WO2012070933A2

WO2012070933A2 - Inflatable element for use interiorly in a holder

Info

Publication number: WO2012070933A2
Application number: PCT/NL2011/000077
Authority: WO
Inventors: Erik Jeroen Eenkhoorn
Original assignee: Erik Jeroen Eenkhoorn
Priority date: 2010-11-26
Filing date: 2011-11-24
Publication date: 2012-05-31
Also published as: JP2013543824A; WO2012070933A3; EP2643205A2; TWI573746B; CN103354792A; JP5863820B2; TW201228904A; KR101846600B1; KR20140002679A; EP2643205B1; CN103354792B; NL1038409C2

Abstract

The invention relates to an inflatable element for use as a damper of fluid oscillations interiorly in a holder (2) with a holder bottom wall, a holder upper wall (31) and holder sidewalls (9', 9", 10', 10"), which holder is suitable for transporting a liquefied gas with its vapour, such as liquefied natural gas or LNG; the element wall (5) comprises an element bottom wall (7), an upper wall (8) and sidewalls (13), which element in the use position floats with its bottom wall (7) on the liquid load (3) and wherein the inflatable element (4) has a thickness (d) smaller than the height between the liquid surface and the upper side wall (31) of the holder and wherein openings ( 11) are provided which extent from the element bottom wall (7) to the element upper wall (8) constituting open fluid connections.

Description

TITLE. Inflatable element for use interiorly in a holder.

The invention relates to an inflatable element for use as a damper of fluid oscillations interiorly in a holder;

the holder is a closed space, suitable for storing a liquid load, in particular the holder is suitable for transporting a liquefied gas with its vapour, such as liquefied natural gas or LNG;

the closed holder is provided with a holder bottom wall, a holder upper wall and holder sidewalls;

the inflatable element comprises an element wall, which defines a closed interior space with a fixed volume for inclusion of an inflating gas, the element wall comprises a element bottom wall, an element upper wall and element sidewalls;

in the use position the inflatable element floats with its element bottom wall on the free liquid surface of the liquid load.

It is known that the cargo in transportable tanks (tank lorries) and road trucks due to various causes, e.g. by accelerating or speeding up or by braking or decelerating, by high speed in bends; or by swerving caused by (near) collisions, may exhibit an undesired dynamical behaviour which even may result in turning over of the vehicle. This effect is for a major part dependant upon the type of cargo contained in the storage tank, the truck or the tanker. For example free movable (low viscous) liquid will easily be brought into motion when subjected to a sudden manoeuvre of the tanker. De back and forth moving or sloshing of the liquid may supply an additional impulse force thereby accelerating turning over of the tanker or truck. Due to statutory regulations in order to prevent sloshing or oscillating of the liquid in the axial longitudinal or driving direction of the tank, baffle plates are mounted inside holders having a volume above a certain limit. These baffle plates have the disadvantage that they only damp axial liquid movements so that non-axial movement of the liquid, like radial or tangential movement, will not be damped or only to a small extend. Furthermore these plates have their own mass and volume, thereby decreasing the capacity of the holder. Moreover these plates are usually fixedly mounted inside the interior of the holder, so that labour-intensive interiorly mounting, inspection, repair en cleaning will be necessary. Furthermore the fixedly mounted plates inside the holder will transmit a portion of the impulse force and the energy of the oscillating liquid to the holder and the holder wall.

In tanker ships for transport by water and/or for storage of liquids and gases at sea also swinging and sloshing of the liquid may occur due to the swell of the water and bobbing of the ship on the water. Gas tankers such as LNG tankers or carriers (LNG, Liquefied Natural Gas) generally contain two or more holders in which gas, cooled to liquid at a temperature of about minus 162 °C at atmospheric pressure, is stored and/or transported . The holders can be of the type 'self supporting', usually in the form of a sphere or can be of the type 'membrane', directly supported by the hull of the ship. The self-supporting holders create a lot of empty, useless, spacing between the spheres, so the capacity of this vessel will be lower than that of the vessels of the 'membrane' type, which make better use of the available space in the hold. Self-supporting holders have a greater resistance to the forces exerted by the sloshing liquid and are therefore preferred for use as storage tanks at sea. For the type 'sphere' the gas is stored under pressure, resulting in the wall thickness of the 'spheres' being significant, which entails high costs and also a high weight.

For holders of type 'membrane' the gas to be transported is present at atmospheric pressure in the liquid form as well as in the vapour form . The fluid 'boils' as a result of the supplied energy due to heat conduction and also due to the energy absorbed in the liquid caused by the sloshing or swelling of the liquid cargo. The swinging or rocking of the liquid in the holders of the gas tanker depends on the swell of the water but also on the degree of loading of the gas tanker. When the degree of loading increases, the ship lies deeper into the water so that the natural frequencies and the vibration and swing frequencies of the ship and the cargo in the holders will change. In gas tankers also the effect occurs that the sloshing and rocking of the liquid will lead to energy absorption and thus to evaporation of liquid, requiring additional cooling or otherwise removing the excess energy. In the following, by the term (Liquified Natural Gas) LNG tanker a gas tanker is meant for storage and/or transportation of the liquefied gas.

These effects make it impossible to fully exploit the capacity of the container and reduce the filling rate in general to values between 10% and 75%. This results in operational constraints, particularly with LNG shuttle tankers operating in the spot market, which are not able to discharge or load the commercially desirable or operationally necessary quantities of gas, e.g. because it is impossible to moor to a buoy, due to the prevailing sea conditions, resulting in lost trade. Also in the exploitation of oil and gas fields by using for LNG tankers as floating storage near a borehole, a maximum capacity is desired at the greatest possible stability in waves or swell of the water. LNG tankers are also used for so-called Yegasification' where ambient heat is used to vaporize the liquid (natural) gas and to deliver the gas to the customers.

The liquid gas constitutes a liquid-vapour equilibrium in the holder depending on the temperature and the pressure. The pressure and temperature are selected such that under atmospheric conditions the gaseous product in the holder essentially is present as a boiling liquid. The free space above the liquid is therefore completely filled with vapour or gas of the product in liquid state.

From US 3, 120,902 inflatable elements are known which can be used as a floating roof or cover on open digester tanks filled with water. The roof of the digester tank is provided with a central tube of metal, which at the bottom side is open to the interior of the digester tank in order to collect biogas formed therein, and which at the top is fitted with a pressure relief valve and a downstream channel in order to continue processing of the collected digester gas in a gas combustion or other gas processing device. This roof is not suitable for insertion into an (existing) holder for liquefied gas in order to act as a damper for oscillations of the liquid gas during transport.

It is well known to provide the interior of a holder of a transport or storage device with an inflatable bag, airbag, buffer cushion or balloon and to pressurize it by means of an inflating gas, such as nitrogen or air, by using for example a compressor or inflating gas from a high pressure storage tank so that the balloon fills the majority of the free space of the holder, and thus limits the sloshing of the liquid and the formation of vapour. Preferably, this inflatable element creates a shape and/or force closed connection to the holder interior wall, whereby a good damping effect is obtained of movement or swinging motion of the fluid. A suitable embodiment constitutes an inflatable element which is provided with an accordion wall or otherwise stretchable or foldable wall or walls, which fold in and fold out or stretch and shrink, respectively, at the supply or discharge of inflating gas into the inflatable element. This type of inflatable element is not suitable for insertion into holders of LNG tankers because the liquid and the vapour must remain in contact in order to enable cooling and discharge of vapour.

Object of the invention is to provide an inflatable element that dampens and also greatly reduces swinging or sloshing of a fluid, such as liquefied gas, in a (transport) holder without necessarily the whole free space being filled with the inflatable element.

This objective is achieved by the invention by providing an inflatable element having a thickness which is smaller than the height between the free liquid surface and the holder upper wall of the holder and wherein the inflatable element is provided with openings which extent from the element bottom wall to the element upper wall, wherein the openings constitute open fluid connections between the liquefied gas and the vaporous gas. With the abovementioned measures the evaporating liquid may flow, by means of the fluid connections formed by the openings in the inflatable element, into the vapour space and the condensed gas may flow back to the liquefied gas, while swinging and sloshing of the liquid is dampened by the inflatable element upon the surface of the liquid.

In a preferred embodiment the inflatable element is provided with a friction flap or stabilizing body near a holder sidewall. Due to this feature the inflatable element obtains additional stability upon its edges, without creating additional resistance during displacement of the element caused by a change in the liquid level.

Preferably the inflatable element is provided with a friction flap or stabilizing body near four opposite holder sidewalls of the holder. In particular the stabilizing body is extending around the entire circumference edge of the inflatable element and constitutes a one-piece circumferential body. By attaching a friction flap for each of the four opposing holder sidewalls and providing an stabilizing body in one piece, the inflatable element can not easily move upward or downward along the holder sidewalls thereby providing the inflatable element with a stabilizing and dampening effect on oscillations of the liquid.

Preferably in the use position the element bottom wall is essentially flat and the element upper wall is arched, curved or multi-arched or curved. Thereby deformation of the inflatable element, caused by fluid motion in the holder, will be more difficult so that liquid oscillations are better damped.

The embodiment is preferred wherein the friction flap is an inflatable body or element comprising a closed internal space for inclusion of inflating gas. With these measures the amount of friction or resistance between the friction flap and the holder interior wall can be adjusted by making the friction flap thicker or wider in horizontal direction and/or by making the friction flap longer in the vertical direction thereby creating an enlarged friction surface between the friction flap and the holder interior wall.

In particular a connecting channel is provided between the interior space of the friction flap and the interior space of the inflatable element. This connecting channel will make the friction flap longer and thicker when the pressure in the interior space of the inflatable element is increased.

The embodiment is preferred wherein the connecting channel is an elongated slit, forming an open fluid connection between the inflatable element and the friction flap. As a result a good fluid connection is formed between the inflatable element and the friction flap so that the clamping force, exerted by the inflatable element on the upright walls of the holder, can be preserved while the stabilizing friction force between the friction flap and the holder walls is maintained.

In an alternative embodiment support elements are provided which extend from the element upper wall of the inflatable element to the holder upper wall of the holder.

In particular the support elements are inflatable elements, which can be adjusted in height by means of supplying or discharging of inflating gas.

These support elements keep the inflatable element in its position on the surface of the liquid so that damping of fluid oscillation will occur. Because the support elements can be extended out or shifted in, e.g. by supplying or discharging inflatable gas, the vertical position of the inflatable element can be adapted to the filling degree of the holder.

In a first alternative embodiment the friction flap is characterized by a substantially horizontal flexible flap, which is connected to an element sidewall of the inflatable element by means of a rotation or bending point.

Particularly the flexible flap is manufactured from a tough, elastic material such as rubber or plastic material. With this embodiment it is possible to provide for a closure, between the inflatable element and the holder walls, that can easily move along the projecting parts of the holder wall like wall bends/twists or wall tongues interiorly in a gas tanker of the type 'membrane'.

A second alternative embodiment of the friction flap is characterized, in that the friction flap is a flexible roll, which is rotatingly mounted around a rotation axis on an element sidewall of the inflatable element.

In particular the flexible roll is manufactured from a flexible and compressible material such as a sponge-like material and/or fibrous material such as hair. The roller rotates about its axis while projecting parts of the wall, like wall bends/twists or tongues, will press the material of the roll together so that moving upwards and downwards of the inflatable element proceeds easily, without causing damage to the wall and/or to the inflatable element.

The invention also relates to a transport or storage device comprising a container with inflatable element.

The invention is further explained by means of a drawing and some embodiments of the inflatable element, whereby features and other advantages will come forward. Fig. 1 is a perspective view of an LNG tanker with a few holders for liquefied gas;

Fig. 2 shows greater detail of a holder of Fig. l, with an inflatable element;

Fig. 3 shows in top view the holder provided with inflatable elements having openings; Fig.4 shows greater detail of a friction flap near a holder sidewall;

Fig.5A shows in side view an alternative embodiment of the inflatable element provided with support elements;

Fig.5B shows a perspective view of the support elements of Fig.5A;

Fig.5C shows a top view of the embodiment of Fig.5A;

Fig6A, 6B, 6C show an alternative embodiment of the friction flap;

Fig.7 shows a roll flap, a second alternative embodiment of the friction flap.

Fig . l shows a transport or storage device with a few holders 2. The transport device in this example is a gas tanker 1, which is provided with eight holders 2 or tanks which are equipped for transporting a liquid load 3; in this example in particular for a liquefied gas such as LNG (Liquefied Natural Gas). A gas tanker suitable for transporting liquefied gas is hereinafter referred to as a LNG tanker. The LNG tanker is provided with means and facilities in order to keep the gas liquefied by maintaining the correct temperature and pressure.

In Fig.2 the holder 2 is shown in more detail. The holder 2 forms a closed space for storing and optionally for transporting a liquefied gas with its vapour; like natural gas or LNG for example. The closed holder has a holder bottom wall, a holder upper wall 31 and holder sidewalls 9', 9", 10', 10". The holder 2 is filled with liquefied gas 3 for about three quarters, so that the liquid top surface approximately is located at three- quarters height of the holder 2. On top of the liquid 3 floats the inflatable element or airbag 4, having an element wall 5, which defines an enclosed interior space 6; the element wall 5 being formed by a flat element bottom wall 7, a multi-curved element upper wall 8 and element sidewalls 13. Friction flaps 20', 20" are provided upon the element sidewalls 13, which provide for a close connection with the holder sidewalls 9', 9", 10', 10" of the holder 2. The inflatable element 4 has a thickness d, which is smaller than the height between the free liquid surface and the holder upper wall 31 of the holder 2; so that the inflatable element 4 only occupies a small portion of the vapour space of the holder. The inflatable element 4 is connected to inflating aid means (not shown) such as an air compressor and a control unit, by which inflating gas, such as air or another gaseous product, can be fed in and out of the inflatable element 4. Also control means, such as control lights, are provided in a control room or area of the gas tanker. The inflatable element 4 of Fig.2 is provided with openings 11 which extend from the element bottom wall 7 to the element upper wall 8. The openings 11 thereby constitute open fluid connections between the liquefied gas and the vaporous gas. The vapour phase is in open contact, through these openings 11, with the liquid phase so that the vaporized liquid can evade through the inflatable element 4 or the condensing vapour can flow back to the liquid. In such holders 2 with liquefied gas, at a temperature much lower than the ambient temperature, energy is lost by heat conduction into the holder 2 and also by absorption of energy in the form of heat as a result of the swinging and sloshing of the liquid the holder. The stabilization of the fluid and the dampening of liquid oscillations limit the flow of energy to the holder 2 and saves energy.

In top view in the holder 2 in Fig.3 is shown the inflatable element 4 with openings 11 provided. The number of openings 11 may vary in number and in size, in general terms can be stated that a regular distribution of these openings 11 on the element top wall 8 is advantageous.

In Fig.4, section IV-IV of Figure 3, a detail is shown of the inflatable element 4 and the wall element 5, in this embodiment formed by element top wall 8 and element bottom wall 7. Some parts of the element wall 5 may be provided with a reinforcing element such as a textile fibre network or carrier. The element bottom wall 7 is preferably provided with a reinforcement to prevent distortion and to maintain a flat surface, which is advantageous for damping the oscillations of the liquid 3. In order to provide the element upper wall 8 of the inflatable element 4 with regular, longitudinally extending, curved surfaces, the inflatable element is provided with connecting parts 12 between the element upper wall 8 and the element bottom wall 7. The inflatable element 4 has a thickness d, which is smaller than the distance between the liquid surface and the holder upper wall 31 of the holder 2. In Fig.4 is furthermore shown the friction valve 20" implemented as an inflatable body with an interior space 21. With its friction walls 23, the friction flap 20" extends parallel to the holder sidewall 10". The friction wall 23 is in contact with the interior side 19 of the holder sidewall 10" and is preferably clamped against it. This creates friction force between the holder sidewall and the friction flap 20" and the inflatable element 4 attached to friction flap 20", so that the inflatable element 4 acts as a damper of liquid oscillations because it is stabilized located on the liquid's surface and thereby hampering the emergence of oscillations of the liquid and dampening liquid oscillations. Friction flaps can be mounted on one, two or all four element sidewalls of the inflatable element 4 or can be configured as a body extending around the entire circumferential edge of the inflatable element 4. The amount of resistance between the holder sidewall and the friction flap can be adjusted by adjusting the amount of air into the interior space 21 of the friction flap.

The friction flap 20', 20" can be provided with separate inflating means or by a control system. Advantageously the interior space 21 of the friction flap may be in open communication with the interior space 6 of the inflatable element 4 so that by inflating or deflating the inflatable element the friction on the walls of the holder 2 can be varied simultaneously. Thereby the connecting channels 22 can be provided between the interior space 6 of the inflatable element 4 and the interior space 21 of the friction flap 20', 20". In a special embodiment, the connecting channels 22 are shaped as elongated slits, which are extending horizontally to a large extend between the inflatable element 4 and the friction flap 20', 20". The friction flap 20', 20" is sometimes referred to as lid or wing.

Because the inflatable element 4 floats on the liquid surface of the liquid load 3 - but not entirely fills the vapour space - the inflatable element 4 will act as a damper of fluid oscillations and have an inhibiting or slowing effect upon the formation of fluid oscillation and also have a dampening effect on the swinging or sloshing motion of the liquid 3 in the holder 2. This dampening effect can even be increased by further inflating the inflatable element 4 so that the friction flap 20' will be unfolded to such an extend that it will make contact with the interior side 19 of the holder sidewall 10" of the holder 2. In this inflated position the interior space 21 of the friction flap 20' will also be completely filled with inflating air, so that friction will occur between the holder sidewall 10" and the friction flap 20', so that the inflatable element has a strong dampening effect on fluid oscillations in the holder 2.

In the alternative embodiment of Fig. 5A, 5B, 5C the friction flaps 20', 20" of the inflatable element 4', still provided with a thickness d and through-openings 11, are replaced by a support elements 30, which extend from the element upper wall 8 of the inflatable element 4 to the holder upper wall 31 of the holder 2. These support elements 30 also keep the inflatable element 4' in position on the surface of the liquid 3 so that also damping of fluid oscillation will occur. The support elements 30 are preferably extendable and retractable so that the vertical position of the inflatable element 4 can be adapted to the degree of filling of the holder 2. The support elements 30 are therefore preferably provided with a separate system for the control and supply and discharge of inflating air. The support elements may include an accordion wall for easily extending and retracting of the support elements 30.

In Fig.6A, 6B, 6C, a first alternative embodiment of the friction flap is shown, which is suitable to be applied in holders 2 of the type 'membrane'. This holder 2 has a thin membrane wall 45. These membrane walls 45 are provided with bends 46 or with an accordion structure or sometimes also with projecting tongues of overlapping membrane, allowing for compensation of the expansion and contraction of the wall material due to the large differences in temperature. These projecting bends or tongues 46 are disadvantageous for the operation of the inflatable element according to the invention. Therefore, the inflatable element 4" in this embodiment is provided with a flexible flap 40, which by means of a pivot 41 is arranged to an element sidewall 13 of the inflatable element 4.

In Fig.6A the inflatable element 4" and the flexible flap 40 is moving downwards upon the liquid surface in the holder 2. In Fig.6B is shown that the flexible flap 40 abuts against the upper side of the wall bend 46 and is slightly tilted about the pivot point 41, relative to the inflatable element 4".

In Fig.6C the flexible flap 40 of the, having moved upwards, inflatable element 4" is tilted so far downwards about the pivot point 41, relative to the element sidewall 13 of the inflatable element 4, that the flexible flap 40 moves along and over the wall bend 46. The flexible flap 40 provides for a good seal with the membrane wall 45 of the holder, during the upward and downward movement of the inflatable element, and also provides for a clamping position of the inflatable element 4 which prevents sloshing and provides for dampening of the liquid.

In a second alternative embodiment of the friction flap in Fig. 7 a flexible roll 50 is applied, which is rotatingly about rotation axis 51 attached to the element sidewall 13 of the inflatable element 4"'. The rotation axis is in a known manner, such as by means of braces or similar, connected to the inflatable element 4"'. The flexible role or roll flap 50 is manufactured from a flexible, compressible, material such as spongy material or loose fibres such as hair. This allows for the roll flap 50 to easily pass obstacles projecting from the membrane wall 45, because the material of the roll is pressed together at the location of the obstacle, such as a wall bend or tongue 46. The flexibility of the material of the flexible roll 50 can be easily adapted to the mechanical strength of the membrane wall 45 or to the membrane mounted thereon or to the need to exert a clamping force by the inflatable element in order to prevent the sloshing of liquid or to dampen swinging of the fluid. The inflatable element 4, 4 ', 4', 4'" may be a single large interior space with thickness d or may be divided into compartments such as portion elements mounted in the longitudinal direction of the holder.

The inflatable element can be loosely inserted in the holder or can be fixedly attached to the holder; but preferably the element is arranged within the holder such, that a small force is exerted on the holder sidewalls of the holder.

The inflatable element can be manufactured from any suitable material such as plastic or fabric.

Claims

Inflatable element for use as a damper of fluid oscillations interiorly in a holder (2);

the holder is a closed space, suitable for storing a liquid load (3), in particular the holder is suitable for transporting a liquefied gas with its vapour, such as liquefied natural gas or LNG;

the closed holder is provided with a holder bottom wall, a holder upper wall (31) and holder sidewalls (9', 9", 10', 10");

the inflatable element (4) comprises an element wall (5), which defines a closed interior space (6) with a fixed volume for inclusion of an inflating gas, the element wall (5) comprises an element bottom wall (7), an element upper wall (8) and element sidewalls (13);

in the use position the inflatable element floats with its element bottom wall (7) on the free liquid surface of the liquid load (3);

characterized, in that the inflatable element (4) has a thickness (d) which is smaller than the height between the free liquid surface and the holder upper wall (31) of the holder and wherein the inflatable element (4) is provided with openings (11) which extent from the element bottom wall (7) to the element upper wall (8), wherein the openings (11) constitute open fluid connections between the liquefied gas and the vaporous gas.

Inflatable element according to claim 1, characterized in that the inflatable element (4) is provided with a friction flap or stabilizing body (20', 20") near a holder sidewall (9', 10').

Inflatable element according to claim 2, characterized in that the inflatable element (4) is provided with a friction flap or stabilizing body (20', 20") near four opposite holder sidewalls (9', 9", 10', 10") of the holder (2).

Inflatable element according to claim 3, characterized in that the stabilizing body (20', 20") is extending around the entire circumference edge of the inflatable element (4) and constitutes a one-piece circumferential body.

5. Inflatable element according to any one of the preceding claims 1 - 4, characterized in that in the use position the element bottom wall (7) is essentially flat and the element upper wall (8) is arched, curved or multi-arched or curved.

6. Inflatable element according to any one of the preceding claims 2 - 4, characterized in that the friction flap (20', 20") is an inflatable body or element comprising a closed internal space (21) for inclusion of inflating gas.

7. Inflatable element according to claim 6, characterized in that a connecting channel (22) is provided between the interior space (21) of the friction flap (20', 20") and the interior space (6) of the inflatable element (4).

8. Inflatable element according to claim 7, characterized in that the connecting channel (22) is an elongated slit, forming an open fluid connection between the inflatable element (4) and the friction flap (20', 20").

9. Inflatable element according to claim 1, characterized in that support elements (30) are provided which extend from the element upper wall (8) of the inflatable element (4') to the holder upper wall (31) of the holder (2).

10. Inflatable element according to claim 9, characterized in that the support elements (30) are inflatable elements which can be adjusted in height by means of supplying or discharging of inflatable gas.

11. Inflatable element according to claim 2, characterized in that the friction flap is a substantially horizontal flexible flap (40), which by means of a rotation or bending point (41) is connected to an element sidewall (13) of the inflatable element (4").

12. Inflatable element according to claim 11, characterized in that the flexible flap (40) is manufactured from a tough, elastic material such as rubber or plastic material.

13. Inflatable element according to claim 2, characterized in that the friction flap is a flexible roll (50), which is rotatingly mounted around a rotation axis (51) on an element sidewall (13) of the inflatable element (4'").

14. Inflatable element according to claim 13, characterized in that the flexible roll (50) is manufactured from a flexible and compressible material such as a spongelike material and/or fibrous material such as hair.

15. Transport or storage device (1) comprising a container (2) with inflatable element (4, 4', 4", 4'") according to any one of claims 1 - 14.