Page 28 - Industrial Plants

Fig. 5- Power vs. time
and SoC of the
battery during the
tug’s cycle. The usage
of the PEM and of the
diesel is shown.

The diesel works now at a power level approximately identify the most suitable for the so-called “power
twice the power requested for the transit speed and the duty”, that means batteries that react fast
specific consumption improves. The time to start the and can provide higher currents in excess of their amp/
main diesel is calculated according to the need of hour rating for short time. The Lithium based technology
beginning the working phase with the battery fully offers these performances. Another key issues is the
charged. During the working phase, the battery can required certification issued by the certification bodies,
assist the main diesel either increasing the continuous in order to provide safe and reliable solution for on
power level or compensating the dynamic power board.
response in order to make any maneuver faster. After
the working phase, a transit phase follows during
which, in the first part, the main propulsion diesel is Power management system
kept on in order to restore the (PMS)
charge of the battery. In the
second part of the transit the PEM The system shown in fig. 2 needs a PMS in order
The integration of a PEM in can be turned on again and the to provide the proper sequences of operation and
parallel to the main diesel main diesel can be switched to coordinate the performances of each component.
helps in reducing the fuel off. Then, after the transit, when The target is to attain the maximum efficiency and the

consumption and improves the tug is in idle, the charge of the best performances for the vessel. The PMS can be
the response time of the battery can be completed by the configured as a system on top of the two propulsion
propulsion system when in auxiliary generator, providing its full lines and coordinates the equipment tied to the dc
maneuvering power. Of course during the cabinet as well as the main diesel, the auxiliary diesel
charging and discharging phases and the shore connection. Among the features
the current given or taken to/from provided, the monitoring of the SoC of the battery is
the battery must be within its essential, in order to define the right time of switching
capability. Another important factor to be calculated is on and off the main diesel and the auxiliary diesel when
the number of cycles that a battery can sustain during in transit or in idle, in order to provide the best energy
its expected life time. In a power cycle as in fig 5 two/ performances.
three charging and two/three discharging phases can
be identified and the DoD could be around 40 to 60%.
Taking into consideration the number of cycles per day Case study

it is easy to identify the requested number for its entire As an example, the data of a typical harbor tug are
life. Typical values go up to 10.000 to 15.000 given. The main diesel is chosen with a power rating of
cycles. There are many types of batteries available on 2250 kW @ 1800 rpm, as shown in fig. 6. The propeller
the market. However between them it is important to curve is shown as well. Since the propeller requires

IndustrIal Plants - May 2017
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