SEPARATION DEVICE

Description

[0001] The invention relates to a device for separating solid particles from a suspension or for concentrating density-divergent substances in a suspension, comprising a hydrocyclone with at least one inlet for the raw liquid, a cylindrical segment, a conical segment, at least one overflow nozzle, and at least one underflow nozzle (discharge). Furthermore, the invention relates to a method for separating solid particles from the underflow stream of a hydrocyclone or for concentrating density-divergent substances in a suspension. BACKGROUND OF THE INVENTION AND STATE OF THE ART

[0002] Hydrocyclones are often used to separate or classify solid particles contained in suspensions, to concentrate them and to separate emulsions such as oil-water mixtures.

[0003] The operation of this separation process is based on the interplay of mass-dependent centrifugal and flow forces. The raw liquid flowing tangentially into the cylindrical part of the hydrocyclone is forced into a circular path, whereby denser solid particles are transported to the outer wall of the hydrocyclone and toward the discharge. A tapered cylinder (cone) leads to an inward displacement of the less dense liquid, resulting in an internal, upward vortex.

[0004] This typically results in low-solids liquid flowing through an overflow nozzle as an overflow stream. However, since the hydrocyclone often does not allow for complete solid-liquid separation, liquid flows unused as an underflow stream in addition to the solid particles to be separated.

[0005] In many cases, liquid loss is not a problem, as only an enrichment of the solid particles in the underflow is required. The enrichment is determined by the design and operating mode of the hydrocyclone. The properties of the concentrated suspension are difficult to influence, but in many technical applications, these properties must be selectively controlled. In other applications, the loss of liquid flowing away with solid particles via the underflow stream must be minimized as much as possible. For example, in waterjet cutting, the separation of solid particles without loss of water from the jet is required.

[0006] To achieve complete solid-liquid separation, the underflow stream can be fed into downstream separation processes. In GB 1,130,339 A, a hydrocyclone is followed by another hydrocyclone. The underflow stream from the first hydrocyclone is again directed tangentially into the second hydrocyclone, where centrifugal or centrifugal force is again used for separation.

[0007] In the closest prior art, WO 2007 / 144631 A2, a sludge container is connected downstream of a hydrocyclone. Depending on the design, this container is used either solely as a solids separation process for separating coarser particles and sand or additionally as a secondary separator for discharging a secondary stream. Similar devices with a secondary separator are also disclosed in EP 1 133 538 A1 and EP 0 313 197 A2. A disadvantage of the secondary separators cited in the prior art is that they must be cleaned manually once several coarser particles have accumulated in the secondary separator. Such cleaning simultaneously interrupts the separation process.

[0008] Other devices used in the prior art, such as sedimentation tanks, have disadvantages such as large space requirements or long residence times due to the low settling velocity of solid particles in higher-viscosity liquids. Filter units incur high costs due to increased maintenance requirements, resulting in longer downtimes. Another disadvantage of filters is sometimes significant pressure drops.

[0009] US 3928186 A describes the sequential separation of lightweight paper fibers from a paper waste suspension. Instead of the underflow stream of a hydrocyclone, the overflow stream, thus producing a low-particle liquid, is fed into a second separation process. BRIEF DESCRIPTION OF THE INVENTION

[0010] The present invention is based on the object of separating separated particles from the underflow (outflow) that have been concentrated by a hydrocyclone in the discharge. Furthermore, the composition of the concentrated suspension should be selectively influenced.

[0011] These objects are achieved by a device for separating solid particles from suspensions, comprising a hydrocyclone with at least a) a hydrocyclone inlet for raw liquid, b) a cylindrical segment, c) a conical segment, d) an overflow nozzle and e) an underflow nozzle, characterized by a secondary separator, comprising a secondary separator inlet, a separation chamber, a dip tube and at least one rinsing inlet and at least one rinsing outlet, wherein the underflow nozzle is fluidically connected to a secondary separator inlet, wherein at least one lateral separation wall with the separation cover and a separation base delimits the separation chamber, wherein a dip tube projects into the separation chamber and functions as an outlet for a secondary flow, wherein the at least one rinsing inlet and the at least one rinsing outlet are fluidically connected to the secondary separator.

[0012] In a generic device, a secondary separator is arranged downstream of the hydrocyclone. The hydrocyclone has at least one hydrocyclone inlet for the raw liquid, at least one segment in the form of a straight circular cylinder shell and a conical segment, at least one overflow nozzle, and at least one underflow nozzle. The underflow nozzle is fluidically connected to a secondary separator inlet, with the underflow flow flowing into the secondary separator via a secondary separator inlet. The secondary separator according to the invention is characterized by a separation chamber, with at least one lateral separation wall comprising the separation cover and a separation base delimiting the separation chamber, with a dip tube extending into the separation chamber and acting as an outlet for a secondary flow, with the secondary separator being fluidically connected to at least one rinsing inlet and at least one rinsing outlet.

[0013] The secondary separator preferably has a circular hollow cylinder shape, but the shape is not limited to a circular hollow cylinder. A secondary separator according to the invention can also have the shape of a general cylinder or a conical shape, and can also be spherical. The lateral separation wall forms the outer surface and is preferably made of aluminum, steel, or plastic.

[0014] The separator cover essentially seals the secondary separator at the top, providing an opening for an inlet. The separator cover can be permanently connected to the lateral separator wall, or it can be designed to be removable. The separator base essentially seals the secondary separator at the bottom, providing an opening for the dip tube. Like the cover, the separator base can be permanently connected to the lateral separator wall, or it can be designed to be removable.

[0015] The secondary separator according to the invention utilizes the angular momentum of the underflow stream coming from the hydrocyclone. The swirl can be further enhanced by an optional fluid guide device in the area of ​​the secondary separator inlet. The centrifugal force acting on the particles is used for solid-liquid separation. Advantageously, no additional external electrical or mechanical energy is required for this separation process.

[0016] The dip tube is arranged such that the opening of the dip tube facing the underflow nozzle and the opening of the underflow nozzle are arranged essentially concentrically. The dip tube is preferably straight throughout, but not necessarily straight throughout, and can be straight only in sections. In one design variant, the dip tube can have a bend or be curved. Furthermore, the dip tube can be displaceable relative to the separation chamber in the direction of the separation floor and / or separation cover. A special design variant provides for a dip tube with a dip tube cover, which is attached to the end of the dip tube facing the underflow nozzle and is permeable to fluids. The dip tube cover can, for example, be flat, conical, or curved.

[0017] A kinked or bent dip tube allows a secondary flow to be directed laterally through the jacket surface of the separation chamber or diagonally through the separation plate. In combination with a separation plate that tapers towards the secondary separator outlet, particles can be removed from the separation chamber as a particle flow in the axial flow direction by periodically or continuously actuating a valve. The axial displacement of the dip tube and its geometric proportions (diameter, length, shape, installation position) enable optimization of the secondary flow with regard to volume flow, continuity, selectivity, and separation efficiency. A dip tube cover prevents particles from directly entering the dip tube and offers additional advantages with regard to the purity and suspension properties of the secondary flow.

[0018] The separator base is preferably flat. In a special design, it has a cone that converges toward the separator cover and from the side separator wall to the dip tube. Alternatively, it is conceivable for the separator base to have a cone that diverges toward the separator cover and from the dip tube to the side separator wall.

[0019] A conical design of the separator plate can have a beneficial effect on separation efficiency. This positively influences the flow behavior of the secondary stream.

[0020] It can also be provided that the separating floor has a recess in each area of ​​the transition to the lateral separating wall, wherein the recess functions as a trough or discharge trough. The recess is preferably annular.

[0021] This ensures that particles or concentrated suspension accumulated in the discharge trough area are less easily swept away by the prevailing flow. A special design provides a removable section of the separator floor near the trough to allow for manual removal of contaminants.

[0022] In one embodiment, the at least one flushing inlet and the at least one flushing outlet can be arranged substantially tangentially to the lateral separator wall and orthogonally to the longitudinal axis of the secondary separator inlet. Alternatively, the at least one flushing inlet and the at least one flushing outlet can be arranged substantially parallel to the secondary separator inlet, with the at least one flushing inlet connected to the separator cover and the at least one flushing outlet connected to the separator base.

[0023] Such a rinsing unit has the advantage that the manual cleaning can be largely relieved of the person maintaining a device according to the invention. Furthermore, as mentioned above, the introduction of a secondary fluid increases the swirl in the secondary separator, increasing the pressure of the particles on the separation wall. The rinsing unit thus further enhances the separation efficiency in the secondary separator according to the invention.

[0024] Furthermore, the task of separating solid particles from the underflow stream of a hydrocyclone or concentrating a suspension is achieved by a process wherein a raw liquid flows into a hydrocyclone as an inlet stream, wherein at least a first solid-liquid separation takes place in the hydrocyclone, with an overflow stream and an underflow stream flowing out of the hydrocyclone. The process is further characterized in that the underflow stream flows into a secondary separator according to the invention, wherein at least a second solid-liquid separation or concentration takes place in the secondary separator, and a secondary stream flows out of at least one secondary separator.

[0025] One process variant provides for the secondary stream coming from the secondary separator to be recirculated into at least one hydrocyclone inlet. In another embodiment, the secondary stream can be recirculated into the overflow stream, for example, continuously, discontinuously, or after any number of separation cycles.

[0026] Recirculating the secondary stream into at least one hydrocyclone inlet has the advantage of increasing the overall separation efficiency and selectivity. This allows the purity and composition of the secondary stream to be controlled according to requirements.

[0027] In another design, a flow sensor can be provided, which, in a special process variant, allows the mass or volume flow of the secondary stream to be measured. The measurement result of the flow sensor provides a variable for controlling a valve or pump.

[0028] Advantageously, the flow conditions in the secondary separator can be dynamically adapted in order to positively influence the separation efficiency or selectivity depending on the requirements.

[0029] Regardless of the design, care is taken to ensure that separated particles are removed from the separation chamber as a particle stream or concentrated suspension. This can be done periodically or continuously. In general, different process variants can be combined. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Fig. 1 shows a hydrocyclone 10 with a downstream secondary separator according to the invention 20 in front view, side view and perspective. Fig. 2 shows a hydrocyclone 10 with inventive secondary separator 20, Inlet flow 1 (raw liquid), overflow stream 2, Underflow stream3, Particle stream or concentrated suspension 4 and secondary current 5. Fig. 3 shows a secondary separator according to the invention in front view and perspective with secondary separator inlet 21, Separator cover 22, side separation wall 23, Separation room 24, dip tube 25, Separation floor 26 and outlet 27. Fig. 4 shows the schematic flow pattern in a secondary separator according to the invention. Fig. 5 shows a special design of a secondary separator according to the invention with a curved dip tube and a valve for the controlled discharge of solid particles or concentrated suspension. Fig. 6 shows a special design of the separator floor and the separator cover 6a Separator floor, which has a towards the separator cover 22 and from the side separation wall 23 to the dip tube 25converging cone 28° has. 6b Separator floor, which has a towards the separator cover 22 and from the dip tube 25 to the side separation wall 23 diverging cone 28" has. 6c Separator cover, which has a direction towards the separator floor 26 and from the secondary separator inlet 21 to the side separation wall 23 diverging cone 29' has. 6d Separation floor, which is partially perforated, open or completely omitted, so that the separated particles or concentrated suspension are discharged freely. 6e Separator floor, which is partially perforated, open or completely omitted, with the separator cover conically extending from the secondary separator inlet 21 to the side separation wall 23diverges so that the separated particles or concentrated suspension are discharged freely. Fig. 7 shows a further design variant of the separating floor, where a recess forms an annular discharge trough 26 ' forms. Fig. 8 shows two variants of a secondary separator according to the invention with flushing inlets and flushing outlets in two views each, which can also be applied to all mentioned designs of the secondary separator. 8a shows tangential flushing inlets 30 (30', 30"), which can also be used as drains and tangential flushing drains 31 (31', 31"), which can also be used as inlets. 8b shows axial flushing inlets 32 (32', 32"), which can also be used as drains and flush drains 33 (33', 33"), which can also be used as inlets. Fig. 9 shows variants of the return of the secondary current5 . 9a shows the return to the inlet stream 1. 9b shows that the secondary current 5 is returned as additional inlet stream. 9c shows the return to the overflow stream 2. Fig. 10 shows an embodiment with a secondary current 5 introduced a) pump 6 or b) control valve 7 with a flow sensor 8. Fig. 11 shows a conceivable structure with a rinsing device and valves for controlling a rinsing process. DETAILED DESCRIPTION OF THE INVENTION

[0031] A key objective of the invention is to provide a device and a method for the effective separation of solid particles from the underflow stream 5 of a hydrocyclone 10 in order to minimize the loss of liquid. A further objective is the selective concentration of a suspension emerging from the underflow of a hydrocyclone. A secondary separator 20 according to the invention has a special geometry for optimal operation. Without limiting the design thereto, preferred embodiments according to Fig. 1 bis 11 described.

[0032] Fig. 1 shows a secondary separator 20 according to the invention, which is arranged directly downstream of a hydrocyclone 10. The raw liquid in the form of a suspension flows tangentially via a hydrocyclone inlet 11 into an upper, cylindrical segment 14' of the hydrocyclone 10. The raw liquid is thereby forced onto a circular path, and a downward vortex is subsequently created. An axial taper of the cylindrical segment 14' forms a conical segment 14. This causes denser solid particles to be increasingly conveyed to the wall of the conical segment 14, whereby the low-particle liquid is driven into the center of the hydrocyclone. The lower mass density of the low-particle liquid leads to an upward flow and consequently to the outflow of a portion of the low-particle liquid through an overflow nozzle 12 as overflow stream 2 ( Fig. 2 ). Particles, residual liquid or concentrated suspension leave the hydrocyclone 10 as underflow stream 3 ( Fig. 2 ) via the underflow nozzle 13 and flows into a secondary separator 20 according to the invention, wherein the underflow nozzle 13 is correspondingly fluidically connected to a secondary separator inlet 21.

[0033] In Fig. 3 A secondary separator 20 according to the invention is shown in detail. The secondary separator inlet 21 is preferably a pipe with a circular cross-section. The dimensioning can be adapted depending on the volume flow and viscosity of the raw liquid. Optionally, the swirl can be further increased by a fluid guide device in the area of ​​the secondary separator inlet 21. The secondary separator inlet 21 is connected to a separator cover 22, for example by welding, gluing, or screwing. The underflow stream 3 ( Fig. 2 ) into a separation chamber 24. This is essentially formed by a circular cylindrical shell surface or lateral separation wall 23 made of, for example, aluminum, steel or plastic.

[0034] One variant can be designed to be transparent in at least one region of the lateral separation wall 23 and / or the separation cover 22 and / or the separation base 26, with this at least one region serving as a viewing window. The separation cover 22 and the separation base 26 essentially seal the hollow cylinder at its end faces in a fluid-tight manner, with openings provided for the at least one inlet 21 and the at least one dip tube 25. The seal can be achieved by a welded connection. Likewise, a detachable screw or clamp connection with corresponding sealing elements can be provided, whereby the separation cover 22 and separation base 26 are removable.

[0035] The dip tube 25 and the outlet 27 are preferably formed from the same tube. The portion of the tube that extends into the separation chamber, which is essentially filled with suspension, is referred to as the dip tube 25. The portion of the tube that leads away from the separation chamber 24 in the direction of flow is referred to as the outlet 27. The tube can be designed like the tube for the secondary separator inlet 21.

[0036] A schematic representation of the flow pattern within a secondary separator 20 according to the invention is shown in Fig. 4 The underflow stream 3 coming from the hydrocyclone 10 has an angular momentum which arises from the functioning of the hydrocyclone 10. In the secondary separator inlet 21, denser particles or suspension components are pressed against the inside of the pipe due to centrifugal force. Upon entering the separation chamber 24, the counteracting centripetal force from the inside of the pipe is eliminated, whereby denser particles are forced against the lateral separation wall 23 and finally come to rest on the separation floor. The less dense liquid remains in the inner region of the separation chamber 24 and experiences buoyancy. The liquid freed of solid particles flows out via the dip tube 25 or via the outlet 27 as secondary stream 5. Optionally, a dip tube cover 25' can be provided to prevent a dense solid particle from directly entering the dip tube 25.

[0037] The advantage over the prior art, in which a hydrocyclone 10 is followed by another hydrocyclone, is, among other things, the abrupt cessation of centripetal force immediately upon the suspension entering the separation chamber 24. This causes the mass to loosen, which prevents clumping, particularly in highly viscous suspensions such as particle-rich biomass or sludge, and thus contributes significantly to increasing separation efficiency. Tests have shown that a secondary separator 20 according to the invention is also suitable for gas-solid or gas-liquid separation.

[0038] Fig. 5 shows a special embodiment of a secondary separator 20 according to the invention. The immersion tube 25 has a bend so that it either penetrates the conically shaped separating base 26 to one side or exits above the cylindrical part of the separating wall (23). The secondary stream 5 flows out via the outlet 27. The separated particles or the concentrated suspension can be discharged downward in the axial flow direction. The introduction of a valve into the particle stream enables the periodic or, preferably, continuous discharge of solid particles or concentrated suspension.

[0039] A special design of the separating floor is in Fig. 6a und 6b shown. In Figure 6a, the conical separator plate 28' converges from the lower region of the lateral separator wall 23 towards the separator cover 22 and the dip tube 25. This influences the flow pattern in the lower region of the separator chamber 24 in such a way that the buoyancy of the less dense liquid is favored. Fig. 6b The variant of a conical separator plate 28" with opposite inclination is shown. This also allows the flow within the secondary separator 20 to be positively influenced depending on the viscosity of a suspension or a gas mixture.

[0040] Fig. 6c 1 additionally shows a special design of the separator cover 22. The cone 29, which diverges downwards from the secondary separator inlet 21 toward the lateral separator wall 23, influences the flow prevailing in the upper region of the separator chamber 24. Particularly for low-viscosity suspensions, an abrupt flow separation, which in the case of highly viscous masses leads to a desired loosening, can be contained in order to counteract turbulence and the associated reduced separation of solid particles at the separator wall 23. Such a cone 29 can be provided for any conceivable embodiment of a secondary separator 20 according to the invention.

[0041] Fig. 6d shows a special design of the secondary separator, where the separator base can be partially perforated, open, or completely open. This design has advantageous properties with regard to concentration, particularly in systems with free discharge against ambient pressure. To reduce turbulence upon entry into the secondary separator and to result in less mixing of the concentrated sludge, the separator cover can also be tapered ( Fig. 6e ).

[0042] Another special embodiment of the separating floor 26 is shown in Fig. 7 shown. The design has a recess 26' in the separator base in the area of ​​the lateral separator wall. The recess preferably forms an annular trough. The separator base can be completely removable or have a removable element only in the area of ​​the recess 26'. This is intended to facilitate cleaning. The advantage of the recess 26' itself is that solid particles settle particularly in this area, whereby the formation of particle accumulations on the otherwise flat separator base 26 can be largely avoided or at least delayed. Such accumulations can represent obstacles to the flow, and in the worst case, solid particles that have already settled are entrained by the low-particle liquid.

[0043] A special embodiment provides a flushing device for a secondary separator 20 according to the invention. Fig. 8a shows tangential flushing inlets and outlets 30, 31. The flushing inlets are preferably positioned horizontally in the upper region of the secondary separator 20 and tangentially to the lateral separation wall 23 and are fluidly connected to the separation chamber 24. Preferably, two flushing inlets 30', 30" are provided, which, in addition to the aforementioned arrangement, are parallel to one another such that incoming liquid flows through both inlets on the circular path of the lateral separation wall 23 in the same direction. The flow entrains previously separated particles, with the flushing liquid flowing out tangentially with the contaminants in the lower region via preferably two flushing outlets 31', 31". These are arranged analogously to the flushing inlets 30, but in the lower region of the secondary separator and offset according to the flow direction.

[0044] Instead of two flush inlets 30', 30" and outlets 31', 31", only one can be provided. Likewise, three inlets or outlets, each offset by an angle of 120°, or more, are conceivable. Likewise, the flush inlets can be used as flush outlets, and the flush outlets can be used as flush inlets. Furthermore, each flush inlet can be used as a flush outlet, and vice versa.

[0045] Fig. 8b shows axially arranged flushing inlets and outlets 32, 33. Preferably, two inlets 32', 32" are provided, which are arranged vertically and parallel to the secondary separator inlet 21, wherein the inlets 32 are fastened to the separator cover 22 and are fluidly connected to the separating chamber 24. Accordingly, preferably two outlets 33', 33" are provided, which are arranged analogously to the inlets 32, but are fastened to the separating base and are fluidly connected to the separating chamber 24.

[0046] Again, instead of two flush inlets 32', 32" and outlets 33', 33", only one of each can be provided. Likewise, three inlets or outlets, each offset by an angle of 120°, or more, are conceivable. Likewise, the flush inlets can be used as flush outlets, and the flush outlets can be used as flush inlets.

[0047] Possible variants of a method according to the invention with regard to the recycling of the secondary current are described in Fig. 9 For example, a recirculation to influence the selectivity in the hydrocyclone feed 11 can be carried out with an inlet stream 1 ( Fig. 9a ). Alternatively, the secondary stream 5 can be recycled into a second inlet located below the hydrocyclone inlet 11. In both cases, the secondary stream 5 is recycled into the separation process. Depending on requirements, the secondary stream 5 can also be recycled directly into the overflow stream 2 ( Fig. 9c ).

[0048] For each design, it can be provided that particles or suspension are continuously, for example with a Fig. 5 shown design, or periodic, with a Fig. 8 illustrated embodiment, are discharged from the secondary separator 20 according to the invention as a particle stream or suspension 4.

[0049] In order to adapt the volume or mass flow to the requirements, different operating modes are possible. Pressure-driven operation provides ( Fig. 10a ), to influence the flow rate of the secondary flow 5 with a pump 6. In self-driven operation ( Fig. 10b ), a control valve 7 is provided instead of the pump 6. For both variants, a flow sensor 8 can be optionally connected downstream, the measurement result of which provides a variable for controlling the pump power or the position of the valve 7. For all operating modes, the secondary flow can be returned to the hydrocyclone inlet ( Fig. 9a ), into a second hydrocyclone inlet ( Fig. 9b ) or into the overflow stream ( Fig. 9c ) can be executed.

[0050] Fig. 11shows a design with valves with which drain sequences for flushing cycles can be implemented. The valves influence the underflow stream 3, the secondary stream 5, as well as the inlet and outlet streams of the flushing device. A preferred drain sequence can include the following steps: close the secondary stream valve, close the underflow stream valve, open the flush drain valve(s), open the flush inlet valve(s), wait time, close the flush inlet valve(s), close the flush drain valve(s), open the secondary stream valve, and open the underflow stream valve.

[0051] The waiting times and the respective pressures of the flushing streams can be adapted to the degree of contamination or the nature of the solid particles.

Claims

1. Apparatus for separating solid particles from suspensions or concentrating suspensions, comprising a hydrocyclone (10) with at least a) a hydrocyclone inlet (11) for raw liquid, b) a cylindrical segment (14'), c) a conical segment (14), d) an overflow nozzle (12) and e) an underflow nozzle (13), and a secondary separator (20), comprising a secondary separator inlet (21), a separator chamber (24) and an immersion tube (25), the underflow nozzle (13) being connected in a fluid-conducting manner to a secondary separator inlet (21), wherein at least one lateral separator wall (23) with the separator cover (22) and a separator base (26) delimits the separator chamber (24), wherein the immersion tube (25) projects into the separator chamber (24) and functions as an outlet (27) for a secondary flow (5), characterized in that the secondary separator 20 comprises at least one flushing inlet (30', 30", 31', 31") and at least one flushing outlet (30', 30", 31', 31"), wherein the at least one flushing inlet (30', 30", 31', 31'') and the at least one flushing outlet (30', 30", 31', 31") are connected to the secondary separator (20) in a fluid-conducting manner.

2. Device according to claim 1, characterized in that the opening of the immersion tube (25) facing the underflow nozzle (13) and the opening of the underflow nozzle (13) are arranged essentially concentrically.

3. Device according to one of claims 1 and 2, characterized in that the immersion tube (25) is kinked or bent in at least one region.

4. Device according to one of claims 1 to 3, characterized in that the immersion tube (25) is displaceable relative to the separator chamber (24) in the direction of the separator base (26) and / or separator cover (22).

5. Device according to one of claims 1 to 4, characterized in that the immersion tube (25) has an immersion tube cover (25'), this being attached in a fluid-permeable manner to the end of the immersion tube that is closer to the underflow nozzle (13).

6. Device according to one of claims 1 to 5, characterized in that the separator base (26) has a cone (28') which merges in the direction of the separator cover (22) and from the lateral separator wall (23) towards the immersion tube (25).

7. Device according to one of claims 1 to 5, characterized in that the separator base (26) has a cone (28") diverging in the direction of the separator cover (22) and from the immersion tube (25) towards the lateral separator wall (23).

8. Device according to one of claims 1 to 7, characterized in that the separator cover (22) has a cone (29') diverging in the direction of the separator base (26) and from the secondary separator inlet (21) to the lateral separator wall (23).

9. Device according to one of claims 1 to 8, characterized in that the separator base (26) has a recess (26') in each region of the transition to the lateral separator wall (23), the recess functioning as a trough.

10. Device according to claim 9, characterized in that the recess (26') has an annular trough (26').

11. Device according to any one of claims 1 to 10, characterized in that the at least one flushing inlet (30', 30'', 31', 31'') and the at least one flushing outlet (30', 30'', 31', 31'' ) are arranged substantially tangentially to the lateral separator wall and orthogonally to the longitudinal axis of the secondary separator inlet (21).

12. Device according to one of claims 1 to 10, characterized in that the at least one flushing inlet (32', 32") and the at least one flushing outlet (33', 33") are arranged substantially parallel to the secondary separator inlet (21), wherein the at least one flushing inlet (32', 32'') is connected to the separator cover (22) and the at least one flushing outlet (33', 33") is connected to the separator base (26).

13. Process for separating solid particles from the underflow stream (3) of a hydrocyclone (10) or for concentrating a suspension, wherein a raw liquid flows as an inlet stream (1) into a hydrocyclone (10), wherein a first solid-liquid separation takes place in the hydrocyclone (10), wherein an overflow stream (2) and an underflow stream (3) flow out of the hydrocyclone (10), characterized in that the underflow stream (3) flows into a secondary separator (20), in particular according to one of claims 1 to 12, wherein at least a second solid-liquid separation takes place in the secondary separator (20) and a secondary stream (5) flows out of at least one secondary separator (20), wherein a secondary fluid flows into the secondary separator (20) and out of the secondary separator (20) via at least one flushing inlet (30', 30'', 31', 31") and at least one flushing outlet (30', 30", 31").

14. The method according to claim 13, characterized in that the secondary stream (5) is recirculated into the at least one hydrocyclone inlet (11).

15. Method according to claim 14, characterized in that the mass or volume flow of the secondary stream (5) is determined by means of a flow sensor (8).