US2781907A

US2781907A - Apparatus and process for the vortical separation of liquid suspensions

Info

Publication number: US2781907A
Application number: US451654A
Authority: US
Inventors: Freerk J Fontein
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 1953-08-26
Filing date: 1954-08-23
Publication date: 1957-02-19
Anticipated expiration: 1974-02-19
Also published as: DE933261C; GB751076A; NL78356C; FR1112090A; NL78336C; BE531264A

Description

Feb. 19, 1957 F. J. FONTEIN 2,781,907

APPARATUS AND PROCESS FOR THE VORTICAL SEPARATION OF LIQUID SUSPENSIONS Filed Aug. 23, 1954 s Sheets-Sheet 1 14 1s s l W 5 /1ww@%-' 13 M /w r WWW Feb.- 19, 1957 F. J. FONTEIN 2,781,907

APPARATUS AND PROCESS FOR THE VORTICAL SEPARATION OF LIQUID SUSPENSIONS Filed Aug. 23, 1954 5 Sheets-Sheet 2 m PIC-3.2

Feb. 19, 1957 F. J. FONTEIN APPARATUS AND PROCESS FOR THE VORTICAL SEPARATION OF LIQUID SUSPENSIONS 3 Sheets-Sheet 3 Filed Aug. 25, 1954 FIG.3

United States Patent 6 APPARATUS AND PROCESS FOR THE VORTICAL SEPARATION OF LIQUID SUSPENSIONS Freerk J. Fontein, Heerlen, Netherlands, assignor to Stamicarbon N. V., Heerlen, Netherlands Application August 23, 1954, Serial No. 451,654 Claims priority, application Netherlands August 26, 1953 10 Claims. (Cl. 209-211) The invention relates to the concentration and classification of particles suspended in a liquid, by means of a hydro-cyclone having two centrally arranged discharge apertures disposed on the axis of the hydrocyclone, and being furthermore provided with two reservoirs for collecting the separated fractions.

It is well known that hydrocyclones are very well suited for concentrating solid or liquid particles suspended in a'liquid, and for classifying solid particles, see for example United States Patents 2,543,689, 2,550,341 and 2,654,479. I

As is well known, the concentrations of the fractions obtained by concentrating or thickening suspensions. or.

emulsions, depend among other things on the size of the apertures in the hydrocyclone, the feed pressure, the pressures prevailing in thedischarge apertures, and the concentration of the initial product. In practice, the concentration of the feed frequently tends to fluctuate, so that also the concentration of the separated fractions will vary, unless special measures are taken to prevent this. For example, if a hydrocyclone is fed with water, both fractions will consist of water, and the collecting of the concentrated fraction will have to be entirely discontinned, at least if a fraction of some certain minimum concentration is required.

However, if the feed of a cyclone thickener has a very high concentration, the concentrated fraction (herein after called apex fraction) may become almost solid. If such a ropy apex fraction is being discharged, the hydrocyclone is no longer operating properly, i. e. the concentration of the dilute fraction (hereinafter to be called overflow fraction) rises considerably.

When in classifying processes, i. e. in making separations according to settling rate, problems of this kind may occur due to variation in feed concentration and also 'due to variationin the content of coarse components in fected by arranging that at an increase or decrease in the feed concentration, or at an increase or decrease in the content of coarse components in the feed, the quantity of the apex fraction will increase or decrease respectively.

,In order to realize'this, theapparatus according to the present invention .is so constructed as to comprise a hydrocyclone provided with two centrally arranged discharge apertures (termed apex aperture and overflow aperture) disposed on the axis of the hydrocyclone, and with reservoirs for collecting the separated fractions, said apparatus being characterized in that the liquid level of each reservoir is located below the corresponding discharge aperture, while each of said discharge apertures connects with a suction pipe which opensinto the corresponding reservoir below-the liquid level therein (by the term liquid level of a reservoir is to be understood hereinafter the height of an overflow edge, i. e. the highest possible level of the liquid contained in the reservoir).

With this arrangement, the two suction pipes, in cooperation withthe hydrocyclone, constitute a siphon between the two reservoirs, so that quite apart from thecurrent produced by supplying liquid or suspension to the hydrocyclone, an additional superimposed current force is produced on the material, as by the. tendency ofthe liquid to flow from a higher to a lower level.

The magnitude and direction of the siphonic current produced ultimately depend on the difference in height between the liquid levels in the two reservoirs, on the size of the discharge apertures of the hydrocyclone, and further, a point of utmost importance in the present invention, on the difference between the specific gravities of the liquids or suspensions in the two suction pipes.

When the hydrocyclone is operating properly, the specific gravity of the overflow fraction changes only slightly at a change in the composition of the feed, but the specific gravity of the apex fraction on the other hand increases in accordance with increase in feed concentration or in the content of coarse particles in the feed. Accordingly, the weight of the liquid in the suction pipe for the overflow fraction changes but little, whereas the weight of the liquid in the suction pipe for the apex fraction is subject to great fluctuations. This has the result that at 1 a low feed concentration or at a low content of coarse all ofthe liquid is discharged through the overflow pipe,

and it may even occur that liquid is sucked up through the apex aperture. When the concentration of the feed is high or when the feed contains a large content of coarse particles, the siphon action causes a much larger quantity of suspension to be discharged through the apex aperture. It'will be clear that as a result, the influence of the feed concentration and of the content of coarse particles in the feed on the concentration and composition of the separated fractions is considerably reduced.

Preferably, the height of the liquid level in each reservoir is made adjustable, and the liquid levels are so regulated relatively to one another, that in case liquid alone, that is without particles suspended therein, is supplied to the hydrocyclone, material is sucked up from the apex reservoir. It will be understood that when the suspension or emulsion to be treated is being supplied, no material shold be sucked out of either of the two reservoirs, but in that case the feed must have agiven minimum concentration before an apex fraction can be obtained.

When carrying out the invention, one is to a certain extent free to select the height of the liquid levels in the two reservoirs. For example, the minimum concentration of the apex fraction can be raised by lowering the liquid levels. Suchlowering of the liquid levels also oifers the possibility of operating at a higher feed 0011- on the force of the currents produced; for, the level of the overflow reservoir has to be raised according as the apex aperture is narrower orthe overflow aperture is wider. T

The reservoirs need not be of any one definite shape; for example, they may be constituted by turned up ends of the suction pipes. The reservoirs serve only to prevent air from entering the suction pipes. Naturally it is necessary that, should the apex reservoir have been drained and the siphon have gone dry, the siphon will start operating again as soon as the feed concentration starts rising. Therefore, it is essential that the level of the overflow reservoir be not too low. The siphon can also be prevented from going dry by supplying water or previously thickened suspension to the apex reservoir. The invention can also be utilized when hydrocyclones are connected in parallel. In this case said hydro cyclones are provided with a common overflow chamber and/or a common apex discharge chamber, each said chamber being provided with a suction pipe.

The invention will be further elucidated with the aid of the accompanying drawings, in which Figure 1 diagrammatically illustrates a test assembly of an apparatus constructed according to the invention, connected in parallel with a hydrocyclone of known type;

Figure 2 is a graph illustrating the test results, and

Figure 3 illustrates an apparatus according to the invention in which use is made of a multiple hydrocyclone.

Figure 1 shows a feed pipe 1 for the material to be treated, which, without being segregated, is divided into two portions in a branch pipe 2. One portion passes through the feed pipe 3 of the hydrocyclone 4, which comprises a cylindrical portion 5 and a conical portion 6. The conical portion 6 is provided at its apex with a discharge aperture 7. The cylindrical portion 5 comprises a centrally disposed vortex finder 8 which via the overflow aperture 9, opens into the overflow chamber 10, said chamber being provided with overflow pipe 11.

The other portion of the feed flows from the branch pipe 2 through the feed pipe 13 of the hydrocyclone 14, said hydrocyclone comprising a cylindrical portion 15 and a conical portion 16. The conical portion 16 is provided at its apex with a discharge aperture 17. The cylindrical portion 15 comprises a central vortex finder 18 which via the overflow aperture 19, opens into the overflow chamber 20, said chamber being provided with an overflow pipe 21. The apex aperture 7 and the overflow pipe 11 of the hydrocyclone 4 discharge freely into the atmosphere, but with the hydrocyclone 14 the situation is quite ditferent. The overflow pipe 21 discharges into the reservoir 22 below the liquid level 23 thereof, which is located below the overflow aperture 19. When the liquid has risen to level 23, the reservoir 22 runs over. Mounted on the apex aperture 17 is the discharge pipe 24, which discharges below liquid level 26 into the reservoir 25, said level being located below the apex aperture 17. When the liquid has risen to the level 26, the reservoir runs over. small tanks which serve to prevent air from entering the

suction pipes

21 and 24. Naturally means may be provided in said reservoirs for carrying otf solid particles in case there should be danger of obstruction. 23 is so adjusted that when water alone is being supplied through the pipe 1, the liquid contained in reservoir will be sucked up. Accordingly, if the feed consists of water alone, hydrocyclone 14 does not yield an apex fraction in contrast to hydrocyclone 4, where water is discharged through the apex.

If it should he desired to prevent the reservoir 25 from being drained, liquid or suspension may be supplied to reservoir 25 via the pipe 27 and valve 28.

Figure 2 illustrates the relative performance of the two hydrocyclones when treating a feed of loess, sand and water of different concentrations.

The concentration of the feed in grams per litre has been plotted on the abscissa a, while the concentration of the apex fraction in grams per litre is plotted on the upper part b of the ordinate, and the concentration of particles bigger than 50 microns in the overflow also in grams per litre on the lower part c ofsaid ordinate.

The hydrocyclones used in this test were so positioned as to have their apices pointing downwards and had the following dimensions:

Diameter of cylindrical portion mm 122 Height of cylindrical portion mm 75 Diameter feed aperture mm 30 The reservoirs 22 and 25 may be The level Diameter overflow aperture mm 30 Length of vortex finder in cylindrical portion mm 30 Apex angle of conical portion 20 The apex aperture of the hydrocyclone 4 measured 11 mm. in diameter, the apex aperture of the hydrocyclone 14 being 18 mm. in diameter. This difference in the diameters of the apex apertures was desirable in order that the difference in behaviour between the two hydrocyclones could be brought out clearly in the graph. In this connection it may be pointed out that the partial vacuum in the overflow aperture 19 brought about by the overflow pipe 21 strengthens the thickening elfect of the hydrocyclone 14, which is compensated for by the wider apex aperture 17. It will be clear that this also reduces the danger of the apex aperture 17 becoming obstructed.

Both the liquid level 26 in the reservoir 25 and the liquid level 23 in the reservoir 22 were located mm. below the apex aperture 17. The feed pressure of the two hydrocyclones was 0.5 kg./cm. The suction pipe 21 was 50 mm. in diameter and the suction pipe 24 35 mm., i. e. said pipes were so wide that no appreciable resistance was exerted on the liquid. The dotted lines in Figure 2 show the results obtained with the hydrocyclone 4. An increase in the feed concentration causes an increase in the concentration of the apex fraction and in the content of components bigger than 50 microns in the overflow. At first, the increase of the concentration of the apex fraction proceeds rapidly, but afterwards it gradually slows down until at a feed concentration of g./litre the maximum concentration of 1330 g. per litre has been reached. At that moment the formation of a ropy discharge sets in and a further increase of the feed concentration does not have an effecton the concentration of the apex fraction.

The content of particles bigger than 50 microns in the overflow is nil at first, after which it gradually increases until, at feed concentrations of over 160 grams per litre, the content of coarse components rises rapidly.

From this it appears that with a hydrocyclone of the known type, the concentration of the apex fraction is low when the concentration of the feed is low, and that the concentration of the overflow fraction and the content of coarse components in the overflow fraction are high when the concentration of the feed is high.

The full lines in Figure 2 show the results obtained with the hydrocyclone 14. At low concentrations, the concentration of the apex fraction is higher than the concentration of the apex fraction from hydrocyclone 4, while at high concentrations it is slightly lower. The overflow fraction has a much lower content of coarse components than the overflow fraction from the hydrocyclone 4, especially at'high feed concentrations. The performance of the hydrocyclone 14 therefore is not adversely affected by the formation of a ropy discharge. Very interesting is the behaviour of hydrocyclone 14 at low feed concentrations. For, hydrocyclone 14 and the

liquid levels

23 and 26 are so adjusted, that in case the overflow fraction has a specific gravity of about 1, and the concentration of the apex fraction is lower than 950 grams per litre, liquid or suspension is sucked upwards through the apex suction pipe 24. This explains why at low feed concentrations (e. g. 30 grams per litre) no apex fraction can be discharge at first. The infed particles, with the exception of the finest particles which are not caught by the hydrocyclone, keep circulating in the hydrocyclone, so that the concentration steadily increases until the concentration near the apex has risen to over 950 grams per litre. When this concentration has been attained, the suction pipe 24 fills with suspension of 950 grams per litre, and contains a suspension column which is in equilibrium. According as more particles are caught by the hydrocy clone, said particles can be discharged through the suction pipe 24. Consequently, the concentration of the apex fraction never falls below 950 grams per litre. When the feed concentration increases to over 38 grams per litre, the concentration of the apex fraction rises to a maximum of 1300 grams per litre. So, if the apparatus according to the invention is used under the above circumstances, the concentration of the apex fraction will always vary between the limits of 950 and 1300 grams per litre, without any regulation being required.

Obviously, the lowest value of the concentration of the apex fraction, 950 grams per litre in the example given above, is dependent on the adjustment of the hydrocyclone and the liquid levels.

In another test, also carried out with two hydrocyclones having their apices directed downwards, the dimensions of the hydrocyclones were as follows:

Diameter cylindrical portion mm 350 Height cylindrical portion ....mm 100 Diameter feed aperture "mm" 50 Diameter overflow aperture mm 50 Length of vortex finder in cylindrical portion mm 75 Apex angle of conical portion 20 Diameter of apex aperture ..mm 30 Both hydrocyclones were provided with suction pipes with an inner diameter of 80 mm. which, just like the suction pipes of the hydrocyclone 14 shown in Figure 1, opened into reservoirs, but whereas the liquid level of the two reservoirs pertaining to the one hydrocyclone was 990 mm. below the apex aperture, the corresponding distance for the other hydrocyclone was 240 mm.

The minimum concentration of the apex fraction from the hydrocyclone equipped with the longer suction pipes was about 850 grams per litre, while the corresponding figure for the hydrocyclone with the shorter suction pipes was about 480 grams per litre.

The hydrocyclone equipped with the long suction pipes yielded a ropy apex fraction at a feed concentration of 300 grams per litre; with the hydrocyclone provided with the short suction pipes this phenomenon was observed at a feed concentration of 150 grams per litre. In both cases the concentration of the apex fraction was about 1350 grams per litre.

In the apparatus of Figure 3, a number of hydrocyclones 29, fed through the common feed pipe 30, are connected with a common overflow chamber 31 and with a common apex discharge chamber 32. The overflow chamber 31 is provided with an overflow pipe 33, which is connected with a bent rubber hose 34. The apex discharge chamber 32 is provided with a delivery pipe 35 which is connected with a bent rubber hose 36.

The turned up ends of the

rubber hoses

34 and 36 have the same function as the reservoirs 22 and 25 in Figure 1, namely to prevent air from entering the suction pipes. The liquid levels are formed by the outlets of the rubber hoses. The performance of the apparatus consequently depends on the height to which these outlets have been adjusted.

I claim:

1. A process of treating liquid suspensions which comprises the steps of subjecting said suspension to vertical separation into two fractions in a hydrocyclone, and restricting variation in the composition of the discharged fractions due to variations in feed by conducting each fraction downwardly into a liquid body disposed below the level at which said fraction is discharged from the hydrocyclone, to eifect a siphonic action between said liquid bodies through said hydrocyclone.

2. A process according to claim 1, including the step of controlling the minimum concentration of the apex discharge fraction by varying the relative level of at least one of said liquid bodies.

3. A process according to claim 1, including the step of limiting the minimum concentration of the apex discharge fraction by adjusting the relative levels of said liquid bodies so that liquid alone fed to the hydrocyclone will cause liquid to be sucked up from the liquid body communicating with the apex aperture of said hydrocyclone.

4. Apparatus for the vertical separation of liquid suspensions into two fractions comprising a hydrocyclone having opposed axial discharge apertures, closed conduit means communicating with each of said discharge apertures and extending to a lower level, overflow means communicating with the lower end of each of said conduit means, each of said overflow means being positioned and adapted to maintain a liquid body having a liquid level above the lower end of the associated conduit means and below the level of the appertaining discharge aperture, whereby said liquid bodies may function through said conduit means and hydrocyclone as a siphon to restrict variations in the composition of the discharged fractions due to variations in feed to the hydrocyclone.

5. Apparatus according to claim 4, wherein one of said overflow means comprises an overflow vessel, into which the associated conduit means discharges at a level below the overflow level thereof.

6. Apparatus according to claim 4, wherein one of said overflow means comprises a turned up extension of the lower end of the associated conduit means.

7. Apparatus according to claim 4, wherein the overflow level of one of said overflow means is vertically adjustable.

8. Apparatus according to claim 4, wherein the overflow level of each of said overflow means is adjustable.

9. Apparatus according to claim 4, including means fior supplying liquid to the overflow means communicating with the apex aperture of said hydrocyclone.

10. Apparatus for the vertical separation of liquid suspensions into two fractions comprising a plurality of hydrocyclones each having opposed axial discharge apertures, a common chamber enclosing the overflow apertures of said hydrocyclones, a common chamber enclosing the apex apertures of said hydrocyclones, closed conduit means communicating with each of said chamhers and extending to a lower level, overflow means communicating with the lower end of each of said conduit means, each of said overflow means being positioned and adapted to maintain a liquid body having a liquid level above the lower end of the associated conduit means and below the level of the appertaining discharge apertures, whereby said liquid bodies may function through said conduit means, chambers and hydrocyclones as a siphon to restrict variations in the composition of the discharged fractions due to variations in feed to the hydrocyclone.

References Cited in the file of this patent UNITED STATES PATENTS 1,890,206 Andrews Dec. 6, 1932 1,948,140 Strohl Feb. 20, 1934 2,504,944 Atkinson Apr. 18, 1950 2,648,433 Wright et a1 Aug. 11, 1953 2,671,560 Fontein et a1. Mar. 9, 1954