Process intensification for carbon capture could reduce costs

In conventional solvent-based carbon-capture systems, CO₂-rich exhaust gas contacts gravity-driven solvents in a vertical packed-bed column. A novel approach developed by Carbon Clean Solutions USA Inc. (CCSUS; Cumming, Ga.; www.carboncleansolutions.com) employs centrifugal force from rotating horizontal packed beds to effect the gas-to-liquid contact. The higher g-forces allowed by the rotation improve mass transfer and enable smaller units to be used. Smaller units would lower capital costs compared to traditional carbon capture. The system has the potential to reduce the levelized CO₂ -capture cost to the U.S. Dept. of Energy (DOE) target of $30/ton or less.

Under a $2.9-million cooperative agreement from the DOE’s National Energy Technology Laboratory, GTI (Des Plaines, Ill.; www.gti.energy) is the prime contractor leading the effort with CCSUS to scale up this process-intensification approach from laboratory scale size to a larger, integrated carbon-capture system capable of removing 1 ton/d CO₂ from power-plant fluegas.

The novel carbon-capture approach, known as ROTA-CAP technology, is designed such that CCS’s intensified solvents are pumped into the center of the rotating cylinder, and the centrifugal force from the rotation pushes the liquid outward through the packed-bed gas-liquid contactor (diagram). The CO₂-containing fluegas flows from the exterior of the cylinder, against the flow of solvent.

“A key feature of ROTA-CAP is its use of more highly concentrated solvents than those used in conventional carbon capture,” says David Bahr, CCSUS technology manager, and that can reduce the energy required for regeneration of the CO₂. Although the overall energy savings are partially offset by the rotational energy required in the packed-bed cylinders, validation tests indicate up to 45% energy savings compared to conventional monoethanolamine (MEA) units.

GTI and CCSUS are now designing the larger-scale system, and anticipate completing construction by mid-2019. After laboratory testing at GTI headquarters, the assembly will be moved to the National Carbon Capture Center in Wilsonville, Ala. for long-term testing. “While the current project is focused on capturing CO₂ from fluegas at coal- and natural-gas-fired power plants, the rotating packed-bed intensification approach could be applied to other industrial operations involving gas-liquid contact,” notes GTI technology manager Osman Akpolat.