EP1228807B1 - Device and method for scraping a solid cake out of a centrifuge drum - Google Patents

Description

The invention relates to a device for peeling a solids cake from a centrifuge drum according to the preamble of patent claim 1 and to a method according to the preamble of patent claim 10.

In the case of modern batch filter centrifuges, the process sequence in the centrifuge is divided into the following steps: filling, washing the filter cake, spin-drying the filter cake and the automatic discharge of the filter cake.

In the horizontally as well as vertically mounted peeler centrifuges, the solids discharge takes place in that a paring knife, which is arranged on a so-called scraper, moves into the centrifuge drum, peels off the filter cake and in that the filter cake is conveyed out of the centrifuge by a discharge element. In the simplest case of vertical centrifuges this Austragsorgan consists of holes in the drum base and a so-called. Schurre (steep sliding surface) in the bottom of the centrifuge housing. The solids discharge can only be done at low speed, as at high speed, the solid would not fall through the holes in the drum base and in the chute. In the horizontal peeler centrifuges, the solid after the reamer by a chute or a Schneckenaustrag immediately behind the actual reamer, detected within the centrifuge drum and discharged from the centrifuge. This embodiment has the advantage that the centrifuge can carry out the solids even at high speeds, whereby no time losses arise for a speed change between the spin speed and the discharge speed.

• Die Verlegung des Räumers, so daß der Feststoffaustrag nicht mehr funktioniert. Wenn Teile des angelagerten Feststoffes, der ja normalerweise pulverförmig aus der Maschine ausgetragen wird, sich wieder vom Räumer lösen, gelangen.diese als Klumpen (Agglomerationen von pulverförmigem Feststoff) in den Austragsstrom und können dort den Transportprozeß stören oder die nachfolgenden Verarbeitungsschritte des Feststoffes beeinträchtigen.
• Die Ablagerungen auf dem Räumer führen zwangsläufig zu einer gewissen Übertragungs-Kontamination zwischen den einzelnen Zentrifugenchargen, was bei der Verarbeitung von hochreinen Produkten unerwünscht oder sogar unzulässig ist.
• Bei der Verarbeitung von hochreinen Produkten ist es heute üblich, daß die Produktionsanlagen zwischen den einzelnen Produkterzeugungschargen vollständig gereinigt werden. Diese Reinigung wird in einem automatischen Prozeß durchgeführt und muß reproduzierbar gute Ergebnisse aufweisen. Dies ist insbesondere dann erforderlich, wenn die Anlagen für eine sog. Multipurpose-Produktion, also die Produktion verschiedenster Substanzen vorgesehen ist. Die Ablagerungen auf den Räumern erschweren die automatische und wiederholgenaue Reinigung der Zentrifuge bzw. machen diesen automatischen Schritt unsicher bzw. unmöglich.

All known discharge systems have a common problem, which is that both coarse-grained, crystalline solids with relatively low residual moisture and low Anlagstendenz must be discharged to surfaces, depending on the application but also solids, the very fine, non-crystalline, thereby partially moist, sticky and have a tendency to stick to solids. Both at low speeds of the centrifuge, during the discharge of the solid, but with a significant upward trend at higher speeds of the centrifuge during the discharge process, there is a tendency that the peeled off from the drum solids adhere to the surface of contact with parts of the reamer, thus An increasing product build-up takes place on the clearing and discharge organs. These product deposits on the reamer have several disadvantages. These are in the following:

• The laying of the reamer, so that the solids discharge no longer works. If parts of the deposited solid, which is normally discharged in powder form from the machine, come off the reamer, they arrive as lumps (agglomerations of powdery solid) in the discharge stream and can interfere with the transport process or interfere with the subsequent processing steps of the solid.
• The deposits on the scraper inevitably lead to a certain transmission contamination between the individual centrifuge batches, which is undesirable or even inadmissible in the processing of high-purity products.
• In the processing of high-purity products, it is common today that the production plants are completely cleaned between the individual product production batches. This cleaning is done in an automatic Process performed and must reproducibly have good results. This is particularly necessary if the facilities for a so-called. Multipurpose production, ie the production of various substances is provided. The deposits on the scrapers complicate the automatic and repeatable cleaning of the centrifuge or make this automatic step unsafe or impossible.

There have hitherto been proposed various ways of avoiding deposits on the reamer.

The most commonly used method is to coat the surface with a substance which has a low adhesion tendency to the solids, or to mass-produce scrapers from such materials. However, many of these coatings have a much lower resistance to corrosion compared to the highly resistant base material of the centrifuge (stainless steel, nickel-based materials, titanium, etc.), so that they have to be renewed after a relatively short operating time. If the coating has too low or high solubility against the suspension, washing or cleaning fluid, it has too short a service life or can lead to contamination of the products to be processed. The coatings are highly dependent on the solid to be processed, so that the same base materials different coating materials must be used. Finally, the coatings usually consist of plastics which have a lower abrasion resistance, which contributes to a shorter service life and to the problem of contamination.

In contrast, the scraper can be designed as a suction nozzle, wherein the suction nozzle opens into a pipe system that leads from the centrifuge. From the centrifuge, a gas stream is sucked through the suction nozzle, wherein the extracted gas can flow into the housing, either via suitable openings or via a suitable gas supply. In operation, the precipitated solid is entrained by the gas flow and discharged through the piping system from the centrifuge. Such a system is known from DE 33 40 636 C2. This system requires a relatively high gas flow and accordingly requires a high expenditure on equipment. Furthermore, the solids must be separated again from the gas stream, which further increases the expenditure on equipment. Problems also arise, inter alia, in that residual moisture enters the gas stream and must be deposited accordingly, and certain solvents can produce explosive gas mixtures, so that the system must be operated with inert gases. Finally, it should be noted that due to rapid gas flows, the solids may impinge on surfaces in the region of the suction opening and thereby increase the problem of deposits.

Furthermore, screws can also be used as discharge elements, in particular in the case of relatively sticky or viscous solids. However, slugs are relatively difficult to clean and do not meet the cleaning requirements of, for example, the pharmaceutical industry. Therefore, the use of screws for the separation of high purity products is undesirable.

There are devices are known which are designed so that the surface of the reamer, which can be routed through the stream of solids, are swept by a discharge, such as a worm, so that the solid can not permanently build on the reamer. Again, the same problems arise as with snails.

Devices and methods according to the preamble of claim 1 and the preamble of claim 10, respectively, are known from Patents Abstract of Japan, Issue 1998 No. 12, Oct. 31, 1998 & JP 10180143A and FR 663036A. In these devices, a gas stream is directed to a base layer which remains on the filter after peeling the solid to remove this base layer.

Devices in which the discharge of solids from the centrifuge drum is assisted by compressed air are known from GB 768782A and FR 1247364A.

Accordingly, the invention has for its object to provide a device for peeling solids cake from a centrifuge drum and a corresponding method, are effectively avoided in the deposition of solids on the reamer.

The solution of this object is achieved by a device according to the features of claim 1 or by a method according to claim 9; the dependent claims relate to advantageous developments of the invention.

According to the invention, a paring knife device, the so-called scraper, has a gas supply and at least one gas outlet opening which is arranged so that an outgoing gas stream is formed at least in a part of the surface area of the paring knife device. In particular, air or inert gases are used as the gas.

In particular, in the area of the peeling knife, an air or gas stream is introduced in such a way that there is a uniform overflow of those surfaces of the reamer over which the precipitated solid slides and on which there is a tendency for caking. This function is achieved by generating the gas flow between the stream of powdered solid and the reamer surfaces. By this gas flow is achieved that the solid particles are kept so to speak by an air cushion at a distance from the surface of the reamer.

Not only the contact and thus a reduction in the speed of the particles is avoided, which reduces the risk of collision among the individual particles in the flow of solids. The risk that a collision of particles leads to the agglomeration of the solid particles to larger structures, which in turn in contact with the surface, by their higher energy content, could lead to deposits, is excluded.

The introduction of the gas stream may e.g. by a corresponding shaping of the paring knife, by means of which a gas flow applied centrally via a pipe system (or bore system) centrally behind the paring knife is evenly distributed over the region in which the solids flow takes place. Depending on the design of the distribution channel and depending on the design of the fluid outlet or gas nozzle, the gas stream can ideally be abandoned in the flow direction of the solids flow. It is also conceivable to adjust the gas flow at a different angle, e.g. 45 °, perpendicular or even to let escape against the flow of solids, wherein the gas flow is deflected by the flow of solids and thus the sliding over the surfaces of the reamer gas cushion is formed.

The nozzles for discharging the gas stream may e.g. can be formed by two components, such as the reamer and the paring knife, but can also be formed by the corresponding design of slots or holes in a component such as the paring knife, the reamer or a separate component.

It is also irrelevant whether the gas flow through a single nozzle, through multiple nozzles in a line or through a nozzle-provided surface (for example, hole slot plate) is abandoned. Furthermore, the gas stream can be abandoned once in the reamer, or distributed on the Räumerrand on Austragsorgan.

It is only essential that a device is arranged so that, together with the product stream, a gas stream is formed, which forms between the solids flow and the relevant wall of the reamer. It is also conceivable that the gas stream abandoned before the reamer and through the solid stream is blown or is also abandoned behind the reamer and can be formed by devices and / or the driving style of the reamer accordingly. It is conceivable the task of gas flow behind the reamer, wherein the reamer is designed as a serrated knife or corrugated and are formed by an axial movement of the pink knife despite the peeling process between the product and spikes / column, which allow the passage of the gas stream. Also conceivable is a task of the gas flow behind the paring knife, wherein the paring knife is controlled in such a way that short-term Anschälvorgänge alternate with short-term lifting operations of the scraper of the filter cake surface. As a result, a pulsating flow of solids and a pulsating gas flow is generated. Due to the different speeds of the gas flow and the solids flow, however, the system of the gas stream sliding over the reamer surface can be generated with the solids flow passing over it in a sufficient manner.

By the new design, a contact of the solid particles with the relevant surfaces of the reamer is sufficiently prevented, so that a solid deposit can no longer take place.

The proposed design is independent of the centrifuge and scraper materials used, regardless of the product and solvent to be processed, and largely independent of the scraper's geometric design.

Fig. 1

eine schematische Darstellung der erfindungsgemäßen Vorrichtung mit verschiedenen Positionen des Räumers,

Fig. 2

eine Detaildarstellung der Fig. 1.

An embodiment of the invention will be explained with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of the device according to the invention with different positions of the reamer,

Fig. 2

a detailed representation of Fig. 1st

Fig. 1 shows schematically in side view (axial view) a centrifuge drum 1, wherein on the inside of the drum wall, a filter means 11 is provided.

Inside the centrifuge drum 1 a peeling knife device with a strut 21, a knife holder 5 and a paring knife 3 is arranged, the device between a position A, in which the paring knife is removed from the wall of the drum 1, and in a position C, in the peeling blade 3 is located in the region of the drum shell 1, is pivotable. Preferably, the paring knife 3 extends axially along the entire inside length of the drum. It may also be shorter, the reamer should be axially movable.

In operation of the centrifuge, the peeling knife device is in the position A, the drum is rotated, and on the drum inner side of the filter means 11 side facing a solid cake 13 is formed.

When the solid cake 13 has reached a predetermined thickness, with the drum rotating, the paring knife is moved toward the solids cake and peels solids 15 from the solid cake. The solids 15 fall due to gravity in a arranged below the paring knife discharge (Schurre) and are discharged from there to the outside.

In that regard, the structure shown corresponds to conventional constructions, and since otherwise the construction of peeler centrifuges is known to those of ordinary skill in the art, a detailed explanation is omitted here.

Details of the embodiment according to the invention can be seen in particular from FIG. As FIG. 2 shows, holds the blade carrier 5 at its the peeled solids 15 side facing away from a gas connection, which is via channels (not shown) with a gas outlet nozzle 9 at the peeled solids facing side of the blade carrier 5 in combination. The gas outlet nozzle is designed such that it passes the gas supplied via the gas connection 7 as a gas stream over the surface of the knife carrier 5. By this gas flow, which is indicated by the arrows, a gas cushion between the peeled solids 15 and the surface of the blade carrier is formed, so that the peeled solids 15 can not attach to the surface of the blade carrier. Preferably, the gas outlet nozzle 9 is formed as a slot which extends over the entire width of the peeling knife 9.

In the illustrated embodiment, the gas outlet nozzle 9 is located between the paring knife 3 and the knife carrier 5. However, it may also be provided in the paring knife 3, and also several nozzles may be provided along the path of the peeled solids 15 along the knife carrier.

In particular, compressed air is used as the gas, and depending on the purpose of use, other gases, for example inert gases, can also be used.

Although the invention has been explained with reference to a filter centrifuge, but it is generally applicable to peeler centrifuges as sedimentation centrifuges.

Claims (15)

1. An apparatus for scraping a solid cake from the inner wall of a centrifuge drum (1), with a scraping blade device (3,5,21), wherein the scraping blade device (3,5,21) has a scraping blade (3), a blade carrier (5), a gas supply (7) and at least one gas-outlet opening (9), characterised in that the gas-outlet opening (9) is so arranged on the blade carrier that a gas flow emerging from the gas-outlet opening forms a gas cushion between the scraped-off solids and at least one part of the surface region of the scraping blade device (3,5,21).
2. An apparatus according to Claim 1, characterised in that the gas flow is directed parallel or non-parallel to the discharge direction of the scraped off solids.
3. An apparatus according to Claim 1, characterised in that the gas flow is directed at an angle of between 0° and 180° to the discharge direction of the solids.
4. An apparatus according to any one of Claims 1 to 3, characterised in that a gas-outlet opening (9) is provided on the scraping blade.
5. An apparatus according to any one of Claims 1 to 4, characterised in that the gas-outlet opening takes the form of a single nozzle, as a nozzle assembly comprising a plurality of linearly arranged nozzles or as a slotted nozzle assembly.
6. An apparatus according to any one of Claims 1 to 4, characterised in that the gas-outlet opening is provided on the side of the scraping blade device (3,5) remote from the discharge side and the scraping blade device has gas-flow openings.
7. An apparatus according to Claim 6, characterised in that the gas-flow openings are formed by serrations of a scraping blade (3).
8. A scraping centrifuge with an apparatus according to any one of Claims 1 to 7.
9. A method of scraping a solid cake from the inner wall of a centrifuge drum (1), wherein using a scraping blade device solids are scraped off from a solid cake and the scraped-off solids are discharged, wherein the scraping blade device has a scraping blade (3) and a blade carrier (5), characterised in that a gas cushion of flowing gas is created between the scraped-off solids (15) and at least one part of the surface of the scraping blade device facing the scraped-off solids, wherein the gas is fed via a gas-outlet opening on the blade carrier (5).
10. A method according to Claim 9, characterised in that the gas is directed directly on to the surface of the scraping blade device.
11. A method according to Claim 10, characterised in that the gas is introduced between the solid cake (13) and the scraping blade device.
12. A method according to Claim 11, characterised in that the gas is directed through gas-flow openings in the scraping blade device.
13. A method according to Claim 11, characterised in that periodically the solid cake is separated from the scraping blade device so that a pulsating gas flow is created between the scraped-off solids and the scraping blade device.
14. A method according to Claim 9, characterised in that a nozzle is formed behind the scraping blade or by the scraping blade so that a uniform gas flow is formed over the entire length of that part of the scraping blade device which adjoins the scraping blade in the production direction.
15. A method according to Claim 14, characterised in that the nozzle is formed to receive the gas flow from the scraping blade and from the blade carrier.

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