Use of ilmenite as an oxygen carrier in chemical looping combustion-batch and continuous dual fluidized bed investigation

Chemical looping combustion (CLC) is a novel way of burning carbonaceous fuel in which CO2 can be inherently separated. Though this technology is suitable for gaseous fuels, recently efforts have made to adopt this technology for solid fuels such as coal. Ilmenite as a suitable oxygen carrier for coal chemical looping combustion is investigated with respect to relevant chemical looping combustion properties. A parametric study conducted in a bubbling fluidized bed is presented in which the following are examined: ilmenite oxygen carrying capacity, ilmenite reactivity with gaseous and solid fuels with respect to redox cycle number, rate of coal conversion in the presence of ilmenite, and the influence of temperature on gas yield, conversion, and gas speciation during coal CLC. The conversion of syngas with ilmenite is best when ilmenite is fully oxidized; reactivity reduces as ilmenite is reduced. The reactivity of ilmenite with snygas increases with redox cycle number over the first cycles and close to 100% syngas conversion was measured. The carbon conversion was low at 900 °C but improved with increasing temperature. Likewise, the rate of gasification increased with increasing temperature approximately doubling when increasing the temperature from 900 to 950 °C. Furthermore, an equalmolar CO- H2 syngas was combusted at 900 °C in IFK’s CLC dual fluidized bed system using ilmenite as the oxygen carrier resulting in a steady-state conversion of circa 90%.