Experimental study of homogeneous mercury oxidation under O2/CO2 atmosphere

Recently oxy-fuel combustion has been investigated as a potential multi-pollutant control technology for coal-fired power plants. However, mercury in flue gas must be removed before CO2 recovery as it can cause liquid metal embrittlement and material failure of aluminum heat exchangers during CO2 purification and compression. Comparing to air combustion, the flue gas constituents and time-temperature profiles changed in oxy-fuel combustion with flue gas recirculation. This may result in different elemental mercury (Hg-0(g)) transformation behaviors. Experimental tests on homogeneous Hg-0 (g) oxidation by Cl-2, HCl, NO and SO2 were conducted under simulated O-2/CO2 and O-2/N-2 atmosphere at the temperature of 473-1273 K. Results showed that under both O-2/CO2 and O-2/N-2 atmosphere, Cl-2 can significantly promote Hg-0 (g) oxidation while much more HCl and higher temperature (> 873 K) were needed to obtain comparable Hg-0(g) oxidation. Hg-0(g) oxidation by Cl-2 and HCl in CO2 atmosphere was lower than that in N-2 cases, while O-2 exhibited significant promotion effect on Hg-0(g) oxidation, especially under CO2 atmosphere at 1073 K. O-2/N-2 and O-2/CO2 atmosphere showed little difference on Hg-0(g) oxidation by NO and SO2, respectively. Hg-0(g) oxidation by NO was about 5-30%, depending on NO concentration in flue gas, decreased as the temperature increasing. SO2 exhibited limited Hg-0(g) oxidation. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.