A natural gas calorific value measurement method and system based on a thermal conductivity detection principle

Abstract

This invention discloses a method and system for measuring the calorific value of natural gas based on the principle of thermal conductivity detection. The measurement method includes: constructing a linear equation between the weighted average molecular weight of a mixed gas sample and the response signal; fitting the sample data to obtain a first functional relationship expression; constructing a linear equation between the weighted average molecular weight of the mixed gas sample and the calorific value, and fitting it to obtain a second functional relationship expression; obtaining the functional relationship between the calorific value of natural gas and the response signal; and outputting the calorific value of natural gas by collecting the TCD response signals of natural gas with different compositions. The system includes a gas supply system, a detection system, and a data processing system. This invention significantly reduces system complexity and manufacturing costs while ensuring measurement performance, exhibiting good economic efficiency and engineering practicality, and is suitable for various application scenarios such as industrial sites, natural gas pipeline transmission and distribution systems, and home energy management.

Description

Technical Field

[0001] This invention relates to the field of natural gas calorific value detection, and specifically to a method and system for measuring the calorific value of natural gas based on the principle of thermal conductivity detection. Background Technology

[0002] With the widespread application of natural gas in power generation, petrochemicals, city gas, and industrial fuel, accurate measurement of its calorific value is crucial for promoting energy metering standardization, ensuring fair trade, and guaranteeing gas safety. Compared to traditional volumetric metering methods, calorific value-based energy metering can more accurately reflect the actual use value of natural gas. In actual gas supply processes, natural gas sources are diverse, with differences in composition between different gas fields and at different transmission and distribution stages, leading to variations in its calorific value. This time-varying characteristic places higher demands on the real-time performance, continuity, and stability of measurement technologies.

[0003] Currently, the calorific value of natural gas is mainly measured using indirect methods, such as gas chromatography. This method typically involves first separating and quantitatively analyzing the components of the natural gas, then weighting the calorific values ​​of each component to obtain the total calorific value. While this method offers advantages in measurement accuracy, it faces several limitations in engineering applications. On one hand, existing calorific value measurement systems have complex overall structures and are highly dependent on the operating environment, maintenance conditions, and specialized operation. On the other hand, some core components still rely on imports, increasing system costs and hindering the large-scale promotion and application of related technologies. With multi-source grid connection and dynamic allocation becoming increasingly common, gas systems are placing a more urgent demand on calorific value measurement technology for engineering applications.

[0004] Therefore, in view of the problems of insufficient real-time performance, high system complexity, and high application cost of existing natural gas calorific value measurement technologies, there is a need for a more advanced natural gas calorific value measurement method and system that can adapt to changes in calorific value and realize online measurement in order to meet the actual needs of energy metering. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a method and system for measuring the calorific value of natural gas based on the principle of thermal conductivity detection.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for measuring the calorific value of natural gas based on the principle of thermal conductivity detection is provided, which includes the following steps: S1: Construct several groups of mixed gas samples mainly composed of alkane, detect the TCD response signal of each mixed gas sample using a thermal conductivity detector, calculate the weighted average molecular weight of each mixed gas sample, and construct a linear equation between the weighted average molecular weight of the mixed gas sample and the response signal. S2: Based on the TCD response signal and weighted average molecular weight of each mixed gas sample detected by the thermal conductivity detector, generate a graph showing the relationship between the TCD response signal and the weighted average molecular weight, and fit the linear equation between the weighted average molecular weight and the response signal to obtain the first functional relationship expression of the fit. S3: Use a natural gas calorific value measuring instrument to detect the calorific value of each mixed gas sample and generate a weighted average molecular weight versus calorific value graph. S4: Construct a linear equation between the calorific value and the weighted average molecular weight of the mixed gas sample, and fit it to obtain the second functional relationship expression of the fit; S5: Substitute the fitted first functional relationship expression into the fitted second functional relationship expression to obtain the functional relationship between the calorific value of natural gas and the response signal. By collecting the TCD response signals of natural gas with different compositions, inputting them into the functional relationship between the calorific value of natural gas and the response signal, the calorific value of natural gas is output.

[0007] Further, step S1 includes: S11: Construct several groups of mixed gas samples mainly composed of alkanes. Each group of mixed gas samples contains a different amount of alkane gas. Use a thermal conductivity detector to detect the TCD response signal of each group of mixed gas samples. S12: The TCD response signal for each alkane component is , i Number the alkane components in the gas mixture sample; based on the mole fraction of the alkane components. TCD response signal for each alkane component The response signal of the mixed gas sample is obtained by performing a weighted summation. S ; ; in, I This refers to the amount of alkane components in the mixed gas sample; S13: Based on the mole fraction of the alkane component and molecular weight Calculate the weighted average molecular weight of the mixed gas sample ; ; S14: Based on the linear relationship between the response signal and molecular weight of a single alkane component. Construct the weighted average molecular weight of the mixed gas sample With response signal S The linear equation between them: ; in, a The first linear coefficient, b This is the first coefficient term.

[0008] Further, step S2 includes: S21: Based on the response signals of each mixed gas sample S and weighted average molecular weight M Generate a graph showing the relationship between the response signal and the weighted average molecular weight; S22: Utilizing the TCD response signal S Weighted average molecular weight M The data points in the relationship diagram are used to calculate the weighted average molecular weight based on the least squares method. With response signal S By fitting the linear equations between them, the first linear coefficients of the fit are obtained. and the first coefficient term This leads to the first functional relationship expression of the fit: .

[0009] Further, step S4 includes: S41: Calorific value of the mixed gas sample Calculated by weighting the calorific value of each alkane component by molar fraction; ; in, The calorific value of the alkane component; S42: The calorific value and molecular weight of a single alkane component satisfy a linear relationship. Constructing the calorific value of mixed gas samples H Weighted average molecular weight The linear equation between them: ; in, c The second linear coefficient, d This is the second coefficient term; S43: Using data points from the weighted average molecular weight versus calorific value graph, the calorific value of the mixed gas sample is determined based on the least squares method. H Weighted average molecular weight By fitting the linear equations between them, the second linear coefficients of the fit are obtained. Second coefficient term This leads to the fitted second functional relationship expression: .

[0010] Further, step S5 includes: S51: Substituting the fitted first functional relationship expression into the fitted second functional relationship expression, we obtain the functional relationship between the calorific value of natural gas and the response signal: ; S52: Use a thermal conductivity detector to collect TCD response signals of natural gas with different compositions, input the functional relationship between the calorific value of natural gas and the response signal, and output the calorific value of natural gas.

[0011] A natural gas calorific value measurement system is provided, which includes a gas supply system, a detection system and a data processing system; The gas supply system includes a carrier gas tank, a standard gas tank, and a natural gas interface. The carrier gas tank and the standard gas tank are connected to the electronic pressure controller (EPC) of the gas supply system via pipelines. The natural gas interface is connected to the pipeline between the standard gas tank and the gas supply system via a three-way valve. The detection system includes a thermal conductivity detector, and the gas supply system is connected to the thermal conductivity detector; The data processing system includes a signal amplification module and a data analysis module. The TCD response signal detected by the thermal conductivity detector is amplified by the signal amplification module and then sent to the data analysis module. The data analysis module contains a functional relationship between the calorific value of natural gas and the response signal, and outputs the measured calorific value of natural gas based on the amplified TCD response signal.

[0012] The beneficial effects of this invention are as follows: By utilizing the response signal generated by hydrocarbon molecules in a thermal conductivity detector, this invention establishes a functional relationship between the natural gas response signal and the weighted average molecular weight and calorific value of natural gas. Employing a direct sample injection measurement method, it achieves rapid and stable measurement of the calorific value of natural gas. This invention maintains high measurement accuracy and repeatability even when the composition of natural gas changes, effectively reducing the impact of gas source fluctuations on the measurement results. The natural gas calorific value measurement system designed in this invention consists of a gas supply system, a detection system, and a data processing system. It features a simple operation process, low calibration frequency, and a single analysis time of only a few seconds, meeting the requirements for continuous online operation. Compared to traditional natural gas calorific value measuring instruments, this invention significantly reduces system complexity and manufacturing costs while ensuring measurement performance. The overall procurement cost can be controlled at a low level, exhibiting good economic efficiency and engineering practicality. It is suitable for various application scenarios such as industrial sites, natural gas pipeline distribution systems, and home energy management, and has high potential for widespread application. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a natural gas calorific value measurement system.

[0014] Figure 2 The graph shows the relationship between the response signal and the weighted average molecular weight.

[0015] Figure 3 This is a graph showing the relationship between weighted average molecular weight and calorific value. Detailed Implementation

[0016] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0017] A method for measuring the calorific value of natural gas based on the principle of thermal conductivity detection includes the following steps: S1: Construct several groups of mixed gas samples mainly composed of alkanes, detect the TCD response signal of each mixed gas sample using a thermal conductivity detector, calculate the weighted average molecular weight of each mixed gas sample, and construct a linear equation between the weighted average molecular weight of the mixed gas sample and the response signal.

[0018] Step S1 specifically includes the following steps: S11: Construct several groups of mixed gas samples mainly composed of alkanes. Each group of mixed gas samples contains a different amount of alkane gas. Use a thermal conductivity detector to detect the TCD response signal of each group of mixed gas samples. S12: The TCD response signal for each alkane component is , i Number the alkane components in the gas mixture sample; based on the mole fraction of the alkane components. TCD response signal for each alkane component The response signal of the mixed gas sample is obtained by performing a weighted summation. S ; ; in, I This refers to the amount of alkane components in the mixed gas sample; S13: Based on the mole fraction of the alkane component and molecular weight Calculate the weighted average molecular weight of the mixed gas sample ; ; S14: Based on the linear relationship between the response signal and molecular weight of a single alkane component. Construct the weighted average molecular weight of the mixed gas sample With response signal S The linear equation between them: ; in,a The first linear coefficient, b This is the first coefficient term.

[0019] S2: Based on the TCD response signal and weighted average molecular weight of each mixed gas sample detected by the thermal conductivity detector, generate a graph showing the relationship between the TCD response signal and the weighted average molecular weight, and fit the linear equation between the weighted average molecular weight and the response signal to obtain the first functional relationship expression of the fit.

[0020] Step S2 specifically includes the following steps: S21: Based on the response signals of each mixed gas sample S and weighted average molecular weight M Generate a graph showing the relationship between the response signal and the weighted average molecular weight, such as... Figure 2 As shown; The main combustible components of natural gas include straight-chain alkanes such as methane, ethane, and propane. The response signals of these alkane molecules on a thermal conductivity detector (TCD) are positively correlated with the difference in thermal conductivity between the carrier gas and the alkane. Simultaneously, the thermal conductivity of alkanes is inversely proportional to the square root of their molecular weight, exhibiting an approximately linear trend with molecular weight. Combining these two relationships, it can be assumed that the TCD response signals of alkanes with low carbon number are linearly correlated with their molecular weight. For example, methane has a molecular weight of 16.04 and a relative response value of 36; ethane has a molecular weight of 30.07 and a relative response value of 51; propane has a molecular weight of 44.10 and a relative response value of 65; butane has a molecular weight of 58.12 and a relative response value of 85; pentane has a molecular weight of 72.15 and a relative response value of 105; and hexane has a molecular weight of 86.18 and a relative response value of 123. The data above shows that as the molecular weight increases, the response signal of alkanes increases in an approximately arithmetic progression. Linear fitting of these data yields a high correlation coefficient, indicating that within the range of common alkanes in natural gas, there is a certain linear correlation between the response signal and the molecular weight.

[0021] As shown in Table 1 below, this embodiment constructed natural gas with different components as mixed gas samples, and obtained response signals and data on the weighted average molecular weight and calorific value of natural gas from a large number of natural gas samples (no less than 150 groups), including the data in Table 1, to fit the first functional relationship expression and the second functional relationship expression.

[0022] Table 1 Sample Test Data

[0023] In this embodiment, helium is used as the carrier gas in the thermal conductivity detector, with the flow rate controlled at 20-30 mL / min. It should be noted that the working principle of the thermal conductivity detector relies on the difference in thermal conductivity between the carrier gas and the sample gas. Commonly used carrier gases also include hydrogen, nitrogen, or argon. This invention uses helium as an example for data acquisition and model building, mainly because helium has high thermal conductivity, good chemical inertness, and high safety. If other carrier gases are used, the absolute value of the TCD response signal will change, but as long as the carrier gas type remains consistent during calibration, the linear fitting method established in this invention will still be applicable. Users can flexibly choose according to actual gas source conditions, cost, and safety requirements.

[0024] S22: Utilizing the response signal S Weighted average molecular weight M The data points in the relationship diagram are used to calculate the weighted average molecular weight based on the least squares method. With response signal S By fitting the linear equations between them, the first linear coefficients of the fit are obtained. and the first coefficient term This leads to the first functional relationship expression of the fit: .

[0025] It should be noted that actual natural gas samples may contain trace amounts of olefins (such as ethylene and propylene), cycloalkanes, or non-hydrocarbon components such as nitrogen and carbon dioxide. These components contribute differently to the thermal conductivity signal, but since their total integral is usually less than 5%, their impact on the weighted average molecular weight of the mixed gas is relatively small. In the fitting process of this invention, the combined effect of these trace components is included in the relationship between the total response signal corresponding to the calibrated sample and the weighted average molecular weight, and is absorbed into the first linear coefficient and the first coefficient term through least-squares fitting. Therefore, it will not significantly affect the accuracy of the final calorific value measurement.

[0026] S3: The calorific value of each mixed gas sample is measured using a natural gas calorific value measuring instrument, and a weighted average molecular weight versus calorific value graph is generated, such as... Figure 3 As shown.

[0027] Straight-chain alkanes in natural gas, such as methane, ethane, propane, butane, and pentane, belong to the same homologue, differing only in their repeating CH2 units. During combustion, the C-C bonds and CH bonds in alkane molecules break and participate in oxidation reactions. With each additional CH2 unit, the number and type of newly added chemical bonds remain largely consistent, resulting in a stable increasing trend in the heat of combustion released per unit amount of substance. Therefore, within the common component range of natural gas, there is a strong linear correlation between the calorific value and molecular weight of alkane molecules.

[0028] For example, methane has a molecular weight of 16.04 and a calorific value of 37.04 MJ / m³. 3 Ethane has a molecular weight of 30.07 and a calorific value of 64.91 MJ / m³. 3 Propane has a molecular weight of 44.10 and a calorific value of 92.29 MJ / m³. 3 Butane has a molecular weight of 58.12 and a calorific value of 119.66 MJ / m³. 3 Pentane has a molecular weight of 72.15 and a calorific value of 147.04 MJ / m³. 3 Hexane has a molecular weight of 86.18 and a calorific value of 174.46 MJ / m³. 3 The data above show that the calorific value of alkanes increases approximately arithmetically with increasing molecular weight. Linear fitting of these data yields a high correlation coefficient, indicating a significant linear correlation between molecular weight and calorific value within the range of common alkanes found in natural gas.

[0029] S4: Construct a linear equation between the calorific value and the weighted average molecular weight of the mixed gas sample, and fit it to obtain the second functional relationship expression.

[0030] Step S4 specifically includes the following steps: S41: Calorific value of the mixed gas sample Calculated by weighting the calorific value of each alkane component by molar fraction; ; in, The calorific value of the alkane component; S42: The calorific value and molecular weight of a single alkane component satisfy a linear relationship. Constructing the calorific value of mixed gas samples H Weighted average molecular weight The linear equation between them: ; in, c The second linear coefficient, d This is the second coefficient term; S43: Using data points from the weighted average molecular weight versus calorific value graph, the calorific value of the mixed gas sample is determined based on the least squares method. H Weighted average molecular weight By fitting the linear equations between them, the second linear coefficients of the fit are obtained. Second coefficient term This leads to the fitted second functional relationship expression: .

[0031] S5: Substitute the fitted first functional relationship expression into the fitted second functional relationship expression to obtain the functional relationship between the calorific value of natural gas and the response signal. By collecting the TCD response signals of natural gas with different compositions, inputting them into the functional relationship between the calorific value of natural gas and the response signal, the calorific value of natural gas is output.

[0032] Step S5 specifically includes the following steps: S51: Substituting the fitted first functional relationship expression into the fitted second functional relationship expression, we obtain the functional relationship between the calorific value of natural gas and the response signal: ; S52: Use a thermal conductivity detector to collect TCD response signals of natural gas with different compositions, input the functional relationship between the calorific value of natural gas and the response signal, and output the calorific value of natural gas.

[0033] like Figure 1 As shown, a natural gas calorific value measurement system includes a gas supply system, a detection system, and a data processing system; The gas supply system includes a carrier gas tank, a standard gas tank, and a natural gas interface. The carrier gas tank and the standard gas tank are connected to the electronic pressure controller (EPC) of the gas supply system via pipelines. The natural gas interface is connected to the pipeline between the standard gas tank and the gas supply system via a three-way valve. The gas supply system provides a stable and switchable gas source for the detection system. It is a precision pneumatic control unit that connects to natural gas sample gas, standard gas, and carrier gas. It also includes a pressure regulation unit (composed of a high-precision pressure reducing valve) to stabilize the gas source pressure within the set operating range; a flow control unit (composed of an electronic pressure controller) to precisely regulate the flow rate of each gas path according to instructions from the data processing system; and a gas path switching unit (using an electrically controlled two-position three-way valve to automatically switch between sample gas and standard gas). In measurement mode, the system uses natural gas sample gas; in calibration mode, it switches to standard gas, automating the measurement and calibration process.

[0034] The detection system includes a thermal conductivity detector, and the gas supply system is connected to the thermal conductivity detector; The data processing system includes a signal amplification module and a data analysis module. The TCD response signal detected by the thermal conductivity detector is amplified by the signal amplification module and then sent to the data analysis module. The data analysis module contains a functional relationship between the calorific value of natural gas and the response signal, and outputs the measured calorific value of natural gas based on the amplified TCD response signal.

Claims

1. A method for measuring the calorific value of natural gas based on the heat conduction detection principle, characterized in that, Includes the following steps: S1: Construct several groups of mixed gas samples mainly composed of alkane, detect the TCD response signal of each mixed gas sample using a thermal conductivity detector, calculate the weighted average molecular weight of each mixed gas sample, and construct a linear equation between the weighted average molecular weight of the mixed gas sample and the response signal. S2: Based on the TCD response signal and weighted average molecular weight of each mixed gas sample detected by the thermal conductivity detector, generate a graph showing the relationship between the TCD response signal and the weighted average molecular weight, and fit the linear equation between the weighted average molecular weight and the response signal to obtain the first functional relationship expression of the fit. S3: Use a natural gas calorific value measuring instrument to detect the calorific value of each mixed gas sample and generate a weighted average molecular weight versus calorific value graph. S4: Construct a linear equation between the calorific value and the weighted average molecular weight of the mixed gas sample, and fit it to obtain the second functional relationship expression of the fit; S5: Substitute the fitted first functional relationship expression into the fitted second functional relationship expression to obtain the functional relationship between the calorific value of natural gas and the response signal. By collecting the TCD response signals of natural gas with different compositions, inputting them into the functional relationship between the calorific value of natural gas and the response signal, the calorific value of natural gas is output.

2. The method for measuring the calorific value of natural gas based on the thermal conductivity detection principle according to claim 1, characterized in that, Step S1 includes: S11: Construct several groups of mixed gas samples mainly composed of alkanes. Each group of mixed gas samples contains a different amount of alkane gas. Use a thermal conductivity detector to detect the TCD response signal of each group of mixed gas samples. S12: The TCD response signal for each alkane component is , i Number the alkane components in the gas mixture sample; based on the mole fraction of the alkane components. TCD response signal for each alkane component The response signal of the mixed gas sample is obtained by performing a weighted summation. S ; ； wherein, I is the amount of alkane components in the mixed gas sample; S13: Based on the mole fraction of the alkane component and molecular weight Calculate the weighted average molecular weight of the mixed gas sample ; ； S14: Based on the linear relationship between the response signal and molecular weight of a single alkane component. Construct the weighted average molecular weight of the mixed gas sample With response signal S The linear equation between them: ； wherein a is a first linear coefficient, b is a first coefficient term.

3. The natural gas calorific value measurement method based on the heat conduction detection principle according to claim 2, characterized in that, Step S2 includes: S21: generating a response signal for each mixed gas sample S and the weighted average molecular weight M , and generating a graph of the response signal versus the weighted average molecular weight; S22: Utilizing the response signal S Weighted average molecular weight M The data points in the relationship diagram are used to calculate the weighted average molecular weight based on the least squares method. With response signal S By fitting the linear equations between them, the first linear coefficients of the fit are obtained. and the first coefficient term This leads to the first functional relationship expression of the fit: .

4. The method for measuring the calorific value of natural gas based on the thermal conductivity detection principle according to claim 3, characterized in that, Step S4 includes: S41: Calorific value of the mixed gas sample Calculated by weighting the calorific value of each alkane component by molar fraction. ； wherein, the heating value of the alkane component; S42: The calorific value and molecular weight of a single alkane component satisfy a linear relationship. Constructing the calorific value of mixed gas samples H Weighted average molecular weight The linear equation between them: ； wherein c is a second linear coefficient, d is a second coefficient term; S43: Using data points from the weighted average molecular weight versus calorific value graph, the calorific value of the mixed gas sample is determined based on the least squares method. H Weighted average molecular weight By fitting the linear equations between them, the second linear coefficients of the fit are obtained. Second coefficient term This leads to the fitted second functional relationship expression: .

5. The natural gas calorific value measurement method based on the heat conduction detection principle according to claim 4, characterized in that, Step S5 includes: S51: Substituting the fitted first functional relationship expression into the fitted second functional relationship expression, we obtain the functional relationship between the calorific value of natural gas and the response signal: ； S52: Use a thermal conductivity detector to collect TCD response signals of natural gas with different compositions, input the functional relationship between the calorific value of natural gas and the response signal, and output the calorific value of natural gas.

6. A natural gas heating value measurement system characterized by, This includes the gas supply system, detection system, and data processing system; The gas supply system includes a carrier gas tank, a standard gas tank, and a natural gas interface. The carrier gas tank and the standard gas tank are respectively connected to the electronic pressure controller (EPC) of the gas supply system through pipelines. The natural gas interface is connected to the pipeline between the standard gas tank and the gas supply system through a three-way valve. The detection system includes a thermal conductivity detector, and the gas supply system is connected to the thermal conductivity detector. The data processing system includes a signal amplification module and a data analysis module. The TCD response signal detected by the thermal conductivity detector is amplified by the signal amplification module and then sent to the data analysis module. The data analysis module contains a functional relationship between the calorific value of natural gas and the response signal, and outputs the measured calorific value of natural gas based on the amplified TCD response signal.

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