Thermodynamic effects of alkaline earth metals on homogenous mercury oxidation during calcium carbonate (CaCO₃) and coal combustion

ABSTRACT

In this study, the relationship between mercury (Hg) oxidation and alkaline earth metals, particularly the transformation of alkaline earth metals in a flue gas atmosphere, was investigated. The thermodynamic stability of the alkaline earth metals during the process of coal combustion and corresponding interactions among the alkaline earth metals and S-species and Cl-species were calculated and analyzed using chemical thermodynamics software HSC Chemistry. Data demonstrated that the main Ca products in the high (1600 K) and low (800 K) temperature states were calcium sulfate (CaSO₄) and calcium chloride (CaCl₂), respectively. As HCl consumption continued (800–400 K) as a result of addition of calcium carbonate (CaCO₃), oxidation of Hg was suppressed. Based on previous studies, an Hg/C/H/N/O/S/Cl/Ca chemical and phase equilibrium model was designed using the chemical kinetics simulation software CHEMKIN Pro in order to further elucidate the influence of CaCO₃ on oxidation of Hg during the coal combustion process. Data indicated that, as CaCO₃ levels increased, equilibrium temperature fell, further supporting the thermodynamic calculation results. Thus, findings suggested that oxidation of Hg in post-combustion gases might be blocked by addition of alkaline earth metals.

KEYWORDS:

• Calcium carbonate
• mercury
• coal combustion
• alkaline earth metal
• oxidation mechanism
• thermodynamics

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was financially supported by the National Natural Science Foundation of China [grant number 51274262].