U.S. patent application number 13/126130 was filed with the patent office on 2012-02-09 for filter bag, pleatable filtration material therefore, and process of making same.
This patent application is currently assigned to Sefar BDH Inc.. Invention is credited to Luc PARENT, Sylvain VIEUILLE.
Application Number | 20120034134 13/126130 |
Document ID | / |
Family ID | 42128154 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034134 |
Kind Code |
A2 |
PARENT; Luc ; et
al. |
February 9, 2012 |
FILTER BAG, PLEATABLE FILTRATION MATERIAL THEREFORE, AND PROCESS OF
MAKING SAME
Abstract
The pleated filter bag, which can be used in a bag-house type
dust collector, is elongated and has a longitudinal hollow center
with an open end, and a pleated filter wall circumscribing the
hollow center. The pleated filter wall has a felt such as PTFE
fibers felted onto an apertured and pleatable scrim which can be
made of metal, and having a permeability lower than a permeability
of the scrim. A membrane of lower-permeability material, such as an
E-PTFE membrane, covers the support felt on the outer side of the
bag.
Inventors: |
PARENT; Luc; (Saguenay,
QC) ; VIEUILLE; Sylvain; (Gemil, FR) |
Assignee: |
Sefar BDH Inc.
200, rue Clement-Gilbert, bureau 101
Saguenay
QC
G7H 5B1
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20110206564 A1 |
August 25, 2011 |
|
|
Family ID: |
42128154 |
Appl. No.: |
13/126130 |
Filed: |
October 26, 2009 |
PCT Filed: |
October 26, 2009 |
PCT NO: |
PCT/CA09/01539 |
371 Date: |
April 26, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61/108619 |
Oct 27, 2008 |
|
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61/152420 |
Feb 13, 2009 |
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Current U.S.
Class: |
422/177 ; 28/104;
55/382; 55/486 |
Current CPC
Class: |
B32B 2264/0257 20130101;
B01D 39/1623 20130101; B32B 27/12 20130101; B01D 61/147 20130101;
B01D 71/36 20130101; B01D 39/1692 20130101; B01D 2239/065 20130101;
B32B 15/18 20130101; B32B 2255/02 20130101; B32B 27/322 20130101;
B32B 15/14 20130101; B32B 2255/26 20130101; B32B 2264/102 20130101;
B32B 2307/718 20130101; D04H 1/559 20130101; B01D 2239/0407
20130101; B32B 2307/714 20130101; B32B 2262/0253 20130101; B32B
5/30 20130101; B32B 2509/00 20130101; D04H 1/492 20130101; D04H
1/4326 20130101; B32B 2307/306 20130101; B32B 2307/72 20130101;
B32B 15/20 20130101; D04H 1/64 20130101; B01D 63/00 20130101 |
Class at
Publication: |
422/177 ;
028/104; 055/486; 055/382 |
International
Class: |
B01D 50/00 20060101
B01D050/00; B01D 39/08 20060101 B01D039/08; B01D 46/52 20060101
B01D046/52; D04H 1/46 20060101 D04H001/46 |
Claims
1. A pleatable filtration material comprising a felt having PTFE
fibers felted onto a pleatable metallic scrim, a permeability of at
least 20 l/dm.sup.2/minute at 12 mm of water gauge and a weight
between 100 and 1000 g/m.sup.2, the felt having a density between
150 and 1000 g/m.sup.2 and a permeability suitably greater than
that of the scrim and between 20 and 250 l/dm.sup.2/minute at 12 mm
of water gauge; and a membrane laminated onto the felt, made of
E-PTFE and having a permeability of between 3 and 75
l/dm.sup.2/minute at 12 mm of water gauge; wherein the filtration
material can be pleated at room temperature and thenceforth
operably retain its pleats.
2. The pleatable filtration material of claim 1 wherein the PTFE
fibers are spunlaced onto the metallic scrim.
3. The pleatable filtration material of claim 1 further comprising
particles of catalyst having a size of less than 10 microns, at
least one of present on the surface of the PTFE fibers and embedded
into the PTFE fibers.
4. The pleatable filtration material of claim 3 wherein the
particles of catalyst are selected from the group consisting of
titanium dioxide, iron oxide, zeolith, copper oxide, tungsten
oxide, aluminum oxide, cobalt oxide, nickel oxide, chromium oxide,
palladium, nickel, gold, platinum, silver and rhodium.
5. The pleatable filtration material of claim 1 wherein the
membrane has a permeability of between 12 and 50 l/dm.sup.2/minute
at 12 mm of water gauge.
6. The pleatable filtration material of claim 1 wherein the
membrane is laminated directly onto the felt.
7. The pleatable filtration material of claim 1 wherein the
membrane is laminated onto the felt via a binder which has
resistance characteristics at least comparable to that of the PTFE
fibers.
8. The pleatable filtration material of claim 7 wherein the binder
is fluorinated ethylene propylene copolymer (FEP) or a
hexafluoropropylene-tetrafluorethylene copolymer.
9. The pleatable filtration material of claim 1 wherein the metal
scrim has chemical and thermal resistance characteristics at least
comparable to PTFE fibers.
10. A process of making a pleatable filtration material comprising
felting PTFE fibers onto a pleatable metallic scrim, a permeability
of at least 20 l/dm.sup.2/minute at 12 mm of water gauge and a
weight between 100 and 1000 g/m.sup.2, until a felt density between
150 and 1000 g/m.sup.2 in addition to the density of the scrim and
a permeability greater than that of the scrim and between 20 and
250 l/dm.sup.2/minute at 12 mm of water gauge are reached; and
laminating an E-PTFE membrane having a permeability of between 3
and 75 l/dm.sup.2/minute at 12 mm of water gauge onto a face of the
felted PTFE fibers.
11. The process of claim 10 wherein the step of felting is done by
hydro-entanglement.
12. The process of claim 10, wherein the laminating further
comprises applying a binder in liquid suspension in a solvent onto
the face of the felted PTFE fibers, and subsequently evaporating
the solvent, the relative weight of transferred solid binder being
between about 1% and 10%.
13. The process of claim 10, wherein the laminating is done
directly onto the face of the felted PTFE fibers.
14. The process of claim 10 further comprising pleating the
filtration material at room temperature.
15. A pleated filter bag for use in a bag house dust collector, the
filter bag being elongated and comprising a longitudinal hollow
center with an open end, and a pleated filter wall circumscribing
the hollow center, the pleated filter wall having a felt felted
onto an apertured and pleatable scrim and having a permeability
lower than a permeability of the scrim and appropriate for
filtration, and a membrane having a permeability substantially
lower than the permeability of the felt and covering the felt on
the outer side thereof facing the hollow center, wherein all of the
scrim, the felt, and the membrane are resistant to a harsh
filtration environment of the dust collector.
16. The filter bag of claim 15 wherein the scrim is made of
metal.
17. The filter bag of claim 15 wherein the felt has PTFE fibers and
the membrane is made of E-PTFE.
18. The pleatable filtration material of claim 17 wherein particles
of catalyst are at least one of present on the surface of the PTFE
fibers and embedded into the PTFE fibers.
19. The filter bag of claim 15 wherein the felt is spunlaced onto
the scrim by water jets.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national stage filing under 35 U.S.C.
.sctn.371 based upon international application no.
PCT/CA2009/001539, filed 26 Oct. 2009 and published in English on 6
May 2010 under international publication no. WO2010/048709, which
claims priority to U.S. provisional application Nos. 61/108,619,
filed 27 Oct. 2008 and 61/152,420, filed 13 Feb. 2009. All of the
foregoing are hereby incorporated by reference as though fully set
forth herein.
FIELD
[0002] The specification relates to pleatable materials, or
fabrics, for use in filtration, and more particularly for use as
pleated "filter bags" in baghouse-type dust collectors, for
example.
BACKGROUND
[0003] A dust collector is an equipment to remove particles in an
industrial fume. Typically the collector contains between hundreds
to thousands of cylindrical elements referred to as bags. The bags
are made of a filtration fabric that is porous. As the gas flows
through, the porous filtration fabric collects particles. The
particles can form a cake on the surface after minutes of
operation, and the bags are typically cleaned by a reversed
jet.
[0004] One of the important parameters of the filtration fabric is
the filtration efficiency. The efficiency of filtration of bags is
related to the total surface area. Typically, if the surface area
is increased, then the velocity of gas and particles going through
the fabric will be reduced, which decreases the probability of
undesired particles going through the fabric and can consequently
reduces the particle emissions. Moreover, a higher surface area can
reduce the probability of particles getting embedded into the
fabric in a manner where they resist the reversed jet, thereby
increasing the lifespan of the filter. It is also possible, by
increasing the surface area, to increase the capacity of a dust
collector. It is thus generally sought to increase the surface area
of the bags in dust collectors, where possible.
[0005] Typically, pleated bags have a greater surface area than
non-pleated bags (i.e. simply cylindrical bags). Using pleated bags
instead of non-pleated bags is thus one way of increasing the
surface area without necessarily increasing the overall size of the
dust collector system. In many cases, replacement of non-pleated
bags by pleated bags can increase the surface area by two to three
times.
[0006] Pleated bags can be made using a pleatable material which
keeps its shape after pleating. The pleating can be done with a
pleating machine. Some pleating machines operate at room
temperature.
[0007] Alternately, for some materials which require thermosetting
to retain their pleats, pleating machines having heating blades are
used to fold the fabric and keep pressure on the pleats until the
fabric is cooled back to room temperature. Heretofore, such
processes have been used with polymers that can be thermally formed
and have a relatively small density.
[0008] Some materials that are not thermally formable per se can be
made so by adding a thermo-setting resin. An example of this is
fiberglass felt impregnated with phenolic resin. The temperature of
blades allow setting of the phenolic resin which subsequently acts
to maintain the shape of the pleats. The reaction being
irreversible, the pleats subsequently keep their shape even at high
temperature.
[0009] However, even given the state of the art, some filtration
materials could not be pleated by the known means and therefore
remained known as being unpleatable. Nevertheless, given some
desired characteristics, at least one of these unpleatable
filtration materials remained a popular choice for some specific
applications despite the fact that it was not available in pleated
form. There thus remained a strong need for an equivalent to such
`unpleatable` materials in pleated form due to the many advantages
of pleats in filtration. This called for improvement.
SUMMARY
[0010] As it will appear from the description below, a filtration
material such as a PTFE felt covered by an E-PTFE membrane, which
was traditionally known as unpleatable, can now be made pleatable
by felting with a pleatable scrim, more particularly a pleatable
metallic scrim. There are many metals which are pleatable when
provided in apertured sheets, and the pleatability of a metallic
scrim can take precedence on the pleatability of both the felted
PTFE and the E-PTFE membrane. Felting by hydro-entanglement
(spunlacing) can be better suited than needle-felting when using a
metallic scrim.
[0011] In accordance with one aspect, there is provided a pleatable
filtration material comprising a felt having PTFE fibers felted
onto a pleatable metallic scrim, a permeability of at least 20
l/dm.sup.2/minute at 12 mm of water gauge and a weight between 100
and 1000 g/m.sup.2, the felt having a density between 150 and 1000
g/m.sup.2 and a permeability greater than that of the scrim and
between 20 and 250 l/dm.sup.2/minute at 12 mm of water gauge; and a
membrane laminated onto the felt, made of E-PTFE and having a
permeability of between 3 and 75 l/dm.sup.2/minute at 12 mm of
water gauge, preferably between 12 and 50 l/dm.sup.2/minute at 12
mm of water gauge; wherein the filtration material can be pleated
using a traditional pleater at room temperature and thenceforth
retain its pleats.
[0012] In accordance with one aspect, there is provided a process
of making a pleatable filtration material comprising felting PTFE
fibers onto a pleatable metallic scrim having resistance
characteristics at least comparable to that of the PTFE fibers, a
permeability of at least 20 l/dm.sup.2/minute at 12 mm of water
gauge and a weight between 100 and 1000 g/m.sup.2, until a felt
density between 150 and 1000 g/m.sup.2 in addition to the density
of the scrim and a permeability greater than that of the scrim and
between 20 and 250 l/dm.sup.2/minute at 12 mm of water gauge are
reached; and laminating an E-PTFE membrane having a permeability of
between 3 and 75 l/dm.sup.2/minute at 12 mm of water gauge,
preferably between 12 and 50 l/dm.sup.2/minute at 12 mm of water
gauge onto a face of the felted PTFE fibers.
[0013] In accordance with one aspect, there is provided a pleated
filter bag for use in a bag house dust collector, the filter bag
being elongated and comprising a longitudinal hollow center with an
open end, and a pleated filter wall transversally circumscribing
the hollow center, the pleated filter wall having a felt felted
onto an apertured and pleatable scrim and having a permeability
lower than a permeability of the scrim and appropriate for
filtration applications, and a membrane having a permeability
substantially lower than the permeability of the felt and covering
the felt on the outer side thereof facing the hollow center,
wherein all of the scrim, the felt, and the membrane are resistant
to a harsh filtration environment of the dust collector.
[0014] In accordance with another aspect, there is provided a
filter fabric construction which incorporates a pleatable scrim to
the base felt. The pleatability of the scrim takes precedence on
the pleatability of the remaining components of the filter fabric,
thereby rendering the filter fabric pleatable. This construction,
or associated production method, can make pleatable a material such
as PTFE, which was traditionally known as non-pleatable.
[0015] In accordance with another aspect, there is provided a
pleatable filtration fabric having an E-PTFE laminated PTFE felt.
This filtration fabric is made pleatable while at least
substantially maintaining the thermal and chemical resistance
characteristics of the PTFE by making the PTFE felt with a
pleatable, heat-resistant and chemical-resistant scrim. The
pleatability of the metallic scrim takes precedence in the
combination and makes the entire material pleatable.
[0016] It will be understood that in the instant specification, the
expression "pleatable" is to be understood in the context of
operability in filtration. A pleatable filtration element will
retain its pleats for a reasonable lifespan in the context of a
normal or recommended use. For instance, a felt of polyester with a
polyester scrim can be viewed as a non-pleatable fabric, whereas
spunbounded polyester, which is denser and stiffer, can be viewed
as pleatable.
DESCRIPTION OF THE FIGURES
[0017] In the appended figures,
[0018] FIG. 1 is a perspective view, fragmented, showing an example
of a felt having a pleatable scrim.
DETAILED DESCRIPTION
[0019] One example of a material which was still used in unpleated
form is polytetrafluoroethylene (PTFE), at least partly because of
its exceptional thermal and chemical resistance characteristics
which made the only viable choice for some harsh environments. An
example of an application where unpleated PTFE-based bags were
still used is dust collectors of waste incineration facilities.
Incinerated wastes typically contain plastics which emit aggressive
chemicals such as HCl, H.sub.2SO.sub.4, and HF during combustion.
PTFE was appreciated for resisting to the combination of high
temperatures (.about. 150 to 260.degree. C.) and aggressive
chemicals present in such waste incineration gaseous by-products.
In applications such as waste incineration where tolerated emission
levels were quite low, the PTFE fabric can be covered by a membrane
to get a more efficient degree of filtration. A porous expanded
PTFE membrane (E-PTFE) can be used to this end, laminated on the
PTFE felt.
[0020] Tests attempting to pleat a PTFE felt (with or without
catalyst) with a PTFE scrim failed. After pleating, the shape was
not kept in a satisfactory way. Further, adding resins to the PTFE
was found inefficient, at least partly due to the lack of adhesion
and wetting by many of the tested resins on PTFE fibers.
[0021] The mere continued use of non-pleated PTFE filtration bags
in dust collectors of applications such as waste incineration
facilities, in itself demonstrates the former unavailability of
this material in pleated form, considering the strong incentives
for using pleated bags instead of cylindrical bags.
[0022] As will be detailed below, it will be understood how such
materials and others can now be pleatable by felting the fabric
onto a pleatable scrim. A type of pleatable scrim which can be used
in making a PTFE felt pleatable is a metallic scrim.
[0023] FIG. 1 shows an exemplary sample of a PTFE felt spunlaced
onto a metallic scrim. In this example, the metallic scrim is a
square steel screen. As shown in the cut-out portion on the bottom
and left-hand side corner of the sample, the metallic scrim is
sandwiched between two layers of PTFE felt. In fact, during
hydro-entanglement of the PTFE fibers, the fibers are placed on one
side of the scrim, and partially pass through it, to the other
side. The right-hand side of the sample is shown pleated. The
E-PTFE membrane (not shown in the illustration), can later be
laminated onto one face of the PTFE felt with metallic scrim. The
PTFE felt can act as a support layer for the E-PTFE membrane which
has a permeability substantially lower than the permeability of the
felt. In use, the E-PTFE membrane faces the outside of the
filtration bag and determines the relatively low permeability of
the filtration material. The felt can thus be used to provide a
cushioned support to the membrane, and, in combination with the
metallic scrim, gives mechanical resistance to the membrane which
acts as the actual "filter" during use but which is not practically
usable alone. In fact, in many applications, the stresses which
would be imparted to the E-PTFE membrane by the scrim during use if
it was adhered directly thereto instead of being supported via
felt, would result in an E-PTFE membrane having a very short useful
life. The metallic scrim additionally provides pleatability to the
filtration material because its higher pleatability takes
precedence in the assembly.
[0024] The felt can be made of expanded porous or non-expanded PTFE
fibers. The felt can be made by spunlacing the fibers onto the
metallic scrim by a water jet--a process commonly referred to as
hydro-entanglement. Hydro-entanglement can allow to avoid or reduce
damage to the metallic scrim which could result if using
conventional needle felting instead. The felt can have a density
between 150 and 1000 g/m.sup.2, preferably between 250 and 700
g/m.sup.2, and a permeability between 20 and 250 l/dm.sup.2/minute
at 12 mm of water gauge, preferably above 100 l/dm.sup.2/minute,
for example.
[0025] The metallic scrim can be made of galvanized steel,
stainless steel, aluminum, aluminum alloy, bronze, brass, copper,
copper-based alloy, nickel, nickel-based alloy, or any suitable
metal or alloy, provided it has suitable pleatability and
resistance, and that it is ductile enough to be pleated without
breaking. The metal can be a woven mesh, a punched metal sheet or
any method that will create a metal sheet with suitable apertures
in it. The permeability of the material should be greater than the
permeability which is desired of the felt, preferably at least 20
l/dm.sup.2/minute at 12 mm of water gauge. The weight of the metal
scrim can be between 100 and 1000 g/m.sup.2, preferably between 300
and 700 g/m.sup.2 for example. Metallic scrims of various known
types of metals can have chemical and temperature resistance
characteristics suitable for harsh applications.
[0026] The felted support layer can be treated with a binder prior
to lamination of the membrane, or the binder can be omitted. The
fibers of the felt can act in a binding manner in certain
applications. If used, the binder can be a fluorinated ethylene
propylene copolymer (FEP) or a
hexafluoropropylene-tetrafluorethylene copolymer, for example, or
any other suitable binder. The binder can be provided at a
concentration of between 25-50% by weight in a liquid suspension,
and be either sprayed on a selected side of the support layer or
transferred thereon using a roll. The material can then be heated
in an oven at .about.120 to 240.degree. C., to evaporate the
solvent. After evaporation, the weight of transferred solid binder
can represent a relative weight of between 1% and 10% (relative to
the weight of the fabric).
[0027] The membrane, which can be made of commercially available
E-PTFE, preferably has a permeability between 3 and 75
l/dm.sup.2/minute at 12 mm of water gauge, more preferably between
12 and 50 l/dm.sup.2/minute at 12 mm of water gauge. The membrane
can be laminated on the side having the binder at a temperature of
270.degree. C.
[0028] It will be noted that in some instances, PTFE felt for use
in applications such as incinerators can have particles of catalyst
deposited on the surface or embedded into the PTFE fibers. This can
be desirable in a pleatable fabric and typically does not affect
pleatability. For example, some catalysts help reducing emissions
of dioxin, furan or nitrous oxide from waste incineration. The
catalyst typically is typically provided a volume less than 20% of
the volume of the PTFE fibers. Examples of catalysts include
titanium dioxide (TiO.sub.2), iron and cobalt (provided in the form
of oxides), nickel, platinum and palladium. Other examples of
catalysts include zeolith, copper oxide, tungsten oxide, aluminum
oxide, chromium oxide, gold, silver, rhodium etc. If used, the
catalyst should be provided in a particles size of less than 10
microns, but can be of any suitable shape, such as spheres,
whiskers, plates, flakes, etc.
[0029] A resulting pleatable filtration material, or fabric, can
include PTFE fibers spunlaced to a steel scrim, covered by a
membrane. Such a fabric can be pleated using a traditional pleater
operating at room temperature. The use of a pleatable metallic
scrim can render the use of heated pleater blades unnecessary. An
exemplary embodiment thereof is provided below:
Example 1
[0030] PTFE fibers are spunlaced onto a 400 g/m.sup.2 stainless
steel scrim by hydro-entanglement. After entangling the total
weight is 800 g/m.sup.2. The permeability of the material at this
step is about 200 l/dm.sup.2/minute. The resulting felted support
material is then sprayed with a suspension of FEP particles to add
about 25 g/m of FEP particles after drying at 150.degree. C. Then,
an E-PTFE membrane is laminated thereon with the temperature of the
FEP particles raised to 270.degree. C. The resulting filtration
material has a weight of 825 g/m.sup.2, and a permeability between
15 and 30 l/dm.sup.2/minute at 12 mm of water gauge, and is
pleatable at room temperature.
Example 2
[0031] Titanium dioxide particles of less than 10 microns in size
are mixed with a PTFE dispersion. The titanium dioxide can
correspond to 1-90% by volume, preferably 25-85% by volume, for
example. The paste is extruded and calendered to form a tape. The
tape is slitted along the length, expanded and processed over a
rotating pinwheel to form fibers. These fibers with catalyst on the
surface are spunlaced onto a 500 g/m.sup.2 stainless steel 316
scrim by hydroentanglement. After entangling the total weight is
900 g/m.sup.2. The E-PTFE membrane is laminated directly on the
surface of the catalytic felt, the fibers acting as the binding
agent. The resulting material has a weight of 900 g/m.sup.2, a
permeability between 15 and 30 l/dm.sup.2/min at 12 mm of water
gauge and is pleatable at room temperature.
[0032] It is to be understood that above example is given for
illustrative purposes only. Alternate embodiments can be realized.
For instance, thicker or thinner fabrics can be realized using more
or less spunlaced PTFE, and different E-PTFE membranes. The
pleatable metallic scrim can be applied to materials other than
PTFE. Further, other scrim materials than metals can have similar
pleatability and resistance characteristics. The use of a catalyst
is optional. Given the above, the scope is indicated by the
appended claims.
* * * * *