EP2788672A1

EP2788672A1 - Pressure vessels in ships

Info

Publication number: EP2788672A1
Application number: EP11793754.0A
Authority: EP
Inventors: Francesco Nettis; Darrell HAWKINS; Christian LENA; Gianfranco NISO; Vanni Neri TOMASELLI; Giorgio VIGNA
Original assignee: Blue Wave Co SA
Current assignee: Blue Wave Co SA
Priority date: 2011-12-05
Filing date: 2011-12-05
Publication date: 2014-10-15
Also published as: CN104105920A; WO2013083150A1

Abstract

A ship comprising a plurality of pressure vessels, there being a first set of pressure vessels of a first length, a second set of pressure vessels of a second length, and a third set of pressure vessels of a third length, the first, second and third lengths differing from one another. The vessels are typically arranged vertically, and the ship can be a multi-hull ship.

Description

PRESSURE VESSELS IN SHIPS

The present invention relates to pressure vessels mounted within a ship, and in particular arrangements for mounting numerous such vessels in a ship so as to maximise cargo volumes, cargo masses, and ship performance at sea, including speed and stability. In particular the pressure vessels are for transporting CNG, whereby the ships are CNG transportation ships.

The detrimental effects of the burning of fossil fuels on the environment are becoming more and more of a concern and have spurred great interest in alternative energy sources. While progress is being made with solar, wind, nuclear, geothermal, and other energy sources, it is quite clear that the widespread availability of economical alternate energy sources, in particular for high energy use applications, remains an elusive target. In the meantime, fossil fuels are forecast to dominate the energy market for the foreseeable future.

Among the fossil fuels, natural gas is the cleanest burning and therefore the clear choice for energy production. There is, therefore, a movement afoot to supplement or supplant, as much as possible, other fossil fuels such as coal and petroleum with natural gas as the world becomes more conscious of the environmental repercussions of burning fossil fuels. Unfortunately, much of world's natural gas deposits exist in remote, difficult to access regions of the planet. Terrain and geopolitical factors render it extremely difficult to reliably and economically extract the natural gas from these regions.

The use of pipelines and overland transport has been evaluated, in some instances attempted, and found to be uneconomical. Interestingly, however, a large portion of the earth's remote natural gas reserves is located in relatively close proximity to the oceans and other bodies of water having ready access to the oceans. Thus, marine transport of natural gas from the remote locations would appear to be an obvious solution. The problem with marine transport of natural gas lies largely in the economics. Ocean-going vessels can carry just so much laden weight, and are typically relatively slow. The current cost of shipping natural gas by sea reflects this fact, the cost being calculated on the total weight being shipped, that is, the weight of the product plus the weight of the container vessel in which the product is being shipped, plus delivery times, or numbers of ships required.

If the net weight of the product is low compared to the tare weight of the shipping container, the cost of shipping per unit mass of product becomes prohibitive since a large amount of the shipped weight is efficiency wastage. This is particularly true of the transport of compressed fluid, e.g. CNG, the weight of which might be less than the weight of the pressure vessel containing it, especially when transported in the conventional Type I steel pressure vessels (cylinders).

This problem has been ameliorated somewhat by the advent of Type II, Type III and Type IV pressure vessels. Type II vessels comprise a thinner metal cylindrical center section, but with standard thickness metal end domes in which only the cylindrical portion is reinforced with a composite wrap. The composite wrap generally constitutes glass or carbon filament impregnated with a polymer matrix. The composite is usually "hoop wrapped" around the middle of the vessel. The domes at one or both ends of the vessel are not composite wrapped. In Class II pressure vessels, the metal liner withstands about 50% of the stress and the composite withstands about 50% of the stress resulting from the internal pressure of the contained compressed fluid. Class II vessels are lighter than Class I vessels but are more expensive. Type III vessels comprise a thin metal liner that is reinforced with a filamentous composite wrap (around the entire vessel). The stress in Type III vessels is shifted virtually entirely to the filamentous material of the composite wrap; the liner need only withstand a small portion of the stress. Type III vessels are much lighter than type I or II vessels but are again substantially more expensive. Type IV vessels comprises a polymeric, essentially gas-tight, liner that is fully wrapped with a filamentous composite. The composite wrap provides the entire strength of the vessel. Type IV vessels are by far the lightest of the four approved classes of pressure vessels but are also the most expensive. Indeed, the use of Type III and Type IV vessels, coupled with the trend to make these vessels very large - cylindrical vessels 18 meters in length and 2.5 or 3.0 meters in diameter are currently being fabricated and vessels that are 30 or more meters in length and 6 or more meters in diameter are contemplated - has resulted in a major step forward in optimizing the economics of ocean transport of compressed fluids. Nevertheless, the efficiency with which these pressure vessels get be used on a ship could be improved. Additionally, the manufacture of even lighter pressure vessels, in terms of the ratio between the weight of the vessel and the weight of the fluid contained therein, would be of benefit. According to the present invention there is provided a ship comprising a plurality of pressure vessels, there being a first set of pressure vessels of a first length, a second set of pressure vessels of a second length, and a third set of pressure vessels of a third length, the first, second and third lengths differing from one another. In preferred arrangements, the difference is at least 15cm or at least 30cm or at least 1 % of the length of the longest pressure vessel.

Differences as a result of usual allowable manufacturing tolerances, or tank expansion characteristics between when the vessels are either filled or empty, are not considered to be "differences in length" for the purpose of this invention.

Typically a ship of the prior art would have a uniform pressure vessel length, or perhaps a set of two different pressure vessel lengths, for allowing the manufacture of the pressure vessels to be standardised. This keeps the design costs for the vessels to a minimum. However, by providing vessels of different lengths, loading efficiencies within the ship can be improved, as discussed below.

Preferably at least one of the sets of pressure vessels are arranged in an array. Mounting the sets of pressure vessels in arrays allows regular spacings to be provided between pressure vessels. This is important to meet safety regulations.

According to a second aspect of the present invention there is provided a ship comprising a plurality of pressure vessels, there being a first set of pressure vessels of a first length and a second set of pressure vessels pressure vessels of a second length, the first and second lengths differing from one another, and wherein the ship is a multi-hull ship, with the longer of the vessels being arranged to extend within the deeper parts of the hull, and the shorter of the vessels being arranged to extend within the less deep parts of the hull. With this arrangement, space is not lost at the foot of each hull of the multi-hull ship. Again in preferred arrangements, the difference is at least 15cm or at least 30cm or at least 1 % of the length of the longest pressure vessel, and differences as a result of usual allowable manufacturing tolerances, or tank expansion characteristics between when the vessels are either filled or empty, are not considered to be "differences in length" for the purpose of this invention.

A third set of pressure vessels of a third length, differing from the first and second lengths by at least 30cm, can also be provided, for example for arranging in side areas of the hulls, or at the fore or aft areas of the hulls.

By providing pressure vessels of different lengths, a greater extent of the space available within the single or multi hulls can be utilised.

Bear in mind too that where the cargo is CNG - the preferred cargo, the weight of that CNG is such that the ship is unlikely to be overloaded thereby - the density of CNG at transportation pressures and temperatures, say 200 to 275bar, and 10-30°C, for example, is perhaps a quarter to a fifth of that of water, and perhaps half to a third of that of LNG. As a result, there can be plenty of buoyancy capacity within a ship to accommodate pressure vessels over a greater extent (width and length) and depth of the ship, especially compared to when loading a ship with LNG (liquefied natural gas).

CNG is a form of natural gas, typically a raw natural gas, whereby it can be stored and transported, while in that compressed state (potentially at pressures of between 200 and 300 bar at room temperature (20°C), i.e. typically at around 250 bar), within a volume that occupies a very small fraction of the volume it would occupy as a gas at atmospheric pressure. Typically the volume reduction is about 99%, i.e. it occupies perhaps only 1 % or less of the volume it would occupy as a gas at atmospheric pressure. The transportation of CNG by using pressure vessels is therefore a commercially viable option. The ships are therefore preferably CNG transportation ships.

By the use of multiple different lengths of pressure vessel, it is also possible to optimise the distribution of the cargo around the ship. Preferably the pressure vessels are arranged vertically on the ship. With this arrangement, the pressure vessels can be arranged with their tops all level - to facilitate the design of any pipework arranged above the vessels - even though the bottoms of the vessels may be arranged at different levels. Alternatively, the tops can be arranged to define different levels. This could be used to control the location of the centre of mass of the ship. For example, shorter vessels may be arranged towards the sides and/or ends of the ship, with longer pressure vessels being arranged towards the middle of the ship. This can keep a centralised core of the cargo near the centreline of the ship, which can assist with ship stability. This can also optimize the vertical position of the centre of mass of the ship, reaching a compromise between the ship stability and the maximum exploitation of spaces. Likewise it can be used keep the centre of mass close to the longitudinal centre of the ship, again to assist with ship stability. In particular, if the ship's essential engineering structure, including items such as engine rooms, accommodation quarters and the like, are arranged towards the rear of the ship, the rear imbalance can be balanced out by the provision of longer pressure vessels towards the front of the ship. Alternatively, and according to the ship design concept, the longer pressure vessels can be arranged towards the rear of the ship in order to guarantee a good visibility for the ship master and to maximize the total gas capacity of the ship. In this case, the shorter pressure vessels can be arranged towards the front of the ship.

Preferably the pressure vessels are Type II, Type III or Type IV pressure vessels, or other forms of pressure vessel comprising a composite structure, rather than an all steel or all metal structure. Such composite pressure vessels are lighter per m³ of storage space therein.

Preferably the pressure vessels are made out of corrosion-resistant materials in contact with the cargo. Preferably they are able to carry a range of gases, such as natural gas (methane) with C0₂ allowances of up to 14% molar, and/or H₂S allowances of up to 1.5% molar, and also such as H₂ and/or C0₂ gases, without suffering from corrosion. The preferred use, however, is CNG transportation. CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄, C₇H₁₆, C₈H₁₈, C₉+ hydrocarbons, C0₂ and H₂S, plus potentially toluene, diesel and octane in a liquid state.

Preferably pressure vessels will also be able to accommodate "well-stream" fluids using direct loading from a well, which would most likely include condensed species and chemical compounds, so that they can be transported to a dedicated processing facility. This transportation of untreated gas may be called "the shuttle producer" concept.

A further advantage of composite pressure vessels in relation to the present invention, compared to all steel pressure vessels, is that whereas all steel pressure vessels are typically fabricated away from shipyards, and delivered to the shipyard for fitting to a ship, each steel pressure vessel being of a standard size to minimise design cost, and to facilitate such transportation (in terms of being of a size to fit on a train or a truck, and of a consistent size to allow the train or truck to be used for delivering numerous such pressure vessels, composite pressure vessels can be made larger, both in terms of their length and their diameter, whereupon such transportation can become impractical, and thus the composite pressure vessels are more typically manufactured at or nearby the shipyard. This then allows them to be made to custom sizes, or to a more numerous range of sizes, since the transportation thereof is less of an issue - they can be craned into position, or delivered on customised transport means that does not need to be accomodatable on roads or standard train tracks.

This thus means that the manufacture of numerous different lengths of pressure vessel is easy to achieve, without requiring extensive redesign costs of the infrastructure of the shipyard/transport network.

Additionally, the structure of composite pressure vessels often takes the form of a tubular member (cylinder section) with end caps, with the winding process being easily adapted to accommodate longer or shorter cylinder sections. For example, for Type III and IV pressure vessels, the use of a thin (substantially non-load sharing) liner allows the use of lighter and less complex manufacturing tools, such as moulds. These moulds usually have a cylindrical section constituted my modules, which can be added together, or disposed of/cut down, as required for meeting a desired pressure vessel length. Furthermore the filament winding technique then involved in Type III and IV pressure vessel production is significantly flexible - to manage different lengths, only the span of the fiber and resin dispenser has to change. As a result, the manufacture of multiple different lengths of pressure vessel is easily achievable, even to the point that the lengths can even be customised.

According to the present invention, it would therefore be desirable to provide a ship as defined above where at least some of the pressure vessels are of a custom length. Given the diameter of some of these vessels, even a 15cm change in length of a vessel can add a considerable amount of volume to a single vessel, and when multiplied by the number of vessels contained on a ship - e.g. 100 or more - the potential for additional stowage space for the cargo is considerable. For example, 15cm for a 2m (diameter) pressure vessel adds 0.47m³ of storage space just for that one vessel, and multiply that by 100 and you have an additional 47m³ of storage - the equivalent of an additional 15m long 2m pressure vessel.

Regarding the multi-hull ship, custom lengths would be particularly beneficial on such a ship, especially where arranged vertically, since the shape of the hull in a multi hull ship is tortuous, with troughs (the hulls) and at least one ridge (between the hulls). Custom pressure vessel lengths would thus allow such a hull to be very efficiently filled.

Such custom lengths would equally be beneficial in a mono-hull ship where the hull has steeply curving sides or ends.

The preferred use of the present invention, however, is in multi-hull ships, since traditionally multi hull ships were not loadable efficiently with cargo, often with just the hulls accommodating cargo, rather than the ridge or ridges too. The present invention can address that by allowing the full width and length of the ship to be used as cargo space, assuming that there is a useable space thereat. Finally, an advantage of the present invention in relation to multi hull vessels is that their faster transport speeds can be utilised more effectively since previously there was a limitation upon the available cargo space, but the present invention allows a greater utilisation of that cargo space while still allowing the faster performance of the multi-hull arrangement to be utilised. The present invention will now be described in further detail, purely by way of example, with reference to the accompanying drawings in which:

Figure 1 schematically shows a ship with a plurality of pressure vessels mounted vertically therein;

Figure 2 shows a cross section through the hull of the ship of Figure 1 ;

Figure 3 shows an alternative arrangement of pressure vessels on a ship;

Figure 4 shows a cross section through the ship of Figure 3; Figure 5 shows a cross section through a twin-hull ship; Figure 6 shows an alternative arrangement of pressure vessels within a twin-hull ship; Figure 7 shows an arrangement of pressure vessels in a tri-hull ship; Figure 8 shows an alternative arrangement of pressure vessels in a tri-hull ship;

Figure 9 shows schematically the pressure vessels arranged in containers;

Figures 10, 1 1 and 12 show further schematic details of the containers, and possible piping therefor; and

Figure 13 shows an enlarged view of the topside piping for fluid loading and offloading, including valved manifolds.

Referring first of all to Figure 1 there is shown a cargo ship fitted with a plurality of sets of pressure vessels, the sets being arranged vertically, in arrays across the width and length of the ship.

These vessels can be interconnected in groups so as to facilitate loading and offloading, and each set may comprise one or more groups of vessels. As illustrated there are five different sets of pressure vessels, each set being an array of pressure vessels, and each set having a different length.

A first set of pressure vessels with a first length - e.g. 20m is provided at the front of the ship. At the front of the ship, the hull tends to curve upwardly, so a full depth pressure vessel cannot be located towards the front of the ship without necessarily having its top raised high above the deck of the ship. Additionally, it is advantageous not to have a very heavy load arranged towards the front of the ship so a shorter vessel reduces the weight of the cargo (CNG) at the front of the ship.

Behind that first set of pressure vessels a second set of pressure vessels is located. This second set of pressure vessels is a set of longer pressure vessels - e.g. 25m.

Since the hull will now have a substantially constant depth, the pressure vessels can now extend closer to the bottom of the hull so as to maximise the cargo capacity of the hull. However, the height of those vessels is chosen such that the tops are level with the tops of the first set of pressure vessels. This can be because this area is still generally towards the front of the vessel, and an excessive weight there would still potentially be desirable. Further, by having a common top height the arrangement of vessel inspection scaffolds for accessing the tops of the pressure vessels is more easy to arrange.

Behind that second set of pressure vessels, there is then provided a third set of pressure vessels. This third set comprises full height pressure vessels - say 30m, and can offer a larger storage volume per vessel, yet still having a common footprint to the previous vessels. As a result, these vessels, when loaded, comprise a larger mass than those previous vessels. By arranging this mass towards the middle of the length of the ship, good ship stability is achievable. Such vessels may therefore extend along a substantial part of the ship for maximising the load capacity of the vessels. Further, these vessels can be arranged to extend well above the deck of the ship, again since the weight of CNG is relatively low, compared to water, whereby they can be tall without destabilising the ship. Vessels with a length of 60m would be possible, for example. Behind that third set of pressure vessels, two further sets of pressure vessels are provided, one having a fourth length and the fifth set having a fifth length. These sets of pressure vessels are even shorter than the first set, and are arranged such that they are wholly contained underneath the deck of the ship. They are arranged to occupy any available space around the engine room or other essential structures of the ship, such as the bridge.

Referring next to Figure 3, an alternative arrangement is shown. In this arrangement the fourth and fifth sets of pressure vessel are not present - often the design of the ship will not permit pressure vessels to be arranged in that aft section of the ship. Further, forward of that section, in place of the three sets of pressure vessels, only two are provided. As a result, all the bottoms are commonly arranged. This assists with the arrangement of the loading and offloading pipes - these CNG pressure vessels are typically loaded and offloaded with CNG via the bottom of the vessels. However, the arrangement of Figure 1 is also possible - different bottom levels for different sets of pressure vessels.

Referring next to Figure 2 - a cross section through these full length vessels - as can be seen, the tops and bottoms of these pressure vessels are all level across the width of the ship. This is achievable since many cargo ships have relatively flat hulls. Referring though to Figure 4, a non flat hull is shown, and in that embodiment the bottoms of the vessels are not all level across the width of the ship. Instead, there are two distinct lengths of pressure vessel - longer length ones towards the centreline of the ship, and shorter ones to the sides of the ship. This is to allow for the fact that the hull can taper or curl at the sides.

Still referring to Figure 4, it can also be seen that the tops of the vessels also are not all level. This is optional, but it can allow a concentration of the load of the cargo towards the centre line of the ship - shorter pressure vessels will be lighter, and putting the shorter pressure vessels along the sides can further concentrate the mass of the cargo into the middle and centre of the ship, thus further improving the ship's stability - the centre of gravity can be lower.

This arrangement of pressure vessels can be combined with the arrangement of Figure 2, wherein two different heights are provided along the longitudinal length of the ship - short vessels towards the front of the ship, and longer ones along the main central part of the ship, whereby four lengths of pressure vessel are actually provided - two long lengths towards the middle, and two shorter lengths towards the front. Obviously various other combinations including smaller groups or smaller sets can be fitted onto a given ship so as to maximise the containment volume of the ship. Further, the different sets of pressure vessels need not all have the same diameter.

Pressure vessels can also be manufactured at other lengths to those listed above. For example any required length of pressure vessel can be made as a custom-made pressure vessel, e.g. lengths of between 1 m and 80m, and more usually lengths of between 2 and 60m. As a result, pressure vessels can be custom designed and manufactured to have any desired length so as to best suit its desired position within a given hull design, or a given pressure vessel securement frame within that hull (e.g. for arranging the pressure vessels in appropriate groups, or in appropriate parts of the hull, as necessary with complex hull designs such as multi-hull ship designs). The pressure vessels can therefore be arranged to custom fit the shape of the hull, or to fit in any available position on a ship. Further, the heights van be varied to as to best distribute the mass of the cargo on the ship for optimum at-sea performance/stability, when the pressure vessels are fully laden with CNG.

Referring next to Figures 9 to 12, the pressure vessels 10 can be arranged in their arrays within modules or compartments 40 - in the illustrated embodiment a 4x7 array. Other array sizes are also to be anticipated, and can be chosen or designed to fit appropriately in the ship's hull in their chosen positions. A set might be a single array.

Preferably the distance between pressure vessel rows within the modules or compartments will be at least 380mm, or more preferably at least 600 mm, for external inspection-ability reasons, and to allow space for vessel expansion when loaded with the pressurised gas. For example, the vessels may expand by 2% or more in volume when loaded (and changes in the ambient temperature can also cause the vessel to change their volume). The amount of the change will vary according to the structural material used for their construction. For example, a 1 % volumetric expansion may occur if carbon fiber composites are used in the reinforcement, whereas, up to 2% volumetric expnasion may occur if glass fiber reinforcements for the composites are used).

Preferably the distance between the modules or compartments (or between the outer vessels 10A and the walls or boundaries 40A of the modules or compartments 40, or between adjacent outer vessels of neighbouring modules or compartments 40, such as where no physical wall separates neighbouring modules or compartments 40, will be at least 600mm, or more preferably at least 1 m, again for external inspection-ability reasons, and/or to allow for vessel expansion.

Each pressure vessel row (or column) in the array is interconnected with a piping system 60 intended for loading and offloading operations. The piping 60 is shown to be connected at the bottom of the vessels 10. It can be provided elsewhere, but the bottom is preferred.

In a preferred arrangement, the piping connects via a 12 inch (30cm) opening 7 at the bottom 12 of each vessel 10. The connection is to main headers, and preferably through motorized valves. The piping is schematically shown, by way of an example, in Fig. 10, Fig. 11 and Fig. 12.

The main headers can consist of three different pressure levels (high - e.g. 250bar, medium - e.g. 150bar, and low - e.g. 90bar), plus one blow down header and one nitrogen header for inert purposes. The vessels 10 are mounted vertically, such as on dedicated supports that hold the vessels in order to avoid horizontal displacement of vessels relative to one another. Clamps may be used for this purpose, such as ones that secure respectively at the top and the bottom of each vessel. The supports can be designed to accommodate vessel expansion, such as by having some resilience.

Vertically-mounted vessels have been found to give less criticality in following dynamic loads due to the ship motion and can allow an easier potential replacement of single vessels in the module or compartment- they can be lifted out without the need to first remove other vessels from above (the hull surrounding the vessels, when arranged horizontally, would prevent longitudinal removal). This vertical arrangement also allows a potentially faster installation time, again since the vessels or modules can be just lowered into place from above.

Mounting vessels in vertical position also allows condensed liquids to fall under the influence of gravity to the bottom, thereby being off-loadable from the vessels, e.g. using the 12 inch opening 7 at the bottom 12 of each vessel 10, for separation from the CNG at the start of the off-load cycle - offloading of the gas will also usually be from the bottom of the vessel 10.

With the majority of the piping and valving 60 positioned towards the bottom of the modules/bottom of the vessels, this helps to maintain the center of gravity also in a low position, which is recommended or preferred for improving stability of the ship at sea.

Modules or compartments 40 can be kept in a controlled environment with an inert gas, or nitrogen gas or other fluids rich in C0₂ or other fire-mitigating compounds, being between the vessels 10 and the modules' walls 40A, thus helping to prevent fire occurrence or fire hazard.

Maximization of the size of the individual vessels 10, such as by making them up to, or beyond, 6m in diameter and/or up to, or beyond, 30m in length, reduces the total number of vessels needed for the same total volume contained. Further it serves to reduce connection and inter-piping complexity. This in turn reduces the number of possible leakage points, which usually occur in weaker locations such as weldings, joints and manifolds. Preferred arrangements call for diameters of at least 2m and lengths of at least 10m.

A set of pressure vessels may comprise multiple modules, such as an array of modules.

One dedicated module might want to be set aside for liquid storage (condensate) using the same concept of interconnection used for the gas storage - the condensate of each pressure vessel will settle to the bottom of the pressure vessel, so flow passageways can direct the condensate to the dedicated module, e.g. when commencing the off-load procedure. The modules and pressure vessels are thus potentially all connected together to allow this distribution of such liquid from other modules 40 to the dedicated module. In and out gas storage piping is linked with metering, heating and blow down systems and scavenging systems, e.g. through valved manifolds. See, for example, Figs 9 and 13 for a schematic arrangement of valved manifolds. They can be remotely activated by a Distributed Control System (DCS) - not shown, but well known in the art of fluid distribution between pressure vessels.

All modules are typically equipped with adequate firefighting systems, as foreseen by international codes, Standards and rules.

Further, instead of arranging the vessels vertically, they can be arranged horizontally, or in arrangements containing both horizontal and vertical pressure vessels, especially when space constraints provide limited upward space.

The present invention therefore provides a ship that can be fitted with a range of pressure vessels that can maximise, or increase compared to single length pressure vessels, the containment capacity within the hull of that ship, and this is achievable without negatively affecting the buoyancy, stability or performance of the ship since the intended cargo - CNG - is relatively lightweight, whereby the capacity of a ship will not be exceeded by that increased storage volume capacity. Indeed, CNG cargo ships typically are designed to counter the fact that the cargo weight will be low compared to cargos such as coal and oil, whereby the increased storage capacity will be welcomed by ship designers.

The increased capacity can also then drive down the transportation cost of CNG since more of it can be transported per journey, and since the speed of the ship can be maximised - by ensuring the balance and stability of the ship is optimised while still offering a large storage capacity, so much so that high speed multi-hull vessels become viable as a cargo vessel - the full extent of the ship's footprint can be fitted with pressure vessels, rather than just the hull sections. See for example, figures 5 to 8, where Figure 5 shows a twin-hull ship in section with custom length pressure vessels fitted to the contour of the hull, Figure 6 shows long and short lengths of pressure vessel, with the longer vessels being located to fit into the depths of the hulls, and the shorter length vessels being fitted across the ridge section of the hull, Figure 7 shows a tri-hull ship in section with custom length pressure vessels fitted to the contour of the hull, and Figure 8 shows long and short lengths of pressure vessel, with the longer vessels being located to fit into the depths of the hulls, and the shorter length vessels being fitted across the ridge sections of the hull.

Obviously other hull designs can also be accommodated by the use of the various sets of pressure vessels of different lengths so as to optimise the cargo capacity of the vessel.

Bear in mind too that the sets may comprise linear arrays of vessels - e.g. lines of vessels extending along parts of the length of the ship, rather than necessarily groups that extend across parts of the width of the vessel.

Preferably the pressure vessels are made of composite materials, either as a reinforcement, or as the primary structure of the vessel, e.g. for the cylindrical section thereof, or as both the cylindrical section thereof and the dome or end sections thereof, so as to be lightweight compared to steel pressure vessels. This ensures that the packing of the large number of pressure vessels onto the ship will not overburden the ship purely as a result of the empty weight of the vessels.

The pressure vessels can be provided to carry a variety of gases, such as raw gas straight from a bore well, including raw natural gas, e.g. when compressed - raw CNG or RCNG, or H₂, or C0₂ or processed natural gas (methane), or raw or part processed natural gas, e.g. with C0₂ allowances of up to 14% molar, H₂S allowances of up to 1 ,000 ppm, or H₂ and C0₂ gas impurities, or other impurities or corrosive species. The preferred use, however, is CNG transportation, be that raw CNG, part processed CNG or clean CNG - processed to a standard deliverable to the end user, e.g. commercial, industrial or residential.

CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄, C₇H₁₆, C₈H₁₈, C₉+ hydrocarbons, C0₂ and H₂S, plus potentially toluene, diesel and octane in a liquid state, and other impurities/species.

The present invention has therefore been described herein purely by way of example. Modifications in detail may be made to the invention within the scope of the claims appended hereto.

Claims

CLAIMS:

1. A ship comprising a plurality of pressure vessels, there being a first set of pressure vessels of a first length, a second set of pressure vessels of a second length, and a third set of pressure vessels of a third length, the first, second and third lengths differing from one another by at least 15cm.

2. A ship comprising a plurality of pressure vessels, there being a first set of pressure vessels of a first length and a second set of pressure vessels pressure vessels of a second length, the first and second lengths differing from one another by at least 15cm, and wherein the ship is a multi-hull ship, with the longer vessels being arranged to extend within the deeper parts of the hull, and the shorter vessels being arranged to extend within the less deep parts of the hull.

3. The ship of claim 2, wherein a third set of pressure vessels of a third length, differing from the first and second lengths by at least 30cm, is also provided.

4. The ship of any one of the preceding claims, wherein at least one of the sets of pressure vessels is arranged with its pressure vessels in at least one array.

5. The ship of any one of the preceding claims, wherein the pressure vessels are arranged in a plurality of containers.

6. The ship of any one of the preceding claims, wherein the pressure vessels have minimum spacings provided therebetween of 380mm.

7. The ship of any one of the preceding claims, at least some of the pressure vessels containing CNG at a pressure greater than 30bar but less than 300bar, when at an ambient temperature of between 10°C and 30°C.

8. The ship of any one of the preceding claims wherein at least 80% of the pressure vessels on the ship have at least part of their length raised above the level of the deck or sides of the ship.

9. The ship of any one of the preceding claims, wherein at least 80% of the pressure vessels on the ship are arranged vertically on the ship.

10. The ship of claim 9, wherein access points for loading and offloading compressed fluid into the pressure vessels are located at the bottoms of at least 80% of the pressure vessels.

1 1. The ship of any one of the preceding claims, wherein the different sets of pressure vessels are arranged to define at least two different bottom levels, spaced at least 30cm out of plane of one another.

12. The ship of any one of the preceding claims, wherein the different sets of pressure vessels are arranged to define at least two different top levels, spaced at least 30cm out of plane of one another.

13. The ship of any one of the preceding claims, wherein shorter vessels are arranged towards the sides of the ship, with longer pressure vessels being arranged towards the centreline of the ship.

14. The ship of any one of the preceding claims, wherein shorter vessels are arranged towards the ends of the ship, with longer pressure vessels being arranged towards the middle of the length of the ship.

15. The ship of any one of the preceding claims, wherein at least 80% of the pressure vessels are Type II, Type III or Type IV pressure vessels.

16. The ship of any one of the preceding claims, wherein at least 80% of the pressure vessels comprise a composite structure.

17. The ship of any one of the preceding claims, wherein custom length pressure vessels are included on the ship, the custom lengths featuring at least two different lengths other than the first or second lengths, these other lengths differing from those first two lengths by at least 15cm.

18. The ship of any one of the preceding claims, wherein the ship is a multi-hull ship comprising at least the two different lengths of pressure vessel arranged vertically within the hull, the vertically arranged pressure vessels being spaced across the width of the hull in one or more arrays, with the longer ones of the pressure vessels in the deeper parts of the hull and the shorter ones of the pressure vessels in the lands between those deeper parts of the hull.

19. A ship substantially as hereinbefore described with reference to any one of Figures 1 to 8.