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

摘要

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 ΔG°_((298 K|)_(H_2+0.5 O_2→H_2O)) 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.