Editing CO2 Shipping

== Overview ==
'''CO<sub>2</sub> shipping''' is the transport of [[Carbon dioxide|CO<sub>2</sub>]] in a refrigerated, pressurised liquid state using specialised marine tankers (often referred to as liquefied CO<sub>2</sub> (LCO<sub>2</sub>) 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.<ref name="ClarksonsIntro">Clarksons, “Liquid CO₂ carriage by sea: An introduction”.<br/>Key points include: need for pressure + refrigeration (avoid dry ice), history of shipping since late 1980s, and indicative vessel fleet/capacities.</ref><ref name="ZEPExec">ZEP/CCSA, ''Guidance for CO₂ transport by ship'' (March 2022)</ref>

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.<ref name="GCCSIShippingProspects">Global CCS Institute, ''Needs, Opportunities and Prospects for CO₂ Shipping in CCS Projects'' (Nov 2025).</ref>

== History ==
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.<ref name="ClarksonsIntro"/><ref name="LarvikAbout">Larvik Shipping, “About us”. </ref>

Through the 2000s–2010s, studies evaluated CO₂ shipping as a CCS transport mode, including design conditions (pressure/temperature), terminal concepts, and costs.<ref name="IEAGHG2004">IEAGHG, ''Ship Transport of CO₂'' (2004).</ref>

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.<ref name="NorlightsPioneer">Northern Lights, “Northern Lights' first CO₂ transport ship ready for delivery” (Nov 2024).</ref><ref name="ReutersNL">Reuters, “Shell, Equinor, TotalEnergies open Norwegian CO₂ storage facility” (Sep 2024).</ref>

== Physical Properties and Phases ==
The CO<sub>2</sub> phase diagram includes two points that are central to ship transport design:
* '''Triple point''': below this temperature/pressure combination, CO<sub>2</sub> cannot exist as a liquid and will form solid (“dry ice”).<ref name="NISTSpanWagner">Span & Wagner (NIST), “A New Equation of State for Carbon Dioxide …” </ref>
* '''Critical point''': above this temperature/pressure, CO<sub>2</sub> becomes a supercritical fluid; below it, CO<sub>2</sub> can be transported as a compressed liquid if temperature and pressure are appropriately controlled.<ref name="ABSCO2Requirements">ABS, ''Requirements for Liquefied Carbon Dioxide Carriers'' (2025).</ref>

'''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.<ref name="ZEPPTBands">ZEP/CCSA (2022)</ref><ref name="GCCSIShippingProspects"/>

== System Design and Operation ==
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).<ref name="IEAGHG2020">IEAGHG, ''The Status and Challenges of CO₂ Shipping Infrastructure'' (Oct 2020). </ref><ref name="ReutersNL"/>

=== CO<sub>2</sub> conditioning and liquefaction ===
Captured CO<sub>2</sub> 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.<ref name="IEAGHG2020"/>

=== Port/terminal intermediate storage ===
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).<ref name="IEAGHG2020"/><ref name="ReutersNL"/>

=== Ship cargo containment and handling ===
Dedicated CO<sub>2</sub> carriers generally use pressurised, insulated cargo tanks ( “Type C” pressure vessels) with refrigeration/pressure control to keep CO<sub>2</sub> 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.<ref name="ABSCO2Requirements"/><ref name="ZEPShipConditions">ZEP/CCSA (2022)</ref>

=== Loading/unloading operations ===
Loading is typically performed using dedicated loading arms/hoses with emergency release systems. Unloading commonly transfers LCO<sub>2</sub> 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.<ref name="GCCSIShippingProspects"/><ref name="ZEPPTBands"/>

== CO₂ Stream Quality and Impurities ==
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).<ref name="ZEPImpurityLogic">ZEP/CCSA</ref><ref name="IEAGHG2020"/>

=== Typical Impurity Considerations ===
Common impurity groups and why they matter:
* '''Water (H<sub>2</sub>O)''': primary driver for corrosion and hydrate/ice risks.
* '''Oxygen (O<sub>2</sub>)''': can accelerate corrosion and participate in acid-forming reactions with sulphur species.
* '''Sulphur oxides (SOx) / hydrogen sulphide (H<sub>2</sub>S)''': toxicity (H<sub>2</sub>S) and strong acid formation pathways when combined with O<sub>2</sub> and water.
* '''Nitrogen oxides (NOx)''': potential acid formation and materials impacts.
* '''Non-condensables (N<sub>2</sub>, Ar, H<sub>2</sub>, CH<sub>4</sub>)''': 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.<ref name="ZEPImpurityLogic"/><ref name="IEAGHG2020"/>

=== Indicative Specification Ranges ===
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.<ref name="ZEPShippingSpecs">ZEP/CCSA (2022)</ref>

{| class="wikitable"
|+ Indicative impurity specifications for CO₂ shipping (examples from published sources). ''NS: Not Specified''
! 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 (CH<sub>4</sub>) || 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.
|}
<ref name="ZEPShippingSpecs"/>

''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.<ref name="ZEPWholeChain">ZEP/CCSA (2022)</ref>

== Safety and Risk Management ==
CO<sub>2</sub> 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 CO<sub>2</sub>. CO<sub>2</sub> is not without hazard, however

SIGTTO CHART

CO<sub>2</sub> is non-flammable, but LCO<sub>2</sub> shipping presents distinct hazards including:
* '''asphyxiation''' (CO<sub>2</sub> is denser than air and can accumulate in low-lying or confined spaces),
* '''toxicity''' (if contaminants such as H<sub>2</sub>S 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).<ref name="ZEPSafetyHazards">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.</ref>

== Notable CO₂ Shipping systems ==
{| class="wikitable"
|+ Selected CO<sub>2</sub> shipping systems (operational, demonstration, and CCS value-chain applications)
! System / vessel(s) !! Region !! Primary purpose !! Indicative scale / features !! Status (as reported)
|-
| Small-scale European food-grade CO<sub>2</sub> tanker fleet (''Helle'', ''Gerda'', ''Embla'', ''Froya'') || Europe || Food/beverage and industrial CO<sub>2</sub> logistics || Historically ~1,200–1,800 tonnes capacity-class vessels serving short-haul European routes || Operational fleet described in industry overview.<ref name="ClarksonsIntro"/>
|-
| [[Northern Lights]] (Longship) LCO<sub>2</sub> 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 CO<sub>2</sub> 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.<ref name="NorlightsPioneer"/><ref name="NLPhoenix">Northern Lights, “Northern Lights welcomes Northern Phoenix” (Dec 2025).</ref>
|-
| [[Project Greensand]] CO<sub>2</sub> carrier ''Carbon Destroyer 1'' || Denmark / North Sea || CCS shipping from onshore capture sites to offshore injection at Nini West/Nini reservoir || Dedicated offshore CO<sub>2</sub> carrier intended for regular routes between Port Esbjerg and Nini West; designed for liquefied CO<sub>2</sub> transport with onboard cooling/pressure systems. || Vessel construction/launch milestones reported in 2025; injection operations targeted 2026. <ref name="GreensandCarrier">Greensand Future, “First European built offshore CO₂ Carrier …” (May 2025).</ref>
|-
| Japan LCO₂ transport demonstration vessel ''EXCOOL'' || Japan || CCUS R&D and demonstration of LCO<sub>2</sub> marine transport || Demonstration test ship developed for CO<sub>2</sub> transport trials under Japanese CCUS demonstration programmes. || Delivered/used for demonstration testing (reported 2023–2024).<ref name="ExcoolDemo">Baird Maritime, “Vessel Review | Excool … liquefied CO₂ carrier demonstrator” (Mar 2024).</ref>
|}

== References ==
<references/>