Direct Air Capture by Monoethanolamine Absorptionwith Heat Pump Enhancements

This study investigates a direct air capture (DAC) process using a monoethanolamine (MEA) absorption process, further enhanced by the integration of heat pump modifications such as lean vapor compression (LVC) and stripper overhead compression (SOC) in the regeneration stage to reduce reboiler requirement. The process is modeled using Aspen Plus and incorporating the CCSI model adapted and suited for DAC environmental conditions. Technical performance was investigated through a sensitivity analysis of various environmental and process parameters, including MEA emission, air inlet temperature and humidity, and factors such as solvent loading, capture rate, gas velocity, and liquid to gas ratio. A scrubber section above the absorber was installed to mitigate MEA emission. The implementation of LVC and SOC results in a significant reduction in regeneration consumption of 25% compared to conventional MEA-based processes but the cost of capture is similar to that of the conventional process, due to additional capital investment. The regulatory limits on MEA emission at the air outlet have a significant impact on the dimensions of the scrubber section and therefore the overall cost of capture is reduced by 8% for the 6 ppm-mol emission limit in comparison to the 0.1 ppm-mol limit. Detailed techno-economic analyses were performed for design cases with capture scales ranging from 0.1 to 1 MtCO₂/yr, with capture costs ranging from 1091 to 1283 €/tCO₂.