AU598505B2 - Cyclone separator - Google Patents

Description

CO0M MO0N WE A LTH OF A 0 S TR A PI A PATENTS ACT 1952 COMPLETE SPECIFICATION (original) FOR OFFICE USE Application Number: Lodgedt ,6 17,50-21.? Complete Specification Lodged:z Accepted: Published: Priority: 0 0 Related Art: 0 00 4 004 0 00 00 4 900 .4 00 4 00 0 0 09 00 004 0 40 94 0 9 04 0 000,~0 0 00 0 00 4 0,0 0 0 4 Name of Applicant:- SECTION DIRE ION SEE OO NAME DIRECTED Ccu-cc~o Address of Anni 4 t-An S HERB=Uttk- hJA,, C -t IN HE, STATE OF VICTORIA COMONWEALTH OF, AUSTRALrIA Actual Inventor(s): Address for Service: DAVIES COLLISON Patent Attorneys, I1 Little Collins Street, Helbourne, 3000.

Complete specification for the in-Vention entitled: "CYCLONE SEP.RATOR" The following statement is a full description of this invention, including the best method of performing it known to me :t- I- i

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la CYCLONE SEPARATOR This invention is about a cyclone separator. This separator may find application in removing a lighter phase from a large volume of a denser phase, such as oil from water, with minimum contamination of the more voluminous phase. Most conventional cyclone separators are designed for the opposite purpose, that is removing a denser phase from a large volume of a lighter phase, with minimum contamination of the less voluminous phase.

This invention is a cyclone separator defined as follows. The cyclone separator has a generally cylindrical first portion with feed means for feeding liquid to be separated to the separator,, and, adjacent to the first portion and substantially coaxial therewith, a generally cyclindrical/tapered second portion open at its far i end. The first portion has an axial overflow outlet opposite the second portion in its end wall). The second portion comprises a flow-smoothing taper converging towards its said far end, where it leads into a substantially coaxial generally cylindrical third portion. The internal diameter of the axial overflow outlet is do, of the first portion is dl, of the divergent end of the taper comprised in the second portion is d 2 of the convergent end of the taper is d 3 and of the third portion is also d 3 The internal length of the first portion is 11 and of the second portion is 12. The total inlet cross-sectional area of the feed means measured at the point of entry normal to the inlet flow is Ai. The shape of the separator is governed by the following relationships: 10 1 2 /d 2 4 0.04 4A /d 2 0.10 i 1" l d /d 0.1 d 1 d 2 d >d d2 3 The half-angle of the convergence of the taper is 20' to preferably up to The taper is preferably frustoconical.

-2- Optionally the half-angle is such that half-angle (conicity) arctan ((d 2 d i.e. of such slight angle that the tapa~r occupies the whole length of the second portion.

Preferably, d 3/d 2is from 0.4 to 0.7. Preferably, where the internal length of the third portion is 1 31 3 1/d 3 is at least 19 and may be as large as desired, preferably at least 40. 1 1 /d I may be from 0.5 to 5, preferably from 1 to 4. d 1/d 2may be from 1 to 3.

For maximum discrimination with especially dilute lighter phases, it was thought necessary to remove, through the axial overflow outlet, not only the lighter phase hut also a certain volume conttihuted by a near-wall flow travelling radially inwardly towards the axis (where, in operation, the lighter phase tends to collect an its way to the axial overflow outlet). It was accordingly 4 I1 15 proposed to provide, within the axial overflow outlet, a further concentric outlet tube of the desired narrowness, thus creating a third outlet from the cyclone separator into which the lighter phase is concentrated. While this design works entirely satisfactorily, it is complicated hy reason of having three outlets and we now unexpectedly find that, when using merely a small axial overflow outlet, the near-wall flow tends to detach itself from the end wall before reaching that outlet, and recirculates (and is Ire-sorted') within the cyclone separator, leading to a welcome simplification. Furthermore, the proportion of heavy fine solids in the overflow outlet falls because of advantageous chcrnges in the flow pattern. (Such solids are generally preferably absent in that outlet).

Preferably d oId 2is at least 0.008, more preferably from 0.01 to 0.08, most preferably 0.02 to 0.06. The feed Aree- advantageously spaced axially from the axllal overflow outlet. Pressure drop in the axial overflow outlet should not he excessive, and therefore the length of the "d 0"1 portion of the axial overflow outlet should be kept low. The outlet may widen by a taper or step.

A flow-smoothing taper may he interposed between the first portion and the second portion, Preferably in the form of a r 3 frustoconical internal surface whose larger-diameter end has a diameter d I and whose smaller-diameter end has a diameter d 2 and whose conicity (half-angle) is preferably at least 10°. For space reasons it may he desired to curve the third portion gently, and a radius of curvature of the order of 50 d 3 is possible.

The actual magnitude of d 2 is a matter of choice for operating and engineering convenience, and may for example b 10 to 100mm.

Further successively narrower fourth, fifth portions may be added, but it is likely that they will increase the energy consumption to an extent outweighing the benefits of extra separation efficiency.

The invention extends to a method of removing a lighter phase from a larger volume of a denser phase, comprising applying the phases to the feed of a cyclone separator as set forth above, the phases being at a higher pressure than in the axial overflow <o outlet and in the far end of the third portion. The pressure drop to the end of the third portion (clean stream) is typically only a about half that to the axial overflow outlet (dispersion-enriched Sstream), and the method must accommodate this feature.

20 This method is particularly envisaged for removing oil (lighter phase) from water (denser phase), such as oil-field production water or sea water, which may have become contaminated with oil <as a result of spillage, shipwreck, oil-rig blow-out or routine operations such as bilge-rinsing or oil-rig drilling.

The feed rate (in m 3 of the phases to the cyclone separator preferably exceeds 6.8d22 where d 2 is in metres. The method preferably further comprises, as a preliminary step, eliminating gas from the phases such that in the inlet material the volume of I any gas is not more than i%.

o a 30 Where however the gas content is not too large, the gas itself may he treated as the lighter phase to he removed in the method. As liquids normally become less viscous when warm, water for example being approximately half as viscous at 50 0 C as at c, the method is advantageously performed at as high a temperature is convenient.

4 1 The invention extends to the products of the method 2 (such as concentrated oil, or cleaned water).

3 The invention will now be described by way of example 4 with reference to the accompanying drawing, which shows, schematically, a cyclone separator according to the 6 invention. The drawing is not to scale.

7 A generally cylindrical first portion 1 has a single 8 feed means comprising a group of feeds at the same 9 circumferential location which feed means is directed tangentially into the first portion 1, and is slightly 11 displaced axially from a wall 11 forming the 'left-hand' end 12 as drawn, although, subject to forming an axisymmetric flow, 13 the disposition and configuration are not critical. Coaxial 14 with the first portion 1, and adjacent to it, is a generally cylindrical second portion 2, which opens at its far end 16 into a coaxial generally cylindrical third portion 3. The 17 third portion 3 opens into collection ducting 4. The feed 04 18 means may be slightly angled towards the second portion 2 to o 19 impart an axial component of velocity, for example by from the normal to the axis.

21 The first portion 1 has an axial overflow outlet 22 opposite the second portion 2.

23 In the present cyclone separator, the actual 0 24 relationships are as follows;:- 25 dl/d 2 2. This is a compromise between energy-saving 26 and space-saving considerations, which on their own would 27 lead to ratios of around 3 and 1.5 respectively.

28 Taper half-angle 40' (T 2 on Figure).

29 d 3 /d 2 °t 30 1 1 /dl 1.0. Values of from 0.5 to 4 work well.

31 1 2 /d 2 is about 22. The second portion 2 should not be 32 too long.

33 The drawing shows part of the second portion 2 as 34 cylindrical, for illustration. In our actual example, it tapers over its entire length.

36 13/d3 40. This ratio should be as large as possible.

37 38 u ZS 4 a 5 0 p pP P 00 0000 o o 0000 o op pP 0 000 0 00 o o P 000 o 00 pp 0 0*00 d0 d 2 0.04. If this ratio is too large for satisfactory operation, excessive denser phase will overflow with the lighter phase through the axial overflow outlet 10, which is undesirable.

If the ratio is too small, minor constituents (such as specks of grease, or bubbles of air released from solution by the reduced pressure in the vortex) can block the overflow outlet 10 and hence cause fragments of the lighter phase to pass out of the 'wrong' end, at collection ducting 4. With these exemplary dimensions, about 1% by volume (could go down to 0.47) of the material treated in the cyclone separator overflows through the axial overflow outlet 10. (Cyclones having d oId o 0f 0.02 and 0.06 were also tested successfully) 'Ai/vd 2 1/16. This expresses the ratio of the inlet feed cross-sectional area to the first portion cross-sectional area.

15 d 2= 58mm. This is regarded as the 'cyclone diameter' and for many purposes can he anywhere within the range 10 100nn, for example 15 60mm; with excessively large d 21tlienrgcosmtn becomes large to maintain effe~ctive separation while with too small d 2 unfavourable Reynolds Number effects and excessive shear 20 stresses arise. Cyclones having d 2= 30mm proved very serviceable.

The cyclone separator can be in any orientation with insignificant effect.

The wall 11 is smooth as, in general, irregularities upset the desired flow patterns within the cyclone. For best performance, all other internal surfaces of the cyclone should also be smooth.

However, in the wall 11, a small upstanding circular ridge concentric with the outlet 10 may be provided to assist the flow moving radially inward near the wall, end the outer 'f'-inge' of the vortex, to recirculate iv~ a generally downstream direction for 30 resorting. The outlet 10 is a cylindrical bore as shown. Where it is replaced by an orifice plate lying flush on the wall 11 and containing a central hole of diameter d 0leading directly to a rele' qely large bore, the different flow characteristics appear to have a sJ<.ghtly detrimental, though not serious, effect on performance. vie outlet 10 may advantageously be divergent in the pp P P 0 000 0 00 Pp p 0 00 000 PP 0p 0* 4 0 04 00400*t t -6direc-tion of overflw, with the outlet orifice in the wall 11 having the diimeter. d and the outlet widening thereafter: at a o cone half-angle of up to 10 In this way, a smaller pressure drop is experienced along the outlet, which must be balanced against the tendency of the illustrated cylindrical bore (cone half-angle of zero) to encourage coalescence of droplets of the lighter phase, according to the requirements of the user.

To separate oil from water (still by way of example), the oil/water mixture is introduced at 500C through the feeds 8 at a pressure exceedir;g that in the ducting 4 or in the axial overflow outlet 10, and at a rate preferably of at least 160 litre/minute, with any gas in the inlet limited to i% by volume. The size, geometry and valving of the pipework leading to the feed 8 are so arranged as to avoid excessive break-up of the droplets (oi bubbles) of the lighter phase, for best operation of the cyclone separator.

For the same reason (avoidance of droplet break-up), still referring to oil and water, it is preferable for no disparsant to have been 000 added. The feed rate (for best performance) is set at such a level that (feed rate/d 2 8 6.8 with feed rate in m 3/s and d in 2 2 metres. The mixture spirals within the first portion I and its angular velocity increases as it enters the second portion 2. A flow-smoothing taper T 1 of angle to the axis 100 is interposed between the first and second portions. Alternatively worded, 100 is the conicity (half-angle) of the frustrum represented by T

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The bulk of the oil separates within an axial vortex in the 0 4 9 second portion 2. The spiralling flow of the water plus remaining oil then enters the third portion 3. The remaining oil separates within a continuation of the axial vortex in the third portion 3.

,k The cleaned water leaves through the collection ducting 4 and may be collected for return to the sea,, for example, or for further cleaning, for example in a similar or identical cyclone or a bank of cyclones in parallel.

The oil entrained in the vortex moves axially to the axial overflow outlet 10 and 'may be collected for dumping, storage or 00 9 0 0 S00 0 40 04 0 0 00 t 4 *rr 07 I0 7 further separation, since it will still contain some water. In this case too, the further separation may include a second similar or identical cyclone.

The smallness of the axial overflow outlet 10 in accordence with the invention is especially advantageous in the case of series operation of the cyclone separators, for example where the 'dense phase' from the first cyclone is treated in a second cyclone, from which the 'dense phase' is treated in a third cyclone. The reduction in the volume of 'light phase' at each stage, and hence of the other phase unwantedly carried over with th 'light phase' through the axial overflow outlet 10, is an important advantage, for e'ample in a boat being used to clear an oil spill and having only limited space on board for oil containers; although the top priority is to return impeccably de-oiled seawater to the sea, the 15 vessel's endurance can be maximised if the oil containers are used to contain only oil and not wasted on containing adventitious sea-water.

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Claims (19)

1. A cyclone separator having a generally cylindrical first portion withfeed means for tangentially feeding liquid to be separated to the separator, and, adjacent ti, the first portion and substantially coaxial therewith, a tapered second portion open at its far end, the first portion having an axial overflow iutlet opposite the second portion, the second portion comprising a flow-smoothing taper converging towards its said far end, where it leads into a substantially coaxial generally cylindrical third portion, the internal diameter of the axial overflow outlet being d 0 of the first portion being dl, of the divergent end of the taper comprised in the second portion being d 2 of the convergent end of the taper being d 3 of the third portion being also d 3 tha internal length of the first portion beingI 11 and of the second portion being 12, the total inlet cross-sectional area o4 the feGd Vmeans measured at the points of entry normal to the inlet flow being Ai, the shape of the separator being governed by the following relationshipst- l2/d 2 2 0.0404A/vdl 0.10 dl> d 2 d2 d 2 3 do/d 2 0.1

2. A cyclone separator according to claim 1, wherein the half-angle of the convergence of the taper is 20' to 2',

3. A cyclone separator according to claim 2, wherein said half-angle is 20' to 19.

4. A cyclone s~parator according to any preceding claim, Wherein d 3 /d 2 is from 0.4 to 0.7. A cyclone separator according to any preceding claim, wherein the internal length of the third portio, is 13 and 1 3 /d 3 is at least t.t U. Is -9-

6. A cyclo-ne separator 11/d 1is from 0,5 to

7. A cyclon.- separator from 1 to 4.

8. A cyclone separator d/d 2 is from 1.5 to 3.

9. A cyclone separator d 0/d 2 is at least 0.008. A cyclone separator from 0.01 to 0.08.

11. A cyclone separator from 0.02 to 0.06.

12. A cyclone separator according to any preceding claim, wherein according to Claim 6, wherein 1 1 /d I is according to any preceding claim, wherein according to any preceding claim, wherein according to Claim 9, wherein d 0/d 2 is actording to Claim 10, wherein d 0 /d 2 is according I I 'I' comprising, interposed between the 15 portion, a flow-smoothing taper.

13. A cyclone separator according to any preceding claim, further first portion and the second tu Claim 12, wherein the taper of Claim 12 is in the form of a frustoconical internal surface whose larger-diameter end has a diameter d I and whose smaller- diameter end has a diameter d 2

14. A cyclone separator according to Claim 13, wherein the conicity (half-angle) of the frustoconical taper is at least I0 Q A cyclone separator according to any preceding claim, wherein d, is from 10 mm to 100 mm.

16. A cyclone separator accordting to Claim I substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

17. A method of removing a lighter phase from a larger volume of a denser phase, comprising applying the phases to the feed means of a cyclone separator according to any preceding claim, the phases being at a higher pressure than in the axial overflow outlet and i the far end of the third portion.

18. A method according to Clpi; wherein the feed rate (in m3/s) of the phases to the cyclone separator exceeds 6.8d2 8 (where d 2 is in metres).

19. A method according to Claims 17 or 18, wherein the lighter phase is gas. A method according to Claim 17 or 18, wherein the lighter phase is oil and the denser phase is water.

21. A method according to Claim 17, 18 or 20, further comprising, as a preliminary step, eliminating gas from the phases such that in the inlet material the volume of any gas is not more than h%.

22. A liJhter phase which has been concentrated relative to a denser phase by subjecting the phases to a mmethod according to any of Claim 17 to 21, and collecting the material leaving by the 0 axial overflow outlet. S. 23. A denser phase from which a lighter phase has been removed by subjecting the phases to a method according to any of Claims a 17 to 21, and collecting the material leaving by the far end of the third portion,

24. A cyclone separator as claimed in any one of Claims 1 to wherein said second portion is partially cylindrical. A cy ne-sepa-Maor-as-claimed-in-any--onaf£ClLmna 1>to 1 and 24 wherein said feed means comprises a plurality of substantially identical substantially equally circumferentially spaced tangentially directed feeds. 26, A cyclone separator asblaimed in claims 1 to 15 and 24 wherein said feed means iompris a a plurality of substantially identicai substan wi y equally circumferentially spaced tingentially directed Dated this 12thday of January, 1987 .NOEBr ARRGIA' I by his Patent Attorneya ^DAVInS 4 COLLISON