Method and apparatus for measuring trace and ultra-trace oil content

Abstract

The present application relates to oil content detection technical field, especially trace and ultratrace oil content measurement method and device, the measurement device of the present application includes low temperature enrichment device, extraction device and infrared spectrometer, low temperature enrichment device includes dewar vessel and U-shaped tube, extraction device includes extractant container, input pipe, lead-out pipe and extraction liquid quantitative pipe, still be equipped with mass flow meter on U-shaped tube, according to the total mass of measured gas and the oil concentration of extraction liquid measured by the infrared spectrometer, the oil content in gas is calculated.The present application also provides a kind of measurement method, using liquid nitrogen cold trap type enrichment mode, through effective extraction, the oil content measurement in gas is converted into the measurement of oil concentration in liquid extractant, accurate measurement is carried out using infrared spectrophotometry.The measurement device and method of the present application, the measurement range is wider for 1500ppmW-1ppbW, reliable measurement in ultratrace and trace range is realized.

Description

Technical Field

[0001] This invention relates to the field of oil content detection technology, and more specifically, to a method and apparatus for measuring trace and ultra-trace oil content. Background Technology

[0002] Oil content in gases is an important indicator for evaluating the quality of gas products. The determination of trace oil in industrial compressed gases is a key research area both domestically and internationally, primarily aimed at accurately measuring trace, ultra-trace, and super-trace levels of oil concentration in compressed gases. In the oxygen production industry, the oil content of compressed air can also affect the safety of oxygen production equipment. If the oil content in nitrogen, helium, or air used in aerospace launches is too high, it will damage the gas supply pipelines, fuel delivery systems, and engine systems of satellites and rockets. When nitrogen, helium, and air are used in the defense industry, especially the aerospace industry, the oil content requirements are very high.

[0003] The concentration of oil in gases is generally below 100 ppm, and due to the complex composition of oils, direct measurement is usually impossible. Quantitative enrichment of the sample beforehand is necessary. Common absorption methods include solvent absorption, adsorption materials, and condensation enrichment. Analytically, the main components of oils are long-chain alkanes or aromatics, and they are found in gases around 29-30 cm⁻¹. -1 2960cm- 1 and 3030cm -1 Characteristic absorption peaks are present at each location, corresponding to the asymmetric stretching vibration frequencies of the CH bonds in the CH3- group, the CH bonds in the -CH2- group, and the CH bonds in the aromatic ring, respectively. Infrared spectrophotometry is divided into infrared spectrophotometry and non-dispersive infrared spectrophotometry. Infrared spectrophotometry can measure the characteristic absorptions of methyl, methylene, and aromatic rings separately, and corrects for the mutual interference between aliphatic and aromatic hydrocarbons. It is suitable for the analysis of oils from different sources or types, and can achieve accurate quantitative analysis results without the need for specific standard oils.

[0004] In the cryogenic environments of liquid hydrogen and liquid helium, lubricating oil components can solidify into particles, causing accidents in high-speed turbine expanders or blockages in system pipelines. This can severely degrade the cooling performance of the entire helium liquefaction unit or refrigerator, a common occurrence in cryogenic systems of large scientific facilities. Therefore, the oil content in the helium working fluid must be below 10 ppb. For safety, the purity of the helium or hydrogen working fluid needs to be monitored in real time, and an emergency procedure must be initiated if the oil content exceeds the limit. Since this involves ultra-trace and trace measurements, reliable enrichment schemes and analytical methods are required.

[0005] To prevent oil contamination from causing serious accidents in cryogenic systems, various hydrogen / helium refrigerators or liquefiers require monitoring and analysis of the oil content in the high-purity helium working fluid during actual operation. Generally, the oil content is required to not exceed 10 ppbW (ug / kg). Currently, the oil module of Linde's WE34M-3 / SM38 multi-component analyzer is mainly used in cryogenic engineering. Its working principle utilizes the photoelectric effect, where alternating current discharges between two metal electrodes, stimulating the gas to emit light. A sensor containing a photodiode and a signal amplifier convert the photocurrent into a voltage value, which is then converted into the concentration of the analyte by an AD converter. To detect the oil content in helium, the oil needs to be pyrolyzed into highly volatile gaseous hydrocarbons containing only 1-3 carbon atoms, which are then sent to the WE34M-3 for detection. Oil mist in helium is separated and concentrated through a filter. The concentration time is set between 10 minutes and several hours. Excessive oil mist usually overloads the filter. Sometimes, if the concentration time is too short, the oil will be squeezed through the filter, resulting in inaccurate measurements and contaminating the equipment. In the pyrolysis chamber, the pyrolysis products are measured in molecular form of hydrocarbons, CxHy containing 1-3 carbon atoms, in vpm. The measurement result is multiplied by a correction factor (from the correction for oil mist, the mass of oil mist deposited on the filter during the concentration stage), and then divided by the total mass of helium passing through the filter during the concentration stage to obtain the mass ratio of oil mist in the helium, in ppb. However, the above testing method and equipment have the following problems: 1) The oil content testing range is narrow. The oil content in pure helium ranges from 0-250 ppb; however, in cryogenic engineering, the oil content often reaches the level of hundreds of ppm. When the oil content is greater than 250 ppb, the concentration, filtration, and pyrolysis of the photoelectric analysis and the analysis chamber cause contamination, the instrument data cannot reflect the actual oil content, and the instrument may even be damaged due to contamination. 2) Each component of the oil needs to be calibrated, and the carrier gas can only be helium; however, the oil composition in actual cryogenic engineering varies, sometimes being a mixture of several components. 3) With only one solution, accurate comparisons are not possible. In actual cryogenic engineering, oil contamination accidents still occur in cryogenic systems even when test data shows compliance.

[0006] Therefore, it is necessary to solve the problem of analyzing trace (parts per million, ppm) and ultra-trace (parts per billion, ppb) oil content in large-scale cryogenic engineering. Since the composition of the compressor lubricating oil used in the cryogenic refrigeration cycle varies, and the oil contaminants from other equipment such as vacuum pumps and the environment are unknown, it is necessary to develop a method and apparatus that can accurately measure the trace and ultra-trace oil content covering various oil contaminants. Summary of the Invention

[0007] To overcome the aforementioned technical problems, this invention provides a method and apparatus for measuring trace and ultra-trace oil content. Utilizing a liquid nitrogen cold trap enrichment method, through effective extraction, the measurement of oil content in the gas is transformed into the measurement of oil concentration in the liquid extractant. Accurate measurement is performed using infrared spectrophotometry, making it suitable for environmental analysis in special fields such as aerospace where strict control of oil and gas samples is required.

[0008] The present invention provides a device for measuring trace and ultra-trace oil content, including a low-temperature enrichment device for enriching and sampling trace and ultra-trace oil components in a gas, an extraction device for extracting oil components, and an infrared spectrometer for analyzing the oil content of the extracted liquid.

[0009] The cryogenic enrichment device includes a Dewar container for holding liquid nitrogen, a U-shaped tube immersed in liquid nitrogen, and gas flowing through the U-shaped tube to form a liquid nitrogen cold trap to enrich and sample the oil components in the gas.

[0010] The extraction device includes a container for storing extractant, an input tube for introducing extractant into the U-shaped tube, an output tube for discharging extractant, and an extraction liquid metering tube. The extractant in the input tube flows in from the gas inlet near the U-shaped tube, and the extracted extract flows out from the gas outlet near the U-shaped tube. After flowing through the output tube, it is stored in the extraction liquid metering tube, which is also used to measure the volume of the extractant.

[0011] A mass flow meter is also provided on the U-shaped tube to measure the total mass of the gas passing through. Based on the measured total mass of the gas and the oil concentration of the extract measured by the infrared spectrometer, the oil content in the gas is calculated.

[0012] Preferably, the U-shaped tube is a partition wall heat exchange steel tube or glass tube, and glass microspheres are filled inside the U-shaped tube. The interface of the glass microspheres on both sides of the U-shaped tube is higher than the interface of the liquid nitrogen, which is used to increase the contact area between the gas and the extractant, which is beneficial to the extraction of oil components.

[0013] Preferably, the diameter of the glass microspheres is 0.5-2 mm, and the porosity of the glass microspheres after filling is 50-85%.

[0014] Preferably, a dust filter with an accuracy of 1-5 μm is provided on both the air inlet and outlet faces of the U-shaped tube; a brake control valve is provided at both the gas inlet and gas outlet of the U-shaped tube.

[0015] Preferably, the air inlet and outlet ends of the U-shaped tube are located outside the Dewar container, which is used to adjust the U-shaped tube vertically.

[0016] Preferably, a brake control valve is provided on both the input pipe and the output pipe;

[0017] The extraction liquid metering tube is connected to the infrared spectrometer via two conduits, one for automatic sample injection and the other for liquid drainage. A brake control valve is provided at the upstream point of the two conduits where no flow split occurs, and a brake control valve is also provided on the conduit used for liquid drainage.

[0018] Preferably, the extractant is trichlorotrifluoroethane or carbon tetrachloride.

[0019] Preferably, the Dewar container is also provided with a liquid nitrogen inlet and an outlet, a liquid nitrogen level gauge is provided inside the Dewar container, a thermometer is provided inside the U-tube, and a heater is provided outside the U-tube. After the cold trap enrichment and sampling, the sample is heated to quickly restore it to room temperature before extraction.

[0020] Preferably, the measuring range of the measuring device

[0021] It is 1500ppmW-1ppbW.

[0022] The present invention also provides a method for measuring trace and ultra-trace oil content using the apparatus described above, comprising the following steps:

[0023] S1: Use a liquid nitrogen cold trap to enrich and sample trace and ultra-trace oil components in the gas;

[0024] S2: Add extractant to extract the enriched sample;

[0025] S3: According to the HJ637-2018 standard for the determination of petroleum and animal oils in water quality, the oil concentration of the extract is measured by the infrared spectrometer, and then the oil mass in the extract is calculated.

[0026] S4: The total mass of the gas passing through is measured using a mass flow meter;

[0027] S5: Calculate the oil content in the gas based on the total gas mass obtained in step S4 and the oil mass obtained in step S4.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The present invention provides a method and apparatus for measuring trace and ultra-trace oil content. Utilizing a liquid nitrogen cold trap enrichment method, and through effective extraction, the measurement of oil content in the gas is transformed into the measurement of oil concentration in the liquid extractant. Accurate measurement is performed using infrared spectrophotometry, with a measurement precision of 1500 ppmW-1 ppbW, covering a wide measurement range and enabling reliable measurement in the ultra-trace and trace ranges. It can conveniently, quickly, and accurately locate contamination sources in cryogenic engineering, thereby further addressing oil contamination issues in cryogenic systems based on these sources. Since each substance oxidized or degraded by oil absorbs infrared light of different wavelengths at the molecular level with slight variations, it can be identified based on infrared spectroscopy. It is suitable for environmental analysis in aerospace and other special fields where strict control of oil and gas samples is required, and has a wide range of applications. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the device for measuring trace and ultra-trace oil content according to the present invention;

[0031] Explanation of reference numerals in the attached drawings: 1-Low-temperature enrichment device; 11-Dewar container; 12-U-tube; 121-Mass flow meter; 122-Glass microspheres; 123-Dust filter; 13-Level gauge; 2-Extraction device; 21-Extractant container; 22-Inlet pipe; 23-Outlet pipe; 24-Extractant metering pipe; 3-Infrared spectrometer; 4-Brake control valve; 5-Two-way conduit. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the embodiments of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0033] like Figure 1 The diagram shows a schematic of the device for measuring trace and ultra-trace oil content of the present invention, which includes a low-temperature enrichment device 1 for enriching and sampling trace and ultra-trace oil components in a gas, an extraction device 2 for extracting oil components, and an infrared spectrometer 3 for analyzing the oil content of the extracted liquid.

[0034] The cryogenic enrichment device 1 includes a Dewar container 11 for holding liquid nitrogen, a U-shaped tube 12 immersed in liquid nitrogen, and gas flowing in the U-shaped tube 12 to form a liquid nitrogen cold trap to achieve enrichment and sampling of oil components in the gas.

[0035] The extraction device 2 includes a container 21 for storing extractant, an input tube 22 for inputting extractant into the U-shaped tube, an output tube 23 for outputting extractant, and an extraction liquid metering tube 24. The extractant in the input tube 21 flows in from the gas inlet adjacent to the U-shaped tube 12, and the extracted extract flows out from the gas outlet adjacent to the U-shaped tube 12. After flowing through the output tube 23, it is stored in the extraction liquid metering tube 24. The extraction liquid metering tube 24 is also used to measure the volume of the extraction liquid.

[0036] A mass flow meter 121 is also provided on the U-shaped tube 12 to measure the total mass of the gas passing through. Based on the measured total mass of the gas and the oil concentration of the extract measured by the infrared spectrometer 3, the oil content in the gas is calculated.

[0037] The U-shaped tube 12 is a partitioned heat exchange steel tube or glass tube, and is filled with glass microspheres 122. The interface between the glass microspheres on both sides of the U-shaped tube 12 is higher than the liquid nitrogen interface, which increases the contact area between the gas and the extractant, thus facilitating the extraction of oil components. Preferably, the diameter of the glass microspheres 122 is 0.5-2 mm, and the porosity of the glass microspheres 122 after filling is 50-85%.

[0038] The U-shaped tube 12 is equipped with dust filters 123 on both the inlet and outlet faces, with a preferred accuracy of 1-5 μm. Braking control valves 4 are provided at both the gas inlet and outlet of the U-shaped tube 12, which can quantitatively control the gas quality for enrichment and extraction in the liquid nitrogen cold trap.

[0039] The air inlet and outlet ends of the U-shaped tube 12 are located outside the Dewar container 11, and are used to adjust the U-shaped tube 12 up and down.

[0040] Both the input tube 22 and the output tube 23 are equipped with brake control valves 4 for controlling the addition of the extractant and the collection of the extract. The extract quantitative tube 24 is connected to the infrared spectrometer 3 via two conduits 5, one for automatic sample injection and the other for draining. A brake control valve 4 is located upstream of the two conduits 5 where there is no flow split, and a brake control valve 4 is also located on the draining conduit, for controlling the entry of the extract sample into the infrared spectrometer 3 for measurement and analysis, and for draining the extract. Preferably, the extractant is trichlorotrifluoroethane or carbon tetrachloride. If the oil concentration of the extract exceeds the upper limit of the infrared spectrometer 3, the extract can be diluted before sampling and measurement; dilution can be performed multiple times.

[0041] The Dewar container 11 is also equipped with a liquid nitrogen inlet and outlet. A liquid nitrogen level gauge 13 is installed inside the Dewar container 11, and a thermometer is installed inside the U-shaped tube 12. To prevent oil droplets from condensing on the inner wall of the sampling tube and to ensure sample integrity, a heater or heat insulation treatment is provided outside the U-shaped tube 12. After enrichment sampling in the cold trap, the sample is heated to quickly return to room temperature before extraction. A vibration device can also be installed to achieve vibration extraction, making the extraction more efficient and uniform.

[0042] The present invention also provides a method for measuring trace and ultra-trace oil content using the apparatus described above, comprising the following steps:

[0043] S1: Use a liquid nitrogen cold trap to enrich and sample trace and ultra-trace oil components in the gas;

[0044] S2: Add extractant to extract the enriched sample;

[0045] S3: According to the HJ637-2018 standard for the determination of petroleum and animal oils in water quality, the oil concentration of the extract is measured by the infrared spectrometer, and then the oil mass in the extract is calculated.

[0046] S4: The total mass of the gas passing through is measured using a mass flow meter;

[0047] S5: Calculate the oil content in the gas based on the total gas mass obtained in step S4 and the oil mass obtained in step S4.

[0048] According to the national standard HJ637-2018, determination of petroleum and animal / vegetable oils in water quality—infrared spectrophotometry—the molecular functional groups are located at 2930 cm⁻¹. -1 (CH3), 2960cm -1 (CH2), 3030cm -1 Aromatic hydrocarbons are a major component of oils used in cryogenic engineering, and can all be characterized by these three functional groups. Therefore, a reference oil solution (methyl, methylene, and aromatic hydrocarbons) covering the molecular characteristics of various oils used in cryogenic engineering is prepared. Standard samples with different oil concentrations are prepared, and the absorbance of the standard samples is measured using an infrared spectrometer to obtain a linear relationship between oil concentration and absorbance of the oil solution. Then, the absorbance of the extract sample is measured using an infrared spectrometer, and the oil concentration of the extract sample is calculated based on the above linear relationship. Preferably, the extract sample needs to be analyzed 10 times using infrared spectrometry. Only data with a relative standard deviation (RSD) of less than 0.5% are valid to avoid random measurement errors.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] The present invention provides a method and apparatus for measuring trace and ultra-trace oil content. Utilizing a liquid nitrogen cold trap enrichment method, and through effective extraction, the measurement of oil content in the gas is transformed into the measurement of oil concentration in the liquid extractant. Accurate measurement is performed using infrared spectrophotometry, with a measurement precision of 1500 ppmW-1 ppbW, covering a wide measurement range and enabling reliable measurement in the ultra-trace and trace ranges. It can conveniently, quickly, and accurately locate contamination sources in cryogenic engineering, thereby further addressing oil contamination issues in cryogenic systems based on these sources. Since each substance oxidized or degraded by oil absorbs infrared light of different wavelengths at the molecular level with slight variations, it can be identified based on infrared spectroscopy. It is suitable for environmental analysis in aerospace and other special fields where strict control of oil and gas samples is required, and has a wide range of applications.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for measuring trace and ultra-trace oil content, characterized in that, It includes a low-temperature enrichment device for enriching and sampling trace and ultra-trace oil components in gases, an extraction device for extracting oil components, and an infrared spectrometer for analyzing the oil content of the extracted liquid. The cryogenic enrichment device includes a Dewar container for holding liquid nitrogen, a U-shaped tube immersed in liquid nitrogen, and gas flowing through the U-shaped tube to form a liquid nitrogen cold trap to enrich and sample the oil components in the gas. The U-shaped tube is a partitioned heat exchange steel tube or glass tube; a brake control valve is provided at both the gas inlet and gas outlet of the U-shaped tube; The extraction device includes a container for storing extractant, an input tube for introducing extractant into the U-shaped tube, an output tube for discharging extractant, and an extraction liquid metering tube. The extractant in the input tube flows in from the gas inlet near the U-shaped tube, and the extracted extract flows out from the gas outlet near the U-shaped tube. After flowing through the output tube, it is stored in the extraction liquid metering tube, which is also used to measure the volume of the extractant. A mass flow meter is also provided on the U-shaped tube to measure the total mass of the gas passing through. Based on the measured total mass of the gas and the oil concentration of the extract measured by the infrared spectrometer, the oil content in the gas is calculated. The U-shaped tube is filled with glass microspheres, and the interface between the glass microspheres on both sides of the U-shaped tube is higher than the liquid nitrogen interface, which increases the contact area between the gas and the extractant, thus facilitating the extraction of oil components. Dust filters with an accuracy of 1-5µm are provided on both the air inlet and outlet faces of the U-shaped tube.

2. The measuring device for trace and ultra-trace oil content according to claim 1, characterized in that, The diameter of the glass microspheres is 0.5-2 mm, and the porosity of the glass microspheres after filling is 50-85%.

3. The measuring device for trace and ultra-trace oil content according to claim 1, characterized in that, The air inlet and outlet ends of the U-shaped tube are located outside the Dewar container, and are used to adjust the U-shaped tube vertically.

4. The measuring device for trace and ultra-trace oil content according to claim 1, characterized in that, A brake control valve is provided on both the input pipe and the output pipe; The extraction liquid metering tube is connected to the infrared spectrometer via two conduits, one for automatic sample injection and the other for liquid drainage. A brake control valve is provided at the upstream point of the two conduits where no flow split occurs, and a brake control valve is also provided on the conduit used for liquid drainage.

5. The measuring device for trace and ultra-trace oil content according to claim 1, characterized in that, The extractant is trichlorotrifluoroethane or carbon tetrachloride.

6. The measuring device for trace and ultra-trace oil content according to claim 1, characterized in that, The Dewar container is also equipped with a liquid nitrogen inlet and outlet. A liquid nitrogen level gauge is installed inside the Dewar container, a thermometer is installed inside the U-tube, and a heater is installed outside the U-tube. After the cold trap enrichment and sampling, the sample is heated to quickly return to room temperature before extraction.

7. The measuring device for trace and ultra-trace oil content according to claim 1, characterized in that, The measuring device has a measurement range of 1500ppmW-1ppbW.

8. A method for measuring trace and ultra-trace oil content using the apparatus according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Use a liquid nitrogen cold trap to enrich and sample trace and ultra-trace oil components in the gas; S2: Add extractant to extract the enriched sample; S3: According to the HJ637-2018 standard for the determination of petroleum and animal oils in water quality, the oil concentration of the extract is measured by the infrared spectrometer, and then the oil mass in the extract is calculated. S4: The total mass of the gas passing through is measured using a mass flow meter; S5: Calculate the oil content in the gas based on the total gas mass obtained in step S4 and the oil mass obtained in step S4.

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