PL183376B1 - Tank for storing iquefied natural gas - Google Patents

Abstract

The cistern consists of an airtight tank (4) made of sheet steel having on its outer surface a layer of passive anticorrosion sheathing (10) which itself is covered by a layer of hydraulic mortar sheathing (23) which is designed to come in direct contact with the natural soil (13) in the ground without requiring the use of a layer of sand (17) but offering the same possibilities of cathodic protection for the cistern (22) by means of sacrificial anodes (15).

Description

The present invention relates to a liquefied natural gas storage tank, in particular a flame-resistant type pressure tanker, which is designed to contain liquefied natural gas and to be buried in the ground with a connected cathodic protection system having at least one sacrificial anode, including a gas-tight tank made of steel sheet having an inner surface forming a chamber containing liquefied natural gas and an outer surface and a layer of passive anti-corrosion plating covering the entire outer surface of the vessel. Such tanks are known from European Patent Specification No. 713 051.

The traditional approach to securing a conventional tanker truck is to use an anti-corrosive plating made of a passive organic material as partial electrical insulation by an active cathodic protection system containing at least one sacrificial anode. Additionally, large amounts of sand are usually added to the pits where the tanker is to be buried. This sand is placed around the entire cistern, creating a uniform layer that protects the anti-corrosion casing of the cistern from coming into contact with the natural soil in the ground, at the same time not

183 376 interfering with the cathodic protection system. The sacrificial anode (s), usually two, are electrically connected to the tank and buried in natural soil in the ground around the tank.

The aforementioned European Patent No. 713,051 discloses that the tank also includes a secondary layer around the passive anti-corrosive plating that will be a mixture of mineral material embedded in the synthetic material. The second layer should be shock-absorbing. While this publication is about a storage tank that is buried in the ground, it does not mention the material that fills the pit.

French Patent Application No. 2,641,844 discloses a tank designed to contain liquefied natural gas and to be buried in the ground having a plating layer of hydraulic mortar that covers the complete tank in which the liquefied natural gas is stored. This publication also applies to a storage tank that is buried in the ground. However, here also, the publication does not mention the pit filling material.

The problem that arises when using sand to fill pits is the need for pits that are much larger than the size of the tanks themselves. This forces, firstly, to remove the excavated soil from the digging site, and secondly, that significant amounts of sand have to be delivered there. The end result is that installing buried liquefied natural gas tanks is a lengthy and costly process, requiring the work of many workers and tools over a long period of time. Moreover, before a tanker is completely buried in the ground, it is exposed to damage, especially during storage, transport and handling.

U.S. Patent No. 5,207,530 discloses the storage of pressurized natural gas in a reservoir containing a conventional casing grouted in a bore drilled in a subterranean formation. Cementing of the casing in a borehole is a conventional technique in the field of oil or gas wells whereby a bore is first drilled into which a tanker is then inserted and the space between the bore wall and the casing is filled with cement. This publication is not related to the present invention, because according to the invention, the space between the cistern and the wall of the pit is filled with natural soil.

The present invention aims to overcome these problems.

For this purpose, a liquefied natural gas storage tank, in particular a pressure-resistant tank of the flame-resistant type, which is designed to contain liquefied natural gas and to be buried in the ground with a connected cathodic protection system having at least one sacrificial anode, containing a gas-tight tank made of sheet steel having an inner surface forming a chamber in which liquefied natural gas is stored and an outer surface and a layer of passive anti-corrosion plating covering the entire outer surface of the tank according to the invention, is characterized in that it has an additional plating layer of hydraulic mortar completely covering the anti-corrosion plating and adapted to be entered into direct contact with natural soil in the ground, with the thickness of the hydraulic mortar not greater than 20 mm.

The plating layer of hydraulic mortar is directly connected to the layer of anti-corrosion plating at all points.

Furthermore, a tanker according to the invention, in one embodiment, has an intermediate layer of adhesive which is bonded to the plumbing layer to bind the plumbing layer to the anti-corrosion plating layer at all points.

The anti-corrosion plating layer is made of a passive organic material selected from the group of compounds containing epoxy paint.

The adhesive is selected from the group of compounds containing epoxy resins, acrylic resins and styrene-butadiene resins.

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The subject of the invention and the solution from the prior art will be shown in the exemplary embodiments in the drawing, in which Fig. 1 shows a section of the pressure face of a liquefied natural gas tanker buried in a traditional way, Fig. invention.

In both figures, some dimensions have been enlarged to better illustrate the individual elements.

Figure 1 shows a traditional underground cistern 1 intended to contain different amounts of liquefied natural gas 2 with space for vaporized natural gas 3 obtained by natural vaporization of the liquid product, and whose very high pressure to which the gas is exposed compared to the external air pressure is equal to that of the saturated ones. natural gas vapor, and the magnitude of which depends on the temperature of the top layer of the liquid product.

In the tank 1, the gas-tight compartment for liquefied natural gas 2 in its gaseous state 3 is a gas-tight tank 4 made of steel sheet, which provides the mechanical strength of the tank 1 with respect to the very high pressure to which the gas is exposed compared to the external air pressure. It typically has a tubular side wall 5 having an inner surface and an outer surface cylindrically extending about a horizontal axis 6 (extending perpendicular to the plane of the drawing). It also has partially spherical end walls 7 having inner and outer surfaces, these surfaces running in a semicircle about a horizontal axis 6 and being concave with respect to each other along this axis. The inner surfaces of the walls 5 and 7 constitute the surface 8 which forms an inner chamber 29 in which the liquefied natural gas 2 is held with the evaporated natural gas 3. The outer surfaces of the walls 5 and 7 constitute the outer surface 9 of the vessel 4 which, in turn, is completely covered a complete layer of passive anti-corrosive plating 10. This anti-corrosion plating 10 acts as the electrical insulation of the tank 4 and is made of a passive organic material selected from the group consisting of epoxy paint. The anti-corrosion plating 10 has an inner surface 11 which is in direct and continuous contact with the outer surface 9 of the tank 4, both at the level of the tubular sidewall 5 and at the level of the end walls 7. The corrosion protection plating 10 also has an outer surface 12 which in the case of a conventional 1, simultaneously forms the outer layer of the tanker 1.

To bury a traditional tanker 1 it is necessary to dig a huge perpendicular pit 14 into the natural soil 13 in the ground. This pit 14 is much larger than the outer surface 12 of the tank 1 itself, because direct contact of the tank 1 with the natural soil has to be avoided 13. The tank 1 is suspended or wedged in the pit 14 so that it does not touch the natural soil 13. Two are then buried. sacrificial anodes 15 in natural soil 13 on each side of tank 1 in the pit 14. Protector anodes 15 are placed at approximately the same level parallel to the horizontal axis 6. Electrical cables 16 are then led from sacrificial anodes 15 to tank 4, through anti-corrosion plating 10. Once the above is complete, the pit 14 is filled with sand 17 until it completely surrounds and covers the tank 1. The sand acts as a barrier between the exterior surface 12 of the anti-corrosion skin 10 and the natural soil 13 in the ground preventing any possible contact.

Although not shown in Fig. 1, the inside of chamber 29 of reservoir 4 is connected to the user device by a system of conduits and valves mounted in a control well 18 made of a large gas-tight pipe that is gas-tight connected to the reservoir by an anti-corrosion skin 10. The control well 18 runs around it. vertical axis 20 which is perpendicular to the horizontal axis 6. When the cistern 1 is placed in the pit 14 it is aligned with the vertical axis 20, so that the control chamber 18 with its gas-tight pipe 19 protrudes from the sand 17 after filling the pit 14 with sand 17. The chamber control has a movable cover 21 situated above the sand level 17.

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Figure 2 shows a tanker according to the invention. A tank 22, similar to the tank shown in Fig. 1, has the same reference numbers for identical parts.

The difference, however, is that the outer surface 12 of the anti-corrosion skin 10 does not form the outer layer of the tanker 22 because an additional layer of hydraulic mortar skin 23 is provided. An additional layer of hydraulic mortar skin 23 forms a new inner surface 24 which completely covers the outer surface 12 of the corrosion protection skin 10. A new outer surface 25 is created which now forms the outer layer of the tanker 22.

The inner surface 24 of the hydraulic mortar skin 23 obtained by, for example, the projection (application) of the hydraulic mortar is evenly distributed and tightly bound at all points along the outer surface 12 of the anti-corrosion skin 10. This is done using one of two methods. The first of these two methods is to apply a hydraulic mortar directly to the anti-corrosive 10 quickly after spraying the anti-corrosive 10 in liquid form onto the outer surface 9 of the tank 4. Since the anti-corrosive skin is still sticky, when the hydraulic mortar 23 is applied, both skins 10 and 23 will connect at all points, while the anti-corrosion plating 10 dries and hardens. The second method consists in adding a thin intermediate layer of adhesive 26 between the skin 23 of the hydraulic mortar and the outer surface 12 of the skin 10 in such a way that both the skins 10 and 23 are connected at all points. The adhesive 26 can be selected from resin compositions such as epoxies, acrylics, styrene butadiene resins, without limiting the list, and is applied in liquid form to the outer surface 12 of the anti-corrosion skin 10. Fresh hydraulic mortar, i.e., containing water, is applied. then onto the intermediate layer of adhesive 26, while it is still tacky, while it hardening, the hydraulic mortar skin 23 will bond tightly at all points to the outer surface 12 of the corrosion protection skin 10.

Tests have shown that both methods provide a sufficiently effective connection of the hydraulic mortar shell 23 with the corrosion protection shell 10, which in turn is properly connected to the tank 4, providing a system strong enough that no support frames are needed. The mechanical properties of a tank 22 used for storing natural gas 2 and vaporized gas 3 at very high pressure compared to the pressure of the outside air are sufficient for this purpose. However, it is advisable to apply additional reinforcement in the hydraulic mortar skin 23, for example in the form of a fibrous material mixed with the hydraulic mortar before it is applied to the anti-corrosion skin 10.

Preferably, the hydraulic mortar plating 23 should be applied uniformly over the overall anti-corrosion plating 10. Tests have shown that a uniform thickness of no more than 20 mm protects the plating 10 as effectively as the sand layer 17 used in the traditional method shown in Fig. 1 for mechanical insulation. 1 cisterns from soil 13.

Under these conditions, the tanker 22 may be buried as described below.

Pit 27 is dug into natural soil 13 in the ground exactly in the same way as pit 14 in Fig. 1, i.e. with the same dimensions and large enough to accommodate a tank 22. During manufacture, tank 22 is covered with a plating 23 of hydraulic mortar and then it is placed down 27 in such a way that the control well 18 is oriented upwards and oriented along the vertical axis 20. On both sides of the tank 22 there are two sacrificial anodes 15 buried into the natural soil 13 at the level of the horizontal axis 6. Ducts electrics 16 run from sacrificial anodes 15 to tank 4 by passing through plumbing 23 and anti-corrosion plating 10, and through an intermediate layer of adhesive 26 that joins both skins 10 and 23, if used. Pit 27 is then filled with natural soil 13 removed during digging

As a result, the outer surface 25 of the plumbing 23, which constitutes the outer layer of the tanker 22, is in direct contact with the natural soil 13 in the ground.

By comparing Figure 1 and Figure 2 and their descriptions, it will be readily apparent that the digging work required to install the tanker 22 of Figure 2 according to the invention is much less than the corresponding work for installing the tanker 1 of Figure 1 according to the conventional method. If you use a portion of the natural soil 13 excavated in digging the pit 27 to fill it, there will be much less excavated soil left to be removed from the site and there will be no need to bring sand 17 to the work site. This results in a significant reduction in transport work.

Of course, the manner in which the embodiment of the invention has been described above is by no means limiting. It should be emphasized that the components constituting the tanker 22 of Fig. 2 have exactly the same dimensions as the components constituting the tanker 1 of Fig. 1. The tanker 22 according to the invention could be manufactured in exactly the same way as the described tanker 1 made according to the conventional method in with respect to the thickness of the walls of the tank 4 and the anti-corrosive shell 10. Moreover, it is possible to add a hydraulic mortar shell 23 which is thicker than 20 mm without affecting the present invention. It should be mentioned that the thickness of 22mm was chosen as it would provide the required degree of weight for the treatment (installation) of the tank 22. If an additional intermediate layer of adhesive 26 is used, the thickness may be much smaller, possibly a few micrometers, but of course the figure this is exemplified by the many other possibilities that exist.

It has surprisingly been found that an additional layer of hydraulic mortar skin applied to the anti-corrosive skin of the tanker, preferably with a constant thickness of no more than 20mm, is sufficient to protect the anti-corrosive skin from damage during folding, transport and handling. This allowed the use of natural soil in the ground to cover the cistern instead of sand. Additional plating made of hydraulic mortar requires only little expenditure on hydraulic mortar and causes only a slight increase in the total weight of the tanker, creating favorable conditions for its transport and installation.

Moreover, the additional plating layer of hydraulic mortar is hard enough to protect the anti-corrosive shell of a tanker made of a passive organic material selected from the epoxy paint group from dents and nicks caused by falling stones and other objects in the soil in the ground during or caused by with slow movements of the soil during the subsidence of the cistern. The hydraulic mortar skin is also flexible enough to absorb these impacts without transferring the impact energy to the anti-corrosive skin of the tanker.

It also contributes to the protection of the tank itself, as the alkaline nature of the hydraulic mortar creates an area around the steel of such a pH that it will not corrode.

The plating made of hydraulic mortar does not interfere with the functioning of the cathode protective system as it conducts electricity. In fact, its electromechanical behavior is akin to sand, provided that the hydraulic mortar plating is homogeneous and in constant contact with the anti-corrosion tanker plating, which, instead, must be homogeneous and in constant contact with the tank itself. It does not constitute an additional barrier to electrical insulation to that of organic anticorrosive coating, the resistance of which is adjustable. This means that the currents produced by the cathodic protection are sufficient and therefore easy to measure on site and directly comparable to the values measured for sand. Not only is the hydraulic mortar plating compatible with the sacrificial anode cathode protection system discussed above, but the experience gained with conventional installations can be directly applied to the plumbing mortar plating. There are no significant differences between the control values for cathodic protection in a tanker installed using the conventional method and a tanker installed using the method of the invention.

Due to its solid and conductive nature due to the fact that it contains water, the hydraulic mortar prevents air occlusion which may occur in other types of additional layers of insulation sheathing.

Also, the hydraulic mortar plating does not affect the tanker's ability to evaporate liquefied natural gas due to its favorable heat transfer coefficient.

Of course, the hydraulic mortar plating of the additional layer can be reinforced. It is possible to use any of the known reinforcement materials for this purpose. The fibrous materials, for example, can be mixed with the hydraulic mortar during the manufacture of the tanker, more precisely, while an additional plating layer is applied by spraying the hydraulic mortar, for example, on the anti-corrosive plating of the tanker.

However, it is also possible and even preferred that the tank itself is a frame for the hydraulic mortar skin by securing the hydraulic mortar skin to the corrosion protection plating at all points. This can be done by adding a thin direct layer of adhesive between the plumbing and anti-corrosive plating in such a way that the two layers are connected at all points. The adhesive used may be one of the resin compositions, such as epoxy, acrylic, styrene butadiene resins. The adhesive is sprayed as a liquid onto the anti-corrosion plating and then hardens. 'Fresh hydraulic mortar is then applied to the adhesive while it is still sticky and as it hardens, the hydraulic mortar is firmly attached at all points to the anti-corrosion layer. It can achieve the same bonding effect - without an intermediate adhesive layer. This is due to the fact that the anti-corrosion plating itself is sprayed in liquid form onto the tank and then hardens. If the hydraulic mortar is applied directly to the anti-corrosion skin layer while it is still sticky, the two layers will be bonded just as tightly as if there was an adhesive between them. In both cases, the hydraulic mortar plating is placed over the tanker before it is buried in the ground.

Taking into account the fact that the tank according to the invention does not require the use of sand, the procedure for installing and burying the LNG tank is different.

The present invention provides a verified method for installing a flame-resistant type pressure tanker adapted to contain liquefied natural gas and to be buried in the ground with an attached cathodic containment system having at least one sacrificial anode, including a gas-tight steel sheet vessel having an inner surface forming a chamber, which stores liquefied natural gas and an outer surface and a layer of passive anti-corrosion plating covering the entire outer surface of the tank.

At least one sacrificial anode, buried in the ground, is electrically connected to the tank with a connection through a plumbing mortar plating and an intermediate adhesive layer, if used. The tanker is then buried with the outer plating made of hydraulic mortar in direct contact with the natural soil in the ground.

The manner in which the installation is carried out is original to the traditional installation of tanks, the present invention also relates to a liquefied natural gas storage burying installation using a pressure-resistant type tank car of a flame-resistant type, designed to contain liquefied natural gas and to be buried in the ground, including a gas-tight tank made of sheet steel, having an inner surface forming a chamber in which liquefied natural gas is stored

183 376 and the outer surface and a layer of passive anti-corrosion plating covering the entire outer surface of the tank, and electric wires connecting the tank to at least one sacrificial anode, which is also buried and located in direct contact with the natural soil, the electric wires also pass through the anti-corrosion layer.

The tanker according to the invention has a plating layer made of hydraulic mortar through which electric cables also lead, the hydraulic mortar plating forming the outer surface of the tank being in direct contact with the natural soil in the ground.

If an intermediate adhesive layer is placed between the anti-corrosion skin and the hydraulic mortar, the electrical wires pass through this intermediate adhesive layer.

It has surprisingly been found that an additional hydraulic mortar skin layer applied to the anti-corrosive skin of the tanker, preferably with a constant thickness of no more than 20mm, is sufficient to protect the anti-corrosive skin from damage during storage, transport and handling. This allows the use of natural soil in the ground to cover the tanker instead of sand. Additional plating made of hydraulic mortar requires only little expenditure on hydraulic mortar and causes only a slight increase in the total weight of the tanker, creating favorable conditions for its transport and installation.

Moreover, the additional plating layer of hydraulic mortar is hard enough to protect the anti-corrosion tank plating made of a passive organic material selected from the epoxy paint group from dents and nicks caused by falling stones and other objects in the soil in the ground during the tank coating or caused by with slow movements of the soil during the subsidence of the cistern. The hydraulic mortar skin is also flexible enough to absorb these impacts without transferring the impact energy to the anti-corrosive skin of the tanker.

It also contributes to the protection of the tank itself, as the alkaline nature of the hydraulic mortar creates an area around the steel of such a pH that it will not corrode.

The plating made of hydraulic mortar does not interfere with the functioning of the cathode protective system as it conducts electricity. In fact, its electromechanical behavior is akin to sand, provided that the hydraulic mortar plating is homogeneous and in constant contact with the anti-corrosion casing of the tanker, which, instead, must be uniform and in constant contact with the tank itself. It does not constitute an additional barrier to electrical insulation to that of organic anticorrosive coating, the resistance of which is adjustable. This means that the currents produced by the cathodic protection are sufficient and therefore easy to suspend on site and directly comparable to the values measured for sand. Not only is the hydraulic mortar plating compatible with the sacrificial anode cathode protection system discussed above, but the experience gained with conventional installations can be directly applied to the plumbing mortar plating. There are no significant differences between the control values for cathodic protection in a tanker installed using the conventional method and a tanker installed using the method of the invention.

Due to its solid and conductive nature due to the fact that it contains water, the hydraulic mortar prevents air occlusion which may occur in other types of additional layers of insulation sheathing.

Also, the hydraulic mortar plating does not affect the tanker's ability to evaporate liquefied natural gas due to its favorable heat transfer coefficient.

183 376

Of course, the hydraulic mortar plating of the additional layer can be reinforced. It is possible to use any of the known reinforcement materials for this purpose. The fibrous materials, for example, can be mixed with the hydraulic mortar during the manufacture of the tanker, more precisely, while an additional plating layer is applied by spraying the hydraulic mortar, for example, on the anti-corrosive plating of the tanker.

However, it is also possible and even preferred that the tank itself is a frame for the hydraulic mortar skin by securing the hydraulic mortar skin to the corrosion protection plating at all points. This can be done by adding a thin direct layer of adhesive between the plumbing and anti-corrosion plating in such a way that the two layers are connected at all points. The adhesive used may be one of the resin compositions, such as epoxy, acrylic, styrene butadiene resins. The adhesive is sprayed as a liquid onto the anti-corrosion plating and then hardens. Fresh plumbing mortar is then applied to the adhesive while it is still sticky and as it hardens, the plumbing mortar is firmly attached at all points to the anti-corrosion layer. The same bonding effect can be achieved without an intermediate adhesive layer. This is due to the fact that the anti-corrosion plating itself is sprayed in liquid form onto the tank and then hardens. If the hydraulic mortar is applied directly to the anti-corrosion skin layer while it is still sticky, the two layers will be bonded as tightly as if there was an adhesive between them. In both cases, the hydraulic mortar plating is placed over the tanker before it is buried in the ground.

Taking into account the fact that the tank according to the invention does not require the use of sand, the procedure for installing and burying the LNG tank is different.

The present invention provides a verified method for installing a flame-resistant type pressure tanker adapted to contain liquefied natural gas and to be buried in the ground with an attached cathodic containment system having at least one sacrificial anode, including a gas-tight steel sheet vessel having an inner surface forming a chamber, in which liquefied natural gas and the outer surface are stored, and - a layer of passive anti-corrosion plating covering the entire outer surface of the tank.

At least one sacrificial anode, buried in the ground, is electrically connected to the tank with a connection through a plumbing mortar plating and an intermediate adhesive layer, if used. The tanker is then buried with the outer plating made of hydraulic mortar in direct contact with the natural soil in the ground.

The manner in which the installation is carried out is original to the traditional installation of tanks, the present invention also relates to a liquefied natural gas storage burying installation using a pressure-resistant type tank car of a flame-resistant type, designed to contain liquefied natural gas and to be buried in the ground, including a gas-tight tank made of sheet steel, having an inner surface forming a chamber in which liquefied natural gas is stored, an outer surface and a layer of passive anti-corrosion plating covering the entire outer surface of the vessel, and electrical cables connecting the vessel to at least one sacrificial anode, which is also buried and placed in direct contact with natural soil, electric cables also pass through the anti-corrosion layer.

The tanker according to the invention has a plating layer made of hydraulic mortar through which electric cables also lead, the hydraulic mortar plating forming the outer surface of the tank being in direct contact with the natural soil in the ground.

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If an intermediate adhesive layer is placed between the anti-corrosion skin and the hydraulic mortar, the electrical wires pass through this intermediate adhesive layer.

Publishing Department of the UP RP. Circulation of 50 copies

Price PLN 2.00.

Claims (7)

Patent claims 1.A liquefied natural gas storage and burying tank with an attached cathodic containment system having at least one sacrificial anode, containing a gas-tight sheet steel tank having an inner surface forming a chamber for storing liquefied natural gas and an outer surface; and a layer of passive anti-corrosion plating covering the entire outer surface of the tank, characterized in that it has an additional plating layer (23) made of hydraulic mortar, which completely covers the anti-corrosion plating (10) and is intended to come into direct contact with the natural soil (13) in the ground, the thickness of the hydraulic mortar is not greater than 20 mm. 2. A tanker according to claim The method of claim 1, characterized in that the plating layer (23) of the hydraulic mortar has a uniform thickness. 3. A tanker according to claim The skin as claimed in claim 1 or 2, characterized in that the plating layer (23) of the hydraulic mortar is connected to the anti-corrosion plating layer (10) at all points. 4. A tanker according to claim The skin as claimed in claim 3, characterized in that the plating layer (23) of the hydraulic mortar is directly connected to the anti-corrosion plating layer (10) at all points. 5. A tanker according to claim The method of claim 3, characterized in that there is an intermediate layer of adhesive (26) which is connected to the plumbing layer (23) to bind the plumbing layer (23) to the anti-corrosion skin layer (10) at all points. 6. A tanker according to claim 3. The method of claim 3, 4 or 5, characterized in that the anti-corrosion plating layer (10) is made of a passive organic material selected from the group of epoxy paint-containing compounds. 7. A tanker according to claim The method of claim 5, characterized in that the adhesive substance (26) is selected from the group of compounds comprising epoxy resins, acrylic resins and styrene-butadiene resins. * * *