CA1110552A - Rotary drum filter and method of operation for medium cleaning - Google Patents
Rotary drum filter and method of operation for medium cleaningInfo
- Publication number
- CA1110552A CA1110552A CA323,380A CA323380A CA1110552A CA 1110552 A CA1110552 A CA 1110552A CA 323380 A CA323380 A CA 323380A CA 1110552 A CA1110552 A CA 1110552A
- Authority
- CA
- Canada
- Prior art keywords
- sector
- filter
- vacuum
- drum
- filtrate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000004140 cleaning Methods 0.000 title claims abstract description 8
- 238000000034 method Methods 0.000 title abstract description 6
- 239000000706 filtrate Substances 0.000 claims abstract description 37
- 239000004744 fabric Substances 0.000 claims abstract description 25
- 239000002002 slurry Substances 0.000 claims abstract description 19
- 239000007787 solid Substances 0.000 claims abstract description 9
- 239000007788 liquid Substances 0.000 claims abstract description 8
- 230000000694 effects Effects 0.000 claims abstract description 7
- 238000004891 communication Methods 0.000 claims description 4
- 230000006854 communication Effects 0.000 claims description 4
- 238000003825 pressing Methods 0.000 claims description 4
- 239000012065 filter cake Substances 0.000 claims description 3
- 230000002093 peripheral effect Effects 0.000 claims description 3
- 238000001914 filtration Methods 0.000 abstract description 5
- 230000015572 biosynthetic process Effects 0.000 abstract description 4
- 238000005406 washing Methods 0.000 abstract description 4
- 238000005755 formation reaction Methods 0.000 abstract 1
- 239000002904 solvent Substances 0.000 description 10
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 6
- 239000010779 crude oil Substances 0.000 description 5
- 238000010276 construction Methods 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 3
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 230000002708 enhancing effect Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 238000010408 sweeping Methods 0.000 description 2
- 102100026933 Myelin-associated neurite-outgrowth inhibitor Human genes 0.000 description 1
- 230000001174 ascending effect Effects 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000010926 purge Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000011877 solvent mixture Substances 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
- B01D33/067—Construction of the filtering drums, e.g. mounting or sealing arrangements
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
- B01D33/073—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration
- B01D33/09—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration with surface cells independently connected to pressure distributors
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Filtration Of Liquid (AREA)
Abstract
ROTARY DRUM FILTER AND METHOD OF
OPERATION FOR MEDIUM CLEANING
ABSTRACT OF THE DISCLOSURE
A rotary vacuum filter wherein each filtration sector of the filter is backwashed with filtrate and/or separately supplied gas or wash liquid while the sector is submerged in the feed slurry in the tank. As each sector starts to resub-merge in the tank, vacuum is applied so that the sector and associated hydraulic system is quickly and completely filled with filtrate and a thin cake or film of solids forms on the filter medium whereupon with the sector still submerged, vacuum is cut off and a positive pressure is applied by either or both pressured gas or liquid supplied through the valve thus forcing filtrate back through the cloth to effect washing thereof. After the wash, vacuum is reapplied for cake for-mation. The drum includes an internal manifold under each filtration sector. The manifolds are mounted on the interior wall of the drum and are secured directly to the drum wall as structural members. Additionally, each manifold serves as a reservoir for storage of wash liquor.
OPERATION FOR MEDIUM CLEANING
ABSTRACT OF THE DISCLOSURE
A rotary vacuum filter wherein each filtration sector of the filter is backwashed with filtrate and/or separately supplied gas or wash liquid while the sector is submerged in the feed slurry in the tank. As each sector starts to resub-merge in the tank, vacuum is applied so that the sector and associated hydraulic system is quickly and completely filled with filtrate and a thin cake or film of solids forms on the filter medium whereupon with the sector still submerged, vacuum is cut off and a positive pressure is applied by either or both pressured gas or liquid supplied through the valve thus forcing filtrate back through the cloth to effect washing thereof. After the wash, vacuum is reapplied for cake for-mation. The drum includes an internal manifold under each filtration sector. The manifolds are mounted on the interior wall of the drum and are secured directly to the drum wall as structural members. Additionally, each manifold serves as a reservoir for storage of wash liquor.
Description
ROTARY DRUM FILTER AND METHOD OF
OPERATION FOR MEDIUM CLEANING
.
Tllls invention relates to rotary vacuum :Eilters and in pnr~icular to improved ways and means for efEectîve washing of the ~lter cloth without interrupting the fi~tration operation.
In operation of rotary filters, such as rotary drum or disc vacuum filters, as each sector of the filter rotates through feed slurry in the tank, filtrate is drawn through the filter cloth while solids are retained on the surface. After the sector emerges from the slurry, continued application of vacuum further dries the cake and a wash liquor may also be applied to displace the filtrate still in the cake. Thereafter, as the sector nears the point of resubmergence, vacuum is re-leased and a positive pressure is applied to cause the cake to drop off the filter surface to discharge; then the sector is resubmerged to repeat the cycle.
Proper filter operation requires that the ~ilter medium cloth co~erin~ the filter be kept clean. That is, it must be porous. In many operations, some of the solids enter into and plug or bl~nd the pores of the cloth and e~entually cause shut-down for cleaning or replacement o~ the filter medium. In fîltration to separate solid wax from a mixture o~ crude oil and an extraction solvent such as methyl ethyl ketone, the mixture is cooled to solidify wax and the resulting ~ooled slurry i filtered. By its nature, wax is tenacious and additionally the crude oil contains many solid impurities. The result is that the filter medium blinds relatively quickly ~hus requiring 5~
frequent shutdown for cleaning. Such cleaning requires a hot solvent hence the down time is considerable since the entire filter is hea~ed and then recooled.
It is the object o~ this invention to provide, in a rota~y V~Cuu~ filte~, ways and means for reve~se washing o~
~he ~ilter mediu~ during each conti.nuous ~iltration cycle.
It is a further object to provide a method of filter opera~ion for use in separating wax from cooled crude oil and solvent by which the filter cloth is kept in an unblinded con-dition~
An additional important object is the provision of a drum construction in which there is provided a manifold imme-diately underlying each filter sector which provides a reservoir of wash liquor (filtrate) within the drum between the filter surface and the valve. The wash liquor is thus rendered readily available for cloth wash with minimum expenditure of energy.
That is, the filtrate used for cloth wash need not be drawn into a complex hydraulic system, but need travel only a short distance into a simple single compartment manifold or reservoir extending the length of the drum and communicating directly with the sector at s~aced points therealong. The result is that when a re~erse pressure is applied, wash liquor (filtrate) need only be displaced directly from the manifold through the cloth.
An even further object is the pro~ision of a drum con-struction in which the manifold is secured to the inside surface of the drum in such a manner that it is a structural part of the drum cont~ibuting to the strength thereof and eliminating piping 5~ ~
between the manifold and filter sectors on the drum surface.
In accordance with the lnvention, the fllter valve is set so that as each sector initiates re-entry into submergence in ~he slurry, it is subjected to vacuum for a short time suffi-S cient to flll the sector and associa~ed hydraulic system in-cluding Inanifo:lds and conduits with filtrate then, while the sec~or is still subrnerged, a positive pressure is applied to force a portion of fil~rate from the system back through the ~ilter medium into the tank. Pressure for the backwash can be provided by either gas or liquid or both supplied through the filter valve and hydraulic system. In special cases where blinding is especially stubborn, additional cleaning can be accomplished by supplying additional solvent to the cloth. This reverse flow or backwash dislodges solids from the cloth. If additional gas or liquid is used, it is selected to be compatib]e with the material being filtered. For instance, in the separa-tion of wax from crude and methyl ethyl ketone solvent, a clear solution of the solvent may be used. In the normal case where extra pressurized solvent is not required, it is an advantage of the invention that the backwash is accomplished at virtually no solvent cost. This is so because the liquid used for back-wash is drawn from the slurry and is returned thereto without loss or dilution of the slurry.
In order to insure that a sufficient volume of filtrate is available for backwash, the filter is constructed with in-ternal manifolds between the surface sectors and the valve. The proper volume of wash liquid will be determined empirically and the conditions of backwash adjusted accordingly.
As soon as the backwash is completed, the valve again s~
subjects the sector to vacuum and it resumes normal operation whereby filtrate is drawn through the clo-th while solids deposit on the surface thereof and after emergence from the slurry the cake is washed, further dried and discharged.
In summary of the above, therefore, the present invention may be broadly seen as to provide a rotary vacuum filter of the type having a plurality of filter sectors covered by a porous filter medium and mounted so that adjacent sec~ors pass successively in-to submergence in a slurry wherein vacuum is applied to draw filtrate through the filter medium into the filter hydraulic system while causing solids to deposit on the filter medium then after emergency from the slurry~.cake is discharged from the filter medium~ the improvement comprising the steps of collecting a volume of filtrate in a reservoir in the hydraulic system adjacent to and in direct hydraulic communication with the sector, discontinuing vacuum and applying pressure to the filtrate while the sector is still in submergence, continuing the pressure until a selected volume of filtrate from the reservoir has been forced through the filter medium, and thereafter applying vacuum to the filter sector while still in submergence.
The above method may be carried out in a rotary vacuurn filter of the type in which a filter cloth is secured.to overlie a drainage deck on the surface of a filter drum iournalled for rotation through a slurry in a tank, and wherein cake is formed as successive sectors of the filter drum surface are rotated into and out of submergence in the tank while vacuum is applied to the underside of the filter medium through a valve, and vacuum :
is released to effect cake discharge after emeryence from the slurry, the improvemen-t enabliny cleaniny of the filter cloth, the improvement comprising an elonyated manifold secured to the inner surface of the drum adjacent to and in hydraulic communi-cation with each sector r pipiny connectiny the valve to each ~.,. . ~, .
sd ~ ~ -! ~' . ' 5%
r~lanifold to sequentially apply vacuu~ to each sector as it starts -to submerge in the -tank and for continuing the vacuurn until the sector and its associated manifold are at least partially fllled with filtrate, means operative while the sector remains submerged sequentially to dlscontinue vacuum apE~lication, -to apply pressure to the piping to force a selected volu~e oE the filtrate from the sector and manifold back throu~h the cloth into the tank, and to immediately reapply vacuum to the surface of the sector to reform a fil-ter cake thereon while drawing filtrate therethrough.
In order that the invention may be more readily under-stood and carried into effect, reference is made to the accom-panying drawings and description thereof which is offered by way of illustration and not in limitation of the invention, the scope of which is defined by the claims which are also intended to cover equivalents.
FIG. 1 is a perspective view of a rotary drum filter embodying the invention;
FIG, 2 is a front elevational view of a filter valve embodying the invention;
FIG. 3 is a side sectional view of the valve shown in Fig. 2 taken in the plane of line 3-3 of Fig. 2 and looking in the direction of the arro~s:
FIGS. 4-8 are simplified sectional views of a single filter sector going through an operating sequence in which the filter cloth is backwashed pursuant to the invention;
FIG. 9 is a partial sectional view of the drum taken as looking lengthwise of the drum of Fig~ 1 adjacent the surface;
FIG. 10 is an elevational view of a part of the drum surface of the drum of Fig, 9 looking in the directlon of arrows ; 10, the drainage grid being omitted for clarity;
FIG, 11 is a partial sectional vi~w of the struc-ture of FigO 10 taken as looking in the direction of arro~s 11 of Fig~ 10, . g ,~
~ sd/`~
The drawings illustrate a solvent oil dewaxing filter adapted to separating solidified wax from a chilled crude oil and solvent mixture in wh;ch it was initially dissolved at higher temperatures.
The basic filter (L) comprises a vat or tank (2); a cy].... ...inclrical drum (3) in the tank journalled for rotation therein by tr~mnions (4), on the drum and bearings on the ~ank endwalls.
A cover (7) closes the vat with the drum inside. Inspection can be made through any of the glass covered ports (~). In operation, feed slurry to be filtered is introduced into the vat (2) by a convenient inlet and a constant level is maintained therein in accordance with standard practice. The surface of the drum is divided longitudinally extending division strips (9) and out-wardly extending end flange (10) into a plurality of individual filtration sectors (11). Each sector contains a drainage grid (12) overlain by a filter medium ~13) held in place by the usual caulking. As the drum rotates, the sectors continuously pass into submergence in the tank where cake is formed on the drum surface while filtrate is pulled through the cloth. After cake formation, the drum rotates out of emergence and may be subjected to further washing and drying, all under the influence of vacuum originating in a usual pump, not sho~n, and communi-cated to the filter sector through the valve (14) then through axial ports in the trunnion (4), internal conduit (16)~ mani-fold ~17~ and ports (18) in the individual sectors (11).
Vacuum applied to the valve (14) through the large flanged openings (21~ is maintained continually in the large valve chamber (15) whence it communicates through the trunnion ports whenever those ports rotate into registration with the chambPr (15). Thus, the ports are subject ~o vacuum whenever 5~ ~
they are not covered by bridge blocks or directly connected to a separate pressure zone such as shown at (23), Fig.'s ~-8 illustra~e operation of the filter through the wash cycle. ~s ~he leading side of sector (11) starts to submer~e, port t24) at the trunnion registers with a small hole (26) in ~he bridge block which provided communica~ion with the vacuum chamber (15) thus vacuum is applied through a conduit to the lead outlet (18) in the sector and the sector and associated piping commence to fill. Upon continued rotation, the trunnion lead port (24) passes the small opening (26) in the bridge block and vacuum is cut off but the trail port (27) on the trunnion registers with another small hole (28~ in the block and vacuum is then applied to the trailing outlets (18) of the sector until the trail piping is filled. Further rotation brings both lead and trail ports (24) and (27) into registration with the openings (29) which communicate to a pressure source through the pressure zone (23) and conduit (31). The appli-cation of pressure forces the thin cake off the drum surface and is continued until the preselected volume of filtrate in the hydraulic system is forced through the filter cloth back into the tank. ~s noted, in the normal case only a part of the hydraulic system contents need be used in the backwash to pre-pare the cloth for another cycle. The volume of backwash is best determined empirically for a given plant. Adjustments in the v~lve or pressure settings control duration and force of back pressure ~lo~ to thus regulate the back~ash volume.
The filtrate backflow through the submerged filter cloth is a dynamic and uniformly distributed wash which acts evenly across the entire sector. This method will be useful in any fil~ration operation where cake formation occurs quickly so there will be ample time to conduct backwash and to reorm the cake after backwash.
Once the backflow has been completed, continued drum rotation brings successive sectors into register with the large vacuum chamber to effect cake formation and drying prior to discharge.
The man-iEold location and drum construction are best.
ill.ust:ra~ed -in F:igs. 9-11. As shown, each sector (11) is pro-vided with lead and trail ports (1~) adjacent its leading and trai]ing edges. As used herein, the words lead and trail have reference to the direction of drum rotation. As illustrated, all lead ports of a single sector communicate with a common lead manifold (17) and all trail ports of a sector with a common trail manifold (17). A single conduit (16) then connects each mani~old with one of the ports in the trunnion which in turn connect through a valve to a vacuum source. This single pipe arrangement reduces the number of internal pipes and enables the use of larger pipes and ports in the trunnion thus enhancing hydraulic efficiency of the filter.
The manifolds are rectangular. Each manifold of a given sector is located as close as possible to the adjacent manifold of an adjacent sector with the junction therebetween, preferably directly under a di~ision strip. Thus, the trail manifold of any sector is located next to the lead manifold of the next succeeding sector; and the centerline between the manifolds is under the division strip (9) between sectors. The manifolds are utilized as structural members for the drum by securing them along their length, either with a continuous weld or a series of tack welds to the interior wall of the drum.
Also, the ports in the drum wall and those in the top wall of the manifold a~e in registration with each other and their peripheral edges are sealed to~ether, usually by welding.
i5~
A plurality of both lead and trail ports (1~) is provided in each sector. The ports are formed as elongated slots located as close as possible and parallel to a division strip. This insures presentation of maximum opening for liquid ~low when the port is on the low side of the sector. Also, the slot~ed por~ is qu:i~e eas~ to seal weld to a corresponding port in the ~op wall of the manifold with which it registers to provide communica~ion with the manifold.
Location of the slotted opening with respect to the manifold side wall nearest the division strip is important. As shown> one side of the slot should be close aboard the top edge of the manifold sidewall. This will keep one or more slots adjacent the lower edge of the sector at all times while the drum is out of the slurry, whether the sector is ascending or de-scending thus enhancing filtrate removal. The slot location isalso an aid to cake discharge by gas blowback through the trail slot. This is so because when a sector is descending to the discharge level the trail port is at the top and the manifold acts to trap and retain residual or entrained moisture that would otherwise be carried back into the filter cake when pressured gas is supplied through the -trail port for cake dis-charge. Further, location of the ports at the extreme opposite sides of the sector insures sweeping of the complete sector during purge when positive pressured gas is introduced through the trail slot and withdrawn under vacuum through the descending lead slot. Complete sweeping is further enhanced by staggering the lead and trail ports with respect to each other as shown in Fig. lO.
The ~ilter is provided with a drainage grid (12) secured between the division strips ~9) and a filter cloth ~13) -- 8 -- ~
S~ ~
suitably secured in place by conventional caulking and wire windings. A usual deflector blade to guide discharged cake into a cake removal scroll or other conveyor is provided.
The conEiguration and physical location of the manifolds are imporLant for ~wo reasons. First, they provide an improved drum cons~ruc~lon because they are secured to the inner drum surface and ~here are no intervening conduits. Secondly, and ~his is very important to the cyclic wash operation, the mani-folds provide a reservoir of wash liquor (filtrate) just adjacent the filter sector. This means that very little energy is wasted by drawing in the necessary wash volume and very little reverse flow is required to effect uniform flow of the necessary small volume of filtrate for cloth wash. Thus, it is adjacent that use of the manifold as a wash liquor reservoir directly adjacent the filtration sector which minimizes backwash cycle time and energy consumption.
Although the invention has been described in connection with a rotary drum filter, it is not limited thereto as it may be utilized in other rotary filters, such as disc filters, wherein successive filter sectors are rotated into and out of submergence in feed slurry wherein vacuum is applied and cake is formed on the surface of the filter medium while filtrate is drawn therethrough.
While the invention is capable of and has been described as occurring every cycle, it may be operated at a lower fre-quency as the need is determined empirically. In any event, the improved wash reduces down time, increases filtration rate, and increases cloth life. In the case of separation of wax from crude oil and solvent, reduction in shutdown reduc4s wear and tear on materials of construction because the extreme variations _ g _ S.5i~
in temperatures between hot wash (180F.) and normal operation (as low as -lSF.) are drastically reduced.
The invention is not limited to filters having both lead and trail ports, but is readily adaptable to various types of hy~lraulic systems. Also, in the illustrated embodiment, it is not necessary that both lead and trail systems be used for back-wash as either may be used alone. Nor is it necessary that both lead and trail systems be used simultaneously for backwash as it may be desirable to have them backflow in series to effect a prolonged wash. All such variations are within the scope of this invention.
OPERATION FOR MEDIUM CLEANING
.
Tllls invention relates to rotary vacuum :Eilters and in pnr~icular to improved ways and means for efEectîve washing of the ~lter cloth without interrupting the fi~tration operation.
In operation of rotary filters, such as rotary drum or disc vacuum filters, as each sector of the filter rotates through feed slurry in the tank, filtrate is drawn through the filter cloth while solids are retained on the surface. After the sector emerges from the slurry, continued application of vacuum further dries the cake and a wash liquor may also be applied to displace the filtrate still in the cake. Thereafter, as the sector nears the point of resubmergence, vacuum is re-leased and a positive pressure is applied to cause the cake to drop off the filter surface to discharge; then the sector is resubmerged to repeat the cycle.
Proper filter operation requires that the ~ilter medium cloth co~erin~ the filter be kept clean. That is, it must be porous. In many operations, some of the solids enter into and plug or bl~nd the pores of the cloth and e~entually cause shut-down for cleaning or replacement o~ the filter medium. In fîltration to separate solid wax from a mixture o~ crude oil and an extraction solvent such as methyl ethyl ketone, the mixture is cooled to solidify wax and the resulting ~ooled slurry i filtered. By its nature, wax is tenacious and additionally the crude oil contains many solid impurities. The result is that the filter medium blinds relatively quickly ~hus requiring 5~
frequent shutdown for cleaning. Such cleaning requires a hot solvent hence the down time is considerable since the entire filter is hea~ed and then recooled.
It is the object o~ this invention to provide, in a rota~y V~Cuu~ filte~, ways and means for reve~se washing o~
~he ~ilter mediu~ during each conti.nuous ~iltration cycle.
It is a further object to provide a method of filter opera~ion for use in separating wax from cooled crude oil and solvent by which the filter cloth is kept in an unblinded con-dition~
An additional important object is the provision of a drum construction in which there is provided a manifold imme-diately underlying each filter sector which provides a reservoir of wash liquor (filtrate) within the drum between the filter surface and the valve. The wash liquor is thus rendered readily available for cloth wash with minimum expenditure of energy.
That is, the filtrate used for cloth wash need not be drawn into a complex hydraulic system, but need travel only a short distance into a simple single compartment manifold or reservoir extending the length of the drum and communicating directly with the sector at s~aced points therealong. The result is that when a re~erse pressure is applied, wash liquor (filtrate) need only be displaced directly from the manifold through the cloth.
An even further object is the pro~ision of a drum con-struction in which the manifold is secured to the inside surface of the drum in such a manner that it is a structural part of the drum cont~ibuting to the strength thereof and eliminating piping 5~ ~
between the manifold and filter sectors on the drum surface.
In accordance with the lnvention, the fllter valve is set so that as each sector initiates re-entry into submergence in ~he slurry, it is subjected to vacuum for a short time suffi-S cient to flll the sector and associa~ed hydraulic system in-cluding Inanifo:lds and conduits with filtrate then, while the sec~or is still subrnerged, a positive pressure is applied to force a portion of fil~rate from the system back through the ~ilter medium into the tank. Pressure for the backwash can be provided by either gas or liquid or both supplied through the filter valve and hydraulic system. In special cases where blinding is especially stubborn, additional cleaning can be accomplished by supplying additional solvent to the cloth. This reverse flow or backwash dislodges solids from the cloth. If additional gas or liquid is used, it is selected to be compatib]e with the material being filtered. For instance, in the separa-tion of wax from crude and methyl ethyl ketone solvent, a clear solution of the solvent may be used. In the normal case where extra pressurized solvent is not required, it is an advantage of the invention that the backwash is accomplished at virtually no solvent cost. This is so because the liquid used for back-wash is drawn from the slurry and is returned thereto without loss or dilution of the slurry.
In order to insure that a sufficient volume of filtrate is available for backwash, the filter is constructed with in-ternal manifolds between the surface sectors and the valve. The proper volume of wash liquid will be determined empirically and the conditions of backwash adjusted accordingly.
As soon as the backwash is completed, the valve again s~
subjects the sector to vacuum and it resumes normal operation whereby filtrate is drawn through the clo-th while solids deposit on the surface thereof and after emergence from the slurry the cake is washed, further dried and discharged.
In summary of the above, therefore, the present invention may be broadly seen as to provide a rotary vacuum filter of the type having a plurality of filter sectors covered by a porous filter medium and mounted so that adjacent sec~ors pass successively in-to submergence in a slurry wherein vacuum is applied to draw filtrate through the filter medium into the filter hydraulic system while causing solids to deposit on the filter medium then after emergency from the slurry~.cake is discharged from the filter medium~ the improvement comprising the steps of collecting a volume of filtrate in a reservoir in the hydraulic system adjacent to and in direct hydraulic communication with the sector, discontinuing vacuum and applying pressure to the filtrate while the sector is still in submergence, continuing the pressure until a selected volume of filtrate from the reservoir has been forced through the filter medium, and thereafter applying vacuum to the filter sector while still in submergence.
The above method may be carried out in a rotary vacuurn filter of the type in which a filter cloth is secured.to overlie a drainage deck on the surface of a filter drum iournalled for rotation through a slurry in a tank, and wherein cake is formed as successive sectors of the filter drum surface are rotated into and out of submergence in the tank while vacuum is applied to the underside of the filter medium through a valve, and vacuum :
is released to effect cake discharge after emeryence from the slurry, the improvemen-t enabliny cleaniny of the filter cloth, the improvement comprising an elonyated manifold secured to the inner surface of the drum adjacent to and in hydraulic communi-cation with each sector r pipiny connectiny the valve to each ~.,. . ~, .
sd ~ ~ -! ~' . ' 5%
r~lanifold to sequentially apply vacuu~ to each sector as it starts -to submerge in the -tank and for continuing the vacuurn until the sector and its associated manifold are at least partially fllled with filtrate, means operative while the sector remains submerged sequentially to dlscontinue vacuum apE~lication, -to apply pressure to the piping to force a selected volu~e oE the filtrate from the sector and manifold back throu~h the cloth into the tank, and to immediately reapply vacuum to the surface of the sector to reform a fil-ter cake thereon while drawing filtrate therethrough.
In order that the invention may be more readily under-stood and carried into effect, reference is made to the accom-panying drawings and description thereof which is offered by way of illustration and not in limitation of the invention, the scope of which is defined by the claims which are also intended to cover equivalents.
FIG. 1 is a perspective view of a rotary drum filter embodying the invention;
FIG, 2 is a front elevational view of a filter valve embodying the invention;
FIG. 3 is a side sectional view of the valve shown in Fig. 2 taken in the plane of line 3-3 of Fig. 2 and looking in the direction of the arro~s:
FIGS. 4-8 are simplified sectional views of a single filter sector going through an operating sequence in which the filter cloth is backwashed pursuant to the invention;
FIG. 9 is a partial sectional view of the drum taken as looking lengthwise of the drum of Fig~ 1 adjacent the surface;
FIG. 10 is an elevational view of a part of the drum surface of the drum of Fig, 9 looking in the directlon of arrows ; 10, the drainage grid being omitted for clarity;
FIG, 11 is a partial sectional vi~w of the struc-ture of FigO 10 taken as looking in the direction of arro~s 11 of Fig~ 10, . g ,~
~ sd/`~
The drawings illustrate a solvent oil dewaxing filter adapted to separating solidified wax from a chilled crude oil and solvent mixture in wh;ch it was initially dissolved at higher temperatures.
The basic filter (L) comprises a vat or tank (2); a cy].... ...inclrical drum (3) in the tank journalled for rotation therein by tr~mnions (4), on the drum and bearings on the ~ank endwalls.
A cover (7) closes the vat with the drum inside. Inspection can be made through any of the glass covered ports (~). In operation, feed slurry to be filtered is introduced into the vat (2) by a convenient inlet and a constant level is maintained therein in accordance with standard practice. The surface of the drum is divided longitudinally extending division strips (9) and out-wardly extending end flange (10) into a plurality of individual filtration sectors (11). Each sector contains a drainage grid (12) overlain by a filter medium ~13) held in place by the usual caulking. As the drum rotates, the sectors continuously pass into submergence in the tank where cake is formed on the drum surface while filtrate is pulled through the cloth. After cake formation, the drum rotates out of emergence and may be subjected to further washing and drying, all under the influence of vacuum originating in a usual pump, not sho~n, and communi-cated to the filter sector through the valve (14) then through axial ports in the trunnion (4), internal conduit (16)~ mani-fold ~17~ and ports (18) in the individual sectors (11).
Vacuum applied to the valve (14) through the large flanged openings (21~ is maintained continually in the large valve chamber (15) whence it communicates through the trunnion ports whenever those ports rotate into registration with the chambPr (15). Thus, the ports are subject ~o vacuum whenever 5~ ~
they are not covered by bridge blocks or directly connected to a separate pressure zone such as shown at (23), Fig.'s ~-8 illustra~e operation of the filter through the wash cycle. ~s ~he leading side of sector (11) starts to submer~e, port t24) at the trunnion registers with a small hole (26) in ~he bridge block which provided communica~ion with the vacuum chamber (15) thus vacuum is applied through a conduit to the lead outlet (18) in the sector and the sector and associated piping commence to fill. Upon continued rotation, the trunnion lead port (24) passes the small opening (26) in the bridge block and vacuum is cut off but the trail port (27) on the trunnion registers with another small hole (28~ in the block and vacuum is then applied to the trailing outlets (18) of the sector until the trail piping is filled. Further rotation brings both lead and trail ports (24) and (27) into registration with the openings (29) which communicate to a pressure source through the pressure zone (23) and conduit (31). The appli-cation of pressure forces the thin cake off the drum surface and is continued until the preselected volume of filtrate in the hydraulic system is forced through the filter cloth back into the tank. ~s noted, in the normal case only a part of the hydraulic system contents need be used in the backwash to pre-pare the cloth for another cycle. The volume of backwash is best determined empirically for a given plant. Adjustments in the v~lve or pressure settings control duration and force of back pressure ~lo~ to thus regulate the back~ash volume.
The filtrate backflow through the submerged filter cloth is a dynamic and uniformly distributed wash which acts evenly across the entire sector. This method will be useful in any fil~ration operation where cake formation occurs quickly so there will be ample time to conduct backwash and to reorm the cake after backwash.
Once the backflow has been completed, continued drum rotation brings successive sectors into register with the large vacuum chamber to effect cake formation and drying prior to discharge.
The man-iEold location and drum construction are best.
ill.ust:ra~ed -in F:igs. 9-11. As shown, each sector (11) is pro-vided with lead and trail ports (1~) adjacent its leading and trai]ing edges. As used herein, the words lead and trail have reference to the direction of drum rotation. As illustrated, all lead ports of a single sector communicate with a common lead manifold (17) and all trail ports of a sector with a common trail manifold (17). A single conduit (16) then connects each mani~old with one of the ports in the trunnion which in turn connect through a valve to a vacuum source. This single pipe arrangement reduces the number of internal pipes and enables the use of larger pipes and ports in the trunnion thus enhancing hydraulic efficiency of the filter.
The manifolds are rectangular. Each manifold of a given sector is located as close as possible to the adjacent manifold of an adjacent sector with the junction therebetween, preferably directly under a di~ision strip. Thus, the trail manifold of any sector is located next to the lead manifold of the next succeeding sector; and the centerline between the manifolds is under the division strip (9) between sectors. The manifolds are utilized as structural members for the drum by securing them along their length, either with a continuous weld or a series of tack welds to the interior wall of the drum.
Also, the ports in the drum wall and those in the top wall of the manifold a~e in registration with each other and their peripheral edges are sealed to~ether, usually by welding.
i5~
A plurality of both lead and trail ports (1~) is provided in each sector. The ports are formed as elongated slots located as close as possible and parallel to a division strip. This insures presentation of maximum opening for liquid ~low when the port is on the low side of the sector. Also, the slot~ed por~ is qu:i~e eas~ to seal weld to a corresponding port in the ~op wall of the manifold with which it registers to provide communica~ion with the manifold.
Location of the slotted opening with respect to the manifold side wall nearest the division strip is important. As shown> one side of the slot should be close aboard the top edge of the manifold sidewall. This will keep one or more slots adjacent the lower edge of the sector at all times while the drum is out of the slurry, whether the sector is ascending or de-scending thus enhancing filtrate removal. The slot location isalso an aid to cake discharge by gas blowback through the trail slot. This is so because when a sector is descending to the discharge level the trail port is at the top and the manifold acts to trap and retain residual or entrained moisture that would otherwise be carried back into the filter cake when pressured gas is supplied through the -trail port for cake dis-charge. Further, location of the ports at the extreme opposite sides of the sector insures sweeping of the complete sector during purge when positive pressured gas is introduced through the trail slot and withdrawn under vacuum through the descending lead slot. Complete sweeping is further enhanced by staggering the lead and trail ports with respect to each other as shown in Fig. lO.
The ~ilter is provided with a drainage grid (12) secured between the division strips ~9) and a filter cloth ~13) -- 8 -- ~
S~ ~
suitably secured in place by conventional caulking and wire windings. A usual deflector blade to guide discharged cake into a cake removal scroll or other conveyor is provided.
The conEiguration and physical location of the manifolds are imporLant for ~wo reasons. First, they provide an improved drum cons~ruc~lon because they are secured to the inner drum surface and ~here are no intervening conduits. Secondly, and ~his is very important to the cyclic wash operation, the mani-folds provide a reservoir of wash liquor (filtrate) just adjacent the filter sector. This means that very little energy is wasted by drawing in the necessary wash volume and very little reverse flow is required to effect uniform flow of the necessary small volume of filtrate for cloth wash. Thus, it is adjacent that use of the manifold as a wash liquor reservoir directly adjacent the filtration sector which minimizes backwash cycle time and energy consumption.
Although the invention has been described in connection with a rotary drum filter, it is not limited thereto as it may be utilized in other rotary filters, such as disc filters, wherein successive filter sectors are rotated into and out of submergence in feed slurry wherein vacuum is applied and cake is formed on the surface of the filter medium while filtrate is drawn therethrough.
While the invention is capable of and has been described as occurring every cycle, it may be operated at a lower fre-quency as the need is determined empirically. In any event, the improved wash reduces down time, increases filtration rate, and increases cloth life. In the case of separation of wax from crude oil and solvent, reduction in shutdown reduc4s wear and tear on materials of construction because the extreme variations _ g _ S.5i~
in temperatures between hot wash (180F.) and normal operation (as low as -lSF.) are drastically reduced.
The invention is not limited to filters having both lead and trail ports, but is readily adaptable to various types of hy~lraulic systems. Also, in the illustrated embodiment, it is not necessary that both lead and trail systems be used for back-wash as either may be used alone. Nor is it necessary that both lead and trail systems be used simultaneously for backwash as it may be desirable to have them backflow in series to effect a prolonged wash. All such variations are within the scope of this invention.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a rotary vacuum filter of the type in which a filter cloth is secured to overlie a drainage deck on the surface of a filter drum journalled for rotation through a slurry in a tank, and wherein cake is formed as successive sectors of the filter drum surface are rotated into and out of submergence in the tank while vacuum is applied to the underside of the filter medium through a valve, and vacuum is released to effect cake discharge after emergence from said slurry, the improvement enabling cleaning of said filter cloth, said improvement com-prising an elongated manifold secured to the inner surface of said drum adjacent to and in hydraulic communication with each sector, piping connecting said valve to each manifold to sequentially apply vacuum to each sector as it starts to sub-merge in the tank and for continuing said vacuum until the sector and its associated manifold are at least partially filled with filtrate, means operative while said sector remains submerged sequentially to discontinue vacuum application, to apply pressure to said piping to force a selected volume of said filtrate from said sector and manifold back through said cloth into said tank, and to immediately reapply vacuum to the surface of said sector to reform a filter cake thereon while drawing filtrate therethrough.
2. A filter according to Claim 1 in which said means for applying pressure to filtrate in said piping comprises pressurized gas.
3. A filter according to Claim 1 in which said means for applying pressure to filtrate in said piping comprises liquid under pressure.
4. In the operation of a rotary vacuum filter of the type having a plurality of filter sectors covered by a porous filter medium and mounted so that adjacent sectors pass successively into submergence in a slurry wherein vacuum is applied to draw filtrate through said filter medium into the filter hydraulic system while causing solids to deposit on said filter medium then after emergence from said slurry, cake is discharged from said filter medium; the improvement comprising the steps of collecting a volume of filtrate in a reservoir in said hydraulic system adjacent to and in direct hydraulic communi-cation with said sector, discontinuing vacuum and applying pressure to said filtrate while said sector is still in sub-mergence, continuing said pressure until a selected volume of filtrate from said reservoir has been forced through the filter medium; and thereafter applying vacuum to said filter sector while still in submergence.
5. A filter comprising a drum formed as a cylinder equipped with trunnions on opposite ends and adapted to rotate in a tank so that successive portions thereof rotate into and out of submergence in said tank, said drum having its curved outer wall surface divided by longitudinally extending division strips into a plurality of filter sectors extending end to end thereof, a flange at each end of said drum closing the ends of said sectors, a filter medium overlying said filter sectors, a plurality of ports in one of said trunnions extending axially therethrough, a plurality of ports in said drum surface spaced apart along at least one side of said sector close to said division strip, at least one manifold extending the length of the inner wall of said drum located under one side edge of each of said sectors, ports in the top wall of said manifold in registration with said ports in said drum, means sealingly connecting the peripheral edges of said ports in said manifold with the peripheral edges of said ports in said drum, said manifold being connected by a single conduit to a port in one of said trunnions, said manifold being secured directly to the inner wall of said drum, valve means to which said single conduit connects, means included in said valve for selectively applying vacuum and pressure to said conduit and manifold, said means including means to sequentially initiate application of vacuum to said pipe as said sector starts to submerge and to continue said vacuum at least until said manifold is filled with filtrate and said sector is submerged, then to discontinue vacuum and apply pressure to filtrate in said conduit to displace at least part of the filtrate from said manifold through said sector and said filter medium and then to reapply vacuum to said conduit while said sector remains submerged.
6. A filter according to Claim 5 in which the drum has ports along both sides of each of said sectors close to said division strips, a manifold is provided under each side of said sector and has ports in registration and sealingly connected with said ports in said drum wall each of said manifolds being connected to a port in said trunnion by a single conduit, said manifolds are formed so that adjacent walls of adjacent mani-folds are straight, and said manifolds are secured directly to the inner wall of said drum.
7. A filter according to preceding Claim 5 in which said ports in said drum surface and manifold are formed as elongated slots arranged parallel to said division strips.
8. A filter according to preceding Claim 6 in which said ports are formed as elongated slots and in each sector said elongated slots along one side edge thereof are staggered with respect to those along the other side edge thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA383,495A CA1128426A (en) | 1978-03-15 | 1981-08-07 | Rotary filter drum |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US88683678A | 1978-03-15 | 1978-03-15 | |
| US05/886,837 US4157301A (en) | 1978-03-15 | 1978-03-15 | Drum construction for rotary drum filter |
| US886,836 | 1978-03-15 | ||
| US886,837 | 1978-03-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110552A true CA1110552A (en) | 1981-10-13 |
Family
ID=27128813
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA323,380A Expired CA1110552A (en) | 1978-03-15 | 1979-03-14 | Rotary drum filter and method of operation for medium cleaning |
Country Status (8)
| Country | Link |
|---|---|
| AU (1) | AU4510679A (en) |
| CA (1) | CA1110552A (en) |
| ES (1) | ES478684A1 (en) |
| FR (1) | FR2419746A1 (en) |
| IT (1) | IT1192640B (en) |
| MX (1) | MX147795A (en) |
| NL (1) | NL7901975A (en) |
| WO (1) | WO1979000765A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5266168A (en) * | 1991-12-20 | 1993-11-30 | The Black Clawson Company | Gravity type pulp washer or thickener with rotating disrupters |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2289762A (en) * | 1939-05-08 | 1942-07-14 | Oliver United Filters Inc | Method and apparatus for filtering |
| US3027011A (en) * | 1958-01-06 | 1962-03-27 | Whiting Corp | Pulp washer and filter |
| US3262575A (en) * | 1963-08-08 | 1966-07-26 | Dorr Oliver Inc | Rotary drum filters |
| US3630380A (en) * | 1969-08-28 | 1971-12-28 | Dorr Oliver Inc | Rotary vacuum drum filters |
| US3627139A (en) * | 1970-06-22 | 1971-12-14 | Nikolai Alexandrovich Burtsev | Continuous drum vacuum filter |
-
1979
- 1979-03-13 NL NL7901975A patent/NL7901975A/en not_active Application Discontinuation
- 1979-03-13 WO PCT/US1979/000166 patent/WO1979000765A1/en not_active Ceased
- 1979-03-14 FR FR7906500A patent/FR2419746A1/en active Pending
- 1979-03-14 AU AU45106/79A patent/AU4510679A/en not_active Abandoned
- 1979-03-14 CA CA323,380A patent/CA1110552A/en not_active Expired
- 1979-03-15 IT IT21027/79A patent/IT1192640B/en active
- 1979-03-15 ES ES478684A patent/ES478684A1/en not_active Expired
- 1979-05-14 MX MX176921A patent/MX147795A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| IT1192640B (en) | 1988-04-27 |
| IT7921027A0 (en) | 1979-03-15 |
| ES478684A1 (en) | 1980-01-01 |
| FR2419746A1 (en) | 1979-10-12 |
| WO1979000765A1 (en) | 1979-10-04 |
| NL7901975A (en) | 1979-09-18 |
| AU4510679A (en) | 1979-09-20 |
| MX147795A (en) | 1983-01-12 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |