Techno-economic assessment of a synthetic methane production process by hydrogenation of carbon dioxide from direct air capture

Direct air capture (DAC) is widely investigated to capture carbon dioxide (CO₂) emissions from decentralised sources. As an alternative to geological storage, CO₂ from DAC can be reacted with hydrogen (H₂) from water electrolysis driven by renewable energy to produce synthetic methane (CH₄), increasing the penetration of renewable energies and leading to a circular carbon economy. This study presents a techno-economic assessment of an integrated system for DAC based on calcium looping and subsequent methanation of CO₂. Photovoltaics (PV) is considered as renewable energy source. For the DAC plant, heat exchangers represent the most expensive component, followed by blowers/compressors, reactors and gas heaters. The levelized cost of CO₂ removal for DAC ranges within 693–1587 € t_CO2⁻¹ according to the parameters considered. For a methanation plant built in Abu Dhabi (United Arab Emirates), the electrolyzer represents the most expensive component, followed by PV field, H₂ storage tank, and reactors. Altogether, the levelized cost of methane (LCOM) ranges within 4.9–8.2 € kg_CH4⁻¹ for integration with the DAC plant investigated. It reduces to 3.1–3.9 € kg_CH4⁻¹ for integration with point source carbon capture. A comparison between Abu Dhabi and Benevento (Italy) reveals that cities with an uneven distribution of solar energy throughout the year may require a large investment cost for the H₂ storage tank, that makes the LCOM increase. In conclusion, LCOM values provided in this study exceeds the current price of methane, suggesting that further improvements or economic incentives are required to increase the competitiveness of this power-to-gas technology.