Photoacoustic system for NH3 detection in a selective catalytic reactor

摘要

Abstract: A new instrument specifically developed for measuring NH$-3$/ 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 CO$-2$/ combustion gas that absorbs at the same wavelength used for NH$- 3$/, lowering the sensitivity of the technique. A $+13$/CO$-2$/ tunable laser emitting at three wavelengths has been used in order to evaluate simultaneously the CO$-2$/ and NH$-3$/ 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. !2