Abstract: This paper takes a 660-MW ultra-supercritical unit for example to study the NO_x distribution and ammonia slip concentration at the SCR denitration outlets after the ultra-low emission retrofit project. The ammonia slip concentration, NO_x concentration, oxygen volume and temperature are measured and tested. It is observed that the NO_x distribution at the outlets is severely uneven, and the ammonia slip concentration is beyond the designed value. In addition, in the area where the ammonia slip concentration is high, the NO_x concentration is low and the denitration efficiency is high. Also at some sampling points, high ammonia slip and NO_x concentrations are observed due to the heavy damage of catalyst caused by the high flue gas flow speed. The test results indicate that after ultra-low emission retrofit, the ammonia injection needs to be optimized and the flue flow field simulation test shall be carried out to improve the operation effect and economic performance of SCR denitration devices.

Key words: ultra-low emission, nitrogen oxide, SCR denitration, relative standard deviation, ammonia injection optimization, ammonia slip