Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02532748 2006-O1-13
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Loading and offloading system
The iuventlon relates to a loading and offloading system on a vessel
comprising a
hull and within said hull a number of cylindrical tanks.
S A tan7cer comprising s number of cylindrical tanks is described in 'WO
OOI7313~1,
rn the known tanks, which are made of a composite material, the structural
integration with the hull of the vessel may lead to fatigue problems during
the service
Life of the vessel. Especially in high sea slates, partially filled tanks may
lead to
sloshing of the contents and. relatively high mechanical loads on the ta~ol~s,
In case a hydrocarbon is stored in the tanks, the atmosphere above the
hydrocarbon. in the lank is formed by an inert gas, which prevents explosive
mixtures to
be formed iri axder to reduce the risk of explosions, Furthermore, the loading
level o'f
the tanks will determine the drab of the vessel, which may vary.
It is an object of the present invention to pxovide a loadingloffloading
system in
which the above problems are mitigated,
Thereto the present invention is characterised by each tank havil~g a first
and a
second opening and respective valves closing each opening, wherein the tanks
are
supported by a support stntoiut~ in the hull, fine first openings of the tanks
being
connoted to a hydrocarbon intlow/outflow line, the second openings of the
tanks being
connected to a displacement fluid inflow/outflow line, at least ono pump being
connected to the displacement fluid ixd'lowloutflow andlo;r to the hydrocarbon
inflowloutflow line, a control means being connected to the at least ox~e pump
and to
the valves for controlling;
- pumping a first volume of displacement liquid or a l~ydxocarbon into the
tanks via
oxie of the di.spla~cemant fluid in:~lowJoutflow line and the hydrocarbon
111'~OWIOlItflO'V~ lixle, while
.. opening the valve of the other of the displacement fluid inflow/outflow
line and
the hydrocarbon inflow/ou't,~l.ow line and removing a second volume of
hydrocarbon or displacement fluid out of the tank via the valve.
Because the tanks are formed by separate units that are supported within the
hull,
they da not contribute to the slx~ctural integrity of the vessel iti a.
significant manner.
The hull can hence be constructed in a more lilt-weight manner witbout a
reduction ixr
safety of containment. Pressure fluctuations inside the tanks will nqt cause
any bezidi.ng
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stresses in the hull, Ian a preferred embodiment, fine tanks are formed by
cylindric~.l
to ks with spherical end faces to form a pressure vessel. A single layer hull
'will suffice
to provide a reliable containment. 'Upon eonsn'uction or during charage~out
and repair,
the tanks can be separately installed, replaced andlor serviced.
S rn a preferred embodimezlt, the level to ~crluch the tanks are filled is
substantially
constant. 'When oil is removed, the displacement fluid, such as for instance
sea water,
takes up the volume that is freed by the oil, such that the tanks are filled
to a constant
level. This has an advantage that reduced sloshing of the tank contents
occurs, which
reduces fatigue problems. Furthermore, since the tanks are filled to a
Substantially
constant level, no inert gases need to be utilised in order to avoid problems
with
vola'dle organies compounds. Furthermore, corrosion of the tazaks, in case
they era
made of metal such as carbon steel, is reduced as no interfaoe of the
container contents
with air is formed.
By keeping a substantially constant level of fluid in the tanks, a
substantially
1 S constant draft can be achieved, This is particularly advantageous in case
the vessel is
moored to the sea bed, and is attached to a sub sea well via a hydrocarbon
riser, such as
in case of an p'1'S~.
rn a preferred embodiment, a heat insulating material iS present at the
interface of
the hydrocarbon and the expulsion fluid, itt case the hydrocarbon is formed by
oil,
ZO which is transported. upward from a sub sea oil well, and the fluid is
formed by sea
water, the oil may have a temperature of for ir~,stance 65°C, whereas
the sea water is
about 10°C. In order to avoid heat loss which would negatively affect
the oil viscosity
and its flow properties, a movable separating member may be situated in each
tank, at
the interface of the hydrocarbon and the displacement fluid, of substantially
equal site
25 and shape as the cross-section of tank. Such au ins~.laiing member has a
further
advantage that oil-water mixing at the interface is reduced.
Tn a preferred embodinner~t the tanks are connected in groups, for instance of
10
tanks each, to a manifold for admission and removal of oil and water. The
tanks may
have other shapes than cylindrical, such as spherical or rectangular, and may
be
30 supported in a honeycomb structure or a rectangular matri;r, Such as a
space frame
structure.
Some embodiments of a vessel according to the present invention will be
explained in detail with reference to the accompanying drawixigs. In the
drawings:
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li'ig. 1 shows a sol~~.~c side view of an FPSO conxprising multiple
cylindrical
tanlcs according to the present invention,
Fig. 2 and 3 show a partial perspective view of a number of tanks according to
the
pxeSent invention,
Figs. 4a~4g show a sequence of loading and offloading using a vessel according
to the
present invention, and
Fig. 5 shows a lay,QUt of multiple interconnected 'lacks.
Figure 1 shows a vessel (1), such as an FPSO, oomprisiug a hull 3 with a
number
of cylindrical tanl~s 4,~. The vessel 1 comprises a turret 7 which is
atvchored to the
seabed 8 via anchor lines 9, The hull 3 can weathervane around the turret: 7
depending
on the wind and current directions. A hydxocarbon riser 11 is connected to a
sub sea
hydrocarbon well 13, such as an oil well. Oil is for instance transferred from
the well
13 to the tanks 4, 5, via a swivel 15 which connects product piping on the
veSSel with
the geostationary riser on the turret 7. The oil can via the oil
inflow/outfilow line 17
and Che valves 18, 19 be transported into and out of the tat~,s 4, 5.
'Via a pump zl and a water ir~letJoutlet line 22, sea water can be pumped,
into and
out of the tanks A,S via valves 23,25. The pump 21 and the valves 18,19,23,25
are
controlled by a control unit 27, such as a computer, wbiel~ is attached via
electrical or
eleetro-optical cables 29, 30, 31 to the pump 21 and ~ valves 18-25.
figure 2 slows a number of tanks 4, 5 placed on a grid of stiffener beams 33
which provide a hull reinfarcement in th.e longitudinal amd in the transverse
directions.
The tanks are connected via a top manifold 35 to main transport ducts 37, and
at the
bottom to main transport duels 39. As spawn in figure 3, a top grid structure
40 is
situated over the tanks 4, 5 and carries the deck 41, below which the
manifoldxng 35
2S anal the main transparl ducts 37 are situated.
Figure 4a shows at the tank 4 after offloading, wZ~erein the majority of the
tank is
filled with seawater 47. A separator, such as a circular floater 42, separates
i:'he oil 45
from the seawater 47. D~u~ing loading of the tank 4, such as shown in figures
4b and 4c,
the water 4'1 is removed via valves 23, and the oil is admitted via valves 18.
For
offloading, as shown in figures 4d and Vie, oil is removed via valves 18, and
water is
admitted via valves 23.
In figure elf, the control unit 2'~ is seexr, controlling the pump 21. and the
valves 18
and 23. Two level sensors 49,50 are connected to the control unit 27 for
providing input
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tp the control unit about the level of ail and water in the tank ~, A tank
radar transducer
S 1 is coupled to the control knit 27 for providing a position control signal
of the floater
~2 in the tank,
As ~s schematically indicated in figure ~4g, tilting of the vessel does not
result in
any sloshing of liquids in the tank A~.
Finally, figure S shows a group 60 of ten tanks, which have a common
loadingloffloading duct 51 for hydrocarbons 61 and a common supply and
discharge
line 62 for seawater, which is taken in from the sea aria seawa~er inlet
chests 64,65 i~
the hull of the vessel 1.
