Solid fuels in chemical-looping combustion using oxide scale and unprocessed iron ore as oxygen carriers

Chemical-looping combustion (CLC) is a novel technology that can be used to meet demands on energy production without CO2 emissions. The CLC-process includes two reactors, an air and a fuel reactor. Between these two reactors oxygen is transported by an oxygen carrier, which most often is a metal oxide. This arrangement prevents mixing of N2 from the air with CO2 from the combustion. The combustion gases consist almost entirely of CO2 and H2O. Therefore, the technique reduces the energy penalty that normally arises from the separation of CO2 from other flue gases, hence, CLC may make capture of CO2 cheaper. Iron ore and oxide scale from steel production were tested as oxygen carriers in CLC batch experiments with solid fuels. Petroleum coke, charcoal, lignite and two bituminous coals were used as fuels. The experiments were carried out in a laboratory fluidized-bed reactor that was operating cyclically with alternating oxidation and reduction phases. The exhaust gases were led to an analyzer where the contents of CO2, CO, CH4 and O2 were measured. Gas samples collected in bags were used to analyze the content of hydrogen in a gas chromatograph. The results showed that both the iron ore and the oxide scale worked well as oxygen carrier and both oxygen carriers increased their reactivity with time