CA2028823A1 - Method and apparatus for washing cellulosic pulp - Google Patents

Abstract

A pulp washer for washing cellulosic pulp stock. The pulp washer includes an endless porous moving belt (33) that rides on a perforated rigid support plate (17) and the cellulosic stock is fed as a layer or mat (69) onto the upper surface of the belt (33). The mat is progressively reduced in thickness and liquor is extracted from the mat as it moves through the converging path. The mat is then passed through a series of conditioning or washing stations where the mat is subjected to dilution by washing and drainage cycles. Each washing station includes a standpipe (103) that extends upwardly beyond the belt and contains a wash liquid. The upper surface of liquid in the standpipe is exposed to a gas (106), such as air, so that the pressure head of the liquid in the standpipe will drive the liquid through the mat.

Description

WO~OJ107~0 PCT/US90/01319 ~ ~ & i ) J~
~1-- , "Method and Apparatus For W~h~ Cellulosic ~p"
Backqround of the Invention In the pa~ermaking industry wood chips ar~ -~
di~ested at elevated temperatures with a pulping ~`
liquor. In the pulping process, cellulosic bon~ing in~redients are dissolved in the pulping liquor, an~ -after pulping, it is desirable to recover the spent .
liquor from the pulp and process the liquor to recover its heat values, as well as the digesting chemicals~ ;
It is desired that the spent liquor be~ recovered with as high a solids content as ~ossible, since the initial stage of the recovery procedure is the concentratio~ of the liquor by eva~oration. Thus~, to provide the most effect`ive recovery process, a minimum q`uan~tity of wash ~
water should be used to wash the pulp. ~`
Traditionally the most common procedure for recovering the pulpi~g liquor has`involved the use of~ ~ ~
rotary dru~ vacuum filters. As~one filtration does not ;
ordinarily sufficiently wash the pulp, the pul~ is typically reslurried with wash water and refiltered.
This sequence is repeated, usually in countercurrent fashion, to obtain the washing of the pulp and the desired recovery of`the pulpin~ liquor. ~;
Rotary ilter drums reguire a substantial amount of water to wash the pulpo This is due to the necèssary reslurrying operatio~s and due to the fact -that drum filters require very low slurry~consistencies l ~`
`for efficient operation. Thus, recovery of ~he pul~in~
liquor from~ the washing process;~util1zing rotary vacuum drum filters requires~su~tantial ener~y to concentrate t~e diluted pulping liquor in th~e recovery operat1on.
To eliminate ;the difficulties encountered ,, ~ with rotary drum fi~lters, at~empts have been made to `
.
filter the slurry on a moving horizontal belt-type -~-` ` ~filter. For example,~United~States Patent No.

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WO90~10750 PCT/US9OtOl319 .:
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4,046,521 shows a system in which the diluted slurry is ' '' de~osited on a moving horizontal filter belt which :' passes over a series of suction boxes~ l~ash water is applied to the downstream suction box and the water `.
passing through the mat supported on the horizontal belt is fed countercurrentl~ through the various suc- .
tion boxes to the upstream end of the system. ~.
U.S. Patent 4,154,644 also discloses a Dulp ~`
washing system in which the diluted pulp,slurry is ,' applied to the upper surface of a ~oving horizontal filter belt. In patent 4,154,644~ a hood is sealed :' over the porous endless belt and the belt passes over a `,~, series of suction boxes and the liquid withdrawn from ~:' the slurry is recy~led countercurrently. to preceding ~, sections of the ~asher. Gases a.nd vapors drawn into , the suction boxes with the wash~liquid are separated from the liquid and recycled to,,the ho,od to cntrol .the ,,, at~osphere in the hood and maintain the desired pres~
sure differential for operation of the washer. ,.`
As the moving horizontal belt that supports .::.
the pulp ~at travels over a serles of vacuum or suction ., boxes in the systems shown in patents 4,046,621 and `.~., 4,154,644, there is a substantial frictional resistance ,`.
to Tnovement of the helt. The increased ~rictional ,;
resistance requires the drive system to have a substan- ' tialIy greater ~ower require~ent and also causes wear ' of the filter belt, reducing the service life o~f thq 1, ,:
belt.
U.S. patents 4,160,297 and 4,246,669 show ';' pulp washing systems in which a layer or ma~ of pulp is contained between two endless filter belts. In these ~, ................................................................ ..
patents, hori:zontal drums are each mounted in a wash . ;.
tank containing the wash liquid and the pul~.mat con~
talned be~ween the filter belts Dasses under.each of the wash drums and through the liquid contained in the ..
'' `'..

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WOgO/10750 PCT/U~0~01319 _3~J~'3~5'-~

tank. The wash liquid from the tank can pass inwardly through the oulp mat contained between the belts, or alternately, can flow outwardly from the drum through the mat into the tank. A countercurrent wash liquid system is employed in which the wash liquid passes between the wash tanks in a countercurrent manner by gravity flow, Su~mary of the Invention . -The invention is directed to an improved -, .
method and apparatus for treatin~ a liquid slurry con~
taining solid materials, such as a slurry composed of -~
cellulosic pulp stock and di~ester or pulping liquor.
The flowa~le cellulosic slur;ry~is fed as a layer or mat onto the upper surface o`f a moving endless porous belt that rides on a ri~id perforated polymeric support plate. An up~er inclined plate is sDaced from the belt and defines with the belt a converging 1OW path so ~-that the-mat is pro~ressively reduced in thickness as it passes through the converging flow path and liquo-:
.
is extracted from the~mat.
The mat then passes through a series of con-ditioning or washin~ stations where the pulp mat is subjected to dilution by washing liquid and drainage cycles. Fresh water is delivered to the mat at the final downs~eam station and the washing liquid, after :
passin~ through the mat, is pumped in countercurrent flow through the various conditioning staitions to the ! -:
upstream end of the washer. ;
:Each washin~ ~or~cond~itioning station comprises a standpipe which extends upwardly beyond the bel~and the upper surface of~the liquid in the stand-D i pe i s e xpos e d t o~ ~ a ~g a s r~ s uch ~ ~ a s ~a i r ~ S G th a t th è ,~
pressure head of the liquid ~in ~he sta~dpipe will drive :~`
the liquid through~the; DUlp mat. The wash liquid draining through the mat is collected in a sump and is .:

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W~ 90/10750 P~TJUS90/01319 ~
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then pum2ed to the standpipe associated with the nextu~,stream washin~ station, so that in this manner, the wash liquid is circulated in a countercurrent flow with respect to, the flow of the pulp mat through thP wash,er.
Following the final washing or conditioning station, the mat is separated from the endless belt~
As the ~ash liquid is driven through the mat by hydraulic pressure, without vacuum or forced air -~
flow, foaming is minimiz,ed. Further, the ~ir cushion ~-in the standpipe provides improved control of the hydraulic pressure in ,~ach wàshing or conditioning station. ' The washer is a completely enclosed unit, so that th,e~re is no discharge of pollutants into the ``~
atmosphere. The washer comprises a lower housing sec-tion and an upper housing secti,o,n, which is hinged to the lower section along a side,ed,ge and the two housiny sections define a sealed washin,~,, or conditioning cham- ~;
ber. The upper housing section can be pivoted upwardly to an open position to install the belt or for r~,ainten~
ance or repair. The headbox is an integral part of the upper housing section. `
In addition, a seal is provided at the up- -stream end of the conditioning chamber which seals against the helt as it enters the conditioning chamber to preclude discharge of pollutants into the atmos-~,here. Similarly, a second s~al is provided at the dlownstream'en~, of the conditioning chamber which seals ayainst f,'he upper surface~of the pulo mat, as the ~at is discharged from the conditioning chamber.
Any air entràpped in the mat will bubble -upwardly through the wash liquid contained within the conditioning cha~ber and be collected in the head space in the standpipes.- To maintain the desired air cushion ~;
in the headspace, a relief valve cn be incorporated '~ ' i .;

WO9p/107S~ PCTJUS90/01319 :

with the upper end o~ each standpipe and a liquid level control, which senses the liquid level in the standpipe ~
can be incorporated to maintain the proper li~uid level in each standpipe. :
The pulp washer. of the invention provides a low dilution factor and will condition the pulp with a :~
low soda loss as well as a low ~iber losis. i`:
The pulp washer is compact in size and occupies considerably les:s floor space than ~ulp ~-washers, as used in the past. . ~.
Other objects and advantages will appear in the course of the following description~
Describtion of the:Drawinas _. :
The drawings illustrate:the best mode presently contemplated of carrying out the invention.
In the drawings~
. Fig..il.is an-end view of the pulp washsr of the invention;
Fig. 2 is a side elevat:ion of the.pul~ washer ~
of the invention;
~ Fig. 3 is a fragmentary enlarged longitudinal: ..
section of the uDstream end of the washer; .' Fig. 4 :i5 a fragmentary enlarged longitudinal : ~ ...
section of the central portion of th~:washer;
:Fig. 5 is a fragmentary lo~ngi:tudinal section : : of the downstream end of the washer;
1, Fig. !6 is a.transverse section.of the~lwasher;~
: and.
Fig. 7~1S an~ enlarged fragmentary~long:itud~
nal;~section showi~ng the seal at the upstream~end of~
the.washer.; ; ;

W~9p/1~750 PCT/US90~01319 ; .

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Description of the Illustrated Embodiment The drawings illustrate a pulp washer .:.;
composed of a frame l that .supports a closed housing ~
2O Frame l includes a pair of upper horizontal beams 3 ~:
each of which is spaced above a lower horiz.ontal beam ~;
4. As shown in Fig. l, the ends of each pair of beams 3 and 4 are connected by a threaded:screw jack 6, while : :
the opposite end of each lower beam 4 is provided with .`
an upwardly extending extension 7 and a removable block .;
8 is disposed between the ex~ension 7 and the lower -surface of the end of the corresponding upper beam 3O
By removal of the block 8, the lower run of the endless ;.
mat supporting belt can be inserted`in the frame, as `.
will be hereinafter~described.
Housing 2 is composed of a generally trough-shaped lower section lO and an upper section ll which ~
is hinged to the lower sectïon`along the corresponding ..
side edges.
As illustrated in Fig. 6, lower section lO of -`
housing 2 incl~des a pair of spaced side channels l2, the ends of which are connected by ~nd plates 13~ In `
addition, a bott:om wall 14 is conn~cted to the side channels 12 and end plates 13 to provide the trough~
like construction for the lower housing section lO. As ~.
.
shown in Fig. 6, an inverted channel l~ extends inwardly from one of the side channels l2 and a longi-jtudinal:~bea~ l6 is secured to the~,inner upstanding ~
flange of channel 15. ~ similar beam 16 is secured to the web o the opposite side channel 1~2. As shown in Fig. 6, a ri:gid~plate or block 17 i~s supported on the u~per edges of beams l6 and extends ~he length of the .::
housing 2. The plate 17 is preferably formed of a polymer1c material, such as polyethylene, and contains a plura:lity of parallel, elongated slots 18 which extend ~ransverselyiof the pla~e. Plate l7 serves to ::

90/tO7~0 2 3 r~ PCT/US90/01319 support a porous b01t which, in turn, supports a web or ~at of pulp, as will be hereinafter described.
Lower section lO of housing 2 is provided with a'~lurality of spaced transverse divider walls l9, which divide the lower housing section lO into a series of sumps or chambers 20 that are spaced along the length of the housing. As shown in ~ig. 2, six sumps 20a~f are provided in lower section lO.
A vertically adjustable wall member 21 is provided at each end of lower section lO. The wall member 21 is verticalIy adjustabl~e with respect to divider wall l9 through a bolt and slotted connection ~22, and the upper edge of wall member 2l is provided ~;
with an inwardly bent tip or flange 23, which is engaged with a groove in the respecti~e end of pIate 17. Engagement of ed~e 23 with the~groove in plate 17 ' acts to hold the ends of the plate down and~accommod-ates di~ferential heat expansion between~the poly~eric '~
plate 17 and the metal lower housing section lO. -~
The walls 19, along with the end walls 13, def~ine chambers 24 and 25 at the upstream and down- ;"
' stream ends, re-cpectively, of lower section lO.
Upper housing section ll is compos d of~a pa~ir of~ spaced~side~channels 27~which are connected by a top wall or cove~r 28. As shown in Fig. 6, a side channel 29 iS ` secured to the lower portion of the web of éach channel`27 and the side flanges o~ eac'h channel 29 are~wel~ded~to a~plate 30. Each plate~30 extends outward~ly from~ch;annel 29~a~nd~the~outer~portlon~of~
pla~te 30~ s~connected by bolts~to`the lower 1ange of ' the respe~tive~side'channel 27.~ Each channel`~29 is prov1ded~with~a~plura~lity~o vert1cal tubes 31 wh~ich~
a~re-~spaced along~the~length of the~channel. Tubes 31 extend co~olete~ly~throu~h~the'channels~and provide pas~sages~or the;low o~ the wash ll~quid, as will~be herel~na~fter~`described~

~O~0/10750 PCT/USg~/01319 .~.

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As best illustrated in Fig. 6, the lower surface of each plate 30 is provided with a recess 32 ~ .
and the side edges of a porous endless belt 33 are received within the respective recesses. The upper run ~.~
of belt 33 is supported on the upper surface of plate ::
17 and the side edges of the belt are spaced inwardly ~`
of the tubes 31~ ~ith this construction, wash liquid flowlng downwardly through tubes 31 will then flow inwardly through recesses 32 to prevent any fibrous :~:
material from clogging within the recesses~
The abutting side edges of the housing sec- -.
tions 10 and 11 are sealed by gaskets 34. One of the gaskets 34 is carried on the upper flange of a channel 35 that is mounted on the upper flange of side channel 12, while the other gasket 34 is carried by ~he upper .. :
end of a generally L-shaped bracket 36 tha~ extends . ~
upwardly fr`om channel-15.` ~hen the ùpper housing sec- ~;.
tion 11 is in the closed position, the lower surfaces ..
of the respective plates 30 will bear against the gaskets ~4 to provide a seal along the side edges of ...
the housing sections. ~.
Upper housing sect:ion 11 is adapted to be pivoted between a closed and open position. To provide .~
the pivoting action, a group of pivot blocks 37 are .~-mounted on the upper flange of one of the side channels ~;~
12 of lower section 10, while a corresponding group of :~
. l. ,luys 38ia,re .secured to:one of thelside channels 27 of upper s~ction ~1, and the lugs 3~ are pivoted ~o blocks 37~ by pivot shaf t 39 . At the op~osite side of the . .
housing, as illustrated in Fig. 6, the lower end of a screw jack 4Q is secured to a ?ivot block 41 which is pivo~ally connected through pin 42 to lu~ 43 secured to :.
sid~ channel 12 of the lower section lOo Jack 40 can be~swung upwardly and received within a slot in the ~:
flan~e 46 of bracket 47 that is secured to the corres- ~.
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WO90/tO750 PCT/~S90/01319 _g_ . .

ponding side channel 27 of upper section ll. A pair of nuts 48 are threaded on jack 40 and located beneath flange 46, while a second pair o~ retaining nuts 49 are ~'~
engaged with the upper end of the jack and bear against the upper surface of flan~e 46. Engagement of nuts 48 and 49 with jack 40 will lock upper section ll in the .' closed position. By releasing nuts ~9 and threading ..
nuts 4~ on the jack,;the upper housing section l1 can~ ~' be pivoted about shaft~39 relative to the lower : '.' section. In addition:,:the jacks 40 c~an be swung:out~
wardly and downwardl:y to a position where they willlnot '.
interfere with installation of the belt 33 in the '"
housing.
Belt:33:is:~c~arried by~a~drive roller Sl 1ocated at the~d~ownstream end~of~the~housing and~an : idler rol~ler~52~lo.cated at~the upstream end.~ In~
~ trav'ell~ing from~roller 52~;to ro'lle~r 5~1, the:upper run:
~ ~:of porous belt~3:3 ~i~s:~suppor~ted~:on the~upper surf:ace of ;~:plate~17.~ ~elt;33~can~be formed~:of:a~plastic mater1a1:, such as~nylon,~or can~be for~ed;~of:~a~metal, such~as~
: stainless steel~
Ro11ers 5~ and~52~are~each~;supported in~a~
air~of~bearin9~bl~oc~s;s3~:~which~are~s~ecu;F~ed to th~e~s1de~
`';channe1s~ 2~of~1owqr~section~1:0;~:through support~members~
5~4~ As~shown~ in;~Fig.;~;2~ the~:~lower~:run~of be1t~3:~3~1s ~
~trained over a: roller 55 which is located inte~rmed:iate : ~: ~ : :,.``:`
the leng.t~ of~ the'~hou~sing a~nd thelroller'551is`~lsupp~rt~

ed`from~the l~ower sec~tion 1~0 through~supports~56.~As~
previously desc ~bed,~the~lower~run~of~belt 3~can~be~
nstal1e;d;~by~'remov~al~ o~ the~blo~k~s~8 t wh:ile~he~.~upper~
run~;~of~t~he~`.be~lt~;is~ s~talled~ y~ e~lea:sin~g~the jacks~40 and:~ voti~ng~the~3~aG' 'downwar:d~1y;, so th t;~the per~
:run.~of:t~he~ e~1~t~ca~n;~:be:~.i:ns~erted~ e~tween~the upper~and~
'owe~r~housi~ng~sect~ 'ns'.

W0~0/l07~0 ~ PCT/VS90/013t9 :' .
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~ ' Mounted on the upper edge of the end wall l3 ;~
at the upstream end o housing section lO is a ~uide block S7 which ~upports the belt 33. As shown in Fig.

3, guide block 57 is spaced between roller 52 and the upstream end of plate 17. Block 57 can be formed of a polymeric material,~such as nylon. Similarly, a guide block 58 is mounted on the upper edge of end wall 13 at the downstream end of the lower section and serves to guide the belt 33 as the belt travels from the down- ~;
stream end of plate 17 to drive roller 51.
The cellulosic slurry is fed to the upstrelam~
end of upper h~using section ll through a supply conduit 60. As~best shown in Fig. l, supply conduit 60 includes a~vertical plpe 61 which is connected through `` a flexi~le coupling 62 to elbow 63. Elbow 63, in turn, is connected to a horizontal manifold 64 which extends~
transversely~of the housing l and a group' ofiinlet ~` pipes 65 connect the~anifold 64 with the~ enlarged inlet 66 of upper housing section ll. See Fig. 3.
Inlet section 66 defines an inlet chamber 67 which , extends~both upwardly and downwardly f~rom the inlet pipes 65. This results in a~swirling action for the incoming slurry which aids in providi~ng a homogenous ;
mixture of ~ibers and l;iquid.
The incoming slurry~is carried by ~elt 33 into a converging flow path defined by plate ~7 and an ~
inclined mat--confi~ning member 68, ~hich èxtends across ,!' ;
the width of the~housing. ~s~the slurry passes throu~ -the converging~path,~liq;uid is extracted from the slurry to~provide a~ fi~rou~s mat 69 and ~he liquid flows th~r~ough the~slots~in~plate~;l7~into the upstream sump 20a. ~The~mat-confin~in~ member 6~8 includes a flat bottom plate 70~which~is di~sposed at an acute angle with respect to plate;17 and a;group of generally ~
shaped reinforclng members 7~1 are secured to the upper ~ ~ ~::: : : . ;

WQ9Q/1~750 PC~lUS90/01319 -: .

~ 3~
,,.~.
,, surface of plate 70, while a generally ver~ical plate 72 extends upwardly from the upstrea~ end of plate ~
70. The downstream end of plate 70 is secured by bolts .~;
to a pivot strip 73 which exte~ds transversely across .~:~
the upper housing. As the bottoTn plate 70 is somewhat ;.;
flexible, it can be pivoted:in a vertical direction ..
about the connection with stri:p 73.
To lock the mat-confining membex 68 at the -`
desired inclination, a group of lugs 74 are connected .
between the vertical section 72 and the downstream reinforcing ~iember 71 and each lug is provided with an ;
elongated slot 75. Lugs 74 are disposed flatwise .
;against the side channels 27 of the upper section and ~bolts 76 extend through the slots 75, as well as th~rough openings in the channels 27. With;this con- ~-struction, the ~at-confining member 68~can ~e pivoted :in~a vertical pIane relative` to plate 17 to change or vary the angularity` therebe~ween and the member 68 can be 1Ocked into the~desired position by turning down : ~ bolts 76.
To~seal the~upstream end~between housing sections 1~Q and 11, a~sealing unit~77 is employedO
Sealing unit 77, as~ best~il1ustrated:in Fig.~7, includes~an elongated block 78 whi~ch:extends trans~
versely of the~belt 33. The~upstream edge of block~78 ;~
: is~pxovided wi:th a recess and the lower end of end wall i l79~of u~pèr~sect~i;on 11 is secured in thé recessl by !
we1ding or~the~ 1ke.~A~ flexibl~e w1per 80~is mou~nte~d :~
w:ithi:n~a recess~ n~th;e~downstea~ end~o~;~block 78~by ;stri:`p~81~ :and~th~e~out~er genera~lly fl~at:end:82:of~;wiper~
80 rid~es`~aga~nst the~upper~surface~of~belt 33~to~
:p`r~ovide~;a s~eal~a~t~the:~upstrea~ end of:the h~ous:ing. An~y iquid~:leakage~which should~occur~:between~wiper 81 and be1~t:33~is~c:o11ect~ed ~in~he upstrea~ chambe:r 24. ;~

f ' r S ~ !

A second mat-confining member 85 is located downstream of the member 68 and forms an extension thereto, as shown in Fig. 3. Mat-confining me~ber ~5 includes a lower generally f~at plate 86 which extends ;
across the housing and is located~at an acute angle with respect to the support plate 17, to thereby define~ -~
a converging flow pa~h for the~mat 69. The converging flow path aids in co~pressing~and extracting liquid from the mat~ A reinforcing beam 87 is secured to~he . .
upper surfaee of plate 86 and the upstream end of plate 86 is secured to a pivot s~rip 88 that extends trans~
versely across the upper housing section. The flexib-ility~o~ plate 86 enables the plate to ~e tilted or pivoted in a ~ertical~ plane relative to the strip 88.
To pivot~plate ~6, an arm 89 is~connected to ~a cross~ shaft 90 that extends transversely across the upper housing section 11, and a link 91 interconnects ~ ~;
the outer end of arm 89~with the~downstream end of the reinforcing member ~7.
. .
A generally vertical arm 92~is also secured to shaft 90 and~the upper end~of arm 92 is connected through two pair of inflatable air bags 93 and 94 t~o fixed supports 95. ~As shown in Fi~g. 3,~the air bags 93 and 94 are located~ on opposite sides of the arm 92~and by inflating or deflat~inq the bags,` the arm 92 can~be pivoted to thereby pivot link 89;and Divot th~e mat~
cbnfiningi~me~ber 85. For exa`mple, by inflat~ing the air bags 93, member~85~will be~raised,~and conversely by~
inflat~ing bags~94,~ember 85 will;~be;lowere~d. ~djus~t~
able~ stops;~6~a~nd~97 are located on opposi~e sides~o~ ~ -the arm 92~and are~ea~ch~mounted~through~a~fixed bracket ` `~
98;~to~the housing.~Stops 96~and~97 1im`it ~he pivotal~
movement of the arm ~2 ~nd~ thus limit~the ~ivot~l move ment~of mat-confining member 85.

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W090~l0750 PCT/US90~01319 ,_ j ,;

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Upper housing section 11 includs a vertically '.
enlarged section 100 spaced above member 85 and defin-ing a closed liquid chamber 101. The upstream end o.f '.~.' section 100 terminates adjacent the upstream end of :
member 85. The pressure of the liquid within the ;'~'.' cha~er 101 defined by section 100 aids in resisting . .' the upward ~ressure exerted by the ma~ ~9 against ''.
member 85 as the mat: flows through the converging flow . .
path. ~ : ,.. ' A series of wash or conditioni:ng zones are ';.
located along the length of housing 2 and, as shown,in '.`
the drawings, five such zones are provided. ~ stand~
pipe 103a-e is associated with e~ch zone and acts to ~ .' : supply wash liquid to that zone. ~Each standpipe 103 '"
nc~udes a vertical column 104, the lower end of which communica~tes with the liquid chamber 101, whlle the~ ''.. ' upper end'of column~104' i5 in communication:with an enlarge~ generally spherical head 105. Air, or other ''.
gas,~is~located in the headspace 106 above the liquld lev:el in head 105.
The low~r:~end of column:104~of each:standpipe 103 ter~inates: in an ~inclined surface 107 which is ' :~;posit:ione:d: at an acute~angle ~to the horizontal and ald~s ;dir:ecting the~was~h liquid~from .the standpipe in a downs~tream di~rection:within~the`cha~ber l~Ol. :~
:: The lower:end of column 104 of each sta:ndpipe ~103 is pr4vided'w~ith~a hori20nta1 flange 108 th'a:t is ;~ : space~ from;the incllned~su~f~c~e 107,~as shown in Flg~s~
3 a:nd~ and~a::wi~er~:10~: is;asso~c~i`a~ed with:the ;stand~
pl~pes~103b-e.~ Each wlper~10;9,~as~ lustrated:in FIg.

4:,~ha;s~a g~enerally curved~'ou~ter ed~ge~which~rides aga~inst the upper~surface vf~mat~6~, while the opposite ~ '~
end~ of ~ach wlp~er~:is~:~connected ~to:the~fl~ange iO8.~
Wiper lO:9~,:wich.~:exend's across~the width of the hous~ing section ll,;can flex~ or pivot~relative to flange 108 WO9Q~10750 PCT/US90~01319 -; ~12 .) S ~. ~
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and will ride or float on the upper surace of mat 69 to prevent wash liquid from the associated standpipe 103 fro~ 1Owing in an upstream direction.
A conventional relief valve 111 is associated with the upper end of the head 105 of each standpipe :^
and serves to relieve the pressure in headspace 106, if it exceeds a predetermined value. During operation of the pulp washer, any air entrained in the mat 69 will be vented upwardly during the washing operation and will collect in the headspace 106 of standpipes 103.
If th~ pressure in the headspace is increased beyond a predetermined value, the relief valve will open to vent the pressure.
To seal the area where the~mat 69 is dis-charged from the housing, a sealing assembly, indicated generally by 114, is incorporated. Sealing assembly 114, as shown in FigO 5, includes a flexible plate 115 which is disposed at an acute angle with rPspect to plate 17 and the outer or downstream edge of plate 115 rides on the upper surface of mat 69o~ A box-like re- ;
inforcing member 116 is secured ~o the upper surface o plate 115 and extends the width of the plate. The upstream end o plate I15 is connected~to a pivot strip `~
117, which extends transversely~of the upper housing section li. Due to the flexible na;ture of plate 115, the plate can pivot or flex in a vertical direction about the pivo!t~strlp~ll7~
To pivot plate ll5, a pi~Jot shaft 118 extends transversel;y across upper housing section 111, and~a bell crank leve~r ll9~is secured~to shaft 118~ The~
l~wer~ gen~erally horizont~al~arm 12~0 of~lever 119 is connected via~a~link 121 to~the downstream end of re-inforcing~member~ll6, while the vertical arm 122 of leve~r 119 extends upwardly from shaft 118. Inflata~le air bags l23 and l24 are mounted between the ar~s 120 ~ ~ .

WO9~/107~0 PCT/~S90/01319 ~r-;2~.3 ' . ! .~
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and 122 of lever 119 and a fixed angle bracket 125. By inflating the air ba~s 123, arm 120 will be pivoted downwardly to thereby pivot plate 115 downwardly toward plate 117. Conversely, inflating bags 124 will pivot arm 120 clockwise as shown in Fig. 5, thereby tilting the plate 115 upwardly to increase the spacing between ;~
the plate and the support plate 117. -. , , To limit the pivotal movement of the lever 119, a lug 126 is secured to the:upper end of arm 122 .`^,~
and is adapted to engage nuts 127 and 128 which are .
threaded on rod 129 that is carried by fixed bracket 130 attached to angle 125. Engagement of lug 126 with nut 127 will li~it the upward movement of plate 115, ~;.
and conversely, engagement of lug 126 with nut 128 will -`
limit the downward movement of p~late 115. -As plate 115 o sealing assembly 114 rides on ;~
the upper surface of the co~pressed mat 69, it will effectively seal:the downstream end of the housing to the in~rcss of air. `~.:
Any wash liquid leaking past the sealing ~ .
assembly 114 will be collected in chamber 125 that is ~.. `
located at the downstream end of the housing. As pre- ~`
~; viously noted, any wash liquid leaking throu~h the -.
sealing asse~bly at the upstream end o~ the housing 2 wil~l be collected~in chamber:24. In addition, a pro `~
vision is made to collect any wash liquid leaking ~.
~ :between the support plàte 17 and plates 30 at the sides of the housing. Any leakage a~: ~his area will be col ;
lected in the side chambers~132 and 133l respectively, .
at the sides of the housing, as shown in Fig. 6. Con- ."
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dui~ts 134, 135r 136 and 137 are` connected to the lower end:of the respe~ctive~chambers 24, 2S, 132 and 133~ and : the wash liquid is conducted through the conduits to an ::accumu;lation tank, not shown. The wash liquid thus .
;: collected can then be returned to the upsteam end of :

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WO90/l0750 ! ~ ~ ,' 2 ~ J S90/01319 . -16-the liquid chamber 101 throu~h a return conduit 138~
which is ~ounted within an opening in the section 100, as shown in Fig. 3.
The wash liquid is preferably fed counter- ~.
currently through the pulp washer with respect to the :
flow of the mat 69. Irl this regard, a conduit 140 :~.
interconnects the lower erd of each sump 20c-f with the inlet of a pump 141, while the outlet of the pump is connected via conduit 142 to the standpipe 103 of the next upstream zone, so that the wash liquid fro~ each - :
zone will be delivered to the next upstream zone in a `:~.
countercurrent fashion. Fresh wash liquid is introduced into the downstream standpipe 103e through an inlet conduit 143 and the spent wash liquid is dis-charged from the sumps 20a and 20b through outlet con-duits 144, which are connected through pumps 145 to a disposal site. With this arrangement, fresh wash -~
liquid is introduced to the standpipe 103e through ..
inlet condui~ 143 and the wash liquid will then pass through the mat and be collected~in su~p 20f. The ;~
liquid will then flow from sump 20f through conduit 140 to pu~? 141f and will be discharged through conduit 142 to the next upstream~standpipe 103d. This procedure is repeated with the wash liquid~progressing countercur- ;`.
rently through the system and finally being discharged :
through the conduits 144 to a disposal site.
It is conte~plated that a liquid level sensiri~ mechanism can be incorpor~ated~with the stand-pipes 103 to maintain: the::desired liquid level in the .. :.
head 105, as shown~in Flg. 4. ~A~;pair of liquid level -sen~sing probes 145 and 146 are disposed in each head 105 and are~operably~connected to a;valve 107 located in the discharge line 142:that supplies that standpiDe.
If the liquid lèvel in ~he head lO5:falls below a given valu~, as sensed:by~probe 145, the valve will be opened,~ :

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WO 90/10750 PCr/US90/01319 :
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to admit liquid through conduit 142 to the standpipe.
On the other hand, if the liquid level rises above the `
level of probe 146, valve 147 will close to prevent the supply of liquid to the standpipe. With this arrange- -ment, the liquid level is maintained within predeter- ~-mined limits within the standpipe to provide the desired pressure head for driving the liquid through ;-~
the mat 69.
In operation, the cellulosic slurry is fed into the inlet chamber 68 throu~h the feed conduit 60 and the configuration of the inlet chamber promotes `~
swirling of the slurry to inti~ately mix the fibrous material and liquid. The sIurry then flows downs~ream ~`
into the converging flow path between plate 17 and the i-mat-ccnfining members 68 and 85. As the slurry flows in the oonverging path, liquid is extracted fro~ the slurry and flows through the porous belt and through the slots 18 in plate 17 for collection in the sump 20a. As previously noted, the pressure of the wash liquid in section 100 above member 85 resists ~he up-ward pressure of the mat flowing through the conver~ing flow path to prevent upward deflection of me~ber 85. -As the mat enters the liquid chamber 101, the wash liquid is driven throùgh the fibrous mat because ;~
of the pressure head generated through use of the standpipe 103. The air cushion in the upper head 105 `
oflthe stalndp;ipe provides im~roved controi of t~e hy~
raulic pressure in each wash zone , As the mat is conv~eyed on belt 33 through the washer, the wash liquid;is driven through the ~at in t~e various washing zones to provide a thoroughly washed mat which is discharged~from the belt as the -belt passes around ~the roller 51 at the downstrea~ end of the washer. `

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-18- 2 C~

The pulp washer of the invention has a low dilution factor and has low soda and fiber loss.
As the housing is a closed system there is discharge of pollutants into the atmosphereO Due to its compact size, there is a substantial space savings as compared to conventional pulp washers.
Since the wash liquid is driven through the ~at by hydraulic pressure without the use of vacuum or air flow, foamin~ of the liquid is minimized.
Various modes of carrying out the invention are contempla~ed as being within the scope of the fol-lowing claims particularly polnting out and distinctly claiming the subject matter which i5 regarded as the invention.
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Claims (31)

We claim:

1. An apparatus for treating a liquid slurry containing solid material, comprising a supporting frame, a perforated support member, means for mounting the support member in a conveying run, drive means for moving said support member in said conveying run, feed-ing means for feeding a slurry containing solid material onto said conveying run of said support member to form a layer, means disposed downstream of said feeding means and defining a converging flow path with said conveying run whereby said layer is progressively reduced in thickness as it passes through said converg-ing flow path, and supply means disposed downstream of said converging flow path for supplying a wash liquid to the upper surface of said layer, said supply means including a vessel to contain said liquid and extending a substantial distance above said conveying run, the upper surface of said liquid in said vessel being exposed to a gas whereby the head of said liquid will drive said wash liquid through said layer.

2. The apparatus of claim 1 and including a closed housing to enclose said support member and the layer supported thereon.

3. The apparatus of claim 2 wherein said housing comprises a lower section and an upper section, means for pivotally connecting the side edges of said sections together, and means for pivoting one of said sections relative to the other of said sections to thereby open said housing.

4. The apparatus of claim 3, wherein said means for pivoting one of said sections comprises at least one screw jack.

5. The apparatus of claim 1, and including a fixed perforated support to support the conveying run of said support member.

6. The apparatus of claim 5, wherein said perforated support comprises a block of polymeric material containing a plurality of openings.

7. The apparatus of claim 6, wherein said block is composed of polyethylene and said openings comprise a plurality of slits extending transversely of the direction of travel of said support member.

8. The apparatus of claim 1, wherein said means for defining a converging flow path comprises a plate disposed at an acute angle with respect to said support member, and means for biasing said plate toward said support member.

9. The apparatus of claim 8, and including means for pivoting the upstream end of said plate to said frame.

10. The apparatus of claim 9, wherein said biasing means comprises an inflatable air bag.

11. The apparatus of claim 2, and including sealing means at the downstream end of the conveying run and disposed to engage the upper surface of said layer to prevent ingress of air into said housing,

12. The apparatus of claim 11, wherein said sealing means comprises a sealing member extending across the width of said support member, pivot means for pivoting the upstream end of said sealing member to said frame, and biasing means operatively engaged with said sealing member to bias the sealing member toward said conveying run.

13. The apparatus of claim 12, wherein said sealing member is disposed at a converging angle-with respect to said conveying run.

14. The apparatus of claim 1, and including a sump located beneath said support member to collect wash liquid passing through said support member.

15. The apparatus of claim 2, wherein said conveying run includes a plurality of zones spaced along the length of said conveying run, said apparatus including a vessel associated with each zone, a sump associated with each zone and disposed beneath said conveying run to collect liquid passing through said`
support member, and pumping means for each sump, each pumping means being operably connected to a vessel of a different zone whereby operation of said pumping means with deliver wash liquid from the sump to said vessel.

16. The apparatus of claim 14 wherein each pumping means is connected to a vessel of an adjacent upstream zone.

17. An apparatus for treating a liquid slurry containing a solid material, comprising a closed housing, an endless perforated belt disposed within the housing and mounted for travel in an upper conveying run, drive means for driving said belt in said run feeding means for feeding a liquid slurry containing solid material to the upstream end of said conveying run to form a layer, rigid perforated support means for supporting said conveying run of said belt, and supply means for supplying a wash liquid to the upper surface of said layer and including a vessel to contain said liquid and extending upwardly a substantial distance above said conveying run, the upper surface of said liquid in said vessel being exposed to a gas whereby the pressure head of said liquid in said vessel will drive the wash liquid through said layer, and collect-ing means for collecting the wash liquid passing through said layer.

18. The apparatus of claim 17, wherein said housing comprises a lower section and an upper section, means for pivotally connecting the side edges of said sections together, and means for pivoting one of said sections relative to the other of said sections to open said housing.

19. The apparatus of claim 18, and including sealing means located at the downstream end of said conveying run and disposed to engage the upper surface of said layer to prevent ingress of air into said hous-ing.

20. The apparatus of claim 18, wherein said upper and lower sections have mating side edges, and gasket means disposed between said side edges to seal said side edges against the ingress of air.

21. The apparatus of claim 18, wherein said means to pivot one of said sections comprises a threaded jack pivotally connected to said lower section and extending through an opening in said upper section, and nut means threaded on said jack and located beneath said upper section whereby threading of said nut on said jack will pivot said upper section relative to said lower section.

22. An apparatus for treating a liquid slurry containing solid material, comprising a closed housing, an endless perforated belt mounted for travel in said housing in a conveying run, drive means for driving said belt in said conveying run, feed means disposed at the upstream end of said conveying run for feeding a liquid slurry containing solid material onto said conveying run, means disposed at the downstream end of said conveying run for removing said layer from said belt, a series of wash zones spaced along the length of said conveying run, a sump associated with each zone and located beneath said conveying run to collect liquid passing through said belt, a vessel associated with each zone and extending upwardly a substantial distance above said conveying run, the upper surface of liquid in said vessel being exposed to a gas whereby the head of liquid in the vessel will drive said liquid through said layer, and pumping means associated with each zone for pumping liquid from the sump of that zone to a vessel of a different zone.

23. The apparatus of claim 22, wherein each pumping means is connected to a vessel of an adjacent upstream zone.

24. The apparatus of claim 22, wherein each vessel comprises a vertical conduit and an enlarged head disposed at the upper end of each conduit.

25. The apparatus of claim 24, wherein said head is exposed to the atmosphere.

26. The apparatus of claim 1, and including liquid level sensing means disposed in said vessel to sense the level of liquid therein, said sensing means being operably connected to said supply means and con-structed and arranged to supply wash liquid to said vessel when the level of liquid in said vessel decreases below a predetermined level.

27. The apparatus of claim 22, and including liquid level sensing means disposed in each vessel and disposed to sense the level of liquid in said vessel, each sensing means being operably connected to a pump-ing means of a different zone to supply wash liquid from said different zone to said vessel when the liquid level in the vessel recedes beneath a predetermined level.

28. An apparatus for treating a liquid slurry containing solid material, comprising a support-ing frame, a perforated support member, means for mounting the support member in a conveying run, drive means for moving said support member in said conveying run, feeding means for feeding a slurry containing solid material onto said conveying run of said support member to form a layer, a housing located above said support member and defining a liquid chamber, converg-ing means disposed downstream of said feeding means and defining a converging flow path with said conveying run whereby said layer is progressively reduced in thick-ness as it passes through said conversing flow path, said chamber extending above said converging means, biasing means operably connected to said converging means for biasing said converging means toward said support member, and supply means for. supplying a wash liquid to said chamber, said wash liquid passing through said layer, the portion of said wash liquid in said chamber and disposed above said converging means resisting upward deflection of said converging means due to the pressure of said layer.

29. The apparatus of claim 28, wherein said supply means comprises a generally vertical standpipe extending a substantial distance above said chamber and containing said wash liquid, the pressure head of said liquid in said standpipe driving said liquid through said layer.

30. The apparatus of claim 29, and including means for maintaining a substantially constant pressure head in said standpipe.

31. The apparatus of claim 29, wherein said standpipe is constructed and arranged to exert a pres-sure head of sufficient magnitude to drive said liquid by gravity through said layer.