Packed-Fluidized-Beds in Chemical-Looping Combustion: The Effect of Random Packing on Fuel Gas Conversion in a Bubbling Bed

Paper in proceeding, 2022

The present work investigates the use of random metal packings in fluidized beds, with specific application to chemical-looping combustion. The use of 25 mm stainless steel thread saddles (RMSR) and 25 mm stainless steel pall rings (Hiflow) were investigated in a batch fluidized bed. The fuel conversion was investigated, and results are compared with spherical packings in form of 12.7 mm aluminium silicate balls (ASB) and a bubbling bed with no packings. Random metal packings can have void factor >96% and consequently could be expected to have limited impact on pressure drop and solid flux. CLC batch experiments were performed in a stainless-steel reactor with I.D. of 7.8 cm and a height of 1.27 m. Experiments were conducted using three fuels: CH4, CO and syngas (50/50% H2/CO), at temperatures between 840-940°C, and different bed heights. Generally, the fuel conversion increases as the bed height increases. The use of packings has 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 could 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, and bed heights for RMSR and Hiflow packings. In contrast, the ASB packings have low void factor (0.43) and provided mixed results with respect to fuel conversion. The results are interpreted as realization of 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 effective reaction rate kf improves by up to 109% in the bed with RMSR packings, as compared to the bed without packings.