A multi-laser hybrid absorption sensor for simultaneous measurement of NH3, NO, and temperature in denitrification flue gas

The real-time monitoring of NH3, NO, and flue gas temperatures is critical to controlling NOx emissions from coal-fired power plants, reducing ammonia slip, and realizing accurate ammonia injection. However, few previous studies have utilized laser absorption sensors to measure these three indicators simultaneously. In this paper, a multi-laser hybrid sensor is designed based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneous measurement of NH3, NO, and flue gas temperature. The sensor uses a distributed feedback (DFB) laser to target the NH3 and the H2O lines, and a quantum cascade laser (QCL) is used to target the NO line. In the measurements of NH3 and NO using calibration-free wavelength-modulated spectroscopy (CF-WMS), we employ a method to obtain the laser wavelength response by fitting the demodulated signal of a standard gas. Additionally, temperature measurements are obtained using the time-division multiplexing (TDM) strategy and direct absorption spectroscopy (DAS) techniques with the help of the absorption spectrum of H2O. Under static conditions, the relative accuracy of NH3 and NO detected by the sensor is 4.2% and 2%, respectively, and the maximum relative standard deviation of temperature is 1.3%. When tested under flowing conditions, the sensor can accurately capture NH3, NO, and temperature changes. The relative accuracy of NH3 and NO is 4.7% and 2.2%, and the relative standard deviation of temperature is 0.9%. The sensor has great potential in optimizing denitrification processes in thermal power plants.