FR2655861A1 - Gas or liquid storage tanks, equipped with a flame protection structure - Google Patents

Abstract

The invention relates to a gas or liquid storage tank. According to the invention, below the lower part of the tank (1) and facing at least the base of the side walls, a flame protection structure is provided, comprising deflectors (baffles) (5, 6) consisting of metal or concrete plates, optionally lined, on at least one of their faces, with a fire protection coating, the said deflectors being arranged at a sufficient distance from the tank for a large volume of air to be interposed between them and the tank.

Description

 Gas or liquid storage tanks, equipped with a flame protection structure.

 The present invention relates to improvements made to gas or liquid storage tanks.

It relates more particularly to tanks of this type, of spherical or cylindrical shape, horizontal or vertical, with or without thermal insulation, and of various dimensions, which can reach several meters in diameter and several tens of meters in height or length, which are equipped with a flame protection structure.

 It is known that, in the field of thermal insulation and fire protection of metal tanks, different techniques are used, depending on whether they are tanks containing liquids or gases at temperatures higher or lower than the ambient temperature. Precautions must be taken to avoid, on the one hand, the phenomena of condensation in the insulation, when the tanks are at a temperature above OOC, but below ambient temperature, on the other hand, the phenomena of condensation and ice formation in the insulation, when the tanks are at negative temperature.

 The presence of moisture in the insulation increases heat losses, while the formation of ice in the insulation not only causes its destruction, but can also, due to the rapid development of the volume and weight of ice , cause disorders in all or part of the tank. Finally, the condensation water in the insulation, although it is distilled water, becomes aggressive after contact with the materials present.

 To obtain the desired thermal insulation and fire protection, various insulators are used, depending on the temperatures of the products stored and the characteristics of the most likely fire. Insulators of the sprayed or bonded polyurethane type or of the bonded polystyrene type (bonded cell), cannot be used because of their poor heat behavior (low melting point, risk of ignition, release of noxious fumes and gases. ..).

Above 500 C, the double function mentioned above (thermal insulation and fire protection) is ensured by one of the following systems
- ceramic fibers or rock fibers under screwed or riveted sheet metal
- rock fibers flocked under screwed or riveted sheet;
- rock fibers and sprayed cement / vermiculite coating.

 Between 50C and 500 C, the tanks do not have thermal insulation; fire protection is provided by a sprayed cement / vermiculite coating.

 Between OOC and 50C, any penetration of moisture into the insulation must be prevented; the aforementioned double function is ensured by a system of cellular glass bonded and grouted, vapor barrier and coated with sprayed cement / vermiculite.

 Below OOC, moisture must be prevented from entering the insulation and fire protection; the desired dual function is then ensured by a glued and grouted cellular glass system, coated with cement / vermiculite completely free of its free water, and vapor barrier.

 However, the drawbacks of the usual systems combining thermal insulation and fire protection, applied to tanks with a service temperature below OOC, essentially stem from the fact that water penetration into the insulation must be avoided at all costs and in fire protection. The vapor barrier cannot be placed between the insulation and the fire protection, because condensation and freeze / thaw cycles in the fire protection would inevitably lead to cracks and alterations in its behavior over time.

On the other hand, the weight of the protection and the differential expansion and contraction movements between the fire protection and the tank can only lead to cracks or tears in the vapor barrier.

 In order for the vapor barrier to be placed outside the insulation-fire protection complex, it must be free of free water. As the sprayed cement / vermiculite coating is based on hydraulic binder, it is therefore necessary to wait for complete drying before applying the vapor barrier.

 In practice, in the case of a sprayed plaster, total natural drying is practically impossible, even if it takes several months. To achieve this, a long and costly parboiling should be carried out. In both cases, the delay is incompatible with the process of carrying out the work.

 One could consider using prefabricated elements of cement / vermiculite, previously steamed, mechanically fixed on the insulation and covered with a vaporizer, but the joints between these elements must not have a weak point from the point of view of fire protection, and the way to achieve them without the introduction of hydraulic binder has not been satisfactorily resolved.

 Fire protection of the cement / vermiculite coating type has a particular characteristic, upon exposure to fire, by the very fact of the hydraulic binder used in its composition. Indeed, from 1000C, the water of crystallization of the cement is released in the form of vapor and, during all the duration of this vaporization, the temperature of the product remains close to 1000C; this duration is called "vaporization level". When all the water of crystallization is released, the product rises in temperature more or less quickly, depending on its thickness and composition, on the one hand, and depending on the thermal capacity of the support, on the other hand.

 If the support is directly the metal of the wall of the tank, the rise in temperature will be all the more rapid as the thickness of metal is low (low thermal capacity). If the support is thermal insulation (assimilated to a low thermal capacity), the temperature rise of the fire protection will be very rapid, whatever the massiveness of the wall of the tank located behind the thermal insulation.

 It will result from this that the reinforcement placed in the fire protection materials, to ensure their maintenance, will be brought to a very high temperature and will no longer be able to support the cumulative weights of the fire protection and of the insulation, in the case of tanks. large dimensions, such as spheres, for example. It should be noted in this connection that the lower hemisphere of a large sphere can have an external surface of 700 m2, corresponding to an insulation and fire protection weight greater than 15 tonnes; from a certain temperature, the underlying paint is softened and it is not possible to rely on adhesion to support the protection; the total weight is taken up in pure traction towards the equator of the sphere.

 In addition, tanks containing dangerous gases or liquids are periodically subjected to structural checks (absence of corrosion, cracks, fatigue, etc.).

 When these tanks are coated with thermal insulation and / or fire protection, it is necessary to make openings in these coatings in determined locations, to make measurements, or to completely remove these for carrying out an examination. complete surface condition (paint and absence of corrosion). These operations are very expensive and entail a long immobilization of the installation, lasting several months in the case of the spheres.

 In addition, traditional vapor barriers are made of materials which have a non-zero water vapor permeability, which inevitably leads to progressive condensation and ice formation. These phenomena lead to premature aging of the insulation, which makes it necessary to carry out an effective and costly painting of the tank to limit corrosion, on the one hand, and to replace the insulation after a few years of use, on the other hand .

 The invention aims to remedy these drawbacks of the known technique by proposing gas or liquid storage tanks which have two well-separated functions of thermal insulation and fire protection, producing their effects both when the products stored are cold. only when they are at higher temperatures, whatever the conditions of the ambient atmosphere.

 To this end, the invention relates to a gas or liquid storage tank, characterized in that, below its lower part and facing at least the base of the side walls is provided a protective structure against flames, comprising deflectors made of metal or concrete plates, optionally coated on at least one of their faces with a protective coating against fire, said deflectors being placed at a sufficient distance from the tank so that a large volume of air is interposed between them and the tank.

 The deflectors will have shapes and heights appropriate to the dimensions of the tank and the height of protection to be provided. They will generally consist of flat or curved plates, fixed on a frame integral with the tank, or independent of it.

 The plates constituting the deflectors may be made of mild steel sheet, stainless steel sheet or any other material; they may be bare or protected on one or both sides with a fire protection coating such as cement / vermiculite, fiber cement, protective panels such as fibressilicate, or by any other product applied against the deflectors.

 The frame supporting the deflectors will be made of steel and will possibly receive protection intended to reduce its rise in temperature during the fire, thus ensuring their stability for the required time.

 When there is a risk of explosion, the plates and their framework will be reinforced or will be made of reinforced concrete.

 In the most common cases, the deflectors will be placed opposite the wall of the tank or its insulation, at a sufficient distance to allow the circulation of maintenance personnel in the meantime.

The state of the wall, or the state of the thermal insulator, will thus be permanently visible.

 The shape and the assemblies of the deflectors between them will be defined so as to reduce the passage of flames and to allow the flow of rainwater and liquids possibly coming from a pipe or tank leak.

The Applicant has established, in fact, that the presence of a large air gap between the deflectors and the tank contributes to a very significant reduction in heat transfer
- in the case where insulation is applied against the tank, the temperature of the insulation, during the fire, can be lower than its limit temperature of use, in particular when using cellular glass
- in the case where no insulation is applied, the temperature of the tank may be much lower than that which would have been reached in the case of protection applied directly against the tank.

 As a result, the temperature reached by the reservoir will be much lower, not only at the collapse limit temperature, but also at the critical pressure temperature. In most cases, the tank can be re-used after the fire, possibly with the thermal insulation retained.

 Advantageously, screens can be placed around certain pipes, so as to avoid that in the event of a leak, a jet of ignited liquid or gas does not come to lick the wall of the tank.

 The screens will be made of mild or stainless steel sheet or any other material, and will be placed in appropriate places.

 The part of the tank or its supports, located below the deflectors, will be protected against fire by a traditional system, for example cement-vermiculite, cement-fiber, ceramic fiber or any other suitable material.

 Various forms of implementation of the invention will be described below, by way of nonlimiting examples, with reference to the attached schematic drawings.

On these drawings
Figure 1 is an elevational view of a vertical cylindrical tank equipped with a protective structure according to the invention
Figure 2 is a view similar to Figure 1 of a vertical cylindrical tank provided with thermal insulation
Figures 3 and 4 are views, respectively in side elevation and end, of a horizontal cylindrical tank equipped with a protective structure according to the invention
Figures 5 and 6 are views similar to Figures 3 and 4 of a horizontal cylindrical tank provided with thermal insulation
Figures 7, 8 and 9 are elevation views of three vertical cylindrical tanks equipped with three other protective structures according to the invention
Figures 10 and 11 are views in vertical elevation of two spherical tanks equipped with fire protection structures according to the invention
Figures 12 and 13 illustrate the possibility of interposing protective screens between tanks and piping or piping connection flanges.

 Reference will first be made to FIG. 1, where a vertical cylindrical reservoir 1, of circular section, is equipped, around its hemispherical base and at a certain distance from it, with deflectors 5 and 6.

The legs 3 supporting the tank, the bottom of the tank 2, and the frame 4 supporting the deflectors 5 and 6 will advantageously be protected by a thermal insulator, intended to counter their rise in temperature in the event of fire. The frame 4 will be adjacent or concentric to the legs 3.

 The base of the cylindrical lateral wall of the reservoir 1 is therefore protected by deflectors 5, coaxial at the bottom of this cylinder and defining a frustoconical framework, and by deflectors 6, coaxial at the middle part of the reservoir and defining a saturated bone. cylindrical. The deflectors 5 and 6 will consist of metal or concrete plates, bare or coated with a fire protection product, and they will also be carried by the frame 4 or a complementary frame.

 In the case of FIG. 1, the tank 1 is bare, while, in the case of FIG. 2, where the described bodies keep the same reference numbers assigned to the index ', the tank 1' is protected externally by a thermal insulator 7 '.

 Similarly, FIGS. 3 and 4 show a horizontal cylindrical tank 10, resting on legs II and protected at its base from possible flames of a fire by planar deflectors 12, inclined symmetrically in the direction of the median vertical plane of the tank 10, so as to form a V-shaped structure, and supported by a frame 13.

 In the case of Figures 3 and 4, the tank 1 is bare, while in the case of Figures 5 and 6, where the bodies already described in connection with Figures 3 and 4 are designated by the same reference numerals, the tank 10 'is provided externally with a thermal insulator 14'.

 In FIG. 7, a reservoir is seen in all points similar to that of FIG. 2, where the members already described in relation to this figure are designated by the same reference numbers assigned to the index ", with the only difference that the deflectors 6 "are no longer parallel to the axis of the tank 1" and no longer define a cylindrical structure, but are inclined in the direction of this axis to form a frustoconical structure coaxial with the tank 1 '.

 Similarly, FIG. 8 represents a reservoir similar to that of FIG. 1, where the members already described in this figure are designated by the same reference numbers assigned to the index a, with this only difference as the deflectors 6, defining a cylindrical structure coaxial with the reservoir 1, are replaced by two sets of deflectors, respectively 6a and 6'a parallel, inclined in the direction of the axis of the reservoir la, to define two frustoconical structures coaxial with the reservoir la.

 Flame protection structures, similar to those of FIGS. 7 and 8, can also protect horizontal cylindrical tanks, the deflectors being, in this case, no longer inclined towards the axis of the tank to define frustoconical structures, but formed from flat plates parallel to this axis and symmetrically inclined on either side of the vertical median plane of the tank in the direction of this plane.

 In the case of FIG. 9, there is a vertical cylindrical reservoir at all points similar to that of FIG. 8, the members of which already described in relation to this figure are designated by the same reference numbers assigned to the index b, with this only difference that the deflectors 5b arranged at the base of the tank are no longer inclined in the direction of the axis of this tank 1b, but are arranged horizontally to define a planar annular structure forming a floor, perpendicular to the axis of the tank, while the deflectors 6b are arranged vertically and concentrically with the axis of the tank lb, to form a cylindrical structure perpendicular to the horizontal deflectors 5b and adjoining them, to form with them, for the maintenance personnel of the tank, a path circulation of these personnel outside the tank.

 A protective structure similar to that of FIG. 9 could similarly equip a horizontal cylindrical tank, with deflectors defining a horizontal floor and deflectors perpendicular to the previous ones forming vertical side walls, to also form a staff circulation path maintenance.

 In the case of FIG. 10, the spherical tank 20, supported by legs 21, is protected from the flames by a structure comprising sets of deflectors 22 and 23 connected together and arranged coaxially with respect to a vertical axis passing through the center of the sphere. The deflectors 22 arranged below the tank define a spherical or frustoconical structure, while the lateral deflectors 23 define a frustoconical structure. The deflectors 22 are crossed by the feet 21 of the tank and are supported by structures 24 concentric with the feet 21 which are thus protected.

 FIG. 11, where the members already described in relation to FIG. 10 are designated by the same reference signs assigned the index ', represents a reservoir 20' protected from the flames by a protective structure comprising three sets of deflectors 22 ' , 23 'and 25', supported by supports 24 'concentric with the legs 21' arranged coaxially to a vertical axis passing through the center of the reservoir 20 ', to form three substantially frustoconical structures. The side deflectors 23 'and 25' are substantially adjoining, while the deflectors 22 ', arranged below the tank 23', are offset downward relative to the adjacent deflectors 23 '.

 As shown in FIG. 12, a curved deflector 30, forming a screen, may be interposed between the reservoir 31, in the form of a horizontal cylinder or a sphere in the case of the drawing, and a neighboring pipe 32, the concacity of the deflector being turned towards piping.

Such a deflector can also be interposed between two neighboring pipes.

 Similarly, a curved deflector 35, forming a screen, may be interposed between two connection flanges 36a, 37a of two pipes 36 and 37 and a neighboring tank 38, in the form of a vertical cylinder in the case of the drawing, the concavity of the deflector 35 being turned towards the flanges 36a and 37a.

 The invention therefore provides simple and easy to implement means for the protection against flames of cylindrical or spherical tanks for liquids or gases, and for the protection of annexed organs.

Claims (11)

 1. Gas or liquid storage tank, characterized in that, below its lower part, and facing at least the base of the side walls, a flame protection structure is provided, comprising deflectors (5,6 12 12; 22,23,25) consisting of metal or concrete plates, possibly coated, on at least one of their faces, with a protective coating against fire, said deflectors being arranged at a sufficient distance from the tank so that a large volume of air is interposed between them and the tank.  2. Tank according to claim 1, characterized in that the structure formed by said deflectors comprises at least one horizontal part (5b) forming a floor, of sufficient width to allow the passage of maintenance personnel.  3. vertical cylindrical tank (1, 1 ', 1 ", la) according to claim 1, characterized in that it comprises a set of lateral deflectors (5, 6; 5', 6 ', 5", 6 " ; 5a, 6a, 6'a) arranged coaxially with the axis of the reservoir and forming around the latter frustoconical or cylindrical structures substantially continuous.  4. Tank according to claim 3, characterized in that said deflectors are supported by a frame (4, 4 ', 4 ",, 4a) adjoining or concentric to the support legs (3, 3', 3", 3a ") of the tank or by an additional framework.  5. horizontal cylindrical tank according to claim 1, characterized in that said deflectors (12, 12 ') are planar deflectors arranged symmetrically on either side of the median plane of the tank and inclined in the direction thereof so as to form a V-structure.  6. Tank according to claim 5, characterized in that the support legs (11, 11 ') of the tank pass through said deflectors and in that these are supported by a structure adjoining or concentric with these support legs.  7. Spherical tank according to claim 1, characterized in that it comprises at least one set of deflectors (22, 23) arranged coaxially with a vertical axis passing through the center of the tank and forming a conical or frustoconical structure.  8. Spherical tank according to claim 7, characterized in that it comprises a first set of deflectors (22,22 ') of substantially frustoconical shape, arranged below the tank and at least a second set of deflectors (23; 23 ', 25') arranged laterally and forming a frustoconical structure.  9. Spherical tank according to claim 8, characterized in that the deflectors (22 ') arranged below the tank (10') are offset downward relative to the side deflectors (23 ', 25').  10. Spherical tank according to claim 8, characterized in that said deflectors are crossed by support legs (21,21 ') of the tank and are supported by a frame (24,24') adjoining or concentric with these support feet .  11- Tank according to one of claims i to 10, characterized in that curved deflectors (30, 35) forming a screen are interposed between the tank (31, 38) and the pipes (32) or the pipe flanges (36a , 37a) neighboring, said deflectors having their concavity turned towards said pipes or said flanges.