Mitigation of gaseous mercury emissions from waste-to-energy facilities: Homogeneous and heterogeneous Hg-oxidation pathways in presence of fly ashes

Abstract

This study describes the main mechanisms that take part in the mercury homogeneous oxidation pathway in presence of some of the main reactive compounds formed during waste incineration processes (O, HCl, SO and NO). Series of model, synthetic dry flue gases were used to elucidate the effects of HCl, SO, NO and their proportions in the gas on mercury behaviour. Three samples of fly ash collected from a MSWI facility were characterized and evaluated both for Hg heterogeneous oxidation and Hg removal in a laboratory scale device. The results obtained in this study showed that homogeneous mercury oxidation in the models MSWI and coal combustion flue gas atmospheres was 52 ± 5% and 25%, respectively. SO, NO and HCl have a synergetic effect in Hg oxidation in presence of oxygen, but the main differences found are mainly caused by the strong influence of HCl and the likely inhibitory oxidation effects of SO. Surface area together with carbon and chloride content of the fly ashes were correlated with their capacity for Hg-heterogeneous oxidation and adsorption. The sample of fly ash with relatively high content of unburnt carbon and chlorine, and with BET surface (2.42 m/g) was able to remove up to 100% of Hg (g) during 300 min. The results obtained in this study provide a complete overview of the behaviour of mercury during MSWI processes and may help to clarify the fate/behaviour of mercury in a filter (e.g. electrostatic precipitator) providing a deeper knowledge about the impacts of fly ash properties on mercury fate in waste incineration.

New insights on mercury abatement and modeling in a full-scale municipal solid waste incineration flue gas treatment unit

“…In accordance, temperature reduction is a very important step in the flue gas treatment process, since the removal of oxidized mercury compounds (Hg n+ ) can be performed more efficiently, in comparison to elemental mercury (Hg°) (Carey et al, 1998;Ie et al, 2013;Pavlish et al, 2003;Rumayor et al, 2018). Therefore, the increase of the ratio Hg n+ /Hg°in the flue gases will be related to a better mercury removal efficiency in the following steps of the treatment process.…”

“…Then, since this approach does not allow the description of physical processes in the flue gas, the mechanisms related to mercury adsorption by activated lignite were studied in detail considering the process kinetics, as described in Section 2.2.2. It is worth mentioning that as reported by different authors, the fly-ashes may also contribute to the mercury removal from flue gases, via heterogeneous oxidation and/or adsorption processes, depending on their unburned carbon content and mineral composition (Feeley et al, 2009;Hassett and Eylands, 1999;Rumayor et al, 2018). However, since their mercury capture capacity is considerably low in comparison to activated lignite (Karatza et al, 1998;Lighty et al, 2008), the impact of fly-ashes on mercury removal is not considered in this study.…”

“…Most of them are related to the composition of flue gases, depending if they come from coal combustion or MSW incineration processes. In the former case, considering the low chlorine content of coal, some authors have described a strong influence of NO, inhibiting or promoting homogeneous mercury oxidation reactions, depending on its amount in the flue gases (Niksa et al, 2001;Rumayor et al, 2018). In contrast, in the latter case, it has been reported that NO has a weak influence on mercury speciation, due to the presence of high HCl concentrations, whose mercury oxidation effect is dominant in the conditions of flue gas cooling devices (Zhou et al, 2013).…”

Removal of Mercury from Acidic Solutions of Mercury Chloride by Means of Sorbents Prepared by Catalyzed Vulcanization of Vegetable Oils

“…Při spalování odpadů, např. tuhých komunálních odpadů (TKO), jsou nejběžnějšími znečišťujícími látkami přítomnými ve spalinách prach, HCl, NO x , SO 2 a některé těžké kovy (včetně rtuti) 1,2 . Koncentrace plynného chlorovodíku ve spalinách jsou obvykle několikanásobně vyšší než koncentrace SO 2 , a proto se k samostatnému odstranění HCl často využívá rychlé ochlazení spalin a selektivní absorpce HCl do horké vody.…”

Effect of additives on stabilization and inhibition of mercury re-emission in simulated desulphurization slurry

“…Mercury emission in the coal-fired power plants varied in the total amount and speciation depending on the coal species, boiler operating conditions and air pollution control devices (Zhang et al 2008). Generally, there are three forms of mercury in the flue gas: elemental mercury (Hg 0 ), oxidized mercury (Hg 2+ ) and particulate-bound mercury (Hg p ) (Rumayor et al 2017). Hg 0 is stable and insoluble, which makes it hard to be efficiently removed from flue gas without advanced control devices (Pavlish et al 2003).…”