Research On The Detection Of Pollutants In Flue Gas Denitration Process Using Tunable Diode Laser Absorption Spectroscopy Measurement

Accurate online measurement of the NH3 and NO concentration helps to monitor the condition of SCR facilities,determine the optimal amount of ammonia injected and control the ammonia injection angles in order to reduce NOx emission and ammonia leak at the exit of SCR facilities.Considering the problem of monitoring NO emmision of low concentration,this report took advantage of tunable diode laser absorption spectroscopy and wavelength modulation method to carry out theoretical research and experimental vertificaiton for measurement objects and envirenment based on the laboratory test system and further built testing systems in coal-fired fluidized bed units to realise simultaneous online monitoring of ammonia leak and NO concentration.It is believed that this paper should lay a foundation for further application.Considering the requirements of high precision and low concentration,the proper absorption lines were first chosen,which lies at the mid-infrared range of 5.19?m.Then an ICL laser was chosen as the laser source and the related experiment system was built.After that,the influence that varying modulation currents have on 2f signals(especially SNR and linear correlation coefficient)was explored,and the best modulation current were further selected.The measurement results of low-concentration nitric oxide(less than 20 ppm)with the best modulation parameter chosen before were fully evaluated.Meanwhile,in view of the influence of temperature fluctration on NO signals,experiments focusing on the signal changes within temperature range of 200-500 ?were carried out and a three-time polynomial fitting was conducted to get an experimental modifier formula for temperature correction.Also,the measurment results at fluctuating temperatures were carefully evaluated.Forthermore,a WDM optical experiment system was designed to monitor ammonia leak and NO concentration at the same time and on the same optical path.For the actual site measurement,a measuremtn hole was installed in the flue duct of a circulating fluidized bed coal boiler in Jiaxing.By changing the spray ammonia flow,fluctuation of ammonia leak and NO concentration was mainly monitored and compared with related statistics measured by measurement devices in use now.