Thermodynamic and techno-economic comparisons of the steam injected turbocompounding system with conventional steam Rankine cycle systems in recovering waste heat from the marine two-stroke engine

This paper aims at evaluating the merits and drawbacks of the steam injected turbocompounding (SIT) system proposed in the authors’ previous work. First, thermodynamic processes of the SIT systems and conventional steam Rankine cycle systems designed with single-pressure and dual-pressure configurations are introduced, followed by detailed techno-economic descriptions. Based on a 4.9 MW marine two-stroke engine, detailed thermodynamic and techno-economic comparisons among seven waste heat recovery systems are performed. It is concluded that both optimizing the evaporation pressure and adopting the dual-pressure steam generation configuration have almost no positive effect on the thermodynamic performance of the SIT system. The evaporation pressure also plays a less important role in determining the economic indexes of the SIT system. With the fuel-saving potential of 5.2% under the design condition and a depreciated payback period of 4.7 years, the SIT system is a good alternative to the conventional turbocompounding system and the steam Rankine cycle system. The dual-pressure SIT system is not recommended due to its long payback period. Since tankers are more likely to operate at part loads, the payback period of steam-based waste heat recovery systems increases by around 30% compared to that evaluated based on the container operational profile.