Removal of ammonium chloride generated by ammonia slip from the SNCR process in municipal solid waste incinerators

The selective non-catalytic reduction (SNCR) process is one of the methods used to reduce NOx to N2 and H2O by injecting NH3 or urea solution into a high-temperature furnace. Merits of this method include simple handling, low cost, and energy savings. However, a critical problem of the SNCR process is the generation of ammonia slip; in reactions with HCl in flue gas, ammonium chloride is generated and forms detached white plumes near the stack. Using a laboratory-scale experimental apparatus, we examined the possibility of NH4Cl collection and removal by a bag filter (BF). The molar NH3/HCl ratio of the compound collected at the filter was nearly one, regardless of gas temperature, retention time, and concentration, confirming the formation of NH4Cl. The NH4Cl generation ratio increased as reaction temperature decreased, indicating that the collection efficiency of NH4Cl should increase if the BF is operated at the lowest possible temperature while avoiding the critical point causing low-temperature corrosion (e.g., 150 °C). In addition, the use of activated carbon injection in the front of the BF and the dust layer on the BF are expected to capture slipped ammonia at the BF and reduce NH4Cl fume generation in the stack.