Direct capture of carbon dioxide from the atmosphere using bricks of calcium hydroxide

Abstract

Direct air capture (DAC) of CO2 plays a key role in most 1.5°C climate scenarios. The low concentration of CO2 in ambient air results in high contactor volumes, air flow rates, and energy requirements. Here, we investigate a DAC system based on the carbonation of Ca(OH)2 hollow bricks piled in stacks that move counter-currently with respect to the air flow. Capture efficiencies of 50% can be obtained with a contactor approximately 10 m deep, with a pressure drop below 200 Pa at air velocities of 3–4 m/s inside the brick holes. To capture 1 Mt-CO2/year, DAC cost approaches 251 and 131 $/t-CO2 (without contingencies) for a first and an nth-of-a-kind system, respectively, relying on emerging technologies to decarbonize the lime and cement industries. If the carbonated bricks find a value as construction materials, breakthrough decreases in costs can be achieved.