Separator and method for purifying liquid-solid mixture

Abstract

The invention relates to a centrifuge with a rotatable bowl (1) adapted to purify a liquid-solid mixture, including settled and floating solids, from solids in a centrifugal field during batch processing, the bowl (1) comprising a separation chamber (7), a liquid discharge for continuously discharging the purified liquid phase (L) from the separation chamber (7) during batch processing, and at least two solid collection areas (20, 21) provided on different radii of the bowl, one solid collection area being used to collect a first, lighter, floating solid phase (Sl) and the other solid collection area being used to collect a second, heavier settled solid phase (Sh), such that the solid collection areas (20, 21) are filled with the associated solid phase (Sl, Sh) over time while the associated batch is being processed.

Description

[Technical field]

[0001] The present invention relates to a centrifuge and a process for purifying a liquid-solid mixture of solids using such a centrifuge. [Background technology]

[0002] Centrifugal separators are known from the prior art for a variety of separation tasks. For example, German Patent Publication 10 2005 021 331 shows a three-phase separator and a method for three-phase separation with such a separator, in which the heavier liquid phase is discharged via a throttled outlet and the lighter liquid phase is discharged by a paring disk, and the solids are continuously discharged via a solids outlet nozzle.

[0003] On the other hand, German Patent No. 697 12 569 discloses a cleaning separator in which the light liquid phase is conveyed out by a paring disc and the other heavy liquid phase by an outlet element which is pressed by a drive to change its position above the free liquid level, so that this phase is also constantly discharged during operation, the immersion depth of which should, if possible, be kept constant in order to reduce energy consumption.

[0004] All of these separators have been proven for specific separation tasks, however, they are not or are poorly suited to purify and separate a liquid-solid mixture into a medium weight liquid phase (e.g., water) and a first relatively light solid phase and a second relatively heavier solid phase. In a clarifier with water as the intermediate liquid phase, the lighter solids in the first solid phase float to the surface of the water and the heavier solids in the second solid phase sink to the bottom of the clarifier (sedimentation).

[0005] However, such simultaneous purification of liquid-solid mixtures containing both suspended and sinking solids is interesting for various separation tasks, such as the separation and sorting of microplastics from water bodies and bodies of water. Microplastics are generally defined as plastic particles less than 5 mm in size. To date, centrifuges have only been used in isolated cases. Other technologies for the clarification step also exist. These include cascade or differential filtration (filters connected in series with decreasing pore size), suspended solids traps or settling boxes (vessels with settling chambers arranged in a maze), and centrifuges operating in batch mode. However, the latter can only separate the settling solids. German patent 1 178 014 can be cited as an example of such a centrifuge operating in batch mode.

[0006] However, to detect the full range of plastics (polymers) with different densities using centrifugation techniques, it is necessary to detect both the sinking and floating polymers. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to create a centrifuge that is particularly suitable for purifying a liquid-solid mixture of floating and sinking solids. Furthermore, a suitable method for purifying a liquid-solid mixture of floating and sinking solids is created. [Means for solving the problem]

[0008] The present invention solves this problem by means of a (centrifuge) separator according to claim 1 and a method according to claim 13 .

[0009] According to claim 1 there is provided a separator having a rotatable bowl configured for purifying a liquid-solid mixture comprising sinking and floating solids from solids in a centrifugal field during batch processing, so that the liquid-solid mixture can be separated into a liquid phase, a first lighter solid phase of floating solids and a second heavier solid phase of sinking solids, the bowl comprising a separation chamber, a liquid discharge for continuously discharging the purified liquid phase from the separation chamber during batch processing, and at least two solids collection areas provided at different radii of the bowl, one solids collection area configured or operative to collect the first lighter floating solids phase and the other solids collection area configured or operative to collect the second heavier solids phase, the solids collection areas being filled with the associated solid phase over time while the associated batch is being processed.

[0010] Such a separator is particularly suitable for purifying products containing at least one fluid phase with a first density ρL and at least two solid phases with two different density classes ρSl and ρSh. The two solid phases preferably contain plastic particles of different density classes ρSl and ρSh, with ρSl<ρL<ρSh. The lighter and heavier solid phases may likewise be composed of solids of different densities, lighter or heavier than the liquid phase. The lighter solid phase, the liquid phase and the heavier liquid phase are separated from one another and collected separately.

[0011] According to a preferred further development, the bowl is configured such that the liquid phase is discharged from the separation chamber on a central radius, a first solids collection area for the lighter solids phase is located on a smaller radius relative to the central radius, and a second solids collection area for the heavier solids phase is located on a larger radius relative to the central radius. In this way, solids of different densities can advantageously be collected radially further inward and radially further outward in the bowl during operation.

[0012] It is preferred, advantageous and aids the separation process if at least one means for increasing the equivalent fining surface is formed in the separation chamber.

[0013] The means for increasing the equivalent fining surface can be, for example, a disk pack having essentially radially extending ribs or a ribbed insert. The central radius from which the continuous liquid discharge takes place can also be realised in various ways, for example by means of a separating disc or by means of one or more tubes whose inlets are located in the area of ​​the central radius and which lead from the bowl in which the liquid rotates.

[0014] According to an advantageous further development, the bowl can be opened so that the solid phase can be removed from the bowl after the batch has been processed and when the bowl is stationary. For this purpose, it appears to be particularly useful if the bowl can be opened in the lower area and, after the batch has been processed, the solid phase and the remaining liquid can flow out of the bowl via the drain into a container.

[0015] The invention also provides the use of a separator according to any one of the claims for the centrifugation clarification of a liquid-solid mixture comprising settled and suspended solids from solids.

[0016] The present invention also provides a method for centrifugally clarifying a liquid-solid mixture, including settled and suspended solids from the solids, in a centrifuge according to one of the claims, comprising the following steps: Step 100 providing a separator and a batch of liquid-solid mixture, the batch having a medium heavy liquid phase (L) and a lighter solid phase having suspended solids (Sl) and a heavier solid phase having settled solids (Sh); Step 200 rotating the bowl and feeding the liquid-solid mixture into the bowl, thereby causing centrifugation within the separation chamber between the medium-heavy liquid phase, the lighter solids phase having suspended solids, and the heavier solids phase having settled solids, such that the lighter solids phase is displaced by the medium-heavy liquid phase toward the center of the separation chamber and the heavier solids phase flows into the largest diameter region inside the bowl wall; Step 300 collecting the light floating solid phase in the center of the separation chamber in at least one first solids collection area in the center of the disc pack or in the center of the ribs, and collecting the heavy settling solid phase in a second solids collection area in the area of ​​maximum diameter inside the bowl wall; Step 400 opening the bowl after batching and draining or removing the solids from the open bowl. The solids are either examined more closely or discarded.

[0017] The separator and method according to the invention make it possible, in particular but not exclusively, to separate microplastics from water discontinuously in a batch or batch process. This technical solution can also be used to purify water and wastewater from plastics and / or microplastics.

[0018] The specific density of the individual polymers present in microplastics varies greatly. Thus, in a mixture of water (approximately 1.0 g / cm3 in freshwater and 1.02-1.03 g / cm3 in seawater) and microplastics in a gravitational field, sinking and floating microplastic particles (which sink in the water) can be distinguished. Typical density ranges for exemplary plastic types are listed in the table below. PE 0.917-0.965g / cm 3 PP 0.900―0.910g / cm 3 Freshwater approximately 1.0g / cm 3 (reference) Seawater approximately 1.02~1.03g / cm 3 (reference) PS 1.040―1.100g / cm 3 PA 1.020―1.050g / cm 3 PVC 1.160―1.580g / cm 3 PET 1.370―1.450g / cm 3

[0019] The separator according to the invention, which is capable of separating different polymers from a water sample, separates very well both sinking (heavier than water) and floating (lighter than water) particles and allows both particles to be collected separately from each other.

[0020] For analysis, the water sample can be processed in a batch or batch-wise operation, where the separated particles remain in the centrifuge during the batch and can be quantitatively evaluated after the end of the batch. After manually removing the separated microplastics from the bowl, the amount of separated microplastics can be determined and compared to the volume of the water sample processed in each batch.

[0021] It should also be mentioned that the solid-liquid mixture can be pre-filtered with a coarse filter before being fed to the bowl 1 in order to remove larger solids. This is particularly useful when the means for increasing the equivalent clarification surface is a disc pack. Advantageous embodiments of the invention can be found in the other dependent claims. [Brief description of the drawings]

[0022] The invention is explained in more detail below by means of exemplary embodiments and with reference to the drawings. [Figure 1] FIG. 2 is a schematic cross-sectional view of a first bowl according to the present invention having a hood. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a second bowl according to the invention having a hood. [Diagram 3] FIG. 2 shows the separator from FIG. 1 in a cross-sectional view, supplemented with a solids outlet. [Figure 4] A side view of the separator is shown in Figs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] FIG. 1 shows a rotatable bowl 1 with a complete shell and a vertically aligned axis of rotation D, preferably on a radius R0.

[0024] This bowl 1 is configured to purify a liquid-solid mixture of solids, including at least one fluid phase of a first density ρL and at least one solid with two different types of densities ρSl and ρSh. The solids can essentially be polymeric particles (rubber, plastic, polymer) with different densities ρSl and ρSh. ρSl<ρL<ρSh applies: the lighter solid phase Sl and the heavier solid phase Sh are composed of solids of different densities that have in common that they are lighter and heavier than the liquid phase, respectively.

[0025] In the bowl, the liquid is purified in a centrifugal field by two solid phases of different density classes ρSl and ρSh in a batchwise manner, i.e. batch by batch. During the processing of each batch, the liquid phase is continuously and completely discharged from the bowl until the processing of the respective batch is finished. On the other hand, the solid phases of different densities are essentially collected on different radii in two different solid collection areas 20 and 21 in the bowl 1 and remain in these areas of the bowl 1 during the processing of the respective batch. During the centrifugation process, this bowl configuration does not allow the solids to be discharged from the bowl.

[0026] In a further development of such a centrifuge, it is conceivable to empty the solids collection areas 20 and 21 at suitable intervals during operation (auto-draining centrifuge) in order to thus achieve a continuous clarification operation.

[0027] The lighter solid phase Sl essentially contains suspended solids, since this phase is lighter than the liquid phase. The heavier solid phase Sh, on the other hand, contains sinking solids that are heavier than the liquid phase, where the suspended solid phase Sl and the sinking solid phase Sh are composed of solids of different densities. The liquid phase can be water, in particular the water of the body of water to be examined or purified. In addition to natural bodies of water such as rivers, lakes, or oceans, it can also be liquid from washing machines, PET recycling plants, washing lines, or other wastewater.

[0028] At the end of processing each batch, bowl 1 is opened and the solids are removed from bowl 1 for further inspection or optionally discarded.

[0029] To achieve this, the bowl 1 of FIG. 1 is designed as follows. The bowl 1 has an axis of rotation D aligned vertically on a radius R0. The rotatable bowl 1 is mounted on a rotating spindle 2, which is driven by a drive motor, for example directly or via a belt. The rotating spindle 2 is mounted so that it can rotate accordingly.

[0030] The rotating spindle 2 may have a conical configuration in its upper and / or lower circumferential regions. The rotating spindle 2 preferably also has a central cylindrical section. The bowl 1 is surrounded by a stationary hood 3, which does not rotate with the bowl.

[0031] Advantageously, the double-conical bowl 1 has a product feed pipe 4 for the product P to be centrifuged, to which a distributor 5 is connected, which has at least one or more inlet openings 6 through which the incoming centrifuged product is fed into the interior of the bowl 1 and into a separation chamber 7. The feed is fed into the bowl 1 axially from above or axially from below.

[0032] The bowl 1 is preferably provided with a device for increasing the equivalent fining surface. This can be achieved in various ways.

[0033] According to Figure 1, the device for expanding the equivalent fining surface is realized by a disc stack 8 consisting of preferably conical separating discs 81. The separating discs 81 extend to a radius R8.

[0034] However, according to figure 2, the device for expanding the equivalent clarification surface is realized by a ribbed insert 800, which preferably has radial ribs 801 distributed circumferentially in the separation chamber 7. The ribs 801 extend to a radius R800.

[0035] The product feed pipe 4 is guided vertically from above into the bowl 1. A feed line, for example through the spindle from below, is also conceivable (not shown). According to FIG. 1, this arrangement is such that the outlet opening 6 is arranged below a riser channel 82 of a disc stack 8 consisting of conically shaped separating discs 81 .

[0036] In the separation chamber 7, when the bowl 1 rotates sufficiently fast as a result of centrifugal force, the liquid-solid mixture separates into a medium density liquid phase L, a relatively light solid phase Sl of suspended solids, and a relatively heavy solid phase Sh of settled solids. To discharge the intermediate density liquid phase, a device is provided at the central radius of the separation chamber for discharging this liquid phase from the bowl.

[0037] This device can be realized in a variety of ways. According to FIGS. 1 and 2, the device for discharging the liquid phase comprises a separating disk 9, the outer diameter of which is dimensioned so as to project radially into the separating chamber 7 approximately centrally.

[0038] Alternatively, one or more tubes with an inlet can project approximately radially into the center of the separation chamber 7 to discharge this liquid phase, similar to a nozzle separator, and direct the liquid phase radially out of the bowl. However, this variant is disadvantageous in that it consumes high energy.

[0039] In FIGS. 1 and 2, the disc pack 8 is closed at the top by a conical separating disc 9, which here has a (slightly) larger diameter than the disc pack 8.

[0040] The liquid phase with average density ρL is fed via a separating disc 9 to a discharge chamber 10 equipped with a paring disc 11. The paring disc 11 directs the liquid phase L from the rotating system to a drainage pipe 12 outside the bowl. In contrast to a free discharge from the bowl (e.g. nozzle), part of the kinetic energy of the liquid can be converted with the help of the paring disc into pump energy (centripetal pump). Also, a stable operating behavior in the separating chamber can be achieved by setting a constant counter pressure at the outlet of the paring disc.

[0041] Therefore, bowl 1 does not have a solid phase discharge where the respective solid phase can be discharged during the centrifugation of the batch: this discharge takes place only after bowl 1 has stopped and bowl 1 has been opened. Thus, to purify the liquid from the solids, a liquid-solid mixture having settled and suspended solids can be centrifugally treated as follows:

[0042] Step 100 First, in step 100, a separator is provided and a liquid-solid mixture (preferably a batch) is provided.

[0043] Step 200 Bowl 1 is rotated and a liquid-solid mixture is fed into the bowl. This is fed through / via feed pipe 4 and distributor 5 into separation chamber 7. In operation, as bowl 1 rotates, centrifugation takes place in separation chamber 7 between a medium heavy liquid phase L, a lighter solid phase Sl with suspended solids and a heavier solid phase Sh with settled solids. In this way, as bowl 1 rotates, the liquid phase L is clarified from the solid phases Sl and Sh.

[0044] Step 300 The lightest materials (in this case the suspended solids Sl) are pushed in the centrifugal field by the medium heavy liquid phase L into the centre of the separation chamber 7. There is no outlet for the suspended solids, so that these light solids collect in at least one first solids collection area 20 in the centre of the separation chamber 7, for example around the central axis 18.

[0045] Meanwhile, the heavy settling solids Sh flow outwards in the centrifugal field. Since there is no outlet for the heavy settling solids, they are forced into the area of ​​maximum diameter of at least one second solids collection area 21 (here cylindrical inside one section) on the inner wall of the bowl 1 and remain there. In this step, a liquid phase L - preferably water from a body of water - is passed through a device for discharging the liquid phase from a bowl 1 . This means that during processing of the batch, only the liquid phase L leaves the bowl, while the suspended and settled solids Sl, Sh remain in the bowl.

[0046] Step 400 After a batch has been processed, bowl 1 can be opened and the solids accumulated in bowl 1 (which have been separated into at least two different density classes in bowl 1) can be removed from the open bowl 1. The solids can then be further inspected or discarded, for example.

[0047] The liquid-solid mixture is therefore very advantageously clarified in batches in the solid bowl separator. The batch is run as long as the solids collection areas 20, 21 of the bowls allow, i.e. as long as they are not yet full. At the end of the liquid phase a check is carried out with a sensor (not shown). As soon as the sensor detects that the maximum allowable amount of solids in the liquid phase has been exceeded, which means that one or both solids collection areas are full and cannot hold any more solids. Processing of the batch must then be stopped.

[0048] At the end of the batch process, bowl 1 is stopped and opened. The solid phases Sl, Sh can then be removed from the bowl. For this purpose, according to one embodiment, the bowl can be separated into an upper part 14 and a lower part 15 by unscrewing at a separation point 13, preferably in the region of the bottom of the bowl 1, and the separated particles, i.e. the two solid phases Sl, Sh, together can flow out of the bowl together with the residual liquid remaining in the bowl 1 (see FIG. 3). This flowing out solid / liquid mixture is discharged via a drain 16 below the bowl and, as shown in FIG. 4, into a container 17 where it is collected.

[0049] According to figure 2, the disc pack 8 is replaced by a preferably star-shaped ribbed insert 800 with circumferentially distributed and preferably radially aligned ribs 801. This embodiment has a smaller equivalent clarification surface compared to the disc pack 8 but is more suitable for collecting solid particles of irregular size, in particular in that the risk of possible blockages in the disc pack is further reduced and pre-filtration can be avoided. Any particles remaining in the bowl 1 , or on the vane insert, or in the disc pack can then be manually emptied into the container 17 .

[0050] Then, for example, the amount of particles separated can be determined and compared to the volume of liquid (water, wastewater, etc.) that passed through the separator in this batch. Both the number of particles and the total weight of particles separated can be evaluated as "amount". This means that both the number of particles / liter and the particle weight / liter can be determined. The particle value is the sum of suspended and settled particles.

[0051] When carefully opening the bowl 1, it is also conceivable to discharge and collect the settled and floating solids separately. [Explanation of symbols]

[0052] Code list Bowl 1 Rotating spindle 2 Food 3 Product supply pipe 4 distributor 5 Outlet opening 6 Separation room 7 Disk Pack 8 Separation disc 81 Riser Channel 82 Ribbed Insert 800 Rib 801 Separation Disc 9 Discharge chamber 10 Pairing Disk 11 Exhaust pipe 12 Separation point 13 Top 14 Bottom 15 Discharge section 16 Container 17 Shaft 18 Solids collection area 20, 21 Product P Radius R0 Separator disc outer radius R8 Outer radius rib R800 liquid phase L Heavier solid phase Sh Lighter solid phase Sl Rotation axis D Density ρL Density classes ρSl, ρSh

Claims

1. A centrifuge having a rotatable bowl (1), the bowl (1) configured to separate a liquid-solid mixture, including settling solids and floating solids, from solids in a centrifugal field during batch processing; The bowl (1) comprises a separation chamber (7), a liquid discharge section for continuously discharging the purified liquid phase (L) from the separation chamber (7) during batch processing, and at least two solids collection areas (20, 21) provided on different radii of the bowl; A separator in which one solids collection area serves to collect a first, lighter, floating solids phase (Sl) and the other solids collection area serves to collect a second, heavier, settling solids phase (Sh), the solids collection areas (20, 21) filling up with the associated solids phase (Sl, Sh) over time while the associated batch is being processed.

2. 2. A separator according to claim 1, characterized in that the liquid phase is discharged from the separation chamber (7) on a central radius, a first solids collection area (20) for the lighter solids phase (Sl) is located on a smaller radius relative to the central radius, and a second solids collection area (21) for the heavier solids phase (Sh) is located on a larger radius relative to the central radius.

3. 3. A separator according to claim 1 or 2, characterized in that in the separation chamber (7) at least one means for increasing the equivalent fining surface is formed.

4. 4. A separator according to claim 3, wherein the means for increasing the equivalent fining surface are disc packs (8).

5. 4. A separator according to claim 3, wherein the means for increasing the equivalent fining surface is a ribbed insert (800).

6. 3. A separator according to claim 1 or 2, wherein the liquid discharge section comprises a separating disc (9).

7. 3. The separator of claim 1, wherein the liquid discharge section comprises one or more tubes, the inlets of the tubes being located in the region of the central radius, and the liquid being directed from the rotating bowl through the tube inlets.

8. 3. A separator according to claim 1 or 2, wherein the fixed bowl (1) is open so that the solid phase can be removed from the bowl (1) after the batch has been processed.

9. 3. A separator according to claim 1 or 2, wherein when the bowl (1) rotates, no solids discharge is provided for discharging solids during the centrifugal process.

10. 9. A separator according to claim 8, wherein the bowl (1) can be opened in the lower region so that, after processing of the batch, the solid phases (Sh, Sl) and the remaining liquid can be discharged from the bowl via a discharge into a container.

11. 3. A separator according to claim 1 or 2, wherein the liquid discharge comprises a sensor capable of monitoring the density of the discharged liquid phase.

12. 3. Use of a separator according to claim 1 or 2 for centrifugal clarification of a liquid-solid mixture having settled and floating solids from said solids.

13. 3. A method for centrifugal purification of a liquid-solid mixture containing settled solids and suspended solids in a batch process using the separator according to claim 1 or 2, comprising: Step 100: providing a separator and a batch of liquid-solid mixture, the batch of liquid-solid mixture having a medium-heavy liquid phase (L), a lighter solid phase (Sl) having suspended solids, and a heavier solid phase (Sh) having settled solids; Step 200: rotating the bowl (1) and feeding the liquid-solid mixture into the bowl (1), thereby causing centrifugation in the separation chamber (7) between a medium-heavy liquid phase (L), a lighter solid phase (Sl) having suspended solids, and a heavier solid phase (Sh) having settled solids, so that the lighter solid phase is displaced by the medium-heavy liquid phase to the center of the separation chamber and the heavier solid phase flows into the largest diameter area inside the bowl wall; Step 300 is collecting the light floating solid phase (Sl) in the center of the separation chamber in at least one first solids collection area (20) and the heavy settling solid phase (Sh) in a second solids collection area (21) at the area of ​​maximum diameter inside the bowl wall; The method includes step 400 of opening the bowl (1) after batch processing and draining or removing solids from the open bowl (1).

14. 14. The method of claim 13, wherein the solid is a plastic particle.

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