WO2013083169A1

WO2013083169A1 - Multilayer pressure vessel

Info

Publication number: WO2013083169A1
Application number: PCT/EP2011/071805
Authority: WO
Inventors: Francesco Nettis; Paolo REDONDI; Vanni Neri TOMASELLI
Original assignee: Blue Wave Co S.A.
Priority date: 2011-12-05
Filing date: 2011-12-05
Publication date: 2013-06-13
Also published as: EP2788653A1; CN104220802A; KR20140110900A; EA201491122A1

Abstract

The present invention relates to a pressure vessel for containing or transporting pressurized gas. More particularly it relates to such vessels for containing or transporting compressed natural gas. The present invention also relates to a method of storing or transporting gas onshore or offshore. Moreover, the present invention relates to a vehicle for transporting gas, in particular compressed natural gas.

Description

MULTILAYER PRESSURE VESSEL

Field of the invention The present invention relates to pressure vessels for containing or transporting pressurized gas in a ship. More particularly it relates to such vessels for containing or transporting compressed natural gas (CNG).

The present invention also relates to a method of storing or transporting gas onshore or offshore. Moreover, the present invention relates to a vehicle for transporting gas, in particular compressed natural gas.

Background art Conventional pressure vessels for containing or transporting pressurized gas are typically made on the basis of steel only and are heavy in weight. However, the cost of steel is considerable, whereby despite its corrosion resistant properties, it presents difficulties on seafaring vehicles - seafaring vessels have a load-bearing limit based upon the buoyancy of the vehicle, much of which load capacity is taken up by the physical weight of the vessels - i.e. their "empty" weight.

Moreover, on seafaring vehicles inevitable salty water spray creates an undesired and prolonged galvanic coupling between the stainless steel in the pressure vessel and the carbon steel used for the ship structure. This coupling leads to the so-called marine corrosion, which over time deteriorates the metal with the higher difference in, or stronger, electronegativity.

Technical problem to be solved The present invention therefore aims at overcoming or alleviating at least one of the disadvantages of the known pressure vessels.

In particular, an object of the present invention is to provide pressure vessels, which are more resistant to the harsh conditions onboard seafaring vehicles. Summary of the invention

A first aspect of the present invention relates to a pressure vessel, in particular for compressed natural gas containment or transport. The pressure vessel has a generally cylindrical shape over a majority of its length and at least one opening for gas loading and offloading and for liquid evacuation. The pressure vessel comprises a non-metallic internal coating, a metallic liner; and at least one external fiber layer.

Preferably the opening is at the bottom of the vessel. Preferably the vessel is for standing vertically, such that the cylindrical section thereof is substantially vertical.

The non-metallic internal coating may preferably be substantially inert.

The non-metallic internal coating may advantageously have a corrosion resistance of at least that of stainless steel.

The non-metallic internal coating may be selected from the group comprising: HDPE, epoxy resins, PVC, etc. The metallic liner may be acidic gas corrosion resistant.

The metallic liner may be made of low-carbon steel.

The fiber layer may be made of fiber wound about the metallic liner.

The fiber layer may comprise carbon fibers.

The pressure vessel may further comprise an insulating layer interposed between the metallic liner and the carbon fiber layer.

The insulating layer may be a gas permeable layer. The fiber layer may comprise glass fibers. The pressure vessel may further comprise a gas permeable layer interposed between the metallic liner and the fiber layer.

The gas permeable layer may comprise glass fibers.

The pressure vessel may further comprise a gas detector connected to the gas permeable layer for detecting a gas leakage.

The pressure vessel may be of essentially cylindrical shape, inside and outside, along that majority of its length.

The inner diameter of the vessel may be between 0.5 meters and 5 meters.

The inner diameter of the vessel may be between 1.5 meters and 3.5 meters.

The pressure vessel may comprise a manhole for entering and/or inspecting the interior of the vessel. Preferably the manhole is at the top of the vessel. The manhole may be a 24 inch (60cm) manhole, or equivalent, for allowing internal inspection, e.g. by a person climbing into the vessel. The manhole may have closing means for allowing sealed closing of the opening thereof.

A plurality of the inspectable pressure vessels (10) can be arranged in a module or compartment, and the pressure vessels can be interconnected for loading and offloading operations.

Preferably the vessels all have the same height. Some may have different heights, however, to accommodate a variable floor condition - such as the curvature of a hull of a ship. According to a second aspect of the present invention, a method is proposed for storing or transporting gas, in particular compressed natural gas, onshore or offshore. The method provides for using at least one pressure vessel according to any one of the preceding configurations of the first aspect of the present invention. A third aspect of the present invention relates to a vehicle for transporting gas, in particular compressed natural gas, comprising at least one vessel to any one of the preceding configurations of the first aspect of the present invention. The gas-transporting vehicle may be a ship or some other form of transporter, such as a truck or a train.

In the gas-transporting vehicle the pressure vessels may be interconnected. Advantages of the invention

The pressure vessel according to the present invention may allow a reduction in the unit cost in production, compared to equivalent steel vessels. A pressure vessel according to the present invention may also allow a reduction in the galvanic coupling between the vessels and a seafaring vehicle transporting them, as compared to steel vessels.

A further advantage of the present invention may be a reduction in the weight of the pressure vessel compared to equivalent steel vessels - a reduced weight allows a greater volume of fluid to be carried by a ship since ships have a given buoyancy for a given displacement.

Moreover, the present invention may allow less costly carbon steel to be used within the pressure vessel, while still maintaining its resistance to corrosion.

Brief description of the drawings

These and other features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

Fig 1 is a schematic cross section of a first embodiment of a pressure vessel in accordance with the present invention. Fig 2 is a schematic cross section of a second embodiment of a pressure vessel in accordance with the present invention.

Fig 3 is a detailed schematic view in cross section of a third embodiment of a pressure vessel in accordance with the present invention.

Fig. 4 is a schematic perspective view showing interconnecting piping between vessels according to the invention, arranged in a module; Fig. 5 is a schematic side view showing the interconnecting piping between vessels lined up within a module;

Fig. 6 is a schematic top view showing the interconnecting piping between vessels lined up within a module;

Figure 7 schematically shows a section through a ship hull showing two modules arranged side by side; and

Figure 8 schematically shows a more detailed view of the top-side pipework.

Detailed description of the invention

Increased capacity and efficiency requests in the field of CNG transportation, and the common use of steel-based cylinders therefor, has led to the development of steel- based cylinders with a thicker structure, which usually results in a heavy device or a device with a lower mass ratio of transported gas to containment system. This effect can be overcome with the use of advanced and lighter materials such as composite structures. Some existing solutions therefore already use composite structures in order to reduce the weight of the device, but the size and configuration of the composite structures are not optimized, for example due to the limitations of the materials used. For example, the use of small cylinders or non-traditional shapes of vessel often leads to a lower efficiency in terms of transported gas (smaller vessels can lead to higher non-occupied space ratios) and a more difficult inspection of the inside of the vessels. Further, the use of partial wrapping (e.g. hoop-wrapped cylinders) for covering only the cylindrical part of the vessel, but not the ends of it, leads to an interface existing between the wrapped portion of the vessel and the end of the vessel where only the metal shell is exposed. That too can lead to problems, such as corrosion.

Also, transitions between materials in a continuous structural part usually constitute weaker areas, and hence the points in which failures are more likely to occur.

As shown in Fig 1 , a vessel 10 in accordance with the present invention is made of an internal metallic liner 2 capable of hydraulic or fluidic containment. The inside of metallic liner 2 is internally coated with a non-metallic layer 1 , such as a polymeric layer, which is capable of withstanding raw gases. The metal liner 2 is not needed to be provided in a form to provide a structural aim during the CNG transportation, loading and offloading phases.

The metal liner 2 is internally coated with the non-metallic corrosion-proof layer 1 and that liner is capable of carrying non-treated or unprocessed gases. Preferred material may be a carbon-steel coated metallic liner 2 with a thin polymer non-metallic layer 1 such as an epoxy resin, HDPE (High-Density Polyethylene) or PVC (Polyvinyl Chloride). Preferably it has a tensile strength of 50 MPa or higher. Preferably it has a Young Modulus of 3 GPa or higher. Preferably it is able to be substantially chemically inert. Preferably it is corrosion-proof for a wide range of chemical compositions, including chlorides. This construction also allows the vessel 10 to be able to carry other gases, such as natural gas (methane) with C0₂ allowances of up to 14% molar, H₂S allowances of up to 1.5% molar, or H₂ or C0₂ gases. 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. The metal liner 2 preferably only needs to be strong enough to withstand the mechanical stresses arising from manufacturing processes of the vessel, such as those imposed thereon when an external fiber layer 3 is being applied. This is because the structural support during pressurized transportation of gas will be provided instead by the external fiber layer 3.

Where the metal liner 2 is of carbon-steel, it could be selected from an API (American Petroleum Institute) 5L X42 or X60 or ASTM (American Society for Testing and Materials) A516 with a preferred tensile strength of 350 MPa or higher.

The external fiber layer 3 may preferably be selected from a fiber-reinforced polymer based on carbon/graphite fibers, advantageously fully wrapping the vessels 10 (including the vessel ends) and providing the structural contribution during service. When carbon fibers are used in the external fiber layer 3, it is preferred, but not limited thereto, to use a carbon yarn with a preferred tensile strength of 3,200 MPa or higher and/or a preferred Young Modulus of 230 GPa or higher. The yarn may advantageously have 12,000, 24,000, or 48,000 filaments per yarn. The composite matrix is preferred to be a polymeric resin thermoset or thermoplastic. More precisely, if a thermoset resin is used, it is preferred that it should be an epoxy- based resin, or alternatively a vinyl ester or polyester-based resin. This also allows achieving a cost reduction. Since the external fiber layer 3 comprising the carbon/epoxy composite is electrically conductive like the steel used for the metallic liner 2, it is advantageous to provide an additional insulating composite layer with isolating properties in order to avoid possible galvanic coupling. This insulating layer may advantageously be made of glass fibers embedded in epoxy resin, hence matching the resin of the external layer. Concerning glass fibers, it is preferred but not limited to the use of E glass or S glass fiber. Preferably, however, the glass fibers have a suggested tensile strength of 1 ,000 MPa or higher and/or a Young Modulus of 70 GPa or higher. Alternatively, as shown in Figure 2, it may be useful to apply a polymeric coating as an insulating layer 4. In this embodiment it is between the liner 2 and the fiber layer 3. The insulating layer 4 may advantageously be selected from materials such as an epoxy resin, HDPE (High-Density Polyethylene) or PVC (Polyvinyl Chloride). Preferably the coating has a tensile strength of 50 MPa or higher and/or a Young Modulus of 3 GPa or higher.

The insulating layer 4, which typically has only to carry compressive stresses, may have porous characteristics, i.e. it may be permeable to gases in the case of leakage from the steel liner. The insulating layer 4 may advantageously then further comprise an integrated gas detection device able to warn in case of leakage from the inner liner 2. Figure 3 schematically shows a connection to such a device, which may be integrated into the wall of the vessel. Such a device might be operated via a wireless transmission to a receiving unit elsewhere onboard the ship, usually nearby the pressure vessel.

The manufacturing of the external composite layer 3 over the said metallic liner 2 (the first layer) preferably involves a winding technology. This can potentially gives a high efficiency in terms of production hours. Moreover it can potentially provide good precision in the fibers' orientation. Further it can provide good quality reproducibility.

The reinforcing fibers preferably are wound with a back-tension over a mandrel. The mandrel is typically the liner. The liner thus constitutes the male mould for this technology. The winding is typically after the fibers have been pre- impregnated in the resin. Impregnated fibers are thus preferably deposited in layers over said metallic liner until the desired thickness is reached for the given diameter. For example, for a diameter of 6m, the desired thickness might be about 350 mm for carbon-based composites or about 650 mm for glass- based composites.

Since this invention preferably relates to a substantially fully wrapped pressure vessel 10, a multi-axis crosshead for fibers is preferably used in the manufacturing process. The process preferably includes a covering of the majority of the ends 11 , 12 of the pressure vessel 10 with the structural external composite layer 3.

In the case of the use of thermoset resins there can be a use of an impregnating basket before the fiber deposition - for impregnating the fibers before actually winding the fibers around the metal liner 2.

In the case of the use of thermoplastic resins, there can be a heating of the resin before the fiber deposition in order to melt the resin just before reaching the mandrel, or the fibers are impregnated with thermoplastic resin before they are deposited as a composite material on the metal liner. The resin is again heated before depositing the fibers in order to melt the resin just before the fiber and resin composite reaches the metal liner 2. The pressure vessel 10 may be provided with an opening 7 (here provided with a cap or connector) intended for gas loading and offloading and liquid evacuation. The opening may be placed at either end 1 1 , 12 of the vessel 10, but as shown it is preferred to be at the bottom end 12. It can be a 12 inch (30cm) opening for connecting to pipework.

The vessel 10 also has an opening 6 at the top end 11 and it is advantageously in the form of an at least 18-inch (45cm) wide access manhole, such as one with a sealed or sealable cover (or more preferably a 24-inch (60cm) manhole). It is preferably provided according to ASME (American Society of Mechanical Engineers) standards. Preferably the opening is provided with closing means, which allows a sealed closing of the opening during gas transportation, but which allows internal inspection when the vessel 10 is not in use, such as by a person climbing into the vessel through the opening/manhole 6. Fig 4 illustrates an arrangement of a plurality of vessels in modules or compartments 40. The pressure vessels 10 can be arranged in a ship's hull (see Figure 6) in modules or compartments 40 and the vessels 10 can be interconnected for loading and offloading operations, such as via pipework 61. In a preferred configuration, such modules or compartments 40 have four edges (are quadrilateral-shaped) and contain a plurality of vessels 10. The number of vessels chosen will depend upon the vessel diameter or shape and the size of the modules or compartments 40. Further, the number of modules or compartments will depend upon the structural constraints of the ship hull for accommodating the modules or compartments 40. It is not essential for all the modules or compartments to be of the same size or shape, and likewise they need not contain the same size or shape of pressure vessel, or the same numbers thereof.

The vessels 10 may be in a regular array within the modules or compartments - in the illustrated embodiment a 4x7 array. Other array sizes are also to be anticipated, whether in the same module (i.e. with differently sized pressure vessels), or in differently sized modules, and the arrangements can be chosen or designed to fit appropriately in the ship's hull.

For external inspection-ability reasons it is preferred that the distance between the vessels 10 within the modules or compartments 40 be at least 380mm, or more preferably at least 600 mm. These distances also allow space for vessel expansion when loaded with the pressurized gas - 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). Preferably the distance between the modules or compartments 40 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.

Still with reference to Fig 4, each pressure vessel row (or column) is interconnected with a piping system 60 intended for loading and offloading operations from the bottom 12 of each vessel 10, such as through the preferably 12 inch (30cm) opening 7, to main headers, such as through motorized valves.

The main headers can comprise various different pressure levels, for example three of them (high - e.g. 250 bar, medium - e.g. 150 bar and low - e.g. 90 bar), plus one blow down header and one nitrogen header for inert purposes. Also as shown in fig 4, the vessels 10 are preferred to be mounted vertically, preferably on dedicated supports or brackets, or by being strapped into place. The supports (not shown) hold the vessels 10 in order to avoid horizontal displacement of the vessels relative to one another. Clamps, brackets or other conventional pressure vessel retention systems, may be used for this purpose, such as hoops or straps that secure the main cylinder of each vessel.

The supports can be designed to accommodate vessel expansion, such as by having some resilience.

When the vessels 10 are vertically mounted, they are less critical in following dynamic loads resulting from the ship motion. Moreover the vertical arrangement allows an easier replacement of single vessels in the module or compartment 40 when necessary - they can be lifted out without the need to first remove other vessels from above. This configuration can also potentially allow a fast installation time. Mounting the vessels 10 in vertical positions also allows condensed liquids to fall under the influence of gravity to the bottom, thereby being off-loadable from the vessels using, e.g. the 12 inch opening 7 at the bottom of each vessel 10. Offloading of the gas will advantageously also be from the bottom of the vessel 10.

With the majority of the piping and valving 60 installed towards the bottom of the modules, the center of gravity of the whole arrangement will be also in a low position, which is recommended or preferred, especially for improving stability at sea, or during gas transportation.

Modules or compartments 40 are preferably kept in a controlled environment with nitrogen gas being between the vessels 10 and the modules' walls 40A, thus reducing fire hazard. Alternatively, the engine exhaust gas could be used for this inerting function thanks to its composition being rich in C0₂.

By maximizing the size of the individual vessels 10, such as by making them, for example, up to 6 meter in diameter and up to 30 meter in length, for the same total volume contained the total number of vessels 10 may be reduced, which in turn allows to reduce connection and inter-piping complexity, and hence 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.

One dedicated module can be set aside for liquid storage (such as condensate) using the same concept of interconnection used for the gas storage. The modules 40 are thus potentially all connected together to allow a distribution of such liquid from other modules 40 to the dedicated module - a ship will typically feature multiple modules.

In and out gas storage piping may advantageously be linked with at least one of metering, heating, and/or blow down systems and scavenging systems through valve- connected manifolds. They may preferably be remotely activated by a Distributed Control System (DCS).

Piping diameters are preferably as follows:

18 inch, for the three main headers (low, medium and high pressure) dedicated to CNG loading/offloading.

24 inch, for the blow-down CNG line.

6 inch, for the pipe feeding the module with the inert gas.

10 inch, for the blow-down inert gas line.

10 inch, for the pipe dedicated to possible liquid loading/offloading.

All modules are preferably equipped with adequate firefighting systems, as foreseen by international codes, standards and rules. The transported CNG will typically be at a pressure in excess of 60bar, and potentially in excess of 100bar, 150 bar, 200 bar or 250 bar, and potentially peaking at 300 bar or 350 bar.

The pressure vessels described herein can 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. No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

1. A pressure vessel (10), in particular for compressed natural gas containment or transport, with a generally cylindrical shape over a majority of its length and at least one opening (7) for gas loading and offloading and for liquid evacuation, comprising: a non-metallic internal coating (1);

a metallic liner (2); and

at least one external fiber layer (3).

2. The pressure vessel according to claim 1 , wherein the non-metallic internal coating (1) is substantially chemically inert.

3. The pressure vessel according to claim 2, wherein the non-metallic internal coating (1) has a corrosion resistance of at least that of stainless steel.

4. The pressure vessel according to claim 1 or 2, wherein the non-metallic internal coating (1) is selected from the group comprising: high-density polyethylene, epoxy resins, polyvinyl chloride.

5. The pressure vessel according to any one of the preceding claims, wherein the metallic liner (2) is corrosion resistant against acidic gas.

6. The pressure vessel according to any one of the preceding claims, wherein the metallic liner (2) is made of low-carbon steel.

7. The pressure vessel according to any one of the preceding claims, wherein the fiber layer (3) is made of fiber wound about the metallic liner (2).

8. The pressure vessel according to any one of the preceding claims, wherein the fiber layer (3) comprises carbon fibers (2).

9. The pressure vessel according to claim 8, further comprising an insulating layer (4) interposed between the metallic liner (2) and the carbon fiber layer (3).

10. The pressure vessel according to claim 9, wherein the insulating layer (4) is a gas permeable layer.

1 1. The pressure vessel according to any one of the preceding claims, wherein the fiber layer (4) comprises glass fibers.

12. The pressure vessel according to claim 1 1 , further comprising a gas permeable layer (4) interposed between the metallic liner (2) and the glass fiber layer (3).

13. The pressure vessel according to claim 10 or 12, wherein the gas permeable layer (4) comprises glass fibers.

14. The pressure vessel according to claim 10, 12 or 13, further comprising a gas detector (5) connected to the gas permeable layer (4) for detecting a gas leakage.

15. The pressure vessel according to any one of the preceding claims, wherein the pressure vessel (10) is of essentially cylindrical shape along that majority of its length.

16. The pressure vessel according to any one of the preceding claims, wherein the inner diameter of the vessel (10) is between 0.5 meters and 5 meters.

17. The pressure vessel according to claim 8, wherein the inner diameter of the vessel (10) is between 1.5 meters and 3.5 meters.

18. The pressure vessel according to any one the preceding claims further comprising a manhole (6) for entering and/or inspecting the interior of the vessel (10).

19. A module or compartment comprising a plurality of the inspectable pressure vessels (10) as defined in any one of the preceding claims, the pressure vessels being interconnected for loading and offloading operations.

20. A method of storing or transporting gas onshore or offshore, in particular compressed natural gas, using at least one pressure vessel according to any one of claims 1 to 18, or the module or compartment of claim 19, the gas being contained within a pressure vessel thereof.

21. A vehicle for transporting gas, in particular compressed natural gas, comprising at least one vessel (10) according to any one of claims 1 to 18, or a module or compartment of claim 19.

22. The vehicle according to claim 21 , wherein the vehicle is a ship.

23. The vehicle according to claim 21 or 22, wherein there are multiple pressure vessels (10) and they are interconnected.