Chemical-Looping Combustion in Packed-Fluidized Bed Reactor – Fundamental Modeling and Batch Experiments with Random Metal Packings

Journal article, 2022

The conversion of gaseous fuels during chemical-looping combustion (CLC) was investigated in a packed-fluidized reactor. The experimental set-up consisted of a cylindrical laboratory-scale bubbling fluidized-bed reactor with an inner diameter of 78 mm and a height of 1.27 m. Two types of fuel, Syngas (50/50% H2/CO) and carbon monoxide (100% CO) were used. Two different types of packings were assessed and compared with the reference case, which was a bubbling bed with no packings. The investigated packings were 25 mm stainless steel thread saddle rings (RMSR) with a bulk density of 195 kg/m3, and 25 mm stainless steel pall ring (Hiflow) with bulk density of 271 kg/m3. The height of the packed reactor section was kept constant at 1 m. Ilmenite concentrate particles in the size range of 90-212 µm was used as oxygen carrier. The unfluidized bed height was varied between 10 and 60 cm. The results show that the fuel conversion increases as the bed height increases, and that the use of packings have positive effect on fuel conversion. For RMSR packings, the syngas conversion at 840°C improves from 0.84 (for 10 cm bed height) to 1.00 (for 60 cm bed height). This should be compared to the bed with no packings, for which the corresponding improvement was from 0.69 to 0.98. The general pattern is consistent for all fuels, packings and bed heights. The results are interpreted as an improvement in gas-solid mass transfer when packings are used, mainly due to reduced bubble size. Fundamental analysis of the variance in pressure drop over the bed to estimate bubble diameter supports this interpretation. It is also shown that the mass-based first-order effective reaction contact factor kf improves up to 109% in the bed with RMSR packings, as compared to the bed without packings.