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

Stricter legislation on sulphur oxide emissions from ships will apply as of 2015 in emission control areas. Consequently, prices on low sulphur fuels are expected to increase drastically, providing a strong incentive to find alternative ways of complying with the legislation and improving the efficiency of machinery systems. The wet sulphuric acid process is an effective way of removing flue gas sulphur oxides from land-based coal-fired power plants. Moreover, organic Rankine cycles (ORC) are suitable for heat to power conversion for low temperature heat sources. This paper describes the design and modeling of a highly efficient machinery system which includes the removal of exhaust gas sulphur oxides. The system consists of a two-stroke diesel engine, the wet sulphuric process for sulphur removal, a conventional steam Rankine cycle and an ORC. Results of numerical modeling efforts suggest that an ORC 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 the combined cycle thermal efficiency by 2.6%. The findings indicate that the technology has potential in marine applications regarding both energy and the environment; however, further research and development efforts are needed.