Using modified fly ash for mercury emissions control for coal-fired power plant applications in China

Abstract

More than 50% of the mercury emissions in China come from coal-fired power plants. Coal-fired power plants also consume more than 50% of the coal used in China, and this proportion is expected to increase according to Chinese energy planning agencies, despite recent actions aiming at more stringent environmental constrains. This study reports mercury emissions measurements of several power plants in China. The results show that the mercury concentration in the flue gas has variability between 0.19 and 11.30μg/Nm3. At the same time, the co-benefit of mercury removal by the existing pollutant control devices at those plants was highly variable, ranging from 17.8% to 96.7%. This motivated research on developing and testing a modified fly ash sorbent that would be competitive due to its low cost, in relative abundance, and adequate for convenient injection at a power plant. Full-scale injection and adsorption experiments were performed at a 300MW plant. It was found that the use of a modified fly ash provide an additional mercury emissions reduction, in addition to the inherent natural mercury capture by the host unit of 30% due to additional fly ash adsorption. Implementation of this additional control option would help achieve combined mercury removal efficiencies in the 75–90% range.