Utilization of waste heat and cold on the example of an LNG-fueled ultra-large container ship

Increasingly stringent requirements for ship energy efficiency measured in CO 2 emissions per ton-mile are introduced to decarbonize shipping. Because using liquefied natural gas as the least=emission fossil fuel per unit of energy doesn’t meet the CO 2 reduction target and the implementation of low-speed engines powered by alternative zero-carbon fuels is in the state of research and development, as well as the application of wind-assisted propulsion remaining ruled out for ultra-large container ships (ULCS) for construction reasons, it becomes necessary to apply deep utilization of waste heat from exhaust gas, jacket cooling water, scavenge air, and cold from LNG regasification in the electricity generation process. The utilization of waste heat and cold from all available carriers will allow the production of an increased amount of steam to power the steam turbine generators, which, when the ship's electricity demand is covered, makes it possible to switch off diesel generators. As a result, the ship's fuel consumption and emissions of harmful substances will decrease. The authors developed the concept of a waste heat and cold recovery system for all available carriers, combining the gas cycle with a two-stage cascade organic Rankine cycle. The operation of the proposed waste heat and cold recovery system was simulated using Aspen Plus software. The calculations revealed that up to 5832 kW of electric power is achievable, which corresponds to 12.18 % of the main engine brake power. This performance ensures a reduction in the attained EEDI and EEXI values of the CMA CGM Jacques Saade by up to 17 %, which is not achievable with conventional waste heat recovery systems utilizing only a part of the exhaust gas and scavenge air streams. • A combined gas turbine and two-stage cascade ORC waste heat and cold recovery system is proposed for an ULCS. • The available waste heat stream is composed predominantly of medium- and low-temperature carriers to be utilized in the ORC. • The efficiency of electricity generation based on waste heat and cold recovery is determined by the working fluids applied. • The generated electricity is sufficient to supply up to 1006 refrigerated containers and a 17 % reduction of EEDI and EEXI.