DE3239427C2 - - Google Patents

Description

The invention relates to a device for stirring with at least one agitator, which is in a container is arranged.

Solids are often used in process engineering processes mashed with liquids as suspensions, and it takes place between the liquid and the finely dispersed Solid a mass transfer instead.

This can be an extraction, a crystallization and / or be an agglomeration process, and the combination Both processes are often used as stirring processes designated.

In continuous large-scale processes gradually different over the entire stirring process Process conditions changed, e.g. B. the temperature or Degree of supersaturation of a solution.

It is known such leaps in process conditions technically to realize that a chain of Stirring tanks are set up and the conditions for each container can be set separately.

This control of the operating conditions is usually necessary to certain properties of the solid to breed specifically, e.g. B. a very specific particle size distribution, a certain strength of agglomerates.

Often there is a need to grow up Solid and the liquid in different Way to transport through a chain of stirrers.

One differentiates z. B. a cocurrent and a countercurrent flow of the solid to the liquid.  

Since it is practically always the case with such operations are pumpable suspensions in the stirrers, it will be inevitable that with the transported Solid also unwanted liquid carried as a carrier medium becomes.

In some processes, a separation of the Solid is provided at the end of the stirrer chain. Just part of the solid goes into the production line further, a possibly much larger part is about a filter separated and returned to the stirring process. One speaks of a vaccine recirculation and uses it especially where the crystal growth is very high is small or where the particle size is particularly controlled must become.

The solid can be separated from the liquid but also after every single stirred tank of the whole Chain make sense, because then co-current and counter-current flow or recirculations in any variant can be and the process control more flexible becomes.

With such an arrangement, the solid can within recirculate a unit "stirred tank / filter", or it the solid can also be in the penultimate or a previous one Stirred tank are returned. In this way can also countercurrent liquid and solid will.

The invention has for its object a Device for stirring the above mentioned Art to create, which with particularly good flexibility the processes of mixing and mixing Separation in an economical way in a particularly simple device-related arrangement allows.  

To achieve this object, the invention provides that in the container at a predetermined level Screen is arranged, which is substantially horizontal and extends over the entire inner surface of the container, that the screen above the agitator so is arranged that the container interior through the Screen into a stirring room located under the screen and divided a sedimentation room above the screen is that the stirring room and the sedimentation room are only connected by an opening, the one in relation to the cross-sectional area of the container has very small opening area.

According to the basic idea of the invention, the essential technical progress achieved with good Flexibility of process control the processes of mixing and separation can be realized without own filter stations to have to build.

It can be particularly advantageous according to the invention Wise solids and liquids alternate with each other brought into contact and separated again be, the flow rates of solids and liquids largely independent of each other can be adjusted. This means that too the residence times of solids and liquids can be set largely independently of each other.

The invention also opens up the advantageous possibility of To convert existing installations on stirred tanks in such a way that the effectiveness is increased significantly.

According to the invention, the arrangement is advantageous hit so that the screen near the liquid surface is arranged in the container. If the umbrella as close as possible to the surface of the liquid in the container is arranged, the largest part of the container volume available for the stirring process.  

It can preferably be provided that the distance of the Of the liquid surface in the order of magnitude of ten percent of the distance from the bottom of the container lies. Of course, that depends on the invention Screen provided different heights Influencing factors that only arise from the circumstances of the individual case can be derived. It is according to the invention however, to strive for the sedimentation space only as big as absolutely necessary and the stirring space so big as possible.

Several designs are conceivable for the screen, both from the technical arrangement as well as from the can depend on processed materials. Preferably the screen can be used as a flat plate or as a flat plate edge areas angled downwards or as a conical surface be trained, the top of the sedimentation chamber is facing. The umbrella could too be bowl-shaped, with the convex side is facing the sedimentation room. Basically can the surface of the screen can be arranged such that particles sedimented there by gravity in the opening between the sedimentation room and the stirring room be introduced and through this opening into the Arrive in the stirring room.

However, it can preferably be provided that the scraper device is designed such that on the screen sedimented particles towards the opening between the stirring room and the sedimentation room are promoted.

In an alternative preferred embodiment of the Subject of the invention can also be provided that the screen is rotatably mounted in the container and that a scraper device on the top of the screen  is arranged, which is fixedly attached to the container is.

A particularly advantageous embodiment of the subject matter of the invention provides that the opening between the mixing chamber and the sedimentation space as an annular gap between the outer edge of the screen and the inner wall of the container is trained.

A rotating movement of the liquid in the mixing room to prevent, can also preferably be provided that radial baffles on the inner wall of the container are arranged.

When very slow stirring speeds are used can, it may be advantageous that the screen as a fixed Plate is formed, which is attached to the container is that the opening between the sedimentation space and the stirring room in the central region of the container is that the shaft of the agitator through the central opening is passed and that the scraper device is attached to the shaft of the agitator.

Practically all known come as agitators Embodiments are contemplated, and it may be preferred the arrangement must be such that the agitator a blade stirrer, a propeller stirrer, an anchor stirrer or has a coated jet stirrer.

In a further preferred embodiment of the subject matter of the invention it is provided that a propulsion jet stirrer is provided, in which compressed Air flows through a jacket tube from the bottom up that a bell-shaped screen above the casing tube a vertical, rotatably mounted hollow shaft is attached and that the interior of the hollow shaft as an air bubble trigger is trained.  

A rotating movement that may occur to prevent the liquid in the sedimentation chamber, can preferably be provided that in the sedimentation room vertical partitions are arranged.

If the suspension penetrates from the the sedimentation room with particularly high reliability should be avoided, can preferably be provided be that several screens are arranged one above the other. Several arrangements of this type can also be stacked be arranged.

Another advantageous embodiment of the subject matter of the invention provides that the sedimentation room from the Container wall made of spiral inwards vertical walls are arranged, the inner edges of which connected to an overflow weir arranged in the center are, and that between the bottom of the Walls and the rotatable screen formed a narrow gap is. Meet the vertical spiral walls a triple function:

First, the walls force the ascending to clear Liquid into a narrow channel and extend the Sedimentation path from the outer edge to the overflow weir. Disruptions from the agitation zone to the sedimentation zone or clarification zone are not so easy to the overflow area.

Second, the spiral walls prevent it from rotating Movement of the liquid.

Third, the spiral walls do the job of scraper blades. The solid deposited on the screen  is out through the spiral walls promoted and falls there through the annular gap between the Screen and the inner wall of the container back into the mixing room. These spiral walls hardly generate any eddies.

It is special in the arrangement according to the invention advantageous that the opening between the sedimentation chamber and the stirring room at the greatest possible distance from the Overflow weir is arranged.

To enlarge the clarification area, can advantageously be provided that the sedimentation space as a upward expanding space is formed.

For example, if it is desired to have an agitator without Moving parts can preferably be provided be that when using one by one from above shaft-driven agitator projecting into the container the agitator shaft in the area of the sedimentation chamber at a distance, fixed hollow shaft is arranged.

In the arrangement according to the invention, the stirring process can be set very strongly in the stirred space without Breaking up turbulence into the sedimentation chamber, which can also be called a clarification room.

In the device according to the invention, it appears advantageous an agitator with a relatively large Number of stirring arms to use, so that the Peripheral speed of the entire agitator so low can be kept as possible.

Of course, in the arrangement according to the invention, it is advantageous the overflow weir then into the central area  of the container when the opening between the Sedimentation space and the stirring space formed as an annular gap is arranged in the edge region of the container is. Basically, the invention Arrangement in a variety of procedural Processes applicable, for example in the alumina industry. The arrangement according to the invention is also suitable advantageously in so-called countercurrent sedimentation in general.

It is also within the scope of the invention, the container to operate under pressure.

In principle, the arrangement according to the invention could a thickening room or a below the agitation room Thickening zone are provided so that the solid with even higher concentration just still flowable could be.

The invention is described below using, for example described with reference to the drawing; in this show:

Fig. 1 shows a schematic vertical section through a decanter,;

FIG. 2 shows various alternative embodiments of the screen shown in FIG. 1 in a schematic vertical section;

Fig. 3 shows an alternative embodiment of the Ausrührers shown in Figure 1 in a vertical section.

FIG. 4 shows an alternative embodiment of the stirrer shown in FIG. 1 in a vertical partial section;

FIG. 5 shows an alternative embodiment of the stirrer shown in FIG. 1 in a vertical partial section;

Figure 6 shows an alternative embodiment of the stirrer shown in Figure 1 in partial vertical section;

Fig. 7 is a stirred container from above;

Fig. 8 is a partial vertical section through a stirrer with several, one above the other and screens

Fig. 9 is a plan view of a stirred tank with the stirrer drive removed and with spiral partition walls in the sedimentation chamber.

As shown in FIG. 1 14/1 15/1 baffle plates are mounted in an upright stirred container at a container inner wall. The interior of the container is divided by a screen 10/1 into a sedimentation chamber 31/1 arranged above it and a stirring chamber 32/1 arranged below the screen. The sedimentation chamber 31/1 and the stirring chamber 32/1 are connected to one another only by a narrow annular gap 30/1 , which is formed between the screen 10/1 and the inner wall 14/1 of the container.

The screen 10/1 is rotatably connected to a shaft 11/1 , which sets both the agitator and the screen 10/1 in rotation. As shown in FIG. 1, inner stirring blades 12/1 and outer stirring blades 13/1 are attached to a plurality of agitator arms arranged one above the other. The overall designated 25/1 agitator is rotated by the drive motor 19/1 shown in the upper part of FIG. 1.

A cross member 18/1 is installed in the stirred tank above the screen 10/1 . Downwardly directed blades 20/1 are attached to this crossbeam, which are used together as a scraper device to scrape particles sedimented on the screen 10/1 and to convey them outward into the opening 30/1 .

The very high built agitator 25/1 works according to the multi-stage impulse counterflow principle. The inner stirring blades 12/1 and the outer stirring blades 13/1 are each set in such a way that in the vicinity of the shaft 11/1 an upward flow is generated in the suspension, which is deflected under the screen 10/1 and through the outer Stirring blades 13/1 is guided down again.

The baffle plates 15/1 attached to the inner wall of the container 14/1 serve to prevent the suspension from rotating in the stirring space 32/1 .

The suspension rises through the opening 30/1, which is designed as a narrow annular gap, into the sedimentation room and has the opportunity in this room to largely clarify it. The clarification can proceed undisturbed in this Sedimantionsraum 31/1 convenient as the vertebrae and movements from the agitation space 32/1 are kept away by the screen 10/1 from 31/1 sedimentation.

It is therefore practically in the sedimentation room completely calm area.

The clarified liquid, the liquid level of which is designated by the reference symbol 21/1 , can run off via the overflow weir 16/1 into the collecting channel 17/1 and from there through the drain pipe 22/1 in the direction illustrated by an arrow.

The collecting channel 17/1 and the drain pipe 22/1 are arranged stationary in the stirred tank .

The solid, which settles on the screen 10/1 in the sedimentation space 31/1 , is displaced outwards by the blades 20/1 of the scraper device arranged stationary in the stirred tank until it slides over the edge of the screen 10/1 and into the stirring space 32/1 falls behind.

In the arrangement shown in FIG. 1, it is important that the volume of the mixing container is largely available for the stirring process, since the screen 10/1 is arranged very close to the overflow weir 16/1 .

FIG. 2 shows in a summarized representation various alternative embodiments of the screen 10/1 shown in FIG. 1.

In addition to the embodiment of the screen illustrated in FIG. 1, which there has the shape of a flat plate with edge regions that are angled downward, various modifications of this shape of the screen are conceivable.

Fig. 2 shows a screen 10 a, which is simply designed as a flat plate.

The screen 10 b is bowl-shaped, with the concave side facing down.

The screen 10 c further illustrated in FIG. 2 is conical, with the syringe of the cone pointing upwards.

Finally, a toroidal screen 10 d is shown in FIG. 2, which is particularly aerodynamic. The top of the torus is covered with a flat plate.

The screens 10 b to 10 d each have sloping surfaces towards the edge, so that the solid sedimented there can slide relatively easily into the stirred space.

In the embodiment of the stirrer according to the invention shown in FIG. 3, the separation of the stirring space from the sedimentation space arranged above is brought about by a stationary screen 10/3 . The stationary screen 10/3 is designed as a flat plate which is attached with its outer edge to the inner wall 14/3 of the container and which has an opening 30/3 in the central area. Through the opening 30/3 , the connection between the sedimentation space and the stirring space is created.

On the same shaft that also drives the agitator, a crowing arm 23/3 is attached, which has downward-pointing blades 20/3 . By Krählarm from the 23/3 and the attached blades 20/3 24/3 scraper means formed of sedimented on the upper side of the screen 10/3 solid is conveyed inwardly towards the opening 30/3. The solid can get into the stirred space through this opening.

An overflow weir 16/3 for the liquid discharge is arranged as shown in FIG. 3 along the circumference of the stirred tank, as is common in clarifying thickeners.

The suspension, which reaches the sedimentation chamber through the opening 30/3 , flows radially outwards from the area of the drive shaft for the agitator and also upwards and has to travel a relatively long way to the overflow weir 16/3 . The conditions have a positive effect on a good clarification and a correspondingly extensive sedimentation.

The embodiment of the subject matter illustrated in FIG. 3 is preferably applicable when the speed of the agitator can be set sufficiently low so that the blades 20/3 do not stir up the sedimented solid again.

In FIG. 4, an alternative embodiment is shown of an agitator. A propeller 27/4 driven from below rotates within a propeller jacket 26/4 , which is designed as a fixed tube and is attached to a holder 28/4 in the central region of the container. The propeller 27/4 pushes the suspension up in the central area of the container, and after deflection on the screen 10/4 the suspension flows down again in the outer areas of the container.

The screen 10/4 is rotatably arranged and the blades 20/4 located above are fixedly attached to a suitable traverse in the stirred tank. Since the opening 30/4 between the sedimentation space and the stirring space is designed as an annular gap near the container wall, the overflow weir is located in the central area, so that the largest possible path is created for the liquid in the sedimentation space.

In FIG. 5, a so-called Treibstrahlrührwerk is illustrated, wherein within a casing tube 29/5 an air tube is disposed 36/5. The circulating effect or stirring effect is achieved by a driving jet emerging from the air pipe 36/5 and directed downwards, which is driven by a pump arranged outside the container.

The sedimentation space is separated from the agitation space by a screen 10/5 which is stationary in the agitation vessel and has an opening 30/5 arranged in the central area.

The solid sedimented on the screen 10/5 is transported to the center by the blades 20/5 attached to the crowing arm 23/5 and can get back into the stirring space through the opening 30/5 .

Fig. 6 illustrates a so-called air-lift stirrer, in which in a jacket tube 29/6 an air jet emerges from an air tube 36/6. This air jet, which can also be referred to as a propellant jet of compressed air, is directed upward, so that an upward flow is produced in the central region of the stirred tank. The air bubbles are caught by a bell-shaped screen 10/6 and discharged upwards out of the stirred tank via a hollow shaft 35/6 . Moreover, the arrangement of Figure 6 corresponds to FIG. The devices already described above, in which a rotating screen and a stationary scraper means are present.

FIG. 7 shows a stirred container from above, in which partition walls 33/7 directed radially inward into the sedimentation chamber are attached to the container inner wall 14/7 . These partitions serve to prevent the liquid from possibly rotating in the sedimentation chamber.

Instead of the radial partitions illustrated in the upper half of FIG. 7, those partitions which form a closed pattern could also be used as shown in the lower part of FIG. 7. This creates separate, upward-facing channels. For example, as shown in FIG. 7, an arrangement of partitions could be used, which are designed and arranged according to a honeycomb pattern. For the sake of completeness, it should also be added that, as shown in FIG. 7, a drive motor 19/7 for an agitator is attached to a double traverse.

Fig. 8 shows a preferred embodiment of a Ausrührers invention, which can be referred to as multistage impulse countercurrent with an attached three-stage sedimentation. A lower screen 10/8 is rotatably mounted on a shaft 11/8 . The shaft 11/8 also serves to drive an agitator. The suspension enters between this lower screen 10/8 and the container wall through the opening 30/8 into a lower sedimentation chamber . This lower sedimentation chamber is delimited at the top by a further, central screen 10 '/ 8 . The sedimented on the lower, rotating screen 10/8 solid particles are first scraped by the stationary blades 20/8 , which are attached to the stationary central screen 10 '/ 8 , and then through the opening 30/8 in the Brought stirring room. The suspension rises through the opening 30 '/ 8 , which is arranged in the central region of the stirring container, into the middle sedimentation chamber. The sedimented solids there, which are deposited on top of the middle screen 10 '/ 8 , are scraped off by blades 10' / 8 and conveyed towards the center. These blades 20 '/ 8 are attached to an upper screen 10''/ 8 , which rotates together with the shaft 11/8 . Through the opening 30 '/ 8 , the solids scraped off by the blades 20' / 8 reach the lower sedimentation chamber

The progressively clarifying suspension flows around the upper screen 10 '' / 8 and passes through the opening 30 '' / 8 , which is formed as an annular gap between the upper screen 10 '' / 8 and the container wall in the upper sedimentation room. The suspension can then continue to be discharged via the overflow weir 16/8 and through the drain pipe 22/8 . Those solid particles that settle on the upper screen 10 '' / 8 are scraped off by the stationary blades 20 '' / 8 and conveyed to the outside so that they pass through the opening 30 '' / 8 into the middle sedimentation chamber reach.

It can thus the suspension from the agitation on a meandering path through the opening 30/8 , further through the lower sedimentation space , through the opening 30 '/ 8 , further through the middle sedimentation space and finally through the opening 30''/ 8 in the flows into the upper sedimentation room. In the opposite direction, the solid particles scraped off by the blades 20 '' / 8 from the upper screen 10 '' / 8 are conveyed through the opening 30 '' / 88 into the central sedimentation space.

The sedimented solid particles in the middle sedimentation space on the middle screen 10 '/ 8 are through the blades 20' / 8 , which rotate with the upper screen 10 '' / 8 , towards the center and through the opening 30 '/ 8 in the lower sedimentation room promoted. The sedimented in the lower sedimentation chamber on the lower screen 10/8 solid particles / supported by the middle of the stationary screen 10 '8 mounted blades 20/8 outwardly and through the opening in the agitation space 30/8.

An arrangement according to FIG. 8, in which several umbrellas with associated scraper devices and several sedimentation rooms are provided, has proven particularly useful in those cases in which it is to be avoided with particularly high reliability that suspension gets from the agitation room into the sedimentation room and there disturbs the flow calming required for sufficient sedimentation.

Fig. 9 shows a plan view of a stirring container with the stirrer removed. On the inner wall 14/9 of the container, walls 34/9 running spirally inwards are attached. The inner ends of these spiral walls 34/9 open at an overflow weir 16/9 . The spiral walls extend up to a small distance, which can be, for example, on the order of a few centimeters, to the surface of an umbrella rotating under these walls.

The spiral walls serve three purposes:

First, the spiral walls 34/9 force the rising, clarifying liquid into a narrow channel and extend the sedimentation path from the outer wall of the container to the centrally arranged overflow weir. In this embodiment, faults that could possibly still get into the sedimentation space from the agitation chamber do not easily penetrate into the area of the overflow weir.

Second, the spiral walls act similar to the partitions 33/7 illustrated in FIG. 7 and suppress a rotating movement of the liquid.

Third, the spiral walls 34/9 function as the blades of the doctor device. The abge on a screen under the spiral walls solid is conveyed through these walls in the direction indicated by arrows to the outside and falls back into the mixing chamber.

The spiral walls only produce a minimum of Whirl, at least a lot less whirl than other scraper devices.

The direction of rotation of the screen is shown in FIG. 9 by an arrow in the peripheral area. The path of the settled solid relative to the spiral walls is entered in Fig. 9 as an arrow chain.

Experimental investigations with the subject of the invention have clearly shown that in extremely advantageous Way the size of particles that get into the overflow only insignificantly above that by Stoke's law due grain size limit.

Claims (20)

1. Device for stirring, with at least one agitator ( 25 ) which is arranged in a container, the container interior being divided into a stirred space ( 32 ) and a sedimentation space ( 31 ). 2. Device according to claim 1, characterized in that the screen ( 10 ) is arranged in the vicinity of the liquid surface in the container. 3. Apparatus according to claim 1 or 2, characterized in that the distance of the screen ( 10 ) from the liquid surface is in the order of ten percent of the distance from the container bottom loading. 4. Device according to one of the preceding claims, characterized in that the screen ( 10 a / 2 ) is designed as a flat plate. 5. Device according to one of claims 1 to 3, characterized in that the screen ( 10/1 ) is designed as a flat plate with Randbe angled down rich. 6. Device according to one of claims 1 to 3, characterized in that the screen ( 10 c / 2 ) is designed as a conical surface, the tip of which faces the sedimentation space. 7. Device according to one of claims 1 to 3, characterized in that the screen ( 10 b / 2 ) is bowl-shaped, the convex side facing the sedimentation chamber. 8. Device according to one of the preceding claims, characterized in that the scraper device ( 24 ) is designed such that sedimented particles on the screen towards the opening ( 30 ) between the stirring space ( 32 ) and the sedimentation space ( 31 ) be promoted. 9. Device according to one of the preceding claims, characterized in that the screen ( 10/1 ) is rotatably mounted in the container and that on the top of the screen ( 10/1 ) a scraper device ( 24/1 ) is arranged, which is fixedly attached to the container. 10. Device according to one of the preceding claims, characterized in that the opening ( 30/1 ) between the stirring space ( 32/1 ) and the sedimentation space ( 31/1 ) as an annular gap between the outer edge of the screen ( 10/1 ) and the inner wall ( 14/1 ) of the container is formed. 11. Device according to one of the preceding claims, characterized in that radial baffle plates ( 15/1 ) are arranged on the inner wall ( 14/1 ) of the container. 12. Device according to one of claims 1 to 8, characterized in that the screen ( 10/3 ) is designed as a fixed plate which is attached to the loading container that the opening ( 30/3 ) between the sedimentation chamber ( 31 / 3 ) and the stirring space ( 32/3 ) is arranged in the central area of the container, that the shaft ( 11/3 ) of the agitator ( 25/3 ) is passed through the central opening ( 30/3 ) and that the scraper device ( 24/3 ) is attached to the shaft ( 11/3 ) of the agitator ( 25/3 ). 13. Device according to one of the preceding claims, characterized in that the agitator ( 25 ) a blade stirrer ( 25/1 ), a propeller stirrer ( 25/4 ), an anchor stirrer or a coated propulsion jet stirrer ( 25/5 , 25/6 ) having. 14. Device according to one of the preceding claims, characterized in that a propulsion jet stirrer ( 25/6 ) is provided, in which compressed air flows from the bottom upwards through a casing tube ( 29/6 ) that a bell-shaped screen ( 10/6 ) Above half of the casing tube ( 29/6 ) is attached to a vertical, rotatably mounted hollow shaft ( 35/6 ) and that the interior of the hollow shaft is designed as an air bubble trigger. 15. Device according to one of the preceding claims, characterized in that in the sedimentation room ( 31/7 ) vertical partition walls ( 33/7 ) are arranged. 16. Device according to one of the preceding claims, characterized in that a plurality of screens ( 10 , 10 ') are arranged one above the other. 17. Device according to one of the preceding claims, characterized in that in the sedimentation chamber ( 31/9 ) from the container wall ( 14/9 ) are arranged spirally inwardly extending vertical walls ( 34/9 ), the inner edges of which are in the center arranged overflow weir ( 16/9 ) are connected, and that a narrow gap is formed between the lower edge of the walls ( 34/9 ) and the rotatable screen. 18. Device according to one of the preceding claims, characterized in that the opening ( 30 ) between the sedimentation chamber ( 31 ) and the stirring chamber ( 32 ) is arranged at the greatest possible distance to the overflow weir ( 16 ). 19. Device according to one of the preceding claims, characterized in that the Sedi mentation space as an expanding upward Space is formed. 20. Device according to one of the preceding claims, characterized in that at the Use one through one from the top of the container protruding shaft driven agitator in the area the agitator shaft in the sedimentation chamber Distance surrounding, fixed hollow shaft arranged is.