The global merchant fleet comprises over 100,000 vessels, the vast majority of which are powered by conventional fuels. Newbuilds with alternative propulsion account for only a fraction of annual tonnage additions. The mathematical consequence: if shipping is to meet its emission targets, existing vessels must be part of the solution.
This is precisely where carbon capture retrofit comes in. It aims to keep existing vessels economically viable for longer under growing emission pressure. Rather than sending a vessel for recycling after 15 years because it becomes uneconomical under EU ETS and FuelEU Maritime, a retrofit with OCCS could improve the emission balance sufficiently for continued operation to remain economically justifiable.
This sounds convincing in theory. In practice, however, feasibility depends on a whole range of technical, economic, and logistical factors that must be carefully examined before any investment decision is made.
Before a retrofit project can even enter the planning phase, four fundamental questions must be answered. None of them concerns the capture technology itself – all concern the boundary conditions on the vessel and along the logistics chain.
Space requirements: Does the vessel have sufficient contiguous space for absorber, stripper, heat exchangers, and auxiliary systems? On many older vessels, the engine room is so densely packed that a retrofit would only be possible on deck – which brings its own structural and safety challenges.
Energy demand: Amine-based capture systems require substantial heat quantities for absorbent regeneration. This heat must be provided from the exhaust stream or an additional steam generator. On older vessels with already marginal energy budgets, this additional demand can become a disqualifier.
CO2 storage: The captured CO2 must be stored on board – typically in liquid form at low temperatures and moderate pressure. This requires a dedicated tank that affects the vessel's position, weight, and stability.
Port logistics: A CO2 transfer facility must exist at the destination port or along the route. Without a functioning offtake chain, the entire investment is worthless. This question is frequently asked last – but should be answered first.
The honest answer is: OCCS retrofit is currently not economically viable for the majority of the existing fleet. Tight layouts, weak port prospects, or an unfavourable route profile shift the equation so far that other decarbonisation pathways make more sense.
Particularly problematic are vessels below 5,000 DWT. For these units, the space requirement of the capture plant bears no reasonable relationship to the quantity of CO2 captured. Vessels with frequently changing routes and significant short-sea traffic are also poor candidates, as the CO2 offtake chain is not available at every port.
On the other hand, there are fleet profiles where retrofit can genuinely make sense: large container vessels on fixed routes between ports with CO2 infrastructure. Bulk carriers with sufficient deck area and regular calls at Rotterdam or Antwerp. Tankers with a remaining service life of eight to twelve years where a newbuild is not justified but EU ETS costs are steadily rising.
The key question is not whether OCCS works technically but whether it works economically for a specific vessel on a specific route at a specific point in time. This requires an individual assessment – not a one-size-fits-all solution.
A realistic retrofit approach begins with a rigorous pre-screening that passes through three phases before any money is spent on a detailed feasibility study.
Phase 1: Desktop screening (2-4 weeks). Based on available vessel data (GA plan, stability booklet, engine room layout), it is assessed whether sufficient space and weight reserve fundamentally exist. Simultaneously, the route profile is analysed: which ports are regularly called at, and which of these offer CO2 transfer now or foreseeably?
Phase 2: Technical pre-planning (4-8 weeks). If Phase 1 is positive, an initial technical concept study is prepared. This includes a preliminary system layout, an energy balance, a stability rough calculation, and an initial cost estimate. The classification society is engaged at this phase to clarify early which requirements apply.
Phase 3: Economic calculation (2-4 weeks). The technical pre-planning is linked with a detailed CAPEX/OPEX calculation. Savings from reduced EU ETS costs and FuelEU penalties are weighed against investment and operating costs. Only if this calculation yields a positive result under realistic assumptions does the investment in a full feasibility study warrant the effort.
The technical integration of an OCCS plant on an existing vessel differs fundamentally from a newbuild solution. In a newbuild, the plant can be considered in the vessel design from the outset. In a retrofit, it must be inserted into an existing, optimised arrangement – with all the compromises this entails.
The first step is always a detailed 3D scan of the existing engine room and potential installation areas on deck. Modern laser scan technology enables the creation of a precise digital model into which OCCS components can be virtually placed. This step is indispensable, as 2D plans of older vessels are frequently inaccurate or do not reflect later modifications.
The exhaust gas connection presents a particular challenge in retrofit projects. The existing exhaust train must be opened and a bypass installed through which part of the exhaust is routed to the absorber. This requires hot work in the engine room and careful planning to minimise yard time.
The structural loading from additional installations must be assessed by a structural engineer. Particularly for deck installations, local reinforcement of the deck structure is frequently required. The costs for this steelwork can constitute a significant portion of the total budget.
Electrical integration includes additional power draw for pumps, compressors, and control systems. On older vessels, this may require an upgrade of the main switchboard or additional generator capacity – costs that are often absent from early estimates.
Yard time for an OCCS retrofit is typically estimated at four to eight weeks, in addition to regular docking. This downtime must be factored into the economic calculation and balanced against charter revenue.
An OCCS retrofit changes not only the vessel physically but also the entire operational workflow. Operators must prepare for several operational changes.
The crew requires additional training for operating the capture plant. This includes daily monitoring of process parameters, handling of chemicals such as monoethanolamine (MEA), detection and management of leaks, and the CO2 transfer process in port. The Safety Management System must be updated accordingly.
Voyage planning becomes more complex. In addition to weather, tidal windows, and port availability, CO2 tank capacity and the availability of transfer facilities must now be considered. On long voyages without CO2 discharge options, the capture plant may need to be temporarily shut down – with corresponding effects on the emission balance.
Spare parts holdings expand to include a new component group. Seals, membranes, valves, and sensors for the OCCS plant must be stocked. As the technology is still young, supply chains are less established than for conventional vessel systems.
Practical experience with OCCS retrofits is still limited, but early projects provide instructive insights. The collaboration between Mitsubishi Shipbuilding and several Japanese shipping companies has shown that containerised OCCS systems can offer a pragmatic solution to the space challenge. The modules are delivered in standard container sizes and can be positioned on existing container slots.
In Europe, Value Maritime's project with its CO2 capture system on a tanker has demonstrated that the technology works in real operations – but also that economics depend heavily on EU ETS allowance prices. At prices below 80 euros per tonne of CO2, payback becomes difficult; at prices above 120 euros, the calculation improves considerably.
An important lesson from all projects to date: planning time is systematically underestimated. From initial concept to operational plant, typically 18 to 24 months pass – longer than for most conventional vessel modifications. Operators considering OCCS retrofit as an option should begin planning early.
The decision for or against an OCCS retrofit should be based on a structured assessment covering four dimensions.
Technical suitability: Sufficient space (at least 200 m³), weight reserve (at least 3 % DWT), stable energy supply, and an exhaust system that permits a bypass.
Logistical feasibility: Regular calls at ports with existing or planned CO2 infrastructure. Without an offtake chain, any technical solution is useless.
Economic viability: Positive payback considering CAPEX, OPEX, downtime, cargo loss, and EU ETS/FuelEU savings. Sensitivity analysis for different CO2 price scenarios is indispensable.
Timing fit: The vessel should have a remaining service life of at least eight years to amortise the investment. Simultaneously, the next regular docking should be used to avoid additional costs for a separate yard stay.
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