Abstract
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•CO2 capture via enhanced weathering (EW) of limestone with seawater was studied.•A sophisticated model was developed for EW in a packed bubble column reactor.•Key mechanisms adopted in the model were experimentally validated.•CO2 capture rate and energy consumption in continuous operation were investigated.•Trade-off of ground area requirement and energy requirement was revealed.
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.