Carbon dioxide capture from atmospheric air using sodium hydroxide spray

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Climate Science

Background:

• Conventional carbon capture targets large point sources.
• Direct air capture (DAC) addresses diffuse and historical emissions.
• NaOH spray contactors offer a novel approach for DAC.

Purpose of the Study:

• To assess the feasibility of a NaOH spray-based contactor for direct air capture.
• To estimate the cost and energy requirements per unit of CO2 captured.
• To compare prototype performance with theoretical predictions.

Main Methods:

• Constructed and tested a prototype NaOH spray system.
• Measured CO2 absorption, energy consumption, and water loss.
• Employed a numerical model for drop collision and coalescence to scale up.
• Estimated operational costs for a full-scale system.

Main Results:

• Direct air capture of CO2 is technically feasible with off-the-shelf technology.
• Drop coalescence reduces CO2 absorption efficiency but fan/pump energy is manageable.
• Significant water loss (20 mol H2O/mol CO2) occurs but can be optimized.
• Estimated CO2 capture cost is $96/ton-CO2 (base case), ranging from $53 to $127/ton-CO2.

Conclusions:

• NaOH spray-based direct air capture is a viable technology for climate change mitigation.
• Optimizing spray characteristics (e.g., 50 micrometer mean drop diameter) can lower costs.
• Further research on solution recovery and CO2 sequestration is needed for full system cost analysis.