Abstract
An initial phase of laboratory investigation has been completed in pursuit of a global-scale methodology for reduction of CO2 in ambient air through direct air capture (DAC). The methodology presented previously by Agee, Orton, and Rogers provides the background for this study. The laboratory prototype experiment presented has been designed to assess the potential for removing CO2 from ambient air by snow deposition. The approach consists of refrigeration to achieve the required CO2 deposition temperature of 135 K at 1 bar of pressure. The refrigerant of choice is liquid nitrogen (LN2) with cooling (77 K) at the top of a cylindrical 26.5-L Pyrex glass sequestration chamber. A highly conductive aluminum base with 14 instrumentation ports rests at the interface between the LN2 reservoir and the sequestration chamber. The cooling and mixing through Rayleigh–Taylor instability achieves uniform deposition temperature. Insulation to maintain the cooling process is provided to sustain CO2 depletion phase change at 135 K. The coldest temperature achieved in experimentation was 125 K. The required cooling period was 4.5 h, with an additional hour to achieve uniform chamber temperatures ≤ 135 K through top-down convective mixing. Experimental measurements showed a reduction of CO2 in the chamber air from initial values of ~500 ppmv down to 35 ppmv. Discussion is given to the issue of chamber CO2 frost versus CO2 snowflake formation, as well as the overall relevance of the experiment to DAC through refrigeration and storage in Antarctica to reduce atmospheric CO2.
