ISO 17179:2016 specifies the fundamental structure and the most important performance characteristics of automated measuring systems for ammonia (NH3) to be used on stationary source emissions, for example, combustion plants where SNCR/SCR NOx control systems (deNOx systems) are applied. The procedures to determine the performance characteristics are also specified. Furthermore, it describes methods and equipment to determine NH3 in flue gases including the sampling system and sample gas conditioning system.
It describes extractive systems, based on direct and indirect measurement methods, and in situ systems, based on direct measurement methods, in connection with a range of analysers that operate using, for example, the following principles:
- ammonia conversion to, or reaction with NO, followed by chemiluminescence (CL) NOx difference measurement for ammonia (differential NOx);
- ammonia conversion to, or reaction with NO, followed by non-dispersive ultraviolet (NDUV) spectroscopy NOx difference measurement for ammonia (differential NOx);
- Fourier transform infrared (FTIR) spectroscopy;
- non-dispersive infrared (NDIR) spectroscopy with gas filter correlation (GFC);
- tuneable laser spectroscopy (TLS).
The method allows continuous monitoring with permanently installed measuring systems of NH3 emissions, and is applicable to measurements of NH3 in dry or wet flue gases, for process monitoring, long term monitoring of the performance of deNOx systems and/or emission monitoring.
Other equivalent instrumental methods can be used, provided they meet the minimum requirements proposed in ISO 17179:2016. The measuring system can be calibrated with certified gases, in accordance with ISO 17179:2016, or comparable methods.
The differential NOx technique using CL has been successfully tested on some power plants where the NOx concentration and NH3 concentration in flue gas after deNOx systems are up to 50 mg (NO)/m3 and 10 mg (NH3)/m3, respectively. AMS based on FTIR, NDIR with GFC and TLS has been used successfully in this application for measuring ranges as low as 10 mg (NH3)/m3.