CaMn 0.875Ti 0.125O 3 as oxygen carrier for chemical-looping combustion with oxygen uncoupling (CLOU)—Experiments in a continuously operating fluidized-bed reactor system

Abstract

Particles of the perovskite material CaMn 0.875Ti 0.125O 3 has been examined as oxygen carrier for chemical-looping with oxygen uncoupling, and for chemical-looping combustion of natural gas, by 70 h of experiments in a circulating fluidized-bed reactor system. For the oxygen uncoupling experiments, it was found that the particles released O 2 in gas phase at temperatures above 720 °C when the fuel reactor was fluidized with CO 2. The effect increased with increased temperature, and with the O 2 partial pressure in the air reactor. At 950 °C, the O 2 concentration in the outlet from the fuel reactor was in the order of 4.0 vol%, if the particles were oxidized in air. For the chemical-looping combustion experiments the combustion efficiency with standard process parameters was in the order of 95% at 950 °C, using 1000 kg oxygen carrier per MW natural gas, of which about 30% was located in the fuel reactor. Reducing the fuel flow so that 1900 kg oxygen carrier per MW natural gas was used improved the combustion efficiency to roughly 99.8%. The particles retained their physical properties, reactivity with CH 4 and ability to release gas-phase O 2 reasonably well throughout the testing period and there were no problems with the fluidization or formation of solid carbon in the reactor. X-ray diffraction showed that the particles underwent changes in their phase composition though.