Device for holding an inside tank of a cryogenic liquid transport tank

Abstract

The cryogenic liquid transport tank (1) according to the invention comprises an inner reservoir (2), substantially cylindrical in shape, disposed within an outer casing (3). The inner reservoir (2) and the outer casing (3) are coaxial along axis X. The inner reservoir (2) is connected to the outer casing (3) by a support device. The support device is characterized in that it consists of a single cone (4) with axis X located at the center (12) of the tank (1) and connecting the inner reservoir (2) to the outer casing (3). There is only one fixed, strong, and reliable point and no movable support. The latter is more complex to design, and it is impossible to control its potential wear over time. Furthermore, its central position reduces the overhang and balances the loads on each side, thus reducing the stresses generated.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of tanks and more particularly those intended to transport cryogenic liquids by semi-trailers, trailers, carriers and wagons, or even by containers or swap bodies.

[0002] Transporting cryogenic liquids often involves a temperature difference of around 200°C between the liquid and the surrounding air, necessitating thermal insulation of the tank. Traditional insulation solutions use polyurethane or other combustible materials, but these are prohibited by the ADR (Agreement concerning the International Carriage of Dangerous Goods by Road) for products with a temperature below -182°C. Other solid materials, such as perlite, often require greater thickness, resulting in a higher overall mass, to achieve the same level of insulation. Given the maximum permissible gross vehicle weight, any additional mass reduces the transportable product mass. Even for lightweight products like methane, excessively thick insulation would exceed the permitted road transport dimensions.

[0003] For these various reasons, single-walled tanks with rigid insulation are now being abandoned for low-temperature liquid gases.

[0004] Today, the market favors double-walled tanks with a high vacuum between them to prevent heat transfer by conduction. These tanks consist of an inner reservoir containing the cryogenic liquid and an outer shell. However, with a 200°C temperature difference between the walls, radiation is very significant. This is managed either by filling the space between the walls with perlite (a rather heavy solution requiring a substantial thickness to limit conductive heat flow), or by using multi-layer insulation (MLI) like that used around satellites. The high vacuum and MLI solution is currently the most effective on the market. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0005] The use of double-walled tanks raises the issue of supporting the inner tank within the outer shell. These supports must address three main problems: Supporting the mass of the inner tank against gravity, but also against other accelerations it may encounter on the road; Resisting thermal expansion: the outer casing remains at ambient temperature while the inner tank can shrink by up to about 7 mm in diameter and 40 mm in length; Minimizing heat loss by conduction (using low-conductivity materials, small cross-sections and long lengths).

[0006] It is known to incorporate a cone at the rear and a sliding piece at the front. The sliding piece at the front allows the inner tank to slide relative to the outer casing during thermal expansion. However, this solution requires the cold section to slide within a perforated partition. As the cold section contracts upon cooling, play may develop in the connection, which will eventually lead to wear, or even, more seriously, fatigue and possible failure.

[0007] We also know of documents US 3 037 657 A1, FR 1 547 246 A1 and D3: GB 254 220 A1 a cone placed in the center of the tank.

[0008] We also know of a device consisting of two fixed and two movable pads positioned at the bottom. The pads are made of a stack of welded cones to limit conduction. However, controlling the play is difficult: enough is needed to allow movement, but not too much, as this would cause unwanted shocks. Long-term durability is not predictable.

[0009] Chains are also used to suspend the inner tank, or to place it on blocks.

[0010] However, these systems are not reliable enough, as the internal reservoir is not adequately maintained. SUMMARY OF THE INVENTION

[0011] The object of the invention is to address these problems and ensure reliable maintenance of the internal tank while allowing recovery of longitudinal expansion, particularly for tanks installed on semi-trailers, trailers, carriers, wagons, containers or swap bodies.

[0012] The cryogenic liquid transport tank according to the invention comprises an inner reservoir, substantially cylindrical in shape, disposed within an outer casing. The inner reservoir and the outer casing are coaxial along the X-axis. The inner reservoir is connected to the outer casing by a support device. The support device is characterized in that it consists of a single cone with X-axis located at the center of the tank, comprising a base and an apex, and connecting the inner reservoir to the outer casing. The base is positioned behind the apex, above the tank's running gear. There is only one fixed, strong, and reliable point of support, and no movable supports. Movable supports are more complex to design, and it is impossible to control their potential wear over time. Furthermore, the central position of the cone reduces the overhang and balances the loads on each side, thus reducing the stresses generated.

[0013] Advantageously, the apex is fixed to the center of the inner tank. In this case, the base will preferably be positioned behind the apex, above the tank's running gear, to absorb the stresses.

[0014] A key feature of the tank is that the filling pipes are located in its center. These pipes are positioned close to the tank's fixed point and are therefore minimally affected by tank contraction. This conical positioning limits differential expansion and stress in the inter-wall piping, because the further the drains are from the fixed point, the more they are subject to tank wall contractions.

[0015] Advantageously, the cone has perforations. These help to limit heat flow between the inner tank and the outer casing while also reducing the tank's weight.

[0016] Advantageously, the cone is fixed by welding.

[0017] According to a specific design, the cone has a length greater than 400 mm, preferably 500 mm. This helps to limit the heat flow between the tank and the casing. The cone will preferably have a length of 1.10 m.

[0018] Advantageously, the cone has a wall thickness between 3 and 10 mm. Since the tank has only one support point instead of two, the thickness of the cone must ensure sufficient stability of the inner reservoir.

[0019] According to another provision, the tanker is a semi-trailer.

[0020] A key feature of the outer casing is its two-part construction, each part consisting of a half-shell and a base. This makes mounting the tank within the casing easier, as each part is lighter to move than the entire casing.

[0021] According to a specific arrangement, one part of the outer shell is longer than a second part. This occurs when the base of the cone is offset from the center of the tank.

[0022] The invention also relates to a method for assembling a tank with at least one of the preceding characteristics; it is characterized in that it comprises the following steps: Assembly and welding of the cone apex onto the inner tank. Positioning of one section of the outer casing onto the inner tank and welding it to the base of the cone behind the apex, above the tank's running gear. Positioning of the other section of the outer casing onto the inner tank and welding it to the base of the cone to close the outer casing.

[0023] The assembly can be done horizontally or vertically.

[0024] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures, which are given only as examples. BRIEF DESCRIPTION OF THE FIGURES

[0025] [ Fig. 1 ] is a view of a semi-trailer according to the invention; [ Fig. 2 ] is a perspective view of the reservoir of the figure 1 : [ Fig. 3 ] is a side view of the tank; ] Fig. 4 ] is a side view of the tank with half of its casing; [ Fig. 5 ] is a side view of the cistern [ Fig. 6 ] is a perspective of the two-part outer envelope. DETAILED DESCRIPTION

[0026] In the rest of the description we will consider that the front corresponds to the front 10 of tank 1 on the side of the coupling and the rear to the rear 11 of tank 1 where the wheels 5 of the semi-trailer are located.

[0027] As can be seen at the figure 1Tank 1 is a double-walled cylindrical tank consisting of an inner reservoir 2 and an outer casing 3, the whole assembly oriented along a substantially horizontal axis X. A cone 4 is fixed to the center 12 of tank 1 between the reservoir 2 and the casing 3. The cone 4 has a base 40 and an apex 41. The base 40 has a larger diameter than the apex 41. The base 40 is connected to the casing 3 and offset towards the rear of tank 1, while the apex 41 is connected to the center of the reservoir 2.

[0028] It is possible to provide that the middle of the cone is located at the center 12 of the tank or that the base 40 is fixed to the center 12 of the tank 1 without departing from the scope of the present invention. The cone 4 being fixedly connected between the tank 2 and the casing 3 next to the pipes 6, it allows to limit as much as possible the stresses in these pipes 6 during the expansions of the tank 2.

[0029] Since the base 40 is connected close to the running gear 5, it facilitates the resumption of loads from tank 2.

[0030] The cone 4 is perforated with holes 42 in order to lighten it and limit the thermal conduction between the inner tank 2 and the outer casing 3. Here the holes 42 are round and of identical size but they could be of different shape and size.

[0031] Tank 1 has a gap between the walls of reservoir 2 and the outer casing 3. When the cryogenic liquid is loaded into reservoir 2, it will contract due to the cold, while the outer casing 3 will remain at ambient temperature and maintain its dimensions. Since the inner reservoir 2 is fixedly connected to the outer casing 3, the gap between them will increase, but because only the central section is fixed, the movement of the ends will have no effect on the outer casing 2 or the piping 6.

[0032] With the cone 4 placed at the center 12 of the cistern 1, the outer envelope 3 consists of two parts 30 and 31, each with a half-ferrule, respectively 300 and 310, and a bottom, respectively 301 and 311.

[0033] We can see on the figures 4 to 6 that the first part 31 of the envelope 3 is longer than the second part 30. This first part 31 is, in the illustrated example, arranged at the front 10 of the tank while the second part 30 is arranged at the rear 11.

[0034] In the illustrated example, the apex 41 of the cone 4 is placed in the center of the reservoir 2, therefore the base 40 is offset from the center 12 of the tank 1. The two parts of the envelope 3 are therefore of different sizes.

[0035] If, in another configuration, the middle of the cone 4 is at the center 12 of the cistern, its base 40 and its apex 41 are arranged symmetrically with respect to this center 12 and the two parts 30 and 31 of the envelope 3 are of identical size.

[0036] The assembly of tank 1, according to the illustrated method, is done as follows: We assemble and weld the apex 41 of cone 4 onto the middle of the inner reservoir 2 ( Fig. 3 ) ; A first part (here 30) of the outer casing 3 is inserted onto the inner reservoir 2 and welded to the base 40 of the cone 4 ( figure 4 ) ; A second part (here 31) of the outer casing 3 is inserted into the inner reservoir 2 and welded to the base 40 of the cone 4 ( figure 5 ).

[0037] The assembly can be carried out flat (horizontally) or vertically without departing from the scope of the present invention. The advantage of having a two-part casing is that these two parts are easier to handle regardless of the chosen assembly.

Claims

1. Tank (1), for transporting cryogenic liquid, comprising a running gear and a substantially cylindrical-shaped inner tank (2) disposed within an outer casing (3), the inner tank (2) and the outer casing (3) being coaxial with respect to an axis X, said inner tank (2) being connected to the outer casing (3) by a supporting device, the supporting device consists of a single cone (4) having the axis X situated at the centre (12) of the tank (1), comprising a base (40) and a top (41), connecting the inner tank (2) to the outer casing (3), characterised in that the base (40) is disposed behind the top (41) above the running gear of the tank (1).

2. Tank (1) according to claim 1, characterised in that the cone and the top (41) are attached at the centre of the inner tank.

3. Tank (1) according to one of the preceding claims, characterised in that it comprises hoses (6) for filling the inner tank (2), disposed at the centre (12) of the tank (1).

4. Tank (1) according to one of the preceding claims, characterised in that the cone (4) has perforations (42).

5. Tank (1) according to one of the preceding claims, characterised in that the cone (4) has a length greater than 400 mm.

6. Tank (1) according to one of the preceding claims, characterised in that the cone (4) has a wall thickness of between 3 and 10 mm.

7. Tank (1) according to one of the preceding claims, characterised in that the tank (1) is a semi-trailer.

8. Tank (1) according to one of the preceding claims, characterised in that the outer casing (3) consists of two parts (30, 31), each comprising a half-ferrule (300, 310) and a bottom (301, 311).

9. Tank (1) according to the preceding claim, characterised in that a first part (31) is longer than a second part (30).

10. A method for assembling a tank (1) according to one of the preceding claims, characterised in that it comprises the following steps of: - Mounting and welding the top (41) of the cone (4) to the inner tank (2), - Positioning a part (30, 31) of the outer casing (3) on the inner tank (2) and welding it to the base (40) of the cone (4) behind the top (41) above the running gear of the tank (1). - Positioning the other part (31, 30) of the outer casing (3) on the inner tank (2) and welding it to the base (40) of the cone (4) to close the outer casing (3).

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