Performance of an oxy-polishing step in the 100 kWth chemical looping combustion prototype

Journal article, 2021

Unconverted fuel gases are normally present in the gas leaving the fuel reactor of a Chemical Looping Combustion (CLC) process. Depending on several factors, including oxygen carrier and fuel volatiles content, the unconverted gases represent 5–30% of the oxygen needed for full combustion. Further conversion of these fuel components is imperative to achieve adequate combustion and to fulfill the requirements for CO2 storage. An oxy-polishing step using highly concentrated O2 to fully oxidize the fuel components offers a straightforward one-step way to reach complete combustion. However, systematic and detailed investigation is lacking while it is essential for design, scale up and optimization. In this work, the oxy-polishing is studied in a post-oxidation chamber (POC) of a 100 kWth unit using different solid fuels and manganese ores in the CLC process. With various flows of air as oxidation agent, the POC performance was evaluated under stable operations in a wide range of operating conditions. An overall oxygen ratio was defined to analyze the effect of O2 excess in the POC. Experimental results show that the oxidation of fuel gas from the fuel reactor can be greatly enhanced by air entering the POC, with the gas conversion being improved from 87 to 90% before the POC to as high as 99–100% after the POC. Full oxidation in POC can be accomplished with excess of O2. For the cases of incomplete oxidation, CO was normally found in higher concentrations than CH4. In a few cases close to optimum, CO and O2 simultaneously have normalized concentrations below 0.5–1% with a low overall oxygen ratio of around 1.01. The POC performance was further compared to the results from a simple reactor model.