Filter apparatus

Filtration apparatus in which the filter medium is in the form of a mat assembled with a support grid which is caused to traverse through a filter chamber in a zig zag path. The mat and support grid extend between the side walls of the filter chamber and are advanced by turning rolls disposed at upper and lower levels. The support grid for the filter mat extends between sealing flanges projecting from the side walls of the filter chamber and auxiliary support for the support grid may be provided by employing a foraminous shelf extending between the flanges. The filter medium is disposed so that its edges overlie the sealing flanges, thereby preventing flow of gaseous medium around the edges of the filter mat. Sealing engagement between the sealing flanges and the filter mat is assured by the inclusion of a series of apertures spaced along the length of the flanges. The undersurface of the filter mat faces the downstream side of the filter housing so that the reduced pressure downstream of the filter mat is applied to the undersurface of the filter mat and effects firm engagement with the flanges.

FIELD OF THE INVENTION 
The present invention relates to filter apparatus, and more particularly to 
roll filters in which the filter medium comprises a web of filter material 
which is advanced through the filter chamber transversely to the flow of 
gaseous medium therethrough, the particulate material entrapped by the 
filter medium being carried out of the filter chamber with the spent 
filter medium. 
BACKGROUND OF THE INVENTION 
In order to enable the use of a filter medium which does not posses 
sufficient rigidity to be self-supporting, a roll type filter apparatus 
has been provided in which an endless flexible mesh grid is caused to 
travel through the filter chamber and the filter medium comprises a web of 
filter material deposited on the mesh grid and carried by the grid through 
the filter chamber. The supporting grid is in the form of an endless band 
which recirculates through the filter chamber, for example in a zig zag 
path between two series of guide rolls extending respectively across the 
gas inlet and gas outlet sides of this filter chamber. The filter web or 
mat is fed into the filter chamber onto the supporting grid at one end and 
is withdrawn from the other end. In this fashion the gaseous flow through 
the filter chamber is caused to flow through the filter mat deposited on 
the mesh grid thereby filtering out particulate material from the gaseous 
flow. 
With filter apparatus of this character, there is a tendency, particularly 
when the filter medium is dense and offers a high resistence to gaseous 
flow through it, for the gaseous medium to pass around the edges of the 
filter medium between the side walls of the filter chamber and the side 
edges of the filter medium along the marginal portions of the endless 
grid. 
Prior to the present invention, the problem of leakage of dirty air around 
the edges of the filter medium has been addressed by the provision of a 
special trackway in the side edges of the filter chamber which is designed 
to accomodate the filter medium as it is advanced through the filter 
chamber. For example, as shown in U.S. Pat. No. 3,280,538, the 
construction of the trackway for the filter medium is effective if the 
filter medium is readily compressible so that the track arrangement may 
compressively engage the edges of the filter medium and provide a seal 
against the escape of gaseous medium around the edges. Such an arrangement 
not only requires substantial thickness and compressability in the filter 
web, but also requires that the filter web accurately track within the 
guideways so that lateral displacement of the web does not effect 
disengagement of the web from the guideways. Where the filter web is thin 
and flexible and is not possessed of a high degree of compressability, the 
arrangement shown in this patent is not satisfactory. 
A similar arrangement is shown in U.S. Pat. No. 3,552,099 wherein the 
filter web is carried by a wire mesh conveyor having an edge form which 
rides in a track along the side walls of the filter chamber. A sealing 
flap overlies the track to engage against the exposed surface of the 
filter web on the wire conveyor to seal against the web and prevent 
leakage of gaseous medium between the web and the side wall. Where the web 
material is not resistant to abrasion, such a sealing arrangement tends to 
cause separation of the web material and enables leakage through the 
separations produced. 
It has also been proposed as shown in U.S. Pat. No. 3,406,503 to utilize a 
filter blanket having an edge construction formed to travel in a guideway 
in the side walls of the filter chamber, the edge construction either 
being an integral part of the filter blanket or being a strip applied to 
the edge of the filter material and having a beaded construction adapted 
to ride in the guideways. Such an arrangement requires the filter material 
to be designed specifically to accomodate to the trackway arrangement in 
the filter chamber and substantially increases the cost of the filter 
material. 
SUMMARY OF THE INVENTION 
With the foregoing in mind the present invention provides a filter 
arrangement of the roll type in which the filter medium is carried through 
the filter chamber by an endless grid and the side walls are provided with 
a flange construction adjacent to the side edges of the grid so that a 
filter medium may be deposited on the grid to overlap the flange 
construction and thereby thoroughly filter the gaseous flow passing 
through the filter chamber, the flanges being specially constructed to use 
the differential pressure across the filter medium to minimize leakage of 
the gaseous flow around the edges of the filter medium. 
More specifically, the present invention contemplates a filter chamber 
having side walls with guide means therebetween for directing the traverse 
of a grid conveyor through the chamber, the flange construction comprising 
perforate strip means extending outwardly from the side walls to engage 
under the filter web to seal thereagainst as the mesh grid is caused to 
travel through the filter chamber, the filter web being deposited on the 
mesh grid across its full width to constitute a filter medium which 
overlaps the perforate edge strips or flanges at opposite sides thereof. 
A particular feature of the present invention resides in the presence of 
guide supports for the medium between the side walls of the filter chamber 
to assist in maintaining sealing engagement of said medium with the flange 
construction.

DESCRIPTION OF A PREFERRED EMBODIMENT 
As shown in FIG. 1, the filter apparatus comprises a filter chamber 10 
having a dirty air supply chamber 11 at its upper end and a clean air 
discharge chamber 12 at its lower end so that the dirty air is caused to 
flow into the chamber 10 from its upper side and be discharged from the 
bottom side, depositing the particulate matter carried by the gaseous flow 
upon the upwardly facing surface of the filter medium in the chamber. 
The filter medium is disposed in the chamber in a zig-zag array, for 
example between upper and lower turning rolls 13 and 14 respectively. In 
the present instance the rolls 13 and 14 are of uniform diameter and are 
preferably in the form of slatted reels which permit gaseous flow through 
the portions of the filter medium which are disposed in contact with the 
rolls. The rolls are driven at a common speed by an external chain drive 
15 trained over sprockets on the upper rolls 13 at the inlet side of the 
chamber and under sprockets on the lower rolls 14 at the inlet side of the 
chamber. As shown in FIG. 1 and in FIG. 2, the chain 15 is driven by a 
drive sprocket 16 through a drive train 17 from a motor 18. The drive 
sprocket 16 is carried on a shaft which mounts a roller 19 which is 
mounted externally of the filter chamber 10 at one end. Suitable sprockets 
or guide pulleys 20 are positioned to maintain the chain in driving 
engagement with the sprockets and to direct the chain in its return run 
below the sprockets on the rolls 13 and 14. 
The filter medium has means to support it in the chamber 10. To this end, a 
support mesh grid 22 is formed in an endless loop having a zig-zag path 
portion over the rollers 13 and under the rollers 14. The grid exits from 
the filter chamber 10 at the far end and passes around an exit roll 23 and 
thereafter passes downwardly under an idler roll 24 and back through the 
chamber around the roll 19 onto entrance rollers 25 and 26. The journal 
bearings for the exit roll 23 are adjustible to assure proper tracking of 
the grid. The drive for the internal rollers 13 and 14 and the external 
roller 19 advances the support grid 22 in a generally leftward path over 
and under the rollers 13 and 14 and out the far end and then back to the 
right under the idler 24 to the external roller 19 and back to the 
entrance rollers 25 and 26. 
The support grid 22 preferably comprises a woven PTFE/glass fabric 
screening impregnated with PTFE resins. The interstices of the screening 
fabric are suitably square with a weave density of six openings per inch 
in each direction. Such screen fabric is dimensionally stable from 
-415.degree. F. to +600.degree. F. and is resistant to both chemical 
degradation and abrasion. It has good breaking strength and tear strength, 
in thicknesses of 0.030 inch. A screen fabric of this character has 
unidirectional porosity, permitting free flow normal to the plane of the 
fabric but preventing lateral flow within the plane of the fabric. In this 
specification, including the claims, PTFE is to be read as 
polytetrafluoroethylene. 
The filter as shown in FIG. 1 has a transparent wall section 31 and 
encloses the upper and lower turning rolls 13 and 14, forming a filter 
chamber through which the gaseous medium passes downwardly. As shown in 
FIG. 3, the mesh support grid 22 travels parallel to the wall 31 between 
the rollers 13 and 14, and the side walls of the chamber 10 are provided 
with side members 32 extending angularly between the upper and lower rolls 
and having inwardly directed flanges 33 to underlie the support grid 22 of 
the filter medium. As shown in FIG. 1, the flanges 33 of the members 32 
are disposed tangential to the upper and lower rollers so that they track 
in registry with the mesh support grid 22. Between the flanges 33 a 
supplemental guiding support for the mesh grid is formed by a foraminous 
support shelf 35 secured to the flanges 33 and extending laterally below 
the filter medium between the flanges 33 on opposite sides of the chamber. 
The support shelf 35 is preferably comprised of an expanded metal grating 
which is flattened to provide a low coeffecient of friction with the mesh 
grid 22. The guiding support 35 between the flanges 33 serves to stabilize 
the filter medium as it travels in the zig zag path between the rollers 13 
and 14. The stabilization afforded by the travel on the support 35 also 
avoids excessive deflection or vibration of the grid 22 during its advance 
through the filter chamber. 
A filter mat is assembled with the grid 22 and is guided through the 
chamber 10 with the support grid 22. To this end the filter medium is in 
the form of a blanket or filter mat 39 which is deposited onto the support 
grid 22 adjacent the entrance roller 26 so that the grid 22 may carry the 
mat 39 through the chamber. In the present instance the mat 39 is supplied 
from a roll 41 which is journaled for rotation on brackets 42 underlying 
the entrance end of the filter chamber. Thus the free end of the filter 
blanket may be withdrawn from the roll 41 and engaged onto the support 
grid 22 and fed into the filter chamber 10 so that its edges overlap the 
flanges 33 along the opposite side edges of the grid. The filter mat 
confronts the pressure side of the filter chamber so that the pressure 
differential upstream and downstream of the filter mat in the filter 
chamber tends to press the filter mat 39 and the grid 22 against the 
flanges 33 along the edges thereof. The air pressure thus assists in 
engaging the filter medium with the flanges 33. When the filter mat 39 and 
grid 22 pass over the exit roll, the spent filter mat disengages the mesh 
grid, and in the present instance falls into a collecting bin 45 at the 
exit end of the filter chamber prior to the return of the mesh grid 
through the chamber. 
It should be noted that the drive for the grid may be continuous so as to 
continuously introduce fresh filter medium into the filter chamber and 
withdraw the spent filter medium from the exit end of the chamber. 
Alternatively the support grid 22 may be advanced intermittently. In the 
latter case the filter medium is stationary in the filter chamber until 
such time as it is decided to change the filter medium so as to present a 
fresh filtering action. The advance of the filter medium may be initiated 
when proper filtering action is impaired, for example by sensors 
responsive to the loading of the filter media with the particulate 
material removed from the gaseous flow. It has been found effective to 
time the intermittent advance so that the filter medium advances a 
distance corresponding to the length of the filter medium between the 
upper and lower turning rolls 13 and 14. Alternatively the advance may be 
interrupted when the sensor indicates that proper filtering action is 
restored. 
The pressure on the upstream side of the grid is higher than the pressure 
downstream of the grid in view of the pressure drop which is generated by 
the filter medium. Preferably the filter is operated in a push-pull 
fashion with blowers or fans both upstream and downstream of the filter 
chamber. Thus the positive air pressure on the exposed surface of the mat 
39 tends to press the mat against the flanges 33, and the negative air 
pressure pulls the underside of the filter mat against the flanges. The 
use of positive pressure upstream of the filter medium and negative 
pressure downstream of the filter medium permits the filter chamber to be 
operated at a negative pressure with respect to ambient conditions, 
thereby avoiding the need for entry and exit portals for the filter 
medium. The negative pressure causes any air leakage to be directed 
inwardly into the filter chamber. Furthermore when the filter medium is 
loaded with particulate material sufficiently to impair its porosity, the 
positive pressure upstream of the filter medium will cause leakage of 
unfiltered gaseous medium at the entrance and exit ends of the filter 
chamber. This condition may be detected, for example by observing the 
escape of unfiltered gaseous medium. 
In the present instance, the flange 33 constitutes a separate strip element 
welded to a base strip and extending continuously along the path of the 
mesh grid 22 between the entrance roller 26 and the exit roller 23. As 
shown in FIG. 3, the flange 33 has apertures 34 disposed at spaced 
intervals along its length in order to assure the sealing engagement of 
the filter medium, i.e. the mat 39 and its support mesh 22 on the flanges 
33. In the present case, the flange 33 is approximately 1.5 inches in 
width and the apertures are spaced apart by about 4 inches and are located 
between the longitudinal center line of the flange 33 and the free edge 
thereof which is directed toward the interior of the filter chamber. The 
apertures 34 in the flanges serve to dispel any air cushion or coanda 
effect which might tend to maintain the filter medium spaced from the 
flanges 33 or to separate the mat 39 from the support 22. The apertures 34 
thereby assist in maintaining a close engagement of the filter medium on 
the flanges 33. This close engagement inhibits flow of gaseous medium 
through the space between the filter medium and the side walls of the 
filter chamber. 
The filter mat 39 is preferably a paper-like non-woven web of the type 
disclosed in the Klein U.S. Pat. Nos. 4,239,516 and 4,293,278 and the 
entire disclosures of these patents are hereby incorporated into the 
present application by reference. It is sufficient to state that the 
filter mat comprises a loose web of glass fibers intermixed with 
micro-bits of an expanded thermoplastic styrene-polymer or expanded 
thermoplastic lower polyolefin or flexible foam polyurethane and suitable 
organic bonding agent. The mat may contain other additives or other 
consituents which function as molecular sieve particles or gas-absorption 
mechanisms for pollutants. The filter mat may be fabricated in various 
ways to provide the porosity and the filtration characteristics which are 
desired for a particular end use. For example, a filter mat made in 
paper-making apparatus in accordance with Example 1 of the aforesaid Klein 
U.S. Pat. No. 4,239,516, comprising polystyrene micro-bits, glass fibers 
and polyvinyl alcohol, has a porosity value of 602.8 liters per minute per 
square decimeter of surface at a pressure differential of 2.54 cm. of 
water (gauge). Another suitable filter mat is the mat described in Example 
2 of Klein U.S. Pat. No. 4,293,378 which is also made using paper-making 
apparatus. The mat comprises glass fibers, the aforesaid polymer 
micro-bits, and an intimate blend or cobeat of polymer micro-bits, 
cellulose fibers and polyester fibers, together with polyvinyl alcohol as 
a binding agent and melamine-formaldehyde as a wet-stength enhancing 
agent. The porosity of the finished mat is generally from about 300 to 
about 1500 liters per minute per square decimater at a pressure 
differential of 2.54 cm. of water (gauge). The mat possesses excellent wet 
strength, which is on the order of 2 kg./cm. 
Still another suitable filter mat is a non-woven material comprising 
cellulose and rayon filters held together by a suitable organic binder and 
having activated carbon particles dispersed throughout for improved 
adsorption capacity. This mat is also conveniently prepared using standard 
paper-making apparatus and may, if desired, contain polyester fibers and 
the aforesaid micro-bits, the latter serving, inter alia, to prevent 
dusting of the carbon particles from the mat. Such a mat is commercially 
available from Crane & Co., Inc., Dalton, Mass. A mat of this type having 
porosity from about 150 to about 450 liters per minute per square 
decimeter at a pressure differential of 2.54 cm. of water (gauge) is very 
effective, particularly in conjunction with the introduction of an 
atomized water spray into the filter chamber, in filtering smoke-laden 
gases or vapors. 
The use of a support grid which rides on sealing flanges along the marginal 
edges makes it possible to minimize the expense of fabrication of the 
filter mat since the filter mat is not required to have sufficient 
rigidity to be self-sustaining as it is advanced through the filter 
chamber. Furthermore, the edge portions of the filter mat need not be 
specially formed to provide a seal with the side walls of the filter 
chamber and irregular edges may be tolerated without adversely affecting 
the filtering capacity of the apparatus since the irregularities in the 
edges overlie the flanges 33 and do not permit leakage of gaseous medium 
through the irregularities, as would be the case in prior art 
arrangements. The composite filter medium consisting of the mat 39 and 
grid 22 simplifies recovery operations. In some applications, the 
particulate matter can be washed from the filter mat and discarded to 
enable the mat to be recycled. In other applications, the particulate 
matter may be recovered from the mat and salvaged, and the spent mat may 
be discarded. For these several reasons, the present invention provides an 
apparatus which may utilize filter mats which are fabricated and wound 
onto rolls for use in the present apparatus at minimum expense. 
While a particular embodiment of the present invention has been herein 
illustrated and described it is not intended to limit the invention to 
such disclosures but changes and modifications may be made therein and 
thereto within the scope of the following claims.