Chemical looping combustion of biomass in 10-and 100-kW pilots - Analysis of conversion and lifetime using a sintered manganese ore

Artikel i vetenskaplig tidskrift, 2018

Chemical looping combustion (CLC) is a type of carbon capture technology that employs metal oxide particles in a redox reaction to transport oxygen to the fuel. As opposed to first-generation carbon capture concepts, CLC does not include a gas separation step and thus offers the advantage of having no thermodynamic energy penalty in the capture process. Manganese-containing oxygen carriers have been shown to offer a good compromise of gas conversion performance, availability, and cost. On the other hand, previously tested manganese materials have often been challenged with high attrition in continuous CLC. By sintering the ore prior to its use as oxygen carrier, the structure of the particles can be reinforced to increase their durability in the process. In this study, a sintered manganese ore was tested for 56 h in two pilot units of different size. The oxygen carrier worked well in the process, was easily fluidized, and did not exhibit any tendency towards agglomeration. Compared to other manganese materials tested in the same units, a higher lifetime based on fines production was reached, while gas conversion performance was similar. Different biomass fuels, mainly biochar of different sizes and black wood pellets, were employed in the study. A clear correlation between gas conversion and the fuel volatile content was detected; this is consistent with results reported in previous studies. The highest gas conversion reached in both units was similar to 93.5% using wood char. The highest carbon capture efficiency, 99% and 100% in the 10- and 100-kW unit, respectively, was reached with black pellets. To compare the tested material with the state-of-the-art oxygen carrier ilmenite, some tests were conducted with a bituminous coal that had been used in the same pilot with ilmenite. The results indicate a higher conversion performance for the tested manganese material.