Climate-Benign Direct Air CO2 Capture, Utilization, and Storage (DACCUS)

Transitioning towards a carbon managed energy infrastructure is essential to mitigate climate change. Negative emission technologies, such as direct air CO₂ capture (DACC), together with renewable energies will likely to be necessary components in the effort to slow, stop, reverse the flow of carbon dioxide (CO₂) to the atmosphere. The DACC process requires heat and electricity to capture CO₂ from the ambient air, the sources of which may not be climate-benign. We present an approach that combines DACC, long-term CO₂ storage, and geothermal energy production: a climate-benign direct air capture, carbon utilization, and storage (DACCUS). The CO₂ captured from the ambient air, is geologically stored in sedimentary basins, and circulated to the surface in a closed system to extract the available geothermal heat.  The produced heat can be used directly or converted to electricity by a power plant and used in the DACC process.  We investigate the performance of DACCUS systems, including sensitivity analyses of key parameters, such as the sorbent regeneration temperature (80-120°C), the outlet temperature the CO₂ stream from the DACC (70-22°C), and reservoir permeability (1x10^-15-1x10^-11 m²), among others.  The results indicate that DACCUS has a promising potential for using the CO₂ from DACC to produce process energy requirements. For example, with a regeneration temperature of 100°C and a DACC outlet temperature of 70°C, reservoirs with depths equal or above 3.5 km, and geothermal temperature gradients equal or above 35°C/km, can provide sufficient wellhead temperatures. In addition, the maximum DACC capacity for those temperatures increases considerably for reservoir permeability up to 5x10^-14 m², and can provide the make-up CO₂ for that which migrates outside of the region in the aquifer where CO₂ is circulated between the subsurface and the surface. Costs estimates for DACC are $500–600/tCO₂. While also the cost of the integrated system is important, the integration with CO₂-geothermal production could yield substantial savings for DACC ($0.64M - $30.6M annually of avoided electricity costs).