Research

Design and modeling of an advanced marine machinery system including waste heat recovery and removal of sulphur oxides

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Abstract

In order to reduce the formation of acid rain and its harmful effects, stricter legislations on emissions of sulphur oxides from ships applies as of 2015 in emission control areas and globally in 2020 by the international maritime organization (IMO). Consequently, prices on low sulphur fuels are expected to increase drastically compared to those of heavy fuel oil, giving ship owners a strong incentive to find alternative ways of complying with the legislations. In addition, IMO regulations on carbon dioxide emissions and high fuel prices provide incentives for improving the efficiency of the machinery system. The wet sulphuric acid process has shown to be an effective way of removing sulphur oxides from flue gas of land-based coal fired power plants. Moreover, organic Rankine cycles are suitable for heat to power conversion for low temperature heat sources. This paper is aimed at designing and modelling a highly efficient machinery system which includes the removal of exhaust gas sulphur oxides. Numerical simulations are carried out using an open source software developed at Technical University of Denmark called Dynamic Network Analysis (DNA). The machinery system suggested in this paper consists of a two-stroke diesel engine, the wet sulphuric process for sulphur removal and an advanced waste heat recovery system including a conventional steam Rankine cycle and an organic Rankine cycle. The results are compared with those of a state-of-the-art machinery system featuring a two-stroke diesel engine and a conventional waste heat recovery system. The results suggest that an organic Rankine cycle placed after the conventional waste heat recovery system is able to extract the sulphuric acid from the exhaust gas, while at the same time increase power generation from waste heat by 32.9% and the combined cycle thermal efficiency by 2.6%. The findings indicates that the technology has an energetic and environmental potential in marine applications, while still further research and development need to be done before it can be put into operation on ships.