Note: Descriptions are shown in the official language in which they were submitted.
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BEPARATION OF 80LID PARTICULATE MATERIALB
FROM FLUID STREAMS
This invention relates to a method and device for
separating particulate materials from fluid streams.
The term fluid in.the context of the present
invention includes both gaseous fluids and liquid
fluids.
In many situations the ability of a fluid stream
to carry particulate material with it may be
beneficial and this ability may be used for example
for the transport of materials, which may be useful
commodities or waste, from one location to another
where the fluid must be efficiently separated from the
particulate material. In other situations,
particulate material may be an undesirable constituent
of a fluid stream and should therefore be removed
before the fluid is introduced, for example, into
engines and machinery or into industrial processes, or
into the environment, whether it be the environment at
large or a closed environment such as an office
building.
An important application of separation methods is
in the field of removal of particulate waste materials
in, for example, homes, gardens, offices, workshops
and factories involving so-called vacuum cleaning
techniques, either in dedicated cleaning equipment or
as an adjunct to other equipment whose operation
causes particulate waste to be formed. Other
important applications are in the field of systems
which produce particulate-bearing waste gases and
liquids which must be treated in order to comply with
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emission criteria, for example diesel and other
internal and external combustion engines, various
industrial processes, and waste disposal operations.
Separation applications involving the use of
liquids as a fluid include, for example, sand dredgers
and the disposal of liquid waste.
It will accordingly be seen from the disclosure
hereinafter that the potential separation applications
to which the present invention can be applied are very
wide-ranging, and include many that are not
specifically mentioned above but to which the
invention is equally applicable.
There is growing concern about filtration
standards and there have been new developments in
vacuum cleaner technology to provide higher levels of
filtration without the need to use ever finer filters
but by the use of very efficient cyclones. Such
cyclones cannot of themselves assure the size of
particle that had been removed from the fluid stream.
This can only be achieved by passing the fluid through
a porous medium having pores of a size prescribed to
eliminate larger particles.
However, such porous media quickly become blocked
and therefore large areas of such media are required
in order to give an acceptable period of use before
they have to be cleaned. A domestic vacuum cleaner is
one example; the blockage of the cooling duct inlet of
certain electrically powered railway trains by fine
snow is another; also air-conditioning filters are
examples which occur readily to mind.
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There is therefore an existing'problem concerning
the efficiency of conventional filtration systems both
in respect of the life of the filters and the
efficiency of the filtration process itself. There is
in particular a need for a process which can more
effectively remove solid particulate materials from
the vicinity of the front face of the filter, which
maintains the filter in a clean condition, which does
not involve such frequent stoppages in the separation
process, which is more compact and uses a smaller
surface area of filter than previous devices which
have attempted to solve such problems, and which is
able to guide separated particles in a controlled
stream to a place where they can be further processed.
Proposals have previously been made to use
rotating filters. However, such prior devices have
been inefficient in practice either by virtue of their
structure, the amount or area of filter which may be
required, or their mode of operation, and there
remains a need for an efficient method of separating
solid particulate material from fluid flows which
avoids the problems mentioned above.
According to the present invention there is
provided a method of separating particulate material
from a fluid stream which method comprises rotating in
the fluid stream a perforated barrier which permits
the fluid to pass through it, the axis of rotation of
the barrier projecting into the fluid stream, and the
front of the perforated barrier being substantially
normal to the streamlines in a major part of the
incoming flow at the points where the flow meets the
barrier, particles colliding with the barrier being in
consequence imparted with kinetic energy in a
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tangential direction so that they travel towards the
periphery of the perforated barrier entrained in a
diverted portion of the fluid stream. Preferably the
said diverted portion of the fluid stream is guided to
a place where it is separate from the vicinity of the
rotating front surface of the perforated barrier so
that separated particles in the said diverted portion
of the stream are not caught up in the fluid stream
which is approaching the rotating barrier.
It is also a preferred feature of the invention
that a portion of the fluid stream which has passed
through the perforated barrier is fed back around the
barrier to join the diverted portion of the fluid
stream containing the entrained separated particulate
material.
The invention further provides a device for
separating particulate material from a fluid stream,
which device comprises:
a duct for, conveying a fluid stream containing
entrained particulate material;
a perforated barrier which is mounted for
rotation in the duct about an axis which projects into
the fluid flow, said perforated barrier permitting
fluid flow through it, the front of the barrier being
arranged in the duct so that it is substantially
normal to the streamlines in a major part of the
incoming flow at the points where the flow meets the
barrier; and
means for rotating the perforated barrier.
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Preferably, the device further 'comprises a means
for guiding a diverted portion of the fluid stream
which contains particles which have collided with the
front of the barrier and in consequence have been
imparted with kinetic energy in a tangential direction
by the rotation of the barrier, so that said particles
are entrained in said diverted portion of the fluid
stream at the periphery of said surface; said guiding
means being arranged to guide said diverted portion of
the stream to a place separate from the vicini~~y of
the rotating front surface of the barrier so that
separated particles in said diverted portion of the
stream are not caught up in the fluid stream which is
approaching the rotating barrier.
By major part of the incoming flow is meant more
than 50% by volume of the incoming flow.
One of the essential features of the present
invention is that the separation of the particulate
material is due not only to the limited size of
openings in the ,rotating barrier but also to particles
colliding with the rotating barrier and in consequence
being imparted with kinetic energy in a tangential
direction as the fluid stream meets the front of the
rotating barrier. That is, the present invention
combines the conventional filtration technique of
using a barrier containing apertures through which
only particles of a certain maximum size may pass,
with a technique in which rotational kinetic energy
given to the barrier is transferred to particles in
the fluid stream so that the particles together with a
part of the fluid, perhaps 5% to 10%, are given
sufficient kinetic energy in the direction of rotation
of the barrier to thus be driven outward from the axis
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of rotation of the barrier towards the circumference
of the perforated part of the barrier so as to
separate them from the main fluid stream, perhaps 90%
to 95% of the original stream, which passes through
the barrier together with the remainder of very small
particles which are able to pass through the
perforations in the barrier. Thus, the present
invention combines conventional barrier filtration
with the use of an imposed tangential force to produce
a relative separation of particulate material from a
fluid in a controlled manner.
It will be understood that in order to arrange
for the fluid stream containing the particulate matter
to meet the front of the rotating barrier normally the
barrier will usually be rotated in a plane normal to
the fluid stream, although this is not absolutely
essential.
The particulate material which is to be separated
by the method and device of this invention will
usually be solid particulate material. However, it
will be appreciated that in some situations the
particles will perhaps, for example, have a relatively
high liquid content and may be capable of description
as say semi-solid or some other description which
might not strictly be regarded as a solid but which
nevertheless is particulate material which is able to
be separated by the method and device of the
invention.
The perforated barrier may be made like a
conventional filter, for example of porous metal,
sintered metal, porous ceramic material, woven or non-
woven fibres, fibre bundles, tube bundles or any other
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conventional filter material. However, it is not
essential that the perforated barrier be of such
construction, as long as it permits fluid flow through
it. Thus, for example, it could be in the form of a
multi-spoked or multi-bladed wheel, a fundamental
requirement of the rotating perforated barrier being
that it has sufficient surface area facing the fluid
stream in order to strike a high proportion of the
solid particles conveyed in the stream and thus cause
them to be carried by tangential force radially away
from the perforated front surface of the barrier and
thus to physically separate them from the main fluid
flow which passes through the body. It will be seen
that this mechanism allows the passageways through the
barrier to remain unblocked. The size of the
passageways or pores through the barrier are of course
relevant to the size of the particulate material which
can be separated. However, it has been found that the
pore size can be for example 100 m~ and surprisingly
using the method of the invention about 98% of
particles 5 m~c size are separated, that is a pore to
particle size radio of 20 to 1. Thus, not only is the
present invention able to substantially remove much
smaller particles than the fineness of the filter
would indicate but this enables a coarser filter to be
used which is also maintained in a clean and efficient
state for a much longer period of time by using the
method of the invention. Another advantage of the
present invention is that the area of filter material
which is required is much smaller than in prior
devices due to the structure and method of use of the
device. The present invention is particularly
suitable for removing particles in size ranges
including about 2.5 ~.m which have in the past been a
problem in causing clogging of conventional filters.
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One feature of the operation of'the invention is
that particulate material in the stream which meets
the rotating barrier at its axis of rotation will not
tend to be driven outwards, at least immediately,
because of the low tangential kinetic and centrifugal
forces at this point and it tends to build up to a
small hyperbolic mound. This can be avoided by
blanking off the surface of porous material at the
axial point of the rotating body, for example
preferably with paint or varnish.
The actual structure of the perforated barrier
may be such that it contains porous material only in
its central area, and the periphery may be of any
suitable material and may serve as a container for the
porous material.
A preferred shape for the barrier is a disc which
may have a flat or curved face, and may be convex,
conical, ovoid, dome, or bullet-shaped or any other
suitable shape which permits the separated particulate
material to be hit clear of the face of the barrier
and preferably guided so that it does not become
caught up in or interfere with fresh incoming fluid to
prevent it from passing through the barrier.
Although, as is explained above, the rotating
perforated barrier is not necessarily in the form of a
conventional filter, for the sake of convenience the
barrier will be referred to hereafter in this
description as a filter.
Preferably, when the fluid containing the
particulate material is not already in motion as a
stream, the means for causing rotation of the filter
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also includes means for inducing the'flow of the fluid
stream. Conveniently in this situation the filter is
formed integrally with or joined to, for example, the
impeller of a turbo machine or other arrangement in
the fluid duct in order to induce fluid flow, which
can be positioned either in front of or to the rear of
the filter in respect of the fluid flow. The power
means for giving rotation may conveniently be an
electric motor but in the application of the present
invention for example to engines, chemical plant or
other processes other motive power may be available
which may be more convenient or economic to use.
The manner in which the diverted portion of the
fluid stream containing separated particles is guided
and handled immediately after it has been struck
sideways off the revolving filter will depend on the
particular application to which the invention is put.
However, in many situations it will be desirable to
arrange a circumferential shroud around the periphery
of the filter, which may be either fixed or may rotate
with the filter,, and extending in front of the filter
so as to form a gap into which the diverted portion of
the fluid stream together with separated particles is
guided, and from which the diverted flow may be
conducted for example to a chamber where most of the
particles can be separated for example by gravity, or
by magnetic or centrifugal force, from the fluid which
may then, for example, be re-combined with the main
fluid flow, either before the main flow has been
subject to the separation step, or after, depending on
the application. Alternatively, the diverted portion
of the flow with the separated particles still
entrained therein may be introduced into a chemical or
physical process for transforming the particles.
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Optionally two or more of the separation steps of
the invention may be arranged in cascade in order to
provide yet finer separation.
As indicated previously, an important and very
useful application of the present invention is in the
field of removal of waste particulate materials which
are at present handled by various forms of vacuum
cleaning technique. It will be seen that the present
invention offers a way of improving such techniques by
substituting a rotating perforated barrier of the
invention for the conventional filters used in such
equipment and in many cases the change of design in
relation to existing equipment is relatively minor but
confers considerable benefits. Such existing
equipment already incorporates appropriate motive
power, usually in the form of an electric motor,
coupled to some form of impeller to induce the fluid
flow, as well as having a collection means for
separated particulate waste. A rotating fluid-
permeable perforated barrier of the invention needs
therefore only tp be coupled to the impeller of the
device in the duct for the fluid stream and the
existing static filter removed, in order to make use
of the present invention.
Thus, for example, a conventional electric
battery-powered hand-held vacuum cleaner type device
such as of the "Dustbuster" (Trade.Mark) type which is
itself a very efficient device of its kind, can be
adapted as mentioned above to use the present
invention. A specific adaptation of this device is
described hereinafter.
Other types of vacuum cleaner which are designed
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for higher volumes of particulate waste include the
so-called bucket or cylinder type whose common
features comprise a cylinder or other container which
incorporates an air inlet to which a collector hose is
attached and an electrically powered impeller having
in front of it one or more conventional filters being
arranged to catch the particulate waste, at least one
of said filters often being in the form of a porous
bag. It will be seen that such a general arrangement
can readily be adapted by using a device of the
present invention in which the impeller is coupled to
a fluid permeable barrier of the invention in order to
rotate it and thus provide a separation of the
particulate waste, which may for example be diverted
back along with the diverted portion of the air flow
within the body of the container and collected at the
bottom of the container.
A variation of the bucket vacuum cleaner is a
carpet shampooer. In this type of cleaner it is
arranged for carpet shampoo to be sprayed onto the
carpet from near,the end of the collector hose. In
this case the hose conducts solid particulate waste in
an airstream which contains liquid back to the
container. In this case also, as is other cases where
a gaseous fluid may contain liquid particles a
conventional "thrower" device can be fitted on the
front of the rotatable filter. The thrower is a solid
disc which, as the name implies, rotates and throws
liquid particles which are present in the gaseous
stream to the side thus reducing or eliminating the
amount of liquid which reaches the filter itself and
which may cause possible blockage problems when mixed
with the particulate material.
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It will be understood that there are other
apparatus in which it may be desirable to introduce a
liquid into the main gaseous fluid stream and in such
situations it may or may not be necessary or desirable
to incorporate a thrower device before the rotating
filter.
An additional or alternative feature which may be
included in such vacuum cleaning equipment is a pre-
shredder, in other words a rotating blade arrangement
fitted on the front of the rotating filter body which
can cause some size reduction in the particulate waste
before it reaches the filter face itself and thus make
the particulate material more manageable.
Another variation of the vacuum cleaner is the
garden vacuum cleaner which is used to remove leaves
and other garden debris. Such a cleaner can use the
device of the invention in a similar manner as
described before but optionally with a useful
variation in that the main stream of air produced by
the impeller can be ducted to a point near the inlet
of the collecting hose in order to dislodge debris
which is then sucked into the collecting hose. Liquid
such as water or other treatments, either fluids or
particulate matter, can if desired by introduced into
the pressurized air stream. It will be seen that this
kind of arrangement can also be used in a carpet
shampooer so that water or carpet shampoo solution is
introduced into the high pressure stream in order to
carry the shampoo deep into the carpet pile.
As mentioned above, in addition to dedicated
cleaning devices there is also a need for efficient
cleaning devices as adjuncts to other types of
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equipment which produce particles as'a by-product of
their operation, for example, mechanical sanders,
polishers, and woodworking machinery. Accordingly, it
is to be understood that the present invention extends
to any such types of equipment when they incorporate
as a means for removal of particulate matter a device
in accord with the present invention.
It has previously been mentioned that the device
of the invention can be applied to the removal of
particles from the exhaust gases of combustion engines
and other processes. It will be apparent from the
previous description that this may be done by carrying
the diverted portion of the fluid stream, in this case
the gaseous exhaust containing a significant
proportion of carbon-based particles, to a separate
receptacle where they can be removed by conventional
means, for example, by gravity or centrifugal force.
However, this diverted stream containing the carbon
particles may also be added to the inlet air of the
engine so that the particles are combusted or
otherwise processed by chemical or physical reaction.
Additionally, it will be understood that the
device of the invention can be employed in any
chemical or industrial process or equipment in which
particulate material needs to be separated from a
fluid and in which the techniques previously mentioned
can be used, for example separation of the particles
from the diverted stream, recycling of the diverted
stream to the main stream and removal of pollutant
particles from exhaust gases and liquids, including
air and liquid conditioning equipment, and reacting
them subsequently to render them innocuous.
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The invention will now be described by way of
example with reference to the accompanying drawings in
which:
Figure 1 is a diagrammatic representation in
section of the operation of the device of the
invention;
Figure 2 is a diagrammatic representation in
section of the device of Figure 1 in which the filter
incorporates an integral axial turbo machine for
producing fluid flow;
Figure 3 is a diagrammatic representation in
section for the device of Figure 1 in which the filter
incorporates a centrifugal turbo machine for
producing fluid flow;
Figure 4 is a diagrammatic representation in
section of a device similar to that of Figure 3
showing in more detail the recovery of particulate
matter and recirculation of diverted fluid, including
the fluid flows and particular points in the system
which are referred to in Figure 5;
Figure 5 is a Mollier diagram of the device of
Figure 4.
Figure 6 is a diagrammatic representation,
partially in section, of a hand-held vacuum cleaner
incorporating the device of the invention.
Referring to Figure 1, the particle laden fluid
12 approaches the rotating filter disc 1 where
particles 2 unable to pass with the fluid stream 3 are
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thrown off the rotating disc 1 by tangential forces as
shown by the direction arrow. The flow of fluid
through the rotating filter is created by the
application of a differential pressure (p' - p~) which
5 may be provided by any suitable means.
Suitable means for providing a differential
pressure across the rotating filter 1 may themselves
rotate providing a suitable and integrated drive means
10 for the disc 1. Figures 2 and 3 show two suitable
turbo-machinery means, Figure 2 an axial machine and
Figure 3 a radial or centrifugal machine. In both
cases the disc is rotated directly by the machine and
forms an integral part of the rotor 4 for the axial
15 machine and rotor 5 for the radial or centrifugal
machine, respectively. The operation of the rotating
filter disc 1 is as previously described with the
fluid 3 passing through the filter 1 and the blading
of the rotors 4 and 5 respectively being clean of
20 particulate matter 2; the filter disc also remaining
clean.
In those situations where particulate free fluid
is the required product the particles 2 may be hit off
25 the rotating filter disc 1, guided to a place where
they will not become caught up in or interfere with
the incoming flow but may not be recovered. In other
situations such as those of a vacuum cleaner it is
necessary to recover the particles 2 that are struck
30 off the rotating filter disc 1. Referring to Figure
4, dirty fluid 12 containing particles 2 enters a duct
14 at point A induced by the action of the centrifugal
machine impeller 5. This fluid is drawn through duct
14 onto the face of the rotating filter disc 1. Clean
35 fluid 3 is drawn by centrifugal action in rotor 5
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through the rotating filter 1 to be exhausted into a
suitable duct 11 at point E. Particles 2 striking the
rotating filter 1 are thrown off as described above to
be carried by the diverted fluid flow 6 induced by the
action of the shrouded rotating disc 1 to point F in a
suitable volute duct formed with the shroud 7. From F
the fluid and particles pass to G in a suitable
container where with lower fluid velocity a proportion
of the particles 13 settle out for example under the
influence of gravity. The partially cleaned fluid 15
passes through duct 9 to rejoin the main stream 12 at
H.
The flow conditions of the incoming stream 12,
10, the clean stream 3, 11 and the particulate laden
stream 6 and the recycle stream 15, are shown in the
Mollier Diagram of Figure 5.
The precise configuration of the rotating disc is
dependent on the detailed flow conditions and geometry
of the main dirty flow 12 and the cleaned flow .3 which
are themselves dependent on the particular
application.
Figure 6 shows partially diagrammatically a hand-
held vacuum cleaner which incorporates a device
according to the present invention. This vacuum
cleaner is in fact an adaptation of the well-known
"Dustbuster" (Trade Mark) type of hand-held vacuum
cleaner which has been modified in the manner
described earlier.
The cleaner comprises a main portion (21) and a
detachable nozzle portion (22) which exteriorly
comprise two housings of moulded plastic material.
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The main portion (21) houses an electric motor (23)
which has switch means (not shown). The electric
motor is powered by rechargeable batteries (24) and
drives an impeller (25) which is integral with funnel-
s shaped conduit (26) at the front of which is fitted a
dome-shaped perforated barrier of metal mesh (27).
The housing (21) has exhaust vents (28) on each side
to carry away the main stream of air produced by the
impeller. Additionally, however, there is a
circumferential gap (29) between the circumferential
neck of the funnel-shaped conduit (26) and the
impeller (25), and the wall of the main housing (21)
which faces the nozzle portion (22). A function of
this gap is to permit a portion of the airstream which
has passed through the perforated barrier and the
impeller to be fed back around the barrier to join the
diverted portion of airstream containing the entrained
separated particulate material.
The detachable nozzle portion (22) has a nozzle
(31) which leads into an internal conduit (32) for
conveying air with particulate material entrained
therein. The presence of the internal conduit (32)
provides an annular space (33) in which separated
particulate material can collect.
It will be seen that the device shown in Figure 6
operates in much the same way as the device shown at
the right hand side of Figure 4 as described
previously, except that instead of the diverted
portion of the fluid stream containing separated
particles being conducted by means of a shroud and a
duct to a solute duct and/or a separate container for
the particles, in the device of Figure 6 the diverted
stream is contained within the detachable nozzle
SUBSTTTUTE SHEET (RULE 26)
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portion (22) and the particles can collect in the
annular space (33). When the nozzle portion (22)
contains a substantial amount of particulate material
it can be detached from the main portion (21), shaken
or otherwise treated to remove particles from the
nozzle portion and then refitted to the main portion
of the c leaner f or re-use .
It should be noted that although pressure
differences are an essential part of the operation of
the method and device of the invention as exemplified
above it is possible, as explained earlier, to balance
the pressures within the device so that there is a
backflow of fluid from behind the filter to join the
diverted stream, so that no pressure seals are
necessary and no clogging of the gap with particulate
material occurs.
SUBSTTTUTE SHEET (RULE 26)
