Consideration about one way hydrocyclon with ring-shaped aperture for separation.

Hadar, Anton ; Motomancea, Adrian ; Szabo, Adam 等

1. INTRODUCTION

This type of equipment named hydrocyclon was invented by E. Britney more than one century ago. It was a real technical revolution because it substituted a lot of very heavy and large equipments with low productivities and outputs. The large scale utilities to separate the solid factions from any kind of hydromass are made to be used in foodstuff industry, pharmaceutical, chemistry, mining, metallurgy and others.

Although the work principle of hydrocyclons remained unchanged, in the last 2-3 decades same improvements were introduced like as a better record between the supply pipe and hydrocyclon body, the decreasing of inside roughness, the improvement of abrasive protection.

The great drawback of actual hydrocyclons consists in just their work principle namely in the existence of two distorted meaning streams inside them, that "disputed" the fine faction. The main descendant stream recuperates from hydromass the most important part of solid factions, while the central hold stream embezzles, respectively draws in over trickling an important part of fine solid factions. This evidence is accepted by all the most important companies through indication of quality parameter "D50" proper for any type of hydrocyclon and that shows the granulometric class with 50% chances to be found again in bold. For example for a hydrocyclon of 10", D50 = 22-44 [micro]m.

The hydrocyclon's flows varying between 40l/min-40.000 l/min with supply pressures between 1/4 bar. The sorting efficiency depends on some qualitative and technical parameters like internal roughness of the lining that must be 0.7/1.6 nm, the ratio between the supply pipe diameter and hydrocyclon diameter but even the ratio between the supply diameter and trickling diameter (Magyari, 1989).

In connection with the flow inside the hydrocyclon we'll present some novelty considerations unseen by the authors in accessed literature.

The entrance hydromass velocity in hydrocyclon is usually bigger than 10 m/s and the born centrifugal force caused of the rotation of all the fluid volume inside the hydrocyclon conduce to a very fast evolution of all the solid particle to adhere on or in the vicinity of the inside wall of the hydrocyclon. The total moving time of a particle in hydrocyclon is 0.2/1s. The circular moving from the entrance is changed than in a descendant helicoidally one (because of the continuous hydromass contribution), so in the vicinity of the top of the cone a part of the fluid is changed the moving sense in an ascending one like in fig. 1.

[FIGURE 1 OMITTED]

It is obvious that a safe boundary between the two streams of different senses does not exist, but certainly they are mutual influence--surely negative: the ascendant helicoidally stream will drive a main part of the thin faction in over trickling. In the same time in a glass hydrocyclon it can observe that because of the rotation movement in the centre of hydrocyclon is born a depression and as a result of this, appears on air column that is also responsible of the ascending stream.

2. THE CONSTRUCTIVE AND FUNCTIONAL DESCRIPTION OF THE NEW HYDROCYCLON

The existence of these perturbations in the classic hydrocyclon is the main cause of this new solution that we propose here. We want to specify that one of the important destinations of this equipment is to produce very pure fluids (water, even air).

In fig.2, we present the scheme of the one-way hydrocyclon with ring-shaped aperture (Jinescu & Sporea, 2007).

It has a cylindrical shape in its active part with descendent one-way inclusively for purified phase and having a ring-shaped aperture for collecting the dense part of the hydromass. The reduction of the evacuation section surface for water is mode in order to maintain the entrance pressure and it doesn't alternate the separation efficiency. In this case the main important problem is to maintain the solid particles in the vicinity of the cylindrical wall until the ring-shaped aperture.

[FIGURE 2 OMITTED]

That is why on the cylindrical part all the particles will move already on a distance of 0/30 mm from the inside wall and until the ring-shaped aperture, the centrifugal force will restrict this distance to about 0/5 mm, so the hole solid part to be separated by ring-shaped aperture. This is thoroughly possible because the dominant force is radial, the ascending stream being present only in conic way where its effect doesn't affect separation, because the solid particles were already eliminated.

3. SOME ELEMENTS OF CONSTRUCTIVE CALCULUS

In order to study the dynamic behavior of a solid particle in fluid is necessary to accept some simplified hypothesis. One of them is that the particle has a spherical shape. In this case we present in fig. 3a the forces on a spherical particle having a descendent movement in a static fluid and in fig. 3b the forces on the same particle in a fluid having a rotation movement.

[F.sub.w] + [F.sub.a] - G = 0 (4)

[F.sub.w'] - [F.sub.c] = 0 (5)

[F.sub.w] + [F.sub.a] - G = 0 (6)

where (Voinea et al., 1989):

[F.sub.w] = 6[pi] r [eta][V.sub.e] the fluid broke force (The Stokes' law)

[F.sub.a] = 4/3[pi][r.sup.3] [rho]g (Archimedes force); G = 4/3 [pi][r.sup.3][rho]g (The particle's weight); [F.sub.c] = m [V.sup.2.sub.r]/R = 4/3 [pi][r.sup.3]([rho] - [rho]') [V.sup.2.sub.r]/R (The centrifugal force)

For a hydrocyclon feeding on 1.5 bar pressure, neglecting the damages of hydrocyclon resistance it results an entrance velocity (Hadar et al., 2002):

V = [square root of 2gH] = 17.15 [ms.sup.-1] (7)

This tangential velocity will diminish in fluid descendent way and will produce first a rotation movement having:

V = [omega]R = [pi]n/30 R = 17.15 [ms.sup.-1] (8)

The rotation:

n = 30V/[pi]R = 1639rot/min (9)

It is possible to obtain the stationary time of a particle in hydrocyclon using the continuity equation

[V.sub.1] = [pi][d.sub.2] = [V.sub.2] [pi][D.sup.2]/4 (10)

[V.sub.2] = [V.sub.1] [d.sup.2]/[D.sup.2] = 1.1m/s (11)

where: [V.sub.1]--the velocity in supply pipe

[V.sub.2]--the velocity in cylindrical part of hydrocyclon d = 50 mm the supply pipe diameter

D = 200 mm the hydrocyclon diameter.

[FIGURE 3 OMITTED]

For a distance between supply entrance and ring-shaped aperture of 260 mm it is obtained a stationary time of a particle in hydrocyclon

t = 0.26/1.1 = 0.24ms (12)

The route time for a particle of the radial distance (30 mm) until the hydrocyclon wall in order to be picked up by the ring-shaped aperture is calculate using (4) formula for 4a and (5) formula for 4b. Also it is possible to calculate radial velocity.

4. EXPERIMENTAL MEASUREMENTS

The crude sample analysis for a hydromass having 2.64 x [10.sup.3] Kg/[m.sup.3], reveal the next granulometric analysis shown in table 1. (Magyari, 1983).

It is easy to observe that the greatest weight from hydromass is in the interval of 0.071-0.32 mm with 89.12 from whole mass.

4. CONCLUSIONS

Next, we want to present some advantages of this type of hydrocyclon:

--The major advantage of one-way hydrocyclon is that of eliminate the hold stream and controlling of separation process.

--Because of the more simplified circulation inside the hydrocyclon, its flow increases about 20-25% for the same diameter given the used hydrocyclon.

--The accuracy of separation decrease under 10 jim

--The total retriever output increase to 95%.

--The one-way hydrocyclons could separate on one passing mineral with different density because the heaviest would be retrieve in first aperture and the thinnest by the followings.

5. REFERENCES

Hadar, A., Motomancea, A.; Szabo, A.& Gheorghiu, H. (2002), One way hydrocyclon with ring-shaped aperture for separation, Proceedings of International Conference of Machine Systems, T.C.M.M. No. 40, Editura Academiei, p. 95-100, Bucharest, Romania

Jinescu, V., Sporea, N. (2007), The Flow Rate of Corotating Twin Screw Extruder. (II), Mat. Plast., Vol. 44, nr. 1, p. 14-17.

Magyari, A. (1983), Utilaje de preparare a substantelor minerale utile (Equipment for preparing usable mineral substances), Editura Tehnica, Bucuresti

Magyari, A. (1989), Manualul inginerului de mine (Handbook of mining engineers), Editura Tehnica, Bucuresti

Voinea, R.; Voiculescu, D. & Simion, F. (1989), Mecanica Solidului cu Aplicatii in Inginerie (Solid mechanics with engineering applications), Editura Academiei Romane, Bucuresti, Romania.

Tab. 1. The granulometric analysis

 Cumulate
 Cumulate Passing
Granulometric Weight Refusals 100-
Category [mm] Extraction [summation] [summation]
 [v.sub.i] [v.sub.i][%] [v.sub.i][%]

 1-0.63 1.00 1.00 99.00
 0.63-0.32 7.76 8.76 92.24
 0.32-0.15 52.36 61.12 38.88
 0.15-0.071 36.76 97.88 2.12
 0.071-0.032 1.50 99.38 0.62
 0.032-0 0.62 100.00 0.00
 Total 100.00 -- --