Combined cycle is often called as the hybrid power generation system composed of a gas turbine and a steam turbine where the steam turbine is powered by exhaust gas heat from the gas turbine. Emission control requirement of the exhaust gas and the fuel oil price forecast have induced to choose the liquefied natural gas (LNG) as alternative to fuel oil, which offers more options of marine power source including the combined cycle.
This paper reviews technologies related to the marine LNG-fueled combined cycle, primarily: working fluid, exhaust gas heat exchanger, and compact steam prime mover. The case study of the marine combined cycle is also proposed, in which the working fluid is set to water, exhaust gas heat exchanger is set to hi-finned tube heat exchanger and compact steam prime mover is set to hi-speed radial turbine. Supposing the gas turbine with rated power of 22,370kW, operating at 100% of power with 40% efficiency, and steam turbine with 80% efficiency; steam condition at the exit of the heat exchanger is 0.3MPa and 573K to gain larger expansion ratio in the steam turbine and more total output of the combined cycle. The case study predicted 3,381kW output by two-stages of the radial steam turbine and 44.06% total efficiency of this combined cycle.
Pursuing the effective use of energy onboard ship is important from the viewpoint of the economy and the environment. In a marine propulsion power system, most energy is released to environment as exhaust gas and cooling water. Waste thermal energy radiated from the prime mover is collected and converted into electric power using a thermoelectric module which transforms temperature differences into electric energy. The fundamental properties of the thermoelectric module were investigated in this study.
We have successfully developed a technology of semi-permanent use of engines and near zero waste oil with almost no wear and near constant thermal efficiency, with remarkable reduction in engine trouble and parts replacement. The results were verified through ship tests 8 years (33,000h). The technology has been in practical use in many marine and diesel generator engines. Also, we presented our theory and technology for the integration of various lube oils ideally with a TBN close to zero. Empirical tests have started in June 2014 and are on-going. Based on the results, we propose a semi-permanent extension of TBO (Time Between Overhaul) by establishing a monitoring system that indicates whether an overhaul is really required or not.
This paper proposes a new hybrid propulsion system without large-capacity battery and clarifies its characteristics. This proposed system has main engines and diesel generators as power sources. These are connected through the electric power converters and the motor generators. To evaluate the propulsion system, a fuel consumption simulation has been developed. The simulation includes the efficiency data of all apparatus which comprise the propulsion system. The efficiency data varies depending on the load factor and rating of the apparatus. Considering all possible energy flows, the most efficient energy flow and power balance are determined. This simulation was evaluated using a tugboat's propulsion system as a model. In this paper, the characteristics of the fuel consumption model are described as the core unit in the simulation. An efficiency improvement of more than a few percent is expected when the power demand is low.