Optimal load allocation of complex ship power plants

Abstract

In a world with increased pressure on reducing fuel consumption and carbon dioxide emissions, the cruise industry is growing in size and impact. In this context, further effort is required for improving the energy efficiency of cruise ship energy systems.In this paper, we propose a generic method for modelling the power plant of an isolated system with mechanical, electric and thermal power demands and for the optimal load allocation of the different components that are able to fulfil the demand.The optimisation problem is presented in the form of a mixed integer linear programming (MINLP) problem, where the number of engines and/or boilers running is represented by the integer variables, while their respective load is represented by the non-integer variables. The individual components are modelled using a combination of first-principle models and polynomial regressions, thus making the system nonlinear.The proposed method is applied to the load-allocation problem of a cruise ship sailing in the Baltic Sea, and used to compare the existing power plant with a hybrid propulsion plant. The results show the benefits brought by using the proposing method, which allow estimating the performance of the hybrid system (for which the load allocation is a non-trivial problem) while also including the contribution of the heat demand. This allows showing that, based on a reference round voyage, up to 3% savings could be achieved by installing the proposed system, compared to the existing one, and that a NPV of 11 kUSD could be achieved already 5 years after the installation of the system.

Energy and Exergy Analysis of a Cruise Ship

“…In the work of Mondejar et al [29] concerning the optimization of an organic Rankine cycle (ORC) on a small cruise ship, the authors assumed that the existing facilities for fulfilling the heat demand on board are left as they are. Baldi et al [30] attempted to optimize the load allocation among the different engines of the same case study, including considerations related to the efficiency of the heat generation on board. In their work, however, they did not consider the potential for optimizing the design of the system, nor did they take into account the temperature at which the heat has to be delivered to the different users.…”

“…Given the fact that many engines are operated at low load (both main and auxiliary engines), the system would benefit from both an electrification of the system and from the installation of batteries. The electrification of the system was explored in previous literature [30] and showed a relevant potential from both an environmental and an economic point of view. The installation of batteries was also considered in previous work referred to the same case study [40] and proved the potential for yearly savings of 1-2%.…”

Optimising design and power management in energy-efficient marine vessel power systems: a literature review

“…Before the actual system design is optimised, the power management optimisation is studied with a pre-defined system topology consisting of a set of pre-chosen components. Baldi et al (2016) used the mixed integer non-linear programming method to optimise the load sharing in a hybrid power system without batteries. Combining sequential quadratic programming for the continuous variables and using the branch and bound method for the integer variables, the problem was solved with Matlab.…”

Design of the Three-Level Multicriterial Strategy of Hybrid Marine Power Plant Control for a Combined Propulsion Complex

“…Potentially low noise of REM Difficulty of the system [18,19] Independence from air quality The limited power [20,21] Reduction of emission in air Danger [22] Hybrid DEPC with alternative sources of energy (ASE)…”