Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
'7~
U~-1917
This inventîon relates to sedime~tation tanks or
thickeners receiving a continuous supply of a feed pulp or
feed suspension. Such tanks are equipped with a rotary rake
structure for continuously mov:ing the settled feed solids in
the form of sludge to a central collecting zone for withdrawal
through a bottom outlet of the tank, while the separated ox
supernatant liquid may overflow along the per.iphery of the
tank.
By way of example, the invention is herein embodied
in a settling tank wherein the rotary rake structure comprises
rake arms which may be of ~he girder type~ extending rigidly
from a central vertical cage portion supported for rotation
upon the top end of a center pier or column. Fixed to the
underside of each rake arm are raking blades effective ~o
convey the sludge over the tank bottom to the annular sump
surrounding the foot end of the pier, incident to rotation
of ~he rake ~tructu.re by drive mechanism mounted atop the pier.
A discharge conduit and pump means are provided for the with-
drawal o the sludge from the sump. The commercial size of
such settling tanks may be in the order 200 to 300 feet diameter,
and even considerably larger.
; For thickeners of large diameter~ the torque re~uired
for moving the sludge may become very large which calls for a
rake structure and driYe gear mechanism of massive and expensive
design. The~efore~ a reduction in the driving torque requirement
for a given sludge condition assumes practical and economlcal
significance, in that it reduces the cost of the mechanism and
of the power to operate the same.
-- 1 -
It is therefore a main object: of this invention to
provide means whereby the torque rPquirernents, especially for
moving heavy sludge are reducible significantly, reliably,
and economically.
The problem underlying this invention may be further
analyzed as follows:
In what heretofore has been considered normal practice,
the sludge solids are shoved to the center of the thickener
by the rotation of the rake structure. This transportation
or conveyance of the sludge is due to the action of ~he raking
blades normally constructed 50 as to extend vertical to the
plane or tank bottom over which the settled solids are raked,
the blades being set at an angle to their direction of travel
so that they scrape the settled solids in the general direction
of the central discharge point or ~one.
That is to say, the solids are shoved by the vertical
planes of the blades in a direction which has tangential and
radial components, the radial component being directed kowards
the center, the tangential component being directed tangential
to the circular path of movement of the blades. Only the radial
component is useful in effecting the conveyance of the settled
solids to the central discharge point.
The tangential component in turn is smaller than the
velocity of the blades themselves, with settled solids slipping
past the sludge engaging surface of the blades.
Since the settled solids must bs shoved or skidded incident
to the sludge raking operation, the foxce or torque required
is dependent upon the frictional resis~anc~ of the sludge to being
moved or sho~ed relative to the residual layer of solids ~n
the tank bottom~
'
7~
How~ver, the frictional resistance oF particle~ of
sludge bed submerged in a liquid is affected by several
factors. One such is the property of "dilatancy" of certain
non flocculated sludges. The solids in these sludges settle
intc a closely packed state wherein they are inhibited by the
interlocking condition of their shapes from moving past one
another. In order to cause them to slip past one another,
or to become flowable, the solids must become less closely
packea~ This means that the void fraction in the sludge must
increase. That is to say slu~ge must be caused to "dilate" by
somehow having fluid penetrate into the area of slip cr flow~
In other words, in order to move a mass of this material,
a fluid or water must be caused to enter the axea of the
inter~ace between the mass to be moved and the supporting
material, that is a zone of slip or shear.
When the sludge solids are relatively small or fine to
begin with, and particularly if there is in the sludge bed a
gradation of unflocculated ~ines down to a very small size,
the large particle voids are filled with smaller particles.
Cons~quently, the resulting void crevices or voids are of very
small or capillary dimensions which ofer a high hydraulic
resistance to movement of water through them. Therefore, if
fluid must penetrate a substantial layer of settled sludge
solids to reach the aforementioned area of slip or shear the
sludge will exhibit a correspondingly high resistance to such
slip or flow. Under such conditions, settled slud~e solids
impose a high torque load upon the rake structuxe and its drive
mechanism~
One way to alleviate or to eliminate such dilatant behaviox
is to flocculate the ~olids. In the flocculated state the
particles cohere into, or are trapped i~ a structure having
increased void space between the particles. They do not settla
L7~
to the a~orementioned closely packed consistency~ and hence
are less resistant to flo~ tharl when not flocculated.
Soli~s can be flocculated by the addition of various
floccula~ing agents. Consequently, one remedy or compromise
measure to cope with the high flow resistance of a dilatant
pulp, heretofore consisted of t:he liberal addition to the feed
pulp of a flocculating chemical at considerable contlnuous
operating cost.
To solve the aforementionPd problem in handling dilatant
sludges, this invention introduces a new concept in producing
a novel method and means for r~ducing the resistance to slip
or f~ow between the solids being raked and the subjacent layer
- of residual solids on ~he tank bottom.
According to this novel concept, means are provided for
in~roducing dilating water directly at or near the aforernentioned
zones of shear, so that the water does not have to penetrate any
substantial distance through a bed of settled or packed solids.
The invention therefore aims to provide means for causing
sludge or "dilating" supernatant water to be channelled
downwardly ~o the point or area of interface or slip between
the mass of solids being moved and the residual layer underneath.
For that purpose, the mass of settled solids inst ad of
being shoved directly against the aforementioned resistance,
i5 cut or slicecl and lifted from the subjacent layer, thereby
causing dila~ing thin sludge or supernatant to enter by way of
a low resistallce path into the area of the interface.
According to one embodiment, the foregoing objective is
attainable by m~ans of a rotary rake structure provided with
specially shaped raking blades.
In this emhodiment, the ~andard vertically straight
sludge shoving blades are replaced with blades of scoop~shaped
~5~
~o~ /3ura~ r~ L~ rlical sectiorl th(; corlt-~ur com,)rises
~'( 3- ~:i sal ~ t ~ pe~ ~ort:ion merginc~ clownwardly ~7i t~ a
for~axd]y cllrve(~ c~r sc~oped lower portion te~rnillatlr.g in a
le~ac~ ^J ~d~e ~cfectiv(~ to pro~luce the horizon-tall~ c~ recte~l
~ut-ting or siicin~3 effect.
The leadinc3 slicing edge thus cuts and llfts settled
solids a~ay from the suhjacent laver of residual ma-terial, while
pernlitting access of thin sludqe or supernatant liquid from an
upper zone ~o the aforemen~ioned :interface between the mo~in~
solids and the bo-ttom layer with ~,he concurrent dilatin-~ and
flow promoting effect upon the sludge~
For that purpose~ the upper or shoving part of -the blade
may be such as to extend above the layer of settled packed solids,
or at least up into a zone or more fluid pulpl thus affording a
wide channel in back of the ~lade for ~he dilating water to
reach the interface or polnt of separation at the cutting edge.
The spacing of the ~lades along the rake arm ls such that solids
pushed by one blade are not caused to fill the space or flow
channel behind the inwardly ad~acent blade, thus leaving the
channel free for admittiny flui~ pulp into the zone of separation
by the cutting edge.
Where -the height of the blade itself is liml-ted for struct~ral
reasons channel elements may be affixed to the trailing side oE the
contoured blades, reaching upwardly Ear enough to establish flow
channels for thin sludge or "dilating" wa-ter from a superjacent
zone, Also, the addition of such flow channel elem~nts may
facilitate the conversion of an existing rake struc ure when
replacing the conventiorlal straight vertical blades with the newly
cont~u~ed 5COOp shaped blades~
3~ But even pulps or sludges of a flocculen-t nature will
benefit from this inventionO Such is the case whexe the amount
of ~he '!~ield value" of a flocculant pulp will affect the sludge
raking operation with respect to torque requirements.
- 5
~S~7~'~
Ln suc~l slu~y~s~ th~ particles coh~re into a plastlc
s-tructure which resists displacement. However9 th~ "yield
value" of such a sludge is hiqhly dependent upon dilution,
decreasing very rapidly wi~,h t,he introduction of dilutiny
waterO
In the case of such flocculen~ sludges it is common
practice to run the rake arms submerged in a deep layer of
thickening pulp.
With this invention, dilating water may be in~roduce~
or channeled into the bottom zone of the sludge bed~ thereby
reducing the drive torque requirement~
Further significance is attached to this invention
insofar as it can also be app]ied in a manner to greatly
relieve an additional substantial torque load imposed by
the central sludge accumulation upon the scraper blades
operating in the annular sump around the center pier.
According to another embodiment, the vertically
straight standard raking blades may be left unchanged due
to the provision of supplemental transverse blades connected
to the standard raking blades in such a mann~r that liquid
is channelled to the raking blades through downflow duc~s
provided on ~he supplemental means.
Specific features are found in various structural forms
of the invention.
Other features and advantages will hereinafter appear.
Fig~ 1 iS a vertical sectional view of a sedimenta~ion tank
h~ving a center pier supported rotating sludge raking s-truct-llr~
embodying the in~entlon featuri]ng vertically curved raking hlades.
Fig. 2 is a plan vi~w of ~he sedimentation tank, taken
on line 3-3 in Fig. 1, showing the arrangement of rake arms of the
~ludge raking structure.
Fig. 3 is an enlarged detail plan view taken on line 2-2
in Fig. 1, of one of the rake arms provided with sequential groups
of di~rerently shaped rakiny blades embodying the invention.
FigO 4 is a detail plan view taken from Fig. 3, of one of
a first group of vertically curved raking blades provided with
vertical ducts for sludge dilating liquid.
Fig. 5 is a cross-sectional view taken on line 5-5 of Fig~
~.
Fig. 6 is a detail plan view taken from Fig. 3, of one
of a second group of vertically curved raking blades provided
wi~h vertical ducts for sludge dilating liquid.
Fig. 7 is a cross-sectional view taken on line 7-7 of Fig~
6.
Fig~ 8 is a detail plan view taken from Fig. 3, of one of a
third group of plain raking blades.
Fig. 9 is a cro3s-sectional view taken on line 9-9 in Fig,
8.
Fig. 10 iliustrates the sludge dilating functlon of the
curved raking blades in a sludge bed of greater depth.
Fig. 12 is a cross-sectional view of the central part of
- the rake structure taken on line 12-12 in Fig. 1, provided wlth
vertically curved blades operating in the annular sludge collecting
su~[lp .
Fig. 13 is ~nenlarged vertical sectional view caken on
line 13-13 in Fig. 12, further showing sludcJe withdrawal pump~n~
facilities~
Fig~ 14 is a detail rear view of one of the curved blades
-- 7 --
;
taken ~rom Fiq~ 13( provided ~ith vertic~l sludcJe ~ilaii~g 'uct~
Fl~. 15 is one end view of the curved blade taken on
line 15-15 in FigO 14~
Fig, 16 is the opposite end view of the curve-l ~lade,
taken on line 16-16 in FigO 14~
Fig, 17 is a top view of the curved blade, taken on line
17-17 in Fig, 14,
Fig, 18 is a rear ~iew of a curved blade similar to
Fig, 14, provided ~ith a modified vertical sludge dilating duct~
Fig. 19 is a vertical sectional view of the curved blade
taken on line lg-l9 in ~ig. 18,
Fig~ 20 is a top view of the curved blade take~ on line
20-20 in Fig, 18.
Fig. 21 is a plan view of one of the rake arms showing
~5 another embodiment of the invention, wherein a supplemental
linear blade extending transversel~ of the standard raking
blades, pro~ides the supply of dilatant liquid through downflow
ducts rising from the supplemental blade,
Fig, 22 is a partial cross-sectional view taken on line
22-22 in Fig~ 21, showing the attachment of the supplemental
linear blade to the underside of the raking blades.
Fig, 23 is another partial cross-sectional view taken on
line ~3-23 in Fig~ 21, showing the transverse linear supplemental
blade divided into individual sections between respective pairs
of raking blades.
Fig. 24 is a plan view of the rake arms similar to Fig.
21, showing the individual transverse supplemental blades in
staggered arran~ement 7 each with a downflow duct for supplying
dilative liquid to the respective associated raking blades.
Fig~ 25 is ~ pa~t sectional view taken on line 23-23 in
Fi~, 21~
-- 8 --
The in~ention as illustra~ed by way of example in
Figs. 1 and 2, is embodied ln a continuously operating thickening
tank of th~ type wherein a sludge raking structure 10 is
supported fQr rotation upon a center pier 11. A drive
mechanism 1~ of any suitabl~ known construction, is mounted
atop the pie~ providi~g the driving torq~e for the rake structure.
The pier also supports the inner end of an access bridge 13.
The rake structure comprises ~ central vertical cage
portion or cage 14 surrounding the pier, and rake arms of
girder like construction extending rigidly from the cage. As
shown in this ex~mple, the rake structure has one pair of long
rake arms 15 and 16 opposite to one another, and a pair of
short rake arms 17 and 18 disposed at right angles thereto, all
arms having sludge impelling or conveying blades 19 fixed to the
underside thereof. In this gen~ral view of the thickening tank
the blades are shown only diagrammatically, but since they
- embody the invention, their structural ~s well as functional
features are clearly illustrated in the subsequent drawing
figures.
The rake structure operates in a settling tank 20 to
which a feed suspension or feed pulp is supplied through feed
pipe 21 terminating in a feed well 22 which surrounds the top
end portion of the rake structure, and is supported by the pier.
The tank :itself may be of usual construction, comprising
a bottom 24 of shallow inverted conical inclination, and formed
with an annular sump 25 around ~he pier, to which settled
solids or sludge are conveyed by the rake structure. Scraper
blades 26 unit~ry with the rake structure and substantially
conforming to l;he profile of the sump, move the collected
sludge to a point of delivery from the sump, as by way of a
discharge pipe 27.
~5~7~
~iq 3 hows an enldrq~d plan vie~ of one Long rak~
arm 16; whexein are indi(~l~ed sequenticli groups of ralcin~
blades namel~ an innerm~s-t G~oup G--l, an intermedia-~ Group
G-2, both ~mbodying the invention, and an outer Gro~p G--3
which may be of standard blade construction.
The sludge conveylng blades embodying this lnvention
will now be described by reference -to the remaining drawing
Figures 4 to 20.
The structural configuration of the blades 28 of the
innermost Group G-l is shown in detail Figures 4 and 5.
These blades differ from those of the other groups, in that
they are in the form of a shell or scoop of double or compound
curvature presenting the sludge engaging surface.
Accoxdingly, the blades 28 comprise an upper portion 28a
that is vertically straight, but horizontally arcuate in cross-
section. Continuing from the lower arcuate end 29 o this
upper portion and merging therewith, is a lower scoop-shaped
portion 30. This lower portion therefore presents a compound
curvature terminating in a substantially horizontal arcuate
cutting edge 31. A pair of upright channel members 32 and 33
shown in the form of angle irons, are fixed or welded to the
rear or trailing face of the arcuate upper portion, the angle
or apex of these members pointing towards the center of the
tank, that is in the direction of the effective radial component
movement of the sludge being conveyed by the blade.
The blades 28 of gxoup G~l operate in the innermo~t
annular area of the tank bottom where the sludge accumulation
attains its maximum depth, as is schematically indicated in
Fig. 10.
-- 10 --
7~
i?h~ c(mir~und s:!udge ~orl~reyi.ng and sludge dilatlng
~lnc,ion of t:he~ bl~des is such that the phenomeno:n of
su,--~ion ~n~ become~ effective und~rnea~h the scoop-shaped
lower po:~ti.o~ of th.~ blade, wil:l. cause thinner sludge from
a h:igh~r ~o~le t.o flow down -the backside of the blade/ ~s
indicated by the flow arrows A~l
Dilation of ~he sludge is t:hus induced around ~he bi.ade,
increas-'ng the flowabllity of the sludge along with the
attendent saving due to a xeduction in driving torque.
A v~rtical slud~r- pushing surface "S" is presented by
the upper straight portion 282 of the blade.
With the leading edge 31 slicing into the accwnulatio~
of settled solids, the l~wer scoop~shaped portion 30 of the
blade i8 efec-tive to lift this material 34 off the residual
thin layer 35. This causes downward movement or ~uction of
thin sludge~ or else of supernatant r from an upper zone
in~o the space below the curved or scoop shaped portion 30,
thereby effecting dilation of the packed sludge solids in the
immediate vicini~y and around the blade incident to conveyance
of the sludge.
However~ in the case of a deep sludge bed, the sludge
dilating effect may be augmented or intensified by the
provi~ion upon the backside of the bla~e of the aforementlone~
verticai channel members 32 anfl 33. These memh~rs may extend
upwardly far enough to induce downflow of thin sludge or else
of supernatant. These channel members may assume structural
forms other than the one shown, for instance other channel
profiles, or else pipes or ducts.
7~
~I~.< hl.ade~ 36 of ~he se(~or~d ~roup (-,-2 (se~ Fig. 3) a~-,
shown i.n Figs. 6 ar.d 7~ diffe:r from those in the first gr~up
G-l inso~ as the upper p~rtii.on of the blade i~ repres~rlted
by a vertically straig~t plat.e 37 formed wlthout curvature,
and having a s-trai~ht horizont~l. bottom edge portion 38.
Connected to, or merying with this lower edge por-tion of
the plate is a scoop-shaped lc,wer portion 39 formed with a
single curvature and thus presenting an horizontal leading
cutting edge 40. These blades operate over an intermediate
annular part of the tank bottom where the sluclge becl is of
intermediate or moderate height as tentatively illustrated
in Fig. 11.
The compound sludge conveying and sludge dilating
functlon of these intermediate blades is similar in princlple
to that of blades 28, while allowing for a more copious down~
flow of dilating water to the underside of the scoop-shaped
portion, and thus to the forward cutting edge of the blade~
However, a pair of vertical channel members 4Oa and aOb are
also shown, ~imilar to those of the blades in Figs. 4 and 5
20 operating in the inner zone~
The blades 41 of the third Group G-3 may be o
vertically planar standard type as shown in detail Figs. 8
and 9, inasmuch as they operate in the outer annular area of
the tank bottom where the la~er of the settled solids is
only very thin.
Accordi.ng to this invention, it was furthermore found,
especially in dealing with the aforementioned dilatant type
of sludges, that a substantial proportion of the driving torque
was consumed by the scr~per blades that must shove the sludge
accumulation in the annular sump to a point of withdrawal.
~ 12 -
~5~'7~
It ~as fGund ihat:-this represerlted a substall-tial propcrtion
of ~he tor~ue load in spite oi.~ the relatively small meclic.n
diameter "~" of the annular sllmp (see Figs~ 1 and 13). It
was -then theo~`zed that the resistance thus imposed upon the
scrapers was due t~ the fact t:hat the sludge was confined
within the SUIllp and that a torque consuming head on push
by the scrapers was required t:o overcome that resis-tance in
order to move the thus laterally confined mass to a point of
discharge.
~owever, according to the invention~ that part of the
tor~ue requirement consumed by the action of the scrape.rs
in the trench, is also reducible significantly by applying
the above stated principle of the invention relative to
sludge dilatancy. A suitable scraper const~uction for that
purpose is exemplified in the enlarged fragmentary views of
the settling tank in Figs. 12 and 13 and the related figures
: . 14 t~ 20.
In a practical embodiment (see Fig. 13) the anrtulax
sump or sludge collecting trench 42 has a pluxality of bottom
discharge outlets uniformly spaced apart, and connected down-
wardly to respective puntpso By way of example, two pumps P-l and
P-2 are shown, although three puntps may be per~exable in order
to reduce the sludge mass that must be shoved by each scraper
to the respective discharge points in the sump.
The pumps P-l an~ P-2 are contained in an operating
chamber ~3 of concrete construction located underneath the
central portion of the tank bottom, and accessible through
a tunnel 44.
- 13 -
:
~L~5~
In this embodilt~(~nt (S~' E;`i(Js. 1~ and 13), four rac~ially
extending scrapers 45 axe located at the respectivt~ four eors~ers
of the cerltral ver-tical cage portion of the rake structure,
fi~ed -to the undersi.de thereof~ The cage port.ion ~esembles
a vertical bo~ st.ructure of squaxe cross-sectional configurat~on,
comprising an horizon~al bottom frame 46 composecl of :~our
structural members 47, and a corresponding frame at the top
(not visible in Fig. 1 both -top and bottom frames being
interconnected by vertical corner members 48. In Fig. L
suitable transverse bracing members 49 as well as diagonal
bracing 50 and 51 in the sides complete this vertical cage
portion of the rake structure.
For ~upport of the scrapers 45 at the underside of the
cage portion, or bottom frame 46 there are provided inside the
bottom frame 46 and as part thereof, four horizontal }~race
members 52 traversing the respective corners of the frame
(see FigO 12). The inner ends 45a of the scrapers
are fixed to the underside of respectiYe corner brace members
52, as indicated by angular clips 52a ~see Figs. 14 and 15).
A vertical angular gusset plate 53 (see Figs. 12, 13, and 14
rigidly connects the outer end portion of each scraper 45 to
the foot end of the respective adjoining vertical corner
membPr 48 of cage portion 14,
The scrapPr itself, according to one embodiment, comprises
a radially extending plate 54 having a forwardly cur~ed scoop-
shaped lower end portion 55 which may terminate a distance
"d" from the bottom of the annu~ar trench.
This scraper plate as shown, has a transverse top edge
56 and downwardly converging side edges 57 and 58 conforming
to the profile of the annular trench.
- 14 -
,~"o9
A vertical duc~ structur~ 59 open at the top "Tl' and
at the bottom ;'B" i5 welded to the back side of ~he ~cr~pex
pla-te, with the lower end of the duc~ conforming partiaLly to
the curvatur~ ~f the scraper pla~e (see Figs. 15 and 16~.
This duct structure comprises a wide flat box like lo-~ex end
portion 60 hugging the backside of the scraper plate, and a
narrower stack like upper encl portion 61 extencllng upwarcl
beyond the ~o~ edge of the scraper pla-te. This duct thus
rises to a point sufficientl~ high for thin sludge or sùper-
natant to pass through the duct clown to the underside of thecurved lower end portion of the scraper plate, thereby
producing the sludge dilating and torque load reducing effect
described above.
In the embodiment accordin~ to (FigsO 18 to 20) of
scraper blades 62 in the trench, the duct of the preceding
embodiment is replaced by a rearwardly open vertical channel
member 62a~
An auxiliary clean-out scraper plate 63 is fixed tc
the inner e~d of scraper plate 54 at right angles to the
vertiGal plane thereof, and effective adjacent to the foot
end of ~he center pier.
For the purpose of reducing the torque load on an
existing rake structure equipped with the standard raking blades,
and consequ~ntly the load on the drive mechanism, the rake
structure is convertibla by utilizing the teaching of this
invention. Su~h conver~ion can be effect~d by replacing the
existing raking blades with others which are contoured or
sooop shaped or curved in the manner set ~orth above e~boclying
the invention. A~cording to another mode of convexsion, the
lower portion of the standard raking blacles is cut away, and
scoop shaped end portions are subst1tuted, so that the thus
converted blades will meet the requirements of the invention,
- 15
substantially ln a manner indicated in Figs 4, 5, 6, 7, 11
and .12.
The invention. is not limi.ted to the example of the cen~er
pier supported rigid rake structure herein show~. Another
embodiment is found for instance in the settling tank and
non-rigid rake structure shown in the patent to Klopper No.
3r295,835. This rake structure is non-rigid by comparison,
in the sense that a double hin.ge device conne~t~ a tubular
rake arm with the lower end o~ a vertical shaft or member
rotat~d by the drive mechanism. A drive arm located above
or near the liquid o~er10w level is ixed to the shaft~ and
has a drag connection with the rake arm, so that rotation
of the shaft together with the dri~e arm will drag the rake arm
over the tank bottom conveying the sludge to the central outlet
zone, The double hinge device and the drag connection allow the
rake arm to override excessive sludge accumulations even while
continuing the conveyance of the sludge.
In a laboratory scale set-up the invention may be
substantiated by tests whereby the torque load reactions from
differently shaped rak.ing blades are comparatively measurable
for different sludges.
Simulating large scale conditions, such comparative tests
corr~borating the invention, will yield information regarding
the torque resistance of the standard raking blades vs. the
resistance o~ blades that axe cux~ed or scoop shaped in accordance
~ith the in~ention.
Following are the results of such comparati~e tests
taken on an Itabirite iron ore sludge, and also on a prepared
sludge of potatoe starch, both sludges exhibiting the above
described dilatancy charact~ristics. As seen ~rom the test
data below, ~he Itabirite sludge when left with the particles
in their origin21 magnetic state, presents a subs~antially greater
- 16 -
resistance than it does after lt has been subjec-ted to
demagnetlzing treatment.
The following test resul-ls are comparative as between
the standard blades and the shaped or curved blades of the
invention in terms of the meac;ured torque load rea~tion:
A. Itabirite Ty~e Iron_Ore (left in the ma~netic state)_:
Standard Blade Curved Blade
Torque Load
Reaction in 230
Grams 110
.. _ .............. ... _ _ _ . .. _ =
B~ Itabirite t e Iron Ore ( ema netized)
Torque Load
Reaction in 70
Grams 30
~_
C. Potatoe Star~h (300a/1 not thickened)
~ _
Torque Load
Reaction in 100
Grams 75
~5~
In the embodiment of Figs~ 21 and 22~ a rake ~rm ~-l
is equipped with standard or ~ertical.ly strai.g}lt rakiny blades
65.
However, for the purposes of this invention, a supple~nen-t~l
linear "dilating" blade 66 of the length "L" coextensive with
the rake arm, is fixedly connected to the leading end portions
67 of the raking blades at the! underside thereof, and thus
in transverse relationship therewithO
This linear blade is sloped slightly about its longitudinal
axis as indicated by the angle "A" (see Fig. 22). The slope
of this blade is downward in the direction of motion of ~he
rake arm, presenting a longitudinal leading slicing edge E-l
so that it would cut loose and lift a layer of settl.ed solids
just as they were entered by leading ends of the raking blades
of the rake arm structure. At the same timel thxough downflow
ducts 68 rising from this supplemental blade, thin sludge or
supernatant from an upper zone is caused to pass down into
and through the horizontal channel formed by the supplemental
blade, supplying dilating liquid to an associated raking blade
in the manner indicated by flow arrows A-Z in Fig. 21 and
flow arrows A-3 in Fi~. 22.
Also indicated in Fig. 21 is a modified arrangement, in
that ~he length "L" of the linear blade i5 subdivided into
individual aligned sections designated a-l through a~8 7 each
~ection being fi-tted in between, and fixed to a respecti~e
paix of associated raking blades 65. In this way (see Fig. 23),
the lower or leading longitudinal edges ~-2 of these blade
sections may be on a le~el with the bottom edges of the raking
blades.
3~ Accordi~g to another embodiment (see Fiys. 24 and 25),
a rake arm R-2 differs from the one in Figs. 21, 22~ and 23,
by a further modified supplemental blade arrangement~
- 18
In this arrangement, each of the respective rakln~
blades 69 has fixed to the l.eading ~nd thereof a supplemental
blade extending substantially at right angles to the vertical
plane of the raking blade, and thus at an angle "s" relatlve
to the longitudinal extent of the rake arm properO These
individual supplemental ~ladec, designated b-l th.rough b-8,
then present the staggered or stepped appearance in the plan
view of Fig. ~4.
Each of these supplemen.tal blades has rising therefrom
a downflow duct 70 through which dilating thin sludye or
supernatant from an upper zone may pass into and through the
horizontal channel formed by the supplemental b~ade, thus
being supplied to the associated raking blade, in the manner
indicated by flow arrows A-4 in FigD 24 and flow arrows A-5
in Fig. 25.
In summary, this invention provides in con~unction with
the operation of the raking blades, a method and means
to cut and lift a layer of solids to be conveyed over th~ tank
bottom by the raking blades, while pexmitting access of a mo.re
fluid pulp or supernatant fluid from a higher zone in the
sedimentation pool to a space close to the zone where the
cutting and lifting is taking place.
While the invention i5 herein illustrated and exemplified
in an embodi.ment wherein the center pier supports the rake
structure as well as the drive mechanism, the invention is
equally applicable to what is generally termed a traction driven
rake structure. As exemplifled in prior art, the inner end
of th~ rake arm is supported for rotation upon the center pier~
but a self propelled drive mechanism is mounted upon the outer
end of the rake axm for moving it along a peripheral supporting
track or rail. Such a drive arrangement may comprise a
self propelled roller device having a driven support roller
- 19 -
~s~
frictional:ly- engag:irlcJ ~ peripheral track~
Alternativel~, nvn--I`ricti,onal or positive drive means
may be substit~lted r for instarlce cog wheel drive where the
outer end o:E the rake arm is supported by anidler roller upon
S a peripheral trac]c, but is propell,ed by a cog wheel of the
drive mechanism, engaging a periph~ral -toothed raclc.
- .20 ~
