Design study on the integrated utilization system of medium temperature waste heat and lng vaporization cold energy for 200000 dwt lng-powered vessels

The study object for this work is a 215000 ton very large crude carrier - liquefied natural gas - powered vessel, intending to integrate the use of medium tempera-ture flue gas waste heat from the exhaust turbine and cold energy from liquefied natural gas vaporization. It proposes a Rankine cycle power generating system with a two stage booster and three stage lateral nesting following the principle of "temperature matching, stepped utilization", taking into account real demands and circumstances of the vessel. The study shows that in this tonnage vessel, through the design and optimization of the stepped utilization scheme, the cold energy released during the vaporization of liquefied natural gas fuel from the ME-GI host machine and the medium temperature waste heat from the exhaust turbine can be fully utilized, and the system structure is tight and simple. After the non-azeotropic mixed working media was optimized and the operational pa-rameters were optimized using genetic algorithm, the system designed in this paper can reach 54.61% exergy efficiency and 187.83 kW net output of power generation. The annual income of the final designed system can reach CNY 1, 133, 240. The capital recovery cycle is expected to be 5.06 years if the system is put into operation.