Transferring the Carbonation of Biomass Bottom Ash from Batch to Continuous Operation

Biomass incineration residues may be used for CO2 capture and storage by carbonation of waste-borne metal hydroxides. Moist carbonation of these ashes can be performed under mild conditions (ambient pressure and temperature) and accelerated by using a CO2-rich gas. The process requires the wetting of the typically dry-discharged ashes and highly depends on the moisture content. Handling of the moist ashes in continuously operated reactors is challenging, especially due to build-up of incrustations. In this study, the carbonation of biomass bottom ash was performed in fixed-bed and rotating drum reactors. Wetting was performed either manually prior to fixed-bed carbonation or with spray-nozzles. The moisture dependent CO2 uptake was evaluated by a gas balance. Results show that the CO2 uptake in the fixed-bed and rotating drum was consistently between 20 and 35 g/kg, although the CO2 concentration in the rotating drum was significantly lower (10 vol% vs. 100 vol%). In the fixed bed, the uptake strongly depended on the moisture content, while in the rotating drum the effect was less pronounced. Application of such rotating drums allows for a continuous solids feed while combining wetting and carbonation.