Any special design consideration if flue gas has ammonia slip?
If a heater or boiler is equipped with a selective catalytic reduction unit (SCR) with ammonia injection for the NOx control, its stack flue gas will carry a residual ammonia gas (ammonia slip). The presence of ammonia, however, impacts NO2 and SO2 measurements, causing the daily calibration error check to fail and the pollutant measurements to drift significantly. To address the issue, an ammonia scrubber is installed right after the probe filter and maintained hot to keep the ammonia slip in the vapor phase. Should any condensation happen, the moisture would react with ammonia, forming ammonium salts in the downstream sample line which would scrub out NOx and SO2.