Note: Descriptions are shown in the official language in which they were submitted.
CA 02178796 2000-O1-13
METHOD FOR FILTERING OUT PARTICLES
FROM A FLUID
The invention relates to a method for filtering out particles from a
fluid, wherein unfiltered fluid is guided into a filter housing of a filter
apparatus and
filtered fluid is guided from the filter housing. A filter element is
positioned in
rotary manner in the filter housing and may be provided with a substantially
cylindrical configuration and with a structure, through which the fluid flows
from the
outside to the inside.
In general, methods for filtering out particles from a fluid and filter
to apparatus are known, in which a fluid containing contaminants in the form
of
particles is forced or sucked through the pores of a filter medium. The
particles
are left behind on the filter medium, whereas the fluid passes through said
filter
medium. Such a filter medium provided with pores has a certain flow
resistance,
which increases over a period of time with an increasing degree of
contamination
of the filter medium. After a certain time the flow resistance becomes so high
that
the filter medium must be cleaned. This gives rise to considerable manual
effort
and costs.
The object of the invention is to provide a method for filtering out
particles from a fluid which is operable without the need for cleaning a
filter
2 o medium from contamination, which avoids the increase of the flow
resistance
resulting from contamination of the filter medium, and which is therefore more
economical.
According to the invention this object is achieved by a method for
filtering out particles from a fluid, wherein unfiltered fluid is guided into
a filter
2 s housing of a filter apparatus and filtered fluid is guided from the filter
housing, and
wherein a rotary filter element, which has a filter structure and is arranged
in the
filter housing and is rotatable about an axis thereof, is rotated at a speed
which
is sufficiently high that all particles passing in a fluid flow into the area
of the rotary
filter element are affected by its structure and are ejected therefrom,
whereas the
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fluid passes the structure of the rotary filter element substantially freed
from the
particles and flows off from the filter housing.
From a flow standpoint, the filter is designed in such a way that
within the filter the fluid flows along a circular path on the filter element,
the fluid
being able to pass through the filter element, and whereas particles contained
in
the fluid are ejected away by the filter element rotating at a correspondingly
high
speed.
A particularly good filtering action is obtained if the fluid flow
direction coincides with the rotation direction of the filter element.
An advantage of the filter according to the invention is that the
particles to be filtered out cannot jam in the pores of the filter element or
be
deposited on the filter element, and consequently the latter is not
contaminated.
Therefore, there is no need to replace the filter element or clean the same.
Instead the particles to be filtered out sink downwards into the filter
housing and
are deposited there. On its underside the filter housing has a discharge lock
through which the deposited particles can be removed.
The filter for practising the method of the present invention is a filter
for filtering out particles being carried in a fluid. The filter has a
substantially-
cylindrical filter housing into which the fluid enters, and a filter element
rotatably
arranged within the housing. Fluid flow is from the outside to the inside of
the filter
element. The filter element is rotatable at a sufficiently high speed that all
of the
particles in the fluid come into contact with a structure of the filter
element and are
ejected outwardly away from that structure. Fluid flow into the filter housing
is
guided so as to be substantially tangential to the structure of the filter
element,
and the direction of the fluid flow corresponds to the rotation direction of
the filter
element.
The filter element may be cylindrical, and may have a cylindrical
cage. The structure of the filter element may be formed by bars running
substantially parallel to its longitudinal axis, and may be grid-like. The
structure
may have a filter cloth or a porous ceramic material layer. The filter element
may
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comprise a substantially-tubular flexible filter cloth which at the operating
speed
is subject to the centrifugal force of its substantially-cylindrical
filtration
arrangement.
The filter housing may have a substantially-circular cross-section,
and may have a fluid inlet so positioned that the fluid flows substantially in
a
tangential direction into the filter housing. The filter housing may have a
substantially-circular-cylindrical configuration, and on its top the filter
housing may
have an outlet for the fluid which is positioned substantially centrally in
the filter
housing. The filter housing may have a discharge lock on its underside. The
filter
element may have an upper part and a disk-shaped lower part, between which is
located a filter medium; this filter element has a substantially-circular-
cylindrical
outer contour, and the upper part has a discharge opening.
The invention is a process for filtering out particles from a fluid using
a filter that comprises a substantially-cylindrical filter housing into which
the fluid
enters, and a filter element rotatably arranged within the housing. Fluid flow
is
from the outside to the inside of the filter element. The process comprises a
first
step of feeding the fluid into the filter housing at a tangential angle to the
filter
element and in the same direction as the rotation direction of the filter
element.
A second step involves rotating the filter element at a sufficiently high
speed that
all of the particles in the fluid come into contact with a structure of the
filter
element and are ejected outwardly away from that structure.
The invention is next described in greater detail by means of
preferred embodiments utilizing the accompanying drawings, in which:
Figure 1 is a cross-sectional side view of a filter illustrating the
method of the invention;
Figure 2 is a cross-sectional plan view of the filter of Figure 1;
Figure 3 is a schematic representation of the interaction between a
rotating filter element and particles in a fluid;
Figure 4a is a partially-sectioned side view of another filter
illustrating the method of the invention;
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Figure 4b is a cross-sectional plan view of the filter of Figure 4a, the
view being along the line 4b-4b in Figure 4a;
Figure 4c is a cross-sectional side view of a strut of the filter of
Figure 4a, the view being along the line 4c-4c in Figure 4a; and,
Figure 5 is a schematic perspective view of another filter in
accordance with the invention, the view illustrating a series of filter
elements
arranged to act in parallel within a single housing.
According to Figures 1 and 2, the filter has a filter housing 10, in
which is rotatably mounted a filter element 6. The filter housing 10 has a
substantially-cylindrical shape, which is funnel-shaped at its lower end. In a
lower
area of the filter housing is located an inlet 12 for a fluid to be filtered.
The filter
housing 10 and inlet 12 are so designed that the fluid entering through the
inlet
flows substantially at right angles to the longitudinal axis and tangentially
to the
wall of the cylindrical filter housing 10 into the filter. An outlet 13 for
the filtered
fluid is located on the top of the filter housing 10.
The filter element 6 also has substantially-cylindrical outer contours.
The filter element 6 is so mounted in the filter housing 10 that a spacing is
maintained between the wall of the filter housing 10 and the outer contour of
the
filter element 6. In this area the fluid flowing through the inlet 12
tangentially to
the wall of the filter housing 10 flows around the filter element 6 until the
fluid
passes through the filter element and then flows out of the filter via the
outlet 13.
Thus, a flow forms around the filter element 6. The flow rotation direction
coincides with the rotation direction of the rotary filter element 6.
The operation of the filter according to the invention will now be
described having regard to Figure 3. The fluid circulating in the area around
the
rotary filter element 6 has on its circular path a much lower circumferential
speed
than the filter element. This naturally also applies to the particles
entrained in the
fluid on which acts a centrifugal force, directed away from the filter
element, due
to the circular movement.
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However, when the fluid passes through the filter element in order
to leave the filter through the outlet 13 in a cleansed form, the particles
that are
to be filtered are entrained in the direction of the filter element despite
the
centrifugal force. Those particles then strike against the filter element
rotating at
a sufficiently high speed, rebound therefrom, and consequently remain on a
circular path in the area between the filter element 6 and the housing 10.
This
process can be repeated many times, until finally the circulating particles
sink
downwards under the force of gravity, and are deposited in the lower part of
the
filter housing. Since the particles striking against the filter element are
ejected
therefrom due to the high speed of the filter element before they penetrate
the
pores of the filter element and since, due to the centrifugal force acting
thereon,
the particles do not have an adequate energy to remain in the pores of a
filter
medium, no contamination of the filter element occurs.
Optimum flow conditions in the area between the filter element 6 and
the filter housing 10 occur if there is a minimum of turbulence. Particularly
on the
wall of the filter housing there is a laminar surface flow layer. The
particles
preferably sink downwards in that layer. The particles enter that layer on the
one
hand because the centrifugal force acts thereon, and on the other hand on
rebounding from the filter element.
A particularly uniform flow distribution is assisted in that the inlet 12
is located at the bottom, and the outlet 13 at the top, of the filter housing
10. This
leads to an upwardly-directed circular flow in the spacing area, with a very
uniform
distribution of the particle-charged fluid over the entire filter element
surface.
Virtually all standard filter materials can be used as the filter
medium, provided that they have a structure running in a cylindrical
longitudinal
direction. It is also possible to use smooth filter cloths, as will be
described in
greater detail hereinafter.
Filter element 6, suitable for the filter according to the invention, can
essentially have the following structure. Between a disk-shaped upper part and
a disk-shaped lower part is fitted a tubular filter element. In the centre of
the
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upper part there is an opening through which can pass out the filtered fluid.
The
upper part and/or lower part are mounted in rotary manner in the filter
housing.
According to Figure 1, a filter element comprises a perforated sheet.
The meshes of the perforated sheet are arranged in the longitudinal and
transverse directions to the rotation axis of the filter element. The webs of
the
perforated sheet running in the cylindrical longitudinal direction are
essential for
the filtering action.
In another construction, the filter element merely comprises
longitudinally-directed bars, which are uniformly circumferentially
distributed. The
spacing between the bars is e.g. 1 mm, and the bar thickness is e.g. 4 mm. The
filter element has a diameter of e.g. 6 to 8 cm, and a height of e.g. 20 cm.
The
bars or perforated sheet can be covered with a filter cloth, which could then
be
referred to as a "filter medium".
In a third filter element construction, a filter cloth is fitted between the
upper part and the lower part. It is particularly appropriate for the filter
cloth to be
constituted by a fabric, which has thicker threads running in the cylindrical
longitudinal direction, and thinner threads in the circumferential direction.
Compared with a perforated sheet or bars in a filter element covered with a
filter
cloth, the same filtering action is obtained with a lower filter element
rotation
speed. This advantageous effect is due to the denser arrangement of the
vertical
structural elements essential for the filtering action. Nevertheless, the
filter cloth
must naturally have sufficiently large passages for the fluid to be filtered.
Due to
the lower rotary speed, the loading of the bearings and the intensity of the
vibrations if an imbalance occurs are lower.
In another construction the filter element has a hollow ceramic body
which, from its outside to its inside, has pores extending towards the outlet.
This
construction is particularly suitable for filtering liquids.
Figure 4a is a partially-sectioned side view of another embodiment
of a filter according to the invention. The filter housing 10 has a design
essentially
in the form of a cylinder of revolution. At its upper end the filter housing
10 is
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closed by a cover 1, which is fixed by clips 2 to the filter housing. In the
centre of
the cover is located a ball bearing 3, in which is mounted the upper part 5 of
the
filter element 6. The bearing shaft of the upper part 5 is hollow and extends
through the cover 1 through a corresponding opening therein. The hollow
bearing
shaft of the upper part 5 forms the outlet 13 through which the filtered fluid
can
leave the filter.
A rotary seal 4 seals the cover 1 in the vicinity of the ball bearing 3
against the bearing shaft of the filter element 6.
The lower end of the filter housing 10 tapers in a funnel-shaped
manner and ends in a connecting piece with a discharge lock 11. By opening the
discharge lock the dirt which has collected in the lower part of the filter
housing
can be removed. Above the funnel-shaped taper of the filter housing 10 is
located
a bearing block 9, which carries a ball bearing 8 located in the centre of the
filter
housing 10. The bearing block 9 has four radially-directed struts (cf. the
sectional
representation of Figure 4b), which extend radially to the wall of the filter
housing
10, and by means thereof the bearing block 9 is connected to the filter
housing 10.
In the lower area of the filter housing 10, but above the struts of the
bearing block
9, there is an inlet 12 for the fluid that is to be filtered.
A filter medium, e.g. a filter cloth, is positioned between the upper
part 5 and the lower part 7. To the underside of the lower part 7 is fitted a
plurality
of radially-directed laminations, whose lower end is approximately level with
the
inlet 12. The upper part 5, the filter medium and the lower part 7 form a
rotor,
which can be driven from the outside by means of the bearing shaft. By means
of the laminations located on the lower part 7 and which act in the manner of
a
blower or fan, the fluid flowing in through the inlet 12 is given a circular
flow in the
spacing area between the rotating filter medium and the wall of the filter
housing
10.
Figure 4b is a cross-sectional plan view of the filter, by means of
which it is possible to see the central position of the filter element 6
within the filter
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housing 10. It is also possible to see the struts 16 of the bearing block 9,
and the
arrangement of the inlet 12.
Figure 4c is a cross-sectional side view of a strut of the bearing
block 9. The struts 16 have an elongated, elliptical cross-section. The
particles
sinking in the spacing area between the filter element 6 and the wall of the
filter
housing 10 consequently drop between the struts 16, through into the funnel-
shaped taper of the filter housing 10 without being deposited on the struts
16.
Figure 5 is a schematic perspective view of a third embodiment of
a filter according to the invention, in which three filter elements 6 are
juxtaposed
to within a common filter housing 10. A distributing pipe 15 is positioned
laterally at
the bottom of the filter housing 10; it distributes the fluid to be filtered
over three
inlets associated with the three filter elements 6. On the top of the filter
housing
there is a common outlet 13'. In addition, at the top of the filter housing 10
is
provided a drive machine 14, which by means of a drive belt or other suitable
drive
means can rotate the three filter elements 6. The filter housing is subdivided
into
two chambers, one chamber containing the rotating filter element 6. The
outlets
of the three filter elements issue into the second chamber with the common
outlet
13'.
