Characterization of reactive CaCO3 crystallization in a fluidized bed reactor as a central process of direct air capture

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A laboratory-scale, fluidized-bed pellet reactor (BPR) was used to investigate a CaCO3 crystallization process for the recovery of CO2 in a Direct Air Capture (DAC) process. The BPR performance was validated against data from a pilot-scale unit. Subsequently, the pellet growth under process-relevant conditions was studied over a period of 144h.The experimental results with the BPR, containing a bed of pellets sized between 0.65 and 0.84mm, have shown that a calcium retention of 80% can be achieved at a fluidization velocity of 60mh−1 and a calcium loading rate of 3molh −1. This result is consistent with calcium retention observed at pilot scale operation and hence, results from the BPR are considered representative for the pilot scale unit.Starting with a bed of pellets sized between 0.15 and 0.5mm, the average pellet growth rate, G, at the reactor bottom increased from 8.1E-10 to 11E–10ms−1 at the onset and decreased to 4.9E–10m s−1 over the course of a 144h test. The calcium retention over the course the test showed the same trend (initial increase and final decrease) as the pellet growth rate.A theoretical bed growth model was developed and validated against data from the pilot scale and benchtop pellet reactors. The model was used to calculate the bed porosity and total pellet surface area in each control volume. The pellet surface area growth at the bottom of the reactor reproduced the pellet growth and retention data trends.