A method for testing total sulfur content of natural gas

Abstract

The present application relates to a kind of natural gas total sulfur content test method, belong to natural gas sulfur content detection technical field.The natural gas total sulfur content test method of the present application, by setting measurement signal threshold value, and the result of real-time detection is compared with measurement signal threshold value, and then according to the comparison result to the dilution ratio is adjusted, so that measurement signal is controlled in threshold value, realize the detection of different total sulfur concentration of the sample gas to be measured by ultraviolet fluorescence detector, improve the detection range of ultraviolet fluorescence detector.

Description

Technical Field

[0001] This invention relates to a method for testing the total sulfur content of natural gas, belonging to the field of natural gas sulfur content detection technology. Background Technology

[0002] In recent years, with the adjustment and optimization of my country's energy structure, natural gas, as a clean energy source, has gradually replaced fossil fuels such as coal and oil due to its advantages of being green, environmentally friendly, economical, safe, and reliable. However, sulfides in natural gas can adversely affect the safety of its transportation, storage, and use, as well as the environment, for example, by corroding equipment, polluting the environment, and harming human health. Therefore, the sulfur content of natural gas is an essential item in natural gas testing. The national standard GB / T17820 clearly specifies the total sulfur index for various types of natural gas. The national standard GB / T11060.8, "Determination of Sulfur Compounds in Natural Gas - Part 8: Determination of Total Sulfur by Ultraviolet Fluorescence Spectrophotometry," specifies the testing and analysis apparatus and methods for sulfur content in natural gas. The sample gas is taken from the process pipeline through a natural gas sampling probe, where it undergoes primary filtration and pressure reduction. It then enters a high-temperature pyrolysis furnace via the sampling pipeline. Simultaneously, combustion gas (oxygen-containing gas, such as air or oxygen, with an oxygen content sufficient to ensure complete conversion of sulfur compounds in the natural gas to SO2, plus an additional 6%) and dilution gas (oxygen-free inert gas, such as nitrogen or argon) are also fed into the high-temperature pyrolysis furnace. Inside the furnace, the sample gas (natural gas process pipeline gas), combustion gas (oxygen-containing gas, such as air or oxygen), and dilution gas (oxygen-free inert gas, such as nitrogen or argon) are combusted at a fixed flow rate ratio. Under sufficient oxygen conditions, all sulfur-containing substances in the sample gas are converted to SO2, and hydrocarbons are converted to CO2 and H2O. The gas after combustion enters the drying tube from the outlet of the high-temperature pyrolysis furnace for drying and dehydration. The dehydrated gas then enters the ultraviolet fluorescence detection chamber of the analyzer. SO2 in the gas is excited to form SO2 under ultraviolet light irradiation. When SO2 molecules return from the excited state to the ground state, they release fluorescence. The released fluorescence is detected by the ultraviolet fluorescence detector. The sulfur content in the sample gas can be determined based on the signal intensity (voltage signal, i.e., V_measured) detected by the ultraviolet fluorescence detector.

[0003] However, in the above testing and analysis methods, the flow ratio of the sample gas, combustion gas, and dilution gas is fixed. Under standard operating conditions, the total sulfur concentration of the sample gas is generally around 20 ppm. Therefore, conventional ultraviolet fluorescence detectors can only detect a total sulfur concentration of around 20 ppm. When the total sulfur concentration of the sample gas is too high (e.g., greater than 300 ppm), because the flow ratio of the sample gas, combustion gas, and dilution gas is fixed, conventional ultraviolet fluorescence detectors cannot detect the total sulfur concentration in the gas. Summary of the Invention

[0004] The purpose of this invention is to provide a method for testing the total sulfur content of natural gas, which can solve the problem of limited monitoring range in current methods for testing the sulfur content of natural gas.

[0005] To achieve the above objectives, the technical solution adopted by the natural gas total sulfur content testing method of the present invention is as follows:

[0006] A method for testing the total sulfur content of natural gas includes the following steps:

[0007] (1) Based on the zero point and range of the measurement signal of the ultraviolet fluorescence detector, set the measurement signal threshold for adjusting the dilution ratio;

[0008] (2) Mix the sample gas, combustion-supporting gas and diluent gas according to the initially set dilution ratio and then perform ultraviolet fluorescence detection. Based on the comparison between the detection results and the measurement signal threshold, adjust the initially set dilution ratio until the detection results are within the measurement signal threshold determined in step (1).

[0009] (3) Using the adjusted dilution ratio and detection results from step (2), determine the total sulfur content of the sample gas to be tested.

[0010] The natural gas total sulfur content testing method of the present invention sets a measurement signal threshold, compares the real-time detection result with the measurement signal threshold, and then adjusts the dilution ratio according to the comparison result to keep the measurement signal within the threshold, thereby enabling the ultraviolet fluorescence detector to detect sample gas with different total sulfur concentrations and improving the detection range of the ultraviolet fluorescence detector.

[0011] Preferably, the lower threshold is greater than the zero point of the measurement signal and less than the minimum value corresponding to meeting the measurement signal-to-noise ratio requirement, and the upper threshold is less than the measurement signal range of the ultraviolet fluorescence detector.

[0012] Preferably, the dilution ratio is calculated using the following formula: Dilution ratio = q 样 / Q 总 , where q 稀 Q is the flow rate of the sample gas to be tested. 总 The flow rate q of the sample gas to be measured 样 , gas flow rate q 助 and dilution gas flow rate q 稀 The sum of the initial dilution ratios of the sample gas, combustion-supporting gas, and diluent gas is adjusted as follows: the detection result is compared with the measurement signal threshold. If the detection result is within the measurement signal threshold, the sulfur content of the sample gas is determined using the detection result; otherwise, the dilution ratio is adjusted until the detection result is within the measurement signal threshold.

[0013] Preferably, the principle for adjusting the dilution ratio is as follows: if the detection result is greater than the upper limit of the threshold, the dilution ratio is decreased; if the detection result is less than the lower limit of the threshold, the dilution ratio is increased.

[0014] Preferably, the method for reducing the dilution ratio is as follows: reduce the flow rates of the sample gas and the combustion-supporting gas, and increase the flow rate of the dilution gas, wherein the increase in the flow rate of the dilution gas is equal to the sum of the decreases in the flow rates of the sample gas and the combustion-supporting gas.

[0015] Preferably, the reduction rate of the flow rates of the sample gas and the combustion-supporting gas is 10% to 30%.

[0016] Preferably, the method for increasing the dilution ratio is as follows: increase the flow rates of the sample gas and the combustion-supporting gas, and decrease the flow rate of the dilution gas, wherein the decrease in the flow rate of the dilution gas is equal to the sum of the increases in the flow rates of the sample gas and the combustion-supporting gas.

[0017] Preferably, the increase rate of the flow rates of the sample gas and the combustion-supporting gas is 10% to 30%.

[0018] Preferably, in step (3), the total sulfur content of the sample gas to be tested is calculated as follows:

[0019] Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the testing apparatus used in the natural gas total sulfur content testing method according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic flowchart of the natural gas total sulfur content testing method according to an embodiment of the present invention;

[0022] The attached diagram is labeled as follows: 1-Process pipeline; 2-Sampling probe; 3-Pretreatment module; 4-Dilution gas pipeline; 5-Combustion-supporting gas pipeline; 6-Zero-point calibration gas pipeline; 7-Range calibration gas pipeline; 8-Analyzer; 9-Sample gas solenoid valve; 10-Zero-point calibration gas solenoid valve; 11-Range calibration gas solenoid valve; 12-Mixing buffer tank; 13-High-temperature pyrolysis furnace; 14-Constant temperature dehydration module; 15-Ultraviolet fluorescence detection chamber; 16-Central control unit; 17-Tail gas emission pipeline; 18-Dilution gas solenoid valve; 19-Combustion-supporting gas solenoid valve. Detailed Implementation

[0023] The natural gas total sulfur content testing method of this invention is an improved invention. Addressing the problem that, under the current conditions where the flow ratio of the sample gas, combustion gas, and dilution gas is fixed, an excessively high total sulfur concentration in the sample gas can prevent the ultraviolet fluorescence detector from detecting the total sulfur concentration, this invention sets a measurement signal threshold and adjusts the dilution ratio based on real-time detection results. This keeps the measurement signal within the threshold, enabling the ultraviolet fluorescence detector to detect sample gases with different total sulfur concentrations.

[0024] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0025] Example 1

[0026] The method for testing the total sulfur content of natural gas in this embodiment adopts the following approach: Figure 1 The test apparatus shown includes a process pipeline 1, a sampling probe 2, a pretreatment module 3, a dilution gas pipeline 4, an combustion-supporting gas pipeline 5, a zero-point calibration gas pipeline 6, a range calibration gas pipeline 7, an analyzer 8, a sample gas solenoid valve 9, a zero-point calibration gas solenoid valve 10, a range calibration gas solenoid valve 11, a mixing buffer tank 12, a high-temperature pyrolysis furnace 13, a constant-temperature dehydration module 14, an ultraviolet fluorescence detection chamber 15, a central control unit 16, a tail gas emission pipeline 17, a dilution gas solenoid valve 18, a combustion-supporting gas solenoid valve 19.

[0027] The dilution gas pipeline 4 and the combustion-supporting gas pipeline 5 are respectively connected to the mixing buffer tank 12. The test sample gas pipeline, zero-point calibration gas pipeline 6, and range calibration gas pipeline 7 are connected in parallel to the mixing buffer tank 12. A dilution gas solenoid valve 18 and a dilution gas flow meter are sequentially installed on the dilution gas pipeline 4; a combustion-supporting gas solenoid valve 19 and a combustion-supporting gas flow meter are sequentially installed on the combustion-supporting gas pipeline 5; a zero-point calibration gas solenoid valve 10 and a zero-point calibration gas flow meter are sequentially installed on the zero-point calibration gas pipeline 6; and a range calibration gas solenoid valve 11 and a range calibration gas flow meter are sequentially installed on the range calibration gas pipeline 7. A sampling probe 2 and a pre-treatment module 3 are sequentially installed on the test sample gas pipeline. The sampling probe 2 is used to extract the test sample gas from the process pipeline 1 and perform primary filtration and pressure reduction on the test sample gas. The pre-treatment module 3 is used to perform secondary filtration and pressure reduction on the test sample gas from the sampling probe 2. The mixing buffer tank 12, the high-temperature pyrolysis furnace 13, the constant-temperature dehydration module 14, and the ultraviolet fluorescence detection chamber 15 are sequentially connected. The ultraviolet fluorescence detection chamber 15 is connected to the central control unit 16 via signal connection. The central control unit 16 is connected to the solenoid valve 9 for the sample gas to be tested, the solenoid valve 18 for the dilution gas, and the solenoid valve 19 for the combustion-supporting gas. The ultraviolet fluorescence detection chamber 15 transmits the detection result signal to the central control unit 16. The central control unit 16 compares the detection result with the measurement signal threshold and sends a dilution ratio adjustment command to the solenoid valve 9 for the sample gas to be tested, the solenoid valve 18 for the dilution gas, and the solenoid valve 19 for the combustion-supporting gas based on the comparison result.

[0028] The natural gas total sulfur content testing method in this embodiment uses produced gas from a gas well as the sample gas to be tested, such as... Figure 2 As shown, the specific steps include:

[0029] (1) Zeroing and range calibration of the measurement signal are performed using zero-point calibration gas and range calibration gas respectively, and the zero point and range of the measurement signal of the ultraviolet fluorescence detector are determined.

[0030] (2) Based on the zero point and range of the measurement signal of the ultraviolet fluorescence detector, a measurement signal threshold for adjusting the dilution ratio is set. The principle for setting the measurement signal threshold is as follows: the measurement signal threshold is greater than the lower threshold and less than the upper threshold; the lower threshold is greater than the zero point of the measurement signal and less than the minimum value corresponding to meeting the measurement signal-to-noise ratio requirement; and the upper threshold is less than the measurement signal range of the ultraviolet fluorescence detector. In this embodiment, the measurement signal range V of the ultraviolet fluorescence detector is... 测 To avoid signal saturation, a margin of 0.5V is reserved on top of the saturation value of 4V, and the upper limit of the measurement signal threshold is set to 3.5V. Based on the signal-to-noise ratio, the minimum unit of the detection signal is 0.001V, with fluctuations within ±0.001V. Only a signal condition of 0.2V can meet the detection requirement of 1% accuracy of the ultraviolet fluorescence detector. During normal measurement, the measurement signal must be at least 0.2V greater than the zero-point signal, and the lower limit of detection is set to V. 零 +0.2V, the measurement signal threshold is greater than V. 零 +0.2V and less than 3.5V, where V 零 This is to measure the zero point of the signal.

[0031] The dilution ratio is equal to the flow rate q of the sample gas entering the high-temperature pyrolysis furnace 13. 样 The ratio of the dilution ratio to the sum of the flow rates of the sample gas, the combustion-supporting gas, and the dilution gas is calculated using the following formula: Dilution ratio = q 样 / Q 总 , where q 稀 Q is the flow rate of the sample gas to be tested entering the high-temperature pyrolysis furnace 13. 总 The flow rate q of the sample gas to be tested entering the high-temperature pyrolysis furnace 13 样 , gas flow rate q 助 and dilution gas flow rate q 稀 sum.

[0032] (3) The initial dilution ratio is estimated and determined based on historical data. According to the set initial dilution ratio, the sample gas to be tested enters the mixing buffer tank 12 through the sample gas solenoid valve 9, the combustion-supporting gas (air) enters the mixing buffer tank 12 through the combustion-supporting gas solenoid valve 19, and the dilution gas (nitrogen) enters the mixing buffer tank 12 through the dilution gas solenoid valve 18. The flow rate q of the sample gas to be tested... 样 Flow rate q of combustion-supporting gas 助 and the flow rate q of the dilution gas稀 The flow rates are 10 mL / min, 200 mL / min, and 700 mL / min, respectively. The sample gas, combustion-supporting gas, and diluent gas are mixed in a mixing buffer tank 12 and then enter a high-temperature pyrolysis furnace 13 at 1050 ± 50 °C. In the furnace 13, the sample gas undergoes combustion with oxygen in the air under high-temperature heating, followed by dehydration in a constant-temperature dehydration module 14. The dehydrated gas then enters an ultraviolet fluorescence detection chamber 15 for ultraviolet fluorescence detection. The detection result is output to the central control unit 16 as a voltage measurement signal; in this embodiment, the result is 4.0V. The detected gas is discharged through the exhaust pipe 17. Pre-mixing the sample gas, combustion-supporting gas, and diluent gas in the mixing buffer tank 12 ensures uniform mixing, promotes complete combustion, and improves the accuracy of the detection results.

[0033] (4) After receiving the detection result signal, the central control unit 16 compares the detection result with the measurement signal threshold. In this embodiment, if the detection result is greater than the upper limit of the measurement signal threshold, the central control unit 16 issues an adjustment command to reduce the dilution ratio. The adjustment command to reduce the dilution ratio is sent to the sample gas solenoid valve 9, the combustion gas solenoid valve 19, and the dilution gas solenoid valve 18. Under the adjustment command, the sample gas solenoid valve 9 and the combustion gas solenoid valve 19 reduce their opening, thereby reducing the flow rate q of the sample gas. 样 and the flow rate q of the combustion-supporting gas 助 All decrease by 10%, and the dilution gas solenoid valve 18 increases its opening under the adjustment command, thus increasing the flow rate q of the dilution gas. 稀 The increase in the value is equal to the sum of the decreases in the flow rates of the sample gas and the combustion-supporting gas, to ensure the flow rate q of the sample gas is maintained. 样 Combustion-supporting gas q 助 and the flow rate q of the dilution gas 稀 The sum, i.e., the total flow Q 总 The flow rate remains constant. The sample gas, combustion-supporting gas, and diluent gas, after flow rate adjustment, enter the ultraviolet fluorescence detection chamber 15 for analysis and detection after combustion and water removal. The detection result is output to the central control unit 16 in the form of a voltage measurement signal; in this embodiment, the detection result is 3.9V. When adjusting the dilution ratio, ensure the flow rate q of the sample gas remains constant. 样 Combustion-supporting gas q 助 and the flow rate q of the dilution gas 稀 The sum, i.e., the total flow Q 总 Keeping it unchanged can improve the pressure stability of the gas, better adapt to actual testing conditions, and facilitate testing.

[0034] (5) Repeat step (4) to measure the flow rate q of the sample gas. 样 and the flow rate q of the combustion-supporting gas 助 Both were reduced by 10% again, and the flow rate q of the dilution gas was increased. 稀The flow rate q of the dilution gas 稀 The increase in the value is equal to the sum of the decreases in the flow rates of the sample gas and the combustion-supporting gas, until the detection result is less than 3.5V. The detection result within the measurement signal threshold is defined as the target detection value, and the dilution ratio corresponding to obtaining the target detection value is defined as the target dilution ratio.

[0035] (6) Calculate the sulfur content in the sample gas using the detection results within the measurement signal threshold and the target dilution ratio. The calculation method is as follows:

[0036] Example 2

[0037] The difference between the natural gas total sulfur content testing method of this embodiment and the natural gas total sulfur content testing method of Embodiment 1 is only that the detection result in step (2) of the natural gas total sulfur content testing method of this embodiment is 0.1V, and the central control unit 16 in step (3) issues an adjustment command to increase the dilution ratio. The solenoid valve 9 of the sample gas to be tested and the solenoid valve 19 of the combustion-supporting gas increase their opening under the adjustment command, so that the flow rates of the sample gas to be tested and the combustion-supporting gas both increase by 10%. The solenoid valve 18 of the dilution gas decreases its opening under the adjustment command, and the decrease in the flow rate of the dilution gas is equal to the sum of the increases in the flow rates of the sample gas to be tested and the combustion-supporting gas.

[0038] Example 3

[0039] The difference between the natural gas total sulfur content testing method in this embodiment and the natural gas total sulfur content testing method in Example 1 is only that, in step (4) of this embodiment, the flow rate q of the sample gas to be tested... 样 and the flow rate q of the combustion-supporting gas 助 Both decreased by 20%, and the flow rate q of the diluent gas... 稀 Increase the flow rate q of the dilution gas 稀 The increase is equal to the sum of the decreases in the flow rates of the sample gas and the combustion-supporting gas.

[0040] Example 4

[0041] The difference between the natural gas total sulfur content testing method in this embodiment and the natural gas total sulfur content testing method in Example 1 is only that, in step (4) of this embodiment, the flow rate q of the sample gas to be tested... 样 and the flow rate q of the combustion-supporting gas 助 Both decreased by 30%, and the flow rate q of the diluent gas... 稀 Increase the flow rate q of the dilution gas 稀 The increase is equal to the sum of the decreases in the flow rates of the sample gas and the combustion-supporting gas.

Claims

1. A method for testing the total sulfur content of natural gas, characterized in that, Includes the following steps: (1) Based on the zero point and range of the measurement signal of the ultraviolet fluorescence detector, set the measurement signal threshold for adjusting the dilution ratio; (2) Mix the sample gas, combustion-supporting gas and diluent gas according to the initially set dilution ratio and then perform ultraviolet fluorescence detection. Based on the comparison between the detection results and the measurement signal threshold, adjust the initially set dilution ratio until the detection results are within the measurement signal threshold determined in step (1). (3) Using the adjusted dilution ratio and detection results from step (2), determine the total sulfur content of the sample gas to be tested.

2. The method for testing the total sulfur content of natural gas as described in claim 1, characterized in that, The lower threshold is greater than the zero point of the measurement signal but less than the minimum value corresponding to meeting the measurement signal-to-noise ratio requirement, and the upper threshold is less than the measurement signal range of the ultraviolet fluorescence detector.

3. The method for testing the total sulfur content of natural gas as described in claim 1 or 2, characterized in that, The formula for calculating the dilution ratio is as follows: Dilution ratio = q 样 / Q 总 , where q 稀 Q is the flow rate of the sample gas to be tested. 总 The flow rate q of the sample gas to be measured 样 , gas flow rate q 助 and dilution gas flow rate q 稀 The sum of the initial dilution ratios of the sample gas, combustion-supporting gas, and diluent gas is adjusted as follows: the detection result is compared with the measurement signal threshold. If the detection result is within the measurement signal threshold, the sulfur content of the sample gas is determined using the detection result; otherwise, the dilution ratio is adjusted until the detection result is within the measurement signal threshold.

4. The method for testing the total sulfur content of natural gas as described in claim 3, characterized in that, The principle for adjusting the dilution ratio is as follows: if the test result is greater than the upper limit of the threshold, decrease the dilution ratio; if the test result is less than the lower limit of the threshold, increase the dilution ratio.

5. The method for testing the total sulfur content of natural gas as described in claim 4, characterized in that, The method to reduce the dilution ratio is as follows: reduce the flow rates of the sample gas and the combustion-supporting gas, and increase the flow rate of the dilution gas. The increase in the flow rate of the dilution gas is equal to the sum of the decreases in the flow rates of the sample gas and the combustion-supporting gas.

6. The method for testing the total sulfur content of natural gas as described in claim 5, characterized in that, The reduction rate of the flow rates of the sample gas and the combustion-supporting gas is 10% to 30%.

7. The method for testing the total sulfur content of natural gas as described in claim 4, characterized in that, The method to increase the dilution ratio is as follows: increase the flow rates of the sample gas and the combustion-supporting gas, and decrease the flow rate of the dilution gas. The decrease in the flow rate of the dilution gas is equal to the sum of the increases in the flow rates of the sample gas and the combustion-supporting gas.

8. The method for testing the total sulfur content of natural gas as described in claim 7, characterized in that, The increase rate of the flow rates of the sample gas and the combustion-supporting gas is 10% to 30%.

9. The method for testing the total sulfur content of natural gas as described in claim 1 or 2, characterized in that, In step (3), the total sulfur content of the sample gas is calculated as follows:

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