DE2320859A1 - PROCESS AND DEVICE FOR INDUCING PARTICLE GROWTH IN A FLOWING LIQUID SUSPENSION - Google Patents

Description

Method and device for inducing particle growth in a flowing liquid suspension.

The invention relates to a method for inducing
of particle growth in a flowing liquid suspension in preparation for a subsequent separation of the grown particles from the liquid.

The invention also relates to a device for carrying out this of the procedure.

If a liquid in which separate particles are in suspension remains stagnant for some time, it appears that apart from a separation (either deposit or
Flotation), a growth of the particles also takes place. This is a consequence of the fact that if there is some difference in the natural rate of separation between particles,

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for example as a result of different sizes of the particles, since there is a certain probability that two particles will overtake each other and thereby unite with each other.

In laboratory devices, it is known that such ¹ particle growth can be accelerated by stirring so that the residence time can then be reduced in a separating vessel. This is caused by the introduction of speed differences between different parts of the liquid, which increases the likelihood that particles will overtake each other. Correspondingly, as the dimensions of the particles increase, the stirring speed should be reduced 'in order to prevent the growth of the particles from being destroyed by the shear effect between layers of liquid'. Since the speed gradient is essentially in the immediate vicinity of the stirrer, continuous stirring has little or no effect.

Stirring is not suitable for handling large amounts of liquid. However, facilities are already known for this purpose which have a number of parallel baffle plates in a staggered arrangement, whichever is guided through the device Liquid give abrupt changes of direction, in this device, as a result of centrifugal forces, a growth of the Particles will take place due to differences in speed. To achieve a sufficient effect, however, should the dimensions of such a device as well as the residence time the fluid in the facility can be very large.

The purpose of the invention is to remedy these disadvantages.

Accordingly, the invention relates to a method and a device for the treatment of large quantities of a liquid suspension in continuous flow in preparation for

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effective separation of the components in suspension in a suitable separating device. The considerable particle growth achieved according to the invention becomes one lead significantly increased separation with the same capacity, so that the efficiency of the device is increased and the dimensions of a separation system of which the separation device is a part can be reduced while its Yield can be increased.

The method according to the invention is characterized in that the liquid is guided in a vertical direction, that the average flow velocity is maintained at such a value throughout the treatment, that essentially all of the particles in the stream are dragged forward and that the dwell time in this vertical stream is chosen so large that, as a result of differences in the flow velocity of the particles in relation to the liquid flow, a growth of the particles through Conservation of the same and thereby the separation is promoted in a subsequent treatment stage.

The device for continuous through-flow for carrying out the method is characterized by an enclosure for Bounding at least one essentially vertical flow path between an inlet and an outlet, the connection or connectability of these two with a feed line for the suspension to be treated, or the inlet side of a separating device, as well as means for maintaining fluid flow on this flow path.

In particular, the vertical flow can be consecutive in a number of Streams with alternating flow directions can be subdivided, with the flow velocity suitable for particle growth and residence time by an appropriate selection

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the cross-section of these partial flows can be adjusted, and, also the flow rate for the subsequent separating device desired entry speed can be adjusted. The natural velocity gradient between the centrurr of the flow and the flow parts in the vicinity of the boundary walls can be through separating plates, which the said flow in parallel partial flows subdivide, enlarged, these plates provided with corrugations or similar profiles if necessary and e.g. can be mutually displaceable so that the power distribution can be influenced as desired.

Exemplary embodiments of the invention are shown schematically in the drawing shown. Show it:

1 shows a device in a simplified schematic representation. in a vertical longitudinal section,

Fig. 2 shows another embodiment of the device, in a vertical one Longitudinal section,

3 shows a further embodiment of the device, in a vertical section,

4 shows a chamber of the device with different arrangements of auxiliary plates, each in a view from below, and one Number of such plates of different lengths, in cross-section,

Fig. 5 corrugated auxiliary plates in two different positions, in longitudinal section,

Fig. 6 adjustable strips instead of the auxiliary plates according to Fig. 5, in a schematic representation,

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7 shows a device in connection with a separating device, in a three-dimensional view, and

8 shows the device according to FIG. 7, in a vertical longitudinal section.

As already mentioned, the invention is based on the insight that a Particle growth will take place when suspended particles are allowed to overtake one another. this will occur especially in a vertical column of liquid as a result of differences in settling or flotation speed, regardless of whether this column is stationary or moving in a vertical direction. In a moving In addition, the flow velocity in the vicinity of the boundary walls will be lower than in the center of the column because of the friction Current, so that, as a result of the speed gradient, speed differences between adjacent liquid layers will develop, which increases the likelihood that Hit particles, enlarged. While large differences in speed are favorable for the initial growth, during the gradual further growth a limit can be reached because the shear between adjacent current layers with different Velocities will lead to the dissolution of the coalesced particles. To achieve a gradual growth of the particles, such speed differences should be reduced, but then the hit probability will also decrease, so that it takes more time to achieve the same increase in dimensions as with the earlier steeper velocity gradient.

On the other hand, the flow speed is limited by the condition that the towing speed should be greater than

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the natural speed of separation (settling or flotation) when the flow is opposite to that speed. Further, the residence time in such a stream ¹ is limited by the dimensions of the current path, which in turn are related back to the desired velocity, as well as by the desired volume of flow per unit time. Therefore it is generally not very possible to achieve a particle growth in a passage of considerable dimensions which is sufficient for a substantial improvement of a subsequent separation in a separation device.

In Fig. 1 a device is shown, which is based in principle on the above considerations. By means of a supply line the suspension to be treated is fed under a given pressure, namely the static pressure of a higher one Liquid container or the pressure of a feed pump. the The speed of the liquid in the feed line 1 is sufficiently high to counteract a separation of suspended particles therein.

The device includes a container 2 with a front and rear end wall 3 and side walls 4. In this container 2, partitions 5 running parallel to the end walls 3 are provided, which are connected to the bottom of the container 2 and end at some distance from the upper edge of the container, and between these partitions 5 other partitions 6 are provided, which protrude above the normal liquid level in container 2 and terminate with their lower end at some distance from the bottom of the container 2. This way they are consecutive Chambers 7 formed by passage openings 8 either are connected to one another above the partition walls 5 or below the partition walls 6. The lead 1 is on the underside

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connected to the first chamber 7, and in the rear End wall 5, which delimits the last Eammer 7, an outlet opening 9 is provided, which is connected to the inlet opening one in Pig. 1 separating device, not shown, for separating of the suspended particles is in communication.

In the uneven chambers 7 the liquid flows upwards, in the even chambers it flows downwards. Measures should be taken to ensure that the upward speed is in the odd Chambers 7 is greater than the natural settling speed of the components settling down, and / or that the downward speed in the straight chambers 7 is greater is considered to be the natural flotation rate of the components subject to flotation, as the pail is, and the flow in the passage openings 8 should be so great that it allows a separation in these particles counteracts.

The cross section of the first chamber 7 is chosen so that the speed of the liquid leaving the feed line 1 is sufficiently reduced to obtain a certain dwell time in this chamber, and on the other hand the boundary walls of this Chamber produce such a velocity gradient that particle growth is initiated to a considerable extent will. In addition, this first chamber 7 ensures an adaptation of the flow leaving the relatively narrow feed line 1 to the larger width of the container 2.

To achieve a steeper speed gradient without a considerable reduction in cross-section, which has an unfavorable influence on the dwell time would have to be obtained is the distance between the first partition wall 5 and the front end wall selected smaller than the width of the wall 3, so that the speed gradient in

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essentially determined by the partition 5 and the end wall 3 and yet a sufficient cross-section is obtained.

The distances between the partitions 5 and 6 are in the successive Chambers 7 are generally larger, so that a decrease in the velocity gradient is achieved in these chambers in order to counteract the destruction of the growth by shear in this way. This has an increase in the cross section and thus also the dwell time, what for the Maintaining gradual particle growth is beneficial. In addition, the average flow velocity increases in the successive chambers 7, wherein the decrease in speed is particularly selected such that the speed in the vicinity of the outlet opening 9 of the desired feed line speed for the separating device, which is connected to the container 2 and in which the particles grown from the liquid are deposited is essentially the same. Such a separator is, for example, a corrugated plate separator Plates.

The position of the outlet opening 9 is arbitrary as such, and this opening can (deviating from Fig. 1) e.g. also be located near the bottom of the vessel 2, if this is for the connection would be cheaper with the separator. The position of the supply line 1 can also be changed at will.

If, as shown in Fig. 2, the partition walls 5 and 6 are inclined, the speed is gradually reduced and the speed gradient is achieved. Fig. 3 shows an embodiment with coaxial partitions 5 and 6, the it makes it possible to obtain a mode of operation which corresponds to that of the device of FIG. When the coaxial partitions are frustoconical, a working method as in Fig. 2 obtained.

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The speed gradient can, while maintaining the speed distribution in the successive chambers 7 and the average speed in each of these chambers / by subdividing them into one another by means of auxiliary plates parallel sub-chambers are enlarged so that, while the flow cross-section is maintained in a chamber 7, the distance from the wall is reduced and thus the speed gradient is increased.

According to FIG. 4A, the auxiliary plates designated there with 10 parallel to the end wall 3 and therefore also parallel to the partition walls 5 and 6, while FIG. 4B shows the same plates 10 shows, which 'extend parallel to the side walls 4. In the event of 2 can either fan-like diverging or parallel triangular plates adapted to the shape of the chamber be used. In the case of Fig. 3, the auxiliary plates can be cylindrical or they can lie in planes that go through the Axis of the apparatus go.

The auxiliary plates 10 will generally extend over the entire height the relevant chamber 7 extend, and measures should be taken to ensure that the liquid flow is not hindered in the adjacent passage opening 8. In the arrangement of Fig. 4B, these plates can also be in the Passage openings 8 extend into it and meet there with corresponding plates in the adjacent chamber 7. In the meantime it is also possible to provide the auxiliary plates 10 only in part of the chamber 7. Furthermore, according to FIG. 4C, there is the possibility of to make some of the panels 10 shorter than the remaining panels, so that a decrease in the wall effect provided by these panels is already reached within the chamber 7 itself. It is also possible to make some of the auxiliary plates 10 displaceable to a to get a certain amount of regulation.

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In Pig. Figure 5 shows another method of introducing velocity differentials into the stream. Here are corrugated sheets 11 provided, the waves of which run transversely to the flow direction indicated by an arrow in FIG. 5. In Fig. 5A are the waves of two adjacent plates 11 in opposite phase of the wave lines, so that the one in the middle between the two Passage lying flat has alternating narrowing and widening parts. As a result, not only in the transverse direction, but also generates speed differences in the longitudinal direction, which additionally promotes particle growth is achieved. If the two plates 11 are mutually offset by half a wavelength, the situation becomes as shown Fig. 5B is reached. In this case, the clear width of the passageways is the same everywhere, so that essentially the same Effect as achieved with flat plates, but the path length is increased. Meanwhile, the repetitive * changes of direction also lead to additional speed differences in the latter case, so that in the situation according to FIG Growth effect will be greater than in the case of flat plates.

Such corrugated sheets can in turn in the manner of FIG. 4A or FIG. 4B be arranged. The stream in the outer passages, fed by a Corrugated sheet 11 and a flat wall are limited is different of the flow between two corrugated plates 11. In the arrangement according to FIG. 4B, the influence of the outer passages, considered as a whole, is much lower. With a suitable choice of the distance from the flat wall or the width of the outer corrugated sheets 11, it is possible to achieve that the effect of the outer passageways is not too great differs from the average effect of the other passages.

It is also possible to match the walls in question with To provide waves, and there is also the possibility of corrugated and alternately provide flat plates. In the latter case is the The regulating effect according to FIG. 5 is no longer possible, but then the regulating effect, attributed to the arrangement according to FIG. 4C,

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still possible.

The arrangement of flat and especially corrugated plates füb.rt leads to an increase in the flow resistance of the chamber 7 concerned, and also the flow resistance in the case the pig. 5A will be greater than in the case of the Pig. 5B. The flow resistance shows the difference in the liquid level successive chambers 7 · This difference in level is a measure of the force needed to overcome the flow resistance is recorded. From the equations for the liquid flow in a constrained flow path the following relationship can be derived:

/ «2 · ^ν

where with ν the average velocity gradient across to the direction of flow, with P the applied force, with ^ the Viscosity and with V the volume · of the liquid is designated. From this follows ^ h as the level difference:

ρ __

P ce (Ah), and thus ν cd (Ah).

If, for example by means of tests, a suitable value for ν has been determined, the latter can be adjusted by laying the plates in such a way that Δ h is given the corresponding value. This can of course also be achieved automatically, in particular when the maintenance of a given speed gradient ν is desired.

Reducing the flow resistance, in particular by eliminating plates, can also help maintain a strong Liquid flow can be used for flooding the facility.

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In the case of a chamber 7 which is divided by a rather small number of corrugated sheets, there will be an increase in flow resistance of the inner passages by laying corrugated sheets lead to the fact that the flow through the outer passageways increases so that in the latter there is an increase in the speed gradient will occur although the dwell time will become shorter. On the other hand, there will be a decrease in flow resistance in the inner passageways lead to the fact that the flow through the outer passages is reduced, so that the The speed gradient is also reduced, while the dwell time is increased. This more or less conflicting one The effect in the inner compared to the outer passages has the consequence that load fluctuations are compensated to a certain extent. This is an advantage of this inherently simple design.

Instead of corrugated sheets, sheets with other profiles, e.g. triangular or trapezoidal profiles, or plates with transverse ribs or the like. can be used.

Fig. 6 shows another solution in which strips 12 arranged in parallel rows are used and at least the strips in alternating rows can be rotated about a longitudinal axis 13, as illustrated in Fig. 6 with dashed lines is. In this way, the effects of the embodiments of FIGS. 5A and 5B can be mimicked. Also are the passages then connected to one another so that load differences are balanced out. This is also due to the arrangement of openings in the plates 10 or 11 possible.

There is also the possibility of using the corrugated sheets 11 of FIG to be arranged in such a way that the waves extend in the direction of flow. In this case, no speed differences are obtained in the direction of flow.

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In practice, the first chamber 7 of the device according to FIG for a uniform introduction and distribution in the lateral direction of the liquid flow emerging from the feed line 1 be used. This chamber can for example be provided with a corrugated sheet facing the front wall 3 and the adjacent partition wall 5 runs parallel. The following chambers are e.g. provided with corrugated sheets in the arrangement according to Fig. 4 or 5, these can be adjustable. The last chamber 7 is not provided with corrugated sheets, for example, and it can have a smaller cross-section than the preceding chamber 7, since then only the effect of the boundary walls is used in the last chamber. In the meantime, it can be advantageous to provide guide walls in the last chamber 7 which cause a uniform transition to the outlet opening 9.

In addition, it can be advantageous to combine assembled partition walls and panels in separate units, which are made, for example, from synthetic resin molding and built into a robust metal container 2. In this way, assembly is simplified such a device ^1, and can also such assembly units for cleaning and repair easily be removed from the container and they can if necessary be replaced by other Einheitein.

In the above description it was assumed that the liquid is supplied to the first chamber 7 from below, however it is also possible to supply the liquid from above. This will depend e.g. on the number of chambers and the fact whether the circumstances allow the supply line 1 to be mounted in the manner shown in FIG.

7 and 8 show a combination of a plate separator and a simple embodiment of the device according to FIG

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. Invention. This separator consists of a container 14 into which a number of parallel corrugated sheets 15 inclined to the vertical are installed, the corresponding corrugation peaks and wave troughs of said corrugated sheets lie in substantially vertical planes. A side wall of this Container 14 is provided with an inlet opening 16 while the opposite side wall has an outlet opening 17, so that a substantially horizontal flow of liquid in the passages between the plates 15 is obtained. The passages between the plates 15 are at their lower ends with a Collecting funnel 18 in connection, the one for receiving the sediment sliding down in the wave troughs of the plates 15 used separation from the liquid flow in the passages mentioned. Floating components of the liquid become are collected in the wave crests of these plates and move upwards, then at the upper end of the plates 15 can be removed in a suitable manner. The outlet opening 17 is in communication with an outlet chamber 19 for the carrier liquid.

The device according to the invention contains in the embodiment According to FIGS. 7 and 8, only two chambers 7. The feed line 1 opens into the upper end of the first chamber 7 and the outlet opening 9 the second and last chamber 7 is connected to a connecting chamber 20 in connection, which in turn is connected to the inlet opening 16 of the plate separator 14. In the second chamber 7 plates 10 are indicated with dashed lines (see »Fig. 8). The upper ends of these plates 10 are vertical Offset towards one another in order to obtain a uniform distribution of the liquid over the entire cross section of the outlet opening 9.

In the connecting chamber 20, guide means for the flow can used to ensure the uniformity of power distribution

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to improve. These guide elements can consist, for example, of transverse strips or blinds which, if necessary, can be adjustable, or they can consist of a spatial grid with mutually crossing rods. Such guide elements are preferably built as separate, self-contained units which can be inserted removably in guides in the walls of the connecting chamber. As can be seen from FIGS. 7 and 8, the connecting chamber 20 has a downwardly inclined floor in order to guide sediments which have already been deposited in this chamber to the collecting funnel 18. The outlet chamber 19 has such a sloped floor ¹ for the same purpose.

Of course, the number of chambers 7 can also be selected to be greater in this case, and also in the first chamber 7 plates 10 can be provided. In some cases a single chamber 7 may be sufficient, and then the supply line 1 connected at the lower end of the chamber, as indicated in Fig. 7 with 1 '.

It will be evident that various modifications are possible within the scope of the invention. A device according to the invention can for example, be connected in series with the same device if the action of a single such device is not sufficient and the construction of a special facility with a correspondingly larger number of chambers is not economical is.

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Claims (33)

. - 16 - 2320853 claims 1. Process for inducing particle growth in one flowing liquid suspension in preparation for a subsequent separation of the grown particles from the liquid, characterized in that the liquid is guided in a vertical direction that the average The flow rate is maintained throughout the treatment at such a value that essentially all particles are dragged forward in the flow, and that the dwell time in this vertical flow is chosen to be so large will that, as a result of differences in flow velocity of the particles in relation to the flow of liquid, a growth of the particles by their union obtained and thereby the separation is promoted in a subsequent treatment stage. 2. The method according to claim 1, characterized in that the vertical stream is divided into a number of successive streams with alternating flow direction that the Flow velocity in the upward and downward currents greater than the natural settling or flotation velocity of the particles in these streams is chosen, and that the velocity in the horizontal connections between the successive vertical flows is sufficient to prevent separation in these connections. 3. The method according to claim 1 or 2, characterized in that the velocity in the vertical streams at a given point is less than the velocity at which the particle growth is at this point by shear as a consequence of a velocity gradient in the stream in the vicinity of this Point would be destroyed. 309845/0942 4. The method according to claim 3 / characterized in that the Reduced speed in at least a number of successive stream parts gradually or in steps will. 5. The method according to claim 4, characterized / that the The final velocity of the stream is essentially the same as the initial velocity for the subsequent separation treatment is made. 6. The method according to any one of claims 3 to 5, characterized in that that speed differences between the particles encourage additional particle growth be introduced into the vertical stream. 7. The method according to claim 6, characterized in that the additional speed differences in successive vertical parts of the current can be reduced either gradually or in stages. 8. The method according to claims 4 and 7, characterized in that the decreasing speed differences either be generated by a gradual or a stepwise broadening of the vertical current. 9. The method according to any one of claims 6 to 8, characterized in that the additional speed differences are generated by dividing at least part of the vertical flow into a number of parallel flows with a smaller cross-section, and that the total cross-section of these partial flows is adapted to the yield and flow rate . 10. The method according to any one of claims 6 to 9, characterized in that the additional speed differences 309845/0942 ■ - 18 - by bringing about changes in the cross-section and / or in the direction of the current with alternating opposites Sense of flow are introduced in the partial flows. 11. The method according to any one of claims 6 to 10, characterized in that the additional speed differences are regulated or adjusted by changing the length and / or the shape of the partial flows. < 12. The method according to claims 2 and 11, characterized in that that a given pressure difference for regulating or setting the additional speed differences is regulated or adjusted between successive vertical flow parts. 13. Facility for continuous flow for execution of the method according to any one of claims 1 to 12, characterized by a border to limit at least one im essential vertical flow path between an inlet and an outlet, the connection or connectivity these two with a feed line for the suspension to be treated, or the inlet side of a separation device, as well by means of maintaining a flow of liquid on this flow path. 14. Device according to claim 13, characterized by partition walls within the enclosure for delimiting a number of successive ones Chambers in which the direction of flow is alternately opposite. 15. Device according to claim 14, characterized in that the cross section of at least a number of successive chambers increases in the direction of flow. 309845/0942 16. Device according to one of claims 13 to 15, characterized by inclined boundary walls and / or partition walls for delimiting one or more chambers with in
Direction of flow gradually increasing cross-section. 17. Device according to one of claims 13 to 16, characterized in that a transverse dimension is a
Chamber or passage is considerably larger than the other in order to obtain a substantial velocity gradient while maintaining a certain cross section in the direction of the smaller dimension. 18. Device according to claims 14 and 17, characterized in that the various chambers in the direction of
smallest dimension are juxtaposed. 19. Device according to one of claims 15 to 18, characterized
characterized in that the successive chambers by
substantially coaxial walls of curved or polygonal cross-section are delimited. 20. Device according to one of claims 13 to 19, characterized by one or more extending substantially vertically
extending plates arranged in a flow path
and these are divided into a number of adjacent partial passages with a smaller cross-section. 21. Device according to claim 20, characterized by sets of plates following one another in the direction of flow, the distance between the plates being mutually and between
outer panels and the adjacent boundary walls in
gradually increases with the successive sets. 309845/0942 22. Device according to claims 16 and 20 or 21, characterized characterized in that the distance between the plates is mutual and between the outer plates and the neighboring ones Boundary walls gradually increasing in the direction of the flow. 23. Device according to one of claims 20 to 22, characterized marked that at least part of the plates and if necessary, the adjacent boundary walls are provided with repeating profiles. 24. Device according to one of claims 20 to 23, characterized characterized in that the plates extend in the direction of the smaller dimension of the flow path in question. 25. Device according to claim 23 or 24, characterized in that the profiled plates alternate with flat plates. 26. Device according to one of claims 20 to 25, characterized in that alternating plates in their longitudinal direction are movable. 27. Device according to claim 26, characterized by regulating means for automatic adjustment of the displaceable plates. 28. Device according to claim 27, characterized in that the Regulating means work in accordance with the pressure difference between successive chambers. 29. Device according to one of claims 14 to 28, characterized by assembly units of partition walls and / or panels arranged in a container. 30. Device according to one of claims 20 to 29, characterized marked that the plates of the last chamber are different 309845/0942 2320853 have their length and their ends in front of the outlet opening for an even current distribution in this opening different heights. 31. Device according to one of claims 20 to 30 , characterized by perforations arranged in at least one part of the plate. 32. Device according to one of claims 13 to 31, characterized through a substantially horizontal connecting chamber connected to the outlet, which is connected to a subsequent Separating device is connected or connectable. 33. Device according to claim 32, characterized by in the Connection chamber arranged flow guide means. April 12, 1973 Jr / ip * 309845/0942