Development and Test of a Rotating Drum Reactor for the Simultaneous Hydration and Carbonation of Dry Biomass Bottom Ash

Abstract

Carbonation of biomass ash allows for the final storage of CO2 as solid carbonates and may therewith contribute to supply energy with net negative greenhouse gas emissions. Accelerating the reaction under ambient temperature and pressure requires presence of water as reaction space. Therefore, dry-discharged ashes need to be humidified. Here we developed and tested a rotating drum reactor integrating hydration and carbonation of biomass bottom ash (BBA). The bed motion was evaluated with moist quartz sand (QS) as a model material. In the BBA carbonation experiments, liquid-to-solid ratios (L/S) between 0.1 and 0.3 were adjusted with two-fluid nozzles. The reactant gas (10 vol% CO2) was fed either simultaneously with or subsequently to humidification. The CO2 uptake was determined gravimetrically as well as using a gas balance and was compared to results obtained under fixed-bed conditions. In the rotating drum, a favorable slumping motion of the QS was identified at a rotation rate of 7 rpm and a fill level of 20 vol%. Thus, BBA carbonation tests were carried out under these conditions yielding a CO2 uptake between 22 and 31 g/kg within 2 h. Uptake was highest at L/S 0.1 and lowest at L/S 0.3. These results indicate that the rotating drum reactor reduces the required moisture content compared to fixed-bed carbonation. The CO2 feeding mode (simultaneous or subsequent) had only a minor effect on the cumulative CO2 uptake but provided valuable insight into the heat production by hydration and carbonation of BBA in the rotating drum system. Graphical Abstract: [Figure not available: see fulltext.].