Note: Descriptions are shown in the official language in which they were submitted.
-
CA 022137~6 1997-09-09
WO96/2~52 PCr/~D5'/O~
Apparatus for PUrification of Liquids
BACKGROUND OF THE INVENTION
This invention relates to apparatus for the
purification of aqueous liquids, in particular where the
J 5 purification treatment requires the liquid for purification
to be passed through a plurality of treatment stages, each
of which comprises a bed of particulate material.
Such treatment stages include for example beds of
particulate material such as sand, garnet, carbon or
10 anthracite for filtration, ion exchange resin for removal
of anionic and/or cationic impurities or hardness removal,
manganese green sand for iron removal and beds of
particulate material for taste, odour, acid or colour
correction. The description below is directed to ion
15 exchange processes. However, the present invention may
also be used in other purification treatments where liquid
is passed through a bed or beds of particulate materials
not cont~i ni ng ion exchànge resins.
A process of conducting ion exchange on an aqueous
20 liquid consists of a service cycle in which aqueous liquid
for purification is passed through a bed, or several
sequentially arranged beds of different types of ion
exchange materials, to produce a product liquid having the
desired characteristics. The service cycle is followed by
25 a regenerating cycle, in which the ion exchange resin is
regenerated, prior to the ion exchange material becoming
exhausted and thus prior to the ion exchange becoming
inadequate. For a deionising apparatus regeneration is by
flow through the bed of acid or alkali, for cation or anion
30 exchange resins respectively. A water softener exchanges
scale-forming ions such as calcium and magnesium ions with
non-scale forming ions, and regeneration is usually by
using solutions of salts of such ions.
For many types of apparatus regeneration is carried
35 out by flow of regenerating liquid in the same direction
through the bed as the service flow. This is termed co-
flow regeneration. Thus, the flow may be upwards or
CA 022137~6 1997-09-09
W096/28252 PCT/~b5~
downwards through the beds of treatment material. Co-flow
regeneration is adequate for water-softening.
For some apparatus it is advantageous for regeneration
to be conducted counterflow, that is with the regenerant
liquid being passed through the bed in the opposite
direction to the service flow. This is particularly
advantageous for some deionising apparatus, particularly
the type of apparatus sold by the applicant company under
the name "Scion" (trademark) in which the rate of flow of
liquids through the bed is higher than most other apparatus
of this type and the cycle frequency is higher. In such
apparatus improved regeneration is achieved since the resin
at different points in the bed contacts regenerant liquid
having a different, optimum composition.
PRIOR ART
In various known processes, often the different beds
of purification material are carried in separate tanks
which employ individual beds. Conventionally, each tank
may be operated independently of the other.
Z0 To reduce apparatus costs and improve efficiency,
there have also been various attempts at mixing the various
purification materials and inserting them into a single
tank. However, apparatuses which contain such mixed
treatment material have various disadvantages. In
particular some materials need to be replenished more often
than others or regenerated more often than others and once
mixed, the materials cannot be selectively replaced.
It has also been proposed to separate compartments
within a single tank. In ion exchange processes it is
known that to achieve the best results the resin beads
should remain substantially fixed within the bed. However,
the volume of the purification materials used may vary.
For example, it is known that some ion exchange resins
expand or contract, depending upon their level of
ionisation, as they remove impurities from the liquid which
is being purified. Likewise, for particulate filters, in
order to drive out particulate impurities, such beds need
CA 022137~6 1997-09-09
W 096/28252 PCT/~D~ 583
to be backwashed and this requires sufficient space to
allow sufficient expansion of the bed for backwash.
Therefore in order to have a satisfactory apparatus having
more than one bed in a single vessel some flexibility in
~ 5 the size of the separate compartments is required.
In US 3554377, a movable filter-diaphragm for use as
a separator between beds in a single tank multi-layer
apparatus for purification of liquids is disclosed. The
filter-diaphragms are also intended to effect a pre-
filtration of a liquid before entry into the respective bedof treatment material.
The filter diaphragms disclosed in this reference are
free to slide along the inner walls of the receptacle in
which the materials are held, to permit compaction of the
bed in response to pressure of liquid or to permit
expansion of the beds during regeneration or backwash,
whilst still keeping the beds of different filter materials
separate from one another. One filter-diaphragm disclosed
in this reference comprises a layer o~ an inert fabric
material such as woven plastic with a sufficiently small
pore size to provide a filtering function and having an
annular ring or rim of elastomeric material with diverging
flanges to engage with the internal sides of the container.
However because these filter-diaphragms also provide
a filter function, a higher pressure differential will be
formed between sequential beds so that the flow rates of
liquid through the bed will be reduced per unit of energy
to drive the liquid through the apparatus. In addition, a
large pressure drop will occur in the centre of the beds of
filtering material and therefore liquid will tend to flow
along the inner walls of the column and unless there is a
perfect seal at the outer edges of the diaphragm, liquid
will flow around the edges of the diaphragm and inteL ;xing
of neighbouring beds will occur and tend to block with
impurities or particulate purification material. Because
of the high pressure differential such separators may tend
to deform and therefore, they may be unable to provide
CA 022137~6 1997-09-09
W 096/28252 PCT/GB96/00583
satisfactory separation between two beds in addition to
satisfactory slidable movement up and down the internal
walls of the column.
One other filter-diaphragm disclosed in this reference
comprises a disc of plastic foam. However, the pores of
these types of separators tend to block irreversibly with
ion exchange or other purification material. In addition,
for such foam separators to be effective, cutting must be
extremely accurate but even then, such separators are not
satisfactory if the internal cross section of the column is
irregular. Particulate material may escape around the
outer edges of such a separator. This is particular~y a
problem when plastic columns are to be used as the
interiors of plastic vessels tend to be somewhat irregular
so that leakage of particulate material may occur.
Also, in deionisation processes, the regenerants used
may be strong acid or strong alkali. On exposure to such
harsh conditions, foam materials tend to become brittle and
may eventually lose their resilience.
One other known movable separator is known as a
"rolling diaphragm". In a purification column which
includes a rolling diaphragm, a sheet of a porous material
having a diameter greater than the horizontal cross-
sectional area inside the column is arranged between two
separate beds. This type of separator is fixed around its
perimeter to the internal wall at a fixed height within the
column. Such a rolling diaphragm may be subject to a large
pressure differential and in addition because the diaphragm
rolls upwardly or downwardly past its fixed position in the
column it is subject to a large amount of wear and tear and
is liable to break.
SUMMARY OF THE PRESENT INVENTION
The present invention aims to overcome the problems of
the known devices and in addition to provide a useful
separator which can be inserted into the pre-formed plastic
columns conventionally used today. These moulded columns
have a relatively small entry port having a diameter
CA 022137~6 1997-09-09
W 096/28252 PCT/~G~O r~3
considerably less than the internal diameter of the column.
The present invention aims to provide a separator
which can effectively separate two beds but in addition can
move within a column overcoming the problems of the prior
art and which can easily be inserted into a pre-formed
column having an entry port smaller than the cross-
sectional area of the interior of the column in which it is
to be used.
According to a first aspect of the present invention
there is provided a movable separator for use in a liquid
purification column, the separator comprising a flexible
porous container, containing solid particulate separator
material which exerts pressure on the container so that in
use in the column, slidable contact of the container
against the internal walls of the column is effected, the
container where it contacts the internal walls of the
column, comprising resilient material.
The flexible, porous container comprises an inert
fabric material, generally comprising woven or more
preferably moulded plastic mesh. This material should be
substantially unaffected by contact with the regenerating
liquids to be used in a water purification process, and
preferably comprises polyethylene, polypropylene, PVC, PVDC
or polyamide. The most preferred material is Tygan Cloth
or SARAN (trademark of Courtaulds). SARAN comprises PVDC
fibres with a 2/2 twill weave, an air space between the
fibres of 26.3% and pore size 181/567~m. Preferably, the
material does not form any filtering function for
particulate impurities as this causes too large a pressure
drop across the separator which is undesirable. Most
preferably, the material provides substantially no
resistance to flow therethrough. Thus, the pore size of the
pores in the porous material may be any size appropriate to
enable the container to contain the solid particulate
material i.e. to prevent the particulate material from
falling through the pores. Generally the pore size of the
material is at least 50~m or even at least lOO~m.
CA 022137~6 1997-09-09
W 096/28252 PCT/GB~GI'~S'8~
Generally the pore size of the porous material is no
greater than lOmm and preferably no greater than 5mm.
In use, the particulate separator material inside the
container exerts pressure on the side portions of the
container to ensure close contact between the container and
the internal walls of the column, and hence effective
separation between the beds. The contact is slidable
contact such that the separator is free to move upwardly
and downwardly within the column.
The container where is contacts the internal walls of
the column in use, may be formed from solid flexible
material, but it is especially preferred that the portions
of the container which are in slidable contact with the
internal walls of the purification column are porous. This
ensures that in use the pressure drop towards the centre of
the column is kept to a min;~l and more uniform fluid flow
through the column results.
The contact of the movable separator with the internal
walls of the purification column should be such that the
separator is freely slidable up and down the inside of the
column but is sufficiently close to substantially prevent
the passage of particulate material from a lower bed below
the separator to an upper bed above the separator and/or
vice versa. Preferably, in use in the purification column
the sliding fit of the movable separator inside the column
should also restrict flow of liquid between the movable
separator and the internal walls of the column. Thus
contact of the container with the internal walls of the
column is around at least part of the internal perimeter of
the column, preferably with at least 40% of the perimeter,
most preferably at least 60% or even at least 90% of the
internal perimeter of the column, without resulting in a
pressure drop towards the middle of the column. Most
preferably contact of the container with the internal walls
is around substantially the whole internal perimeter of the
column.
CA 02213756 1997-09-09
W 096/28252 PCT/~D~G,/0_~83
The container should be sufficiently large that the
desired volume of particulate material can be held within
the container.
The container of the movable separator of the present
invention comprises a flexible material such that it can be
deformed to be inserted into a purification column through
a small entry port. Particularly when it is an open
container, the container is advantageously substantially
resilient such that it substantially regains its shape once
inside the column. However, if it is not wholly resilient,
the shape of the container can be arranged by inserting a
rod through a port of the column. This is particularly
important for open containers as these may be placed in the
column empty, and the particulate separator material may be
introduced subsequently by pouring through the entry port
of the column. Thus, particularly if the container is
open, preferably it is substantially resilient. However,
if necessary after insertion into the column a rod may be
introduced through a port in the column to lift the side
portions of the container and open the container ready for
receiving the particulate separator material.
Alternatively, the container may be a closed container
such as a porous bag of any shape, which is partially
filled with particulate material prior to insertion into
the column. The bag is formed from flexible material and
its flexibility and the fact that it is only particularly
filled and/or formed from elastic material, together enable
the bag to be inserted through a port having a smaller
diameter than that of the column, even though it already
contains the particulate separator material. After
insertion through the port the container will then lie on
top of a lower bed of particulate purification material
already in the column, the particulate separator material
inside the bag ensuring that the container of the separator
covers substantially the whole horizontal cross-sectional
area of the column, and being in slidable contact with the
internal sides of the column preferably substantially
CA 022137~6 1997-09-09
W096/28252 PCT/GB96/00583
wholly around its perimeter. In this embodiment the part
of the bag which contacts the surface of the bed of
particulate purification material in use forms a base
portion for the container and the parts of the bag which
contact the internal walls of the column in use, form side
portions.
The pressure exerted by the solid particulate
separator material in the container enables the flexible
container to have slidable contact with the internal walls
of the column even though the internal diameter and shape
of the column may be irregular.
When the container is an open container, it may
comprise a base portion and side portions, the side
portions extending upwardly from the base portion to form
a container. In this case, in use the side portions
contact the internal walls of the column. The side
portions may extend above the desired bed depth of
particulate material to no detrimental affect. Generally
the side portions will extend upwardly from the base
portion at least 5 cm and no greater than 40 cm.
The side portions may provide a larger circumference
to the container than the internal circumference of the
column or may extend upwardly and outwardly from the base
portion to enable the container to have adaptable
circumference depending on the internal surface of the
column, or the side portions may be elastic.
It is particularly preferred that the material of the
side portions should be substantially deformable so that
the container may expand slightly (in particular where it
contacts the internal walls of the column) due to the
pressure of the particulate material if the internal walls
of the purification columns are slightly irregular. For
example, Tygan Cloth and SARAN, each as mentioned above
have a degree of deformability in the diagonal direction
but the original shape can be regained. Thus where Tygan
Cloth or SARAN is used to form an open container having a
base portion and side portions, preferably the side
CA 022137~6 1997-09-09
W 096/28252 PCT/GB96/00583
portions are formed so that the Tygan Cloth or SARAN is
cross-cut, the upwardly extending walls having the plastic
strands of Tygan Cloth positioned diagonally, enabling
outward expansion and inward contraction of the side
portions of the container. When the container is open,
the shape and dimensions of the base portion of the porous
material preferably tend towards substantially the shape
and dimensions of the internal horizontal cross-section of
the column in which it is to be used. However, the shape
may vary, for example, if the side portions extending
upwardly from the base portion have sufficient elasticity
to enable them to have slidable contact with the internal
side walls of the purification column, or if they extend
upwardly and outwardly from the base portion as described
above. Preferably however, the shape and dimensions of the
base portion of the porous material are substantially the
same as the internal horizontal cross-sectional shape and
dimensions of the purification column in use. Generally
such columns are cylindrical and therefore the base portion
will be substantially circular.
In this case a similarly shaped top portion may be
provided to form a closed container.
The container may also comprise a reinforcing material
to promote its resilience. In particular where the
container is open and comprises a base portion and side
portions, it may have a reinforcing rim for example at the
periphery of the base portion and/or the upper (open) end
of side portions. Alternatively, reinforcing strips may be
substantially horizontal on a container in use. Such
reinforcement may comprise for example a rubbery or similar
elastomeric material.
The particulate separator material held in the
container may be any particulate material optionally
comprising mixtures of different particulate materials and
in any amount which will exert sufficient pressure to
enable slidable contact of the side portions of the porous
container with the internal walls of the purification
CA 022137~6 1997-09-09
W096/28252 PCT/GB96/00583
column. Generally the average diameter of the particulate
material will be at least 0.5mm, preferably at least lmm or
even 1.5mm. Generally the average diameter of the
particulate material will be no greater than 50mm,
preferably no greater than 25mm and most preferably no
greater than lOmm. If it is desired to increase the weight
of the separator, weights may be added to the container.
Preferably the distribution of the particle size of
the particulate material will be as low as possible so that
the particles are relatively uniformly sized to ensure
substantially consistent resistance to flow of liquid
through the bed of particulate material. Preferably at
least 50% of the particles have a diameter with up to 30%
or most preferably no greater than 10% variance. Suitable
materials are for example gravel or metal particles such as
ball bearings. Mixtures of different particulate materials
may be used. The particle size of the particulate material
may be arranged substantially graded (for example in
layers) such that in use the particulate material closest
to the liquid purification material has a smaller particle
size than that in a layer in the centre of the container.
This helps to prevent passage of purification material into
the movable separator.
Gravel or pebbles are a particularly preferred
suitable particulate material for use in the separator of
the invention. However, if the aqueous liquid purification
process requires strong alkali to be passed through the
movable separator, it is preferred that the pebbles or
gravel should be coated for example with polymeric coating
to increase their chemical resistance.
Preferably the particulate material in the container
has a density greater than the density of the particulate
purification material generally ion exchange material in
the bed below the separator container. Preferably the
density will be greater than 1 g/cm3, more preferably 2g/cm3
and most preferably 5g/cm3, or even above lOg/cm3.
CA 022137~6 1997~09~09
W 096/28252 PCT/GB~G/C~r~3
The amount and density of the particulate separator
material are also dependent upon the pressure required to
- be exerted on the lower bed in the column.
The depth of the particulate separator material is
S such as to form a bed of particulate material in the
container. The bed depth of particulate material will
generally be at least 3 cm, preferably at least 5 cm. Any
depth of particulate material may be provided, depending
upon the height of the purification column and the bed
depth of active purification material, generally ion
exchange resin, which is required. For example the
particulate material in the container may be up to 20cm or
even 30 cm deep.
The invention is particularly advantageous because the
density and amount of particulate material in the container
of porous material can be selected to form a heavy layer.
Thus when positioned above a bed of ion exchange resin in
a column, a movable separator of the invention can enable
free space to be provided in the column but in addition can
effectively fix the bed so that it must remain
substantially stable and cannot mix. It has been found
that during a service cycle, improved performance can be
obtained using ion exchange resin when the resin is held
substantially stable and movement is limited.
The invention is particularly useful in a counterflow
regeneration apparatus and process. It is well known that
for optimum performance when using counterflow regeneration
techniques, there should be no mixing of the resin beads
during any stages of the operational cycle. The advantages
of counterflow deionisation processes are also well known
and the success of such processes is highly dependent on
the presence of an efficient regeneration step. Therefore,
the separators of the present invention can be used to give
enhanced stability to a bed during the regeneration and
service steps and increase the efficiency of the bed,
whilst permitting PYr~n~ion and contraction of the bed
during the operational cycle.
-
CA 022137~6 1997-09-09
W 096/28252 PCT/GB~G/C~
The density and amount of particulate material in the
movable separator can easily be adapted to suit the
particular application. Thus for example where the
regeneration step comprises upward flow, for a higher flow
S rate of regenerant, the container can be arranged to
contain a heavier or more dense bed of particulate material
or a greater volume of particulate separator material, to
ensure stability of the bed and still allow a degree of
expansion of the ion exchange resin bed.
According to a second aspect of the invention, a
movable separator is provided for use in a liquid
purification column, the separator comprising a flexible
porous container, containing solid particulate separator
material which exerts pressure on the container, beneath
lS which is positioned a layer of substantially inert material
having a density below lg/cm3 and in use, in the column,
slidable contact of the separator against the internal
walls of the column is effected.
It is not essential that the container, where it
contacts the internal walls of the column is porous. Thus,
for example the container may comprise a base and side
portions as described above, but in which the side portions
are formed from non-porous, flexible and/or elastic
material such as a rubbery plastic. The use of a layer of
inert material beneath the container ensures that in use,
the pressure of liquid flowing through the movable
separator does not become so great at the internal walls of
the column that purification material is carried past the
sides of the separator. Mixing of neighbouring beds of
liquid purification material is therefore prevented.
The present invention also includes an apparatus for
purification of liquid, the apparatus comprising a liquid
purification column, the column comprising in sequence a
lower bed of liquid purification material, a movable
separator and above the movable separator, an upper bed of
liquid purification material. The movable separator is as
described above. A plurality of beds of liquid
CA 022137~6 1997-09-09
:. ~ ;,,
.. .... ..
13
purification material may also be provided in the column,
optionally, each being separated from the neighbouring bed
by a movable separator as defined above. Preferably the
apparatus is an aqueous liquid purification apparatus.
Preferably the liquid purification materials comprise ion
exchange resin.
The invention also includes a process in which water
for purification is passed through the apparatus described
above, in a service cycle, and in a regenerating cycle,
regenerant liquid is passed through the apparatus.
In this case, the amount and density of the
particulate separator material may be sufficient to
substantially hold down the inert beads to result in a
substantially floating separator, when liquid for
purification is passed through the column.
The density of the substantially inert material must
be lower than the density of the particulate liquid
purification material in the lowar bed and is generally
less than that of water, for example below lg/cm3 and
preferably below 0.9g/cm3 or even 0.8g/cm3. The use of a
combination o~ low density particulate material beneath the
movable separator ensures ease of adjusting the loading of
pressure exerted by the movable separator as not only can
CA 022137~6 1997-09-09
PCT/~b~5/~83
W 096/28252
14
the amount and density of the particulate separator
material be adjusted, but in addition the amount and
density of the low density particulate material can also be
adjusted. Generally, the low density material comprises
inert resin beads but any particulate material having a
density below that of the water purification material in
the lower bed (that is, below the movable separator) may be
used such as hollow spheres or chopped low density plastic.
The low density material may be arranged loose as a bed or
inside a porous divider such as a further porous container
as described above.
Where the particulate separator material is large and
the pores in the container do not prevent carry-through of
ion exchange resin from the ion exchange resin beds above
and below the separator, when positioned in the column, the
apparatus may be used in conjunction with a bed of inert
exchange resin material on one or both sides of the
container. This ensures that any carrythrough of resin is
inert so that the ion exchange beds remain substantially
stable and immobile.
The separator of the invention may optionally be
provided with a honeycomb layer on one or both sides of the
container, especially where inert resin is provided. The
honeycomb layer extends across substantially the whole
cross-sectional area of the column. This substantially
fixes the inert resin and further reduces mobility of the
ion exchange resins and therefore improves the performance
of the separator.
The honeycomb layer may be provided by a layer of foam
which is preferably substantially chemically resistant to
the regenerating li~uids which are to be passed through the
ion exchange column.
Generally at least 60% or even 80% or 90% of the low
density particulate material will have a particle size such
that it will not pass through a mesh having apertures with
a width 0.5mm, preferably it will not pass through a mesh
having apertures with a width lmm. Generally at least 60~
CA 022137~6 1997-09-09
W 096128252 PCT/~5~C~J83
or even 80~ or 90~ of the low density particulate material
will pass through a mesh having apertures with width 20mm
and preferably with width lOmm- The use of inert material
having a particle size greater than that of the particulate
liquid purification material of the lower bed is
advantageous.
It is particularly advantageous for the movable
separator to include a layer of inert material beneath the
container, as it enables the use of up-flow service liquid
purification systems in which in the service flow, liquid
for purification is passed upwardly through the column,
passing firstly through the lower bed of liquid
purification material, then through the low density inert
material and upwardly through the container and upper bed
before leaving the column through an exit port at the top
of the column without intermixing of the beds of
purification material. This is particularly advantageous
as the low density, inert material and amount and density
of the particulate material in the container can be
adjusted so that the apparatus will retain the lower bed in
a substantially fixed position whilst still being allowed
room for expansion. In addition, the inert bed not only
ensures good separation but also contributes to good
distribution of the liquid for purification or regenerant
liquid through subsequent beds irrespective of flow rate.
The regeneration step can be either up-flow or down-
flow, preferably it will be a counter flow, down-flow
regeneration.
The low density material may be for example a cellular
structure in which air is trapped or may be a structure
comprising low density particulate material such as a foam
material in which the low density particulate material is
trapped.
The present invention also comprises a process for
purification of liquids comprising passing liquid for
purification through at least two beds of liquid
-
CA 022137~6 1997-09-09
W 096/28252 PCTIGB96/00583
purification material in a purification column, separated
from one another by a movable separator as described above.
The liquid purification material may comprise for
example, particulate filter material such as carbon,
manganese green sand, garnet, anthracite or sand, or ion
exchange resin which may be weak, strong or mixed anion,
weak or strong cation or a mixed bed resin. Preferably the
liquid purification material is ion exchange resin.
The present invention has been found to be
particularly useful for separating two (or more) beds of
anion exchange resin in particular where one comprises
either weak or mixed base anion resin and a second
comprises strong base anion resin.
Often in a deionisation treatment, beds of both anion
and cation exchange resins are required. There may be one
ion exchange column for anion resins and a separate column
for cation exchange resins or, beds of both anion or cation
may be in the same column. The present invention is
particularly useful for separating two beds of anion
exchange resin because in practice, it is advantageous to
use in a demineralisation apparatus for aqueous liquids
both a weak or mixed base anion resin and strong anion
resin. Weak resins are more easily regenerated requiring
less chemical regenerant than strong resins and will remove
at least some of the impurities in the liquid for
purification. However weak resins will not remove all of
the impurities and so in particular for a deionisation
process, it is necessary to include a bed of strong resin
to ensure removal of all the ionic impurities. It is less
efficient to use only strong resin because regeneration
requires more regenerant and will take longer than for an
equivalent amount of weak resin.
However, conventionally it is difficult to use both
strong and weak or mixed anion resins in the same column
because their densities are too similar to enable operation
of the two beds without inteL i~ing Furthermore, fixed
partitions are undesirable due to eYp~n~ion and contraction
CA 022137~6 1997-09-09
W 096/28252 PCT/GB96/00583
of the anion exchange resin depending upon whether it is in
the ionised or de-ionised form. The present invention
- enables the use of an anion exchange resins comprising weak
or mixed base anion resin in addition to strong base anion
S resin in the same column- In use, liquid for purification
will flow through the weak anion resin, then through the
movable separator and then through the strong base anionic
resin.
The present invention is also useful for separating
two types of cation resin- Cation units often use only one
ion exchange resin type for example a strong cation
exchange resin. However as for the anion exchange resins
discussed above, it is also desirable to use a combination
of weak acid cation ~Ych~nge resin with strong resin. As
explained for the anion resin, since weak resin is more
easily regenerated it is preferable to remove at least some
of the cations using a weak cation resin rather than to
remove all of the cation impurities using strong acid
cationic exchange resin. This ensures more efficient
regeneration and an overall increase in efficiency of the
water purification process.
The invention is also particularly useful for use in
processes which have to be run at high temperatures. Some
ion exchange resins tend to be unsuitable for use at high
temperatures. In addition, since a combination of weak or
mixed resin with strong resin has to be selected with the
resins having relative densities such that the two will
substantially not mix during use. ~he choice of suitable
resins which can be used in conventional processes
therefore is limited and it may be impossible to select the
resins most appropriate for the purification of the
particular liquid for purification- The present invention
overcomes this problem as the separator prevents
intermixing and enables the resin choice to be determined
by the technical consideration of the resin and particular
aqueous liquid source, thus producing increased efficiency.
CA 022137~6 1997-09-09
W 096/28252 PCT/~b5G,~'~3
Expansion and contraction of the beds is still permitted.
The invention is particularly useful for separating a
mixed or weak anion exchange resin from a strong anion
exchange resin where the resin is one which is suitable for
use at high temperatures for example above 30~C or even
above 35~C or 40~C. Thus for a downflow service apparatus,
a cation resin containing column may comprise strong cation
resin positioned beneath mixed or weak cation exchange
resin and separated by a movable separator of the invention
and liquid for purification passes downwardly firstly
through the mixed or weak cation resin and subsequently
through the strong cation resin. Alternatively, the
service flow can be upwardly and the beds of ion exchange
resin in the opposite arrangement. Prior to the present
invention this problem could be overcome by incorporating
a fixed connector. However such a connector does not
operate as a separator and intermixing between the beds
still occurs. Alternatively a stationary separator could
be incorporated in the column and regenerate using a split
flow which reduces operating efficiency. The present
invention overcomes all of these prior art problems.
The present invention enables efficient separation of
two beds of ion exchange material irrespective of their
densities, whllst still enabling sufficient expansion of
the beds throughout the deionisation and regeneration
steps. Thus, the invention enables use of the preferred
ion exchange resin for purification of a particular aqueous
liquid: the most appropriate resins can be selected on
their merits appropriate to a liquid for purification and
irrespective of their respective densities. This results
in considerable benefits to process efficiency.
In addition, because there is no risk of considerable
inte i~ing of the beds which are separated by the movable
separator, ion exchange columns can be packed more fully,
and therefore greater process efficiency results for a
given column size. In conventional processes, sufficient
free space must be left in an ion exchange column to enable
.
} ~
-
CA 022137~6 1997-09-09
W 096/282~2 PCT/GB96/00583
backwashing so that after use and resultant mixing of two
beds of purification material, back-washing could be
- effected in order to reform two separate beds.
There is no need to provide a separate back-wash
facility to the apparatus of this invention. The free
space in a column should therefore be sufficient to allow
~yr~n~ion and contraction of the ion exchange resin at
various stages of the service and regeneration cycles,
depending on the chemical form of the resin but does not
have to be so great as to enable backwash. The free space
may therefore be lower than 20%, or even 15~ or 10% of the
internal volume of the column.
Although the present invention is particularly
directed to deionisation processes, such a movable
lS separator may also be incorporated into water softening
units (for ~Yçh~nge of hardness ions such as calcium and
magnesium and chloride).
If it is decided to incorporate a filter bed
comprising particulate filter bed material in addition to
an ion ~Yc-hAnge resin bed or beds, the apparatus will be
arranged such that in use in a service flow, aqueous
liquids for purification will pass first through the filter
bed and subsequently through ion exchange resin. It is
desirable to leave sufficient space so that the filter can
be backwashed in situ, without having to remove all of the
ion exchange material. Thus for example the separator can
be used to separate an ion exchange resin from a filter bed
comprising for example sand. Generally, in the service
flow, liquid for purification flows downwardly through the
beds of purification material. Therefore, where both a
particulate filer material and ion exchange material are
; provided, in a purificati~on column, preferably the ion
exchange resin will be at the bottom of the column and the
filter bed will be arranged above the ion exchange resin.
Thus, the density and weight of the separator can be
adjusted so it exerts sufficient pressure on the bed below
to substantially pack the lower bed comprising ion exchange
CA 022137~6 1997-09-09
W096/28252 PCT/~br'!~C'83
resin and permit the upper bed to settle so that there is
free space above the bed and on backwashing, the density of
the separator is sufficient to substantially retain packing
of the lower bed so that the filter bed has sufficient free
space to be effectively backwashed. Similar adjustments
can be made depending upon the required degree of the bed
beneath the separator and the free space or expansion space
required by the beds either side of the separator.
Generally, in use, in the service flow, liquid for
purification passes downwardly through beds of particulate
purification material. Thus, in a purification column or
other vessel, the beds of different particulate material
will be arranged such that the material which the liquid is
intended to pass through first is at the top of the
apparatus, the beds for subsequent treatment being beneath
it in sequence, preferably each sequential bed being
separated from a neighbouring bed by a movable separator of
the present invention. A column, or other purification
apparatus may therefore contain a plurality of movable
separators. The apparatus and processes of the present
invention are particularly directed to counterflow ion
exchange processes where in the service flow liquid for
purification flows downwardly through the beds and in the
regeneration and/or cleaning cycle, regenerant and/or
backwash liquid flows upwardly through the beds.
In accordance with a further embodiment of the
invention, a collector/distributor may be incorporated in
the movable separator and if desired, this permits split
flow processes and also enables the use and regeneration of
both anion or cation exchange resins to be used in the same
vessel. In this case, the collector will be provided with
a grommet or other means to allow the collector/distributor
to move with the movable separator. Therefore the
present invention is particularly advantageous because it
enables the use of a single purification column to fulfil
all of the requirements of a water purification system and
it may therefore include beds of anion exchange resin,
CA 022137~6 1997-09-09
W 096/28252 PCT/GB9''005X3
cation exchange resin, filter beds etc in the same vessel.
Thus, very tall columns may be used which require less
- floor space. For example, the height of the vessels may be
above two metres, even above 2.5 or 3 metres. The floor
space required can therefore be reduced considerably to
around lm2 or even 0.5m or 0.25m or below for an ion
exchange system comprising a volume of ion exchange resin
and other filter material of from 1 or even 2m3.
The invention also has the additional advantage that
a fast flow rate in both service flow and in particular
also regeneration flow rate can be permitted without undue
mixing of a bed positioned beneath a separator of the
present invention. In particular in counter flow
processes, regeneration rate can be increased without undue
mixing of a bed as the movable separator can provide a
stabilising weight above the bed whilst still enabling
expansion/contraction of the bed depending upon its stage
of ionisation. The invention is particularly useful for
flow rates in the service flow of the order of 80m3/m2/hour
although rates in the range 20 to 80 m /m2/hour may be used.
The regenerating flow is preferably at a rate of 20-
24m3/m2/hour through the ion exchange resin beds although
the rate may be as low as 4 or 5 m3/m2/hour.
The lifting of conventional constraints on the
purification of liquids has a significant effect on the
cost efficiency of a purification process.
The present invention enables processes to be carried
out at higher flow rates but also increases efficiency of
the process in particular of the regeneration step.
Therefore, the overall time required for removal of unit
concentration of impurities from a unit volume of liquid
for purification and regeneration of the system is reduced.
The overall time required for an effective cycle is
therefore reduced. In the current climate of water
shortages and the high environmental cost of the use of
large quantities of water, any saving to be made on use of
recycled water is therefore highly advantageous.
CA 022137~6 1997-09-09
W 096/28252 PCT/GB~G~C583
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 to 4 illustrate liquid purification columns
in which different arrangements of different purification
materials are shown.
Figure 5 illustrates a deionisation process
incorporating movable separator according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EM~ODIMENT
In each of Figures 1 to 4, 1 represents the
purification column, 2 represents the porous material of
the movable separator and 3 represents the particulate
material of the movable separator. In Figure 1, 4
indicates weak acid cationic exchange resin and 5
represents strong acid cationic exchange resin. In the
service flow, aqueous liquid for purification enters the
column through port 6 and flows downwardly through the weak
acid cationic exchange resin, the movable separator and
subsequently through the strong acid cationic exchange
resin to exit the column through port 7. During the
regeneration, regeneration liquid enters port 7 and flows
upwardly through the column through strong acid cation
resin, through the movable separator, through the weak acid
cation resin and exits the apparatus through port 6. 8
indicates free space within the vessel enabling expansion
and contraction of the beds depending upon their degree of
ionisation. If desired, a further movable separator may be
incorporated upon bed 4 to help prevent mixing of the bed
on rapid regeneration flows. Figure 2 represents the
regeneration and backwash flow of a column in which 9
represents a sand filter bed during regeneration and
backwash and 10 represents strong acid cation exchange
resin which is expanding on regeneration. The movable
separator might move very slowly upwards to allow freeing
of the bed but does not enable significant mixing in the
bed whilst allowing sufficient free space in 9 that
effective backwash of the filter bed can be attained. The
regenerant is flowing through entry port 11 upwardly
CA 022137~6 1997-09-09
W 096/28252 PCT/GB96/00583
23
through the bed 10 and through filter bed 9 to exit from
port 12.
In Figure 3, 13 represents a bed of anionic exchange
bed resin and 14 represents a strong acid cation exchange
resin bed for a water softener apparatus. Aqueous liquid
for softening flows inwardly through port 15, upwardly
through the bed 14, through movable separator and
subsequently through the anion trap 13 before exiting the
column through port 16. On regeneration, acid regenerant
for the strong acid cation bed enters the column through
port 15 and flows upwardly until it reaches the
collector/distributor 17 positioned in the particulate
material 3 of the movable separator. Likewise, salt
solution for regenerating the ionic resin flows downwardly
through port 16 through the ion exchange bed 13 until it
reaches the distributor/separator 17 in the particulate
material of the movable separator. Both regenerating
liquids having regenerated the anionic and cationic resins,
respectively then flow through the collector distributor 17
to exit the column via line 18.
In Figure 4, 19 represents a bed of anionic exchange
resin and 20 represents a bed of cationic exchange resin.
During service flow, liquid for purification enters port 21
and flows upwardly through bed 20, through the movable
separator and through bed 19 to exit the column through
port 22. During regeneration, acid for regenerating the
cationic exchange bed enters the column through port 21 and
fills upwardly through bed 20 and is removed via collector
23 to exit the column along line 24 and base for
regenerating the anion resin enters the apparatus through
port 22, flows downwardly through bed 19 and is removed by
collector 25 to exit the apparatus along line 26.
Figure 5 shows a cation column 27 and an anion column
28. In column 27, a bed of sand filter material 29 is
provided. A basket 30 formed from SARAN mesh contains
gravel 31 (Grading 2-3). A bed 32 of inert resin having a
specific gravity 0.535 and particle size 1.3-1.7mm, a bed
CA 022137~6 1997-09-09
W 096/28252 PCT/~D~G/OOS83
24
33 of cation exchange resin, and a bed 34 of crushed
granite (grading 2-3) and is provided in the column 27.
The crushed granite bed 34 is provided so that the ion
exchange resin in bed 33 (which has smaller particle size)
5 is substantially prevented from escaping from the column
through the port 35. A sand and resin trap 36 prevents any
particulate material which escapes from vessel 27 from
being passed into vessel 28. In vessel 28, bed 37 presents
a bed of weak base anion exchange resin. As before, 30
10 represents the cross section of a basket formed from SARAN.
Stainless steel ball bearings 38 which are substantially
spherical and having an average diameter of 3mm are
provided above a bed of inert resin having a density lower
than that of water and lower than that of the water
15 purification material (strong base anion resin) in bed 39
below.
In use, in a service cycle, water for purification
passes along line 40 enters column 27 through port 41 and
passes downwardly through the free space in 42, through
20 sand filter bed 29, the movable separator comprising
container 30 and inert bed 32 and subsequently through the
bed of cation resin 33 prior to passing through inert bed
34 to exit the column through port 35. Liquid for
purification having passed through this column, it proceeds
25 along line 43, through the sand and resin trap 36 and
subsequently a long line 34 prior to entering column 28
through port 45. It then passes through free space 46,
through the bed of weak base anionic exchange resin, 37 and
subsequent through the movable separator comprising the bed
30 of stainless steel particles in container 30 and bed of
inert low density material 32. It then passes through bed
39 strong base anion resin prior to leaving column 28 r
through port 47, along line 48.
In the regeneration cycle, regenerant enters column 28
35 through port 47 and passes upwardly through the column
where it is passed out of the column through port 45 and
then a valve 49 is lead away along line 50. Either
CA 022137~6 1997-09-09
W 096/28252 PCT/GB96/00583
simultaneously, or sequentially, regenerant is passed along
line 51 and via valve 52, passes into column 27 through
port 35. It passes upwardly through the cation exchange
column past the movable separator and sand filter and then
leaves the vessel through port 41 and is lead away along
line 40.
During the service cycle as the beds of ion exchange
material become exhausted, their volume changes and the
movable separator comprising the container and inert resin
bed moves inside the respective columns so that in each
case, the change in volume of bed beneath the separator can
be accomodated, whilst still being held substantially fixed
and without placing undue pressure on the resin as its
volume changes. During regeneration, as the volume of the
lower beds changes, the movable separator moves again
inside the column. An effective separation of the beds
either side of the movable separator is provided, even
though the internal surfaces of the plastic columns 27 and
28 have irregularities.
