FIELD OF THE INVENTION
This invention relates to the separation of solid particles
from a liquid in which they are dispersed.
BACKGROUND TO THE INVENTION
To remove fine, solid particles a few microns in size from
water (or any other liquid) it is conventional to use semi-permeable materials.
The materials used are porous to water molecules but the pores are sufficiently
small to prevent solid particles passing through. The materials perform micro or
ultra filtration depending on their pore size.
Conventionally a filter based on such material comprises
an elongate core pipe which has rows of holes along it. Elongate leaves of semi-permeable
material having one open side, but otherwise being in the form of sealed pockets,
are fixed to the pipe with their open edges in communication with the rows of holes.
There are mesh-like spacers between the pockets and in the pockets. The sealed pockets
are wound tightly about the pipe, and the wound unit is slid into an elongate outer
When water with entrained solid particles flows into the
casing, it enters solids retention passages bounded between the leaves, the spacers
between the pockets being in the solids retention passages. The water, but not the
solids, permeates through the semi-permeable material into the pockets and thence
to the pipe via the open edges of the pockets and the rows of holes.
After a period of use, the filter becomes blocked, or at
least the flow rate decreases to such an extent that it is necessary to clean the
filter. This is achieved by opening a valve which controls a waste exit from the
casing, and feeding flushing water under pressure into the casing to sweep the water
in the casing, and the solid particles, out of the casing through the waste exit.
JP 09 313899 A
Patent Abstracts of Japan, 1998, no. 04, 31 March 1998
) all describe methods of flushing filter units of the type described.
The object of the present invention is to provide an improved
method of operating a filter unit and an improved filter installation.
BRIEF DESCRIPTION TO THE INVENTION
According to one aspect of the present invention there
is provided a method of operating an upright filter unit which includes a membrane
comprising a permeate pipe and water permeable leaves through which water passes
to reach said permeate pipe, the method comprises feeding raw water to the lower
end of the unit, extracting permeate water from the lower end of the unit, and maintaining
an above atmospheric pressure in the upper end of the unit by means of a permanent
connection to a supply of gas under pressure.
The gas, for the sake of economy, will normally be air
but other gases, could be used.
To clean the membrane the method of operation comprises
terminating the flow of raw water, opening a waste flow line communicating with
the lower end of the unit and instituting flow of flushing water to the upper end
of said unit whilst maintaining the supply of gas to the upper end of the unit so
that water, gas and solid particles flow from said unit through said waste flow
The pressure can, during flushing of the filter unit, be
maintained at a constant valve or can pulstae.
The present invention also provides an installation comprising
an upright of filter unit which includes a membrane comprising a vertical permeate
pipe and water permeable leaves through which water passes to reach said permeate
pipe, an inlet at the lower end of the unit for raw water, an outlet at the lower
end of the unit for permeate, valve means for closing-off the supply of raw water,
an inlet at the upper end of the unit, a supply of gas under pressure which is permanently
connected to the inlet at the upper end of the unit whilst the unit is operating
to separate liquid from entrained solids, a flushing water flow pipe leading to
the inlet at the upper end of the unit, valve means for normally closing said flushing
water flow pipe and which valve means can be opened to connect said flushing water
flow pipe to a source of flushing water under pressure when cleaning is to be undertaken,
and a waste outlet at the lower end of the unit for through which flushing water
and solid particles leave the unit.
The filter unit within the installation may consist of
a membrane comprising a permeate pipe and water permeable leaves through which water
passes to reach said permeate pipe, the membrane having an end cap at each end thereof,
and a casing formed in situ by winding resin coated fibres around the membrane and
The fibres are preferably in the form of glass fibres but
other fibres such as carbon fibres and Kevlar fibres can be used.
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;
DETAILED DESCRIPTION OF THE DRAWINGS
- Figure 1 is a section through a filter unit in accordance with the present invention;
- Figure 2 is an "exploded" view of the filter unit of Figure 1;
- Figures 3 and 4 are pictorial views of opposite sides of a filter installation;
- Figure 5 and 6 are side elevations of opposite sides of the filter installation;
- Figure 7 is a top plan view of the filter installation;
- Figure 8 and 9 are opposite end views of the filter installation; and
- Figure 10 is a circuit diagram of the filter installation.
The filter unit 10 illustrated in Figures 1 and 2 comprises
an elongate, vertical, perforated core pipe 12 around which elongate leaves 14 (Figure
2) are wound. Each leaf 14 is in the form of a sealed pocket and is fabricated using
semi-permeable material which permits water but not solid particles to pass through
it. The inner edge of each pocket is open and it is this edge that is attached to
the pipe 12. The pockets communicate with the interior of the pipe 12 via the multitude
of perforations in the pipe 12. The construction of the pipe 12 and leaves 14 is
conventional. In accordance with conventional nomenclature in the art, the structure
comprising the pipe (designated 12) and water permeable leaves (designated 14) will
be referred to as a "membrane". The membrane is designated 16.
The filter unit, as illustrated in Figure 1, further includes
an end cap 18 at the lower end thereof. The end cap 18 has a central socket 20 which
receives a tube 22. The tube 22 penetrates into the pipe 12 and connects the end
cap 18 to the pipe 12. An outlet bore 24 in the end cap 18 communicates with the
interior of the tube 22 and hence with the interior of the pipe 12 and enables permeate
which has entered the pipe 12 to flow from the filter unit 10. The tube 22 temporarily
connects the end cap 18 to the membrane 16.
The end cap 18 additionally has two more bores 26, 28.
The bore 26 is the raw water feed inlet and the bore 28 is the flushing outlet.
It is through the bore 28 that solid particles are swept from the casing during
the cleaning procedure as will be described hereinafter. There can if desired be
more than one bore 26 and more than one bore 28.
At the upper end of the filter unit 10 there is a further
end cap 30. The end cap 30 has an axial bore 32 through it to which a supply of
air under pressure (not shown in Figures 1 and 2) is attached. There is a space
34 between the end cap 30 and the membrane 16. The upper end of the core pipe 12
is closed by a plug 36.
To fabricate the filter unit 10, the membrane 16 has the
two end caps 18, 30 fitted to it and the composite structure is mounted on a rotatable
mandrel (not shown). The mandrel comprises two co-axial, axially spaced shafts which
enter the bores 24 and 32 thereby rotatably to mount the end caps 18, 20 and the
The end cap 30 includes a sleeve 38 in which the end of
the membrane 16 is fitted thereby providing the requisite temporary connection between
the cap 30 and the membrane 16. The mandrel is rotated and a casing 40 is fabricated
by winding resin coated glass or other fibre strands about the membrane 16 and end
caps 18, 30. The casing 40 joins the membrane 16 to the end caps 18, 30 thereby
to form an integrated unit which does not have any space between the outer surface
of the membrane 16 and the inner surface of the casing 40.
Turning now to Figures 3 to 10, the filter installation
illustrated comprises a base frame 42 on which all the remaining components of the
installation are mounted.
Four filter units 10.1, 10.2, 10.3 and 10.4 of the form
described above are mounted on the frame 42. Pipes 44 are connected to the inlet
bores 32 of the four filter units. Each pipe 44 leads to a valve 46 (Figure 10)
which controls flow from an air supply 48.
The water to be treated enters via an inlet 50 and flows
through a valve 52 to a pipe 54 which connects to the suction side of a pump 56.
The pressure side of the pump is connected to a manifold 58. There is a second inlet
60 for flushing water and a valve 62 is provided between the inlet 60 and the pipe
The manifold 58 is connected by four branch pipes 64 to
the bores 26 of units 10.1, 10.2 etc. Thus the raw water flows into the solids retention
passages of the membranes 16. Each bore 24 is connected to an outlet pipe 66 and
the pipes 66 lead to a permeate outlet manifold 68. The other bore 28 of each end
cap 18 is connected to a pipe 70, and the pipes 70 lead to a manifold 72. There
are valves 74 in the pipes 70, valves 76 in the pipes 66 and valves 78 in the pipes
A pipe 80 connects the manifold 58 to branch pipes 82 which
lead to the inlet bores 32 at the upper ends of the units 10.1, 10.2 etc. There
are normally closed valves 84 in the branch pipes 82. The pipes 82 join the pipes
44 so that the bores 32, for flushing purposes, can be connected simultaneously
to the air supply designated 48 and to the clean water supply 60.
In normal operation the raw water with solid particles
in it is pumped by the pump 56 into the manifold 58, then into the pipes 64, through
the bores 26 and into the membranes 16. The water which flows into the membranes
16 permeates through the leaves 14 and exits via the pipes 12, tubes 22 and bores
24. From the bores 24 the water flows to the pipes 66 and thence to the manifold
68 via the valves 76.
The upper ends of the units 10.1, 10.2 etc are permanently
connected to the air supply 48 thereby to maintain a pressure at above atmospheric
in each unit 10.1, 10.2 etc. The pressure of the raw feed water at the bores 26
is sufficient to balance the air pressure in such manner that the water fills the
casings 40 substantially to the top whilst leaving an air space above the water.
When the filter units become clogged, the valve 52 is shut
and the valve 62 is opened. Simultaneously the valves 74 and 84 are opened and the
valves 76, 78 closed. The valves 74, 84, in normal operation, are closed and the
valves 76, 78 are normally open. Flushing water flows from the pump 56 to the manifold
58 and then to the pipe 80. From the pipe 80 the flushing water flows through the
pipes 82 to the bores 32 with the incoming air which was able to start flowing through
the units immediately the valves 78 were closed to remove water pressure from the
lower ends of the membranes.
The air and flushing water flows through the solids retention
passages of the membranes, out through the bores 28 to the pipes 70 and then to
the manifold 72 carrying the filtered-out particles with it.
Air under pressure is constantly supplied to the upper
end of each filter unit. During flushing the air pressure can be maintained at a
constant value or can be caused to pulsate.