The invention relates to a separation device for a mixture containing a liquid solution and solid microparticles.

Such device is known from the document FR 2484287 and it comprises:

a) an upper part for orienting the mixture to be separated along the descending vortical profile, and

b) a lower conical part, into which the upper part opens, and which provides, by its convergence, the separation of microparticles with regard to the liquid solution, at the separation point M, on the one hand in form of ascending axial spurting of the liquid solution, and on the other of a downward flow of the solid microparticles.

In order to achieve a reasonable separation yield, it is necessary to develop a reasonable centrifugal force inside the upper part of device.

For this, the upper part of this device presents cylindrical form with a relatively large height, and the mixture to be separated is overpressurised and introduced into this cylinder with a very high pressure of the order of 7 to 1 0 bars, in order to guide the mixture of a vortical profile along the walls and to provide it with a centrifugal force sufficient to assure the separation in the lower conical part.

In order to achieve these high pressures, generally a compressor is used, which considerably increases the costs of device commissioning and the required security level. Moreover, relatively large height of the upper cylindrical part makes the vertical dimensions of the device larger, making it difficult to implement it the existing installations.

The invention aims to overcome these inconveniences.

For this, the invention relates to a separation device, comprising:

a) an upper part for orienting the mixture to be separated along the descending vortical profile, and b) a lower conical part, into which the upper part opens, and which provides, by its convergence, the separation of micropartides with regard to the liquid solution, at the separation point M, on the one hand in form of ascending axial spurting of the liquid solution, and on the other of a downward flow of the solid micropartides.

According to the invention, the upper part comprises a pipe coiled into a plurality of spirals, on the upper end of which a mixture to be separated is received, and the lower end of which pours this mixture tangentially onto internal wall of the lower conical part, pipe spirals providing this mixture with descending vortical profile, prior to its introduction into the lower conical part.

The invention presents other interesting aspects, among which:

- the length path travelled by the mixture to be separated inside the tube prior to its introduction into the lower conical part that equals at least one meter.

- the fact that the pipe with spirals comprises different inlet orifices for mixture to be separated, that can be chosen independently from each other, in order to modify the length of the path travelled by the mixture.

- the fact, that the pipe with spirals presents a winding radius predetermined by the size of the particles to be separated.

- the presence of a vertical column for evacuating the liquid solution upwardly from the point M, serving as a support for coiling the pipe with spirals.

- the fact, that the evacuation column presents diameter determined by the diameter of the lower conical part inlet, to avoid the ascent of the mixture to be separated leaving the pipe with spirals through the evacuation column.

The invention also relates to a separation system for a mixture containing a liquid solution, a group of small size micropartides, and a group of bigger size micropartides. The system comprises:

- the above mentioned device, that provides the first separation of the group of big size micropartides with regard to a liquid solution in the mixture with the group of small size micropartides,

- means for pressurizing the liquid solution in the mixture with the group of small size micropartides resulting from the first separation, and - the hydrocyclone receiving the pressurized liquid solution in the mixture with the group of small size microparticles, and that provides a separation of the pressurized liquid solution with regard to the group of small size microparticles.

The invention also relates to a system for separating a liquid solution composed of an aqueous phase and an organic phase in the mixture with the microparticles in suspension.

The system comprises:

- the above mentioned device, that provides the first separation of the liquid solution with regard to microparticles,

- means for forming from the liquid solution resulting from the first separation, an emulsion of the organic droplets in the aqueous phase, and

- a vertical column for separating the organic droplets from the emulsion with regard to the aqueous phase, containing an organic solvent miscible with droplets organic phase, and into which the emulsion is introduced in form of globules that migrate by gravity to the bottom of the column, while the organic droplets contained in each globule migrate as a result of the buoyancy to the top of this globule, where they are captured by the solvent in the column.

The invention will be better understood and other objects, advantages and features of the present invention will become apparent from the following description, in relation to the attached figures, wherein:

- Fig. 1 is a schematic view of the device of the invention,

- Fig. 2a to 2d are graphs representing the granulometric distributions of four types of m ixtures of l iquid solution containing respectively four types of solid microparticles, that is: limestone (Fig. 2a), clay (Fig. 2b), carbon powder (Fig. 2c), and limestone imbibed in fuel oil (Fig. 2d),

- Fig. 3a and 3b are graphs representing granulometric distributions achieved respectively in the overflow and in the underflow of the device, when the mixture to be separated contains limestone microparticles imbibed in fuel oil and when the mixture flow rate had fixed as 450 l/h,

- Fig. 4 schematically represents a short circuit problem, that is avoided according to the invention by an appropriate dimensioning of the device. The device i l lustrated i n the F ig . 1 enables, without excessive energy consumption, a separation, in the liquid mixture containing solid particles, of the liquid solution with regard to the solid particles.

It is applicable especially to the separation of particles with diameter of a few hundreds of microns, or even smaller.

For this, it comprises a lower part forming a cyclone 1 , inside of which the actual separation takes place, and an upper part 2, intended to provide the m ixture to be separated with descending vortical profile, prior to its admission into the cyclone.

Lower part

More specifically, cyclone 1 presents the shape of a cone or a funnel, the widened upper part of which is a part for admission of mixture to be separated, and the lower convergent part is provided with a channel 4 for evacuating the microparticles once the separation is completed, the walls 10 of the intermediate part maintaining the descending vortical profile, that was defined by the upper part of device.

In a classical way, in such type of cyclone 1 , the mixture to be separated is let into the upper part of a cone and tangentially along the internal wall of this cone, that enables to maintain the vortical movement descending gradually to the cyclone bottom, the centrifugal force decreasing and the Stokes force, that is proportional to the particle size, increasing.

However, at the inversion point M, the balance of the centrifugal forces and the Stokes forces is equal to zero, and the mixture experiences a brutal separation and splits into an ascending central spurting 6, consisted mainly of the liquid solution, and that is evacuated by the vertical column 8 or overflow, and into descending flow 7, consisted of humid suspension of agglomerated microparticles evacuated by the channel 4 of the cone 1 , and in other words by the underflow.

Upper part

In order to guide the mixture to be separated of a vortical movement and to provide it with a sufficient centrifugal force upstream from the cone 1 to obtain said separation, according to the invention, an introduction of the mixture to be separated into the cone 1 via pipe with spirals 9 is provided, that replaces energy-consuming pressurizing means and the upper cylindrical part of an important height, of the known devices. This pipe operates simply by gravity and thus does not consume energy.

Moreover, it is coiled into spiral around the vertical column for evacuating the liquid solution, already presented, that enables smaller overall dimensions.

More specifically, m ixture introduction into the pipe inlet is realised at the pressure of the medium to be treated (for example 3 bars), without overpressurization, by an upper end of the pipe 2.

Then the mixture to be separated travels the path defined by the pipe spirals, to finally reach the final spiral 9 of the pipe 2, ended with a term inal bead 1 5 that surrounds the upper part of the underlying cone 2, and is introduced into this part along a tangential direction through the orifice 1 1 formed in this upper part of cone.

Thus, the separator of invention enables, thanks to its upper part in form of a pipe with spirals, to naturally exert a centrifugal force, to reduce the energy consumption in relation to known separators of this type, but also to reduce the overall dimensions defined by its winding around the already existing evacuation column. In fact, the height of the cylindrical part in known type devices is economized.

To optimize the separation, it is possible to change different geometric parameters of device, such as:

- the diameter of a pipe inlet,

- the length of the path travelled by the mixture inside the pipe, that must be sufficient to stabilize the mixture at its arrival to the cone inlet, where it will be agitated again;

- the winding radius of the pipe 2 around the column 8, the position of the separation point M being dependent on, that should be localised above the microparticles 7 suspension in the convergent part of cone, and that is chosen depending on the size of the particles to be separated. Device dimensions

The influence of these parameters on the separation efficiency is described below:

Winding radius of the pipe

Regarding the winding radius R of a admission pipe 2, or a spiral radius, it was experimentally proven, that the best result can be achieved with a winding radius larger than an equilibrium orbit radius R, that corresponds to a vertical speed inside the cyclone equal to zero. Te latter could be calculated by means of a forces balance at the point M:

Centrifugal force = Stokes force

Where η = R, "v," is a tangential speed and "x" is a diameter of the particles to be separated (in this case it is fixed at 100 pm), p _s : solid particles mass density, p: mass density of the liquid medium to be treated, μ: viscosity of the liquid, u: speed of the solid particles displacement in the liquid.

18μ.¾

This winding radius can be found in a zone of increasing radial speed and thus with the maximum centripetal acceleration (about 360 g).

In our case, the winding diameter of 30 mm could be determined.

Spiral height and length of the path travelled in it by the mixture to be separated

For the spiral height (equivalent to the height of the cylindrical part of device of known type), the optimal "H/d _cyC ione = 5" ratio given by Rietema was taken by replacing the cyclone diameter "d" by the winding diameter, which was established according to above paragraph as 30 mm.

It gives H = 150 mm.

For a spiral with diameter of 8 mm, this height H generates 19 coils and thus the length L of the path travelled by the mixture to be separated of 1800 mm. Trials with the path lengths of 2, 1 .5, and 0.5 m have been made. It was possible to modify the path length of the mixture by modifying the position of its inlet point inside the pipe with spirals.

The results achieved with the carbon powder, the solid particles of which meet the distribution illustrated in Fig. 2c, with a feed rate of 450 l/h and flow rate of underflow (particles evacuation through the channel 4) of 60 l/h are given in the following Table 1 .

Table 1 : Influence of length of the path travelled by the mixture in the spiral pipe.

It was found that starting form a path length of 1 m travelled by the mixture to be separated inside the spiral pipe, the separation efficiency is constant and satisfying, because the particles found in the overflow liquid solution present a small diameter (55 Mm on average: see the average diameter of 95% of the particles present in the overflow (overflow D

The length of 1 m for the pipe with spirals seems to be the m inimum length starting of which it is possible to achieve the fine particles separation, only particles of 55 Mm being found in the purified liquid solution. Cone inlet diameter

In order to reduce the risk of short circuit illustrated in Fig. 4, that is the risk that the mixture to be separated introduced by the pipe with spirals 2 into the cone 1 will be directed to the column for evacuating the liquid solution 8 instead of travelling along the cone lateral wall 10 along the vortical profile, and in order to improve the separation along with small loss of the charge, it was decided to use the diameter of the lower part of 80 mm, that represents the ratio of the cylindrical part diameter surpassing the cone / cone inlet diameter = 0.25, that is found in device or in classical cyclone.

In this way, at the cone inlet, the centrifugal force decreases approximately 3 times and the axial speed / radial speed ratio increases. All the trials were performed with such lower part diameter.

As a result of this dimensional part, for the device of invention the following optimal geometrical parameters can be defined:

^■ diameter of the conduit used for the spiral - 8 mm

^■ spiral diameter - 30 mm

^■ length of the path travelled by the mixture inside the spiral - 1000 mm

^■ cone inlet diameter - 80 mm

^■ outlets diameter - 10 mm

^■ cone height - 40 mm

The other experiments were conducted in order to determine:

a) what is the influence of mass density of the solid particles contained in the mixture on the separation efficacy;

b) what is the influence of feed rate on the separation;

c) is it possible to accelerate the separation process by increasing the feed rate, that would allow to reduce the equipment size;

d) is it possible to successfully treat the solutions containing a biphasic liquids (aqueous phase and organic phase) and the particles imbibed in an organic phase?

The experimental results were achieved with device of the optimized geometry defined in the above discussed dimensional part, used with liquid mixtures of different nature particles (limestone, clay, carbon powder and limestone imbibed in fuel oil), the initial granulometric distributions of which are represented on the graphs of Figs. 2a to 2d.

Each figure shows a histogram in form of bars, that corresponds to the proportion of each particle size of the same diameter on a quantity scale from 0 to 1 0% , designated by the reference A.

Figures also show a cumulative distribution curve for particles contained in the analysed medium, that translates itself into scale from 0 to 1 00%, designed by the reference B.

a) Influence of solid particles mass density

Series of experiments aiming to discover the influence of mass density were conducted in the following starting conditions: input flow rate inside the spiral pipe between 250 and 400 l/h; flow rate of the underflow (channel 4) between 60 and 120 l/h. The results achieved with feed rate of 460 l/h and flow rate of the underflow of 60 l/h are shown in the following Table 2:

Table 2: Influence of mass density

The results demonstrate that in all the cases, particle separation is possible with a granulometric distribution indicating that the bigger particles are present essentially in the underflow, and only the smaller particles are present in the overflow. It is thus possible to use the device of the invention for solid/liquid separation for plurality of the solid particles, even if these particles are present in the organic phase (the case of limestone imbibed in fuel oil). b) Influence of feed rate

Series of experiments aim ing to discover the influence of feed rate were conducted in the following starting conditions: input flow rate between 240 and 450 l/h; flow rate of the underflow being 60 l/h. Different solids were used. The results achieved with a limestone - fuel oil - water mixture (three-phase mixture, that is with two liquid phases: organic and aqueous, and one solid phase) are shown in Table 3:

Table 3: Influence of feed rate

These results demonstrate that for all the flow rates, particle separation is possible with a granulometric distribution indicating that preferably, the bigger particles are present in the underflow, while the smaller particles are present in the overflow.

Similar result were achieved for the mixtures devoid of organic phase:

Example with the carbon powder

Table 4; Results achieved with the carbon powder

c) regarding possible dimensional reduction of the apparatus

The increase of a flow rate only slightly improves the apparatus performance, that enables the high flow rates in the accelerators of small dimensions.

d) possible treatment of three-phase mixtures - application in petrochemistry

Figs. 3a and 3b represent graphs illustrating, for the highest flow rate (450 l/h), the granulometric distribution achieved for the limestone - fuel oil - water mixture.

Thus, with the same high flow rate it is possible to use device of invention to separate solids form liquids in the presence of the organic phase.

This result is very interesting in the scope of use of device of the invention upstream the biphasic separator by the phase inversion.

This type of separator enables the effective separation of phases, aqueous and organic, from the liquid solution containing it, and it is mainly used in petrochemistry in order to recover the organ ic solvents dispersed in the waste waters from the petrochemical platform.

However, this waste waters are often present in form of sludge, because they also contain the solid particles, that limit the biphasic separator operation by obstructing perforated plate, that usually enables introduction of solution to be treated in form of globules of emulsion into column containing the organic solvent capturing the globules organic phase during their travel down to the column bottom. The use of device of the invention upstream from such separator will allow the purification of the three-phase mixture of the largest solid particles (69 pm, that are found in the underflow form Fig. 3b), and the liquid solution delivered by it from its evacuation column will contain only solid particles of a small diameter (38 pm, Fig. 3a), and it will be possible to treat said solution by the separator without risk of silting-up the separator perforated plate.

e) Influence of underflow/feed rate ratio

The R _f ratio:

R _f = flow rate of the underflow / feed rate

is an important parameter, that determines the separation efficacy.

The results achieved for R _f between 0.2 and 0.09 clearly show, that in the analysed range of flow rates, this parameter does not influence the degree of separation, that remains equal to about 90%.

From the above experiments, device of the invention allows to separate solid particles of 100 pm or less with respect to a liquid solution.

Thus it can be used as the first means for filtrating the mixture, that will be later filtrated more finely by the second type of separation device, like a hydrocyclone, or as a means for screening the mixture prior to treatment by the other type of device, the operation of which would be limited by the presence of the solid particles of more than 100 pm of diameter, such as above mentioned biphasic separator.