Optimization of advenced liquid natural gas-fuelled combined cycle machinery systems for a high-speed ferry

This paper is aimed at designing and optimizing combined cycles for marine applications. For this purpose, an in-house numerical simulation tool called DNA (Dynamic Network Analysis) and a genetic algorithm-based optimization routine are used. The top cycle is modeled as the aero-derivative gas turbine LM2500, while four options for bottoming cycles are modeled.

Firstly, a single pressure steam cycle, secondly a dual-pressure steam cycle, thirdly an ORC using toluene as the working fluid and an intermediate oil loop as the heat carrier, and lastly an ABC with inter-cooling are modeled. Furthermore, practical and operational aspects of using these three machinery systems for a high-speed ferry are discussed.

Two scenarios are evaluated. The first scenario evaluates the combined cycles with a given power requirement, optimizing the combined cycle while operating the gas turbine at part load. The second scenario evaluates the combined cycle with the gas turbine operated at full load. For the first scenario, the results suggest that the thermal efficiencies of the combined gas and steam cycles are 46.3 % and 48.2 % for the single pressure and dual pressure steam cycles, respectively.

The gas ORC and gas ABC combined cycles obtained thermal efficiencies of 45.6 % and 41.9 %, respectively. For the second scenario, the results suggest that the thermal efficiencies of the combined gas and steam cycles are 53.5 % and 55.3 % for the single pressure and dual pressure steam cycles, respectively.

The gas ORC and gas ABC combined cycles obtained thermal efficiencies of 51.0 % and 47.8 %, respectively.