the IHS Ballast Water Guide - RWO Marine Water Technology

Sponsored by IHS Fairplay Solutions Guide to Ballast Water Treatment Systems
recorded in a ballast water record book.
When ballast water is exchanged, 95% of
the vessel’s ballast water is replaced with
water farther out in the oceans, 200nm from
the coast and at least 200m deep, as the bioorganisms
cannot survive this far from land.
Exchanging water at sea can be dangerous and
introduce excessive stresses and forces that
can cause a vessel to become unstable and
even capsize. BWE was intended to be phased
out by 2016 once ships were equipped with
treatment systems.
Coatings of ballast water tanks must
withstand 15 years without deterioration,
which is a requirement of the International
Association of Classifi cation Societies (IACS)
common structural rules and is inherent
in the SOLAS Performance Standards for
Protective Coatings (PSPC).
System specifi cation
The main considerations are ballast capacity
and pumping rate, water treatment method,
size of system and space available, servicing
and costs.
The ballast capacity and pumping rate
are dependent on the ship type and size.
The International Chamber of Shipping has
pointed out that there are fewer systems
available that are suitable for ships with
ballast capacity larger than 5,000m 3 .
Although multiple systems can be installed,
this increases energy costs.
The ballast capacity of most vessels is
roughly one-third of their deadweight, so
a 115,000dwt Aframax has tanks holding
40,000m 3 of ballast water and a VLCC or
VLOC up to 100,000m 3 .
Most ballast systems have a pump capacity
that enables total ballast capacity to be
emptied or fi lled in about 10 hours. As pretreatment
fi ltration features in many systems
the owner should consider the time lost in the
backfl ushing cycle for cleaning the fi lter.
The degree of pressure loss is dependent on
the maximum operational pressure of existing
ballast pumps, the design of the ballast head
and the location of the installation. Systems
tend to create a pressure loss of between
0.5bar and 2bar, for which the ballast-water
pump will have to compensate.
Concerning the volume of ballast water
treated per hour, optimum pumping rates need
to be established, in order to turn round the
vessel quickly and not confl ict with the speed
at which the cargo empties or tidal levels rise.
A lot depends on vessel size. Systems
can satisfy vessel size by working units in
parallel to match the desired fl ow. Plenty of
ships require pumping rates of no more than
2,000m 3 /h, which some BWTS suppliers
believe is the optimum size to aim at.
Certain makers have yet to gain suffi cient
experience of handling the largest ship
types. A VLCC might require a pump rate of
6,000m 3 /h, which could prove challenging to
some manufacturers.
When implementing the system, the
potential purchaser needs to consider the
system size and space available, not only for
the equipment, but also piping and possibly
upgraded or additional pumps. The degree
of modularity in the system is an important
factor in making the best use of available
space. Space is also needed for maintenance
access and for storage of consumables.
Operating costs (energy, consumables,
crew time, maintenance and servicing) all
should be factored into the capital cost of the
equipment and its installation.
The availability of maintenance, servicing
and consumables are considerations that
are as signifi cant as their cost. The eff ects of
the system on ballast tank coatings and as a
contributor to corrosion in the ballast tank
and pipes should also be taken into account.
© IHS Global Limited 2012 39
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