Retention of mercury by low-cost sorbents: Influence of flue gas composition and fly ash occurrence

Abstract

The present study employs chars obtained from the gasification of different types of biomass as low cost sorbents of mercury at laboratory scale. The influence of gas composition and fly ash occurrence on mercury retention and oxidation by char samples was evaluated. Chars obtained from a mixture of paper and plastic waste showed mercury retention capacities similar to those obtained with a commercial activated carbon. Homogeneous mercury oxidation was mainly promoted by NO 2 and , to a certain extend, by SO 2 +O 2 . The highest heterogeneous mercury oxidation was observed in the chars with the highest mercury retention capacity suggesting that the sorption process also involves the capture of oxidized mercury species. The presence of fly ash particles clearly influenced heterogeneous oxidation but did not affect mercury retention by the char sorbents.

Effect of fly ash composition on the retention of mercury in coal-combustion flue gas

“…Various methods are used to explore the interaction between mercury and fly ash [6][7][8][9][10][11][12][13][14][15][16]. Among them, many authors have focused on the characterization of native fly ash and their properties of mercury retention [8][9][10][11][12].…”

Transformations of mercury in processes of solid fuel combustion – review

“…Jang and co-authors (Jang et al 2014) reported that in combustion, SO 2 reacts with oxidized mercury (HgCl 2 ), generating fi nally particulate mercury in a form of HgSO 4(s) . Fuente-Cuesta et al (2012) suggested that O 2 has a synergistic effect on mercury oxidation, not only affecting it directly, but also via NO 2 .…”

“…The effi ciency of heterogeneous reactions taking place on the surface of fl y ash also depends on the fl ue gas composition, and particularly on the concentration of NO 2 , HCl, NO, and SO 2 (Norton et al 2003, Hower et al 2010, Fuente-Cuesta et a. 2012.…”

“…However, due to the high activation energy of 98.29 kcal/mol (US EPA Grant No. R828168, 2004), a direct reaction between Hg and HCl, leading to the formation of HgCl, is impossible (Fuente-Cuesta et al 2012). The mechanisms of HgCl 2 formation via homogeneous reactions of Hg 0 and atomic chlorine are suggested to proceed according to the following equations (Niksa et al 2001, Zhuang et al 2004, Zhao et al 2006:…”

A comparison of devices using thermal desorption for mercury speciation in solids

“…The emissions of mercury from thermal power stations and other combustion installations account for 55.4% of the total amount of mercury emitted in Europe in 2012 [4]. Coal fired power plants also generate Hg-loaded solid wastes [5], such as fly ashes and gypsum. These sub-products are disposed of in landfills or re-used as raw materials, with the consequent risk of being released to water or to the atmosphere.…”