EP1958698A1 - Method for operating a centrifuge - Google Patents

Abstract

A suspension of the product is introduced into a working region (60) through a drive shaft (20), a drum being rotated continuously during filling. The suspension is centrifuged. The product is dried, during which the drum rotates continuously. A fluid (the drying gas) is injected by nozzle(s) through the annular space (18) and into the interior (60) of the drum (10). The speed of the drum is controlled during drying, such that product cake does not collapse. During centrifugation, the internal pressure in the drum is raised.

Description

The present invention relates to a method for operating a centrifuge.

Centrifuges are well known in the art. They are primarily used in the chemical, pharmaceutical and food industries, in suspensions, i. Substances with a liquid and a solid content to separate the solid phase from the liquid phase and to dry.

In general, conventional centrifuges comprise a drum with a filter disposed in the drum. The filter can be designed as a rigid metal filter. The space between filter and drum wall is also referred to as annulus. The area inside the filter is called working space.

In conventional centrifuges, the suspension is first filled in the working space. This is conventionally done by the drive shaft, which is hollow, so that it can be used as a filling shaft. The drive shaft is further firmly connected to the drum base and serves to drive the drum. Usually, the drive shaft is mounted horizontally.

The suspension is filled with rotating drum in the working space. By acting on the suspension Forces in the radial direction, such as the centripetal force, or the resulting inertial forces, such as centrifugal force, the suspension is pressed outwards to the filter. With a correspondingly high centrifugal force, a stable liquid ring is created. This creates a suspension ring on the filter. The liquid phase now passes through the filter into the annulus and is discharged while the solid phase remains in the working space.

In conventional centrifuges, the solid phase of the product adheres firmly to the filter after the liquid phase has escaped. The solid phase may have a residual liquid content of up to 30%. The firmly adhering to the filter product is called in this state, cake or ring cake, product cake or filter cake.

The centrifuged product with a high residual liquid content in the form present after centrifuging is generally not optimally suitable for further transport for a further process step "drying". It has proved to be particularly advantageous to dry the product directly in the working space. In this way it is prevented to have to spend the still wet and only cumbersome transportable product via a transfer unit in a drying room. For toxic products, the risk for the personnel involved also decreases. Centrifuges in which a product is centrifuged and dried in the same working space are also referred to as centrifugal dryers.

In conventional centrifugal dryers, the cake must be blasted off the filter before drying. For this purpose, shot nozzles and drum bottom openings are provided, which open into the annular space. The annulus itself is divided by webs into several sections, each section having a drum bottom opening having. Furthermore, it is conventionally provided that the firing nozzles can be moved to the drum base openings from the outside. The shot nozzles now inject a generally gaseous fluid at high pressure into the annulus. The fluid now moves in the opposite direction through the filter and dissolves the solid phase of the product pressed by the centrifugal forces into the filter from the filter. This process is also called breaking the filter cake. Optionally, several firing nozzles may be provided so that they inject the fluid into the annulus at the same time, or it may also be provided only a shot nozzle, which successively injects the fluid into the individual sections and thus peel off the filter cake piece by piece.

After the filter cake has been broken off, the product is dried. The drying is conventionally carried out either by fluidized bed drying or fixed-bed drying.

In fluidized bed drying, either a stop-and-go process or a continuous process is typically used. In the stop-and-go process, a hot drying fluid is injected through the barrel bottom openings into the working space by means of the firing nozzles. Then, the drum is further rotated by a certain amount and again submitted a shot with the drying fluid in the working space. Thus, the product is dried by the hot gas and so swirled by the successive rotation of the drum so that the product dries as evenly as possible.

In continuous drying, the firing nozzles are not fully moved up to the drum bottom, but there remains a minimal gap between the nozzles and the Drum base. The drum now rotates continuously at a slow speed and a corresponding control system of the centrifugal dryer causes the weft nozzles to inject the drying fluid whenever there is a drum bottom opening in front of the firing nozzle exit. To simplify the scheme, the drum bottom openings are conventionally formed as slots. In this way, the product is dried by the drying fluid in the continuous drying and again and again caused by the continuous rotation of the drum, so that the drying takes place as evenly as possible.

In the case of fixed-bed drying, the product cake is not initially blasted off. Rather, a hot drying gas is introduced into the working space which separates the product cake from the inside to the outside, i. from the working space in the direction of the annular space, flows through and deprives the product cake while moisture. Thus, the product cake is dried in its ring shape and only then released from the filter. This can, for example, also by blowing off or by eversion of the filter in the case of a filter cartridge centrifuge.

After drying, the dried product, which now usually takes the form of a powder, can be removed from the working space and processed further.

In the conventional methods described above, however, problems occur in the processing of certain products. Especially for products with a broad range of grain sizes and a high proportion of fines, centrifuging is made considerably more difficult.

Already during filling a sedimentation of the larger product parts takes place. Due to their different ratios of mass to surface, the larger proportions of product rapidly move radially outward to the filter. However, the fine fraction first floats in the liquid and settles more slowly to the outside of the filter. In the process, the fine product components clog the interspaces between the larger product parts, so that it is frequently not possible for the liquid phase to flow out through the capillary between the larger product portions. The liquid phase then flows during centrifugation only very slowly or not at all. An increase in the rotational speed of the drum does not solve this problem either. For problematic products, this results in a residual liquid content of the product of up to 70% after centrifuging.

When drying by means of the fluidized bed drying of the above-mentioned products with a broad grain spectrum and high moisture content also occurs quickly clumping of the product. In the conventional fluidized bed drying roll product parts, which are moved by the rotation of the drum up, again and again along the remaining product portions down on the drum base. Thus, the clumping of the product is greatly promoted because during rolling down smaller product particles adhere to larger product particles and thus form ever larger lumps. The clumping of the product during drying, however, entails significant disadvantages. On the one hand, the larger lumps can not be dried satisfactorily because they remain very moist inside, on the other hand, the lumpy product is only very poorly suited for further processing.

In conventional fixed-bed drying, so-called drying cracks often form in the product cake during drying. By virtue of these cracks, the drying gas naturally escapes preferentially due to the lower resistance, so that a large part of the drying gas escapes through the drying cracks without passing through the product per se and exhibiting a drying effect. On the one hand, the drying gas is not used efficiently, on the other hand, the cake can not be dried evenly. In addition, in the vicinity of the drying cracks areas of high heat often occur, in which the product can be damaged or undesired chemical reactions occur.

Thus, an additional and basically superfluous post-processing of the product may be necessary to obtain a processable product consistency.

Furthermore, the filters, in particular metal filters, can not be manufactured with an arbitrarily small mesh size. The minimum mesh size is currently about 10 μm. For products with a high fines content, i. About 20% of the product has a grain size of less than 10 microns, much of the product is lost during conventional drying processes. Especially during the fluidized bed drying, the fine fraction is constantly atomized and escapes together with the drying gas through the filter into the annulus. Thus, conventional processing methods often lose a substantial portion of the product.

Finally, certain products have strict specifications for the way they are processed. Thus, for example, a maximum temperature of the drying gas may be predetermined, since a higher temperature would result in damage to the product or unwanted chemical reactions. As often Even if a very low maximum residual liquid content is specified by about 1%, compliance with the conventional methods is almost impossible. This is the case in particular for products in the food and chemical and pharmaceutical sectors.

To solve the above problems, a method for operating a centrifugal dryer according to claim 1 is proposed.

In the method according to the invention, a fluid is already injected during the centrifuging by means of the firing nozzles through the annular space in the drum. This loosens the product during centrifugation and prevents the product from sticking firmly to the filter. This not only prevents a product having a broad grain size spectrum from being clogged, but also prevents the product from sticking to the filter in the ring form. Thus, the duration of centrifugation is significantly shortened because the liquid phase can flow off faster due to the more porous product.

Of course, the centrifuging step according to the invention with constant loosening of the product cake can also be used separately in any method for the operation of a centrifuge. Thus, the centrifuging step may in particular also be used prior to any conventional drying step, such as conventional fixed bed drying or conventional fluidized bed drying, in any centrifuge manner.

Of course, even during centrifugation by pumping a suitable gas through the Filling shaft, the internal pressure of the drum can be increased to accelerate the escape of the liquid phase.

Furthermore, the speed of the drum during drying may be so high that the product cake does not collapse. This means that, although a drying fluid is injected by means of at least one firing nozzle in the opposite direction through the filter in the working space and the product cake is repeatedly loosened, swirled and dried, however, prevent the action of the drum rotation on the product radial forces that the product cake collapses. Thus, the product cake is kept permanently stationary during drying.

This initially results in the advantage that the product cake itself acts as a filter during drying. In this way it is prevented that the fines content is lost during drying. This results in a much higher product yield and increased efficiency of the process.

During drying, the hot drying gas is injected into the working space by means of the firing nozzles. As already described, due to the forces in the radial direction, which are caused by the drum rotation, the ring shape of the product is also permanently maintained during drying. By injecting the drying gas through the annulus into the working space, i. From outside to inside, a significant advantage over the prior art is also achieved.

In conventional drying processes, the hot drying gas in the case of fixed bed drying flows through the product cake only once from the inside to the outside, ie from the working space out in the direction of the annulus. In the fluidized bed drying, the drying gas flows through the cake once from the outside in the lower drum area and escapes in an upper area of the drum, without traversing the product again.

However, in the proposed process, the hot drying gas first flows through the product cake from outside to inside. Since the hot drying gas must escape again from the working space, it flows through the product cake at another point again from the inside out and escapes into the annulus. The drying gas thus passes through the product cake twice, resulting in a much more effective utilization of the moisture absorption capacity of the drying gas and a faster drying of the product cake. The permanent swirling of the product also increases the porosity of the product, allowing the drying gas to permeate the product more easily and more evenly. To assist the movement of the drying fluid from the inside to the outside, the pressure in the drum can be increased. This can be done by additional pumping of drying gas through the filling shaft.

By introducing a drying gas through the filling shaft into the working space, the two-sided drying of the product ring is also improved. Uniform drying from both sides allows more homogeneous drying of the product, avoiding unwanted localized overheating.

Due to the permanent loosening of the product cake, the formation of drying cracks is avoided in the inventive method. On the one hand, the drying cracks are directly destroyed by the drying gas injected into the working space by means of the firing nozzles, or else the Drying cracks are immediately re-added by whirling finer product proportions. Thus, the drying gas conducted into the working space through the filling shaft is forced to completely traverse the product from the inside to the outside and thus dries the product more effectively.

Finally, the process according to the invention also prevents clumping of the product due to agglomeration. By keeping the product cake stationary during drying, the above-described mechanism of lump formation is prevented, since unrolling and sticking of the moist product portions is no longer possible. Also, an accumulation of the product on the bottom of the drum which occurs after the blasting off, which often represents the beginning of the agglomeration, no longer occurs.

For injecting the fluid into the annulus, at least one firing nozzle is provided for this purpose. In one embodiment, two shot nozzles are used. The firing nozzles are on the one hand at the so-called 6 o'clock position, d. H. at about the bottom of the drum and at the 7 o'clock position, d. H. slightly laterally offset from the lowest point, arranged. In one embodiment of the invention, the firing nozzle is offset at an angle of approximately 30 ° at the 7 o'clock position relative to the firing nozzle at the 6 o'clock position.

The 6 o'clock position is therefore particularly advantageous because the acceleration due to the radial movement of the product still adds up to the acceleration occurring radially outwards. The outward forces are therefore greatest at the 6 o'clock position. Therefore, working at this point with the highest pressure when shooting the fluid to loosen up the cake and the best increase in porosity can be achieved.

In one embodiment of the invention, the annular space is divided into 12 sections, each having a drum base opening in the form of a slot. During one revolution of the drum, the two firing nozzles can inject the fluid into the same drum bottom opening or else into different drum bottom openings. When the firing nozzles inject the fluid into the same drum bottom opening, this means that during a clockwise rotation of the drum, first the shot nozzle in the 6 o'clock position injects the fluid into the particular drum bottom opening and thereafter when the drum has moved on and the particular drum bottom opening in front of the firing nozzle is at the 7 o'clock position, the firing nozzle at the 7 o'clock position injects the fluid into the particular drum bottom opening. In this way, it can be ensured that enough fluid is injected into the drum and a proper swirling effect occurs.

It should be noted at this point that the direction of rotation of the drum and the representation of the firing nozzle positions has been selected by time for the sake of simplicity of explanation only, and is not to be considered as limiting. The direction of rotation of the drum and the exact position of the firing nozzles can vary and always depends on the viewing direction.

In one embodiment of the method, it can be provided that the firing nozzles in each case inject the drum in each case in staggered drum bottom openings. It can be provided that the fluid is injected in each case displaced by a drum base opening with each drum movement. In this way, it is ensured that the product is whirled over the entire circumference of the drum.

In one embodiment of the method, the drum rotates during the filling of the product suspension in the drum. The injection of fluid by means of the firing nozzles can then be done already at the beginning of filling.

As will be explained in more detail below, according to the invention, during the injection of fluid, the drum rotates at a lower rotational speed than is normally the case in conventional centrifuges in the corresponding process steps. With a drum diameter of 400 mm, the speed during injection is about 150 rpm. At this speed, however, no stable liquid ring can build up.

Due to the lower viscosity of the liquid suspension portion, the shear forces from the muddy solid portion, which rapidly builds up into a ring during filling, can be poorly transferred to the liquid portion. Within the already established solid ring therefore forms a kind of lake from the filled suspension. In the method according to the invention, the loosened solid ring is able to entrain a thick layer of the liquid fraction over a certain angular distance before it breaks off again from the solid ring. An approximately 1 mm thin suspension layer but remains over the entire solid ring.

Due to the fluidization of the suspension lake due to the rotation of the drum, a sedimentation of the suspension and a separation of the product components with larger particle sizes of the fines is prevented. This layer formation of the different grain sizes takes place during conventional filling during filling and sits down during centrifuging. In the method according to the invention, however, this is prevented from the beginning.

Due to the permanent fluidization of the solid ring by means of the injected fluid of the solid ring is much more permeable to the overlying suspension ring. Since the overlying suspension ring only has a thickness of about 1 mm and the solid ring is constantly fluidized, the suspension ring filtered off very quickly. As a result, no sedimentation can occur in the liquid ring.

Furthermore, it can be provided that the product throughout the process, i. that during filling, centrifuging and drying, the product is loosened by means of the fluid injected into the working space by the firing nozzles. The filling step may then proceed smoothly to the centrifuging step, then the centrifuging step may then smoothly proceed to the drying step.

In one embodiment of the method, after drying, a so-called homogenization step may be provided. Although in the homogenization step the drum also rotates continuously, but at a speed reduced so that the product cake collapses. As already stated above, due to the permanent loosening of the product cake no break-off is necessary and with a corresponding reduction in the drum speeds, the product cake automatically collapses and the product trickles to the drum bottom. The product now has the form of a dry fine powder that moves up and down together with the drum, but falls back to the bottom of the drum before reaching the apex. Because the product already dried as desired, but no clumping of the product now occurs. Rather, the product is mixed evenly, so that the particle sizes of the product particles are evenly distributed over the entire product and the remaining moisture content is distributed homogeneously over the product.

As already stated, the drum speed during filling, during centrifuging and during drying is chosen so that the product cake is retained and does not collapse even in spite of the fluid injected by means of the firing nozzles. Only when homogenizing a lower speed is selected so that the product falls before reaching the apex of the drum.

Furthermore, the possible speeds are limited by the fact that with increasing speed, the residence time of the drum bottom openings before the firing nozzles at some point is too short to inject a necessary amount for fluidizing fluid quantity. The amount of fluid is then too small to whirl the product cake in the desired manner.

A minimum speed thus always results from the point at which the ring shape of the product cake is no longer preserved and the product cake collapses to a maximum speed results from the amount of fluid that can give the shot nozzles in a given period, as well as the Shape of the drum bottom openings and the associated residence time of the drum bottom openings in front of the firing nozzles.

For a drum with a diameter of 400 millimeters and a subdivision of the annulus into twelve sections, wherein each section has a drum base opening in the form of a slot, the following possible drum speeds for the corresponding method steps could be determined.

However, it should be expressly pointed out at this point that the determined rotational speeds can also be transferred to any other drum sizes by means of mechanical principles. The method according to the invention can in principle be applied to centrifugal dryers of all sizes and with any subdivision of the annular space.

wobei v die Umfangsgeschwindigkeit und r der Radius der Kreisbewegung ist. Für v gilt des weiteren $$\mathrm{v}\mathrm{=}\mathrm{\omega }\mathrm{*}\mathrm{r}\mathrm{.}$$

For the centripetal acceleration a during the circular motion, the following applies: $$\mathrm{a}=\sqrt{\frac{{\mathrm{\nu }}^2}{r}}.$$

where v is the peripheral speed and r is the radius of the circular motion. For v further applies $$\mathrm{v}\mathrm{=}\mathrm{\omega }\mathrm{*}\mathrm{r}\mathrm{,}$$

Thus results for the centripetal acceleration $$\mathrm{a}\mathrm{=}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0003.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^2\mathrm{*}\mathrm{r}\mathrm{,}$$

With the speeds specified here and the drum radius of 200 millimeters, the acceleration acting on the product can thus be determined approximately and thus at least approximately calculated back to the necessary speeds for other drum radii. The necessary rotational speed ω ₂ at a drum radius of r ₂ results at a drum radius of r ₁ equal to 200 mm and the rotational speeds ω ₁ given here below $${\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0003.png"\; state="\{\{state\}\}">\omega </figure-callout>}}_2={\mathrm{<figure-callout\; id="1"\; label="\omega "\; filenames="imgf0003.png"\; state="\{\{state\}\}">\omega </figure-callout>}}_1\mathrm{*}\sqrt{\frac{r1}{r2}}$$

The rotational speeds indicated here for a drum diameter of 400 mm are thus transferable at least approximately without problems to other drum sizes by means of the equation (4).

As an alternative, the accelerations acting on the product cake are also given in g.

For the rotation of the drum with permanent loosening of the product cake by injecting a suitable fluid by means of the firing nozzles through the annulus into the working space a suitable speed of 120 to 150 revolutions per minute was determined with a drum diameter of 400 mm. This corresponds to an acceleration of 5 g acting on the product cake.

The speed of 150 revolutions per minute or the acceleration of 5 g can be used during filling, during centrifuging and during drying. In particular, during drying, a speed of about 150 revolutions per minute leads to a particularly good weiterzuverarbeitenden product. The described drying step according to the invention results in improved and more effective drying and a qualitatively improved end product not only in the described problematic products but generally in all types of products.

In less problematic products that do not clog during centrifugation, of course, during filling and centrifuging with a higher speed of about 500 revolutions per minute with a drum diameter of about 400 mm are used to accelerate the centrifuging. The acceleration acting on the product cake can be up to 55g during filling and up to 600g during centrifuging. For very coarse-grained products, it is even possible to accelerate up to 2000g on suitable centrifuges. During drying, the speed is then lowered again to about 150 revolutions per minute.

For problematic products that clog quickly and significantly slow down centrifugation, the rate of discharge during centrifugation could be doubled by the method of the invention. Thus, an accelerated and therefore economically advantageous processing of the product is possible.

During homogenization, a suitable speed is about 50 to 80 revolutions per minute with a drum diameter of about 400 mm. Considering the accelerations acting on the product cake, the speed should be selected so that the radial outward acceleration due to the circular motion is less than 1g, so that the product falls down in the upper part of the drum due to gravitational acceleration.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or in isolation, without departing from the scope of the present invention.

Figur 1

zeigt eine seitliche Querschnittsansicht eines Zentrifugentrockners, auf dem das erfindungsgemäße Verfahren ausgeführt werden kann.

Figur 2

zeigt eine schematische Frontalansicht einer Trommel mit möglichen Positionen der Schussdüsen und der Trommelbodenöffnungen, um das erfindungsgemäße Verfahren auszuführen.

Figur 3

zeigt das Korngrößenspektrum eines lediglich als Beispiels aufgeführten problematischen Produkts, das durch das erfindungsgemäße Verfahren besonders vorteilhaft zentrifugiert und getrocknet werden kann.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below in detail with reference to the drawings.

FIG. 1

shows a side cross-sectional view of a centrifugal dryer on which the inventive method can be carried out.

FIG. 2

shows a schematic frontal view of a drum with possible positions of the firing nozzles and the drum bottom openings in order to carry out the inventive method.

FIG. 3

shows the grain size spectrum of a problematic product listed only as an example, which can be centrifuged and dried by the method according to the invention particularly advantageous.

FIG. 1 shows a centrifugal dryer on which the inventive method can be carried out. The centrifugal dryer has a drum 10 which comprises a drum shell 11 and a drum base 12 which is fixedly connected to a drive shaft 20 used for filling. The drum base 12 further has drum bottom openings 14. Within the drum 10, a metal filter 16 is arranged. Between the metal filter 16 and the drum shell 11 is an annular space 18, in which the drum bottom openings 14 open. The annular space 18 is divided in the illustrated embodiment into twelve sections, each having a trained as a slot drum bottom opening 14.

Within the filter 16 is the working area 60 in which the product is processed, ie centrifuged and dried, will. Opposite the drum base 12 of the work area 60 is closed by a baffle plate 40, which can be opened. When the baffle plate 40 is open, the product can be transferred from the working space 60 into the area 80 and removed.

Furthermore, a drain 52, through which the liquid phase of the product can flow, and an outlet 54 are provided, through which gases introduced into the working area can escape.

FIG. 2 shows a schematic frontal view of the drum 10. The direction of rotation of the drum 10 is in the present example in the clockwise direction. The vertex 70 of the drum 10 as well as a first weft nozzle 31 and a second weft nozzle 32 are also shown. The first weft nozzle 31 is in the so-called 6 o'clock position and the second weft nozzle 32 is in the so-called 7 o'clock position , The first firing nozzle 31 is offset from the second firing nozzle 32 by about 30 °. Furthermore, further firing nozzles may be provided, such as the third firing nozzle 33, which is located at the eleven o'clock position. The firing nozzles inject a suitable fluid, which is preferably gaseous, into the working area 60 through the drum bottom openings formed as elongated holes 90 through the annular space 18 and the filter 16.

As further prerequisites, the centrifugal dryer used should have a single-motor concept as a drive. This makes it possible to continuously approach all speeds between a standstill and a maximum speed of the drum. This is important in that conventional centrifugal dryers often use a twin-engine concept that includes a main and a geared motor. These are connected via a centrifugal clutch, However, only fully opens at a speed of about 160 revolutions per minute. The gear motor itself runs only up to 5 revolutions per minute. However, since the speed range between 0 and 150 revolutions per minute is currently used in the method according to the invention, this twin-engine concept is not suitable for the present method.

Furthermore, the centrifugal dryer on which the process according to the invention is carried out should have a suitable control system. In particular, the centrifuge dryer must be able to control the injections through the shot nozzles 30 in the millisecond range. The position of the drum 10 must be able to be detected in the minute range (based on the angular position). For this purpose, in particular a play-free and rigid coupling between the drive shaft 20 and the motor is necessary. By a single engine concept, this can be suitably provided.

FIG. 3 shows the grain size spectrum of a typical product that can be processed by the method according to the invention. As FIG. 3 shows, the product has a fines content of about 20%. About 20% of the product has a grain size of 10 μm or less. However, the product shown is not to be considered as limiting the use of the method of the invention. Rather, the method of the invention provides improved centrifugation and drying in all types of products.

In carrying out the method according to the invention, a product suspension is first introduced into the working area 60 in a first step of filling through the drive shaft 20 designed as a filling shaft. The drum 10 rotates continuously during filling. The speed of the drum is chosen so that the forces in Radial direction are so high that forms a ring of the product suspension on the filter 16.

Already during filling, a suitable fluid can be injected into the working space by means of the general shot nozzles designated 30. The shot nozzles 30 are moved close to the drum base, so that there is only a minimal gap between the nozzle head 38 and the drum base 12. It should be noted that the firing nozzles 30 are always fixed while the drum 10 is rotating. In order to be able to move the firing nozzles 30 as desired to the drum base 12, the firing nozzles can be made axially movable. A feed duct 34 is surrounded by a bellows 36 and the firing nozzles 30 can be moved axially by means of a suitable device.

Under a suitable fluid is basically to understand such a fluid that does not cause any chemical reactions in the product and does not damage the product in any other way. The fluid used is usually gaseous.

The firing nozzles 30 initially inject the fluid through the elongated holes in the annular space 18, from which the fluid moves through the filter 16 into the working space 60. The fluid exits the working space 60 at another location in the opposite direction again through the filter 16 and escapes through the drum bottom openings 14 and the outlet 54th

A first nozzle 31 and a second nozzle 32 inject during a first revolution in the same slot 14 'a. During the next drum revolution they inject the fluid into the next, ie offset by one, slot 14 ", etc. This ensures that the product over the entire Drum circumference is whirled up. The whirling up thus always takes place when the corresponding drum section passes the range between 6 and 7 o'clock.

During filling, an initially thin, solid-state ring forms on the filter. Inside this ring is a suspension consisting of the liquid fraction and the remaining solids, continuously adding suspension to a maximum. However, due to the low viscosity of the liquid portion and the associated poor transmission of shear forces in the suspension, the suspension can not build up into a stable ring. The suspension thereby forms a suspension lake within the solid ring. However, the shear forces are large enough that forms an approximately 1 mm thin suspension layer on the inside of the solid ring.

Due to the fluidization of the suspension lake due to the rotation of the drum, however, a sedimentation of the suspension and a separation of the product components with larger particle sizes from the fines during the filling is prevented in the inventive method.

Furthermore, by increasing the porosity of the solid ring due to the injection of fluid by means of the firing nozzles and the resulting rapid filtration of the liquid, a sedimentation of the solids content in the approximately 1 mm thin suspension ring is prevented.

Once the entire amount of suspension has been filled, the filling step is then transferred to the centrifuging step. The drum 10 rotates at a suitable speed during centrifuging, at a drum diameter of 400 mm, for example 150 rpm, or so fast that 5 g act on the cake, and the suspension is constantly loosened up by the injection of fluid by means of the firing nozzles 30. This prevents the smaller particle size of the product from being trapped between the larger particle size portions of the product and clogging the capillaries needed to complete the liquid phase. Also, the filter itself is not clogged by the fine product components, since it is regularly flowed through in the opposite direction of the fluid gas.

Of course, for less problematic products which do not clog quickly and can also be centrifuged in a conventional manner, it is also possible to carry out the filling and centrifuging step in the manner known hitherto and only during drying with the permanent injection of a suitable one according to the invention gaseous fluid to begin. For example, the filling and centrifuging at a drum speed of 500 rev / min. or with a radial acceleration of 55 g, and only to dry the drum speed to 150 U / min. be lowered.

The centrifuging step blends into the step of drying. The rotational speed of the drum 10 is about 150 rpm with a drum diameter of 400 mm during drying. The annular structure of the product cake is retained and the product cake does not collapse. The firing nozzles 30 now inject a hot drying gas into the working space 60. As already described, the hot drying gas must penetrate the product cake twice. As a result, a particularly high drying efficiency is achieved. In addition, the product cake is dried evenly from two sides. By constantly loosening the product cake over the In addition, there is no clumping of the product due to the entire circumference and the stationary maintenance of the ring shape of the product cake. By maintaining an annular cake throughout the drying process, the product itself acts as an additional filter which prevents the fines of the product from escaping through the filter 16.

In addition, hot drying gas can also be introduced into the working chamber 60 through the drive shaft 20. This can additionally increase the drying speed of the product. By preventing drying cracks in the product by the continuous loosening, the drying gas in the working space 60 can not easily escape through the drying cracks, but completely passes through the product, thereby further increasing the drying efficiency.

After the product has been dried as desired, the step of drying is followed by a homogenization step. The drum speed is lowered in a drum with a diameter of 400 mm from 150 U / min to about 50 to 80 U / min or to a radial acceleration of less than 1 g. The product cake now collapses. The product now has the form of a fine powder which collects at the bottom of the drum 10 and is entrained by the drum 10 in the direction of the apex 70 of the drum 10. However, before reaching the apex 70, the product trickles down again in the direction of the low point of the drum 10. In this way mixing and homogenisation of the product is achieved, whereby after a short time the different grain sizes and residual moisture content are distributed evenly throughout the product. In addition, by the shot nozzles 30, in turn, a gas can be injected into the working space 60, in addition to the product loosen. However, this is not absolutely necessary during the homogenization step.

Following the homogenization step, the dried product can be removed as a fine powder.

It should again be noted that the above speeds are to be understood merely as an example of a centrifugal dryer with a drum diameter of 400 mm. For other drum diameters, other speeds must be selected which produce the same effects. In particular, the speed during drying should be chosen so that the ring shape of the product cake is always maintained.

By means of the method according to the invention described above, economically meaningful centrifuging and drying of products prone to clumping becomes possible in the first place. In contrast to conventional methods, which have produced in such problematic products only a sludge consisting of sludge with a high liquid content, a dry fine powder can be obtained by the inventive method.

Moreover, the process according to the invention provides a shorter drying time for all types of products, ie also for those products which hitherto were considered to be non-problematic, due to the higher porosity of the product during processing. The inventive method is thus not on the example. In FIG. 3 but can advantageously be applied to all types of chemical and pharmaceutical products, as well as food and all kinds of centrifuges.

Claims (6)

Method for operating a centrifuge with a drive shaft (20) used for filling, a drum (10) adjoining the drive shaft and having a drum shell (11) and a drum base (12), a filter (16) with one inside the drum Filter located working area (60), between the filter (16) and the drum shell (11) formed annular space (18), at least one in the drum base (12) formed drum bottom opening (14) which opens into the annular space (18), and at least one firing nozzle (30, 31, 32, 33) arranged to inject a fluid through the at least one drum bottom opening (14) into the annulus (18), comprising the following step: - Centrifuging a suspension of a product, wherein during centrifugation, a fluid is injected by means of at least one firing nozzle (30, 31, 32, 33) through the annular space (18) in the working area (60). The method of claim 1, wherein during centrifugation, the drum (10) rotates at a speed dependent on a diameter of the drum (10) which results in a similar acceleration of the product in the radial direction, such as a speed of about 150 revolutions per minute at a diameter of the drum (10) of about 400 mm. The method of claim 1 wherein the drum (10) rotates at a speed during centrifuging causes a radial acceleration in the product cake about in a range of 1 to 10 g. A method according to any one of claims 1 to 3, wherein during filling the drum (10) rotates at a speed dependent on a diameter of the drum (10) which causes a similar acceleration of the product in the radial direction as a speed of about 150 revolutions per minute with a diameter of the drum (10) of about 400 mm. Method according to one of claims 1 to 3, wherein the drum (10) rotates during filling at a speed which causes a radial acceleration in the product cake in a range of about 1 to 10 g. A method according to claim 3 or 5, wherein the acceleration caused is 5 g.

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