Solid bowl centrifuge

A solid bowl centrifuge for dewatering sludge exhibiting a conical solid bowl and an inner rotor part which revolving at different speeds and has apparatus for axially transporting solid components for improved separating and reduced energy consumption. The sludge is introduced at a tapered end and solid components are discharge at an expanded end. Introduction of sludge is effected through a radial inlet channel(s). Surface elements are attached to the inner rotor by holder arms and are located at a slight distance from the inner wall of the solid bowl drum. A surface element free axial passage channel is defined between the inner rotor wall and the solid bowl drum extending at least 50% of the radial distance between the rotor wall and the drum. A baffle plate is mounted on the inner rotor at the wide end of the drum leaving an annular gap or passage between a compacting space and a sediment discharge which exhibits a radially inwardly directed sediment outlet channel(s). The separated liquid is drained through a liquid outlet channel(s) from the compacting space. The liquid outlet is mounted on the inner rotor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a solid bowl centrifuge and more particularly to a 
sludge dewatering centrifuge with a conical bowl drum. 
2. Description of the Related Technology 
DE-OS No. 3 301 099 incorporated by reference herein shows a centrifuge 
where the solids settling on the inner wall of the solid bowl drum and the 
liquid clear phase are discharged from a conically expanded zone of the 
solid bowl centrifuge. Baffle plates are attached to the solid bowl drum 
and an internal rotor, they penetrate the settling slurry phase in the 
entire radial fill level. The baffle plates agitate the slurry phase by 
imparting axially and circumferentially directed flow components. These 
baffle plates simultaneously affect the solid and the liquid phase and 
cause a mixing effect which acts against the desired separation of the 
soild and liquid phases. In addition to this swirl produced by the baffle 
plates, a further disadvantage lies in the relatively high amount of 
energy required to operate the centrifuge as both phases are thrown 
radially outward upon their discharge from the solid bowl drum without 
energy recovering measures. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved solid bowl 
centrifuge for increased separation effect with a reduction in energy 
consumption. 
According to the invention the solid bowl centrifuge for dewatering of 
sludge has a conical solid bowl drum and an inner rotor part which rotates 
relative to the drum. The inner rotor part exhibits devices for the 
axially transporting solid sludge components. The sludge is introduced at 
a conically tapered end of the centrifuge drum and the solid sludge 
components are discharged at a conically expanded end of the solid bowl 
drum. The sludge is introduced through one or more radial sludge inlet 
channels. Apparatus for axially transporting solid sludge components 
settling on the inner wall of the solid bowl drum is provided which 
exhibits one or more surface elements attached to the inner rotor part. 
The surface elements may be moved at a slight distance from, and at an 
appropriate relative velocity past the inner wall of the solid bowl drum. 
The surface element may advantageously be arranged on holding arms, where 
an axial passage channel free of surface elements is provided between the 
inner rotor and the surface elements. The channel may advantageously 
amount to at least 50% of the radial distance between the wall of the 
inner rotor part and an inner wall of the solid bowl drum. A baffle plate 
may be mounted in the area of the conically expanded end of the solid bowl 
drum on the inner rotor part. The baffle plate and the inner wall of the 
solid bowl drum define an annular gap at the wide end of the drum. The 
annular gap represents the passage opening from a compacting space located 
in front of the baffle plate to a sediment discharge space located behind 
the baffle plate. Advantageously one or more radially inwardly directed 
sediment outlets connected a sediment discharge channel lead from the 
sediment discharge space outside the solid bowl drum. The liquid separated 
from the sediment is drained from a compacting space by one or more liquid 
outlet channels mounted on the inner rotor part which extend radially 
inward and pass into a liquid discharge channel leading outside the solid 
bowl drum. 
The invention provides for accumulating the clear phase or liquid 
components in the radially inner area of the drum. The components of the 
heavy phase or solids have sedimented out, to a very large extent, from 
the radially inner area. An unimpeded axial flow with a light spiral flow 
component may be established in a radially inner flow space without 
entrainment of heavy phase components, sedimenting in the radially outer 
area, by said flow. The heavy phase components are held within or in the 
area of surface elements located in a radially outer area of said drum and 
are somewhat shielded against flow of the clear phase in the radially 
inner area. Swirling caused by baffle plates which extend simultaneously 
through both phase zones is thereby prevented. Although DE-OS No. 3 301 
099 (FIG. 3) shows surface elements mounted on holding arms, which may be 
moved at a slight distance past the inner wall of the solid bowl drum and 
which extend only slightly in the radial direction these surface elements 
are flanked on both sides by closed helical blades defining flow channel 
with a small flow cross section. High flow velocities are generated in the 
flow channel and no quieted flow favoring sedimentation of the clear phase 
may be established. 
According to the invention quiet guidance of the flow is further favored by 
the radially directed slurry inlet channels which insure that the slurry 
is introduced with a flow component already accelerated to the 
circumferential velocity in the vicinity of the inner wall of the solid 
bowl drum. The development of a radial velocity profile comprising shear 
flows interfering with the separation process may thereby be avoided and 
the sedimentation process may begin effectively at the onset or initial 
portion of the drum (feed side). 
In addition to shielding the sedimented heavy phase against the flow 
prevailing in the radially inner zone, of the lighter clear phase largely 
depleted of heavy components, the surface elements employed, for example, 
in the form of a ribbon screw impart intense shear stress to the 
sediments. The sediments are backed up against the baffle plate under the 
increasing compression effect and spill against the axial transport 
direction of the ribbon screw over the inner edge of the screw or surface 
elements. These shear forces acting during this constant shifting of 
layers of the sedimented phases, favor the further compacting of the solid 
phase components. 
To optimize these consolidating effects occurring in front of the baffle 
plate, a throttle with a variable throttle cross section may be placed in 
the sediment discharge area. The throttle may be actuated by a device 
measuring the viscosity of the sediment, connected in line with the 
throttle. 
A further advantageous device for optimization of the consolidation effect 
developing in front of the baffle plate, a variable throttle may be 
arranged in the clear phase discharge area. This throttle may be actuated 
by a device measuring viscosity located in the sediment discharge area. 
The cross-sectional area of the throttle may be varied by an axial 
displacement of the baffle plate, whereby the width of the annual gap 
bounded by the edge of the baffle plate and the inner wall of the drum may 
be regulated in the area of the conically expanding drum. The throttling 
device may be advantageously a device for varying the level of material 
taken up through the radial outlet channels. 
A plurality of openings closed by closure flaps are provided in an annular 
zone of the solid bowl drum to limit the sediment discharge space to the 
outside in order to insure continuous operation of the solid bowl 
centrifuge and secure against clogging by coarse particles. 
Coarse particles may settle in recesses formed by such closed openings. 
Accumulated course particles are detected by a course matter sensor 
mounted on the baffle plate. Integration of the accumulation and the 
coarse matter sensor tends to brake or block the relative motion of the 
baffle plate and outer drum. A torque sensor device located in the drive 
unit for the inner rotor part and the solid bowl drum detects the breaking 
and generates a control pulse to actuate a brief opening of the closure 
flaps. Coarse particles may be discharged to the outside into an annular 
collecting gutter in this fashion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The solid bowl centrifuge 1 comprises a closed conically expanding solid 
bowl drum 2 and an inner rotor part 3 coaxially supported therein. The 
solid bowl drum 2 exhibits hollow shafts 6 and 7 on its two frontal 
surfaces 4 and 5. The shaft parts 8 and 9 of the inner rotor part 3 
extends through hollow shafts 6 and 7, respectively. The hollow shafts 6 
and 7 are bearingly supported in a housing 10 which encloses the solid 
bowl drum 2. The inner rotor part 3 is supported in the hollow shafts 6 
and 7 by the shaft parts 8 and 9. 
A v-belt pulley 11 and 12 each is located on the hollow shaft 6 and the 
shaft part 8, respectively at the conically tapering end of the solid bowl 
drum 2. The solid bowl drum 2 and the inner rotor part 3 may thereby be 
driven at a slight difference rpm. This may be achieved by utilizing 
pulleys 11 and 12 having slightly different diameters. 
A feed channel 13 for sludge is located at the conically tapering end of 
the solid bowl drum 2 in the form of a hollow bore provided in the shaft 
part 8. The feed channel 13 may branch inside the solid bowl drum 2 into 
radial sludge inlet channels 14. 
The inner rotor part 3, inside the solid bowl drum 2, carries thin holder 
arms 15 exhibiting a plurality of surface elements 16. The surface elments 
16 are arranged at a slight distance from the inner wall for the solid 
bowl drum 2 and only extend a small distance radially. The surface 
elements are arranged so as to impart a transport impulse to sludge 
particles introduced into the drum 2 upon rotation of the inner rotor part 
3. The transport impulses are directed toward the conically expanded end 
of the drum 2. In place of individual surface elements, a continuous 
ribbon screw 116 may also be used (FIG. 2). Similarly, conveying means 
with essentially the same action, such as paddle screws and scrapers set 
obliquely with respect to the principal axis of the solid bowl centrifuge, 
may be employed. The number and profile of the holder arms may 
advantageously be minimized in order to minimize their affect on the 
radially inner flow path and avoid introducing unnecessary swirling. 
A baffle plate 17 is mounted within the drum 2 at the conically expanded 
end on the inner rotor part 3. The edge of the plate and the inner wall of 
the drum 2 define an annular gap 18. The baffle plate 17 divides the space 
enclosed by the solid bowl drum 2 between frontal surface 4 and 5 into a 
compacting space 19 and a sediment discharge space 20. An annular space or 
surface 21 of the drum 2, associated with the sediment discharge space or 
area exhibits a plurality of openings 22 distributed over the 
circumference and closed by the closure flaps 23. 
The baffle plate 17 carries radially inward directed sediment outlet 
channels 24 on the side facing the sediment discharge space 20. The radial 
outlet channels 24 lead to axial sediment outlet channels 25 located in 
the shaft part 9. 
The sediment oulet channels 25 open into an annular, non-revolving 
collector vessel 26. A sediment discharge shaft 27 branches off the 
collector vessel 26. 
A plurality of radially directed liquid outlet channels 28 branch off from 
the compacting space 19. The liquid outlet channels 28 are spaced from the 
baffle plate 17, and pass into an axial liquid discharge channel 29. A 
non-revolving line connection 30 is located at the end of the axial liquid 
discharge channel 29. 
A coarse matter sensor 31 is fastened to the baffle plate 17, arranged in 
the area of the openings 22 at a small distance from the annular surface 
21. 
The closure flaps 23 are connected to a hydraulic actuation device 32, 
which may be activated by a torque sensor device (not shown) located in 
the drive 33. The annular surface 21 is surrounded by a non-revolving 
collector gutter 34. 
In actual operation, the sludge is introduced into the solid centrifuge 1 
in the vicinity of the inner wall of the solid bowl drum 2 by the feed 
channel 13 and the sludge inlet channels 14. In this fashion the sludge 
undergoes a large degree of acceleration, to the circumferential velocity 
of the solid bowl drum 2, upon its entry into the compacting space 18. 
This introduction of the sludge in a relatively quiet flow contributes to 
allowing the sedimentation process of the solid phase to begin very close 
to the conically tapered or narrow end of the solid bowl drum. The solid 
phase is seized in the radially outer zone by the surface elements 16 and 
conveyed toward the conically expanded or wide end of the drum 2. The 
radial height of the solid phase increases in the direction of conical 
expansion and in the area of the baffle plate 17, exceeds the radial 
height of the surface elements 16. The components of the solid phase back 
up at the baffle plate 17 and spill over the radially inner edge of said 
elements, against the axial transport direction due to the throttle 
effects in the sediment discharge zone. In a repeated sequence the 
sediment components are exposed to a constant shear stress, which leads to 
further compacting of the solid components. 
The solid sediment components arrive in the sediment discharge space 20 
through the annular gap 18. The sediments then pass through the sediment 
outlet channels 24 and the sediment discharge channels 25 into the fixed 
collector vessel 26. The collector vessel 26 may be emptied by the 
sediment discharge shaft 27. 
During operation coarse particles may settle in the area of the openings 
22. The coarse material accumulates and begins to impact on the coarse 
matter sensor 31, which revolves with the baffle plate 17. The sensor acts 
as a brake on the system whereby the impact causes a retardation of 
rotation in the drive unit 33. The torque sensor device senses the 
retardation caused by accumulation of coarse material and produces a 
control pulse transmitted to the closure flap actuating device 32 thereby 
opening the closure flaps 23. The opening process is only of a short 
duration, therefore, the removal of coarse particles may be carried out 
without interruption of the normal operation of the solid bowl centrifuge. 
The clear phase (liquid) forming and accumulated in the radially inner area 
of the compacting space 19 is drained through the liquid outlet channels 
located on the inner rotor part 3, the liquid discharge channel in the 
shaft part 9 and a fixed line connection 30. 
The height of the solid phase backing up in front of the baffle plate may 
be adjusted by a variable throttle located in the sediment discharge area. 
The throttle setting may be effected advantageously as a function of 
measured values of a device measuring viscosity of the sediment 
discharged. 
In another embodiment of the invention a variable throttle may be arranged 
in the clear phase discharge zone, which may be controlled as a function 
of the measured values of a viscosity measuring device for the sediment 
being discharged. 
By the two aforementioned throttles it is possible to affect the 
consistency or residual humidity of the sediment, in order, for example, 
to prevent clogging in the sediment discharge area as a result of the 
excessive dewatering of the sediment, or a too rapid flow of the sediment 
due to insufficient dewatering.