|
In recent years, due to the construction of large storage tanks and gas pipelines, there is an urgent demand for gas remote sensors with high sensitivity and fast response in the fields of petrochemical, gas, coal mine and electric power, and gas remote sensors carried by vehicles, drones and intelligent robots have become a hot spot in industrial applications. At present, the gas remote sensor based on TDLAS is still limited to methane. The near infrared absorption lines of ethane are weak, the absorption spectra of propane and butane are bands not characteristic peaks, so it is difficult to achieve the high sensitivity of alkane gas except for methane. Therefore, the actual industrial applications mostly use Fourier transform spectroscopy (FTIR) or photoionization detector (PID).The emergence of inter band cascade lasers (ICL) makes it possible to detect alkane and olefin gases with high sensitivity. Most propane detection schemes mostly use the absorption peak of 3370nm. Considering avoiding the influence of water vapor and carbon dioxide in the air, the absorption peak of 3364nm for propane is selected in this paper. In this band, the ICL laser is used to measure methane, ethane, propane and n-butane at the same time. A TDLAS measurement system with open optical path is constructed by placing a hollow reflector at a distance of 50 meters. The return light is collected and concentrated through the lens into the detector, and the absorption signal of alkane gas within 50 meters is obtained. In this paper, the absorption signals and harmonic signals of four kinds of gases at 15 meters and 50 meters are given respectively. According to the harmonic signal and noise, the detection limit of the gas to be measured is better than 50ppm∙m. According to the different gases to be measured in gas and petrochemical fields, a method of mixture identification is proposed to measure the recognition effect of mixture. Looking forward to the future, the response sensitivity of mid-infrared detectors continues to be improved, and alkane gas sensors without reflector at the end will become possible.
|
