Optimization of waste heat recovery from the exhaust gas of marine diesel engines

In this article, some configurations of waste heat recovery systems are described, analysed and compared, in order to find the optimal plant layout. Starting from the availability of performance data of a two-stroke diesel engine, adopted for the propulsion plant of a crude oil tanker ship, the authors examined different solutions for the waste heat recovery from the diesel engine exhaust gas ensuring the best fulfilment of the vessel needs in terms of mechanical, electric and thermal energies. The considered waste heat recovery systems can adopt either steam turbine and gas turbine or simply steam turbine for power generation. As regards the steam plant, two basic layouts are considered, optimized and compared: the first plant scheme is a typical steam plant currently adopted for waste heat recovery purposes and the second one is a solution proposed by the authors. Considering the different options, in this article, four different system layouts, applied to the mentioned diesel engine, are singly optimized and compared between them in order to find the most suitable plant and the steam cycle parameters that provide its best operation at the engine normal continuous rating. The performance of the optimized waste heat recovery systems is evaluated also by comparing them under off-design engine load conditions, in the engine power range between 50% and 100% of its maximum continuous rating.