EP2497565A1 - Mixing silo - Google Patents

Abstract

The mixing silo (8) has a cylindrical container with a conical outlet. Multiple vertically arranged separating walls, a central middle tube running in the direction of cylinder longitudinal axis and a silo wall are connected with each other such that multiple chambers (7) are formed, which are separated from each other and are filled with granules. The emptying openings of the individual silo chambers open into the cone of the silo, and the emptying openings are not lockable.

Description

The invention relates to a mixed silo for free-flowing finely divided solids, in particular for powdery, fibrous and / or granular mix, in particular plastic granules, especially suitable for mixing plastic granules, with excellent mixing quality with simultaneous simplified and improved washability to avoid cross-contamination. In particular, the subject of the invention is a mixed silo for the homogenization of optionally inhomogeneous polymer granulate batches in the form of a product stream from a polymer granulate production.

In this mixing process additional fine abrasion should be avoided as far as possible and no foreign contamination may result from granule residues from previous mixing and filling processes of other types of granulate in the silo.

The resulting in the production of thermoplastics in the reactor granular product is plasticized in an extruder and formed in a granulation into single strands, which are cut by means of a rotating knife in the granulator to granules. In a further step, this product can be compounded with other components.

Compounding in polymer processing is the preparation of the finished plastics molding compound, the compound, from the plastic raw materials with the addition of fillers and reinforcing agents, plasticizers, adhesion promoters, lubricants, stabilizers, etc. The compounding takes place predominantly in extruders and comprises the processing operations conveying , Melting, dispersing, mixing, degassing and pressure build-up.

In the granulation, the melt is then pressed through the openings of a nozzle plate, so that in the case of strand pelletizing first melt strands are produced, which then result in the granulation cylinder granules or cut in the case of Kopfgranulierung directly at the exit to the nozzle plate and then lenses - or spherical granules result. The granulation can be carried out, for example, in a liquid stream which cools the granules and largely avoids agglomeration. Subsequently, the granules are dried and sieved to deposit agglomerates formed despite cooling.

Following granulation after production or after compounding, the product is usually conveyed pneumatically to a mixing silo.

The granules are homogenized in the mixing silo to compensate for fluctuations in the manufacturing process and optionally subsequently transported pneumatically into the storage silos.

The mixing silos known from the prior art are generally operated as a gravity mixer or Umwälzmischer. For both types, there are numerous proposals in the prior art to achieve by appropriate installations in the silo container even with a single pass of the bulk material high mixing quality, ie a good homogenization of different and usually successively filled in the silo container bulk materials, or - in the case of Recirculating mixers - to keep the number of revolutions and thus the mixing time short.

Depending on the requirements and design, an acceptable quality of mixing is thus already achieved at maturity. The DE 41 12 884 C2 gives in the background description a comprehensive overview of the prior art, which is based essentially on the installation of funnel-shaped internals in the cone area of the mixing silo.

A disadvantage of the subject of the DE 41 12 884 C2 However, that is necessary to use in the bottom area of a silo a separate, multi-bladed funnel, which significantly increases the production cost and maintenance of the mixing silo, since such a structure is very difficult to clean.

Another solution is the so-called pipe mixers, where vertical pipes with siphoning openings in the silo lead from different heights granules to the outlet. For example, multiple-pipe blenders are used, in which the pipe channels are arranged on the inner wall to the cone area and reach a degree of mixing in pure leakage. A disadvantage is the construction-related corresponding effort for cleaning with water to avoid contamination.

The aim of all versions is to achieve an acceptable mixing quality with the lowest installation and operating costs and the simplest cleaning effort.

Subjecting the prior art to a subsequent analysis reveals those strengths and weaknesses that have been well documented in the literature.

For example, the show DE 12 98 511 and the EP 60 046 A1 each a mixed silo, whose interior is divided by radially extending from the container outer wall to its central axis, vertical plate segments in several chambers, which successively fill due to correspondingly stepped upper edges of the sheet segments in a suitable position of the filling opening according to the overflow principle, which often one - however batch size dependent - vertical premix instead of the otherwise occurring purely horizontal stratification is achieved.

Disadvantage of DE 41 12 884 C2 , of the DE 12 98 511 and the EP 60 046 A1 but is that the inlet and outlet cross sections of the mixing cross are each formed approximately equal and thus only one limited mixing of the bulk material can be done at the same time poor cleaning options to avoid cross-contamination.

Furthermore, from the DE 22 19 397 already known as Umwälzmischer Mischsilo known in which the central riser is surrounded by another, contrast, much shorter tube, so that this further tube with the central tube defines a first annulus and the silo tank wall or its conical bottom a second annulus. During recirculation or bulk material removal, different settling velocities of the bulk material set in the two annular spaces, so that bulk material fractions originating from different height levels in the outlet area are blended or mixed with one another. On a similar principle is also based on the DE 30 29 393 A1 known gravity Umwälzmischer in which the circulation is not made via a center tube but via a running outside of the silo tank, vertical riser.

DE 21 58 579 A1 describes a device for the continuous mixing of granular bulk material, the construction of which, however, in particular by the existing fittings (separately controllable metering devices) within the silo and through the partially filled hopper causes a cross-contamination during product change. In addition, the handling of such a device is much more difficult. Similar devices are in JP 56 111028 A and JP 59 053836 U discloses, in which the individual chambers are also lockable and the device causes a construction-related in operation cross-contamination.

All these known mixing silos have the disadvantage that the internals provided in the silo container are exposed to considerable static and dynamic loads. Although the known mixing silos without exception are designed for mass flow conditions, there are also bulk material deposits which make it much more difficult to wash out the silo container. The requirement for easy leaching of the silo container before filling with another type of bulk material, however, is increasingly asked.

It was therefore an object to provide a silo, with the help of which largely homogeneous mixtures of polymer granules can be produced, which are obtained in the form of an optionally inhomogeneous polymer granulate product stream. Moreover, the mixing process in such a silo must as far as possible cause the generation of very fine particles, by the mixing process itself, such as e.g. Avoid abrasion or granule fragments.

1. i. eine Mehrzahl von senkrecht angeordneten Trennwänden, ein zentrales, in Richtung der Zylinderlängsachse verlaufende Mittelrohr und die Silowand mit einander verbinden, so dass mehrere von einander getrennte Kammern entstehen, die jeweils von oben mit Granulat befüllbar sind und am unteren konischen Ende des Silos jeweils eine Öffnung zur Entnahme des Granulats aufweisen, und zwar der Gestalt, dass alle Entleerungsöffnungen der einzelnen Silokammern in den Konus des Silos einmünden und die Entleerungsöffnungen gegebenenfalls nicht absperrbar sind;
2. ii. eine Vorrichtung mit der Möglichkeit zur beliebigen Verteilung des in das Silo eingeführten Granulats in alle Zylinderkammern des Silos; und gegebenenfalls
3. iii. eine oder mehrere gegebenenfalls flexibel bzw. automatisiert teleskopierbar zu positionierende, bevorzugt aber fest angeordnete Vorrichtungen zur Spülung aller Bereiche des Silo-Innenraums mit Flüssigkeit zur Entfernung von Produktresten aus dem Silo.
4. iv. eine Totraum-freie Silokonstruktion, die insbesondere die Siloeinbauten sowie sämtliche Stutzen, Konen und Flansche betreffen

A further object of the invention was to provide a silo which, after completion of the emptying operation, is substantially free of residual quantities of the granules previously conveyed therein. The inventive task has been solved by providing a cylindrical vertical mixing silo comprising a cylindrical container with a conical outlet, characterized by the following features:

1. i. a plurality of vertically arranged partition walls, a central, running in the direction of the cylinder longitudinal axis central tube and the silo wall with each other, so that a plurality of separate chambers arise, each of which can be filled from above with granules and the lower conical end of the silo each having an opening have to remove the granules, namely the shape that all discharge openings of the individual silo chambers open into the cone of the silo and the emptying openings may not be shut off;
2. ii. a device with the possibility of arbitrary distribution of the introduced into the silo granules in all cylinder chambers of the silo; and optionally
3. iii. one or more optionally flexible or automated telescopically positioned, but preferably fixedly arranged devices for flushing all areas of the silo interior with liquid for removing product residues from the silo.
4. iv. a dead space-free silo construction, which particularly affect the silo installations as well as all nozzles, cones and flanges

This method according to the invention makes it possible, as compared with a method known from the prior art, to largely avoid the production of ultrafine particles with uniformly good or even improved homogenization. Furthermore, the use of a device for rinsing the mixing silo makes it easy and safe to clean any granules and dust residues still present in the silo, so that contamination with subsequent granulate batches can be ruled out with certainty.

The method can be used both for homogenizing granules whose divergence is caused for example by the polymer granulate product stream due to the smallest fluctuations in the upstream process, as well as for the homogenization of various product granules (eg, blends).

Preferred polymer granules are polycarbonate granules of a homopolycarbonate or a copolycarbonate, in pure form or as a mixture with other components. The polycarbonates may contain conventional additives as additional components, such as mold release agents, flow aids, heat stabilizers, UV and / or IR absorbers, flame retardants, dyes and fillers, and other polymers.

The polycarbonate granules can also be added to the conventional additives for these thermoplastics additives such as fillers, UV stabilizers, IR stabilizers, heat stabilizers, antistatic agents and pigments, colorants; if appropriate, the demolding behavior, the flow behavior, and / or the flame retardancy can be improved by adding external mold release agents, flow agents, and / or flame retardants (eg, alkyl and aryl phosphites, phosphates, phosphanes, low molecular weight carboxylic acid esters, halogen compounds, salts , Chalk, quartz powder, glass and carbon fibers, pigments and combinations thereof. Such compounds are described, for example, in US Pat WO 99/55772 , Pp. 15-25, and in " Plastics Additives ", R. Gächter and H. Müller, Hanser Publishers 1983 , described).

The mixed silo according to the invention must contain at least 2 chambers, but preferably more than 2 chambers, more preferably 6 chambers. These chambers may have different sizes, but preferably they should be the same size and also have the same height in the mixing silo. The chambers are open within the silo at their upper and lower ends over the entire cross section. The respective lower ends of the chambers are adapted to the design of the conically narrowing silo and may optionally be individually lockable. In the lowest point of the cone-shaped silo, into which all chambers open, a mixing space (1) is created in which the simultaneous confluence of all partial flows from all the filled chambers produces the homogenized polymer-granulate mixture which can be transferred from there to other storage or filling stations. Devices is transported. The mixing chamber (1) can be shut off from the granulate removal line (2) through a fitting (3) so that defined granulate quantities can be stacked in the silo. The partitions that form the silo chambers and extend from the central center tube to the silo inner wall may be formed straight or curved, preferred are curved partitions, such as in Fig. 1 , shown. The partitions are designed so that no acute angle between adjacent chamber walls arise, so that deposits of polymer granules can be avoided in these areas. Such acute angles between adjacent chamber walls may be achieved by attaching additional segments (4) as shown in FIG Fig. 1 , be bypassed shown. Throughout the granulate-conducting silo interior, the formation of so-called undercuts or gaps or joints of any kind is optionally deliberately avoided by constructive measures to exclude deposits of granular residues at these sites (dead space-free construction). This applies in particular to the connecting flange (1a) of the removable silo discharge cone (mixing chamber 1). In this way, it is ensured that in the treatment of subsequent different types of granulate lots in this mixed silo contamination with product residues from previous granulate lots, which were mixed in this mixed silo, is avoided with certainty. The risk of such cross-contamination is also prevented in a preferred embodiment by rinsing, for example with water, preferably with deionized water, after completion of the emptying of the mixing silo. Except water can other liquids can be used, singly or as a mixture. The mixed silo according to the invention is made of materials which have a sufficiently smooth surface and do not permit contamination of the polymer granules to be treated with foreign substances, such as, for example, abrasion. Suitable materials for this are, for example, plastic, aluminum alloys or steel, aluminum alloys and steel are preferably used, and the steel grades 1.4301, 1.4541 and 1.4571 are particularly preferred.

In a preferred embodiment, the emptying openings of the individual silo chambers can not be shut off in the cone of the silo.

In a further preferred embodiment, the mixing space (1) below the silo chambers up to the shut-off valve (3) has a volume of not more than 2%, preferably not more than 1%, more preferably not more than 0.5% and at least 0.1%, preferably at least 0, 2% of the total volume of the mixed silo. The total volume of the mixing silo in this context is the addition of the volume of all chambers (7) and the volume of the mixing chamber (1).

Homogenization of optionally inhomogeneous polymer granules, e.g. From a continuous granulate manufacturing process is carried out by filling the silo chambers with the granules and then draining the granules. This is done in such a way that the granule stream (5) entering the silo is conveyed by means of a mobile granule feeding device, such as e.g. a rotary tube distributor (6) in individual chambers (7) of the mixing silo (8) is introduced in defined amounts. It is important for the success of the homogenization, in granules whose inhomogeneity due to variations in the manufacturing process, important that a sufficiently large number of chambers is filled in the mixing silo, and that each filled into the chambers granules a minimum lower amount per filling cycle do not fall below the chamber. Filling cycle here means the time interval between the start and end of the granule filling a chamber before switching to the next chamber. At an extreme undershooting of such a minimum amount per filling cycle, such. in the case of a continuous rotation of the rotary tube distributor across all chambers, no adequate separation of the entire amount of polymer granules pending for homogenization into sufficiently large and possibly different granule subsets would be possible. Only by stacking sufficiently large quantities of granules with sufficiently different properties in several different chambers of the mixing silo can be sufficient homogenization in the silo discharge by the simultaneous and continuous outflow of granules from all chambers of the mixing silo and the continuous mixing of all these streams in the cone of the mixing silo be effected.

Regardless of the total number of chambers in the mixed silo, but at least 2, the number of chambers to be filled depends on the size of the polymer granulate batch to be homogenized and the size of the mixing silo. It must be filled at least 2 chambers with vorzugsweiser same amount of granules (volume or mass) to ensure approximately equal granular effluent at the lower ends of the chambers in the mixing space of the silo. Would remain due to an unsuitable filling of the silo chambers residues of granules in one or more chambers that could not be mixed with at least one additional partial flow from one of the silo chambers, the mixing quality of the entire lot would be impaired. If more than 2 chambers are present in the mixing silo, then preferably more than 2 mixing chambers of the mixing silo are filled, in particular 6 chambers of equal size are filled, each with almost the same high level, if this allows the size ratio of mixed silo to polymer granulate batch. For static reasons, in each case opposite silo chambers are preferably filled.

In a preferred embodiment, the silos are filled in the following manner: The silos stand on 4 load cells each, which are used in weighing modules as support frames. This is a continuous weight measurement of the silos is given. With the weight data, the product feed amounts can be controlled, i. the pneumatic conveyors are switched on or off and the rotary distributor is brought into the appropriate filling position.

The filling of the open-topped silo chambers is done in a further preferred embodiment by a granular distributor, which can distribute the preferably centrally introduced on the silo roof granulate specifically targeted to individual silo chambers in any way. For this purpose, in particular a granular distributor tube is suitable, as in Fig. 2 is shown and which is hereinafter called "rotary tube distributor". This rotary tube distributor is mounted centrally on the roof of the silo (9) and consists of a rotatable tube (10) of suitable length and suitable curvature, which can reach each silo chamber with the outlet device. The tube is preferably rotatably mounted in a holder (11) on the imaginary longitudinal axis of the cylindrical silo in the roof center and can be rotated to change or adjustment of the filling position, for example by a motor; this in turn can be controlled by suitable operating devices. The filling positions can be signaled by appropriate initiators on the silo chambers. The rotary tube is tightly connected via a suitable flange to the granulate feed line (12) on the roof (13) of the silo. The diameter of the rotary tube largely corresponds to that of the granule feed line. The entire construction, in particular in the area of the flange connection of the rotary tube, is free of undercuts or gaps in which residual quantities of granules could remain. Suitable materials for the production of the rotary tube are steel or aluminum alloys, preferred materials are steel, in particular stainless steel (1.4301, 1.4541, 1.4571).

The control of the various positions of the chambers in the mixing silo through the rotary distributor is preferably carried out by means known from the prior art initiators, which are arranged for each chamber in the rotary tube housing. As soon as the rotary tube reaches the initiator of the chamber to be approached with a switching flag after starting, the drive is switched off. The filling is preferably carried out in a 6-chamber mixing silo in the order chamber -1, -4, -2, -5, -3 and -6 (opposite chambers).

The granule mixing process is a purely gravimetric process, dispensing with additional granule-conveying processes, e.g. Pumping in circuits or mixing by pressure impulse turbulence. As a result, the additional formation of granular abrasion is largely avoided.

In a particularly preferred embodiment, the mixed silo according to the invention contains, as further constituent, one or more devices for rinsing all areas of the silo interior with water or another liquid, for removal of product residues still remaining from the silo, as in FIG Fig. 3 shown. This device is preferably installed on the silo roof (13) and designed so that all chambers of the silo, the rotary tube distributor and the interior of the silo roof can be sprayed with water with it. This flushing device is preferably a spherical spray head (14a) with a plurality of water nozzles, so that parts of the plant can be flushed with water in an environment of nearly 360 °. The draining water leaves the mixing silo through the shut-off valve (3) at the bottom of the mixing chamber (1) of the silo. The spray head can be rigid or rotatable and can sit on a fixed lance which projects into the space to be flushed. An alternative embodiment shows the Fig. 4 , Here, the spray ball (14b) is driven into the interior with a driven telescopic lance for the rinsing process. After the flushing process, the spray ball moves back and is sealed off, for example via a rotary flap (14c) to the interior, so that the spray ball is protected against product dusts, which may clog the water nozzles, if necessary.

The spray heads are rinsed in a preferred embodiment after the rinsing process with compressed air and dried. On the compressed air flushing can in the embodiment according to Fig. 4 (14b) are waived. The spray heads are preferably made of stainless steel, 1.4404, but may also consist of other metal alloys.

In a preferred embodiment, the rinsing process is an automated process with preferably 2 rinse sections. After the conveying process, the conveying switch is adjusted so that the inlet is blocked in the direction of the silo. Then the delivery line is flushed in the direction of the silo inlet. After completion of the first rinsing process, the silo is rinsed. For this purpose, the spray balls above the individual chambers and the spray balls in the region of the silo roof (Rotary tube manifold, manhole) acted upon with water. After completion of the flushing is blown with compressed air through the spray balls and dried.

Both rinsing processes are preferably monitored by a flow measurement. For a successful flush, the water flow rate must exceed a minimum limit.

If necessary, the silo interiors can be dried by air. Alternatively, a so-called dripping time can preferably be provided for drying, in which the shut-off valve (3) remains open, so that residual moisture can run off.

Fig.1.

ist ein Silo-Querschnitt und zeigt die Aufsicht von oben eines erfindungsgemäßes Mischsilo mit den Unterteilungen in einzelne Kammern.

Fig.2.

zeigt als Vorrichtung zur beliebigen Verteilung des in das Silo eingeführten Granulats in alle Zylinderkammern des Silos als Beispiel einen sog. Drehrohrverteiler.

Fig. 3

zeigt einen Längsschnitt durch ein erfindungsgemäßes Mischsilo mit einem am Dach des Silos befindlichen und flexibel zu positionierenden Spülkopf.

Fig. 4

zeigt den Silokopf mit den Spüleinrichtungen, insbesondere die beiden Betriebsstellungen der teleskopierbaren Lanze mit Sprühkugel

The following drawings illustrate the construction and the function of the mixing silo according to the invention and the apparatuses used therein:

Fig.1.

is a silo cross section and shows the top view of an inventive mixed silo with the subdivisions into individual chambers.

Fig.2.

shows as a device for arbitrary distribution of the introduced into the silo granules in all cylinder chambers of the silo as an example a so-called. Rotary tube distributor.

Fig. 3

shows a longitudinal section through an inventive silo with a located on the roof of the silo and flexible to be positioned flushing head.

Fig. 4

shows the silo head with the purging, in particular the two operating positions of the telescopic lance with spray ball

Claims (10)

Mixed silo containing a cylindrical container with conical outlet, characterized in that : i. a plurality of vertically arranged partition walls, a central, running in the direction of the cylinder longitudinal axis central tube and the silo wall with each other, so that a plurality of separate chambers (7) arise, which are each filled from above with granules and the lower conical end of the silo each having an opening for removal of the granules, namely the shape that all discharge openings of the individual silo chambers open into the cone of the silo and the emptying openings are not shut off; ii. a device with the possibility of arbitrary distribution of the introduced into the silo granules in all cylinder chambers of the silo (filling device (6)). Mixed silo according to claim 1, characterized in that one or more devices for flushing all areas of the silo interior with liquid for removing product residues from the silo is present. Mixed silo according to claim 2, characterized in that the devices for flushing all areas of the silo interior are fixed or flexible (telescopic) are arranged. Mixed silo according to one of claims 1 to 3, characterized in that the product-contacted areas are designed as dead space-free constructions Mixed silo according to one of claims 1 to 4, characterized in that the filling device of the rotary kiln type is distributor and is mounted centrally on the roof of the silo and consists of a rotatable tube of suitable length and suitable curvature. Mixed silo according to claim 5, characterized in that there are mounted initiators for determining the filling positions. Mixed silo according to one of claims 1 to 6, characterized in that the mixing chamber (1) below the silo chambers to the shut-off valve (3) has a volume of not more than 2% and at least 0.1% of the total volume of the mixing silo (addition of the volume of all chambers ( 7) and the volume of the mixing chamber (1)). Mixed silo according to claim 7, characterized in that the mixing space (1) below the silo chambers to the shut-off valve (3) has a volume of not more than 1% and at least 0.2% of the total volume of the mixing silo. Use of a mixed silo according to any one of claims 1 to 7, characterized in that polymer granules are filled into the silo chambers and then the granules are discharged. Use of a mixing silo according to claim 8, characterized in that after draining the granules, the mixing chambers are rinsed out.

Images