US2772805A

US2772805A - Floating roof liquid storage tank structure

Info

Publication number: US2772805A
Application number: US475226A
Authority: US
Inventors: Grundig Henry
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1954-12-14
Filing date: 1954-12-14
Publication date: 1956-12-04
Anticipated expiration: 1973-12-04

Description

the rim 13 and the tank/wall or the seal ring 16 and may be held in fluid-tight sealing relation to the ring and rim as by means of annular clamps secured to each and designated inthe drawings by the

numerals

19 and 20. Any conventional means to prevent rotation of the roof may be provided. Also, as in the conventional floating roof structure, the roof as sh'own in the drawings is provided with means for supporting the roof in vertically spaced relation to the tank bottom, when the contents may be reduced to less than the volume of liquid displaced by the roof. Such support means ordinarily consist of a plurality of tubular members extended through the upper and lower surfaces of the roof and each adapted to receive a support legvr which may be extended from or withdrawn into the lower end of a tubular member. A typical support means is generally illustrated in the drawings wherein the tubular member is designated by the numeral 21 and the extension leg by the numeral 22. Reinforcing plate 23, secured to the tank bottom, is provided to receive the lower end of the leg 22. kThe support means as now contemplated, however, dilTer from those conventionally employed. Whereas in the conventional structure these supports are designed Vto hold the roof at a level such that the rim is from three to four feet above the tank bottom, according to the pres-v ent invention, at its lowermost level the roof is supported with the rim at a distance above the tank bottom which is about four inches less than the diameter of the nozzle 3 and orice 4although preferably not less than twelve inches above the tank bottom.

As a feature of the roof'construction according to the present invention the rim 13 in the area of juxtaposition to the nozzle 3 and orifice 4 is provided with an arcuate notch portion as indicated by the numeral 31, while the adjoining lower deck portion 11 of the lloating roof is provided with an arcuately indented portion 32 forming a channelled course extending radially inward from the rim notch 31. As shown, this indented portion 32 has an initial radius of curvature at the rim substantially equal to that of 4the notch portion 31, both having a radius substantially greater than that of the nozzle 3. Also as shown, the channelled course 32 has the general form of the surface of the smaller of two `co-nical portions divided by the intersection of la plane with a right circular cone, from the apex thereof to a chord in the base which chord is equal to or less than the diameterY of the base. Other conic forms or shapes also may be utilized in producing the` indented portion 32, but preferably the edge portions,'designated in the drawings -by the

numerals

32a and 32b thereof will be substantiallycongruent with those of` a conic section of a ,circular cone whereinthe'radiusof the base of the cone is substantially equal to the radius of curvature of the rim notch portion 31, and wherein the arcuate measure of the rim notch portion is not substantially more than 180. The specific relationships contemplated would provide a rim notch portion 31 constituting a circular segment having a rise such that with the roof fully depressed the apogee of the segment arc will be spaced from the tank oor by a vertical distance at least equal to the diameter of the nozzle 3, and in any event so.

that the distance will not be less than the greatest vertical distance between the tank oor and the circumference of orice 4. The width of theV segment, that is the straight line distance between the opening of the notch should be somewhat greater than the diameter of the:

nozzle or orifice and preferably slightly less than the Width of the area enclosed by the weir 7. Y 'Y y The conic forms or shapes contemplated by the relationships as set forth above have been represented in Figs. 3, 4 and 5. In these figures, like parts have been designated by the same numerals. As shown, Fig. 3v represents the conformation of the

edge portions

32a and 32b of the channelled course which is also specically illustrated by Figs. l and 2, 'and wherein the corresponding conic section is formed by a plane which cuts thecone from the apex thereof through a chord in the base thereof. Such a conicsection has a generally triangular form and the curve of intersection is two intersecting straight lines meeting at the apex designated by the numeral 32e. In the form represented by Fig. 4, the

edge portions

32a and 32b correspond to those of a conic section formed by a plane which cuts through the cone in parallel relation to a plane tangent to the surface of such cone, and wherein the curve of intersection is a parabola. The third form, shown by Fig. 5, has edge portions 32a and 32h which correspond to those of a conic section formed by a plane which cuts through the cone in non-parallel, angular relation to a plane tangent to the surface of the cone,` and wherein the curve of intersection is a hyperbola.

In addition, the sealing ring 16 also is provided with a notch portion 33 which extends upwardly from the lower edge of the ring to a depth greater than the depth of the notch portion 31 in the tank roof rim 13. The notch portion 33 as shown is disposed in opposed and aligned relation to the nozzle and rim notch portion 31. This notch portion should have a dimension at the opening adequate to receive the upper edge of the weir freely, and should have a depth such that when the roof is depressed the greatest vertical distance between the uppermost level of the notch portion and the tank iloor is not lessithan the greatest vertical distance between the tank Hoor and the circumference of the orifice 4.

When' constructed in the foregoing manner, the roof supports lmay be positioned so as to permit withdrawal of liquid therefrom to a depth substantially below the upper level of the inlet-outlet nozzle 3 and orifice 4, while maintaining surface contact of the roof with the residual liquid inventory, and without substantially reducing or interfering with flow into lor from the tank through the nozzle 3. In the apparatus as described, the dam or weir 7 substantially prevents the entrance of undesired sludge or residual liquid into the nozzle 3. The notched portions 31 and 3'3 avoid llow restriction of the nozzle by either the seal ring 16 or the roof rim 13. The indented portion 32, as described and shown, provides for substantially free communication between the nozzle 3 and the tank beyond the darn 7. By permitting the iioatingv roof to descend ducing a vapor space between the roof and the remainto a lower level ythan possible with conventional structures, the apparatus as described permits withdrawal of greater quantities of liquid from the tank without proing liquid contents. In the storage of volatile and nammable liquids, by this means not only are evaporation losses substantially reduced, but also i'n eliminating a vapor space above the liquid the hazards of iire and explosion v are substantially minimized. In addition, by reducing the required minimum tank inventory, a greater working capacity is obtained. The increased working capacity in gallons which is obtained for each Vfoot of reduction in residuall tank inventory is equal to 7.48957 W2. 'Ihus in e a tank having a diameter of feet, a two foot reduction in residualinventory is equal to an increase in working capacity of the tank of more than'264,000 gallons. v

As a specifici example of a tank and oating roof structure according to the present invention, a tank having a: :ddiameter ot` 150 feetv and a height of about 48 feet would be provided with a floating roof having a diameter of about 148 feet, 10 inches. would be spaced radially from the tank wall by a distance of about7 inches. In a typical roof of such diameter the (-13) would have a vertical dimension of about 3 feet, 5 inches, extending above the upper deck (12) of the roof structure by a distance of about 2 inchesto provide for vattachment along one edge of a flexible annular closure element (18), the other edge of the closure being attached to the upper edge of an annular seal ring or The annular shoe would have a verticalk dimension of about 3 feet, 111/2 inches, and would be sup- When centered, this roof ported to extend above the upper deck by a distance of about 6 inches, and below the lower deck (11) by a distance of about 21/2 inches.

A conventional tank structure of this character, would be provided with an inlet or outlet orifice (4) and nozzle (3) about 20 inches in diameter. As compared with this conventional arrangement in the structure according to the present invention the axis of the inlet or outlet orifice nozzle would be spaced from the tank bottom at a distance substantially equal to the radius of the nozzle, namely ten inches above the bottom. As previously indicated a dam or weir member (7) is provided to enclose an area in the immediate vicinity of the nozzle and orifice. In the tank contemplated this dam would be about sixteen inches high, the ends being secured to the tank wall on each side of the orice at a distance from the orice of about twenty inches and the midpoint of the dam would be spaced from the orifice, radially of the tank at a distance of about forty inches. The supports (22), provided to hold the roof above the tank bottom when the contents are reduced to less than the volume displaced by the roof, in the present structure contemplated would be arranged to provide a distance of about-sixteen inches between the ri-m (13) and the bottom wall (2) of the tank. Also, in the roof structure contemplated by the present invention the indented portion (32) provided in the lower deck of the roof, opens through a notch portion (31) in the rim of the roof wherein the notch portion has a radius of curvature of about twenty inches, and an opening width at the rim edge having a straight line distance between the edges of about forty inches. The uppermost point in the notch portion would be about twenty inches above the tank floor with the roof fully depressed.

The indented portion (32) would have initial dimensions identical with those of the notch portion (31), and at a distance from the outer wall of the tank equal to that of the midpoint of the plate forming the weir (7), a radius of curvature of about ten inches. Likewise in this speciiic example, the seal ring notch portion (33) would have a radius Vof curvature such that the circular segment formed would provide a straight line distance between the lower edges of the notch opening aqual to about sixty inches. The uppermost point in the notch portion would be about twenty inches above the tank oor with the roof in a fully depressed position.

What is claimed is:

1. In a storage tank, including a bottom wall, a cylindrical upright wall extending upwardly from said bottom wall, a conduit connection nozzle opening into said tank through said upright wall immediately adjacent said bottom wall, a oating roof in said tank, including a oor and a vertical peripheral rim portion, said roof adapted to be supported primarily on the surface of a liquid contained in said tank, and thereon to be positioned at various levels within the tank as said liquid is introduced and withdrawn, said roof also including rigid support means extended downwardly from said floor adapted to establish a lower most position for said roof at a level which is below a horizontal plane tangent to said nozzle and in vertically spaced relation to the tank bottom wall, a vertical sealing ring resiliently supported on said roof rim in substantially parallel radially spaced relation thereto and in substantially fluid tight surface contact with the inner surface of the tank wall, an arcuate notch portion extending upwardly in said ring, an arcuate notch portion extending upwardly in said rim, and a channelled course defined in the roof floor opening downwardly therefrom, said channeled course extending radially inward from said rim and coincident at its outer end with said rim notch portion, each of said sealing ring and rim notch portions having a radius of curvature greater than that of said nozzle and disposed in opposite alignment with said nozzle radially of said tank and roof.

2. An apparatus according to claim t1 wherein said arcuate, roof rim, notch portion is substantially a segment of a circle, wherein t-he surface of said channelled course substantially corresponds to that of t-he smaller of two cone portions formed by the intersection 1of a plane with a right circular cone having a base radius equal to that of said rim notch portion, the intersect-ion of said plane with said cone extending through the base of said cone :along a chord thereof, and wherein Fthe Ilater-al edge portions of said channelled course substantial-ly correspond to the curve lof intersection of said plane with said ycone.

3. An appara-tus acc-Ording yto claim 2 wherein said curve of intersection of said plane `with said .cone is ytwo intersecting straight ylines.

4. An apparatus according to claim 2 wherein said curve of intersection of said plane with said cone is ta parabola.

5. An apparatus according 'to claim 2 `wherein said curve yof intersection of :said plane with said cone is a hyperbola.

6. An apparatus according to claim 1, including an elongated plate having a lateral dimension lat least equal to the radius of said nozzle, wherein .said plate is secured in edgewise relation to the bottom wall of said tank, extending Vertioa'llly lupward therefrom, and wherein said plate is secured lat each end to the upright wall of said tank in opposed relation diametrically of said nozzle and radially spaced therefrom, said rplate forming -a weir enclosing an area of the tank bottom wall extending inwardly from 'the opening of said nozzle through the upright wall, and also wherein the straight line distance between the intersection of said sealing ring notch portion with the `lower edge of said ring is greater than the lateral dimension of the area enclosed -by said elongated plate vertically :below said not-ch portion.

7. An :appara-tus according to claim 6, wherein said channelled course extends radially inward of said tank roof Ibottom to a distance substantially greater than the inward extension of the :area of said tank bottom wall which is enclosed `by said elongated plate.

References Cited in the tile of this patent UNITED STATES PATENTS