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 m(2) year of space, depending on the feed CO2 concentration. These would increase to 5.7-8.2 GJ and 7.1-13.1 m(2) 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 CO(2 )removal options previously reported, while the space requirement quantification provides essential information for future feasibility assessment of this scheme.

Automated summary

Enhanced weathering of calcite with seawater using air enriched with CO2 was investigated in this study. A mathematical model of the reactor was constructed and validated with experimental data, revealing the performance in terms of energy consumption and CO2 capture rate. The major energy requirements were found to be for liquid pumping, gas compression, and CO2 enrichment. The study also quantified the space requirement for capturing 1 tonne of CO2, taking into account degassing of the weathering product in the ocean.