Assessment of reasonable opportunities for direct air capture

Abstract

This work explores the possibility of using CO _2 captured directly from the atmosphere for several applications that require low to moderate purities. Comparisons of the minimum and real work for separating CO _2 from air, natural gas combined cycle flue gas and pulverized coal combustion flue gas are proposed and discussed. Although it is widely accepted that the separation of CO _2 from air to high purity is more energy-intensive than separating CO _2 from more concentrated sources, this study presents select cases where the separation of CO _2 from air to low and moderate purities is energetically equivalent with the work required for flue gas CO _2 separation. These energetically-competitive cases are shown to be dependent on the percent capture and final CO _2 purity desired. In particular, several technologies can be considered as CO _2 utilization opportunities in which dilute CO _2 may be an adequate feedstock. Specifically, this study is focused on enhanced oil recovery and microalgae cultivation technologies, which appear to be the most beneficial near-term applications for utilization of CO _2 from direct air capture.

Keywords

• direct air capture
• negative emissions
• carbon capture