Abstract
Power production from coal combustion is one of two major anthropogenic sources of mercury emission to the atmosphere. The aim of this study is the analysis of the carbon footprint of mercury removal technologies through sorbents injection related to the removal of 1 kg of mercury from flue gases. Two sorbents, i.e., powdered activated carbon and the coke dust, were analysed. The assessment included both direct and indirect emissions related to various energy and material needs life cycle including coal mining and transport, sorbents production, transport of sorbents to the power plants, and injection into flue gases. The results show that at the average mercury concentration in processed flue gasses accounting to 28.0 µg Hg/Nm3, removal of 1 kg of mercury from flue gases required 14.925 Mg of powdered activated carbon and 33.594 Mg of coke dust, respectively. However, the whole life cycle carbon footprint for powdered activated carbon amounted to 89.548 Mg CO2-e·kg−1 Hg, whereas for coke dust this value was around three times lower and amounted to 24.452 Mg CO2-e·kg−1 Hg. Considering the relatively low price of coke dust and its lower impact on GHG emissions, it can be found as a promising alternative to commercial powdered activated carbon.
Highlights
Industrial activities, electricity production, or dedicated use of mercury lead to anthropogenic Hg emissions into the atmosphere [1,2,3,4]
Taking into account the mass of coal required for the production of the sorbents (1.3 Mg coal·Mg−1 coke dust (CD); 2.8 Mg coal·Mg−1 powdered activated carbon (PAC)) and the by the sorbents under consideration, Carbon footprint (CF) of the extraction stage are 13.720 Mg CO2 ·kg−1 Hg for PAC and
Such a significant reduction of CF is caused by avoiding the emission of methane, which in the process of electricity generation is burned to carbon dioxide which has 28 times lower global warming potential (GWP) than methane
Summary
Industrial activities, electricity production, or dedicated use of mercury (e.g., gold mining) lead to anthropogenic Hg emissions into the atmosphere [1,2,3,4]. The dominant source of mercury emissions to the air in Poland is the combustion processes in the energy production sector, emitting, e.g., over 6 Mg Hg in 2017, which is around 54% of the whole mercury emissions in the country [7]. To prevent or reduce mercury emissions into the atmosphere from coal combustion, BAT recommends special methods [9]. In the situation with significant mercury content in the combusted coal and the insufficient effectiveness of passive methods of its removal, it is necessary to apply additional technologies, the so-called active methods [11]. The BATs for the active removal of mercury from the flue gas include powdered activated carbon (PAC) injection [12,13]. PAC particles containing adsorbed Hg can be more removed in, e.g., electrostatic precipitator (ESP) or fabric filters (FF) [14]
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