Solid bowl centrifuge

Abstract

The invention relates to a solid bowl centrifuge for processing a suspension Su in a centrifugal field, comprising a housing (100) and a rotor (200) that is rotatably mounted in the housing (100), wherein the rotor (200) comprises at least the following: a rotatable drum (210) with an axis of rotation D, wherein the drum (210) has a cylindrical section (211) and a conical section (212), a screw (230) arranged in the drum (210) and rotatable relative to the rotatable drum (210) at a differential rotational speed, a supply pipe (217) which projects into the drum (210) and is arranged concentrically to the axis of rotation D and through which the suspension Su to be processed can be directed into a separation chamber (219) of the drum (210), at least one liquid outlet (214) arranged in the cylindrical section (211) of the drum (210), at least one solids discharge (218) which is arranged in the conical section (212) of the drum (210) and is arranged in the centre or near the centre of the drum (210), and the solid material Fe leaves the drum (210) in an axial direction or substantially in an axial direction with respect to the drum (210), wherein the supply side of a pump (400) is attached to the solids discharge (218), which is designed in such a way that a counterpressure can be influenced upstream of the pump or in the drum (210) by controlling the pump.

Description

[0001] Solid bowl screw centrifuge

[0002] The invention relates to a solid bowl screw centrifuge according to the preamble of claim 1.

[0003] A solid-bowl screw centrifuge (also called a decanter) can be used to separate a solid phase from a suspension. Optionally, the suspension, once cleared of solids, can be separated into different liquid phases in a design with two liquid outlets. Solid-bowl screw centrifuges are ideally suited for processing relatively high solid concentrations in the feed stream, are comparatively robust, achieve excellent separation results, and ensure effective drying of the solids.

[0004] In this context, solids are understood to mean solids that have been dehydrated as far as possible, but in practice they often still contain so much residual moisture that they behave like sludge.

[0005] Known solid-bowl screw centrifuges with a frame that is non-rotatable or non-rotating during operation have a rotor that is rotatable or rotates relative to the frame, which in turn has a rotatable bowl and a screw within it that rotates at a speed different from that of the bowl. For the discharge of the solids, essentially radially aligned solids discharge openings are provided in a conical section of the bowl.

[0006] If the energy loss caused by the discharge of solids or sludge from the bowl of the solid bowl screw centrifuge is to be as small as possible, the radius on which the solids discharge openings are located in the drying zone or in the conical section of the bowl must also be as small as possible.

[0007] If a solid-bowl screw centrifuge is to be operated in such a way that the so-called pond depth – this results from the difference between the inner diameter of the bowl and the diameter of the liquid weir to which the suspension extends inside the bowl – is as large as possible, this requires the solids to be discharged as close to the rotation axis as possible. For this purpose, the radius at which the solids discharge openings are located in the drying zone or in the conical section of the bowl must be as small as possible. A solid-bowl screw centrifuge advantageously designed in this direction is described in DE 102019 126 325 A1.

[0008] It is also desirable to be able to change the position of the separation zone within the separation chamber, while minimizing energy loss during solids discharge, so that the solids leave the drum “drier” or “wetter” as required.

[0009] The invention has the object of creating a solid bowl screw centrifuge that essentially meets the above requirements.

[0010] The invention solves this problem by the subject matter of claim 1.

[0011] Accordingly, a solid bowl screw centrifuge for processing a suspension Su in a centrifugal field is provided with a housing and a rotor rotatably mounted in the housing, which has at least the following:

[0012] - a rotatable drum with a rotation axis D, the drum having a cylindrical section and a conical section,

[0013] - a screw arranged in the drum, which can rotate relative to the rotating drum at a differential speed,

[0014] - an inlet pipe extending into the drum and arranged concentrically to the axis of rotation D, through which the suspension Su to be processed can be fed into a separation chamber of the drum,

[0015] - at least one liquid outlet arranged in the cylindrical section of the drum and

[0016] - at least one solids discharge which is arranged in extension of the conical section of the drum and which is arranged in the center or near the center of the drum, so that the solid Fe leaves the drum in the axial direction or substantially in the axial direction with respect to the drum, wherein the inlet side of a pump is attached to the solids discharge, which pump is designed in such a way that a back pressure can be influenced by controlling the pump on the flow side upstream of the pump or in the drum.

[0017] This simple design provides a very good opportunity to easily adjust the position of the separation zone within the separation chamber, while minimizing energy loss during solids discharge, so that the solids can exit the bowl "drier" or "wetter" as needed. In a particularly preferred embodiment of the invention, the solids discharge does not rotate with the bowl during operation of the solid bowl screw centrifuge. This allows the solids discharge to be connected to the downstream lines or a pump in a simple design and with minimal manufacturing effort.

[0018] According to a further, particularly preferred embodiment of the invention, the solids discharge is fluidly connected to one or more openings in the drum. This creates a solids discharge that is easy to manufacture.

[0019] In another particularly preferred embodiment of the invention, the solids discharge is connected to the rotating rotor via a sliding seal. This provides a simple structural isolation of the pump at the solids discharge from the rotor's rotational movement, and the solids flow is pressure-tightly sealed from the environment.

[0020] Furthermore, in another particularly preferred embodiment of the invention, the solids discharge is continued as a pipe in the extension of the conical section of the drum, coaxial with the rotational axis D of the drum. This provides a simple way to direct the solids flow outside the solid bowl centrifuge and thus an optimal installation location for the pump.

[0021] Furthermore, in another particularly preferred embodiment of the invention, the pump is a positive displacement pump. This advantageously makes the pump robust with respect to the fluid to be pumped—namely, the solid phase—and self-priming with respect to its flow-dynamic properties.

[0022] According to a further, particularly preferred embodiment of the invention, it is appropriately provided that the pump is an eccentric screw pump or a rotary lobe pump.

[0023] In a further particularly preferred embodiment of the invention, the volume flow rate (volume flow / time) through the solids outlet can be varied by the pump via the pump speed. This advantageously and easily brings about the changeability of the position of the separation zone within the separation chamber. Likewise, in a further particularly preferred embodiment of the invention, the pump can generate a positive or negative counterpressure in the solids discharge, with the pump being controlled by a control device designed for this purpose. This makes it easy and therefore advantageous to adjust the solids to leave the drum "drier" or "wetter" as required.

[0024] The object is also achieved by the method according to claim 11, which is characterized by the following method steps:

[0025] - Providing a solid bowl screw centrifuge according to claim 1 or any preceding claim;

[0026] - Increasing or decreasing the volume flow rate of the solid Fe through the pump by the control device and thereby influencing the back pressure in the drum, thereby influencing the position of the separation zone in the drum.

[0027] This method perfectly complements the device according to the invention in order to achieve a changeable position of the separation zone within the separation chamber with the lowest possible energy loss during solids discharge, so that the solids leave the drum "drier" or "wetter" as required.

[0028] Further advantageous embodiments of the invention can be found in the subclaims.

[0029] The invention is described in more detail below with reference to exemplary embodiments and the drawings. Features described in connection with these exemplary embodiments can also be used in other—not shown—embodiments of the invention and are therefore also usable as features in claims. They show:

[0030] Figure 1: a schematic sectional view of a rotor of a solid bowl screw centrifuge according to the invention with a horizontal axis of rotation;

[0031] Figure 2: a schematic view in section of a rotor of a solid-shell

[0032] State-of-the-art screw centrifuge.

[0033] The following description of the figures describes one or more embodiments of a solid-bowl screw centrifuge. The individual features of these embodiments can also be combined with embodiments not shown and are also suitable as advantageous embodiments of the subject matter described in one or more of the main and subclaims.

[0034] First, the construction of Fig. 2 will be described, which is further developed according to the invention in Fig. 1.

[0035] Fig. 2 shows a solid bowl screw centrifuge with a frame 100 that is non-rotatable or non-rotating during operation - which can preferably be designed as a type of housing - and a rotor 200 that is rotatable or rotating during operation.

[0036] The rotor 200 has a rotatable drum 210 with a horizontal axis of rotation D. However, the axis of rotation D can also be oriented differently in space, particularly vertically. The rotor 200 also includes a screw 230 arranged in the drum 210, the axis of rotation of which coincides with the axis of rotation D of the drum 210.

[0037] The drum 210 has a cylindrical section 211 and an axially adjoining conical section 212. The cylindrical section 211 is closed here by a substantially radially extending drum cover 213. In the conical section 212, the drum 210 is preferably conical on the inside and outside (relative to the drum shell).

[0038] The screw 230 also has a cylindrical section 231 and an axially adjoining conical section 232. It is arranged within the drum 210. During operation, the screw 230 can be rotated at a speed different from that of the drum 210.

[0039] The worm 230 has worm flights 233 and a worm hub 234. The worm 230 is preferably constructed in one piece, but it can also be assembled from the worm hub 232 and the worm flights 231.

[0040] The screw flights 233 can have a progressive or degressive pitch. The pitch can be linear or have sections with varying pitches. Depending on the pitch direction of the screw flights 233, the screw 230 rotates in the same direction as or opposite to the drum's rotation direction.

[0041] An inlet pipe 214 extends into the drum 210, running concentrically to the rotational axis D here. The inlet pipe opens into a distributor 215 through which a suspension Su to be processed can be guided radially into a separation chamber 216 of the drum 210. The inlet pipe 214 can either be guided into the drum 210 from the side of the cylindrical drum section 211 or it can be guided into the drum 210 from the side of the conical drum section 212.

[0042] One or more liquid outlets 217 can be formed in or on the drum cover 213. These can be designed in various ways, such as openings in the drum cover 213 that have a type of overflow weir, or in another way, such as a paring disc.

[0043] At least one solids discharge 218 is formed at the end of the conical section 212.

[0044] The drum 210 is designed as a solid-shell drum. In the rotating drum 210, at least one liquid phase Fl is clarified from solids Fe. The at least one liquid phase Fl exits the liquid outlet 217 at the drum cover 213. The solids Fe, however, are transported by the screw 230 toward the solids discharge 218 and ejected from the drum 210 there.

[0045] A first drum shaft section 219 can be axially connected to the drum cover 213 or to the actual drum 210, which is connected in a rotationally fixed manner to the drum 210, and a second drum shaft section 220 can be radially connected to the conical drum section 212 with respect to the drum 210, which second drum shaft section is also connected in a rotationally fixed manner to the drum 210.

[0046] Axially adjoining the cylindrical section 231 of the worm 230 is a first worm shaft section 235, which can be connected to the worm 230 in a rotationally fixed manner. A worm bearing 236 is mounted on the first worm shaft section 235. The conical section 232 of the worm 230 is also supported here. The conical section 232 of the worm 230 has a second worm shaft section 237. Another worm bearing 238 is mounted on the second worm shaft section 237.

[0047] A drive device 300, which may have one or two motors, serves to drive the rotor 200. At least one gear 310 may be connected downstream of the drive device 300, on which two pulleys 320, 330 are schematically shown here, indicating that the gear 310 may have at least two interfaces for feeding a respective torque of the motor(s) into the gear 310 in order to drive the drum 210 and the worm 230. Alternatively (not shown here), the rotor 200 may also be driven in another way.

[0048] According to Fig. 2 (and preferably also according to the invention), the gear 310 rotates the drum 210 on the one hand and the worm 230 on the other hand.

[0049] The drum 210 can be rotatably mounted by two drum bearings 221, 222 arranged axially offset in the direction of the rotation axis.

[0050] The drum bearings 221, 222 may advantageously be arranged between the drum 210 and the frame 100 or one or more elements connected to the frame 100 so that the drum 210 can be rotated relative to the frame 100.

[0051] The screw bearings 236, 238, however, can be arranged radially between the screw 230 and the drum 210, so that the screw 230 can be rotatable relative to the drum 210.

[0052] The term "bearing" should not be defined too narrowly in this regard. Each of the bearings 221, 222, 236, and 238 can consist of one or more individual bearings, which are then arranged axially directly adjacent to one another, so that they can each be considered functionally as a single bearing.

[0053] In one possible design variant (not shown), one of the screw bearings 238 in the area of ​​the solids discharge 218 can be omitted. This can be provided, for example, in a vertical arrangement of the solid bowl screw centrifuge.

[0054] The mounting of the drum 210 in or on the frame 100 as well as the mounting of the screw 230 in the drum 210 can also be designed differently than shown.

[0055] In a preferred embodiment, the above features can also be incorporated into the solid-bowl screw centrifuge of Fig. 1, as well as other variants of the invention. However, in these variants, the solids discharge 218, in particular, is designed differently.

[0056] The solids discharge 218 is arranged here in the center or near the center of the drum 210. In the solid-bowl screw centrifuge in Fig. 1, the solids discharge 218 is in fluid communication with one or more solids discharge openings 223 in the drum 210. Preferably, the one or more solids discharge openings 223 are aligned axially or substantially in the axial direction with respect to the drum 210, in other words, coaxially with the rotational axis D of the drum 210. This advantageously reduces shear forces that arise when the solid Fe exits the drum 210.

[0057] In the design of the solid-bowl screw centrifuge according to Fig. 1, the solids discharge 218 is connected to the rotor 200 via a sliding seal 224. Thus, the solid Fe to be discharged is guided through the solids discharge openings 223 at the axial end of the rotating drum 210 during operation of the solid-bowl screw centrifuge, via the seal 224, into a non-rotating solids discharge (section) 218, which is arranged here as an axial extension of the drum 210. It can be designed like a pipeline, as shown here by way of example, and have a conical and an adjoining cylindrical section. This solids discharge section 218 is connected to the inlet side of a pump 400.This pump 400 is preferably a positive displacement pump, particularly preferably an eccentric screw pump or a rotary lobe pump, in which the volume flow rate through the solids outlet 218 can be varied via the pump speed.

[0058] If the volume flow rate through the pump 400 is less than the unaffected volume flow rate of the solid Fe solely due to the transport of the screw 230, then the pump 400 generates a positive back pressure in the drum 210. If the volume flow rate through the pump 400 is greater than the unaffected volume flow rate of the solid Fe solely due to the transport of the screw 230, then the pump 400 generates a negative back pressure in the drum 210.

[0059] The pump 400 is thus designed such that, by appropriate control—depending on requirements—a backpressure can be influenced on the flow side upstream of the pump or in the drum 210. The pump 400 is controlled by a control device designed for this purpose (not shown here). The control device acts on corresponding actuators that influence the speed of the pump 400, such as a frequency converter, which in turn acts on the pump motor. This control device can also be integrated into the control system of the solid-bowl screw centrifuge.

[0060] By varying the backpressure in the solids discharge, the position of the separation zone in the solids bowl centrifuge can be easily and advantageously adjusted virtually continuously, thus optimally adjusting the moisture content of the discharged solid Fe as required. If pump 400 generates a positive backpressure in the solids discharge 218, the position of the separation zone changes toward the liquid outlet 217. The solid Fe thus leaves the bowl 210 drier.

[0061] If the pump 400 generates a negative back pressure in the solids discharge 218, the position of the separation zone changes in the direction of the solids discharge 218. The solid Fe therefore leaves the drum 218 moister.

[0062] The following procedure is specified for influencing a separation zone between two defined positions in the bowl 210 of a solid bowl screw centrifuge:

[0063] In a first method step, a solid bowl screw centrifuge according to claim 1 or one of the preceding claims is provided.

[0064] In a subsequent process step, the volume flow rate of the solid Fe through the pump is increased or decreased by the control device and thus the back pressure in the drum, thereby influencing the position of the separation zone in the drum.

[0065] This creates a simple process for changing the position of the separation zone within the separation chamber with the lowest possible energy loss during solids discharge, so that the solids or sludge leaves the drum “drier” or “wetter” as required.

[0066] List of reference symbols

[0067] 100 frames

[0068] 200 rotor

[0069] 210 Drum 211 Cylindrical section 212 Conical section 213 Drum cover

[0070] 214 Inlet pipe 215 Distributor 216 Separation chamber 217 Liquid drain

[0071] 218 Solids discharge 219 Drum shaft section 220 Drum shaft section 221 Drum bearing

[0072] 222 Drum bearing 223 Solids outlet opening 224 Seal

[0073] 230 screw 231 cylindrical section 232 conical section 233 screw flight

[0074] 234 Worm hub 235 Worm shaft section 236 Worm bearing 237 Worm shaft section

[0075] 238 worm bearings

[0076] 300 Drive system 310 Gearbox 320 Pulley 330 Pulley

[0077] 400 pump

[0078] D axis of rotation Su suspension Fe solids Fl liquid phase

Claims

Claims 1 . A solid-bowl screw centrifuge for processing a suspension Su in a centrifugal field, comprising a housing (100) and a rotor (200) rotatably mounted in the housing (100), which rotor has at least the following: a) a rotatable drum (210) with a rotational axis D, the drum (210) having a cylindrical section (211) and a conical section (212), b) a screw (230) arranged in the drum (210) and rotatable at a differential speed relative to the rotatable drum (210), c) an inlet pipe (217) projecting into the drum (210) and arranged concentrically to the rotational axis D, through which the suspension Su to be processed can be guided into a separation chamber (219) of the drum (210), d) at least one liquid outlet (214) arranged in the cylindrical section (211) of the drum (210), e) at least one solids discharge (218),which is arranged in extension of the conical section (212) of the drum (210) and which is arranged in the center or near the center of the drum (210) and the solid Fe leaves the drum (210) in the axial direction or substantially in the axial direction with respect to the drum (210), characterized in that f) the inlet side of a pump (400) is attached to the solids discharge (218), which is designed in such a way that a back pressure can be influenced by controlling the pump on the flow side upstream of the pump or in the drum (210).

2. Solid bowl screw centrifuge according to claim 1, characterized in that the solids outlet (218) does not rotate with the drum (210) during operation of the solid bowl screw centrifuge.

3. Solid bowl screw centrifuge according to claim 1 or 2, characterized in that the solids discharge (218) is in fluid communication with one or more solids discharge openings (223) in the drum (210).

4. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the solids discharge (218) is connected to the rotor (200) via a sliding seal (224).

5. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the solids discharge (218) is continued as a pipe coaxial to the axis of rotation D of the drum (210) in extension of the conical section (212) of the drum (210).

6. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the pump (400) is a positive displacement pump.

7. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the pump (400) is an eccentric screw pump or a rotary lobe pump.

8. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the volume flow rate through the solids outlet (218) can be varied by the pump (400) via the pump speed.

9. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that a positive or a negative counterpressure can be generated in the solids outlet (218) by the pump (400).

10. Solid bowl screw centrifuge according to one of the preceding claims, characterized in that the pump (400) is controlled by a control device designed for this purpose. 11 . Method for influencing a separation zone between two defined positions in the drum (210) of a solid-bowl screw centrifuge, characterized by the following method steps: a) providing a solid-bowl screw centrifuge according to one of the preceding claims 1 to 10; b) increasing or decreasing the volume flow rate of the solid Fe through the pump (400) by the control device and concomitantly influencing the back pressure in the drum (210), thereby influencing the position of the separation zone in the drum (210).

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