Studying And Instrument Of In-situ VOCs Monitoring System Based On TDLAS

Nowadays the air pollution is becoming more and more harder. The detection of pollutant, flammable or explosive gases is of great importance to the environmental protection and production safety. As important components of air pollutant, volatile organic compounds (VOCs) are harmful for the environment and human. Most of VOCs are toxic for animals and plants, and some of them may generate photochemical smog in the sunlight, which can cause severe secondary pollution. But till now, by conventional monitoring methods VOCs can not be on line detected rapidly and accurately.As a rapid accurate on line gas monitoring method, tunable diode laser absorption spectroscopy (TDLAS) has been used in monitoring many kinds of air pollutants, such as SO2, NH3, CO, CO2 and so on. TDLAS system is an in-situ monitoring system, and it is characterized with long period of calibration, short response time and high accuracy. TDLAS can be used broadly in in-situ monitoring of many kinds of harmful gases, but because of spectral character variance between inorganic gas and VOCs it is hard to monitor VOCs directly with classical TDLAS system.Based on spectral characters of VOCs and the TDLAS technique, we did some improvement on the structure of classical TDLAS system. Using two ways of theoretic derivation and experimental verification, we solved the following problems, including half-peak breadth of VOCs being much wider than those of inorganic gases, spectra aliasing and the absorption bands of VOCs being close to middle-infrared band.After we built a new system for monitoring VOCs, we did linear calibration of the system and evaluated its capability. This investigation has expended the monitoring scope of TDLAS, and provided a rapid and exact in-situ system for analyzing VOCs.