High Efficiency Waste Heat Recovery from Dual Fuel Marine Engines

The paper presents an original variable layout steam plant for the Waste Heat Recovery (WHR-VL) from marine dual fuel (DF) engines, designed considering the different exhaust gas stack temperature limits, depending on the engine fuel type: generally no less than 160 °C for diesel oil and without limits for natural gas (NG). Using diesel oil, a single pressure superheated steam plant configuration is adopted, while a dual pressure system is proposed for the NG fuel mode of the engine. In both WHR-VL plant layouts, the produced steam is mainly delivered to a steam turbine for the ship electric energy production, while a smaller amount meets the ship thermal loads. Starting from data of a marine four stroke DF engine, the WHR-VL steam plant components are sized and optimized through a mathematical code, according to a numerical procedure described in the paper. The WHR-VL plant data and performance, for different engine fuel modes and loads, are compared with those of a more traditional WHR single pressure steam plant, developed and optimized for the waste heat recovery of the same dual fuel engine.