Detection And Analysis System For CO₂Gas Based On TDLAS

With the rapid development of economy and the significantly improved livingcondition, people start to worry about the problems of resources and environment lyingbehind. Eco-environment protection and the treatment of pollution, with the exhaust oftoxic gas as the main source, are the focus issues drawing attentions from manycountries around the world. The carbon dioxide discharged by industrial production,civil coal firing and automobile exhaust could lead to the greenhouse effect,desertification and other serious problems. Therefore, the real-time monitoring ofcarbon dioxide is of great significance. Non-contact detection for optical gas hasachieved a fast development in recent years and makes up the deficiency of traditionalmeasurement methods for gas density in both the accuracy and speed. The detectionfor the density of carbon dioxide in this thesis is based on the tunable diode laserabsorption spectroscopy (TDLAS), which is a high resolution technique with excellentsingle mode property, high accuracy, fast response, good versatility and otheradvantages.The Lambert-Beer’s law is used as the basic theoretical foundation for the systemand also combined with some relevant theory of TDLAS for detection of gasconcentration, which are used for the theoretical derivation of wavelength modulationand harmonics detection technology, including the determination of theoreticalexperimental parameters for harmonics detection times, modulation depth, etc..Besides, by applying the relevant knowledge on molecular spectrum of gas andspectral line shape, the study of two important elements, the temperature and thepressure, is conducted. The TDLAS system is also designed and constructed. Duringthe construction, the optimum working condition for the laser is gained through thecharacteristic test for the tunable diode laser. The density test of carbon dioxide for thissystem is also run, which are used to detect gases at different temperature and pressureas well as modify the impact of measuring the concentration values for temperatureand pressure. Finally, the software programming in host computer is performed byusing LabVIEW and the inversion formula of gas density is obtained through linearfitting, meanwhile measuring standard gas concentration to get a satisfactoryexperimental result，so the online detection of the carbon dioxide density is basicallyrealized.