RELATED APPLICATIONS

This application is a continuation-in-part of Application Serial No. 07/920,342 filed in the same of the inventor on July 29, 1992.

TECHNICAL FIELD

This invention relates to storage tanks with a floating roof and a stillpipe for storing products which contain volatile substances . The floating roof has a first opening designed to slide tightly along a vertical stillpipe which itself has a series of second openings distributed along its length to permit product flow for the products in the tank to the inside of the stillpipe. More particularly the invention relates to an improved sealing device movably mounted in the stillpipe to reduce the flow of volatile substances from the inside of the stillpipe to the atmosphere through the stillpipe openings which are located above the roof.

BACKGROUND ART

Tanks with a floating roof and a stillpipe are generally intended for storing reltively large volumes of petroleum products . The stillpipe is provided with a number of holes or slits along its length intended to insure that the level of the product is the same on the inside of the stillpipe as it is on the outside in the tank. The gauging of the level of the product was formerly performed by manual measuring with a measuring tape or with a float. Presently the gauging is generally performed with microwaves (radar) such as for instance in U.S. Patent No. 4,641,139.

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Presently day environmental laws in numerous countries now impose rigid limits for pollution from substances that are harmful to the environment. This necessitates that tanks of different types must be designed in such a way that the outflow of volatile substances, such as by evaporation, must be limited.

DISCLOSURE OF THE INVENTION

According to the invention a sealing device in the stillpipe is characterized firstly in that it comprises a floating body provided with at least on outward seal designed to move or glide tightly against the inner circumference of the stillpipe. The volyme/weight relationship of the floating body is such that the floating body, floating in the product encloses in its interior a portion of the product surface. The inside of the floating body communicates freely with the product through at least a third opening while a fourth opening to the inside of the stillpipe above the floating body is sufficient to allow the gas pressure in the inside of the floating body to commuicate with the stillpipe above the floating body. The floating body is built to the extent necessary from material which allows direct gauging of the product level with microwaves.

It is thus an object of the invention to provide a device of the foregoing type which is simple in design and safe in utilization, the device should also permit level gauging of the product level with micorwaves.

The device of the invention may be designed in various ways within the scope of the invention.

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In one embodiment the floating body is formed like a pipe downwardly open through said third opening and on top provided with a cap from a material that is penetrable to micrwaves and provided with a small fourth opening. This cap may be formed in the shape of a funnel. The pipe is suitably provided with a number of annular flexible seals spaced around the outer circumference ot the pipe .

In one embodiment the pipe is designed with an inner constriction forming a substantially central channel with a relatively small cross section. The floating body is designed in such a way that while floating in said product the floating body presents the product surface below said channel. The constriction should be disigned without sharp changes of diameter and when viewed in a longitudinal section comprise an hour-glass shape.

Considering the fact that the stillpipe when used for gauging with microwaves usually contains a downwardly diverging cone, the stillpipe thus in the upper end only shows a restricted cross-section automatically restorable to its original dimension. This design allows the cross-section of the floating body to be temporarily reduced so that it may be put down through the cross-section of the stillpipe which is only partially open.

In one suitable embodiment of the device according to the invention said pipe is deformable and the cap consists of a cupola or cone constructed from flexible material. A central frame is provided connected to the pipe and to the cupola by flexible links. The frame is provided, at its lower end, with centering guide elements. The flexible links in this case act like the corresponding links in an umbrella enabling the cupola to bend out of the pipe to their original dimensions.

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In an alternative embodiment of the device the floating body is designed like a hollow sphere from flexible material substantially filling up the cross-section of the stillpipe. The volume/weight relationship of the floating body is such that the product surface within the body, when the floating body floats in the product, is located substantially at a symmetry plane through the center of the sphere .

BRIEF DESCRIPTION OF DRAWINGS

The invention is now described in more detail with reference being made to the accompanying figures wherein,

Fig.l is a schematic drawing showing a partial longitudinal section of a storage tank with a floating roof and a stillpipe.

Fig. 2A and 2B show a longitudinal section of a storage tank and a cross-section thereof;

Fig. 3 shows a schematic diagram of a longitudinal section of an alternative embodiment of the invention;

Fig. 4A and 4B show a longitudinal section and a cross- section of an alternative embodiment of the invention;

Fig. 5 schematically illustrates a longitudinal section of a further embodiment of the device ot the invention; Fig. 6 schematically illustrates a further alternative embodiment of the device of the invention;

Fig. 7 schematically illustrates a further alternative embodiment of the device of the invention.

Fig. 8 and 9 schematically illustrate in perspective a further embodiment of the device of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to Fig. 1 there is shown a tank 1 with a floating roof 2 and a stillpipe 3. A rubber sleeve 4 seals the

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stillpipe 3 against the roof 2. A jacket pipe 5 is attached to roof 2 and depends around the stillpipe 3. A number of alongated holes or slits 6 are spaced along the stillpipe 3. A conical insert 7 may be present in the stillpipe 3 intended to guide a microwave when gauging with such. A microwave source may be suitably disposed above or within the upper end of the stillpipe as shown at 7A.

The device as shown in Figs. 2A and 2B comprises a floating body in the form of pipe 8 made from cellular plastic with a lower ballast 9 around a lower opening 10. The floating body floats in the product in tank product surface 11. A number of annular flexible seals 12 are proveded around the pipe 8 with inernal spacing to seal pipe 8 against the stillpipe 3. A conical plastic cap 13 with a central relatively small opening 14 covers the upper part of pipe 8. The cap 13 may be provided with narrow radial slots 15 going out from its center to allow for annual gauging. The slits 15 reduce the evaporation from the product surface within the floating body.

Fig. 3 illustrates an alternative embodiment of a device according to the invention with a cap in the form of a plastic funnel 16 attached to a pipe 36 in its upper conical formed end which fits the plastic funnel 16. A snap-in closure 17 which is not completely gas-tight keeps the plastic funnel 16 attached to the pipe 36 forming a connection between the interior 18 of the floating body and the atmosphere which levels out any differnece in gas pressure. The pipe 36 is made from metal plate and the hollow interior 8 is filled with air. A vlave 20 is provided in ballast 9 for reasons of manufacture. The plastic funnel 16 is provided with a spout 19 extending below the surface 11 of the product.

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In Fig. 5 there is shown an embodiment of the divece wherein the floating body is made from metal plate and contains a hollow interior filled with air. The inside wall of the floating body is formed rotationally symmetrically and contains three sections . The three sections comprises an upper space 22 with a relatively large cross-section gradually tapering downwardly with continous change to a central channel 23 with a relatively small cross-section and gradually downwardly enlarging to a lower space 24 with a relatively large cross-section.

The volume /weight relationship of the floating body causes it to float in the product . The floating body may also be constructed from plastic and may be filled with cellular plastic. The outer wall of the floating body may be provided with a number of annular seals 12 as previosly described. The floating body may also be provided with a plastic cap, not shown, with a relatively small openng for equalizing the interior gas pressure in the lower space or channel 24 and the atmosphere.

If there is a conical insert 7 in the stillpipe 3 as shown in Fig. 1, the device according to the invention may be designed in such a way as to permit deforming to an extent necessary to allow it to be introduced through the limited cross-section formed by the conical insert and then autmatically regain its original dimensions. In such a deformable embodiment the floating body illustrated in Figs . 4A and 4B comprises a flexible ring part 25 with outer flexible seal rings 12 and a flexible cap 13 with a central opening 14.

In the alternative embodiment of Fig. 6 the floating body 21 comprises a flexible ring part 26 with a cupola 27 of flexible material. A central frame 28 is provided with

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flexible links 29 connected to the ring part 26 and the cupola 27. At the lower part of frame 28 there are provided guide elements 30 for centering the device in the stillpipe 3. Frame 28 and flexible links 29 act as the corresponding means in a common umbrella. Thus the device may be folded together to a substantially smaller cross-section so that it may be inserted through a reduced cross-section in stillpipe 3 if necessary. A channel is provided between openings 32 and 33 in the central part of frame 28 for equalizing gas pressure in the inner chamber 31 of the floating body.

A further embodiment of the device is shown in Fig. 7. The floating body is designed from a flexible material as a hollow sphere 34 of substantially the same dimension as the cross-section of stillpipe 3. Holes 35 are arranged in the sphere 34 so that the volume/weight relationship of the floating body is such that the product surface substantially is located at a symmetrical plane through the center of the sphere when the floating body floats in the product. In practice this embodiment of the device according to the invention can only be used within a limited range of density of the product . The ability of the floating body to cover holes in the stillpipe is also limited.

A further and preferred embodiment of the invention is shown in Figs. 8 and 9 which illustrate two shapes for this embodiment. The floating body is comprised of outer pipe 40 and 41 preferably of metal such a steel. Mounted on the outer surfaces of the pipes are spaced annualar 42-45 & 46- 49. The seals are preferably disposed at substantially equal spacings from one another and serve the same purpose as the seals previosly described in connection with Figs. 2A and 5. Four seals are illustrated and a number in excess of two is preferable. The float is sufficiently long and the seals sufficiently close to one another to effectively prevent gas

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flow from the surface of the liquid in the tank through the elongated holes 6.

Within the pipes are inserted funnels 50 and 51 having upper annular edges coinciding with the upper edges of the pipes. At the bottom ends the narrow portions of the funnels 50 and 51 are attached to bottom plates 51 and 53 attached to the pipe and the funnel to form openings or holes 54 and 55. The funnels thus have upper frustoconical portions connected to lower narrow and substantially cylindrical portions. The function of the selaing devices of Figs. 8 and 9 is the same as described for the embodiments of Figs. 2 and 5.

It will be readily seen by one of ordinary skill in the art that the present invention fulfills all of the objects set forth above. After reading the foregoing specification, one of ordinary skill will be able to effect various changes, substitutions of equivalents and various other aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.

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