WO1991015418A1

WO1991015418A1 - Floating roof of synthetic material for liquid storage tank

Info

Publication number: WO1991015418A1
Application number: PCT/NL1991/000044
Authority: WO
Inventors: Piet Hugo Alphonsus Van Der Kuil; Alexander Faber; Robert Kroesbeek
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-03-22
Filing date: 1991-03-22
Publication date: 1991-10-17
Anticipated expiration: 1992-09-22
Also published as: FI915467A0; JPH05504924A; AU7781191A; FI915467A7; CA2057921A1; TW221684B; NL9000684A; KR920701015A; EP0473778A1

Abstract

The improvement relates to a method for the installation of a floating roof structure in a closed liquid storage tank and also it relates to the tank roof structure obtained thereby. It is the purpose of the invention to compose out of a great number of interconnectable synthetic modules or synthetic sandwich boards (3) backed up by a large number of prefabricated low frame profiles (4), an integral floating roof structure (1) of extremely lightweight construction. Furthermore it is particularly important as a feature that this floating roof structure (1), by its own rigidity and its overall strongness, can fully operate itself as a building site because of the fact that the traverse frame profiles (4) used for strenghtening the roof surface structure by interconnecting sandwich modules (3) have a height of e.g. no more than 2 times the single height of a module, i.e. no more than 15 cm. The level of liquid in the storage tank is now covered to a high degree, and apparently it is now possible to suppress even the recent tolerable rate of vaporization enormously, thereby contributing much to the desired degree of environmental purity.

Description

FLOATING ROOF OF SYNTHETIC MATERIAL FOR LIQUID STORAGE TANK

The invention relates to a method for the installation of a floating roof structure in a dosed liquid storage tank and further it relates to a floating roof obtained thereby.

In view to steadily increasing requirements in environmental legislation for the storage of volatile liquid products it becomes a tendency to avoid the creation of a level of liquid underneath the floating roof as such creation could give rise to substantional environmental problems.

Storage tanks for liquid products may have a diameter from e.g. 8 to nearly 88 meters and in the latter case enormous volumes of liquid vapour must be discharged to the open air. This encounters extensive environmental problems because mostly such stored volatile liquids dangerously affect the breathing of human beings and animals.

Metal floating roof structures are known which may sink down as a result of liquid movements and/or leakage, resulting again In the creation of a level of liquid. Also there do exist floating roofs which are underneath covered with an aluminium foll yet giving rise to locally created levels of liquid, causing the aforementioned disadvantages. Moreover a floating tank roof structure must be sufficiently strong to be usable as a building site for carrying out repair activities.

According to the invention a floating roof structure, also serving as a building floor may be installed in a closed storage tank for liquid, which roof is composed of a number of interconnected synthetic modules thereby carrying out the following steps:

a. a great number of fully enclosed sandwich module board elements of reinforced synthetic material, provided with a core of hard foam and also being locally provided with insert pieces of screwable material, are lengthwise so positioned that they constitute altogether an uninterrupted flat working floor surface, which by providing of corresponding roundings for the tank wall, will correspond in its shape and its size with the floating roof to be installed, whereas this working floor is supported, at least for a substantial part, by a temporary and premounted fiat horizontally positioned roof support scaffolding structure which is located underneath and at a certain distance from the tank bottom;

b. at the upper side of the working floor and in a direction which is perpendicular to the longitudinal axis of sandwich module boards there are positioned a number of oblong transverse frame profiles which are fixedly connected to the sandwich module boards by means of fasteners thereby providing for a stiff integral roof structure;

c. thereafter the roof structure is provided with operational means such as: i. a manhole in order to carry out activities underneath the roof structure;

ii. at choice a number of roof structure supporting legs, which may or may not be adjustable;

iii. a number of cable bushings for the use of anti-rotation cables to prevent an undesirable rotation of the roof structure;

iv. at choice a number of drainages for condense liquid;

v. at choice a number of air inlet and air discharge means; whereafter the horizontal roof support scaffolding structure is dismounted and taken out of the tank allowing the floating roof structure to rest upon its own supporting legs or to rest upon a number of fixed supporting legs which ware installed before on the bottom of the tank;

d. the longitudinal and traverse seams between adjacent modules of the working floor for the roof structure are sealed off at the bottom side of the roof structure by means of self-adhesive tape thereby forming a totally flat surface, whereafter for the prevention of gas and air inclusions, the seam slit is further fitted up with synthetic material of the skin material of the sandwich module, the self adhesive tape being removed or not after hardening;

e. the flexible tank wail seal is thereafter mounted to the circumferential edge of the roof structure.

In a preferred embodiment of the invention the floating roof structure is built up of sandwich module boards and traverse frame profiles, characterized in that a traverse frame profile has a polygonal vertical cross section and is composed by two preferably rectangular tubular profiles, one on top of the other, particularly a lower square tubular profile and on top of it an upper rectangular tubular profile, resting upon its short rectangular side.

It is effective to build up the tank roof structure according to still another embodiment of the invention with a number of cut-off profiles each time having a length of at least two times the width of a sandwich module is applied for, in such a way that every time the utmost ends of the lowermost square tubular profiles and also the utmost ends of the upper rightangled tubular profiles are always located in the central portion of the sandwich module.

It appears that for easy handling the length of a cut-off profile preferably amounts 1,000 mm whereas the total integral cross section of the traverse frame profile amounts to 50 x 50 and 50 x 30 square mm respectively.

Thereby the stiffness of the built up tank roof structure may be efficiently obtained while using a standard sandwich module having a width of 500 mm, a length of 6,000 mm and a thickness of 50 mm.

In order that a sandwich module possesses sufficient rigidity it may be provide in a direction perpendicular to its longitudinal axis with integral insert pieces of screwable material at regular distances preferably made of hard screwable polylamlnated wood (Multiplex), which pieces are incorporated in the foamed core material for the fixind of screws and suchlike fixing elements in and to the sandwich module.

According to the invention at its bottom side, the tank roof structure is entirely flat except for the presence of a required manhole flange and various

bushings (for cables, air inlets, air outlets, supporting legs) respectively so that it is virtually impossible that spaces are created having a level of liquid. At the one hand the floating tank roof structure is light enough to float upon the level of liquid whereas at the other hand it is pertinently unsinkable, this embodiment of its structure constitutes such a rigidity that no liquid volumes are collected upon the tank roof and thus no unallowable vaporization will occur.

By using a great number of adjustable support legs provided for underneath the floating tank roof structure, the entire roof structure is equally supported on various locations wlth respect to the bottom of the storage tank and all provisions are available to make the operational use of the tank roof structure profitable, thereby excluding any disadvantages which inherently affect existing floating tank roof structures.

According to another embodiment of the invention there are provided air inlet and air discharge means for a tank roof structure consisting of a potshaped housing, having a number of parts, provided with at least one fixing flange for connecting it with the opening in a sandwich module and a cup shaped cover of the housing being provided with a number of air inlet and discharge openings respectively which are covered by a flexible non-return valve, a vertically movable bar being centrally petitioned in the cover, which bar is provided at its upper end above the cover with an eyelet for connection to a cable and within the housing under the cover and perpendicular thereto said bar is provided with a number of closed discs, each having an outer circumferential downwardly directed cupshaped edge, whereas the inner side of said housing is provided with a number of corresponding downwardly directed funnel-shaped concentric baffles, in such a way that vapors passing through said means are forced to escape via this labyrinth seal.

Also according to the invention there is provided for in a permanent fixation by means of a magnet keeping the floating roof structure in place by means of anti- of the tank by means of anti-rotation cables characterized in that a flat magnet is provided having horizontally and centrally respectively in at least two mutually perpendicular directions a number of anti-tilting elements, one and the other such a way that a possible tilting point or tilting Ine with respect to said fe located substantially far away and outwardly from the utmost borderline of the circumferential edge if the permanent magnet which holds to the bottom of the storage tank.

The invention will now be further described with reference to the accompanying drawing of an embodiment shown at different scale dimensions.

Fig. 1 is a schematic upper view of a floating tank roof structure aocordlng to the invention;

Fig. 2 shows schematically and in cross section the location of the tank roof structure which is supported upon the bottom of the tank by means of a great number of support legs;

Fig. 3 shows separately a synthetic module as part of the flat surface of the tank roof;

Fig. 4 te partially a cross section through a preferred embodiment of the tank roof structure taken at the sealing off against the wall of the tank;

Fig. 5 also shows a partial cross section of another preferred embodiment of a tank roof structure as shown in Fig. 4;

Fig. 6 is a cross section of the traverse frame profiles which are applied for to render the required stiffness and strongness to the tank roof structure;

Fig. 7 shows a special anchoring structure to fix the position of the floating tank roof;

Fig. 8 is a cross section of a bushing in the tank roof in use for a dipstick gauging tube and for anti-rotation cables;

Fig. 9 is a cross section of a sampling device provided for in the tank roof, provided with a star-shaped flexible non-return valve;

Fig. 10 is a liquid vapour-overpressure drain valve provide with a labyrinth seal avoiding liquid to arrive upon the tank roof;

Fig. 11 is a cross section of the manhole structure for the tank roof.

According to the invention the method basically consists in the composition of on entire floating tank roof 1, shown in Fig. 1 and 2, which has a flat synthetic board covering 2 having floating properties. The strongness and the stiffness of the synthetic covering 2 is obtained by interconnecting a great number of sandwich modules 3 to form a flat surface while using traverse frame profiles 4, each of which is constituted by a number of tubular, preferably rectangular profile which are traversally coupled to the sandwich modules 3 In a special manne Prior to building up a floating tank roof 1 at the Inside of a storage tank 5 there is erected upon the bottom 7 of the tank, at a workable level of e.g. 80 cm, a scaffolding having a flat upper surface (not shown here) upon which the sandwich modules 3 are positioned. After completion of the tank roof structure this scaffolding must be dismounted and finally be carried away through the manhole 8. Upon this flat supporting surface ad sandwich modules 3 are now horizontally positioned according to Fig. 1 and nearby the wal 9 of the tank the sandwich modules 3 are adapted to the rounded shape. Internally these sandwich modules 3, see Fig. 3, are provided with a foamed core material 10 which is composed from e.g. a flat core of hard foam sandwiched between two glass fiber reinforced outer skins 11. It is obvious that the sandwich module 3 is entirety unsusceptible for affection by the liquid stored in the tank 6; this being important in the event of mechanical damage to the tank roof structure. The thickness of the sandwich module 3 is e.g. 50 mm whereas the outside dimension of a single, preferably rightangled, in the drawing shown square profile 5, embodiment amounts to 50 x 50 mm. Figs. 4 and 5 show the arrangemert of the traveree frame profiles 4 in a direction perpendicular to the longitudinal axis of the oblong sandwich module 3. One tubular profile 5 which has a rectangular cross section, having an overall length of e.g. 100 cm, is bondwtse placed upon a first lower row of tubular profiles 5, see Fig. 6, and it is effective to let the longitudinal seam 12 between adjacent sandwich modules 3 coincide with an abutting seam 12' between the square profiles 5. It is advantageous for obtaining a greater resistance against bending to compose a traverse frame profile 4 from a lower square tubular profile on top of which in an upright position, a narrower rightangled tubular profile is positioned. The traverse frame profile is a reversed T-profile composition; dimensions 50 x 50 mm and 50 x 30 mm respectively. At the one hand installation takes place with short standard lengths, at the other hand It simplifies a quick mounting and disassembly respectively. In the hard foam core material of a sandwich module 3 and upon regular distances there is integrally Incorporated an insert piece 13 of hard screwable material sufch as polylamlnated wood (Multiplex), which will stand the fixation of fixing elements, like screws 14.

After all preparations have been made and the tank roof structure has been completed, all longitudinal and traverse seams 12 between adjacent sandwich modules 3 must be sealed off against liquid. To that purpose the seams 12 are now at the bottom side of the tank roof structure entirety sealed off with self- adhesive tape and than these seams are fined up from the top side with the same material of which the skin covering 11 is made. After hardening out there is created an integral roof which fulfills all required properties with respect to its own floating power. The self-adhesive tape may be removed after hardening out of the filled out seam, however this is not always necessary.

After the tank roof structure has been completed, the seaftng 15 must be installed its construction being here described in a global way only. In Fig. 4 an endless sealing tip 16 is liquid tight connected by means of a colar 17 to the edge of the tank roof 1 and the position of the tank roof 1 1s defined also by a spring element 18 the one end 19 of which is connected to a seal lip 16 whereas the other end

20 is fixed, through a spring loop 21, to the tank roof 1. Fig. 5 shows another wall seal in cross sectional view, consisting of a flexible bumper 16' which is fixed to the tank roof 1 by means of a distance holding device 18'. Fig. 7 shows a bushing 22 in the sandwich module 3 for an anchoring cable 23. The upper end of this anchoring cable 23 is fixed to the fixed roof of the storage tank 6 and its lower end 24 is connected to the upper side of a permanent magnet 26 by means of a spring 25, it is the purpose to anchor the magnet 26 to the bottom 7 of the tank, the presence of a number of anti-rotation cables 23 thereby holding the position of the floating tank roof 1. The magnet 26 is provided with protrusions 27 e.g. from strip material which is fixed to the body of the magnent 26 by means of clamping or the like thus bringing the tilting point far away from the permanent magnetic surface, thereby guaranteeing the permanent location of the magnet 26 with respect to the bottom 7 of the tank. The extra advantage of this faculty, which is uhbreakably connected to the tank roof structure, is the total avoidance of socalled hot spotwelding to the bottom 7 of the tank.

In Fig. 8 another bushing 28 is shown for a fixed gauging tube (not shown here). A flexible collar or cup 29 is clamped between a fixed flange 30 which b bolted by means of bolts 14' around an opening in the tank roof 1 and a removable flange 31 so that the tank roof 1 can move in an upward and downward direction with respect to the fixed gauging tube. If necessary, the whole tank roof 1 may be sunk for half of its thickness into the liquid without affecting its effectiveness. For taking liquid samples from the storage tank there is provided a sampling device, Fig. 9, consisting of a funnel-shaped mouth 33 for receiving and centering a bottle shaped container (not shown) which is lowered by means of a star- shaped cut flexible valve 34 to sample liquid from the tank content. The annular protruding edge 35 at the lower side of the funnel-shaped mouth 33 rests upon and is guided respectively in u tubular passage 36, provided with a flange 37 and a counter flange 38 for its attachment to the opening bi the tank roof 1. At the level of the flange 37 there are provided in the tubutar widened portion a number of air openings. The Valve 34 is attached to the throat of the funnel-shaped mouth 33 by means of a hinge 39 and can be opened by means of a cable 40. The other cable end is connected to a hook 41 whioh is adjustably in its height attached to the tank roof 1. The valve 34 is automatically opened in the event that the lower end of the hook 41 (not fully shown) is running up against a stop, e.g. the bottom 1 of the tank.

If as a result of weather conditions e.g. liquid vapour is collected under the tank roof 1 which must be discharged, there are a number of dischargers 32 provided upon openings in the tank roof 1, see Fig. 10. A discharger 32 consists of a pot shaped housing 42 which is downwardly attached to a tubular passage 45 provided with attachment flanges 43 and 44 respectively and connected to the tank roof 1. The passage 45 has air openings 46 and it diverges downwardly to a funnel 47. The housihg 42 is covered by a cup-shaped lid 48 which is provided with passage ways 49 which are closabie by means of a flexible non-return vaive

50. A central rod 51 having an eyelet 53 can be operated by a cable 23' from the upper side and so be lifted or closed. Attached to the rod 61 and to the housing 42 are cooperating labyrinth baffles and discs 64 and 66 respectively which obstruct the escape of vapour. To enable a fast escape however the lid 48 is operated by means of the cable 23'.

Fig. 11 shows details of a manhole. The manhole cover 66 rests upon a tubular collar flange 57 circumferential edge of the manhole 8. The flange is attached by means of screws 14' screwed in the hard polylaminated (Multiplex) material within the sandwich module 3. In the central portion upon the manhole cover 56 there is a passage opening in which a discharger 32, see Fig. 2, can be installed and further handgrips are provided at the upper and bottom side respectively of the manhole cover 66.

Fig. 2 schematically shows the adjustable support legs 60 which are guided by and attached to the tank roof 1 by means of tubular guidlngs 61. At choice such support legs may have a fixed length and are attached to the tank roof 1 by means of a tubular guiding 61 or the support tegs 60 and their guidlngs 61 are provided of adjustable locking devices, known per se.

The floating tank roof 1 is of very light construction and it has a high floating power and, by its enormous own rigidity resulting from the use of sandwich modules and low traverse frame profiles, is also an ideal building floor for carrying out maintenance activities. The smooth surface underneath it prevents all existing disadvantages with known tank roofs. Considering the very smal height of the tank roof 1, e.g. 50 mm of the sandwich module plus two times 50 mm for the composing tubular profiles 5 of the traverse frame profile 4, its total height is no more than 15 cm (I) at the location of these traverse frame profiles 4.

In Fig. 1 the simple and systematic building up of the tank roof structure by the new method is made visible. The modular arrangement makes it possible to make tank roofs of different dimensions having the same favorable floating power. The use of the sandwich structure having a hard outer skin make no longer a problem of possible damages and their quick repair.

Since the construction is realized with simply operable sandwich modules and whereas the tubular profiles are easily handled during mounting and demounting because of the small length, this novel method offers great advantages end extra safety for the environment, now that even for very great tanks only a minimum evaporation will occur and so it remains controllable. Apart therefrom this floating roof together with its synthetic sandwich modules has a specific heat insulating function for the liquid which is stored in the tank. Patent claims:

Claims

PATENT CLAIMS

1. Method for the installation of a floating roof structure in a closed storage tank for liquid, which roof is composed of a number of Interconnected synthetic modules thereby carrying out the following steps:

a. a great number of fully enclosed sandwich module board elements of reinforced synthetic material, provided with a core of hard foam and also being locally provided with insert pieces of screwable material, are lengthwise so positioned that they constitute altogether an uninterrupted flat working floor surface, which by providing of corresponding roυndings for the tank wall, will correspond in its shape and its size with the floating roof to be installed, whereas this working floor is supported, at least for a substantial part, by a temporary and premounted flat horizontally positioned roof support scaffolding structure which is located underneath and at a certain distance from the tank bottom;

b. at the upper side of the working floor and In a direction which is perpendicular to the Iongitudinal axis of sandwich module boards there are positioned a number of oblong transverse frame profiles which are fixediya) Roof connected to the sandwich module boards by means of fasteners thereby providing for a stiff integral roof structure; c. thereafter the roof structure is provided with operational means such as

i. a manhole in order to carry out activities underneath the roof structure :

ii. at choice a number of roof structure supporting legs, which may or may not to adjustable;

iii. a number of cable bushings for the use of anti-rotation cables to prevent art undesirable rotation of the roof structure;

iv. at choice a number of drainages for condense liquid; v. at choice a number of air inlet and air discharge means; whereafter the horizontal roof support scaffolding structure is dismounted and taken out of the tank allowing the floating roof structure to rest upon its supporting legs or to rest upon a number of fixed supporting legs whloh installed before on the bottom of the tank;

d. the longitudinal and traverse seams between adjacent modules of the working floor for the roof structure are sealed off at the bottom side of the roof structure by means of self-adheslve tape thereby forming a totally flat surface, whereafter for the prevention of gas and air inclusions, the seam slit is further filled up with synthetic material of the skin material of the sandwich module, the self adhesive tape being removed or not after hardening;

e. the flexible tank wall seal is thereafter mounted to the circumferential edge of the roof structure.

2. Floating roof structure which is composed, according to claim 1, of sandwichb) module boards and traverse frame profiles, characterized in that a traverse profile has a polygonal vertical cross section and is composed by two preferably rectangular tubular profiles, one on top of the other, particularly a lower tubular profile and on top of it an upper rectangular tubular profile, resting its short rectangular side.

3. Roof structure according to claim 2, characterized in that a number of cut-off profiles each time having a length of at least two times the width of a sandwich module is applied for, in such a way that every time the utmost ends of the lowermost square tubular profiles and also the utmost ends of the upper rightangied tubular profiles are always located in the central portion of the sandwich module.

4. Roof structure according to daim 3, characterized in that a cut-off profile has a length of about 1,000 mm whereas the total integral cross section of the traverse frame profile amounts to 50 x 50 and 50 x 30 square mm.

5. Roof structure according to daim 4, characterized in that the sandwich module preferably has a width of 500 mm and a length of 6,000 mm at a thickness of 50 mm.

6. Sandwich module to be used for a roof structure according to claim 5, characterized in that locally, in a direction perpendicular to its longitudinal axis, integral insert pieces of screwable material are provided at regular distances, preferably of hard screwable polylaminated wood (Multiplex), which pieces are incorporated in the foamed core material for the fixing of screws and suchlike fixing elements in and to the sandwich module.

7. Roof structure according to claims 2-5, characterized in that its bottom side is entirely flat except for the presence of a required manhole flange and various bushings (for cables, air inlets, air outiets, supporting legs) respectively.

8. Roof structure according to claim 7, characterized in that the floating roof structure is provided with a great number of adjustable support legs which equally support the entire roof structure on various locations with respect to the bottom of the tank.

9. Air inlet and air discharge means for a roof structure according to any one of the foregoing daims- 2-5 and 7-8, characterized that a pot-shaped housing, consisting of a number of parts, is provided with at least one fixing flange for connecting it with the opening in a sandwich module and a cup shaped cover of the housing being provided with a number of air inlet and discharge openings respectively which are covered by a flexible non-return valve, a vertically movabls bar being centrally positioned in the cover, which bar is provided at its upper end above the cover with an eyelet for connection to a cable and within the housing under the cover and perpendicular thereto said bar is provided with a number of closed discs, each having an outer circumferential downwardly directed cupshaped edge, whereas the inner side of said housing is provided with a number of corresponding downwardly directed funnel-shaped concentric baffles, in such a way that vapors passing through said means are forced to escape via this labyrinth seal.

10. Permanent magnet fixing means for keeping the floating roof structure according to claims 2-5 and 7-8 respectively in place with respect to the bottom of the tank by means of anti-rotation cables characterized in that a flat permanent magnet is provided horizontally and centrally respectively in at least two mutually perpendicular directions of a number of anti-tilting elements, one and the other in such a way that a possible tilting point or tilting line with respect to said magnet is located substantially far away and outwardly from the utmost borderline of the circumferential edge of the permanent magnet which holds to the bottom of the storage tank.