The combustion of coal can result in trace elements, such as mercury, being released from power stations with potentially harmful effects for both human health and the environment. Research is ongoing to develop cost-effective and efficient control technologies for mercury removal from coal-fired power plants, the largest source of anthropogenic mercury emissions. A number of activated carbon sorbents have been demonstrated to be effective for mercury retention in coal combustion power plants. However, more economic alternatives need to be developed. Raw biomass gasification chars could serve as low-cost sorbents for capturing mercury since they are sub-products generated during a thermal conversion process. The aim of this study was to evaluate different biomass gasification chars as mercury sorbents in a simulated coal combustion flue gas. The results were compared with those obtained using a commercial activated carbon. Chars from a mixture of paper and plastic waste showed the highest retention capacity. It was found that not only a high carbon content and a well developed microporosity but also a high chlorine content and a high aluminium content improved the mercury retention capacity of biomass gasification chars. No relationship could be inferred between the surface oxygen functional groups and mercury retention in the char samples evaluated.
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.
Mercury displays a different reactivity and behaviour depending on its speciation.Determination of the mercury species present in combustion flue gases is important for proposing effective control technologies. The Ontario Hydro (OH) method is accepted as the only wet-chemical method suitable for measuring total and speciated mercury in flue gases. However, the continuous development of combustion technologies has the effect of modifying the operational variables and the composition of the resulting flue gases, leading to measurement biases in mercury determination. In this work, an alternative method based on the use of an ionic exchanger resin is proposed for the determination of gaseous oxidised mercury. The results show that for sampling flue gases containing reactive gases over long periods of time, the use of this resin is a suitable method for determining gaseous elemental and oxidized mercury, even in the presence of large amounts SO 2 or NO 2 . Application of the OH method when elevated amounts of SO 2 or NO 2 are present in the gas composition leads to an overestimation of the amount of oxidised mercury due to the oxidation of the mercury in the KCl impinger solution.
Hybrid direct carbon fuel cells (HDCFCs) are now considered as one of the most efficient options for the generation of clean energy from mineral coals. This work sheds light on the reaction mechanism of the HDCFC operated with raw and pre-treated mineral coals which have been thoroughly characterised and tested.
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