Energy Conversion and Management: X (Oct 2023)
Techno-economic optimization of hybrid-electric power plants onboard cruise ships
Abstract
This work aims at assessing energy, environmental and economic performances of hybrid-electric plants installed onboard large-size cruise vessels fuelled by Liquefied Natural Gas. Specifically, hybrid-electric power plants coupling combined gas electric and steam plants, reciprocating engines and lithium-ion battery pack are considered. By adopting cogeneration efficiency, carbon dioxide emissions, nitrogen oxide emissions and costs as objective functions, optimal performances were assessed by a Mixed Integer Linear Programming code, following a two-step procedure. First, the MILP code has been applied considering 8-days long, phase-mean operating profiles to identify an optimal design of the engine room. Second, power plant performances have been investigated by applying MILP code to hourly demand profiles, in order to provide more detailed insight on working schedule. Overall, as main outcome of the phase-mean analysis, the potential of combined gas electric and steam plants and lithium-ion batteries in promoting a more efficient energy utilization, reduced environmental impact and enhanced cost savings is proved. Specifically, combined gas electric and steam plant was shown to optimize objective functions during navigation and maneuvering, whereas batteries improved energy and environmental performances in the most demanding ship operating conditions. Furthermore, optimal sizing of lithium-ion battery pack was determined at 40 MWh, despite its economic competitiveness resulted to deeply rely on carbon tax. On the other hand, the hourly analysis showed that controlling the combined gas electric and steam plant and batteries according to a mixed spinning reserve-peak shaving strategy optimizes the performance of power plant even in port conditions, with almost no role played by reciprocating engines. In detail, in comparison to a reference non-hybrid electric power plant, batteries are shown to improve cogeneration efficiency and greenhouse gas emission savings by nearly 2%, whereas nitrogen oxide emissions and costs were reduced by 12% and 2%, respectively.
