Multistage steam recovery for CO2 direct air capture via S-TVSA: Enhanced solid sensible heat recovery through stepwise phase-change integration

• Novel multistage steam recovery process for CO 2 direct air capture via S-TVSA. • Rigorous multi-objective optimization evaluating energy and productivity trade-offs. • ∼90% sensible heat recovery, exceeding current best available technology (∼50%). • ∼20% lower specific energy consumption than best available technology. • ∼23% lower net removal cost than best available technology under baseline condition. A cost- and energy-efficient direct air capture (DAC) process is essential for large-scale CO 2 removal. This study proposes a novel multistage steam recovery process for DAC based on steam-assisted temperature–vacuum swing adsorption (S-TVSA) using solid sorbents. In this process, reactor pressurization via steam and subsequent depressurization for water evaporation and sorbent cooling (evaporation cooling) are performed in multiple stages. Outflow gases from each evaporation-cooling stage, predominantly composed of steam, are spontaneously transferred to the corresponding steam-pressurization stage. This stepwise pressure-swing configuration expands the pressure swing range compared to the current best available technology (BAT), namely the single-stage steam recovery process. A numerical proof-of-concept was conducted using unsteady S-TVSA process simulations coupled with multi-objective optimization. The results showed that, compared to the single-stage process, the multistage configuration enhances recovery of solid sensible heat through improved coupling with H 2 O evaporation during evaporation cooling. Approximately 90% of the solid sensible heat can be internally recovered, which is significantly higher than that achieved with BAT (∼50%), resulting in approximately 20% lower specific energy consumption. A simplified techno-economic analysis indicates a consistently lower levelized cost of DAC. When indirect emissions are considered, the net removal cost is further reduced by ∼23% under baseline conditions. Overall, the proposed concept establishes a thermodynamically improved, phase-change-mediated strategy for internal heat recovery between solid phases, addressing the long-standing challenge of solid sensible heat recovery in temperature-swing adsorption processes. Beyond DAC, this approach is broadly applicable and offers substantial potential for energy and cost savings in adsorption-based separation systems.