U.S. patent application number 11/338394 was filed with the patent office on 2007-07-26 for blend of polytetrafluoroethylene, glass and polyphenylene sulfide fibers and filter felt made from same.
Invention is credited to Kishio Miwa, Arthur Russell Nelson, Roy B. Parker.
Application Number | 20070173159 11/338394 |
Document ID | / |
Family ID | 38286149 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070173159 |
Kind Code |
A1 |
Miwa; Kishio ; et
al. |
July 26, 2007 |
Blend of polytetrafluoroethylene, glass and polyphenylene sulfide
fibers and filter felt made from same
Abstract
An improved intimate cardable fiber blend containing
polytetrafluoroethylene fibers, dual glass fibers and polyphenylene
sulfide fibers and a filtration felt including a needled batt of
the intimate cardable fiber blend made by mechanically blending the
polyphenylene sulfide fibers and glass fibers with
polytetrafluoroethylene fibers, carding the blend to form a
nonwoven batt and needling the batt to provide a felt.
Inventors: |
Miwa; Kishio; (Madison,
AL) ; Nelson; Arthur Russell; (Midlothian, VA)
; Parker; Roy B.; (Simpsonville, SC) |
Correspondence
Address: |
SIROTE & PERMUTT, P.C.
P.O. BOX 55727
2311 HIGHLAND AVENUE SOUTH
BIRMINGHAM
AL
35255-5727
US
|
Family ID: |
38286149 |
Appl. No.: |
11/338394 |
Filed: |
January 24, 2006 |
Current U.S.
Class: |
442/320 ;
428/373 |
Current CPC
Class: |
D04H 1/74 20130101; Y10T
428/2929 20150115; D04H 1/4382 20130101; B01D 39/1623 20130101;
D04H 1/4218 20130101; D04H 1/4318 20130101; Y10T 442/50 20150401;
B01D 39/2017 20130101 |
Class at
Publication: |
442/320 ;
428/373 |
International
Class: |
D04H 1/08 20060101
D04H001/08; D02G 3/00 20060101 D02G003/00 |
Claims
1. An intimate blend of fibers comprising polyphenylene sulfide
fibers, glass fibers and fluoropolymer fibers.
2. The blend according to claim 1 including from about 20% to about
70% glass fibers.
3. The blend according to claim 2 including from about 30% to about
50% glass fibers.
4. The blend according to claim 3 wherein the glass fibers are dual
glass fibers.
5. The blend according to claim 3 wherein the glass fibers are
between about 1.5 inches and 4 inches in length and have a diameter
of about 6 microns.
6. The blend according to claim 1 wherein the blend includes from
about 40% to about 60% polyphenylene sulfide fibers.
7. The blend according to claim 6 wherein the polyphenylene sulfide
fibers are between about 2.0 inches and about 4.5 inches in length
and have a denier per filament of between about 2 and about 7.
8. The blend according to claim 1 including from about 5% to about
30% polytetrafluoroethylene fibers.
9. The blend according to claim 8 including from about 7% to about
20% polytetrafluoroethylene fibers.
10. The blend according to claim 1 including from about 40% to
about 60% polyphenylene sulfide fibers, from about 30% to about 50%
glass fibers and about 10% polytetrafluoroethylene fibers.
11. The blend according to claim 1 wherein the polyphenylene fibers
are present in an amount less than that of the glass fibers.
12. The blend according to claim 1 wherein the ratio of glass
fibers and polyphenylene fibers to fluoropolymer fibers is about 9
to 1.
13. The blend according to claim 1 wherein the ratio of glass
fibers and fluoropolymer fibers to polyphenylene fibers is from
about 2 to 3 to about 3 to 2.
14. The blend according to claim 1 wherein the ratio of
fluoropolymer fibers and polyphenylene fibers to glass fibers is
from about 1 to 1 to about 7 to 3.
15. The blend according to claim 1 wherein for every one part
fluoropolymer fibers there is between about 3 to about 5 parts
glass fibers and between about 4 to about 6 parts polyphenylene
sulfide fibers.
16. The fiber blend according to claim 1 comprising about one part
polytetrafluoroethylene staple fibers, about 3 to about 5 parts
glass staple fibers and about 4 to about 6 parts polyphenylene
sulfide staple fibers.
17. A filter comprising a membrane-type filter laminated to a
filter felt prepared from the intimate fiber blend of claim 1.
18. The filter according to claim 17 wherein the membrane-type
filter is a polytetrafluoroethylene membrane.
19. An improved filter felt comprising a needled batt of the
intimate fiber blend of claim 1.
20. The felt according to claim 19 having a weight ranging between
about 14.8 ounces per square yard to about 18.2 ounces per square
yard.
21. The felt according to claim 19 having a thickness ranging
between about 0.074 inches to about 0.088 inches.
22. The felt according to claim 19 wherein the supporting scrim is
made of at least one of polyphenylene sulfide fibers and
polytetrafluoroethylene fibers.
23. The felt according to claim 19 wherein the felt exhibits a PM
2.5 emissions result of about 0.0000249 grams per dry standard
cubic meter according to ASTM Test Method D6830-02.
24. The felt according to claim 19 wherein the felt exhibits a
total mass emissions result of about 0.0000249 grams per dry
standard cubic meter according to ASTM Test Method D6830-02.
25. The felt according to claim 19 wherein the felt exhibits an
initial residual pressure drop of about 2.28 centimeters of water
gauge according to ASTM Test Method D6830-02.
26. The felt according to claim 19 wherein the felt exhibits a
residual pressure drop increase of about 1.39 centimeters of water
gauge according to ASTM Test Method D6830-02.
27. The felt according to claim 19 wherein the felt exhibits an
average residual pressure drop of about 3.03 centimeters of water
gauge according to ASTM Test Method D6830-02.
28. The felt according to claim 19 wherein the felt exhibits a
filter sample weight gain of about 1.82 grams according to ASTM
Test Method D6830-02.
29. The felt according to claim 19 wherein the felt exhibits a PM
2.5 removal efficiency of about 99.99981% according to ASTM Test
Method D6830-02.
30. The felt according to claim 19 wherein the felt exhibits a
total mass removal efficiency of about 99.99985% according to ASTM
Test Method D6830-02.
31. The felt according to claim 19 wherein the felt exhibits a
permeability of about 25.2 cubic feet per minute to about 40.4
cubic feet per minute.
32. The felt according to claim 19 wherein the felt exhibits a
Mullen Burst strength average of about 252 pounds per square inch
to about 298 pounds per square inch.
33. The felt according to claim 19 wherein the felt exhibits,
according to ASTM Test Method D6830-02, less PM 2.5 emissions than
that of a 100% polyphenylene sulfide fiber filter felt material
having a weight per square yard substantially equal to the weight
per square yard of the felt.
34. The felt according to claim 19 wherein the felt exhibits a
Mullen Burst strength average greater than that of a 100%
polyphenylene sulfide fiber filter felt material having a weight
per square yard substantially equal to the weight per square yard
of the felt.
35. The felt according to claim 19 wherein the felt exhibits a
greater resistance to burn-through from a spark than that of a 100%
polyphenylene sulfide fiber filter felt material having a weight
per square yard substantially equal to the weight per square yard
of the felt.
36. The felt according to claim 19 wherein the felt exhibits a
burn-through temperature greater than that of a 100% polyphenylene
sulfide fiber filter felt material having a weight per square yard
substantially equal to the weight per square yard of the felt.
37. A process for preparing the filter felt of claim 19 comprising,
mechanically blending about 3 to about 5 parts glass staple fibers
and about 4 to about 6 parts polyphenylene sulfide staple fibers to
every one part polytetrafluoroethylene staple fibers, carding and
crosslapping the fibers with a carding machine, and needling the
batt onto one or both sides a scrim of polyphenylene sulfide
fibers.
38. The felt according to claim 19 wherein the felt resists
melt-through by one or more stainless steel ball bearings of 1/4 to
1/2 inch, heated to about 343.degree. C., when the heated one or
more ball bearings are placed on the filter felt while the filter
is stretched horizontally across a frame.
39. An intimate fiber blend comprising about one part
polytetrafluoroethylene staple fibers, about 3 parts glass staple
fibers and about 6 parts polyphenylene sulfide staple fibers
wherein the polyphenylene sulfide staple fibers are present as 2.7
denier polyphenylene sulfide staple fibers and the
polytetrafluoroethylene staple fibers have a denier per filament of
between 3.5 and 6.7.
40. An intimate fiber blend comprising about one part
polytetrafluoroethylene staple fibers, about 4 parts glass staple
fibers and about 5 parts polyphenylene sulfide staple fibers
wherein the polyphenylene sulfide staple fibers are present as 2.7
denier polyphenylene sulfide staple fibers and the
polytetrafluoroethylene staple fibers have a denier per filament of
between 3.5 and 6.7.
41. An intimate fiber blend comprising about one part
polytetrafluoroethylene staple fibers, about 5 parts glass staple
fibers and about 4 parts polyphenylene sulfide staple fibers
wherein the polyphenylene sulfide staple fibers are present as 2.7
denier polyphenylene sulfide staple fibers and the
polytetrafluoroethylene staple fibers have a denier per filament of
between 3.5 and 6.7.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an intimate fiber blend and
more particularly to an intimate fiber blend including
polytetrafluoroethylene, glass and polyphenylene sulfide fibers and
a filter felt made therefrom.
BACKGROUND OF THE INVENTION
[0002] Use of bag filters as filters for collecting the dust
emitted, for example, from refuse incinerators, coal boilers and
metal melting furnaces, is well-known. In these applications, bag
filters are required to exhibit heat resistance, since the exhaust
gas temperatures are in a high temperature range of 150.degree. C.
to 250.degree. C., depending on application. The conventional
filter media used at such high temperatures are made of felt
produced by laminating a ground fabric and a web using
polyphenylene sulfide fibers, metaaramid fibers, polyimide fibers,
fluorine fibers or glass fibers, etc., and entangling the fibers
using a needle punch or jet water stream, etc.
[0003] Filters containing polytetrafluoroethylene fibers are
advantageous because they have outstanding resistance to high
temperatures, chemical attack and abrasion. However, commercially
available filters containing these fibers are expensive and often
permit passage of more particulate matter (PM) than is desirable
under today's increasingly rigorous environmental standards.
Polyphenylene sulfide fibers also have excellent properties such as
heat resistance, barrier properties and chemicals resistance, but
like filters containing polytetrafluoroethylene filter felt,
polyphenylene sulfide filter felts permit passage of more
particulate matter than is desired, though typically not as much as
polytetrafluoroethylene felts. Such filter media exhibit another
shortcoming. Polyphenylene sulfide fiber filters have poor
burn-through resistance when contacted by sparks, which are often
present in the effluent of incinerators, coal boilers and metal
melting furnaces. The holes that result from spark burn-through can
result in decreased filtration performance of such filters.
[0004] An alternative to filter felts for use in bag filters are
membrane-type filters. Generally, membrane filters are expected to
have a greater filter efficiency than that of filter felts. In
part, that is because membrane filters have pores of a controlled
and predetermined size through which particulate laden air can
pass. The pores are small enough to capture particulate matter that
conventional filter felts cannot. However, the small pore size of
today's membrane filters often causes them to produce an
undesirably high pressure drop across the filters which relates to
decreased air permeability and ultimately decreased filtration
performance. This is particularly true for membrane filters
designed to capture fine particles, i.e., particles less than 2.5
micrometers in diameter, which are believed to pose the greatest
health risks. Consequently, the overall filtration performance of
such membrane filters is offset by poor air permeability.
[0005] Another shortcoming of membrane filters is that they are
often too fragile to be implemented in a certain application. For
example, the filtration of hot gases produced from the manufacture
of asphalt regularly occurs in an environment that can damage
membrane filters, which results in the decrease service life of
such filters. This happens in part because of the nature of the
equipment used in the asphalt industry and its inadequate upkeep.
In addition, membrane filters are expensive to use compared, for
example, to polyphenylene sulfide fiber filter felts.
[0006] The benefit of the filter felt of the present invention is
its unexpected ability to meet or exceed the filtration efficiency
of membrane filters while providing a lower pressure drop across
the filter. This allows for a more cost effective filtration design
for a bag house. In addition, the present invention is intended to
solve the above problems by providing a filter felt having good
heat and burn-though resistance properties and improved strength as
a filter medium when used at high temperatures of 150.degree. C. to
250.degree. C. in refuse incinerators, coal boilers, metal melting
furnaces, etc. Further, the filter felt of the present invention
will likely exhibit a longer service life than conventional 100%
polyphenylene sulfide filter felts when used extensively at high
temperatures of 190.degree. C. to 205.degree. C.
SUMMARY OF THE INVENTION
[0007] This invention provides an intimate cardable fiber blend
containing 5% to 15% of 2 to 25 denier per filament
polytetrafluoroethylene fibers, 25% to 55% of 0.1 to 1 denier per
filament glass fibers and 1 to 10 denier per filament polyphenylene
sulfide fibers. The invention also provides an improved filter felt
comprising a needled batt of the intimate cardable fiber blend.
Preferably, the blend includes 30% to 50% by weight glass fibers
having lengths ranging between 1.5 inches and 4 inches and a more
preferably lengths of about 1.5 inches with an average diameter of
6 microns. Further, it is preferred that the fiber blend includes
approximately 10% by weight of 3 to 7 denier per filament
polytetrafluoroethylene fibers having lengths ranging between 2.0
inches and 4.5 inches and more preferably lengths of about 3 inches
and a denier per filament of 3.5 to 6.7. In addition, the
polyphenylene sulfide fibers preferably represent from 40% to 60%
by weight of the blend and are 2 to 7 denier per filament
polyphenylene sulfide fibers having lengths ranging between 2.0
inches and 4.5 inches and more preferably lengths of about 3 inches
and a denier per filament of 2.5 to 3.
[0008] This invention also provides a process for preparing the
filter felt by (1) mechanically blending the polyphenylene sulfide
fibers and glass fibers with polytetrafluoroethylene fibers, (2)
further blending the fibers in a carding machine, forming a
nonwoven batt, if necessary by crosslapping, (3) combining layers
of the batt to form a layered batt of a desired thickness, (4)
needling the batt to provide a felt and, (5) optionally, heat
setting the felt by heating on a tenter frame. Preferably the
filter felt contains a supporting scrim which most preferably is a
woven fabric of polyphenylene sulfide fibers, although other
synthetic fibers are contemplated such a polytetrafluoroethylene
fibers. The mechanical blending can be accomplished by any means
known in the art, for example, by hand or in a picker or by
creeling the fibers in one creel and then forming a tow which is
crimped and cut to the desired cut length or in a mechanical
blending device like a fiber opener.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
[0009] This invention relates to an intimate blend of fibers and a
filter felt made therefrom, the blend including glass fibers,
polytetrafluoroethylene fibers and polyphenylene sulfide fibers.
The combination of the fibers unexpectedly results in a filter felt
exhibiting improved resistance to burn-through by sparks, hot
embers and the like, improved filter efficiency and improved
strength and degradation characteristics.
[0010] Useful glass fibers are typical continuous or spun glass
fiber available commercially from Owens-Coming and AGY. The glass
fibers can be cut to desired staple length on a Lummus cutter. For
ease of processing, crimped glass fibers or dual glass fibers can
be used. The term "dual glass fiber" as used herein means a glass
fiber made from two or more glass compositions having different
coefficients of expansion. Dual glass fibers may also be known as
irregularly-shaped glass fibers or bi-glass fibers. These glass
fibers are not straight, but instead curl after spinning producing
a natural, random twist. Dual glass fiber is sold by Owens-Coming
under the MIRAFLEX name. The preferred glass fiber is "DE" type
glass fiber.
[0011] The term "fluoropolymer fiber" as used herein means a fiber
prepared from polymers such as polytetrafluoroethylene, and
polymers generally known as fluorinated olefinic polymers, for
example, copolymers of tetrafluoroethylene and hexafluoropropene,
copolymers of tetrafluoroethylene and perfluoroalkyl-vinyl esters
such as perfluoropropyl-vinyl ether and perfluoroethyl-vinyl ether,
fluorinated olefinic terpolymers including those of the
above-listed monomers and other tetrafluoroethylene based
copolymers. For the purposes of this invention, the preferred
fluoropolymer fiber is polytetrafluoroethylene fiber.
[0012] The fluoropolymer fiber can be spun by a variety of means,
depending on the exact fluoropolymer composition desired. Thus, the
fibers can be spun by dispersion spinning; that is, a dispersion of
insoluble fluoropolymer particles is mixed with a solution of a
soluble matrix polymer and this mixture is then coagulated into
filaments by extruding the mixture into a coagulation solution in
which the matrix polymer becomes insoluble. The insoluble matrix
material may later be sintered and removed if desired. One method
which is commonly used to spin polytetrafluoroethylene and related
polymers includes spinning the polymer from a mixture of an aqueous
dispersion of the polymer particles and viscose, where cellulose
xanthate is the soluble form of the matrix polymer, as taught for
example in U.S. Pat. Nos. 3,655,853; 3,114,672 and 2,772,444.
Preferably, the fluoropolymer fiber of the present invention is
prepared using a more environmentally friendly method than those
methods utilizing viscose. One such method is described in U.S.
Pat. Nos. 5,820,984; 5,762,846, and 5,723,081. In general, this
method employs a cellulosic ether polymer such as methylcellulose,
hydroxyethylcellulose, methylhydroxypropylcellulose,
hydroxypropylmethylcellulose, hydroxypropylcellulose,
ethylcellulose or carboxymethylcellulose as the soluble matrix
polymer, in place of viscose. Alternatively, if melt viscosities
are amenable, filament may also be spun directly from a melt.
Fibers may also be produced by mixing fine powdered fluoropolymer
with an extrusion aid, forming this mixture into a billet and
extruding the mixture through a die to produce fibers which may
have either expanded or un-expanded structures. For the purposes of
this invention, the preferred method of making the fluoropolymer
fiber is by dispersion spinning where the matrix polymer is a
cellulosic ether polymer.
[0013] The fluoropolymer fiber can be made into the desired staple
length using any number of means known in the art. Preferably, the
fluoropolymer fiber is cut into staple by a Lummus cutter.
Polytetrafluoroethylene staple fiber is sold by Toray Fluorofibers
(America), Inc.
[0014] The polyphenylene sulfide fibers used in the present
invention are known to be excellent in heat resistance, chemical
resistance and hydrolysis resistance. Preferably, the fibers
contain 90% or more of fibers made of a polymer containing the
phenylene sulfide structure --(C.sub.6H.sub.4--S).sub.n-- (n is an
integer of 1 or more) as a component of the fibers. The
polyphenylene sulfide fibers can be cut into the desired staple
length by any number of means known in the art, including by using
a Lummus cutter. Methods for preparing polyphenylene sulfide fibers
are described in U.S. Pat. Nos. 3,898,204 and 3,912,695.
Polyphenylene sulfide staple fibers are sold by Toray Industries,
Inc.
[0015] The filter felt of this invention can be prepared by any
means known in the art. For example, the felt can be prepared by
(1) making a fiber blend containing about 10%
polytetrafluoroethylene fibers, 40% to 60% polyphenylene sulfide
fibers and 30% to 50% glass fibers in a picker, (2) passing the
blend through a suitable carding machine to provide a web of an
intimate blend of polytetrafluoroethylene, polyphenylene sulfide
and glass fibers, (3) cross-lapping the carded web from the carding
machine and combining the resulting batt into a layered batt, if
necessary, to provide the desired weight, preferably between 5 and
25 ounces per square yard and most preferably about 16 ounces per
square yard, (4) lightly needling the layered batt on one or both
sides using a needle loom, and (5) further needling the batt both
sides of a woven polyphenylene sulfide scrim to produce a felt. The
batts of blended fibers may also be prepared using an air-lay. If
desired, the felt can be heat set by placing the uncompacted felt
on a tenter frame and passing the felt through an oven.
[0016] A preferred embodiment of the present invention includes an
intimate fiber blend and filter felt made therefrom comprising
about one part polytetrafluoroethylene staple fibers, about 3 parts
glass staple fibers and about 6 parts polyphenylene sulfide staple
fibers wherein the polyphenylene sulfide staple fibers are present
as 2.7 denier polyphenylene sulfide staple fibers and the
polytetrafluoroethylene staple fibers are present as 6.7 denier
polytetrafluoroethylene staple fibers and 3.5 denier
polytetrafluoroethylene staple fibers.
[0017] A further preferred embodiment of the present invention
includes an intimate fiber blend and filter felt made therefrom
comprising about one part polytetrafluoroethylene staple fibers,
about 4 parts glass staple fibers and about 5 parts polyphenylene
sulfide staple fibers wherein the polyphenylene sulfide staple
fibers are present as 2.7 denier polyphenylene sulfide staple
fibers and the polytetrafluoroethylene staple fibers are present as
6.7 denier polytetrafluoroethylene staple fibers and 3.5 denier
polytetrafluoroethylene staple fibers.
[0018] Another preferred embodiment of the present invention
includes an intimate fiber blend and filter felt made therefrom
comprising about one part polytetrafluoroethylene staple fibers,
about 5 parts glass staple fibers and about 4 parts polyphenylene
sulfide staple fibers wherein the polyphenylene sulfide staple
fibers are present as 2.7 denier polyphenylene sulfide staple
fibers and the polytetrafluoroethylene staple fibers are present as
6.7 denier polytetrafluoroethylene staple fibers and 3.5 denier
polytetrafluoroethylene staple fibers.
[0019] The present invention will be explained further in detail by
the following example.
EXAMPLE
[0020] A test filter felt according to the present invention was
prepared by producing a first fiber blend containing 5% by weight
of polytetrafluoroethylene fibers having an average length of 3
inches and a denier per filament of 3.5; 5% by weight of
polytetrafluoroethylene fibers having an average length of 3 inches
and a denier per filament of 6.7; 50% by weight of polyphenylene
sulfide fibers having an average length of 3 inches and denier per
filament of 2.7, and 40% by weight of DE fiber glass having an
average length of 3 inches and average diameter of 6 microns. A
second fiber blend was prepared containing 5% by weight of
polytetrafluoroethylene fibers having an average length of 3 inches
and a denier per filament of 3.5; 5% by weight of
polytetrafluoroethylene fibers having an average length of 3 inches
and a denier per filament of 6.7; 60% by weight of polyphenylene
sulfide fibers having an average length of 3 inches and denier per
filament of 2.7, and 30% by weight of DE fiber glass having an
average length of 3 inches and average diameter of 6 microns.
[0021] Each of the first blend and the second blend was blended
mechanically and further blended in a commercial carding machine to
provide a first web and a second web, respectively, of an intimate
blend of polytetrafluoroethylene, polyphenylene sulfide and glass
fibers. Thereafter, each of the carded webs from the carding
machine was cross-lapped to provide a pair of batts having the
desired weights. To produce the test filter felt, the batt of the
first blend was needled using a needle loom on one side of a woven
polyphenylene sulfide scrim and the batt of the second blend was
needled using the needle loom on the other side of the
polyphenylene sulfide scrim.
TEST RESULTS AND MEASUREMENTS
Basis Weight and Thickness
[0022] The test filter felt had an average weight of 16.4 ounces
per square yard with a range of 14.8 to 18.2 ounces per yard and an
average thickness of 0.082 inches with a range of 0.074 to 0.088
inches.
Air Permeability
[0023] The test filter felt exhibited an air permeability average
of 35.1 cubic feet per minute with a range of 25.2 to 40.4 cubic
feet per minute.
Mullen Burst Strength
[0024] The burst strength of the test filter felt was measured
using the Mullen Burst Test. The Mullen Burst Test uses a circular
material sample that has been clamped over a diaphragm and inflated
with oil. Pressure is applied until the test fabric bursts. The
pressure (in pounds per square inch) at which the fabric bursts is
the bursting strength. The burst strength of the test filter felt
as measured by a Mullen Burst Test averaged 268 pounds per square
inch with a range of 252 to 298 pounds per square inch.
Ball Bearing Test
[0025] The test filter felt's resistance to melting was tested
using a ball bearing test. The test includes suspending the test
filter felt across one open horizontal frame and a control felt
consisting of a 100% polyphenylene sulfide fiber felt having a
weight per square yard substantially equal to the weight per square
yard for the test filter felt across another open horizontal frame.
One or two stainless steel ball bearings of 1/4 to 1/2 inch are
heated to about 343.degree. C. in a Blue Max type oven or a muffle
furnace. This is above the melting point of polyphenylene sulfide
fiber. A high temperature pad is placed beneath each of the frames
to receive the ball bearings if they penetrate the test filter felt
or the control felt. The heat sink effect of the steel is high so
residence time in the oven is required. A heated ball bearing is
placed on each of the test filter felt and control felt, and the
felts are observed. In the test, the heated ball bearing failed to
penetrate the test filter felt. However, the control felt was
melted and penetrated by the heated ball bearing.
Burn-Through Resistance
[0026] The test filter felt's resistance to burn-through from
sparks, for example, as encountered by bag houses in coal fired
boilers, asphalt plants and metal working facilities, was measured
using a hot ember test. The potential for burn-through of the test
filter felt was measured against a control filter felt consisting
of 100% polyphenylene sulfide felt with scrim having an average
weight of 16 ounces per square yard. The test consisted of
contacting a red hot ember at the end of a wooden stick to the test
filter felt and the control filter felt.
[0027] In the test, the control felt initially resisted
burn-through when contacted by the red hot ember but eventually the
glowing ember penetrated the control felt. The test felt resisted
burn-through when contacted with red hot ember even when
substantial pressure was exerted by the ember against the test
filer felt. No holes were burned through the test filter felt.
Filter Performance
[0028] Testing of the resulting test filter felt was conducted
using an ETS, Inc. Filtration Performance Test Apparatus to
determine the filter sample's performance with respect to outlet
particulate emissions (PM2.5), outlet particulate emissions (total
mass), initial residual pressure drop, increase in residual
pressure drop, average residual pressure drop, mass weight gain of
the filter sample, average filtration cycle time and number of
filtration cycles. Testing was conducted in accordance with ASTM
Test Method D6830-02 and with the test specifications and
conditions as detailed in the Generic Verification Protocol for
Baghouse Filtration Products (BFP) developed by the Air Pollution
Control Technology Verification Center (APCTVC) which is part of
the U.S. EPA's Environmental Technology Verification (ETV) Program
and is operated in partnership between RTI and EPA. The protocol
was adapted from the German VDI Method 3926, and modified for ETV.
One exception to the protocol specification was that the test
program consisted on one run rather then three runs as specified in
the protocol.
[0029] The test run consisted of three test phases. To simulate
long term operation, the filter sample was first subjected to a
conditioning period which consisted of 10,000 rapid pulse cleaning
cycles under continuous dust loading. During this period, the time
between cleaning cycles was maintained at three seconds. No filter
performance parameters were measured during the conditioning
period.
[0030] The conditioning period was immediately followed by a
recovery period, which allowed the filter felt sample to recover
from the rapid pulsing. The recovery period consisted of 30 normal
filtration cycles under continuous dust loading. During a normal
filtration cycle, the dust cake was allowed to form on the test
filter felt until a differential pressure of 1,000 Pa (4.0 inch
w.g.) was reached. At this point, the test filter felt was cleaned
by a pulse of compressed air. Immediately after pulse cleaning the
pressure fluctuated rapidly inside the test duct. Some of the
released dust immediately re-deposited on the test filter felt. The
pressure then stabilized and returned to normal. Thus, the residual
pressure drop across the filter felt was measured three seconds
after conclusion of the cleaning pulse. It was monitored and
recorded continuously throughout the recovery and performance test
period.
[0031] The performance test period immediately followed the
recovery period for a cumulative total of 10,030 cycles after the
test filter felt was installed in the test apparatus. The
performance test period was six hours in duration and during this
phase normal filtration cycles and constant dust loading were
maintained and recorded. Outlet mass and PM 2.5 dust concentrations
were measured using an inertial impactor located downstream of the
test filter felt. The weight gain of each impactor stage substrate
was measured to within 0.00001 grams.
[0032] Test conditions throughout the test were as follows: Test
dust: Pural NF Alumina (1.5.+-.1.0 micron mass mean diameter);
Inlet dust feed rate: 100.+-.20 grams/hr. (18.4.+-.grams/scm);
Filtration Velocity: 120.+-.6 m/hr; Gas Temperature: 25.degree.
C..+-.2.degree. C., and Pulse Cleaning Pressure: 75 psi.
[0033] A control filter felt manufactured by Southern Felt was also
tested using the test method and specification described above. The
control filter felt consisted of standard 100% polyphenylene
sulfide filter felt having a weight ranging between 16 to 19 ounces
per square yard.
[0034] The test results for the performance test phase are
summarized in Table 1. TABLE-US-00001 TABLE 1 Parameter Standard
PPS Test Felt PM2.5 Emissions (g/dscm) 0.0000815 0.0000249 Total
Mass Emissions (g/dscm) 0.0000830 0.0000249 Initial Residual
Pressure Drop (cm w.g.) 3.15 2.28 Residual Pressure Drop Increase
(cm w.g.) 0.51 1.39 Average Residual Pressure Drop (cm w.g.) 3.43
3.03 Filter Sample Weight Gain (grams) 1.58 1.82 Average Filtration
Cycle Time (seconds) 122 111 Number of Filtration Cycles (or
Pulses) 176 195
[0035] Detailed information for the performance test phases is
provided in Table II. TABLE-US-00002 TABLE II Parameter Standard
PPS Test Felt VERIFICATION TEST RESULTS Mean Outlet Particle Conc.
0.0000815 0.0000249 PM 2.5 (g/dscm) Mean Outlet Particle Conc.
0.0000830 0.0000249 Total mass (g/dscm) Initial Residual Pressure
3.15 2.28 Drop (cm w.g.) Change in Residual Pressure 0.51 1.39 Drop
(cm w.g.) Average Residual Pressure 3.43 3.03 Drop (cm w.g.) Mass
Gain of Filter Sample (g) 1.58 1.82 Average Filtration Cycle Time
(s) 122 111 Number of Pulses 176 195 RESIDUAL PRESSURE DROP At
Start of: Conditioning Period (cm w.g.) 0.18 0.24 Recovery Period
(cm w.g.) 3.06 2.23 Performance Test Period (cm w.g.) 3.15 2.28
Pulse Pressure (psi) 75 75 REMOVAL EFFICIENCY (%) Dust Conc
(g/dscm) 18.10 16.80 PM 2.5* 99.99942 99.99981 Total Mass**
99.99954 99.99985 * ( Dust .times. .times. Concentration .times. *
.times. 0.7735 ) - PM .times. .times. 2.5 .times. .times. Outlet
.times. .times. Concentration Dust .times. .times. Concentration
.times. * .times. 0.7735 * .times. 100 ##EQU1## ** ( Dust .times.
.times. Concentration - Total .times. .times. Mass .times. .times.
Outlet .times. .times. Concentration Dust .times. .times.
Concentration * .times. 100 ##EQU2##
Comparison to Membrane-Type Filter Media
[0036] Performance testing using the ETS, Inc. Filtration
Performance Test Apparatus was conducted in accordance with ASTM
Test Method D6830-02 on a control filter felt laminated with a
Textratex.RTM. expanded polytetrafluoroethylene membrane style 8005
available from Donaldson Company, Inc. of Bloomington, Minn. The
test specifications and conditions were as detailed in the Generic
Verification Protocol for BFP developed by the APCTVC. The membrane
exhibited PM 2.5 emissions of 0.00005 g/dscm and an initial
pressure drop of 8.46 cm w.g. versus 0.0000249 g/dscm and 2.28 cm
w.g., respectively, for the test filter felt. In addition, the
membrane exhibited a filter sample weight gain of 0.16 grams versus
1.82 grams for the test filter felt.
[0037] As will be apparent to one skilled in the art, various
modifications can be made within the scope of the aforesaid
description. Such modifications being within the ability of one
skilled in the art form a part of the present invention and are
embraced by the claims below.
* * * * *