Investigation on the ammonia emission characteristics in coal-fired power plants of China

Abstract

The coal-fired power plants in China have basically completed the upgrade and transformation for the ultra-low emission, and the reduction in traditional pollutant emission is significant. However, excessive ammonia emission has become one of the major concerns due to its adverse effects on environmental protection facilities and atmospheric environment. In this paper, four typical coal-fired power plants which have completed the ultra-low emission retrofits were measured on site to investigate the whole process emission characteristics of ammonia. The ammonia in the flue gas was classified into the gaseous ammonia, the filterable ammonia or the total ammonia, based on different sampling systems. Besides, the ammonia in the captured fly ash, desulfurization slurry, desulfurization wastewater, and gypsum was also analyzed to provide a quantitative overview of ammonia emission. Results showed that there was only gaseous ammonia detected at the outlet of SCR devices. Most gaseous ammonia was converted into filterable ammonia when it passed through the air preheater. Filterable ammonia, the predominant form of ammonia that made up about 65% to 95% of the total ammonia, could be effectively captured by the dust removers, with over 80% of it being removed. Higher ammonia concentration was measured from the fly ash collected in the rear storehouses. The concentration of ammonia emitted at the WFGD outlet was less than 0.5 mg/Nm3, with no more than 0.3 mg/Nm3 being discharged after the further removal by WESP. Discharging with the captured fly ash was the main pathway for ammonia emission, which should be considered in the further pollution control in coal-fired power plants.