Utilization of Waste Heat for Carbon Capture on Ships

Utilization of Waste Heat for Carbon Capture on Ships

Executive summary

Using shipboard waste heat to drive carbon-capture systems (OCCS / Onboard Carbon Capture and Storage) is technically feasible and often essential: most CO₂ capture methods (amine absorption, thermal sorbent regeneration, certain DAC variants, CO₂ liquefaction) require heat that can be supplied from engine exhaust, jacket cooling circuits, or auxiliary boiler streams instead of burning additional fuel. Proper integration (heat-integration, WHR units, ORC for electricity, heat pumps) reduces the parasitic fuel penalty and improves economics — but space, weight, solvent management, SOx/NOx compatibility, and operational variability remain major design and regulatory challenges. Recent industry studies and techno-economic reports (DNV, MARAD/US, MDPI reviews, peer-reviewed papers) quantify the tradeoffs and demonstrate pilot-scale feasibility for selected ship types and operating profiles. DNV+2Maritime Administration+2

1. Why use waste heat for shipboard carbon capture?

Most capture technologies need a recurring thermal input for sorbent/solvent regeneration or CO₂ conditioning (cooling/liquefaction). On ships the largest continuous heat sources are:

• Main engine exhaust (very high temperature and large flow).

• Jacket cooling / scavenge air / charge-air cooler circuits (moderate temperature but high mass flow).

• Auxiliary boilers and economizers (if present).

Using these streams for regeneration avoids burning additional fuel in a separate boiler and reduces net CO₂ emitted per tonne captured (i.e., lowers the system’s parasitic load). Heat integration also often reduces electricity demand (e.g., for compressors) if steam/hot water is available for direct solvent regeneration or pre-heating. Multiple technical assessments find waste-heat integration is a key enabler of OCCS feasibility. ScienceDirect+1

2. Which capture technologies are most compatible with shipboard WHR?

Below are the capture options and how waste heat can be used:

• Amine absorption (conventional solvent scrubbing) — requires low-pressure steam (80–120 °C range typical for many regenerations, depending on solvent). Onboard, steam can be produced by capturing exhaust heat via an exhaust gas boiler (WHRU) or by using jacket-water heat with heat pumps to reach regeneration temperatures. Amine systems are mature and well-studied for ships, but solvent volatility and degradation (esp. in SOx presence) must be managed. ACS Publications+1

• Thermal swing adsorption (TSA) & solid sorbents — many sorbents regenerate at 80–150 °C or higher; waste heat can be used directly for TSA beds or indirectly via hot water/steam loops. TSA systems can be more compact and avoid liquid solvent handling, but sorbent lifetime and heat transfer design are critical. ScienceDirect

• Temperature- or pressure-swing adsorption with low-grade heat assistance — hybrid cycles can be optimized so that low-grade waste heat regenerates the adsorbent and compressors supply pressure differentials. Integration with ORC or electrical WHR can supply compressor power. University of Strathclyde

• Membrane and cryogenic separation — membrane systems mainly use electrical energy (compressors) and benefit less from low-grade thermal streams; cryogenic liquefaction (for storage of captured CO₂) requires refrigeration — WHR can be used to run an ORC to produce electricity to drive cryo compressors or to supply heat for intermediate stages in liquefaction. Maritime Administration+1

• Solid sorbent DAC-like approaches — emerging materials (amine-functionalized solids) regenerate at moderate temperatures and are promising where low-grade heat is plentiful. Research is ongoing for maritime adaptation. MDPI

(Choice depends on vessel type, available waste-heat temperature, space constraints, and desired capture rate.)

3. How much waste heat is available on ships — and is it enough?

Typical marine diesel engines convert ~30–50% of fuel energy to shaft power; the remainder is lost as heat in exhaust, jacket water, scavenge air, and cooling systems. Several studies and TEAs quantify usable waste heat and show that:

• Exhaust gas and jacket cooling together often provide a substantial thermal resource able to supply a meaningful fraction of the heat required for solvent regeneration — but not always 100% at all operating points. The available thermal energy varies strongly with engine load, vessel trading pattern, and ambient (sea) temperature. MDPI+1

• MARAD and other techno-economic reports show capture rates using waste heat integration ranging widely (example: 30–75% capture in modeled cases, depending on fraction of exhaust processed and heat availability). Where waste heat is insufficient at lower loads, solutions include partial capture, bypassing some exhaust, or supplementing heat with auxiliary boilers or ORC electricity. Maritime Administration+1

In short: for many ship types (LNG carriers, cruise ships, tankers on long sea passages) waste heat is a large and useful resource, but designers must map heat availability vs expected load profile to size the capture system correctly. ScienceDirect

4. Practical heat-integration patterns for shipboard capture

Common integration architectures in studies and pilots:

1. Direct WHRU → solvent stripper

   Exhaust gas passes through a Waste Heat Recovery Unit (WHRU) / economizer to generate hot water/steam that feeds the amine stripper/regenerator. This avoids combustion and is simple when exhaust temp and flow are sufficient. Maritime Administration

   
   

2. Jacket water + heat pump

   Use jacket cooling water (lower temperature) combined with a heat pump to lift temperature to the solvent regeneration range; heat pumps let you use low-grade heat more efficiently at the cost of electrical consumption. Useful when exhaust heat is not continuously available. University of Strathclyde

   
   

3. ORC (Organic Rankine Cycle) electrical supply

   Convert exhaust/jacket heat to electricity via ORC to drive compressors and pumps (e.g., membrane or cryo systems) or to power heat pumps for regeneration. ORC introduces additional complexity and footprint but provides flexible electric power. MDPI+1

   
   

4. Hybrid (partial exhaust + auxiliary)

   When available waste heat fluctuates, process a fraction of the exhaust gas (bypass remainder) and store captured CO₂ in liquefied form; use auxiliary boilers only if needed. This limits parasitic fuel burn and reduces system size. MARAD TEA models this partial-processing approach. Maritime Administration

Each architecture trades off complexity, space, CAPEX/OPEX, and capture fraction.

5. Key technical challenges

• Solvent / sorbent compatibility with marine exhaust: High SOx (if low-sulfur fuels are not used), particulate, and trace contaminants accelerate solvent degradation or foul sorbents — requiring upstream SOx/particulate removal (e.g., scrubbers, filters). Studies stress the need for robust gas pretreatment. Maritime Administration+1

• Variable load and intermittent heat: Ship engines operate across wide load ranges; WHR sizing must consider worst-case (low heat) and best-case (high heat) operating points. Heat storage (buffer tanks) and hybridization (heat pump/auxiliary boiler) are mitigation options. Lighthouse+1

• Space & weight: Carbon capture units, CO₂ compressors, storage tanks (for liquefied CO₂), and WHR hardware require significant space — a major constraint on retrofit installations. Newbuilds can incorporate OCCS more easily. DNV

• Energy penalty & economics: Even with WHR, capture imposes a parasitic load (electrical and thermal). Techno-economic analyses find costs per tonne captured are high today, but fall with optimization, partial capture strategies, and scale. Policy incentives, carbon pricing, or utilization routes (CCU) change project economics significantly. Maritime Administration+1

• Regulatory & liability issues: Handling, storing, and transporting captured CO₂ on ships raises safety, insurance, and class-approval questions; many class societies and regulators are actively developing guidance. Early engagement with class societies (DNV, ABS, ClassNK) is recommended. DNV+1

6. What pilot and modeling studies say (selected findings)

• MARAD / US studies and techno-economic assessments modeled practical OCCS designs and found that waste-heat integration can reduce the net energy penalty compared to cases where extra fuel is burned for regeneration — but capture fraction and parasitic power remain sensitive to ambient and load profiles. Typical additional electrical power demand reported in case studies ranged from several hundred kW upward depending on ship size and design choices. Maritime Administration+1

• Peer-reviewed design studies (e.g., amine-based designs for LNG-fuelled ships) provide detailed thermal balances and cost estimates, and show that waste-heat supply from exhaust and jacket water frequently provides a large share of the regeneration heat required — especially for ships running at high, steady loads. ACS Publications+1

• Reviews and meta-analyses summarize that no single OCCS design fits all vessels; best candidates today are long-trading, high-utilization ships (bulk carriers, tankers, LNG carriers, large ro-ro/cruise) where steady waste heat is available and space/weight tradeoffs are manageable. MDPI+1

These studies are the best current evidence base for choosing WHR-centric OCCS architectures.

7. Practical roadmap for a waste-heat-driven OCCS pilot

1. Preliminary feasibility (0–2 months)

   • Perform energy and mass balances for the vessel: map exhaust/jacket heat availability vs duty cycle.

   • Identify space, weight, and power margins; engage class society early.

2. Concept & selection (2–4 months)

   • Select capture technology best aligned with heat availability (amine vs TSA vs hybrid).

   • Model heat-integration (WHRU sizing, buffer tanks, heat pumps, ORC if needed).

3. Detailed engineering & procurement (4–10 months)

   • Design exhaust pretreatment (particulate/SOx removal), stripper/adsorber layout, compressors, CO₂ conditioning and storage (liquefaction if required).

   • Include controls to modulate capture rate or bypass when heat is insufficient.

4. Build & install (10–16 months)

   • Bench test key subsystems (regenerator, sorbent beds) with representative exhaust simulant.

   • Retrofit installation with monitoring and safety interlocks.

5. Sea trials & data collection (16–22 months)

   • Measure capture fraction, parasitic power, solvent degradation rates, and operational impacts across typical trade routes and ambient conditions.

   • Iterate on control strategy (partial capture, buffering) to optimize net emissions and fuel penalty.

6. Decision & scale

   • If KPIs meet targets, plan fleet rollout or refine for newbuild integration. Maritime Administration+1

8. Policy, economics, and deployment drivers

• Carbon pricing and regulations will largely determine OCCS uptake; without price signals or mandates, CAPEX/OPEX for OCCS is difficult to justify for many owners today. Governments and classification societies are piloting standards and incentives. sites.usp.br+1

• Value-adding CCU (conversion of captured CO₂ to chemicals or fuels) or shore-based storage arrangements can improve project economics but require logistics and market development. ACS Publications

• Newbuild integration is a more immediate practical path: vessels designed from the outset can integrate WHR and capture equipment more compactly and economically than retrofits. DNV and other bodies recommend considering OCCS during early design. DNV

9. Conclusions & Recommendations

• Waste heat is the single most important enabler to make onboard carbon capture materially less energy-intensive. Direct WHRU → stripper integration, heat pumps, and ORC hybrids are the primary engineering patterns. Maritime Administration+1

• Best initial targets are high-utilization, long-distance ships where heat availability is steady and space can be planned (newbuilds or selected retrofits). MDPI

• Key near-term R&D needs: solvent/sorbent resilience to marine exhaust contaminants, compact low-weight CO₂ liquefaction and storage, and robust control strategies for variable loads. SSRN+1