Cleaning Apparatus and Method
This invention relates to an apparatus for cleaning storage tanks, and more particularly for disturbing and/or removing settlement deposits from the bottom of large storage tanks. The invention is particularly suitable for disturbing settlement deposits in tanks for oil but is also suitable for use with other kinds of deposits.
In the oil industry, oil in various states is generally stored in very large tanks, typically of 100m. in diameter or more. Such tanks are cylindrical and may be partially buried in order to better resist hydrostatic pressure therein. Typically a floating roof is provided to prevent evaporation and to provide shelter from rain.
Oil is, of course, pumped into and out of such tanks, which for reasons of economy are generally maintained as full as possible. Solids held in suspension will settle and accumulate in the base of the tank. Over a period such solids may build up to a depth of several metres, thus reducing the effective volume of the tank significantly. Nevertheless, such solids are a valuable source of energy since they may typically be 95% recoverable oil products.
Removal of such solids is highly problematic since access openings are few. Typically a roof may have one or two manholes and a number of small openings about 75 mm. in diameter. Openings may also be provided around the base of the tank, but these are often wholly or partially occluded by settled solids. Many existing tanks were built without adequate thought to the removal of deposits, and cannot now be modified.
Finally, these storage tanks are usually located on tank farms at a minimum spacing. Access for cleaning plant is accordingly restricted.
Prior apparatus for removal of settlement solids has proved ineffective or has become unusable due to legislative changes. Large plant is not generally usable because of space constraints on a tank farm. Temporary apparatus mounted on a tank is often
unacceptable because the additional loadings may exceed design limits for the tank. The typical light tank roof is in any event unable to bear a significant load. Permanent apparatus increases installation costs significantly whereas the use is only occasional; furthermore maintenance costs can be very significant.
What is required is a means of disturbing and/or removing settlement solids which is relatively inexpensive, which can be installed and used only when required, which is adaptable to the type of settlement solids, which is widely adjustable in use to reflect changing conditions within the tank, and which can be used with existing tanks.
According to a first aspect of the present invention there is provided a lance for disturbing solids in the base of a liquid containing tank, the lance comprising a cylinder adapted to fit through an aperture in the roof of a tank, the cylinder having an inlet connectable to a source of pressurised liquid, and a jetting outlet and a mixing outlet provided through the wall of the cylinder, whereby liquid entering through said inlet is expelled through said outlets to disturb solids in the base of the tank.
Such solids are typically propelled into suspension in the liquid where they can be removed by a suitable pump.
Preferably more than one jetting outlet is provided. A plurality of jetting outlets having different orientations are preferably provided. The jetting outlets are preferably provided with replaceable jets whereby the jet area may be changed to suit settlement conditions. The jetting outlets are preferably provided in the distal end of the lance, that is to say the end of the lance, in use, remote from the tank roof. The jetting outlets may be spaced about a housing which is connected to the distal end of the cylinder. A plurality of mixing outlets are preferably provided. The mixing outlets are provided along the length of, and spaced around, the cylinder.
The lance may preferably be provided with separate inlets for communicating liquid to the jetting and mixing outlets. In such an embodiment said inlets may be connectable to separate sources of pressurised liquid. Alternatively both inlets may be connectable
to a common source. In such an embodiment valve means may be provided between the pressurised liquid source and the inlets so as to apportion the flow from the source between the inlets.
Where two inlets are provided the lance may take the form of inner and outer cylinders with one inlet being in fluid communication with the interior of the inner cylinder, and the other inlet being in fluid communication with an annular space defined between the cylinders. In such an embodiment the jetting outlets may be in fluid communication with the interior of the inner cylinder, and the mixing outlets in communication with the annular space.
The or each source of pressurised fluid is preferably adapted to supply fluid in a pulsed manner rather than in a continuous flow.
The lance may be rotatable in use so as to assist with the mixing of tank solids with liquid ejected from the outlets. The lance may be provided with rotation means which, in use, remain external to the tank. The lance may be mounted on a turntable which is rotatable by appropriate drive means. Alternatively the lance may be connected to a bell crank arrangement operable to effect rotation thereof. In yet a further embodiment the lance may be rotatable by virtue of a rack and pinion arrangement.
The lance may be provided with a foot adapted, in use to rest on the base of a tank. A bearing may be provided between the foot and the lance so as to enable the lance to be rotated freely. The lance may be provided with vertical adjustment means thereby allowing the depth within a tanlc at which the lance is positioned to be varied. The lance may be of a modular construction comprising a plurality of sections which may be assembled so as to provide a lance having a desired length and configuration.
According to an alternative embodiment of said first aspect of the present invention there is provided a lance for disturbing solids in the base of a liquid containing tank, the lance comprising a cylinder adapted to fit through an aperture in the roof of a tank, the cylinder having an inlet connectable to a source of pressurised liquid, and a jetting
outlet and a mixing outlet provided through the wall of the cylinder, whereby liquid entering through said inlet is expelled through said outlets to disturb solids in the base of the tan, the lance further including flow apportionment means provided between the source of pressurised liquid and said outlets, said flow apportionment means acting to split the flow from said source between said outlets.
Preferably said flow apportionment means enable the split to be varied. The flow apportionment means enable the flow to be directed between the outlets according to user requirements. For example more flow could be directed initially to the jetting outlet so as to disturb solids within the tank. Subsequently the proportion directed to the mixing outlet can be increased so as to agitate the liquid/solids mixture.
In yet a further embodiment of said first aspect there is provided an apparatus for disturbing solids in the base of a liquid containing tank, the apparatus comprising a body adapted to fit through an aperture in the roof of a tank, the body having an interior cavity connectable via an inlet to a source of pressurised liquid, the body having a plurality of lances extending therefrom, said lances having jetting and mixing outlets therein in fluid communication with said body cavity, said outlets being provided at different levels, in use, within the tank.
In such an embodiment said lances may be defined by a plurality of concentric cylindrical members extending from said body. Preferably the apparatus includes flow apportionment means provided between the pressurised liquid source and the inlet so as to apportion the flow from the source between the outlets.
According to a second aspect of the present invention there is provided a method of disturbing solids in the base of a liquid containing tank, the method comprising the steps of:
introducing a lance through the roof of the tank, the lance comprising a cylinder having an inlet connected to a source of pressurised liquid, and a jetting outlet and a mixing outlet provided through the wall of the cylinder;
placing the outlets in the vicinity of solids in the base of the tank; and directing pressurised liquid to the outlets to disturb solids in the base of the tank.
Such a method enables solids to be placed in suspension in the liquid, and pumped out of the tanlc by any suitable means when the concentration of solids in the liquid reaches a predetermined level.
In preferred embodiment the method includes the additional step of; varying the proportion of pressurised liquid supplied to each of the jetting and mixing outlets from the source.
Preferably the supply of pressurised liquid is a pulsed supply. Preferably also the method includes the step of rotating the lance.
The method may comprise a two stage process comprising: a first stage of supplying a solvent to the outlets to disturb recoverable solids in the base of the tank, and a second stage of supplying a carrying fluid to the outlets to disturb non-recoverable solids in the base of the tanlc.
It will be appreciated that the order of the above referenced stages may be reversed.
Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompany drawings in which:
Figure 1 is a schematic illustration of a tank farm installation; Figure 2 is a transverse section through a typical oil storage tank; Figure 3 shows cross-sectional side view a lance according to an embodiment of the invention;
Figure 3 a shows an end view of the lance of figure 3
Figure 4 shows a cross-sectional side view of a lance similar to that of figures 3 and 3 a;
Figure 5 shows a schematic arrangement of a pump; Figure 6 shows schematically another lance according to the invention; Figure 7 shows a schematic side view of a storage tank and cleaning system according to the present invention; and Figure 8 shows an alternative embodiment of a storage tanlc and cleaning system according to the present invention.
Figure 1 illustrates a typical tank farm installation with tanks 11, 12, 13 separated at a minimum distance by containment walls 14. The tanks may be in the size range 60-200m in diameter. Pipework, not shown, connects the tanks to other installations for filling and discharging.
Figure 2 illustrates schematically a typical cylindrical tank 20 having a base 21 side wall 22 and relatively light roof 23. Manholes 24, 25 are provided at the base and in the roof. The roof is also provided with a plurality of openings 26 (two shown), usually about 75 mm. in diameter which are normally closed by a cap. The openings 26 typically have a short sleeve (not shown) extending downwardly into the tank, which sleeve co-operates with upwardly extending spigots (not shown) of the tank base 21 to locate the roof 23. Within the tank solids 27 may build up to several metres in depth, the remainder of the tank being filled with, for example, unrefined crude oil 28.
Eventually, after many drainings and chargings, the depth of solids may build up to an unacceptable level. This period may be of the order of 3-15 years depending on the quality of the oil. Solids must be removed by a device because of the danger to human health within the tank.
Typically, the solids are fluidised by a quantity of solvent, for example light cut oil (LCO); and the solids are pumped out as a suspension either directly to a distillation plant or to a filtration plant which removes the solids for further use. Repeated fluidisation of solids may be required until the depth of solids remaining is minimal. It will be appreciated that the solids present in a tank may comprise a combination of recoverable material, such as waxy hydrocarbon deposits, and waste material such as
sand and grit. The fluidisation of the solids may therefore be achieved in a two stage process comprising a first stage of using a solvent to capture the recoverable material, followed by a second stage of using a carrying fluid to capture waste material for extraction and subsequent disposal. The carrying fluid may comprise a heavy oil having suitable characteristics, such as viscosity, which enable it to, in effect, pick up the sand and grit.
An apparatus according to the invention is illustrated schematically in Figures 3 and 3 a. The apparatus, generally designated 30, comprises an elongate lance 32 adapted to fit through an aperture 26 of a storage tank, and a manifold 33 which, in use, remains exterior to the tank. The lance 32 comprises a cylindrical outer wall 34 within which there is provided an inner conduit 36. The inner conduit 36 is co-axial with the longitudinal axis 40 of the outer wall 34. The inner conduit 36 has an outer diameter which is less than the inner diameter of the wall 34 and hence an annular flow space 38 is provided between the wall 34 and the conduit 36. The lance 32 may be of a modular construction comprising a plurality of sections joined in an appropriate manner. In the embodiment shown the lance 32 comprises two sections.
Connected to the distal end of the lance 32, which is to say the end remote from the manifold 32, is a nozzle member 42. The nozzle member 42 serves to both close off the annular flow space 38 and provide nozzles 44 in fluid communication with the inner conduit 36. In the embodiment shown the nozzle member 42 is provided with four nozzles 44. Three of the nozzles 44 are spaced at 120 degree intervals around the side of the nozzle member 42 while a fourth downwardly depending nozzle 44 is provided in the base of the member 42. The side nozzles 44 are provided with a slightly downward inclination.
Mixing apertures 46 are also provided in the outer wall 34, which apertures 46 are in fluid communication with the annular flow space 38. The mixing apertures 46 are spaced around the outer wall 34. Additional sets of mixing apertures (not shown) may spaced along the length of the outer wall 34. Located on the base of the nozzle member 42 is a bearing assembly 48 having a foot 50 adapted to, in use, rest against the base of
21 of a storage tank 20. The bearing assembly 48 permits the lance 32, in use, to rotated about its longitudinal axis 40. The bearing assembly 48 has a hollow core 52 so as not to obstruct the downwardly depending nozzle 44. Apertures 54 of the bearing assembly 48 permit fluid communication across the bearing assembly when the foot 50 is in contact with storage tanlc base 21.
The manifold 33 is provided with two inlets 56, 58. The first inlet 56 permits fluid to be supplied to the inner conduit 36. The second inlet 58 is connected to an accumulation chamber 60 which in turn is in fluid communication with the annular flow space 38. The accumulation chamber 60 further acts as a stop limiting the insertion depth of the lance 32. Figure 4 shows a similar lance configuration to figures 3 and 3 a but without the bearing assembly 48.
In use the lance 32 is inserted into a storage tank 20 such that the nozzle member 42 extends into the solids accumulation 27. Pressurised liquid, typically a solvent such as LCO, is then supplied via the inlets 56, 58 to the inner conduit 36 and/or the annular flow space 38 and subsequently to the nozzles 44 and apertures 46. The nozzles 44 are configured so as to emit a jets of fluid adapted to cut into the solids, whereas the apertures 46 are adapted to emit fluid jets which promote the mixing of solids dislodged by the nozzle jets with LCO present in the tank 20.
The apparatus 30 is rotatable about its longitudinal axis 40 as indicated by arrow 41, in use, so as to dislodge and mix solids in a plurality of radial directions. The apparatus 30 is rotatable by actuation means provided exterior to the tank 20. Typically the apparatus 30 may be rotatable through an arc of around 170 degrees by the provision of a bell-crank arrangement. Alternatively orientation of the apparatus 30 may be varied by mounting on a turntable at an angle to the vertical. An air stepper motor may periodically rotate the lance 32 through a small angle. The apparatus 30 may also be provided with means (not shown) which are operable to, in use, move the apparatus towards and away from the tank base 21 as indicated by arrow 39.
A plurality of such lances 32 may be inserted through corresponding apertures 26 of the roof 23 of a tanlc 20
A high pressure pump is utilised to supply liquid to the inlets 56, 58. An example of such a pump is shown in Figure 5. The pump, generally designated 62 comprises a hydraulic cylinder 64 and two pneumatic cylinders 66. The working pistons 68, 70 of the cylinders 64,66 are linked by a connecting member 72. In use, the pneumatic cylinders 66 are operated so as to actuate the hydraulic cylinder 64. The cylinders 64,66 are double acting so that an output from the hydraulic cylinder 64 is available on both the extension and contraction strokes of the pneumatic cylinders 66. Typically the pneumatic cylinders may operate on a compressed air supply of around 10 bar, with the hydraulic cylinder being configured to supply liquid to the inlets 56, 58 at a pressure of around 50 bar.
It will be understood that a pump 62 of this configuration supplies pressurised fluid to the inlets 56, 58 in a pulsed flow manner. Interspersed between the pump 62 and the inlets 56, 58 there is provided a flow apportionment valve which enables the outlet from the pump 62 to be split between the inlets 56, 58. The valve enables the flow to be split such that 100 percent is directed to the nozzles 44, 100 percent is directed to the aperture s 46 , or any desired apportionment in between.
Operation of the apparatus 30 is continued until a significant quantity of solids is in suspension, and the LCO/solids mixture is pumped out by other means for processing. A fresh charge of LCO is then introduced, and the process repeated until the solids have been removed.
It will be appreciated that there are many variables which can be adjusted in real time, including pulsing rate, pulsing pressure, rate of increase of pulsing pressure, apportionment of flow from the pump between the inlets 56, 58, and rotation of the lance 32. Furthermore, the nozzles 44 and apertures 46 can be arranged in any desired orientation, and the jet size can be readily changed. The length of the lance 32 is also readily changeable by means of the addition or removal of tubular sections thereof.
Figure 6 shows an alternative embodiment of a lance 73. The lance comprises a body 74 which is insertable into an aperture 26 in the roof of a storage tank 20. The body 74 includes an internal chamber 75 and a flange 76 which serves to limit the insertion depth of the body 74. Extending downardly from the body 74 are a plurality of concentric cylinders 77 which are arranged so as to provide flow paths 78 terminating at nozzles 80 positioned at varying depths within the tank. In the embodiment shown there are provided five cylinders 77 defining three flow paths 78 with nozzles 80 provided at three separate depths.
The body 74 is provided with a single inlet 82 which comprises two concentric inlet paths 84, 86. The inner inlet path 84 communicates with the innermost cylinder 77 and nozzles 80 via a conduit 88 traversing the internal chamber 75. The outer inlet path 86 is com ected to the internal chamber 75 which in turn feeds the outer flow paths 78 and nozzles 80.
The apparatus described is relatively light compared with the prior art, and imposes no significant load on the roof of a standard oil tanlc.
A plurality of such lances may be inserted tlirough corresponding apertures in the roof of a tanlc.
Figure 7 illustrates an alternative arrangement. A tank 90 has a solids layer 92 over which is pumped a solvent layer 94, typically LCO. A lance 96 passes through a standard 75 mm opening to just above the solids/LCO boundary. Connected to the lance 96 are actuation means 110 which are operable to rotate the lance 96 about is longitudinal axis 112 as indicated by arrow 114. A second lance 98 extends through a second 75 mm opening into the LCO.
A double acting pump 100 of the type described above, illustrated schematically, connects the lances 96, 98 via a pipe 102, and pumps LCO in the direction of arrow
104. Intermediate the pump and the first lance 96 is a flow apportionment valve 106 of the type described above.
In use, LCO is circulated by the pump 100, and solids are scoured out by the lance 96 as previously described. Circulation continues until the LCO is ready for processing. A sampling device 116 is connected via a sampling line 118 to the pump outlet. The sampling device 116 monitors the LCO being drawn from the tank 90 and enables the suspension of solids within the LCO to be determined. Thus when the saturation point of the LCO is reached, operation of the apparatus can be ceased and the LCO/solids mixture removed from the tank 90 for processing. Information from the sampling device 116 may be utilised to alter or modify the operation of the lance 96 and/or pump 100. For example, depending upon the amount of solid matter suspended in the LCO, the rotation of the lance 96 may be altered as may the pressure or flow rate of the pump 100, or the operational state of the flow apportionment valve.
Figure 8 illustrates a similar system to that shown in figure 7. In this embodiment LCO is drawn from a separate tanlc 108 rather than from within the tank 90 being cleaned. A continuous bleed of LCO may be drawn off for reprocessing or passage through a filtration plant before return to the tank 90. In this embodiment the sampling device 116 and sampling line 118 are separate from the cleaning apparatus, with the sampling line being routed directly into the tank 90.
Although this invention has been described in relation to oil tanks, the apparatus and method is suitable for any storage tank in which solids may be disturbed into suspension in a liquid which overlies them.