Method and device for measuring trace and ultratrace amounts of oil

Abstract

The present invention relates to the technical field of oil content detection, in particular to a method and device for measuring trace and ultratrace oil content. The measuring device of the present invention comprises a low-temperature concentrator, an extractor and an infrared spectrometer, the low-temperature concentrator comprises a Dewar vessel and a U-shaped tube, the extractor comprises an extraction solvent vessel, an inlet tube, an outlet tube and an extract quantification tube, and the U-shaped tube is further provided with a mass flowmeter for calculating and obtaining the oil content in the gas based on the total mass of the measured gas and the oil concentration of the extract measured by the infrared spectrometer. The present invention further provides a measuring method, which uses a liquid nitrogen cooling trap concentration method to effectively extract and convert the measurement of the oil content in the gas into the measurement of the oil concentration in the liquid extraction solvent, and performs accurate measurement using infrared spectroscopy. The measuring device and method of the present invention have a relatively wide measuring range of 1500 ppmW to 1 ppbW, and realize reliable measurement in the ultratrace and trace ranges.

Description

[Technical field]

[0001] The present invention relates to the technical field of oil content detection, in particular to a method and device for measuring trace and ultra-trace oil content. [Background technology]

[0002] The oil content in gas is one of the important indicators for evaluating the quality of gas products. The problem of the method for measuring the amount of oil in industrial compressed gas is one of the basic problems that are being studied intensively at home and abroad, mainly to accurately measure the oil concentration at the minute, trace and ultra-trace levels in compressed gas. In the oxygen generation industry, the oil content in compressed air also affects the safety of oxygen generators. If the nitrogen gas, helium gas or air used in rocket launch has too high an oil content, it will harm the gas supply pipes, fuel transportation system and engine system of satellites and rockets. When nitrogen gas, helium gas, air, etc. are used in special industrial sectors, especially the spaceflight industrial sector, the requirements for their oil content are higher during the use process. In our national standards, there are no restrictions on the oil content in air and helium gas, and there are no corresponding testing methods. There is still no mature and simple analytical method for measuring the amount of oil in gas. The main methods for measuring oil content are gravimetric method and spectrophotometric method, and the gravimetric method is applied to measure the high content of oil in liquids.

[0003] The concentration range of oil content in gas is generally less than several hundred ppm, and the oil composition is complex and generally cannot be measured directly. The sample needs to be quantitatively concentrated in advance. Commonly used absorption methods include solvent absorption, material adsorption, and condensation concentration. In the analysis method, the main components of the oil are long-chain alkanes or arenes, and the 2930 cm -1 , 2960cm -1 and 3030cm -1Each of them has characteristic absorption peaks corresponding to the asymmetric stretching vibration frequency of the CH bond in the CH3- group, the asymmetric stretching vibration frequency of the CH bond in the -CH2- group, and the asymmetric stretching vibration frequency of the CH bond in the aromatic ring. Infrared spectroscopy is divided into infrared spectrophotometry and non-dispersive infrared spectroscopy. Infrared spectroscopy can measure the characteristic absorption of the methyl group, methylene group, and aromatic ring, respectively, and correct the mutual influence between aliphatic hydrocarbons and aromatic hydrocarbons. It is applied to the analysis of oils from different sources or types, and can perform accurate quantitative analysis without determining special standard oils.

[0004] In the temperature range of liquid hydrogen and liquid helium, lubricating oil components turn into solid particles in a low-temperature environment, which can cause accidents in the high-speed turbo expander of the core moving parts or block the piping of the low-temperature system, resulting in a significant decrease in the refrigeration performance of the helium liquefier or the entire refrigerator, which is a common accident in low-temperature systems such as big science equipment. Therefore, it is required that the oil content in the helium gas working material is lower than 10ppb. For safety reasons, it is necessary to monitor the purity of the helium gas or hydrogen gas working material in real time, and if the oil content exceeds the standard, an emergency treatment program will be entered. This is because the measurement is in the ultra-trace and trace ranges, so a reliable concentration scheme and analysis method are required.

[0005] In order to avoid serious accidents in low-temperature systems caused by oil contamination, various hydrogen / helium refrigerators or liquefiers need to monitor and analyze the oil content in high-purity helium gas working material during actual operation, and it is generally required that the oil content does not exceed 10 ppbW (i.e. ug / kg, where W indicates the mass ratio of concentration). Currently, the oil module of Linde's multi-component composition analyzer WE34M-3 / SM38 is mainly used in low-temperature processes, and its operating principle is to use the photoelectric effect, that is, an alternating current is discharged between two metal electrodes to stimulate the gas to emit light. The photocurrent is converted into a voltage value by a sensor including a photodiode and a signal amplifier, and the concentration of the measured substance can be obtained through an AD conversion device. In order to detect the oil content in helium gas, the oil needs to be pyrolyzed into gaseous hydrocarbons that are more volatile and contain 1 to 3 carbon atoms, and then sent to the WE34M-3 for detection. The oil mist in the helium gas is separated and concentrated by a filter, and the concentration time is set to 10 minutes to several hours. Too much oil mist generally results in overloading of the strainer, and if the concentration time is too short, the oil will be pushed through the strainer, contaminating the device. The pyrolysis products in the pyrolysis chamber are measured as hydrocarbon compounds in molecular form, containing 1 to 3 carbon atoms in CxHy, and the unit is vpm. The measurement result is multiplied by a correction factor (correction from oil mist, the mass of oil mist deposited on the strainer in the concentration stage) and divided by the total mass of helium gas that passed through the filter in the concentration stage to obtain the mass ratio of oil mist to helium gas, and the unit is ppb. However, the above test method and device have the following problems. First, the oil content test range is narrow, the oil content range in pure helium is 0-250ppb, but in low-temperature processes there are often hundreds of ppm grades, and when the oil component content is greater than 250ppb, it will contaminate the photoelectric analysis concentration filtration and decomposition distillation as well as the analysis room, so the instrument data cannot reflect the actual oil content, and even the instrument will be contaminated and damaged. Second, the carrier gas is only helium gas, and it is necessary to standardize the oil of each type of component, and the oil components in the actual low-temperature process are different, and may be a mixture of multiple components.Third, with only one scheme, it is not possible to compare the measurement accuracy. In an actual low-temperature process, the test data may show a pass, but an oil contamination accident may occur in the low-temperature system.

[0006] Therefore, it is necessary to solve the problem of analyzing trace (parts per million, ppm) and ultratrace (parts per billion, ppb) oil content in large-scale low-temperature processes. Because the components of the compressor lubricating oil used to perform the low-temperature refrigeration cycle are different, and the oil contaminant components from other devices such as vacuum pumps and the environment are unknown, it is necessary to research methods and devices that can accurately measure trace and ultratrace oil content including various oil contaminant components. Summary of the Invention [Problem to be solved by the invention]

[0007] In order to overcome the above technical problems, the present invention provides a method and device for measuring trace and ultratrace oil content, and utilizes a liquid nitrogen cooling trap concentration method to effectively extract and convert the measurement of oil content in gas into the measurement of oil concentration in liquid extraction solvent, and uses infrared spectrophotometry for accurate measurement, which is applicable to environmental analysis in special fields such as space flight where oil and gas samples are strictly controlled. [Means for solving the problem]

[0008] The present invention provides a measuring device for trace and ultratrace oil content, which comprises a low-temperature concentrating device for concentrating and sampling trace and ultratrace oil components in a gas, an extracting device for extracting the oil components, and an infrared spectrometer for analyzing the oil content of the liquid after extraction. The low-temperature concentrator includes a Dewar vessel for storing liquid nitrogen and a U-shaped tube for immersion in liquid nitrogen, and the gas flows through the U-shaped tube to form a liquid nitrogen cooling trap to realize concentrated sampling of oil components in the gas; The extraction device comprises a container for storing an extraction solvent, an import pipe for importing the extraction liquid into the U-shaped tube, an outlet pipe for outlet of the extraction liquid, and an extraction liquid quantification tube, the extraction solvent in the import pipe flows into the gas inlet adjacent to the U-shaped tube, the extracted extraction liquid flows out of the gas outlet adjacent to the U-shaped tube, flows through the outlet pipe, and is stored in the extraction liquid quantification tube, and the extraction liquid quantification tube is further for measuring the volume of the extraction liquid, The U-tube is further provided with a mass flow meter for measuring the total mass of the gas passing through and calculating and obtaining the oil content in the gas based on the measured total mass of the gas and the oil concentration of the extract measured by the infrared spectrometer.

[0009] Preferably, the U-tube is a steel tube or a glass tube for heat transfer type heat exchange, the U-tube is further filled with glass bubbles, and the interfaces of the glass bubbles on both sides of the U-tube are higher than the interfaces of the liquid nitrogen, in order to increase the contact area between the gas and the extraction solvent, which contributes to the extraction of oil components.

[0010] Preferably, the diameter of the glass bubbles is 0.5 to 2 mm, and the porosity of the glass bubbles after filling is 50 to 85%.

[0011] Preferably, a dust filter having a precision of 1 to 5 um is provided on both the intake end surface and the exhaust end surface of the U-shaped tube, and an automatic control valve is provided on both the gas inlet and the gas outlet of the U-shaped tube.

[0012] Preferably, the intake end face and exhaust end face of the U-tube are located outside the Dewar vessel, for realizing vertical adjustment of the U-tube.

[0013] Preferably, both the inlet pipe and the outlet pipe are provided with automatic control valves, One branch of the extract quantification tube is connected to the infrared spectrometer by a two-way catheter for automatically supplying liquid, and the other branch is for draining liquid. An automatic control valve is provided at a point upstream of the two-way catheter where the flow is not divided, and an automatic control valve is also provided in the catheter for draining liquid in the two-way catheter.

[0014] Preferably, the extraction solvent is trichlorotrifluoroethane or carbon tetrachloride.

[0015] Preferably, the Dewar vessel is further provided with a liquid nitrogen inlet and outlet, a liquid nitrogen level gauge is provided inside the Dewar vessel, a thermometer is provided inside the U-tube, and a heater is provided outside the U-tube, and after concentrated sampling is performed in the cold trap, the sample is quickly returned to room temperature by heating before being extracted.

[0016] Preferably, the measurement range of the measurement device is 1500 ppmW to 1 ppbW.

[0017] The present invention further provides a method for measuring trace and ultratrace oil contents by the above-described device, Step S1: Concentrating and sampling trace and ultratrace oil components in the gas using a liquid nitrogen cooling trap; Step S2 of extracting the concentrated sample by adding an extraction solvent; Step S3: measuring the oil concentration of the extract using the infrared spectrometer according to the HJ637-2018 measurement standard for petroleum and animal and vegetable oils in water, and calculating the mass of oil in the extract; Step S4 of measuring the total mass of the gas that has passed through using a mass flow meter; and step S5 of calculating and obtaining the oil content in the gas based on the total mass of the gas obtained in step S4 and the mass of oil obtained in step S4. Effect of the Invention

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: In the method and device for measuring trace and ultratrace oil content according to the present invention, the method of concentration by liquid nitrogen cooling trap is used to effectively extract, and the measurement of the oil content in the gas is converted into the measurement of the oil concentration in the liquid extraction solvent, and the infrared spectrophotometry is used to perform accurate measurement, with a measurement accuracy of 1500ppmW~1ppbW, a wider measurement range, and reliable measurement in the ultratrace and trace ranges is realized, and the pollution source in the low-temperature process can be easily, quickly and accurately found, thereby further solving the problem of oil pollution in the low-temperature system according to the pollution source, and various substances produced by the oxidation or decomposition of oil have slightly different degrees of absorption of infrared rays of different wavelengths at the molecular level, so that they can be distinguished according to the infrared spectrum, which is applicable to the environmental analysis of strict control of oil and gas samples in special fields such as space flight, and has a wide range of applications. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing an apparatus for measuring trace and ultratrace amounts of oil content according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be described in more detail below by specific embodiments with reference to the drawings. The following description is a preferred embodiment of the present invention, and 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.

[0021] FIG. 1 is a schematic diagram showing a measuring device for trace and ultratrace oil content according to the present invention, which includes a low-temperature concentrating device 1 for concentrating and sampling trace and ultratrace oil components in a gas, an extracting device 2 for extracting the oil components, and an infrared spectrometer 3 for analyzing the oil content of the liquid after extraction. The low-temperature concentrator 1 includes a Dewar vessel 11 for storing liquid nitrogen and a U-shaped tube 12 for immersion in liquid nitrogen. Gas flows through the U-shaped tube 12 to form a liquid nitrogen cooling trap, thereby realizing concentrated sampling of oil components in the gas. The extraction device 2 includes a container 21 for storing an extraction solvent, an import pipe 22 for importing the extraction liquid into the U-shaped pipe, an outlet pipe 23 for outlet of the extraction liquid, and an extraction liquid quantification pipe 24, in which the extraction solvent in the import pipe 22 flows in from a gas inlet adjacent to the U-shaped pipe 12, and the extracted extraction liquid flows out from a gas outlet adjacent to the U-shaped pipe 12, flows through the outlet pipe 23, and is stored in the extraction liquid quantification pipe 24, and the extraction liquid quantification pipe 24 is further used to measure the volume of the extraction liquid. The U-tube 12 is further provided with a mass flowmeter 121 for measuring the total mass of the gas passing through and calculating and obtaining the oil content in the gas based on the measured total mass of the gas and the oil concentration of the extract measured by the infrared spectrometer 3.

[0022] The U-tube 12 is a steel tube or glass tube for heat transfer type heat exchange, and glass bubbles 122 are further filled into the U-tube, and the interfaces of the glass bubbles on both sides of the U-tube 12 are higher than the interface of liquid nitrogen to increase the contact area between the gas and the extraction solvent, which contributes to the extraction of oil components. Preferably, the diameter of the glass bubbles 122 is 0.5 to 2 mm, and the porosity of the glass bubbles 122 after filling is 50 to 85%.

[0023] The intake end face and exhaust end face of the U-shaped tube 12 are both provided with dust removal filters 123 having a precision of preferably 1 to 5 um, and the gas inlet and gas outlet of the U-shaped tube 12 are both provided with automatic control valves 4 that can quantitatively control the mass of gas to be concentrated and extracted in the liquid nitrogen cooling trap.

[0024] The intake end surface and exhaust end surface of the U-tube 12 are located outside the Dewar vessel 11, and serve to adjust the vertical movement of the U-tube 12.

[0025] The inlet pipe 22 and outlet pipe 23 are both provided with an automatic control valve 4 for controlling the addition of the extraction solvent and the collection of the extract. The extract metering pipe 24 is connected to the infrared spectrometer 3 by a two-way catheter 5, one branch of which is for automatically sending the extract, and the other branch is for draining the extract. An automatic control valve 4 is provided at a non-divergent upstream point of the two-way catheter 5, and an automatic control valve 4 is also provided at the drainage catheter of the two-way catheter for controlling the extraction sample to be put into the infrared spectrometer 3 for measurement and analysis, and the extraction liquid to be discharged. Preferably, the extraction solvent is trichlorotrifluoroethane or carbon tetrachloride. When the oil concentration of the extract exceeds the upper limit of measurement of the infrared spectrometer 3, the extract may be diluted and then sampled for measurement, or may be diluted multiple times.

[0026] The Dewar vessel 11 is further provided with an inlet and outlet for liquid nitrogen, a liquid nitrogen level gauge 13 is provided inside the Dewar vessel 11, a thermometer is provided inside the U-tube 12, and a heater or heat insulation is provided outside the U-tube 12 to prevent oil droplets from condensing on the inner wall of the sampling tube to ensure complete sampling. After concentrated sampling with a cold trap, the sample is quickly returned to room temperature by heating before extraction. A vibration device may also be installed to realize vibration extraction, making the extraction more effective and uniform.

[0027] The present invention further provides a method for measuring trace and ultratrace oil contents by the above-described device, Step S1: Concentrating and sampling trace and ultratrace oil components in the gas using a liquid nitrogen cooling trap; Step S2 of extracting the concentrated sample by adding an extraction solvent; Step S3: measuring the oil concentration of the extract using the infrared spectrometer according to the HJ637-2018 measurement standard for petroleum and animal and vegetable oils in water, and calculating the mass of oil in the extract; Step S4 of measuring the total mass of the gas that has passed through using a mass flow meter; and step S5 of calculating and obtaining the oil content in the gas based on the total mass of the gas obtained in step S4 and the mass of oil obtained in step S4.

[0028] Based on the People's Republic of China Standardization Law HJ637-2018 Infrared spectrophotometric method for the determination of petroleum and animal and vegetable oils in water, molecular functional groups 2930cm -1 (CH3), 2960cm -1 (CH2), 3030cm -1 (Aromatic hydrocarbons) are the main components of oils used in low-temperature processes, and all of them can be represented by these three functional groups. Therefore, standard oil solutions of standard oils (methyl group, methylene group, and aromatic hydrocarbons) containing various oil molecular characteristics in low-temperature processes are mixed to prepare standard samples with different oil concentrations, and the absorbance of the standard samples is measured using an infrared spectrometer to obtain a linear relationship between the oil concentration and the 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 linear relationship. Preferably, the extract sample needs to be infrared analyzed 10 times, and only data with a relative standard deviation (RSD) of each data within 0.5% is valid, to avoid random errors in measurement.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: The method and device for measuring trace and ultratrace oil content of the present invention uses the concentration method of liquid nitrogen cooling trap to effectively extract and convert the measurement of oil content in gas into the measurement of oil concentration in liquid extraction solvent, and uses infrared spectrophotometry to perform accurate measurement, with a measurement accuracy of 1500ppmW~1ppbW and a wider measurement range, realizing reliable measurement in ultratrace and trace ranges, and can easily, quickly and accurately find the pollution source in low-temperature process, thereby further solving the problem of oil pollution in low-temperature system based on the pollution source. Since various substances produced by oxidation or decomposition of oil have slightly different degrees of absorption of infrared rays of different wavelengths at the molecular level, they can be distinguished based on the infrared spectrum, which is applicable to environmental analysis of strict control of oil and gas samples in special fields such as space flight, and has a wide range of applications.

[0030] Finally, it should be noted that the above embodiments are merely for illustrating the technical solutions of the present invention, and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments, or equivalently replace some or all of the technical features therein, but these modifications or replacements do not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present invention. [Explanation of symbols]

[0031] 1 Low temperature concentrator 11 Dewar vessel 12 U-tube 121 Mass Flowmeter 122 Glass Bubbles 123 Dust removal filter 13 Liquid level gauge 2 Extraction device 21 Extraction solvent container 22 Import pipe 23 Outlet pipe 24 Extract metering tube 3. Infrared spectrometer 4 Automatic control valve 5 Bidirectional Catheter

Claims

1. An apparatus for measuring trace and ultratrace oil content, comprising: The present invention is provided with a low-temperature concentrator for concentrating and sampling trace and ultra-trace oil components in a gas, an extractor for extracting the oil components, and an infrared spectrometer for analyzing the oil content of the liquid after extraction, The low-temperature concentrator includes a Dewar vessel for storing liquid nitrogen and a U-shaped tube for immersion in liquid nitrogen, and the gas flows through the U-shaped tube to form a liquid nitrogen cooling trap, thereby realizing concentrated sampling of oil components in the gas; The extraction device comprises a container for storing an extraction solvent, an import pipe for importing the extraction liquid into the U-shaped tube, an outlet pipe for outlet of the extraction liquid, and an extract liquid quantification tube, the extraction solvent in the import pipe flows into the gas inlet adjacent to the U-shaped tube, the extracted extract flows out of the gas outlet adjacent to the U-shaped tube, flows through the outlet pipe, and is stored in the extract liquid quantification tube, and the extract liquid quantification tube is further for measuring the volume of the extraction liquid, The U-shaped tube is further provided with a mass flowmeter for measuring the total mass of the gas passing through it and calculating and obtaining the oil content in the gas based on the measured total mass of the gas and the oil concentration of the extract measured by the infrared spectrometer.

2. 2. The device for measuring trace and ultratrace oil content as described in claim 1, characterized in that the U-tube is a steel tube or glass tube for heat transfer type heat exchange, the U-tube is further filled with glass bubbles, and the interfaces of the glass bubbles on both sides of the U-tube are higher than the interfaces of liquid nitrogen, thereby increasing the contact area between the gas and the extraction solvent and contributing to the extraction of oil components.

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

4. The device for measuring trace and ultra-trace oil content as described in claim 1, characterized in that the U-shaped tube is provided with a dust filter having an accuracy of 1 to 5 um on both the intake end and the exhaust end, and an automatic control valve is provided on both the gas inlet and the gas outlet of the U-shaped tube.

5. The device for measuring trace and ultratrace oil content as described in claim 1, characterized in that the intake end face and exhaust end face of the U-shaped tube are located outside the Dewar vessel, and are intended to enable the U-shaped tube to be adjusted up and down.

6. The inlet pipe and the outlet pipe are both provided with automatic control valves; The device for measuring trace and ultratrace oil content as described in claim 1, characterized in that one branch of the extract quantification tube is connected to the infrared spectrometer by a two-way catheter for automatically sending liquid, and the other branch is for draining liquid, and an automatic control valve is provided at a non-diverging point upstream of the two-way catheter, and an automatic control valve is also provided in the catheter for draining liquid in the two-way catheter.

7. 2. The apparatus for measuring trace and ultratrace oil content according to claim 1, characterized in that the extraction solvent is trichlorotrifluoroethane or carbon tetrachloride.

8. The apparatus for measuring trace and ultratrace oil content according to claim 1, characterized in that the Dewar vessel is further provided with a liquid nitrogen inlet and outlet, a liquid nitrogen level gauge is provided inside the Dewar vessel, a thermometer is provided inside the U-tube, and a heater is provided outside the U-tube, and after concentrated sampling is performed using a cooling trap, the sample is quickly returned to room temperature by heating before being extracted.

9. The apparatus for measuring trace and ultratrace oil content according to claim 1, characterized in that the measurement range of the measuring apparatus is 1500 ppmW to 1 ppbW.

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