CO 2 capture from air and co-production of H 2 via the Ca(OH) 2–CaCO 3 cycle using concentrated solar power–Thermodynamic analysis

Abstract

The thermodynamics of a solar thermochemical cycle for the capture of CO 2 from air are analyzed. The cycle encompasses 3 reactors: an aerosol-type carbonator for capturing CO 2 from air using a spray of Ca(OH) 2 aqueous solution, a solar calciner for thermally decomposing CaCO 3 into CaO using concentrated solar energy, and a conventional slaker for regenerating Ca(OH) 2. Two approaches are examined: (1) a closed-material cycle that delivers pure CO 2; and (2) an open-material cycle that, additionally, co-produces hydrogen. The 2nd approach features the same components as those of the closed-material cycle, except that the calciner co-produces CaO and syngas by the combined CaCO 3-decomposion and CH 4-reforming processes, and syngas is further processed to separate streams of H 2 and CO 2. Its thermodynamic efficiency, defined as the ratio of Δ G 298 K ∘ | H 2 + 0.5 O 2 → H 2 O for the H 2 produced to the thermal energy input (solar energy+heating value of CH 4) is 22.7%. The solar chemical reactor technology for the calcination and for the combined calcination-reforming is presented.