GB2332233A

GB2332233A - Flexible shroud for a guide pole inside a floating-roof tank

Info

Publication number: GB2332233A
Application number: GB9825592A
Authority: GB
Inventors: Archibald Bryden
Original assignee: JOHN MOWLEM CONSTRUCTION PLC
Current assignee: JOHN MOWLEM CONSTRUCTION PLC
Priority date: 1997-12-09
Filing date: 1998-11-24
Publication date: 1999-06-16
Anticipated expiration: 2018-11-24
Also published as: GB9825592D0; GB2332233B

Abstract

A floating-roof tank (10) comprises a cylindrical tank shell (11) in which a floating-roof (12) is fitted. Deck legs (13) limit the downward movement of the roof when the tank is empty. The roof is provided with a perimeter sealing system (14) which prevents loss of liquid or vapour at the annular joint between the roof and tank. A hollow guide pole (15), which is slotted along its length, is provided extending through the roof being connected to the tank shell (15A, 15B). The guide pole prevents rotation of the roof with respect to the shell and a roller bearing arrangement (16) guides the roof in its vertical movement with respect to the guide pole. The pole may be used to extract samples from the tank or indicate fluid level. A shroud (20) which is sleeve-like, vapour impermeable and capable of folding covers the pole where it extends above the roof. The shroud is secured to the roof near the roller bearing arrangement and near the top of the pole (15A) and moves vertically with the roof.

Description

1 FLOATING-ROOF TANKS 2332233 This invention relates to float-ing-roof

tanks for the bulk storage of hydrocarbons and other volatile liquids.

Floating-roof tanks are well known. The main purpose of the floating-roof is to minimise vapour loss from the stored volatile liquid to achieve economy, environmental protection and safety. The tank shell is normally cylindrical and the roof -'s provided with an annular sealing system around its perimeter to permit rise and fall is of the roof with minimal vapour leakage. The rooL prevented from rotation within the tank shell frequent'y by a vertical guide pole or pipe located radially inwardly oil the tank shell, passing through -the roof, and being secured at its upper and lower ends to the tank shell. The hollow interior oil the guide)ole, since iz prot-rudes above -the roof- at all times, is usually used as an access for --ak-nc samples from the stored liquid and it may include a float gauge to indicate the stored liquid level. these purposes and to ensure that the liquid within -::he pole is representative of the bulk stored liquid, the pole -s slotted or apertured along its length. The slots or apertures permit liquid mixing to occur.

disadvantage of the known floating-roor ta-k It is a t'-at at least intermittently a significant length of the apertured guide pole is exposed:o atmospheric condi---'lons 2 above the roof and give rise to significant unwanted vapour losses.

It is an object of the present -inventlon to provide a new and improved form of floating-roof tank.

The present invention provides a floating-roof tank for the bulk storage of volatile liquids, the tank having a generally vertical guide pole passing through the roof to prevent rotation of the roof with respect to the cylindrical tank shell, be-Ing hollow, the guide pole being secured at its ends to the tank shell and being apertured along its length to enable sampling of the stored liquid, whiere-in the improvement comprises an essentially vapour- surface of guide pole extensible movement c--:

sleeve-like shroud secured to the ex)osed the roof and extending over that part of the which is above the roo, the shroud being and compressible to accommodate vertica- he roof.

Preferably the shroud is formed of a fabric ma--er-a-'.

The shroud may be formed of a plurality of sleeve sections which are -!c-. ned end-to-end. Conveniently a flexible '--.-t --o--d extends -i- oarallew--h each sleeve sec--t'on, the cord leength being such as to be the --mt-ina -actor in --he extensLbil-ty c-' each sleeve section.

An embodiment of the present w-1-1 now be desc---Jbed by way of example with reference to tnn accomQanvinc drawings, in which:- 3 Fig. Fig. wi th the Fig As comzrises roof 12 verticallS tank shel 1 illustrates a known floating-roof tank; 2 illustrates a floating-roof tank M accordance present invention; and 3 illustrates a detail of the Fig. 2 tank.

is shown in Fig. 1 a floating-roof tank 1C a cylindrical tank shell 11 in which a floating- is fitted and which is free to rise and fall according to the volume of liquid within the 1 11. The roof 12 carries a plurality of deck legs 13 which are distributed over the area of the roof and which limit the downward movement of the roof so that, for example, when the tank is empty of stored liquid access is possible beneath the roof to clear debris and silt from the ", co- of the tank. The roof 12 is provided with a perimeter sealing system 14 which prevents loss of liquid -2 and the or vapour at the annular joint between the roof -ank shell 11. A guide pole 15 is provided extend-ng through the roof 12 being connected to the tank shell 11 at ts upper and lower extremities 15A, 15B. The guide pole is provided to prevent rotation of the roof 12 with respect to the shell 11 and a roller bearing arrangement 16 is fitted to the roof to guide the roof in its vertical movement with respect to the guide pole 1-5.

The guide pole 15 is conveniently made of steel and is -he roof 12, spaced slightly inboard of the Outer edge of + SOmm. - 'de pole 15 typically by a distance of about 7 L he gu- 4 typically is about 18m in length, has a bore of 200, 250 or 33Omm. i. diameter and its wall -s provided with apertures or slots about 10Omm. in length and about 25mm in width and spaced apart by about 100m=.

In accordance with the present -invention and as shown in 7Ja. 2 the guide pole 15 where 't projects above the roof 12 -'s covered by a shroud 20 whJch is sleeve-like and essentially vapour impermeable and which is capable of f olding vertcal movement of the roof 12.

he shroud 20 is nreferably made of a fabric-like material incorporating or coated with a polymer such as PVC polyurethane, PVC Nitri-le or Teflon to -render the fabric essentally vapour impermeable and to -mDart resistance to degradation characteristics having regard to the fact that the interor of the shroud 20 is exposed to vapours from Such a shroud mav have an extended the stored 'L-cluid.

-eng--.- of aboui 10 or 18m and a colla:)sed length of only 5 to 2m.

he sleeve-like shroud 20 _Js secured a- its lower end to the e=osed surace of t-e roof 12 in the vicinity of -6 ---ne roller bearing arrangemen- so that the ower end ot' the shroud 20 moves vert-ically with the roof 12. it S upper end the shroud 2C is secured to the guide pole 15 in the vic-nity of the connection 15A, whereby the upper end -'s:ixed.

-he s'-roud 2C - ",ike a bellows or --oncer-na to accommodate which is Fig. 3 illustrates part of one form of the composed of sleeve sections 21A (typically 2m in overlap) by means and are free to shroud 20 21B etc.

length) joined end-to-end (with an of collars 22A, 22B etc which fit around slide over the guide po-le 15. Collars 22A, 22B are each formed with inner and outer rings between which the sleeve sections are clamped. Slotted apertures in the pole 15 are shown at 17. The sleeve sections 217k, 21B are individually extensible and contractable and one or more cords 24 extends in parallel, being clamped at 25A, 25B to the collars 22A, 22B, the sectional cord length being slightly less than that of the sleeve section so as to be the limiting factor in the extensibility of each sleeve section. The cords 24 may be made of nylon but preferably are made of steel and electrically connected at 1-he-'r ends to provide electrical conduct L.ors for removal o: static electricity.

iz w-J-11 be understood that the shroud 20 may be retrofitzed to an existing tank 10 in which case to avoid dismantling portions of the tank 10 the shroud 20 -nay Jni- is wrapped in situ around -ially be in sheet form which the pole 12 and fastened long itudinal ly, for example with a zip fastener or a loop-and-hoo',, fastener (velc--o RTim). The fastening may extend vertically or hel-ica-','y. Collars 22A, 22B for this purpose are initially segmented.

1 ',y secured zothe upper Ihe shroud 20 is convenient- 6 extremity of the guide pole 15 by means of a circular tie or -fastener (e.a. a Jubilee clip) and at the roof 12 by means of a dead weight or cold weld clamp.

By virtue of the present invention the shroud 20 foils wind around the he effects of slotted guide pole 15 and -he thereby substantially prevents loss of vapours through t apertures 17.

However, iL is Lo be noted that the volume enclosed by -zhe shroud -'s variable and depends upon --',,ie vertical pcsition of the roof. Changes in roof position occur relatively slowly and particularly when the roof rises the vo",ume chancre within the shroud 20 -i S preferably accommodated by seepage through the fastenings of the shroud (either at top/bottom or via the longitudinal zip or -lap valve -f-tted velcro fastener) or by means of a special to Ithee free end of the gu-de pole 15.

7

Claims

1 A floating-roof tank for the bulk storage of volatile -ical guide pole liquids, the tank having a generally vert passing through the roof to prevent rotation of the roof with respect to the cylindrical tank shell the guide pole being secured at its ends to the tank shell, being hollow, and being apertured along its length to enable sampling of the stored liquid, wherein the improvement comprises an essentially vapour- impe rmeabl e sleeve-like shroud secured -io the exposed surface of the roof and extending over that part of the guide pole which is above the roof, the shroud being extensible and compressible to accommodate vert-lcal movement of the roof.

2. A 'Lloating roof tank as claimed in claim 1, wherein the shroud is formed of a fabric material.

3. A floating roof tank as claimed in either preceding c!a-4rr,, wherein the shroud is formed of a plurality off sleeve sections which are joined end-zo-end.

4. A floating roof tank as claimed in claim 3, wherein a flexible but in extensible cord extends in parallel -w-izh each sLeeve section, the cord length being such as to be e ' b llmitinc factor in the extens- ility of each sleeve sect ion.

8 A floating roof tank as claimed in any preceding claim, wherein the upper end of the shroud is secured to the upper end of the guide pole in 7-he vicinity of its connection to the tank shell.

6. A floating roof tank as claimed in any preceding claim, wherein the shroud is formed as a wrapping around the guide pole with a longitudinally-extending fastener.

7. A floating roof tank as claimed in claim 6, wherein the fastener is a zip fastener or a lloop-and-hook fastener.