A natural gas hydrocarbon dew point analysis calibration system and calibration method

Abstract

The present invention relates to a natural gas hydrocarbon dew point analysis and calibration system, belonging to the technical field of natural gas hydrocarbon dew point analysis and calibration, comprising an online standard substance generating device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point instrument to be calibrated, an automatic weighing device and a data processing system; the online standard substance generating device generates n-butane gas with a concentration of 10%, and the outlet gas is used for quantitative analysis of the standard substance, a gas source for the calibration device and a standard gas source for the instrument to be calibrated. After adopting the above method or structure, the present invention has the following advantages: this patent adopts a method of online generation of standard substances combined with precise determination of gas chromatography and dew point calculation simulation, and through the coordinated use of the hydrocarbon dew point calibration device and the automatic weighing device, realizes effective traceability and accurate calibration of the natural gas hydrocarbon dew point analyzer, makes up for the traceability shortcomings of the natural gas hydrocarbon dew point analyzer, and ensures the accuracy of the hydrocarbon dew point analysis detection value.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas hydrocarbon dew point analysis and calibration, and in particular to a natural gas hydrocarbon dew point analysis and calibration system and calibration method. Background Art

[0002] During long-distance natural gas pipeline transportation, temperature and pressure fluctuations can cause changes in the natural gas's hydrocarbon dew point. When the critical point is exceeded, liquid hydrocarbons precipitate, causing corrosion and damage to equipment such as pipelines and compressors. Therefore, real-time monitoring of natural gas's hydrocarbon dew point is crucial. Conventional hydrocarbon dew point measurements are performed using online chromatographs to determine the contents of C1, C7, and C8. Many of these devices require a probe inserted directly into the pipeline and require specialized technicians to operate, combining multiple gas quality and metering parameters into a single instrument.

[0003] Heavy hydrocarbons in natural gas can easily liquefy and form condensate in cold environments and at pipe reducers. This can cause pipeline blockages and compressor failures, seriously impacting natural gas pipeline safety. Currently, GB17820-2018 "Natural Gas" requires that liquid hydrocarbons be absent from natural gas under the pressure and temperature conditions at gas transfer points; GB 50251-2015 "Code for Design of Gas Pipeline Engineering" requires that the hydrocarbon dew point of gas entering the pipeline be below the minimum ambient temperature. Due to the compositional characteristics of natural gas, it exhibits the physicochemical properties of retrograde condensation. To test the hydrocarbon dew point of natural gas, GB / T 27895-2011 "Determination of Natural Gas Hydrocarbon Dew Point - Visual Measurement with a Cooled Mirror" and SY / T7484-2020 "Determination of Natural Gas Hydrocarbon Dew Point - Automatic Measurement with a Cooled Mirror" utilize visual and automated methods, respectively, using a cooled mirror analyzer.

[0004] Compared with the relatively abundant hydrocarbon dew point analysis and detection instruments and corresponding national / industry standard analysis methods on the market, there is currently a lack of corresponding standard devices and calibration methods to calibrate and trace the value of hydrocarbon dew point analysis instruments, which makes it impossible to effectively guarantee the accuracy of the detection data of hydrocarbon dew point analysis instruments.

[0005] In view of the above, it is necessary to propose a natural gas hydrocarbon dew point analysis calibration system and calibration method to solve the above problems. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problems and provides a natural gas hydrocarbon dew point analysis calibration system and calibration method. It adopts the method of online generation of standard substances combined with precise determination of gas chromatography and dew point calculation simulation. Through the coordinated use of hydrocarbon dew point calibration device and automatic weighing device, effective traceability and accurate calibration of natural gas hydrocarbon dew point analysis instrument are achieved.

[0007] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0008] A natural gas hydrocarbon dew point analysis and calibration system comprises a standard substance online generating device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system;

[0009] The online standard substance generator generates n-butane gas with a concentration of 10%, and the outlet of the online standard substance generator is connected to the gas chromatograph, the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated through a three-way connection.

[0010] The gas chromatograph analyzes the actual concentration of n-butane gas emitted by the online standard substance generator, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration;

[0011] Comparing and correcting the dew points between the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated;

[0012] The automatic weighing device performs standard control on the n-butane gas, and then feeds it back to the hydrocarbon dew point calibration device through dynamic feedback. The n-butane gas from the automatic weighing device is analyzed for venting air composition and input into the gas chromatograph.

[0013] Preferably, the linear equation for predicting hydrocarbon dew point by the model is:

[0014] y=0.0024x5-0.0633x4+0.6602x3-3.6449x2+14.833x-48.681.

[0015] Preferably, the model predicts that the difference between hydrocarbon dew points within the pressure range of 0 to 10 bar is within the range of -0.12 to 1.54°C.

[0016] Preferably, the gas chromatograph is a flame ionization detector (FID) or a thermal conductivity detector (TCD), or a combination of the two.

[0017] A natural gas hydrocarbon dew point analysis calibration method comprises the following steps:

[0018] The generated gas from the online generator of the standard substance is analyzed by gas chromatography to determine its accurate concentration x;

[0019] The precision pressure controller precisely controls the pressure of the generated gas, and the mass flow meter accurately measures the flow rate of the generated gas as v;

[0020] The temperature in the system is dynamically fed back in real time by a platinum resistance temperature sensor, and the result is fed back to the refrigerator. The refrigerator dynamically adjusts the cooling power and realizes precise temperature control through the refrigerant outlet and refrigerant reflux. Under the condition of x concentration, the hydrocarbon dew point of the sample gas is T0. The temperature is adjusted from T0+3℃ to T0-3℃ from high to low, with an initial temperature step of 1℃. When liquid condensation is found to flow out into the reference liquid storage container, the temperature T1 at this time is recorded and the temperature is adjusted from T1+1℃ to T℃ from high to low, with a temperature step of 0.1℃. During the adjustment process, the equilibrium time for each temperature point is 30 minutes. The concentration of n-butane in the vented air is analyzed by online gas chromatography. When the n-butane concentration is 0, it proves that all n-butane in the sample gas has condensed. The initial condensation temperature T is determined, which is the hydrocarbon dew point of the sample gas.

[0021] During the temperature control process, the adjustment and control can be considered successful only if the temperatures of the four platinum resistance temperature sensors are within the range of ±0.01℃ from the set value;

[0022] All platinum resistance temperature sensors must be calibrated or certified by standard platinum resistance thermometers to ensure that the temperature data is traceable to the international unit of measurement, Kelvin (K).

[0023] The flow directions of the generated gas and the refrigerant outlet are opposite to each other, ensuring sufficient heat exchange of the sample;

[0024] The sample condensate liquid after heat exchange enters the multi-way selection valve, and the sample automatically enters the reference liquid storage container or the standard liquid storage container;

[0025] The mass change of the reference liquid storage container or the standard liquid storage container is transmitted to the data processing system through the mass sensor for data processing;

[0026] When the multi-way selector valve switches to the standard liquid storage container, the data processing system automatically tares and resets the weighing device, and records the mass of the hydrocarbon liquid in the standard liquid storage container within the time t;

[0027] The reference liquid storage container and the standard liquid storage container are connected to the outside through pipes for air discharge, and the air discharge pipes are equipped with one-way valves to prevent gas or air from flowing back and affecting the weighing accuracy;

[0028] When the vented air enters the gas chromatograph, real-time online analysis is performed to determine whether there is any n-butane overflow in the vented air.

[0029] Preferably, the switching principle of the multi-way selector valve is as follows: during the process of determining the hydrocarbon dew point, the sample enters the reference liquid storage container, and after the hydrocarbon dew point T of the sample gas is determined, it is switched to the standard liquid storage container, and the time t is recorded. The theoretical condensate mass is m, which is calculated as follows:

[0030] After adopting the above method or structure, the present invention has the following advantages:

[0031] This patent adopts a method of online generation of standard substances combined with precise determination of gas chromatography and dew point calculation simulation. Through the coordinated use of hydrocarbon dew point calibration device and automatic weighing device, it realizes the effective traceability and accurate calibration of natural gas hydrocarbon dew point analyzers, fills the traceability shortcomings of natural gas hydrocarbon dew point analyzers, and ensures the accuracy of hydrocarbon dew point analysis detection values.

[0032] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present invention will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 is a flow chart of the system of the present invention;

[0035] Figure 2 is a connection diagram of the calibration method of the present invention;

[0036] Figure 3 This is a simulated diagram of the dew point of 10% n-butane in nitrogen according to the present invention.

[0037] As shown in the figure: 1. Online standard substance generator; 2. Precision pressure controller; 3. Mass flowmeter; 4. Platinum resistance temperature sensor; 5. Refrigerator; 6. Refrigerant outlet; 7. Refrigerant reflux; 8. Condensate liquid; 9. Multi-way selection valve; 10. Condensate liquid inlet for reference liquid storage container; 11. Air vent for reference liquid storage container; 12. Condensate liquid inlet for standard liquid storage container; 13. Air vent for standard liquid storage container; 14. Reference liquid storage container; 15. Standard liquid storage container; 16. Air vent; 17. Data processing system. DETAILED DESCRIPTION

[0038] The following describes in detail embodiments of the present application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application.

[0039] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0040] The present invention will be described in further detail below in conjunction with the full text.

[0041] Combined with attachment Figure 1-Figure 3 , a natural gas hydrocarbon dew point analysis and calibration system, comprising a standard substance online generating device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system;

[0042] The online standard substance generator generates n-butane gas with a concentration of 10%, and the outlet of the online standard substance generator is connected to the gas chromatograph, the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated through a three-way connection.

[0043] The gas chromatograph analyzes the actual concentration of n-butane gas emitted by the online standard substance generator, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration;

[0044] Comparing and correcting the dew points between the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated;

[0045] The automatic weighing device performs standard control on the n-butane gas, and then feeds it back to the hydrocarbon dew point calibration device through dynamic feedback. The n-butane gas from the automatic weighing device is analyzed for venting air composition and input into the gas chromatograph.

[0046] The linear equation for predicting hydrocarbon dew point of the model is:

[0047] y=0.0024x 5 -0.0633x 4 +0.6602x 3 -3.6449x 2 +14.833x-48.681.

[0048] The model predicts that the difference between hydrocarbon dew points within the pressure range of (0 to 10) bar is within the range of (-0.12 to 1.54)°C.

[0049] The gas chromatograph is a flame ionization detector (FID) or a thermal conductivity detector (TCD), or a combination of the two.

[0050] A natural gas hydrocarbon dew point analysis calibration method comprises the following steps:

[0051] ① The generated gas from the online generator of the standard substance is analyzed by gas chromatography to determine its accurate concentration x;

[0052] ②The precision pressure controller precisely controls the pressure of the generated gas, and the mass flow meter accurately measures the flow rate of the generated gas as v;

[0053] ③ The temperature in the system is dynamically fed back in real time by a platinum resistance temperature sensor, and the result is fed back to the refrigerator. The refrigerator dynamically adjusts the cooling power and realizes precise temperature control through the refrigerant outlet and refrigerant reflux. Under the condition of x concentration, the hydrocarbon dew point of the sample gas is T0. The temperature is adjusted from T0+3℃ to T0-3℃ in a descending order, with an initial temperature step of 1℃. When liquid condensation is found to flow out into the reference liquid storage container, the temperature T1 at this time is recorded. The temperature is adjusted from T1+1℃ to T℃ in a descending order, with a temperature step of 0.1℃. During the adjustment process, the equilibrium time for each temperature point is 30 minutes. The concentration of n-butane in the vented air is analyzed by online gas chromatography. When the n-butane concentration is 0, it proves that all n-butane in the sample gas has condensed. The initial condensation temperature T is determined, which is the hydrocarbon dew point of the sample gas.

[0054] ④ During the temperature control process, the adjustment and control can be considered successful only if the temperatures of the four platinum resistance temperature sensors are within the range of ±0.01℃ from the set value;

[0055] ⑤ All platinum resistance temperature sensors must be calibrated or certified by standard platinum resistance thermometers to ensure that the temperature data can be traced back to the international unit of measurement, Kelvin (K);

[0056] ⑥ The flow directions of the generating gas and the refrigerant outlet are opposite to each other to ensure sufficient heat exchange of the sample;

[0057] ⑦ After heat exchange, the sample condensate liquid enters the multi-way selection valve, and the sample automatically enters the reference liquid storage container or the standard liquid storage container;

[0058] ⑧The mass change of the reference liquid storage container or the standard liquid storage container is transmitted to the data processing system through the mass sensor for data processing;

[0059] ⑨ When the multi-way selector valve switches to the standard liquid storage container, the data processing system automatically tares and resets the weighing device, and records the mass of the hydrocarbon liquid in the standard liquid storage container within the time t;

[0060] ⑩The reference liquid storage container and the standard liquid storage container are connected to the outside through pipes for air discharge, and the air discharge pipes are equipped with one-way valves to prevent gas or air from flowing back and affecting the weighing accuracy;

[0061] When the vented air enters the gas chromatograph, real-time online analysis is performed to determine whether there is any n-butane overflow in the vented air.

[0062] The switching principle of the multi-way selector valve is as follows: during the hydrocarbon dew point determination process, the sample enters the reference liquid storage container. After the hydrocarbon dew point T of the sample gas is determined, it is transferred to the standard liquid storage container and the time t is recorded. The theoretical condensate mass is m, which is calculated as follows:

[0063] Standard substance online generator:

[0064] ① The device principle can be the dynamic dilution generation principle or the permeation tube generation principle, generating n-butane gas with a theoretical concentration of 10%;

[0065] ②The gas pressure at the generator outlet is continuously adjustable within the range of (1-10) bar, ensuring the selection of multiple calibration pressure points;

[0066] ③ The generator outlet is equipped with a three-way connection, which enables simultaneous sampling of the hydrocarbon dew point instrument to be calibrated and the hydrocarbon dew point calibration device;

[0067] ④ The n-butane and nitrogen used are both national certified standard substances to ensure traceability. The n-butane is the high-purity n-butane gas standard substance GBW(E)060061; the nitrogen used is the ultra-high-purity nitrogen standard substance GBW06343;

[0068] Gas Chromatograph (GC):

[0069] ①The function of the gas chromatograph is to analyze the actual concentration of n-butane gas of 10% of the theoretical concentration that occurs dynamically;

[0070] ② In order to prevent the analytical error introduced by the linearity of the analytical instrument, the gas standard substance used is the n-butane gas standard substance GBW(E)062325, which has the same or close concentration as the generated gas;

[0071] ③ The detector configured for the gas chromatograph can be one of the flame ionization detectors (FID) and thermal conductivity detectors (TCD), or a combination of both, for the analysis of high-concentration n-butane gas standard substances and exhaust gas composition generated online;

[0072] ④The concentration of generated gas is determined by single-point precise matching method (external standard method);

[0073] The model predicts hydrocarbon dew point:

[0074] ① Calculate the hydrocarbon dew point model based on the concentration of generated gas analyzed by gas chromatograph;

[0075] ② The prediction of hydrocarbon dew point is based on the physical property state equation established by Peng-Robinson;

[0076] ③ Table 1 and Figure 1 The dew point simulation data and the simulated linear graph of 10% n-butane in nitrogen are shown respectively. The simulated point data are fitted to the linear equation y = 0.0024x 5 -0.0633x 4 +0.6602x 3 -3.6449x 2 +14.833x-48.681;

[0077] ④ The difference between the hydrocarbon dew point of the fitting equation and the simulation data in the pressure range of (0 to 10) bar is in the range of (-0.12 to 1.54) °C;

[0078] ⑤ In order to avoid the influence of simulation error and ensure the accuracy and reliability of hydrocarbon dew point, the temperature input value of the downstream hydrocarbon dew point calibration device is changed from (T0+3)℃ to (T0-3)℃ based on the calculated dew point T0 to determine the accurate value, such as Figure 3 and as shown in Table 1;

[0079] Table 1 Simulated dew point data of 10% n-butane in nitrogen

[0080]

[0081]

[0082] like Figure 2As shown, the online standard substance generating device 1 is connected to the precision pressure controller 2 and the mass flowmeter 3 of the automatic weighing device in sequence, and the temperature in the system is dynamically fed back in real time through the platinum resistance temperature sensor 4, and the result is fed back to the refrigerator 5. The precise temperature control and circuit closed loop are achieved through the refrigerant outlet 6 and the refrigerant reflux 7. The condensate liquid 8 after heat exchange in the refrigerator 5 can enter the reference liquid storage container condensate liquid inlet 10 of the reference liquid storage container 14 and the standard liquid storage container condensate liquid inlet 12 of the standard liquid storage container 15 respectively through the multi-way selection valve 9. The mass changes of the reference liquid storage container 14 and the standard liquid storage container 15 are transmitted to the data processing system through the mass sensor for data processing. The reference liquid storage container vent air 11 and the standard liquid storage container vent air 13 are connected to the external vent air 16, and then enter the gas chromatograph for real-time online analysis to analyze whether there is n-butane overflow in the vent air.

[0083] A natural gas hydrocarbon dew point analysis calibration method comprises the following steps:

[0084] ① The generated gas from the standard substance online generating device 1 is analyzed by gas chromatography to determine its accurate concentration x (mol / mol);

[0085] ② The precision pressure controller accurately controls the pressure of the generated gas at 101.325kPa, and the mass flow meter accurately measures the flow rate of the generated gas as v (L / min);

[0086] ③ The temperature in the system is dynamically fed back in real time by the platinum resistance temperature sensor 4, and the result is fed back to the refrigerator 5. The refrigerator 5 dynamically adjusts the cooling power through the refrigerant outlet 6 and the refrigerant reflux 7; to achieve precise temperature control; under the condition of x (mol / mol) concentration, the hydrocarbon dew point of the sample gas is T0, and the temperature is adjusted from T0+3℃ to T0-3℃ in a descending order, with an initial temperature step of 1℃. When liquid condensation is found to flow out into the reference liquid storage container 14, the temperature T1 at this time is recorded, and the temperature is adjusted from T1+1℃ to T℃ in a descending order, with a temperature step of 0.1℃. During the adjustment process, the equilibrium time for each temperature point is 30min. The concentration of n-butane in the vented air is analyzed by online gas chromatography. When the n-butane concentration is 0, it is proved that all n-butane in the sample gas has condensed, and the initial condensation temperature T is determined. dew , which is the hydrocarbon dew point of the sample gas;

[0087] ④ During the temperature control process, the adjustment and control can be considered successful only if the temperatures of the four platinum resistance temperature sensors 4 are within the range of ±0.01℃ from the set value;

[0088] ⑤ All platinum resistance temperature sensors 4 must be calibrated or certified by standard platinum resistance to achieve temperature data traceability to the international unit of measurement, Kelvin (K);

[0089] ⑥ The flow directions of the generated gas and the coolant outlet 6 are opposite to each other to ensure sufficient heat exchange of the sample;

[0090] ⑦ After heat exchange, the sample condensate liquid enters the multi-way selection valve 9, and the sample automatically enters the reference liquid storage container 14 or the standard liquid storage container 15;

[0091] ⑧ The mass change of the reference liquid storage container 14 or the standard liquid storage container 15 is transmitted to the data processing system 17 through the mass sensor for data processing;

[0092] ⑨ The switching principle of the multi-way selector valve is as follows: During the process of determining the hydrocarbon dew point, the sample enters the reference liquid storage container. After the hydrocarbon dew point T of the sample gas is determined, it is transferred to the standard liquid storage container and the time t is recorded. The theoretical condensate mass is m, which can be calculated as follows:

[0093] Where: m-mass of n-butane condensate, in g; M-relative molecular mass of n-butane, 58.12 g / mol; P-sample inlet pressure, in Pa; t-time for the sample to enter the standard liquid storage container, in min; v-flow rate of the sample gas, in L / min; x-n-butane component content, in mol / mol; R-gas constant, with a value of 8.314510 Pa·m3 / (mol·K); T-sample inlet temperature, in Kelvin (K).

[0094] When the multi-way selector valve 9 switches to the standard liquid storage container 15, the data processing system 17 automatically tares and resets the weighing device, and records the mass of the hydrocarbon liquid in the standard liquid storage container within the time t;

[0095] ⑩ The reference liquid storage container vent 11 and the standard liquid storage container vent 13 are connected to the external vent 16 through pipes, and the pipes are both equipped with one-way valves to prevent gas or air from flowing back and affecting the weighing accuracy;

[0096] When the vent air 16 enters the gas chromatograph, real-time online analysis is performed to analyze whether there is n-butane overflow in the vent air.

[0097] This patent adopts a method of online generation of standard substances combined with precise determination of gas chromatography and dew point calculation simulation. Through the coordinated use of hydrocarbon dew point calibration device and automatic weighing device, it realizes the effective traceability and accurate calibration of natural gas hydrocarbon dew point analyzer.

[0098] The present invention and its embodiments are described above. This description is not restrictive. What is shown in the full text is only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without creatively designing, they shall all fall within the scope of protection of the present invention.

Claims

1. A natural gas hydrocarbon dew point analysis and calibration system, characterized in that: It includes a standard substance online generating device, a gas chromatograph, a hydrocarbon dew point calibration device, a hydrocarbon dew point meter to be calibrated, an automatic weighing device and a data processing system; The online standard substance generator generates n-butane gas with a concentration of 10%, and the outlet of the online standard substance generator is connected to the gas chromatograph, the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated through a three-way connection. The gas chromatograph analyzes the actual concentration of n-butane gas emitted by the online standard substance generator, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration; Comparing and correcting the dew points between the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated; The automatic weighing device performs standard control on the n-butane gas, and then feeds it back to the hydrocarbon dew point calibration device through dynamic feedback. The n-butane gas from the automatic weighing device is analyzed for venting air composition and input into the gas chromatograph; The hydrocarbon dew point calibration device includes a precision pressure controller and a mass flow meter that are sequentially connected to an online standard substance generator. The temperature in the system is dynamically fed back in real time via a platinum resistance temperature sensor. The result is fed back to a refrigerator. The temperature is precisely controlled and the circuit is closed through a refrigerant outlet and refrigerant return. After heat exchange in the refrigerator, a condensate liquid is obtained. The automatic weighing device includes a reference liquid storage container condensate liquid inlet and a standard liquid storage container condensate liquid inlet, through which the condensate liquid can enter the reference liquid storage container and the standard liquid storage container respectively through a multi-way selection valve. The mass changes of the reference liquid storage container and the standard liquid storage container are transmitted to the data processing system through a mass sensor for data processing. The air discharged from the reference liquid storage container and the air discharged from the standard liquid storage container are connected to the external air discharge, and then enter the gas chromatograph for real-time online analysis to analyze whether there is n-butane overflow in the air discharge.

2. A natural gas hydrocarbon dew point analysis and calibration system according to claim 1, characterized in that: The linear equation for predicting hydrocarbon dew point by the model is y=0.0024x 5 -0.0633x 4 +0.6602x 3 -3.6449x 2 +14.833x-48.681; x is pressure, y is dew point temperature.

3. The natural gas hydrocarbon dew point analysis and calibration system according to claim 1, characterized in that: The model predicts that the difference between hydrocarbon dew points within the pressure range of 0 to 10 bar is within the range of -0.12 to 1.54°C.

4. The natural gas hydrocarbon dew point analysis and calibration system according to claim 1, characterized in that: The gas chromatograph is a flame ionization detector (FID) or a thermal conductivity detector (TCD), or a combination of the two.

5. A calibration method based on the natural gas hydrocarbon dew point analysis calibration system according to claim 1, characterized in that: The following steps are involved: ① The generated gas from the online generator of the standard substance is analyzed by gas chromatography to determine its accurate concentration x; ②The precision pressure controller precisely controls the pressure of the generated gas, and the mass flow meter accurately measures the flow rate of the generated gas as v; ③ The temperature in the system is dynamically fed back in real time by a platinum resistance temperature sensor, and the result is fed back to the refrigerator. The refrigerator dynamically adjusts the cooling power and realizes precise temperature control through the refrigerant outlet and refrigerant reflux. Under the condition of x concentration, the hydrocarbon dew point of the sample gas is T0. The temperature is adjusted from T0+3℃ to T0-3℃ in a descending order, with an initial temperature step of 1℃. When liquid condensation is found to flow out into the reference liquid storage container, the temperature T1 at this time is recorded. The temperature is adjusted from T1+1℃ to T℃ in a descending order, with a temperature step of 0.1℃. During the adjustment process, the equilibrium time for each temperature point is 30 minutes. The concentration of n-butane in the vented air is analyzed by online gas chromatography. When the n-butane concentration is 0, it proves that all n-butane in the sample gas has condensed. The initial condensation temperature T is determined, which is the hydrocarbon dew point of the sample gas. ④ During the temperature control process, the adjustment and control can be considered successful only if the temperatures of the four platinum resistance temperature sensors are within the range of ±0.01℃ from the set value; ⑤ All platinum resistance temperature sensors must be calibrated or certified by standard platinum resistance thermometers to ensure that the temperature data can be traced back to the international unit of measurement, Kelvin (K); ⑥ The flow directions of the generating gas and the refrigerant outlet are opposite to each other to ensure sufficient heat exchange of the sample; ⑦ After heat exchange, the sample condensate liquid enters the multi-way selection valve, and the sample automatically enters the reference liquid storage container or the standard liquid storage container; ⑧The mass change of the reference liquid storage container or the standard liquid storage container is transmitted to the data processing system through the mass sensor for data processing; ⑨ When the multi-way selector valve switches to the standard liquid storage container, the data processing system automatically tares and resets the weighing device, and records the mass of the hydrocarbon liquid in the standard liquid storage container within the time t; ⑩The reference liquid storage container and the standard liquid storage container are connected to the outside through pipes for air discharge, and the air discharge pipes are equipped with one-way valves to prevent gas or air from flowing back and affecting the weighing accuracy; When the vented air enters the gas chromatograph for real-time online analysis, it is used to analyze whether there is n-butane overflow in the vented air; The gas chromatograph analyzes the actual concentration of n-butane gas emitted by the online standard substance generator, predicts the hydrocarbon dew point through a model, and then feeds back to the hydrocarbon dew point calibration device for calibration; A dew point comparison is performed between the hydrocarbon dew point calibration device and the hydrocarbon dew point meter to be calibrated.

6. The calibration method according to claim 5, characterized in that: The switching principle of the multi-way selector valve is as follows: during the hydrocarbon dew point determination process, the sample enters the reference liquid storage container. After the hydrocarbon dew point T of the sample gas is determined, it is transferred to the standard liquid storage container and the time t is recorded. The theoretical condensate mass is m, which is calculated as follows: M is the relative molecular mass of n-butane, P is the sample inlet pressure, v is the flow rate of the sample gas, R is the gas constant, and T is the sample inlet temperature.

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