Carbon Capture, Storage and Usage (CCUS)

Carbon Capture, Utilisation and Storage describes a set of processes that capture CO₂ from flue gases, process gas streams or directly from the atmosphere, and either store it permanently — typically in geological formations — or use it as a feedstock in industrial processes such as enhanced oil recovery, chemical production or materials manufacture.

CCUS is distinct from Carbon Capture and Storage (CCS), which refers specifically to permanent geological storage, though the terms are often used interchangeably. Carbon Capture and Utilisation (CCU) refers specifically to the use of captured CO₂ as a feedstock.

Several technologies are used for industrial CO₂ capture, with the appropriate choice depending on the CO₂ concentration in the source stream, the flow rate, the required CO₂ purity and the operating conditions.

Post-combustion capture uses an amine solvent to absorb CO₂ from dilute flue gas streams after combustion. Pre-combustion capture removes CO₂ from a hydrogen-rich synthesis gas stream before combustion — this approach is used in hydrogen production from natural gas with CCS (blue hydrogen). Oxyfuel combustion burns the fuel in a pure or enriched oxygen atmosphere to produce a concentrated CO₂ flue gas, simplifying capture.

Captured CO₂ must be conditioned — dried, purified and compressed — for transport and storage or for use in downstream processes. CO₂ compression to pipeline or injection pressure requires multi-stage compression with intercooling. Water must be removed to prevent corrosion in pipelines and compressors.

The CO₂ purity specification for transport and storage — covering water content, O₂, N₂ and other impurities — is set by the pipeline operator and the storage site or receiving facility requirements.

Blue hydrogen is a key application for CCUS in the near-term energy transition. In SMR-based hydrogen production, CO₂ can be captured from the PSA tail gas (which is predominantly CO₂ and hydrocarbons), from the reformer flue gas, or from both streams to maximise overall CO₂ capture rate.

The choice of capture point affects the overall capture efficiency, the cost and the engineering complexity. Pre-combustion capture from the PSA tail gas captures a significant fraction of the CO₂ but may not achieve capture rates required by some blue hydrogen certification standards without additional flue gas treatment.

Refineries are large sources of industrial CO₂ emissions from process heaters, steam generation and process reactions. CCUS is one of the pathways for refinery decarbonisation alongside electrification of heating, fuel switching and process optimisation.

CO₂ capture from refinery flue gas streams is technically feasible using post-combustion amine absorption. The economic viability depends on the CO₂ price, the cost of transport and storage, and the availability of suitable storage infrastructure.

Howe Baker provides engineering services for CCUS projects from concept through to EPC delivery. This includes front-end engineering and feasibility studies, CO₂ capture system design, CO₂ conditioning and compression design, and integration of CCUS with existing or new process plant.