The Research On High Temperature Measurement By Tunable Diode Laser Absorption Spectroscopy Technique

The pollution problems is becoming more and more serious as the economy developed and the rapid industrialization process in the recent years, because of the emission of large amounts of waste gases produced by coal-fired power plants and metallurgy, and combustion of urban solid waste. As one of the most important parameter, the temperature used for monitoring and control in process industries which has been applied in continuous emission monitors and in the optimization of combustion, and which could improve the environmental protection and energy conservation.The measurement method of temperature can be divided into two main categories: contact and non-contact. The former must contact the target as the own temperature which only shows the temperature of the contact point. The sensors of this category normally have long response time and low dynamic measured range. The latter have fast response and large dynamic range because of without contacted target that are inaccessible due to hostile environments and geometry limitations. Therefore, the non-contact method of temperature measurement is fit for high temperature and hash environment.As one of superior sensitivity and high-resolution technique, Tunable diode laser absorption spectroscopy (TDLAS) also has features of non-invasive and high-selectivity. The most widely applied TDLAS instrumentations are based on distributed feedback (DFB) lasers which are robust and easily couple to the fibers, so the technique has strong ability of anti-electromagnetic interference for field application. Meanwhile, TDLAS is non-extractive assessment of combustion process which debases the doubts of the people concerned. The paper shows the research on temperate measurement by TDLAS, and all the study in progress are based on water spectrum between7150-7200cm-1using the DFB laser (NEL Company, NLK1E5GAAA).In order to clear the research content and well purpose, the beginning of this paper describe the technique development for high temperature measurement. The HITEMP molecular spectroscopic database for high temperature modeling of the spectra of molecules in the gas phase is described. It also provides an overview of the basic theory of absorption spectroscopy and the basic principles of temperature measurement method by TDLAS, then explains the experimental apparatus and its main parameters. The innovation of the paper is to define the concepts of "Two-spectrum group" instead of "Two-line" which used to measure temperature appeared in the previous literature for innovation. The water vapor spectrum in the1392nm region is systematically analyzed to find the best "Two-spectrum group" for sensitive measurement of temperature using a single tunable diode laser. The development of "Two-spectrum group" design-rule approach establishes a new paradigm to optimize tunable diode laser sensors for temperature measurement. Three "Two-spectrum group" are selected for temperature sensor by theory simulation. Through the experimental verification of temperature sensor, the "Two-spectrum group"7164.8993cm-1and7165.8203cm-1are established for industrial application, then explain the experimental error and data analysis.In addition, the design of system software for theory simulation, data acquisition and data fitting are introduced. Finally, concluding remarks and further research made a number of recommendations.