Feature 4 | Cranes & Cargo handling
More space for bulk
Shipboard storage space constraints are challenged by a new approach from
MacGregor Bulk.
F
igure 1 shows an illustration of a typical
bulk handling system concept of the
type found on most existing supply
vessels, including vessels under construction.
The basic principle of this concept is that the
bulk storage tanks are pressure vessels and that
compressed air is used for discharging the bulk
cargo. Typically, the bulk tanks are designed
for a maximum operating pressure of 5.6bar.
Typical volumes are 30m
3
-80m
3
, diameters
4m-5m, and heights 5m-6m. The bottom part
of each tank is covered with aeration panels
to fluidise the cargo when discharging to rig.
The valves for selecting the tank to be filled or
emptied are usually butterfly-type.
MacGregor Bulk claims that the main Figure 1: typical bulk shipboard storage system today.
weakness in this scenario is the basic principle
of such systems, where pressure vessels are
used as bulk tanks. A circular footprint is
not an optimum shape for efficient use of
valuable space on an offshore service vessel,
because it limits available below deck space
for other liquid cargos and equipment. In
addition, the complicated piping layout and
inconvenient location of pipes and valves is
further disadvantaged by the use of butterfly
valves, claims the company - the piping layout
demands a considerable amount of attention
during design, fabrication, and installation
phases. Even operators of the system point Figure 2: Macgregor’s high volume bulk handling system. since the hopper is not
out the clogging problems they regularly face performing the discharge operation it is not subjected to pressure and therefore a
in the areas where pipes branch out and the rectangular shape can be used.
difficulties encountered in maintenance due
the inconvenient location between main deck
and top of the tanks, the company claims. vessel market and, in 2005, received its first and Blow Pump configuration the dry bulk
In its solution MacGregor Bulk draws on order from Qatar Shipping Co for dry bulk capacity is increased by some 50%-75% within
the 50 year experience of its Nordströms brand handling systems for two anchor handling tug the same space occupied by conventional
- the pneumatic conveying systems that have supply vessels for Halul Offshore Services, with spherical bulk tanks.
been installed on more than 60 cement carriers delivery this year. Today the total number of Existing bulkheads form the walls, and
sized between 1000dwt and 40,000dwt, and systems on order has grown to some 50 units. the main deck forms the roof of the hopper.
at more than 15 marine cement terminals, In MacGregor’s high volume BHS Some 2.2m space is needed under the
where conveying rates in excess of 650t/hour concept, cargo is received and stored in a hopper for the blow pump. The inclination
of cement through a single line have been hopper integrated into the vessel’s hull and of the hopper is 15
o
. The complete area of
achieved. The technology has been used for the discharge is performed by a blow pump, the floor is covered with aeration panels.
transferring huge quantities of bulk cement using compressed air. The advantage of this For segregating different cargos, the hopper
from ship to shore silos and vice versa. approach is that the hopper is not required may be further divided into two or more
As a result of a market study, MacGregor to be pressurised and can be shaped to fit the compartments by adding transversal and/or
Bulk has tailored its Nordströms dry bulk overall hull design and utilise the available longitudinal partitions.
handling technology for the offshore supply space more effectively. With this Hopper MacGregor Bulk uses a two-way valve
90 The Naval Architect February 2008
NA Feb 08 - p90+91.indd 90 05/02/2008 09:53:56
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