NZ299292A - Above ground fuel or industrial chemical storage tank comprises inner tank supported inside an outer tank to control leakage from inner tank - Google Patents

Description

299292 PATENTS FORM NO 5 FEE NO 4: $260.00 PATENTS ACT 1953 COMPLETE SPECIFICATION After Provisional No 299 292 Dated 3 September 1996 STORAGE TANK I Eric Alexander Sinclair a New Zealand citizen of 30 Mercer Street Drury RD2 NZ hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: i? 9 2 § 2 STORAGE TANK FIELD OF THE INVENTION This invention concerns above ground tanks for fuel, industrial chemicals and other compounds which are subject to storage safety regulations.

BACKGROUND OF THE INVENTION Above ground tanks avoid most of the problems which afflict below ground tanks but leakage is a danger which is countered in safety regulations by stipulation that the tank must be mounted within a blind which is of sufficient capacity to contain the leaked contents of the tank. The provision of a large tray surrounding the tank is expensive and requires extra installation space.

On farms the tanks hold hydrocarbon fuel. The bund beneath the tank collects spilled hydrocarbon which floats on the accumulated rain water. Sometimes spairks from electric fence energisers ignite the exposed fuel in the bund. Overflows from bunds cause problems in rural areas.

Whereas it is possible to manage risks such as corrosion, failures of components and ground movement by design, the installer prefers to have assurance that if the tank contents are class 3 goods, the contents are stable and safe.

A further risk is that of damage by fire or impact by vehicles in urban locations and perforation by rifle fire I » » 299292 in rural locations. If tank, users can have safe above ground tanks, they may install them in preference to below ground tanks.

Regulations require that tanks are installed a minimum distance from a source of ignition but fire risk must be managed partly by ensuring that the tank contacts will be proof against ignition in the event of an external fire, for a period sufficient to allow fire appliances to arrive and operate. In rural areas above ground tanks are at risk of accidental perforation from rifles. Tanks up to 2001 are installed on farms and industrial premises. They are made of 3mm steel plate. Over this capacity they are made of 5mm steel plate.

This invention addresses these problems.

SUMMARY OF THE INVENTION This invention provides an above ground storage tank for hazardous liquids comprising an inner tank for the storage of liquid, supported inside an outer tank wherein the volumes of the iuner and outer tanks are similar, the outer tank being capable of fluid tightness and flow means enabling the content of the inner tank to be controlled Thus in the event of a leak from the inner tank the contents will be entirely contained within the outer tank intellectual property office of n.z. 2 4 apr 1998 2992°' from which they may be recovered. Accordingly the inner tank may rest contiguously within the outer tank with the tank walls in contact along a common axis. More usually the tanks will be cylindrical and coaxial. Conversely the tanks are constructed as a double wall cylinder. Clearly the invention is applicable to cross-sections other than rectangular and circular.

The interstitial space defined by the inner and outer tanks may be inspectable and\or drainable. The inner tank may be divided into compartments by one or more partition walls. The walls may be a double skin and the space between may be inspectable and\or drainable. The interstitial space may be of substantially constant section.This may be set by spacers fixed to the outer face of the inner tank. The space may be 20-50mm. The spacers may be drilled so that the interstitial space is at uniform pressure. The t«nk and compartment walls may be made of metal plate and the whole assembly welded. The outer tank may be supported on a sled or vertical cradles.

A feature of the invention may be means to monitor the pressure of the interstitial space together with optional means to raise the pressure above atmospheric. A fall in pressure would indicate the outer tank may not be capable of retaining the contents of the inner tank should a leak occur . Investigation would reveal which tank was at fault. The pressure range may be 7-35kPa. 4 299292 As soon as pressure falls to a predetermined value , in practice about 7kPa, or the slop tank HIGH level is reached or other predetermined safety threshold is exceeded, all dispensing from the inner tank is interrupted. These operations lend themselves to microprocessor control. Similarly the space may be filled with inert gas or may be monitored under vacuum.

For special applications such as locations which require fireproof tanks a protective layer may surround the outer tank. A layer of heat resistant or impact resistant or heat reflective material may be usied such as phenolic resin, concrete, or sintered metal or an equivalent. The purpose of such a layer is to keep flammable contents below flash point. Any vapour produced by the rising temperature of the contents is vented safely by the vent provided in the manhole. This insulating layer may be rendered additionally impact resistant by the provision of an exterior metal case. The heat resistant layer may be 10, 20, 30, 40, 50 mm thick.

The extra layer may be tiles adhered to the tank surface; preformed sections of a composite shell ; a layer built by application with a gun.

DESCRIPTION OF THE DRAWINGS Certain embodiments of the invention are now described with reference to the accompanying drawings in which 299292 Fig 1 is a fragment of a double compartment sled tank; Fig 2 is a section of a corner fragment; Fig 3 is a section of the joint between the tank wall and the compartment wall showing the interstitial space Fig 4 is a diagram of the controls showing how the space pressure switch is integrated.

Fig 5 is a section through a fragment of a tank with a heat resistant structure.

Fig 6 is a section of a corner fragment of a version with a mounded end plate.

Referring now to Figs 1-3 the sleds 2 rest on the ground connected by ties (not shown) . They support cradles 4 in which the tank assembly rests. The inner tank 6 is about 3800mm long with an outer diameter of 1900mm and is made of 5mm steel plate. Circular end walls 8 are welded in position and 40x10mm spacers are welded to the outer surface of the inner tank at intervals. The paired partition walls 12 divide the inner the inner tank 6 into compartments 14,16. Spacers 18 are welded to end plates 20. When the inner tank 6 is slid into the outer tank 22 the manholes 24 cut in both tanks register. The end plates 26 of the outer tank contact a ring of spacers 18 in which position they are welded. In this way the space 25 between the tanks is controlled in volume.

The construction is economic in materials in that it is 6 299292 only necessary for the outer tank to be slightly larger than the inner tank to permit one to enter the other. Space 25 communicates with inspection ports 28 for the purpose of inserting a gas probe or other diagnostic instrument . The manholes 24 have the customary charge discharge and vent conduits.

In Fig 4 a STOP-START relay 30 controls the pump motor 32. The motor is routinely cancelled by the float switch 34 of the slop tank 36 and the overfill cutoff 38 as is usual but additionally by the pressure switch 40 which senses interstitial pressure.

In use the interstitial space is pressurised as part of the commissioning of the tank assembly and after testing for gas tightness, pressure is checked periodically by reference to the gauge 42 which accompanies the pressure switch. If pressure is lost during an inspection it is reapplied.

Referring now to Figure 5 the inner tank 6 is made of 6 mm steel plate. The outer tank 22 is made of 3 mm steel plate and there is an intermediate skin 44 of 3 mm plate. Between the intermediate skin and outer plate there is an impervious hard phenolic resin layer 46, 20 mm thick. Thus tanks in service station locations which could suffer collision by vehicles or in countries which experience civil unrest involving small arms fire, have additional 7 299292 means of protection.

In Fig 6 a tank for farm use has an inner skin 6, an outer skin 22 separated by spacers 10 and closed by mounded end plate 48.

In a non-illustrated version, arcuate tiles are adhered in a continuous jacket around the outer tank. They are made of poorly heat conductive ceramic which delay the transmission of severe external heat to the tank interior. Such tiles are known from the literature. 8 199292

Claims (21)

CLAIMS:

1. An above ground storage tank for hazardous liquids compromising: (a) an inner tank for the storage of liquid supported inside an outer tank wherein the volumes of the inner and outer tanks are similar, the outer tank being capable of fluid-tightness (b) flow means enabling content of the inner tank to be controlled.

2. An above ground storage tank as claimed in claim 1 having means to monitor the condition of the interstitial space.

3. An above ground storage tank as claimed in claim 1 or 2 with means to inspect the interstitial space.

4. An above grc nd storage tank as claimed in any one of claims 1 to 3 wherein the interstitial space is drainable.

5. An above ground storage tank as claimed In any one of the preceding claims wherein the inner and outer tanks are coaxial and spacers are located between the tanks.

6. An above ground storage tank as claimed in any one of the preceding claims wherein the interstitial space is of 9 intellectual property office of n.z. 0 k ADD 10QQ 299292 constant thickness.

7. An above ground storage tank as claimed in any one of the preceding claims wherein the tanks are made of welded metal plate.

8. An above ground storage tank as claimed in any one of the preceding claims wherein the inner tank has two or more compartments.

9. An above ground storage tank as claimed in claim 8 wherein the compartments are separated by a double wall.

10. A method of operating a tank as claimed in claim 1 wherein the interstitial pressure is maintained at 7-35kPa.

11. A method as claimed in claim 2 wherein the monitor interrupts fluid flow to or from the inner tank in response to a change in the interstitial pressure.

12. A method as claimed in any one of claims 2-11 wherein the interstitial space is evacuated in use or filled with inert gas.

13. An above ground storage tank as claimed in any one of claims 1-9 having a protective layer interposed between the inner and outer tanks. 10 intellectual propfflty office ofnz - 5 may 1998 received &S292

14. An above ground storage tank as claimed in claim 13 wherein a protective layer surrounds the outer tank.

15. An above ground storage tank as claimed in claim 14 wherein the layer is heat or impact resistant material or heat reflective material.

16. An above ground storage tank as claimed in claims 14 and 15 wherein the heat resistant layer is phenolic resin, concrete, or sintered metal.

17. An above ground storage tank as claimed in claims 14, 15 and 16 wherein the layer is enclosed by a metal case.

18. An above ground storage tank as claimed in any one of the preceding claims wherein the outer tank has a layer of tiles which increase resistance to fire.

19 A method of operating a tank as claimed in claim 1 comprising charging the space between the inner and outer tanks with fluid causing heat transfer between the tanks. r - ■ ■ .i —r

20. An above ground storage tank constructed and adapted for use substantially as herein described with reference to Figures 1 to 4.

21. An above ground storage tank constructed and adapted Intellectual property office x1 ofnz -5 may 1998 pprciv/cn 299292 for use substantially as herein described with reference to Figure 5. 22 An above ground storage tank constructed and adapted for use substantially as herein described with reference to Figure 6. Steel Tanks Ltd by their Attorneys Kramer W Kramer 12 intellectual property office ofnz - 5 may 1998 Received J