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 image 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.