Reducing the carbon footprint of LNG shipping: Implementation of a combined waste heat recovery system in the onboard incinerator for lower environmental impact

The shipping industry is committed to reducing CO₂ emissions by at least 40 % by 2030. Liquefied Natural Gas tankers play a critical role in achieving this target; however, these vessels typically rely on incineration for waste disposal during extended voyages. This study proposes an integrated waste heat recovery system for an LNG vessel's incinerator, considering the range of historically traveled routes, spanning both cold and hot regions. The system combines a conventional Rankine cycle, an organic Rankine cycle, and a Seebeck effect heat-to-electricity harvester. The steam Rankine cycle harnesses waste heat from exhaust gases, while the organic Rankine captures low-grade thermal waste energy using fluids selected based on their energy recovery potential, environmental impact, and safety profile. A series of operational scenarios were examined, with R1234ze(Z) identified as the most effective organic fluid. The proposed system can recover up to 264.57 kW of net power, thereby reducing CO₂ emissions by 86.67 tons annually. A multi-objective optimization identifies the optimal operating point under realistic conditions, guiding operators on the most favorable times to run the incinerator for maximum energy recovery. This innovative system, which accounts for geographic location, supports the maritime sector's decarbonization goals by enhancing energy efficiency and reducing emissions.