Recently, as an era of a high oil price advents, efforts to save fuel costs by improving energy efficiency of marine vessels and to secure an environmentally friendly feature in operation of a marine vessel are being made.
In general, in an operation of a marine vessel, most energy is consumed by a main engine for propelling the marine vessel, and about 25% of fuel consumed for the operation of the main engine is practically disposed of in air as an exhaust fume. Accordingly, a variety of devices for recovering part of waste heat by using the exhaust fume are actively being introduced.
FIG. 1 is a schematic view illustrating a waste heat recovery device for a marine vessel of a related art. Referring to FIG. 1, in the waste heat recovery device for a marine vessel of a related art, a heat recovery device (boiler) 121 is installed at an exhaust pipe through which an exhaust fume is exhausted from an engine 110 of a marine vessel and then heat of the exhaust fume is recovered (heated under uniform pressure) so that high temperature steam is generated to be used as a variety of energy sources.
However, in the waste heat recovery device for a marine vessel of a related art, since waste heat of an exhaust fume is recovered through only the heat recovery device 121 having a single structure, waste heat of an exhaust fume that is still in a high temperature state even after having passed through the heat recover device 121 is not recovered and discharged into the air so that energy is wasted.
Also, a heat recovery device for recovering heat from coolers to cool the heat generated from the engine itself is not provided.
On the other hand, an operation rate of the engine 110 varies during the operation of a marine vessel. For example, the engine 110 of a marine vessel may be operated with a full load for about ⅔ of the entire operation days and with a load lower than the full load for the rest of the operation days. As such, when the engine 110 is operated with a load lower than the full load, a relatively low amount of exhaust fume is generated compared to the exhaust fume generated when the engine 110 is operated with a full load.
A change in the amount of an exhaust fume causes a change in heat capacity flowing in with the Rankine cycle, which has a severe influence on efficiency of the Rankine cycle. Accordingly, electricity may be stably generated when the above issue is considered in the development of a waste heat recovery device for a marine vessel which may drive a turbine by recovering a large amount of waste heat of an exhaust fume of an engine compared to the related art.