Migration and Emission Characteristics of Ammonia/Ammonium through Flue Gas Cleaning Devices in Coal-Fired Power Plants of China

To investigate the up-to-date migration and emission characteristics of NH₃/NH₄⁺ in coal-fired power plants (CFPPs) after implementing ultralow emission retrofitting, typical air pollution control devices (APCDs) in CFPPs, including flue gas denitrification, dust collectors, combined wet flue gas desulfurization (WFGD), and wet precipitators are involved in field measurements. The results show that most of the excessive injected and/or unreacted ammonia from the flue gas denitrification system, whether selective catalytic reduction (SCR) or selective noncatalytic reduction (SNCR), is converted into particle-bound NH₄⁺ (>91%), and the rest (less than 9%) is carried by flue gas in the form of gaseous NH₃, with a concentration value of 0.15–0.54 mg/(N m³) at the denitrification outlet. When passing through dust collectors, particle-bound NH₄⁺ concentration decreases substantially along with the removal of particle matter. In WFGD, the dissolution and volatilization effects affect the gaseous ammonia concentration, which decreases when using limestone slurry and a 20% solution of ammonia as a desulfurization agent, while liquid ammonia solution with a high concentration (99.8%) may cause the flue gas NH₃ concentration to increase considerably by 13 times. Particle-bound NH₄⁺ concentration is mainly influenced by the relative strength of desulfurization slurry scouring and flue gas carrying effects and increases 2.84–116 times through ammonia-based WFGD. Furthermore, emission factors of NH₃ for combinations of APCDs are discussed.