GB2134414A - A sludge dislodging machine - Google Patents

Abstract

The machine comprises a chamber defined by a fixed disc 15 and half-cylinder 18, and having an inlet 6 and an outlet. A nozzle housing 2,3 is rotatable about the chamber, and carries two nozzles 4,5. The longitudinal axis of each nozzle is at an angle to the axis of rotation of the housing, e.g. at 90 DEG , and the orifice of each nozzle is of elongated cross-section with the length of the major axis being at least twice that of the minor axis and preferably between 5:1 and 20:1. A rotor 12 within the inlet 6 is rotated by the flow of cleaning fluid, e.g. oil, and drives the housing 2,3 through reduction gearing. <IMAGE>

Description

SPECIFICATION A sludge dislodging machine This invention concerns a tank cleaning machine, especially for removal of or dislodging of sludge from the bottom of a storage tank and also to prevent sludge from re-precipitating on the bottom.

The accumulation of sludge on the bottom of crude oil storage tanks results in a number of operational problems, for example the capacity of the storage tank is reduced, 'dams' formed by the sludge deposits may trap pools of water which later form water slugs in the outflow from tank, the sludge causes uneven landing of the legs of the floating roof and alternative use of the tank for other oil types and products is prevented. The sludge accumulates despite the operation of normal tank mixers and it must be periodically removed by physically entering the storage tank. This is costly, a potential hazard to personnel and give rise to problems with the disposal of large amounts of sludge.

A machine suitable for removing sludge from the bottom of a storage tank is described and claimed in our U.K. patent application 8029639. This comprises a central body, a casing rotatable about said body and provided with two substantially diametric nozzles arranged so that liquid emerging therefrom sweeps substantially only in one plane, a turbine for rotating the casing about the central body and means ensuring that when the casing is continuously rotated, alternately one nozzle is closed for substantially 180 rotation whilst the other nozzle is open. Although in use such machines have proved very successful, a disadvantage is that high pumping rates are needed since the liquid velocity of the liquid emerging from the nozzle decays in the longitudinal direction.

We have now devised a machine which substantially overcomes these difficulties by the use of nozzles having certain shaped orifices.

According to this invention a machine suitable for dislodging sludge from the bottom of a storage tank comprises a chamber having an inlet and an outlet, a nozzle housing rotatable about the chamber and means for rotating the housing about the chamber.

There is at least one nozzle secured to said housing with the longitudinal axis ofthe nozzle being at an angle to the axis of rotation of the housing and the construction of the chamber, nozzle housing and nozzle are such that liquid flowing out of the outlet of the chamber can emerge through the nozzle. The orifice ofthe nozzle is of elongated cross-section with the length of the major axis being at least twice that of the minor axis.

Using this machine oil or liquid from the storage tank may be recirculated through the machine and the jet produced by the rotating nozzle re-suspends the sediments in the crude oil and thus facilitates removal or disposal by subsequent processing.

In order that the nozzle housing can rotate about the chamber the cross-sections of the housing and chamber perpendicular to the axis of rotation will have to be circular. In practice the chamber and nozzle housing will both be cylindrical or have substantial portions which are cylindrical.

Although the machine will function with only one nozzle usually there will be two such nozzles, preferably located diametrically with respect to the cross-section of the nozzle housing. If the sludge dislodging machine is intended to be located at or near the centre of the tank bottom then the machine can be designed so that liquid can emerge from the two nozzles simultaneously. However if it is intended that the machine be located near the tank wall then preferably liquid only emerges from one nozzle at any one moment and that when a nozzle is pointed towards the tank wall liquid is prevented from emerging from that nozzle at that particular moment.

The machine is described and claimed in our U.K.

application 8029639 is one such machine.

The or each nozzle must be secured to the nozzle housing so that the longitudinal axis of the nozzle is at an angle to the axis of rotation of the housing. This angle is usually substantially 90".

The construction of the chamber, nozzle housing and nozzle are such that liquid entering the inlet of the chamber can emerge through the nozzle and out into the tank and towards the sludge located therein which it is desired to dislodge. This means that the outlet or outlets of the chamber will register with an inlet or inlets in the nozzle housing at some time during the complete rotation of the nozzle housing about the chamber. The inlet or inlets in the nozzle housing will in turn communicate with the nozzle or nozzles attached to the nozzle housing.

There are means for rotating the nozzle housing about the chamber. Usually a turbine will be used and this is conveniently located in the chamber downstream of the inlet thereof. A gearing system can translate rotation of the turbine blades into rotation of the nozzle housing about the casing.

Other means for rotating the nozzle housing about the chamber comprise a flexible drive connecting the impeller shaft with a motor.

The shape of the nozzles is not critical but it is convenient if they are shaped like truncated cones tapering towards their extremities, the taper ensuring that the jet of liquid emerging has a comparativeliy small angle of spread. The cross-section ofthe cones can be circular but it is convenient if it is substantially the same as the shape of the nozzle, e.g. rectangular or elliptical.

It is an essential feature of the present invention that the orifice of the nozzle is of elongated crosssection wherein the major axis is at least twice that of the minor axis. Preferably this ratio is at least 4:1 and is usually between 5:1 and 20:1, for example 10:1 or 15:1. Usually the orifice will be rectangular, but alternatively it could be elliptical.

Especially when the machine is being used for dislodging sludge from the bottom of a storage tank it will be desirable that the orientation of the or each nozzle is such that when the machine is operating the minor axis ofthe orifice will be in the upright position, usually substantially vertical. This means that usually the major axis of the orifice of the or each nozzle will be substantially perpendicular to the axis of rotation of the nozzle housing.

A form of machine suitable for use near the side wall of a storage tank is similar except for the shape of the orifices of the nozzles, to that which has been described and claimed in U.K. patent application 8029639. In this embodiment the chamber comprises a central body which will inevitably be circular in cross-section and is conveniently a disc which is stationary when the machine is in use. This body, e.g. disc, is usually bolted to the inlet pipework.

Since the machine is designed to be suspended above but near the floor of a storage tank, this pipework will usually be fixed to the top of the machine. Alternatively this machine could be used upside down with the inlet on the bottom.

Although the machine is primarily designed to be suspended just above the floor of the storage tank it is possible for it to sit on a base in which case the base will have to be designed to cope with the fact that the floor of a storage tank is often sloping, e.g.

the base will have adjustable legs.

The nozzle housing rotatable about the central body is preferably cylindrical and is provided with two substantially diametric nozzles. These nozzles should preferably be situated so that when the machine is suspended above or seated on the floor of a storage tank and the nozzles rotate the jet of liquid is between 20 cm and 40 cm above the floor of the tank. If the machine sits on a base, the housing will have to be free to rotate with respect to the base, e.g. it will be free to rotate within a circular recess.

The nozzles are arranged so that liquid emerging therefrom sweeps in a stream substantially only in one plane. When the machine is operating and suspended above or seated on the bottom of the tank it is preferable that the jets are substantially parallel to the bottom wall of the tank and so the nozzles should be designed to project substantially at right angles to the longitudinal axis of the machine.

It is essential that when the machine is in use liquid emerges substantially only from one nozzle at a time. This is necessary because the machines are usually located near the wall of the tank and it is highly desirable to prevent a jet of liquid emerging from a nozzle impinging on the tank wall at close quarters with possible damage to the tank wall.

Accordingly it is preferred that the machine be located within a tank adjacent to the side wall thereof and arranged so that when the machine is operating substantially no liquid impinges on the side wall to which the machine is adjacent.

This blanking mechanism can take various forms but one simple form is to extend the central body, e.g. disc, along the longitudinal axis ofthe machine with a substantially half cylinder which is also housed within the casing, the half cylinder being large enough to shutoffthe inlet to one ofthe nozzles as the nozzle housing rotates. This means that liquid entering the machine and flowing within the housing and towards the nozzles will only be able to emerge laterally from the housing over an arc which is generaily no more than 180 . It is only when one of the nozzles rotates through this are that liquid can emerge from the machine, i.e. through one of the nozzles. In practice, it is preferred that the half cylinder be somewhat greater than a half cylinder i.e.

extend through an arc of 180"two 200 . However in some cases the arc could be anything between 160 to 200 .

An alternative arrangement is for the central body to be in the form of a cylinder with a window therein extending round the wall of the cylinder for approxi mately 180 and being positioned so that when the housing rotates about this cylinder liquid can emerge from the window and through a nozzle.

In orderto be able to rotate the nozzle housing about the central body, a turbine is preferred and it is preferred that the central body houses the turbine which is rotated by flow of liquid through the machine. The turbine shaft usually has a gear and through a gear train the nozzle housing is caused to rotate about the central body. In the preferred embodiment the turbine is located in the upper part of the machine above the disc constituting the central body and within the substantially half cylin der. The turbine shaft extends downwards through an aperture in the disc and at its lower end is provided with a gear, for example a worm which engages with a gear train, rotation of which causes the casing to rotate about the central body, e.g. the disc.

The speed of rotation of the machine is fairly critical and in practice it is found desirable that when used for removal of sludge from the bottom of a storage tank, the nozzle housing makes one complete revolution in between 2 and 4 hours, e.g. about 3 hours.

Although in some cases one machine may be quite sufficient for cleaning the sludge from the bottom of a storage tank it may often be desirable or even necessary to use more than one such machine.

One convenient arrangement when cleaning a tank having a circular side wall is to use two but preferably three, substantially equispaced machines suspended above the floor of the tank and adjacent to the wall. The sweeping stream from the nozzle from each machine will cover the whole of the floor of the tank with little overlap of each sweep.

Generally, the number of machines required depends on the size of the tank and the pumping capacity available.

A machine is designed to be located at or near the centre of the tank bottom can be of similar construction to that described in GB 8029639 but without the blanking mechanism. Thus, it will usually have a nozzle housing having two nozzles, preferably diametrically located and this nozzle housing is rotatable about a central body in which is located a turbine. Liquid can be circulated through the central body past the turbine causing rotation of the turbine blades. By means of gearing the rotation of the turbine blades can be translated into rotation of the nozzle housing and hence the nozzles. The liquid emerges through the rotating nozzles in a sweeping jet. By locating the machine near the bottom of the tank this sweeping jet can be located substantially parallel to the floor of the tank and so dislodge the sludge settling at the bottom of the tank.

In the embodiments of this invention although the turbine is usually powered by recirculating the oil the turbine could be supplied with water under pressure, e.g. 6 to 14 kg/cm2. This may if desired be heated and may contain a detergent, a chemical emulsifier or demulsifier. If it was then desired to use the tank again for oil storage all traces of water would have to be removed before re-using the tank.

This invention also concerns method of dislodging sludge from the bottom of a storage tank and the method comprises circulating a liquid through a sludge dislodging machine located near the bottom of the storage tank, e.g. one of the machines just described. The machine has one or more rotatable nozzles, the orifices of which are shaped so that the liquid emerging therefrom emerges as a jet elongated in the tangential direction as the nozzle rotates, The nozzles are caused to rotate and sludge is thereby dislodged and sediments are resuspended in the stored liquid. Usually the axis of rotation of the or each nozzle is substantially vertical and usually the plane of rotation of the nozzle is substantially parallel to the plane of the floor of the tank.However if the tank floor slopes slightly downward towards its centre as is quite often the case, the plane of rotation of the nozzle will usually be horizontal so that the emerging jet of liquid will usually be substantially horizontal. The jet of liquid expands however and therefore a substantial component of the emerging jet flow will be substantially parallel to the tank floor.

The invention is now described with reference to the drawings in which: Figure 1 shows a view in perspective of a sludge dislodging machine especially for use near the side wall of a tank; Figure2 shows this machine installed suspended above the floor of a circular tank, the wall of which is part cut away; Figure 3 shows a view of this sludge dislodging machine in part section; Figure 4 is a plan view of three sludge dislodging machines of Figure 1 installed suspended above the floor of the circular tank; and Figure 5shows a view of a sludge dislodging machine in part section, this machine being designed for mounting near or at the centre of a storage tank.

Referring to Figures 1 and 2 of the drawings the sludge dislodging machine 1 comprises a rotatable casing having a lower portion 2 and an upper portion 3 to which two nozzles 4 and 5 are attached. The axis of the nozzles 4 and 5 is substantially at right angles to the longitudinal axis of the machine. It can be seen that the orifices 35 of the two nozzles 4 and 5 are rectangular and the ratio of the major axis to the minor axis is 10:1.

The sludge dislodging liquid, for example oil, enters the machine at the top (at 6 in Figure 1) via the elbow pipe 7. This pipe 7 passes through an aperture 10 of the wall 11 of the tank and is provided with a flange 8 to which another pipe 9 is attached.

Referring now to Figure 3 within the opening 6 at the top of the machine there is a turbine 12 having a shaft 13. The turbine blades are surrounded by a turbine shroud 36 supported from the upper cylindrical portion 3 of the machine by fins 37. The shaft 13 passes through an aperture 14 in a disc 15. To prevent liquid, e.g. oil penetrating the lower part of the machine there is a seal 38 comprising a stainless steel bellows to which is attached a canopy 39 which is fixed to the disc 15. In the annular space between portion 3 of casing and disc 15 there is a half cylindrical casing 18 which extends upwards from the disc 15. Although casing 18 is substantially half-cylindrical, in the immediate proximity of the disc 15 it does completely envelope the disc 15 and therefore completely occupies the annular space between disc 15 and portion 3 of casing.This casing 18 is fixed to disc 15 by welding butthe upper and lower portions (3 and 2) of the outer casing are free to rotate about the casing 18.

The lower end of the shaft 13 is provided with a worm 19 which meshes with worm wheel 20. This worm wheel 20 is carried on shaft 21 the other end of which is worm 22. This worm 22 engages with worm wheel 23 and is carried on shaft 24, part of which is broken away for clarity. This shaft 24 carries a worm 25 which engages with worm wheel 26 carried on shaft 27. This shaft 27 also carries a spur gear 28 and this engages with a ring gear 29. This ring gear 29 is welded to the lower portion 2 of the rotatable casing and to the base plate 32.

The machine of Figures 1 to 3 operates as follows: The oil is recirculated, entering the machine 1 through aperture 6 and causing turbine 12 to rotate.

As the turbine shaft 13 rotates by means of worms 19,22 and 25, worm wheels 20,23 and 26, spur gear 28 and ring gear 29 the outer casing rotates about the disc 15 and half cylinder 18. Since the nozzles 4 and 5 are attached to upper portion 3 of the outer casing they also rotate in a substantially horizontal plane as shown at 34. Since these nozzles 4 and 5 are diametrically placed the flow of oil shown at 33 can only enter one nozzle at a time (as shown in Figure 3, nozzle 4). As the nozzles rotate in the horizontal plane eventually the entry to nozzle 5 will be free of blanking by casing 18 and oil will enter this nozzleS.

At the same time the entry to nozzle 4 will be blanked off by casing 18 and so oil will be unable to enter nozzle 4. In this manner as the nozzles rotate oil will emerge from only one nozzle at a time and in a substantially horizontal sweep.

Figure 4 shows three equispaced sludge dislodging machines la, 1b and 1c. Provided there they are correctly orientated so that substantially no oil emerges from a nozzle directly pointing at the side wall, it can be seen that substantially the whole of the diameter of the tank bottom is swept by oil emerging from the three machines.

Referring to Figure 5 which shows a similar machine to that shown in Figures 1,2 and 3 except that it is designed for mounting near or at the centre of a storage tank, there is a rotatable casing having a lower portion 42 and an upper portion 43 to which two nozzles 44 and 45 are attached. The axis of the nozzles 44 and 45 is substantially at right angles to the longitudinal axis of the machine. It can be seen that the orifices of the nozzle 44 and 45, one of which is shown at 75, are rectangular and the ratio of the major axis to the minor axis in this case is 10:1.

Within the opening 46 there is a turbine shroud 76 supported by fins 77 to the upper cylindrical portion 43 of the machine. Within this shroud there is the turbine 52 having a shaft 53 which shaft passes through an aperture 54 in a disc 55. The axis of rotation of the turbine will usually be substantially at the centre of the storage tank. To prevent liquid, e.g.

oil penetrating the lower part of the machine there is a seal 78, comprising a stainless steel bellows to which is attached a canopy 79 which is fixed to the disc 55. The rotatable casing is free to rotate about the disc 55.

The lower end of the shaft 53 is provided with a worm 59 which meshes with worm wheel 60. This worm wheel 60 is carried on shaft 61 the other end of which is worm 62. This worm 62 engages with worm wheel 63 and is carried on shaft 64, part of which is broken away for clarity. This shaft 64 carries a worm 65 which engages with worm wheel 66 carried on shaft 67. This shaft 67 also carries a spur gear 68 and this engages with a ring gear 69. This ring gear 69 is bolted to the ring lower portion 42 of the casing which is fixed to the base plate 72.

The machine of Figure 5 operates as follows: The oil is recirculated, entering the machine through aperture 46 and causing turbine 52 to rotate.

As the turbine shaft 53 rotates by means of worms 59,62 and 65, worm wheels 60,63 and 66, spur gear 68 and ring gear 69 the outer casing rotates about the disc 55. Since the nozzles 44 and 45 are attached to upper portion 43 of the outer casing they also rotate in a substantially horizontal plane as shown at 74. The flow of oil is shown at 73 for nozzle 44 and as the nozzles 44 and 45 rotate in the horizontal plane the flow of oil out of the nozzles will be in a substantially horizontal sweep.

Claims (13)

1. Amachine suitable for dislodging sludge from the bottom of a storage tank comprising a chamber having an inlet and an outlet, a nozzle housing rotatable about the chamber, means for rotating the housing about the chamber, at least one nozzle secured to said housing with the longitudinal axis of the nozzle being at an angle to the axis of rotation of the housing and the construction of the chamber, nozzle housing and nozzle being such that liquid flowing out of the outlet ofthe chamber can emerge through the nozzle, wherein the orifice ofthe nozzle is of elongated cross-section with the length of the major axis being at least twice that of the minor axis.

2. A machine according to claim 1 in which the nozzle housing has two nozzles.

3. A machine according to either of claims 1 and 2 wherein the longitudinal axis of the nozzle is at an angle of 90 to the axis of rotation of the housing.

4. A machine according to any one of the preceding claims wherein the means for rotating the housing about the chamber comprises a turbine.

5. A machine according to any one of the preceding claims wherein the nozzles are similar in shape to truncated cones with the cross section of the cones being rectangular or elliptical.

6. A machine according to any one of the preceding claims wherein the length ratio of the major axis to the minor axis is between 5:1 and 20:1.

7. A machine according to any one of the preceding claims wherein the major axis of the orifice of of the or each nozzle is substantially perpendicular to the axis of rotation of the nozzle housing.

8. A machine according to claim 1 substantially as hereinbefore dscribed with reference to Figures 1 to 3 of the drawings.

9. A machine according to claim 1 substantially as hereinbefore described with reference to Figure 5 of the drawings.

10. A method of dislodging sludge from the bottom of a storage tank which comprises circulating a liquid through a sludge dislodging machine located near the bottom of the storage tank, said machine having one or more rotatable nozzles, the orifices of which being shaped so that the liquid emerging therefrom emerges as a jet elongated in the tangential direction as the nozzle rotates, wherein the nozzles are caused to rotate and sludge is dislodged and sediments are re-suspended in the stored liquid.

11. A method according to claim 10 wherein the axis of rotation of the or each nozzle is substantially vertical.

12. A method according to either of claims 10 and 11 wherein the plane of rotation of the nozzle is substantially horizontal.

13. A method according to either of claims 10 and 11 wherein said sludge dislodging machine is the machine according to any one of claims 1 to 9.