WO1996017666A1

WO1996017666A1 - Apparatus for reducing the pressure in a liquid stream

Info

Publication number: WO1996017666A1
Application number: PCT/GB1995/002859
Authority: WO
Inventors: Geoffrey Childs
Original assignee: Richard Mozley Limited
Priority date: 1994-12-07
Filing date: 1995-12-07
Publication date: 1996-06-13
Also published as: GB9524967D0; GB9424678D0; AU3991395A; GB2296106A

Abstract

Apparatus (11) for reducing the pressure in a liquid stream, especially one bearing abrasive particles, comprising at least two tapering cavities (19) each having an inlet (51) directed tangentially of its wider end (20) and an outlet (21) at its narrower end, the two cavities (19) being connected in series in such a way, that in use, the outlet stream from a first of the two cavities (19) is directed to the inlet (51) of the second cavity (19) such that energy in the flowing stream is dissipated and thus the pressure reduced in its passage from the inlet (25) to the first cavity (19) to the outlet (21) from the second cavity (19).

Description

APPARATUS FOR REDUCING THE PRESSURE IN A LIQUID STREAM

The present invention relates generally to apparatus for reducing the pressure in a liquid stream and to a method of reducing the pressure in a liquid stream.

When, during industrial processes, high pressure liquid streams result (often as a by-product) it is necessary to reduce the pressure in the stream before this can be safely discharged. Conventionally, pressure reduction is achieved by passing the stream through a narrow aperture, typically in a plate, downstream from which the pressure in the stream is lower than upstream thereof.

In some circumstances the conventional pressure-reducing technique is not appropriate. For example, if the flowing liquid is heavily charged with particles, especially abrasive particles, wear at the edges of the holes which, in order to achieve the pressure-reduction effect, must be of relatively small dimensions, causes these to enlarge thereby degrading the pressure-reduc ion effect. Moreover, because the holes are necessarily small the risk of blockage due to obstruction by coagulation or aggregation of the particles carried by the stream is a significant risk. This is especially significant in the case of effluent from oil treatment processes where the particulate material carried by the stream may have oil adherent to its surface. Another inherent disadvantage in the traditional technique utilising an apertured plate lies in the fact that upstream of the plate the collection chamber must be contained within a separately formed pressure vessel capable of withstanding the forces exerted by the stream. In many cases the regulations governing the structure, maintenance and operation of a pressure vessel makes this an unattractive option.

The present invention seeks to provide apparatus for reducing the pressure in a liquid stream which, whilst effectively acting to lower the pressure, is less susceptible to blockage or clogging than conventional apertured plate pressure reducers, and which may be formed to dimensions that avoid the necessity for a separate pressure vessel (for example allowing standard pipe fittings to be used instead) thereby making the production, maintenance and operation simpler and more economical.

According to one aspect of the present invention, therefore, apparatus for reducing the pressure in a liquid stream, especially one bearing abrasive particles, comprises at least two tapering cavities each having an inlet directed tangentially of its wider end and an outlet at its narrower end, the two cavities being connected in series in such a way that, in use, the outlet stream from a first of the two cavities is directed to the inlet of the second cavity so that energy in the flowing stream is dissipated and thus the pressure reduced in its passage from the inlet to the first cavity to the outlet from the second cavity.

By directing the inlet stream to a tapering cavity tangentially of its wider end the flow within the cavity adopts a vortex configuration. In such a vortex the outlet aperture through which the stream within the tapering cavity must flow creates a pressure differential across it which is greater, in relation to its size, than the pressure differential across a correspondingly dimensioned aperture in an apertured plate to which the stream is delivered in a direct, non-vortex flow. In this respect the tapering cavity acts as a so-called "blind" hydrocyclone, that is one having an underflow outlet but no overflow outlet.

Preferably there is provided at least one further tapering cavity having an inlet directed tangentially of its wider end and an outlet at its narrower end, , so connected that, in use, the outlet stream from the said second tapering cavity is directed to the inlet of the said further tapering cavity. This said further tapering cavity may be provided with an overflow outlet passage from the wider end thereof leading from a hollow vortex- finder extending axially of the said further tapering cavity and having an inlet opening at the end thereof nearer the narrow end of the said further tapering cavity.

When used in oil treatment apparatus, in which there may be a high pressure stream of discharge water bearing oil impregnated sand, the action of the first and second tapering cavities to create vortex flow and sharp changes in pressure, may cause a certain level of separation of oil from sand, and in the said further tapering cavity the differential specific gravities of the oil, sand and water can be exploited to locate a point in the vortex where the oil can be separated from the sand and water to exit through the said overflow outlet passage (perhaps in company with a certain proportion of water) to be taken on to a further part of the oil-treatment process.

In another embodiment of the invention there may be further provided a secondary inlet passage leading to a point in the path of the stream through the apparatus between the outlet of the second tapering cavity and the inlet to the said further tapering cavity. Means may be provided for delivering a secondary stream of fluid to the said secondary inlet passage, and likewise there may be provided means for varying the pressure of the said secondary stream at least at or in the region of the said secondary inlet passage. Because the pressure in the flowing fluid stream drops in transfer from one tapering cavity to the next and because the charge of particles and/or other material in the liquid may not be constant, the instantaneous pressure at any point within the apparatus may vary over time. The additional or secondary inlet is provided to allow the option of introducing clean water to the flowing stream at lower pressure to ensure that the particulate material is adequately diluted to be carried in the stream at the lower pressure without risk of settlement, blockage or clogging. Apparatus may, of course, be provided with both a stage having an overflow outlet passage and one

(not necessarily the same stage) having a secondary inlet passage.

The tangential inlet passages to the wider ends of successive tapering cavities may be so positioned as to direct the stream of liquid passing therethrough to circulate in the same direction or in opposite directions in successive cavities. Since the pressure reduction is at least in part achieved by the dissipation of energy in creating the vortex within the tapering cavity, an arrangement in which the direction of swirl is reversed at each successive stage advantageously maximises the energy consumption thereby increasing the effectiveness of the apparatus in reducing the pressure in the flowing stream.

In a preferred embodiment of the invention each said tapering cavity is formed in a plate-element having substantially parallel flat major faces, with the axis of the tapering cavity formed therein lying substantially orthogonally of the said major faces and passing entirely through the element with its wider end opening in to one major face and its narrower end opening in to the opposite major face.

The tapering cavities are thus formed in effect as cyclone chambers, and may have a first portion defined by a cylindrical side wall and a second portion defined by a conical side wall, the cylindrical side wall being contiguous with the wider end of the conical side wall and receiving the tangential input.

Each said plate-like element may have a depression or hollow in the major face into which the wider end of the tapering cavity opens, and a channel communicating between the said depression or hollow and the perimeter of the said wider end of the said tapering cavity whereby to convey, in use, liquid arriving at the said depression or hollow from the outlet of a preceding tapering cavity to the wider end of the tapering cavity in a generally tangential relation thereto.

Apparatus according to the invention may thus be formed from a plurality of such plate-like elements, held together in a stack by any convenient means, with contacting faces forming a liquid-tight seal and the channel and depression or hollow effectively forming, respectively, a transfer passage and a reception chamber in cooperation with the flat face of the adjacent said plate-like element. By suitably forming the plate-like elements the outlet from one tapering cavity can open directly into the depression or hollow defining the reception chamber of the next adjacent plate-like element so that successive stages of the apparatus can be formed using exactly identical elements merely located in different orientations to one another in dependence on their position in the stack. In a preferred embodiment of the invention the plate-like elements are held together in a stack by bolts passing through the elements and secured by nuts.

In embodiments of the invention having a secondary inlet and/or an overflow outlet passage these may be formed in an insert plate located between two adjacent elements defining the or a second tapering cavity and the or a further tapering cavity. It will be appreciated that although three tapering cavities have been defined hereinabove, there may in practice be more than one such first, second or third tapering cavity depending on the flow rate and pressure differential it is desired to achieve.

In embodiments having means for varying the pressure of the said secondary inlet stream such means may comprise an adjustable restrictor valve, and the means for varying the pressure of the said secondary inlet stream may further include means for effecting dynamic control of the variations thereof. Such dynamic control may act either to follow variations in instantaneous pressure resulting from unpredictable variations in flow rate, stream pressure or concentration, or may be utilised to modify the performance of the apparatus, for example by periodically back washing the cavities and passages by increasing the pressure at the secondary inlet, thereby causing reverse flow and minimising the risk of gradual accretions leading to blockages.

the present invention also comprehends a method of reducing the pressure in a flowing liquid stream, comprising the steps of causing a vortex flow in the said stream in a tapering vortex chamber and allowing the stream to flow from the vortex through an outlet aperture in to at least one tapering vortex chamber having an outlet aperture at least at its narrower end.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an external side view of a first embodiment of the invention;

Figure 2 is a plan view of an element forming a tapering chamber of the embodiment of Figure 1; Figure 3 is a sectional view taken on the line III - III of Figure 2;

Figure 4 is a cross-sectional view through a stacked assembly of elements such as those shown in Figures 2 and 3;

Figure 5 is an external side view of a second embodiment of the invention;

Figure 6 is a schematic partial sectional view through a part of the embodiment of Figure 5; Figure 7 is an external side view of a third embodiment of the invention; and

Figure 8 is a schematic partial sectional view of a part of the embodiment of Figure 7.

Referring now to the drawings, the pressure reducing apparatus illustrated in Figures 1 to 4 comprises an external vessel in the form of a pipe section generally indicated 11, having flange connectors at each end, namely an inlet end flange connector 12 and an outlet end flange 13. The pipe section 11 is intended to be connected in a pipeline to receive at its inlet a liquid under a relatively high pressure, for example in the region of 27 bar, and to deliver from its outlet, to an outlet line (not shown) the same liquid under a reduced pressure, say in the region of between atmospheric pressure and 5 bar. It is anticipated that the pipe section 11 will be installed vertically with the inlet flange 12 directly above the outlet flange 13, but this is not necessarily an essential condition.

Within the pipe section 11 is a stacked array 14 of individual identical elements 15. In the embodiments illustrated in Figure 4 there are five such elements which, with a flow rate anticipated to be in the region of two cubic metres per hour may be fitted within a pipe section of 4 inch (100mm) internal diameter. Each element 15 of the stack 14 comprises a circular disk having a cylindrical side wall 16, a flat upper face 17 and a flat lower face 18. The upper and lower faces 17 and 18 are closely parallel to one another and finished to a high level of flatness, for example by lapping, to provide a water tight seal when two such elements are placed in face-to-face contact under pressure.

The upper face 17 of each element 15 is formed with a cyclone cavity 19 having a wider end 20 opening into the face 17 and a narrower end 21 opening into the face 18. The cavity 19 has a cylindrical first portion 22, and a conically tapered second portion 23. The wide end 20 of the cavity 19 lies almost entirely to one side of a diametral plane defined by the line X-X of Figure 2. On the other side of the diametral plane X-X is formed a hemispherical cavity 24 defined by the line Y-Y of Figure 3 the centre of which is equidistant from the diametral plane X-X as the axis of the cyclone cavity 19, defined by the line Z-2. In this way contiguous elements 15, laterally inverted about the diametral plane X-X have respective cavities 24 and outlets 21 aligned with one another as can be seen in Figure 4.

Also formed in the upper surface 17 of each element 15 is an arcuately curved groove or channel 25 extending from an outlet 50 from the hemispherical cavity 24 tangentially to an outlet 51 into the cylindrical portion 22 of the cyclone cavity 19. Thus, as can be seen in Figure 4, a liquid, such as, for example, water bearing a charge of oily sand, entering the hemispherical cavity 24 in the upper most element 15 is conveyed along the arcuate channel 25 to enter tangentially into the cylindrical wall portion 22 of the cyclone cavity 19. A flat circular upper plate 26 placed over the upper surface 17 of the upper most element 15, and having an inlet opening 27 through which the inlet stream can enter the hemispherical cavity 24 defines each chamber and passage formed by the cavities 19 and 24 and the channel 25.

The section line III-III defining the section illustrated in Figure 3 lies on a diametral plane perpendicular to the diametral plane X-X. Equally spaced on either side of the diametral plane defined by the section line III- III, and lying on the diametral plane X-X are two through holes 28, 29 for receiving clamping bolts held at each end by respective nuts 30, 31. Each element 15 is also formed with two further through holes 31, 32 the function of which will be explained in more detail hereinbelow.

As will be appreciated from a consideration of Figures 1 and 4, when the apparatus illustrated is connected in a pipeline by the flanges 12, 13, a high pressure stream entering the hemispherical cavity 24 of the first element 15 in the stack 14 through the opening 27 in the plate 26, is directed from there along the curving channel 25 to enter tangentially into the cylindrical portion 22 of the cyclone cavity 19 where it adopts a swirling, cyclonic condition. The swirling liquid passes down the tapering portion 23 and out through the narrow opening 21. Because of the energy dissipation in the vortex, and the helical flow of the fluid stream the apparent resistance to flow exerted by the passage 21 is much greater than the actual dimensions of the opening 21, thereby creating a significant drop in pressure equivalent to that which would be produced by a plane hole of smaller dimensions. Because it has larger dimensions, however, the hole 21 is subject to less wear than would be a hole of smaller dimensions. In order to resist wear, especially in circumstances where the apparatus may be used with a liquid such as wash water bearing a charge of sand, each element 15 is preferably made from a highly resistant material such as a ceramic.

The reduced-pressure stream exiting from the aperture 21 in the first element 15 enters the hemispherical chamber 24 in the second element 15 of the stack 14 which, as can be seen in Figure 4, is coaxially aligned therewith. The liquid then flows from this cavity 24 along passage 25 to the next cyclone cavity 19 where it is again caused to swirl down the tapering passage and through the aperture 21.

In an alternative embodiment, shown in broken outline in Figure 2, there may be a further curved channel like the channel 25, on the opposite side of the diametral median plane defined by the section line III-III. Successive elements 15 may have one or the other of the channels 25, 25' obstructed by a correspondingly shaped insert such that each adjacent cyclone chamber 19 receives a stream from an opposite tangent so that the direction of rotation of adjacent cyclones is opposite from one another thereby increasing the amount of energy absorbed. In the embodiment illustrated in Figures 1 and 4 chree further such elements 15₃ to 15₅ are provided, each acting in exactly the same way to reduce the pressure of the stream flowing therethrough until the last element 15₅ is reached. Adjacent this element is an outlet plate 33 through which the stream, now at ambient or close to ambient pressure exits to flow through the outlet into the delivery pipe (not shown) connected to the flange 13.

The embodiment illustrated in Figures 1 to 4 acts purely as a pressure reducing hydrocyclone where the entirety of the inlet stream entering the aperture 27 in the plate 26 flows out through the aperture 34 in the outlet plate 33.

In the embodiment of Figures 5 and 6 there is a modification which allows the further separation of oil which may be adherent on the surface of the sand in the inlet stream, and which may be separated by the cyclonic action through the first few stages to be separated from the outlet stream for onward transmission to other treatment stages. Such separation is beneficial since the inlet stream may in many cases be the discharge from oil treatment processes on its way to be returned, for example, to the sea and any further separation of residual oil contamination is an advantage. In the embodiment of Figures 5 and 6 the same reference numerals as allocated in Figures 1 to 4 have been used for the same or corresponding components. This embodiment differs by the addition of a separator plate 35 between the last element 15₅ and the penultimate element 15. This separator plate has a passage 36 in alignment with the outlet opening 21 of the element 15 4 and the hemispherical cavity 24₄ of the element 15₅ allowing the stream exiting from the opening 21 of the cyclone cavity 19 in the penultimate element 15₄ to enter the hemispherical collection cavity 24 of the last element 15₅ and to pass along its curved transfer passage 25 to the last cyclone cavity 19. The lower face of the insert plate 35 has a downwardly projecting vortex finder 37 coaxial with the axis of the cyclone chamber 19, and the vortex finder 37 communicates with an internal passage 38 leading to a radial outlet 39 coupled to an outlet connector 40 having a connection flange 41. The vortex finder 37 is shaped and dimensioned to provide an outlet route for any oil separated from the water-borne sand and which, in the cyclone 19, would therefore (being lighter than the particles of sand themselves) occupy the radially innermost part of the cyclonic stream within the cyclone 19. Oil-bearing water is therefore extracted through the passages 38, 39 and the outlet connector 40 whilst sand- bearing water passes through the underflow opening 21 and the final outlet passage 34 in the plate 33.

In the embodiment of Figures 7 and 8 there is illustrated a further-modified embodiment having the overflow outlet illustrated in Figures 5 and 6, and a further inlet connection 42 having a connection flange 43. As can be seen in Figure 8 the inlet connection 42 is joined to a separator plate 44 having a passage 45 which leads from the connector 42 to a transverse passage 46 which connects the small end outlet 21 of the cyclone cavity 19 in the last element 15₅ with the passage 34 in the end plate 33. By introducing a fresh liquid in the direction of the arrow A of Figure 8 through the coupling 42 into the passage 45, a number of different effects may be achieved. If the pressure of the fresh wash water A matches or is just greater than that of the liquid flowing through the passage 46 from the last cyclone stage 15₅ this will augment the flow of depressurised water to compensate for the volume loss of oil through the outlet 40. The outlet flow rate will therefore match the inlet flow rate of pressurised liquid. At higher pressures the outlet flow may be held stationary, thereby allowing on/off control of the flow, whilst at higher pressures yet the flow through the cyclone stack may be reversed allowing back washing of the apparatus and release of any blockages which may have occurred. Rapid variation or pulsing of the backwash pressure can also assist in releasing any blockages. Although reference has frequently been made to the depressurisation of a high pressure water stream contaminated with oily sand, it will be appreciated that the principles of the invention may be applied to apparatus suitable for depressurising any stream of liquid and the apparatus for the present invention may, therefore, find application in a wide range of uses.

Claims

1. Apparatus for reducing the pressure in a liquid stream, especially one bearing abrasive particles, comprising at least two tapering cavities each having an inlet directed tangentially of its wider end and an outlet at its narrower end, the two cavities being connected in series in such a way, that in use, the outlet stream from a first of the two cavities is directed to the inlet of the second cavity such that energy in the flowing stream is dissipated and thus the pressure reduced in its passage from the inlet to the first cavity to the outlet from the second cavity.

2. Apparatus as claimed in Claim 1, in which there is provided at least one further tapering cavity having an inlet directed tangentially of its wider end and an outlet at its narrower end, so connected that, in use, the outlet stream from the second tapering cavity is directed to the inlet of the said further tapering cavity.

3. Apparatus as claimed in Claim 2, in which there is further provided an overflow outlet passage from the wider end of the said further tapering cavity leading from a hollow vortex-finder extending co-axially of the said further tapering cavity and having an inlet Opening at the end thereof nearer the narrow end of the said further tapering cavity.

4. Apparatus as claimed in Claim 2 or Claim 3, in which there is further provided a secondary inlet passage leading to a point in the path of the stream through the apparatus between the outlet of the said second tapering cavity and the inlet to the said further tapering cavity.

5. Apparatus as claimed in Claim 4, in which there are further provided means for delivering a secondary stream of fluid to the said secondary inlet passage, and means for varying the pressure of the said secondary stream at least at or in the region of the said secondary inlet passage.

6. Apparatus as claimed in any preceding claim, in which the tangential inlet passages to the wider ends of successive tapering cavities are so positioned as to direct the stream of liquid passing therethrough to swirl in opposite directions in successive cavities.

7. Apparatus as claimed in any preceding claim, in which each said tapering cavity is formed in a plate-like element having substantially parallel flat major faces, with the axis of the tapering cavity lying substantially orthogonally of the said major faces.

8. Apparatus as claimed in any preceding claim, in which the said tapering cavities are formed as cyclone chambers with a first portion defined by a cylindrical side wall and a second portion defined by a conical side wall.

9. Apparatus as claimed in Claim 7 or Claim 8, in which each said plate-like element has a depression or hollow in the major face into which the wider end of the tapering cavity opens, and a channel communicating between the said depression or hollow and the perimeter of the said wider end of the said tapering cavity whereby to convey, in use, liquid arriving at the said depression or hollow from the outlet of a preceding tapering cavity to the wider end of the tapering cavity in a generally tangential relation thereto.

10. Apparatus as claimed in any of Claims 7 to 9, in which the said plate-like elements are held together in a scack by bolts passing through the elements and secured by nuts.

11. Apparatus as claimed in Claim 3 or Claim 4 and any of Claims 5 to 10, in which the said secondary inlet and/or the said overflow outlet passage are formed in an insert plate located between two adjacent elements defining the or a second tapering cavity and the or a further tapering cavity.

12. Apparatus as claimed in any of Claims 5 to 11, in which the said means for varying the pressure of the said secondary inlet stream comprises an adjustable restrictor valve.

13. Apparatus as claimed in any of Claims 5 to 12, in which the means for varying the pressure of the said secondary inlet stream includes means for effecting dynamic control of the variations thereof.

14. A method of reducing the pressure in a flowing liquid stream, comprising the steps of causing a vortex flow in the said stream in a tapering vortex chamber and allowing the stream to flow from the vortex through an outlet aperture into at least one further tapering vortex chamber having an outlet aperture at least at its narrower end.