In situ, portable and robust laser sensor for simultaneous measurement of ammonia, water vapor and temperature in denitrification processes of coal fired power plants

Simultaneous measurement of the ammonia, flue gas temperature and water vapor concentration in denitrification (deNOx) processes is of great importance for improving the deNOx efficiency of coal-fired power plants (CFPPs) and maximizing energy conservation and emission reduction. A portable, robust, low-cost and low-power laser sensor was developed based on wavelength modulation spectroscopy (WMS) with a single near infrared diode laser, which covers the optimized NH3 spectral line at 6612.73 cm(-1) and H2O line pair at 6612.02 and 6609.85 cm(-1). A calibration-free for WMS with varied modulation amplitude (WMS-VMA) was proposed to improve the performance of the tri-spectral line analysis. A probe, based on Herriott cell structure, coupled with deformation resistance, dust-proof, air-tight and anti-seismic, was design to adapt to the harsh environment of CFPPs. Lab-based sensor evaluation showed that the measurement accuracies for the temperature, H2O and NH3 concentration are 2.9 %, 4.8 % and 5.1 %, respectively. Allan variance analysis shows that the sensor has good stability, and the measurement sensitivity at five-second resolution are 0.1 ppm and 0.03 % for NH3 and H2O concentration, respectively. Furthermore, the feasibility of the sensor system was also verified by field tests at both deNOx inlet and outlet in a practical CFPP, denoting great potential of ammonia injection optimization in deNOx process.