SE465604B - SET FOR SEPARATION OF A SUBJECT FROM A SCIENTIFIC WITH THE PARTICULAR MATERIAL - Google Patents

Description

15 20 25 30 35 465 604 of very expensive substances.

As an alternative to the separation technique described above, it has been proposed that a liquid from which a substance should be separated should be supplied to the lower part of a treatment chamber containing a bed of particles; which are free to move relative to each other; and then caused to flow through this particle bed from below and upwards in such a way that the particles are kept in a fluidized or floating state in the treatment chamber.

Such a fluidization technique would require a smaller overpressure of the supplied liquid than the previously described separation technique.

However, the capacity of a separation plant in this case would instead be limited by the fact that the flow rate of the liquid through the particle bed cannot be too great. This flow rate must not be greater than the particles being held by gravity in the bed and not being carried by the upwardly flowing liquid out of the treatment chamber.

Another technique; which has been proposed to bind a certain substance in a liquid to particles, means that the particles are kept suspended in the liquid by stirring for a time and then - after they have attracted the said substance in the liquid - separated from the liquid by gravity separation or centrifugal separation.

A disadvantage of this technique is that it takes a relatively long time to create the required contact between the particles and all parts of the liquid for the separation of the substance in it.

An object of the present invention has been to provide a new method of separating a substance from a liquid by bonding the substance to small particles, which method enables a substantially greater separation capacity than the methods described above and thus can be applied on a much larger scale than these. Another object of the invention has been to enable the use of significantly smaller particles than those that could have been used previously. These objects can be achieved according to the invention in that a body of liquid with a predetermined density is kept in rotation together with small particles with a density lower than that of the liquid, and that liquid, from which said substance separated, brought into contact with the particles in such a way that they are kept suspended in the rotating liquid.

The invention thus relates to particles which are lighter than a liquid being kept in a floating state in a rotating liquid body, while the liquid from which a substance is to be separated is caused to bypass the floating particles.

If desired, particles can be kept suspended throughout the rotating liquid body. Preferably, however, particles are kept suspended in only one layer of the liquid body; wherein the liquid to be liberated from said substance is caused to flow through the suspension layer.

The main part of the liquid should flow between the suspended particles in the direction from the axis of rotation of the rotating liquid body towards the radially outer part of the liquid body.

Because the particles are lighter than the liquid; the particles floating in liquid will, by the centrifugal force, strive to move radially inwards; wherein the force acting on the particles in this direction is greater the further from the axis of rotation the particles are located. Therefore, the inflow of liquid from which said substance is to be separated can be made very large without risk of the particles leaving the treatment chamber together with radially outwardly flowing liquid. The force to which the particles are subjected by the flow of the supplied liquid is independent of the distance of the particles from the axis of rotation.

If the particle size were to vary slightly in the suspension layer, this does not matter so much, since extremely small particles, which are easily carried by the supplied liquid, are still retained in the vicinity of the other particles as a result of the radially outward increasing centrifugal force. By the same mechanism, a particle is immediately returned radially inwards, if it has been affected by temporary forces and is carried too far out of the axis of rotation.

The liquid body held in rotation can have any desired shape. If it has such a shape that the flow cross-section of the supplied liquid increases radially outwards; the balancing effect on the suspended particles becomes even greater; since the force caused by the flow of the liquid on the particles then decreases with increasing distance from the axis of rotation of the liquid body; while the opposite centrifugal force increases.

An increasing flow cross-section of the supplied liquid may be desirable especially in the radially outer part of the suspension layer in order to safely retain the particles therein. In the main part of the suspension layer, however, it may be desirable to instead have a radially outwardly decreasing flow cross-section for the supplied liquid. Thereby, namely, if desired; a substantially uniform distribution of the particles in the suspension layer is achieved along the flow path of the liquid therethrough. If the particles have a certain size distribution, this may be taken into account when designing the flow path of the liquid through the suspension layer in order to achieve the desired distribution of the particles therein.

As will be appreciated, any desired distance between the particles in the suspension layer can be achieved by appropriate selection of centrifugal force in and liquid flow through the suspension layer. This distance can t.o.m. changes by regulating the centrifugal force and / or the liquid flow during the separation process.

Advantageously, a merely slightly modified conventional centrifugal separator can be used for carrying out the method according to the invention, wherein both the said liquid and the particles can be kept in rotation in the form of a substantially annular body. The invention is applicable in connection with substantially all such separation processes in which conventional liquid chromatography may be used. In addition, the invention makes it possible to solve many separation problems with the aid of the separation technique in question, which at present cannot be solved in an economically acceptable manner. Thus, the invention makes it possible on an industrial scale to separate very small amounts of valuable or harmful substances from disturbing amounts of highly dilute solutions.

For example, the quality of some dryer; such as beer or wine; improved by the removal of certain substances. Another example is that wastewater can be purified from non-desirable substances; before it is released into the wild.

The choice of material for the particles to be used must be made taking into account the liquid; where a substance should be separated; partly to the mentioned subject. Since many process liquids have a density of about 10, often particles with a density lower than 10 must often be selected.

Different types of plastic material may be considered. For example, polyethylene or polypropylene can be used as the base material in the particles.

In the same way as is generally known in connection with conventional liquid chromatography, the particles must; to be used in the method according to the invention; usually prepared; so that they can attract and bind a substance to be separated from a liquid.

In this case, the particles are given an active surface in one or another of several known ways; which e.g. chemically or physically can bind the said substance to the particles; when the liquid comes in contact with them.

For example, it is possible to give the particle surfaces a certain charge, so that they can attract and bind particulate matter; which has the opposite charge. Also well-known principles for so-called affinity chromatography can be applied in connection with the present invention.

It is also possible to use particles; which are capable of absorbing a substance in a liquid. In such cases, the substance in question penetrates into the particle body itself; where it is retained. As in the case of conventional liquid chromatography, it is often desirable that the particles used in the separation process of the invention can be reused many times. The same technique can be applied as in conventional liquid chromatography to liberate particles from substances which have bound to the particles during a separation process.

The particle size should be as small as possible but must be adapted to the chosen combination of centrifugal force produced and the size of the liquid flow in the centrifugal field in question. Preferably, particles in the order of 0.1 - 10 μm are used.

The invention is described in the following with reference to the accompanying drawing. In this, Fig. 1 schematically shows a so-called open centrifuge rotor of a kind which can be used in the practice of the invention.

Fig. 2 shows a part of the centrifuge rotor in Fig. 1 slightly modified. Fig. 3 shows a so-called closed centrifuge rotor which can alternatively be used in the practice of the invention.

Fig. 1 shows a part of a centrifuge rotor comprising a rotor body 1, which is supported by a vertical drive shaft 2. The rotor body 1 delimits a separation chamber 3; wherein a stack of conventional frustoconical separating discs 4 is arranged coaxially with the rotor 4. The stack of separating discs 4; which have axially aligned so-called distribution hole 5; rests on a conical bottom plate 6. This plate has corresponding holes 7 located in line with the distribution holes 5.

The bottom plate 6 together with the lower part of the rotor body 1 forms a chamber 8, which communicates with the separation chamber 3 via the holes 7 in the bottom plate 6. In the chamber 8 a channel 9 opens, which extends axially through the drive shaft 2.

On top of the stack of separation discs 4 rests a conical partition wall 10, which together with the upper part of the rotor body 1 delimits a number of channels 11. These channels 11 extend from a radially outer part of the separation chamber 3 towards the center of the rotor and open. 465 604 in a first outlet chamber 12, which is formed by the radially inner parts of the rotor body 1 and the partition wall 10.

Radially inside the first outlet chamber 12, the radially inner part of the partition wall 10 forms a second outlet chamber 13. The separation chamber 3 communicates via a overflow drain 14 with this second outlet chamber 13.

Both outlet chambers 12 and 13 are designed as radially inwardly open annular grooves, and into these extend stationary outlet means 15 and 15, respectively. 16; which may be in the form of conventional so-called shell discs. Both outlet means are supported by a stationary inlet pipe 17, which extends from the outside of the rotor into a central inlet chamber 18 in the rotor formed radially inside the frustoconical separating discs 4. The part of the inlet pipe 17 present in the inlet chamber 18 is perforated; so that a liquid supplied through the inlet pipe can be sprayed radially outwards and distributed along the axial extent of the inlet chamber.

At the radially outermost part of the separation chamber 3, the rotor body 1 has a number of outlet openings 19 evenly distributed around the center axis of the rotor. In a known manner, these outlet openings can be arranged to be opened and closed during the operation of the rotor.

During its operation, the centrifuge rotor described above will contain a liquid; partly very small particles; which have a density which is less than the density of the liquid. Thereby, the liquid will form a rotating body; filling the largest part of the separation chamber 3, comprising the spaces between the separation plates 4; and a part of the central inlet chamber 18, the particles being suspended in a cylindrical, sleeve-shaped layer 20 of the liquid body, located closest to the axis of rotation of the rotor. The layer 20 extends radially inwards to the level of the overflow drain 14, whereby liquid supplied to the rotor via the inlet pipe 17 will be sprayed towards the inside of the layer 20. The layer 20 can be divided into different sectors by means of radial and axially extending carrier wings (not shown) supported radially inside the separating discs 4 of the base plate 6 and the partition wall 10.

The centrifuge rotor in Fig. 1 is intended to operate in the following manner.

Liquid, from which a certain substance is to be separated, is supplied via the inlet pipe 17 and sprayed against the inside of the rotating sleeve-shaped liquid layer 20, which contains particles. Through this liquid supply, the particles will be maintained in a floating state in the rotating liquid body. The larger the liquid supply through the inlet pipe 17 is made, the greater the distance obtained between the particles in the liquid body.

During the passage of the supplied liquid through the layer 20, it is effectively brought into contact with the surfaces of the particles, which are prepared in a known manner to attract the substance to be separated from the liquid.

When the liquid has passed through the layer 20 and is released from all or a part of said substance, it flows further radially outwards through the spaces between the separating discs 4 to the radially outer part of the separating chamber 3. From there the liquid flows via the channels 11 again radially inwards to the outlet chamber 12, from where it is removed by means of the stationary outlet means 15.

During the separation operation described above, new particles can be supplied to the rotor and spent particles removed from the rotor either continuously or intermittently. New particles can be supplied through the channel 9 in the drive shaft 2 and, via the chamber 8 and the distribution holes 5, pumped into the spaces between the separating disks 4. The fed new particles will thus move in countercurrent to the liquid flowing radially outwards in the rotor. As a result, a corresponding amount of particles which have separated the above-mentioned substance from the supplied liquid is displaced out of the inlet chamber 18 via the overflow drain 14 to the outlet chamber 13. By means of the stationary outlet means 16, the particles are removed from the outlet chamber 13. According to a alternatively by intermittently displacing particles out of the separation chamber 3, the outflow of liquid through the stationary outlet means 15 can be temporarily interrupted, while new liquid is still supplied via the inlet pipe 17. In this case the liquid surfaces in both the outlet chamber 12 and the separation chamber 3 (or the separation chamber 18) ) to move radially inwards.

New particles are suitably supplied to the centrifugal rotor suspended in a liquid of a suitable kind, for example a part of the liquid which has left the centrifugal rotor after being freed from the above-mentioned substance. In a known manner, particles which have been used in the described separation operation, i.e. has been removed from the centrifuge rotor via the outlet chamber 13, reconditioned and used again. If necessary, the particle suspension which is supplied to the rotor via the channel 9 can be more dilute, i.e. contain fewer particles per unit volume of the particle suspension than the particle suspension discharged from the rotor by the outlet means 16. The composition of the discharged particle suspension is determined by the particle density desired in the layer 20 of liquid-fluidized particles.

By using conical separation discs 4 of the type described, particles which have the task of attracting the said substance in the supplied liquid can be effectively prevented from accompanying liquid too far on its path radially outwards in the rotor.

However, it may be appropriate to dimension the separation discs in such a way that a large part of the particle suspension is formed radially inside the separation discs in order to avoid the particle suspension becoming too dense.

In the above it has been assumed that the centrifuge rotor has a separate inlet for new particles. Alternatively, new particles can be supplied to the centrifugal rotor through its ordinary inlet for the said liquid, i.e. they can be mixed with the liquid before it is fed to the centrifuge rotor.

Fig. 2 shows an embodiment of a centrifuge rotor arranged for such a supply of new particles. 10 15 20 25 30 35 -Iš- O \ LH ON- CD # 5 10 Fig. 2 shows a perforated inlet pipe 17a which carries an outlet member 16a. The outlet means extends radially into an outlet chamber 13a, which is connected to the separation chamber of the rotor via a number of holes 21 in a partition wall 22. The holes 21 are located at a level radially outside the free liquid surface formed in the inlet chamber 18 by the liquid body rotating therein.

In the radially innermost layer of the liquid body, which layer in Fig. 2 is designated 20a, particles are kept in a suspended state by liquid supply via the perforated inlet pipe 17a. As can be seen, the partition wall 22 extends radially inwardly to a level within the layer 20a, so that particle suspension cannot flow into the outlet chamber 13a any other way than through the holes 21. These are level with the radially outer part of the layer 20a.

In the embodiment in Fig. 2, the centrifugal rotor has truncated conical separating discs 4a§ which at their radially innermost edges support annular members 23, which extend substantially horizontally.

The members 23 have a radially outwardly increasing thickness; whereby the spaces between them converge radially outwards. This is a design of the members 23; which enables a substantially unchanged or t.o.m. decreasing flow cross-section can be achieved for liquid; flowing radially outwardly through the particle suspension layer 20a.

The members 23 have axially 24 holes 24 located axially in line with each other and with the holes 21; whereby particles; which has separated a certain substance from the passing liquid, can leave the layer 20a at the current radial level and flow out into the outlet chamber 13a. Therein, if desired, by means of the outlet means 16a, a free liquid surface located radially outside the free liquid surface in the inlet chamber 18a can be maintained. In this case, it is anticipated that the holes 21 form a restriction of the suspension flow out into the outlet chamber 13a.

In an embodiment of the centrifugal rotor according to Fig. 2, new particles are preferably supplied to the layer 20a together with the liquid introduced through the inlet pipe 17a. This allows the new particles to be initially suspended in the radially innermost part of the layer 20a and to - as they separate the said substance from the liquid and thereby become heavier in certain applications of the invention - move radially outwards and finally leave the layer 20a via holes 24 and 21.

Fig. 3 shows an alternative embodiment of a centrifuge rotor, by means of which the method according to the invention can be performed.

Parts of the centrifuge rotor in Fig. 3; which correspond to parts of the centrifugal rotor in Fig. 1; have been assigned the same reference numerals as the latter with the addition of the letter_b.

The centrifugal rotor in Fig. 3 has a inlet pipe 25 for liquid, from which a blank is to be separated; extending into the rotor via the channel 9 in the drive shaft 2. The inlet pipe 25; which is rotatable together with the rotor; is perforated along its stretch in the inlet chamber 18b.

The rotor body 1 carries at its upper part a pipe 26 and a impeller 27 connected to the pipe; The tube 26 and the impeller 27 are sealingly surrounded by a stationary pump housing 28; having an outlet conduit 29. The interior of the tube 26 communicates with the channels 11b of the rotor and with the interior of the impeller 27; whereby the latter is arranged to pump liquid from the separation chamber 3b via the channels 11b out into the pump housing 28 and further through the outlet line 29.

Similarly, the conical partition wall 10b is connected at its upper part to a tube 30; extending coaxially through the tube 26; and carries a impeller 31. The upper part of the tube 30 and the impeller 31 are sealingly surrounded by a stationary impeller housing 32; having an outlet conduit 33. The interior of the tube 30 communicates with the inlet chamber 18b and with the interior of the impeller 31; whereby the latter is arranged to pump particle suspension from the inlet chamber 18b out into the pump housing 32 and further through the outlet line 33. 465 604 12 A centrifuge rotor according to Fig. 3 operates in substantially the same way as a centrifuge rotor according to Fig. 1. The only difference is that the whole the flue chamber 18b is filled with particle suspension during operation and that the separation operation inside the rotor can be carried out at superatmospheric pressure and without the liquid and the particles coming into contact with the atmosphere surrounding the rotor.

Claims (10)

10 15 20 25 30 35 .Du Ch CI1 ON C3 .Read 13 Patent claims A method of separating a substance from a liquid by binding the substance to small particles which are kept in motion, characterized in that a body of liquid with a predetermined density is kept in rotation together with small particles having a density lower than that of the liquid. of the liquid, and that liquid, from which said substance is to be separated, is brought into contact with the particles in such a way that they are kept suspended in the rotating liquid body. 2. A method according to claim 1, characterized in that the main part of the liquid, from which said substance is to be separated, is caused to flow between the suspended particles in the direction from the rotating axis of the rotating liquid body towards the radially outer part of the liquid body. 3. A method according to claim 1 or 2, characterized in that the liquid, from which said substance is to be separated, is caused to flow through a layer (20) of the rotating liquid body, in which the particles are kept suspended. 4. A method according to claim 3, characterized in that liquid is continuously removed from the radially outer part of said layer (20). 5. A method according to any one of the preceding claims, characterized in that new particles are added and used particles are removed from the liquid body while it is kept in rotation. 6. A method according to any one of the preceding claims, characterized in that the liquid body and the particles are kept in rotation as a substantially annular body. A method according to any one of the preceding claims, characterized in that liquid is led from the rotating liquid body radially outside the suspended particles to a space (12), in which the rotation maintained during 465 604 10 15 14 is allowed to form a free, preferably annular liquid surface , which is maintained at a predetermined radial level. 8. A method according to any one of the preceding claims, characterized in that a free surface of the rotating body of liquid and particles is kept at a predetermined level in a chamber (3), which is delimited by a rotating body (1) § by means of a overflow drain (14) from said chamber (3). A method according to any one of claims 3-7, characterized in that new particles are supplied to said layer (20a) of the rotating liquid body at a first level and that used particles are removed from the layer (20a) at a second level (21) radially outside the first level. 10. A method according to any one of the preceding claims, characterized in that the liquid, from which said substance is to be separated, is caused to bypass the suspended particles along a flow path, the flow cross-section decreases and in which the centrifugal force increases, seen in the flow direction of the liquid.