CO2 capture from air and co-production of H2 via the Ca(OH)2–CaCO3 cycle using concentrated solar power–Thermodynamic analysis

The thermodynamics of a solar thermochemical cycle for the capture of CO2 from air are analyzed. The cycle encompasses 3 reactors: an aerosol-type carbonator for capturing CO2 from air using a spray of Ca(OH)2 aqueous solution, a solar calciner for thermally decomposing CaCO3 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 CO2; 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 CaCO3-decomposion and CH4-reforming processes, and syngas is further processed to separate streams of H2 and CO2. Its thermodynamic efficiency, defined as the ratio of ΔG298K∘|H2+0.5O2→H2O for the H2 produced to the thermal energy input (solar energy+heating value of CH4) is 22.7%. The solar chemical reactor technology for the calcination and for the combined calcination-reforming is presented.