EP1180400A1

EP1180400A1 - Cyclone separation apparatus

Info

Publication number: EP1180400A1
Application number: EP01306516A
Authority: EP
Inventors: Albert Edward Wraith; Michael David Slack
Original assignee: Newcastle University Ventures Ltd
Current assignee: Newcastle University Ventures Ltd
Priority date: 2000-08-02
Filing date: 2001-07-30
Publication date: 2002-02-20
Also published as: GB0018825D0

Abstract

A cyclone separation apparatus 1 is described for at least partially separating one or more materials carried in a fluid. The apparatus 1 includes a cyclone body 2 having a generally part conical part 6 in which fluid entering through inlet 4 is encouraged to follow a helical path around a centrally located elongate member 12. The elongate member 12 serves to stabilise the flow of fluid through the cyclone body 2, and a coaxial arrangement 8 of tubes 9, 10 is provided at the narrow end of the part conical part 6 to extract the separated components of the fluid.

Description

The present invention relates to cyclone separation apparatus, and relates particularly to cyclone separation apparatus for at least partially separating one or more materials carried in a fluid.
Cyclone separation apparatus are known for separating components of fluid streams according to density. In particular, hydro-cyclones are used for separating mixtures of fluid substances, such as solid particles dispersed within liquids, for example mineral tailings in water, mixtures of liquids, for example water contaminated with oil, and separating liquid containing entrained gases, for example air in water requiring removal by an air purge system. Gas cyclones are also known for separating particulates supported in a stream of gas, i.e. separating particles, which may be solid or liquid, carried in a gas, for example dust particles emitted by an industrial process.
Cyclone separation apparatus of the type described above separate the components on the basis of their differential densities, and in the case of particles, also on the basis of their size related behaviour in the viscous fluid when influenced by acceleration forces. Cyclones operate by causing fluid or fluids to be separated to exercise a helical path within a conical chamber, which movement results in separation under the influence of centrifugal action.
Cyclones are attractive devices for separating substances since they have relatively few moving parts, the centrifugal forces encouraging separation being derived entirely from the motion of fluid through the device. As a result of the small number of moving parts, cyclones also require relatively low maintenance compared with other separation apparatus. For example, filters and sieves require frequent attention or replacement.
A known cyclone separator consists of an upper cylindrical chamber, into which fluid is introduced tangentially through one or more inlet apertures, or by means of a curved volute. The fluid is thus forced to rotate in a spiral manner within the upper chamber, before entering a lower conical chamber, in which the flow is constrained into a helical motion of diminishing radius. An exhaust tube is arranged axially in the upper cylindrical section to extract one of the separated components of the flow, the exhaust tube typically extending into the cyclone chamber as far as the junction of the upper cylindrical section and the lower conical section. A further chamber is typically provided at the narrower base part of the conical section to collect the other separated component. Means are also often provided for periodic flushing out of this component from the chamber.
In operation of the known cyclone separator, the denser components, or heavier particulate materials, are concentrated in the radially outer part of the flow helix by means of centrifugal action, and consequently find their way to the lower collection chamber. Less dense fluid, possibly entraining lighter particulate materials, is better able to follow the flow in the radially inner part of the helix and reverse its axial direction, and flow up the exhaust tube, thus achieving separation.
The efficiency of known cyclones of this type is judged by the ability of the cyclone to adequately separate substances. For example, a cyclone may be required to separate a stream of particle laden water such that heavier, valuable, particles are removed, and in such instances, the cyclone will be designed such that particles above a given size and mass will be directed to the lower chamber, whilst lighter particles will remain entrained in the water, and so exit via the exhaust tube. A so-called "cut point" will generally be decided upon before design of the cyclone commences, the "cut point" representing the size of particles for a given density for which half of the particles will be collected in the lower chamber, and half will remain in the exhausted water. As well as the "cut point", the performance of the cyclone with regard to other particle sizes in the region of the "cut point" is also important. For example, in many applications, a sharp "cut" is required.
Cyclone separators are also used to separate liquids, for example water polluted with small amounts of oil. In this example, the cyclone will be required to provide a high efficiency of separation, possibly with a requirement for no more than one thousandth of the original concentration of oil in water remaining in the exhaust flow. A number of variations in the arrangement of the inlet and outlet of the fluid flow are possible, as well as the means for extracting the denser fraction.
Known cyclone separators suffer from a number of drawbacks. Firstly, known cyclone separators are incapable of separating gases from liquids with any useful efficiency. Known separators also suffer from so-called "bypassing", in which large or dense particulate material or dense liquid, on entering the upper chamber at a small axial radius, is insufficiently propelled radially outwards by centrifugal action, and can therefore find a direct path into the exhaust tube, thus detrimentally affecting the sharpness of the "cut", and hence lowering the separation efficiency. A further drawback is that although the main flow through the separator may be continuous, removal of the denser fraction following separation must be performed as a batch process, as a result of which the main flow through the unit must be temporarily halted. A further drawback affecting liquid flows in known cyclones results from a low pressure region arising along the axis of the cyclone chamber, which encourages the formation of an air vortex, which then destabilises the helical flow, causing loss of cyclone action. This drawback severely limits the flow rate that can be achieved in a liquid separation cyclone. A further drawback results from the required differential pressure that must be applied between the inlet and the outlet of the cyclone in order to drive the required flow of fluid through the device. A further deficiency is that a particular cyclone design geometry is very rigid in its potential applications, since process variations requiring small changes in "cut point", or variation in the densities of the fluid media to be separated, cannot be easily accommodated within a particular cyclone design, i.e. the cyclone, once designed, is very inflexible in its potential application.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
According to an aspect of the present invention, there is provided a cyclone separation apparatus for at least partially separating one or more materials carried in a fluid, the apparatus comprising:-
a cyclone body having a longitudinal axis, at least one inlet for receiving fluid prior to separation treatment thereof, at least one outlet for discharging a respective portion of said fluid subsequently to separation treatment thereof, and a first portion having a substantially part conical internal surface having a first end of larger diameter and a second end of smaller diameter, wherein said apparatus is adapted to cause liquid received at a said inlet to undergo helical motion about said longitudinal axis from said first end of said first portion towards said second end thereof; and
an elongate member arranged substantially along said longitudinal axis.
By providing an elongate member arranged substantially along the longitudinal axis of the cyclone body, this provides the advantage of stabilising flow of fluid through the apparatus. In the case of a hydro cyclone, the provision of the elongate member provides the advantage of inhibiting the formation of cavitation or gas filled voids within the fluid. The stabilisation of flow in the vicinity of the longitudinal axis of the cyclone body, resulting from the provision of the elongate member, further provides the advantage of allowing incorporation of an efficient collection arrangement consisting of one or more conduits arranged at the narrower end of the first portion of the cyclone body. The provision of the elongate member further provides the advantage of reducing the effects of bypassing, thus improving the sharpness of the "cut" i.e. the separation efficiency of the apparatus.
In a preferred embodiment, the elongate member includes a tapering portion located in use substantially in the first portion of the cyclone body.
By providing a tapering portion of the elongate member, this provides the advantage of further stabilising the flow of fluid through the apparatus.
The tapering portion may have a taper angle substantially equal to the taper angle of the first portion of the cyclone body.
The tapering portion may be substantially part-conical.
In a preferred embodiment, the cyclone body has a second portion having a substantially cylindrical internal surface, and the second portion extends from the first portion and is provided with the or each said inlet.
The elongate member may include a substantially cylindrical portion located in use substantially within the second portion of the cyclone body.
The elongate member may be displaceable in a direction substantially parallel to the longitudinal axis.
The elongate member is preferably rotatable about the longitudinal axis.
By enabling the elongate member to rotate about the longitudinal axis, for example actively by means of a motor or passively by means of fluid drag, this enables the characteristics of the apparatus, such as the "cut point", or separation efficiency, to be adjusted.
In a further preferred embodiment of the invention, the elongate member is adapted to allow passage of at least one gas therethrough.
This provides the advantage of enabling the apparatus to separate entrained gas from a liquid, the helical motion of the liquid displacing entrained gases radially inwards to the wall of the elongate member.
The elongate member may be hollow.
The apparatus may further comprise suction means for removing gas from the elongate member.
In a preferred embodiment, the or each said outlet includes a respective conduit having a respective end arranged substantially coaxially with the longitudinal axis.
This provides the advantage of allowing a continuous separation process, eliminating the need for batch collection of the heavier separated component.
At least one said conduit may be displaceable relative to the first portion of the cyclone body in a direction substantially parallel to the longitudinal axis.
This provides the advantage of allowing the "cut point" of the separation apparatus to be adjusted, thus making the apparatus much more flexible in its application than prior art devices. This also provides the advantage of enabling adjustment of the "cut point" of the apparatus to be carried out during operation thereof. Also, by selection of the relative diameters of the coaxial collection tubes, large variations in the concentration of the separated components may be accommodated.
The apparatus may further comprise pressurisation means for applying a pressure difference between the or each said inlet and the or each said outlet.
According to another aspect of the invention, there is provided a cyclone separation apparatus for at least partially separating one or more materials carried in a fluid, the apparatus comprising:-
a cyclone body having a longitudinal axis, at least one inlet for receiving fluid prior to separation treatment thereof, at least one outlet for discharging a respective portion of said fluid subsequently to separation treatment thereof, and a first portion having a substantially part-conical internal surface having a first end of larger diameter and a second end of smaller diameter, wherein the apparatus is adapted to cause fluid received at a said inlet to undergo helical motion about said longitudinal axis from said first end of said first portion towards said second end thereof, and wherein the or each said outlet includes a respective conduit having a respective end arranged substantially coaxially with the longitudinal axis.
Preferred embodiments of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which:-
Figure 1 is a plan view of a cyclone separation apparatus of a first embodiment of the present invention;
Figure 2 is a cross-sectional elevation view of the apparatus of Figure 1; and
Figure 3 is a cross-sectional elevation view, corresponding to Figure 2, of a second embodiment of the present invention.
Referring to Figures 1 and 2, a cyclone separation apparatus 1 has a cyclone body 2 having an upper cylindrical part 3 provided with an inlet duct 4 for introduction of fluid to be separated. The inlet duct 4 is connected to an entrance aperture 5, the purpose of which is to introduce the fluid to be separated tangentially to the internal surface of the cylindrical part 3.
The cyclone body 2 also has a lower part conical part 6, the lower part of which defines a sleeve 7 within which a splitter 8 comprising coaxial inner 9 and outer 10 exhaust tubes are slidably located. The tubes 9', 10 are coaxial with longitudinal axis 11 of the cyclone body 2 and are slidable in a direction parallel to the axis 11 in sleeve 7.
A solid tapering member 12 is rotatably mounted to the cyclone body 2 within a sleeve 13 and includes an upper generally cylindrical part 14 and a lower, conical tapering part 15, the taper angle of which is generally equal to the taper angle of the part conical part 6 of the cyclone body 2.
The operation of the apparatus of Figures 1 and 2 will now be described.
Fluid to be separated is propelled through the cyclone body 2, either by the application of positive pressure at the inlet duct 4, or by means of negative pressure applied to the exhaust tubes 9, 10. Fluid entering the cyclone chamber defined by the cyclone body 2 from the inlet aperture 5 is constrained by the walls of the cyclone body 2 to rotate in a circular fashion, and to undergo helical motion about longitudinal axis 11. Axial flow takes place under the influence of the differential pressure applied between inlet 4 and the outlets 9, 10, the resulting helical flow being of decreasing radius between the inlet 4 and outlets 9, 10.
Particulate matter entrained within the fluid, or in the case of mixed fluids, the fluids themselves, are influenced by centrifugal forces acting within the helical fluid flow. In the case of particulate material denser than the fluid, the helical motion serves to increase the concentration of the denser particulates in the radially outward layers of the fluid, and particulates less dense than the fluid are displaced by fluid entering the radially outward layers, and are thus forced into the radially inner layers.
Variations in relative density between the particulate matter and the supporting fluid thus results in a gradation of particles according to their respective densities, across the radial layers of fluid. Such gradation is exploited by the coaxial collection tubes 9, 10, the inner tube 9 collecting the less dense, or smaller particulate, and the outer tube 10 collecting the heavier fraction. In the case where particulate materials are supported in a medium of less density, such as solid or liquid particles supported in air, then particle size, as well as density, predominates in establishing the ultimate concentration within the cyclone chamber. In the case of mixed liquids, such as oil and water, the denser liquid will concentrate in the radially outer fluid layers, while the less dense liquid is constrained to the radially inner part of the cyclone chamber. To maximise the efficiency of separation, the diameter of the coaxial tubes 9, 10 is carefully chosen, with particular attention to the expected relative concentrations of the different fluids.
The elongate member 12 inhibits chaotic flow conditions which would otherwise be present close to the longitudinal axis 11 of the cyclone body 2, and which would diminish the separation efficiency of the cyclone, and possibly also lead to bypassing. The use of the elongate member 12 minimises the formation of a chaotic fluid core, and thus permits a design in which both fluid exhausts 9, 10 are positioned in a convenient position at the base of the cyclone body 2, whilst maintaining stable separation.
In the arrangement of Figure 2, the exhaust tube assembly 8 consisting of the coaxial tubes 9, 10 is free to be moved axially within the sleeve 7 in order to adjust the characteristics of the device. For example, movement of the exhaust tube assembly 8 could be controlled in response to signals from fluid detectors (not shown) in the outlet tubes 9, 10, to permit automatic adjustment of the relative concentrations of separated fluids in the outlet tubes 9,10. Also, the elongate member can be moved axially within a sleeve 13 at the top of the cyclone body 2 in order to adjust the characteristics of the device.
Referring to Figure 3, in which parts common to the embodiment of Figure 2 are denoted by like reference numerals but increased by 100, the elongate member 112 is constructed from a porous material and is provided with a central bore 130 communicating with an evacuation exhaust system 131. In operation, gases entrained in liquid entering the cyclone body 102 are displaced by the centrifugal action of the cyclone to occupy the boundary layer adjacent the elongate member 112 located along the axis 111. The gases are free to diffuse through the porous material of the elongate member 112 and can then be collected from the central 130 bore of the elongate member 112 by means of the evacuation system 131. This offers a much more effective means of separating gases from liquids than is possible with cyclones of the prior art.
It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

A cyclone separation apparatus for at least partially separating one or more materials carried in a fluid, the apparatus comprising:-

a cyclone body having a longitudinal axis, at least one inlet for receiving fluid prior to separation treatment thereof, at least one outlet for discharging a respective portion of said fluid subsequently to separation treatment thereof, and a first portion having a substantially part conical internal surface having a first end of larger diameter and a second end of smaller diameter, wherein said apparatus is adapted to cause liquid received at a said inlet to undergo helical motion about said longitudinal axis from said first end of said first portion towards said second end thereof; and

an elongate member arranged substantially along said longitudinal axis.
An apparatus according to claim 1, wherein the elongate member includes a tapering portion located in use substantially in the first portion of the cyclone body.
An apparatus according to claim 2, wherein the tapering portion has a taper angle substantially equal to the taper angle of the first portion of the cyclone body.
An apparatus according to claim 2 or 3, wherein the tapering portion is substantially part-conical.
An apparatus according to any one of the preceding claims, wherein the cyclone body has a second portion having a substantially cylindrical internal surface, and the second portion extends from the first portion and is provided with the or each said inlet.
An apparatus according to claim 5, wherein the elongate member includes a substantially cylindrical portion located in use substantially within the second portion of the cyclone body.
An apparatus according to any one of the preceding claims, wherein the elongate member is displaceable in a direction substantially parallel to the longitudinal axis.
An apparatus according to any one of the preceding claims, wherein the elongate member is rotatable about the longitudinal axis.
An apparatus according to any one of the preceding claims, wherein the elongate member is adapted to allow passage of at least one gas therethrough.
An apparatus according to claim 9, further comprising suction means for removing gas from the elongate member.
An apparatus according to any one of the preceding claims, wherein the elongate member is hollow.
An apparatus according to any one of the preceding claims, wherein the or each said outlet includes a respective conduit having a respective end arranged substantially coaxially with the longitudinal axis.
An apparatus according to claim 12, wherein at least one said conduit is displaceable relative to the first portion of the cyclone body in a direction substantially parallel to the longitudinal axis.
An apparatus according to any one of the preceding claims, further comprising pressurisation means for applying a pressure difference between the or each said inlet and the or each said outlet.
A cyclone separation apparatus for at least partially separating one or more materials carried in a fluid, the apparatus comprising:-
a cyclone body having a longitudinal axis, at least one inlet for receiving fluid prior to separation treatment thereof, at least one outlet for discharging a respective portion of said fluid subsequently to separation treatment thereof, and a first portion having a substantially part-conical internal surface having a first end of larger diameter and a second end of smaller diameter, wherein the apparatus is adapted to cause fluid received at a said inlet to undergo helical motion about said longitudinal axis from said first end of said first portion towards said second end thereof, and wherein the or each said outlet includes a respective conduit having a respective end arranged substantially coaxially with the longitudinal axis.