Chemical-looping combustion in packed-fluidized beds: Experiments with random packings in bubbling bed

Abstract

Chemical-looping combustion (CLC) in packed-fluidized bed reactor was investigated. Experiments were carried out in a cylindrical laboratory-scale bubbling fluidized-bed reactor with an inner diameter of 78 mm and a hight of 1.27 m. Ilmenite concentrate particles in the size range 90–212 μm was used as oxygen carrying fluidizing solid. Two different types of random packings were used: aluminum silicate balls (ASB) with a diameter of 12.7 mm and bulk density of 1439 kg/m3 and 25 mm stainless steel thread saddles (RMSR) with bulk density of 204 kg/m3. The superficial gas velocity was 0.3 m/s. The fuels were CO and CH4. The bed temperature was 840 °C for CO and 940 °C for CH4. The height of the packed bed was kept constant at 1 m. The fluidized oxygen carrier bed height was varied from 2 cm to 40 cm. Results showed that fuel conversion in packed-fluidized beds is highly dependent on oxygen carrier bed height and the nature of the packing. Packed-fluidized beds with RMSR packing resulted in a significant improvement in fuel conversion, compared to a bubbling bed with no packing. With 30–40 cm bed height, CO conversion was ≈99.5% with RMSR packing and 91–96% without packing. The corresponding numbers for CH4 were ≈84% and ≈78%. Further, the RMSR packing has very high void factor (0.96). Thus, it should have limited effects on particle inventory, pressure drop and throughput. The most likely mechanism for improved fuel conversion is improved gas-solid mass transfer due to be reduced bubble size. The ASB packing has low void factor (0.43) and provided mixed results with respect to fuel conversion.