For this assessment the most important factors are safety,
durability and blockage, since these cannot be compromised.
Spillage and maintenance have been graded as
nominally important, since they are unwanted, but they
can be dealt with. Power and costs have been rated as
less important and may act as final decision criteria.
From this assessment it is clear that Concept 2 is the
most promising. In the next section, this concept is finalized
for both platform types and practical realizations are
presented.
4.4.5 Final concept
In collaboration with Dutch and international companies,
suitable machines were selected for each of the basic
functions and information regarding costs, dimensions,
weights and power consumptions were provided.
4.4.5.1 Transshipment
The Dutch company Deltapompen B.V. was consulted for
the selection of the slurry pumps. For the transshipment
slurry pump they selected a pump with a capacity of 300
m³/h, which uses 90 kW of electrical power. This pump
will cost € 19,000, including the motor and the mounting.
Similar to the slurry pump that extracts the small particles
from the ocean, this pump will be made from the
corrosion resistant material super duplex and is able to
pump slurries with a maximum particle size of 50 mm.
This pump is suitable for both platform types.
4.4.5.2 Transport
There are two options for the transportation of the collected
debris: buying or chartering a vessel. Which is the
most economical depends on the type of platform to be
used.
SWATH Vessel
For a SWATH vessel platform, which cannot hold a buffer,
the constant nearby mooring of a vessel is required to
perform continuous processing. This also implies that
two vessels are required, due to the transportation time.
This would result in very high costs when a vessel is chartered.
For this platform type, the only practical economic
option is to buy a vessel.
The SWATH vessel platform needs to be supplied with
marine gas oil every 14 days to keep its generators running.
It makes sense to synchronize the transport vessel
periods, so that they can also transport fuel and other
supplies. In 14 days, The Ocean Cleanup Array would collect
approximately 899 m³ of plastic debris. Since the
Voraxial Separator produces a 50-50 mix of plastic and
water, as explained in Section 4.2, twice the amount of
cargo capacity is required. Thus, required cargo capacity
of the transporting vessels is 1,798 m³.
To calculate the order of magnitude of the costs of transportation,
a tanker vessel of sufficient size has been chosen
as a baseline. The specifications of this vessel are
stated in Table 4.15. It should be noted that this vessel
does not have a bow thruster, so it is not capable of using
Dynamic Positioning (DP), necessary for the continuous
mooring of the vessel during the 14-day loading period.
A calculation based on actual data is not possible, so the
fuel consumption of Dynamic Positioning is assumed to
be 50% of the fuel consumption of sailing. An example
given to support this assumption is the MSV Fennica,
which uses 30 MT of fuel at normal sailing speed and 15
MT of fuel for Dynamic Positioning (offshore).