Bi-Level Optimization of the Energy Recovery System from Internal Combustion Engines of a Cruise Ship

In recent years, ship builders and owners have to face a great effort to develop new design and management methodologies that lead to a reduction in consumption and emissions during the operation of the fleet. In the present study, the optimization of an on-board energy system of a large cruise ship is performed, both in terms of energy and of the overall dimensions of the system, while respecting the environmental constraint. In the simulation, a variable number of identical Organic Rankine Cycle (ORC)/Stirling units is considered as an energy recovery system, bottoming the main internal combustion engines, possibly integrating with the installation of photovoltaic panels, solar thermal collectors, absorption refrigeration machines and thermal storages. The optimization takes into account the effective optimal management of the energy system, which is different according to the different design choices of the energy recovery system. Two typical cruises are considered (summer and winter). To reduce the computational effort for the solution of the problem, a bi-level strategy has been developed, which prescribes managing the binary choice variables expressing the existence or not of the components by means of an evolutionary algorithm, while all the remaining choice variables are obtained by a mixed-integer linear programming model of the system (MILP) algorithm. The entire procedure can be defined within the commercial software modeFRONTIER^®.