Waste Heat Recovery for Ships
Waste heat recovery is a growing field of research in internal combustion
efficiency improvements. A conventional gasoline internal combustion
engine converts about 30% of the energy in the fuel into mechanical work.
With a efficient diesel, the figure is about 35%. The rest of the energy
is lost in the form of waste heat, through the cooling system and the
This is largely because of metallurgical limits of materials currently
used in internal combustion engines. With no real alternatives in the near
future, aluminium and iron are still the most viable materials for engine
construction. A number of experiments were carried out using ceramics for
engine construction. While theoretically ceramics can provide a higher
efficiency in thermal combustion (due to the higher temperatures they can
withstand), production engines using ceramics cannot be expected in the
near future. So engineers are exploring ways to harness the energy wasted
to the environment.
BMW and Honda have both tried experiments with Rankine cycle units that
can provide additional electricity, reducing the load on the alternator
and improving the fuel efficiency a bit. Systems like those are however
too expensive for automotive use. A better fit would be use in
applications where initial cost is a smaller fraction of the high-running
costs--applications such as ships, for instance. Opcon, a Swedish energy
and environmental technology group is now about to install a waste
recovery system on a Wallenius ship. The pilot installation will
potentially save about 4 to 6% of fuel. Wallenius's statistics show that
the company uses about 200,000 to 250,000 tons of bunker fuel a year for
their fleet of over 150 vessels.
Wallenius is interested in both the fuel savings and the environmental
credit that comes with lesser carbon and sulphur dioxide emissions. "The
opportunities that Opcon Powerbox offers for utilising waste heat and
reducing fuel consumption on board our ships are among the most
interesting we have seen in this field. A fuel saving of between four and
six per cent is considerable in this context. In future we see
opportunities to use this technology and make savings of up to ten per
cent. We aim to install Opcon Powerbox on all of our new vessels and on
most of our existing ones in future. We want to be among the leaders in
the shipping sector in reducing energy consumption and cutting emissions,"
says Per Croner, CEO of Wallenius Marine AB.
Opcon's Powerbox runs on the organic rankine cycle (similar to Honda's and
BMW's) and uses waste heat to vaporise a working fluid that then expands
in a screw type compressor. The Lysholm screw compressor is connected to a
generator that will produce electricity. After passing through the screw
compressor, the fluid is cooled and pumped back to continue the cycle.
Maximum efficiency and hence electricity generation is governed by the
difference in temperature between the hot and cold side.
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