Mixed Oxide Oxygen Carriers for Chemical-Looping Combustion

Doctoral thesis, 2017

Chemical-Looping Combustion is a promising method for combustion with inherent carbon dioxide capture. Oxygen is provided to the fuel with a solid oxygen carrier. The oxygen carrier is circulated between the reactor for fuel oxidation and another reactor where it is reoxidized with air. A good performing oxygen carrier is vital for this process. An oxygen carrier is typically a metal oxide and this work focus on evaluating oxygen carriers based on mixed metal oxides. A method was developed to determine the reduction reaction enthalpy of oxygen carriers in a fluidized-bed batch reactor. The method was verified using a nickel based oxygen carries with known enthalpy. Different oxygen carriers based of the iron-titanium oxide ilmenite were evaluated to determine the reaction enthalpy in a chemical-looping process. Oxygen carriers manufactured with spray drying technology were developed through a screening process. Starting with 79 different materials those deemed promising were tested in a fluidized-bed batch reactor. The ability to release oxygen, reactivity with fuel and fluidization behavior were the most important parameters and based off the results 10 materials were chosen to be investigated in a small continuous Chemical-Looping reactor system. Based off these results 2 materials were examined in a larger continuous Chemical-Looping reactor system where fuel power up to 6 kW were used. Oxygen carrier particles based on calcium manganite performed best with substantial release off oxygen and high to complete conversion on fuel. The material CaMn0.775Ti0.125Mg0.1O3-δ performed best in all three reactor systems. In addition to the oxygen release and reactivity these particles also proved durable with unaffected reactivity and low attrition after 99 h of continuous chemical-looping operation.