Valves for Carbon Capture and Storage (CCS) - CO2, Amine, Supercritical Service

Carbon capture and storage (CCS) is expanding rapidly as an industrial decarbonisation technology. Commercial-scale CCS projects include the Quest CCS (Shell Canada, 1 Mt/yr CO2), Boundary Dam (SaskPower, 1 Mt/yr), Sleipner (Equinor, North Sea, 1 Mt/yr), and numerous projects under development for blue hydrogen production, gas power plants, and industrial point sources (cement, steel). Each stage of the CCS chain - capture, compression, transport, and injection - has distinct valve requirements.

Post-Combustion Capture - Amine Absorption

Post-combustion capture using amine solvents (MEA, MDEA, piperazine, and blended amines) is the dominant capture technology for power plants and industrial sources. The amine absorber-stripper circuit is highly corrosive: amine solution at pH 8-11, temperatures from ambient to 130°C in the stripper reboiler; CO2-loaded amine is mildly acidic (pH 7.5-8.5); heat stable salts, oxidative degradation products, and foaming all create corrosive by-products; SS 316L is the standard body material for amine service; standard carbon steel corrodes in amine solutions above 80°C due to carbonate-amine attack.

CO2 Compression - High-Pressure Gas

Captured CO2 must be compressed from atmospheric (or slightly above) to pipeline pressure - typically 100-200 bar for transport in a supercritical state. Interstage cooler and separator valves handle wet CO2 gas with trace impurities (SO2, NOx, H2S depending on source). Key material considerations: wet CO2 forms carbonic acid (H2CO3) when combined with water - pH drops to 4-5, causing rapid corrosion of carbon steel; SS 316L or duplex 2205 for all wetted internals in compression interstage service; NACE MR0175 compliance where H2S exceeds 50 ppm (common in pre-combustion or natural gas sweetening capture systems).

Supercritical CO2 Pipeline Transport

Above 31.1°C and 73.8 bar (the CO2 critical point), CO2 exists as a supercritical fluid - with properties between liquid and gas. Supercritical CO2 is dense (600-900 kg/m3), has low viscosity, is highly soluble in most elastomers (causing explosive decompression damage), and is an excellent solvent for organic materials including PTFE lubricants and valve greases. Pipeline block valve requirements: API 6D full-bore ball valves (pig-friendly bore); NACE MR0175 for CO2 with H2S impurity; metal seats (not PTFE seats - supercritical CO2 permeates and degrades PTFE over time); explosive decompression rated elastomers (HNBR or FFKM rather than standard NBR) for valve body seals; emergency shutdown actuators (ESD) with SIL 2 rating for pipeline isolation.

CO2 Injection Well Valves

CO2 injection wellhead valves are the final interface between the surface compression/transport system and the geological storage reservoir. Requirements: API 6A wellhead design; extremely tight shutoff (Class VI or better) to prevent CO2 migration; metal seats for long-term sealing reliability (PTFE seats degrade in supercritical CO2 over years); NACE MR0175 if H2S co-injection; remote actuated (ESD shutdown on detection of surface CO2 leak); regular leak detection testing (pressure decay testing) to verify ongoing seal integrity.