Cost evaluation of CO₂ sequestration by aqueous mineral carbonation

A cost evaluation of CO₂ sequestration by aqueous mineral carbonation has been made using either wollastonite (CaSiO₃) or steel slag as feedstock. First, the process was simulated to determine the properties of the streams as well as the power and heat consumption of the process equipment. Second, a basic design was made for the major process equipment, and total investment costs were estimated with the help of the publicly available literature and a factorial cost estimation method. Finally, the sequestration costs were determined on the basis of the depreciation of investments and variable and fixed operating costs. Estimated costs are 102 and 77 €/ton CO₂ net avoided for wollastonite and steel slag, respectively. For wollastonite, the major costs are associated with the feedstock and the electricity consumption for grinding and compression (54 and 26 €/ton CO₂ avoided, respectively). A sensitivity analysis showed that additional influential parameters in the sequestration costs include the liquid-to-solid ratio in the carbonation reactor and the possible value of the carbonated product. The sequestration costs for steel slag are significantly lower due to the absence of costs for the feedstock. Although various options for potential cost reduction have been identified, CO₂ sequestration by current aqueous carbonation processes seems expensive relative to other CO₂ storage technologies. The permanent and inherently safe sequestration of CO₂ by mineral carbonation may justify higher costs, but further cost reductions are required, particularly in view of (current) prices of CO₂ emission rights. Niche applications of mineral carbonation with a solid residue such as steel slag as feedstock and/or a useful carbonated product hold the best prospects for an economically feasible CO₂ sequestration process.