CCS Capture Types

The cheapest carbon to capture is the carbon you never have to dilute out of a mixed gas stream. That insight explains why some CCS projects are cost-competitive today while others remain aspirational.

CO2 capture methods differ by where and how they intercept the carbon. Post-combustion treats flue gas after burning; the CO2 is dilute (roughly 4-15% of exhaust), requiring energy-intensive separation. Pre-combustion converts fuel to a hydrogen-CO2 mixture before burning, yielding a concentrated CO2 stream that is cheaper to separate. Oxy-combustion burns fuel in pure oxygen rather than air, producing exhaust that is almost entirely CO2 and water, sidestepping separation at the cost of an energy-intensive air separation unit. Direct air capture (DAC) pulls CO2 from ambient air at only 0.04% concentration, making it by far the most expensive per ton.

If capture cost scales with the energy needed to separate CO2 from surrounding gases, which method should be cheapest per ton?

Concentration drives cost. Pre-combustion and oxy-combustion, because both produce concentrated CO2 streams. Post-combustion runs roughly $16-76/ton at industrial sources (up to ~$61/ton for gas power plants). DAC costs $300-1,000/ton currently. The US 45Q tax credit pays $85/ton for geological storage and $180/ton for DAC, calibrated to these differences. Most existing commercial CCS operates on naturally high-concentration streams (gas processing, fertilizer production), not power plants. DAC is the only method that addresses historical emissions, which is why it commands separate, higher subsidies.

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