CO2 Compression Options for CCUS

CO₂ compression is an often overlooked part of CCS. It’s a lot more than a little black box at the edge of the capture process flow diagram. CO₂ compression from near-atmospheric to pipeline pressure consumes about 10% of the power output from a power generation facility with capture. In fact, the compression parasitic load is about half of the parasitic load for solvent-based capture. Yet, opportunities for reducing compression costs are limited, with some compressors already approaching maximum achievable efficiency. Other challenges can include the need to design for large swings in flow rate and discharge pressure, reconciling equipment selection between small-scale and full-scale projects, and special designs for some processes that capture CO₂ at less than atmospheric pressure.

Discharge pressure and flow must be maintained within relatively narrow ranges for many centrifugal compressors and downstream solutions using low cost multistage centrifugal pumps with great turndown capabilities can be used to take larger pressure and flow swings allowing the more expensive machines to run at their sweet spots. Some capture processes such as membranes result in CO₂ capture at less than atmospheric pressure and require creative compressor solutions to reduce the overall cost of CCS.

Many demonstration and first-mover industrial CCS projects are better suited by compressors other than centrifugal compressors, which are likely to be selected for full-scale projects. These can include multistage centrifugal blowers, screw compressors, reciprocating compressors, multistage centrifugal pumps, and others. This paper will provide a broad overview of CO₂ compression options for different suction pressures, flow rates, and discharge pressures and for project scales ranging from small-scale demonstration to full-scale commercial projects. Emerging CO₂ compression technologies will also be discussed. A generalized comparison of refrigeration-based liquefaction followed by pumping vs. straight compression will also be presented.