Solid fuels in chemical-looping combustion

The feasibility of using a number of different solid fuels in chemical-looping combustion (CLC) has been investigated. A laboratory fluidized bed reactor system for solid fuel, simulating a chemical-looping combustion system by exposing the sample to alternating reducing and oxidizing conditions, was used. In each reducing phase 0.2 g of fuel in the size range 180-250 μm was added to the reactor containing 40 g oxygen carrier of size 125-180 μm. Two different oxygen carriers were tested, a synthetic particle of 60% active material of Fe2O3 and 40% MgAl2O4 and a particle consisting of the natural mineral ilmenite. Effect of steam content in the fluidizing gas of the reactor was investigated as well as effect of temperature. A number of experiments were also made to investigate the rate of conversion of the different fuels in a CLC system. A high dependency on steam content in the fluidizing gas as well as temperature was shown. The fraction of volatiles in the fuel was also found to be important. Furthermore the presence of an oxygen carrier was shown to enhance the conversion rate of the intermediate gasification reaction. At 950 °C and with 50% steam the time needed to achieve 95% conversion of fuel particles with a diameter of 0.125-0.18 mm ranged between 4 and 15 min depending on the fuel, while 80% conversion was reached within 2-10 min. In almost all cases the synthetic Fe2O3 particle with 40% MgAl2O4 and the mineral ilmenite showed similar results with the different fuels.