Note: Descriptions are shown in the official language in which they were submitted.
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FILTER FOR REMOVING SOLIDS FROM LIQUIDS
FIELD OF THE INVENTION
THIS INVENTION relates to filters for removing solids from liquids. The
filter is particularly, but not exclusively, intended for the purpose of
removing solids
from water in the purification of the water for drinking and other purposes
such as for
use as boiler water.
BACKGROUND TO THE INVENTION
Water which is, without treatment, usable for drinking, agricultural or
industrial purposes is in extremely short supply. The sea, which constitutes
the most
abundant source of water, carries a heavy load (30000 to 40000 parts per
million) of
dissolved solids. Depending on the particular geographic region it also
carries a
load of silt and/or sand in suspension. It must therefore be filtered and
desalinated
before it can be used for any purpose whatsoever.
Water from rivers, lakes and underground sources is usually
contaminated with dissolved solids and with solid material which is suspended
or
dispersed in the water. There can in addition be biological material requiring
micro
or ultra filtration to remove it.
The object of the present invention is to provide a filter which is an
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improvement over known filters.
BRIEF DESCRIPTION OF THE INVENTION
According to one aspect of the present invention there is provided a
filter which comprises a casing having an inlet for water to be filtered, a
first stage
filter within the casing for removing solid material from the water entering
the casing
and a second stage filter within the casing to which the water flows from the
first
stage filter, and which second stage filter includes reverse osmosis membranes
for
performing ultra filtration or micro filtration and/or for removing solids
that are
dissolved in the water.
In the preferred form said casing is of elongate form, said first and
second stage filters being adjacent to one another in the direction of the
length of
said casing.
According to a further aspect of the present invention there is provided
a filter comprising an elongate casing bounding an elongate space, an inlet to
said
space for water to be purified, an outlet from said space for permeate water,
an
outlet from said space for brine, a first stage filter in said space for
removing solids
from the water which has entered said space through said inlet, a chamber
forming
part of said space and a second stage filter, the second stage filter
including reverse
osmosis membranes for performing ultra filtration or micro filtration and/or
for
removing solids that are dissolved in the water, the first stage filter, the
chamber and
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the membranes being positioned so that water flows in the direction of the
length of
the casing to pass through said first stage filter to said chamber and through
the
second stage filter to said outlets from the chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show how
the same may be carried into effect, reference will now be made, by way of
example,
to the accompanying drawings in which:
Figure 1 is a diagrammatic section through a filter in accordance with the
present invention, Figure 1 also showing the piping connected to the filter;
Figure 2 is a front view of a disc of the filter of Figure 1, Figure 2 being
to a
larger scale than Figure 1;
Figure 3 is a section through the disc on the line III-III of Figure 2;
Figure 4 is a rear view of the disc;
Figure 5 is a view, to a larger scale than Figures 2 to 4, of a spiral flow
guide;
Figure 6 is a section, to a greatly exaggerated scale, illustrating the manner
in
which a part of the filter operates;
Figure 7 is a pictorial view of a reverse osmosis cartridge;
Figure 8 is a section through a further form of filter;
Figure 9 is an end view of the filter of Figure 8;
Figure 10 is an "exploded" diagrammatic view of the filter of Figures 8 and 9;
Figure 11 is a pictorial view, to a larger scale, of part of the filter of
Figures 8
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to 10;
Figure 12 is a section through another form of filter;
Figure 13 is an end view of the filter of Figure 12; and
Figure 14 is an "exploded" diagrammatic view of the filter of Figures 12 and
13.
DETAILED DESCRIPTION OF THE DRAWINGS
The filter shown in Figure 1 is designated 10 and comprises a plurality
of porous pipes, the pipes being designated 12. Each pipe 12 has a hairpin
bend 14
therein, and the ends of the pipes are attached to a disc 16 which fits in a
cylindrical
casing 18. Seals (not shown) are provided between the casing 18 and the disc
16,
the seals fitting in the grooves 20 (see particularly Figure 3) which are
formed in the
outer periphery of the disc 16.
Opposite ends of the casing are closed by end caps 22 and 24 which
are held in place by two part locking ring structures 26. The outer ring 28 of
each
locking ring structure 26 is embedded in the wall of the casing 18 when the
casing is
manufactured using glass fibre reinforcing and resin. The inner ring 30 is in
the form
of a removable split ring which is decreased in diameter before being inserted
into
the ring 28. The inner rings 30 can be removed by reducing their diameters and
sliding them out of the casing 18 thereby to release the end caps.
2p O-rings (not shown) seal between the end caps 22 and 24 and the
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casing 18, the O-rings being in grooves 32 and 34 of the end caps 22 and 24.
The end cap 22 and the disc 16 define a chamber 36 which contains
the pipes 12. A tube 38 extends through the end cap 22, across the chamber 36
and
terminates in communication with a central bore 40 of the disc 16. A bore 42
passes
through the end cap 22 and communicates with the chamber 36. A pump 44 is
connected to the bore 42 by a pipe 46 and feeds the water to be filtered to
the
chamber 36 from a source 48. The pump 44 is also connected to a reservoir 50
of
clean, filtered water. Valves 52, 54 enable filtered or raw water selectively
to be
pumped by the pump 44.
The disc 16 has bores 56 therethrough, each end of each pipe 12
communicating with a respective bore 56 and the pipes hanging in U-formation
below the disc 16 in the chamber 36. The bores 56 are not arranged axially but
at an
angle (see Figures 2 to 4) so that water entering the conical vortex chamber
designated 58 formed in the upper face of the disc 16 swirls in the chamber
58. As
will be seen from Figures 2 and 4 the bores 56 are arranged in a spiral array.
A spiral flow guide 60 is integral with, or secured to, the disc 16 and is
within the vortex chamber 58. The guide lies within the peripheral flange 62
that
protrudes from the main body of the disc 16.
The chamber 58 constitutes one end portion of the space designated
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64 which is bounded by the disc 16 and the end cap 24.
Within the space 64 there is a hollow envelope 66 comprising two
sheets of membrane material through which water can permeate. The two sheets
are welded or otherwise secured together around their peripheries. Any type of
membrane material can be used. For example ultra filtration membranes, micro
filtration membranes or reverse osmosis membranes can be employed. When the
sheets are welded together two tubes 68 and 70 are welded in. The tube 68
extends
from the envelope 66, through the walling of the casing 18 to a shut-off valve
72.
The valve 72 is connected to a source 74 of air or water under pressure.
The tube 70 passes through a central bore 76 of the end cap 24,
emerges from the casing 18 and is connected to a valve 78. A plurality of
side-by-side envelopes 66 forming a pack can be provided. Spacers 80 inside
the
envelopes 66 and further spacers (not shown) between the envelopes 66 prevent
collapse of the envelopes in normal operation and also prevent excessive
expansion
of the envelopes 66 when they are internally pressurized.
An outlet bore 82 for water containing any last remaining solids passes
through the end cap 24. A pipe 84 leads from the bore 82 to a T-piece 86. The
other
pipes which connect to the T-piece are designated 88 and 90. The pipe 88 leads
to
a valve 92 and the pipe 90 to a valve 94.
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Between the valve 94 and the pump 44 there is a T-piece 96. A valve
98 is connected between the pipe 46 and the T-piece 96. A branch pipe 100
leads
from the pipe 46 to a valve 102. The tube 38 is connected by a pipe 104 to a
valve
106.
In use water containing solids that are to be filtered out is withdrawn
from the source 48 by the pump 44 and fed under pressure to the chamber 36 via
the T-piece 96, the valve 98 and the pipe 46. The pipes 12 filter out the bulk
of the
solids in the water as will be described hereinafter.
The water which penetrates the walls of the pipes 12 through the pores
in the pipe walls enters their interiors, flows along the bores of the pipes
12, enters
the bores 56 and then flows into the vortex chamber 58.
The angle at which the bores 56 enter the vortex chamber 58, and the
provision of the spiral guide 60, promotes swirling of the water in the vortex
chamber
58 and in the part of the space 64 immediately above the vortex chamber 58.
The valve 106 is fully open at start-up and the pressure in the space
64 causes an initially strong water outflow through the central bore 40, tube
38 and
pipe 104. This results in the creation of the vortex at the centre of the
chamber 58.
The bulk of the solids not filtered out by the pipes 12 enters the bore
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40. It will be understood that all the water that enters the bore 40 is
flowing to
waste. The flow rate through the valve 106 is thus adjusted after start up
until the
minimum outflow of water is obtained consistent with the continued existence
of the
vortex. By adjustment of this flow rate it is possible to achieve a flow
pattern in which
the so-called overflow vortex which normally exists co-axially with the main
vortex is
suppressed. Experimental work has shown that the main vortex extends a
distance
above the disc 16, steadily diminishing in strength and eventually becoming
undetectable. Above the main vortex there is an upward flow of water but
little or no
overflow vortex capable of carrying particles upwardly with it.
The final stage in the filtering process takes place when the water
permeates through the membrane material constituting the envelopes 66. Solid
particles remain on the outside of the envelopes 66 and water which is
substantially
devoid of solid particles flows through the tube 70 to the valve 78 and then
to a
storage reservoir, water main or point of use.
The pressure at the outlet bore 76 of the filter 10 is monitored and,
when a pressure loss of sufficient magnitude is detected, an automatic
cleaning
sequence is initiated.
The main part of the cleaning sequence involves closure of the valves
52, 98, 92 and 106 for a brief period and opening of the valves 54, 94 and 102
for a
brief period. This results in clean water being drawn from the reservoir 50
and
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pumped by the pump 44 through the valve 94 to the space 64. The increase in
pressure in the space 64 results in a commensurate increase in pressure in the
pipes 12. The reverse flow through the pores of the pipes 12 cleans the pipes
as will
be described hereinafter. Cleaning of the pipes 12 is thus effected by
temporarily
increasing their internal pressure above their external pressure.
The material dislodged from the outside of the pipes 12 exits from the
chamber 36 via the bore 42, pipe 100 and valve 102.
The reverse flow of water causes the vortex in the chamber 58 to
collapse. When the valves 52, 98, 92 and 106 re-open, and valves 54, 94 and
102
re-close, the valve 106 must be fully opened and then subsequently adjusted to
re-establish the vortex.
Because clean water is being fed to the space 64, flow of water
through the envelopes 66 is not interrupted during the cleaning procedure for
the
pipes 12.
To clean the envelopes 66, the valve 72 is opened briefly, typically for
a second or less, and hence the envelopes 66 are inflated by air or water
under
pressure. Simultaneously the valve 78 is closed briefly. The external spacers
between the envelopes 66 prevent them over inflating and bursting. The sudden
expansion of the envelopes dislodges solid material which has adhered to the
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outside thereof and the general flow from the space 64 to the bore 82 carries
away
the dislodged solid material which exits through the valve 92.
It will be understood that there is a tube 68 and a tube 70 for each
envelope 66. The tubes 68 and 70 lead to common manifolds.
The pipes 12 are of rubber, a rubber compound or a synthetic plastics
material which has a surface to which the solid material will not adhere
strongly. The
type of surface required can be compared to that of a motor vehicle tyre.
Whilst mud
will adhere to the tyre, the bond is not strong and the mud can, if dry,
easily be
knocked off or, if wet, can easily be washed off.
Each pipe 12 has therein a plurality of pores which extend from the
outer surface of the pipe to the inner surface of the pipe. One such pore,
designated
108, is shown in Figure 6. The pore 108 is, at the external surface of the
pipe, wider
than at the internal surface of the pipe. Preferably the diameter at the outer
end of
the pore is in the region of five microns and at the inner end of the pore is
of the
order of one micron or two microns. The pipe wall thickness is about 15mm.
Grains of solid material, designated 110 in Figure 3, lodge in the pores
108 and, within a short period of time after start up (from a few seconds to a
few
minutes), each pore 108 has therein a mass of grains which act as a filter
allowing
water to permeate into the hollow interior of the pipe 12 but preventing other
solid
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material from passing through. It will be understood that as the water passes
through the filter constituted by the grains in each pore 108, the solid
material that
was entrained therein is deposited onto the outer surface of the pipe 12. This
accumulation of solid material is designated 112 in Figure 6. When flow in the
reverse direction through the pores 108 occurs as described the accumulations
of
solid material are swept away.
It has also been found that the pressure drop across each pore 108
should not be excessive. If the pressure drop is excessive the grains 110 in
the
pores 108 and the solids accumulation 112 are sucked into the pores 108 with
such
force that it becomes difficult to dislodge the accumulation 112 of material.
The
pores 108 are thus blocked and flow through the filter from the pipe 46,
through the
pores 108 in the pipes 12 to the hollow interiors of the pipes and thence to
the vortex
chamber 58 drops significantly.
The envelopes 66 can be replaced by a spirally wound membrane, for
example, a reverse osmosis membrane in the form of a cartridge 114 as shown in
Figure 7. Such a filter will be described in more detail with reference to
Figures 12,
13 and 14.
The cartridge 114 comprises a central pipe 116 around which reverse
osmosis packages 118 each comprising two sheets 120, 122 of complex polymer
and an intervening spacer 124 are wound. The pipe 116 has holes 126 in it, the
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holes being in rows extending along the pipe. Water in the permeate passages
designated 128 enters the pipe 116 through these holes. The salt retention
passages are designated 130.
Two sheets 120 and 122 are welded together around three of their
edges to form each package 118. The fourth edges are not welded together but
secured by adhesive to the pipe 116 on opposite sides of a row of holes 126 in
the
pipe 116. Thus each row of holes 126 is in communication with the permeate
passage 128 of a respective package.
In Figure 7, simply for illustrative purposes, the membrane sheets 120
and 122 of the top package 118 are shown separated so that the spacer 124 can
be
seen. The other packages 118 are shown as having the edges of the sheets 120
and 122 welded togther so that the spacer 124 is concealed.
The number of packages 118 used depends on the number of rows of
holes 126 because each package must be positioned so that its permeate passage
128 communicates with a respective row of holes.
Once wound onto the pipe 116, the membrane sheets 120 and 122 of
each package 118 are in face-to-face contact with the sheets 120 and 122 of
the
adjacent packages 118.
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Once all the packages 118 have had the inner edges of their sheets
120 and 122 adhered to the pipe 116, the packages are wound tightly around the
pipe 116 and then taped to prevent them unwinding. An outer sleeve (not shown)
is
then provided to prevent the packages 118 bursting when pressure is applied to
the
sheets 120 and 122 upon feed water being introduced into the cartridge 114.
The
outer sleeve fits into the casing 18.
It will be understood that the passages 130 are open at both axial ends
of the wound cartridge.
The cartridge is used in conjunction with two end caps designated 132
and 134. The end cap 132 comprises a disc 136 and a flange 138 which extends
around the periphery of the disc 136. The cap 132 is at the end of the
cartridge from
which the brine stream emerges. The disc 136 has in it a central hole 140
which
registers with the pipe 116 and a plurality of holes 142 through which the
brine
stream flows. There is a gap of, for example, two to four centimetres between
the
end of the cartridge and the disc 136. The function of the end cap 132 is to
cause a
back pressure immediately adjacent the exit ends of the brine passages. The
axes
of the holes 140, 142 are parallel to the axis of the pipe 116.
The end cap 134 is at the inlet end of the cartridge. It comprises a disc
144 having a central hole 146 which registers with the pipe 116 and a
plurality of
holes 148 between the hole 146 and a peripheral flange 150 that extends around
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the periphery of the disc 144. The disc 144 can be against the end of the
cartridge
or up to four centimetres from the cartridge.
The axes of the holes 148 are not parallel to the axis of the pipe 116
but are at an angle to it. This results in the discrete streams of water which
pass
through the holes 148 and impinge on the end of the cartridge 114 doing so at
an
angle and not along paths parallel to the pipe 116. The orientation of the
holes is
such that the streams swirl in the same direction as the packages are wound.
It will be understood that the cartridge 114 is positioned with the end
cap 134 adjacent the disc 16 and the end cap 132 at the other end of the
casing 18
adjacent the end cap 24.
Turning now to Figures 8 to 11 this illustrates a filter 152 which
comprises a casing 154 in which there is a membrane cartridge 114 of the type
described with reference to Figure 7 and a pre-filter designated 156. The
prefilter
156 comprises three cylinders 158 including walls of mesh screening material.
The
cylinders 158 are in a chamber 160. The inlet to the chamber 160 is designated
162. The water flows through the walls of the mesh cylinders 158 into the
interiors
of the cylinders and from the interiors of the cylinders 158 to a further
chamber 164
via bores 166. The chamber 164 is bounded on one side by a disc 168 on which
the
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cylinders 158 are mounted and in which the bores 166 are formed and on the
other
side by the end cap 134 of the cartridge 114.
The brine outlet from the cartridge 114 is designated 170 and the
permeated water outlet is designated 172, these being in an end cap 174.
The cartridge 114 and disc 168 are held in place by spacers
designated 176, 178 and 180. The inlet 162 is in an end cap 182, there being
ring
structures 184 and 186 for holding the end cap 182 and the end cap 174 in
place.
Piping generally designated 188 connects the interiors of the cylinders
158 to an outlet 190 in the end cap 182. A waste pipe 192 leads from the
chamber
164 through the end cap 182 to waste.
During normal operation water with solids entrained in it enters the
filter through the inlet 162, flows through the mesh cylinders 158, through
the bores
166, across the chamber 164 and thence into the salt retention passages of the
cartridge 114. Permeate emerges through the outlet 172 and brine emerges
through the outlet 170.
To clean the filter, water under pressure is supplied to the outlet 172,
the water flowing from the permeate passages through the membranes to the salt
retention passages. On emerging from the salt retention passages into the
chamber
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164, some of the water can flow to waste through the pipe 192.
The remainder of the water flows through the bores 166 into the
cylinders 158. A portion of the water entering the cylinders 158 flows through
the
mesh to clean the outside surfaces of the cylinders. The remainder of the
water
flows through the piping 188 to the outlet 190 carrying with it solid material
which
had previously passed through the mesh of the cylinders 158.
The piping shown in Figure 1 is modified to enable a cartridge to be
cleaned by removing the tube 68 and connecting the valve 72 and water source
74
directly to the bore 7fi. The valve 78 is closed whilst membrane cleaning
takes
place.
Turning finally to Figures 12, 13 and 14 this illustrates a filter similar to
that shown in Figure 1 but which has a cartridge 114 in place of the envelopes
66.
Furthermore it is similar in construction to the filter of Figures 8 to 11 but
in place of
the mesh cylinders 158 it has pipes 12 as described with reference to Figure
1.
The end cap 134 of Figure 14 is shown as having a pattern of holes
that differs from that shown in Figure 10. Otherwise, where applicable, like
reference numerals have been used in Figures 12, 13 and 14 on the one hand and
8
to 11 on the other hand.
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The filter of Figures 12 to 14 is cleaned in the same way as described
above in relation to the filter of Figures 8 to 11.
Filters which include the vortex chamber 58 are operated in a vertical
position as shown in Figures 1 and 12. The filter of Figures 12 to 14 hence
has to
be operated in a vertical position. The filter of Figures 8 to 11 can be
operated
horizontally.
The pipes 12 can remove all solids above twelve microns in size. The
filter cylinders 158, depending on the mesh used, remove all solids above
about 20
micron. The type of prefilter selected depends on the solids load of the feed
water
and the desired final water quality.
It is possible, in place of the hoses 12 and the cylinders 158, to use a
disc filter, preferably a self cleaning disc filter, or any other type of
filter which will
remove solid material down to the requisite size before the water flows to the
cartridge 114 or envelopes 66 for ultra or micro filtration or for the removal
of
dissolved solids.
If small balls of a rubber-like material are placed in the chamber 160,
these are displaced by the flowing water and tend to "bounce" around in the
chamber keeping the solids in suspension and thus assisting in preventing
clogging
of the filter.
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It is also possible to clean membranes by suddenly closing a valve in
the permeated water pipe. The shock wave passing in the reverse direction
shakes
loose solids in the salt retention passages. A similar effect can be obtained
by
feeding air under pressure into the permeate water pipe.
It is also possible to provide electrical coils around the cartridge 114 as
described in the specification of PCT application PCT/GB9810054 (WO 98/30501 )
for the purpose of enhancing the performance of the cartridge. In Figures 8
and 12
the coils are designated 194, 196 and 198. They are embedded in the walls of
the
casing as the casing is fabricated.
