Sulfur trioxide emissions from coal-fired power plants in China and implications on future control

SO3 is a significant gaseous precursor of secondary particulate matter and is also a key for the overall improvement of ambient air quality. In this study, SO3 emission characteristics for coal-fired power plants (CFPPs) from field experiments and existing studies are collected to study the SO3 transformation and removal characteristics and to determine the temporal and spatial distribution of SO3 emissions from CFPPs. The formation ratio of SO3 in boilers and selective catalyst reduction system is 0.9 +/- 0.5% and 40.52 +/- 19.23%, respectively. The formed SO3 is then removed by dust collectors and desulfurization systems in sequence, approximately 26.52-82.96% and 56.48-96.32%, respectively. Due to the development of air pollution control devices, SO3 emission in 2015 (71.0 kt) is almost equal to the emission in 2000 (70.9 kt) although coal consumption kept increasing. Some areas of the North China Plain have the highest distribution density of CFPPs, which implies more stringent SO3 emission limit may need to be considered in these regions for future control. Also, the monitoring method and control technologies should be developed simultaneously for better application of the emission limit.