ES2973509T3 - insulation system - Google Patents

Abstract

The present invention relates to a cryogenic insulation system for oceangoing vessels. The method and system involve the steps of sequentially applying a plurality of layers to the exterior surface of the tank. The layers include a first layer of foam applied to the tank, a second gas/liquid impermeable liner applied to the first layer, and an outer liner layer applied to the second layer. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

insulation system

Technical field

The present invention relates to the transportation of liquefied gases and particularly (but not exclusively) liquefied natural gas (LNG). Specifically, the invention relates to a new insulation arrangement for a particular type of LNG tank, known in the industry as an IMO Type C LNG tank. Such tanks can be used to transport LNG as cargo, but can also be used as a fuel tank for ocean-going vessels, allowing the LNG to be used as fuel for a ship with consequent environmental benefits. The invention can also be applied to other tanks for transporting cryogenic liquids such as liquefied propane gas (LPG) or liquefied ethylene gas (LEG).

Background of the invention

International Maritime Organization (IMO) regulations stipulate the types of tanks that can be used to transport LNG on ships. A common tank used for LNG is a Type C tank that is shaped like a sphere or cylinder that acts as a pressure vessel to contain the LNG. The standards stipulate a series of technical characteristics that a tank must have for its safe use to be certified.

Cryogenic liquids such as LNG are transported and stored at extremely low temperatures, i.e. -163 degrees C, and these temperatures must be maintained to keep the gas in liquid form.

One technique for insulating such a tank is to apply spray foam insulation to the outside of the tank. Typically, polyurethane is applied or sprayed onto the exterior of the LNG tank. Such spray foam materials are convenient to apply and cost effective and are very popular with boat builders due to the cost effective nature of the insulation that can be applied. Yambén is very easy to apply.

The combination of Type C LNG tanks and spray foam insulation allows LNG to be transported safely either in large volumes as cargo or as fuel for a ship. The present invention, as described herein, provides an effective way to insulate a ship's LNG fuel tank.

However, although existing insulation systems are widely accepted in the industry as fit for purpose, the present inventor has established an improved insulation system and method using a new foam spray technique.

Specifically, the new system and method further enhances the advantages of spray foam insulation and prolongs insulation efficiency. It can also advantageously provide an additional fire barrier to an LNG tank.

Examples of existing prior art include US 8,297,468, which relates to storage containers or fuel tanks for liquefied natural gas; and US 4,106,424, which refers to large maritime containers for storage of liquefied gases.

GB1516150A describes thermally insulated containers for liquefied gas. GB1516150A does not describe a first layer on the outer surface of a tank that is a layer of sprayed polyurethane foam comprising a plurality of individual polyurethane sublayers, wherein the sublayers have different densities.

KR20130053727A discloses a method of constructing cargo tanks for LPG.

Brief description of the invention

According to the present invention, a method according to claim 1 and an LNG tank according to claim 12 are provided.

Also described in the specification, but not covered by the appended claims, is a method of insulating a tank for containing liquefied gas, said method comprising the steps of sequentially applying a plurality of layers to the outer surface of the tank, said sequential layers comprising :

(A) a first layer of foam applied to the tank;

(B) a second waterproof coating applied to the first layer;

where each of said layers surrounds a previous layer.

Optionally, after step (B), an additional coat of:

(C) An outer coating layer applied to the second layer.

The above advantageously provides a multi-layer insulation system in which a layer of foam is encapsulated or sealed between the tank itself and another impermeable layer. Specifically, the first layer may be provided with a gas-tight metallic vapor barrier. This forms a vapor tight barrier around the foam and tank that was not previously conceived.

Advantageously, the barrier is a metal barrier that provides the waterproof property of the insulation system. The metal barrier may include a self-adhesive layer to connect it to the foam or may be applied with a separate adhesive.

The combination of a tank, a foam insulating layer and an impermeable vapor barrier has not been previously considered and therefore a liquefied natural gas tank is also provided comprising a first layer of foam surrounding the tank and a second waterproof barrier surrounding the first foam layer.

Therefore, an LNG fuel tank may be provided with foam insulation and a barrier surrounding the foam that is impermeable to vapor and liquids, as will be explained later in this document.

Advantageously, the impermeable barrier provides multiple advantages.

For example, it prevents damage to the foam layer during use. More importantly, the waterproof barrier prevents moisture from entering cavities or open cells within the foam layer itself, which can damage and degrade the foam.

Furthermore, the inventor has established that said impermeable layer prevents the emission of CO2 (also known as a foaming agent) and the entry of air into the foam cells, which advantageously prevents aging or degradation of the foam layer. The foaming agent is used to expand the foam and remains in the cells after expansion. This could migrate from the cells over time and reduce the thermal properties of the insulation.

Currently, polyurethane (PU) foams are blown with a combination of CO2, obtained through the chemical reaction between precisely dosed amounts of water in the polyol mixture and the isocyanate component, and with high molecular weight blowing agents such as hydrofluorocarbons (i.e. HFC-365mfc). , HFC-227ea and/or HFC-245fa) and/or other fluorinated or chlorofluorinated olefins (i.e., HCFO-1233zd, HFO-1336mzz). Other suitable foaming agents may also be used now or in the future. While CO2 can easily diffuse out of the foam cells, high molecular weight blowing agents will substantially remain within the foam cells for periods far in excess of those required for a reasonable economic life. Therefore, these blowing agents are called "permanent", while CO2 is called a "non-permanent" blowing agent. Therefore, the aging of the thermal properties of such PU products is predominantly caused by the diffusion of air into the product cells and the diffusion of CO2 outwards, if diffusion-tight coatings do not prevent both. things.

Therefore, the use of a new combination of a foam layer with a waterproof encapsulant layer significantly minimizes the aging of the thermal properties of the insulating layer by preventing the entry of ambient air (oxygen) into the cells within the foam and the CO2 release from within the foam cells.

The present insulating layer significantly reduces the aging of the polyurethane foam, thus substantially improving the operational life of the insulating layers.

The term impermeable is intended herein to refer to a layer that prevents gas and liquid from passing through the layer in any direction.

The first layer of foam can be applied to the tank surface using various techniques. The foam layer can be applied, for example, by a spray technique using a spray gun. This allows the foam to be easily and quickly applied to large tank surfaces.

It is particularly convenient to apply expanded polyurethane foam in this way.

Specifically, the foam layer may be a premix of polyol and isocyanate.

The foam layer may be a single foam layer in some applications. However, to maximize insulating properties, the foam layer may be formed from a plurality of individual polyurethane sublayers, each applied over a previous layer.

The sublayers may have any suitable thickness. For an LNG application, the foam layer may be formed from a plurality of sublayers, each layer having a thickness of between 5 mm and 35 mm. In such an application, to meet the insulation needs for sea voyages, the total thickness can be 300 mm measured from the outer wall of the tank.

Furthermore, the individual layers are applied with different (different) densities.

Specifically, in an LNG application, a sublayer closer to the tank may have a density greater than 50 kg/m3 and a later layer may have a density greater than 40 kg/m3. The inventor has shown that such a combination of layers and different densities optimized the insulating properties and mechanical resistance of the insulating layer. Both are important in an LNG application.

In another arrangement, not covered by the appended claims, the densities of the foam layers may be substantially the same. This simplifies the application process and provides uniform foam density. It has further been established that thermal performance can be further improved if the first 50 mm of foam layer measured from the tank surface has a density greater than 50 kg/m3 and the remaining depth of the foam layer has a density greater than 40 kg/m3.

To further improve the structural integrity of the foam layer, the layer (or sublayers) may be provided with glass fibers within the foam. This can be incorporated into the sprayed polyurethane mixture or applied as one or more mesh layers. This acts advantageously as a crack preventative.

A polyurethane primer is applied to the tank before the foam is applied. This improves the bond strength between the foam and the tank surface.

As described above, the impermeable layer is impermeable to gas and liquid, but specifically prevents air from penetrating and CO2 from diffusing out of the foam cells.

Advantageously, the waterproof layer may be an aluminum foil with a polymeric backing layer and an optional self-adhesive coating. Such a combination of aluminum foil and polymer backing provides the desired waterproof quality in combination with flexibility and ease of application to the outer surface of the foam layer. In this way a vapor-tight barrier is formed.

Furthermore, the polymeric layer is advantageously sealed if punctured due to the elastic nature of the material. Therefore, the integrity of the waterproof seal is not compromised if the layer is accidentally punctured.

The waterproof layer may use a polymeric backing layer such as butyl rubber.

The waterproof layer may further be provided with a self-adhesive layer facing the foam side of the waterproof layer to provide a bonding surface to hold the layer in position against the foam. The insulating layer can be further enhanced with the inclusion of an optional fire retardant layer or coating. For example, a third fire retardant layer may be provided between the waterproof layer and the coating coating. This fire retardant layer may be a mineral wool layer such as a rock wool/mineral wool fire retardant layer. Other similar A60 insulating or fire retardant layers can also be used.

Advantageously, the outer layer of the insulating system may be in the form of a layer of aluminum, galvanized steel or stainless steel surrounding the previous layer. This can be installed, for example, as a plurality of panels or rings that are tessellated to encapsulate the preceding layers. The coating provides structural strength to the insulation system and protects the interior layers. In effect, the outer coating layer and the tank wall create a cavity in which the insulating foam, waterproof layer and fire retardant are safely contained and protected.

Advantageously, the method described herein can be applied to any type of cryogenic transport tank, including, for example, an IMO type C tank.

Also provided in the patent specification, but not covered by the appended claims, is an IMO type C tank comprising an outer insulating layer, said layer comprising:

(A) a first layer of foam applied to the tank;

(B) A second waterproof coating applied to the first layer.

Optionally, the tank can be provided with an additional layer around layer (B), i.e.:

(C) A third layer of coating surrounding the second layer.

Said tank may further comprise an optional third fire retardant layer between the second waterproof layer and the coating layer as described above.

The term liner is used herein to refer to a layer that includes, but is not limited to, an aluminum sheet with a layer of butyl rubber bonded thereto.

A further aspect of an invention described herein extends to an ocean-going vessel (such as a cryogenic transport vessel) according to claim 15.

Brief description of the drawings

An exemplary embodiment of the invention will now be described with reference to the following figures. According to one (or more) embodiments of the present invention, the figures show the following:

Figure 1 shows an insulated tank according to the invention with the plurality of layers cut.

Figure 2 shows the insulating layer according to the invention and each of the sublayers.

Any reference to prior art documents in this specification should not be considered an admission that such prior art is widely known or part of the common general knowledge in the field. As used in this specification, the words "comprises", "comprising" and similar words are not to be construed in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to."

The invention is described in more detail with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples.

Figure 1 shows an LNG tank 1 incorporating an insulation system as described herein. Such a tank 1 comprises an inner tank body 2 which in Figure 1 is generally cylindrical but other shapes may also benefit from the insulation system described herein. The tank body comprises 3 supports (only 1 shown) which are the means for supporting the tank on the deck/structure of the ship.

The insulating layer consists of 4 main layers, each with different properties and thicknesses:

• The first layer is a 5 layer of spray foamed polyurethane.

• The second layer 6 is a waterproof layer of aluminum foil with a polymer backing.

• The third layer (optional) 7 is a fire retardant layer of mineral/glass wool; and

• The outer layer 8 is a metal cladding which may (as shown in Figure 1) be in the form of a plurality of panels, each of which abut one another to encapsulate the insulation system.

As shown in Figure 1, each layer surrounds the previous layer with tank 2 housed within the insulation system.

In a non-layer 7 arrangement, outer layer 8 can be applied directly onto layer 6.

Figure 2 shows a cross section of the insulation system shown in Figure 1.

Similar reference numbers refer to the same layers. As shown, the main thickness of the insulation system is the polyurethane layer. A polyurethane primer is applied to the outer surface of tank 2 to help bond the polyurethane foam layer 5 to tank 2.

The application of the insulating layer will be described below.

The invention is not limited to the specific embodiment described below, which provides an IMO type C tank with an average thermal conductivity K value of approx. 0.085W/m2 K and has a total insulation thickness of 300 mm of PU foam and 50 mm of Rockwool fire retardant wool. This represents only one example of the application of the invention.

Stage 1: foam application

The foam applied is a premix of polyol and isocyanate manufactured by Tagos Srl. These components are brought together and sprayed onto the surface of the tank using a conventional spray gun. A polyurethane primer is applied to the tank surface prior to foam application to improve the bond strength between the foam and the tank surface.

The foam is sprayed onto the surface of the tank in several layers to create the specified total insulation thickness of approximately 300 mm. The thickness of each layer is 5 to 35 mm.

The first 50 mm of foam has a density of 60 kg/m3 and the remaining 250 mm has a density of 40 kg/m3. Foam density variation will be obtained using different polyol formulations that have the correct installed and free-growth applied foam density specification. Alternatively, to simplify installation a single density could be used for all foam layers; However, this example is not covered by the accompanying claims.

Stage 2 - Application of the waterproof layer

After application of the spray foam, an aluminum foil with a butyl rubber backing is applied over the entire exterior surface of the foam to form a vapor-tight barrier. This can be by using a self-adhesive layer on the metal or by using a separate adhesive. The vapor barrier will close or seal itself in the event of an accidental puncture due to the elasticity of the backing.

Stage 3 and 4: Optional coating and fire retardant layer

The metallic coating can be selected from various materials and thicknesses. In this specific modality, the coating is 0.6 mm thick stainless steel (SS 316L).

Band of metal strapping to be applied in a sufficient circumferential and longitudinal pattern around the tank to make a fastening arrangement for the metal covering. The metal covering is attached by overlapping joints to the strapping tape using rivets or screws. Each joint between facing sheets is sealed with sealant.

Before applying the coating, a layer of insulation similar to a layer of A60 fire insulation can be applied to the entire surface of the waterproof layer and secured with conventional steel strapping. A suitable material is that manufactured by Rockwool. The thickness can be between 3 and 80 mm.

The 0.6mm SS 316L coating is then applied outside of the Rockwool insulation attached to the strapping band outside of the Rockwool. Metallic coating and fire blankets provide integrated mechanical and fire protection.

Optionally, a glass reinforced polyester (GRP) will be applied to the outer surface of the stainless steel coating. The thickness of GRP can be >2mm and this protects the stainless steel from the effects of seawater in cases where the tank is located on the deck of a ship.

Each layer is applied so that it surrounds the previous layer. The insulation system keeps the LNG at the required low temperature inside tank 2.

Advantageously, a fuel or cargo tank on an oceangoing vessel incorporating this system has improved operational life and reliability due to the fact that the insulating foam layer does not degrade as is the case with conventional insulation systems.

Although the invention has been described by way of example, it should be appreciated that variations and modifications can be made without departing from the scope of the claims.

Claims (15)

1. A method for insulating a tank (1) to contain liquefied gas, said method comprising the steps of sequentially applying a plurality of layers to the exterior surface of the tank, said sequential layers comprising: (A) a first layer of foam (5 ) applied to the tank and surrounding it; (B) a second waterproof coating (6) applied to and surrounding the first layer; wherein the first layer is a sprayed polyurethane foam layer comprising a plurality of individual polyurethane sublayers, wherein the sublayers have different densities; furthermore, wherein a polyurethane primer is applied to the exterior surface of the tank before applying the first layer of foam. 2. A method as claimed in claim 1, wherein the foam layer is a premix of polyol and isocyanate. 3. A method as claimed in any preceding claim, wherein each sublayer is between 5 mm and 35 mm thick. 4. A method as claimed in claim 1, wherein a sublayer closest to the tank has a density greater than 50 kg/m3 and a subsequent layer has a density greater than 40 kg/m3, and optionally wherein the first 50 mm of foam layer measured from the surface of the tank has a density greater than 50 kg/m3 and the remaining depth of the foam layer has a density greater than 40 kg/m3. 5. A method as claimed in any of the preceding claims, wherein the foam layer further comprises glass fibers within the foam. 6. A method as claimed in any of the preceding claims, wherein the second impermeable layer is gas/liquid impermeable and is in the form of an aluminum sheet with a polymeric backing layer and an optional self-adhesive coating. 7. A method as claimed in claim 6, wherein the polymeric support layer is butyl rubber. 8. A method as claimed in any of the preceding claims, wherein a third fire retardant layer (7) is provided surrounding the waterproof coating and a coating is provided surrounding the third fire retardant layer and wherein the layer fire retardant is a layer of mineral wool, and optionally where the mineral wool layer is rock wool or glass wool. 9. A method as claimed in any preceding claim, wherein a coating layer is in the form of a layer of aluminum, galvanized steel or stainless steel surrounding the previous layer. 10. A method as claimed in any preceding claim, wherein the method includes an additional step (C) of applying an outer coating layer which is applied to the second layer. 11. An LNG tank (1) comprising an outer insulating layer, said layer comprising (A) a first layer of foam (5) applied to the tank and surrounding it; and (B) a second waterproof coating (6) applied to and surrounding the first layer; wherein the first layer is a sprayed polyurethane foam layer comprising a plurality of individual polyurethane sublayers, wherein the sublayers have different densities; furthermore, wherein a polyurethane primer is applied to the exterior surface of the tank before applying the first layer of foam. 12. An LNG tank as claimed in claim 11, further comprising a third layer: (C) A third layer of coating surrounding the second layer. 13. An LNG tank as claimed in claim 12, further the third layer comprises a third fire retardant layer (7) between the second impermeable layer and the coating layer. 14. An LNG tank as claimed in any of claims 11 to 13, wherein the impermeable coating is a metallic layer. 15. A ship comprising a tank according to any of claims 11 to 14.