CaMn0.875Ti0.125O3 as oxygen carrier for chemical-looping combustion with oxygen uncoupling (CLOU) – experiments in a continuously operating fluidized bed reactor system

Artikel i vetenskaplig tidskrift, 2011

Particles of the perovskite material CaMn0.875Ti0.125O3 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 O2 in gas phase at temperatures above 720°C when the fuel reactor was fluidized with CO2. The effect increased with increased temperature, and with the O2 partial pressure in the air reactor. At 950°C, the O2 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 in the order of 30% was located to the fuel reactor. Reducing the fuel flow so that 1900 kg oxygen carrier per MW natural gas was used improved the combustion efficiency to above 99.8%. The fuel conversion decreased considerably at lower temperatures though. The particles retained their physical properties, reactivity with CH4 and ability to release O2 in gas phase reasonably well throughout the testing period and there were no problems with the fluidization or formation of solid carbon in the fuel reactor. X-ray diffraction showed that the particles underwent changes in their phase composition though.