Several ways to detect oil content in compressed air

Thread Content

With the widespread application of compressed air, different industries have different requirements for compressed air quality. The main factors that affect the quality of compressed air are oil, water, and solid particles. However, oil content is the most difficult to detect. Because of this, different detection methods and detection methods have emerged in the industry. At present, common methods for measuring oil content generally include gravimetric method, ultraviolet spectrophotometry, infrared spectrophotometry, chemical indicator tube method, particle size spectrometer method, photochemical ionization detector method, gas chromatography-mass spectrometry technology, etc. 1. Gravimetric method Gravimetric method is a method in which a certain amount of sample gas is placed in a container or medium (filter paper, filter membrane) with a constant weight, evaporated, dried, and weighed at a constant weight to determine the analysis result. Gravimetric method is the earliest method used to determine oil content. Currently, many people still use gravimetric method to determine water bodies with high oil content. When using the gravimetric method, it is necessary to strictly control the dryness and wetness of the sampling tube, absorbent cotton quantitative filter paper and the influence of dust contamination, and strictly prevent other oil contamination. During the sampling and analysis process, absolutely no additional debris is allowed to adhere to the container or medium being weighed. The balance must be weighed quickly and accurately. This is because mechanical and dust impurities in the air during sampling will affect the accuracy of the oil content. However, the low sensitivity of the gravimetric method determines that it is not suitable for accurately measuring the oil content in the gas. Because the oil content in the gas is quite low, it is obviously inappropriate to use the gravimetric method to determine it. 2. Infrared spectrophotometry UV spectrophotometry has become one of the methods widely used in China due to its short test time, simple sampling structure, and high test accuracy. The UV spectrophotometric determination method is based on the characteristic absorption of aromatic compounds with conjugated bonds and benzene rings contained in oil in the ultraviolet region. Therefore, this method can be used to determine the concentration of substances with conjugated double bond structures to determine the oil concentration in gas samples. 3. Chemical indicator tube method The main manufacturers of instruments using the principle of chemical indicator tube method are Johnson Controls of the United States and Dräger of Germany. Johnson Controls' oil indicator is equipped with a gas detection agent that reacts with the oil to form a colored layer. Quantitative analysis is performed based on the depth of the color layer or the length of the discolored layer. Dräger's oil detection tube method captures oil mist into the indicator layer of the oil detection tube. Under the action of a catalyst, it reacts with the concentrated sulfuric acid in the oil detection tube to produce a black product. There is a correlation between the color depth and the oil content. The oil content in the air is detected through colorimetry. This method generally only determines whether the oil content is greater than a certain value and cannot obtain a specific value. This method is simple to sample, but it takes a long time and can only detect a general range of oil content without specific values. 4. Particle size spectrometer method The particle size spectrometer is an instrument that uses the scattering principle of light to count suspended particles, so it cannot distinguish suspended oil and solid particles. However, this method can be used to measure the oil content of specific gases (for example, only containing oil particles). Its biggest advantage is that the measurement speed is fast and can be measured in real time. 5. Photochemical Ionization Detector Method In recent years, Germany's Beko and Sears have each launched online oil content testing instruments, using the photochemical ionization detector method. This method is a method of measuring hydrocarbon vapor content through a PID (photochemical ionization detector). From a principle perspective, this method mainly measures oil vapor, so it is generally used to monitor changes in oil content in compressed air online. However, since this type of instrument mainly targets hydrocarbons, and oil impurities are only part of the hydrocarbons, it is difficult to accurately measure the total oil content. 6. Gas chromatography-mass spectrometry technology Gas chromatography-mass spectrometry technology is mainly used to measure oil vapor. The principle is to use activated carbon to absorb oil vapor, and then use gas chromatography-mass spectrometry technology for analysis and measurement. As the requirements for the oil content of compressed air become higher and higher, and the proportion of oil vapor becomes larger and larger, this method will also become an important method for oil content measurement. The following are several common detectors currently available: 1. Dräger Aerotest Dräger Aerotest Alpha compressed air quality detector is a relatively simple, common and fast way to test compressed air quality. It has only 4 detection channels and can detect the concentration of oil, water, carbon monoxide and carbon dioxide in compressed air individually or simultaneously. It is most commonly used to detect the concentration of water and oil in compressed air. It is also a dedicated detector for GMP certification in the biopharmaceutical industry. Main advantages and features: 1. Used to detect the oil content, water content, CO, CO2, etc. of low-pressure compressed air. This product has been widely used in GMP certification in the domestic biopharmaceutical industry and mainly detects the oil and water content in compressed air. 2. Breathing air quality can be detected through quantitative analysis of contaminants in compressed air according to appropriate purification standards. Can meet the requirements of different standards (such as: DIN3188 standard). 3. The Dräger detection tube can be used to quantitatively detect water vapor H2O, oil, carbon dioxide CO2, carbon monoxide CO and other pollutants in compressed gas. 4. The quick plug-in interface of the Dräger compressed air tester can be connected to various types of air supply system interfaces. 5. No power supply is required for compressed air testing. 6. All components of the detector can be packed into a hard suitcase, making it easy to carry and operate. As follows, the detection value of the Dräger oil tank is shown in the reference chart.: It should be noted that the Dräger detector can only be used to detect oil mist in compressed air. Oil vapor cannot be displayed and cannot detect the actual value. It can only detect the approximate oil content range and the detection limit.: 0.05mg/m3 oil mist. 2. Hillside SUTO S120 Hillside SUTO S120 uses the photoionization detector method, which is a method of measuring hydrocarbon vapor content through PID (photoionization detector). It is an oil vapor sensor used to measure the oil content of compressed air and other gases within the allowed range of specification parameters. The S120 oil vapor sensor can be used for long-term monitoring of the oil vapor content of compressed air and industrial gases. It can also be used in conjunction with the S551 to provide sampling monitoring as a portable device. The automatic calibration design is adopted to ensure the stability and high accuracy of the instrument. The S120 will monitor and display the sensor's pollution status and lifespan to the user. When it detects "exceeding the use range", the sensor will block the sampling gas to prevent contamination. The instrument is easy to carry, simple to operate and highly accurate. Main advantages and features: 1. Measure the oil vapor content of compressed air or other gases. 2. Connect through the sampling tube and quick interface. 3. Can be used as fixed or portable application. 4. Measure small oil content as low as 0.001 mg/m3. 5. PID sensor, high accuracy. 6. LED indicator light prompts service and alarm. 7. Connect SUTO display and data logger or third-party display and control device. 8. IP 65 housing provides good protection even in harsh industrial environments. 9. The built-in display (optional) of the residual oil detector can directly display the actual value. 3. The German cs instruments gas measuring instrument OILCHECK 400 compressed air oil content detector. The principle adopted by the German cs instruments gas measuring instrument OILCHECK 400 compressed air oil content detector and Hills SUTO S120 is the photoionization detector method, which can continuously measure with high precision except liquid oil, mist oil and vapor form. The low detection limit is 0.001mg/m³, which can monitor level 0 air quality ISO 8573. Different from the S120, it adopts a fixed bracket method and can be installed at the back end of the compressed air system for online monitoring at any time to monitor the quality of compressed air in real time, effectively ensuring equipment production and product quality. Advantages and features: ·PID sensor with long-term performance, high-precision residual oil measurement (oil vapor) measurement (photoionization detector) and ideal choice for mobile measurement. The PID sensor can obtain accurate measurement results in about 30 minutes. Automatic zero-point calibration can obtain long-term stable measurement results. The integrated mini-catalyst is reliable and generates a reference gas for zero point calibration. The reference gas with the help of an activated carbon filter will affect the measurement accuracy due to the aging and saturation of the activated carbon filter. The Zheng type catalyst that generates "zero air" will not age or wear, there is no need to replace the activated carbon filter, and sampling can be easily done through PTFE hose or stainless steel tube. Catalytic oxidation technology is the best solution to remove oil from compressed air. Stable oil-free compressed air can be obtained without replacing the oil-free machine, and it can reach level 0 status. Different from conventional oil removal filters, catalytic oxidation oil removal equipment uses core material catalysts to promote a chemical reaction between oxygen in compressed air and oil pollution under a certain temperature environment, ultimately generating carbon dioxide and water. Oil stains can be removed from the molecular level with no consumables or losses. Class 0 oil-free compressed air can be obtained stably for a long time.