Is solid calcium looping a scalable technology for mega-ton carbon dioxide removal?

Atmospheric CO 2 removal at Gton scale is necessary to limit global temperature rise. This study provides essential insights into the energy, area, and water requirements of solid calcium looping for large-scale CO 2 removal, combining experimental results with an upscaled system context. Thermogravimetric analysis (TGA) characterizes the products, while scanning electron microscopy (SEM) qualitatively assesses sorbent performance. Experiments in a climate chamber focus on carbonation kinetics, varying relative humidity, temperature, and slaking ratios. Results demonstrate that relative humidity above 70 % significantly enhances carbonation rates, favoring the placement of facilities in high-humidity locations. The optimal slaking ratio is identified as one mole of water per mole of CaO. Carbonation at 20 °C yields faster reaction kinetics than at 12 °C, with both temperatures achieving a carbonation degree of 66 mol.% in three and four days, respectively. Lower temperatures require a larger area to achieve similar annual capture rates. Cyclic testing shows stable capture capacity and carbonation kinetics over nine cycles. For a one-million-ton-per-year capture unit, the process requires 4.9–6.2 GJ/ton CO2 for electric heating, with air contactor areas reduced to 0.08–0.12 km 2 using vertically stacked sorbent trays. Water consumption reaches 0.7 ton H2O /ton CO2 at the optimal slaking ratio but can be minimized in high-humidity, water-scarce locations by omitting slaking, at the expense of larger area requirements. While only northern Europe currently meets the conditions for implementing the technology, considering both electricity grid CO 2 intensity and weather, the potential of solid calcium looping for large-scale CO 2 removal remains promising, warranting further exploration of logistics and practicalities in real-world applications. • Solid calcium looping demonstrates potential for Mton CDR. • Viability of solid calcium looping relies on successful process management. • Relative humidity > 70% enhances carbonation kinetics. • Stoichiometric slaking conditions enhances carbonation kinetics. • Stable sorbent performance observed over multiple cycles.