CO2 Shipping
Overview
[edit]CO2 shipping is the transport of CO2 in a refrigerated, pressurised liquid state using specialised marine tankers (often referred to as liquefied CO2 (LCO2) carriers). It has used at small scale to supply food, beverage, and industrial gas markets in the North Sea, and is now being developed at larger scale as part of value chains that connect dispersed emitters to regional storage hubs.[1][2]
Ship transport is often considered when:
- multiple capture sites need to connect to a common storage location,
- offshore transport between capture and storage locations is required, or
- volumes are modest/variable and flexibility is valued compared with fixed pipelines.[3]
History
[edit]CO₂ has been shipped by sea since the late 1980s, initially using converted dry cargo vessels for short-haul European supply to the food and beverage sector.[1][4]
Through the 2000s–2010s, studies evaluated CO₂ shipping as a CCS transport mode, including design conditions (pressure/temperature), terminal concepts, and costs.[5]
In the mid-2020s, large, purpose-built LCO₂ carriers began entering service to support CCS hub-and-spoke models (e.g., Northern Lights/Longship), with dedicated vessels and terminals designed for multi-user CO₂ logistics.[6][7]
Physical Properties and Phases
[edit]The CO2 phase diagram includes two points that are central to ship transport design:
- Triple point: below this temperature/pressure combination, CO2 cannot exist as a liquid and will form solid (“dry ice”).[8]
- Critical point: above this temperature/pressure, CO2 becomes a supercritical fluid; below it, CO2 can be transported as a compressed liquid if temperature and pressure are appropriately controlled.[9]
Insert phase diagram with overview of low, medium and high
Typical shipping temperature/pressure regimes. Industry guidance commonly discusses more than one “standard” operating band, reflecting trade-offs between refrigeration duty, tank wall thickness, and cargo density. For early CCS shipping, two common cryogenic bands are often cited: approximately 5.5–7 bar(g) at around -50 °C (“low pressure”) and ~15–18 bar(g) at around -30 °C (“medium pressure”), with some projects also considering closer-to-ambient transport linked to ship-to-offshore offloading concepts.[10][3]
System Design and Operation
[edit]A liquid CO₂ shipping chain typically comprises: (i) CO₂ conditioning and liquefaction at (or near) the capture site, (ii) intermediate storage and loading at a terminal, (iii) ship transport in insulated pressure tanks, and (iv) unloading, buffer storage, and onward transfer to utilisation or geological storage (often via pipeline from a receiving terminal).[11][7]
CO2 conditioning and liquefaction
[edit]Captured CO2 is dried and treated to control impurities (especially water and reactive acid-formers) and is then compressed and refrigerated to a target liquid condition suitable for storage and ship loading. Liquefaction concepts may use multi-stage compression with refrigeration and/or Joule–Thomson expansion depending on the selected pressure/temperature band and integration opportunities.[11]
Port/terminal intermediate storage
[edit]Because ship arrivals are discrete, intermediate storage is used to buffer between continuous capture and batch ship loading. Terminals commonly include:
- insulated storage tanks (sized to ship cargo parcels and scheduling),
- pumps/compressors to match ship loading conditions,
- metering and sampling for custody transfer, and
- safety systems (gas detection, ventilation, emergency shutdown, controlled venting).[11][7]
Ship cargo containment and handling
[edit]Dedicated CO2 carriers generally use pressurised, insulated cargo tanks ( “Type C” pressure vessels) with refrigeration/pressure control to keep CO2 in the intended liquid state and manage boil-off or heat ingress. Operating windows are selected to avoid crossing into solid formation regions and to maintain stable two-phase margins under expected weather, routing, and loading/unloading conditions.[9][12]
Loading/unloading operations
[edit]Loading is typically performed using dedicated loading arms/hoses with emergency release systems. Unloading commonly transfers LCO2 to receiving tanks and then to pumps/compressors for onward transport. Some CCS concepts consider direct ship-to-offshore offloading to reduce onshore terminal infrastructure, but these place different constraints on ship design and operating pressure.[3][10]
CO₂ Stream Quality and Impurities
[edit]Impurity control in CO₂ shipping is driven by:
- corrosion and materials compatibility (e.g., water + CO₂ → carbonic acid; reactive combinations can form stronger acids),
- phase behaviour (non-condensables shift the phase envelope and can increase required pressure or cause two-phase instability),
- solid formation/plugging (dry ice risk increases near the triple point; some contaminants raise freezing/solidification risks),
- toxicity (e.g., H₂S), and
- operability (hydrate/ice formation, sloshing behaviour, metering accuracy, and venting characteristics).[13][11]
Typical Impurity Considerations
[edit]Common impurity groups and why they matter:
- Water (H2O): primary driver for corrosion and hydrate/ice risks.
- Oxygen (O2): can accelerate corrosion and participate in acid-forming reactions with sulphur species.
- Sulphur oxides (SOx) / hydrogen sulphide (H2S): toxicity (H2S) and strong acid formation pathways when combined with O2 and water.
- Nitrogen oxides (NOx): potential acid formation and materials impacts.
- Non-condensables (N2, Ar, H2, CH4): affect vapour pressure and may increase ship tank pressure for a given temperature.
- Trace contaminants (amines, NH₃, aldehydes, Hg): may be capture-process-specific and require case-by-case assessment for compatibility and emissions controls.[13][11]
Indicative Specification Ranges
[edit]Published shipping specifications vary by project, but early CCS projects have referenced stringent ppm-level limits for several contaminants. One widely cited comparison shows (i) a Northern Lights shipping specification (ppm mol) alongside (ii) EU recommendations used for broader transport discussions.[14]
| Component | Northern Lights example (ppm mol) | EU recommendation example | Notes |
|---|---|---|---|
| CO2 | NS | >99.7% by volume | Total purity basis differs across documents and contracts. |
| H2O | ≤30 | <50 ppm | Water control is central for corrosion/ice risk. |
| O2 | ≤10 | NS | Often tightened for corrosion control. |
| H2S | ≤9 | <200 ppm | Toxicity and acid formation risks. |
| SOx | ≤10 | NS | Acid formation and materials risk. |
| NOx | ≤10 | NS | Acid formation and materials risk. |
| CO | ≤100 | <2000 ppm | Typically managed for safety/compatibility and monitoring. |
| H2 | ≤50 | <0.3% by volume | Non-condensable; affects phase behaviour/pressure. |
| NH3 | ≤10 | NS | Capture-process dependent. |
| Amine (total) | ≤10 | NS | Capture-process dependent. |
| Methane (CH4) | NS | <0.3% by volume | Non-condensable; affects phase behaviour/pressure. |
| Argon (Ar) | NS | <0.3% by volume | Non-condensable; affects phase behaviour/pressure. |
| Formaldehyde | ≤20 | Not defined | Trace contaminant; process dependent. |
| Acetaldehyde | ≤20 | Not defined | Trace contaminant; process dependent. |
| Mercury (Hg) | ≤0.03 | Not defined | Materials/health considerations. |
| Cadmium (Cd) / Titanium (Ti) (sum) | ≤0.03 | Not defined | Trace metals; contract-specific. |
Note: Specifications must be developed on a whole-chain basis (capture → conditioning → terminal → ship → receiving terminal → storage), because temperature/pressure selection and impurity limits are coupled; lower-temperature shipping can require more stringent impurity control.[15]
Safety and Risk Management
[edit]CO2 is a relatively safe substance to transport in comparison with other flammable or combustible materials. SIGTTO produced a chart shown the potential hazard pathways applicable and not applicable to CO2. CO2 is not without hazard, however
SIGTTO CHART
CO2 is non-flammable, but LCO2 shipping presents distinct hazards including:
- asphyxiation (CO2 is denser than air and can accumulate in low-lying or confined spaces),
- toxicity (if contaminants such as H2S are present),
- cryogenic injury and cold burns (from cold surfaces, jets, or dry ice particles),
- embrittlement/structural damage (localised sub-zero temperatures during rapid depressurisation),
- overpressure/relief events (heat ingress, boil-off, or operational upsets), and
- marine risks (collision/grounding, hose/arm release, mooring failure).[16]
Notable CO₂ Shipping systems
[edit]| System / vessel(s) | Region | Primary purpose | Indicative scale / features | Status (as reported) |
|---|---|---|---|---|
| Small-scale European food-grade CO2 tanker fleet (Helle, Gerda, Embla, Froya) | Europe | Food/beverage and industrial CO2 logistics | Historically ~1,200–1,800 tonnes capacity-class vessels serving short-haul European routes | Operational fleet described in industry overview.[1] |
| Northern Lights (Longship) LCO2 carriers (e.g., Northern Pioneer, Northern Pathfinder, Northern Phoenix) | Norway / North Sea | CCS hub shipping from capture sites to Øygarden receiving terminal, then pipeline to offshore storage | Dedicated 7,500 m³ CO2 carriers; reported transport conditions of ~19 bar(g) and down to ~-35°C. | Ships delivered/added during 2024–2025; project designed for multi-user CCS logistics.[6][17] |
| Project Greensand CO2 carrier Carbon Destroyer 1 | Denmark / North Sea | CCS shipping from onshore capture sites to offshore injection at Nini West/Nini reservoir | Dedicated offshore CO2 carrier intended for regular routes between Port Esbjerg and Nini West; designed for liquefied CO2 transport with onboard cooling/pressure systems. | Vessel construction/launch milestones reported in 2025; injection operations targeted 2026. [18] |
| Japan LCO₂ transport demonstration vessel EXCOOL | Japan | CCUS R&D and demonstration of LCO2 marine transport | Demonstration test ship developed for CO2 transport trials under Japanese CCUS demonstration programmes. | Delivered/used for demonstration testing (reported 2023–2024).[19] |
References
[edit]- ↑ 1.0 1.1 1.2 Clarksons, “Liquid CO₂ carriage by sea: An introduction”.
Key points include: need for pressure + refrigeration (avoid dry ice), history of shipping since late 1980s, and indicative vessel fleet/capacities. - ↑ ZEP/CCSA, Guidance for CO₂ transport by ship (March 2022)
- ↑ 3.0 3.1 3.2 Global CCS Institute, Needs, Opportunities and Prospects for CO₂ Shipping in CCS Projects (Nov 2025).
- ↑ Larvik Shipping, “About us”.
- ↑ IEAGHG, Ship Transport of CO₂ (2004).
- ↑ 6.0 6.1 Northern Lights, “Northern Lights' first CO₂ transport ship ready for delivery” (Nov 2024).
- ↑ 7.0 7.1 7.2 Reuters, “Shell, Equinor, TotalEnergies open Norwegian CO₂ storage facility” (Sep 2024).
- ↑ Span & Wagner (NIST), “A New Equation of State for Carbon Dioxide …”
- ↑ 9.0 9.1 ABS, Requirements for Liquefied Carbon Dioxide Carriers (2025).
- ↑ 10.0 10.1 ZEP/CCSA (2022)
- ↑ 11.0 11.1 11.2 11.3 11.4 IEAGHG, The Status and Challenges of CO₂ Shipping Infrastructure (Oct 2020).
- ↑ ZEP/CCSA (2022)
- ↑ 13.0 13.1 ZEP/CCSA
- ↑ 14.0 14.1 ZEP/CCSA (2022)
- ↑ ZEP/CCSA (2022)
- ↑ ZEP/CCSA (2022) discusses CO₂ accumulating in low points creating asphyxia hazard, and describes leakage depressurisation leading to Joule–Thomson cooling, potential steel embrittlement, and solid CO₂ particle formation with inhalation risks.
- ↑ Northern Lights, “Northern Lights welcomes Northern Phoenix” (Dec 2025).
- ↑ Greensand Future, “First European built offshore CO₂ Carrier …” (May 2025).
- ↑ Baird Maritime, “Vessel Review | Excool … liquefied CO₂ carrier demonstrator” (Mar 2024).