EP3769847A1 - Continuous drying centrifuge - Google Patents

Abstract

The invention relates to a centrifuge for separating a material to be screened into a solid and a liquid with a screen drum (1) which is arranged within a housing (10) and rotatably mounted about an axis of rotation (100), the length of which extends from a first side (1a ) extends in the transport direction (50) of the material to be screened to a second side (1b) and has a screen jacket (11), the centrifuge at least one air flow element (80, 81a, 81b, 81c, 85, 86) and / or at least one dehumidifying element ( 45) in order to generate an, in particular dehumidified, air stream within the housing (10). The invention also relates to a method for separating a material to be sieved into a solid and a liquid by means of a continuously operating centrifuge, the liquid being mechanically separated from the solid by means of a rotating sieve drum (1), the solid being further dried within the centrifuge by means of an air flow generated by an air flow element (80, 81a, 81b, 81c, 85, 86) takes place

Description

The invention relates to a centrifuge for separating a moist material to be screened into a solid and a liquid with a sieve drum arranged inside a housing and rotatably mounted about an axis of rotation, the longitudinal extent of which extends from a first side in the transport direction of the material to be screened to a second side and has a sieve jacket. The invention also relates to a method for separating a material to be screened.

The term screening material means a suspension or a moist solid which can have solid particles of different particle sizes.

Such centrifuges are known. During the separation, a certain proportion of the liquid naturally remains on or in the solid, which is referred to as residual moisture. It has been found to be disadvantageous that the residual moisture of the solids achieved in known centrifuges is too high and does not meet the requirements for a dry solids.

The object of the invention is therefore to develop a continuously operating centrifuge in such a way that a sufficiently low residual moisture content of the solids to be separated is achieved.

This object is achieved according to the invention by a centrifuge according to claim 1 and a method according to claim 13. Advantageous further developments of the invention are given in the dependent claims.

Particularly advantageous in the centrifuge for separating a material to be sieved into a solid and a liquid with a sieve drum arranged inside a housing and rotatably mounted about an axis of rotation, which extends with its longitudinal extent from a first side in the transport direction of the material to be sieved to a second side and a Has sieve jacket, it is that the centrifuge has at least one air flow element and / or at least one dehumidifying element in order to generate an, in particular dehumidified, air flow within the housing.

The sieve drum has a sieve casing which forms at least part of the sieve drum, in particular its longitudinal extension. In particular, part of the sieve drum, in particular its longitudinal extent, can be designed as a solid jacket, in particular a solid jacket drum.

The centrifuge according to the invention can basically be any type of continuously operating centrifuge, in particular a sieve screw centrifuge, a sieve screw centrifuge with pre-thickening, a decanter centrifuge, a sieve decanter, a vibrating centrifuge, a sliding centrifuge or a pusher centrifuge. The term “continuously operating centrifuge” means a centrifuge in which no sequentially separated steps are required in order to separate the material to be screened into its components.

The terms drum and sieve drum are used synonymously in the following remarks.

All centrifuge types have in common that a drum rotates and thus generates a centrifugal force by means of which the introduced material to be screened is transported to the drum shell.

Decanter centrifuges work according to the so-called countercurrent principle. The drum is partially designed as a solid jacket drum with at least one cylindrical section and a conical section, the first side closing the cylindrical section of the drum and the second side closing the conical section at its smaller diameter, with a flange with a or more openings is arranged. The flange forms an edge which protrudes inwardly in relation to the radial course of the centrifuge compared to the drum. The screenings to be separated are placed in the middle of the drum. The sedimented solid is conveyed in the direction of the second side by the screw, which revolves at a differential speed to the drum, while the clarified liquid overflows over the flange on the first side of the drum. A liquid level, which is established on the first side due to the course of the drum and the edge formed by means of the flange, determines the ratio between a clarifying part and a dry part of the drum. The liquid level defines the liquid level that is created when the material to be screened is processed by rotating the drum. The liquid level can also be referred to as the sump height, the clarifying part as the sump and the dry part as the dry beach. The differential speed between the worm and the rotor is usually realized by a high-performance drive, in particular by means of V-belts.

The pre-thickened sieve screw centrifuge is basically a previously described decanter centrifuge, in which a section with a sieve jacket is connected to the second side of the drum so that liquid, in particular with small solid particles, can exit through the sieve jacket. Larger solid particles are transported by means of the screw to the free end face of the sieve drum and transported away at a free edge of the sieve drum. In such a centrifuge, the material to be screened can thus be separated into three components: liquid over the first side of the drum; Liquid, optionally with fine solid particles, over the sieve casing of the sieve drum; larger solids over the free edge of the sieve drum following the second side of the drum.

A sieve decanter is structurally a sieve screw centrifuge with a pre-thickening, the section having the sieve casing connected to the second side of the drum being cylindrical. This section of the sieve drum having the sieve jacket can have a diameter that is the same or a larger than the diameter to which the section adjoins.

In contrast to the screw sieve centrifuge, the pusher centrifuge transports the material to be sieved, in particular the solids, in the transport direction along the axial course of the drum by an oscillating movement of a push floor, in particular parallel to the axis of rotation of the drum. The transport of the material to be screened, in particular the solids, along the axial course of the drum in the transport direction takes place in the vibrating centrifuge by means of an axial vibration of the drum itself superimposed on the rotary movement of the sieve drum The solids separated from the sieve drum are pushed in the transport direction until it leaves the sieve drum. The vibrating centrifuge and the pusher centrifuge therefore each have no screw conveyor for transporting the material to be screened, in particular the solids, along the axial course of the drum.

The sliding centrifuge also does not have a screw conveyor. The solid particles slide individually, i.e. not in a closed form, over stepped sieve trays of the sieve drum, whereby the solids deposited on the sieve drum slide by overcoming the very low frictional force between the sieve material and the sieve drum by a downhill force in the transport direction of the sieve material until it slides into the sieve drum , especially at the large diameter of the sieve drum.

In the following, the invention is described using the example of a screw-type centrifuge, the invention not being related to screw-type centrifuges limited. Rather, the invention can be used analogously in the other types of centrifuge described above.

The example described below does not require any elements other than those according to claim 1 that are essential for the invention.

In this example of the screw sieve centrifuge, the sieve drum is conical and widens from the first side with a first diameter in the direction of transport of the material to be sieved to the second side with a second larger diameter. A screw conveyor with a screw flight arranged on the outside of the screw conveyor is arranged within the screening drum, the screw flight corresponding to the inner course of the screening drum. The screw conveyor rotates with a differential speed compared to the rotating sieve drum, so that the material to be sieved is evenly distributed and accelerated. The screw conveyor rotates at a higher speed than the rotating screening drum so that the material to be screened is transported in the direction of transport. The material to be screened is usually introduced in the form of a solid-liquid mixture on the first side of the screen drum in the vicinity of the smallest screen drum diameter. On the first side, the main part of the liquid is separated from the material to be screened radially via the screen drum. The solids deposited on the sieve drum, which is also referred to as solids cake, are transported by means of the transport screw in the transport direction to the second side of the sieve drum until it leaves the sieve drum over the edge of the second side of the sieve drum. There is a gap between the sieve drum and the corresponding screw flight, in particular from 0.5 mm to 4 mm, so that rotation of the sieve drum and the screw is easily possible.

According to the invention, during the transport of the solids deposited on the sieve drum in the transport direction, an air flow generated to the solids by means of the air flow element is supplied. Alternatively or in addition to this, the air flow is dehumidified by means of the dehumidifying element. According to the invention, this means that the air flowing into the housing is dehumidified inside or outside the housing. Dehumidification is understood to mean a reduction in the relative and / or absolute humidity of the air.

According to the invention, this air flow is not the air flow of a known centrifuge, which naturally arises from the rotation of a drum of a known centrifuge. Rather, according to the invention, it is an air flow which is enlarged and / or dehumidified compared to the known prior art, which is generated by means of the air flow element and / or is dehumidified by means of the dehumidifying element. According to the invention, such an air flow is used to effectively dry the solid within the centrifuge. This enlarged and / or dehumidified air flow penetrates the solid or flows past the solid and dries it during the transport in the transport direction during the separation process. The dehumidifying element enables a reduction in the relative and / or absolute humidity of the air in the air flow and thereby improves drying by increasing the ability of the air flow to absorb moisture. In this way, the residual moisture in the separated solid is effectively reduced. Subsequent drying of the solid can thus be dispensed with.

According to the invention, in addition to the mechanical separation of the solid and the liquid, further drying of the screenings deposited on the screen drum in the form of a solid cake by convection by means of a continuously operating centrifuge is made possible. The mechanical separation takes place in particular in that the liquid from the material to be screened pressed against the screen jacket is separated radially via the screen drum, while the solid remains on the screen drum. Furthermore, this solid remaining on the sieve drum is further freed of the residual liquid during its transport in the transport direction by means of the air flow generated by the air flow element and / or dehumidified by means of the dehumidifying element by convection by drying the solid by means of the air flow and the liquid portion absorbed in the air flow is transported away with the air flow. The residual liquid leaves the solid in liquid or gaseous form. As a result, a solid with a low residual moisture, in particular below 5%, in particular below 3%, in particular below 1%, in particular below 0.5%, in particular below 0.2%, in particular below 0.1%, in particular below 0, 05%, based on the mass of the solid provided.

This provides a continuously operating centrifuge with a high throughput rate, with a solid with a low residual moisture being achieved at the same time.

In the case of the other types of centrifuges, the method of operation of the drying according to the invention is analogous. In the case of the sieve screw centrifuge with pre-thickening, the decanter centrifuge and the sieve decanter, the solids are additionally sedimented prior to drying. With the vibrating centrifuge, the sliding centrifuge or the pusher centrifuge, the solids deposited on the drum are not transported in the transport direction by means of a transport screw.

When an air flow element is arranged, an air flow that is 1.5 to 5 times greater than that of known centrifuges can be achieved according to the invention.

When a dehumidifying element is arranged, the air flowing into the housing and / or the air inside the housing and / or the air flowing out of the housing can be dehumidified. With a cumulative arrangement of an air flow element and a dehumidifying element, at least one dehumidifying element can be arranged downstream and / or one dehumidifying element upstream of the air flow element and / or a dehumidifying element within an assembly with the air flow element. Depending on the design and / or position of the air flow element, the air flowing into the housing and / or the air inside the housing and / or the air flowing out of the housing can be dehumidified.

If a dehumidifying element is arranged, the air of the air flow can be increased by a temperature of 5 ° C to 50 ° C, in particular 10 ° C to 40 ° C, in particular 15 ° C to 30 ° C, by means of the dehumidifying element, in particular a heating element, especially heated. In other words, the air in the air flow can be preconditioned. In particular, the air can be preconditioned inside and / or outside the housing. In particular, the temperature of the air during the preconditioning can be increased by 5 ° C to 50 ° C, in particular by 10 ° C to 40 ° C, in particular by 15 ° C to 30 ° C, in particular heated, in particular independently of the previous air temperature, will. In particular, the air can be heated to a temperature of up to 500.degree. C., in particular up to 100.degree. C., in particular up to 80.degree. C., in particular from 15.degree. Such preconditioning of the air increases the water absorption capacity of the air and thus improves drying by reducing the relative humidity of the air.

In particular, the centrifuge can have an inlet line or a feed pipe, by means of which the material to be screened is introduced directly or indirectly into the screening drum. In particular, the material to be screened can be introduced into the screen drum near the first side of the screen drum. The term near the first side encompasses a range of up to 25%, in particular up to 50% of the longitudinal extent of the screening drum starting from the first side.

In particular, the sieve drum can be at least partially cylindrical and / or at least partially conical. In particular, that part of the sieve drum having the sieve casing can be at least partially cylindrical and / or at least partially conical. In particular, the part of the sieve drum having the sieve jacket can be at least partially conical, widening along an acute angle, in particular from 5 ° to 30 °, in particular from 10 °, in particular from 20 °. In particular, the screening drum can widen from the first side with a first diameter in the transport direction of the material to be screened to the second side with a second larger diameter.

In particular, the sieve drum can be designed in several parts, in particular from a carrier basket and a sieve basket fastened to the carrier basket, in particular wherein the sieve basket can comprise several sieve segments.

In particular, the sieve drum can be partially designed as a solid jacket drum.

In particular, the centrifuge according to the invention can be used for the separation of polymer granules or polymer pellets. The terms polymer granulate or polymer pellets include both pure polymers and polymer compounds.

Particularly when a screw is arranged, in particular in the case of the screen screw centrifuge, the screw flight of the screw can be partially interrupted, in particular in the central region of its longitudinal extent. In this case, the worm partially has no worm thread. In this way, the material to be screened, in particular the solids, only partially slides over the screen drum in this area and / or is only pushed in the transport direction by the screen material subsequently deposited on the screen drum and is not pushed by the worm gear in this part. This means that the material to be sieved remains in the sieve drum longer and is therefore dried longer so that the residual moisture can be further reduced.

Alternatively or cumulatively, the screw can be cylindrical, the sieve drum being at least partially conical. In this way, the screenings deposited on the sieve drum will remain longer in the screen drum in the widening area of the screen drum due to the larger gap between the screw and the screen drum, because in this area the screenings separated only when there is a larger layer of the screenings on the screen drum by means of the Worm gear in Transport direction is pushed. This means that the screenings are dried longer so that the residual moisture can be further reduced.

In particular, such a screw can have one or more recesses or recesses in its base body. In this way, the air flow can be further optimized, in particular enlarged, and the drying can be improved.

In particular, the axis of rotation about which the screen drum is rotatably mounted can be oriented horizontally or at an angle to the horizontal or vertically.

At least one of the air flow elements is preferably formed by one or more lamellae projecting beyond the sieve casing of the sieve drum, in particular in the radial direction of the sieve drum. When the screen drum rotates, such lamellae generate a negative pressure around the screen jacket of the screen drum. This negative pressure is increased compared to a sieve drum without such slats. In this way, air, in particular more air, flows from the interior of the sieve drum over the sieve casing and over the solids deposited on the sieve casing and dries the solids in the process. Thus, an air flow is generated by means of the lamella (s), which leads to less residual moisture in the solid. A sieve drum designed in this way can be referred to as a fan drum.

In particular, several lamellae can be arranged, which are evenly distributed over the outer circumferential course of the screening drum. Such lamellae can also be referred to as blades. The lamellas can extend over the entire length of the sieve drum. Alternatively or cumulatively, lamellae extending over part of the longitudinal extent of the sieve drum can be arranged. In the case of lamellae which extend over part of the longitudinal extent of the sieve drum, several lamellae can be arranged along the longitudinal extent.

In particular, the lamellae can vary with respect to their extension in the radial direction starting from the sieve drum along the longitudinal extent of the sieve drum. In this way, different pressure ratios and thus locally different air volume flows can be implemented along the longitudinal extension of the sieve drum. In particular, the lamellae can run at an acute angle, in particular from 1 ° to 45 °, to the longitudinal extension of the sieve drum.

As an alternative or in addition to the described fan drum, at least one of the air flow elements is preferably formed by one or more ventilation elements, in particular a ventilation fan. In the simplest case, the ventilation element can be implemented through an opening to the surroundings of the housing. In particular, the ventilation element can be arranged on the housing, in particular in a housing area facing the second side of the sieve drum. In particular, the ventilation element can be designed as a ventilation fan and / or air pump. Such a ventilation element increases the air flow flowing into the housing, in particular towards the sieve drum, in particular from the vicinity of the housing, and thereby improves the drying of the solid.

In particular, the ventilation element can have at least one dehumidifying element for dehumidifying the air flow, in particular a heating element and / or a filter and / or a separation cyclone, whereby the drying performance is further improved. This is because air with less humidity increases the air's ability to absorb moisture.

As an alternative or in addition to the described fan drum and / or the ventilation element, at least one of the air flow elements is preferably formed by one or more ventilation elements, in particular a ventilation fan. In particular, the ventilation element can be arranged on the housing, in particular in a housing area facing the screen jacket. Such a venting element increases the air flow flowing out of the housing, so that a greater negative pressure in the Housing, in particular around the screen jacket. In this way, more air is sucked through the screen jacket and the solids deposited on it, which improves drying. In the simplest case, the ventilation element can be implemented through an opening to the surroundings of the housing.

In the event that the air flowing out through the ventilation element is supplied to the housing in a circulating air mode, in particular by means of a ventilation element, the ventilation element can have at least one dehumidifying element for dehumidifying the air flow, in particular a heating element and / or a filter and / or a separation cyclone, exhibit.

At least one of the air flow elements is preferably formed by one or more lamellae protruding beyond the screen jacket of the screen drum, the lamellae being connected to the screen drum in a materially and / or non-positively and / or form-fitting manner. In particular, the lamellae can engage in retaining grooves in the screening drum, in particular be pressed in. In particular, the slats can be attached to one or more rings. Such rings can in turn be pushed onto the screen drum in the axial direction and fixed to the screen drum. Such rings allow easy assembly and disassembly of lamellae on the screening drum.

In particular, the lamellae can be welded and / or glued and / or screwed and / or riveted to the sieve drum. In particular, a magnetic connection between the lamellae and the sieve drum can be produced by means of at least one, in particular electric, magnet.

Preferably, at least one of the airflow elements is formed by one or more lamellae protruding beyond the sieve casing of the sieve drum, the lamellae having a metal and / or a plastic, in particular reinforced plastic, in particular fiber composite material and / or steel as a component. A plastic contributes Weight reduction of the slats. A metal is used to make the slats more robust.

At least one of the air flow elements is preferably formed by one or more lamellae protruding beyond the sieve casing of the sieve drum, at least one of the lamellae being straight or curved, in particular curved backwards, in the radial direction of the sieve drum. Lamellas in particular have the advantage that less solids are deposited on them. Curved fins, on the other hand, create a larger airflow. Of course, a combination of straight and curved, in particular backward curved, lamellae on the screening drum is also possible.

At least one particularly vertical bulkhead is preferably arranged between the housing and the screening drum. In particular, an annular gap of 0.5 mm to 2 mm can be provided between the sieve drum and the bulkhead. In particular, the bulkhead can be sealed against the sieve drum, in particular by means of a sliding seal and / or a contactless seal and / or a Teflon ring seal and / or a mechanical seal.

In particular, the bulkhead can be materially and / or non-positively and / or positively connected to the housing. The bulkhead allows a functional subdivision of the screening drum into at least two sections with regard to their axial extent. In other words, such a bulkhead divides the surrounding housing into at least two sections. This is advantageous because such a subdivision allows the air flow generated by the air flow element to be used in a targeted manner in one of the sections of the sieve drum. In particular, it is advantageous to generate the air flow in a section of the sieve drum in which the material to be sieved has already covered part of the longitudinal extent of the sieve drum in the transport direction and therefore already has only a little liquid. In particular, the air flow element can therefore be arranged in the region of the centrifuge in which the air flow element has a Air flow generated behind the bulkhead in the direction of transport of the material being screened. In this way, the drying of the screenings is made more efficient within a so-called drying zone.

The bulkhead can be sealed against the sieve drum in such a way that the seal acts like a membrane in that it is air-permeable, but not liquid-permeable.

In particular, one or more further such bulkheads can be arranged in order to functionally subdivide the sieve drum into further sections.

Preferably at least one vertical bulkhead is arranged between the housing and the sieve drum, which divides the axial extent of the sieve drum into a dewatering zone, in particular in the transport direction of the screened material in front of the bulkhead, and into a drying zone, in particular in the transport direction of the screened material behind the bulkhead.

According to the invention, however, this does not mean a strict, geometrically precise subdivision of the two screen drum zones. Rather, the dewatering zone and the drying zone can at least partially overlap. However, the air flow generated by the air flow element is advantageously concentrated in the drying zone.

Such a subdivision is advantageous because it allows the air flow generated by the air flow element to be used in a targeted manner in the drying zone of the sieve drum. It is advantageous to generate the air flow in a section of the sieve drum in which the material to be sieved has already covered part of the longitudinal extent of the sieve drum in the transport direction and therefore already contains only a little liquid. In particular, the air flow element can therefore be arranged in the area of the centrifuge in which the air flow element generates the air flow in the transport direction of the material to be screened behind the bulkhead. In this way, the drying of the screenings within the drying zone is made more efficient.

In the case of lamellae on the sieve drum, the lamellae can only extend over the drying zone of the sieve drum. If a ventilation element is arranged, this ventilation element can be arranged behind the bulkhead in the direction of transport of the material to be screened in order to generate the air flow in a targeted manner in the drying zone.

In particular, the bulkhead can be assigned to the first side of the sieve drum. The wording that the bulkhead is assigned to the first side of the sieve drum means that the bulkhead is arranged in the first half, in particular the first quarter, in particular the first 20%, in particular 10%, in the transport direction of the material to be screened.

In particular, the bulkhead can be sealed off from the sieve drum in such a way that the seal acts like a membrane in that it is air-permeable, but not liquid-permeable.

In particular when the sieve drum is designed as a fan drum, the longitudinal course of the lamella (s) in the area of the bulkhead can be interrupted. In this way, an effective seal between the bulkhead and the sieve drum can be achieved.

At least one particularly vertical bulkhead is preferably arranged between the housing and the sieve drum, which partition is assigned to the second side of the sieve drum.

The wording that the bulkhead is assigned to the second side of the sieve drum means that the bulkhead is in the last quarter, in particular the last 20%, in particular 10%, in particular 5%, in particular 3% of the longitudinal extent of the Screen drum, in particular on the second side, in particular on a free edge of the screen drum is arranged.

In particular, this bulkhead can be sealed against the sieve drum, in particular by means of a sliding seal and / or a contactless seal and / or a Teflon ring seal and / or a mechanical seal, in particular in such a way that the seal acts like a membrane, being air-permeable, but not is liquid-permeable. This prevents the liquid separated in front of the bulkhead in the direction of transport of the material being screened from reaching the area falling out of the screen drum. Thus the low residual moisture of the solid is realized. Furthermore, an air stream, coming from the second side of the sieve drum at the free edge at which the separated solid material leaves the sieve drum, flows towards the outer jacket of the sieve drum, can further minimize the residual moisture. This so-called countercurrent flowing through an annular gap between the sieve drum and the housing, in particular a bulkhead on the housing, prevents the liquid previously separated on the sieve drum from being transferred to the solid falling on the free edge of the sieve drum, in particular into a solid on the free edge the sieve drum arranged solids housing arrives.

The dehumidifying element is preferably designed as at least one heating element and / or condensation dryer and / or filter and / or separating cyclone. The separating cyclone is a passive component that separates the liquid from the air. In particular, such a dehumidifying element can be arranged inside, outside or on the housing. In particular, several dehumidifying elements can be arranged. In the case of a condensation dryer, the humid air can be guided by means of the air flow element or several air flow elements over cooling fins and / or cooling fins, the temperature of which is below the dew point of the air. The water from the air condenses and collects as condensation on the cold surface, which then collects in a separate container. In particular, the cooled and dehumidified air can subsequently be heated, in particular by means of a heating element.

The centrifuge is preferably designed as a sieve screw centrifuge, with one, in particular hollow inside, inside the sieve drum. Transport screw is arranged with a screw flight arranged on the outside of the transport screw, in particular that the screw flight corresponds to the inner course of the sieve drum. The screw conveyor can have a first axial opening on its first end face facing the first side of the screening drum and / or a second axial opening on its second end face opposite the first end face. An inlet line for introducing the material to be screened into the sieve drum can be guided via the second axial opening of the screw conveyor, in particular the material being screened is introduced into the drum screen via the first axial opening of the screw conveyor. The screw conveyor can have at least one conical section and / or at least one cylindrical section. Alternatively or cumulatively, the material to be screened can be fed to the screening drum via an axial opening in the screw conveyor.

The invention also relates to a method for separating a material to be screened, in particular polymer pellets, into a solid and a liquid by means of a continuously operating centrifuge, the liquid being mechanically separated from the solid by means of a rotating drum screen

It is particularly advantageous in the method according to the invention for separating a material to be screened, in particular polymer pellets, into a solid and a liquid by means of a continuously operating centrifuge, with the liquid being mechanically separated from the solid by means of a rotating sieve drum, it is that within the Centrifuge, the solid is dried by means of an air flow generated by an air flow element and / or by means of an air flow dehumidified by a dehumidifying element.

After the liquid has been separated from the solid by means of the rotating sieve drum, the solid formed as a result still has a certain liquid content, since liquid adheres to the solid particles. Due to the inventive drying of the solid by means of an air flow generated by an air flow element and / or by means of one of a Dehumidification element dehumidified air flow, a further drying of the solid takes place, so that a very low residual moisture can be achieved.

According to the invention, the air flow is generated by the ventilation element already described and / or the ventilation element already described and / or by the already described lamellae protruding beyond the sieve casing of the sieve drum. In particular, the air flow can be generated by means of an active and / or passive air flow element. According to the invention, an active air flow element means an air flow element with its own, in particular electric, drive which actively supplies air into the housing and / or sucks air out of the housing. For example, the active elements are fans and / or pumps. According to the invention, a passive airflow element means an airflow element which, due to its design and / or its position, serves to generate an airflow without using its own drive. For example, the passive elements are openings in the housing or lamellae in the fan drum.

In this way, according to the invention, in addition to the mechanical separation, there is also a further separation of the solid and the liquid by convection. It is used to reduce the residual moisture in the solids processed using the process.

The method is also not restricted to any specific type of centrifuge, but rather can be carried out using any of the centrifuges described in the introduction.

In particular, the speed of the sieve drum can be 500 to 2000 revolutions per minute. If a screw conveyor is arranged, it can rotate 3 to 30 revolutions per minute faster than the sieve drum, ie have a speed difference compared to the sieve drum of 3 to 30 revolutions per minute.

In particular, in a screw-type centrifuge, the speed difference between the screw and the drum and / or the geometry of the screw flight, in particular its screw pitch, can be set in such a way that the solids deposited on the drum remain longer on the drum. The smaller the screw pitch, the smaller the distances between the successive blades of the screw flight and the longer the length of time the material to be screened remains on the screen drum. In particular, the worm thread of the worm can be designed degressively. That is, the screw flight, which is assigned to the first side of the screening drum, has a greater screw pitch than the course of the screw flight following in the transport direction of the material to be screened, which has a correspondingly smaller screw pitch. In particular, the dwell time of the material to be screened, in particular in a drying zone of the screen drum, can thereby be extended.

Furthermore, a longer dwell time of the solid on the sieve drum can be achieved, in particular by means of a low differential speed, in particular of 3 to 30 revolutions per minute. In this way, the solids are dried for a longer period in order to achieve an even lower level of residual moisture.

In particular, the method according to the invention can be used for separating polymer pellets or polymer granules.

In particular, the method can be carried out in recirculation mode. For this purpose, the air discharged by means of a venting element, in particular after it has been preconditioned, in particular by means of a dehumidifying element, in particular by means of a venting element, can be fed back to the housing of the centrifuge.

It is advantageous in the method if the material to be screened has an elevated temperature of 40 ° C. to 100 ° C., in particular 80 ° C., in particular 60 ° C., in particular 40 ° C., before it is introduced into the sieve drum. Under these boundary conditions, improved drying effects can be implemented. In particular, the material to be screened can be heated to a temperature of 40 ° C. to 100 ° C., in particular to 80 ° C., in particular to 60 ° C., in particular to 40 ° C., before it is passed into the sieve drum. For this purpose, one or more additional heating elements can be provided for heating the material to be screened. In particular, the centrifuge according to the invention itself can have one or more additional heating elements for heating the material to be screened.

The air of the air flow is preferably increased, in particular heated, by a temperature of 5 ° C to 50 ° C, in particular 10 ° C to 40 ° C, in particular 15 ° C to 30 ° C, by means of the dehumidifying element, in particular a heating element. In other words, the air in the air flow is preconditioned. In particular, the air inside and / or outside the centrifuge can be preconditioned. In the event that the centrifuge has a housing, the air inside and / or outside the housing can be preconditioned. Such preconditioning of the air increases the water absorption capacity of the air and thus improves drying by reducing the relative humidity of the air.

In particular, the air can be heated to a temperature of up to 500 ° C, in particular up to 100 ° C, in particular up to 80 ° C, in particular from 15 ° C to 85 ° C, in particular from 20 ° C to 50 ° C. In particular, the temperature of the air during the preconditioning can be increased by 5 ° C to 50 ° C, in particular by 10 ° C to 40 ° C, in particular by 15 ° C to 30 ° C, in particular heated, in particular independently of the previous air temperature, will.

The longitudinal extent of the sieve drum is preferably divided into a dewatering zone and a drying zone, in particular the drying taking place within the drying zone. This can be done using the bulkhead already described.

According to the invention, however, this is not a strict, geometrically precise subdivision of the two screen drum zones, but a functional subdivision meant. Rather, the dewatering zone and the drying zone can at least partially overlap. However, the air flow generated by the air flow element is advantageously concentrated in the drying zone.

Such a subdivision is advantageous because it allows the air flow generated by the air flow element to be used in a targeted manner in the drying zone of the sieve drum. It is advantageous to generate the air flow in a section of the sieve drum in which the material to be sieved has already covered part of the longitudinal extent of the sieve drum in the transport direction and therefore already contains only a little liquid. In particular, the air flow element can therefore be arranged in the area of the centrifuge in which the air flow element generates the air flow in the transport direction of the material to be screened behind the bulkhead. In this way, the drying of the screenings within the drying zone is made more efficient.

Fig. 1

eine Teilansicht eines Querschnitts durch eine Siebschneckenzentrifuge nach dem bekannten Stand der Technik;

Fig. 2

eine Teilansicht eines Querschnitts durch eine erfindungsgemäße Siebschneckenzentrifuge nach erstem Ausführungsbeispiel;

Fig. 3a

eine perspektivische Ansicht und einen Querschnitt einer ersten Siebtrommel mit gekrümmten Lamellen gemäß der Erfindung;

Fig. 3b

eine perspektivische Ansicht und einen Querschnitt einer zweiten Siebtrommel mit geraden Lamellen gemäß der Erfindung;

Fig. 3c

eine perspektivische Ansicht und einen Querschnitt einer dritten Siebtrommel mit an Ringen befestigten Lamellen gemäß der Erfindung;

Fig. 4

eine schematische Ansicht einer erfindungsgemäßen Zentrifuge nach zweitem Ausführungsbeispiel;

Fig. 5

eine schematische Ansicht einer erfindungsgemäßen Zentrifuge nach drittem Ausführungsbeispiel;

Fig. 6

eine schematische Ansicht einer erfindungsgemäßen Zentrifuge nach viertem Ausführungsbeispiel;

Fig. 7

eine Teilansicht eines Querschnitts durch eine erfindungsgemäße Schubzentrifuge.

A centrifuge according to the known prior art and several exemplary embodiments of the invention are shown in the figures. Show it:

Fig. 1

a partial view of a cross section through a screen screw centrifuge according to the known prior art;

Fig. 2

a partial view of a cross section through a screw sieve centrifuge according to the invention according to the first embodiment;

Fig. 3a

a perspective view and a cross section of a first screening drum with curved lamellae according to the invention;

Figure 3b

a perspective view and a cross section of a second screening drum with straight lamellae according to the invention;

Figure 3c

a perspective view and a cross section of a third screening drum with lamellae attached to rings according to the invention;

Fig. 4

a schematic view of a centrifuge according to the invention according to a second embodiment;

Fig. 5

a schematic view of a centrifuge according to the invention according to a third embodiment;

Fig. 6

a schematic view of a centrifuge according to the invention according to the fourth embodiment;

Fig. 7

a partial view of a cross section through a pusher centrifuge according to the invention.

The figures are not shown to scale.

The Figure 1 Figure 11 shows a partial view of a cross section through a centrifuge according to the prior art. It is a screw sieve centrifuge. A drum configured as a sieve drum 1 rotatably mounted within a housing 10 can be seen. A screw 2, which follows the conical shape of the sieve drum 1, is arranged inside the sieve drum 1. The sieve drum 1 and the screw 2 rotate at different speeds about the axis of rotation 100 in order to separate the material 90 in the form of a suspension into a solid and a liquid, the filtrate. The axis of rotation 100 of the sieve drum 1 is aligned horizontally. Due to the different speeds of the rotations of the sieve drum 1 and the screw 2, a relative movement occurs between the sieve drum 1 and the screw 2, whereby the screened material 90 is transported along the sieve drum 1 in the transport direction 50 due to the screw thread 20 arranged on the outside of the screw 2.

The sieve drum 1 has a first side 1 a, on which the material to be sieved 90 is guided into the sieve drum 1 via the inlet line 9. Furthermore, the sieve drum 1 has a second side 1b with a larger diameter compared to the first side 1a. The screw 2 has an opening 21 for the passage of the screenings 90 to the screening drum 1. The inlet line 9 is guided over an axial opening of the screw 2. Via the inlet line 9 and the opening 21, the screenings 90 are passed into the screening drum 1 near the first side 1a.

The screenings 90 entering the sieve drum 1 are separated by the rotation of the screen drum 1 in such a way that the liquid of the screenings 90 passes through the screen casing 11 of the screen drum 1 according to the arrows 30, after which it is diverted from the housing 10 through discharge lines 31 and 32 . The solids part of the screenings 90, however, is transported by means of the worm thread 20 of the screw 2 in the transport direction 50 of the screenings 90 over the longitudinal extent of the screening drum 1 until the solids on the second side 1b of the screening drum 1 falls on the free edge according to arrow 35.

This type of separation can be referred to as mechanical separation.

The Figure 2 shows a partial view of the cross section through the sieve screw centrifuge according to the invention according to a first embodiment. The screw thread 20, which is not visible in the cross-section, is also shown schematically across the screen drum 1. This centrifuge basically works according to the principle of the centrifuge Figure 1 , whereby in addition to the mechanical separation, an additional separation takes place by convection in the form of drying of the solid according to the invention. In an area of the housing 10 facing the second side of the sieve drum 1, a ventilation element 80 in the form of a ventilation fan is arranged, which generates an air stream 40 flowing into the housing 10 in order to dry the solid.

Furthermore, a first bulkhead 15 for functional subdivision of the longitudinal extension of the sieve drum 1 into a dewatering zone 1c in the transport direction 50 in front of the bulkhead 15 and a drying zone 1d in the transport direction 50 behind the bulkhead 15 is arranged between the housing 10 and the sieve drum 1.

Furthermore, a second bulkhead 16 is arranged between the housing 10 and the sieve drum 1, which partition is assigned to the second side 1b of the sieve drum 1, namely is arranged on the free edge of the sieve drum 1. This second bulkhead 16 is sealed off from the sieve drum 1 in such a way that it is air-permeable, but not liquid-permeable.

The air flow generated by means of the ventilation element 80 for drying the solid can be divided into different types. This creates an air stream according to the arrows 41, which penetrates the solids deposited on the sieve drum 1 and the sieve casing 11 itself and thereby dries the solids. In connection with this air flow according to the arrows 41, there is also an air flow according to the arrows 43 which flows along the screw flight 20 and can be referred to as a cross flow.

Furthermore, this creates an air flow according to the arrows 42, which comes from the second side 1b of the sieve drum 1 at the free edge at which the separated solid leaves the sieve drum 1, against the transport direction 50 of the screenings 90 into the screw flight 20 and to the outer shell the sieve drum 1 flows between the sieve drum 1 and the bulkhead 16. This countercurrent prevents the liquid previously separated on the sieve drum 1 from reaching the free edge of the sieve drum 1 and thus the falling solids.

By means of the discharge line 31, mainly liquid in the drainage zone 1c is discharged. By means of the discharge line 33, liquid is discharged in liquid and gaseous form in the drying zone 1d.

Thus, by means of the ventilation element 80, an air flow for drying the solid is generated. This air flow in its described types ensures a lower residual moisture in the solids processed by means of the centrifuge. The first bulkhead 15 concentrates the air flow on the drying zone 1d and thereby further improves the drying. The second bulkhead 16 also prevents the previously deposited on the sieve drum 1 Liquid arrives at the solid falling on the free edge of the sieve drum 1 and thereby also improves drying.

In an exemplary embodiment not shown, the sieve drum 1 according to the first exemplary embodiment can be designed as a fan drum, which is based on the Figures 3a to 3c is explained in more detail below.

The Figure 3a shows a perspective view and a cross section AA of a first screening drum 1 with lamellae 81a according to the invention which are curved backwards with respect to the radial direction of the screening drum 1. The lamellae 81a extend almost over the entire longitudinal extent of the sieve drum 1. In alternative embodiments, however, the lamellae 81a can also extend over a possibly smaller part of the longitudinal extent of the sieve drum 1.

The Figure 3b shows a perspective view and a cross section BB of a second screening drum 1 with lamellae 81b according to the invention which are straight with respect to the radial direction of the screening drum 1. The lamellae 81b extend almost over the entire longitudinal extent of the sieve drum 1. In alternative embodiments, however, the lamellae 81b can also extend over a possibly smaller part of the longitudinal extent of the sieve drum 1.

The Figure 3c shows a perspective view and a cross-section CC of a third screening drum 1 with lamellae 81c according to the invention which are curved backwards with respect to the radial direction of the screening drum 1. The lamellae 81c are attached to the screening drum 1 by means of rings 800 pushed onto the screening drum 1 and each extend only over part of the longitudinal extent of the screening drum 1. Two successive rings 800 form an assembly with the lamellae 81c attached. Rings 800 of this type permit simple assembly and disassembly of lamellae 81c on the screening drum 1.

The so-called fan drums according to Figures 3a to 3c have in common that they create a negative pressure around the screen jacket 11 due to the Generate rotation of the sieve drum 1. This creates an air flow for drying the solid, so that drying is improved.

The Figure 4 shows a schematic view of a centrifuge according to the invention according to the second embodiment. The air flow 40 supplied to the housing 10 is dehumidified by means of a dehumidifying element 45 in the form of a heating element in order to increase its water absorption capacity. For this purpose, the ambient air 400 with a temperature of 5 ° C to 25 ° C is heated by 25 ° C by means of the dehumidifying element 45. That means: the temperature of the ambient air 400 is increased by 25 ° C. As a result, the relative humidity of the supplied air stream 40 is reduced, whereby its water absorption capacity increases. This improves drying. Furthermore, a ventilation element 85 in the form of a ventilation fan is arranged on the discharge line 33 in order to further increase the air flow within the housing 1 and to improve drying. The discharge line 33 and the venting element 85 are located in a region of the housing 10 facing the sieve casing of the sieve drum 1.

The Figure 5 shows a schematic view of a centrifuge according to the invention according to a third embodiment. This is in addition to the centrifuge after Fig. 4 a ventilation fan 86 is arranged as a ventilation element and can be optionally connected to the dehumidifying element 45. The ventilation fan 86 can be switched on as required. The ventilation fan 86 when switched on increases the air flow 40 additionally. Furthermore, a separating device for separating the diverted stream into a liquid part 330 and a gaseous part 331 is arranged on the discharge line 33, the venting element 85 in the form of a venting fan being connected downstream of the gaseous part.

The Figure 6 shows a schematic view of a centrifuge according to the invention according to a fourth embodiment. This is in addition to the centrifuge after Fig. 4 a ventilation fan 86 is connected upstream of the dehumidifying element 45. The ventilation fan 86 additionally increases the air flow 40. Unlike in the centrifuge according to Fig. 5 the ventilation fan 86 is not optional, but mandatory.

The Figure 7 shows a partial view of a cross section through the pusher centrifuge according to the invention. Deviating from the previously described screw sieve centrifuges, this is a pusher centrifuge with a push floor 7, which is driven in an oscillating manner according to the double arrow 71. Here, the material to be screened 90 is transported in the direction of transport 50 by continuously pushing the solid previously deposited on the drum 1 by means of the solid newly deposited on the drum 1 and by means of the push floor until it reaches the drum 1 at the free edge according to arrow 35 leaves. The sieve drum 1 is designed as a fan drum with lamellae, not shown. Due to the rotation of the sieve drum 1 about the axis of rotation 100, these lamellae generate a negative pressure around the sieve casing of the sieve drum 1 and thus also an air flow 41. Furthermore, the air in the air flow 41 is dehumidified by means of a dehumidifying element (not shown) in the form of a heating element. This air stream 41 penetrates the sieve casing of the sieve drum 1 and the solids deposited thereon, the solids being dried. In this way, the residual moisture in the solid is minimized.

Claims (15)

Centrifuge for the separation of a material to be screened (90) into a solid and a liquid with a sieve drum (1) which is arranged inside a housing (10) and rotatably mounted about an axis of rotation (100), the length of which extends from a first side (1a) extends in the transport direction (50) of the material to be screened (90) to a second side (1b) and has a screen casing (11), characterized in that the centrifuge has at least one air flow element (80, 81a, 81b, 81c, 85, 86) and / or has at least one dehumidifying element (45) in order to generate an, in particular dehumidified, air flow within the housing (10). Centrifuge according to Claim 1, characterized in that at least one of the air flow elements (80, 81a, 81b, 81c, 85, 86) is formed by one or more lamellae (81a, 81b, 81c) protruding beyond the sieve shell (11) of the sieve drum (1) is trained. Centrifuge according to Claim 1 or 2, characterized in that at least one of the air flow elements (80, 81a, 81b, 81c, 85) is formed by one or more ventilation elements (80), in particular a ventilation fan (86). Centrifuge according to one of the preceding claims, characterized in that at least one of the air flow elements (80, 81a, 81b, 81c, 85, 86) is formed by one or more ventilation elements (85), in particular a ventilation fan. Centrifuge according to one of the preceding claims, characterized in that at least one of the air flow elements (80, 81a, 81b, 81c, 85, 86) through one or more over the sieve casing (11) of the sieve drum (1) protruding lamellae (81a, 81b, 81c) is formed, wherein the lamellae (81a, 81b, 81c) are cohesively and / or non-positively and / or positively connected to the screening drum (1). Centrifuge according to one of the preceding claims, characterized in that at least one of the air flow elements (80, 81a, 81b, 81c, 85, 86) is formed by one or more lamellae (81a, 81b, 81a, 81b,) protruding beyond the sieve casing (11) of the sieve drum (1). 81c), the lamellae (81a, 81b, 81c) having a metal and / or a plastic, in particular reinforced plastic, in particular a fiber composite material and / or a steel as a component. Centrifuge according to one of the preceding claims, characterized in that at least one of the air flow elements (80, 81a, 81b, 81c, 85, 86) is formed by one or more lamellae (81a, 81b, 81c), with at least one of the lamellae (81a, 81b, 81c) being straight or curved, in particular curved backwards, in the radial direction of the screening drum (1). Centrifuge according to one of the preceding claims, characterized in that at least one particularly vertical bulkhead (15, 16) is arranged between the housing (10) and the sieve drum (1), in particular that the bulkhead (15, 16) opposite the sieve drum (1 ), in particular by means of a sliding seal and / or a contactless seal and / or a Teflon ring seal and / or a mechanical seal. Centrifuge according to one of the preceding claims, characterized in that at least one particularly vertical bulkhead (15) is arranged between the housing (10) and the sieve drum (1), which divides the axial extension of the sieve drum (1) into a dewatering zone (1c), in particular in the transport direction (50) of the screenings (90) in front of the bulkhead (15), and in a drying zone (1d), especially in the transport direction (50) of the screenings (90) behind the bulkhead (15). Centrifuge according to one of the preceding claims, characterized in that at least one particularly vertical bulkhead (16) is arranged between the housing (10) and the sieve drum (1), which partition is assigned to the second side (1b) of the sieve drum (1). Centrifuge according to one of the preceding claims, characterized in that the dehumidifying element (45) is designed as a heating element and / or condensation dryer and / or filter and / or separating cyclone. Centrifuge according to one of the preceding claims, characterized in that the centrifuge is designed as a sieve screw centrifuge, with a transport screw (2), in particular hollow inside, with a screw flight (20) arranged on the outside of the transport screw (2) inside the sieve drum (1) ) is arranged, in particular that the screw thread (20) corresponds to the inner course of the sieve drum (1). A method for separating a material to be screened (90), in particular polymer pellets, into a solid and a liquid by means of a continuously operating centrifuge, the liquid being mechanically separated from the solid by means of a rotating sieve drum (1), characterized in that within The centrifuge is used to dry the solid by means of an air flow generated by an air flow element (80, 81a, 81b, 81c, 85, 86) and / or by means of an air flow dehumidified by a dehumidifying element (45). The method according to claim 13, characterized in that the air of the air flow by means of the dehumidifying element, in particular a heating element, to a temperature of 5 ° C to 50 ° C, in particular 10 ° C to 40 ° C, in particular 15 ° C to 30 ° C ° C is increased, in particular heated. Method according to claim 13 or 14, characterized in that the longitudinal extension of the sieve drum (1) is divided into a dewatering zone (1c) and a drying zone (1d), in particular that drying takes place within the drying zone (1d).

Images