Note: Descriptions are shown in the official language in which they were submitted.
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The pre~ent invention relates to a method for the filtration of
a suspension or emulsion and also to apparatus for carrying out the
method.
In the filtration of a suspension or emulsion, it is previously
known tc supply the suspension (or emulsion) to a filter bed consisting
of a filter medium of particles enclosed in a tank. The suspension
flows upwardly through the filter bed and, in some appropriate manner, ~ ;
the filtered liquid phase obtained by the filtratlon is discharged from
the filter bed through outlet means provided with some appropriate cover
means, for instance, jalousi wall or screen, to prevent the filter medlum
from escaping with the filtered liquid phase~ In one such type of
filtration apparatus it is also known, in order to obtain a continuously
operating filtration apparatus, i.e. without shutting off the filtration
during the cleaning of the filter medium, to allow the filter medium,
while the filtration is going on, to flow downwardly through the filtra-
tion tank, remove the dirtied (contaminated) filter medium in the
course of filtration from the ba~e of the tank to a pipe positioned out-
side of the tank, allow the dirtied filter medium to pass through a
washing devlce, and return the cleaned filter medium from the washing -~
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device to the surface of the filter bed ln the tank. In another known
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filtration apparatus, likewise provided with a washlng device positioned
outside of the filtration tank but without filtration in counter-current
between the filter medium and the suspension, the filtration oE the filter ;-
medium takes place during the flow thereof in counter-current to the ;
wash liquid which is taken out from the pipe for delivering the suspension
to be filtered.
The object of the present invention i8 to provide a continuously
operating filter which, by simple means, provides reliable operation,
high capacity in relation to required space, substantially always the
same filtering capacity and efficient washing of the filter medium. `~
The filter, besides utilizing the advantage of an effective use of
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the filter bed by counter-current flow (known per sP) between the filter
medium and the suspension during the filtration, also utilizes the
advantage of improved washing by counter-current flow between the filter
medium and the wash liquid (likewise known per se but in another filtering
application3.
The present invention, as mentioned above in connection with the
statement of prior art, relates to a method for the filtration of a sus-
pension or emulsion wherein the suspension is supplied to ~ zone of filter
medium of particles forming a filter bed, flows in the direction upwardly
through the filter bed during the filtration and is discharged from the
filter bed as filtered liquid phase. During filtration the filter medium
flows in a direction downwardly through the filter bed zone in counter-
current to the suspension past the inflow of the suspension into the filter
bed. The filter medium is thereafter transported from the filter bed to a
wash path and washing of the dirtied filter medium takes place during
flow in counter-current to a wash liquid. The washed filter medium is
then returned to the top surface of the filter bed zone.
The novel and characterizing features of the method according ;
to the invention is that at least a part of the filtered liquid phase
is discharged from the filter bed zone for maintaining above this zone
a zone of filtered liquid phase, that the transport of the dirtied
filter medium takes place upwards through a defined passage of the filter
bed zone, and that said counter-current washing of the dirtied filter
medium along the wash path takes place during flow of the dirtied filter
medium in counter-current to the filtered liquid phase utilized as wash
liquld, which liquid phase is supplied to the wash path from said zone of
filtered liquid phase.
Thus, according to the invention, the total filtering and washing
process can take place within the filtration apparatus and the filtered
or clarified liquid obtained by the filtration is, in a simple and
advantageous manner, utilized as wash liquid.
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Within the E~me of the present lnvention and as will become evident
hereinafter, further improvements are provided with a view to making the -
washing as well as the filtration still more effec~ive. During the wash-
ing the relative velocity between the filter medium and the wash liquid
is momentarily increased at least once which creates espeeially favourable
conditions for washing the filter medium. Decelerating the filter medium
at least once and increasing the contact tim~ between the filter medium ,~'
and the wash liquid results in an increased effectiveness of the washing
and also breaks caked aggregates of filter medium caused by the dirtying.
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Also, according to the invention, the quantity of the wash liquid flowlng
along the wash path can be controlled. As to the quantity of filter medium
transported to the wash path, this quantity can, according to the invention,
also be automatically controlled in order to constantly achieve an
appropriately adapted flow of filter medium to the wash path and this
control can be made by sensing quantity or pressure of the suspension
before its supply to the filter bed zone. Finally, by a method
according to the invention, air supplied for the transport of
the dirtied filter medium can be prevent from infiltrating
the filter bed zone by being previously ~rapped and dis- -
- 20 charged, whereby risk for local fluidizing of the filter bed, which could
result in substantiaI reduction of the ~iltering capacity of the filter
bed, is eliminated.
The invention also relates to a filtration apparatus for carrying ;~
out the above-mentloned method. The filtration apparatus includes a zone
of filter medium particles forming a filter bed, inlet means for the suspension
or emulsion to be filtered positioned in the lower part of the filter
bed zone for su~pension flow during the filtration in the direction up-
wards ~hrough the filter bed, a space located below said inlet means and
being in free communication with the filter bed zone, to which space the
filter medium continuously is supplied by flow in the direction downwards
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through the filter bed zone, and a transport device for hauling the
filter medium supplied to said space and dirtied by the filtration
up to a wash device which is arranged and constructed for washing in
; counter-current between the filter medium and a wash liquid alld provided
with means for returning the washed filter medium to the top surface of the
filter bed. In the filtration apparatus of the present invention there
is maintained, above the filter bed zone, a zone of filtered liquid
phase obtained by the filtra~ion. The transport device comprises a pump
havlng a pipe extending upwardly through the filter bed zone to at least
the upper part of said zone of filtered 'iquid phase and i9 connected
to the upper part of the wash device. The lower part of the wash device
is provided with at least one inlet means which is connected to said zone
of filtered liquid phase. In a preferred embodiment of the invention which,
in respect to operation and construction, is simple, the wash device is
immersed in said zone of filtered liquid phase and has its lower end
located above the filter bed zone.
The invention is illustrated by way of e~ample with reference to the
accompanying drawings in which:
Fig. 1 is a vertical section of a filtration apparatus in accordance
with this invention;
Fig. 2 i9 an enlarged view of the upper portion of the filtration
apparatus shown in Fig. 1 illustrating more clearly the wash device; and
Fig. 3 is a top schematic view illustrating a filtration unit composed
of a number of the Eiltration apparatu~es shown in Fig. 1.
Referring to Fig. 1, there i8 shown a particle filter medium 1
confined in a tank having walls 2 and a funnel or cone-shaped bottom 3.
The base of the cone preferably conforms to the shape of the tank as deflned
by the walls 2.
The filter medium may be sand or other materials, such as particles
of a plastics material or mixtures of several materials. A mixture of
several grain slze fractions can be used in a continuously operatlng filter
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according to the invention which is contrary to conventional techniques,
depending on what is to be ~filtered and how effective the filtration
is to be carried out. A man skilled in the art can, by tests, determine
the most suitable material and grain size in each particular case.
The suspension or emulsion to be filtered is supplied, as shown
by arrow A, to the tank through inlet 4 which preferably is located as
shown near the bottom of the tank. The flow of the suspension into the
filter bed takes place in the lower part of the filter bed via a number
of pipes 5 having outlets 6. A roof 7 is arranged above the outlet of
each pipe to prevent the filter medium from being in direct contact with
the outlets and to expose a larger surface of the filter medium to the
supplied suspension. By this, the risk of clogging the filter owing to
substantial momentary dirtying of the filter medium close to the pipe
outlets is reduced. The roof 8 have a V-shaped croæs-sect~on and owing to
this and to the arrangement of the pipe outlets with roofs, the movement
of the filter medium downwards is considerably reduced. The arrange-
ment of having the pipe outlets 6 in the lower part of the filter bed
~ provides an advantage in that the filter medium being the dirtiest,
; i.e. the filter medium passing the roof~ and the pipe outlets, continues
downwards and is no more utilized for filtration. By this the risk of
clogging is reduced since new filter medium can be exposed to the incoming
suspension. The incoming suspension flows, in co~mter-current to the
filter medium, upwardly through a zone of the filter bed towards
increasingly cleaner Eilter medium. The filtered liquid phase obtained
during the flow of the suspension upwards through the filter bed zone is ~-
kept as a zone 8 of filtered liquid phase above the filter bed and
its surface level is, in the embodiment shown, fixed by discharging the
filtered liquid phase from the filtration apparatus via a weir 9
to an outlet (arrow B).
In the tank bottom 3, down into which the dirty filter medium flows,
the intake of some conveying or pumping devlce 10 is located.
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As appears from the illustrated embodlment, the conveying device extends
centrally through the apparatus and can for lnstance consist of a mammoth
pump. Such a pump operates with air as transport medlum and the air is
supplied from above downwardY along a pipe 11 extending alongside a tran~-
port pipe 12 forming a part of the conveying device. The air is ~upplied
to the transport pipe 12 through hole~ ~n~t shown) in the lower part of
the pipe. The fil~er medium i8 transported (arrow C) by the air through
the pipe 12 up to a wash device 13 (de~cribed hereinafter~ positioned
above the filter bed.
If the air conducted into the mammoth pump for some reason should - ;
extrude through the lower part of the transport pipe 12 and infiltrate
the filter medium, there is a risk of local fluidizing of the filter
medium resulting in a substantial reduction of the filtering capacity of
the filter. In arder to prevent such a disturbance, a funnel 14,
turned upside down, is placed above and around the lntake of the pump.
The funnel catches the escaped alr and discharges the same through holes
in the top end of the funnel into a pipe 15 extending alongside the
transport pipe. The funnel also eerves as guide means for the flow of
; the filter medium downwards 80 that a uniform flow profile (flow character-
istic) is obtained over the cross-section of the apparatus.
The above-described roof~ 7 positioned above the outlets 6 of
the inlet pipes contrlbute, as well as the funnel 14, to achieve desired
flow proile. Such rooE~ can, although not shown, in order to still
more ensure desired flow profile, be arranged ln the filter bed at other
places and wlthout being associated with inlets of the suspension into
the filter bed through the outlets 6.
The wash device 13 is ~hown in larger scale in Fig. 2. The filter
medium to be washed arrives from the upper end of the transport pipe 12,
turns ~arrow D) and flows downward~ along a wash path formed by the space
between the tran~port pipe 12 and an outer pipe 16. The outer pipe 16 is
preferably concentrically arranged relative to the transport plpe 12.
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The filter medium can, owing to its dirtiness, contain clumps and these
are broken up by striking a plate 17 or the like positioned in the flow
path of the filter medium. The veloclty of fall of the filter medium
is also decelerated by the plate 17. The filter medium hits thereafter,
further down in the wash path, an intermediate partition 18 provided with
holes 19, preferably followed by a number of additional intermediate
partitions o~ similar shape. In the embodiment shown there are five
intermediate partitions. The holes 19 in two adjacent partitions are
preferably displaced in relation to each other, so that a vertical free
; lO passage for the filter medlum is prevented. Owing to this, there is a
frequent deceleration of the filter medium during its passage thr~ugh
the wash device. The filter medium flows downwardly counter-current to
an upwardly flowing wash liquid. The velocity of the wash liquid becomes
momentarily higher when it flows through the holes in the intermediate
partitions which results in particularly favourable conditions for the
washing of the filter mediu~.
The filtered liquid phase in zone 8 positioned above the filter
bed is used as wash liquid. The wash device is in this respect immersed
in the filtered liquid phase in zone 8 and, as shown with arrow E in
2~ the illustrated embodlment, the ~sh liquid, i.e. the filtered liquid
phase, is supplied to the wa~h path througb an opening 20 between the
lower end of the outer pipe 16 and the transport pipe 12 and Plows upwards
along the wa~h path. The wash liquld which becomes dlrty during the
washing, i.e. the re~ect, is discharged from the wash path as shown
with arrow F, flows over a weir 21 and i9 discharged from the apparatus
as shDwn with arrow G. Thig weir can be adjustable as to its height
and width position, thereby making it possible to control the quantity
of wash liquid. For instance, the quantity of wash liquid is increased
upon lowering of the weir. The quantity of wash liquid is also automatic-
ally increased when the level of the filtered liquid above the filterbed rises, for instance by increased load on the filtration apparatus.
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In order to gulde the filter medium~ discharged from the transport
pipe 12, downwardly to the wash path and in order to separate the reject
from the incoming Eilter medium, a pipe 22 is arranged between the outer
pipe 16 ~nd the transport pipe 12, such pipe 22 being lowered a distance
past the top end of the transport pipe.
The pipe 22 projects out beyond the outer pipe 16, and air supply
pipe 11 and alr discharge pipe 15 pass through the pipe 22. The pipe 22
also encloses a device 23 for capturing air from the transport pipe 12
containing filter medium. In the illustrated embodiment this capturing
device consists of downwardly facing cones and upwardly facing truncated
cones, alternately arranged.
Although not shown, a part of the filtered liquid phase can, if
desired, be taken out within the filter bed zone below its top surface
by arranging outlet pipes for filtered liquid phase. The inlets to such
outlet pipes preferably are located substantially vertically above the
outlets of inlet pipes 6. Also, if desired, roofs can be placed over
the inlets to such pipes in conformity with the roofs 7 located above the
; outlets of inlet pipes 6. By taking out the filtrated liquid phase
through such outlet pipes having their inlets positioned within the filter
2Q bed zone, below the top surface thereof, a satisfactory filtrated liquid
phase is ensured also upon, for instance, possible shutdowns in the wash
device, in which case the filtered liquid phase existing above the filter
bed could be dirty.
Below the bottom end of the wash device a cone 24 is arranged for
spreading the filter material coming from the wash device out over the
top surface of the filter bed. Moreover, the cone 24 is provided with a
suitable number of holes 25 in order to obtain a supply of filter medium
particles to the surface of the filter bed positioned below the cDne.
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Besides the above described automatic control of the wash liquid
quantity, also an automatic control of the quantity of filter medium
supplied to the wash can, although not shown~ be accomplished. By placing
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a quantity sensing or pressure sensing means ln the supply pipe for
the suspension (in ~ig, 1 indicated with the arrow A) a signal indicating
a change, for instance a pressure lncrease owing to accumulation of
suspended material in the filter bed, is obtained. This signal can~in
a manner known per se~be used for the control of the capacity of the
conveying or pumpin~ device 10 so that the transported quantity of
filter medium to the wash device is increased or decreased.
In the embodiment described above and shown on the drawings, the
wash device is immersed in the zone 8 of filtered liquid phase and
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the filtered liquid phase is from this zone admitted as wash liquid
into the wash device through the opening 20. The filtered liquid
phase utilized for the washing can, however, alternatively be laterally
admitted through one or several openings in the outer pipe 16 at the
lower portion thereof. In another alternative embodiment, not shown,
in which likewise filtered liquid pha~e from the zone 8 i9 utilized as
wash liquid, at least a part of the wash device is immersed in and
separately arranged relative to the filter bed and one or several pipes
are drawn from the zone 8 to the lower portion of the wash device for
the supply of the wash liquid to the wash device so positioned.
A ~iltration apparatus according to the invention, for instance,
the preferred embodiment described above and shown in Figs. 1 and 2,
makes a construction with comparatively small dimension~ possible and
thereby the advantage is achieved that the apparatus i~ easy to handle
and ea~y to attend in operation. Moreover, owing to the act that all
elements required for the contimlously operating apparatus are positioned
within the apparatus and furthermore that certain devices, for instance
the wash device and the conveying or pumping device, can be formed as
units, the apparatus is well adapted to be built as a module. When greater
filtration capacities than one single apparatus can produce are required
it is possible to build together, in a simple and advantageous way,
several apparatuses into one large filtrat~on plant. Such a filtration
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plant is exemplified and somewhat schematically shown in Fig. 3 and
comprises a group of eight module-built filtration apparatuses joined
together. All devices and elements required for the operation of a
filtration apparatus according to the invention, for instance a filtra-
tion apparatus as shown in ~igs. 1 and 2, are embodied in each module.
However, the walls 2, which border against each other in the group, are
removed (the dashed lines in Fig. 3 are intended to illustrate the upper ~-
edge of the bottoms 3). Furthermore, for each row 29 of filtration
apparatuses there is a common outlet 26 for the filtered liquid phase
discharged from each filtration apparatus (arrow B in Figs. 1 and 2)
and for both rows 29 there is a common outlet 27 for the re~ect from the
wash device (arrow G in Figs. 1 and 2). It is apparently not necessary
to arrange these common outlets 26 and/or 27 as shown but such an arrange-
ment obviously simplifies the construction. The outer wall 28 enclosing
the filtration apparatus can consist of walls 2 in each filtration
apparatus, but alternatively all walls 2 in each filtration apparatus can
be removed and a separate outer wall be built around the filtration
plant.
As is al80 eYident from Fi8. 3, each apparatus module has a hexagonal
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form in cross-section. This form sl~ows ~imple joining to larger filtra-
tion plants. Other forms are, however, possible to u~e, for instance,
square, which also allows simple ~oining. A square form can, however,
compared with for instance hexagonal form be less suitable owlng to the
fact that the filter medium situated in the corners is decelerated in its
movement downwards and thus less active in the filtration. -~
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