Energy, Exergy, Economic and Environmental (4E) analysis of integrated direct air capture and CO2 methanation under uncertainty

Direct Air Capture (DAC) technologies are gaining interest in the concept of carbon utilization and Power-to-Gas (PtG), as the economic valorization of the CO2 into methane provides a viable pathway to allow DAC systems to mature. However, research on DAC mainly focuses on isolated systems, and the system performance depends on parameters that are highly uncertain. To study the integration of DAC in PtG, we developed a DAC-PtG model, performed an Energy, Exergy, Economic and Environmental (4E) analysis and implemented uncertainty quantification to consider the uncertain environment. The results illustrate that the DAC-PtG system is autothermal when introducing a two-stage mechanical vapor recompression unit at the DAC outlet. The exergy efficiency ranges between 51.3% and 52.6% within 3 standard deviations, for which the uncertainty is driven by the ambient conditions and the uncertain heat of desorption. The methane issued from DAC-PtG has a lower carbon footprint than fossil methane when the carbon footprint of the electricity supply is below or equal to 0.12 kgCO2-eq/kWh. The Levelized Cost of Synthetic Natural Gas (LCSNG) ranges between 130 euro/ MWh and 744 euro/ MWh, following an uncertain electricity price and uncertain expenses related to DAC and electrolysis. Therefore, bulk manufacturing, further maturing of these technologies and more demonstration projects are required to reduce the uncertainty of the LCSNG. Future works will consider intermittent renewable energy sources to supply power.

Automated summary

Direct Air Capture (DAC) technologies are being studied for integration with Power-to-Gas (PtG) systems in order to convert CO2 into methane. The performance of the DAC-PtG system depends on uncertain parameters, and the study analyzes the system using Energy, Exergy, Economic and Environmental (4E) analysis. Introducing a two-stage mechanical vapor recompression unit at the DAC outlet makes the DAC-PtG system autothermal. Uncertainty in exergy efficiency is driven by ambient conditions and the heat of desorption. The carbon footprint and cost of the methane produced by DAC-PtG depends on the electricity supply and expenses related to DAC and electrolysis.