Storage Tank, Transport System Therewith and Method for Operating It
Storage tank comprising—an outer container ( 2 ) having a first closable opening ( 23 ), and—an inner bladder container ( 3 ) disposed within said outer container ( 2 ) and having a second closable opening ( 30 ), said outer container ( 2 ) and inner container ( 3 ) being sealed with respect to each other, said inner container ( 3 ) being adapted to be filled and or emptied with a liquid through said second closable opening ( 30 ), a space ( 8 ) between the outer container ( 2 ) and the inner container ( 3 ) being adapted to be filled with liquid through the first closable opening ( 23 ). The outer container ( 2 ) is rigid with at least one flexible portion incorporated in the rigid outer container and configured to flex so as to expand and contract to compensate volume variations caused by pressure and or temperature variations to which the storage tank ( 1 ) is subjected.
1 . A storage tank comprising
an outer container having a first closable opening; and
an inner container disposed within said outer container and having a second closable opening;
wherein said outer container and inner container are sealed with respect to each other, wherein said inner container is adapted to be filled and/or emptied with a liquid through said second closable opening, and wherein a space between the outer container and the inner container is adapted to be filled with liquid through the first closable opening; and
wherein the outer container is rigid and comprises at least one flexible portion configured to flex so as to expand and contract to compensate volume variations caused by pressure and/or temperature variations to which the storage tank is subjected.
2 . The storage tank according to claim 1 , wherein said at least one flexible portion comprises a first surface which is linked to an adjacent surface of the outer container by a smooth rounded or chamfered transition portion of the outer container.
3 . The storage tank according to claim 1 , wherein the outer container comprises a closed body having a transversal polygonal cross-section, said at least one flexible portion being formed by at least one side wall and/or end wall of said body.
4 . The storage tank according to claim 3 , wherein said body of the outer container comprises a substantially rectangular transversal cross-section.
5 . The storage tank according to claim 1 , wherein the outer container comprises a closed cylindrical body having a circular transversal cross-section, said at least one flexible portion being formed by at least one end wall of said body.
6 . The storage tank according to claim 1 , wherein the outer container is made of a polymer material or a homogenous material.
7 . The storage tank according to claim 1 , wherein the inner container is made of an elastomer.
8 . The storage tank according to claim 1 , further comprising a hollow rigid member connected to the second closable opening and extending inside the inner container, the hollow rigid member being configured for use in emptying and filling the inner container.
9 . The storage tank according to claim 8 , wherein said hollow rigid member comprises a rod and an end body at a distal end relative to said second closable opening, said end body having rounded side walls projecting on either side of said rod.
10 . The storage tank according to claim 9 , wherein said rod comprises through bores, wherein said rounded walls of said end body surround a part of the rod in which the through bores ( 902 ) are formed, and wherein said rounded walls are spaced one from the other.
11 . The storage tank according to claim 8 , further comprising at least one channel having a plurality of apertures along its length, said at least one channel being disposed against the hollow rigid member and/or an inner face of a wall of the outer container.
12 . The storage tank according to claim 1 , further comprising monitoring means connected to the inner container and/or the outer container and being configured to monitor volume variations inside the storage tank.
13 . A transport system comprising a cage and a plurality of storage tanks according to claim 1 , said storage tanks being disposed within said cage, and said cage comprising a suspension element configured to enable the suspension of the cage from a lifting machine.
14 . A method of operating the storage tank according to claim 1 , said method comprising:
at a topside facility, filling the inner container with a liquid and filling the space between the inner container and the outer container with a liquid;
closing the first and second closable openings;
transporting the storage tank to a subsea location with the closable openings closed;
at the subsea location, connecting the second closeable opening of the inner container to a subsea installation and opening the first closable opening of the outer container to the surrounding seawater;
emptying liquid from the inner container and allowing seawater into the space between the outer container and the inner container to thereby compensate for volume changes of the inner container; and
disconnecting the inner container from the subsea installation and closing the first and second closable openings before the storage tank is lifted from the subsea location and transported back to a topside facility for refilling.