Effect of flue gas impurities on the performance of a chemical looping based air separation process for oxy-fuel combustion

Integrated Chemical Looping Air Separation (ICLAS) offers an energy efficient and cost effective option for large-scale oxygen generation in oxy-fuel type power plants. Oxygen production in the ICLAS is achieved by reduction of oxidised metal oxides in an environment of steam/recycled flue gas (CO2-rich) using a dedicated reduction reactor. This paper provides the results of a thermodynamic investigation into the effect of flue gas impurities on the reduction of three metal oxide oxygen carriers (Cu, Mn and Co oxides) under conditions pertinent to an oxy-fuel coal-fired power plant. Relevant calculations were carried out using the Fact-sage 6.1 thermodynamic equilibrium calculation software package. Different gas streams, namely crude/wet, dry, pure CO2 and steam were considered in the simulations together with the additional hypothetical impure flue gas stream having larger concentrations of CO, SO2 and NO. Effects of SO2, NO, CO and O2 contents of the flue gas on oxygen carrier conversion and oxygen decoupling process were investigated in detail. It was established that the successful reduction of metal oxides in the presence of flue gas impurities can only be achieved at higher temperatures due to increased partial pressure of O2 and the formation of metal sulphates at temperatures less than 800–900 °C. This may increase the operating and capital costs of the CLAS based oxygen production.