the Hybrid Cutter Dredger: a study on technical and economical feasibility

Growing concern about global warming and climate change intensified the research into more efficient ways of operation in the maritime industry. These researches triggered the use of electrical batteries in hybrid systems. Van Oord aims to operate more efficiently, which implies using less fuel and thus emitting less carbon dioxide. A way to achieve this might be the use of batteries for hybrid power plants on board of their cutter suction dredgers. This will investigate what the potential carbon dioxide reduction of a hybrid system could be. Since the competitiveness of the Van Oord fleet should not be affected a certain cost perspective is taken into account as well. The objective of this thesis is to find a battery capacity that achieves a fuel and running hour reduction in such a way that it is cost effective. The cutter suction dredger’s operational profile has a fluctuating nature in terms of power demand. In this study several operational profiles are examined and one most representative operational profile is constructed. This operational profile has large peaks and troughs which favours the use of a certain peak shaving system like a battery. Moreover, the average loading of the diesel engines is quite frequently far off the optimal 85% load. In order to optimise the power demand from the diesel engines and ensuring efficient operation, models are developed to simulate the behaviour of the diesel engine, the battery and the hybrid system as a whole. As a start the effect of transients in the load profile of the diesel engine on its efficiency is investigated. It is found that the efficiency of a larger medium speed diesel engine running on constant speed with a sufficient air excess ratio, is not affected by transients in the load profile. The data collected in this analysis is used to develop a fuel consumption model which estimates fuel consumption as function of the load of the engine. In addition, the diesel engine the battery pack is modelled. The model of the battery pack is based on multi dimensional lookup tables that hold the non-linear relations between terminal voltage, state of charge and current. For the battery a separate lifetime calculation is developed, which estimates the battery lifetime for different charge/discharge profiles. The fuel consumption model and the battery model are tested and perform as intended. In order to combine the fuel consumption model and the battery model, a power management system is developed. This power management system uses binary logic to optimise the system performance. The set-points of the power management system are tuned in an iterative way. Due to a structured simulation approach the simulation results can be converted to trend lines. These trend lines enable the determination of the optimal battery capacity with respect to reduction of fuel consumption, reduction of running hours, investment cost and battery lifetime. The optimal capacity for the battery is 4516 ℎ. With this battery the system is not cost effective. However, technical feasibility is proven and fuel consumption is reduced. A yearly fuel reduction of 75 ton HFO and 142 ton MDO is achieved. This results in a reduction of carbon dioxide of 687 ton annually. With this system every ton of carbon dioxide reduction will cost Van Oord €575. The performance of the hybrid system can be improved by extending the battery lifetime. This is done by adjusting the power management settings according to the actual residual battery capacity. This method reduces the cost per ton carbon dioxide reduction to €128. Furthermore the effect of running on MDO instead of HFO is investigated, this results in a marginal improvement in cost perspective. Every ton of carbon dioxide reduction will cost €554. The actual annual carbon dioxide reduction will not change. Unfortunately the proposed hybrid system will only reduce carbon dioxide emission in a cost effective way when the HFO price rises to €700 per ton and the battery price per ℎ halves. In combination with a Liquefied Natural Gas (LNG) fuelled power plant the hybrid system can be used. It is proven that energy demand can be stored in and provided by a battery with a reasonable size. Due to the response of a gas engine the battery is not an extra any more, but it becomes a necessity.Mechanical, Maritime and Materials EngineeringMarine and Transport TechnologyShip Design, Production and Operation