Ammonia (NH3) slip

The accurate measurement of unreacted ammonia (NH3), or ammonia slip, is of concern for utility boiler systems employing urea- or ammonia-based selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) processes for NOx control. NH3 slip has important impacts upon deposition, plugging and potential corrosion of cold-end equipment located downstream of the SCR or SNCR system. Excessive NH3 slip can also impact ammonia adsorption in the fly ash and can contribute to stack plume and visibility problems. The levels of NH3 slip will also indicate the proper operation of the SCR/SNCR systems and the NOx reduction process. Over the last few decades there has been increasing concern about man-made pollution of the atmosphere. The dilution of pollutants in the atmosphere makes the concentrations very low, often below 1 ppb, and therefore difficult to measure. There are numerous reported measurements of trace gases in the atmosphere and measurements of some gases such as CO and NOx, are done routinely in many cities. In addition to measuring the gases in the atmosphere, it is important to monitor the many sources of emission, where traffic, agriculture and industry are the most important types. Industrial processes are often large-scale point sources with gas abatement systems which can be optimised to reduce the emissions.