CA2012832C - Traveling bridge filter with surface wash - Google Patents

Abstract

A liquid filtration system is provided which includes a traveling bridge device mounting and backwash means for successively cleaning each of a plurality of filter cells formed in a filtration tank. Both surface wash and backwash means are included in a single hood structure adapted to sealingly engage each filter cell, successively, as the traveling bridge carriage traverses the tank. The surface wash means includes a surface wash conduit for supplying liquid under pressure to the upper surface layer of each cell. The backwash means includes a backwash conduit for creating suction within each filter cell.

Description

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~ . ~RAVELING R~T~ FILT~R WIT~ SURF~ OE WAS~

This invention relates generally to liquid ~ filtration ~ystems and, more ~specifically, to traveling bridge-type cle~ sr device~ for ~equentially cle~ni n~ a plura].ity o~ downward flow, su~y~ e~l ~olid~ f~lter units located within a relatively large filtration tank.
It i~ ~ell known in the art ~o utilize filtration tank3 divided into a plurality of filter cell~, one adjacent the other, and all contai~ing a multi-layer arrangement o~ granular ~ilter media ~uçh a~ sand, gravel and the like. In downward flow filtration ~y~tem~ o~ ~hi8 type, w24ter or o~her liguid con~a{ning ~ p~n~e~ solid partic}e3 ~ 8 i~,L,G~c~ into the ~iltration tanX from above and clarified water i8 drawn off from a ch.-~er beneath the filter c~ . During downward flow through the individual c~118, parti~ulat~ ~atter ~,en~L-A~d within tha layer~ of g~n~ r ~iltar media.
~ ually, th~ partic~lat~ matter clog~ thQ filter media, thereby re~lc~ n~ ~ha filtering capability o~
tho ~y~tem. Thu~, thera i8 a need ~or periodic cl~n~q of thu filgsr cellq. It i3 al80 known to maintaln s~h units in co~t~ n-~o~ operation duri~g cl~n~n~ by tho u~ o~ trav~ling bridge devic~s which move from one filter cell to the next, to backwash individual cells while permitting the filtration process to continue in the remaining cells.
Example~ of traveling bridge apparatu~ of thi8 , . . ~ . .

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~ . type may be seen in U.S. Patent Nos. 4,540,487;
4,486,307; 4,133,766; 3,984,3~6; 2,235,227, and 649,409. Typically, traveling bridge system~
include an overhead carxiage, movable along tracks, guideways or the like, which carries, e.g., a backwash hood succe~sively ~nga~eable with th~ upper end of each ~ilter cell. For a downflow t~pe filter, water or other treatment liguid is generally introduced into the cell from below, in a counterflow arrany~ t to the normal filtering direction. The backwash hood typically includes a suction head for drawing out fluid and debri~ forced to the surface of ~he filter cell a~ a result of the backwa~h. As the backwash of an individual cell is completed, the traveli~g bridge will index the backwa~h hood to the next ad~acent cell. See, for example, U.S. Patent ~o. 4,308,141, in which a modular filter 8y3tem i~ dlscloRed, and wherein a traveling bridge type backwa~h system is indexed to successive filter unlt~.
Thare are al~o known in the prior art devices for bre~k~ng up a mat or lay~r of material which :
forms on th~ s~r~ace o~ a filter ~ed. For example, in U.S. Patent No. 2,33~,749, a pair of surface rakin~ --h~n~ ~m are utilized on either 3ide of a backwa~h eai~son. In U.S. Patent No. 2,194,071, a ov~rhead s~rfac~ wa~h ~ystem is di~closed wherein a spray head having fixed ~t~ i8 sus~~nded from a carriage, enabling wa~h liquid to be d~rected do~.~wdrdly onto the upper surface o~ the filter bed ~ a~ the carriage move~ along the length of the ~ank.
A conv~ntional, 3tationary backwa~h 3ystem is utilized to wash the loosened material upwardly into ,.. :, . .;. ~ .
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one or more stationary discharge troughs.
U.S. P~ent Nos. 4,152,265 and 4,454,034 disclose traveling bridge filtration systems which combine backwash operations with the u~ ation of mechanical scarifying blades which are said to break up and loosen the mat on the surface of the bed.
In the present invention, a unique combination of filter cell cleaning devices is provided in a traveling bridge configuration. In one exemplary embodiment, an elongated, rectangular filtration tank is divided into a plurality of individual cells by a plurality of laterally spaced, substantially parallel partitions ext~n~i ng across the width of the tank. The tank i8 further provided with tracks or guideways supporting a traveling bridge for ~v~ -nt along the top of the tank, in a direction transverse to the orientation of the upright partition~. In an exemplary embodiment of the invention, the traveling bridge compri~es a carriage from which i8 ~uspended surface wash means as well as backwa~h means, located wi~hin a ~ingle hood assembly, a~a..g~d ~or ~equential ~ealing engagement with each filt2r cell.
The single surface wash/backwash hood assembly of thi~ exemplary emko~ t of the invention e~tends acro~s substantially the full width of the tank, l.e., along substantial}y the entire length of ~he indi~idual filter cells. The hood per se includes a pair o~ lower side wall portions which are spaced apart a distance corresponding to the distance between the individual cell partitions, as well as upper side wall portions which are inclined toward each other and which intersect at a hood . . ~ . , ~ . . .
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Located within the hood, and extending substantially parallel to, and midway between, the lateral lower side wall portions o~ the hood, is a surface wash manifold, extending substantially acro~s the width of the tank, and provided at spaced positions along it~ leng~h with a plurality of discharge nozzles from which liquid is dispen~ed under pres~ure onto the upper surface of the filter bed. The surface wash manifold is connected to a substantially vertically oriented s~rface wash conduit which extends upwardly through the hood to fir~t fluid surface wash pump mounted on the traveling bridge carriage.
In the exemplary embodiment, water i5 supplied to the pump from a clean water trough ad~acent the tank, although it will be appreciated that water may also be supplied from any fresh or clean water source.
A horizontal backwash manifold i~ al80 located within the hood, above the ~ur~ace wa~h manifold, and generally coextensive therewith. The bacXwa~h mani~old ~8 preferably located in the area of the lnclined upper wall portions of the hood. The backwash manifold is connected substantially m~dway along its lens~h to a ~ertical suction conduit ~hlch also extends upwardly, through the hood, to a second fluid bacXwa~h pump mounted on the travellinq bridge carriage. This second pump is a suction pump, ~he inle~ side of which is connected to the vertical suction conduit.
The horizontal backwash manifold is provided with a plurality of uniformly arranged aperture3 ,. ..
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2 ~ 3 !':~' ~ extending along its length and about its periphexy to uniformly draw liguid and accompanying debris upwardly out of ~ filter cell in a dire~tion opposite the normal filter flow direction to thoroughly backwash the ~ilter media.
In order to index the hood assembly to successive cells along the length of the filtration tanX, the hood assembly 1~ rec:iprocable vertic~lly a distance sufficient to enable the hood as~embly to disengage from the cell partitions or wall~, and to clear the adjacent cell partitions during lateral mo~ nt to the ne~t cell. To this end, portions of the vertical surface wash conduit and vertical backwa~h conduit, respectively, may be provided with fle~ible, e.g., bellows-type, connectors whlch permit a relatively small degree of vertical mov~ nt of the hood structure vis-a-vis the vertically fixed carriage.
Accordingly, in it3 broadest aspect, the ! pre~ent invention relates to a traveling bridge filtar cle~n~ng sy~tem including a liguid filtration tank divlded into a plurality o~ ad~acent ~ilter cells, each of ~he cells cont~ nl ng filter medla; R
traveli~g bridge carriage located above the tank and movable along the tank, the carriage mounting sur~ace wash means and backwa~h means within a single hood a-~embly adapted to ~ealingly enga~e successive ones of the filter cells.
For eac~ individual cell, the carriage mounted first and second pumps may b~ ~imultaneously activated 30 that the mat or crust of material present on ~he upper surface of the filter bed is broken up by the surface wash, while at the same ~' ' '. , ~' ~:

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~ . time, the backwash expand~i and cleans the filter media from below, drawing dirt and debris as well as the broken surface ~ru~t or mat mat~rlal upwardly into the suction conduit locatad in the hood assembly. In this way, tha filter media i~
effectively cleaned, the formation of mudballs i~
preventsd, and the ~ull filtration capability of ~he cell is re~tored.
It will therefore be appreciated that the present invention provide~ a unique combination of surface wash and backwash means in a single hood assembly within a traveling bridge filter cleaning system, which effectively cleans successive cells of a multi-cell tank without disturbing the filtering proces~ in the ~ -1 n~ ~g cell~.
Additional object~ and advantages of the subject invention will become apparent from the detailed descriptlon which follows.
Embodiments of the invention will ~e described with reference to the accompanying drawings, in which:

FIGUR~ 1 is a schematic ~ide view of a traveling bridge type flltration ystem ln accordance with the invention;

FIGURE 2 i3 a 3ch~ ~tic plan view of the - filtration tank shown in FIGUR~ 1 with the traveling bridge components L~ ed ~or clarity; and FIGURE 3 is a schematic end view of a traveling bridge filtration system shown in FIGUR~ 1.

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Referring now to FIGURES 1-3, a su~pended solids filtration apparatus in acc~rdance with this invention includes a substantially rectangular tank 10 comprising side wall~ 12, e!nd walls 14 and a bottom wall 16. The tank is dlivided into a plurality of filter cells 18 by generally upright, spaced partition~ 20 which extend from one side of the tanX to ~he other, in a substantially parallel arrangement, and substantially transversely of the direction of elongation of the tank. It will be appreciated, however, that the shape of the tank and the orientation of the filter cell partition~ may be varied in accordance wi~h de~ign requirements, etc.
The tank include~ an underdrain or subfloor 22 resting on the partitions 20, and which supports a multi-layer filter media bed compri~ing, preferably, layers of gravel 24, sand 26 and anthracite 28 (or other suitable filter media). The ~pace between bottom wall 16 and ~ubfloor 22 compri~eq a chamber 30 which for~s a claarwell. The filtered water flows past a weir area 32 including a vertical baffle 33 and out o~ the tank via an outlet 34.
Under normal CiL~l ~ances, the water or other flu~d to be treated ~8 ~upplied to the tank at a level above the filter media by any quitable m~ans (not shown) and ~h~ tank i8 filled to a level 36.
In accordanc~ with one exemplary embodiment of this invention, sur~ace wash and backwash means are movably supported on a carriage 38 provided with a plurality of wheels 40 which are guided along tracX~
or guideways 42 on an upper extension 44 of the .
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~ . tank. It will be appreciated that the tracks or guideways may also be part of an overhead framewor~
or the liXe, ~eparate from thoa tanX design.
Further, in thi~ regard, it i3 to be noted that the carriage and controls for tndl~i ng the carriage are not part of thi~ invention, alld may be of any conYentional constructlon.
The carr~age 38 support~ a oombined sur~ace wa~h and backwash device 46 in s~t~pende~
relationship vis-a-vi~ the carriage.
The cr 'ined surface wash/ba~kwash devic.e 46 of this inv~ntion includes a single hood ~tructure 48 which extends acro3~ the tank, along ~ub~tantially the entire length of ~he filter cells 18. The hood 48 include~ a pair of lower side wall portion3 50 which are ~p~eA apart a di~tance corre~pon~ng substantially to the distance between the ~ilter cell partitions 20. Tapered wall portion~ 52 extend inwardly and upwardly from the parallel side wall portion to an apex 54, although it will be - under~tood that other hood configurations may bs u~ilized.
Located withln th~ hood 48, and e~t~n~ng substantially parallel to the ~id~ wall portions 50 i~ a surface wa~h manifold 56 provided with a plurality of nozzles 58 ext~n~ ng from ei~her side :
o~ tha manifold, and ln- 8p~e~ relation~hip along the length thcreof. A surface wa~h fluid ~upply conduit 60 extend~ substantially vertically upwardly from the mani old and out of the hood 48 to a pump 62 mounted on the carriage 38. It will be under~tood that conduit 60 i3 connected to the outlet ~ide of th~ pump, while a cond~it 64 i~

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~ . connected to the inlet ~ide of the pump. Conduit 64 3Upplies li~uid to the pwmp and, in one exemplary Pmbodiment, the supplied liqui~d originates in a trough 66 mounted to one ~ide of the filtration tank. The trough 66 receiYe3 filtered water from the weir area 32, and to thi~ ~end, a pipe 68 extend~
between the trough and the wei:r area thereby providin~ a ready ~upply of liquid for the surfacQ
wash pump.
Alternatively, fre~h clean water from any suitable source may be ~upplied to the surface wash device.
The laterally spaced, substantially parallel ~ide wall~ ~0 are provided along their lowermo~t surface~ with se~lin~ means ~uch as rubber gasket~
68 which ara secured ~her~to by any ~uitable mean~, enabllng air and water ~ight ~eal~ to be establlshed between the hood 48 and individual filter cell~ 18.
The backwash device include3 a backwash ~uction conduit 72 which exte~d~ do~ ardly from a suction pump 74 mounted on the carriage 38. The ~uction conduit 72 ~tend~ through the hood 48, appro~imat~ly midway along th~ length of the hood, and i8 cvn~ ed to a horizontal backwa~h ma~i~old 76 which ~tends generally parallel to the cell partition~ 20 and 8ubstantially acros~ the antire width of th~ tank, wi~hin an upper portion o~ the hood, ~etween th~ incli~ed portions 52 of the hood sidewalls. The manifold 76 ~s also provided with a plurality of parforation~ (not ~hown) which provida for substantially uniform ~uction within the hood 48 across the respective cell 18.
It will he appreciated that in a cell cleaning . ~ .

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~ operation, carriage 38 will successively index the surface wash and backwash means within the hood 48 to the individual filter cells~ 18, in the direction of the arrow 7B in EIGURE 1. At the same time, it will be appreciated that means mu~t be provided to move the bood 48 vertically toward the cells 18.
The -v~ -~t is required to enable sealing engagament between the hoo~ 48 and an individual cell 18. After cleaning, tha surface wa~h/backwa~h hood i~ retracted vertically upwardly away from the cells a relatively small distance, e.g., on the order of two ;n~hes~ to provide clearance which permit~ horizontal in~; ng of the hood assembly to the next cell. The vertical reciprocatory v~- -nt may be effected by any conventional mean~ (not shown), such as hydraulic cylinders, ~acks, etc., along with conventional control~.
In order to permit relative movement between the hood 48 and carriage 38, flexible couplings 78, 80 are interpo~ed in conduits 72, 60, respectively.
The couplings may be in the nature of a bellow~ or any other ~uit~ble flexing mean~.
It is . fur~her ~eature of the invent~on that the tank includ~, a~ one end thereof, horizontal and vertical wall portion 82, 84 to create an e~tended tank portion which accc odate~ the traveling brldge carriage when not in use, enabling unre~tricted acce~ fro~ above to all of the filter cells.
In operation, after the carriage has been moved to one end of the tank, i.e., to the far right in FIGURE 1, t~e surf~ce wa~h/backwash hood i~ lowered into position, beneath water level 36, such that the seals or gasXats 68 engage the upper end~ of the - : :

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partitions 20 of the fir~t filter cell 18. After surface wash and backwash are completed as to the first cell, the hood assembly is retracted upwardly and moved laterally Yia carriage 38 to the next filter cell 18 and thereafter lowered into position so that the hood 48 engages the second filter cell, et~. This procedure may be repeated until the last cell i~ reached at the far le~t ~ide of the tank (FIGURE 1).
It will be appreciated that as the hood assembly is lowered into po~ition over a subjacent filter cell, qasXets 68 on the hood wall~ establish a hydraulic seal which isolates the filter cell 18 from the re ~; ni n~ cells in the tanX, and wh~ch prevents debris in the one cell from moving into one or bo~h ad;acent cells.
During surface wash, pump 62 supplie3 water under pres ure to the horizontal surface wash manifold 56 via conduit 60. The water is di~charged through the plurality of nozzle~ 58 and brea~s up any crust or mat-like material Which has formed on the surfac~ o~ th~ fllter bed. Suitable ~crePnln~
material may be used if des~red to cover the perforations in the manifold 56 to prevent clogg~ng of the p~rforation~ with dislodg~d debris, filter media, etc.
BacXwa~h i~ carrl~d ou~ simultaneou~ly with the abov2 d~scribed surface wash. During backwash, -Ruct1on i8 created in the hori~ontal ~uctio~
manifold 76 via pump 74, drawing water upwardly, countercurrent to the normal flow, through the underdrain or sub floor 22, filter media layers 24, 26, 28, hood 48, manifold 76 and backwa~h suction , . , : '', ' : ' .-: :.. ~:
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conduit 7~, all thç while cleansing the filter media and removing particulate matter, including that dislodged in the ~urface wash operation. From pump 74, the backwa~h liquid is discharged through a ho~e to a trouqh or drain (not shown) in a conventional ~nn~r .
While the invention has been described in connection with what i~ pre~ently considered to be the most practical and preferred embodiment, it i8 to be understood that the invention i~ not to be limited to the disclo~ed embo~ -nt, but on the contrary, i8 intended to cover various modifications and eguivalent arr~n~ -nts included within the spirit and ~cope of the appended claims.

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Claims (18)

WHAT IS CLAIMED IS:

1. In a traveling bridge filter cleaning system including a liquid filtration tank divided into a plurality of adjacent filter cells, each of said cells containing filter media, a traveling bridge carriage located above said tank and movable along said tank, said carriage mounting a surface wash manifold and a backwash manifold within a suspended hood assembly adapted to sealingly engage each of said cells, aid surface wash manifold including a plurality of nozzles extending therefrom, said surface wash manifold and said plurality of nozzles being substantially fixed relative to said hood assembly.

2. A traveling bridge as defined in claim 1 wherein said hood assembly comprises a pair of side walls, having upper and lower portions, the lower portions of said sidewalls provided with sealing means for sealingly engaging partitions in said tank which define said filter cells.

3. A traveling bridge filter system as defined in claim 1 wherein each of said cells is provided with at least three layers of filter media supported by a porous underdrain.

4. A traveling bridge as defined in claim 1 wherein said backwash manifold extends substantially horizontally along substantially the entire length of said hood assembly.

5. A traveling bridge as defined in claim 4 wherein said surface wash manifold is located beneath said backwash manifold, and is substantially coextensive therewith.

6. A traveling bridge as defined in claim 5 wherein said carriage mounts a surface wash pump for supplying liquid under pressure to an upper surface of each of said filter cells, successively, through said surface wash manifold, and a backwash pump for creating suction with each of said filter cells, successively, through said backwash manifold.

7. A filtration system for suspended solids within a liquid comprising a tank divided into a plurality of individual filter cells, each cell defined by a pair of laterally spaced partitions extending across the tank, said tank including a subfloor supported by said partitions above a bottom wall of said tank; said subfloor also supporting a multi-layer filter media bed in each of said filter cells; a traveling bridge including a carriage movable along said tank and and indexable to each of said filter cells; and wherein said carriage supports a hood assembly including surface wash means and backwash means for successive engagement with each of said filter cells, said surface wash means including means for supplying pressurized water for breaking up surface crust material formed on the liquid.

8. A filtration system as defined in claim 7 wherein said filter cells are of the downward flow-type and wherein clarified liquid flows through a chamber located between aid bottom wall and said subfloor and into a weir area.

9. A filtration system as defined in claim 7 wherein said tank is provided with means for guiding said carriage along said tank, and wherein said tank is provided with extended wall areas permitting said carriage to be moved beyond said filter cells, thereby permitting unrestricted access to said filter cells.

10. A combined surface wash and backwash device for a traveling bridge filter system wherein the device is carried by a carriage movable across a plurality of adjacent filter cells, the device comprising:
a hood assembly adapted to successively engage in sealing relationship with each of the filter cells, said hood carrying a surface wash manifold including a plurality of nozzles fixedly secured within said hood assembly for discharging fluid onto filter media within the filter cells in a first direction, and a backwash manifold for withdrawing fluid from the filter cell in a second direction opposite to the first direction.

11. A device as defined in claim 10 wherein said surface wash manifold extends substantially the entire length of the filter cell.

12. A device as defined in claim 11 wherein said backwash manifold also extends substantially the entire length of the filter cell.

13. A device as defined in claim 10 and further including surface wash pump means and backwash pump means for simultaneously supplying fluid to and withdrawing fluid from, each of said filter cells, successively.

14. A device as defined in claim 10 wherein said backwash manifold is perforated along its length so that fluid may be uniformly withdrawn from the filter cell.

15. A device as defined in claim 10 wherein said surface wash manifold is operatively connected to a surface wash pump mounted on said carriage.

16. A device as defined in claim 15 wherein said surface wash pump draws filtered fluid from said trough mounted to one side of the tank.

17. A filtration system for suspended solids within a liquid comprising a tank divided into a plurality of individual downward flow-type filter cells, each cell defined by a pair of laterally spaced partitions extending across the tank, said tank including a subfloor supported by said partitions above a bottom wall of said tank; said subfloor also supporting a multi-layer filter media bed in each of said filter cells; a traveling bridge including a carriage movable along said tank and indexable to each of said filter cells; wherein said carriage supports a hood assembly including surface wash means and backwash means for successive engagement with each of said filter cells, said surface wash means including means for supplying pressurized water for breaking up surface crust material formed on the liquid; and wherein clarified liquid flows through a chamber located between said bottom wall and said subfloor and into a weir area.

18. A filtration system as defined in claim 17 wherein said tank is provided with means for guiding said carriage along said tank, and wherein said tank is provided with extended wall areas permitting said carriage to be moved beyond said filter cells, thereby permitting unrestricted access to said filter cells.