WO2012008826A1

WO2012008826A1 - Cargo tank for holding liquids

Info

Publication number: WO2012008826A1
Application number: PCT/NL2010/050457
Authority: WO
Inventors: Gert Jan Vossnack
Original assignee: Trilobes B.V.
Priority date: 2010-07-15
Filing date: 2010-07-15
Publication date: 2012-01-19

Abstract

The invention relates to a cargo tank (10) for holding a liquid, the cargo tank comprising at least: - a first tank section (12A), - a second tank section (12B), and - a third tank section (12C), which together define a tank volume (14), wherein each tank section is defined by a curved tank wall (16) which is curved in such a way that the tank wall is substantially free of bending moments when the cargo tank is filled with a liquid, wherein the cargo tank comprises at least a first and a second constricted transition (13A,13B), wherein in the first constricted transition the tank wall of the first tank section meets the tank wall of the second tank section and wherein in the second constricted transition the tank wall of the second tank section meets the tank wall of the third tank section.

Description

Title: Cargo tank for holding liquids

Field of the art

The present invention relates in general to cargo tanks for holding liquids. The invention relates in particular to cargo tanks for holding fruit juice, in particular on board ships. The invention relates in particular to cargo tanks for holding orange juice on a vessel for transport over water on board a vessel.

Description of the prior art

Cargo tanks for holding fruit juices and other liquids are known. In the field of the art, existing ships are sometimes converted from one type of cargo to another type of cargo. Currently, general bulk carriers are sometimes converted into ships for transporting liquids such as fruit juices. In such an operation, the ship is fitted with one or more cargo tanks for holding fruit juices.

One problem of a known cargo tank is that it has a rather complex shape inside. This makes it difficult to clean the cargo tank, and remainders of juice or other liquid tend to stay behind in the cargo tank after emptying of the cargo tank, and even after cleaning of the cargo tank. These remnants may start to rot or degrade, and when the cargo tank is used for a subsequent transport of liquid, the remnants disadvantageously affect the quality of the new load of liquid. This may result in a buildup of contamination which cannot be removed by normal cleaning procedures. The complex shape makes the cargo tank unsuitable for perishable cargos.

Another problem associated with liquid cargo tanks for ships is that often, the tank is required to fit in a predetermined shape within the hull of an existing vessel. Hull

compartments of cargo ships often have dimensions which are designed to match to constructional considerations. For instance, a vessel of a certain length may have four or five compartments lengthwise and one or two compartment across the width of the ship. Such a configuration imposes restrictions on the dimensions of the liquid cargo tank, for instance that a tank must be elongate according to a certain length/width ratio.

It is also possible that the cargo bay of a ship has a certain height, and that the liquid cargo tank must extend over the entire height of the cargo bay of the ship. This imposes a minimal height on the liquid cargo tank.

It is also possible that the height of the ship itself must be limited because the ship must be able to pass underneath certain bridges across certain canals or waterways. This imposes a maximum height on the liquid cargo tank. Furthermore, cargo ships are quite large. Hence, the liquid cargo tanks which are to fit in the cargo bays also need to be quite large. This creates extra requirements of structural strength for the cargo tanks and the ability to withstand the pressure of the liquid inside the cargo tank. As a result of movements of the ship additional loads are placed on the tank creating extra requirements on structural strength.

It is also possible that a liquid cargo tank needs to be fitted in a container ship, i.e. that the liquid cargo tank should comply with the dimension of a standard container.

All these circumstances impose restrictions on the dimensions of the liquid cargo tank.

Furthermore, ships have sizes which vary enormously, and therefore for each ship, the requirements for the cargo tanks may be different.

However, cargo tanks for liquids have their own, different set of criteria for optimal design. For instance, the tank wall is generally curved in such a way that substantial bending moments are avoided and that the tank wall is only or almost only loaded under tensile stress when the tank is filled with a liquid. This allows a relatively thin tank wall.

Other criteria also apply, such as a certain required inclination of the tank floor for easy emptying of the liquid. Also, the cargo tank may need to have a predetermined volume or a certain minimal height, such that a man can stand in the cargo tank and still be able to - fairly easily - reach the entire inner wall of the tank for cleaning or inspection.

Furthermore, in some cases the liquid cargo tanks may need to be mobile, in that they can be loaded and unloaded from a vessel. This requirement creates extra technical demands.

The set of requirements for the cargo bay wherein the cargo tank should fit do not always match the set of criteria for optimal cargo tank design. In practice, sometimes a less optimal cargo tank is designed and fitted in an existing cargo bay, or an optimal tank is designed which does not fit very well in the cargo bay, i.e. which leaves a substantial unused space within the vessel.

EP0658494A is known, which discloses a tank container. A disadvantage of this container is that the form is limited to certain aspect ratios of length/width/height as can be seen from figure 3, which shows a top view. If for instance the width of the cargo tank would need to be varied relative to the length due to criteria originating from the cargo space of a ship, this would not be possible or only be possible in a very limited way. Therefore, the applicability of the tank of EP0658494A is quite limited in practice.

Furthermore, EP0658494A is difficult to clean, and remnants of liquid tend to stay behind in the tank after emptying. In many cases, a person should then enter the tank in order to clean the cargo tank from the inside. Because of the complicated form of the tank, this is difficult and takes a long time. US3814290 is further known which also discloses a cargo tank. US3814290 also has the disadvantage of a limited possibility to vary the length/width/height ratios.

US3814290 also has a complex inner shape, which requires intensive cleaning after emptying.

In the field of the art, box shaped cargo tanks for liquids are also known. The box shaped tanks have substantially flat outer walls which are stiffened by stiffening members such as girders or beams connected to the substantially flat walls. However, these cargo tanks have the disadvantage of being very heavy. This is due to the fact that substantial bending moments are created on the flat walls and girders or beams of substantial size and weight are required to create sufficient stiffness to compensate these moments.

There is a need in the field of the art for a better match between cargo spaces of ships and liquid cargo tanks. At the same time, the cargo tank should have a limited weight, so a better match should not result in a substantially increased weight of the cargo tank. Object of the invention

It is an object to provide a cargo tank which improves at least one aspect of the prior art.

It is an object of the invention to provide a cargo tank for liquids which. h has more freedom of variation in length/ width/height ratios.

It is another object of the invention to provide a cargo tank for liquids of which the inside is easier to clean.

It is another object of the invention to provide a cargo tank with an optimized construction weight compared to the prior art

The invention

In order to achieve a least one object, the invention provides a cargo tank for holding a liquid, the cargo tank comprising at least:

• a first tank section,

· a second tank section, and

• a third tank section,

which together define a tank volume, wherein each tank section is defined by a curved tank wall which is curved in such a way that the tank wall is substantially free of bending moments when the cargo tank is filled with a liquid, wherein the cargo tank comprises at least a first and a second constricted transition, wherein in the first constricted transition the tank wall of the first tank section meets the tank wall of the second tank section and wherein in the second constricted transition the tank wall of the second tank section section meets the tank wall of the third tank section.

The invention results in a cargo tank with a highly variable width/length ratio. The invention also results a in a cargo tank which has a relatively light construction.

In an embodiment, the first, second and third tank sections have a bulbous form, when seen in top view. In an embodiment, the first, second and third tank sections have the form of a part of a circle, when seen in top view. Depending on the form, the bending moments are zero, substantially zero or some bending moments may occur.

The first, second and third section may substantially have the form of a lobe.

In an embodiment, a frame is externally mounted to the tank sections, the frame comprising at least a first and a second portal which extend substantially around the cargo tank and are positioned respectively at the first and second constricted transition in order to provide rigidity to the cargo tank at the first and second restricted transition when the cargo tank is filled. The external frame allows a simpler inner form of the cargo tank

In an embodiment, the first and second portals have a substantially inverted staple shape or a substantially square-shape or a substantially rectangular shape. This forms fits around the cargo tank in a simple way.

In an embodiment, an outer perimeter of the first and second portals - when seen in side view - does not extend substantially beyond a box-shaped perimeter defined by the width and height of the tank sections, such that the width and height of the cargo tank are determined by the tank sections and not by the portals, in this way, the volume which is taken by the cargo tank is used efficiently, i.e. a large portion of the volume of an outer box defined by the cargo tank is available for holding liquid by the tank sections.

In an embodiment, wherein the inner tank volume is substantially free from any constructional elements which span the cross-section of the cargo tank at the first and second restricted transition. A simpler inner form of the volume is created.

In an embodiment, the first, second and third tank sections have a rounded roof wall, wherein the side wall which defines the curved shape gradually goes over in the rounded roof wall. Depending on the application, the roof can also be flat or conical shaped per tank section. In an embodiment, the cargo tank is elongate, when seen in top view. In an embodiment, the cargo tank has a length/width ratio of more than 2:1 .

In an embodiment, the cargo tank comprises a discharge opening and a floor, wherein said floor is inclined in the direction of the discharge opening in order to allow a liquid to flow towards the discharge opening when the cargo tank is emptied.

In an embodiment, the discharge opening is positioned at one end of the cargo tank, and wherein the floor of the cargo tank is substantially straight and is inclined in the direction of the discharge opening. The inclined floor makes it possible to empty the cargo tank very easy. The floor is inclined in the longitudinal direction. The discharge opening is provided at an end tank section.

In an embodiment, the cargo tank comprises a floor construction with substantial form rigidity, the constructional form comprising longitudinal beams and transversal beams which are mounted together, wherein the floor construction supports the tank wall, and wherein the first and second portals are mounted to the floor construction at their lower ends. In this way, a strong construction is obtained.

In an embodiment, the floor construction has a varying height which has a minimum at one end of the elongate cargo tank and has a maximum height at another end of the elongate cargo tank. This feature allows an easy construction of the inclined floor of the cargo tank. The floor construction has a minimum height near the discharge opening, so that emptying of the cargo tank is possible by gravity.

In an embodiment, the floor construction comprises at least one transverse beam at each of the first and second transition zone, wherein each transverse beam is connected with the lower ends of the first and second portals. The portals in effect have the form of a closed loop by the lateral beam in the floor construction. The closed loop portals are very strong and allows large cargo tanks. The size of the closed loop portals may be adapted to the size of the cargo tank.

In an embodiment, the cargo tank comprises 3, 4, 5, 6, 7, 8, 9 or 10 bulbous tank sections connected to one another at respective constricted transitions. The cargo tank will comprise one end tank section at each end and a plurality of middle tank sections in between.

In an embodiment, the cargo tank comprises straight outer side walls which are provided on the outside of the tank sections, thereby providing the cargo tank with a substantially rectangular shape when viewed in side view and in top view, such that the form is suitable to be used as a container of standard dimensions in container shipping, such as 1 TEU, 2 TEU, 3 TEU. The cargo tank may also comprise a substantially flat roof, for easy stacking of one cargo tank on top of another cargo tank.

In an embodiment, the first second and third tank section have a diameter, and the constricted transition has a length, and the diameter of the tank sections is at most 20% greater than the length of the constricted transition.

The invention further relates to a method of converting a non-liquid carrying cargo vessel into a liquid carrying cargo vessel, the method comprising inserting at least one cargo tank of claim 1 into a cargo compartment of the ship.

The invention also relates to a vessel comprising at least one cargo tank according to the invention. List of figures

The invention is explained in more detail in the text which follows, with reference to the figures, which show a number of embodiments, which are given purely by way of non- limiting examples.

Figure 1 shows a schematic view from above of a cargo tank according to the invention.

Figure 2 shows a schematic front view of a cargo tank according to the invention. Figure 3 shows a schematic side view of a cargo tank according to the invention, taken from the right side in figure 2.

Figure 4 shows a schematic top view of a cargo tank according to the invention. Figure 5 shows a schematic bottom view of a cargo tank according to the invention. Figure 6 shows a schematic perspective bottom view of a cargo tank according to the invention.

Figure 7 shows a schematic perspective top view of a cargo tank according to the invention including outer walls.

Figure 8A shows a detail of a constricted transition.

Figure 8B shows acting forces in the detail of Figure 8A. Detailed description of the figures

Turning to figures 1 -9, a cargo tank 10 according to the invention comprises three tank sections 12A, 12B, 12C. The cargo tank 10 may comprise more tank sections. The tank sections 12A, 12B, 12C define a single inner volume 14. In top view, the tank sections 12A, 12B, 12C have a shape of a part of a circle. The tank sections have a tank wall 16 which extends around the volume 14 and defines the volume. The tank wall 16 may be provided with stiffeners 17 which are ribs which extend around the outer side of the tank sections. The tank wall 16 extends vertically. The tank wall 16 defines a cross-section of a tank section - when seen in top view - which is substantially uniform over the height of the tank section. The cargo tank has a length 50, a height 51 and a width 52. The height of the cargo tank 10 may be varied over a considerable range.

The tank sections have a rounded roof 18. The roof 18 may also be flat or conical. The tank wall 16 gradually goes over in the roof 18. In the roof 18, at least one utility device 19 is provided such as a sight glass, a venting opening, a level indicator a pressure sensor or a different utility device 19. In the wall 16, an entry opening may be provided for an operator, an inspector or a cleaning crew..

The tank sections 12A, 12B, 12c are supported by a floor construction 22. The floor construction has a certain thickness and comprises beams which are mounted to one another and extend in different directions. Longitudinal beams and transverse beams are mounted to one another to form a rigid floor construction

The tank section 12A is connected to tank section 12B at a transition 13A. Here, the side wall 16 of the first tank section 12A and the side wall 16 of the second tank section 12B meet one another and are connected to one another. The walls 16 extend at an angle relative to one another at the transition, when seen in top view.

At transition 13A, a first portal 15A is provided. At transition 13B, a second portal 15B is provided. The portals 15A, 15B each comprise two vertical beams 22 and a horizontal beam 23. The vertical beams 22 extend parallel to the transition 13A. The horizontal beams 23 extend over the roof 18 of the cargo tank 10 from one side to another side.

The portals are mounted to the floor 20 of the cargo tank. The portals 15A, 15b are also mounted to the transitions 13A, 13b over the height of the side wall 16.

Horizontal supports 67 are provided which are constructed to support outer side walls 66, see figure 7.

Turning to figure 2 a front view of the cargo tank 10 is shown. The floor construction has a minimum height 26 at one end and a maximum height 27 at another end.

The height 28 of the side wall 16 thus varies over the length of the cargo tank 10. The side wall 16 has a maximum on the left side in figure 2 and a minimum on the right side in figure 2. The floor 21 is inclined over an angle a. A combined discharge/filling opening 30 is provided at the left side of the cargo tank 10.

The height of the portals 15 does not exceed the height of the roof 18.

Turning to figure 3, it is shown that the portals 15B stay within a box-shaped perimeter 34 define by the width and height of the cargo tank 10. The box perimeter is shown in dashed lines. Figure 3 shows the side of the cargo tank where the floor has the maximum height 27. It can be seen that the portals 15 extend around the constricted transition 13.

Turning to figure 4, the cargo tank is shown in top view. It is visible that the tank sections are part of a circle. The left and right tank sections 12A, 12B have a more complete form of a circle and are cut-off only on one side. The middle tank section 13B is a circle part which is cut-off at the left and right side.

Support members 25 are mounted near the floor 21 between the floor 21 and the vertical beams 22, to stiffen the connection between the portals 15 and the floor 21. The support members 25 may have a triangular form.

The floor construction 20 may have recesses 40 in the four corners. In these locations, structural strength is not really required. The recesses 40 create a space to fit equipment like coolers, heaters, pumps, pipes and valves etc.. The width 44 of the cargo tank 10 at the constricted transition 13 is about 80 percent of the maximum width (or diameter) 45 of the cargo tank 10. Some variation between 72 and 88 percent may occur. The centers of the sections 18 are positioned at a distance 47 from one another, see figure 4.

For circular tank walls 16, the mathematical relation between the distance between the tank part vertical centerlines, diameter and width 44 is : width 44 = ((diameter 45)² - (distance centers 47)²)^{0 5} ).

The number of middle section 12B may be increased in order to increase the length 50 of the cargo tank without increasing the width 52.

Turning to figures 5 and 6, the underside of the floor construction 20 is shown. A bottom plate 22 is provided on which the cargo tank 10 rests on the underground.

Longitudinal beams 60 extend longitudinally, transversal beams 62 extend transversally. A transversal beam 62A, 62B is provided at each constricted transition 13A, 13B. The transversal beams 62A, 62B are firmly connected to a respective portal 15A, 15B.

Smaller beams 64 extend across the floor 21 .

Turning to figure 7, the cargo tank 10 is shown with outer side walls 66 which allow the cargo tank to be deployed as a container-type cargo tank. The side walls 66 also provide protection.

Turning to Figures 8A and 8B, the transition 13A is shown in more detail. The beam 22 is connected to the side walls via intermediate members 58. Other kinds of connections are also possible. The side wall 16 of tank section 12A and the side wall 16 of tank section 12B are welded directly to one another. The intermediate member 58 is welded onto the outer side of the transition and the vertical beam 22 is welded to the intermediate plate 58. The forces 80, 81 of the side walls even out in the longitudinal direction of the cargo tank, but add up in the transverse direction. The force 82 exerted by the vertical beam

compensates for this and maintains equilibrium.

Operation

When the cargo tank 10 is filled with a liquid, the forces of the liquid bring the side wall 16 under tension. The side wall 16 remains substantially free of bending moments. The tension forces of the side walls meet in the transitions 13A, 13B. Generally, the transitions 13A, 13B will be weld connections.

Here, the portals 15A, 15B exert an inward force on the transitions 13A, 13B, such that the shape of the cargo tank remains the same.

Because there is no inner partition wall 8 like the one shown in figures 3, 4 of

EP0658494, there is no inner construction to provide form stability to the cargo tank 10. Instead, the external portals 15A, 15B provide form stability and rigidity from the outside. This allows a simpler inner form of the cargo tank 10. The forces of the side walls 16 are transferred into the side beams 22 wherein they are converted into bending moments. The bending moments are transferred into the upper beam 23 and into the floor 20 of the cargo tank, in particular into lateral beams 62A, 62B. Thus, a construction is obtained which is less optimal in terms of forces, i.e. more bending moments are created than in the tank of EP0658494. However, this disadvantage results in a simpler inner form. This results in easier emptying and cleaning of the cargo tank, which is a considerable advantage in the transport of many liquids for consumption, such as fruit juices.

Furthermore, the portals 15 allow the tank to have a considerable size in

combination with an acceptable weight, which is required for ships.

Because there may be three, four, five six or more tank sections 12, the width/length ratio of the cargo tank 10 can be varied widely. This results in the possibility to convert most existing dry cargo ships into liquid cargo ships. Other liquids may also be transported. When the cargo tank 10 is emptied, the discharge opening 30 is opened. Due to the inclination of the floor and the simple inner form of the cargo tank, the emptying will go very easy.

It will be obvious to a person skilled in the art that the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention. The invention is limited only by the claims.

Claims

1 . Cargo tank for holding a liquid, the cargo tank comprising at least:

• a first tank section,

• a second tank section, and

• a third tank section,

which together define a tank volume, wherein each tank section is defined by a curved tank wall which is curved in such a way that the tank wall is substantially free of bending moments when the cargo tank is filled with a liquid, wherein the cargo tank comprises at least a first and a second constricted transition, wherein in the first constricted transition the tank wall of the first tank section meets the tank wall of the second tank section and wherein in the second constricted transition the tank wall of the second tank section meets the tank wall of the third tank section.

2. Cargo tank according to claim 1 , an inner tank volume being substantially free from any constructional elements which span the cross-section of the cargo tank at the first and second restricted transition.

3. Cargo tank of claim 1 or 2, wherein the first, second and third tank sections have the form of a part of a circle, when seen in top view.

4. Cargo tank of any of the previous claims, comprising a frame which is externally mounted to the tank sections, the frame comprising at least a first and a second portal which extend substantially around the cargo tank and are positioned respectively at the first and second constricted transition in order to provide rigidity to the cargo tank at the first and second restricted transition when the cargo tank is filled.

5. Cargo tank according to any of the previous claims, wherein the first and second portals have a substantially inverted staple shape or a substantially square-shape or a substantially rectangular shape.

6. Cargo tank according to any of the previous claims, wherein an outer perimeter of the first and second portals - when seen in side view - does not extend substantially beyond a box-shaped perimeter defined by the width and height of the tank sections, such that the width and height of the cargo tank are determined by the tank sections and not by the portals.

7. Cargo tank according to any of the previous claims, wherein the cargo tank is elongate when seen in top view, in particular having a length:width ratio of more than 2:1 .

8. Cargo tank according to any of the previous claims, wherein a discharge opening is positioned at one end of the cargo tank, and wherein the floor of the cargo tank is substantially straight and is inclined in the direction of the discharge opening.

9. Cargo tank according to any of the previous claims, wherein the cargo tank

comprises a floor construction with a substantial form rigidity, the constructional form comprising longitudinal beams and transversal beams which are mounted together, wherein the floor construction supports the tank wall, and wherein the first and second portals are mounted to the floor construction at their lower ends

10. Cargo tank according to any of the previous claims, wherein the floor construction has a varying height which has a minimum at one end of the elongate cargo tank and has a maximum height at another end of the elongate cargo tank.

1 1 . Cargo tank according to any of the previous claims, wherein the floor construction comprises at least one transverse beam at each of the first and second transition zone, wherein each transverse beam is connected with the lower ends of the first and second portals.

12. Cargo tank according to any of the previous claims, comprising 3, 4, 5, 6, 7, 8, 9 or 10 or more bulbous tank sections connected to one another at respective constricted transitions.

13. Cargo tank according to any of the previous claims, comprising straight outer side walls and a straight outer roof wall which are provided on the outside of the tank sections, thereby providing the cargo tank with a substantially rectangular shape when viewed in side view and in top view, such that the form is suitable to be used as a container of standard dimensions in container shipping, such as 1 TEU,

2 TEU, 3 TEU.

14. Cargo tank according to any of the previous claims, wherein the first second and third tank section have a diameter, and wherein the constricted transition has a length, and wherein the diameter of the tank sections is at most 20% greater than the length of the constricted transition.

15. Method of converting a non-liquid carrying cargo vessel into a liquid carrying cargo vessel, the method comprising inserting at least one cargo tank of claim 1 into a cargo compartment of the vessel.

16. Vessel comprising at least one cargo tank of claim 1 .