EP0454045B1 - Centrifugal drier - Google Patents

Description

The invention relates to a centrifuge dryer with a horizontally mounted drive shaft, a drum connected to it, a filter arranged inside the drum, which surrounds a work space that is conically enlarged from the connection side of the drive shaft, and an axially displaceable baffle plate that forms an end face of the work space. and with a centrifuge housing encapsulating a drum and baffle plate.

Filter centrifuges are used to mechanically separate solids from suspensions after chemical, biological or fermentative processes have expired. A centrifuge of the type described above, which is known from DE-A 30 42 948, contains in a cylindrical drum region a rotating push floor which is driven by axially oscillating movements by a push cylinder guided by the drum shaft. The suspension is distributed to the cylindrical drum area from a feed pipe that opens into the drum by means of a feed pot that rotates with the moving floor, from where the solids are conveyed from the moving floor into a conical drum area after a short dwell time and then thrown off into a stationary collecting housing by centrifugal force. To at the from Moving floor on the solid entrainment movement to prevent early wear of the filter surface on the inside of the drum, its openings consist of axial longitudinal slots, which, for reasons of strength, must not be less than a certain minimum width, so that products with grain sizes below 40 µm cannot be treated. A disadvantage is the regulation of the centrifuge throughput, which is only possible by supplying the suspension, since the product transported from the moving floor into the drum cone passes from there into the collecting housing in an uncontrolled manner. Since the dwell time of the product along the drum cone cannot be controlled, this type of centrifuge is only suitable for fast-filtering, coarsely crystalline mass products of low quality. Product washing to remove mother liquor is impossible because of the inhomogeneous density of the product that slides uncontrollably over the drum cone.

For emptying a centrifuge drum, a peeling device is known from DE-A 33 40 636, for example, which peels off the product layer adhering to the drum by means of a peeling head arranged on a telescopic discharge tube after the centrifuging operation has ended. Such devices cause seal abrasion and thus contamination in the product during their movements. In addition, peeling devices have deposition surfaces which are wetted by suspension and, after they have dripped off, cause an unwashed product to crust over. A crust reinforced by peeling dust can flake off in the case of centrifugal vibrations and contaminate the end product.

Peeling devices are also problematic in that a residual layer always remains in the drum, the compression of which causes increasingly longer filtration times for the subsequent batches. To remove the residual layer, the centrifuge must be stopped and opened, solvent vapors being drawn off while the residual layer is being scraped off and scooped out. Foreign particles get into the product, and workers and the environment are polluted.

The object of the invention is to provide a centrifuge dryer which, while eliminating the above-described disadvantages of known centrifuges in discontinuous or continuous operation with mechanical and / or thermal separation technology, and from which the product is completely emptied in a moist or dry state without avoiding a peeling device that a residual layer remains on the filter.

• besteht der Filter aus einem über seine gesamte Länge konischen Metallgewebeeinsatz,
• ist auf der als Füllrohr ausgebildeten Antriebswelle die geschlossene Stirnwand des Arbeitsraumes mitdrehend befestigt,
• ist an seinem erweiterten Ende der Arbeitsraum von einem nach innen offenen stationären Ringkanal umgeben, an den wenigstens eine Produktförderleitung angeschlossen ist,
• ist die Stauscheibe zwischen einer das erweiterte Ende des Arbeitsraumes abdichtenden Verschlußstellung und Öffnungsstellungen für einen einstellbaren Austritt zum Ringkanal verschiebbar, mit dem die Verweilzeit des Produktes im Arbeitsraum gesteuert wird.

According to the solution to this problem according to the invention

• the filter consists of a conical metal mesh insert over its entire length,
• the closed end wall of the working space is attached to the drive shaft, which is designed as a filling tube,
• the working area is surrounded at its extended end by an inwardly open stationary ring channel to which at least one product delivery line is connected,
• the baffle plate is displaceable between a closed position sealing the enlarged end of the working space and open positions for an adjustable outlet to the ring channel, with which the dwell time of the product in the work space is controlled.

If the conical drum containing the metal filter insert is perforated, at least one distributor line extending along the jacket with radially inwardly directed nozzles can be provided within the centrifuge housing near the outer drum circumference, which is used to supply washing liquid, backwash the filter surface and / or supply Use compressed air or hot gas. Pressure surges with hot gas can be exerted through the nozzles in order to detach and remove the dehumidified product from the filter. The flowability of the product along the conical drum wall can be increased by external supply of hot gas.

At the mouth of the drive shaft, a guide device can be provided, with which, by means of a variable pre-pressure, suspension or washing liquid impinges on the desired length of the filter cone.

At least one blade projecting into the ring channel is attached to the end of the drum, and one or more tangential nozzles for introducing conveying gas can be provided in the ring channel.

The cone shell of the drum and the conical circumference of the filter cone enclosing the working space can have several adjoining longitudinal areas with different opening angles have, for example 15 ° on a first longitudinal third for the initial filtration, while a smaller angle on the second longitudinal third causes a slower feed of the product.

In a further embodiment of the centrifuge dryer according to the invention, the mouth of a washing tube, which is preferably guided through the drive shaft into the work space, can be designed such that the smooth-walled work space, free of internals, is washed free of adhering mother liquor, regardless of the product washing. If the washing pipe inserted into the drum has nozzles directed towards an inner circumferential area of the working space, the product can be washed on the continuous path along the drum wall between the initial filtration and the final reduction in the final moisture. In this mode of operation, too, the product is discharged completely, in that the entire filter cake is pushed continuously along the drum wall to the ring channel.

In addition to the outlet gap, which can be finely adjusted via the baffle plate, the dwell time of the product in the work area is also influenced by additional parameters, such as drum speed, friction, viscosity or thixotropy of the product mixture, temperature, strength of the compressed gas surges injected from the outside, etc., so that the filter cone is completely emptied through pulsation promotion without additional mechanical aids.

With the help of the baffle plate and its setting option, you can choose between batch operation and continuous operation. The baffle plate is preferably mounted on an axis guided in the adjacent end wall of the centrifuge housing and axially movable by an adjustment drive. The end of the drum can have a cylindrical or conical outlet collar for receiving a sealing surface of the baffle plate.

• besteht die Trommel aus einem am mitdrehenden Trommelboden befestigten geschlossenen Mantel, der sich in Richtung auf sein freies Ende zylindrisch oder konisch verjüngt erstreckt;
• ist der konische Ringraum zwischen dem Trommelmantel und dem mit seinem verjüngten Ende am Trommelboden anschließenden Metallfilterkonus durch axiale, den Filterkonus abstützende Stegwände in Druckkammern unterteilt;
• enthalten die Druckkammern im Trommelboden wenigstens eine Diffusoröffnung, der auf dem gleichen Umkreis in der Rückwand des Zentrifugengehäuses mit geringem Abstand gegenüberliegend eine obere und eine untere Druckgasdüse zugeordnet ist;
• ist jede Düse mit einer Ventilsteuerung versehen, die während der Überdeckungsdauer von Diffusor und Düse diese zu intermittierenden Druckgasstößen öffnet.

According to a preferred development of the centrifuge dryer according to the invention

• the drum consists of a closed jacket attached to the rotating drum base, which extends cylindrically or conically tapered towards its free end;
• the conical annular space between the drum shell and the metal filter cone adjoining with its tapered end at the drum base is divided into pressure chambers by axial web walls supporting the filter cone;
• contain the pressure chambers in the drum base at least one diffuser opening, which is assigned on the same circumference in the rear wall of the centrifuge housing with a small distance opposite an upper and a lower compressed gas nozzle;
• Every nozzle is equipped with a valve control, which opens these to intermittent bursts of compressed gas during the overlap period of the diffuser and nozzle.

This proposal results in a pressure chamber centrifuge drum with a solid jacket and a replaceable, multi-layer sintered metal mesh filter cone with a low Surface friction. The annular space between the solid jacket and the filter insert is divided into several chambers, each containing a diffuser opening through which compressed gas is injected by means of fixed nozzles to detach the product from the filter and to simultaneously flow and dry the product. The open drum end carries a flange as a system for the axially displaceable baffle plate, which, as a gas-tight seal, enables the working space in the filter cone to be filled or washed as a sealed container by the drive shaft.

The process steps of filling / washing / drying / spinning are carried out in the work area, which is free from internals exposed to wetting with mother liquor and ensures the highest level of product purity. After dry spinning, the working space can be subjected to excess pressure in order to reduce the capillary rise in the residual moisture remaining in the product layer adhering to the filter cone and to achieve the lowest final moisture levels. Escaping gas pressure is impossible due to the sealed baffle plate.

After the end of the filtration, the product layer is blown off the filter cone by supersonic flow impulses injected into the pressure chambers and the pressure increase thus induced. The product forms, for example, a pile that fills 50% of the work area and is moved at a reduced speed like a drum dryer. In this phase, hot gas is injected into the pressure chambers below, which is now the circulated Product flows through from below and due to the high gas velocity causes a turbulent product flow with high heat exchange and efficient drying. Since the product is only in a partial area of the filter cone and constantly falls down due to the rotation, the inflowing gas passes through the filter cone, cleaned with dust, and escapes through the diffusers into the centrifuge housing, from where it is passed on through connecting pieces. For this purpose, the housing can have an upper valve-controlled connecting piece for the extraction of drying gas containing solvent or washing liquid.

During the drying phase taking place in the negative pressure, normal pressure or positive pressure range, the baffle plate remains in a gas-tight system in the drum flange, so that no leakage flows occur. In order to empty the working space after drying, the baffle plate is removed from the drum flange by means of an axial drive unit and brought into a mode of operation which rotates with the drum or is uncoupled by means of a switching device.

An expedient embodiment provides that the free ends of the drum shell and the filter cone are connected to one another in a sealed manner and carry axially directed driver bolts on a circumferential flange which extend through assigned openings of the baffle plate. The driver bolts can have a limited length and, in the case of the outlet gap to the ring channel, a baffle plate which largely exposes them can disengage from their openings.

The free end of the drum is surrounded by an inwardly open ring channel from which one or more product delivery lines originate. The baffle plate is displaceable between a position closing the access to the ring channel and a position releasing the exit from the working space. By means of compressed gas surges supplied through the respective lower pressure chamber, the product arrives from the filter cone with the drum rotating slowly and can be circulated there by mechanical aids and / or by means of injected compressed gas and can be led out via a tangential outlet. When changing the product, the centrifuge housing including the drum and ring channel can be flooded and washed when the drum rotates, whereby the washing liquid takes the same route as the product otherwise.

According to a further embodiment, the diffuser openings can consist of curved elongated slot slots arranged on the same pitch circle. - It is expedient if the edge of the diffuser openings protrudes beyond the inner circumference of the drum shell. The face of the nozzle housing can cover the diffuser opening at least in the radial direction.

Fig. 1

einen einstufigen, vorzugsweise für einen Chargenbetrieb ausgelegten Zentrifugentrockner nach der Erfindung im Längsschnitt,

Fig. 2

einen dem Aufbau von Fig. 1 ähnlichen Zentrifugentrockner mit innerem Waschrohr für Durchlaufbetrieb,

Fig. 3

eine Variante des Zentrifugentrockners nach Fig. 1 mit einer Druckkammer-Zentrifugentrommel,

Fig. 4

eine Teildarstellung aus Fig. 3 mit abgeändertem Mitnehmerbolzen,

Fig. 5

einen vergrößerten Längsschnitt durch die Zentrifugentrommel in Fig. 3 und

Fig. 6

einen vergrößerten Querschnitt der Zentrifugentrommel nach Fig. 3.

Embodiments of the centrifuge dryer according to the invention are explained below in connection with the drawings. Each shows schematically Further features and advantages of the invention result from the description of exemplary embodiments of the centrifuge dryer according to the invention in conjunction with the drawings, which show details essential to the invention, and from the claims. The individual features of the claims can be implemented individually or in groups in any combination in further embodiments of the invention. Each shows schematically

Fig. 1

a single-stage, preferably designed for batch operation centrifuge dryer according to the invention in longitudinal section,

Fig. 2

1 similar to the structure of Fig. 1 centrifuge dryer with an inner washing tube for continuous operation,

Fig. 3

1 a variant of the centrifuge dryer according to FIG. 1 with a pressure chamber centrifuge drum,

Fig. 4

3 with a modified driving pin,

Fig. 5

an enlarged longitudinal section through the centrifuge drum in Fig. 3 and

Fig. 6

3 shows an enlarged cross section of the centrifuge drum according to FIG. 3.

1, a horizontally mounted hollow shaft 7 is connected to a frequency-controlled drive motor 1 via a V-belt drive 2. The shaft 7 carries a conical perforated centrifuge drum 4, in which a circumferentially closed filter cone 3 is held, which can consist of woven-together sintered metal sieves. The hollow shaft 7 carries a deflection hood 8 in front of the mouth in order to guide the supplied suspension in the direction of the arrow to the smallest drum circumference. The hollow shaft 7 is supported in a bearing housing 18 on a machine stand 15 and carries a connection 5 held by means of a mechanical seal for the supply of suspension or washing liquid.

A centrifuge housing 17 is fixedly connected to the bearing housing 18 and is sealed against the shaft 7 via a shaft seal 14 and closed by a cover through which a circular baffle plate 9 can be axially displaced. The baffle plate 9 is mounted on a central axis 20 which is moved by a drive unit 19 arranged on the outside of the cover.

The baffle plate 9 can be moved along a stationary guide 21 into an inner guide surface at the extended end of the drum 4 in order to close the working space 23 in a discontinuous operation. A product cake A drawn above the central axis is formed from the filtered suspension. The product, freed from mother liquor, is washed and centrifuged dry. Then at reduced speed and when the baffle plate 9.1 is open, the product is emptied into a ring channel 10, which is sealed off at the periphery of the extended drum end and is open to the inside, has any suitable cross section, is supported on the centrifuge housing 17 or on its cover, and bears a guide 21 solely on account of the centrifugal force , against which the baffle plate lies in its open position 9.2. When spinning dry, the drum 4 can be pressurized via the hollow shaft. Thereafter, hot gas pressure surges can be introduced from one or more distribution lines 16 with a slowly rotating drum, which completely detach the product cake A from the heated filter surface 3. The hot gas entering the drum 4 escapes via a rotating filter attached to the baffle plate 9 through the axis 20 into a vacuum line.

In continuous operation, according to FIG. 2, a defined outlet gap is set by the baffle plate 9 and the drum 4 is constantly subjected to suspension. The mother liquor is spun off over a first cone length a and collected in a discharge nozzle 6. On a second cone length b, the product is washed with washing liquid injected through the pipeline 25 and then centrifuged dry on a cone length c. The centrifugally moist product flows off without residue into the ring channel 10, in which the blades 11 attached to the drum circumference feed the product to a current dryer 12 or, via the indicated down pipe 13, to a vacuum dryer or container.

Radially inwardly directed nozzles extend from the distribution line 16, which in certain cases can consist of a single longitudinal slot and are used optionally for supplying washing liquid, backwashing the filter surface and / or for supplying compressed air or hot gas.

3 to 6, a drum base 30 is fastened on the end of the hollow shaft 28, which is inserted into the centrifuge housing 17 in a sealed manner, from which a cylindrical drum shell 32, or a drum drum 32 which is slightly tapered towards its free end, extends. Between the inner end of a drum flange 34 and the drum base extends a sintered filter fabric consisting of a stiffened metal filter cone 36, on the outside of which, at circumferential intervals, U-profiles 38 are welded as a receptacle for web walls 40 which extend radially inwards from the drum jacket 32 and which extend into the conical annular space Subdivide gas-tight pressure chambers 42 from one another. Each pressure chamber contains a circular or elongated diffuser opening 44 in the drum base 30, through which pressure surges are injected in its upper positions by one or more nozzles 46 arranged in the fixed rear wall 45 of the housing at selectable intervals. The pressure rise resulting from the supersonic flow in the pressure chamber 42 has the effect that the product layer adhering to the inside of the filter cone 36 is detached and falls over the entire segment surface.

A baffle plate 52 is rotatably mounted on an axis 50, which is sealed in the housing cover 48 and which, as in the example according to FIGS. 1 and 2, can be displaced between an end position closing the working space 53 and the exit to the ring channel 54, more or less opening intermediate positions. The drum flange 34 carries a socket with an annular surface 56 for the circumference 58 of the baffle plate. Suspension or washing liquid are fed through the hollow shaft 28 and through an inner tube 60 to the conical ring nozzles 28a or 60a. This enables fully automatic loading, since the co-rotating liquid emerging from the ring nozzles in the shape of a trumpet can be directed to any desired area of the inner wall of the filter cone and the baffle plate due to its variable pre-pressure, particularly when the working area is completely washed. On the drum flange 34 projecting in the ring channel 54 blades 64 and driver bolts 66 are fixed, which protrude sealed through openings in the baffle plate 52 and transmit the drum rotation. 4, the driver bolts 66 are shortened so that the baffle plate is uncoupled from the driver drive from a certain opening size of the ring channel and is held in place by locking bolts 68.

In centrifuging operation, filtered mother liquor or washing liquid passes through the filter cone 36 into the pressure chambers 42 and flows from there along the drum shell through the diffuser openings 44 into the housing 17 or through its collecting connection 72. In order to ensure the fluid drainage in the case of a cylindrical drum jacket 32, the entire apparatus is operated during of the spin operation slightly inclined, namely raised at the left end in Fig. 2. After the dry centrifugation, the hollow space 28 is pressurized with gas pressure to reduce the capillary rise in the residual moisture remaining in the product.

To detach the product layer adhering to the filter cone 36, hot gas can first be blown into the pressure chambers 42 with low-pressure surges in order to heat the filter cone and to dry the sticky base layer of the product. After this pre-drying, high-pressure shocks occur, under which the product layer breaks and falls off. At the same time, the filter cone is cleaned from the outside in.

After cleaning the filter cone in the five pressure chambers according to FIG. 6, for example, hot gas is introduced in pressure surges via the lower nozzle 47 in order to convectively dry the product as an eddy current. The product collected in the lower half of the work area is constantly shifted at low speed, thus accelerating drying. The injected gas exits through the upper half of the cone.

Since the gas enriched with solvent and other liquid vapors in the work space, freed from the product in the filter and flowing out of the pressure chambers 42 may already condense in the centrifuge housing 17, from where it is fed to a condenser in a short distance, there is a high usable temperature difference for drying available to the case where the product is removed from the filter drum by means of a peeling head and accompanied by a convective drying gas in cocurrent to a product separation filter and therefore must have an exhaust gas temperature that is at least 30 ° higher than the dew point.

Because the convective hot gas flow is separated from the product transport, only about half the amount of heat required there is required for heating the drying gas for the same drying time in relation to the known peeling process. The product obtained using the new gas routing achieves significantly lower final humidities compared to current drying or vacuum contact drying, which are in the ppm range.

After the drying in the working space 53 in the overpressure or underpressure range has ended and the outlet to the ring duct has been opened, the gas pressure surges which continue to exert on the product cause pulsation promotion, in which the pulsating conveying gas drives the product through the ring duct into a dust separator or another destination.

• Niedriger Oberflächenreibwert des metallischen Filterkonus,
• Konuswinkel des auswechselbaren Filterkonus,
• Trommeldrehzahl,
• Druckgas-Impulsströmung in Verbindung mit verstellbarer Stauscheibe.

The desired complete emptying of the product from the work space free of built-in parts without remaining residual layer is achieved without a peeling device by combining the following parameters:

• Low surface friction of the metallic filter cone,
• Cone angle of the exchangeable filter cone,
• Drum speed,
• Compressed gas impulse flow in connection with adjustable baffle plate.

Claims (17)

1. A centrifugal drier comprising a horizontally supported drive shaft, a co-rating drum linked to said drive shaft, a filter mounted inside the drum and enclosing a work area conically flaring from the link side of the drive shaft, an axially displaceable baffle disk forming one end face of the work area, and with a centrifuge housing encapsulating the drum and the baffle disk,
   characterized by following features:

   - the filter (3; 36) consists of a wire-cloth which is conical over its entire length,

   - the closed end face (30) of the work area (23; 53) is affixed in co-rotating manner to the drive shaft (7; 28) designed as a filling pipe,

   - the work area is enclosed at its flaring end by an inwardly open stationary annular duct (10; 54) which connects to at least one product conveyance conduit,

   - the baffle disk (9; 52) is displaceable between a closed position sealing the flaring end of the work area (23; 53) and open positions for adjustable discharge to the annular duct controlling the product's dwell-time in the work area.
2. Centrifugal drier as in claim 1, characterized in that at least one manifold conduit (16) with radially inward discharge nozzles for washing liquid, filter cleaning medium and/or compressed air and hot gas is mounted inside the centrifuge housing and parallel to the drum periphery.
3. Centrifugal drier as in claim 1 or 2, characterized in that a deflector means (8) is provided at the mouth of the drive shaft and effective, by means of variable intake pressure, to direct the suspension or the washing liquid to impinge on any desired lengthwise position of the filter cone.
4. Centrifugal drier as in one of the preceding claims, characterized in that at least one bucket (11; 64) entering the annular duct is affixed to the end of the drum (4; 32).
5. Centrifugal drier as in one of the preceding claims, characterized in that one or more tangential nozzles to introduce conveying gas are provided in the annular duct (10).
6. Centrifugal drier as in one of the preceding claims, characterized in that the conical periphery of the filter cone (23; 53) enclosing the work area comprises adjoining zones with different angles of aperture.
7. Centrifugal drier as in one of the preceding claims, characterized in that the mouth of a wash pipe (25) preferably passing through the drive shaft (7) into the work area is of such design that independently of product washing, the smooth-walled work area free of integrated accessories can be flushed clear of adhering mother liquor.
8. Centrifugal drier as in one of the preceding claims, characterized in that by combining and suitably dimensioning the parameters: filter-cone angle, angular speed, surface friction and external impulsive loading of compressed gas on the filter cone, this filter cone shall be comopletely emptied of its product by means of impulsive conveyance and in the absence of mecnanical accessories.
9. Centrifugal drier as in one of the preceding claims, characterized in that the baffle disk (9; 52) rests on a shaft (20; 50) guided in an adjacent end face of the centrifuge housing (17) and axially displaced by an adjustment drive.
10. Centrifugal drier as in one of the preceding claims, characterized in that the flaring drum end comprises a cylindrical or conical discharge flange (34) to receive a sealing surfache of the baffle disk (9).
11. Centrifugal drier as in one of claims 1 or 3, throught 10, characterized by following features:

    - the drum consists of a closed casing (32) affixed to a co-rotating drum bottom (30) and extending cylindrically or conically tapering towards its free end;

    - the conical annular space between the drum casing (32) and the metal filter cone (36) joining by its tapered end the drum body is devided into pressure chambers (42) by axial webs (40) bracing the filter cone;

    - the pressure chambers comprise at least one diffuser aperture (45) in the drum bottom, said aperture being associated to an upper and a lower compressed-gas nozzle (47) a slight distance away on the same circle in the back wall (45) of the centrifuge housing;

    - each nozzle is provided with a valve control (70) which during the overlap of diffuser and nozzle opens this nozzle for intermittent impulses of compressed gas.
12. Centrifugal drier as in claim 11, characterized in that the diffuser apertures (44) consist of curved elongated slots arranged on the same circle.
13. Centrifugal drier as in either of claims 11 and 12, characterized in that the edges of the diffuser apertures (44) project beyond the inside periphery of the drum casing (32).
14. Centrifugal drier as in one of claims 11 through 13, characterized in that the end face of the nozzle housing overlaps the diffuser aperture at least radially.
15. Centrifugal drier as in one of the preceding claims, characterized in that the free ends of the drum casing (32) and of the filter cone (36) are connected to each other in sealing manner and bear axial drive bolts (66, 67) on a circumferential flange that extend through associated apertures in the baffle disk (52).
16. Centrifugal drier as in claim 15, characterized in that the drive bolts (67) present a restricted length and, when the baffle disk (52) substantially clears the discharge gap to the annular duct (54), disengage from the apertures of said baffle disk (52).
17. Centrifugal drier as in one of the preceding claims, characterized in that the housing (17) comprises an upper, valve-controlled hook-up stub to evacuate drying gas containing solvent or washing liquid.

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