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Maritime decarbonisation knowledge guide
Onboard Carbon Capture and StorageIs Retrofitting an Existing Ship Worth It?
Most existing ships will still need to use carbon-based fuels over the next decade and beyond. Energy-efficiency measures cannot reduce emissions to zero, while zero- and near-zero-emission fuels are not yet widely available. Installing oCCS therefore allows a ship to capture CO2 before the exhaust leaves the funnel, reducing actual emissions and carbon costs while helping the vessel remain operational under increasingly stringent decarbonisation requirements. To deliver genuine emission reductions, the captured CO2 must also be stored safely onboard, offloaded in port and sent to permanent storage or an eligible utilisation pathway.
Exhaust pretreatment → capture → compression/liquefaction → storage
Illustrative; not to scale
TRL 7–8Marine technology readiness of amine post-combustion capture
30–40%Capture rates common in current commercial cases
15–30%Typical energy/fuel penalty range for amine systems
10+ yearsRemaining life more likely to support payback
Term explained
What does oCCS mean?
oCCS stands for onboard carbon capture and storage. The lower-case o emphasises that the system is installed onboard. It does more than capture CO2: it also conditions and temporarily stores the CO2 onboard until it can be handed over to the downstream chain in port.
oonboardCarried out aboard the ship
CCCarbon CaptureCapturing carbon from exhaust or fuel-processing streams
SStorageConditioned and temporarily stored pending offloading
The big picture
Why must shipowners assess oCCS now?
For shipowners, this is not only an environmental issue; it is about whether a ship can remain commercially competitive throughout its remaining life. Carbon emissions are increasingly becoming a direct operating cost, while the Carbon Intensity Indicator (CII), regional carbon pricing and charter markets continue to intensify decarbonisation pressure. Yet the supply, price and port infrastructure for alternative fuels remain uncertain, and many existing ships are unsuitable for a complete fuel conversion. oCCS is therefore an important option for protecting asset value, reducing part of the vessel's carbon exposure and buying time for the fuel transition.
Fuel switching
Reduce lifecycle carbon intensity at the fuel source, subject to fuel supply, tankage, engine, safety and remaining asset-life constraints.
Onboard carbon capture
Separate carbon after or before combustion, store it and transfer it into the downstream carbon chain, without necessarily changing the existing fuel or engine.
Why owners care
Four pressures make the assessment necessary
If a ship has more than ten years of remaining life and frequently trades in carbon-priced regions, waiting for every alternative fuel to mature fully could mean years of continuing carbon costs and an early loss of competitiveness in chartering and operations.
Systems such as the EU Emissions Trading System (EU ETS) increasingly translate each tonne emitted into allowance-surrender obligations, surcharges and voyage costs. Eligible captured quantities may reduce part of this carbon-cost exposure.
Mid-life ships are often too young to scrap, yet may be too old to justify full conversion to a new fuel. oCCS can reduce the risk of premature commercial obsolescence.
Retaining the existing engine and fuel arrangement lets owners defer an irreversible fuel choice while green-fuel supply, pricing and bunkering networks mature.
Cargo owners, charterers and financial institutions increasingly focus on actual carbon intensity. Verifiable emission-reduction capability helps reduce the risk of exclusion from carbon-sensitive markets.
A necessary assessment does not mean mandatory installation on every ship. Investment may not be justified at present for vessels with short remaining lives, low carbon-price exposure or no CO2 offloading route. For ships with long remaining lives, high exposure on European Economic Area (EEA) routes, regular port calls and the ability to establish a downstream carbon chain, however, oCCS is already a strategic option that cannot be ignored.
The most important decision principle: installing capture equipment does not by itself constitute an emission reduction. Captured quantities can translate into compliance value and owner returns only when the CO2 is reliably measured, safely stored, offloaded and transported into a permanent storage or utilisation pathway recognised by the applicable regulations.
How it works
From funnel to permanent storage
A complete oCCS solution is not a single machine. It is a six-stage chain involving the ship, port, transport operator and storage site.
Capture
Separate carbon from exhaust or fuel-processing streams.
Conditioning
Purify, dehydrate and compress the CO2 to meet downstream specifications.
Onboard storage
Store it as a liquid, in solution, as solid carbon or in mineral form.
Offloading
Transfer it ship-to-shore, ship-to-ship or in ISO tank containers.
Onshore transport
Move it by pipeline, liquefied CO2 (LCO2) carrier, road or rail.
Final outcome
Permanent geological storage or recognised long-term utilisation.
The chain is only as strong as its weakest link. In 2026, the main weaknesses lie in port reception, specification compatibility, cross-border regulation and an auditable chain of custody—the complete record of CO2 flows and responsibilities from onboard capture through transfer and transport to final storage—rather than in capture chemistry alone.
Technology status
Mature solutions remain limited
Amine post-combustion capture is currently the most mature pathway and already has commercial LR-classed applications. Other pathways have potential, but most remain at the marine-demonstration or proof-of-concept stage, or are better suited to newbuildings.
Current front-runner
Amine post-combustion chemical absorption
Exhaust gas is first scrubbed and cooled, then enters an absorber where it contacts lean amine, which retains capacity to absorb CO2. The resulting CO2-rich amine is heated in a regenerator to release a high-concentration CO2 stream. The CO2 is then compressed, dehydrated and liquefied before entering onboard storage tanks.
This page assigns TRL 7–8, indicating that the pathway lies between system-prototype demonstration in an operational environment and a complete system that has been tested and qualified. An actual retrofit to an existing ship still requires ship-specific integration and approval.
Amine regeneration requires substantial heat. The design must also address sulphur oxides (SOx), nitrogen oxides (NOx), corrosion, solvent degradation, amine emissions or slip, nitrosamine by-products, absorber size and approximately 15–30% additional fuel consumption.
| Technology pathway | Marine TRL | Main advantages | Main limitations | Current position |
|---|---|---|---|---|
| Amine chemical absorption Post-combustion amine | 7–8 | No change to the main engine or existing fuel system; commercial, classed installations already exist | Regeneration heat, equipment volume, solvent/corrosion and exhaust pretreatment | Most mature |
| Calcium-based mineralisation Calcium looping | 5–6 | Produces solid CaCO3; avoids low-temperature LCO2 tanks | Approximately 2.27 t of CaCO3 per 1 t of CO2; solids handling and onshore regeneration | Under demonstration |
| Membrane separation Membrane | 4–5 | No liquid chemicals; potential for modularisation | Sensitive to SOx, NOx, moisture and particulates; requires continuous differential pressure and power | Early stage |
| Cryogenic separation Cryogenic | 3–4 | High-purity CO2; no amine solvent | Power for compression/refrigeration; risks of low-temperature embrittlement, boiling liquid expanding vapour explosion (BLEVE) and dry ice | Ship-type specific |
| Pre-combustion reforming/pyrolysis Pre-combustion | 4–6 | Handles concentrated carbon streams; pyrolysis can produce solid carbon | Limited to gaseous fuels; hydrogen safety, reactor space and thermal management | More suited to newbuildings |
| Oxy-fuel combustion Oxy-fuel | 2–3 | Theoretical capture rate approaches 100% | Large oxygen-production plant, high power demand, pure-oxygen fire hazards and engine modifications | Continue to monitor |
Gross vs. net
Capture rate ≠ net emission-reduction rate
Net benefit = captured quantity − added energy emissions
Unless waste heat from main-engine exhaust, jacket water or the scavenge-air cooler is used effectively, the capture system's additional fuel consumption will substantially erode its emission-reduction benefit.
Retrofit integration
The greatest challenge is often not the equipment itself
The General Arrangement (GA), funnel, tanks, piping and electrical systems of an existing ship were not designed with oCCS in mind. Whether the system can actually be delivered through detailed design and construction matters more than whether it appears to “fit” on drawings at the Approval in Principle (AiP) stage. AiP means that the classification society accepts the concept in principle; it does not mean detailed design is complete or final approval has been granted.
Exhaust routing and bypass
- Locate downstream of exhaust cleaning and cooling
- Provide full-flow bypass capability
- Automatic bypass on high backpressure
- Redundant upstream backpressure measurement
Steam, waste heat and power
- Approximately 3–4 MJ of regeneration heat per kg of CO2 captured by an amine system
- Verify spare capacity in the auxiliary boiler and exhaust-gas economiser
- Loads from compression, refrigeration, ventilation and the uninterruptible power supply (UPS)
- Include low-load and in-port scenarios
Storage capacity and voyage length
- Define capture rate, storage volume and voyage length together
- Capture stops when the tanks are full
- Weight, stability and longitudinal strength
- Penalties in cargo capacity, twenty-foot equivalent unit (TEU) slots and deadweight tonnage (DWT)
CO2 and amine safety
- Low-level CO2 detection and oxygen-deficiency monitoring
- Forced ventilation and accumulation analysis
- Volatile organic compound (VOC), pH and leak detection
- Continued accessibility and availability of life-saving appliances and muster stations
Emergency shutdown and materials
- Open bypasses, stop pumps and close isolation valves
- Include ventilation and alarms in the cause-and-effect matrix
- Low-temperature embrittlement and wet-CO2 corrosion
- Compatibility of solvents, gaskets and elastomers
Piping, adjacency and approval
- Pipe routing, supports and thermal expansion
- Drip trays, tank adjacency and hazardous areas
- Application by analogy of relevant provisions of the International Bulk Chemical (IBC) Code or International Gas Carrier (IGC) Code
- Address flag-State interpretations and exemptions early
7–8 barLow-pressure option, approximately −50 °C
15–20 barMedium-pressure option, approximately −26 to −20 °C
5.18 barCO2 triple-point pressure; dry ice must be avoided
60–70 TEUReport example: space penalty for 1,470 t of LCO2
Regulation & value chain
Capturing CO2 is not enough; the quantity must qualify for regulatory recognition
oCCS spans class safety, IMO environmental rules, regional carbon pricing, cross-border CO2 transport, port reception and final storage. These regimes are not maturing at the same pace.
EU ETS
Conditional recognitionThe applicable eligibility, permanence and MRV requirements must be met, supported by complete downstream evidence. Intermediate losses, emissions from onshore regeneration and the intended utilisation pathway must still be clearly attributed.
FuelEU Maritime
Not currently recognisedoCCS has not yet been incorporated into greenhouse-gas-intensity or penalty calculations. Ship-specific projects should continue to check the latest progress of the Article 30 review.
IMO
Framework under developmentThe report states a 2028 target for the oCCS environmental framework and a 2029 target for interim safety guidelines. Early projects must still proceed through class and the flag State.
London Protocol
Geographically constrainedCross-border transport of CO2 for sub-seabed geological storage generally requires the relevant Contracting Parties to have accepted—or provisionally applied—the 2009 amendment to Article 6 of the London Protocol, and the countries concerned to have entered into an agreement or arrangement. Activity is currently concentrated around the North Sea.
LR class framework
Established pathwayThe EACCS class notation, EACCS READY descriptive note, Approval in Principle (AiP) and ShipRight Risk Based Certification (RBC) can form a ship-specific pathway covering design, risk assessment, construction, commissioning and in-service assurance.
Best-fit segments
Operating conditions matter more than ship type alone
A vessel's true suitability depends jointly on remaining life, carbon-price exposure, offloading availability and whether the ship can absorb the equipment and cargo-capacity penalties.
More favourable near-term candidates
- Medium-range (MR) tankers/chemical tankers on fixed European Economic Area (EEA) routes
- Liquefied natural gas (LNG)-fuelled ships and LNG carriers
- Container ships on fixed rotations
- Short-sea ships, feeder container ships and RoPax vessels with frequent port calls
Potentially viable subject to conditions
- Very large crude carriers (VLCCs)/Suezmax tankers: ample space but long voyages
- Large bulk carriers: high reduction potential but infrequent offloading
- Global tramp trade: weaker current carbon-price exposure
- Container ships: power and TEU-slot penalties require detailed calculation
Currently weaker commercial cases
- Approximately five years of remaining life
- Primarily trading in unpriced regions
- No credible reception chain at ports of call
- Unable to accept structural, energy or cargo-capacity penalties
Decision gates
Confirm the closed loop before selecting equipment
The right starting point is not to ask which supplier offers the highest capture rate. It is to place a specific ship on a specific route and determine whether the technical, regulatory and commercial chains can all work at the same time.
Asset life
Does the ship have approximately ten years or more of commercially viable operating life remaining?
No → defer retrofit in most cases
Regulatory exposure
Does the actual route incur a quantifiable carbon cost?
Include only confirmed benefits in the base case
Reception chain
Which ports of call can receive the CO2? Have specifications, flow rates and responsibility boundaries been confirmed?
No named and confirmed reception pathway → do not proceed to final investment decision (FID)
Storage balance
Can the tanks hold the captured quantity from the longest leg? How long will capture stop once they are full?
Verify with a voyage-by-voyage mass balance
Integration margins
Are the steam, power, waste heat, GA, stability and cargo-capacity penalties acceptable?
A ship-specific concept design is required
Safety and approval
How will HAZID, HAZOP and ESD requirements be addressed, and how will class, flag-State and regulatory interpretations be resolved?
Start Approval in Principle (AiP) and ShipRight Risk Based Certification (RBC) early
Monitoring, reporting and verification (MRV)
How will captured quantities, additional energy use, offloading losses and final storage be audited?
Establish a verifiable CO2 chain of custody
For surveyors & project managers
Where should survey and project management focus?
Issues most likely to drive major drawing revisions, repeated flag-State correspondence and site rework should be resolved progressively from the concept-design/Approval in Principle (AiP) stage.
01Fix the route and offloading destination first: interface conditions for the terminal, barge or ISO tank containers should form part of the design basis.
02Close out space and energy issues: pipe routing, tank location, and heat and power balances cannot be left until the production-drawing stage.
03Link HAZID and HAZOP to detailed design: risk controls must be traceable to valves, ESD, ventilation and the cause-and-effect matrix.
04Include MRV in the inspection and test plan (ITP): calibration, data retention, performance drift, custody-transfer metering and proof of storage must all be verifiable.
Source map
Sources and reading context
This page is based on Lloyd's Register's “Applying Onboard Carbon Capture & Storage to Existing Ships” and is intended to help readers establish the overall framework quickly.
Visit the official Lloyd's Register (LR) project/research report page
Applying Onboard Carbon Capture and Storage to Ships
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Original document section guide
- Executive summary: pp. 4–9
- Technology status: pp. 17–25
- System integration: pp. 27–34
- Regulatory framework: pp. 35–41
- The business case: pp. 42–46
- Developing the carbon value chain: pp. 47–53
- Conclusions and risk register: pp. 54–57