Note: Descriptions are shown in the official language in which they were submitted.
CA 02214538 1997 - 09 - 22
W0 96129135 PCT~ C~6
~ LIQUID/SOLIDS SEPARATOR
BACKGROUND TO TE~E II~ ENTION
This invention relates to a clarifier/thickener or separator of the type adapledto be used to separate suspended solids from a liquid.
Clarifiers/thickeners of the above kind are used in many different
applications and have particular relevance in the clarification of water. and
thickening of slimes produced in mining and mineral processino operations.
However, it is to be understood that the invention is not limited to use in
any particular application.
Generally liquid and suspended solids are fed into the inlet of the separator
at relatively low density. Within the separator. a large portion of the solids
is separated out of the liquid and a clear liquid is then discharged, usually
at the top of the separator, and the solids which usually settle under the
influence of gravity are withdrawn from the separator at the lower end
thereof. The clarified liquid is frequently re~erred to as "overflow". The
high density solids, in the form of a sludge, is frequently drawn out of the
bottom outlet from the separator. This sludge material is frequently termed
"underflow" .
In operation, the largest of the solid particles generally will separate under
gravity to the lower region of the separator. The smaller particles, known
as colloidal solids. will generally not settle within an acceptable time frame.
Clarifiers/thickeners therefore rely on the addition of a coagulant or
SUBSTITUTE SHEET ~RULE 26)
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W O96t29135 PCT/GB96/00688
flnrr~ nt which provides an cLr~ c bridg~ng m~rh~ni~m 1;~.L~ _-,.. small
particles. This bn~l~ine m~rh~nicm results in l~ger particles being forrned
u~ich ~ill then settle under tne inflllrnr.- of gravity
ln ordcr to join together the particles need to "collidc" ~vith each othcr, and
for this reason energy must be appliet to the liquid. Energy is gerl~r~lly
prov~dcd by caus~g the liquid to flow ~hrough the s~,~....t~,.. With the
correct energy input particles will remain togcthcr after colli~inn
Prior art clanfiers/thir~r~n~-rs have oftcn suffered f~om one or more
disadv~nt~es ('~Pr~lly what i~ uircd is ~at the s~ r will operate
to an ~c~-~t~hl~ dcgree of cffic;~nry, bc relatively ~I~to~ ;r and
m~ e ~ee, and will require ~r~t~hle lcvels of floer~llPnt
SUI~I~RY 0~ T~F, IIWF.I~TI~
According to a first aspcct of the inven~ioIL a s~,P-~Iul is provided for
b~ solids and liquids from a fecd r~t~ri~1 ~~ a mix of solids
and liqu~ds, the S~ r cnmrri~:in~
a tank having a top, generally vertical side walls, ant a CC~ ;C~I1Y
tapcred bottom;
a clarified liquid outlet at or near thc ~op of ~e t~nk;
a sludge outlct ~om tbe tapered bottom of the tank; and
a generally ve~ically aligned feed conduit located within the tanlc
- -
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W O96/29135 PCTJ~35~V.~fgg
- 3 -
ne~r thc top thereof;
thc fced cond~ut i"Ch~ing a feed section and a rli~ , scction, the
feed section being a~lapted to recei~e feed m~terial and the disch~rge
section being adapted to discSargc fced m~trr~l into the tank below
the top thercof. the di~L~ section being of ~vider ~ mPter th~n
the feed section.
The dischargc section preferably tapers ~.~L,~ y iQ a dllw~ d dircction.
The feed conduit may be centrally located and vertically ali~ed within the
tank.
~ft.~l~ the feed sectîon is cylintlrir~l, and the discharge section is of
h1 cone shape, and dle axis of the feed section and the ~1ischarge
section are .~ Pnt with each other and w~th the ver~cal a cis of the tank.
The dis~d~;c scction may t ~ ...ir.~fr i~l a lower cdgc which is ~ ~T,~ y
eq~ 1ly spaoed away ~rom the vertical side walls of ~e tank around the
en~rc p- ~ ;~ of the tank, th~reby ~1Pfinin~ an ar~nular throat ~.h._.~. said
lo~ver cdgc and ~e vertical side vvalls
The wid~h of the throat may be ~,_L..~ 5% and 15% of the ~ let~ of the
~c.
Preferably, tbc width of thc throat is a~loY;~ tf~ly 10% of the rli~mPt~r of
th~ tank
,
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W 096/29135 PCT/GB96/00688
The upper sulface of the corle shaped discharge section may define, together
with thc vertic~l side walls of the t~nl~, an upw~rtly di~erging scttling bed.
The half cone sngle of ~e discharge sec~ion may be ~.,L~ 20~ and 45~.
Preferably, the half cone angle ofthe discl~., section is ~ ly 30~.
The ~ t- ~- may include a recycle conduit ~hich extends upwardly within
~e tank from a region bdow the discharge section to the top or near the top
of ~e tank
The recycle conduit may be locatet wi~hin the feed r~nrl--it, p.~f~.~ly
coaxially the,lG~i~
The recycle conduit may . U~ ~ an upper right-circular cylinlln~ l section,
and a lo~er, downwardly diverging, conical section
The discharge scG~on may col~ c a du ~ "w~ ~gi.lg col~ical section,
with the low~r con-c I section of the recycle conduit nes~ng wit~n the
a~c sec~ion.
The cone an~les of the discharge section and the lo~rer conical sec~on are
preferably :iU~ iAlly the same.
The .~ , may filrther inclu~e a pluralit~ of downwardly converging
truncated cones s~ n~A, one bdow the odler, w~t~in the tank, the
lowermost t~l..c~d cone leading towards the tapercd bottom of the tan~;.
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W ~96129135 PCT)GBgC)~
Preferably, the ~a.~lor has three tIunc~tcd corles.
The L,u~ lcd cones sre preferably sll~Pn-lcd from and lie below tbe feed
condu~t.
The 5~ ma~ inclqde a launder at or ne r the top of the tank i~to which
cl~ifi~~~3 liquid v ill flow in use.
The feed conduit may l~ave an open uppcr end into which clarified liquid
may flo~ m use
P~f~ably~ the levels of the launder and the upper end of the feed conduit
can be adjustcd relative to each other to thereby providc means for
selectively va~y~ng the relative E,~n .,..lages of clar~fied liquid whic~ flow
into the feed conduit and the launder IL~e~,Lively.
The launder msy be of ar~ular shape and surround, but be spaced from, the
upper end of the feed condu~t.
T}le launder p~e~Lly ii;-CU~c~ s a ~eir over vhich thc rl~ifie~l liquid
will flow into the la~nder, the wcir ~mpn~ing a plurality of V-shaped
notches
The V-shaped rlotches a~e plef~,aLly c~vcnly spaced around the launder
~ ~e launder may b~ adjus~ble relati~e to the open upper end of the feed
con~ t
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W O 96/29135 PCT/GB96/00688
The lev~1 of the open end of the feed conduit may also be adjus~ble relative
to the launder
The open uppel end of ~e feed conduit may include a weir over which
clar~eied liquid will flow into the fced cr~n~it, the weir rnmrncin~; a
plurality of V-shaped notches ~paced around the upper end of thc feed
conduit.
The feed m~t~l rnay be fed into the feed contuit through a lateral supply
conduit which joins into the feed conduit below the upper end of the feed
conduit.
The latcral supply conduit may have an auxiliary conduit feedin~ into it, the
auxiLia~y conduit being uscd to h,~ lu~c floec~ nt into the feed m~ten~
use.
According to a second a~pect of ~c inYentiOn, there is ~rovided a feed
condn~t for a liquids/solids ~ .., said ~eed conduit c~..,.l.. ;~;..~ a
cylinriri~ul feed scction, ~nd a do-~vn~artly di~ g discharge section which
is fLlced to and coaxially aligned with the feet sectio4 the fe-cd conduit beingadapted to be l.lo~ d wi~ its axis generally ver~cal within a liquidslsolids
~c~
The f-ed section may be nght circular cylinrlrir~l, and the rlix~ section
conical.
The feed conduit may fi~ther includc a recycle conduit which extend~
through and is ccax~ally aligned uJith ~e fced sccuon and the discharge
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WID 96129135 ~9C'rJ~C~OD~
.. -- 7
section.
Thc recycle conduit may hsve an upp~r, right circular cylindrical sec~on,
and a lower, do~,..v~dly liv~.g,..g, con~cal sechon.
According to a th~rd aspect of the invention, there is provided a solids
C~ t~ lus foruse ~ithin a liquids/solids s~ t~r, said solids
co~ rdlion app_ratus compris~ng a plurality of aligned, L[.~ tl-~ nght
anglcd cones, adapted to be mounted one below the other wit~ a
liquids/solids S~,~JA'dtUr, e_ch cone bcing oriented so as t~ be do~nwardly
convergent.
T~c cone-angles of all of the truncated concs are preferably 5nhA~t~ltiAIIy thc
same.
Acc-..di.lg to a four~ aspcct of thc invention there is provided a method of
~araLing a solids/liqLuds ~nixed feed ~t~n~l in a seF~ ~o~ tank vvhich has
g~n~Ar~lly ve~cal. side walls and a feed conduit inr11lrlin~ a dow~ ly
discha~ge sectiol~ centr211y lor~t~d ~vithi~ the tank and spaccd
away from tbe walls of the tank thereby rlefinin~ an annular throat ~L~
the ta~k and the disch~5~ scction7 ~e m~thod ~.~cludi~g ~e steps of:
i"L".,.l. ~ ;."~ the f~d ma~rial into the tank through the feed ~nn~nit;
.
adding a flncc~ nt to the feed m~t~rial either before or after it has
entered the tank.-
allowing the feed m~t~l to pass through thc discharge section;
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W 096129135 PCTI~kSC~'~C6
allowing heavier solid par~icles to settle under the ;"ll.~ e of
~ra~ty towards th~ bottom of the tank,
allowing lighter solid pa~ticles to pass upwardly through thc throat;
selecting a~d m....;l... ;n~ the flow of feed rr~a-~n~l ~nto the tank so
lhat a bcd of solid partic]es forms within thc tank above the throat,
and
~hlll&~ g rl~nfied liquid from the top of the t~nk above the bed,
and sludge from the bottom of thc tank.
The me~od m~y indude the step of diverting a ~,-c..~ge of the ~l~nfi~l
liquid into the feed conduit to mix v~ith the feed m~tr.n~l
The mcthod may ~nclude ~e step of ~arying the p.,.C~ of clarified
liquid introduccd into the feed conduit so as to ~ary the specific gravity of
m~ l passing into the feed conduit and thercby opt;mi~ thc scparation
".. t~ . ,yI;re of the ~ rJl.
An rmho~ ..t of the irlvention is d~srnh~ bclouv by way of ~ le with
,ef~ ,e to the ~ rlpA.~y~g drawings. I~e draw~ngs, h~ r, are
mercly il~ of how the invention might be put into cffect so that the
specific form and a~em~nt of the various features showll is not to be
lm~l~r5tnorl as limiting on the ~nYention.
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W 096/2913~ P~J~ 8
~RIEF DESCRIPTIO~ OF T~IE DRAwrNGs
Figure 1 show5 a cross-cPr~ion~l side view throu~ a typical
rl~ ifier/thi~L-rn.-r acc~ to the invention; arld
FiEure 2 shows a plan view of ~e cl~rifi~tthi~ n-~ shown in F~gure
1.
I)ETAILED DES(,~~ 0~ OF AN EMBODIMENT
As shown in the dra~ings, a s~ 10 for scy~ e solids from liquids
in a feed m~ten~l inr~ rc a ~~en r~lly vertically . ~ 3;r~g tank 12 havislg
ver~ical side walls 14, a ~ y open top 16 and a duw-~w~lly l~ g
or cone shaped bottom 18. The tank 12 sho~n in t~e J~wi.~ is o~rcular
in cross-section, but tbe tanl~ rnay be square or rec~ nl~r in cross ~liu~l
and would operate in ~ ;"11y the same ma~ncr as is A~s~be~l below.
Thc taolc 12 has a ol~rifi~d liquid outlct 20 ~ocsted ne r the top 16, and a
sludge ou~et 22 ~ u~L which sludge which ~as cnllert~d in ~etapered
bottom will be discl,a~h~d.
A feed conduit 24 is loca~od wi~in ~e tank 12 near ~e upper end thereof.
I~e feed conduit is EEr~~r~lly vertically aligned and inrlllA~s a feed section
26 and a ~i~rh~r~e section 28 which is located below ~e fced section 26
Ihe fced sechon 26 ~s preferably of cylindrical form. The disc~e section
28 ~ of larger ~i~m~t~r ~orn ~e feed section 26 and is preferably of
do~LLwardly di~g~g fo~m as shown. Thc cross-seotional shapc of ~e
d~scharge secb.on should match that of ~e tank so t~a~ the lower edge 30 of
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W 096/29135 PCT/~k5C~'C~G~8
- 10
the discharge section is equally spaced from the walls 14 of the tank around
the ent~re lower ~ e.y of the discharge section 28.
Fced m~tPn~l is supplied to the feed conduit ~4 through a feed pipe 32
which passes through the sidc ~;uall 14 of the tank and extends into the feed
conduit :24. The discharge end 34 of t~e feed pipc 32 rnay be d~ .w~L~lly
directed as shovrn in the drawings to tirect i~ feed m~t~ri:~l
dOw,lwaldly The feed pipe has a floec~ nt supply pipe 36 c....nr. t~
hereto by means of which flccc~ nr is added to the feed m~r~ri~l as it
travels in the feed pipe 32.
The d;s~ ,c section 28 is, as mPntio"~A above, prehrably cor~ically
shaped. The half-cone angle of the discharge section may bc b~.LW ~ll about
20~ and 45~ and is p.cf..~.bly about 30~. The axes of the feed section and
the discharge section are p.c~.~ly coi~ nt w~th the axis 38 of the t~
throat 40 is defined ~l~, _.,.. the lower edge 30 of the disch . ~c section
28 ~nd the-side walls 14. As m~rltinn~l above, the throat 40 is preferably
Of ~ ."~1 .. .t width around the entire ~. il~h~,. y of the discharge section. The
wid~ of thc throat may be b~ ~ 5% and 1~% of the total width of the
tanlc 12 In the ~c~lcd a~ng~ne~lt the ~idth of the throat 40 is about
10% of the ~liz.. t~l of ~e tank 12
A recycle conduit 42 i~ located within the tank, co-axi~lly wi~ ~e feedconduit 24. The recvcle conduit includes an upper cylindncal section 44,
and a lower truncated conical section 46. The conical section 46 is
down~ardly d~ g as shown and is ne~d within the dia~ ,e scction
28. An annular gap 48 is thus defined ~L~ Ll the dischar~e section 28 and
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W O 96/29135 PCT/GB~61'C~YB
thc conical section 46.
T.o~t~d below the recycle conduit 42 is a solids concentra~on apparatus S0
The solids ~ r .~t~lio~ C cn~rnC~c 8 plur~ity of d~ ly
co..~ ~ h~ c~d codes 52. The cones 52 lead one into the other and
serve to direct solids s~g withiD ~e tank lZ towarts thc sludgc outlct 22.
Thc concs 52 are ~ ~ from thc rcoycle conduit 42 by a pl~ity of
S~ -Cr rodc 54
The cl~nfie~i liquid outlet 20 is ~ with clarificd liqu~d from the
s~ o- via a lal~nder ~6. The launder is of annular shape and is :~U~JpOl L~,~
in po~ ... from a gantry 58 locatcd a~ thc top of the tank 12. The launder
lc~ci~ J liqu~d which has been clarified in thc tanlc 12. The liquid flows
iuto the l~u~ter over a u~ir ~hich is defined by both the radially inner ed~e
6Q and the radially outer edge 62 of ffie launder 56. The weir is dcf~et by
a scries of V-shaped notchcs.
In the rmho.l.. l~ shown in the dLaw ~ sthc eleva~on of the laurlder 56,
relative to the tank, is var~able The upper end 64 of the feed condnit also
servcs as a ~re~r for clarificd liquid. As shown the upper end 64 of thc feet
conduit is also providet wit~ a series of V-shaped nt~t~ BSr ~arying ~e
ele~ ou of the launder 56 relativc to ~e upper end 64 of thc feed conduit
the rclative ~ .5 Of rlsrifi~ liquid which flows into the laundcr and
into the feed conduit can be varied. This feature is di~ more detail
below.
In use, feed m~t~i which W~ill5 a mix of solids and liquids will be
i~troduccd through ~e feed pipe 32. A con~olled volurne of flc~rc~ nt will
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- 12 -
be addcd to the feed materia~ ~ria Ihe flrJcr~ nt supply pipe 36. T~e feed
m~trri~l as it enters the feed conduit 24, will move downwardly t~wards the
disch~rge section 28. As the feed mAt~n~l enters the disch~-gc section and
moves radially oun~ards through the gap 48 its flow velocity will slow and7
in so doing, the hcavicr and l~r~er solit paracles in the flow will begirl to
settlc towarts ~e lower reg~orls of ~e tank. The flocG~ nt w~ll assist
par~dcs to join to~ether.
Lighter and smaller solid particles will tend to move around the lower edge
30 of ~e ~lischa~gc section 28. The liquid and similar particles will then
move upvvardly through the throat 40 into a settling bed or "floc bed",
inl~lirzlted by the shade~d area 66 locatet above ~e throat 40. It will ~e notedthat the floc bed 66 is upwardly div~ d Ih~,.efulc as the liquids and
smaller solids flow up~1vardly there will be a ~.,d_~y for the flow velocity
to dc~"cusc~ Thus, at thc ~In~ r~ of the ~oc bed 66 ~e relatively rapidly
upwardly mov~ng solid particles will tend to collide with the ~lnA~ of the
floc bed 66. Solid parncles will collide with each other ~e~by inc.c~g
the collectivc size of the p~hcles. As the solid particles increase in s~ze
they ~ill tend to beg~n settli~g duw..wdl dly, back through the throat7 towards
the bottom af the tank. The floc bed 66 thus acts su~ 1~ lilcc a s~eYe to
~ap upwardly flow~ng solid par~icles. Liq~d will pass up throu~ h the floc
bed towards the launder but eve~ small solids ~ill be ~apped in ~e ffoc
'oed.
The floc bed 66 will form naturally ss a cw~ ce of the upwardly
diverging config~ration of the flow path above the ~lia~h~7t: section 28
Thus, the cone-shaped form of the ~ rh~r~~e section senres firstly to slow the
velocity of flow to allow larger pa~icles to settle7 and then secondly, as after
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' - 13 -
flo~ has passed through the throa~, to agaiIl slow the flow velocity above the
throat to allow ~e floc bed 66 to form
It is i~O~l~t that the densi~y of the feed ~ tPr~ is O~l;r'.i5~,d for proper
y of ~e settlc-r. For this reason it is ~fef~Lle~ ~hat at le t some of
the rl~nfiP~ liquid ~hich is available for discharge from the settler is fed
back into the feed conduit 24 for mixing with fiesh feed rnaterial. For this
reason ~e relative elevations of the launter ~6 and the upper cnd of ~c fecd
condu~t should be adjustable. This can be ac~ieved by either raising or
lowerLng the lalmder, or b~ raising or lower-ng the fced ~n~ it In the
e~nborlim~nt shown the cl.~liull of the launder 56 is adjustable and for this
reason a flexible co~ E pipe 67 is fittet L~ n the launder ~6 and ~e
r.lArifi~ liquid outlet 20. The V-s~aped notches which define the lC~
we~Is cnsure relati~ely preclsc control of flow ~ to ~he fe~d conduit and
ntler Dilution of the fed m~t~ results in lcss ~or~lllAnt rnnc~mrti~n
and higher settling rates.
As solid partieles settle they will pasS towArds ~e tapered bottom 18. The
jower part of the t nk is rcfcrred to as the c~nn.cn~ inn zone. I'hc cones 5
serve to dc-..~L. solid m~trri~l passing dcswll~.lly into ~he ~on~o~ At~sT~
zone so th~t m~teri:ll drawn ollt of the sludge outlet 22 is slu~lge-like in
nah~re
As solid m~trri~l d~u~ on the upper surfacE of the cones 52 it w~ll begin
to slide do~n the inner s~ rS,ccS ofthose cones throughthe ~ throats
of ~e cones until it deposits _s sl~dge ~n the cone shaped bottom 18
Liquid, ~l~ricted by arrows 68, will move in an upward direction ant will
move upward into the con~ shaped lowcr section of the recycle conduit. It
,
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- 14 -
is ellvisa~cd that ~e liquid 68 will be moving upwardly at a rela~vely low
upward flow rate so as not to Gal'Ty ~th it many solid partiGles moving
downward in this consolidation zone
One distinct adYa~ of ~e r~r~fi~lr~tion of the cones ~2 is that tho cones
serve to guude solid p~t~cles mov~g down in this con~nliA~tinn zone
towards the cenlle of the conc shaped bottom 18. lt ~ill be noted thal a
solid particle build up as in~lir~t~d at rllrn~r~l 70 occurs below thc lo~ver
most cone 52. The ad~ ,c of this is t~at discharge whiGh takes place
through the outlet 22 will tend to draw sludge f:rom this ceDtral region and
t~us the problem of op~n sludge f~ee ~ E~.s (~o~n as "rat holes") be~ng
formed in the sludge will, to a large extent. be ~limin5~A Instead,
discharge which does take place throu~h the outlet 22 will tend to
cnn~in~ t~ the solid sludge m~t~ l and dlis slud~e material w~ll generally
be g~uded lo~ ds the centre of the bottom 18 ~ereby rl~ in~ any such
"rat holes" that may tend to occur.
It is envisaged tha~ a s~ of ~e t~pe rlP.crsi~eA ~hnll have a number ofadvant~ges. T~e ~Alur will, it is envisaged, remove sllcp~ solids
over a wide range of flow rates and solids levels. It will also rcmove
particles of vaTying ~;ti~os and provide a lL,lal~ clear overflow.
Controllable nnrl~lnw ~3~nci1i~s over a ~1v~de range of ~l~n$iti~c is Also
pnCcihl~ The s~ or ~. also be used to achieve classificatiorl of solid
particles by mun;~ the feed flow rate, flocc~ nt ar~rlition lcvcls and
optimicin~ or adjusting the annular op~ing to suit the required cl~sc,ifie~ti~ n
Clearly there may be mul*ple inlets and a s~r~ratnr shown irl the drawi~gs
a relativel~ simple example of the ~nanner i~ which the invenhon may be
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uscd. As prcv~ously m~ntjonfA thc i~ rdt~ does not nccd to be circular
in cross-section. A square or rectangular s~p~ may be u5ed. Thus,
whes~ thc term "cone" is uscd in this sp~ifir~inn it is not jT1t'ndffl to only
rcfer to circular cones. T~e tum should be tal~en to include v~thin its scope
pyramid or other shapcd concs.
There src manS~ advanta~es to bc obt~in~d by using a rl~rifir~ "~l~ " ~ of
tl~ type r~ ~A herein Firstly, dilution of the feed rnay be ~lltrm~tjr~l ly
controllet over a fi~ll range of opeIational con~lihonC a~d could be changed
to cope wi~ r1~n~e~ in feed flou~ rates and feed material liquid/solids ratios.
'rhe chanE~e in area of the an~ular passage le~Lds to a very high rate of
rn~xi~g tuc to the cha~ge in fced ~- lo~ s T~is is particularly
adv,...t~o~s when multiple units are employed i~ couIlter cunent
"Iittic~n (washing) wheD high mixing eff;ri~nnicc are ~quired. The
chan~e iu cross-section of the r1s~ti f~ ..cL ~ r up~ard of the annular throat
40 quickly ct~hilic~c the depth of the floc bed and also i~ as.,s thc
;erlry of the floc bed since the upw~-t velority ~d~d on the floc
particlcs rapidly dcc~c~s~s This will le ~ to more collisions ~L~e.,.l
particles and larger flocs v~ quickly occur th~ lowin~ the lar~er floc
particlcs to ~II under gra~rity through the t~roat 40 th~eby ~ ly
~-ple1in~ the floc bed of solids.
The tischarge f~om the cnncolidz~tlnn cone is ccc~nti~lly ~bove thc ~ erflow
diacl~ .. The buL~ of the high density sludge is thus allo~ed to build from
'~ the centre ounv~rds ~ereby enCl~ring minimicing ~le effect of "rat holes" and
blo~L ~grs or cu~ a~ ~;n~ which often reslllts f~om "rat holes" f ~ning
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W 096/29135 PCTI~C~ 6
It is en~.r~saged that corrosiorl/eros~on lates will be low due to the slow
movernent of solids in a do~Lw~L,d directiorL It will also be y~preciated that
there are no mov~n~ parts of the a~.ltuS Thc ~~ lus will be seif-
r~ nin~ and it is envisaged that it wil] havc a lo~ fl~e~ nt rr n~.. rLion
due to the larger particles tending to settle lmt~ gravity so they will no~ be
carried up into the floc bed The floc bed abovc thc annular throat 40 is
self-b~n~jn~
It should be noted that the form of the throat 40 can be vancd. For
example, a downwardly depcnrlins~ 53~irt could be ,.~ h~ to the lower edge
of the discharge sec~ion 28. Such a skirt will than defiIle an annular
cylind~icall~r shaped throat which will bave the effect of lowen~g the top of
the floc bed but Would possibly ~I,lo~. the ~ y of the floc bed.
,
