.

[0025] A system for real-time measurement of calorific value of LNG gasified natural gas, comprising: a mass flow meter of natural gas after LNG gasification and a data acquisition controller thereof, a thermometer and a pressure gauge and a data acquisition controller thereof, a communication cable, a station control system and a TCP / IP centralized control interface and an external data transmission interface, a calorific value calculation and analysis computer, a built-in database and a calculation program module based on the method for real-time measurement of calorific value of LNG gasified natural gas as claimed in any one of claims 1 to 8, and a calorific value measurement display module of the station control system; ... The controller connects the collected real-time data to the station control system and its TCP / IP centralized control interface and external data transmission interface via a communication cable, and is connected to third-party equipment via the station control system and its TCP / IP centralized control interface and external data transmission interface; the calorific value calculation and analysis computer is used to receive real-time data transmitted via the station control system and its TCP / IP centralized control interface and external data transmission interface, and run the built-in database and calculation program module to realize real-time analysis and calculation of calorific value data, and save the calculation results on site; or, the calculation results are further distributed to the calorific value metering and display module of the station control system through the external communication interface for real-time display.

[0026] Furthermore, the natural gas mass flow meter after LNG gasification and its data acquisition controller are: a Coriolis mass flow meter, and a data acquisition controller including data acquisition and remote transmission functions of the mass flow meter itself;

[0027] Thermometers and pressure gauges are the temperature gauges and pressure gauges located at the closest distance to the mass flow meter, and both should have the function of remote data transmission.

[0028] The present invention adopts the above technical solution, which has the following advantages:

[0029] 1. Based on the thermophysical properties of LNG itself and 2000 sets of LNG thermophysical property databases, the present invention realizes the high-precision mathematical correlation between the calorific value of natural gas after LNG gasification and the measured temperature, pressure, density and nitrogen content, avoiding the dependence of the traditional cumbersome method on the component analysis of the natural gas after LNG gasification.

[0030] 2. The present invention can directly perform online real-time calorific value measurement and analysis after online real-time measurement of temperature, pressure, density and estimated nitrogen content, and can be applied to all process units of LNG plants. The measurement results can be directly transmitted to the station control system (DCS system) for unified application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of a method for real-time measurement of calorific value of LNG gasified natural gas in an embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of the system structure for real-time measurement of calorific value of LNG gasified natural gas in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The existing calorific value measurement method for LNG receiving stations, LNG liquefaction plants, and LNG storage stations is mainly one: that is, a sampling port is reserved in the pipeline after LNG gasification, and a gas chromatograph is installed at the sampling port. The gas chromatograph is used to analyze and calculate the LNG calorific value data of the sampled sample at intervals of 4 to 5 minutes. However, this method has two main problems: first, a single gas chromatograph analysis device costs nearly one million yuan, which is expensive to invest in and difficult to deploy in large numbers. Usually, there is only one gas chromatograph installed on the gasification external transmission main pipeline for an LNG receiving station, LNG liquefaction plant, and LNG storage station, and an indirect method of calorific value transfer is used for the adjacent separate gasification external transmission pipeline; second, the gas chromatograph has a long time period of 4 to 5 minutes, and it is impossible to achieve second-level measurement. It cannot be applied to the actual situation where the LNG quality changes rapidly in the process, and the LNG gasification external transmission is mixed and the quality changes continuously.

[0034] Therefore, the present invention provides a method and system for real-time metering of the calorific value of natural gas after LNG gasification, based on the thermal physical properties of natural gas after direct LNG gasification, according to the basic relationship between the temperature, density and calorific value of natural gas after LNG gasification, a mathematical correlation formula of the calorific value of natural gas after LNG gasification is established, a mass flow meter of natural gas after LNG gasification is installed to measure the dynamic density value of the pipeline in real time, a thermometer and a pressure gauge with remote transmission function are installed near the mass flow meter, a data communication channel is established by connecting the data receiving port of the station control room through the data transmission port of the mass flow, and a host computer calculation program and an explosion-proof industrial computer are installed to realize real-time monitoring, metering and analysis of the calorific value of natural gas after LNG gasification at the monitoring point.

[0035] In order to make the purpose, technical solution and advantages of the embodiment of the present invention more clear, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiment of the present invention. It is Benfa Based on the described embodiments of the present invention, the present invention is described in detail. All other embodiments obtained by ordinary technicians in the field are within the scope of protection of the present invention.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] In one embodiment of the present invention, a method for real-time measurement of calorific value of LNG gasified natural gas is provided, which involves the measurement of calorific value of LNG gasified natural gas products at LNG receiving stations, LNG liquefaction plants, and LNG storage stations, and has the advantages of universality, low cost, and rapid installation and deployment in large quantities. In this embodiment, Figure 1 As shown, the method comprises the following steps:

[0038] 1) Based on the ρ-T preset relationship table of the pre-established built-in database, a corresponding mathematical fitting relationship is established;

[0039] 2) According to the measured density ρ of the LNG mass flow meter real , and the measured values ​​T of the nearest thermometer and pressure gauge real and P real , query the temperature T in the built-in database to find the corresponding measured temperature T real Next, and the current measured density ρ realThe closest density value ρ is then determined to determine the typical LNG corresponding to the density value ρ in the built-in database, so as to calculate the density value ρ of the natural gas after gasification of the current typical LNG at a temperature of 20°C. 20 ;

[0040] 3) According to the density ρ-pressure P relationship, according to the measured pressure P real and the measured density ρ real Calculate the density of LNG at 20°C and 1 atmosphere pressure 20 / 101.325kpa ;

[0041] 4) Based on the density value ρ 20 / 101.325kpa Calculate the HHV at reference / combustion temperature 20 / 20°C and pressure 101.325 kPa 20℃ , and then calculate the Wobbe number WI at 20℃ 20℃ , complete the real-time measurement of the calorific value of LNG gasified natural gas.

[0042] In the above step 1), based on the pre-established ρ-T preset relationship table of the built-in database, the corresponding mathematical fitting relationship is established as follows:

[0043] ρ real =b1+b2×(T real +160)+b3×(T real +160) 2

[0044] In the formula, ρ real Indicates the measured density value, T reAl represents the measured temperature value, b1~b3 are the first calculation coefficients.

[0045] In the above step 2), the temperature in the built-in database is queried to find the density value closest to the current measured density at the corresponding measured temperature, which is: real ∣} formula calculation, find the density value closest to the current measured density at the corresponding measured temperature; where ρ is the density closest to the current measured density ρ real The closest density value, ρ real ∣ is the measured density value.

[0046] In the above step 3), the density of LNG at 20°C and 1 atmosphere is calculated according to the density-pressure relationship and the measured pressure and density:

[0047] ρ 20 / 101.325kpa =ρ 20 ×[1+β×(P real -101.325) / 10]

[0048] In the formula, ρ 20 / 101.325kpais the density of LNG at 20°C and 1 atmosphere; β = 0.19235 / 100; ρ 20 is the density value of the current typical LNG at a temperature of 20°C; P real The actual measured pressure.

[0049] In step 4), the reference / combustion temperature conditions of 20 / 20°C and pressure of 101.325 kPa are calculated based on the density value. High Heating Value HHV 20℃ , including the following steps:

[0050] 4.1) Based on the density of LNG at 20°C and 1 atmosphere and the HHV at the reference / combustion temperature conditions of 20 / 20°C and 101.325 kPa 20℃ According to the relationship between the molar content of nitrogen, Mol N2 Divide into three groups of intervals;

[0051] In this embodiment, according to the molar content of nitrogen, Mol N2 Divide into three groups of intervals: 0≤N2<0.3%; 0.3%≤N2<0.6%; N2≥0.6%.

[0052] The interval formula of 0≤N2<0.3% is:

[0053]

[0054] The formula for the interval 0.3%≤N2<0.6% is:

[0055]

[0056] The formula for the interval N2≥0.6% is:

[0057]

[0058] The second coefficients a1-a4 in each interval formula have different values.

[0059] 4.2) Estimated and manually set the nitrogen molar content Mol N2 value, select one of the interval formulas to calculate the high heating value HHV 20℃ .

[0060] In step 4), the Wobbe number WI at 20°C is calculated. 20℃ for:

[0061] WI 20℃ =HHV 20℃ / (ρ 20℃ / 1.205) 0.5

[0062] Among them, HHV 20℃It is the high calorific value under reference / combustion temperature conditions of 20 / 20℃ and pressure of 101.325kpa.

[0063] In one embodiment of the present invention, a system for real-time measurement of calorific value of LNG gasified natural gas is provided, which involves a series of analysis processes, hardware equipment, and control system communications. First, it includes establishing a system consisting of a mass flow meter for natural gas after LNG gasification and its data acquisition controller, a thermometer and a pressure gauge, a communication cable connected to a station control system, a station control system data output interface, a communication cable from the station control system data output interface to a calorific value calculation and analysis computer, a calorific value calculation and analysis computer, a built-in database, and a calculation program module. In this embodiment, Figure 2 As shown, the system includes:

[0064] LNG gasified natural gas mass flow meter and data acquisition controller thereof, thermometer and pressure gauge and data acquisition controller thereof, communication cable, station control system and TCP / IP centralized control interface and external data transmission interface, calorific value calculation and analysis computer, built-in database and calculation program module based on the method for real-time measurement of calorific value of LNG gasified natural gas in the above-mentioned embodiments, calorific value measurement and display module of station control system;

[0065] After LNG gasification, the natural gas mass flow meter and its data acquisition controller, the thermometer and the pressure gauge and their data acquisition controller connect the collected real-time data to the station control system and its TCP / IP centralized control interface and external data transmission interface via communication cables, and are connected to third-party equipment via the station control system and its TCP / IP centralized control interface and external data transmission interface;

[0066] The calorific value calculation and analysis computer is used to receive real-time data transmitted via the station control system and its TCP / IP centralized control interface and external data output interface, and run the built-in database and calculation program module to realize real-time analysis and calculation of calorific value data. and Save the calculation results locally; or distribute the calculation results to the station control system through an external communication interface. Value measurement display module for real-time display.

[0067] In the above embodiment, the natural gas mass flow meter after LNG gasification and its data acquisition controller are: Coriolis mass flow meter (such as Emerson, 2 inches or 3 inches), and include a data acquisition controller with data acquisition and remote transmission functions of the mass flow meter itself. The interface forms include Modbus RS485, TCP / IP, 4-20mA DC HART, pulse signal and Ethernet port.

[0068] Thermometers and pressure gauges are the temperature gauges and pressure gauges located at the closest distance to the mass flow meter, and both should have the function of remote data transmission.

[0069] In the above embodiment, the communication cable connected to the station control system is a mass flow meter, as well as a thermometer and a pressure gauge, which are directly connected to the centralized control communication module of the plant control system (DCS system) through a cable via a data acquisition controller and a Modbus RS485 and TCP / IP interface.

[0070] In the above embodiment, the station control system data output interface is the external data transmission interface of the centralized control communication module of the plant control system (DCS system). The interface can be connected using a third-party device to read the data of the centralized control communication module of the plant control system (DCS system) from the outside.

[0071] In the above embodiment, the communication cable from the data output interface of the station control system to the calorific value calculation and analysis computer is a communication transmission cable connecting the data output interface of the station control system and the interface of the third-party device.

[0072] In the above embodiment, the calorific value calculation and analysis computer realizes real-time analysis and calculation of calorific value data by reading real-time data of the centralized control communication module of the station control system (DCS system), running the built-in database and the calculation program based on a specific method, and saves the calculation results locally, or further distributes the calculation results to the calorific value metering display module of the control system (DCS system) through an external communication interface.

[0073] In the above embodiment, the built-in database is 2000 groups of typical LNG formed by 2000 ships of LNG measured by a third-party organization, which is a group of typical LNG consisting of six parameters: specific components, pressure, temperature, density, calorific value, and Wobbe number. Each group of LNG is calculated for physical properties by Aspen commercial software, and a corresponding relationship table between temperature T and natural gas density ρ after LNG gasification in the range of [-50°C, 60°C] with an interval of 1°C is established. The six parameter tables of components, pressure, temperature, density, calorific value, and Wobbe number of 2000 groups of typical LNG in saturated state and the ρ-T corresponding relationship table of each group of typical LNG in the range of [-50°C, 60°C] together constitute the built-in database.

[0074] In summary, for the current calorific value measurement of natural gas after LNG gasification at LNG receiving stations, LNG liquefaction plants, and LNG storage stations, the only practical engineering technology is a technical method of gas chromatography analysis and calculation. The advantage is that the specific quantity of each component is determined one by one through chromatographic analysis, and then the calorific value is calculated through a formula. The disadvantage is that in the LNG field, the simplified characteristics of the thermal properties of natural gas after LNG gasification are ignored, and the complex analysis and calculation process of general gases is still applied, which is not only expensive, but also increases the uncertainty of the results due to the large time lag of the analysis process (4 to 5 minutes), resulting in low cost-effectiveness and large measurement deviation. The present invention makes full use of the 2,000 LNG physical property parameters measured by a third party accumulated over many years to establish a database and a calculation method based on a specific method. Calculation program, through mass flow meter and its data acquisition controller, temperature Gauges and pressure gauges, connected to the station control system The data acquisition and analysis system is established by communication cables, station control system data output interface, communication cables from the station control system data output interface to the calorific value calculation and analysis computer, the calorific value calculation and analysis computer, the built-in database and the calculation program module.

[0075] The system provided in this embodiment is used to execute the above-mentioned method embodiments. Please refer to the above-mentioned embodiments for specific processes and detailed contents, which will not be repeated here.

[0076] Embodiment, the present invention is further described by the following specific embodiment. The implementation steps in this embodiment are as follows:

[0077] Step 1: Given the gasification and export area of ​​a certain LNG receiving station, a 3-inch Coriolis mass flowmeter is installed in the bypass pipeline, a pressure gauge and a temperature gauge with remote transmission function are installed nearby, and a calorific value calculation and analysis computer is arranged in the plant control room (DCS). The TCP / IP interfaces of the mass flowmeter, pressure gauge and temperature gauge are connected to the TCP / IP centralized control interface of the plant control room (DCS) through a communication cable, and the TCP / IP interface of the calorific value calculation and analysis computer is connected to the TCP / IP centralized control interface of the plant control room (DCS) through a communication cable.

[0078] The second step is to establish a built-in database for the LNG gasification natural gas calorific value calculation and analysis computer and a calculation program based on a specific method. The specific steps include:

[0079] (1) Establishing a mathematical fitting relationship for the ρ-T correspondence table in the built-in database;

[0080] ρ real =b1+b2×(T real +160)+b3×(T real +160) 2

[0081] In this embodiment, b1 = 7.566158E-01; b2 = -0.934821E-00; b3 = -1.423408E-03. For example, E-03 represents e -3 .

[0082] (2) According to the measured density ρ of the mass flow meter real , is 0.7758kg / m 3 , and the T of the nearest thermometer and pressure gauge real At 16°C and P real is 443.5 kPa. Query the temperature T in the built-in database and use Min{|ρ-ρ real ∣}Calculate the formula and find the corresponding measured T real Next, and the current measured density ρ real (0.7758kg / m 3 ) is closest to the density ρ value, which is 0.7786kg / m 3 , and then determine the typical LNG gasified natural gas corresponding to the density ρ parameter in the built-in database. Then, apply the mathematical fitting relationship to calculate the density value ρ of the current typical LNG gasified natural gas at a temperature of 20°C 20 , is 0.7332kg / m 3 .

[0083] (3) Apply the density ρ-pressure P relationship. According to the measured pressure P real , density ρ real Calculate the density of LNG at 20°C and 1 atmosphere pressure 20 / 101.325kpa . The result is 0.6877kg / m 3 .

[0084] (4) High calorific value (HHV) under reference / combustion temperature conditions of 20 / 20°C and pressure of 101.325 kPa 20℃ The density of natural gas after LNG gasification is ρ 20 / 101.325kpa According to the nitrogen molar content Mol N2 Divide into three groups: 0≤N2<0.3%, 0.3%≤N2<0.6%, N2≥0.6%. In this embodiment, N2 is 0.2%, select the first group 0≤N2<0.3% interval formula to calculate, and get HHV 20℃ The value is 38.96MJ / Sm 3 .

[0085] In this embodiment, a1=6.177861E+02; a2=-8.625425E-01; a3=3.3711066E-03; a4=0.

[0086] (5) Calculate the Wobbe number WI at 20°C20℃ It is 48.325.

[0087] The third step is to run the data acquisition and analysis system established in the above steps to collect data in real time, analyze and calculate the LNG calorific value data in real time, and save the calculation results on the spot, or further distribute the calculation results to the calorific value metering display module of the control system (DCS system) through the external communication interface.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for real-time measurement of calorific value of LNG gasified natural gas, characterized in that: include: Based on the ρ-T preset relationship table of the pre-established built-in database, a corresponding mathematical fitting relationship is established; According to the measured density of the LNG mass flow meter and the measured values ​​of the nearest thermometer and pressure gauge, the temperature in the built-in database is queried to find the density value closest to the current measured density at the corresponding measured temperature, and then the typical LNG corresponding to the density value in the built-in database is determined to calculate the density value of the gasified natural gas of the current typical LNG at a temperature of 20°C; Calculate the LNG density at 20°C and 1 atmosphere pressure based on the measured pressure and density through the density-pressure relationship. Calculate the HHV based on the density value at reference / combustion temperature conditions of 20 / 20°C and pressure of 101.325 kPa 20℃ , and then calculate the Wobbe number WI at 20℃ 20℃ , complete the real-time measurement of the calorific value of LNG gasified natural gas.

2. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 1, characterized in that: Based on the ρ-T preset relationship table of the pre-established built-in database, the corresponding mathematical fitting relationship is established as follows: ρ real =b1+b2×(T real +160)+b3×(T real +160) 2 In the formula, ρ real Indicates the measured density value, T real represents the measured temperature value, b1~b3 are the first calculation coefficients.

3. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 1, characterized in that: Query the temperature in the built-in database to find the density value closest to the current measured density at the corresponding measured temperature: real |} formula calculation, find the density value closest to the current measured density at the corresponding measured temperature; where ρ is the value closest to the current measured density ρ real The closest density value, ρ real | is the measured density value.

4. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 1, characterized in that: The density of LNG at 20°C and 1 atmosphere is calculated based on the density-pressure relationship and the measured pressure and density: r 20 / 101.325kpa =ρ 20 ×[1+β×(P real -101.325) / 10] In the formula, ρ 20 / 101.325kpa is the density of LNG at 20°C and 1 atmosphere; β = 0.19235 / 100; ρ 20 is the density value of the current typical LNG at a temperature of 20°C; P real The actual measured pressure.

5. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 1, characterized in that: Calculate the HHV based on the density value at reference / combustion temperature conditions of 20 / 20°C and pressure of 101.325 kPa 20℃ ,include: Based on the density of LNG at 20℃ and 1 atmosphere and the HHV at reference / combustion temperature conditions of 20 / 20℃ and pressure of 101.325kpa 20℃ According to the relationship between the molar content of nitrogen, Mol N2 Divide into three groups of intervals; By estimating and manually setting the molar content of nitrogen Mol N2 value, select one of the interval formulas to calculate the high heating value HHV 20℃ .

6. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 5, characterized in that: According to the molar content of nitrogen, Mol N2 Divide into three groups of intervals: 0≤N2<0.3%; 0.3%≤N2<0.6%; N2≥0.6％。 7. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 6, characterized in that: The interval formula of 0≤N2<0.3% is: The formula for the interval 0.3%≤N2<0.6% is: The formula for the interval N2≥0.6% is:

8. The method for real-time measurement of calorific value of LNG gasified natural gas according to claim 1, characterized in that: Calculate the Wobbe number WI at 20°C 20℃ for: WI 20℃ =HHV 20℃ / (r 20℃ / 1.205) 0.5 Among them, HHV 20℃ It is the high calorific value under reference / combustion temperature conditions of 20 / 20℃ and pressure of 101.325kpa.

9. A system for real-time measurement of calorific value of LNG gasified natural gas, characterized in that: include: LNG gasified natural gas mass flow meter and data acquisition controller thereof, thermometer and pressure gauge and data acquisition controller thereof, communication cable, station control system and TCP / IP centralized control interface and external data transmission interface, calorific value calculation and analysis computer, built-in database and calculation program module based on the method for real-time measurement of calorific value of LNG gasified natural gas as claimed in any one of claims 1 to 8, calorific value measurement and display module of the station control system; After LNG gasification, the natural gas mass flow meter and its data acquisition controller, the thermometer and the pressure gauge and their data acquisition controller connect the collected real-time data to the station control system and its TCP / IP centralized control interface and external data transmission interface via communication cables, and are connected to third-party equipment via the station control system and its TCP / IP centralized control interface and external data transmission interface; The calorific value calculation and analysis computer is used to receive real-time data transmitted via the station control system and its TCP / IP centralized control interface and external data output interface, and to run the built-in database and calculation program module to realize real-time analysis and calculation of calorific value data, and save the calculation results on site; or, the calculation results are further distributed to the calorific value metering and display module of the station control system through the external communication interface for real-time display.

10. The system for real-time measurement of calorific value of LNG gasified natural gas as claimed in claim 9, characterized in that: The natural gas mass flow meter after LNG gasification and its data acquisition controller are: Coriolis mass flow meter, and a data acquisition controller including the data acquisition and remote transmission functions of the mass flow meter itself; Thermometers and pressure gauges are the temperature gauges and pressure gauges located at the closest distance to the mass flow meter, and both should have the function of remote data transmission.

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