Effects of NH4Br additive on mercury transformation and removal during CFB coal combustion

Abstract

ABSTRACTBACKGROUNDMercury emission from coal‐fired power plants has caused widespread concern. Halogen is considered to be a good mercury oxidant and many researchers have added it into the coal for mercury removal. However, the mechanism of mercury transformation is still not clear. Effects of NH4Br additive on mercury transformation and removal were studied on a 6 kWth circulating fluidized bed (CFB) coal combustor. The main goal of this work is to explore in detail the mercury transformation mechanism in the presence of bromine.RESULTSResults showed that the concentration of Hg0 and Hg2+ in the flue gas was 2.003 and 2.434 µg m−3, respectively, while Hgp was 14.866 µg m−3 during the raw coal combustion. By adding more NH4Br, the content of Hg0 and Hg2+ decreased while the content of Hgp increased. At an NH4Br addition amount of 0.3%, Hg0 transformation rate and Hgg removal rate reached maximum values of 78.85% and 76.83%, respectively. Some mercury compounds (such as HgS(red), HgO, HgSO3) were further oxidized by active bromine with NH4Br addition.CONCLUSIONThe added NH4Br generates active bromine in the furnace, which promotes both homogeneous and heterogeneous oxidation of mercury. Adding NH4Br into coal benefits mercury removal during coal combustion. © 2016 Society of Chemical Industry