Device and method for on-line measurement of the sulphur content of a gas in a gas pipeline

Abstract

The present application belongs to the technical field of oil and gas storage and transportation, and discloses a device and method for online measurement of gas sulfur content in a sulfur-containing gas field pipeline. The device comprises a natural gas compressor, a gas tank (variable volume or fixed volume), a temperature control refrigeration system, a computer, a pressure sensor, a temperature sensor, and multiple automatic valves. By introducing the natural gas sample in the pipeline into the gas tank, the temperature and / or volume of the sample are accurately adjusted under the control of the computer, the pressure, temperature, and volume data in two different states are obtained, the compression factor ratio of the gas is calculated, and the hydrogen sulfide concentration is indirectly determined based on the preset mapping relationship between the compression factor ratio and the hydrogen sulfide concentration. This method does not require optical or electrochemical sensitive elements, avoids the interference of field dust and moisture, has the advantages of simple structure, high reliability, and low maintenance cost, and is suitable for long-term stable online monitoring of sulfur-containing natural gas pipelines.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas storage and transportation technology, specifically relating to a device and method for online measurement of gas sulfur content in pipelines of sulfur-containing gas fields. Background Technology

[0002] During natural gas extraction and transportation, the presence of hydrogen sulfide (H2S) can cause serious corrosion problems, threatening the safe operation of pipelines and equipment. Therefore, real-time and accurate monitoring of its concentration is crucial. Currently, the detection methods for H2S content in natural gas are mainly divided into two categories: offline laboratory analysis and online monitoring, but both have their own limitations.

[0003] Traditional offline analysis methods, such as chemical titration or laboratory gas chromatography, require manual sampling and delivery to the laboratory for analysis. These methods suffer from significant time lag, cannot provide real-time data, and the sampling and transportation processes may introduce errors or alter the representativeness of the samples, making it difficult to meet the immediacy requirements of continuous pipeline safety monitoring.

[0004] To address the real-time issue, various online monitoring devices have been developed. One type is based on optical principles, such as ultraviolet fluorescence analyzers. These determine the concentration of H2S molecules by measuring their absorption or fluorescence response to specific ultraviolet light. However, the detection windows of these optical devices are easily contaminated or fogged in the dusty, humid, and potentially condensate-containing environments where pipeline natural gas is transported, leading to severe signal attenuation, baseline drift, frequent maintenance and calibration, poor long-term operational stability, and high costs for the core optical modules. Another common type of online device is the detector using electrochemical sensors. Although the initial cost is lower, these sensors suffer from short lifespans, susceptibility to interference from other gas components, or poisoning failure, resulting in insufficient reliability. They are typically used only for safety alarms rather than precise measurement. Finally, there are online gas chromatographs. While they offer high analytical accuracy, they are complex, bulky, and have extremely high purchase and maintenance costs, long single analysis cycles, and relatively slow response times.

[0005] A thorough analysis of the existing online monitoring technologies reveals that they all rely on the direct detection of specific physical or chemical properties of sulfur or H2S molecules (e.g., light absorption characteristics, electrochemical reactions, or chromatographic retention characteristics). This direct detection approach leads to several shortcomings: the high-sensitivity specialized components used for direct detection (such as optical components, specific sensors, and precision chromatographic systems) are often complex in structure, expensive, and extremely sensitive to external working environments (cleanliness, temperature, interfering components). Therefore, under the harsh and variable application conditions in oil and gas fields, reliability, stability, and economy are difficult to achieve simultaneously. Summary of the Invention

[0006] The purpose of this invention is to provide an apparatus and method for online measurement of gas sulfur content in pipelines of sulfur-containing gas fields. This invention solves the problems of existing online hydrogen sulfide detection technologies, which rely on direct detection principles such as optics and electrochemistry, and are prone to contamination, failure, instability, and high cost in harsh industrial environments, thus failing to achieve long-term reliable online monitoring.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] The device for online measurement of sulfur content in gas within a pipeline in a sulfur-containing gas field includes a natural gas compressor, a variable-volume gas tank, a temperature-controlled refrigeration system, a computer, pressure sensors, temperature sensors, and multiple automatic valves.

[0009] The natural gas compressor is connected to the main gas transmission line via a first automatic valve;

[0010] The variable volume gas box is connected to the natural gas compressor via a second automatic valve and is housed within the temperature-controlled refrigeration system, which contains the pressure sensor and temperature sensor.

[0011] The variable-capacity gas box is also connected to the main gas supply line via a third automatic valve;

[0012] The computer is communicatively connected to the natural gas compressor, variable volume gas tank, temperature control and refrigeration system, pressure sensor, temperature sensor and various automatic valves. It is used to control the entire process of sampling, adjustment, measurement and exhaust. Based on the pressure, temperature and volume values ​​of the gas in the variable volume gas tank under two different temperature-pressure states, it calculates the compressibility factor ratio of the gas under the two states, and determines the hydrogen sulfide concentration according to the preset correspondence between the compressibility factor ratio and the hydrogen sulfide concentration.

[0013] Furthermore, the temperature-controlled refrigeration system is a two-stage compression vapor refrigeration cycle system, and its refrigerant is an aqueous solution of ethylene glycol.

[0014] Furthermore, the concentration of the ethylene glycol aqueous solution is 50% to 60%.

[0015] Furthermore, the variable volume air box has an annular structure, and its volume can be adjusted between 50 mL and 500 mL.

[0016] Furthermore, the variable volume air box is made of nickel-based alloy, and its dynamic sealing mechanism uses multi-layer polytetrafluoroethylene sealing rings.

[0017] Furthermore, the polytetrafluoroethylene sealing ring has 4 to 6 layers.

[0018] The present invention also discloses a method for online measurement of gas sulfur content in a sulfur-containing gas field pipeline using the device described above, characterized by comprising the following sequential steps:

[0019] (a) Sampling steps: Open the first automatic valve and the second automatic valve, start the natural gas compressor, fill the variable volume gas tank with the natural gas sample from the gas pipeline to the first volume V1, close the third automatic valve, the second automatic valve and the first automatic valve, and stop the natural gas compressor;

[0020] (b) First state measurement step: Start the temperature control and refrigeration system, adjust the gas in the variable volume gas box to the first temperature T1 and maintain the first volume V1, and measure the first pressure P1;

[0021] (c) Second state measurement step: The gas in the variable volume gas box is adjusted to the second temperature T2 by the temperature control and refrigeration system, and the volume of the variable volume gas box is adjusted to the second volume V2, and the second pressure P2 is measured; wherein, the second temperature T2 is different from the first temperature T1;

[0022] (d) Concentration calculation steps: The computer calculates the compressibility factor ratio of the gas in the second state and the first state based on V1, P1, T1 and V2, P2, T2, and determines the hydrogen sulfide concentration in the natural gas sample according to the preset mapping relationship between the compressibility factor ratio and the hydrogen sulfide concentration.

[0023] (e) Exhaust reset procedure: restore the gas in the variable volume gas box to the ambient temperature, open the third automatic valve, the second automatic valve and the first automatic valve, adjust the volume of the variable volume gas box to the minimum, exhaust the gas back to the main gas supply line, and then close all automatic valves and equipment.

[0024] Furthermore, in step (c), the values ​​of the first temperature T1 and the second temperature T2 are such that the ratio of the compressibility factor of the natural gas sample in the first state and the second state is more sensitive to changes in hydrogen sulfide concentration than a preset threshold.

[0025] Furthermore, in step (d), the compression factor ratio is calculated using the following formula:

[0026] ;

[0027] in, The compression factor in the first state. The compression factor in the second state. The pressure in the first state, The volume in the first state. The absolute temperature in the first state. The pressure in the second state, The volume in the second state. This represents the absolute temperature in the second state.

[0028] Furthermore, in step (a), before sampling, the volume of the variable-volume gas box is at its minimum value; in step (e), after exhaust, the volume of the variable-volume gas box returns to the minimum value.

[0029] On the other hand, the present invention also discloses another device for online measurement of gas sulfur content in a sulfur-containing gas field pipeline, including a natural gas compressor, a fixed volume gas box, a temperature control and refrigeration system, a computer, a pressure sensor, a temperature sensor and multiple automatic valves, wherein the natural gas compressor is connected to the main gas transmission pipeline through a first automatic valve;

[0030] The fixed-volume gas tank is connected to the natural gas compressor via a second automatic valve and is housed within the temperature-controlled refrigeration system, which contains the pressure sensor and temperature sensor.

[0031] The fixed-volume gas box is also connected to the main gas supply line via a third automatic valve;

[0032] The computer is communicatively connected to the natural gas compressor, fixed-volume gas tank, temperature control and refrigeration system, pressure sensor, temperature sensor and each automatic valve. It is used to control the entire process of sampling, adjustment, measurement and exhaust. Based on the pressure and temperature values ​​of the gas in the fixed-volume gas tank at two different temperature states, it calculates the compressibility factor ratio of the gas at the two states and determines the hydrogen sulfide concentration according to the preset correspondence between the compressibility factor ratio and the hydrogen sulfide concentration.

[0033] The volume of the fixed-volume gas box is fixed during manufacturing and cannot be adjusted during use.

[0034] Furthermore, the temperature control refrigeration system is a two-stage compression vapor refrigeration cycle system, with ethylene glycol aqueous solution as the refrigerant, an effective temperature control range of -40 degrees Celsius to 50 degrees Celsius, and a temperature control accuracy of not less than ±0.1 degrees Celsius.

[0035] Furthermore, the volume of the fixed-volume gas box is any fixed value between 50 ml and 500 ml.

[0036] Furthermore, the computer is configured to control the temperature control and refrigeration system to sequentially bring the gas in the fixed-volume gas tank to at least two different predetermined measurement temperature points, and to maintain a constant volume of the fixed-volume gas tank at each predetermined measurement temperature point, measuring the corresponding pressure and temperature values; the at least two different predetermined measurement temperature points are optimized based on the concentration range of the main components of the background natural gas in the target gas field, so that the compressibility factor ratio calculated from the predetermined measurement temperature points and the corresponding pressure values ​​has a maximum sensitivity to changes in hydrogen sulfide concentration or exceeds a preset sensitivity threshold.

[0037] The testing method is as follows, including the following sequential steps:

[0038] (a) Sampling procedure: Open the first and second automatic valves, start the natural gas compressor, and fill the fixed-volume gas tank with natural gas samples from the main gas pipeline to a fixed volume. Then, close the third automatic valve, the second automatic valve, and the first automatic valve to stop the natural gas compressor;

[0039] (b) First state measurement procedure: Start the temperature control and cooling system to adjust the gas in the fixed volume gas box to the first predetermined measurement temperature point. And maintain a fixed volume The pressure remains unchanged, and the first pressure is measured. ;

[0040] (c) Second state measurement step: Adjust the gas in the fixed volume gas box to the second predetermined measurement temperature point through the temperature control and refrigeration system. Maintain a fixed volume The second pressure was measured without change. Among them, the first predetermined measurement temperature point With the second predetermined measurement temperature point different;

[0041] (d) Concentration calculation steps: The computer calculates the concentration based on a fixed volume. First pressure First predetermined measurement temperature point And the second pressure Second predetermined measurement temperature point Calculate the ratio of the compressibility factor of the gas in the second state to that in the first state. Based on the preset mapping relationship between the optimized compressibility factor ratio and hydrogen sulfide concentration, the hydrogen sulfide concentration in the natural gas sample is determined. ;

[0042] (e) Exhaust reset procedure: restore the gas in the fixed volume gas tank to the ambient temperature, open the third automatic valve, the second automatic valve and the first automatic valve, start the natural gas compressor, exhaust the gas in the fixed volume gas tank back to the main gas pipeline, and then close all automatic valves and equipment.

[0043] Furthermore, the first predetermined temperature measurement point Second predetermined measurement temperature point The following optimization selection method is used to determine the selection in advance:

[0044] Step 1: Based on the concentration range of the main components of the background natural gas in the target gas field, determine the concentration variation range of each component of the background natural gas, and select the benchmark value vector of each component concentration of the background natural gas. ;

[0045] Step 2: Within the effective temperature control range of the temperature-controlled refrigeration system, select multiple candidate temperature points to form a candidate temperature point set. ;

[0046] Step 3: For the set of candidate temperature points Each pair of temperature points in ,in Calculate the vector of concentration benchmark values ​​for each component of the background natural gas. Below, compression factor ratio Regarding hydrogen sulfide concentration The absolute value of the partial derivative over the entire target measurement concentration range The integral value on The partial derivatives are calculated using the numerical difference method, with a difference step size of [missing information]. Taking 0.1%, the Simpson numerical integration method was used to divide the concentration range into 150 equal intervals for calculation;

[0047] Step 4: Select the integral value The largest temperature pair is taken as the optimal temperature pair and denoted as the first predetermined measurement temperature point. Second predetermined measurement temperature point .

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] This invention abandons the traditional approach of directly detecting sulfur or H2S molecules, creatively transforming sulfur content measurement into a physical measurement of the compressibility factor ratio of a natural gas mixture. By precisely altering the temperature and pressure of the sample gas using a variable-volume gas chamber and a temperature-controlled refrigeration system, the H2S concentration is inferred from the compressibility factor ratio calculated based on these two sets of state parameters. This method fundamentally avoids reliance on complex optical devices, consumable electrochemical sensors, or precision chromatographic systems, making the entire measurement system unaffected by on-site dust, humidity, and complex components. Furthermore, the completely enclosed sampling and measurement process prevents the gas sample from contacting the external environment, avoiding issues such as optical window contamination and sensor poisoning, significantly improving long-term operational stability and reliability in harsh industrial environments.

[0050] This invention consists of a natural gas compressor, a variable-volume gas tank (or a fixed-volume gas tank), a conventional pressure / temperature sensor, and a standard refrigeration unit, eliminating the need for expensive dedicated analytical modules. The overall structure is simple, easy to manufacture, and easy to integrate and install. By avoiding the periodic replacement of high-value consumables (such as chromatographic columns, special light sources, and sensor probes), it significantly reduces the equipment's long-term maintenance costs and total life-cycle operating expenses, resulting in substantial economic benefits.

[0051] This invention automates the entire process of sampling, condition adjustment, measurement, calculation, and exhaust by coordinating the operation of a natural gas compressor, various automatic valves, and a variable-volume gas tank (or a fixed-volume gas tank) under computer control. The entire measurement cycle can be completed without interrupting the main pipeline's gas transmission and can be performed cyclically at a set frequency, achieving true online, continuous, and real-time monitoring. This provides timely and accurate data support for pipeline corrosion early warning and safe production.

[0052] This invention optimizes the measurement temperature point, making the compressibility factor of the mixed gas extremely sensitive to changes in H2S concentration, thus ensuring the accuracy of the indirect measurement method. The annular design of the variable-volume gas chamber and the precision volume adjustment mechanism (or the integrated design of a fixed-volume gas chamber), combined with high-precision pressure and temperature sensors, ensure the accuracy of state parameter measurements, providing a reliable basis for the final concentration calculation. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0054] Figure 1 This is a schematic diagram of the device structure described in Embodiment 1 of the present invention.

[0055] Figure 2 This is a graph showing the compressibility factor of natural gas containing different proportions of H2S.

[0056] Figure 3 It represents the change in the ratio of the compressibility factor of natural gas containing different proportions of H2S at -20℃ and 0℃.

[0057] Figure label:

[0058] 1 Natural gas compressor, 2 Variable volume gas tank, 3 Temperature control refrigeration system, 4 Computer, 5 Pressure sensor, 6 Temperature sensor, 7 First automatic valve, 8 Second automatic valve, 9 Third automatic valve. Detailed Implementation

[0059] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0060] In the description of the embodiments of the present invention, it should be understood that the terms "length", "vertical", "horizontal", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0061] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "multiple" means two or more, unless otherwise explicitly specified.

[0062] In the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0063] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above" and "over" the second feature include the first feature being directly above or diagonally above the second feature, or simply indicating that the first feature is at a higher horizontal level than the second feature. "Below" and "below" the second feature include the first feature being directly below or diagonally below the second feature, or simply indicating that the first feature is at a lower horizontal level than the second feature.

[0064] The following disclosure provides many different implementations or examples for carrying out different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the embodiments of the present invention. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of the present invention; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0065] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0066] Example 1: This example is based on the real gas law. For a fixed mass of the same gas, its state satisfies the following relationship: ,in For pressure, For volume, The compression factor, The number of moles. The gas constant is This refers to absolute temperature. Within a closed system ( (Unchanged), the ratio of the compressibility factors of two different states (state 1 and state 2) can be calculated by the following formula:

[0067] ;

[0068] In this context, subscripts 1 and 2 represent state 1 and state 2, respectively.

[0069] Compressibility factor of gas mixture It is related to the properties and concentrations of each component, especially highly correlated with the concentration of the strongly polar gas H2S. Therefore, by accurately measuring the concentrations under both states... , , Calculate From this, the H2S concentration can be deduced.

[0070] Establishment of the mapping relationship between compressibility factor ratio and H2S concentration:

[0071] The preset compressibility factor ratio and its correspondence with hydrogen sulfide concentration are obtained in advance and stored in the computer through any of the following methods:

[0072] (1) Experimental calibration method: Prepare multiple standard natural gas samples with known hydrogen sulfide concentrations (e.g., H2S concentrations of 0%, 1%, 3%, 5%, and 10%, with the remaining components being methane, ethane, carbon dioxide, etc., and their proportions simulating the composition of an actual gas field). Using this device or a PVT experimental system of equivalent precision, measure the pressure values ​​of each sample at the selected first temperature T1, first volume V1, and second temperature T2, second volume V2. Calculate the compressibility factor ratio according to the above formula, and establish a database or fitting curve of the concentration-ratio correspondence.

[0073] (2) Thermodynamic model calculation method: Based on the main component range of natural gas in the target gas field (such as CH4: 85-95%, CO2: 1-5%, C2H6: 0.5-3%, H2S: 0.1-10%), the compressibility factor under different H2S concentrations in the T1, V1 and T2, V2 states is calculated and the ratio is calculated to form a mapping table.

[0074] For illustrative purposes, a simplified mapping example is given below (e.g., background gas is 95% CH4 and 5% CO2, measurement conditions are T1=0℃, V1=100mL, T2=-20℃, V2=100mL), as shown in Table 1:

[0075] Table 1:

[0076]

[0077] See Figures 1-3 This embodiment discloses an online device for measuring the sulfur content of gas in a natural gas pipeline in a sulfur-containing gas field. The natural gas compressor 1 is connected to the main gas pipeline via a first automatic valve 7. The variable volume gas tank 2 is connected to the natural gas compressor 1 via a second automatic valve 8 and is housed within the temperature control and refrigeration system 3. The pressure sensor 5 and temperature sensor 6 are installed inside the variable volume gas tank 2, and it is connected to the main gas pipeline via a third automatic valve 9. The computer 4 is communicatively connected to the natural gas compressor 1, the variable volume gas tank 2, the temperature control and refrigeration system 3, the pressure sensor 5, the temperature sensor 6, the first automatic valve 7, the second automatic valve 8, and the third automatic valve 9.

[0078] The temperature-controlled refrigeration system 3 uses a 55% ethylene glycol aqueous solution as the refrigerant. The volumetric variable-capacity gas box 2 has a volume adjustment range of 50 mL to 500 mL, and in this embodiment, its initial minimum volume is 50 mL. The volumetric variable-capacity gas box 2 is made of nickel-based alloy, and its dynamic sealing mechanism uses 5 layers of polytetrafluoroethylene sealing rings.

[0079] Based on the above-mentioned device, this embodiment also proposes a method for online measurement of gas sulfur content in natural gas pipelines of sulfur-containing gas fields, the method comprising the following steps:

[0080] S1: Initial Setup. Keep the natural gas compressor 1 and temperature-controlled refrigeration system 3 off, and keep the first automatic valve 7, second automatic valve 8, and third automatic valve 9 closed. Adjust the volume of the variable-volume gas tank 2 to the minimum value of 50 mL. Open the third automatic valve 9 to balance the internal pressure of the variable-volume gas tank 2 with the main gas pipeline pressure (in this example, the main pipeline pressure is 10.0 MPa), and then close the third automatic valve 9. At this time, the pressure inside the variable-volume gas tank 2 is approximately 10.0 MPa, and the temperature is ambient temperature of 20°C (293.15 K).

[0081] S2: Sampling Procedure. Sequentially open the first automatic valve 7 and the second automatic valve 8, start the natural gas compressor 1, and fill the variable-volume gas tank 2 with natural gas. Simultaneously, increase the volume of the variable-volume gas tank 2 from 50 mL to a first volume V1 = 100 mL. Once the volume reaches 100 mL and the pressure stabilizes, close the second automatic valve 8 and the first automatic valve 7, and stop the natural gas compressor 1. At this point, the variable-volume gas tank 2 contains a sealed natural gas sample, with a pressure slightly higher than the main pipeline pressure, denoted as P_sample (e.g., 10.2 MPa).

[0082] S3: First-state measurement procedure. Start the temperature-controlled cooling system 3 to cool the gas in the variable-volume gas tank 2 to the first temperature T1 = 0℃ (273.15 K), while maintaining the volume V1 = 100 mL. After the temperature stabilizes, measure the first pressure P1 = 9.45 MPa and the first temperature T1 = 273.15 K using the pressure sensor 5 and temperature sensor 6.

[0083] S4: Second State Measurement Step. Continue adjusting the temperature control and refrigeration system 3 to further cool the gas in the variable volume gas tank 2 to the second temperature T2 = -20℃ (253.15 K). Simultaneously, adjust the volume of the variable volume gas tank 2 from V1 = 100 mL to the second volume V2 = 90 mL. After the temperature and volume stabilize, measure the second pressure P2 = 9.20 MPa and the second temperature T2 = 253.15 K.

[0084] S5: Concentration Calculation Steps. Computer 4 receives the above measured values: V1 = 100 mL, P1 = 9.45 MPa, T1 = 273.15 K, V2 = 90 mL, P2 = 9.20 MPa, T2 = 253.15 K. The compressibility factor ratio is calculated according to the formula:

[0085] ;

[0086] in, The compression factor in the first state. The compression factor in the second state. The pressure in the first state, The volume in the first state. The absolute temperature in the first state. The pressure in the second state, The volume in the second state. This represents the absolute temperature in the second state.

[0087] S6: Exhaust Reset Procedure. Control the temperature-controlled refrigeration system 3 to stop refrigeration, allowing the gas in the variable-volume gas tank 2 to naturally return to ambient temperature (approximately 20°C). Then, sequentially open the third automatic valve 9, the second automatic valve 8, and the first automatic valve 7. Start the natural gas compressor 1, adjusting the volume of the variable-volume gas tank 2 from 90mL to the minimum value of 50mL, venting the gas back to the main gas pipeline. After exhausting, close the first automatic valve 7, the second automatic valve 8, and the third automatic valve 9, stopping the natural gas compressor 1 and the temperature-controlled refrigeration system 3. The system returns to its initial preparation state, awaiting the next measurement cycle.

[0088] Example 2: This example is an optimization based on Example 1, specifically addressing the issues of mechanical complexity and unoptimized temperature selection in the variable volume air box 2.

[0089] 2.1 The device is optimized as follows:

[0090] The variable-volume gas box 2 in Example 1 is replaced with a fixed-volume gas box. The volume of the fixed-volume gas box is determined to be 200.0 ml during manufacturing, with a manufacturing tolerance of ±0.1 ml, and the volume cannot be adjusted during use.

[0091] The fixed-volume gas tank is manufactured using a nickel-based alloy through a one-piece molding process, with a mirror-polished inner wall and no moving parts or dynamic sealing mechanisms. The fixed-volume gas tank is also housed within the temperature-controlled refrigeration system 3, connected to the natural gas compressor 1 via the second automatic valve 8, and connected to the main gas pipeline via the third automatic valve 9.

[0092] The temperature control and refrigeration system 3 adopts an improved two-stage compression vapor refrigeration cycle system, using a 55% ethylene glycol aqueous solution as the refrigerant. The effective temperature control range is extended to -35°C to 50°C, with a temperature control accuracy of ±0.05°C within the -30°C to 30°C range. The control program of the computer 4 has been modified accordingly, eliminating the volume regulation control module and adding a temperature optimization selection module and a high-precision temperature control module.

[0093] 2.2 Temperature Optimization Selection Process:

[0094] In this embodiment, the first predetermined measurement temperature point T1_opt and the second predetermined measurement temperature point T2_opt are predetermined through the following detailed optimization selection method, which is completed before the device is put into use:

[0095] Step 1: Determining the range of natural gas components:

[0096] For a high-sulfur gas field in northeastern Sichuan, the concentration range of the main components of the background natural gas was determined as follows:

[0097] Methane (CH4) concentration range: 85% to 92%, with a baseline value of 88.5%;

[0098] Carbon dioxide (CO2) concentration range: 3% to 7%, with a baseline of 5.0%;

[0099] Ethane (C2H6) concentration range: 1.5% to 3.5%, with a baseline value of 2.5%;

[0100] Nitrogen (N2) concentration range: 2% to 5%, with a baseline value of 3.5%;

[0101] Concentration range of other heavy hydrocarbon components (C3⁺): 0% to 0.5%, with a baseline value of 0.5%.

[0102] The baseline vector of the concentrations of each component in the background natural gas is denoted as:

[0103] ; where superscript Indicates transpose. The reference value for methane concentration. A baseline value representing carbon dioxide concentration. The reference value for ethane concentration. The reference value for nitrogen concentration. The reference value indicates the concentration of other heavy hydrocarbon components.

[0104] Step 2, Selection of candidate temperature points:

[0105] The effective temperature control range of the temperature-controlled refrigeration system 3 is -35 degrees Celsius to 50 degrees Celsius. A set of candidate temperature points is selected at 5-degree Celsius intervals. The unit is Celsius. In thermodynamic calculations, it needs to be converted to absolute temperature. The conversion formula is: ,in Represents absolute temperature. It indicates the temperature in Celsius.

[0106] Step 3, Sensitivity integral value calculation:

[0107] The target measurement range for hydrogen sulfide concentration is: to For the candidate temperature point set Each pair of temperature points in ,in Calculate the sensitivity integral value :

[0108] ;

[0109] in:

[0110] Indicates that the background natural gas composition is The concentration of hydrogen sulfide is At that time, temperature The compression factor below With temperature The compression factor below The ratio, i.e. ;

[0111] For the mixed gas at temperature The compressibility factor under the given conditions is obtained by calculating the Peng-Robinson equation of state.

[0112] Indicates the ratio of compression factor Regarding hydrogen sulfide concentration The partial derivatives;

[0113] The partial derivatives are calculated using the numerical difference method: ,Pick ;

[0114] The integral was calculated using Simpson's numerical integration method, dividing the concentration range... The calculation is performed by dividing the data into 150 equal intervals.

[0115] Step 4, Optimal Temperature Pair Selection:

[0116] Calculate the sensitivity integral value for all temperature pairs. Find out The temperature pair with the highest value is selected as the optimal temperature pair. The calculation results are shown in Table 2 below (selected high-sensitivity region):

[0117] Table 2:

[0118]

[0119] As can be seen from the table above, temperature has an effect on... The sensitivity integral value is the largest, at 0.04321. Therefore, the optimal temperature pair is determined as follows:

[0120] First predetermined temperature measurement point: ;

[0121] Second predetermined measurement temperature point: ;

[0122] Step 5: Optimize the establishment of mapping relationships;

[0123] Use the optimal temperature and background natural gas component concentration benchmark vector The optimal compressibility factor ratio was calculated based on the Peng-Robinson equation of state when the hydrogen sulfide concentration varied from 0% to 15%. Establish optimized mapping relationship table 3:

[0124] Table 3:

[0125]

[0126] The optimized mapping table is pre-stored in computer 4.

[0127] 2.3 Online Measurement Implementation Process:

[0128] S1, Initial state preparation:

[0129] Keep the natural gas compressor 1 and the temperature control refrigeration system 3 in the off state, and keep the first automatic valve 7, the second automatic valve 8, and the third automatic valve 9 in the off state. The volume of the fixed-volume gas tank is a fixed value. milliliters.

[0130] S2, Sampling steps:

[0131] The first automatic valve 7 and the second automatic valve 8 are opened sequentially to start the natural gas compressor 1 and fill the fixed-volume gas tank with natural gas. Once the pressure in the fixed-volume gas tank is balanced with the pressure of the main gas pipeline (10.0 MPa in this example), the second automatic valve 8 and the first automatic valve 7 are closed, stopping the natural gas compressor 1. At this point, the fixed-volume gas tank contains a sealed sample of 200.0 ml of natural gas, with an initial pressure of... Megapascals, initial temperature Kelvin (ambient temperature 20 degrees Celsius).

[0132] S3, First-state measurement steps:

[0133] The temperature control and cooling system 3 is activated to precisely adjust the gas in the fixed-volume gas box to the first predetermined measurement temperature point. Kelvin (30.0 degrees Celsius). The temperature control process lasted approximately 3 minutes. After the temperature stabilized within the range of 303.15 ± 0.05 Kelvin, the readings were measured using pressure sensor 5 and temperature sensor 6.

[0134] First pressure Megapascal

[0135] First temperature Kelvin

[0136] S4, Second State Measurement Step:

[0137] Adjust the temperature control and refrigeration system 3 to precisely regulate the gas in the fixed-volume gas box to the second predetermined measurement temperature point. Kelvin (-30.0 degrees Celsius). The temperature control process lasted approximately 5 minutes. After the temperature stabilized within the range of 243.15 ± 0.05 Kelvin, the following was measured:

[0138] Second pressure Megapascal;

[0139] Second temperature Kelvin;

[0140] S5, Concentration Calculation Steps:

[0141] Computer 4 receives the above measurement values:

[0142] Fixed volume milliliters, first pressure Megapascals, the first temperature Kelvin, Second Pressure Megapascals, the second temperature Kelvin.

[0143] Calculate the optimized compressibility factor ratio according to the formula for compressibility factor ratio under a fixed volume. : in, As the primary pressure, The first temperature, As the second pressure, This is the second temperature.

[0144] Substitute the values: Computer 4 queries a pre-stored optimized mapping table and calculates the hydrogen sulfide concentration using linear interpolation. : when At that time, it is between 1.0687 in the optimized mapping table (corresponding to...) ) and 1.1026 (corresponding to )between.

[0145] The interpolation calculation formula is:

[0146] ;

[0147] in, To determine the concentration of hydrogen sulfide, For the lower hydrogen sulfide concentration in the mapping table, The higher hydrogen sulfide concentration in the mapping table To calculate the optimized compression factor ratio, for The corresponding optimized compression factor ratio, for The corresponding optimized compression factor ratio.

[0148] For a lower hydrogen sulfide concentration, This represents the optimized compressibility factor ratio corresponding to a lower hydrogen sulfide concentration. For a high concentration of hydrogen sulfide, This represents the optimized compression factor ratio corresponding to higher hydrogen sulfide concentrations.

[0149] Substitute into the calculation: Therefore, the concentration of hydrogen sulfide in the natural gas sample was determined to be 2.74% (rounded to two decimal places).

[0150] S6, Exhaust Reset Procedure:

[0151] The temperature-controlled refrigeration system 3 stops cooling, allowing the gas in the fixed-volume gas tank to naturally return to ambient temperature (approximately 293.15 Kelvin). Then, the third automatic valve 9, the second automatic valve 8, and the first automatic valve 7 are opened sequentially. The natural gas compressor 1 is started to vent the gas in the fixed-volume gas tank back to the main gas pipeline. After venting is complete, the first automatic valve 7, the second automatic valve 8, and the third automatic valve 9 are closed, stopping the natural gas compressor 1 and the temperature-controlled refrigeration system 3. The system returns to its initial preparation state, awaiting the next measurement cycle.

[0152] In Example 1, the dynamic sealing mechanism (multi-layer PTFE sealing ring) of the variable-volume gas box 2 is susceptible to wear and leakage under high pressure and frequent expansion / contraction conditions, requiring regular maintenance and replacement, which affects the long-term operational reliability of the device. The volume adjustment process introduces volume measurement errors, and the coupled operation of temperature and volume changes increases control complexity. Unoptimized temperature selection results in suboptimal measurement sensitivity, limiting further improvement in hydrogen sulfide concentration detection accuracy. Simultaneous adjustment of temperature and volume increases the time required for a single measurement and reduces the frequency of online monitoring.

[0153] This embodiment uses a fixed-volume air box, completely eliminating the dynamic sealing mechanism and removing any moving or wearing parts, thus greatly simplifying the mechanical structure of the device. Experimental data shows that after 1000 continuous measurement cycles, the failure rate of the device in this embodiment is 0, while the leakage failure rate due to sealing ring wear in Embodiment 1 is 3.2%.

[0154] The volume of the fixed-volume air box is calibrated during manufacturing, with a calibration accuracy of ±0.05%, while the repeatability of the volume adjustment mechanism in Example 1 is ±0.5%, reducing the volume measurement error by an order of magnitude.

[0155] This embodiment optimizes the selection of the first predetermined measurement temperature point. =30℃ and the second predetermined measurement temperature point At -30°C, the compressibility factor ratio showed a sensitivity of 0.00346 / % to hydrogen sulfide concentration, while in Example 1, the sensitivity of temperature to (0°C, -20°C) was 0.00182 / %, representing a 90.1% increase in sensitivity.

[0156] 2.5 Comparative Experimental Data:

[0157] To verify the technical effectiveness of this embodiment, under the same experimental conditions, the measurement performance results of this embodiment (fixed volume + temperature optimization) and Embodiment 1 (variable volume) are compared as shown in Table 4:

[0158] Table 4:

[0159]

[0160] The comparative data above fully demonstrates that this embodiment has achieved significant progress in measurement accuracy, reliability, efficiency, and cost through two improvements: a fixed-volume gas chamber and optimized temperature selection.

[0161] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0162] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for online measurement of sulfur content in gas within a sulfur-containing gas field pipeline, comprising a natural gas compressor, a variable-volume gas tank, a temperature-controlled refrigeration system, a computer, a pressure sensor, a temperature sensor, and multiple automatic valves, characterized in that: The natural gas compressor is connected to the main gas transmission line via a first automatic valve; The variable volume gas box is connected to the natural gas compressor via a second automatic valve and is housed within the temperature-controlled refrigeration system, which contains the pressure sensor and temperature sensor. The variable-capacity gas box is also connected to the main gas supply line via a third automatic valve; The computer is communicatively connected to the natural gas compressor, variable volume gas tank, temperature control and refrigeration system, pressure sensor, temperature sensor and various automatic valves. It is used to control the entire process of sampling, adjustment, measurement and exhaust. Based on the pressure, temperature and volume values ​​of the gas in the variable volume gas tank under two different temperature-pressure states, it calculates the compressibility factor ratio of the gas under the two states, and determines the hydrogen sulfide concentration according to the preset correspondence between the compressibility factor ratio and the hydrogen sulfide concentration.

2. The device for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 1, characterized in that, The temperature-controlled refrigeration system is a two-stage compression vapor refrigeration cycle system, and the refrigerant is an aqueous solution of ethylene glycol.

3. The device for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 2, characterized in that, The concentration of the ethylene glycol aqueous solution is 50% to 60%.

4. The device for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 1, characterized in that, The variable volume air box has an annular structure, and its volume can be adjusted between 50 mL and 500 mL.

5. The device for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 1 or 4, characterized in that, The variable volume air box is made of nickel-based alloy, and the dynamic sealing mechanism uses multi-layer polytetrafluoroethylene sealing rings.

6. The device for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 5, characterized in that, The polytetrafluoroethylene sealing ring has 4 to 6 layers.

7. A method for online measurement of gas sulfur content in a sulfur-containing gas field pipeline using the apparatus described in any one of claims 1 to 6, characterized in that, Includes the following sequential steps: (a) Sampling steps: Open the first automatic valve and the second automatic valve, start the natural gas compressor, fill the variable volume gas tank with the natural gas sample from the gas pipeline to the first volume V1, close the third automatic valve, the second automatic valve and the first automatic valve, and stop the natural gas compressor; (b) First state measurement step: Start the temperature control and refrigeration system, adjust the gas in the variable volume gas box to the first temperature T1 and maintain the first volume V1, and measure the first pressure P1; (c) Second state measurement step: The gas in the variable volume gas box is adjusted to the second temperature T2 by the temperature control and refrigeration system, and the volume of the variable volume gas box is adjusted to the second volume V2, and the second pressure P2 is measured; wherein, the second temperature T2 is different from the first temperature T1; (d) Concentration calculation steps: The computer calculates the compressibility factor ratio of the gas in the second state and the first state based on V1, P1, T1 and V2, P2, T2, and determines the hydrogen sulfide concentration in the natural gas sample according to the preset mapping relationship between the compressibility factor ratio and the hydrogen sulfide concentration. (e) Exhaust reset procedure: restore the gas in the variable volume gas box to the ambient temperature, open the third automatic valve, the second automatic valve and the first automatic valve, adjust the volume of the variable volume gas box to the minimum, exhaust the gas back to the main gas supply line, and then close all automatic valves and equipment.

8. The method for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 7, characterized in that, In step (c), the values ​​of the first temperature T1 and the second temperature T2 are such that the ratio of the compressibility factor of the natural gas sample in the first state and the second state is more sensitive to changes in hydrogen sulfide concentration than a preset threshold.

9. The method for online measurement of gas sulfur content in a sulfur-containing gas field pipeline according to claim 7, characterized in that, In step (d), the compression factor ratio is calculated using the following formula: ； in, The compression factor in the first state. The compression factor in the second state. The pressure in the first state, The volume in the first state. The absolute temperature in the first state. The pressure in the second state, The volume in the second state. This represents the absolute temperature in the second state.

10. A device for online measurement of sulfur content in gas within a sulfur-containing gas field pipeline, comprising a natural gas compressor, a fixed-volume gas tank, a temperature-controlled refrigeration system, a computer, a pressure sensor, a temperature sensor, and multiple automatic valves, characterized in that: The natural gas compressor is connected to the main gas transmission line via a first automatic valve; The fixed-volume gas tank is connected to the natural gas compressor via a second automatic valve and is housed within the temperature-controlled refrigeration system, which contains the pressure sensor and temperature sensor. The fixed-volume gas box is also connected to the main gas supply line via a third automatic valve; The computer is communicatively connected to the natural gas compressor, fixed-volume gas tank, temperature control and refrigeration system, pressure sensor, temperature sensor and each automatic valve. It is used to control the entire process of sampling, adjustment, measurement and exhaust. Based on the pressure and temperature values ​​of the gas in the fixed-volume gas tank at two different temperature states, it calculates the compressibility factor ratio of the gas at the two states and determines the hydrogen sulfide concentration according to the preset correspondence between the compressibility factor ratio and the hydrogen sulfide concentration. The volume of the fixed-volume gas box is fixed during manufacturing and cannot be adjusted during use.

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