Coal combustion experiments at a lab-scale furnace with a capacity of 10,000 kcal/h were conducted in order to investigate the speciation changes and mass distribution of mercury with limestone injection in conditions of air and oxy-fuel combustion. Mass distribution and concentration of mercury in flue gas at oxy-fuel combustion were higher than those at air combustion. With limestone injection, the reduction of mercury from flue gas by adsorption into limestone could be clearly observed at both air and oxy-fuel combustion conditions. In the speciation of mercury, the particulate mercury in flue-gas was dominant with around 50% and the portion of elemental mercury was higher than that of oxidized mercury as shown at other coal combustion cases. At oxy-fuel combustion, most of particulate mercury seemed to be bounded to limestone more easily in comparison to air combustion, so that the elemental mercury in flue gas resulted to be more dominant at oxy-fuel combustion. (C) 2014 Elsevier B.V. All rights reserved.