Direct Air Capture (DAC) is a crucial Negative Emissions Technology (NET) for mitigating global warming. One of the main challenges in DAC processes is the high energy and economic costs associated with airflow systems in large-scale air contactors. Recently, there has been a growing interest in using hydrated lime to capture low concentrations of CO2 (~450 ppm) from the atmosphere, particularly at higher air relative humidity. Cooling towers, commonly used in various industrial units to cool process water, provide an ideal environment for hydrated lime-based DAC systems as they expose large flows of ambient air to water. This study assessed the feasibility of integrating vertically oriented parallel flat plates of Ca(OH)2 into the upper section of an industrial mechanical draft cooling tower to simultaneously perform the dual tasks of water cooling and CO2 capture from the passing air. Results of an unsteady-state Shrinking Core Model (SCM) showed that 425 cooling towers of 20×20 m2 cross-sectional area accommodating 5-m-long Ca(OH)2 vertical plates of porosity 0.55, thickness 2 cm, and distance between adjacent plates of 2 cm can achieve an annual CO2 capture rate of 1 million tons if the carbonated plates are replaced 4 times a year (3-month cycle duration). By utilizing a scaled-up centralized calcination unit for the regeneration of the recycled sorbent, the estimated final cost of the proposed DAC process is around $93.5 to $269.3 per ton of CO2 captured, which makes the proposed system a cost-competitive alternative among the state-of-the-art DAC technologies.

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