Comparison of Saturated and Superheated Steam Plants for Waste-Heat Recovery of Dual-Fuel Marine Engines

From the working data of a dual-fuel marine engine, in this paper, we optimized and compared two waste-heat-recovery single-pressure steam plants—the first characterized by a saturated-steam Rankine cycle, the other by a superheated-steam cycle–using suitably developed simulation models. The objective was to improve the recovered heat from the considered engine, running with both heavy fuel oil and natural gas. The comparison was carried out on the basis of energetic and exergetic considerations, concerning various aspects such as the thermodynamic performance of the heat-recovery steam generator and the efficiency of the Rankine cycle and of the combined dual-fuel-engine–waste-heat-recovery plant. Other important issues were also considered in the comparison, particularly the dimensions and weights of the steam generator as a whole and of its components (economizer, evaporator, superheater) in relation to the exchanged thermal powers. We present the comparison results for different engine working conditions and fuel typology (heavy fuel oil or natural gas).