CA2271824A1 - Improved composition and design of a filter fabric useful in pulp and paper making apparatus - Google Patents
Improved composition and design of a filter fabric useful in pulp and paper making apparatus Download PDFInfo
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- CA2271824A1 CA2271824A1 CA002271824A CA2271824A CA2271824A1 CA 2271824 A1 CA2271824 A1 CA 2271824A1 CA 002271824 A CA002271824 A CA 002271824A CA 2271824 A CA2271824 A CA 2271824A CA 2271824 A1 CA2271824 A1 CA 2271824A1
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- Prior art keywords
- filtering medium
- medium according
- fibers
- filter fabric
- warp
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
- B32B5/24—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer
- B32B5/26—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer another layer next to it also being fibrous or filamentary
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/08—Filter cloth, i.e. woven, knitted or interlaced material
- B01D39/083—Filter cloth, i.e. woven, knitted or interlaced material of organic material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
- B32B5/024—Woven fabric
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/02—Types of fibres, filaments or particles, self-supporting or supported materials
- B01D2239/0208—Single-component fibres
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/04—Additives and treatments of the filtering material
- B01D2239/0471—Surface coating material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/04—Additives and treatments of the filtering material
- B01D2239/0471—Surface coating material
- B01D2239/0492—Surface coating material on fibres
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
- B01D2239/0604—Arrangement of the fibres in the filtering material
- B01D2239/0613—Woven
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
- B01D2239/065—More than one layer present in the filtering material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
- B01D2239/065—More than one layer present in the filtering material
- B01D2239/0659—The layers being joined by needling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/12—Special parameters characterising the filtering material
- B01D2239/1233—Fibre diameter
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- Engineering & Computer Science (AREA)
- Textile Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Filtering Materials (AREA)
Abstract
Filtering mediums are disclosed composed of fabric having a plurality of fibers where the surfaces thereof are coated with an ethylene chlorotrifluoroethylene copolymer. The fibers may also be extruded ethylene chlorotrifluoroethylene copolymer.
Description
IMPROVED COMP08ITIOH l,HD DSBIGN
AHD PAhE33 ~IN~3 APP~1RATU8 . 1 ~~11C1C~iR0 OF T88 INPE19TIOH
AHD PAhE33 ~IN~3 APP~1RATU8 . 1 ~~11C1C~iR0 OF T88 INPE19TIOH
2 1. Meld of the Invention.
V
V
3 The present invention relates to filter 4 fabric which is particularly useful in a rotary drum vacuum separator washer or the like for use in pulp 6 and paper making apparatus.
7 2. Descr~otion~,of the Prior Art.
g For many years, rotary drum filters have 9 been used in the pulp and paper industry to separate suspended and processed pulp particles from the 11 fluids (black liquor) used in the manufacture of 12 paper. These filters operate on the principle of 13 the bottom arc of a rotating drum contacting a 14 reservoir of pulp suspended in liquid and applying a vacuum to draw the pulp suspension onto the drum 16 and to draw the fluid through a perforated screen 17 surface such as a fabric or wire cloth which covers 18 the drum. The solids are thereby deposited on the 19 covering filter while the process liquors are drawn into the core of the drum. At a later point in the 21 drum rotation cycle, the deposited cake or layer of 22 pulp is removed from the surface of the filter.
23 Removal is accomplished by means such as a doctor 24 blade or board set in close proximity to or against the "surface" of the drum (see for example, U.S.
26 Patent No. 4,505,137, the disclosure of which is 27 incorporated by reference and U.S. Patent Nos.
7 2. Descr~otion~,of the Prior Art.
g For many years, rotary drum filters have 9 been used in the pulp and paper industry to separate suspended and processed pulp particles from the 11 fluids (black liquor) used in the manufacture of 12 paper. These filters operate on the principle of 13 the bottom arc of a rotating drum contacting a 14 reservoir of pulp suspended in liquid and applying a vacuum to draw the pulp suspension onto the drum 16 and to draw the fluid through a perforated screen 17 surface such as a fabric or wire cloth which covers 18 the drum. The solids are thereby deposited on the 19 covering filter while the process liquors are drawn into the core of the drum. At a later point in the 21 drum rotation cycle, the deposited cake or layer of 22 pulp is removed from the surface of the filter.
23 Removal is accomplished by means such as a doctor 24 blade or board set in close proximity to or against the "surface" of the drum (see for example, U.S.
26 Patent No. 4,505,137, the disclosure of which is 27 incorporated by reference and U.S. Patent Nos.
1 3,363,744: 3,403,786; 3,409,139 and 4,138,313). The 2 composition and design of the drum covering plays an 3 important role in separating the object (pulp) from 4 the process liquids. This filtering device must have sufficient tortuosity to effectively remove the 6 suspended particles while simultaneously allowing a 7 large volume of the liquid fraction to flow through 8 the medium and into the drum core.
9 The continuous cycle of paper-making process imposes a high degree of fatigue on the filter 11 device covering as a result of the constant 12 flexing/compression of the rotation. In addition, 13 the filter cover is continually abraded by hard 14 deposits in the solids of the filtrate such as mineral deposits and other foreign material, as well 16 as by the pulp removal mechanism.
17 Further demands are also made on the filter 18 cover since the process takes place at elevated 19 temperatures and the aqueous suspension frequently contains harsh chemicals such as bleach and 21 chlorides from bleach, peroxides, processing aids 22 and acids.
23 These hostile environments may shorten the 24 useful life of the filter.
The trapping of particles of mineral deposits, 26 lignin-based products or particles from corrosion 27 by-products within the matrix of the filter layer is 28 especially deleterious: such precipitates tend to 1 adhere to the filaments of the filter, thereby 2 "blinding" or plugging the filtration process.
3 When any of these hostile conditions render the 4 filter wrap ineffective, the overall manufacturing process must be stopped and a replacement filter 6 wrap must be installed. This obviously entails the 7 high cost of lost production as well as the expense 8 to install a new filter cover.
9 It has been a continuing goal of the industry to extend the useful life of the filtering medium.
11 Moreover, the trend in the pulp processing industry 12 is towards increasingly stressful and stringent 13 operating conditions and temperatures.
14 Thus, advances in both the composition and design of the filter layer covering these rotating 16 drums is desirable to minimize both the plugging and 17 mechanical and/or corrosive wear, i.e. to extend 18 their useful life.
19 In terms of composition, these filter matrices are generally made of either stainless steel or 21 extruded polymer. The typical format of the filter 22 materials is a woven textile-type mat or screen.
23 It should also be noted that U.S. Patent No.
24 5,407,736 - McKeon describes the use of a monofilament formed from the combination of a 26 polyester resin and a fluoropolymer resin for a 27 paper making fabric having improved abrasion 28 resistance.
1 Each of these other prior types of composition 2 has advantages and disadvantages.
3 Stainless steel is heavy, and very difficult 4 and costly to install. Stainless steel can handle a wide range of operating temperatures and 6 conditions. However, the most serious drawback of 7 stainless steel is that mineral deposits and other 8 sticky contaminants readily adhere to the matrix, 9 causing pluggage and stoppage and resulting process downtime.
11 Polymeric filters, generally made of woven PVDF
12 monofilament, are lightweight, less costly and easy 13 to handle and install. While not as temperature 14 tolerant as stainless steel, PVDF filter fabrics nevertheless withstand operating temperatures up to 16 275 degrees F. PVDF filter fabrics are not quite as 17 smooth as stainless steel mesh since the brittle 18 skin of the monofilament is frequently fibrillated 19 during both the weaving as well as in actual use.
As in the case of stainless steel, the most 21 serious disadvantage of PVDF is the adherence of 22 sticky components from the pulp slurry to the 23 monofilament yarns of the fabric. The hairy fibrils 24 may exacerbate this adhesion, which eventually leads to the plugging and shortened life of the filter.
27 It is an object of the present invention to 28 provide a filtering medium particularly suited for WO 98/30385 PCT/US98In0425 1 use in vacuum separators of the type used in pulp 2 and paper making processes and apparatus.
3 It is a further object of the present invention 4 to provide a filtering medium exhibiting an increase in useful temperature and pH range as compared to 6 prior filtering mediums used in paper making 7 processes.
8 It is a still further object of the present 9 invention to provide a filtering medium for use in paper making apparatus or the like which exhibits an 11 extended useful life and is less susceptible to 12 plugging of openings as compared to prior media used 13 for that purpose.
14 In accordance with a preferred embodiment of the present invention, a filtering medium suited for 16 use on a rotary drum vacuum filter for processing 17 pulp comprises a fabric comprising extruded 18 monofilament E-CTFE fiber, preferably woven of 19 fibers of approximately 12 mil diameter.
~FSCRIPTION OF DRAWING
21 Figure 1 is a plot of test results for two 22 filter media, a prior art filter made of KYNAR~ PVDF
23 filter material (manufactured by ATOCHEM) and a 24 filter made of HALAR~ E-CTFE fiber according to the present invention (manufactured by Ausimont, 26 U.S.A.).
27 DESCRIPTION OF PREFERRED EMBODIMENT.
28 A filter medium suitable for use in vacuum 29 separators of the type used in paper making 1 processes comprises a fabric woven of extruded 2 monofilament E-CTFE. The fabric is wrapped around 3 a conventional vacuum drum assembly.
4 In order to provide an increase in both the useful temperature and pH range of the filter, 6 fabric constructions similar to PVDF filter fabric 7 was woven of HALAR~ E-CTFE polymer and tested.
8 The HALAR and KYNAR filter fabrics which were 9 tested were made with identical yarn size and fabric construction. The fabrics were KYNAR and a HALAR
11 Twinflex filtration fabric made by Barrday, Inc. of 12 Cambridge, Ontario, Canada. Twinflex weave is a 13 design developed by Barrday in which face and 14 backing fabrics are woven together. The face side of the fabric is a plain weave and provides the 16 filtration function. In plain weave, each weft yarn 17 passes successively over and under each warp yarn 18 with each row alternating. The back side of the 19 fabric is a leno weave and it adds strength and stability to the fabric. The size of the yarn is 12 21 mil (12/1000") in both cases. Mesh opening is the 22 distance between two adjacent yarns expressed in 23 "mils." Open area in a fabric is an indication for 24 straight through drainage. The open area of a fabric is calculated as follows:
26 open area (%)_ [1-(warp count) x (warp 27 diameter)] x [1-(weft count) x (weft 2g diameter)] x 100.
WO 98/30385 PCTlUS98I00425 1 The fabric specifications were as follows:
3 Style MFN-2801 MFN-3901 ' 4 Material Kynar Halar Weave Dual Layer Dual Layer 6 Thread Count 42 Warp x 30 42 Warp x 30 7 Face Cloth Fill Fill 8 Yarn Diameter 12 Warp x 12 12 Warp x 12 9 (mil) Fill Fill Mesh Opening 12 Warp, 12 Warp, 11 (mil) 21 Fill, 21 Fill, 24 Diagonal 24 Diagonal 12 % Open Area 32 32 13 Shrink 10 to 12% Warp 10 to 12% Warp 2 to 3% Fill 2 to 3% Fill 14 Flow Rate xxxx GPM, xxxx GPM, CFM > 1000 CFM >~ 1000 Weight 18.5 oz/yd~ 18.5 oz/yd=
16 pH Operating 1 through 14 1 through 14 17 Range 18 Maximum 265F, 129C 300F, 150C
19 Operating Temperature 22 The capability of higher temperature range was 23 verified in actual field use, as might be expected 24 from the higher melting point of HALAR~ E-CTFE
polymer (464 degrees F) as compared to PVDF.
26 The useful pH range Was also broadened by -27 converting to a fabric constructed wholly of HALAR~
28 E-CTFE polymer.
29 To verify proper flow through of process liquids and filtration efficiency, identical fabric 31 weave constructions of HALAR~ E-CTFE and PVDF were ( 32 also compared in short-term testing and indeed, no 33 significant differences were found.
1 Thus assured that the conversion to an 2 identical fabric construction made of HALAR~ E-CTFE
3 could be made to take advantage of the higher 4 temperature resistance and the wider pH tolerance offered by HALAR~ E-CTFE, the change was made and 6 side-by-side long term field testing was initiated.
7 Surprisingly, however, these actual field 8 trials revealed an unexpected phenomena. Referring 9 to Figure 1, the relative liquid flow rates (initial flow rate taken as 100%) over a period of twenty 11 four weeks was plotted for similar filter made of 12 Ausimont HALAR~ E-CTFE fiber and ATOCHEM KYNAR~ PVDF
13 fiber. As the exposure time for the two fabrics 14 lengthened, the PVDF fabric construction began to plug, or blind at a rate consistent with typical 16 performance of PVDF fabric weaves in this end use 17 and under these conditions. The HALAR~ fiber, 18 however, maintained a surprisingly higher flow 19 through rate, essentially exhibiting very little change in performance. These actual field test 21 data, and the slopes of the flow-through performance 22 curves are depicted graphically in Figure 1.
23 This data shows that the same sticking 24 phenomena that plugs PVDF and stainless steel filter fabrics is substantially minimized or eliminated 26 when a HALARm fiber is employed, even under the same 27 use conditions. This surprising result was not 28 indicated by initial flow-through measurements, nor 1 would this behavior have been predictable from the 2 chemistry of the two fabric constructions.
3 This unexpected degree of less plugging 4 substantially extends the useful life of the E-CTFE
filter fabrics.
6 This result was completely unexpected since 7 both the closely chemically related E-CTFE and PVDF
8 fluoropolymers have very similar surface energy and 9 coefficients of friction (drag).
While the monofilament yarns of the E-CTFE
11 fabrics did have less fibrils on the surface (E-CTFE
12 is less brittle than PVDF), this is believed to have 13 only a minor effect.
14 To better understand this unexpected result, the tested fabric constructions were then dried and 16 the fiber surface morphology was examined by Atomic 17 Force Microscopy. This very advanced technique of 18 examining surface roughness revealed new information 19 not normally available to those skilled in this art.
It was found that the E-CTFE fiber surfaces were 21 discernibly smoother and they thus provide much 22 fewer sites than the PVDF filaments for particle 23 anchorage and buildup.
24 The reason for the ultra-smooth extruded surface of HALAR~ E-CTFE monofilament is still not 26 completely understood. However, it is clear that 27 the HALAR yarn surfaces would be much easier to keep 28 free of contamination buildup. In turn, this would 29 maintain the E-CTFE woven fabric filter effectiveness while greatly extending its useful life.
l0
17 Further demands are also made on the filter 18 cover since the process takes place at elevated 19 temperatures and the aqueous suspension frequently contains harsh chemicals such as bleach and 21 chlorides from bleach, peroxides, processing aids 22 and acids.
23 These hostile environments may shorten the 24 useful life of the filter.
The trapping of particles of mineral deposits, 26 lignin-based products or particles from corrosion 27 by-products within the matrix of the filter layer is 28 especially deleterious: such precipitates tend to 1 adhere to the filaments of the filter, thereby 2 "blinding" or plugging the filtration process.
3 When any of these hostile conditions render the 4 filter wrap ineffective, the overall manufacturing process must be stopped and a replacement filter 6 wrap must be installed. This obviously entails the 7 high cost of lost production as well as the expense 8 to install a new filter cover.
9 It has been a continuing goal of the industry to extend the useful life of the filtering medium.
11 Moreover, the trend in the pulp processing industry 12 is towards increasingly stressful and stringent 13 operating conditions and temperatures.
14 Thus, advances in both the composition and design of the filter layer covering these rotating 16 drums is desirable to minimize both the plugging and 17 mechanical and/or corrosive wear, i.e. to extend 18 their useful life.
19 In terms of composition, these filter matrices are generally made of either stainless steel or 21 extruded polymer. The typical format of the filter 22 materials is a woven textile-type mat or screen.
23 It should also be noted that U.S. Patent No.
24 5,407,736 - McKeon describes the use of a monofilament formed from the combination of a 26 polyester resin and a fluoropolymer resin for a 27 paper making fabric having improved abrasion 28 resistance.
1 Each of these other prior types of composition 2 has advantages and disadvantages.
3 Stainless steel is heavy, and very difficult 4 and costly to install. Stainless steel can handle a wide range of operating temperatures and 6 conditions. However, the most serious drawback of 7 stainless steel is that mineral deposits and other 8 sticky contaminants readily adhere to the matrix, 9 causing pluggage and stoppage and resulting process downtime.
11 Polymeric filters, generally made of woven PVDF
12 monofilament, are lightweight, less costly and easy 13 to handle and install. While not as temperature 14 tolerant as stainless steel, PVDF filter fabrics nevertheless withstand operating temperatures up to 16 275 degrees F. PVDF filter fabrics are not quite as 17 smooth as stainless steel mesh since the brittle 18 skin of the monofilament is frequently fibrillated 19 during both the weaving as well as in actual use.
As in the case of stainless steel, the most 21 serious disadvantage of PVDF is the adherence of 22 sticky components from the pulp slurry to the 23 monofilament yarns of the fabric. The hairy fibrils 24 may exacerbate this adhesion, which eventually leads to the plugging and shortened life of the filter.
27 It is an object of the present invention to 28 provide a filtering medium particularly suited for WO 98/30385 PCT/US98In0425 1 use in vacuum separators of the type used in pulp 2 and paper making processes and apparatus.
3 It is a further object of the present invention 4 to provide a filtering medium exhibiting an increase in useful temperature and pH range as compared to 6 prior filtering mediums used in paper making 7 processes.
8 It is a still further object of the present 9 invention to provide a filtering medium for use in paper making apparatus or the like which exhibits an 11 extended useful life and is less susceptible to 12 plugging of openings as compared to prior media used 13 for that purpose.
14 In accordance with a preferred embodiment of the present invention, a filtering medium suited for 16 use on a rotary drum vacuum filter for processing 17 pulp comprises a fabric comprising extruded 18 monofilament E-CTFE fiber, preferably woven of 19 fibers of approximately 12 mil diameter.
~FSCRIPTION OF DRAWING
21 Figure 1 is a plot of test results for two 22 filter media, a prior art filter made of KYNAR~ PVDF
23 filter material (manufactured by ATOCHEM) and a 24 filter made of HALAR~ E-CTFE fiber according to the present invention (manufactured by Ausimont, 26 U.S.A.).
27 DESCRIPTION OF PREFERRED EMBODIMENT.
28 A filter medium suitable for use in vacuum 29 separators of the type used in paper making 1 processes comprises a fabric woven of extruded 2 monofilament E-CTFE. The fabric is wrapped around 3 a conventional vacuum drum assembly.
4 In order to provide an increase in both the useful temperature and pH range of the filter, 6 fabric constructions similar to PVDF filter fabric 7 was woven of HALAR~ E-CTFE polymer and tested.
8 The HALAR and KYNAR filter fabrics which were 9 tested were made with identical yarn size and fabric construction. The fabrics were KYNAR and a HALAR
11 Twinflex filtration fabric made by Barrday, Inc. of 12 Cambridge, Ontario, Canada. Twinflex weave is a 13 design developed by Barrday in which face and 14 backing fabrics are woven together. The face side of the fabric is a plain weave and provides the 16 filtration function. In plain weave, each weft yarn 17 passes successively over and under each warp yarn 18 with each row alternating. The back side of the 19 fabric is a leno weave and it adds strength and stability to the fabric. The size of the yarn is 12 21 mil (12/1000") in both cases. Mesh opening is the 22 distance between two adjacent yarns expressed in 23 "mils." Open area in a fabric is an indication for 24 straight through drainage. The open area of a fabric is calculated as follows:
26 open area (%)_ [1-(warp count) x (warp 27 diameter)] x [1-(weft count) x (weft 2g diameter)] x 100.
WO 98/30385 PCTlUS98I00425 1 The fabric specifications were as follows:
3 Style MFN-2801 MFN-3901 ' 4 Material Kynar Halar Weave Dual Layer Dual Layer 6 Thread Count 42 Warp x 30 42 Warp x 30 7 Face Cloth Fill Fill 8 Yarn Diameter 12 Warp x 12 12 Warp x 12 9 (mil) Fill Fill Mesh Opening 12 Warp, 12 Warp, 11 (mil) 21 Fill, 21 Fill, 24 Diagonal 24 Diagonal 12 % Open Area 32 32 13 Shrink 10 to 12% Warp 10 to 12% Warp 2 to 3% Fill 2 to 3% Fill 14 Flow Rate xxxx GPM, xxxx GPM, CFM > 1000 CFM >~ 1000 Weight 18.5 oz/yd~ 18.5 oz/yd=
16 pH Operating 1 through 14 1 through 14 17 Range 18 Maximum 265F, 129C 300F, 150C
19 Operating Temperature 22 The capability of higher temperature range was 23 verified in actual field use, as might be expected 24 from the higher melting point of HALAR~ E-CTFE
polymer (464 degrees F) as compared to PVDF.
26 The useful pH range Was also broadened by -27 converting to a fabric constructed wholly of HALAR~
28 E-CTFE polymer.
29 To verify proper flow through of process liquids and filtration efficiency, identical fabric 31 weave constructions of HALAR~ E-CTFE and PVDF were ( 32 also compared in short-term testing and indeed, no 33 significant differences were found.
1 Thus assured that the conversion to an 2 identical fabric construction made of HALAR~ E-CTFE
3 could be made to take advantage of the higher 4 temperature resistance and the wider pH tolerance offered by HALAR~ E-CTFE, the change was made and 6 side-by-side long term field testing was initiated.
7 Surprisingly, however, these actual field 8 trials revealed an unexpected phenomena. Referring 9 to Figure 1, the relative liquid flow rates (initial flow rate taken as 100%) over a period of twenty 11 four weeks was plotted for similar filter made of 12 Ausimont HALAR~ E-CTFE fiber and ATOCHEM KYNAR~ PVDF
13 fiber. As the exposure time for the two fabrics 14 lengthened, the PVDF fabric construction began to plug, or blind at a rate consistent with typical 16 performance of PVDF fabric weaves in this end use 17 and under these conditions. The HALAR~ fiber, 18 however, maintained a surprisingly higher flow 19 through rate, essentially exhibiting very little change in performance. These actual field test 21 data, and the slopes of the flow-through performance 22 curves are depicted graphically in Figure 1.
23 This data shows that the same sticking 24 phenomena that plugs PVDF and stainless steel filter fabrics is substantially minimized or eliminated 26 when a HALARm fiber is employed, even under the same 27 use conditions. This surprising result was not 28 indicated by initial flow-through measurements, nor 1 would this behavior have been predictable from the 2 chemistry of the two fabric constructions.
3 This unexpected degree of less plugging 4 substantially extends the useful life of the E-CTFE
filter fabrics.
6 This result was completely unexpected since 7 both the closely chemically related E-CTFE and PVDF
8 fluoropolymers have very similar surface energy and 9 coefficients of friction (drag).
While the monofilament yarns of the E-CTFE
11 fabrics did have less fibrils on the surface (E-CTFE
12 is less brittle than PVDF), this is believed to have 13 only a minor effect.
14 To better understand this unexpected result, the tested fabric constructions were then dried and 16 the fiber surface morphology was examined by Atomic 17 Force Microscopy. This very advanced technique of 18 examining surface roughness revealed new information 19 not normally available to those skilled in this art.
It was found that the E-CTFE fiber surfaces were 21 discernibly smoother and they thus provide much 22 fewer sites than the PVDF filaments for particle 23 anchorage and buildup.
24 The reason for the ultra-smooth extruded surface of HALAR~ E-CTFE monofilament is still not 26 completely understood. However, it is clear that 27 the HALAR yarn surfaces would be much easier to keep 28 free of contamination buildup. In turn, this would 29 maintain the E-CTFE woven fabric filter effectiveness while greatly extending its useful life.
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Claims (22)
1. A filtering medium having extended life comprising a fabric comprising a plurality of fibers, wherein at least the surface of said fibers comprises a coating of the copolymer ethylene chlorotrifluoroethylene (E-CTFE).
2. A filtering medium according to Claim 1, wherein said fibers are monofilament fibers formed from extruded E-CTFE.
3. A filtering medium according to Claim 2, wherein said fibers are woven to provide a filter fabric having at least one layer.
4. A filtering medium according to Claim 3, wherein said filter fabric has a front layer and a back layer, said front layer being formed by a plain weave having warp and weft threads, wherein each weft thread is passed successively over and under each warp thread with each row alternating, and said back layer being formed by a leno weave, and wherein said filter fabric is formed by weaving said front layer and said back layer together in a double weave.
5. A filtering medium according to Claim 4, wherein said filter fabric has an open area according to the following formula: Open Area = [1-(Warp Count X Warp Diameter in mils)] X [1-(Weft Count X Weft Diameter in mils)].
6. A filtering medium according to Claim 5, wherein said filter fabric has an open area of less than fifty percent.
7. A filtering medium according to Claim 5, wherein said filter fabric has an open area of about one-third.
8. A filtering medium according to Claim 5, wherein said front layer has a warp count greater than its weft count of threads and mesh openings substantially equal to the diameter of individual fibers.
9. A filtering medium according to Claim 8, wherein said fibers are between about 8 mils and 30 mils in diameter.
10. A filtering medium according to Claim 9, wherein said fibers are approximately 12 mils in diameter.
11. A filtering medium according to Claim 9, wherein said filter fabric is wrapped around a vacuum drum assembly.
12. A filtering medium having extended life for use in pulp and paper making vacuum separator apparatus comprising a fabric comprising a plurality of fibers, wherein at least the surface of said fibers comprises a coating of the copolymer E-CTFE.
13. A filtering medium according to Claim 12, wherein said fibers are monofilament fibers formed from extruded E-CTFE.
14. A filtering medium according to Claim 13, wherein said fibers are woven to provide a filter fabric having at least one layer.
15. A filtering medium according to Claim 14, wherein said filter fabric has a front layer and a back layer, said front layer being formed by a plain weave having warp and weft threads, wherein each weft thread is passed successively over and under each warp thread with each row alternating, and said back layer being formed by a leno weave, and wherein said filter fabric is formed by weaving said front layer and said back layer together in a double weave.
16. A filtering medium according to Claim 15, wherein said filter fabric has an open area according to the following formula: Open Area = [1-(Warp Count X Warp Diameter in mils)] X [1-(weft Count X Weft Diameter in mils)].
17. A filtering medium according to Claim 16, wherein said filter fabric has an open area of less than fifty percent.
18. A f filtering medium according to Claim 16 , wherein said filter fabric has an open area of about one-third.
19. A filtering medium according to Claim 16, wherein said front layer has a warp count greater than its weft count of threads and mesh openings substantially equal to the diameter of individual fibers.
20. A filtering medium according to Claim 19, wherein said fibers are between about 8 mils and 30 mils in diameter.
21. A filtering medium according to Claim 20, wherein said fibers are approximately 12 mils in diameter.
22. A filtering medium according to Claim 20, wherein said filter fabric is wrapped around a vacuum drum assembly.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US3492497P | 1997-01-10 | 1997-01-10 | |
| US60/034,924 | 1997-01-10 | ||
| PCT/US1998/000425 WO1998030385A1 (en) | 1997-01-10 | 1998-01-07 | Improved composition and design of a filter fabric useful in pulp and paper making apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2271824A1 true CA2271824A1 (en) | 1998-07-16 |
Family
ID=21879494
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002271824A Abandoned CA2271824A1 (en) | 1997-01-10 | 1998-01-07 | Improved composition and design of a filter fabric useful in pulp and paper making apparatus |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2271824A1 (en) |
| WO (1) | WO1998030385A1 (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5422159A (en) * | 1994-12-08 | 1995-06-06 | Ausimont U.S.A., Inc. | Fluorpolymer sheets formed from hydroentangled fibers |
-
1998
- 1998-01-07 WO PCT/US1998/000425 patent/WO1998030385A1/en active Application Filing
- 1998-01-07 CA CA002271824A patent/CA2271824A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1998030385A1 (en) | 1998-07-16 |
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