Note: Descriptions are shown in the official language in which they were submitted.
2132399
i
The invention relates to a method and apparatus for
the separation and dewatering of a slurry of solids con-
tained in liquid (e.g., water) in various concentrations.
Such solids may be in the form of a manure slurry or may
originate in industrial processes, or in animal-intensive
operations for processing animals or their parts or plants,
and mixed with fibres, e.g., animal hairs or vegetable
fibres. Such slurries all have the same general physical
characteristics.
It has long been recognized that it would be advanta-
geous to remove water mechanically from various solids and
by-product sludge, such as, for example, sewage sludge and
fluid manure slurries. The use of mechanical dewatering
would reduce the weight of material to be disposed or
transported or the amount of water to be evaporated during
various thermal drying steps often employed in the produc-
tion of solid fertilizers or soil conditioners. Many dif-
ferent types of mechanical dewatering apparatus have been
developed, but none is believed to have gained widespread
usage and acceptance.
One of the simplest machines for the separation of
solids and liquid is the screw press separator, wherein the
screw turns within a progressively narrowing housing toward
the discharge for achieving a gradual compression of the
solids being separated. However, the operation of such
machines in actual practice showed that the narrowing sec-
tions had a detrimental effect on the throughput, the field
of application and the flexibility of the screw press
2132399
separator. Whenever the quantity of the introduced mixture
or its consistency varied, for example, due to a variation
of the content of fibrous solids, the solids were com-
pressed in the narrowing areas, with the result that the
separator became clogged.
One attempted solution to this problem was providing
for the passage of the released water through the housing
wall to a strainer basket of reduced diameter, so that a
counter pressure could be built up. Although in such sepa-
rator the uniform screw driven toward the discharge diddewater the aqueous suspension, no compression effect was
provided to obtain a high proportion of the dry substance.
Screw-type finishers, wherein the conveying means com-
prised a screw or auger of relatively high pitch, were also
commonly used to separate liquids from solids. Such fini-
shers provided increased axial forces for conveying large
amounts of solids through the finisher. However, it was
found that such screw finishers did not provide adequate
drying action for finishing admixtures of the type referred
to above, wherein it is extremely important to remove
essentially all of the liquid or liquor from the solids.
In the patent literature, U.S. Patent No. 3,235,087
patented February 15, 1966 by R.A. Andrews et al, provided
an apparatus for separating liquids from solids. The appa-
ratus included a housing having end walls with an inlet inone of the end walls and an outlet in the other of the end
walls. A cylindrical screen was mounted within the housing
and extended between the end walls. An impeller member was
2132399
_ i f 3
mounted for rotation about an axis in the housing and
within the confines of the screen. The impeller member
included a cylinder member extending between the end walls.
A screw was carried on the cylinder member, the screw
having a plurality of flights, the flights extending from
a point short of the inlet to an intermediate point between
the end walls. The impeller member further included a
paddle extending from the intermediate point to a point
adjacent the outlet means. The paddle was of helical
configuration but it extended generally longitudinally with
respect to the axis. The last of the flights changed pitch
and merged into the paddle. Thus the screw and the paddle
defined cylindrical surfaces of revolution closely spaced
from the inside surface of the screen. A motor provided
rotation of the impeller member in a direction to cause
solids to be conveyed from the inlet means to the outlet
means.
U.S. Patent No. 4,214,377 patented July 29, 1980 by V.
Moffet provided a mechanical dewatering process. That
dewatering process included the steps of passing a feed
stream of organic solids into the first end of a cylin-
drical chamber dewatering zone having a cylindrical porous
wall, with the inner surface of the porous wall being
attached to longitudinal support rods which extended from
the first end to the second end of the porous wall. The
feed stream was pressurized to a super atmospheric pressure
by rotating a centrally-mounted screw conveyor which
extended between the first end and a second end of the
2132399
dewatering zone while constricting the opening at the
second end of the dewatering zone. The blade of the screw
conveyor had a helical outer edge which was separated from
the inner surface continuous and unagitated cylindrical
layer of filter media comprising fibres derived from the
feed stream was maintained in an annular space located
between the inner surface of the porous wall and the outer
edge of the screw conveyor. Simultaneously, organic solids
were transferred through the centre of the dewatering zone
from the first end to the second end of the dewatering
zone. Water was withdrawn radially from the dewatering
zone through the porous wall and the cylindrical layer of
filter media. A dewatering zone effluent stream having a
higher organic solids content than the feed stream was
withdrawn from the second end of the dewatering zone.
U.S. Patent No. 4,260,488 patented April 7, 1981 by
E. Condolios provided a device for compacting and draining
fluid sludge containing fibrous materials. Such device
included a vertical vessel including an upper cylindrical
portion and a lower conical portion. A supply pipe for the
sludge to be treated extended tangentially at a level below
the top of the cylindrical portion of the vessel. A plur-
ality of rotating perforated blades having a vertical axis
was installed in the cylindrical portion below the supply
pipe. A conical rotating screw having a vertical axis was
installed in the conical portion of the vessel. The coni-
cal screw included at least one blade having a pitch corre-
lated to the fibrous sludge to be treated so that com-
2132399
s
pressed sludge at this level was not solidified and stillcontained interstitial water. The conical portion had a
lower end with an outlet orifice for compressed sludge. A
spillway was provided at the upper end of the cylindrical
portion of the vessel for the discharge of a part of the
interstitial water contained in the sludge. A horizontal
cylindrical chamber was secured to the conical portion of
the vessel at the outlet orifice. That chamber included a
downstream portion having a wall constituted as a grating
for the discharge of remaining interstitial water contained
in the sludge. A rotating screw was installed in the cham-
ber and extended beneath the outlet orifice. The chamber
had an outlet orifice at an end thereof for discharge of
compacted sludge. A flexible outlet was provided at the
orifice, the outlet having a conical shape and a free end
with an outlet diameter which was smaller than its inlet
diameter.
U.S. Patent No. 4,520,724 patented June 4, 1985
provided a screw drier for plastic materials. That drier
consisted of a support chassis or casing and a normal screw
of known screw conveyor type in a cylindrical channel on
top. At one end of the channel, the screw was supported
and rotated via tapered roller bearings. The remaining,
longer section of the screw was suspended. The first sec-
tion of the screw shaft was solid to withstand the stressesof the support in rotation. The second section of the
shaft was equipped with helical vanes or turns, for its
entire length, and was hollow to lighten it. The third and
2132399
_ 6
final section was also hollow, and had openings which
allowed the water expelled from the inside of the material
being dried to come out through the inside of the shaft
rather than through the openings in the casing of the
drier.
The material to be dried was introduced from above
through a hopper in the channel of the drier, and was
advanced by the screw conveyor for a distance equal to the
opening of the hopper. In the next section of the drying
channel near the outlet, the material was pressed out with-
out the aid of the vanes of screw. Therefore, the shaft of
the screw was equipped with turns only in the section
between the flanges connecting the hopper to the drying
channel, corresponding to the entrance. The final turn of
the screw went beyond the flanges connecting the hopper to
the drying channel, corresponding to the entrance. The
entire section of the last turn was thicker than the other
turns. The increased thickness began at the shaft and
tapered off toward the top, so that the turn had a trun-
cated conical section. Water was expelled through multipleopenings in the drier casing corresponding to the outlet
section downstream from the flanges connecting the input
hopper. To facilitate water expulsion in the high pressure
area, a fairly dense distribution of openings was provided
in the area extending from the flange connecting the inlet
hopper to just beyond the section of the last turn, des-
cending at 90 to the shaft. The high pressure area thus
began immediately after the last turn, and it is here that
2132399
most water is expelled. The distribution of the openings
may be less dense in the next section. In order to facili-
tate compression inside the drying channel, contraction
devices are provided at its outlet consisting of a fixed
collar, shaped like a truncated cone, applied along the
terminal peripheral edge and tapering toward the inside.
A hinged flap door adjustable in height at the top edge of
the channel, was also provided. The flap door cooperated
with the collar to slow the advance of the material by
reducing the diameter of the channel at the outlet.
U.S. Patent No. 4,291,619 patented September 29, 1981
by A.J. Hunt et al provided a screw press with controllable
rear door. The press utilized an elongate cylindrical
barrel or cage divided into a feed and pressure section and
a pressing chamber section. The walls of the pressing
chamber section and of a portion of the feed and pressure
section were formed from a filter screen through which
extracted liquids could pass. The feed and compression
screw was formed from a cylindrical body having large pitch
spiral threads attached thereto and disposed in the feed
and pressure section of the press barrel. A concentric
drive shaft through the screw body was utilized to turn the
feed screw via a hydraulic drive unit. The front portion
of the feed and pressure section was an enclosed inlet
region with an inlet opening at the top thereof to allow
gravity feed of materials into the press.
A circular door was disposed at the end of the press-
ing chamber, such door having tapered edges mating with an
2132399
_ 8
opening in the chamber and bulkhead. The circular door was
slidably engaged with the feed and pressure screw drive
shaft which extended through the door and was supported at
its outer end by a bearing frame or pillow block. External
inward pressure on the door will therefore maintain the
door tightly closed until outward pressure from inside the
chamber overcame the external pressure and forced the door
to slide rearward along the drive shaft. An hydraulic
pressure system was used having hydraulic actuators
attached to the rear frame of the press with their actu-
ating rods applying pressure to the rear door through a
throw-out type bearing assembly. Hydraulic pressure was
applied to the hydraulic actuator pistons in a direction to
force the rods outward. An adjustable pressure relief
valve was connected between the inlet and outlet lines of
the hydraulic actuators suitable to relive at a selected
pressure above that applied to the actuators. Thus, when
the pressure of the material in the pressing section of the
barrel against the inner surface of the door exceeded the
hydraulic pressure such that the relief valve bypassed, the
door would be forced backward along the drive shaft
allowing the material to extrude out of the opening in the
rear plate in the form of a highly compressed plug or log.
The door also included a plurality of cutter bars attached
and projecting from its inside surface. As the door was
opened by the internal pressure, a clutch switch was mech-
anically closed, causing an electric clutch anchored to the
drive shaft and to the door to engage, thereby rotating the
21323~9
g
door at the speed of the drive shaft. The cutters then
pared away the compressed plug or log which built up in the
pressing section during operation, allowing the chips to be
collected and carried away.
U.S. Patent No. 5,009,795 patented April 23, 1991 by
D. Eichler, entitled "Process for the Dewatering of Solids
Suspended in Water and Screw Press Separator Therefor", was
alleged to provide an improvement in such screw press sepa-
rators. The basic concept of that invention involved a
change in the formation and shape of the solid plug, in
order to obtain an operation free of interference of the
machine, independently of different types of liquid manure
and fluctuations in mixture consistency. The solid plug
was located in all stages of dewatering in a cylindrical
strainer basket, and the screw press separator was con-
figured so that no solids could accumulate between conical
or tapering parts. The necessary counter pressure acting
on the plug was built up by the internal stressing of the
compressed elastic solids by friction against the walls the
friction directed parallel to the direction of advancement
of the plug. The plug began to form rearwardly of the
straining basket under a rising pressure which increased
from the outlet of the helical screw to the end of the
straining basket and then declined toward the solids dis-
charge opening. This pressure rise in the part of the
straining basket after the plug left, the screw was essen-
tial for the further dewatering of the solids retaining on
the straining surface.
2132399
-- ' 10
It is seen that the above patented solutions did not
fully solve the problem. Accordingly, an object of a broad
aspect of the present invention then, is to broaden the
field of application and improve the flexibility of the
aforedescribed types of screw press separators, to increase
the dry substance content of the solids, and to provide a
novel and structurally-superior means for building up the
necessary counter pressure acting on the solid plug.
An object of another aspect of the present invention
is to provide such apparatus which is extremely simple and
rugged in construction and adapted to be manufactured eco-
nomically.
By one broad aspect, the present invention provides a
screw press separator for separating and deliquefying a
slurry of solids and liquids comprising: a cylindrical
housing; a radial inlet means for the inflow of the solids-
containing liquid slurry into the cylindrical housing; a
cylindrical strainer basket extending rearwardly within the
housing, the strainer basket having a cylindrical outlet
end and apertured cylindrical walls for the passage of
separated liquid therethrough; a cylindrical discharge
chamber extending rearwardly from the outlet end of the
strainer basket and defining a solids discharge opening at
a terminal end thereof, the cylindrical discharge chamber
being provided with longitudinally-extending members
serving to prevent a plug of solids situated therein from
rotating; an auger disposed both in the cylindrical housing
and in the strainer basket, the auger including a shaft
2132399
-- 11
extending through the housing, through the strainer basket
and through the cylindrical discharge chamber, and auger
flights affixed to an outer periphery of the shaft, the
auger flights beginning in the housing at a location
S communicating directly with the radial inlet means and
terminating adjacent the terminus of the strainer basket;
a spring-loaded door assembly at the exit of the cylin-
drical discharge chamber, the door assembly being opera-
tively-connected to the shaft of the auger so that the door
assembly rotates with the shaft, the inner face of the
upstream end of the door assembly being provided with a
plurality of longitudinally-extending, disintegrating
members, the door assembly being movable between a blocking
position in which it blocks the solids discharge opening,
and an unblocking position in which it provides such solids
discharge opening; and a motor for driving the auger for
advancing the solids-containing liquid slurry rearwardly
within the cylindrical housing and through the strainer
basket to separate the liquid from the solids, to pass such
liquid through the strainer basket and to propel solids in
the form of a plug into the cylindrical discharge chamber;
whereby the solid plug which is so-formed is then dis-
charged, in the form of discrete particles, by way of the
spring-loaded door assembly at the solids discharge
opening.
By one variant thereof, the cylindrical discharge
chamber is provided with a plurality of longitudinally-
2132399
_ 12
extending keystocks as the members which prevent rotation
of the plug of solids.
By another variant thereof, the spring-loaded door
assembly comprises two plates separated by spring members
which are, in turn, fixed to each of the plates, the
upstream plate being adapted to be slidable with respect to
the shaft, and the downstream plate be~ng secured to the
shaft.
By a variation thereof, the spring members are
manually adjustable to vary the compressive resistive
thereof, to vary the extent to which the plug is compacted
by resistive pressure of the door assembly.
By another variation thereof, the longitudinally-
extending disintegrating members on the upstream plate
comprise a plurality of tearing bolts.
By another variant thereof, the apertured cylindrical
walls of the strainer basket comprise longitudinally-
slotted screen elements.
By yet another variant thereof, the screw press sepa-
rator includes a cylindrical chamber concentrically sur-
rounding the strainer basket to provide a concentric mantle
therearound for the accumulation of liquid therein, the
mantle including a liquid outlet means therefrom.
By another aspect, the present invention provides a
method for separating and deliquefying solids contained in
a slurry, comprising the steps of:
A) introducing the slurry into a screw press sepa-
rator, the screw press separator comprising a cylindrical
2132399
-_ 13
housing, a radial inlet means for the inflow of the solids-
containing liquid slurry into the cylindrical housing, a
cylindrical strainer basket extending rearwardly within the
housing, the strainer basket having a cylindrical outlet
end and apertured cylindrical walls for the passage of
separated liquid therethrough, a cylindrical discharge
chamber extending rearwardly from the ~outlet end of the
strainer basket and defining a solids discharge opening at
a terminal end thereof, the cylindrical discharge chamber
being provided with longitudinally-extending members
therein, an auger disposed both in the cylindrical housing
and in the strainer basket, the auger including a shaft
extending through the housing, through the strainer basket
and through the cylindrical discharge chamber, and auger
flights affixed to an outer periphery of the shaft, the
auger flights beginning in the housing at a location
communicating directly with the radial inlet means and
terminating adjacent the terminus of the strainer basket,
a spring-loaded door assembly at the exit of the cylin-
drical discharge chamber, the door assembly being opera-
tively-connected to the shaft of the auger so that the door
assembly rotates with the shaft, the inner face of the
upstream end of the door assembly being provided with a
plurality of longitudinally-extending disintegrating
members, the door being movable between a blocking position
in which it blocks the solids discharge opening, and an
unblocking position in which it provides the discharge
opening, and a motor for driving the auger for advancing
2132399
_ 14
the solids-containing liquid slurry rearwardly within the
cylindrical housing and through the strainer basket to
separate the liquid from the solids, to pass such liquid
through the strainer basket and to propel solids in the
form of a plug into the cylindrical discharge chamber; B)
rotating the auger to advance the slurry into the strainer
basket, thereby to separate the liquid from the solids, to
pass such liquid through the strainer basket and to propel
solids in the form of a plug into the cylindrical discharge
chamber; C) preventing such solid plug in the cylindrical
discharge chamber from rotating; D) urging the plug to pass
into the cylindrical discharge chamber to apply a predeter-
mined force to the spring-loaded door assembly; E) disinte-
grating the plug by means of the disintegrating members on
the interior face of the upstream face of the door assembly
which is rotating along with the auger; and F) removing
discrete solids through the space between the end of the
cylindrical discharge chamber and the front face of the
upstream face of the upstream plate of the rotating spring-
loaded door assembly.
By one variant thereof, the method includes the stepsof: providing the spring-biased door with spring means for
controllably moving the door between a blocking position in
which it blocks the solids discharge opening, and an
unblocking position in which it provides the solids dis-
charge opening; biasing the door toward the blocking posi-
tion by means of the spring means; and adjusting the spring
means to vary an initial compressive force applied by the
2132399
`_ 15
door assembly to the plug to vary the extent to which the
plug is compacted.
In the accompanying drawings,
Fig. 1 is a longitudinal section through a screw press
separator according to the invention;
Fig. 2 is an enlarged longitudinal section of the
auger shown in Fig.1;
Fig. 3 is a partial, longitudinal section view of the
end of the screw press separator showing the discharge
chamber with the keystocks therein, and the spring-loaded
door assembly with its disintegrating members thereon, in
its blocking position; and
Fig. 4 is a partial, longitudinal section view of the
end of the screw press separator showing the discharge
chamber with the keystock therein, and the spring-loaded
door assembly with its disintegrating members thereon, in
its unblocked position.
Depicted in Figs. 1 and 2 is a screw press separator
10 for the conversion of a liquid/solids slurry into its
constituent liquid and solid elements. The screw press
separator 10 includes an inflow and control zone A, an
initial feed and compression zone B, a liquid removal and
compression zone C, and a solids discharge zone D.
A radial inlet pipe 15 affixed to cylindrical barrel
12 is provided for directly feeding the slurry into auger
chamber 11 thus filling the auger space, and thence
directly into the auger 17 to impinge upon and be taken up
by, the flights generally indicated as 16, and also
2132399
16
specifically as flights 2S,26 of the auger 17. Any over-
flow is returned directly to the pit source of the slurry.
It is preferred to agitate and mix the slurry before it is
fed into the separator. In general, the slurry is normally
fed by means of a rotating pump (not shown) in an amount
which is preferably in excess of what is needed. The
excess may be recycled by means of an overflow pipe (not
shown) provided adjacent to the feeder. Thus, the screw
press separator 10 receives influent slurry in a radial
manner, which assists in having the influent slurry go
directly to the auger 17, with no dead space in the auger
chamber 11 of the screw press separator 10.
The auger 17 is mounted for rotation within the barrel
12 by means of a longitudinal shaft 18 rotatably-mounted in
a sealed bearing 19, mounted in a main end plate 20. Shaft
18 is driven by a motor (not shown) attached to the shaft
18 and supported in a conventional manner on base 21.
Cylindrical barrel 12 includes a cylindrical separa-
tion chamber 22. Cylindrical separation chamber 22 incor-
porates a cylindrical strainer basket 23, preferably in theform of a longitudinally-slotted screen. While not essen-
tial, a concentric cylindrical mantle 24, which also
includes a liquid withdrawal pipe 28, may be provided
therearound. The auger 17 extends into the separation
chamber 22 for substantially its entire length.
As seen in Fig. 2, the auger 17 includes an infeed
series of flights 25 disposed in auger chamber 11. The
flights 25 have a consistent pitch, and are of a selected
2132399
17
first thickness. Although any reasonably necessary pitch
will be useful, the pitch of the infeed flights will
usually vary from 4" to 9", but is generally 6" to 8". The
thickness of these auger flights generally may be 1/4".
The remaining flights 26, which are in the separation
chamber 22, are of greater thickness than the infeed
flights 25. The thickness of these~ auger flights 26
generally may be about 3/8" thick. The flights 25,26 are
preferably of stainless steel.
As seen now in Fig. 1, the terminal end 27 of the
auger 17 ends near the end of the cylindrical strainer
basket 23, thereby providing the deliquefying zone "C".
The liquid which is removed may be simply discarded, or may
be withdrawn from mantle 24 via the liquid outlet pipe 28.
A cylindrical discharge chamber 29 is provided at the
end of the cylindrical barrel 12. The discharge chamber 29
includes a support spider assembly, indicated schematically
as 50 and a spring-loaded door, indicated schematically as
75.
These assemblies are seen in more detail in Figs. 3
and 4, As seen therein, the discharge chamber 29 is defined
by a hollow, open-ended collar 51 provided with a flange
52, and an extension shaft 53 of the shaft 18 of the auger
17 passing therethrough.
A support frame 50 is secured to the flange 52, as by
welding. The support frame 50 is in the form of a spider
55 having a plurality of forward, longitu~;nAlly-extending
fingers 56. Only one such finger 56 is shown, but there
2132399
~ 18
may be three or more such fingers 56 equiangularly-disposed
about the collar 51. An outer disc 57 providing the open-
end of the collar 51 is used to install a plurality of
axially-extending keystocks 58. The spider 55 supports a
bearing 59 within which the terminus 60 of the extension
shaft 53 is supported and is adapted to rotate.
The extension shaft 53 supports a spring-loaded door
assembly 75. The spring-loaded door assembly 75 is
situated at the solids discharge end 32 (see Fig. 4) of the
discharge chamber 29. This spring-loaded door assembly 75
includes a pair of longitudinally-spaced-apart plates,
namely an inner (upstream) plate 76 and an outer (down-
stream) plate 77. The plates are separated by a plurality
of coil springs 78. The load on the coil springs 78 may be
varied by suitable means known to those skilled in the art.
Outer (downstream) plate 79 is secured by means of clamping
block 81 to extension shaft 53 of the shaft 18 of the auger
17. The inner (upstream) plate 78 is slidably located with
respect to extension shaft 53 by means of bushing 83 which
is secured to the inner face of inner plate 78 and is also
adapted to rotate along with the extension shaft 53. Inner
plate 78 is also is provided with a plurality of longitudi-
nally-extending tearing bolts 84 on its inner (upstream)
face.
As thus seen in Figs. 3 and 4, the discharge chamber
29 is provided with a plurality of internal longitudinally-
extending flutes or square, cross-section, rectangular
keystocks 58. As an example only, four of such keystocks
2132399
19
58 are welded at four locations 90 apart, with respect to
the inner annulus of the discharge chamber 29. As one
example only, the approximate dimensions of the keystocks
58 is approximately 4" in length and 3/8" in cross-section.
The function of the keystocks 58 is to retain the solid
plug and to prevent such solid plug, which is formed by the
auger 17, from rotating inside the discharge chamber 29 due
to the rotation of the extension shaft 53. The egressing
solid plug is disintegrated by means of the tearing or
stripping bolts 84. In one example only, each such bolt 84
has an approximate dimension of 5 13/16" in length and 3/4"
in diameter. The non-rotating plug egresses from the dis-
charge chamber 29 and its solid consistency is destroyed by
coming into contact with the moving stripping bolts 84.
The pressure of the plug compresses inner plate 76 towards
outer plate 77, as seen in Fig. 4, leaving an egress solids
outlet door 32 between the end of the discharge chamber 29
and the beginning of the inner plate 76. Consequently, the
solid fragments fall through the open egress door 32 and
fall to the ground. Alternatively such solids may be
collected by a conveyor belt (not shown) located imme-
diately below the egress door 32 for transportation else-
where.
It will be appreciated that, without the keystocks 58
and tearing bolts 84, the auger 17 would impart rotation to
the solid plug. Such rotation would be augmented by the
rotating door assembly 75. The screw press separator would
2132399
~ 20
then cease to operate, as the solid plug would be spinning
in situ without removal of solid material.
The screen of the strainer basket 23 is preferably
longitudinally-slotted of one-quarter millimetre to one
millimetre in slot size and it is commercially-available.
It is preferable to use such longitudinally-slotted screen
as opposed to a type of screen which has~apertured holes or
the like. These apertured screens tend to catch soiid ele-
ments, e.g., straw, in the slurry which the auger 18 cuts
off, thus embedding the solid elements in the screen and
tending to clog it and render it inoperable. With slots,
the auger 18 tends to pull the solid elements back into the
plug and out of engagement with the screen. The auger 18
within the strainer basket 23 extends radially to the
lS screen of the strainer basket 23. Thus, the distance
between the inner diameter of the strainer basket 23 and
the outer diameter of the flights 26 of the auger 17 is
small, e.g., 0.020 - 0.030". A close tolerance, e.g., plus
or minus 0.010" is maintained for this distance.
More control of the liquid expressing procedure using
the apparatus of aspects of this invention is provided due
to the back pressure build-up. The spring-loaded rear door
assembly 75 enables selective control of the back pressure
by applying compressive forces by means, well-known to
those skilled in the art, without the need for any taper or
wedge in the barrel.
In one example of operation, an aqueous manure slurry
to be separated is typically pumped from a pit and arrives
2132399
21
through a pipeline into the separator. It is also prefer-
able to agitate the manure slurry in the pit. The aqueous
manure slurry is introduced in excess and fills the sepa-
rator. Any overflow is returned via by-pass piping to the
pit. This, in return agitates the manure in the pit and
inhibits sedimentation of the solids in the liquid manure
slurry. At the commencement of a deliquefying operation,
the spring-loaded door assembly, which rotates with the
auger, is virtually closed to build up back pressure. Such
back pressure establishes a dam for the liquid which is
forced radially and outwardly out of the openings provided
in the cylindrical strainer basket. The screw press auger
in the separator into which the aqueous manure slurry is
fed seizes a portion of the aqueous manure slurry corres-
ponding to the intake capacity of the screw press andtransports it in a self-regulating manner by means of the
inflow flights of the auger to a separation chamber. A
layer of solids adjacent to the housing wall passes into
the separation chamber in the form of a growing filter cake
and finally exits the auger as a solid plug filling the
volume of the cylindrical discharge chamber.
The auger transports the solid plug through the sepa-
ration basket to the discharge chamber, while the pressure
is rising toward the terminal end of the auger due to the
reaction created by the spring-loaded rear door assembly.
During that stage, a dewatering of the solids accumulated
in the plug occurs. The solids, which are densified due to
the dewatering, are transported by the auger toward the
21 3239,9
~ 22
terminal end of the auger, and are accumulated within the
last screw turns and shaped into a plug. The increasing
pressure leads to additional dewatering and deposition of
solids onto the plug. This plug is moved to the cylindri-
cal discharge chamber from the strainer basket. The plug
travels along the screw shaft, the end of the shaft pro-
jecting forwardly past the discharge opening and being
connected to the spring-loaded door assembly. Within the
cylindrical discharge chamber, the keystocks prevent the
plug from rotating, but permit it to apply pressure to the
spring-loaded door assembly. Under the action of the pres-
sure generated by the screw press, and the back pressure of
the spring-loaded door, the plug produced in this manner is
pushed to the discharge opening upstream plate of the
spring-loaded door assembly and urges that door rearwardly
to provide the egress opening. The plug is broken up by
the tearing bolts located on such upstream plate of the
rotating spring door. The pieces of the plug so formed,
discharge through the egress opening.
