Trigeneration pathways for maritime decarbonization in liquefied natural gas tankers: A case study on waste energy recovery from an auxiliary engine

The decarbonization of maritime transport poses a major challenge for the shipping industry, increasingly driven by international regulations that introduce economic instruments such as the European Union Emissions Trading System and the upcoming International Maritime Organization’s carbon levy. This study proposes an integrated trigeneration system to reduce emissions from natural gas-fueled vessels by recovering waste energy from an auxiliary engine of a case-study liquefied natural gas tanker. The configuration combines a parallel organic Rankine cycle, cold energy recovery, thermoelectric generators, and a carbon capture heating module to simultaneously produce electricity, cooling, and heating, thereby reducing carbon dioxide emissions. Ship’s operational routes from 2019 to 2024 were analyzed to account for varying air and seawater temperatures. The selected auxiliary engine operates under steady conditions and presents considerable thermal losses from both combustion and liquefied natural gas vaporization. The cold energy from natural gas regasification meets the air conditioning demand, while the parallel organic Rankine cycle recovers heat from the alternator cooling system, engine jacket water, and exhaust gases to generate onboard electricity. Thermoelectric generators are strategically installed on the engine block to harness dispersed thermal energy. Residual exhaust heat is utilized in the carbon capture heating unit to regenerate the amine solvent of a carbon capture and storage system. Energy and exergy analyses were performed, using five ultra-low global warming potential working fluids. Results indicate significant reductions in specific liquefied natural gas consumption, avoiding up to 7,014.88 tons of CO 2 -equivalent emissions annually. From an economic standpoint, the proposed system achieves a lower abatement cost than purchasing EU ETS allowances or paying the forthcoming IMO Tier 1 Remedial units.