Filter apparatus

A filter apparatus and filtering system which is particularly applicable for extracting particulated material from hot gases comprising a collector overlying a portion of the upstream face of the filter element for applying a reduced pressure to the particulate filter cake formed thereover to effect a dislodgement and recovery of the filtered particulate material. The collector is movable to progressively traverse substantially the entire upstream face of the filter element to effect a cleaning thereof by removal of the filter cake without interruption of the operation of the filtering system. The invention further encompasses a separator for cleaning the granular filter medium withdrawn from the filter apparatus and for recycling the cleaned filter medium back to the filter apparatus.

BACKGROUND OF THE INVENTION 
A variety of filtration devices have heretofore been used or proposed for 
use in extracting finely divided particulate material entrained in gaseous 
streams. A prevalent problem associated with prior art filter devices is 
in the need for intermittently disrupting operation to enable a cleaning 
and removal of the filtered material from the filter element. A further 
problem has been the inability of such filter systems to effectively 
filter particulate matter from high temperature gas streams such as the 
gaseous effluent from coal gasification processes whereby the gaseous 
stream can be directly employed as a fuel for the operation of gas 
turbines without encountering damage to the operating components as a 
result of erosion and wear due to entrained abrasive particles. In some 
instances, it has been necessary to first cool the coal gasification 
product to a low temperature to enable filtration resulting in a 
substantial loss and waste of the sensible heat in the fuel gases. 
Similar problems have also been encountered in connection with the recovery 
of finely particulated products in hot gaseous streams such as in the 
spray drying of various food products. The necessity to employ relatively 
low temperatures to accomodate the filtration system results in reduced 
efficiency of the spray drying process and in some instances also 
adversely effects the quality of the product. The relatively large volume 
of entrained solids in such spray drying processes necessitates frequent 
cleaning and removal of the filtered product from the upstream layer of 
the filter device which has occasioned frequent interruptions in the 
operation of such prior art systems further detracting from their 
efficiency. 
Many of the problems and disadvantages associated with filtering systems of 
the types heretofore known are overcome in accordance with the filter 
apparatus and system of the present invention whereby gaseous streams can 
be efficiently and effectively subjected to filtration without prior 
cooling, whereby the filter cake accumulated on the filter element can be 
effectively and efficiently removed without interruption of the filtering 
operation, and wherein the filter medium itself can be periodically 
withdrawn, cleaned and recirculated back to the filter element. 
SUMMARY OF THE INVENTION 
The benefits and advantages of the present invention are achieved by a 
filter apparatus which comprises a housing defining a fluid passageway 
formed with a fluid inlet and a fluid outlet having a filter element 
therein which is interposed between the inlet and the outlet. A collector 
is positioned within the housing and is formed with an inlet port 
overlying a portion of and disposed contiguous to the upstream face of the 
filter element and the filtered particulate material in the form of a cake 
thereover. The collector includes discharge means for discharging the 
collected particulate material to a position exteriorly of the housing and 
is provided with a conduit in communication therewith for effecting a 
reduction in the fluid pressure therein below the fluid pressure in the 
housing of a magnitude sufficient to cause the particulate material 
adjacent to the inlet port to become dislodged from the upstream face of 
the filter element. Drive means are provided for effecting relative 
movement of the inlet port and the filter element in a manner to 
progressively traverse substantially the entire area of the upstream face 
for collecting the particulate material thereon. 
In accordance with a further embodiment of the present invention, the 
filter element comprises a pair of foraminous walls between which a 
temperature resistant granular filter medium is disposed such as ceramic 
spherical particles. The filter chamber containing the filter medium is 
suitably connected to a discharge conduit through which the filter medium 
is periodically withdrawn and is passed through a separator including a 
gas jet oriented in a direction countercurrent or cross-flow to the 
direction of travel of the filter medium for removing the fine sized 
particles from the surfaces thereof which are subsequently recovered. The 
granular filter medium in a cleaned condition is removed from the 
separator and recirculated to the filter chamber of the filtering system. 
Additional benefits and advantages of the present invention will become 
apparent upon a reading of the description of the preferred embodiments 
taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now in detail to the drawings and as best seen in FIG. 1, the 
filtering system of the present invention comprises a filter assembly 10 
connected at its upper end to a gas inlet conduit 12 through which a gas 
is supplied containing entrained particulate matter. In those instances in 
which the gas contains large quantities of contaminating particles, it is 
preferred to first pass the gas stream through a preliminary course dust 
removal cyclone 13 in which most of the large particles are removed. A gas 
outlet conduit 14 is connected to the side portion of the filter assembly 
through which the filtered gas is discharged. A discharge conduit 16 is 
connected to the base of the filter assembly and is provided with a valve 
18. The discharge conduit is connected at its lower end to a hopper 20 for 
storing the particulate material or product extracted from the gas stream. 
In the specific embodiment shown in FIG. 1, the hopper 20 is connected to 
a blower 22 for applying a reduced pressure to the interior of the hopper 
for the purposes subsequently to be described and the discharge of the 
blower is connected to a suitable bag filter 24 for extracting any 
entrained particulate matter in the exhaust gas stream. The gas discharged 
from the bag filter 24 through a conduit 25 may suitably be combined with 
the filtered gas in the outlet conduit 14 and may be repressurized, if 
desired. 
A hopper 26 is disposed at an elevated position relative to the filter 
assembly 10 and contains a granular filter medium which is adapted to be 
periodically withdrawn through a supply conduit 28 for replacing the 
filter medium in the filter assembly. A discharge conduit 30 is connected 
to the lower portion of the filter assembly 10 for periodically 
withdrawing the granular filter medium from the filter assembly and for 
transferring the withdrawn filter medium to a separator 32 in which the 
contaminating particulate matter on the surfaces thereof is removed. The 
cleaned filter medium is recycled to the filter medium storage hopper 26 
through a recycle conduit 34. 
The cleaning of the filter medium in the separator 32 is effected by a high 
velocity jet in a manner to be more fully described in connection with 
FIGS. 4 and 5 and the entrained contaminating particles are withdrawn 
through a conduit 36 connected to the upper end of the separator 32 and 
are passed through a suitable cyclone or bag filter 38. The gas employed 
for cleaning the filter medium in the separator in accordance with a 
preferred practice of the present invention may comprise a portion of the 
filtered gas which is bled from the gas outlet conduit 14 through a valve 
40, repressurized in compressor 43 and transferred through conduit 42 into 
the lower end portion of the separator. Similarly, the exhaust gas from 
the separator discharged from the cyclone or bag filter 38 can be returned 
to the gas inlet conduit 12 for admixture with the incoming gas to be 
filtered via a conduit 44 equipped with a valve 46. It will be apparent 
from the arrangement shown in FIG. 1, that the filtering system is adapted 
to operate on a continuous basis during which the filtered particulate 
matter in the incoming gas stream is intermittently or continuously 
removed from the filter element for collection in the hopper 20. 
Interruption of operation preferably is effected at periodic time 
intervals during which the granular filter medium is replaced in the 
filter assembly as a result of accumulation of particulate matter therein 
which may suitably be sensed by an increased pressure drop across the 
filter element. 
Referring now to FIGS. 2 and 3 of the drawings, the filter assembly 10 
comprises a three dimensional housing defining a passageway through which 
the incoming gas stream passes and in the specific preferred embodiment 
shown includes a circular cylindrical wall 48 which is supported at its 
lower end on a circular base or flange 50 and along its upper end portion 
by an annular manifold ring 52. A conical-shaped cover 54 formed with an 
annular flange 56 along its lower edge is disposed in overlying 
relationship on the upper edge of the manifold ring 52. The peripheral 
portion of the annular flange 56 and the base 50 are provided with 
apertures for receiving the ends of through-bolts or tie rods 58 for 
removably clamping the assembly together. 
The upper end portion of the cover 54 is provided with an inlet port 60 
which is connected to the gas inlet conduit 12 (FIG. 1) for introducing 
the gas stream to be filtered into the housing. A foraminous plate or 
screen 62 is mounted downstream of the inlet port 60 which acts as a 
diffusor for uniformly distributing the incoming gas over the upstream 
face of a filter element 64 and for further effecting an agglomeration of 
the particulate entrained matter therein facilitating filtration thereof. 
The filter element 64 is comprised of an inner foraminous wall or screen 66 
and an outer foraminous wall or screen 68 which are of a circular 
cylindrical configuration and are disposed concentric to each other 
defining therebetween a filter chamber 70. The base 50 and the manifold 
ring 52 are suitably grooved as shown in FIG. 2 to slidably receive and 
retain the lower and upper edges, respectively, of the walls 66, 68 in 
appropriate spaced position. The circular base 50 is provided with a 
plurality of outlet ports 72 at circumferentially spaced intervals which 
are disposed in communication with the lower end of the filter chamber 70 
providing for a gravitational discharge of the granular filter medium 74 
from the chamber into an annular discharge manifold 76 affixed to the 
lower side of the base. The discharge manifold 76 is in turn connected to 
one or a plurality of discharge conduits 30 (FIG. 1) for transferring the 
withdrawn filter medium to the separator. The upper annular manifold ring 
52 is formed with an annular chamber 78 which is disposed in communication 
with a plurality of inlet ports 80 disposed at circumferentially spaced 
intervals which in turn are connected to one or a plurality of supply 
conduits 28 (FIG. 1) for receiving granular filter medium from the filter 
medium storage hopper. The base of the annular manifold ring is formed 
with a plurality of circumferentially spaced discharge ports 82 for 
discharging the filter medium by gravity into the upper end of the filter 
chamber 70. The introduction of cleaned filter medium and the withdrawal 
of filter medium from the filter chamber 70 is controlled by means of 
valves 84, 86 as shown in FIG. 1 located in the supply conduit 28 and 
discharge conduit 30, respectively. The replenishment of the filter medium 
is performed periodically in consideration of the accumulation of 
particulate matter in the interstices thereof as evidenced by an increase 
in the pressure drop across the filter element. The time interval between 
changes of the filter medium will vary in consideration of the quantity of 
particulate matter in the incoming gas stream, its size and size 
distribution, the distance between the inner and outer foraminous walls 
defining the depth of the filter element, the size and configuration of 
the filter medium and the operating pressure of the filtration system. 
The filter medium itself can comprise any particulate material which 
preferably is of a spherical shape and of substantially the same size to 
provide for uniformity in the porosity of the filter element along its 
length and depth. Preferably the filter medium is comprised of a 
temperature resistant material such as ceramic pellets which are able to 
withstand the high temperature of the gas stream being filtered. The 
operating temperature range of the filter system can range from about room 
temperature up to the design limits of the supporting metal structure. For 
example, gas streams derived from coal gasification processes which can 
satisfactorily be handled in accordance with the present invention can 
broadly range from about 100.degree. F. to as high as about 1800.degree. 
F. The foraminous inner and outer walls 66, 68 similarly are comprised of 
a high temperature resistant material such as stainless steel or nickel 
base alloys and may be in the form of a screen or perforated metal sheet. 
In accordance with a preferred practice, the filter medium comprises 
spherical particles which may range in diameter from about 0.02 inch up to 
about 0.25 inch and which are all of substantially the same size. The 
depth of the filter element through which the gas passes may range from 
about 1/2 inch up to about 6 inches and preferably from about 1 to about 2 
inches depending upon the particular flow rate of the gas stream and the 
nature or characteristics of the particulate matter therein. 
In accordance with a preferred practice, there is a controlled relationship 
between the diameter of the spherical filter medium and the thickness of 
the filter bed with respect to pressure drop, ease of cake initiation and 
particulate collection efficiency. When the filter is clean, that is 
before any cake formation has taken place, there is some penetration of 
the particles into the bed of filter medium before the cake is formed. 
Generally, a range of 20 up to about 100 layers of spheres, and preferably 
from about 30 to about 50 are employed to maintain high collection 
efficiency without undue pressure drop across the filter element. During a 
filtration cycle, once the filter cake or layer is initiated, the filter 
cake itself acts as the filter and very few particles enter the filter 
medium. However, some time period is required for the cake to be formed, 
and it is during this cake build up period that most particles get into 
the filter medium bed. It has been observed that particles that are 
retained in the filter bed are from about 2 to about 3 orders of magnitude 
smaller than the filter medium spheres; that is, when the filter medium is 
from about 1 to about 5 millimeters in diameter, the dust or particulate 
material entering the media range from about 0.2 to about 5 microns, 
respectively, and these particles are collected because they adhere to the 
filter medium or to the other particles previously deposited on the filter 
medium. As the gas and entrained particles enter the filter bed during 
cake formation, each layer of spherical filter medium catches a percentage 
of the entrained particles entering that layer. For example, 80% of such 
contaminating particles are entrapped in the first layer while 80% of the 
escaping particles, or 16%, are entrapped in the second layer, etc. The 
foregoing relationship is generally true in those instances in which all 
of the contaminating particles are of substantially the same size and 
shape. It will be appreciated, that smaller particles tend to penetrate 
further through the filter bed. Eventually, a sufficient quantity of 
particles penetrate through all of the layers of the filter medium bed at 
which point some of such particles escape into the filtered gas on the 
downstream side of the filter bed. At that point, the filter medium must 
be replaced with a fresh charge of cleaned spherical filter medium. Once a 
filter cake of significant thickness is established, the entry of 
contaminating particles into the filter medium is substantially reduced. 
As the filter cake increases in thickness, a pressure drop across the 
filter cake increases in a manner approximately proportional to the 
thickness of the accumulated cake. In order to avoid excessive pressure 
drop as a result of cake build up, the filter cake is continuously or 
intermittently removed to maintain efficiency of the filtering operation. 
After the removal of the filter cake from a selected portion of the 
upstream side of the filter element, a new filter cake builds up during 
which some further penetration of contaminating particles into the filter 
bed occurs. Ultimately, the pressure drop across the filter element is not 
appreciably lowered by filter cake removal due to the accumulation of 
contaminating particles within the interstices of the filter medium itself 
at which point the filter medium is replaced with a fresh batch. 
As best seen in FIGS. 2 and 3, a collector assembly 88 is rotatably mounted 
within the housing and includes a tubular shaft 90 connected by means of a 
sealed slip connection to the discharge conduit 16 (FIG. 1). The tubular 
shaft is journaled in a stepped collar 92 affixed to the underside of the 
base 50 defining a rotational axis coinciding with the center of curvature 
of the inner wall 66 of the filter element. 
The tubular shaft 90 terminates at its upper end in a circular flange 94 
the lower surface of which is disposed in sliding bearing contact against 
the upper surface of the base 50. A shroud or baffle 96 in the shape of a 
horn is affixed to the upper surface of the flange 94 and terminates along 
its outer periphery in a collector port 98 the edges of which are disposed 
contiguous to the inner foraminous wall 66 and the accumulation of 
particulate matter in the form of a filter cake on the upstream face of 
the filter element. 
The circumferential width of the collector port 98 can be varied to 
encompass from about 5% to as much as about 25% of the area of the 
upstream face of the filter element. The collector port 98 is of a height 
to substantially overlie the entire height of the upstream filter face. 
While circumferential widths of the collector port greater than about 25% 
can be employed, the use of collector assemblies of such increased area 
reduces the available effective area of the filter element reducing the 
filtering capacity of the system without providing for any material 
advantages. Generally the area of the collector port relative to the area 
of the upstream face of the filter element is controlled within a range of 
about 5% to about 10%. 
The collector assembly 88 serves to effectively remove the filtered 
material or cake from the upstream face of the filter element by an 
intermittent application of a reduced pressure to the filter cake causing 
a dislodgement thereof and is recovered within the interior of the baffle. 
The high efficiency of filter cake removal in accordance with the present 
invention is believed to result from the sudden reduction in pressure 
adjacent to the powder cake whereby the cake and the gas entrapped therein 
momentarily expands causing simultaneous cake expansion and breakup 
accompanied by a blowback or puffback caused by the expanding gas in the 
filter medium. The dislodged cake fragments drop through the influence of 
gravity and gas flow into the interior of the collector assembly which is 
sloped to facilitate transfer thereof to the tubular shaft 90, discharge 
conduit 16 to the collector hopper. 
The imposition of reduced pressure to the interior of the collector 
assembly adjacent to the filter cake can be effected when the filter 
system is operated under high pressure, for example, above about 2 
atmospheres by simply venting the interior of the collector assembly to 
the hopper at atmospheric pressure by opening the valve 18 (FIG. 1) of the 
discharge conduit 16. When the filter system operates at or about 
atmospheric pressure, the reduced pressure is effected by operation of the 
blower 22 (FIG. 1) to provide a sufficient pressure reduction to effect 
cake dislodgment. Ordinarily, a pressure reduction of a magnitude of 2 is 
sufficient to effect substantially complete removal of the accumulated 
cake. For example, with the gas inlet pressure at a magnitude of about 2 
atmospheres, the application of atmospheric pressure to the interior of 
the collector assembly is adequate. 
The progressive movement of the collector assembly across the upstream face 
of the filter element can be performed continuously by a slow incremental 
rotation or intermittently by an indexing of the collector assembly from 
one overlying location to the next overlying location. Preferably the 
collector assembly is intermittently advanced and the reduction in 
pressure within the interior thereof is effected on a pulsed basis after 
attaining the new position. Appropriate indexing movement of the collector 
assembly can be achieved such as shown in FIG. 2 by means of a variable 
speed motor 100 having a drive sprocket 102 affixed to the output shaft 
thereof which is drivingly connected to a roller chain 104 which in turn 
is trained about a driven sprocket 106 affixed to the tubular shaft 90. 
The frequency at which the collector assembly is advanced can be varied in 
accordance with the rate of build up of powder cake on the upstream face 
of the filter element. The specific schedule of cake removal depends on 
the severity of service, type of service, allowable increase in pressure 
drop occasioned by the cake build up and other related factors. Typically 
for the extraction of particulate contaminants from a coal gasification 
product stream, operating at about 2 atmospheres of pressure and at a 
temperature of about 1600.degree. F., a schedule of about from 1 to about 
6 complete revolutions of the collector assembly per hour is satisfactory. 
With the circumferential width of the collector port being about 
60.degree., 84% of the upstream face of the filter element is available 
for filtration. The indexing of the collector assembly accordingly can be 
effected in 60.degree. increments requiring 6 advances to complete one 
revolution. 
Referring now in detail to FIGS. 4 and 5 of the drawings, the separator 32 
for cleaning the filter medium comprises an elongated tubular housing 108 
the major length of which is angularly inclined and terminates in a 
substantially upright top portion which is connected to the exhaust 
conduit 36 (FIG. 1). The lower end portion of the housing is formed with a 
removable section 110 which is connected to the main housing 108 by means 
of annular flanges 112. A flat plate or ramp 114 is affixed to the 
interior of the housing 108 along which the filter medium moves downwardly 
by the action of gravity in the form of a layer on being introduced into 
the separator by the discharge conduit 30 (FIG. 1). The lower portion of 
the housing 118 below the ramp 114 is sealed adjacent to the flange 112 by 
an arcuate section 116. 
The lower section 110 of the separator is formed with an arcuate segment 
118 the upper face of which is disposed substantially flush with the face 
of the adjacent annular flange 112. A plate or ramp section 120 is affixed 
to the interior of the lower section in spaced relation with respect to 
the upper edge of the arcuate section 118 defining therebetween an orifice 
or slit 112 the axis of which is oriented along the upper surface of the 
main ramp 114. The ramp section, arcuate segment and adjacent wall of the 
lower section 110 define in combination a manifold chamber 124 which is 
connected to the conduit 42 (FIG. 1) for supplying a high pressure gas 
which is discharged in the form of a planar jet through the slit 122 in a 
direction countercurrent to the downward travel of the filter medium along 
the upper surface of the ramp 114. The impingement of the gaseous jet on 
the surfaces of the filter medium effects removal of minute particles of 
contaminants thereon which are entrained in the gas stream and pass 
upwardly and outwardly of the housing through the exhaust conduit 36. In 
accordance with a preferred construction, the lower edge of the orifice or 
slit 122 is positioned in alignment with the upper surface of the ramp 
114. The filter medium upon passing beyond the gaseous jet travel 
downwardly by gravity along the ramp section 120 and are removed from the 
separator through the recycle conduit 34 for return to the filter medium 
storage hopper 26 (FIG. 1). 
In accordance with a specific embodiment of the separator shown in FIGS. 4 
and 5, the housing 108 is 6 inches in diameter and filter medium is 
introduced through the inlet conduit 30 at a rate of about 2 pounds per 
minute at a velocity of about 70 feet per second. The slit is of a width 
of 0.020 inch and the cleaning gas is introduced into the manifold chamber 
at a rate of 23 cubic feet per minute for discharge from the slit. The 
fine particulate contaminants are blown off the surfaces of the filter 
medium and pass upwardly through the separator chamber out through the 
exhaust conduit 36. When the cleaning gas comprises a high temperature gas 
such as derived from a coal gasification process, the cleaning operation 
is performed employing hot gases at a temperature at least above that 
which would occasion any condensation to form due to the moisture and 
other volatile content in the gas stream. 
Referring now to FIGS. 6-8 of the drawings, an alternative satisfactory 
embodiment of the filter system is illustrated in which the filter medium 
separation and recycling system is self-contained and in which the filter 
element rotates relative to the stationary collector assembly. As shown, 
the filter apparatus comprises a cylindrical plenum 126 defining a chamber 
and which is tapered along its lower portion terminating in an outlet port 
128 which is adapted to be connected to a discharge conduit such as the 
discharge conduit 16 of FIG. 1 equipped with a valve 18 and a bag filter 
for recovering the particulated material discharged therethrough. The 
plenum 126 is closed at its upper end by means of a circular top wall 130 
to which a gas inlet conduit 132 is connected through which a gas 
containing entrained particulate matter is introduced into the interior of 
the plenum. The gas inlet conduit 132 corresponds to the conduit 12 of 
FIG. 1 and may also be suitably provided with a cyclone such as the 
cyclone 13 of FIG. 1 to effect a preliminary removal of course particulate 
matter from the incoming gas stream. 
A rotary filter assembly 134 is disposed within the plenum 126 and is 
mounted for rotation about a substantially vertical axis. The filter 
assembly comprises an outer element comprising a lower impervious conical 
wall portion 136, a foraminous or porous intermediate cylindrical wall 
portion 138 and an upper cylindrical imperforate wall portion 140. The 
lower conical wall portion 136 is rotatably supported in a conical bearing 
142 connected by a spider (not shown) to the interior wall of the plenum 
126. The base of the conical wall portion terminates in an outlet 
connected by a slip connection to a filter medium discharge conduit 144 
which extends downwardly toward the base of the plenum. The discharge 
conduit 144 is equipped with a screen element 146 along the lower portion 
thereof for permitting entrained particulate matter to fall downwardly 
through the action of gravity toward the outlet port 128 while retaining 
the granular filter medium within the conduit. 
The filter assembly further includes an inner element disposed 
concentrically within the outer element and including an imperforate 
dish-shaped base 148, a cylindrical foraminous or porous intermediate 
section 150 which extends longitudinally of and for substantially the same 
length as the foraminous cylindrical wall portion 138 of the outer 
element, and an imperforate tapered tubular upper wall section 152. The 
upper tubular end of the wall portion 152 is connected by means of a 
sealed slip joint to a stationary outlet conduit 154 through which the 
filtered gas is discharged. The inner filter element and outer filter 
element are maintained in appropriate concentric spaced relationship and 
are drivingly coupled together by means of a plurality of baffles or webs 
156 extending axially and radially therebetween and are of a configuration 
to minimize any interference with the downward gravitational flow of the 
granular filter medium 158 interposed between the inner and outer filter 
elements. The radial distance between the inner and outer filter elements 
of the rotary filter assembly 134 can be controlled to achieve the desired 
depth of the filter medium in consideration of the parameters previously 
discussed in connection with the embodiment illustrated in FIG. 2. 
A controlled continuous or intermittent rotation of the filter assembly is 
achieved as best seen in FIG. 6 by a coaxial shaft 160 extending 
vertically through the gas outlet conduit 154 and secured by means of a 
spider 162 to the upper wall portion 152 of the inner element. The shaft 
160 extends through a rotary seal 164 provided in the wall of the outlet 
conduit and is connected at its upper end to a sprocket 166 affixed 
thereto. The sprocket 166 is connected by means of a roller chain 168 to a 
driven sprocket 170 affixed to the output shaft of a variable speed 
electric motor 172. 
In accordance with the foregoing arrangement, a slow incremental rotation 
or an intermittent indexing of the filter assembly is effected in a manner 
similar to that previously described in connection with the collector 
assembly 88 of the embodiment shown in FIG. 2. The rotation of the filter 
assembly causes the upstream face thereof incorporating the powdered 
filter cake thereover to be advanced adjacent to a collector manifold 174 
stationarily positioned adjacent to a circumferential portion of the 
upstream face. As may be best seen in FIGS. 7 and 8, the collector 
manifold 174 is of a generally semi-circular cross-section and is formed 
with an elongated rectangular collector port 176 which overlies a 
circumferential section of the foraminous intermediate wall portion 138 of 
the outer element of the filter assembly. The upper end of the collector 
manifold is closed while the lower portion thereof terminates and is 
disposed in communication with a downwardly angularly inclined discharge 
conduit 178 which is connected to a storage hopper system (not shown) 
similar to the hopper 20 schematically illustrated in FIG. 1. The 
imposition of a reduced pressure to the interior of the collector manifold 
effects a dislodgement and recovery of the particulated filter cake on the 
adjacent upstream face of the filter assembly in accordance with the 
parameters and mode of operation as previously described in connection 
with the collector assembly 88 of FIG. 2. 
The embodiment shown in FIGS. 6-8 includes an integrated self-contained 
filter medium cleaning and recirculation system as a satisfactory 
alternative to the external separater 32 and recycle conduit previously 
described in connection with FIGS. 1 and 5. As shown, the lower end of the 
filter medium discharge conduit 144 is disposed in communication with a 
vertically oriented conveyer tube 180 within which a screw conveyer 182 is 
rotatably mounted. The upper end of the shaft of the screw conveyer 182 
projects outwardly of the top wall 130 of the plenum and a suitable driven 
sprocket 184 is affixed thereto. The driven sprocket is drivingly coupled 
by means of a roller chain 186 to a drive sprocket 188 mounted on the 
output shaft of a variable speed electric motor 190. The upper portion of 
the conveyer tube 180 is formed with an outlet or discharge chute 192 for 
discharging the granular filter medium into the annular region between the 
inner and outer filter elements. 
As best seen in FIG. 6, the discharge chute 192 is formed with a conduit 
194 the discharge end of which transversely intersects the axis of the 
chute and the granular medium discharged therethrough. The conduit 194 is 
adapted to be connected to a high pressure source of air such as the 
conduit 42 and compressor 43 illustrated in FIG. 1 which is discharged in 
the form of a jet in impinging relationship against the filter medium 
particles to effect a removal of the minute particulate contaminants 
thereon. The contaminating particles removed become entrained in the 
cleaning jet gas stream and are transferred through the discharge end of 
the chute into the interior of the plenum for passage through the filter 
assembly. The cleaned filter medium in turn passes downwardly through the 
action of gravity and is discharged into the upper end of the filter 
assembly. 
The operation and recycling of the filter medium including a separation and 
cleaning thereof is performed in consideration of the same parameters as 
previously discussed in connection with the system shown in FIG. 1. 
Accordingly, when the pressure drop across the filter medium attains a 
preselected level indicative of entrappment of filtered particles within 
the interstices of the granular filter medium, the motor 190 is energized 
effecting upper conveyance of filter medium through the conveyer tube 
which is accompanied by a downward gravitational movement of the filter 
medium in the annular region of the filter assembly and through the 
discharge conduit 144. As previously mentioned, the provision of the 
screen element 146 in the medium discharge conduit effects a preliminary 
separation of entrained contaminating particles from the filter medium 
which are recovered through the discharge port 128. The remaining 
contaminating particles are removed by the cleaning action of the gas jet 
in the discharge chute 192. The recirculation and cleaning action of the 
filter medium is continued until the entire internal portion of the filter 
assembly has been replenished with cleaned filter medium. 
It will be noted in FIG. 6, that the depth of the filter medium 158 within 
the annular region between the inner and outer filter elements is 
controlled so as to provide a depth above the upper ends of the foraminous 
intermediate wall portions 138 and 150 greater than the radial depth of 
the filter medium between the inner and outer filter elements. This 
results in an increased resistance against axial flow of gas within the 
plenum downwardly through the open end of the outer filter element and 
preferentially induces flow in a radial inward direction from the 
foraminous outer wall portion 138 through the annular filter medium and 
through the inner foraminous wall section 150 and thence outwardly through 
the gas outlet conduit 154. 
While the recycling, cleaning and replenishment of the filter medium in the 
two embodiments shown in the drawings can be performed without 
interruption of the filtration cycle, it is also contemplated that a 
plurality of individual filter assemblies can be employed which are 
connected in parallel to enable individual ones to be disconnected 
temporarily from the inlet gas flow during periods in which the filter 
medium is being changed. This provides for further assurance that no 
contaminating particles pass through the filter assembly and remain 
entrained in the outlet gas product. 
While it will be apparent that the invention herein disclosed is well 
calculated to achieve the benefits and advantages as hereinabove set 
forth, it will be appreciated that the invention is susceptible to 
modification, variation and change without departing from the spirit 
thereof.