The Detection Of Heavy Element In Flue Gas By Laser-Induced Breakdown Spectroscopy

With the need for sustainable development and the improvement of environmentalprotection consciousness, people began to generally concern about the hazards of airpollution. How to effectively control the emissions of flue gas pollutants has graduallybecome an emerging and cutting-edge area in combustion research, also become thefocus of attention of the government departments and research institutes. The premise ofcontrol of flue gas pollutant emissions is that the concentration of pollutants in the fluegas is real-time online measurements. In thesis, the detection of combustion flue gas byLaser-Induced Breakdown Spectroscopy was introduced, to achieve the real-time onlinemonitoring of a variety of pollutants emissions in the combustion process; it will havepositive and far-reaching impact on prevention of air pollution. In order to solve theproblem of using the LIBS technology to real-time detect heavy metals in the flue gas, aseries of studies were carried out and the main work is as following:(1)Set up a LIBS flue gas monitoring device which consists of the detection system,the simulated flue gas system, the actual flue gas produce system. Through theintegration of the sample chamber and integration of the entire system, the real-timeonline qualitative analysis of Ni, Cd, Hg, Fe, Mg, Cu, Ca, Al, Pb, Sr, Ba, Na, Kelements has been achieved in the flue gas, it laid the foundation for the following work.(2)To improve detection capability of the LIBS and meet the demand to the actualflue-gas detection, much critical technology was studied systematically, such asimproving the detection sensitivity, expanding the wavelength region, efficient signalprocessing method and so on. Except of the simple’s character and content, the signalintensity of the LIBS also has relationship with the system parameter. We got the bestsystem parameter, which is the laser’s energy is100mJ, the delay time is500ns, the gatewidth is3μs and the accumulating time is20. For there is low concentration ofpoisonous emission particulate in the gas, the sample compression technology was usedto improve the detection sensitivity, and the inlet diameter is24mm. the outlet diameteris1mm. The sample was sprayed from the large area to the laser plasma area by thesmall export.(3) The study of the detection device calibration system. Spectral calibration ofheavy metal elements in flue gas is much more complex than other forms of sample calibration. Due to there is no standard sample for calibration, so this article hasdesigned two sets of calibration system for liquid-solid transformation calibrationsystem and dry fluidized bed calibration system. By the calibration system produce aknown concentration of sample to be calibrated and draw up the calibration curve of thevarious analysis elements. The atomic physics parameters database was established ofvarious elements used for the quantitative analysis of the characteristic lines andcalculated on the basis of various heavy metal elements for rapid quantitative analysis.The detection limit of Ni(5.09mg/m~3), Cd(1.00mg/m~3), Hg(6.17mg/m~3), Pb(60.64mg/m~3), Sr(0.64mg/m~3), Ba(0.83mg/m~3) has been got by calibration curve.The results will provide the basis for the monitoring of gas pollutants in thedirection of the development of practical technologies.