GB2074886A - A backwashable filter - Google Patents
A backwashable filter Download PDFInfo
- Publication number
- GB2074886A GB2074886A GB8111721A GB8111721A GB2074886A GB 2074886 A GB2074886 A GB 2074886A GB 8111721 A GB8111721 A GB 8111721A GB 8111721 A GB8111721 A GB 8111721A GB 2074886 A GB2074886 A GB 2074886A
- Authority
- GB
- United Kingdom
- Prior art keywords
- filter
- filter medium
- clamping band
- basket
- backwashable
- 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.)
- Granted
Links
- 238000011001 backwashing Methods 0.000 claims abstract description 17
- 239000007788 liquid Substances 0.000 claims abstract description 14
- 239000002184 metal Substances 0.000 claims description 5
- 238000001914 filtration Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- 229920000297 Rayon Polymers 0.000 description 5
- 238000010276 construction Methods 0.000 description 5
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000002245 particle Substances 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- 239000004744 fabric Substances 0.000 description 2
- 229920003043 Cellulose fiber Polymers 0.000 description 1
- 238000007688 edging Methods 0.000 description 1
- 229920000126 latex Polymers 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000004627 regenerated cellulose Substances 0.000 description 1
- 239000000565 sealant Substances 0.000 description 1
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
- D21D5/02—Straining or screening the pulp
- D21D5/16—Cylinders and plates for screens
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
- B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
- B01D29/13—Supported filter elements
- B01D29/15—Supported filter elements arranged for inward flow filtration
Abstract
A backwashable filter includes a generally cylindrical housing, an inlet opening into the housing and an outlet opening from the housing, a cylindrical filter basket within the housing and arranged between the inlet and the outlet openings, and a backwashing arm bearing against the inside of the filter basket and being rotatable around the inside face of the filter basket. The filter basket comprises a perforate core (1), a filter medium (3) wrapped around the perforate core (1) and a perforate flexible outer clamping band (4) wrapped around the outside of the filter medium (3) with tensioning means (9, 10, 11) to apply tension to the clamping band (4) to clamp the filter medium (3) tightly against the perforate core (1). This clamping band (4) constrains the filter medium (3) and so prevents it flexing with rotation of the backwashing arm and this enhances its life. The performance of the filter is also increased since leakage of the liquid to be filtered around edges of the filter medium is more easily prevented particularly when split clamping rings (12) are also provided. <IMAGE>
Description
SPECIFICATION
A backwashable filter
This invention relates to backwashable filters and, in particular, bachwashable filters capable of use in the filtration of viscose and other viscous liquids.
Backwashable filters have been used for filtering a variety of materials by they have found particular use in the filtration of viscose before it is extruded to form regenerated cellulose film or regererated cellulose fibre. British Patent
Specification No 1,111,914 describes the general construction and use of such a filter and its application to the filtration of viscose. This specification shows a filter having a generally cylindrical housing with an inlet opening into the centre of the housing and an outlet opening from the outside periphery of the housing. A cylindrical filter basket is located coaxially within the housing and arranged between the inlet and the outlet, and a backwashing arm is rotatably mounted about the central axis of the housing and bears against the inside face of the filter basket.In use, the liquid to be filtered is forced into the inside of the filter basket and then the liquid passes out through the filter basket into the space between the outside of the basket and the housing and thence through the outlet. Debris filtered from the liquid is trapped in the filter basket. The backwashing arm is hollow and the part which bears against the inner face of the filter basket includes an elongate slot extending parallel to the axis of the housing. In use, the pressure inside the backwashing arm is less than the pressure in the space between the outside of the filter basket and the inside of the housing and, therefore, as the backwashing arm is rotated against the inside face of the filter basket some of the filtered liquid passes in reverse flow through the filter basket and into the backwashing arm.In its reverse flow through the filter basket the filtered liquid carries with it the debris which has been trapped in the filter basket and so, as the backwashing arm is rotated, it continually backwashes the filter basket at the same time as the majority of the filter basket is being used for filtration.
This type of filter has met with considerable success but, in spite of that, it does possess several disadvantages which are particularly marked when it is used to filter viscose and other visous liquids. The filter basket includes an inner and an outer cage between which the filter medium is located. In the past, the filter medium has usually been formed by a woven stainless steel wirecloth. The outer perforated cage is formed in two halves. It is important that the perforations in both the inner and the outer cages are aligned with one another so that the liquid to be filtered can pass through the filter basket. The way that the filter basket is prepared and the way that the alignment is achieved is described fully in
British Patent specification No 1,1 1 1,914.The relative position of the inner and outer cages and that of the perforations in them depends upon the
thickness of the filter medium positioned between
them and therefore, the inner and outer cages
have to be made and matched for one particular
thickness of filter medium. Thus, for example, if it
is desired to change the thickness of wirecloth to
be used as the filter medium, and usually this
occurs when it is desired to change the gauge of
the wire cloth, a fresh filter basket has to be
manufactured. When the inner and outer cages -are perforated together in a single operation as
disclosed in Specification No 1,1 1 1,914 this is a
relatively awkward operation to perform using
conventional machine tools in view of the
relatively large size of the filter baskets and the
large number of perforations which have to be
machined into the cages.
In spite of the precautions mentioned in British
Patent Specification No 1,111,914 it is difficult to get an exact match between the inner and outer cages whilst allowing for the thickness of the filter medium between them and we have found that, in practice, there is usually some clearance between the filter medium and the inner and outer cages.
When the filter is being used, the differential pressure across the filter medium urges the filter medium against the inside of the outer cage.
However, the portion of the wirecloth adjacent the backwashing arm, being subjected to a reverse flow of the filtered liquid, is urged against the outer surface of the inner cage. As the backwashing arm is continually rotating, this means that when there is any clearance between the inner and outer screens the wirecloth is being continually flexed and this leads to early failure of the wirecloth filter medium due to the metal fatigue
In view of the difficulty in matching the inner and outer cages with the thickness of the filter medium it is difficult to ensure that a fluid-tight seal is formed around the top and bottom ends of the filter medium. Naturally any leakage of the material to be filtered around the top and bottom ends leads to this material being ineffectively filtered and so reduces the overall efficiency of the filter.
In general, filter media such as wirecloth are
manufactured in the form of flat sheets and therefore, to form them into a cylinder so that they can be used with this type of filter, it is necessary to have at least one join extending parallel to the axis of the filter.
Considerable difficulty has also been found in
providing an effective seal along the joins in the filter material which extend in an axial direction as well as around both the top and bottom ends.
According to this invention a backwashable filter includes a generally cylindrical housing, an
inlet opening into the housing and an outlet
opening from the housing, a cylindrical filter
basket within the housing and interposed between the inlet and outlet, and a backwashing arm
bearing against the inside of the filter basket and
being rotatable about the axis of the filter basket, the filter basket comprising a perforate core, a
filter medium wrapped around the perforate core,
and a perforate flexible outer clamping band wrapped around the outside of the filter medium with tensioning means to apply tension to the
clamping band and thereby clamp the filter medium tightly against the perforate core.
Thus, as the filter medium is tightly clamped between the clamping band and the perforate core, it cannot flex during backwashing and this increases the life of the filter element. The filter element is wrapped around the perforate core and
clamped in this position by the clamping band,
and thus, it is possible to obtain a much tighter
seal at the top and bottom ends of the filter
medium and along the axial join of the filter mediun
so reducing the amount of leakage of the
unfiltered liquid past the filter element. Further, it is simple and straightforward to exchange a particular filter medium for one of different thickness since the outer clamping band accommodates a range of filter media of different thickness.
Preferably the filter basket includes clamping rings adjacent the top and bottom ends of the filter medium and arranged to clamp the top and bottom ends of the filter medium against the perforate core to prevent any leakage of the liquid to be filtered around the top and bottom ends of the filter medium. The clamping rings may engage the filter media directly but preferably they bear against the outside of the clamping band. The top and bottom ends and the axial join of the filter medium may be impregnated with an impermeable sealant, for example a rubber latex composition, to ensure the integrity of the seals at the top and bottom ends and the axial join.
The perforate flexible clamping band may include apertures similar to those in the perforate core but, in this case, it is preferred that the size and pitch of the apertures is different from that in the core so that there is a substantially constant overlap between the apertures in the clamping band and those in the core irrespective of the relative alignment between the two. However, it is preferred that the clamping band is made from a wire mesh or lattice work and so has a largely open configuration. The band may be made by a combination of a wire mesh adjacent the filter medium to provide support for it and an outer lattice work support to provide the main structural strength of the clamping band.
When the clamping band is formed by a woven wire mesh, it is preferred that wires of the wire mesh which extend in an axial direction of the basket are precrimped into a serpentine shape and wires of the mesh which extend in a circumferential direction around the basket clamping band are substantially straight before being wrapped around ths core and filter media.
We have found that when a typical woven wire
mesh is used in which the wires extending in both of these directions have a serpentine configuration there is some give in the circumferential direction of the wire mesh when it is wrapped around the perforate core and this give allows some flexing of the filter medium. However, when the clamping band is made from a wire
mesh having precrimped wires extending in the
axial direction and straight wires in the direction
which is, in use, the circumferential direction, the
give in the circumfernetial direction is
substantially eliminated and this enables the filter
medium to be clamped more tightly against the
perforate core.
When the clamping band is formed by or
includes a lattice work, it may include a lattice
work of substantially straight rods extending in the
axial direction and connected to a number of outer
spaced circumferentially extending bands or,
alternatively, it may include an array of parallel
circumferentially extending rings connected to a
number of outer, axially extending rods.
The tensioning means preferably includes bars
connected to axially extending edges of the
clamping band and screwthreaded means
associated with the bars to draw them together to
apply tension to the clamping band and thereby
clamp the clamping band tightly around the
outside of the filter medium.
Particularly when the clamping band is made
from a lattice work it may be manufactured in two
or more parts fixed together to form the complete band. This arrangement facilitates the manufacture of the band. Only a single tensioning means is necessary when the band is formed in two or more parts although tensioning means may be provided between the parts. The inner core may include one or more locating pegs projecting outwards from it. In this case the filter medium and the clamping beand are arranged to located on this or these locating peg or pegs. Usually the pegs are located between the axially extending edges of the filter medium and the clamping band.
The pegs define the location of the clamping band relative to the perforate core and also prevent rotation of the filter medium and the clamping band relative to the core.
Preferably the filter medium is an in-depth filter medium such as a sintered fleece of stainless steel fibres. With such an in-depth filter medium debris is trapped throughout the thickness of the filter medium to provide it with a greater dirt holding capacity. It is also possible to provide a sandwich of a number of different layers of in-depth filter medium, one on top of the other and so increase the degree of fineness of filtration which can be achieved by the filter without limiting its throughput. When the filter basket includes a number of layers of different porosity the larger particles tend to get trapped in the more porous layers whereas the finer particles pass through the more porous layers and are only trapped in the downstream, less porous layers. This means that the downstream less porous layers are not clogged prematurely by large particles of debris.
The particular construction of the filter medium can thus be varied to suit a particular material which is to be filtered. With the filter constructed in accordance with this invention whilst the filter basket can accommodate filter media having a wide range of thickness, in extreme cases it may be necessary to provide a clamping band which is longer or shorter.
We have found using one example of filter in accordance with this invention that we have been able to replace an existing three stage viscose filtration plant in which the first stage included a backwashing filter substantially as described in
British Patent Specification No 1,111,914 having a filter medium formed by 16 micron wirecloth, with a single stage filter including an in-depth filter medium. We have also found that the volume of material used in the backwashing of the filter medium and withdrawn through the backwashing arm has been reduced from 50% to 8% whilst, at the same time, the throughput of the filter has been increased from 39 litres per minute to 70
litres per minute.
Particular examples of a filter in accordance with this invention will now be described with
reference to the accompanying drawings; in which:~
Figure 1 is a diagrammatic perspective view of two parts of a first example of filter basket;
Figure 2 is a section through a part of the first
example of filter basket showing the clamping
arrangement;
Figure 3 is a scrap section through the first
example of filter basket;
Figure 4 is a part axial section through part of a
first example of filter basket;
Figure 5 is a perspective view of part of the
clamping band used in the second example of
filter basket;
Figure 6 is a cross-section through the
clamping arrangement of the second example of
filter basket;
Figure 7 is a vertical section through part of the second example of filter basket;;
Figure 8 is a cross-section through the clamping means of the third example of filter basket;
Figure 9 is a side elevation of the clamping means of the third example; and,
Figure 10 is a vertical cross-section through the third example of filter basket.
The basic construction and arrangement of a backwashing filter in accordance with this invention is substantially similar to that described in British Patent Specification No 1,111,914 and will therefore not be discussed in detail. The filter differs only in the construction of its filter basket and examples of three different filter baskets will now be described.
A first example of filter basket includes a perforated cylindrical core 1 including holes 2, a filter medium 3, and a clamping band 4. An axially extending region of the core does not include any
holes and axially extending edges of the filter
medium 3 and clamping band 4 are arranged
adjacent this unperforated region of the core 1.
Also the top and bottom of the core 1 is
unperforated. Metal edging strips 5 are fixed to
the adjacent axially extending edges of the filter
medium 3. The filter medium 3 is wrapped around the core 1 and the strips 5 are bolted together by
nuts and bolts 6. The filter medium 3 is formed by a fleece of sintered stainless steel fibres 7 having a wire mesh protection or support screens 8 on its opposite faces. One or both of the protection or support screens 8 may be sintered onto the fleece 7. This arrangement is clearly shown in Figure 3 but in all other Figures the filter is simply shown as a wire cloth for clarity. The screes 8 provide protection for the fleece 7 and some mechanical strength for the filter medium 3.
The clamping band 4 is formed from woven stainless steel wire mesh the wires of which extending in a direction parallel to the axial direction of the filter basket are pre-crimped into a serpentine shape whereas the wires of the mesh which extend around the filter basket are substantially straight before the clamping band is wrapped around the core. This is shown clearly in
Figure 3, but the conventional symbol used in
Figure 2. Tensioning means including metal bars 9 and bolts 10 and 1 1 are used to apply tension to the clamping band 4. The bars 9 are welded to the axially extending edges of the clamping band 4.
The clamping band 4 is wrapped around the core 1 and filter medium 3 and the clamping bars 9 are pulled together by bolts 10 which pass through one of the bars 9 and are screwthreaded into the other bar 9. Further bolts 11 which are screwthreaded into the other of the bars 9 bear against the one of the bars 9. The bolts 11 are then tightened and the bolts 10 and 1 1 tightened in sequence to maintain the faces of the clamping bars 9 generally parallel. The bolts 10 are tightened to ensure that the clamping band 4 is tensioned to clamp the filter medium 3 tightly a#gainst the inner core 1.
The bars 9 do not extend to the top and bottom edges of the clamping band 4 and neither do the metal strips 5. Split clamping rings 12 are located adjacent both the top and bottom ends of the filter medium 3 and around the outside of the clamping band 4 and the filter medium 3 are clamped tightly against the core 1 and to prevent leakage of unfiltered liquid around the top and bottom ends of the filter medium 3.
The second example is generally similar to the first and similar parts have been given the same reference numbers. However, in this example, the clamping band is made from a lattice work of axially extending round rods 13 supported by circumferentially extending rigns 14. The axially extending rods 13 may have a wedge-shaped cross-section. The construction of the tensioning means for this example are substantially indentical to those in the first example.
The third example is again generally similar to the second example but, in this case, the outer screen is formed by a lattice work of circumferentially extending round wires 15 held together by axially extending support bars 16. In this example the clamping bars 9 include fixed opposed pairs of projections 17 which replace the bolts 11. With this example the circumferentially extending round wires 15 form an effective seal at both the top and bottom ends of the clamping band and consequently separate split clamping and so has a largely open configuration.
5. A backwashable filter according to claim 4, in which the band is made by a combination of a wire mesh adjacent the filter medium to provide support for it and an outer lattice work support to rings 12 are not required.
Claims (1)
1. A backwashable filter including a generally cylindrical housing, an inlet opening into the housing and an outlet opening from the housing, a cylindrical filter basket within the housing and interposed between the inlet and outlet, and a backwashing arm bearing against the inside of the filter basket and being rotatable about the axis of the filter basket, the filter basket comprising a perforate core, a filter medium wrapped around the perforate core, and a perforate flexible outer clamping band wrapped around the outs#ide of the filter medium with tensioning means to apply tension to the clamping band and thereby clamp filter medium tightly against the perforate core.
2. A backwashable filter according to claim 1, in which the filter basket includes clamping rings adjacent the top and bottom ends of the filter medium and arranged to clamp the top and bottom ends of the filter medium against the perforate core to prevent any leakage of the liquid to be filtered around the top and bottom ends of the filter medium.
3. A backwashable filter according to claim 2, in which the clamping rings bear against the clamping band.
4. A backwashable filter according to any one of the preceding claims, in which the clamping band is made from a wire mesh or lattice work provide the main structural strength of the clamping band.
6. A backwashable filter according to claim 4, in which wires of the wire mesh extending in the axial direction of the basket are pre-crimped into a serpentinve shape and wires of the mesh extending in a circumferential direction around the basket are substantially straight before being wrapped around the filter medium and core.
7. A backwashable filter according to claim 4 or 6, in which the lattice work is formed by substantially straight rods extending in the axial direction and connected to a number of spaced outer circumferentiaily extending bands.
8. A backwashable filter according to claim 4 or
6, in which the lattice work is formed by an array of parallel circumferentially extending rings
having a number of axially extending rods
connected to their outer faces.
9. A backwashable filter according to any one of the preceding claims, in which the tensioning
means includes bars connected to axially extending edges of the clamping band and screwthreaded means associated with the bars to draw them together to tension the clamping band and thereby clamp the clamping band tightly around the outside of the filter medium.
10. A backwashable filter according to any one of the preceding claims, in which the filter medium comprises a sintered fleece of metal fibres.
11. A backwashable filter according to claim 1, constructed substantially as described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8111721A GB2074886B (en) | 1980-04-22 | 1981-04-13 | Backwashable filter |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8013158 | 1980-04-22 | ||
| GB8111721A GB2074886B (en) | 1980-04-22 | 1981-04-13 | Backwashable filter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2074886A true GB2074886A (en) | 1981-11-11 |
| GB2074886B GB2074886B (en) | 1983-09-28 |
Family
ID=26275270
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8111721A Expired GB2074886B (en) | 1980-04-22 | 1981-04-13 | Backwashable filter |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2074886B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0072672A2 (en) * | 1981-08-14 | 1983-02-23 | Eli Ivan Robinsky | Filtering apparatus and a method of filtering a liquid-solids suspension |
| EP0733734A2 (en) * | 1995-03-24 | 1996-09-25 | Jylhäraisio Oy | Straining method and screen |
-
1981
- 1981-04-13 GB GB8111721A patent/GB2074886B/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0072672A2 (en) * | 1981-08-14 | 1983-02-23 | Eli Ivan Robinsky | Filtering apparatus and a method of filtering a liquid-solids suspension |
| EP0072672A3 (en) * | 1981-08-14 | 1984-08-01 | Eli Ivan Robinsky | Filtering apparatus and a method of filtering a liquid-solids suspension |
| EP0733734A2 (en) * | 1995-03-24 | 1996-09-25 | Jylhäraisio Oy | Straining method and screen |
| EP0733734A3 (en) * | 1995-03-24 | 1998-06-10 | Jylhäraisio Oy | Straining method and screen |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2074886B (en) | 1983-09-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |