The Online Monitoring System of VOCs Emitted by Stationary Pollution Source Based on FTIR
Lü Shi-long1, ZHAO Hui-jie1, REN Li-bing2, WANG Xin3, WEI Hao-yun1, LI Yan1*
1. State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, Tsinghua University, Beijing 100084, China
2. Wuhan Tianhong Environmental Protection Industry Co., Ltd., Wuhan 430223, China
3. College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, China
Abstract：VOCs (Volatile organic compounds) not only cause global environmental pollution, but also have negative impact on people’s daily life. Efficient and accurate monitoring of VOCs has become a hot issue in China’s atmospheric environment governance. Compared with other gaseous pollutants, VOCs are more volatile and easily react with other gaseous pollutants. The complexity of their physical and chemical characteristics sets higher requirements on existing detection methods. Among various gas detection methods, spectral detection technology has been widely used due to its advantages of convenience, rapidity, and accuracy. As an important spectrum detection technology, FTIR (Fourier transform infrared spectroscopy) is multi-channel, which could analyze hundreds of pollutants and calculate real-time pollutant concentrations as well, solving the problems caused by the complex nature of VOCs gas. This paper has tested the online monitoring system of VOCs emitted by stationary pollution source, which is based on FTIR. The infrared interference signal emitted by the interferometer is absorbed by the target gas in the 10-m path length gas pool and subjected to Fourier Transform to obtain the infrared spectrum containing the characteristic absorption peak of the gas. In addition, the comparison between the infrared spectrum and standard database helps with identification of the target gas and concentration measurement. This system covers a spectral range of 650～4 000 cm-1. Since most VOCs have relatively independent absorption peaks in the mid-infrared fingerprint area, the analysis of multiple gases can be completed with a spectral resolution of 1 cm-1 and a concentration detection range of 1.6～319.47 mg·m-3 (Take Benzene as an example). What’s more, the system analyzes and tests dozens of VOCs, such as toluene, acetone, and ethyl acetate, obtaining infrared spectra of different gases, which coincides well with the standard database and can be differentiated according to the absorption peaks of different gases. In order to obtain the exact gas concentration, instruments need calibration as well as to reduce the adsorption of gas in the inner chamber and the mirror and control the water vapor content, a temperature control system is added to monitor the temperature of the gas pool in real time. Meanwhile, with xylene standard gas with different concentrations inflated, this experiment uses the five-point calibration method to obtain the relationship between the analytical concentration and the standard concentration, leading to a relative deviation of the analytical concentration less than 0.06%. To verify the performance of the system in actual working scenario, this paper selects a coating workshop to monitor the VOCs pollution caused by volatilization of solvents and diluents in coating process for one week obtaining concentration changes of benzene, methyl ethyl ketone, isopropyl alcohol and ethyl acetate. Concentration safety threshold is set to guarantee safe operations. From the long-time data analysis, the system MTBF (Mean Time Between Failure) is as long as 1 000 h, which provides a lasting, stable and reliable real-time monitoring.
Key words：FTIR; VOCs; Gas analysis; Online monitoring
吕世龙，赵会杰，任利兵，王 昕，尉昊赟，李 岩. FTIR固定污染源VOCs在线监测系统[J]. 光谱学与光谱分析, 2018, 38(10): 3106-3111.
Lü Shi-long, ZHAO Hui-jie, REN Li-bing, WANG Xin, WEI Hao-yun, LI Yan. The Online Monitoring System of VOCs Emitted by Stationary Pollution Source Based on FTIR. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2018, 38(10): 3106-3111.
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