US2817441A

US2817441A - Process for separating mixture of solid particles into fractions by means of a hydrocyclone

Info

Publication number: US2817441A
Application number: US360464A
Authority: US
Inventors: Jan N J Leeman; Freerk J Fontein
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 1953-03-02
Filing date: 1953-06-09
Publication date: 1957-12-24
Anticipated expiration: 1974-12-24
Also published as: GB726510A; BE526735A; FR1097313A; DE1022532B

Description

2,817,441 ES INTO Dec. 24,1957 J. N. J. LEE-MAN ETAL PROCESS FOR SEPARATING MIXTURE OF SOLID PARTICL FRACTIONS BY MEANS OF A HYDROCYCLONE Filed June 9, 1953 FlG.l

linvenl'oks Jan 71$. Lee man FreerK J. Fonfein B3 ATTO II 11 95 United States Patent "ETRO'CESS .FOR "SEPARATINGMIXTURE- F SOLID PARTICLES INTO FRACTIONS BY MEANS OF HYDROCYCLONE i Jan. N. J. 1 Leeman, Brunssum, ,and Freerk J. t Fontein, .He11len,.Netherlands, assignors to Stamicarbon'N. V.,

The present invention relates to a methodsfor separating zmixturesofsolidtparticles into fractionsbyumeans of :a hydrocyclone.

The: term ihydrocyclone. as used in this. specification and-the: claims: hereof designates apparatus known. per se .comprisinga chamber which is peripherallybounded by .asmooth' surface of revolution (by which we mean a .surfacetgeneratedlby the rotation of a straightor a curved line aboutgancaxis) xandmtapering towards one end, the apparatus including one or more feedpassages'leading substantially tangentially into the chambernear the wider end thereoftand twouaxial discharge apertures, viz.,. one :atfithe apex ofthe chamber and hereinafter called the apexaaperture. and one intthe wider end of the chamber and hereinafter called the overflow aperture. The chambermay; comprise conjoined cylindrical and conical portions :and the tapering wall may conformrto the wall of a true cone or may beslightly. curved to present'a. concave or convex surface to the inside of the chamber. .The overflow aperture may be and preferably is defined by a short, conduit, hereinaftercalled a vortex, finder extendingaxially into the wider end of the chamber. The dimensionsl ,of a hydrocyclone and the diameters of the feed apertures and outlets are such that, whena liquidis con tinuously introduced into the feed conduit(s) at a suffi- "c'iently high pressure, arotary current is generated in the chamber, which current has an inner vortex directed to- Wardsthe vortex finder and another vortex around the first one, which moves axiallyin the opposite direction.

Within .the inner vortex there is an air core, provided there is no backpressure on the outlets. The chamber which generally is substantially conical, preferably has a mean angleof'taper of from 5 to 30,but angles up to .9.0.also havebeen successfully employed.

It.is old to use hydrocyclones for the separation of solid ,particlesaccordingto grain size (classification) and for separation according to specific gravity (washing).

If, a.mixture ofsolidparticles-is to be classified the mixture .is fed continuously under pressure into a hydrocyclone of suitable dimensions, together with a liquid whose specific gravity is lower than thatof the particles to be .classificd. The fraction which then leaves the hydrocyclone continuouslvthrough the apex aperturecontains substantially all the big particles and a small portion of the small particles, the fraction leaving the hydrocyclone continuously through the overflow aperture conmedium as hereinafter defined. The fraction which then leaves the'hydrocyclone continuously through the apex- Laperturecontainssubstantially only particles the specific Jgravity of which ishigher than the specific gravity of sepanrationttogether with separating medium, thefraction conrtinuously leaving the hydroeyclone through the overflow aperture containing substantially-all particles with a -spe- 2,817,441 C6 Patented Dec. 24, 1 957 cific gravity lower than the specific gravity of separation together with separating medium.

tThe-expres'sion liquid separating medium as used above means an entirely liquid medium havinganintermediate specific, gravity, i. e., a specific gravity which is higher than the specific gravity of the specifically light particles and lower than the specific gravity of the specifically heavy particles constituting the fractions to *be separated, or a mediumvcomprising a liquid with-solid particles considerably smaller than the particles to be separated in suspension,'and having an intermediate specific gravity as aforesaid at a concentration'ofthe suspension: particles of: fifty percent or less.

The: suspension iparticles utilized in a: separating medium of thesecond of the aforesaid kinds, arewgenerallysmaller than '200. microns and are often of a "size of 60-microns or less, depending on :the size. of the particles to be sepa- 'rated,:the specificitgravity oflthecparticles in the suspension and the. conditions under which the separation takes place.

iIncarrying out the hydrocyclonic method of separation, especially if large hydrocyclones are used, the energyconssurnption is atrpresent rather high. For example for a hydrocyclone witha diameter of 1,000mm. it is necessary :to employ a feed pressure corresponding to about a head of 12"m. of separating medium, :andlarger hydrocyclones require still higher"pressures. [in general the feed presvsure should. amountztov the pressure exerted by a column offeed which has aheightof six times the axial length of the hydrocyclone.

If the feed pressure is too low, 3 theabove mentioned hollow air core is not formed and the separation is 'not sufficiently :accurate, :in particular when large "hydrocy- .clonesforinstance with a: largest diameter of more than .350wmm. are used. :In washing operations, specifically light particles then get into .the apextfraction, while, in classification at varying loads, too many fine particles enter the apex fraction of 'thehydrocyclone. Therefore it is :usual totfeed the separating medium together with the mixture to be separated into thehydrocycloneunderco'nsiderable pressure by means of a pump. The use -'of tpumpstothisendtis accompanied, however, with'serious drawbacks,-viz. the risk of blockage and of "breaking up' tof the particles to be separated. A pump furthermore consumes much energy.

Now it is the object of the present inventionto provide a method of operating a hydrocyclone wherein the pressure it used 1 is :significantly below the pressure hitherto re- :quired but wherein satisfactory results .in washing and classification 1 are obtained. .of this invention to provide such method wherein the It is in particularthe object "hydrocyc'lone is mounted in such a way that its axis makes a considerable angle with the vertical. Preferably the axis should be arranged either horizontally or so that the lowest generatrix of the hydrocyclone is substantially horizontal or in an intermediary position.

We have found that with a hydrocyclone in such inclined positionithe desired sharpness of separation can be obtained at a much lower pressure than h'ith'erto was necessary. The rapidly rotating current which is gen- :erated in a *hydrocvclone when a high feed pressure is employed, gives rise to centrifugal forces which are much-greater th'an 'th'e *force of gravity, so that the position of a hydrocyclone operated at high pressure generally is of secondary importance. Nevertheless hydrocyclones used in classification and washing have previously been operated with their axis substantially vertical, the apex pointing downwards, and with feed pressures corresponding with. a feed head of at least six times the axial length of the hydrocyclone.

The invention is based on the discovery that the reason why big hydrocyclones which are positioned vertical need a comparatively high feed pressure is that, owing to their great length, these hydrocyclones contain such a tall liquid column that gravity becomes an important factor and influences the operation of the hydrocyclone. If, however, the hydrocyclone is given a sufficient tilt this phenomenon cannot occur.

In washing there is no air core if the feed pressure is too low and the hydrocyclone is positioned vertical. In that case specifically light particles may reach the apex aperture of the hydrocyclone, moving along the axis. If the hydrocyclone is tilted sufliciently there is an air core generally, and the specifically light particles cannot reach the apex aperture. Besides, if the hydrocyclone is positioned horizontal, there is no component of the gravitatio'nal force which can move the specifically light particles in the direction of the apex aperture.

If, in classifying, there is no air core, much liquid laden with fine particles leaves through the apex aperture, unless this aperture be chosen very small and its size be varied Whenever there is a change in the composition of the feed. The latter demand is hard to meet in practice. If the hydrocyclone is tilted sutficiently an air core :is formed, however, and the apex fraction will always have a high concentration, so that practically only the coarse particles leave the hydrocyclone through the apex aperture.

It stands to reason that the shape and the dimensions of the hydrocyclone moreover have to satisfy demands known in themselves; e. g., in general the discharge and feed apertures must be smaller than the overflow aperture.

With a vertical hydrocyclone the feed pressure (H) (expressed in metres of separating medium) has to be 'a't least about 6 times the axial length (L) of the hydrocyclone. Now it has appeared that, if the axis of the hydrocyclone makes an angle or with the vertical, the feed pressure need be only 6 times L cos a, or, expressed in a formula, ,6 H equal to or greater than the absolute value of L cos cc. However, this is of importance only if L H, because in the case that L H the axis of hydrocyclone may also be vertical.

According to one preferred mode of realising the invention the hydrocyclone is put with its axis substantially horizontal (or about 90 The influence of gravity is then as small as possible and the ratio of H to L cos a is infinitely large. It goes without saying that under those circumstances H cannot be made arbitrarily small, but must be great enough so that a rotary current is generated in the hydrocyclone.

A special advantage of a hydrocyclone which is positioned more or less horizontal is that, when this cyclone is fed from a tank situated higher than the cyclone, the feed conduit to the hydrocyclone may be straight. The feed conduit to a vertically arranged hydrocyclone usually has a bend in practice, which causes wear.

According to another preferred mode of realisation a conical hydrocyclone is so positioned that 90 ot is substantially equal to half of the apex angle and that the apex of the hydrocyclone is lower than its overflow aperture. This position otters the advantage that all the liquid can flow out of the hydrocyclone, which is of importance in case of shut-down and revision.

In order that the hydrocyclone may operate Well it is furthermore desirable that the liquid which has been discharged through the vortex finder cannot flow back to the vortex finder, as otherwise fine or specifically light particles might move to the apex aperture through the core of the cyclone and enter the apex fraction. In practice this involves, that the vortex finder must not discharge into a back-pressure chamber.

The invention, which is especially suitable for making separations by means of hydrocyclones having an axial length between 0.7 and 9 m. with a feed head in the range from 0.4 to 5.7 times the axial length of the hydrocyclone will be further explained with the help of the drawings.

Figure l is a section through a hydrocyclone which is so positioned that the lowest generatrix is horizontal.

Figure 2 is a view of a washing apparatus comprising a deep wash box and a hydrocyclone with its axis positioned horizontal.

In Figure 1, 1 is a hydrocyclone, consisting of a cylindrical section 2 and a conical section 3. The feed conduit 4 discharges tangentially into the cylindrical section 2 through the feed aperture 5, the cylindrical section being closed by a plate 6 in which the vortex finder finder 7 is provided. The conical section 3 is provided with an apex aperture 8. The hydrocyclone is fed from the feeder tank 21. The level of the liquid in this tank is at a height H above the feed aperture 5. The axial length of the hydrocyclone is denoted by L, the angle between the axis of the hydrocyclone and the vertical by a.

The hydrocyclone 1 is mounted on a horizontal floor 10 by means of supports 9 and in such a manner that the lowest generatrix of the conical section 3 is horizontal, or or=half the apex angle of the hydrocyclone. 11 is a collecting tank for the light fraction discharged through the vortex finder 7 and 12 is a collecting tank for the heavy fraction discharged through the apex aperture 8. The collecting tank 11 is so constructed that the fraction removed through vortex finder 7 cannot flow back to pipe 7.

Example 1 Different samples of raw bituminous coal having particle sizes ranging from 0.5 to 10 mm., from Staatsmijn Emma, were washed in a conical hydrocyclone of the following dimensions:

Axial length of hydrocyclone mm Diameter of the cylindrical section mm Length of the cylindrical section mm Diameter of the feed aperture mm Diameter of the vortex finder mm Length of the vortex finder mm Diameter of the apex aperture mm 150 Apex angle degrees 20 Test Nr 1 Heavy traction (tons/hour) Light fraction (tons/hour) Spec. grav. suspension. Spec. gravity of separation Enclosed area Tro'np curve (cm. Probable deflection... (eart probable) (For the meaning of enclosed area Tromp curve and probable deflection or cart probable see e. g. Coll. Eng. 1950, pp. 128-13O and 159, Cheradame and others).

Such good results cannot be obtained with the hydro- QYGlQHe in the vertical position.

Example 2 Raw coal fines were washed in a conical hydrocyclone of the following dimensions:

Axial length of the hydrocyclone -mm 1780 Diameter of the cylindrical section mm 700 Length of the cylindrical section mm 420 Feed aperture mm 86 176 Diameter of the vortex finder mm 300 Length of the vortex finder "mm" 420 Diameter of the apex aperture mm 220 Apex angle "degrees" 20 The axis of the hydrocyclone was horizontal and the hydrocyclone was fed from a tank situated at a height of 5.90 m. above the cyclone. The separating suspension had a specific gravity of 1.53 and consisted of Water and magnetite, 95% by weight of which was smaller than 50 The feed contained a large percentage of slush, owing to which the viscosity of the suspension was high, which had an unfavourable influence on the result. The enclosed area of the Tromp curve of the particles of 1-2 mm. was 62 cm. and the probable deflection amounted to 0.08, which, under the given conditions may be called very good.

Example 3 A mixture of sand and loess in water was classified in a conical hydrocyclone of the following dimensions:

Axial length of the hydrocyclone mm 945 Diameter of the cylindrical section mm 350 Length of the cylindrical section n mm 150 Diameter of the feed aperture mm 70 Diameter of the vortex finder .mm 230 Length of the vortex finder mm 150 Diameter of the apex aperture mm 70 Apex angle degrees 20 The hydrocyclone was so positioned that its axis was horizontal and it was fed from a tank situated at a height of 3 m. above the cyclone. Under these conditions its capacity amounted to 53.3 in. per hour.

The suspension contained 50 grams of solid material per litre. The grain distribution in the feed and the results of the classification appear from the following table:

With the same hydrocyclone in the vertical position the classification is considerably worse at the same feed pressure and more fine particles get into the discharge fraction.

Fig. 2 shows a diagram of an attractive application of the invention. Here the feed conduit of the horizontal hydrocyclone 13 is directly coupled, via valve 14, to the short discharge pipe 15 of the deep wash box 16.

The column of suspension from the feed aperture of hydrocyclone 13 to the overflow trough 17 of wash box 16 provides the feed pressure H.

The mixture to be separated, e. g. raw coal, is introduced into the wash box at 18. The coal fraction is removed through the overflow trough 17, the shales and iniddlings through the discharge pipe 15. The latter fraction is subsequently separated in hydrocyclone 13 into a waste fraction, caught in the collecting tank 19, and a fraction consisting of middlings, caught in collecting tank 20. When operating in this manner the amount of energy required to make the separation between the waste and the middlings is very small.

We claim:

1. A process of separating a mixture of solid particles into fractions, which comprises the steps of continuously feeding the mixture together with a liquid medium under pressure tangentially into a hydrocyclone having an axial length of at least 0.7 metre, whereby separated fractions are discharged from axial overflow and apex apertures at opposite ends of said hydrocyclone, the axis of said hydrocyclone being inclined relative to the vertical at a considerable angle, and adjusting the feed pressure of said mixture and medium to a value, expressed in head of feed, substantially less than six times the axial length of said hydrocyclone but large enough to maintain a central air column in said hydrocyclone.

2. Process according to claim 1, in which the hydrocyclone axis is horizontal.

3. Process according to claim 1, in which said hydrocyclone is conical and the angle of inclination between the hydrocyclone axis and the horizontal is substantially equal to one-half the apex angle of the hydrocyclone.

4. Process according to claim 1, in which the discharge fraction from the overflow aperture is prevented from reentering the hydrocyclone.

5. Process according to claim 1, in which the discharge fraction from the apex aperture of the hydrocyclone discharges into air.

6. Process according to claim 1, in which the hydrocyclone is fed by the static head of a wash box positioned directly there-above.

7. A process of separating a mixture of solid particles into fractions, which comprises the steps of continuously feeding the mixture together with a liquid medium under pressure tangentially into a hydrocyclone having an axial length of at least 0.7 metres, whereby separated fractions are discharged from axial overflow and apex apertures at opposite ends of said hydrocyclone, the axis of said hydrocyclone being inclined relative to the vertical at a considerable angle, and adjusting the feed pressure of said mixture and medium to a value expressed in head of feed, within the range of from 0.4 to 5.7 times the axial length of the hydrocyclone.

Watts May 26, 1953 Fontein Feb. 9, 1954

Claims

1. A PROCESS OF SEPARATING A MIXTURE OF SOLID PARTICLES INTO FRACTIONS, WHICH COMPRISES THE STEPS OF CONTINUOUSLY FEEDING THE MIXTURE TOGETHER WITH A LILQUID MEDIUM UNDER PRESSURE TANGENTIALLY INTO A HYDROCYLONE HAVING AN AXIAL LENGTH OF AT LEAST 0.7 METRE, WHEREBY SEPARATED FRACTIONS ARE DISCHARGED FROM AXIAL OVERFLOW AND APEX APERTURES AT OPPOSITE ENDS OF SAID HYDROCYCLONE, THE AXIS OF SAID HYDROCYCLONE BEING INCLINED RELATIVE TO THE VERTICAL AT A CONSIDERABLE ANGLE, AND ADJUSTING THE FEED PRESSURE OF SAID MIXTURE AND MEDIUM TO A VALUE, EXPRESED IN HEAD OF FEED, SUBSTANTIALLY LESS THAN SIX TIMES THE AXIAL LENGTH OF SAID HYDROCYCLONE BUT LARGE ENOUGH TO MAINTAIN A CENTRAL AIR COLUMN IN SAID HYDROCYCLONE.