NOVELTY - Processing carbon dioxide in an algae cultivation and processing system (14) involves: generating energy products and accepting a by-product of carbon dioxide (151) from a fossil-fuel based system; using the by-product carbon dioxide from the fossil-fuel based system to produce algae from either or both solar radiation and artificial illumination, recovering the oil content of the algae and providing streams of oxygen and algae oil to the fossil-fuel based system.    USE - For processing carbon dioxide in algae cultivation and processing system (claimed).    ADVANTAGE - The present process reduces the consumption of fossil energy in the energy production; maximizes the use of renewable (solar) energy; minimizes the use of fossil fuel; and minimizes emissions of carbon dioxide to the atmosphere.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a system for capturing and sequestering the carbon dioxide produced in a fossil-energy production system through establishing synergism between the conventional fossil-energy production system and renewable energy production, comprising units provided within the fossil-energy production system for recirculating a portion of the product gases from the complete combustion of a hydrocarbon fuel such that the stream of recirculated gases contains pure carbon dioxide that can substitute for the nitrogen content of air; units for substituting the oxygen in air by the pure stream of oxygen from the renewable-energy production system with the recirculating stream of pure carbon dioxide to produce the oxidant for combusting a hydrocarbon fuel; units for capturing the carbon dioxide in the remaining portion of the product gases from combustion and exporting the captured carbon dioxide to the renewable-energy production system; a renewable-energy production system for the cultivation and processing of algae that receives the captured carbon dioxide from the fossil-energy production system and produces a stream of pure (near 100%) oxygen; units in the renewable-energy production system for processing the algae biomass to produce a combustible algae oil and a carbon-rich algae biomass residue; units in the fossil-energy production system to receive the stream of pure oxygen and to combine this stream in proportion with the recirculated stream of essentially pure carbon dioxide to produce the oxidant for combusting the hydrocarbon fuel that contains the equivalent of the oxygen content of air; and units for increasing the proportion of oxygen in the oxidant thereby reducing the carbon dioxide content.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a system for the cultivation of algae and for processing the algae for the production of its oil, of by-product oxygen, and of the processing of oil-free algae for the production of methane.    Algae cultivation and processing system (14)    Gas separation unit (118)    Algae/liquid separation device (128)    Oil-free algae biomass (142)    By-product carbon dioxide (151)