Photoacoustic system for NH3 detection in a selective catalytic reactor

A new instrument specifically developed for measuring NH3 concentrations at the inlet and outlet of an SCR reactor is described. It is based on the photoacoustic technique and can perform an online and in-situ n-point measurement grid. The major problem is the severe interference of CO2 combustion gas that absorbs at the same wavelength used for NH3, lowering the sensitivity of the technique. A 13CO2 tunable laser emitting at three wavelengths has been used in order to evaluate simultaneously the CO2 and NH3 concentration. The integrated measurements have been done by a simple differential absorption technique by using a pyroelectric detector; the spatially resolved measurements have been carried out through the analysis of the acoustic wave generated by the laser beam and collected by four microphones perpendicularly disposed. Experimental tests on a 35 MW industrial plant and comparison with traditional sampling methods are presented.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.