Photoacoustic NH₃ Monitoring with Waveguide CO₂ Lasers

Abstract

Ammonia is not a natural constituent of fossil fueled power plant emission, but nitrogen oxides and sulphur dioxide are. In various schemes for denitrification and desulphurization, ammonia is introduced either as a reducer of NO_X as in the Selective Catalytic Reduction (SCR) process or as a neutralizer for acids developed in the denitrification, as in the corona based CORONOX process. In either case one wants to monitor the efficiency of the process and to be able to document compliance with NH3 emission limits. Thus, there is an increasing need for ammonia measurements in smoke stacks, and the monitor needs to be:

• moderately sensitive, corresponding to 1 ppm detection limit;

• very selective, so as to monitor NH3 regardless of known and unknown components in the smoke;

• automatic;

• moderately fast, corresponding to 1 measurement per 10 minutes for normal monitoring, and 1 per minute for reactor characterization and process optimization.