Field measurements of NOx and mercury from oxy-fuel compression condensates at the Callide Oxyfuel Project

The Callide Oxyfuel Project (COP) is the world's largest operating oxy-fuel plant and has successfully demonstrated the retrofitting capability for oxy-fuel to capture CO2. The compression of the raw flue gas at the COP has also demonstrated that NOx and Hg can also be removed as part of the liquid condensate. This work presents field tests conducted on the condensates to determine the stability of captured NOx and Hg species when depressurised. These tests involved sampling liquid condensate directly into a customised aeration vessel and measuring the evolved gases over an 8-12 h period. The low-pressure condensate (similar to 4 bar) showed that 3-18% of captured NOx species and 0.5-1.2% of the Hg were volatile, while the high-pressure condensate (24 bar) re-emitted 2-68% of captured NOx and 0.05-12.5% of the captured Hg. These tests showed that volatile Hg was related to volatile NOx and that this volatility of condensates changed with time as the compression plant operated from start-up. Equilibrium calculations of HNO2 in the gas and liquid phases supported the volatility measurements, suggesting that the rate of oxidation of HNO2 to HNO3 in the condensed phase is slow. Overall, the conditions which favoured NOx stability in the condensates, namely longer residence and higher pressure also favoured Hg stability. This work has shown that emissions from an oxy-fuel compression plant must include those emanating from depressurised condensates and suggest that the re-emitted species may not the same as in typical combustion flue gas, but the result of higher-pressure conversion. (C) 2015 Elsevier Ltd. All rights reserved.