Apparatus and method for cleaning storage tanks

Abstract

An apparatus for cleaning a liquid storage tank comprises a barrier 4 alterable between a deflated configuration and an inflated configuration. In its deflated configuration the barrier may be inserte

Description

The present invention relates to an apparatus and associated method for cleaning storage tanks. Liquid storage tanks often require the removal of contaminants, typically in the form of gas that may be released from the liquid and in the form of solids either in suspension in the liquid or that is deposited as sludge at the bottom of the tank. Sludge can be particularly problematic as it reduces the usable space in a storage tank and can be difficult and costly to remove, sometimes requiring the draining of the tank and associated downtime. The problem of cleaning waste solids from tanks is particularly acute where tanks have limited access such as a hatch, as only equipment of restricted size may be used. The present invention seeks to address these issues. According to a first aspect of the present invention there is provided an apparatus for cleaning a liquid storage tank comprising: a barrier alterable between a deflated configuration and an inflated configuration; wherein in its deflated configuration the barrier may be inserted into a tank via an upper opening of the tank; in its inflated configuration at least a portion of the barrier is inflated with a fluid such that it is substantially planar and may cover the surface of a body of liquid stored in a tank; wherein the apparatus comprises a waste extraction hose configured to convey waste from an underside of the barrier. Advantageously an apparatus made in accordance with the present invention may be employed with tanks that have limited access. Furthermore, the apparatus of the present invention may be used with existing tanks to isolate the liquid stored therein from air, so eliminating risk of oxidation, contamination or explosion. In some embodiments the apparatus comprises: a hub member; an inflatable peripheral member; a plurality of inflatable arms connecting the hub member to the peripheral member; portions of sheet material extending between adjacent arms and the peripheral member disposed therebetween; wherein in its deflated configuration the peripheral member and arms are deflated; in its inflated configuration the peripheral member and arms are inflated with a fluid; in its inflated configuration the peripheral member, arms and portions of sheet material define a substantially planar barrier that may cover the surface of a body of liquid stored in a tank. In some embodiments the waste extraction hose is adapted to fluidly connect the underside of the barrier to a waste collection unit located inside or outside of the tank. In some embodiments the waste extraction hose is adapted to fluidly connect an underside of the barrier to outside of the tank. In some embodiments the apparatus comprises a pump or compressor. In some embodiments the barrier comprises at least one peripheral flange configured to form a seal between the barrier and a side wall or side walls of the tank. In some embodiments the at least one peripheral flange is formed of rubber material. In some embodiments the at least one peripheral flange extends from the barrier such that when the barrier is in use the flange contacts a side wall or side walls at an angle. In some embodiments the liquid storage tank is an oil storage tank, or a crude oil storage tank and the oil has a specific gravity of around 0.85 to 0.92. In some embodiments the barrier is substantially impermeable to waste gas and the apparatus is adapted to extract waste gas from an underside of the barrier. In some embodiments the apparatus comprises at least one switch configured to automatically initiate extraction of waste gas when a predetermined quantity of gas has collected under the barrier. In some embodiments a switch is actuatable by float switch positioned at an underside of the barrier. In some embodiments the barrier is at least partially permeable and the apparatus comprises at least one conduit configured to fill the inflatable arms and peripheral member with a liquid having a higher specific gravity than the liquid stored in the tank such that the barrier sinks through the liquid stored in the tank towards a bottom of the tank; and the apparatus is adapted to extract waste solids from an underside of the barrier. Beneficially, installation of the apparatus creates a temporary barrier enabling the extraction of sludge without disturbance to the stored product. Current cleaning methods include jetting with water or diesel. Agitation in this way, creating a turbulent mixture of useful product, precipitates and water is an inefficient way to recover valuable product and dispose of voluminous waste. In some embodiments the barrier comprises a mesh or a partially permeable membrane configured to filter liquid stored in the tank as it passes through the membrane. In some embodiments the apparatus comprises at least one extraction tool at an underside of the barrier. In some embodiments the tool extends from a hub member. In some embodiments the tool comprises one or more of an Archimedes screw, an agitator, a vacuum hose, a heater, one or more jets of gas and / or liquid, a scraper, a macerator, a vibration tool, an air lift pump. In some embodiments the underside of the barrier comprises at least one heating member extending along at least parts of inflatable arms, or comprises at least one heating member extending along at least parts of inflatable arms and a peripheral member. In some embodiments a heating member comprises a tube conveying warmed fluid. In some embodiments the apparatus comprises at least one non-return valve on the upper side of the barrier configured to hinder return of liquid to the underside of barrier. According to a second aspect of the present invention there is provided a method of cleaning a liquid storage tank comprising the steps of: providing an apparatus made in accordance with some of the preceding statements of invention; inserting the barrier in its deflated configuration into the storage tank; inflating the barrier inside the tank; positioning the barrier in its inflated configuration such that it sits atop liquid in the tank; extracting waste gas from below the barrier. According to a third aspect of the present invention there is provided a method of cleaning a liquid storage tank comprising the steps of: providing an apparatus made in accordance with some of the preceding statements of invention; inserting the barrier in its deflated configuration into the storage tank; inflating the barrier inside the tank; allowing the barrier to sink to a position near a bottom of the tank; extracting waste solids from below the barrier. In some embodiments the barrier is inflated with fluid that has a specific gravity of around 1.0 to 1.3. In some embodiments the barrier is inflated with the fluid is water or saline solution. In order that the present invention may be more fully understood a specific embodiment will now be described by way of example with reference to the accompanying schematic drawings, of which: Figure 1 is a cross-section of an oil storage tank and an apparatus made in accordance with the present invention outside of the tank in its deflated configuration, the apparatus being designed to fit a tank of circular cross-section; Figure 2 is a cross-section of the oil storage tank of Figure 1 with the apparatus inside the tank in its inflated configuration; Figure 3 is a plan view of the barrier of the apparatus in its inflated configuration; Figure 4 is an expanded view of the peripheral member of the apparatus abutting a side wall of the tank; Figure 5 is a cross-section of the oil storage tank of Figure 1 with the apparatus inside the tank in its inflated configuration, the apparatus having sunk to near the bottom of the tank; Figure 6 is a cross-section of an apparatus made in accordance with the present invention comprising an Archimedes screw; Figure 7 is a cross-section of an apparatus made in accordance with the present invention comprising an air lift pump; Figure 8 is a cross-section of an apparatus made in accordance with the present invention comprising a vibration tool and a submersible pump; Figure 9 is schematic of a heating system; Figure 10 is a plan view of an apparatus made in accordance with the present invention, the apparatus being designed to fit a tank of rectangular cross-section; and Figure 11 is a schematic view illustrating non-return valves on an apparatus as the apparatus sinks through liquid stored in a tank; Figure 12 is a schematic view illustrating non-return valves on an apparatus whilst the apparatus being used for sludge extraction; and Figure 13 is a cross-section of an apparatus made in accordance with the present invention comprising a flexible perforated extraction hose. An apparatus 1 for cleaning a liquid storage tank may be inserted into an oil tank 2 via an openable and closable access hatch 3 when a barrier 4 of apparatus 1 is in a deflated configuration. In some embodiments a protective funnel may be provided so that it may be positioned at an access hatch 3 to assist the insertion and removal of apparatus 1 through the hatch 3. Such a funnel may be made of a cushioning material such as rubber and may be substantially hyperboloidal in shape. Barrier 4 is shaped such that it has a concave underside when inflated. Once inside tank 2 the barrier 4 of apparatus 1 may then be inflated by means of a hose that is one for the service lines 6 such it forms a substantially planar barrier that sits atop oil 5 stored in tank 2. Barrier 4 may be inflated with a fluid (either gas or liquid) selected to match the purpose of apparatus 1, as in some instances it may be desired for barrier 1 to remain atop liquid stored in a tank, whereas in other instances it may be desired for barrier 1 to sink within a tank, as shall be further explained below. Barrier 4 comprises a hub member 7, a substantially circular inflatable peripheral member 8, a plurality of substantially linear inflatable arms 9 connecting hub member 7 to peripheral member 8 and substantially sector-shaped portions of sheet material 10 extending between adjacent arms and the peripheral member disposed therebetween. In some embodiments inflatable arms 9 may be enhanced by inflatable semi-rigid ribs. Peripheral member 8 may comprise one or more pressure relief valves 28. Extending circumferentially around the side of peripheral member 8 are located rubber flange members 11 that are adapted to contact the side wall 2a of tank 2 to form a seal between barrier 4 and side wall 2a. In the present embodiment three rubber flange members 11 are provided on barrier 4. Flange members 11 extend from the side of barrier 4 at an angle such that they extend downwardly when barrier 4 is in use. In other embodiments they may extend upwardly or substantially horizontally when the barrier is in use or a combination of upwardly and / or downwardly and / or horizontally extending flange members may be provided. Angling gaskets 11 both enhances the seal that is formed between gaskets 11 and side wall 2a as waste gas evolves from oil 5 and enhances the ability of gaskets 11 to clean side wall 2a in those embodiments comprising a sinking barrier. Embodiment 1 - impermeable barrier In one embodiment of the present invention barrier 4 is substantially impermeable to gas, with sheet material 10 being formed of an impermeable material. In this embodiment inflatable peripheral member 8 and inflatable arms 9 are inflated with a gas (air or an inert gas such as nitrogen) by means of a hose comprised in service lines 6 such that barrier 4 sits atop oil 5. Service lines 6 comprise a waste gas extraction hose that passes through hub member 7 such that the extraction hose fluidly connects the underside of barrier 4 with a pump (not shown) located outside of tank 2. Gases that evolve from oil 5 remain trapped under barrier 4 and may be periodically pumped from tank 2 by means of the extraction hose. Pumping may be actuated manually, by means of a timer, or by means of remote monitoring equipment located at barrier 4. For example, a float switch (not shown) may be positioned at an underside of barrier 4. As gas evolves and deforms barrier 4 the float switch is displaced, and at a predetermined level the float switch actuates the pump by means of service lines 6. Depending upon requirements and the nature of the gas that is evolving in a tank the waste gas may either be dispersed in the atmosphere or collected for use. When apparatus 1 is to be removed from tank 2 it may be deflated and extracted via access hatch 3. Embodiment 2 - semi-permeable barrier In a second embodiment of the present invention barrier 4 is semi-permeable, with sheet material 10 being formed of a mesh filter. In this embodiment inflatable peripheral member 8 and inflatable arms 9 are inflated with a gas, and then the gas is replaced with a liquid (typically water or brine) that has a higher specific gravity than the oil 5 in tank 2. Air / water stop valves are commercially available to allow replacement of gas with liquid, and to shut automatically at a predetermined water pressure. Barrier 4 is filled evenly with liquid to prevent capsize. This may be achieved by using independent filling hoses perforated to a set size adapted to the filling pressure and flow reaching peripheral member 8. Ropes (not shown) with graduation marks may be attached to peripheral member 8 to ensure that barrier 4 sinks evenly. Water has a higher specific gravity (1.0 for fresh, 1.03 for saline) than oil (0.85 to 0.92) resulting in barrier 4 gradually sinking towards the bottom of tank 2. Clean oil passes through the mesh filter of sheet material 10 whereas waste solids are retained below barrier 4. Thus, as barrier 4 descends it filters waste solids from oil 5 within tank 2. In some embodiments non-return valves may be provided for the mesh filters on the upper side of barrier 4. Such valves may be in the form of overlapping sheets of substantially impermeable material that are configured to prevent return of clean product to the underside of barrier 4 as sludge 12 is extracted. Figures 11 and 12 illustrate how such non-return valves may operate. During the descent of barrier 4 through a liquid impermeable valve sheets 27 that are attached to inflatable arms 9 and peripheral member 8 allow liquid to pass from the underside of barrier 4 through sheet material 10. During extraction of sludge from beneath barrier 4 suction forces impermeable valve sheets 27 to lie flat so as to prevent the return of liquid from above barrier 4 to its underside. Further, as barrier 4 descends flanges 11 scrape side wall 2a of tank 2 thereby skimming any waste solids from side wall 2a. As may be seen from Figure 5, barrier 4 may descend until it meets a layer of sludge 12 that has been deposited at the bottom of tank 2. Apparatus 1 may then be used to extract sludge 12 from tank 2 by means of an extraction hose 15 that is comprised in service lines 6 and fluidly connects the underside of barrier 4 at hub member 7 with a waste collection unit (not shown) located outside of tank 2. To facilitate extraction of sludge 12 from all parts of the tank bottom one or more spacers, such as a cage feet, or one or more inflatable annular rings may be attached to the underside of barrier 4 to prevent a partial suction vacuum from blocking the path of sludge for extraction. A variety of methods of extracting sludge 12 from beneath barrier 4 may be employed. In some embodiments waste solids may be siphoned and in other embodiments one more pumps may be employed. A submersible pump may suck sludge 12 into extraction hose 15 or pumps may be located outside of tank 2. A robot may be deployed to traverse the bottom of tank 2 and convey sludge into an extraction hose. In some embodiments, as illustrated in Figure 6 an Archimedes screw 13 may be operated to remove sludge 12. In some embodiments an extraction member may be disengaged from the underside of barrier 4 as an axle is from a wheel, via bearings or O rings. This allows the extraction member to rotate and for a horizontal part 16 of the extraction member, with or without a series of apertures or an Archimedes screw, to extract sludge 12 from all parts of the tank bottom. Figure 13 illustrates such an arrangement where an outer sleeve 29 allows the introduction of a flexible extraction pipe 30 which can be advanced or withdrawn, and rotated. Flexible extraction pipe 30 comprises a plurality of openings 31 through which sludge 32 may be extracted into pipe 30 by means of suction. In large tanks a programmable robot may cover the entire bottom surface, raking out sludge and driving flexible Archimedes screw 13 to raise the sludge. For harder residues where a more robust Archimedes screw is required universal Cardan joints 14 can link a series of screws, for example just below the central extraction point of the apparatus. A Cardan joint is not a constant velocity joint, so some vibration occurs in use. This is in practice a small advantage as it may loosen sludge 12 for extraction. In other embodiments such as that depicted in Figure 7 an air lift pump may be employed to extract sludge 12 from tank 2. In this embodiment compressed air is introduced through an air hose 17 (which could be of around 25mm internal diameter) to extraction hose 15 (100 to 300mm diameter). As the air expands it creates a partial vacuum which sucks up sludge 12 through perforated cage 18. More viscous sludge such as waxes may clog air lift pump arrangement. In such circumstances a steam, hot water or diesel spray system may also be employed to loosen solid waste. In some embodiments as illustrated in Figure 8 a vibration tool 20 may be employed to loosen sludge, which may be thixotropic; thus shear stress by vibration diminishes its viscosity allowing for it to be more readily extracted by a submersible pump 21 positioned at hub member 7 of barrier 4. In some embodiments one or more heating members in the form of one or more hot water pipes 22 may be provided to heat sludge 12 such that it is readily extracted. Such pipes may be attached to the underside of inflatable arms 9 and peripheral member 8, and an exemplary flow path for such a pipe system is illustrated in Figure 9. Any shape or configuration of barrier may be provided depending upon the requirements of a tank. For example, as illustrated in Figure 10 a rectangular barrier may be provided comprising two hub members 23, inflatable arms 24, peripheral member 25 and sheet members 26. In some embodiments an intermediate collection tank (not shown) may be positioned on the tank roof and a pipe (optionally of larger diameter) may allow sludge 12 to be drained from this to larger tanks at ground level beside the tank, where treatment of sludge 12 can be carried out. Apparatus 1 may be constructed of any suitable materials such as is medium or heavy sheet plastic. For example, polyvinyl chloride (PVC) may be employed for non-flammable applications or antistatic polyethylene (PE) be employed for use with flammable liquids. Polypropylene (PP) may also be used. For high-risk applications a three-layer PE sheet, consisting of PE, aluminium foil (acting as a Faraday cage) and PE with dissipative coating may be used. The present invention is not limited to use with tanks containing volatile oils, and may be employed to assist the cleaning of a tank containing any liquid. Vegetable oils, fruit juices and other liquids will have residues of different characteristics. Selection of the extraction method will be dependent on these characteristics. Water based product (wines, fruit juices) may require a fluid that is heavier than water such as brine to enable a barrier to sink to the bottom of a tank. Alternatively, or in addition a barrier may be weighted to sink by providing one or more weights on the barrier. In some embodiments, an apparatus for use with small tanks in specialist applications may comprise a set of ribs that curve from the centre to the peripheral member so that when the unit is rotated sludge is guided centripetally to a central extraction point. Where additional elements (a cage, heating coils, etc) underneath the unit are required this may make removal of the unit through an access hatch of the tank difficult. In such circumstances ropes may be attached to anchor points on the peripheral member to haul the apparatus. In this specification an apparatus / method / product "comprising" certain features is intended to be interpreted as meaning that it includes those features, but that it does not exclude the presence of other features. Many variations are possible without departing from the scope of the present invention as defined in the appended claims.

Claims

1. An apparatus for cleaning a liquid storage tank comprising:a barrier alterable between a deflated configuration and an inflated configuration;whereinin its deflated configuration the barrier may be inserted into a tank via an upper opening of the tank;in its inflated configuration at least a portion of the barrier is inflated with a fluid such that it is substantially planar and may cover the surface of a body of liquid stored in a tank; whereinthe apparatus comprises a waste extraction hose configured to convey waste from an underside of the barrier.

2. The apparatus of claim 1 comprising:a hub member;an inflatable peripheral member;a plurality of inflatable arms connecting the hub member to the peripheral member; portions of sheet material extending between adjacent arms and the peripheral member disposed therebetween; whereinin its deflated configuration the peripheral member and arms are deflated;in its inflated configuration the peripheral member and arms are inflated with a fluid;in its inflated configuration the peripheral member, arms and portions of sheet material define a substantially planar barrier that may cover the surface of a body of liquid stored in a tank.

3. The apparatus of claim 1 or 2 wherein the waste extraction hose is adapted to fluidly connect the underside of the barrier to a waste collection unit located inside or outside of the tank.

4. The apparatus of claim 1 or 2 wherein the waste extraction hose is adapted to fluidly connect an underside of the barrier to outside of the tank.

5. The apparatus of any preceding claim comprising a pump or compressor.

6. The apparatus of any preceding claim wherein the barrier comprises at least one peripheral flange configured to form a seal between the barrier and a side wall or side walls of the tank.

7. The apparatus of claim 6 wherein the at least one peripheral flange is formed of rubber material.

8. The apparatus of claim 6 or 7 wherein the at least one peripheral flange extends from the barrier such that when the barrier is in use the flange contacts a side wall or side walls at an angle.

9. The apparatus of any preceding claim wherein the liquid storage tank is an oil storage tank, or a crude oil storage tank, and the oil has a specific gravity of around 0.85 to 0.92.

10. The apparatus of any preceding claim wherein the barrier is substantially impermeable to waste gas and the apparatus is adapted to extract waste gas from an underside of the barrier.

11. The apparatus of claim 10 wherein the apparatus comprises at least one switch configured to automatically initiate extraction of waste gas when a predetermined quantity of gas has collected under the barrier.

12. The apparatus of claim 11 wherein a switch is actuatable by float switch positioned at an underside of the barrier.

13. The apparatus of any of claims 1 to 9 wherein the barrier is at least partially permeable and the apparatus comprises at least one conduit configured to fill the inflatable arms and peripheral member with a liquid having a higher specific gravity than the liquid stored in the tank such that the barrier sinks through the liquid stored in the tank towards a bottom of the tank; andthe apparatus is adapted to extract waste solids from an underside of the barrier.

14. The apparatus of claim 13 wherein the barrier comprises a mesh or a partially permeable membrane configured to filter liquid stored in the tank as it passes through the membrane.

15. The apparatus of claim 13 or 14 comprising at least one extraction tool at an underside of the barrier.

16. The apparatus of claim 15 when dependent upon claim 2 wherein the tool extends from a hub member.

17. The apparatus of claim 15 or 16 wherein the tool comprises one or more of an Archimedes screw, an agitator, a vacuum hose, a heater, one or more jets of gas and / or liquid, a scraper, a macerator, a vibration tool, an air lift pump.

18. The apparatus of any of claims 13 to 17 wherein the underside of the barrier comprises at least one heating member extending along at least parts of inflatable arms, or comprises at least one heating member extending along at least parts of inflatable arms and a peripheral member.

19. The apparatus of claim 18 wherein a heating member comprises a tube conveying warmed fluid.

20. The apparatus of any of claims 13 to 19 comprising at least one non-return valve on the upper side of the barrier configured to hinder return of liquid to the underside of barrier.

21. A method of cleaning a liquid storage tank comprising the steps of:a. providing an apparatus made in accordance with any of claims 10 to 12;b. inserting the barrier in its deflated configuration into the storage tank;c. inflating the barrier inside the tank;d. positioning the barrier in its inflated configuration such that it sits atop liquid in the tank;e. extracting waste gas from below the barrier.

22. A method of cleaning a liquid storage tank comprising the steps of:a. providing an apparatus made in accordance with any of claims 13 to 20;b. inserting the barrier in its deflated configuration into the storage tank;c. inflating the barrier inside the tank;d. allowing the barrier to sink to a position near a bottom of the tank;e. extracting waste solids from below the barrier.

23. The method of claim 22 wherein the barrier is inflated with fluid that has a specific gravity of around 1.0 to 1.3.

24. The method of claim 22 or 23 wherein the barrier is inflated with the fluid is water or saline solution.17

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