Modelling of a concentrated solar power - photovoltaics hybrid plant for carbon dioxide capture and utilization via calcium looping and methanation

Increasing the share of renewable energies and reducing the emissions of carbon dioxide are two of the major challenges of this century. Effective use of solar energy can contribute to both targets. In this study, it is investigated an integrated process in which concentrated solar power is used to perform carbon dioxide capture from a combustion power plant through the calcium looping cycle in a dual interconnected fluidized bed system. Carbon dioxide is then reacted with hydrogen obtained from water electrolysis to produce methane (power-to-gas). Electrolytic cells may be powered by photovoltaics or excess renewable energies, thus reducing their curtailment. The integrated process was studied by means of model computations. Steady state operation of the different units was considered. Intrinsic variability of the solar energy was managed with implementation of a seasonal and/or daily thermochemical energy storage strategy. Design and operational conditions assumed as a reference were those of a combustion plant of municipal solid waste located in Manfredonia (Italy). Parameters were chosen so as to reproduce realistic conditions. Model results suggest that carbon dioxide capture can range from 30% to 85%. Input thermal power of the concentrated solar power must range between 50 and 175 MW, for 12 h of operation. A share of this energy can be integrated in the power cycle for electricity generation, upgrading the potentiality of the original combustion plant. Size of cubic storage vessels required for continuous operation of the system ranges from 10 to 70 m according to the implemented strategy. Methane yield ranges within 3-12 × 10 tons per year, and production of H needs a photovoltaic field of 4-5 km if built in Manfredonia. Altogether, the integrated plant has an overall efficiency of 20-22% and allows, simultaneously, for carbon dioxide capture, continuous integration of solar energy in the energy production cycle and carbon dioxide utilization for methane production.