Potential of enhanced weathering of calcite in packed bubble columns with seawater for carbon dioxide removal

Enhanced weathering of minerals is one option being considered for removing CO₂ from the atmosphere to help combat climate change. In this work, we consider the weathering of calcite with seawater in a reactor using air enriched with CO₂. A mathematical model of the packed bubble column reactor was constructed with the key mass transfer and chemical reaction components validated with experimental data. The modelling results for a continuous process reveal the performance in terms of the specific energy consumption and the CO₂ capture rate, which are affected by parameters including particle size, superficial velocities of gas and liquid, reactor bed height and feed CO₂ concentration. The major energy requirements are for pumping liquid and compressing gas, and for CO₂ enrichment; energy needed for supplying solid particles (mining operations, transport and comminution) was found to be comparatively minor. A trade-off was possible between ground area requirement (determined by CO₂ capture rate) and energy requirement. To capture 1 tonne of CO₂ at the reactor, optimal designs were predicted to consume 2.1–2.3 GJ of electricity and occupy 1.8–5.2 m² year of space, depending on the feed CO₂ concentration. These would increase to 5.7–8.2 GJ and 7.1–13.1 m² year per tonne of CO₂ captured, after allowing for degassing of the weathering product in the ocean. This increased energy intensity is still within the range of the CO₂ removal options previously reported, while the space requirement quantification provides essential information for future feasibility assessment of this scheme.