Method and system for real-time metering of liquid calorific value of LNG (Liquefied Natural Gas)

Abstract

The invention relates to the field of LNG metering and operation, and discloses a method and system for real-time metering of an LNG liquid calorific value, and the method comprises the steps: building a corresponding mathematical fitting relational expression based on a pre-built rho-T preset relation table of a built-in database; according to the actually-measured density and actually-measured values of a thermometer and a pressure meter at the nearest position, the temperature in the built-in database is inquired to find a density value closest to the current actually-measured density at the corresponding actually-measured temperature, and a typical LNG density value corresponding to the density value in the built-in database is determined; according to the actually measured pressure and the actually measured density, the LNG density value at the temperature of-160 DEG C and under the atmospheric pressure is calculated; calculating a high calorific value under a reference / combustion temperature condition of 60 / 60 DEG F and a pressure of 14.696 psia and a high calorific value under a reference / combustion temperature condition of 15 DEG C / 15 DEG C and an atmospheric pressure based on the density value to obtain a high calorific value HHV20 DEG C under a reference / combustion temperature condition of 20 DEG C / 20 DEG C and an atmospheric pressure; and according to the density value and the high calorific value HHV20 DEG C, the gaseous density and the WI20 DEG C at 20 DEG C are calculated, and LNG liquid calorific value real-time metering is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of LNG metering and operation, and in particular to a method and system for real-time metering of LNG liquid 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 LNG liquid is a technical method based on LNG liquid sampling and gasification and chromatographic analysis. However, due to the inherent defects of a single LNG liquid sampling and chromatographic analysis equipment costing tens of millions of RMB and the sampling process being prone to gasification, which leads to inaccurate sampling, the cost-effectiveness ratio is high, and the sampling position is layered, resulting in large measurement deviations. Under the design and operation conditions of widespread LNG quality-based storage and quality-based external transmission, the existing technical methods still have the inefficiency problem of taking 4 to 5 minutes to complete the chromatographic analysis at the fastest speed, which is limited by the high calorific value metering equipment and the lack of reservation for the design sampling port. It is not applicable to the reality that the quality of LNG changes rapidly in the process, the external LNG is mixed and the quality is constantly changing, and it is impossible to achieve real-time measurement in seconds.

[0003] Another technology that is being studied and initially applied in engineering is the Raman chromatography laser direct measurement of the calorific value of LNG. This technology eliminates the sampling device required by the existing sampling method, but it also has the problems of high cost, the need to reserve installation ports, and the need to further improve the accuracy of data analysis. It is difficult to install it in LNG receiving stations, LNG liquefaction plants, and LNG storage stations. It also has the problem of low efficiency, with the fastest chromatographic analysis taking 4 to 5 minutes to complete, and cannot achieve real-time measurement in seconds. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method and system for real-time metering of LNG liquid calorific value, which can realize real-time online metering of LNG liquid calorific value in seconds and simultaneous online metering of multi-pipeline LNG liquid calorific value at LNG receiving stations, LNG liquefaction plants, and LNG storage stations, so as to meet the calorific value balance, trade handover and process control within the station and plant.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for real-time measurement of LNG liquid calorific value, which includes: establishing a corresponding mathematical fitting relationship based on a pre-established ρ-T preset relationship table of a built-in database; querying the temperature in the built-in database according to the measured density of the LNG mass flowmeter or the LNG density meter, and the measured values ​​of the nearest thermometer and pressure gauge, so as to find the density value closest to the current measured density at the corresponding measured temperature, and then determine the typical LNG corresponding to the density value in the built-in database, so as to calculate the density value of the current typical LNG at a temperature of -160°C; calculating the LNG density value at -160°C and one atmosphere according to the measured pressure and the measured density through the density-pressure relationship; calculating the high heating value GHV under the reference / combustion temperature conditions of 60 / 60℉ and a pressure of 14.696psia based on the density value. BTU / SCF,60F , and the high heating value HHV at reference / combustion temperature conditions of 15°C / 15°C and 1 atmosphere 15℃ , get the high heating value HHV under reference / combustion temperature conditions of 20℃ / 20℃ and 1 atmosphere pressure 20℃ ; According to the density value and high heating value HHV 20℃ Calculate the gas density ρ at 20°C 20℃ Hehuabaishu WI 20℃ , complete the real-time measurement of LNG liquid calorific value.

[0006] 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:

[0007] ρ real =b1+b2×(T real +160)+b3×(t real +160) 2

[0008] In the formula, ρ real Indicates the measured density value, T real represents the measured temperature value, b1~b3 are the first calculation coefficients.

[0009] Further, the density of LNG at -160°C and 1 atmosphere is calculated based on the measured pressure and density:

[0010] ρ -160 / 101.325kpa =ρ -160 ×[1+β×(P real -101.325) / 10]

[0011] In the formula, ρ -160 / 101.325kpa is the density of LNG at -160℃ and 1 atmosphere; β=0.19235 / 10000; ρ -160is the density value of the current typical LNG at a temperature of -160°C; P real The actual measured pressure.

[0012] Further, based on the density value, the GHV at the reference / combustion temperature condition of 60 / 60°F and pressure of 14.696 psia is calculated. BTU / SCF,60F ,include:

[0013] Based on high heating value GHV BTU / SCF,60F and LNG density value ρ -160 / 101.325kpa 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 the molar content of the first group of nitrogen Mol N2 The interval formula is used to calculate the high calorific value GHV BTU / SCF,60F :

[0015]

[0016] Among them, a1~a4 are the second calculation coefficients.

[0017] Furthermore, the HHV at reference / combustion temperature conditions of 15°C / 15°C and 1 atmosphere pressure is calculated. 15℃ ,include:

[0018] Set the first conversion factor γ G-HHV15 , the reference / combustion temperature condition 60 / 60℉, pressure 14.696psia high heating value GHV BTU / SCF,60F Converted to reference / combustion temperature conditions 15℃ / 15℃, high heating value HHV at 1 atmosphere pressure 15℃ :

[0019] HV 15℃ =GHV BTU / SCF,60F ×γ G-HHV15 .

[0020] Furthermore, the HHV at reference / combustion temperature conditions of 20°C / 20°C and 1 atmosphere pressure is calculated. 20℃ ,include:

[0021] Set the second conversion factor γ 15-20 , the reference / combustion temperature condition 15℃ / 15℃, high heating value HHV under 1 atmosphere pressure 15℃ Converted to reference / combustion temperature conditions 20℃ / 20℃, high heating value HHV at 1 atmosphere 20℃ :

[0022] HV 20℃ =HHV15℃ ×γ 15-20 .

[0023] Further, according to the density value and high heating value HHV 20℃ Calculate the gas density ρ at 20°C 20℃ Hehuabaishu WI 20℃ ,include:

[0024] Calculate the gas density ρ at 20℃ based on the density value 20℃ ;

[0025] Based on high heating value HHV 20℃ and the gas density ρ at 20°C 20℃ Calculate the Huabai number WI 20℃ .

[0026] Furthermore, Huabai Number WI 20℃ for:

[0027] WI 20℃ =HHV 20℃ / (ρ 20℃ / 1.205) 0.5

[0028]

[0029] Wherein, c1~c3 are the third calculation coefficients.

[0030] A system for real-time measurement of LNG liquid calorific value, comprising: an LNG mass flow meter or an LNG density meter and a data acquisition controller thereof, an LNG thermometer and an LNG pressure meter and a data acquisition controller thereof, a station control system and a TCP / IP centralized control interface and an external data transmission interface, an LNG calorific value analysis computer, a preset built-in database and a calculation program module based on the method for real-time measurement of LNG liquid calorific value as described in any one of claims 1 to 8, and a calorific value measurement display module of the station control system; an LNG mass flow meter or an LNG density meter and a data acquisition controller thereof, an LNG thermometer and an LNG pressure meter and a data acquisition controller thereof 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 the centralized control communication module of the plant control system via the station control system and its TCP / IP centralized control interface and external data transmission interface; the LNG calorific value analysis computer is used to receive real-time data transmitted to it 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.

[0031] Further, the LNG mass flowmeter or LNG density meter and its data acquisition controller are: a Coriolis mass flowmeter for cryogenic fluid LNG, or an online LNG density meter with a density direct measurement function, and includes a data acquisition controller with data acquisition and remote transmission functions provided by the LNG mass flowmeter or LNG density meter itself;

[0032] LNG thermometer and LNG pressure gauge are the temperature gauge and pressure gauge located at the closest distance to the LNG mass flow meter or LNG density meter, and both have the function of remote data transmission.

[0033] The present invention adopts the above technical solution, which has the following advantages:

[0034] 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 LNG and the measured temperature, pressure, density and nitrogen content, avoiding the dependence of the traditional cumbersome method on the analysis and testing of the composition of LNG components one by one.

[0035] 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

[0036] Figure 1 is a flow chart of a method for real-time measurement of LNG liquid calorific value in an embodiment of the present invention;

[0037] Figure 2 It is a schematic diagram of the system structure for real-time measurement of LNG liquid calorific value in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] In order to solve the problem that the real-time online measurement of LNG liquid calorific value in seconds and the simultaneous online measurement of LNG liquid calorific value in multiple pipelines cannot be achieved in LNG receiving stations, LNG liquefaction plants and LNG storage stations, the present invention provides a method and system for real-time measurement of LNG liquid calorific value. Based on the thermophysical properties of LNG and according to the basic relationship between the temperature, density and calorific value of LNG, a mathematical correlation formula of the LNG liquid calorific value properties is established, an LNG mass flowmeter is installed to measure the dynamic density value of the pipeline in real time, a thermometer and a pressure gauge with a remote transmission function are installed near the LNG mass flowmeter, a data communication channel is established by connecting the data receiving port of the station control room through the data transmission port of the LNG Coriolis mass flow, and a host computer calculation program and an explosion-proof industrial computer are installed to achieve real-time monitoring and measurement, and analysis of the LNG calorific value of the monitoring point.

[0039] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0040] 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.

[0041] In one embodiment of the present invention, a method for real-time measurement of LNG liquid calorific value is provided, specifically, the calorific value measurement of LNG liquid products and LNG liquid process control at LNG receiving stations, LNG liquefaction plants, and LNG storage stations, which can achieve online real-time measurement of LNG liquid calorific value and online real-time accurate measurement in seconds, 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:

[0042] 1) Based on the ρ-T preset relationship table of the pre-established built-in database, a corresponding mathematical fitting relationship is established;

[0043] 2) According to the measured density ρ of LNG mass flow meter or LNG density 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, through Min{|ρ-ρ real ∣} Formula calculation to find the corresponding measured temperature T real Next, and the current measured density ρ real The density value ρ closest to the typical LNG corresponding to the density value ρ in the built-in database is determined to calculate the density value ρ of the current typical LNG at a temperature of -160°C -160 ;

[0044] 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 -160℃ and 1 atmosphere pressure -160 / 101.325kpa ;

[0045] 4) Based on the density value ρ -160 / 101.325kpa Calculate the GHV at reference / combustion temperature conditions of 60 / 60°F and pressure of 14.696 psia BTU / SCF,60F , and the high heating value HHV at reference / combustion temperature conditions of 15°C / 15°C and 1 atmosphere 15℃ , get the high heating value HHV under reference / combustion temperature conditions of 20℃ / 20℃ and 1 atmosphere pressure 20℃ ;

[0046] 5) According to the high heating value HHV 20℃ Calculate the gas density ρ at 20°C 20℃ Hehuabaishu WI 20℃ , complete the real-time measurement of LNG liquid calorific value.

[0047] In the above step 1), based on the ρ-T preset relationship table of the pre-established built-in database, a corresponding mathematical fitting relationship is established, specifically:

[0048] ρ real =b1+b2×(T real +160)+b 36 ×(T real +160) 2

[0049] In the formula, ρ real Indicates the measured density value, T real represents the measured temperature value, b1 to b3 are the first calculation coefficients. In this embodiment, b1 = 4.598158E+02, b2 = -1.414823E-00, and b3 = -3.943498E-03. For example, E-03 represents e -3 .

[0050] In the above step 3), the density of LNG at -160°C and 1 atmosphere is calculated based on the measured pressure and measured density:

[0051] ρ -160 / 101.325kpa =ρ -160 ×[1+β×(P real -101.325) / 10]

[0052] In the formula, ρ -160 / 101.325kpa is the density of LNG at -160℃ and 1 atmosphere; β=0.19235 / 10000; ρ -160 is the density value of the current typical LNG at a temperature of -160°C; P real The actual measured pressure.

[0053] In step 4), the higher heating value GHV at reference / combustion temperature conditions of 60 / 60°F and pressure of 14.696 psia is calculated based on the density value.BTU / SCF,60F , including the following steps:

[0054] 4.1) Based on High Heating Value (GHV) BTU / SCF,60F and LNG density value ρ -160 / 101.325kpa According to the relationship between the molar content of nitrogen, Mol N2 Divide into three groups of intervals:

[0055] The first group of intervals is 0≤N2<0.3%; the second group of intervals is 0.3%≤N2<0.6%; the third group of intervals is N2≥0.6%. In this embodiment, N2 is 0.2%.

[0056] 4.2) Estimated and manually set the nitrogen molar content Mol N2 Value, select the molar content of the first group of nitrogen Mol N2 The interval formula is used to calculate the high calorific value GHV BTU / SCF,60F :

[0057]

[0058] Wherein, a1-a4 are second calculation coefficients. In this embodiment, a1=6.297192E+02, a2=-9.825821E-01, a3=4.4741213E-03, a4=0.

[0059] The calculation formula for the second set of intervals is:

[0060]

[0061] In this embodiment, a1=2.572999E+03, a2=a2=-9.606137E+00, a3=1.399806E-02, a4=0.

[0062] The calculation formula for the third group of intervals is:

[0063]

[0064] In this embodiment, a1=6.085036E+03, a2=-2.517325E+01, a3=3.121225E-02, and a4=0.

[0065] In step 4), the HHV at the reference / combustion temperature of 15°C / 15°C and 1 atmosphere is calculated. 15℃ (MJ / Sm3), is:

[0066] Set the first conversion factor γ G-HHV15 , the reference / combustion temperature condition 60 / 60℉, pressure 14.696psia high heating value GHV BTU / SCF,60FConverted to reference / combustion temperature conditions 15℃ / 15℃, high heating value HHV at 1 atmosphere pressure 15℃ :

[0067] HV 15℃ =GHV BTU / SCF,60F ×γ G-HHV15 .

[0068] In this embodiment, the first conversion coefficient is set to: G-HHV15 =0.037333.

[0069] In step 4), the HHV at the reference / combustion temperature of 20°C / 20°C and 1 atmosphere is calculated. 20℃ ,for:

[0070] Set the second conversion factor γ 15-20 , the reference / combustion temperature condition 15℃ / 15℃, high heating value HHV under 1 atmosphere pressure 15℃ Converted to reference / combustion temperature conditions 20℃ / 20℃, high heating value HHV at 1 atmosphere 20℃ :

[0071] HV 20℃ =HHV 15℃ ×γ 15-20 .

[0072] In this embodiment, the second conversion coefficient is set to: 15-20 =0.982438.

[0073] In the above step 5), according to the density value and the high heating value HHV 20℃ Calculate the gas density ρ at 20°C 20℃ Hehuabaishu WI 20℃ , including the following steps:

[0074] 5.1) Calculate the gas density ρ at 20°C based on the density value 20℃ ;

[0075] 5.2) Based on high heating value HHV 20℃ and the gas density ρ at 20°C 20℃ Calculate the Huabai number WI 20℃ .

[0076] Among them, Huabai number WI 20℃ for:

[0077] WI 20℃ =HHV 20℃ / (ρ 20℃ / 1.205) 0.5

[0078]

[0079] Wherein, c1~c2 are the third calculation coefficients. c1~c3 are obtained by the regression equation given by the built-in 2000 sets of LNG thermophysical property database.

[0080] In this embodiment, c1=8.412233815077151E-01, c2=-2.817486818129847E-03, c3=5.722123959447615E-06.

[0081] In one embodiment of the present invention, a system for real-time measurement of LNG liquid calorific value is provided, which is used to implement the methods in the above embodiments, involving a series of analysis processes, hardware equipment, and control system communications. First, it includes establishing a system including an LNG mass flow meter or an LNG density meter 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 an LNG calorific value calculation and analysis computer, an LNG 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:

[0082] LNG mass flow meter or LNG density meter and data acquisition controller thereof, LNG thermometer and LNG pressure meter and data acquisition controller thereof, station control system and TCP / IP centralized control interface and external data transmission interface, LNG calorific value analysis computer, preset built-in database and calculation program module based on the method for real-time measurement of LNG liquid calorific value in the above-mentioned embodiments, calorific value measurement display module of station control system;

[0083] LNG mass flow meter or LNG density meter and its data acquisition controller, LNG thermometer and LNG pressure meter and its 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 connect to the centralized control communication module of the plant control system via the station control system and its TCP / IP centralized control interface and external data transmission interface;

[0084] The LNG calorific value 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 to run the built-in database and calculation program modules 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.

[0085] In the above embodiment, the LNG mass flowmeter or LNG density meter and its data acquisition controller are: a Coriolis mass flowmeter (e.g., Emerson, 2-inch or 3-inch) for cryogenic fluid LNG, or an online LNG density meter with a density direct measurement function, and a data acquisition controller with data acquisition and remote transmission functions provided by the LNG mass flowmeter or LNG density meter (Emerson, 2-inch or 3-inch) itself. The interface forms include Modbus RS485, TCP / IP, 4-20mA DC HART, pulse signal and Ethernet port.

[0086] LNG thermometer and LNG pressure gauge are the temperature gauge and pressure gauge located at the closest distance to the LNG mass flow meter or LNG density meter, and both have the function of remote data transmission.

[0087] In the above embodiment, the communication cable connected to the station control system is an LNG mass flow meter or an LNG density 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 data acquisition controller and a Modbus RS485 and TCP / IP interface.

[0088] 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.

[0089] In the above embodiment, the communication cable from the data output interface of the station control system to the LNG 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.

[0090] In the above embodiment, the LNG calorific value calculation and analysis computer realizes real-time analysis and calculation of calorific value data by reading the 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 the specific method, and saves the calculation results on the spot, or further distributes the calculation results to the calorific value metering display module of the control system (DCS system) through the external communication interface.

[0091] 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 6 parameters including specific components, pressure, temperature, density, calorific value, and Wobbe number. Each group of LNG is subjected to physical property calculations using Aspen commercial software, and a corresponding relationship table between temperature T and LNG liquid density ρ in the range of [-162°C, -145°C] with an interval of -1°C is established. The 6 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 [-162°C, -145°C] together constitute the built-in database.

[0092] 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.

[0093] Embodiments: The present invention is further described below by way of specific embodiments.

[0094] Step 1: Given the LNG tanker loading area of ​​a certain LNG receiving station, a 3-inch LNG Coriolis mass flowmeter is installed on a tanker loading skid, a pressure gauge and a temperature gauge with remote transmission function are installed nearby, and an LNG calorific value calculation and analysis computer is arranged in the LNG tanker control room or the plant-wide central control room (DCS). The TCP / IP interfaces of the mass flowmeter, pressure gauge and temperature gauge are all connected to the TCP / IP centralized control interface of the LNG tanker control room or the plant-wide central control room (DCS) through a communication cable, and the TCP / IP interface of the LNG calorific value calculation and analysis computer is connected to the TCP / IP centralized control interface of the LNG tanker control room or the plant-wide central control room (DCS) through a communication cable.

[0095] The second step is to establish the built-in database and calculation program module of the LNG calorific value calculation and analysis computer. The specific steps include:

[0096] (1) Establish a mathematical fitting relationship for the ρ-T correspondence table in the built-in database:

[0097] ρ real =b1+b2×(T rrsl +160)+b3×(T real +160) 2

[0098] (2) Based on the measured density ρ of the LNG mass flow meter or LNG density meter real , is 455.2kg / m 3 , and the T of the nearest thermometer and pressure gauge real is -153.5℃ and P realis 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 (455.2kg / m 3 ) is closest to the density ρ value, which is 455.7kg / m 3 , and then determine the typical LNG corresponding to the density parameter ρ in the built-in database. Then use the fitting relationship in step (1) to calculate the density value ρ of the current typical LNG at a temperature of -160°C -160 , is 468.006.kg / m 3 .

[0099] (3) Apply the density ρ-pressure P relationship. According to the measured pressure P real , density ρ real , calculate the LNG density value ρ at -160℃ and 1 atmosphere pressure -160 . The result is 468.026.kg / m 3 .

[0100] (4) High Heating Value (GHV) at reference / combustion temperature conditions of 60 / 60°F and pressure of 14.696 psia BTU / SCF,60F and LNG density value ρ -160 / 101.325kpa According to the nitrogen molar content Mol N2 Divide into three groups. In this embodiment, N2 is 0.2%. Select the first group of formulas to calculate GHV BTU / SCF,60F The value is 1149.830 BTU / SCF.

[0101] By estimating and manually setting the molar content of nitrogen Mol N2 value, automatically select the interval formula.

[0102] (5) High Heating Value (GHV) at 60 / 60°F and 14.696 psia BTU / SCF,60F Converted to reference / combustion temperature conditions 15℃ / 15℃, high heating value HHV at 1 atmosphere pressure 15℃ (MJ / Sm 3 ), set the conversion factor γ G-HHV15 The calculated result is 42.827MJ / Sm 3 .

[0103] (6) High calorific value HHV 15℃ Further converted to high heating value HHV at reference / combustion temperature conditions 20℃ / 20℃ and 1 atmosphere pressure 20℃ The calculated result is 42.173MJ / Sm 3 .

[0104] (7) Calculate the gas density ρ at 20°C 20℃ 0.776Kg / m3, Wobbe number WI 20℃ It is 52.555.

[0105] The third step is to run the data acquisition and analysis system established in the above 7 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.

[0106] In summary, for the current LNG receiving station, LNG liquefaction plant, LNG storage station, the only practical engineering technology for LNG liquid calorific value measurement is a technical method based on LNG liquid sampling and gasification and chromatographic analysis calculation. The advantage is that the specific quantity of each component is determined by chromatographic analysis one by one, and then the calorific value is calculated by formula. The disadvantage is that the simplified characteristics of LNG thermal properties are ignored in the LNG field, and the complex analysis and calculation process of general gas is still applied, which is not only expensive, but also increases the uncertainty of the results due to the addition of low-temperature LNG sampling and gasification operations in the analysis process, resulting in low cost-effectiveness and large measurement deviation. The present invention makes full use of 2000 LNG physical property parameters measured by a third party accumulated over many years, establishes a database and a calculation program based on a specific method, and establishes a data acquisition and analysis system through an LNG mass flow meter or an LNG density meter 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 an LNG calorific value calculation and analysis computer, an LNG calorific value calculation and analysis computer, a built-in database and a calculation program module.

[0107] 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 LNG liquid calorific value, 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 or LNG density 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 current typical LNG at a temperature of -160°C; The density of LNG at -160℃ and 1 atmosphere is calculated based on the measured pressure and density through the density-pressure relationship. Calculates the GHV based on the density at reference / combustion temperature conditions of 60 / 60°F and pressure of 14.696 psia BTU / SCF,60F , and the high heating value HHV at reference / combustion temperature conditions of 15°C / 15°C and 1 atmosphere 15℃ , get the high heating value HHV under reference / combustion temperature conditions of 20℃ / 20℃ and 1 atmosphere pressure 20℃ ; According to density value and higher heating value HHV 20℃ Calculate the gas density ρ at 20°C 20℃ Hehuabaishu WI 20℃ , complete the real-time measurement of LNG liquid calorific value.

2. The method for real-time measurement of LNG liquid calorific value 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 LNG liquid calorific value according to claim 1, characterized in that: The density of LNG at -160℃ and 1 atmosphere is calculated based on the measured pressure and density: p- 160 / 101.325kpa =ρ -160 ×[1+β×(P real -101.325) / 10] In the formula, ρ -160 / 101.325kpa is the density of LNG at -160℃ and 1 atmosphere; β=0.19235 / 10000; ρ -160 is the density value of the current typical LNG at a temperature of -160°C; P real The actual measured pressure.

4. The method for real-time measurement of LNG liquid calorific value according to claim 1, characterized in that: Calculates the GHV based on the density at reference / combustion temperature conditions of 60 / 60°F and pressure of 14.696 psia BTU / SCF,60F ,include: Based on high heating value GHV BTU / SCF,60F and LNG density value ρ -160 / 101.325kpa 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 the molar content of the first group of nitrogen Mol N2 The interval formula is used to calculate the high calorific value GHV BTU / SCF,60F : Among them, a1~a4 are the second calculation coefficients.

5. The method for real-time measurement of LNG liquid calorific value according to claim 1, characterized in that: Calculate the HHV at reference / combustion temperature 15°C / 15°C and 1 atmosphere 15℃ ,include: Set the first conversion factor Y G-HHV15 , the reference / combustion temperature condition 60 / 60°F, pressure 14.696psia high heating value GHV BTU / SCF,60F Converted to reference / combustion temperature conditions 15℃ / 15℃, high heating value HHV at 1 atmosphere pressure 15℃ : HHV 15℃ =GHV BTU / SCF,60F ×γ G-HHV15 。 6. The method for real-time measurement of LNG liquid calorific value according to claim 1, characterized in that: Calculate the HHV at reference / combustion temperature 20°C / 20°C and 1 atmosphere 20℃ ,include: Set the second conversion factor γ 15-20 , the reference / combustion temperature condition 15℃ / 15℃, high heating value HHV under 1 atmosphere pressure 15℃ Converted to reference / combustion temperature conditions 20℃ / 20℃, high heating value HHV at 1 atmosphere 20℃ : HHV 20℃ =HHV 15℃ ×γ 15-20 。 7. The method for real-time measurement of LNG liquid calorific value according to claim 1, characterized in that: According to density value and higher heating value HHV 20℃ Calculate the gas density ρ at 20°C 20℃ Hehuabaishu WI 20℃ ,include: Calculate the gas density ρ at 20℃ based on the density value 20℃ ; Based on high heating value HHV 20℃ and the gas density ρ at 20°C 20℃ Calculate the Huabai number WI 20℃ .

8. The method for real-time measurement of LNG liquid calorific value according to claim 7, characterized in that: Huabai Number WI 20℃ for: WI 20℃ =HHV 20℃ / (r 20℃ / 1.205) 0.5 Wherein, c1~c3 are the third calculation coefficients.

9. A system for real-time measurement of LNG liquid calorific value, characterized in that: include: LNG mass flow meter or LNG density meter and data acquisition controller thereof, LNG thermometer and LNG pressure meter and data acquisition controller thereof, station control system and TCP / IP centralized control interface and external data transmission interface, LNG calorific value analysis computer, preset built-in database and calculation program module based on the method for real-time measurement of LNG liquid calorific value as claimed in any one of claims 1 to 8, calorific value measurement display module of station control system; LNG mass flow meter or LNG density meter and its data acquisition controller, LNG thermometer and LNG pressure meter and its 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 connect to the centralized control communication module of the plant control system via the station control system and its TCP / IP centralized control interface and external data transmission interface; The LNG calorific value 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 to run the built-in database and calculation program modules 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 LNG liquid calorific value according to claim 9, characterized in that: LNG mass flowmeter or LNG density meter and its data acquisition controller are: Coriolis mass flowmeter for cryogenic fluid LNG, or online LNG density meter with density direct measurement function, and includes a data acquisition controller with data acquisition and remote transmission functions of the LNG mass flowmeter or LNG density meter itself; LNG thermometer and LNG pressure gauge are the temperature gauge and pressure gauge located at the closest distance to the LNG mass flow meter or LNG density meter, and both have the function of remote data transmission.

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