Thermodynamic and Economic Studies of a Combined Cycle for Waste Heat Recovery of Marine Diesel Engine

In the present study, the thermodynamic and economic performance of a combined thermodynamic cycle formed by an ORC and a Kalina cycle, which can simultaneously recover waste heat of exhaust gas and cooling water of marine engine, has been analyzed. Two typical marine engines are selected to be the waste heat source. Six economic indicators are used to analyze the economic performance of this combined thermodynamic cycle system with different marine engine load and under practical comprehensive operating condition of marine engine. The results of the present study show that the combined thermodynamic cycle system with R123 as organic working fluid has the best performance. The system with cis-butene has the worst economic performance. Under practical comprehensive operating conditions of ships, R123 has the shortest Payback Periods, which are 8.51 years and 8.14 years for 8S70ME-C10.5 engine and 5G95ME-C10.5 engine, respectively. Correspondingly, payback Periods of Cyclopentane are 11.95 years and 11.90 years. The above values are much shorter than 25 years which are the lifetime of a marine ship. Under practical comprehensive operating conditions of ships, the combined cycle system can provide output power which is at least equivalent to 25% of engine power. Considering that R123 will be phased out in near future, cyclopentane may be its good successor. Cyclopentane can be used safely by correct handling and installing according to manufacturer's instructions.