Thermodynamic analysis of waste heat recovery systems in marine diesel engine

Energy efficiency, energy saving, renewable and sustainable energy issues are of great importance today as energy demand increases and the negative impacts of current energy use reach noticeable dimensions. So, the maritime sector faces greater challenges in energy efficiency and fuel consumption. At the beginning of these difficulties are the emissions from the diesel engines and the fuel costs which are the first place when considering the ship operating costs. When waste heat recovery methods are applied, there will be a reduction in the amount of total CO2 (carbon dioxide), NOx (nitrogen oxides) and SOx (sulfur oxides) emissions per unit fuel per unit fuel as well as fuel savings. Waste heat recovery systems generate heat without using additional fuel and without emissions, and generate power using this heat energy recovered. In this study, waste heat recovery systems are discussed by using a two-stroke six-cylinder low-speed diesel engine and analyzes were made for power turbine generator, steam turbine generator and combined system for three different ambient conditions and three different diesel engine operating loads were taken into consideration and exergy destructions, exergy destruction rates, exergy efficiencies, power outputs and efficiency increases of waste heat recovery systems components were calculated. Furthermore, the payback period was calculated based on the cost of the fuel saved per year and the cost of installation of the waste heat recovery systems. As a result of the thermodynamic analyses, it was seen that the highest exergy destruction rate occurred in diesel engine in all heat recovery systems, three diesel engine operating loads and three ambient conditions. The lowest payback period has been occurred in 100 percentage diesel engine operating load and winter conditions in power turbine generator system.