LAUSR

Ammonia has been recently recognized as promising carbon-free fuel towards decarbonizing both the power and industrial heating sectors. However, fuel slip during ammonia combustion is of high concern because of the low reactivity and high toxicity of the chemical, motivating the development of sensitive sensor for real-time monitoring of ammonia emission in combustion flue gases. In this work, a near-infrared absorption spectroscopic sensor was developed for trace ammonia (NH3) measurements in high-temperature flue gas environments with water vapor (H2O) concentration as high as 40% (mole fraction), which is particularly suitable for monitoring fuel slip in ammonia combustion system. The sensor used a distributed feedback (DFB) laser to target the NH3 absorption line near 6612.73 cm-1. Proof-of-concept tests were conducted in a high-temperature multi-pass cell with a controlled temperature of 500 K and pressure of 1 atm. A custom-designed variable humidity generator was used to provide reference NH3/N2 mixture with controlled H2O concentration (10%-40%) to simulate ammonia combustion flue gases. Direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) were both used to ensure a relatively large dynamic range. H2O-induced broadening effects on the measured absorption profile were quantified. The developed sensor was firstly validated against NH3/N2 mixtures with different H2O concentrations with a lower detection limit of 70 ppb achieved. Real-time measurement of NH3 slip in the flue gases from CH4/NH3/air flames and CH4/NH3 co-firing industrial furnace were performed as a demonstration of the sensor for time-resolved ammonia monitoring with sufficient accuracy, sensitivity, and time response.