CA1110981A

CA1110981A - Process and apparatus for the centrifugal treatment of fluids containing impurities in suspension

Info

Publication number: CA1110981A
Application number: CA316,564A
Authority: CA
Inventors: Jean-Francois Vicard
Original assignee: LAB SAS
Current assignee: LAB SAS
Priority date: 1977-11-22
Filing date: 1978-11-21
Publication date: 1981-10-20
Also published as: JPS5481561A; DE2850690A1; FR2409076A1; BR7807589A; FR2409076B1; DE2850690C2; JPS622854B2; ZA786427B; US4170555A; IN149088B

Abstract

A B S T R A C T
In a process for the centrifugal treatment of liquid of liquid or gaseous fluids containing impurities in sus-pension, of the type in which the fluid to be treated is injected tangentially in a first end of an apparatus of circular transverse section in which this fluid forms a first, substantially cylindrical rotating layer, whilst at the other end, and starting from the periphery, a frac-tion containing heavy impurities is collected, then cleared fluid, then possibly a fraction containing impu-rities lighter than the fluid, it being provided to re-cycle at least one fraction of the fluid leaving the apparatus by tangential injection at a point located at a radial distance different from that of the point of injection of said fluid, so as to create in the apparatus at least one second, substantially cylindrical layer con-centric to the first, in contact therewith and rotating in the same direction substantially according to the same law of variation of the linear speed as a function of the radius.

Description

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The present invention rel~1es to apparatus in which a fluid containing impurities in suspension which are more dense and/or possibly lighter than said fluid is rotated at high speed, with a view to effecting separation thereof.
The fluid injected tangentially in such an apparatus is known to have a tendency to rotate therein according to the so-called irrotational regime, this beinq advantageous for the separation of the impurities. However, the friction against the wall tends to hinder the stable establishment of this regime.
It is an object of the invention to remedy this drawback.
In one particular aspect the present invention provides a process for the centrifugal treatment of liquid or gaseous fluids containing impurities in suspension, of the type in which the fluid to be treated is injected tangentially in a first end of an apparatus of circular transverse section in which this fluid forms a first, substantially cylindrical rotating layer, whilst at the other end, and starting from the periphery, a fraction containing heavy impurities is collected, then clearer fluid, then possibly a fraction containing impurities lighter than the fluid, it being provided to recycle at least one fraction of the fluid leaving the apparatus by tangential injection into the first end thereof, the fraction to be recycled independently of the initial fluid to be treated is injected at a point located at a radial distance different from that of the point of injection of the fluid, so as to create in the apparatus at least one second, substantially cylindrical layer concentric to the first, in contact therewith and rotating in the same direction substantially according to the same law of variation of the linear speed as a kg/~b .,"~ ,. . - .- . ~ , . , ` :

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function of the r~ ius.
In anoth-er aspect the present inven~.i.on provldes dn apparatus for the centrifugal treatment of a ]iquid or gaseous fluid containg imi~urities in suspension, comprising: a substan-tially cylindrica~ bo~y having first and second ends; a plurality of tangential inl~ts disposed at the first end concentrically to each other and opening in the same direction to create within the body, ~pon injection of the fluid, a succession of concentric annular rotating fluid layers; a plurality of tangential outlets at the second end to collect the fluid from the layers, with the radially outermost of tne outlets collecting a fluid fracti.on con-taining the heaviest impurities and the radially innermost of the outlets collecting a fluid fraction containing the lightest impuri-ties; and means to re-inject the fluid fraction collected from one of the layers by one of the tangential outlets through the tangential inlet for the layer immediately radially interior to the one of the layers.
The invention will be more readily understood on reading the following description with reference to the accompanying drawings, in which:
Fig. 1 is a longitudinal section through an apparatus according to the invention with two successive rotating layers.

.,.,~. --la-kg/ob Figs. 2 and 3 are transverse sections thereof along II-II and IIl-III (Fig. 1).
Fig. J~ shows a partial vertical section of a variant embodi-ment of the lower part.
Fig. 5 is a I~artial vertical section showing a possible struc-ture of the section of the tangential inlet nozzles.
To simplify explanations, it will be assumed hereinafter that the fluid treated is a liquid.
The apparatus shown in Fig. 1 comprises a vertical cylindri-10 cal body 11. This body is partly closed at its upper eod by a plate composed ol two concentric annular portions 2 and 3, the outer portia

2 being located at a level lower than that of the inner portion 3 and these two portions being connected by a vertical sleeve 4. The outer portion 2 is pierced with an opening forming inlet of a flat tangential 15 nozzle 5, which is sliglltly inclined downwardly and of which the flat section extends over the whole raclial width ol this portion. Similarly, a like no zz le 6 is associated with the inner portion 3. It will be noted that, to render the drawing more clear, the no~les 5 and 6 have been shown in section in the san~e plane whilst for constructive reasons 20 they are advantageously offset somewhat angularly about the vertical .
axis of the body 1, as shown in Fig. 2.
The connecting sleeve 4 extends downwardly below portion 2.
On the other hilnd a second sleeve 7 is provided which defines portion O

3 internally and which also penetrates downwardly, but less than the 25 first sleeve 4. The upper end of the second sleeve 7 receives an insulator 8 which supports an axial electrode 9, which extends down-wardly through the whole of the body 1 and extends beyond the bottom the r eof .
The lower end of the body 1 is partially closed by an i~nllul.lr 30 plate 10. Three tangential outlets 11, 12 and 13, slightly inclinecl dowll-.. _ ____.___.__ ___. _, ., . _. _, ,.. ~ ., . . _, . ~ . ... . . . . .

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wardly, opell in this plate and, there again, they have been shown in section in the s~me rcldial plane in Fig. 1, whilst in fact they are offset angularly, as shown in Fig. 3. The outermost outlet ll is o reduced radial width. It is followed by the outlet 12 which is wider, 5 and these two outlets ll ;lnd lZ together correspond in a transverse plane to a radidl zone identical to that to which the portion 2 ol the upper l~late corresponds, i. e. the nozzle 5; in other words, the total width of ll and oZ 12 is essentially equal to the distance separating the sleeve 4 from tbe peripher<ll ~vall ol the body l. ~s to the third outlet 10 13, the radial zorle which it concerns is substantially the same às that to which nozzle 6 correspollds, i. e. the zone defined in a trans-verse plane by the two sleeves 4 and 7.
In the central opening oJ the lower plate lO there is mounted a downwardly oriented divergent pipe 14, the inner diameter ol this 15 ,vi~e corresponding substantially to the inner diameter of sleeve 7. ~s is clearly shown in E`ig. l, the electrode 9 extends beyond the pilue l~l.
The no~.le 5 is tl-e one supplying tlle a~-paratus, as iu(ljc.l~ecl by arrow lS. It is connected to a suitable device (not shown) wllich sends it the suspension to be treated under pressure. The out~et ll 20 corresponds to the separated slurry (arrow 16, Fig. 3). It is connec-ted to a corresponding draining rec:eptacle via a valve or the like enabling the rate of flow to be regulated as a function of the rate of flow of the heavy particles separated with a view to reducing the quan-tity of liquid which accompany them. The outlet 12 is connected to 25 nozzle 6 by an outer pipe represented schematically as 17 and in which is inserted a Venturi 18 comprising at its throat an injector 19 sup-plied under a relatively high pressure with an auxiliary fluid (arrow 20) which will be assumed to be air, to give a specific idea. As to outlet 13, it is connected to a suitable pipe (not shown) adapted to collect the trecltec~ Lli(l.
Operation is as follows: the liquid to be treated is iuje(.ted into the apparatus through nozzle 5. It constitutes inside said appara-tus a cylin~lric.ll layer A whictl tends to rotate in irrotational regime with lormation of a theoretically hyperbolic axial vortex but which, if the speed of injection is sufIiciently high, may be assimilated to a cylindrical surface. Under the effect of the centri-fugal force, Ihe heavy impurities are progressively concentr.ltecl towards the l>eriphery. The rotating mass is furthermore animated 10 by a descending movement so that more or less concentrated slurry 0 i~ obtained at outlet 11 and relatively clear liquid at outlet 12. The slurry is drained, whilst the relatively clear liquid flows through pipe 17 and arrives at the Venturi 18, which, under the effect of the injector 19, acts as a pump to give it a higher dynamic and!or static 15 pressure. It thus arrives at nozzle 6 which injects it a8ain tangen-tially into the body 1 inside which it constitutes a second cylindrical layer B vvh;ch also tends to follow the irrotational regime. This layer is located inside layer A and if the power of the Venturi injec-tor 18 as well as the form of the nozzle 6 are suitably regulated, its 2Q law of movemellt is substantially the same as that of said layer A, ao that, at the boundary of the two layers, the linear speeds are sub-stantial].y equal and no eddy is therefore formed It will be recalled on this subject that the irrotational move-ment is defined by formula vr = k in which v is the speed at any point, 25 r the radial distance of this point ~,vith respect to the a~is and _ a constant. For the two layers A and B to rotate in harmony, it suffices that the constant k be the same in both cases The sleeve 4 separ~tes the two layers when they begin to rotate in order to give them time to take the irrotational regime regularly. The sleeve 7 acts in the . ~

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same way to allow the regu1ar formation oI the central vortex, reierenced C, at tl-e centre oi whichthe electrode 9 is insulated.
Within the l~yer 13 ~he centrifugal field is more intense than in layer A, with the result that residual heavy impurities are further separated and rejectecl into layer A to be evacuated through outlet ll.
The clear li(~uid is collected from outlet 13 The latter rnay be regulated so that a small quantity of clear liquid overflows through pipe ~4, taking along possible light impurities such as lloating particles and scum. If thè auxiliary fluid injected at l9 is air, fine bubbles rejected inwardly and which thus tend to pro-rnote the separation ot these light impurities by flotation, aplJear in layer B.
l`he electrode 9 serves in known manner to promote the agglo-meration of the particles and separation thereof.
When the licluid does not contain light impurities and when it is desired to use it for atomisation (for example in a dust-removal chamber), the outlet 13 may be eliminated or obturated. Tlle clcar licluid then escapes totally through the central pipe 14 and is divided into fine droplets, on leaving same, due to its ene rgy of rotation.
~`ig. 4 shows a variant which may be used when it is clesired to collect the light impurities without any effect of atomisation. l-1ere, the pipe 14 is replaced by a simple axial pipe comprising a rirst por-tion 22 with large diameter in which the electrode 9 extends, lollc)wed by another portion 23 of smaller diameter where the energy o1 rotatio 2 5 i s di s si pat ed Fig. 5 indicates how the inlet nozzles 5 and 6 may be sectioned with a view to promoting the establishment of the irrotational regime As is shown, their section takes the form of a recumbent rectangular trapezium so that the height of this section reduces on approaching tlle cl~is, lhe upper side of the trapezi~um being able to be conc~ve in order better to correspond to the conditions inlposed by tlle irrotational reginle To tl~e s.~ e en(l, tlle w~lls ol the l~ortions Z and 3 of the 5 upper plate may be E~rovided to be helical, so that they are adapted to the helical n~ovement of the liquid streams, the opening oi each of the nozzles then being in a radial plane. In the case of nozzles sectioned as in F`ig. 5, the stream constituted by the helical wall must be deformed progressively to be connected to the section of 10 the nozzle.
It is Lurther possible to reduce the formation of eddies to-wards the noz~les by l-nultiplying the latter for each portion 2 or 3 of the plate. Four nozzles 5 may thus be provided, disposed at 90 with respect to one another on the portion 2 of the plàte and 15 four nozzles 6 oriented at 45 with respect to the prece-lirlg ones on portion 3. The turbulence is then distributed and absolbe(l better The preceding l`igures have shown an apparatlls in wllill two concentric layers A and B rotate, but it is understood tl-at the numt~er of such layers may be greater than two.
2U It ha~ L~een assun-ed hereinl-elore that the fluid treatecl was a liquid, but tl-e invention is also applicable to gases. In such a case there is no longer formation of a vortex such as C and if there are no light impurities, the lower plate may be hermetically closed, the electrode 9 stopping thereabove. The outlet 13 may then be central, 25 if desired

Claims

WHAT IS CLAIMED IS:

1. In a process for the centrifugal treatment of liquid or gaseous fluids containing impurities in suspension, of the type in which the fluid to be treated is injected tangentially in a first end of an ap-paratus of circular transverse section in which this fluid forms a first, substantially cylindrical rotating layer, whilst at the other end, and starting from the periphery, a fraction containing heavy impurities is collected, then clearer fluid, then possibly a fraction containing impurities lighter than the fluid, it being provided to recycle at least one fraction of the fluid leaving the apparatus by tangential injection into the first end thereof, the fraction to be recycled independently of the initial fluid to be treated is injected at a point located at a radial distance different from that of the point of injection of said fluid, so as to create in the apparatus at least one second, substantially cylindrical layer concentric to the first, in contact therewith and rotating in the same direction substantially according to the same law of variation of the linear speed as a function of the radius.

2. The process of Claim 1, in which the fluid to be treated is injected tangentially in a first zone adjacent the periphery of the apparatus, so that a rotating layer is formed against this periphery, whilst there is collected towards the second end, in the radial zone concerned by this rotating layer, on the one hand a fraction of fluid containing heavy impurities, on the other hand a clearer fraction which is at least part-ly recycled, wherein this clearer fraction is re-injected immediately inside the first rotating layer formed by the fluid to be treated and there is collected at the second end of the apparatus and in the radial zone concerned by the second rotating layer thus created, on the one hand the treated fluid, on the other hand fluid containing possible light impurities.

3. The process of Claim 2, wherein, between the first and the second layer, there is created an intermediate layer of circulation in closed circuit, the inlet of which is connected in parallel to that of the second layer and the outlet of which is for its part connected in parallel to that of the first layer.

4. An apparatus for the centrifugal treatment of a liquid or gaseous fluid containing impurities in suspension, comprising:
a substantially cylindrical body having first and second ends;
a plurality of tangential inlets disposed at said first end concentrically to each other and opening in the same direction to create within said body, upon injection of said fluid, a succession of concentric annular rotating fluid layers;
a plurality of tangential outlets at said second end to collect the fluid from said layers, with the radially outermost of said outlets collecting a fluid fraction containing the heaviest impurities and the radially innermost of said outlets collecting a fluid fraction containing the lightest impurities;
and means to re-inject the fluid fraction collected from one of said layers by one of said tangential outlets through the tangen-tial inlet for the layer immediately radially interior to said one of said layers.

5. The apparatus of Claim 4, wherein the re-injection means com-prise a Venturi with injector supplied with a fluid under pressure, the Venturi being disposed between the outlet of said one of said layers and the inlet for the layer immediately radially interior.

6. The apparatus of Claim 4, in which each tangential inlet is formed by a nozzle extending over a radial distance, wherein the section of each nozzle is in the form of a recumbent rectangular trapezium with its small base oriented towards the axis of the apparatus.

7. The apparatus of Claim 6, wherein the oblique side of the trapezium section of each nozzle is concave in form.

8. The apparatus of Claim 4, wherein the first end comprises sleeves which penetrate therein over a distance to separate the successive cylindrical layers in an initial zone where their regime of rotation has not yet been regularly established.

9. The apparatus of Claim 4, comprising at its second end, respective outlets for respective fluid fractions containing the heaviest impurities, clearer fluid to be recycled and finally treated fluid, and a central outlet for impurities lighter than said fluid.

10. The apparatus of Claim 4, including an axial electrode, wherein said electrode extends at the second end beyond the body of the apparatus through a central pipe.

11. An installation for the centrifugal treatment of fluids con-taining impurities in suspension, comprising, mounted in parallel on the same supply and evacuation circuits, a plurality of apparatus as defined in Claim 4, wherein all these apparatus have a common recycling pipe with a single delivery means inserted therein.