Oxy-fuel combustion is the ideal option among low carbon combustion technologies for post CO2 capture. Mercury in CO2-enriched flue gas must be removed efficiently because mercury can cause metal embrittlement and aluminum corrosion during post CO2 processing. To date, there is little research that has reported mercury speciation, emissions, and removal from the oxy-fuel combustion systems. Therefore, a comprehensive review of mercury chemistry and mercury removal from the oxy-fuel combustion system is necessary. This paper reviews the formation, emission, and removal of mercury from oxy-fuel combustion systems. The aim is to evaluate and summarize the fate of mercury and the status of mercury-control technologies for the oxy-fuel combustion process. It is recommended that the modification of existing ESP, SCR, or FGD systems to enhance mercury control should be developed. The investigation of mercury capture by activated carbon or other low-cost sorbents requires further research to evaluate its suitability for oxy-fuel combustion plants. The installation of additional mercury oxidation catalysts downstream of an SCR unit, where mercury would be oxidized along the economizer exit exhaust, is a promising solution. It is also recognized that the injection of a chemical oxidizing agent to control mercury emissions requires further investigation to realize the full potential of this application.
In order to clarify the effect of sodium on the heterogeneous adsorption of NO on a char surface, several reasonably simplified saturated and unsaturated char models were selected as research objects, and Na atoms were decorated on the char models. Each char model and NO adsorption product were optimized by using density functional theory at the GGA-PBE (generalized gradient approximation-Perdew–Burke–Ernzerhof) level to obtain the adsorption energy of NO on different models. The results indicate that the addition of Na atoms catalyzes the adsorption of NO molecules by an saturated char structure, the adsorption form is changed from physisorption to chemisorption, and the adsorption energy is increased from −15.6 to −98.2 kJ/mol. The adsorption energy of NO molecules with an unsaturated armchair-type char structure containing edge active sites is affected by sodium atoms, increasing from −211.7 to −303.6 kJ/mol, while the adsorption capacity of the zigzag-type char structure for NO molecules is hardly affected by Na atoms. This study provides a theoretical basis for the development of clean utilization technology of high-alkali coal.
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