Note: Descriptions are shown in the official language in which they were submitted.
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DUST COLLECTOR WITH REVERSE AIR CLEANING
Back4lo~n~ of the Invention
The present invention relates generally to dust collectors
for use as industrial air filters and the like and, more
particularly, to dust collectors of the type which include an
arrangement for self-cleaning the filter elements mounted in the
dust collector.
In general, self-cleaning industrial dust collectors have
traditionally fallen into two separate and distinct categories,
namely, so-called reverse air dust collectors and so-called pulse
jet dust collectors.
Typical examples of the reverse air dust collectors are
disclosed in Wheaton U.S. Patent No. 4,157,899; Bourne U.S. Patent
No. 3,648,442; Barr U.S. Patent No. 3,951,627; and Goodrich U.S.
Patent No. 4,878,926. In all of these dust collectors, the
filters are in the form of a long bag made of a fabric material,
and these filter bags are self-cleaned at periodic intervals by
a continuous flow of cleaning air directed into the interior of
the bags which flow outwardly through the interstices of the
fabric material in a direction opposite to the normal flow of air
to be cleaned, whereby particles of foreign matter which have
collected on the exterior surface of the filter bag are removed
therefrom. Because of the nature of the fabric from which bag
filters are made, namely, the flaccid material with the relatively
large interstices in the fabric, they are most effectively and
efficiently cleaned by the continuous flo~ of cleaning air,
although it has been proposed to let the pressure of the cleaning
air build up and be released in bursts of air as disclosed, for
example, in Bosworth U.S. Patent No. 4,655,799.
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With the advent of pleated paper filters, it was found
that such filters could be used in many applications of industrial
dust collectors, and the use of the smaller size of the pleated
paper filter elements reduced significantly the size of the dust
collector and increased the cleaning efficiency of the filter.
These pleated paper filters are formed of a somewhat porous and
generally stiff paper that is fluted with V-shaped indentations.
Because of the inherent stiffness of the paper filter medium,
these filters could not be properly self-cleaned using a reverse
flow of cleaning air as described above and, instead, required the
use of so-called pulse jets, which consist of a nozzle positioned
above the interior opening of each pleated paper filter cartridge
to produce a quick, high pressure pulse of air within the
"interior" of the filter cartridge that caused the pleated side
walls of the paper filter medium to bow outwardly and release some
of the foreign particles on the outer surface of the filter
cartridge. A typical pulse jet cleaning system of this general
type is described in Frey U.S. Patent No. 4,218,227. While these
pulse jets are effective in cleaning pleated paper filter
cartridges, the equipment and operating costs necessary to
generate the pulse jets add a significant expense to the
manufacture and operation of dust collectors that utilize pulse
jet cleaning.
Recently, pleated filter cartridges have been made from
a more resilient material, such as thermoformable spun-bonded
polyester as described in greater detail in U.S. patent
application Serial No. 08/082,666, filed June 25, 1993, which is
incorporated herein by reference. It has been found that the use
of these new filter cartridges with conventional pulse jet
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cleaners of the type described above results in more effective
cleaning of the filter cartridges by the pulse jets, but dust
collectors utilizing these new filter cartridges still have the
disadvantage of relatively high equipment and operating costs as
described above.
Summary of the Invention
In accordance with the present invention, it has been
found that the use of pleated filter cartridges with the new more
flexible filter media in combination with a continuous stream of
reverse air to clean such filter elements results in a dust
collector which offers the efficient and effective filtering
associated with typical pulse jet cleaned pleated filter
cartridges and the significant cost saving available from reverse
air cleaning as compared with pulse jet cleaning.
More specifically, the present invention includes a dust
collector for removing foreign particles from an air stream, such
dust collector comprising a housing including a grid plate having
a plurality of openings therein arranged in a predetermined
pattern wherein such openings are arranged in concentric circles,
and an air blower assembly which is mounted for rotation within
the housing and just above the grid plate. The air blower
assembly includes a plenum chamber having a radial extent along
the grid plate and the plenum chamber is rotatable along the upper
surface of the grid plate and has air discharge openings
positioned to direct air downwardly into the aforesaid grid plate
openings progressively as the plenum chamber is rotated above the
grid plate. The air blower assembly also includes an air blower
for generating a generally continuous and steady stream of air
through the discharge openings in the plenum chamber at a
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predetermined flow rate. A pleated filter cartridge is mounted
on the grid plate at each of the openings therein, and each
cartridge depends downwardly from the grid plate. Each filter
cartridge is provided with a plurality of pleats, with each pleat
formed by an inner apex and two side walls extending outwardly
from the apex at a predetermined angle, and each filter cartridge
is formed of a material having a particular resiliency that will
cause the material to normally be disposed in a relaxed state for
general filtering operation with the filter pleat side walls
disposed at the aforesaid predetermined pleat angle. However, in
response to the aforesaid continuous stream of cleaning air being
directed into the filter cartridge at the aforesaid predetermined
flow rate, the pleats move to an expanded state at which the pleat
angle increases to a second value greater than the predetermined
pleat angle whereby foreign particles are removed from the outer
surface of the filter cartridge.
In the preferred embodiment of the present invention, the
blower assembly includes a stanchion mounted for rotation above
the grid plate, with the plenum chamber being mounted on the
stanchion for rotation therewith, and with an air blower and drive
motor therefor also mounted on the stanchion for rotation
therewith, the air blower and motor being positioned on the
opposite side of the stanchion from the plenum so that the plenum
chamber counterbalances at least some of the weight of the air
blower and the drive motor. Also, it is preferred that each
filter cartridge include a perforated support tube, with the
resilient filtering material being disposed circumferentially
about the support tube, and wherein the expanded pleat angle
during cleaning is at least 10 greater than the relaxed
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predetermined pleat angle, and the filter cartridge material is
preferably a thermoformable, spun-bonded polyester material.
Brief Description of the Drawinqs
Figure 1 is a side elevational view of a dust collector
embodying the present invention;
Figure 2 is a front view of the air blower assembly
illustrated in Figure 1, but rotated 90;
Figure 3 is a detailed view of the pleated filter
cartridge;
Figure 4A is a diagrammatic illustration of the pleated
filter cartridge in its relaxed state; and
Figure 4B is a diagrammatic view similar to Figure 4A, but
showing the filter media in its expanded or cleaning position.
Description of the Preferred Embodiment
Looking now in greater detail at the accompanying
drawings, Figure 1 illustrates a dust collector embodying the
present invention which includes a housing 10 provided with a grid
plate 12 extending horizontally across the housing 10 to divide
it into an upper clean air chamber 14 and a lower dirty air
chamber 16. The grid plate 12 is conventional, and includes a
plurality of openings 18 that are arranged in concentric,
circumferential patterns, only one of which is illustrated in
Figure 1, and a pleated filter cartridge 20 is mounted at, and
extends downwardly from, each of the openings 18.
A blower assembly 22, which is substantially identical to
the blower assembly described in aforesaid U.S. Patent No.
4,878,926, which is incorporated herein by reference, includes a
vertically extending stanchion 24 mounted for rotation about the
vertical axis of its extending length in a bearing 26 affixed to
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the grid plate 12 and an upper bearing 28 ca`rried in a support 30.
Adjacent the lower end of the stanchion member 24, a centrifugal
blower 32 and its drive motor 34 are rigidly fixed to a plenum
chamber 36 that extends radially outwardly with respect to the
stanchion member 24 across the upper surface of the grid plate 12,
and the plenum 36 has a plurality of nozzles or outlets 38 that
are arranged to coincide with the aforesaid circumferentially
arranged openings 18 in the grid plate 12 as the plenum chamber
36 is rotated across the upper surface of the grid plate 12, all
in a manner described in greater detail in the aforesaid U.S.
Patent No. 4,878,926. The stanchion 24, with the blower 32, drive
motor 34, and plenum 36 mounted thereon, is rotated by a motor 40
operating through a conventional speed reducer unit 42 which is
connected to a drive gear 44 that meshes with a larger driven gear
44' secured directly to the stanchion member 24. The upper end
of the stanchion member 24 is fixed to a conventional slip ring
assembly 46 which receives electrical current from any convenient
source. As the stanchion member 24 rotates, electrical current
is transferred from the fixed portion of the slip ring assembly
to the rotatable portion thereof, and the electrical current is
carried by an electrical line (not shown) that passes down the
center of the stanchion member 24 to the blower motor 34.
As explained in greater detail in the aforesaid U.S.
Patent No. 4,878,926, the reverse air cleaning system described
above offers significant advantages in initial cost and operating
cost, and by virtue of the arrangement of the air blower 32 and
the horizontally extending plenum chamber 36, there is a
significant reduction, as compared with conventional blower
assemblies of this type, in the frictional losses of the air flow
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from the impeller of the blower 32 through the plenum chamber 36
and outwardly from the plenum outlets 38. As will be described
in greater detail below, this arrangement permits the blower
assembly 22 to generate, at each of the plenum outlets 38, a
constant and continuous air flow at a predetermined flow rate,
preferably about 500 cfm.
As best seen in Figures 3, 4A, and 4B, each of the filter
cartridges 20 includes an annular mounting plate 50, which is used
to mount the filter cartridges 20 to the lower face of the grid
plate 12, and a perforated support tube 52 depending downwardly
from the mounting plate 50 to a circular, air impermeable end
plate 54 fixed to the support tube 52. The filter cartridge 20
also includes filter media 56 having a generally cylindrical
configuration that includes a multiplicity of pleats 58 extending
longitudinally from one end of the filter cartridge 20 to the
other. The filter media is preferably a thermoformable spun-
bonded polyester filter media, which is commercially available
from SF Air Filtration AG, Von ~oll Aerial 43, CH-4710 Klus-
Balsthal, Switzerland, as Model No. SF-2651. Pleated filter
cartridges with this type of filter media are described in greater
detail in U.S. patent application Serial No. 08/082,666, filed
June 25, 1993, which is incorporated herein by reference, and
filter cartridges of this general type are also disclosed in U.S.
Patent No. 5,207,812.
In operation, filter cartridges 20 are secured to the grid
plate 12 with the upper opening in each pleated filter cartridge
20 corresponding to each of the grid plate openings 18, and dirty
air is introduced into the dirty air chamber 16 through an inlet
(not shown) and the dirt air passes through the filter media 56
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of each pleated filter cartridge 20 so that foreign particles
entrained in the air are deposited on the exterior surface of the
filter cartridges 20 and the cleaned air flows from the interior
of each filter cartridge 20, up through the grid plate openings
18, and into the clean air chamber 14 where the air is discharged
through an outlet opening (not shown), all in a conventional
manner. The blower assembly 22 is constantly rotated by the motor
40 so that the plenum 36 moves across the upper surface of the
grid plate 12 and air from the blower 32 is continuously
discharged through the nozzles 38 which move across ~he above-
described circumferentially arranged openings 18 in the grid plate
12. As a nozzle 38 passes over a grid plate opening 18, the
continuous stream of air emitted therefrom flows downwardly into
the interior of the adjacent filter cartridge 20, and this
cleaning air then flows outwardly through the filter media 56 in
a direction opposite to the normal air flow through the filter
cartridge 20, whereby the foreign matter collected on the exterior
surface of the filter media 56 is gradually cleaned therefrom.
As best seen in Figures 4A and 4B, the flow of cleaning
air into the interior of the filter cartridges 20 results in the
filter media 56 expanding from its relaxed state illustrated in
Figure 4A to an expanded state illustrated in Figure 4B, and the
foreign matter trapped in the pleats of the filter media 56 is
released from the surface of the filter media 56.
More specifically, as explained in greater detail in the
aforesaid U.S. patent application Serial No. 08/082,666, each of
the pleats 58 is formed by two side walls 60 extending from an
apex 62, and at the relaxed position of the pleats 58 illustrated
in Figure 4A, the side walls extend from the apex 62 at a
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predetermined pleat angle 64. When the cleaning air causes the
filter media 56 to move to its expanded position, this pleat angle
64 increases to a second angle that is at least 10 greater than
the pleat angle in the relaxed condition of the filter media 56.
It has been found that utilizing filter cartridges formed
of a material that is more resilient than conventional pleated
paper filter cartridges, such as the above-described
thermoformable spun-bonded polyester filter media, in combination
with a continuous flow of cleaning air introduced into the filter
cartridges 20 at a predetermined flow rate provides a sufficient
force to cause the filter media 56 to expand from its relaxed
position (Figure 4A) to its expanded position (Figure 4B) to
release the foreign matter collected in the pleats 58 without
requiring the high energy, high cost pulses that heretofore have
been required to clean conventional pleated paper filter
cartridges having a paper filter media that is too rigid to permit
cleaning by a continuous reverse air cleaning apparatus.
By virtue of this unique combination, the dust collector
of the present invention, as compared with conventional pleated
paper pulse-jet cleaned dust collectors, is less expensive to
build, less expensive to maintain, and provides more trouble-free
operation. More importantly, tests indicate that the combination
of the cleaning system described above and the filter cartridges
results in an approximately thirty percent savings in cleaning
energy cost as compared with the utilization of such cleaning
system with conventional filter bags as disclosed in the aforesaid
U.S. Patent No. 4,878,926.
It will therefore be readily understood by those persons
skilled in the art that the present invention is susceptible of
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broad utility and application. Many embodiments and adaptations
of the present invention other than those herein described, as
well as many variations, modifications and equivalent arrangements
will be apparent from or reasonably suggested by the present
invention and the foregoing description thereof, without departing
from the substance or scope of the present invention.
Accordingly, while the present invention has been described herein
in detail in relation to its preferred embodiment, it is to be
understood that this disclosure is only illustrative and exemplary
of the present invention and is made merely for purposes of
providing a full and enabling disclosure of the invention. The
foregoing disclosure is not intended or to be construed to limit
the present invention or otherwise to exclude any such other
embodiments, adaptations, variations, modifications and equivalent
arrangements, the present invention being limited only by the
claims appended hereto and the equivalents thereof.
