GB2071748A

GB2071748A - Floating roof liquid storage tanks

Info

Publication number: GB2071748A
Application number: GB8107048A
Authority: GB
Original assignee: Motherwell Bridge and Engineering Co Ltd
Current assignee: Motherwell Bridge and Engineering Co Ltd
Priority date: 1980-03-19
Filing date: 1981-03-06
Publication date: 1981-09-23
Also published as: GB2071748B

Abstract

A floating roof liquid storage tank 10 is provided with an inflatable body 20 located adjacent the tank floor 14 and beneath the roof 12. Body 20 is inflated and deflated by means 23 which may transmit air or water to the body 20 which can be in the form of interconnected bags 21 made of flexible material such as nitryle/pvc or polyether/polyurethane. The floating roof 12 has legs 13 and when these rest on tank floor 14 liquid 15 from tank 10 can be drawn off by weir device 25 whilst bags 21 are inflated so that the undersurface of roof 12 remains wetted by liquid 15 at all times while allowing more of the residual stored product to be drawn off. When the liquid 15 is oil this inhibits collection of explosive gases at the undersurface of roof 12. <IMAGE>

Description

SPECIFICATION Floating roof liquid storage tanks This invention relates to floating-roof liquid storage tanks.

Floating-roof liquid storage tanks are commonly used for the storage of oil, the underside of the floating roof being in contact with the stored oil volume at all times in order to avoid the presence of a potentially hazardous vapour volume within the tank. For a variety of practical reasons such floating-roofs are provided with legs which limit the downward travel of the roof as the tank is emptied and this in turn means that the tank cannot be emptied completely if the vapour volume is to be avoided. The resulting dead storage volume, or 'heel', is a source of annoyance to operators who wish to take full advantage of the storage tank capacity for process and delivery purposes.

It is an object of the present invention to provide a means of reducing the dead storage volume in a floating-roof liquid storage tank whilst maintaining the underside of the floating-roof in contact with the residual stored liquid.

According to the present invention there is provided a floating-roof liquid storage tank housing an inflatable body adjacent the floor of the tank, means being provided for inflating said body with a medium, the arrangement being such that, when inflated, the body displaces liquid stored within the tank and, when deflated, the body permits substantially full use of the tank capacity for storage of said liquid.

Preferably said body is made of flexible material such as nitryle/p.v.c. or polyether/polyurethane.

Conveniently said medium is water. Said body may be formed by a plurality of interconnected discrete members and the inflating means may be arranged to inflate and/or deflate said discrete members from one or more locations.

Said body may be inflated with a gaseous medium such as air or a medium which is more dense than the liquid stored in the tank. In either case it is preferred that the body be contoured to prevent fouling with the support legs of the floating-roof.

Preferably the body is tethered to the floor of the tank to prevent the body, particularly in its uninflated state, wandering under the influence of currents caused by filling and emptying the tank of stored liquid and which might otherwise cause the body to foul the support legs of the floating roof or the roof drain downpipe when the latter is fitted internally of the tank.

An embodiment of the present invention will now be described by way of example with reference to the accompanying schematic drawing.

The drawing shows part of a floating-roof storage tank 10 having a peripheral wall 1 a floating-roof 12 with leg supports 13. The roof 12 is shown in its lowermost position with supports 13 resting on the floor 14 of the tank. It will be noted that floor 14 is not necessarily planar since it is customary for the tank floor to be slightly coned. The roof 12 has a generally flat central area 1 2A which is peripherally bounded by an annular pontoon 1 2B with a flexible sealing skirt 1 2C which is in wiping contact with the tank wall 11.

The tank 10 contains a volume of stored oil 1 5 and the surface 1 5A of this oil is in contact with the whole of the undersurface of the roof 12 except at the skirt 12C. The roof 12 is shown schematically and may be either of conventional single or double deck design.

Housed within the tank 10 is an inflatable body 20 in the form of several interconnected bags 21, a fill/empty pipe 22 extending from the body 20 through the wall 11 of the tank 10 to a means 23 for inflating or deflating the body 20 as will be explained. It will be appreciated that with the body 20 in its deflated condition the stored oil 1 5 can be withdrawn from the tank 10 through the customary wall-mounted draw-off pipe (not shown) but when the roof 12 reaches the position shown with the leg supports grounded on the floor 14 this discharge of oil is stopped either automatically or manually in order to maintain oil surface 1 5A in contact with the undersurface of roof 12.At this point the body 20 may be inflated thereby effectively increasing the volume beneath the roof 12 and further oil may be removed either through the same draw-off pipe or through a special weir-type draw-off device 25 mounted on floor 14 and mating with a chamber 24 mounted on roof 12 when the latter is in its grounded condition.

The means 23 for inflating and deflating the body 20 is arranged to deflate the body 20 when the tank 10 is being filled with oil 1 5 to be stored and to inflate the body 20 when the tank 10 is being emptied. The precise point in the emptying cycle at which the body 20 is inflated is not critical but so long as the roof 12 is in its grounded condition it is important that the body 20 remains inflated to avoid a vapour-filled space arising between the roof 12 and the surface 15A of the stored oil 15. Thus the body may be inflated before the roof 1 2 reaches its grounded condition.

The means 23 will require a pressure head to establish inflation of the body 20 and this may be by means of a pump or a volume of water stored in an adjoining storage tank.

The inflatable bags 21 may conveniently be those sold by British Hovercraft Corporation Limited as described in their brochure SP 3861 which provide a deflated bag volume of less than 10% of the inflated bag volume and in relation to the total storage volume of the tank the deflated bag volume is negligibly small.

1. A floating roof liquid storage tank housing an inflatable body adjacent the floor of the tank, means being provided for inflating said body with a medium, the arrangement being such that, when inflated, the body displaces liquid stored within.

the tank and, when deflated, the body permits substantially full use of the tank capacity for

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Floating roof liquid storage tanks This invention relates to floating-roof liquid storage tanks. Floating-roof liquid storage tanks are commonly used for the storage of oil, the underside of the floating roof being in contact with the stored oil volume at all times in order to avoid the presence of a potentially hazardous vapour volume within the tank. For a variety of practical reasons such floating-roofs are provided with legs which limit the downward travel of the roof as the tank is emptied and this in turn means that the tank cannot be emptied completely if the vapour volume is to be avoided. The resulting dead storage volume, or 'heel', is a source of annoyance to operators who wish to take full advantage of the storage tank capacity for process and delivery purposes. It is an object of the present invention to provide a means of reducing the dead storage volume in a floating-roof liquid storage tank whilst maintaining the underside of the floating-roof in contact with the residual stored liquid. According to the present invention there is provided a floating-roof liquid storage tank housing an inflatable body adjacent the floor of the tank, means being provided for inflating said body with a medium, the arrangement being such that, when inflated, the body displaces liquid stored within the tank and, when deflated, the body permits substantially full use of the tank capacity for storage of said liquid. Preferably said body is made of flexible material such as nitryle/p.v.c. or polyether/polyurethane. Conveniently said medium is water. Said body may be formed by a plurality of interconnected discrete members and the inflating means may be arranged to inflate and/or deflate said discrete members from one or more locations. Said body may be inflated with a gaseous medium such as air or a medium which is more dense than the liquid stored in the tank. In either case it is preferred that the body be contoured to prevent fouling with the support legs of the floating-roof. Preferably the body is tethered to the floor of the tank to prevent the body, particularly in its uninflated state, wandering under the influence of currents caused by filling and emptying the tank of stored liquid and which might otherwise cause the body to foul the support legs of the floating roof or the roof drain downpipe when the latter is fitted internally of the tank. An embodiment of the present invention will now be described by way of example with reference to the accompanying schematic drawing. The drawing shows part of a floating-roof storage tank 10 having a peripheral wall 1 a floating-roof 12 with leg supports 13. The roof 12 is shown in its lowermost position with supports 13 resting on the floor 14 of the tank. It will be noted that floor 14 is not necessarily planar since it is customary for the tank floor to be slightly coned. The roof 12 has a generally flat central area 1 2A which is peripherally bounded by an annular pontoon 1 2B with a flexible sealing skirt 1 2C which is in wiping contact with the tank wall 11. The tank 10 contains a volume of stored oil 1 5 and the surface 1 5A of this oil is in contact with the whole of the undersurface of the roof 12 except at the skirt 12C. The roof 12 is shown schematically and may be either of conventional single or double deck design. Housed within the tank 10 is an inflatable body 20 in the form of several interconnected bags 21, a fill/empty pipe 22 extending from the body 20 through the wall 11 of the tank 10 to a means 23 for inflating or deflating the body 20 as will be explained. It will be appreciated that with the body 20 in its deflated condition the stored oil 1 5 can be withdrawn from the tank 10 through the customary wall-mounted draw-off pipe (not shown) but when the roof 12 reaches the position shown with the leg supports grounded on the floor 14 this discharge of oil is stopped either automatically or manually in order to maintain oil surface 1 5A in contact with the undersurface of roof 12.At this point the body 20 may be inflated thereby effectively increasing the volume beneath the roof 12 and further oil may be removed either through the same draw-off pipe or through a special weir-type draw-off device 25 mounted on floor 14 and mating with a chamber 24 mounted on roof 12 when the latter is in its grounded condition. The means 23 for inflating and deflating the body 20 is arranged to deflate the body 20 when the tank 10 is being filled with oil 1 5 to be stored and to inflate the body 20 when the tank 10 is being emptied. The precise point in the emptying cycle at which the body 20 is inflated is not critical but so long as the roof 12 is in its grounded condition it is important that the body 20 remains inflated to avoid a vapour-filled space arising between the roof 12 and the surface 15A of the stored oil 15. Thus the body may be inflated before the roof 1 2 reaches its grounded condition. The means 23 will require a pressure head to establish inflation of the body 20 and this may be by means of a pump or a volume of water stored in an adjoining storage tank. The inflatable bags 21 may conveniently be those sold by British Hovercraft Corporation Limited as described in their brochure SP 3861 which provide a deflated bag volume of less than 10% of the inflated bag volume and in relation to the total storage volume of the tank the deflated bag volume is negligibly small. CLAIMS

the tank and, when deflated, the body permits substantially full use of the tank capacity for storage of said liquid.

2. A tank as claimed in claim 1, wherein said body is made of flexible material.

3. A tank as claimed in either preceding claim, wherein said body is tethered to the floor of the tank.

4. A tank as claimed in any preceding claim, wherein said body is formed by a plurality of interconnected discrete members and the inflating means is arranged to inflate and/or deflate said discrete members from at least one location.

5. A tank as claimed in any preceding claim, wherein a weir-type draw-off device is mounted on the floor of the tank and mates with a vented chamber formed in the floating roof of the tank when said roof is at a predetermined distance from the tank floor, said inflatable body being located wholly within said distance when inflated.

6. A floating roof liquid storage tank substantially as hereinbefore described with reference to the accompanying drawing.