SCREW CENTRIFUGE FOR WET MECHANICAL SEPARATION OF SOLIDS

Description

[0001] The invention relates to a screw centrifuge for the wet mechanical separation of solids according to their density, comprising a rotating cylindrical drum with two conical drums connected thereto and openings for the discharge of the separated substances as sinking material and floating material and the separation liquid, and a rotating shaft with openings for the introduction of the solids to be separated, wherein a baffle plate is arranged on the shaft in the axial direction between the introduction opening for the substances to be separated and the discharge opening for the sinking material, and the shaft has two screws, one for the sinking material and one for the floating material, wherein the screw for the sinking material has a helix for transporting the sinking material to the opening for the discharge of the sinking material.

[0002] Such screw centrifuges are known, for example, from EP 0 553 793 B1. EP 1 020 227 A1 also discloses a screw centrifuge according to the preamble of claim 1, wherein the area between the baffle plate and the opening for the discharge of a third phase is designed as a classification zone.

[0003] Such machines have a limited throughput for light or floating matter. If the established throughput is increased, the machine blocks the product. Other similar machines are known from DE 195 16 636 A1 or EP 1 485 205 B1. Such machines are used for three-phase separation of mixtures of substances, e.g. different plastic fractions and a separation liquid. By selecting the appropriate density of the separation liquid, several different fractions can be separated in multi-stage processes. Furthermore, DE 3134935 A1 describes a decanter centrifuge for the separation of one solid phase and two liquid phases. Separation of light or floating matter is not possible here. The decanter centrifuge of DE 2612696 also does not allow separation of floating matter. It separates light and heavy solids, which settle or are carried to the inner circumference of the centrifuge bowl by gravity.US 2528974 describes a centrifugal separator for separating solids from liquids, which also does not allow three-phase separation. The spiral separator of US 4781822 separates two types of particles according to density and size, respectively.

[0004] The aim of the invention is therefore to achieve better separation and higher throughput in a three-phase separation.

[0005] The invention is therefore characterized in that the screw for the floating material is designed as a multi-flight screw and has spirals for transporting the floating material to the opening for the discharge of the floating material, the screw for the sinking material comprises an external spiral which is designed as a parallel spiral, wherein the parallel spiral consists of one or more additional narrow ribbon spirals, the external spiral has an overlap with the internal spirals of the screw for the floating material, the external spiral is arranged parallel to the spiral for transporting the sinking material around the spirals for transporting the floating material, wherein the external spiral is connected to the spirals for transporting the floating material at different points and the spirals are counter-rotating.This allows the throughput to be increased significantly while maintaining the same separation quality and residual product moisture, while also achieving a significant reduction in clogging / blocking of the machine despite higher throughputs.

[0006] A favorable embodiment of the invention is characterized in that the screw flight for the sinking material extends to the drum, and the screw flight for the floating material has a smaller outer diameter than the inner diameter of the screw flight for the sinking material. Due to this measure and the counter-rotating nature of the two screws, the light material floating on the separation liquid can be transported by the inner flight to the light material discharge, while the heavy material sinks, collects on the drum wall, and is transported by the outer flight to the opposite discharge. The separation liquid is separated separately via nozzles.

[0007] A favorable development of the invention is characterized in that the part of the cover of the screw flight for the sinking material is directly connected, preferably welded, to the flight for the floating material. This eliminates the need for any additional supports that could impede the path of the separated material.

[0008] An advantageous development of the invention is characterized in that the screw for the sinking material is designed as a multi-flight screw. With a suitable selection of flights and pitch, the total capacity of a screw can be increased.

[0009] The amount of product conveyed by each spiral flight (the product "pile" in front of the spiral) is significantly reduced compared to a single-flight spiral. This supports process stability, the separation of product fractions, the transport of the respective fraction, and the separation from the separation medium with significantly increased product throughputs.

[0010] The invention will now be described by way of example with reference to the drawings, in which Fig. 1 a state-of-the-art screw centrifuge Fig. 2 a screw centrifuge according to the invention Fig. 3 a cut through Fig. 2 along line III-III shows.

[0011] In Fig. 1 the separation device 10 consists of a cylindrical drum 11 that is conical at both ends. Inside the drum 11 there is a two-part conveyor screw 12 with screw flights 13 for discharging the sinking material 16 and with screw flights 23 for discharging the floating material 17. By means of different designs of the screw flights, e.g. outer diameter, counter-rotating flights, the sinking material 16 and the floating material 17 are transported to oppositely arranged discharge openings 14, 15: the sinking material 16 to one or more discharge openings 14, the floating material 17 to one or more discharge openings 15. The separation liquid 18 separated from the sinking material and the floating material is discharged via one or more nozzles 19 on the heavy material side of the separation device 10. A baffle plate 20 prevents the floating material 17 from being caught by the spirals 13 for the sinking material 16 during the separation process and from reaching the sinking material discharge 14.The mixture of solids and separation liquid to be separated is fed into the vessel interior via an axially arranged feed pipe 21 through one or more feed openings 22. By rotating the drum 11 and the conveyor screw 12, the mixture, for example a suspension, is set in rotation and a centrifugal field is generated in the suspension. The conveyor screw 12 is typically driven at a speed different from the drum speed. Due to the difference in density between the solids and the separation liquid, the solids separate within a short period of time, with the light solid (floating material 17) settling on the surface of the separation liquid 18 and the heavy solid (sinking material 16) sinking to the inner surface of the drum 11.The floating material is now captured by the screw flight 23 and conveyed to the discharge opening 15. The sinking material 16 is captured by the screw flight 13, conveyed to the discharge opening 14, and, due to the conical shape of the outer surface of the drum 11, lifted out of the separation liquid and conveyed out of the drum 11 via the discharge opening 14. The conical part of the drum 11 in the area of ​​the discharge opening 15 facilitates the separation of the floating material 17 from the separation liquid 18.

[0012] Fig. 2 now shows a screw centrifuge according to the invention, whereby an analogous representation to Fig. 1 was selected. Identical parts are identified by the same reference numerals as in Fig. 1 In order to improve throughput while maintaining the same separation selectivity and residual moisture, the transport of the settling material 16 via helix 13 to the discharge opening 14 is supplemented by additional parallel helixes 13'. This extension consists of one or more additional narrow (belt) helix(s) 13', which are arranged parallel to helix 13 around the helix 23 (and 23') for the floating material 17. The counter-rotation results in better separation of the solids. The helix(s) 13, 13' is / are connected to the helix(s) 23, 23' at various points, e.g., welded. This supports the helix(s) 13, 13'; separate supports are not required, which can restrict the screw flights and lead to clogging / blocking of the machine.According to the invention, the screw flight 23, 23' for the floating material 17 is designed with two flights, which allows for better conveying and thus a higher throughput. The product to be processed (feed material) often consists of plastic mixtures of different densities, which are to be separated into floating and sinking material fractions. Depending on the application, the separation leads to a separation selectivity of well over 99% for the individual fractions. In this way, in addition to lumpy plastic mixtures or films, fibrous materials such as carpet remnants made of polypropylene, polyamide and latex, among others, can be separated in a two-stage process and thus recycled. The separated solids are also subjected to a certain degree of washing during the separation process before being discharged.For even more effective separation, the two screw flight groups for sinking and floating material can also be installed with different pitches as required for the process, allowing the machine to be perfectly tailored to the process.

[0013] In Fig. 3 is a cut through Fig. 2along the line III-III. It shows a section through the individual screw flights. The upper part shows the section through the first flight 23 of the screw 12 for separating the floating material 17. The lower part shows a section through the second flight 23' for the floating material. However, additional screw flights can also be used, so that the screw then has three or more screw flights if necessary. The flight 13' for the sinking material 16 is shown on the outer circumference. In a single-flight flight for the sinking material 16, only the flight 13' appears, as shown in the upper part. In a double-flight flight, the flight 13" is also present, as shown in the lower part of the drawing.

[0014] The invention is not limited to the examples in the drawings. The edges of the coils can also be protected from excessive wear by wear pieces.

[0015] In summary, the invention relates to a screw centrifuge for the wet-mechanical separation of solids according to their density, which has a rotating cylindrical drum with two conical drums connected to it, with openings for the discharge of the separated substances as sinking matter and floating matter and the separation liquid, and a rotating shaft with openings for the introduction of the solids to be separated, wherein the shaft has two counter-rotating screw flights, with a baffle plate arranged on the shaft in the axial direction between the inlet opening for the substances to be separated and the discharge opening for the sinking matter. In addition, the outer flight of the screw for the sinking matter overlaps with the inner single- or multi-flight flight of the screw for the floating matter, wherein the flights are counter-rotating. The outer flight of the screw for the sinking matter can also be multi-flight.This allows for a particularly high throughput while maintaining high levels of selective separation and maintaining low residual moisture. The invention also relates to a conveyor screw for such a screw centrifuge.

Claims

1. Screw centrifuge for wet mechanical separation of solids according to their density by means of a rotating, cylindrical drum (11) with two conical drums connected to it and which has openings (14, 15) for discharge of the separated material as settleable solids (16) and floating solids (17) and of the separating liquid (18), and with a rotating shaft (12) with openings (22) for infeed of the solids to be separated, where a baffle disc (20) is arranged on the shaft in axial direction between the infeed opening (22) for the substances to be separated and the discharge opening (14) for the settleable solids (16), where the shaft (12) has two screws, one for the settleable solids (16) and one for the floating solids (17), where the screw for the settleable solids (16) has a flight (13) for the transport of the settleable solids (16) to the discharge opening (14), characterised in that the screw for the floating solids (17) is designed as a multi-channel screw and has flights (23,23') for the transport of the floating solids (17) to the discharge opening (15), the screw for the settleable solids (16) comprising an outer flight (13', 13"), which is designed as a parallel flight (13', 13"), where the parallel flight (13', 13") is comprised of one or several additional narrow ribbon flights (13', 13"), where the outer flight (13', 13") surrounds the inner flight (23, 23') of the screw for the floating solids (17), the outer flight (13', 13") is arranged parallel to the flight (13) for the transport of the settleable solids (16) surrounding the flights (23,23') for the transport of the floating solids (17), where the outer flights (13',13") are connected to the flights (23,23') at various points and the flights (13 ,13', 13", 23, 23') working in opposite directions.

2. Screw centrifuge according to Claim 1, characterized in that the screw flight (13, 13', 13") for the settleable solids (16) extends as far as the drum (11) and the screw flight (23, 23') for the floating solids (17) has a smaller outer diameter than the inner diameter of the screw flight (13', 13") for the settleable solids (16).

3. Screw centrifuge according to Claim 1 or 2, characterized in that the part of the screw flight (13', 13") for the settleable solids (16) that surrounds the flight (23, 23') for the floating solids (17) is directly connected to it, preferably by welding.

4. Screw centrifuge according to one of Claims 1 to 3, characterized in that the screw for the settleable solids (16) is designed as a multi-channel screw.

5. Transport screw for a screw centrifuge according to one of Claims 1 to 4, comprising a shaft (12) and two screws, one for the settleable solids (16) and one for the floating solids (17), where the screw for the settleable solids (16) has a flight (13) for the transport of the settleable solids (16), characterised in that the screw for the floating solids (17) is designed as a multi-channel screw and has flights (23,23') for the transport of the floating solids (17), the screw for the settleable solids (16) comprising an outer flight (13', 13"), which is designed as a parallel flight (13', 13"), where the parallel flight (13', 13") is comprised of one or several additional narrow ribbon flights (13', 13"), where the outer flight (13', 13") surrounds the inner flight (23, 23') of the screw for the floating solids (17), the outer flights (13', 13") are arranged parallel to the flight (13) for the transport of the settleable solids (16) surrounding the flights (23,23') for the transport of the floating solids (17), where the outer flights (13',13") are connected to the flights (23,23') at various points and the flights (13 ,13', 13", 23, 23') working in opposite directions.

6. Screw conveyor according to Claim 5, characterized in that the screw for the settleable solids (16) is designed as a multi-channel screw.