EP0142698B1 - Method and apparatus for the pneumatic unloading of centrifuges - Google Patents

Abstract

A method and an apparatus for pneumatically evacuating a vertical centrifuge (12), the drying gas moving as a secondary flow (54) being converted-prior to its combination with the mixture of product and gas conveyed through the discharge pipe-into a turbulent longitudinal flow essentially enclosing the discharge pipe as far as its downstream end, in order to prevent caking of the centrifuged material within the discharge pipe or in conveying lines (20) attached thereto and also to shorten the length of the drying pipe.

Description

The invention relates to a method for emptying centrifuges, in particular vertical centrifuges, in which the centrifuged product is released into a discharge pipe through the closed centrifuge housing by peeling off the wall of the rotating centrifugal drum and in the heated drying gas in a primary stream into the centrifuge and into a secondary stream is passed into a drying section connected to the discharge pipe and carrying the product-gas mixture.

In a method of the aforementioned type known from DE-A-20 56 893, the gas-tight centrifuge housing of a centrifuge to be emptied is included in a closed conveyor circuit by passing heated drying gas into the centrifuge by means of a pressure line and a discharge tube provided with a peeling head to one Suction line connects, in order to then feed the product conveyed out of the centrifuge by means of a gas circulation device through a drying section to a cyclone filter bunker. In this way, the sensitive or poisonous product, which may or may not be sterile, is peeled out of the centrifugal drum and conveyed further within a closed circuit without this solvent becoming volatile solvent coming into contact with the ambient air.

According to a variant of this method, it is proposed to connect the outlet of the heating device arranged in the closed conveyor circuit for reheating the drying gas cooled in the condenser directly to the suction line via a shunt line, so that the centrifuge is partially bypassed. This type of gas routing should be used with relatively wet centrifugal products that tend to stick to start drying during the peeling and discharge process.

In the implementation of this known method it is considered disadvantageous that the connecting line between the centrifuge and the junction of the shunt line in the main pipe remains ineffective with regard to the drying of the product and is only a pneumatic conveying path. On this conveyor line, the product-gas mixture coming from the centrifuge can cool down to the dew point of the solvent very soon, so that the moist product cakes in the pipeline and clogs after a short period of operation, resulting in expensive downtimes of the system. quite apart from the possible endangerment of the entire batch if the products are to be kept sterile. In order to avoid excessive cooling, it is necessary to increase the inlet temperature of the drying gas into the centrifuge, which means, for example, products with a low melting point, particularly in the area of a telescopic arrangement used to steal the discharge and peeling tube in the centrifugal drum when passing from one into the Bake the following pipe on the inner walls, making further adjustment of the discharge pipe impossible.

Furthermore, when the known method is used, it can be seen that the product bakes on the drying tube in the region of the confluence of the conveying section, where the drying gas introduced in the secondary stream presses the partially still moist product against the wall opposite the confluence or also melts there. In this context, there is always the risk of extensive pipe blockage with expensive cleaning and follow-up costs.

The invention is based on the object of further developing and improving the above-mentioned method for emptying centrifuges in such a way that baking of the product to be conveyed within the discharge pipe or in the subsequent transport line is avoided to a large extent and, furthermore, by reducing the outlay on equipment Shortening the necessary drying tube length is made possible.

This object is achieved in that the drying gas carried in the secondary stream is transferred before being combined with the product-gas mixture conveyed through the discharge pipe into a turbulent longitudinal flow which essentially envelops the discharge pipe up to its downstream end.

The amount of drying gas introduced in the secondary flow, which concentrically surrounds the product-gas mixture as it emerges from the discharge pipe, ensures intensive swirling, so that the greatest possible exchange takes place between the hot drying gas and the product moisture. This process can roughly be compared to the principle of atomization drying, which also considerably shortens the length of the tube that is otherwise required for drying the current. Since the secondary flow is brought concentrically to the discharge pipe before the combination with the product-gas mixture, there is the advantageous possibility of maintaining a higher temperature in the secondary flow, this heat either before the combination with the product-gas mixture Discharge tube is released and therein the drying process promotes or can be largely introduced into the mixture when a z. B. sensitive to abrupt changes in temperature on the way of the Centrifugal drum has been pre-dried through the discharge tube or has already been partially heated. As a result, the drying tube length is also advantageously shortened in order to dryly separate the product discharged from the centrifuge in the downstream cyclone bunker filter. These aspects which result from the use of the method according to the invention are of particular importance if products which change frequently are centrifuged in order to utilize the processing plant as far as possible.

The invention also relates to a pneumatic discharge device, in particular for a vertical centrifuge, for carrying out the above-described method according to the invention. The state of the art for this is a discharge device according to DE-A-20 56 893 already mentioned at the outset with a discharge tube which can be moved in a centrifuge centrifuge drum and has a peeling head at the preceding end, a centrifuge housing which is involved in a pneumatic conveying circuit and a connection housing arranged thereon in a sealed manner , in which the discharge pipe is guided and radial and axial adjusting devices for the discharge pipe are arranged, the pneumatic conveying circuit having a branch line for supplying a primary flow of a heated drying gas into the centrifuge and a branch line for supplying a secondary flow of the heated drying gas into one with the discharge pipe in Related drying line includes.

In order to achieve the improvement in drying intended by the process by shortening the drying distance and to avoid caking of the product and blocking of the adjusting device of the peeling head, it is proposed according to the invention for the pneumatic discharge device that the discharge pipe at its downstream end passes through the free end of the connection housing and seals protrudes from this by at least one length corresponding to its axial setting stroke, which is surrounded by a jacket tube connected to the free end of the connection housing and merging into a drying section, into which a pipe socket opens immediately behind the connection housing and which connects to the branch line of the drying gas leading to the secondary flow of the drying gas Funding group is connected.

Since the cladding tube for the secondary flow of drying gas is flanged directly to the rear end of the connection housing and passes downstream into the drying section, the upper or downstream end of the connection housing is sealed off from the ambient atmosphere. This fact is exploited according to the invention in order to allow the connecting pipe to pass smoothly through the entire connecting housing and in particular sealed at the downstream end through the free end of the connecting housing and to protrude into the cladding tube without interruption or telescopic extension. Without the cladding tube, the drying tube leading to the bunker filter (suction line of the pneumatic conveying circuit) would have to be inserted rigidly and statically sealed into the upper end of the connection housing and combined with a telescopically displaceable discharge tube in order to provide the necessary freedom of movement for adjusting the discharge tube and to ensure the peeling elbow connected there, ie both the longitudinal movement and the rotational movement of the discharge tube. The inevitably resulting diameter widening in such an arrangement between the discharge pipe and suction line connection leads to an undesirable gas swirling at this point and to caking of the product on the pipe walls. The caking movements of the discharge tube are blocked by such caking. With the proposal according to the invention, not only are these operational difficulties eliminated, but at the same time significant structural savings are achieved. Within the continuous discharge tube, which is therefore free of changes in diameter, there are no undesired swirls and no more caking. With regard to the sealing, there is the important advantage that the discharge tube can be finely ground and polished on the outside and can be sealed with a seal arranged at the upper end of the connection housing. This seal and the finely ground circumference of the discharge tube have the further advantage that the annular space formed with the cladding tube can be kept free with the aid of the secondary flow of the drying gas, otherwise there is a risk of product dust falling backwards as a result of an increase in diameter. The drying gas subsequently introduced flows upward concentrically to the inner discharge pipe and swirls the product-gas mixture coming out of the discharge pipe for the purpose of additional intensive drying.

In an embodiment of the discharge device according to the invention, it is proposed that the insertion socket be connected laterally to the cladding tube directly behind the free end of the connection housing. This ensures that the secondary flow in every case keeps the lower end of the annular space in the cladding tube free of product deposits and thus also the passage and sealing of the discharge tube.

The inlet connection for the secondary flow of the drying gas can be connected to the casing tube essentially perpendicularly to the axis thereof, in order to ensure concentric guidance of the casing pipe even over a small axial length To achieve secondary current. If necessary for other reasons, the inlet connector can also be inclined and / or connected tangentially to the cladding tube.

According to a further feature of the discharge device according to the invention, an end plate can be held between the free end of the connection housing and a fastening flange of the cladding tube, which contains a sealing passage for the discharge tube and which defines the annular space formed between the discharge tube and the cladding tube in the axial direction up to the mouth of the insertion socket fills out. The cover plate is thus used to avoid dead spaces or to place the bushing in its place.

In a further embodiment of the discharge device, it is proposed that the discharge pipe be surrounded within the connection housing at a concentric distance by an immersion pipe, the preceding end of which is connected to the discharge pipe and is guided in a sealed manner at least in the region of the upstream end of the connection housing. This measure aims, among other things, at a favorable introduction of the axial and radial adjusting forces for the peeling movements of the discharge pipe and, in terms of construction, simplified connection options for the servomotors driving these movements.

The outer circumference of the immersion tube can be guided both by an adjusting ring supported between the ends of the connection housing and by a sliding ring arranged on the end of the connection housing facing the centrifuge.

• Fig. 1 eine Übersicht über den zur erfindungsgemäßen Austragvorrichtung bildenden pneumatischen Förderkreis,
• Fig. 2 einen Längsschnitt durch das auf einem Zentrifugengehäuse befestigte Anschluß gehäuse mit Austragrohr, Schälkrümmer und Hüllrohr für Sekundärgasstrom und
• Fig. 3 einen waagerechten Schnitt durch das Anschlußgehäuse nach Fig. 2 in Höhe des Antriebszylinder für die Drehbewegung des Austragrohres.

Further details and advantages of the invention result from the following description of exemplary embodiments of the method according to the invention and the discharge device according to the invention in conjunction with the drawings which show details essential to the invention. They show, largely schematically,

• 1 shows an overview of the pneumatic conveyor circuit forming the discharge device according to the invention,
• Fig. 2 shows a longitudinal section through the attached to a centrifuge housing connection housing with discharge tube, peeling elbow and cladding tube for secondary gas flow and
• Fig. 3 is a horizontal section through the connection housing of FIG. 2 at the level of the drive cylinder for the rotary movement of the discharge tube.

1, a sealed centrifuge housing, in which a centrifugal drum 12 is rotatably mounted, is supported on a centrifuge frame 14. On the top of the sealed centrifuge housing 10, a connection housing 16 is fastened in a sealed manner, the details of which are explained below in connection with FIGS. 2 and 3. In the connection housing 16, a rotatable and height-adjustable discharge pipe 60 is guided, the lower end of which continues into a pipe bend 62 and a peeling head 64, on which peeling knives are arranged laterally and below. Due to the sensitive radial and axial adjustment of the discharge tube with the elbow, 10 very thin product layers can be removed from the centrifugal drum, which is driven at a suitable speed, for the purpose of centrifuge emptying when the centrifuge housing is closed.

The peeling process is accompanied by pneumatic conveying, wherein drying gas heated up via a primary flow branch 52 shown in FIG. 1 is introduced into the centrifuge housing and the discharge pipe 60 is connected to a pneumatic suction line. According to Fig. 1, the centrifuge is included in a pneumatic conveyor circuit which comprises successive units and assemblies. The upper end of the connection housing 16 is followed by a cladding tube 18 described in more detail below, followed by a drying tube section 20 by means of an unspecified compensating piece, in which the residual moisture is extracted from the peeled product with the aid of the drying gas before it is removed via a cyclone separator 22 with a filter 24 arranged therein falls dry into a bunker 26. In the exemplary embodiment shown, the bunker 26 is equipped as a mixing container with a screw mixer 28.

From the upper end of the cyclone separator 22, the conveying circuit continues via the suction line 30, a safety filter 32 into a condenser 34, where the carrier medium is freed from the solvent vapors carried along. A droplet separator 36 is connected downstream.

The delivery cycle continues with a high-pressure fan 38 and a measuring and metering device 40 with which the remaining solvent content of the carrier medium can be adjusted. So that the ignitability of the mixture remains low and a 0 content remains less than about 6%, an N ₂ supply is provided as required. Behind the blower 38, a pressure line 42 continues into a heating device 44, which can consist of a heat exchanger. A bypass line 46 and a downstream mixing valve 48 enable sensitive temperature control of the drying gas which is now prepared for product treatment and which still flows through a safety filter 50. After a shut-off and control valve 58, the heated drying gas is divided into a primary flow conducted into the centrifuge via a primary branch 52 and a connection 56 on the centrifuge housing 10, and into a primary flow leading to the cladding tube 18 via a secondary branch 54 Secondary current. The distribution ratio is, for example, 1: 3 instead of the distribution ratio of 1: 1 mentioned in claim 4.

The enlarged representation of the connection housing 16 fastened on the centrifuge 10 in FIG. 2 shows its subdivision into a lower section 68, a middle section 70 and an upper section 72 for reasons of simplified production, maintenance and repair. The discharge tube 60 extends through the connection housing 16, the lower end of which extends into the elbow 62, to which the peeling head 64 is fastened with an enlarged opening, from which a lateral peeling knife edge 66 can be seen. The discharge tube 60 is connected to a dip tube 76 of larger diameter via a lower flange connection 74.

In the upper position of the discharge tube, which is retracted into the connection housing 16, the immersion tube 76 extends essentially up to the upper inner end of the connection housing, so that a sufficient support length remains within the connection housing in the extended state. The dip tube 76 is guided on its circumference in the region of the lower end of the connection housing at 78 on both sides of a seal 80 free of gas and dust.

Between the lower section 68 and the central section 70 of the connection housing, a support ring 84 is clamped, on which an adjusting ring 86 is supported and rotatably supported on the circumference. Support ring 84 and adjusting ring 86 include the immersion tube 76 with bearing play, so that with respect to the lower guide 80 in the connection housing there is a favorable large distance between the bearings or guides of the support tube.

As can also be seen from FIG. 3, a feather key 88 is attached to the circumference of the dip tube 76, which extends through a recess 90 of the adjusting ring 86 and serves as a driver connection between the adjusting ring and the dip tube. The adjusting ring 86 is provided over a part of its circumference with a circumferential toothing 92 which is in engagement with a rack 94. The rack 94 forms part of a piston rod 96 of a hydraulic cylinder 98 and is provided with pistons 100, 102 at both ends. If the cylinder 98 is acted on at one of its ends in accordance with FIG. 3, the adjusting ring 86 is rotated by the piston rod movement until the radius running through the center of the parallel key 88 is in the axis 82. In this position, the parallel key 88 is aligned with a recess 104 in the supporting ring located underneath and can now be moved downwards.

For the axial adjustment of the discharge tube 60, a drive cylinder 110 is supported in the connection housing 16 on the adjusting ring 86 in an axially parallel arrangement to the discharge tube, the piston rod of which protrudes through openings in the adjusting ring and the supporting ring and is articulated with a piston rod eye 108 on a driving lug 106 attached to the dip tube 76. In Fig. 2 a proximity switch 112 and the associated sensing marks 114 on the parallel key 88 can be seen, which emits signals for the operator in the end positions of the longitudinal adjustment.

2, the discharge tube 60 is extended through an opening in the upper section 72 of the connection housing 16 into the cladding tube 18 and forms an essentially concentric annular space 118 therewith. The length of extension of the discharge tube 60 upward from the connection housing 16 is determined approximately the vertical adjustment stroke corresponding to the drive cylinder 110 in order to be able to completely empty the centrifugal drum and after an additional remaining length. This ensures that the discharge pipe 60 in the extended end position is still surrounded by an annular space 18 before the secondary flow of the drying gas, which is led through the inlet pipe 120 connected to the cladding pipe 18, the product gas emerging from the upper end of the discharge pipe -Mixture can achieve.

The cladding tube 18 is connected with its lower flange to the connection housing 16 in a sealed manner on an end plate 116, for example made of PTFE plastic. The end plate 116 extends upwards into the annular space 118 until it is approximately flush with the lower edge of the insertion piece 120. The end plate thus forms an axially extended guide and seal for the ground and polished outer circumference of the discharge tube 60. The upper flange 126 of the cladding tube 18 connects to the z. B. Curved drying section 20 shown in FIG. 1.

Claims (11)

1. Method for evacuating centrifuges, in particular vertical centrifuges, wherein the centrifuged product being peeled from the wall of the rotating centrifuging drum (12) is fed to a discharge pipe (60) passing through the closed centrifuge housing (10),

and wherein a heated drying gas is fed in a primary flow to the centrifuge and in a secondary flow to a drying path (20) connected to the discharge pipe and guiding the mixture of product and gas,

characterized

in that the drying gas guided in the secondary flow prior to being combined with the mixture of product and gas conveyed through the discharge pipe (60) is converted into a turbulent longitudinal flow substantially concentrically enclosing the discharge pipe as far as its downstream side.

2. Method per claim 1, characterized in that the drying gas is circulated in a closed conveying loop through the drying path (20) joining the intake of the secondary flow, through a product separator (22), through a condensing path (34) and finally is reheated before being split into primary and secondary flows.

3. Method per claims 1 or 2, characterized in that the drying gas is circulated in the closed loop by a high pressure blower (38) mounted between the condenser and the heating path (34 through 44) and after being temperature controlled is again split into primary and secondary flows.

4. Method per one of the above claims, characterized in that the heated drying gas is split in the ratio of about 1 : 1 into the primary flow and secondary flow.

5. Pneumatic discharge apparatus in particular for a vertical centrifuge to implement the method of one of the claims 1 through 4, with a discharge pipe (60) movable within a centrifuging drum (12) and provided at the leading end with a peeling head (64), with a centrifuge housing (10) included in a pneumatic conveyance loop and a connecting chamber (16) sealingly mounted thereon, through which passes the discharge pipe and with in which are mounted radial and axial adjustment means for the discharge pipe, said pneumatic conveyance loop comprising a branch line (52) to feed a primary flow of heated drying gas into said centrifuge, and a branch line (54) to feed a secondary flow of heated drying gas into a drying path (20) connected to said discharge pipe (60),
characterized in that the discharge pipe (60) passes hermetically at its downstream end through the free end of the connecting chamber (16) from which it projects by a length corresponding to its axial adjustment stroke, said length being enclosed by an enclosing pipe (18) connected to the free end of the connecting chamber (16) and merging into the drying path (20), a pipe stub (120) issuing directly behind the connecting chamber into said enclosing pipe and being connected with said branch line (54) of the conveying loop passing the secondary flow of the drying gas.

6. Pneumatic discharge apparatus per claim 5, characterized in that the intake pipe stub (120) is connected directed behind the free end of the connecting chamber (16) laterally to the enclosing pipe (18).

7. Pneumatic discharge apparatus per claims 5 or 6, characterized in that the intake pipe stub (120) for the secondary flow of the drying gas is connected essentially perpendicularly to the axis of the enclosing pipe (18) to this enclosing pipe.

8. Pneumatic discharge apparatus per one of claims 5 to 7, characterized in that a closing disk (116) is mounted between the free end of the connecting housing (16) and a mounting flange (122) of the enclosing pipe (18) and contains a sealing feed-through for the discharge pipe (60) and filling the annular space formed between the discharge pipe (60) and the enclosing pipe (18) in the axial direction as far as the intake of the feed pipe stub (120).

9. Pneumatic discharge apparatus per one of claims 5 through 8, characterized in that the discharge pipe (60) is concentrically enclosed within the connecting chamber (16) by a spaced immersion pipe (76) of which the front end is connected to the discharge pipe and is guided hermetically at least in the area of the upstream end (68) of the connecting chamber (16).

10. Pneumatically discharge apparatus per claim 9, characterized in that the outer circumference of the immersion pipe (76) is guided both by an adjustment ring (86) supported between the ends of the connecting chamber (16) and by a slip-ring (78) mounted at the end (68) of the connecting chamber (16) adjacent to centrifuge.

11. Pneumatic discharge apparatus per claims 9 or 10, characterized in that a doubly-acting adjustment cylinder is provided as the rotational drive means for the adjustment ring (86) which includes a piston-rod (96) designed as a gear- rack (94) tangential to the adjustment ring (86) and engaging an outer toothing (92) of the adjustment ring (86), and in that the adjustment ring (86) supports on its top side an adjustment cylinder (110) mounted axially parallel to the discharge pipe (80), said adjustment cylinder including a piston rod (108) guided through an opening in the adjustment ring and which is connected at its free end with the immersion pipe (76).

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