Development And Performance Improvement Of A Multifunctional Portable Ammonia Escape Laser Detector

Detection of ammonia slip concentration in denitrification（de NOx）process is of great significance for improving denitrification efficiency and realizing energy conservation and emission reduction.The current ammonia slip laser sensor system for de NOx detection has a single function and does not simultaneously detect the water vapor concentration and flue gas temperature,which also affect the de NOx efficiency.In addition,in practical application,in-situ portable detection instruments are required to better understand the distribution of ammonia slip concentration and to optimize ammonia injection.Therefore,in view of the actual requirements of simultaneous and in-situ detection of ammonia slip,water vapor concentration and temperature in denitrification process,a multi-functional portable ammonia slip laser sensor system was developed.Firstly,a highly sensitive and high-precision multi-parameter detection method based on a single near-infrared laser is developed.Firstly,the absorption spectral bands of NH₃and H₂O were optimized,and 6609.5-6613cm^-1was determined as the detection band,which could be covered perfectly by a single 1.512μm distributed feed back（DFB）laser.Then based on wavelength modulation spectroscopy（WMS）developed varied modulation amplitude of WMS-2f/1f calibration-free method,reduce the interference between absorption lines at the same time improve the signal-to-noise ratio（SNR）of the harmonic signal.Finally,the multi-component gas concentration inversion algorithm is developed to realize the high sensitivity and high precision detection of NH₃and H₂O concentration and temperature.Secondly,the multi-function portable ammonia slip laser sensor system has been developed and improved.Firstly,the design and construction of the ammonia slip laser sensor system of the first version are introduced.Later,problems such as poor vibration resistance,easy condensation of the lens,low integration of the host,low SNR and low detection accuracy are found in the application,which often lead to measurement failure.Then the first version of the laser sensor system has been improved.By adding a mirror structure,the length of the fixed part is reduced and the vibration resistance of the cavity is enhanced.The location of the built-in long optical path gas cell is replanned and designed to avoid lens condensation.The laser control circuit board with small volume is adopted to ensure the precise control of the laser and improve the integration of the host.empirical mode decomposition（EMD）algorithm was used to suppress the standard fringe and noise in harmonic signals,and the measurement sensitivity was improved by 42.76%.Kalman filtering algorithm was used to carry out real-time filtering of tunable diode laser absorption spectroscopy（TDLAS）measurement results,and the detection accuracy was improved by three times.The improved and completed laser sensor system consists of a multi-function,miniaturized,low power consumption,low cost sensor host and a portable,robust,plughable sampling probe.Thirdly,the performance of ammonia slip laser sensor system is evaluated both in laboratory and field.Lab experiments showed that the measurement accuracies for NH₃and H₂O concentration and temperature are 5.1%,4.8%and 2.9%,respectively.Allan variance analysis shows that the sensor has good stability,and the measurement sensitivity at five-second resolution are 0.1ppm and 0.03%for NH₃and H₂O concentration,respectively.Furthermore,the feasibility of the sensor system was also verified by field tests at both de NOx inlet and outlet in a practical coal-fired power plant,denoting great potential of ammonia injection optimization in de NOx process.