CO₂ recycling for oxy-power-to-gas and oxy-power-to-methanol. Clean alternatives for energy storage

Carbon dioxide is the largest single contributor to global warming and current atmospheric concentrations are increasing at the fastest ever observed rate. Carbon capture and storage (CCS) and carbon capture and utilization (CCU) have been proposed as essential alternatives to reduce CO₂ emissions. Unfortunately, there are important energy penalties when CO₂ is separated from flue gases, as well as social issues concerning underground storage. Besides, most of the CCU methods actually release the captured CO₂ after the lifetime of the generated product. Other possibility to reduce global CO₂ emissions is the massive deployment of renewable energy. The main challenge that arises in this scenario is the management of the fluctuating renewable production. To tackle this problem, Power-to-X technologies (PtX) store surplus electricity in form of an energy vector by using H₂ from electrolysis as precursor. In particular, Power-to-Methane and Power-to-Methanol combine H₂ coming from electrolysis with CO₂ to produce synthetic methane and methanol. Both options are classified as energy storage and CCU methods as they use CO₂ to produce synthetic fuels. The conventional concepts release again the CO₂ when synthetic fuels are used. In this work we present novel and clean alternatives combining oxyfuel combustion and Power-to-X technologies to keep CO₂ in closed loops. These options make use of the oxygen produced in the electrolysis to feed, with recirculated CO₂, an oxyfuel boiler that satisfies a thermal demand and produces a flue gas mainly composed by CO₂ and H₂O. CO₂ is recycled, together with H₂, to produce valuable fuels in Power-to-X. This work overviews the state-of-the-art of these technologies and presents some examples for the application of these systems.