Investigation of hydrogen obtainment from sea water using waste heat on ships, energy and exergy analysis

Increasing population and demands, as well as high-volume use of the transportation sector, increases the importance of alternative energy sources day by day. Maritime vehicles, which are one of the prominent and highly used transportation vehicles in world trade, have been the subject of many researches on renewable energy sources for a greener environment. One of the most important of these studies is the production of electricity from the waste heat of diesel engines with high exhaust gas temperatures in marine vehicles. Waste heat recovery system is generally applied to increase engine efficiency and reduce the amount of CO2. In this thesis study, hydrogen production was achieved by using electricity produced from the waste heat from the exhaust of a cargo ship's diesel engine. While electricity production is provided by the rankine cycle (RC), hydrogen production is provided by the electrolysis of sea water. Seawater is purified by reverse osmosis before electrolysis and converted into hydrogen. After the concept design of the system was made, energy and exergy analysis was applied. For the hydrogen production system from seawater, the percentage rates of exergy destruction of the components were calculated from largest to smallest as follows: 55% electrolyzer, 21% compressor, 9% high pressure pump (5-6), 7% reverse osmosis (4-5), 4% high pressure pump, 3% low pressure pump (between 3-4), 1% reverse osmosis (between 6-7). Since exergy destruction in sediment filter, thin film membrane and mixed bed resin is very low, it is accepted as 0%. For the Rankine cycle, the percentage rates of exergy destruction are as follows, from largest to smallest: 86% turbine, 12% economizer, 1% pump, 1% condenser. As a result, in this study, both waste heat was utilized and the energetic possibility of obtaining hydrogen from seawater through electrolysis was demonstrated.