Surrogate modelling-assisted comparison of reactor schemes for carbon dioxide removal by enhanced weathering of minerals using seawater

Abstract

Reactor-based enhanced weathering of minerals represents one of the options for CO2 removal from the atmosphere to control the concentration of greenhouse gases for stabilising the climate. Earlier studies have modelled two reactor types, namely trickle-bed reactor and packed bubble column. However, their CO2 removal potential has not been compared. Building on the previous studies, this work further develops the mechanistic reactor models to enable them to consistently describe continuous weathering of minerals using seawater. Addressing the computational demands of the mechanistic models, a surrogate modelling-based optimisation procedure is developed to allow each reactor type to be rigorously optimised for minimising two competing objectives, namely energy consumption and space requirement. This has allowed the Pareto fronts of the two reactor types to be produced and compared. When applied to calcite weathering which is predominantly controlled by gas–liquid mass transfer, the packed-bubble column has been shown to consistently outperform the trickle-bed reactor, thanks to its superior mass transfer performance. However, when considering the weathering of forsterite, packed-bubble column performance is significantly worsened compared to calcite weathering, primarily because its low dissolution rate shifts the controlling mechanism of the process from gas/liquid mass transfer to solid dissolution. These results provide new insights to inform the future evaluation of reactor-based enhanced weathering schemes in terms of reactor design selection and the implication of mineral types.