MXPA96002732A - Method and drain apparatus capi - Google Patents

Abstract

The present invention relates to a method for reducing the moisture content of a fiber fabric in a fabric manufacturing process, comprising the steps of: a) holding the fabric on an air permeable fabric, b) slightly pressing the tissue between the air permeable fabric and the capillary membrane of a capillary dewatering roller having defined pores therein which are configured to induce a negative capillary suction pressure where the tissue is transported around a peripheral segment of the capillary dewatering roller; and c) pull a vacuum inside the capillary drain roller, the vacuum not being greater than the negative capillary suction pressure of the capillary pores

Description

METHOD AND CAPILLARY DRAIN APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the drainage of paper tissues in a papermaking process, and more particularly, to the use of capillary forces to remove water from non-pressurized wet tissues without a virtually general compaction of the fabric during the manufacturing process for make paper 2. Brief Description of Previous Art U.S. Patent No. 3,262,840 issued to Hervey relates to a method and system for removing liquids from fibrous articles such as paper and textiles using a porous polyamide body. The porous polyamide body is, for example, a porous and elastic sintered nylon roll. In this method, a wet paper fiber fabric is passed through a series of pressure fastening points, each of which includes at least one porous nylon roll. Apparently, the liquid is transferred from the wet paper fiber fabric into the porous nylon rollers by a combination of the pressure that is applied by the clamping point rollers, some degree of capillary action on the porous roller and assistance of emptiness. However, the transfer is virtually limited in this process because it must occur during a relatively short period of time in which the fabric passes between the attachment point and the opposed rollers. Hervey further discloses that the water taken in the porous nylon roller is then either blown out of the pores by pressurizing a chamber within the roller or removing it from the pores by applying an external vacuum to the roller. This blowing out of the water from the pores also tends to clean the pores.

U.S. Patent No. 4,556,450 issued to Chuang et al. Describes a method and apparatus for removing fluid from tissues through the use of capillary forces without compacting the tissue. The tissue passes over a peripheral segment of a rotating cylinder having a cover containing capillary-sized pores. The internal volume of the rotating cylinder breaks in at least two and as many as six chambers which are separated from each other by stationary parts and seals. At least one of the chambers has an induced vacuum there to increase the capillary flow of water from the sheet. Another chamber includes positive pressure to expel water from the pores out of the cover after the leaf has been removed. Presumably, the pores are cleaned by this expulsion of water. All the water taken from the sheet is kept inside or just below the pores and is expelled from the capillary cover in each revolution of the cylinder. A few roofing materials are discussed including a sintered sintered Double Dutch Twill Weave as taught in U.S. Patent No. 3,327,866 issued to Pall.

U.S. Patent No. 4,357,758 to Lampinen teaches a method and apparatus for drying objects such as paper tissues using a fine porous suction surface saturated with a liquid and placed in hydraulic contact with a liquid that it was placed under reduced pressure with reference to the tissue that is being dried. The suction surface of porous and fine liquid is located on the outside of a rotating drum and the water is removed from the drum apparently through the use of pumps which rotate with the drum. Lampinen does not seem to make any provision for cleaning the pores.

The prior art fails to teach the light knuckle pressing of the tissue against the capillary membrane to ensure a hydraulic contact between the water contained in the tissue and the water in the pores of the capillary membrane without general compaction of the tissue. This promotes a greater and faster drainage through the use of the capillary membrane. further, the light pressing of the tissue against the capillary membrane with a knuckle surface is not taught in combination with a non-sectored capillary drain roller which is maintained at a single pressure, that pressure is near but does not exceed the pressure of Effective capillary breakdown of the main flow pore diameter of the capillary membrane. In addition, the prior art fails to discuss the washing and cleaning of the capillary membrane from the outside of the capillary drain roller to the interior thus draining any particles trapped in the pores inside the drum. This is also possible because the drum is not sectioned and maintained at a single vacuum pressure, and furthermore, because the capillary pores are pores of non tortuous path substantially straight.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for removing a portion of the liquid contained in a continuous wet porous fabric in a papermaking process without substantially general compaction of the fabric using capillary forces.

It is another object of the present invention to provide a capillary dewatering surface on a rotating capillary dewatering drum which can be cleaned through the use of external high pressure water sprays which clean the surface of the drum and drain the trapped contaminant particles inside. of the capillary pores inside the drum.

Still another object of the present invention is to provide a method and apparatus for removing a portion of liquid contained in a continuous wet porous fabric in a paper making process wherein the hydraulic interface between the water contained in the continuous wet porous fabric and the water within the capillary pores of the capillary dewatering membrane is improved by lightly pressing the continuous wet porous tissue with a knuckle fabric open against the capillary dewatering membrane.

Still a further object of the present invention is to provide a method and apparatus for removing the water removed from a continuous wet porous fabric in a process for making paper from the capillary pores of the capillary membrane through the use of a dewatering roller. unseparated capillary maintained at a single vacuum pressure approaching but not exceeding the effective capillary breakage pressure of the main flow pore diameter of the capillary pores of the membrane.

Briefly stated, the foregoing and numerous other objects, features and advantages of the present invention will become readily apparent from reading the detailed description, clauses and drawings given herein. These objects, features and advantages are achieved through the use of a capillary dewatering roller that includes a capillary dewatering membrane having a composite structure. The capillary dewatering membrane consists of at least two and therefore as four layers. The upper layer is the capillary surface itself against which the wet tissue is placed. The main pore diameter of the pores of the capillary membrane should be about 10 microns or less. Backing this upper capillary layer are one or more support layers. In addition to supporting and stabilizing the capillary membrane, these relatively open layers allow water to flow easily through them and into the perforated roller. This allows the capillary vacuum to be evenly distributed under the upper capillary membrane. The fact that the successive layers have larger and larger openings allows any contaminant to then pass through or up to the upper capillary layer to continue to be defined in the center of the dewatering roll.

The capillary dewatering roller is an unsecured roller and is kept under a constant vacuum which approximates the negative capillary suction pressure Cp in which: Cp = 2s Cos? where s is the interfacial tension of water-airé "-» solids,? e the water-air-solids contact angle and r is the capillary pore radius.If the contact angle in both the capillary orifice and the capillaries of the leaf is dewatered to cer (perfectly humid) then the radius of curvature of the water meniscus in the water-air interface is around d almost equal to R. This would be true inside both the capillary membrane and inside the leaf A balance sheet is reached, the dewatered sheet is then moved out of the capillary medium, the vacuum source which is connected to the interior of the capillary dewatering roller simulates the capillary suction force, Cp. promoting the flow of water through capillary pores with water on the underside of the capillary membrane has continued to be removed.

A cleaning shower is provided which flushes the surface of the capillary debris roll between the point where the tissue leaves the surface of the capillary membrane and the point where the tissue is lightly pressed against the surface of the capillary membrane. The cleaning shower also serves to push any particles lodged in the capillary pores to the center of the roller where they are carried out with the water. The pores of a non-tortuous, substantially straight path facilitate the cleaning approach from the outside to the inside.

The capillary dewatering roller of the present invention can be used in a variety of a plurality of paper making processes to improve the energy efficiency of the process. One such process is to deliver a supply from a head box to the forming fabric to form an embryonic tissue. The embryonic tissue is then dewatered by vacuum while it is held on the forming fabric so that the fabric is in the range of from about 6% to about 32% dry. Very possibly multiple vacuum boxes will be necessary to achieve a 32% drying. The fabric is then transferred with vacuum from the forming fabric to the open knuckle transfer fabric and while it is held on such a transfer fabric, the fabric is lightly pressed against the surface of the capillary membrane of the capillary dewatering roll of the present invention. Alternatively, part or all of the vacuum dewatering can be done while the fabric is in the transfer fabric. The fabric is drained to the range of from about 33% to about 43% dry by the capillary dewatering roller. Additional drying can be achieved by placing the multiple capillary dewatering rolls in series. The fabric drying can then be completed by a variety of means including the use of a continuous dryer, a Yankee dryer, a surface dryer fired with high temperature gas, steam heated bottle dryers, -etc.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic display of a part of a capillary dewatering system that is constructed according to the preferred embodiment of the invention; Figure 2 is a Coulter Porometer pore size distribution curve of a tissue hand sheet from ® as manufactured by the Scott Paper Company at 10 Cottonelle brand pounds per basis weight of ream; Figures 3A, 3B and 3C are graphic representations of the controlled capillary dewatering process according to the preferred embodiment of the invention; Figure 4 is a fragmentary cross-sectional representation of a capillary dewatering composite structure according to a preferred embodiment of the invention; Figures 5A and 5B represent ideal and realistic pore configurations; Figure 6 is a graphical representation of a differential flow distribution of Coulter porometer for a micrometer capillary membrane Nuclepore 5 according to the invention; Figure 7 is a representation of a preferred capillary vacuum roll hole pattern according to the preferred embodiment of the invention; Figure 8 is a graphic representation of the effect of putting the drying level on the capillary dewatering roller; Figure 9 is a diagrammatic representation of a tissue papermaking machine according to the invention, with a capillary dewatering roll, a continuous air dryer, and a crepe dryer.

Figure 10 is a diagrammatic display of a machine for making tissue paper according to the invention, with a capillary dewatering roller and a crepe dryer, but not through an air dryer.

Figure 11 is a diagrammatic representation of a papermaking machine according to the invention with a capillary dewatering roller, a high temperature surface dryer and a crepe dryer; Y '"~ - Figure 12 is a diagrammatic representation of a machine making conventional woven paper with an air dryer and a crepe dryer.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring now to Figure 1, there is shown the capillary dewatering drum 10 of the present invention having a capillary membrane compound 12 therein. A wet fabric W held on an open-knuckle carrier fabric 14 is contacted against the capillary membrane composite 12 of the rotating capillary drainer drum 10. A clamping point roller 16 lightly presses the tissue W against the capillary membrane composite 12 so that the tissue W is slightly compacted in the knuckle areas of the open knuckle carrier fabric. 14. "Light compression" as defined here is to press a linear force within the range of from less than one (by almost counterbalancing the weight of the clamping point roll) to about 150 pli (pounds of force per linear inch). More preferably, the clamping point roller 16 compresses the tissue 19 against the composed of capillary membrane 12 at a linear force that is virtually within the range of 20-50 pli. The purpose of the light knuckle compression of the tissue against the capillary membrane is to ensure the hydraulic contact between the water contained in the tissue and the water in the pores of the capillary membrane without a general compaction of the tissue. This promotes a faster and greater drainage through the use of the capillary membrane.

The invention should be operative at higher linear pressures, perhaps as high as 400 pli, even though undesired compaction of the tissue at such pressures may occur.

The fabric is not subjected to a general compaction but is compacted slightly in discrete places where the fabric is compacted by the knuckles of the carrier fabric 14. The fabric W, even when it is held on the carrier fabric 14, is transported around the a peripheral segment of the rotating capillary dewatering drum 10. After moving around a peripheral segment of the capillary dewatering drum 10, the fabric is removed from contact with the capillary membrane composite 12 while still holding onto the transfer cloth 14. a cleaning shower 18 which sprays the water against the surface of the capillary membrane 12. The cleaning shower 18 washes the outside of the membrane 12 and furthermore, drives through the capillary pores of the membrane 12 any particles lodged there so that the particulates are carried through the membrane compound 1 into the center of the drum 10. The water is removed from the center or the capillary drain drum 10 by means of a siphon 20 In operation, the capillary drain drum is subjected to an internal negative pressure. In other words, a vacuum is pulled over the interior of the drum 10 by a vacuum source 1 which approximates the effective capillary breaking pressure of the main flow pore diameter of the pores of the capillary membrane 12. The pressure of Effective capillary break is the level of pressure (vacuum) where the air flow through the wet capillary membrane does not exceed 10% of the air flow through a dry membrane at the same pressure (vacuum). The capillary roller 10 is generally operated at a pressure (vacuum where the air flow does not exceed 3% to 5% of the air flow through a dry membrane at the same pressure level (vacuum and can be operated with less than 10%). a vacuum level Figure 2 is a Coulter Porometer d ® pore size distribution curve a Cottonelle brand tissue hand sheet as manufactured by Scott Paper Company at 10 pounds per reweigher base weight. The maximum frequency distribution occurs at a pore diameter of about 50 microns.The diameter of the main flow pore size is about 36 microns.

This indicates that the majority of the free water contained in such a wet handsheet is in the pore size range of 30 miera or greater. This is represented conceptually in Figure d of Figure 3a which shows a schematic pore size distribution curve. The shaded area below this pore size distribution curve represents the amount of free water trapped within such pores. The concept of controlled capillary drainage under the present invention is basically to remove such free water by contacting the wet sheet with a dry capillary medium which has a smaller capillary pore size, for example, a capillary medium having a peak of distribution of capillary pore size to 8 microns. The schematic pore size distribution curve for the capillary medium is shown as a dotted line in Figure 3a. If this capillary medium of 8 microns has sufficient pore volume, it will absorb from the largest pores within the leaf until a state of equilibrium is reached. At such a state of equilibrium, there will no longer be free water in the leaf in pores of 8 microns or larger in diameter. In this state, the water within the capillary medium of pore size of 8 microns and part of the residual water within the sheet are then in a continuous phase. Within this continuous phase, there is a negative capillary suction pressure Cp, where: C "= 2s Cos? As mentioned above, if the contact angle in both the capillarity and the sheet is zero, then the radius of curvature of the water meniscus in the air-water interference is about equal to r. Therefore, the smaller the radius r, the greater the amount of water that will be absorbed from the leaf into the capillary medium, provided that the capillary medium has sufficient volume to retain the water that is being absorbed, or is provided with means to remove the water from the capillary medium to be absorbing water from the sheet.

Looking at Figure 4 there is shown the representative cross-sectional view taken on lines 4-4 of Figure 1. From such a cross section it can be seen that the capillary dewatering membrane 12 is actually a composite structure consisting of at least two and preferably of as many as four layers. The upper layer is the capillary surface 22 against which the wet tissue is placed. The main flow pore diameter (as measured by a Coulter Porometer, manufactured by Coulter Electronics, Inc. of Hialeah, FL) should be less than about 10 microns to induce sufficiently high capillary vacuum levels to facilitate a good drainage . The smaller the capillary pore diameter, the higher the drainage levels, and the drier the sheet is when it is discharged from the capillary surface 22. Supporting the capillary surface layer 22 are the support layers 24, 26 and 28 These support layers 24, 26 and 28 and the capillary membrane surface 22 are wrapped around the outer side of a perforated vacuum roller 30. In addition to supporting and stabilizing the capillary surface membrane 22, these relatively open layers 24, 26 and 28 allow water to flow easily through them to the interior of the perforated vacuum roll -30, thereby allowing capillary vacuum to be uniformly distributed across the capillary membrane 22. The fact that the successive layers 24 , 26 and 28 open, each successive layer internally having pore size openings larger than the previous layer, allows any contaminating material to pass through the capillary layer. top to continue to be drained to the inside of the center of the roller and outward.

Layers 22, 24, 26 and 28 are formed in a compound through combinations of rubber (plastic) or sintered-joint (metals). An example (see Example A below) of a composite membrane structure acceptable for use with the present invention should be a Double Dutch Twill woven mesh membrane (as can be obtained from Tetko Inc. of Briarcliff Manor, NY) bonded-sintered to 3 coarser support layers successively. An example (see Example B) would be a Nuclepore nucleation view membrane (as manufactured by Nuclepore Corporation of Pleasanton, CA) which is glued to a nonwoven polyester fabric which in turn is glued to a nonwoven fabric. woven polyester mesh.

The composite capillary membrane 12 is flexible enough to be wrapped around a perforated cylinder 30 which has a diameter in the range of from 2 feet to 12 feet or more. The seams can be glued, buttoned, stapled, overlapped and / or welded. Tests have shown that while the seam in either the machine direction or the machine direction is less than a quarter of an inch width and as long as the drain time is 0.15 seconds or longer, they will not be visible. wet strips in the paper when removing it from the capillary drain roller 10. It seems that there is sufficient diffusion through the sheet to facilitate the drainage. Wider seams of about 1/8 inch may tend to show wet marks. Similarly, contaminated or clogged spots about 1/4 of an inch in diameter or less will not leave wet marks on the fabric.

EXAMPLE A - Drain from Ho to Backing Fabric # 1 (24) -150x150 mesh, ss square fabric Backing Fabric # 2 (26) -60x60 mesh, ss square fabric Backing Fabric # 3 (28) -30x30 mesh, ss square fabric Membrane Surface Cap. (22) -woven Double Double Twill type mesh -swoven mesh, simple trajectory Mesh Account -325x2300 Equivalent to Pore Length - 110 μm Coulter Size MFP -9.19 μm 1 / d -12.0 Air Permeability (? P-0.5" H:?) -5 - 10 cfm / square foot Supply -65% Pine / 35% Eucalyptus Weight Base -14 pounds / 2880 square feet Line Speed -500 fpm Residential Time -0.46 seconds Clamping Point Roller Load -27 lbs / linear inch Hair Roller Vacuum ("H2?) -111 Pre-Capillary Drum Dryness -24.9% Post-capillary Drum Dryness - 38.2% EXAMPLE B - Sheet Drain Backing Fabric # 1 (24) -Polyester non-woven Backing Fabric # 2 (26) -Polyester Mesh - Albany #? 135 (30x36 square fabric) Membrane Surface Cap (22) -Nuclepore 5.0 μm Type -Nucleation Track Equivalent Pore Length -10 μm Coulter Size MFP -5.35 μm 1 / d -1.9 Air Permeability (? P-0.5"H:?) -3.5 cfm / square foot Supply -70% NSWK / 30% Eucalyptus Weight Base -14 pounds / 2880 square feet Line Speed -500 fpm Residence Time -0.46 seconds Loading Roller Clamping Point (pli) -45 0 Hair Roller Vacuum ("H20) -134134 Pre-capillary Drum Dryness -23., 1% 23% .3% Post-capillary drum dryness -39., 7% 32% .7% With the capillary drain roller 10 of the present invention, a thin capillary membrane 22 containing thin capillary pores but not much bulk or thickness was used. The longer the pore is, the longer the time for the water to be absorbed from the sheet due to viscous pulling forces. In addition, with thinner and larger capillary pores, there is an opportunity for a clogging of the pores by fine contaminants or an accumulation of coating and the pores are more difficult to clean. Because the capillary membrane surface 22 is relatively thin and therefore does not have the volumetric capacity to hold the volume of water to be absorbed from the sheet, a vacuum source is connected to the underside of the capillary membrane for simulate the capillary suction force Cp, and promote the flow of water through the capillary pores. This allows the water that is removed from the sheet to pass completely through the capillary membrane surface 22 and the support layers 24, 26 and 28 so that the water can be continuously removed from the inside of the drum 30. Since the water is continuously removed from the capillary membrane surface 22, an additional volume for further absorption by the capillary membrane surface 22 is continuously created. The vacuum level inside the vacuum drum 30 should be as close to Cp as possible to promote maximum sheet drainage. However, if the vacuum is greater than Cp, the capillary water seal and air will begin to escape through it. If this happens in any great extent, the vacuum energy is wasted and the capillary drain effect is compromised.

The smaller the capillary pore diameter, the higher the drainage levels, and the drier the leaf will be as it leaves the capillary surface. However, the smaller the pore diameter, the more difficult it is to keep the pores from being contaminated or clogged. These capillary membranes with main pore diameters of around 5 microns have worked well in the tests. (The main flow pore diameter refers to the equivalent pore diameters of noncircular cross-section pores). Such capillary pore size membranes have produced high levels of sheet dryness and have tended to remain clean. Pore sizes from 0.8 to 10 microns have ran at vacuum levels of from 3 inches of Hg to about 15 of Hg. The preferred pore diameter is in the range of from about 2 to about 10 microns.

Preferably, the capillary pore should be as short as possible and then open rapidly downwards above the minimum pore diameter (see Figure 5A). In this way, capillary forces can be generated with a reduced flow resistance. In addition, pore contamination is minimized. Any particles that pass through the minimum pore diameter will not tend to be trapped and therefore this type of pore design facilitates an outward cleaning of the capillary drain roller 10. In practice, the preferred design is to maintain the pore as short as possible with respect to its diameter. The ratio of the actual equivalent capillary pore path length, 1, to the equivalent pore diameter, d, should be small (see Figure 5B). The pore aspect ratio (1 / d) should be in the range of from about 2 to about 20. Preferably, the pore aspect ratios should be less than 15. Straight pores are preferred. The more tortuous the trajectory, the harder it is to keep the pore open and clean. Labyrinth structures (for example spurious types, sintered metals, ceramics) are the most difficult to keep clean and are not preferred.

The permeability of the capillary membrane 22 is also of importance since it affects the volume of water that can be removed in a given period of time. The permeability is related to the pore size, the pore aspect ratio, and the pore density and can be characterized by the Frazier Number (volume of air flow per unit area area at 0.5"H20? P). desired relatively high permeabilities Therefore, Frazier Numbers above 3 are preferred. Per lower permeability membranes (Frazier Number of about 0.8) have been conducted in an acceptable manner.

As previously mentioned, capillary pores with a non-tortuous or straight trajectory are preferred. Direct capillary pores are produced by a nucleation track technique (eg, Nuclepore or Poretics) which serves well as the surface membrane 22 of the present invention for draining wet tissues. Such capillary pores have an excellent pore aspect ratio (1 / d) making them good to keep them clean as well as for drainage. They also have a small pore size range as measured by the Coulter porometer. In other words, the pore size distribution for the capillary pores produced by the nucleation track technique is relatively small. This is shown in the graph of Figure 6 in which the pore size distribution schemes of the pore structure of 5 micron Nuclepore against the percentage of differential flow. As mentioned above, a nucleation track membrane can be obtained from Nuclepore Corporation. The disadvantage of the membranes 22 manufactured by the nucleation track technique is that the membranes are somewhat fragile. However, these types of membrane are effective for draining non-compressed wet sheets such as the capillary or outer layer 22 of the composite membrane 12.

Capillary membranes 22 have also been successfully run using woven polyester mesh fabrics such as PeCap 7-5 / 2 (see Example C) which is available from Tetk Inc. of Briarcvliff Manor, NY. In addition, the Double Dutch Twill woven wire meshes as described in US Pat. No. 3,327,866 issued to Pal et al. Have been used as an acceptable capillary layer in the process of the present invention for draining fabrics. wet. As noted in the Pall et al. Patent, these woven wire meshes can be calendered and bonded-sintered to fix the openings in place and smooth the surface. Other membranes may also be acceptable as long as they fall within the ranges for the preferred diameter, pore aspect ratio, and permeability.

EXAMPLE C - Sheet Drain Backing Fabric # 1 (24) - Polyester Mesh - Albany # 5135 (30x36 square fabric) Membrane Surface Cap. (22) -PeCap 7-5 / 2 Type - Polyester monofilament fabric Equivalent Pore Length -65 μm Coulter Size MFP -6.26 μm 1 / d -10.4 Air Permeability (? P-0.5"H :?) -0.9 cfm / square foot Supply -60% Pine / 40% Eucalyptus Weight Base -14 pounds / 2880 square feet Line Speed -500 fpm Time of Residence -0.46 seconds • C ^ arga of Clamping Point Roller (pli) -34 Capillary Roller Vacuum ("H2?) -186 Pre-Capillary Drum Dryness -32 .5% Dryness of Post-Capillary Drum -42. 8% The use of methods (eg, steam showers) to reheat the woven sheet and reduce the viscosity of water before the capillary drain roll has resulted in higher dryness levels for the fabric exiting the capillary dewatering roll. Such a method, together with the use of small pores, higher vacuum levels and / or longer residence times on the capillary drain roll can result in levels of dryness coming out of the capillary drain roll of approximately 50%. Dryness levels as high as 52% have been achieved in the laboratory using capillary drainage. The use of two or more capillary drain roller 10 in series can present practical means to obtain virtually longer residence times at the high operating speeds of commercial paper machines. Each roller can successively have smaller pore diameter pore diameter diameters 22 and high capillary vacuum levels to facilitate cleaning.

The design of the membrane composite, particularly the upper capillary pore surface 22, contributes to being able to maintain both the capillary surface 22 and the overall membrane composite 12 clean. Membrane contamination is a major problem experienced in capillary drainage systems. Poplar pore sizes are easily clogged. As indicated above, the present invention preferably uses capillary pores having a pore diameter in the range of 2 to 10 microns with the smallest pore aspect ratio (1 / d) of 20 or less. In addition, the pores are essentially straight and non-tortuous, and the membrane has a permeability with the increasing flow area after the minimum restriction presented to the capillary membrane surface 22. Once the paper tissue has left the roller capillary drain 10, the capillary surface is intermittently exposed to the external high-pressure showers 18 which clean the composite membrane during the operation of the capillary drain roller 10. The high-pressure showers 18 work from the outside of the composite membrane 12 towards the center of the dewatering roller 10. The energy and moment in the spraying forces causes any particles lodged in the pores through the minimum restriction (which is generally located on the outer side of the membrane compound 12), to the outside of the lower side of the capillary layer 22 and through the larger openings successively of the composite layers 24, 26 and 28. The c Ontaminants are therefore drained to the center of the roller with the water from the shower and the water is absorbed from the paper tissue. The waste left on the surface of the capillary membrane is drained out by that portion of the water shower tangentially deflected by the solid part of the capillary membrane surface 22.

In the design of a suitable pressure shower 18 for cleaning purposes, with the shower 18 directed virtually and radially to the capillary drain roller 10 so that the shower sticks on the membrane surface 22 at virtually the right angles, it is believed that If the water still has a 1/2 inch hydraulic head after penetrating the composite membrane 12, the shower must have been strong enough to clean the composite membrane. The aforementioned hydraulic head is the height of the water column on the rough side (inside the roller 10) of the composite membrane 12 when the shower water is hit vertically upwards and perpendicularly to the fine capillary side in a membrane (outer surface) of roller 10).

The different combinations of nozzle sizes, configurations, separations and pressures can produce the desired half inch inch hydraulic head. A spray manifold which has been found to work well on an experimental paper machine with a capillary drain roller 10 consisted of Spraying Systems Company nozzles model No. 1506 operating at 690 psig located 2.5 inches from the surface on the membrane 22 This configuration penetrated a 325 x 2300 mesh, Double Dutch Twill composite membrane with a 0.65 inch hydraulic head. The corresponding penetration anchors of the composite membrane 12 was 1.5 inches. Since the spacing between the adjacent nozzles was 3 inches, from centerline to centerline, while the effective cleaning width per nozzle was only 1.5 inches, the shower was oscillated in the direction of the cross machine to ensure 100% of covering of the composite membrane 12. The oscillation frequency was varied with the line speed to maintain the maximum intermittent time that a particular area of the membrane 12 was not hit by the spray at 14 seconds. This resulted in any part of the membrane 12 being washed only 0.2% of the total time. Values as low as 0.04% have been achieved. By way of example, on the experimental paper machine which included a capillary dewatering roller 10, the spray nozzles were oscillated in the direction of the cross machine at a rate of 0.214 inches / second. Such an experimental paper machine was operated at a line speed of 5 fpm and the capillary drain roller 10 on such an experimental paper machine had a diameter of 2 feet.

It should be noted that different membrane designs require different shower combinations. For example, it appears that the 5 micron core capillary surface would require pressures of only 100 to 200 psi to maintain adequate cleanliness if it is used as the capillary surface layer 22 for the capillary dewatering roller 10 of the experimental paper machine discussed. in the preceding paragraph.

The perforated vacuum cylinder 30 requires being made of a non-corrosive material. Stainless steel is preferred even when bronze can also be used. The orifice size and distribution should be such as to provide a uniform vacuum to all areas on the underside of the capillary membrane composite 12. For example, the vacuum roller 30 may have holes of a diameter of 1/8. inch over 1/2 inch staggered centers as shown in figure 7. If desired, the slots can be cut on the surface to facilitate water drainage and vacuum uniformity.

The vacuum is introduced to a capillary drain roller 10 through a stationary central stump. There are no multiple internal chambers in the capillary drain roller 10 that is being operated at different pressure or vacuum levels. Such multiple internal chambers being operated at different pressures or vacuum levels can create significant operating problems such as runoff from one chamber to another, wear of the cylinder stumps, and unbalanced loads on the rotating cylinder. The only air run-off inside the roller of the present invention comes through the mechanical seals in the central stumps and those larger pores where the effective capillary breaking pressure is exceeded. This air flow is relatively small and is substantially less than the air flow in the corresponding vacuum dewatering box.

Because the entire interior of the capillary dewatering cylinder 10 is maintained at a uniform vacuum level with respect to the atmosphere, the shell is subjected to a uniform pressure difference. The shell thickness is therefore determined by normal stress analysis techniques. With the unseeded vacuum roller 30 there are no major unbalanced forces, so that bearing loads are minimized. The shell should be designed for a differential of about 25 inches Hg (max).

As mentioned above, the water can be removed from the interior of the roller 10 by means of a siphon 20 which terminates at or near the inner wall of the cylinder 30. It is preferred to continuously remove the water from below the composite membrane 12 to through the vacuum drum shell 30. A continuous water film is not required under the capillary surface membrane 22 or under the composite membrane 12. Any water film will produce an increased centrifugal force at the higher paper machine speeds to which the capillary dewatering roller 10 will be operated; this must be off-center by a corresponding increase in capillary vacuum. There are a number of alternate ways to remove this water including a spoon for water.

The clamping point roller 16 is intended to establish a hydraulic contact between the water in the tissue W and the water in the capillary pores of the membrane surface 22. Some of the water is pushed from the tissue in the area of the knuckles the transfer cloth 14. This water fills any hollow volume in the capillary membrane surface 22 and reduces the interfacial resistance to the movement of water from the tissue W into the pores of the capillary membrane surface 22. In addition, the fiber network of the tissue is put into more intimate contact with the capillary surface 22 and some of the entrapped air can be removed from the W tissue. These factors should help to dewater the tissue W.

The clamping point roller 16 must apply a very light load to the sheet which is held between the carrier cloth with knuckles 14 and the capillary membrane surface 22. The clamping point roller 16 should preferably have a relatively smooth cover. It has been successfully used a soft rubber cover having a hardness of P & J of about 150. Forces of about 10 to 45 pli have been applied for the clamping roll 16 producing an average value of about 11 to 38 psi at the clamping point between the clamping point roller 16 and the capillary dewatering roll 10. Values of around 20 pli (around 20 psi at the point of attachment) or lower appear to be sufficient to promote the beneficial factors mentioned above. The lower the pressure at the point of attachment, the less opportunity for compression of the general tissue. A soft and very wide fastening point is preferred allowing the paper to be lightly pressed sclo into the knuckle area of the transfer fabric 14 to ensure that there is no virtual overall compression of the fabric W. The use of the knit roller clamping 16 increases the dryness outside the capillary dewatering drum 10 of the present invention by about 2 to 7 percentage points (eg, Example B). This is a large amount of water and a major advantage of the system of the present invention.

Typically, the open knuckle transfer fabric 14 is a woven polyester fabric normally found in a continuous dryer process (for example, Albany 5602 Ceno is manufactured by Albany International of Albany, NY). Other types of transfer fabrics may be acceptable including plastic or metal wires, forming type fabrics, non-woven fabrics, or even certain paper felt felts in wet differential. The open knuckle transfer fabric 14 should be air permeable and should not substantially compress the sheet when pressed against the surface of the capillary membrane 22. Typically, the pressure or knuckle areas of the transfer cloth 14 should be less than about 35% of the surface area of the fabric 14 and more preferably, in the range of 15% to 24% of the surface area of the fabric 14.

The residence time during which the wet fabric W and the surface of capillary membranes 22 are in contact with one another is a function of the amount of wrap around the capillary drain drum 10, the diameter of the capillary drain drum 10, and the speed of operation. The reference time can be defined by the equation: t = 0.5236DA / V where: t = residence time (second) D = roller diameter (foot) A = wrapping angle in degrees V = tangential velocity (fpm) The wrapping angles from around 200 ° to 315 ° are expected. The greater the wrapping angle, the more drainage will be achieved. Residence times of at least 0.15 seconds are desired and up to 0.35 seconds are preferred. Even when the leaf will become drier with more residence time, the rate of change is quite slow above 0.15 seconds. A test run with a Dutch Twill composite membrane showed a decrease in dryness of only about 1% (39% down to 38%) as the residence time decreased from 0.46 seconds to 0.24 seconds.

The capillary dewatering system of the present invention has demonstrated the ability to dewater uncompressed moist tissues to dryness levels approaching 43%. For pre-ium tissue supplies the method and capillary dewatering apparatus of the present invention has achieved dryness levels of from about 36% to about 42% dry. The dryness on the capillary dewatering drum 10 is a function of the supply, the basis weight, the level of refinement, the permeability and the membrane pore size, the capillary vacuum level, the clamping roller and the residence time.

During the capillary dewatering step of the present invention, the density and thickness of the tissues remain the same as or better than those of a corresponding continuously creped and dried tissue tissue (see Product Examples 1A IB, 2A and 2B). ). No general compression of the fabric took place allowing the production of a more bulky low density fabric. Product Examples 1A and 2A are standard through Scott air-creped tissue products. Product Examples IB and 2B are air dried, capillary dried tissue products made with the process of the present invention. The supply for Product Examples 1A and IB was homogenously mixed of 65% pine and 35% eucalyptus. The supply for Product Examples 2A and 2B was a homogeneous mixture of 70% NSWK and 30% eucalyptus.

PRODUCT EXAMPLES 1A AND IB Single Layer Tissue Products 1A1B Speed (fpm) 500500 Clamping Point Roller Load (pli) -27 Capillary Roller Vacuum ("H20) -111 Pre-Capillary Roller Dryness (%) -24.9 Post-capillary Roller Dryness (%) -38.2 Dryness Continuous Pre-Dryer (%) 30,538.2 Base Weight (pound / 2,880 square feet) 16,816.5 Thickness (mils / 24 layer @ 1.0 Kpa) 297303 MDT (ounce / inch) 18,719.2 CDT (ounce / inch) 9.39.1 Apparent Density (gm / cc) 0.09060.0871 PRODUCT EXAMPLES 2A AND 2B One Layer Tissue Products 1A1B Speed (fpm) 500500 Loading of Clamping Point Roller (pli) -34 Capillary Roller Vacuum ("H20) -130 Pre-capillary Roller Dryness (%) -30.2 Post-capillary Roller Dryness (%) -39 Dryness of Continuous Pre-Dryer (%) 30,939 Base Weight (pound / 2,880 square feet) 16,315.7 Thickness (mils / 24 layer § 1.0 Kpa) 274290 MDT (ounce / inch) 18,522.0 CDT (ounce / inch) 8.411.0 Apparent Density (gm / cc) 0.09540.0867 Another advantage of the capillary drain system of the present invention is that the dryness outside the capillary drain drum 10 is relatively independent of the incoming drying of the fabric W. For any given set of conditions, the dryness of the fabric W outside the drum of capillary drainage 10 would not give more than about 1% since the dryness of the tissue inside is varied from about 14% to about 30% (e.g., figure 8). The dryness of the fabric outside tends to increase slightly as the incoming dryness increases above about 30%. This has several benefits. First, by being able to remove extremely large volumes of water (for example, 14% dryness within 38% of dryness outside is equivalent to 4.51 gw removed each gf), the number of dewatering stations or energy intensive vacuum used in the general papermaking process can be reduced or perhaps even eliminated. Second, the capillary dewatering system acts as a softening device for moisture streaks. The non-uniformities in humidity that go inside the capillary drain roller 10 are greatly reduced or flattened. If the continuous dryer is used in the next phase of drying, this results in better drying in the continuous dryer and fewer streaks on the continuous dryer fabric.

An additional advantage of the capillary drainage system of the present invention is its relative insensitivity to the basis weight. Changes in the basis weight from about 12 pounds per ream to about 25 pounds per ream do not seem to result in any major changes in the drying of the capillary dewatering roller. A test produced less than a one percentage point difference. This feature again tends to reduce the undesirable effects associated with base weight non-uniformities and allow a range of products to be run (from lightweight facial tissue to heavy paper towel) on the same paper machine.

The capillary dewatering roller 10 can be used in combination with continuous dryers, Yankee dryers, gas surface temperature dryers, steam heated dryers, or combinations thereof. For example, looking at Figure 9 below, a head box 50 is shown delivering a supply to a forming wire 52 constituting the wet embryonic tissue thereon. The fabric W is vacuum dewatered by means of the vacuum boxes 54. The fabric W is then transferred to a continuous dryer cloth with knuckles 56 when the fabric is in the range of from about 10% to about 32% dry by means of a vacuum 58. If desired, the sheet can be further dewatered and shaped by a vacuum box 59, even when this box is not required. The continuous knit dryer fabric 56 carries the fabric to the capillary dewatering roller 10 with the dryness of the fabric being in the range of from about 125 to about 32% upon entering it into the capillary dewatering roller 10. The knit roller of clamping 16 presses the fabric W and the continuous dryer fabric with knuckle 56 against the capillary membrane 12 of the capillary drainage roller 10. The dryness outside the capillary drainage roller will be in the range of from about 33% to about of 43% dry. The continuous dryer fabric 56 then carries the fabric through a continuous dryer 60. The fabric W in the dryness in the range of from about 65% to about 95%, is then transferred to the Yankee dryer 62 that is being pressed on it by the press roll 64. The fabric is then creped from the Yankee dryer 62 when the fabric is at a dryness of from about 95% to about 99% by weight, and running through the rolls of calandria 66 A process for making alternating paper using the capillary dewatering drum 10 of the present invention is shown in FIG. 10. The components used in such a process are virtually identical to those shown and described in FIG. 9. Therefore, similar components in the Figure 10 are numbered as they were in Figure 9. The only difference in the process shown in Figure 10 is that the continuous dryer has been removed. Thus, with the capillary dewatering roller 10 receiving a fabric at a dryness of 12% to about 32% dry with the fabric W coming out of the roller 10 at a dryness of from about 33% to about 43% dry , the fabric is only in the range of from about 33% to about 43% dry as it is transferred to the surface of the Yankee dryer. Creping occurs from 95% to 99% dry. The tissues made with the use of the capillary dewatering roller in this manner (FIG. 10) had a thickness, density and feel values equal to or better than those of a comparable base weight tissue product made with creping and drying processes. continuous and without capillary drainage (see Product Examples 3A, 3B, 4A and 4B). Product Example 3A was made with the entire continuous drying process followed by the Yankee crepe dryer. The Example 3B Product was made with the capillary dewatering process of the present invention followed by drying with an air dryer and then a Yankee crepe dryer. Product Example 4A is a creped product and was made with the capillary drainage process of the present invention with complete drying only on the Yankee dryer, not with the continuous dryer. The Product of Example 4B is a conventional dry felt and compressed tissue product. The supply for making the Products of Examples 3A, 3B, 4A and 4B was a homogeneous mixture of 70% NS K and 30% eucalyptus.

PRODUCT EXAMPLES 3A AND 3B Two-Layer Tissue Products 3A3B Speed (fpm) 500500 Hair Roller Vacuum ("H20) -115 Pre-Hair Roller Dryness (%) -32 Post-Hair Roller Dryness (%) -39.7 Pre-Crepe Dryer Dryness (%) 35.739.7 Two layers Base Weight (pound / 2,880 square feet) 20,922.2 Thickness (mils / 24 layer @ 1.0 Kpa) 463516 MDT (oz / inch) 12,312.2 CDT (ounce / inch) 5.75.6 Apparent Density (gm / cc) 0.07250.0691 Finished Product Handfeel * 1.001.04 * Normalized to all continuous drying equal to 1.00 PRODUCT EXAMPLES 4A AND 4B Two-Layer Tissue Products 4A4B Speed (fpm) 500500 Capillary Hair Vacuum ("H20) 115-Pre-Capillary Roller Dryness (%) 27.3-Post-capillary Roller Dryness (%) 39.8-Continuous Pre-Dry Dryer (%) 39.826.2 Two layers Base Weight (pound / 2,880 square feet) 21,820.6 Thickness (mils / 24 layer @ 1.0 Kpa) 48934ÍT MDT (ounce / inch) 9.810.7 CDT (ounce / inch) 4.44.1 Apparent Density (gm / cc) 0.07160. 0966 Finished Product Handfeel * 1.010.91 * Normalized to all continuous drying equal to 1.00.

The ability of the capillary drain system to remove water after substantial compression of the fabric makes it economically advantageous to retrofit a conventional wet compressed paper machine to one that can produce soft absorbent and low density towel and tissue products. For example, the wet press felt run may be replaced by a continuous knuckle dryer fabric and the capillary drain system of the present invention, and be skipped in the space left between the forming fabric and the Yankee crepe dryer, as it was shown in figure 10. The sheet can then be transferred to the Yankee dryer at about 33% to 43% dry and creped to the normal crepe dryness of paper machine. As shown in Examples 3A, 3B, 4A and 4B given above, the resulting low density soft product is very similar to that made with a continuous Yankee dryer-dryer combination as shown in Figure 12. The cost of retrofitting using the capillary drain system, however, is lower and can be achieved with less interruption to the operation of the paper machine. JEJL process of the resulting paper machine will also use less energy than the retrofit of the continuous dryer.

Similarly, the capillary drainage system can be used in combination with a continuous dryer to retrofit a machine to make wet compressed paper if more drying before the Yankee is required. It can also be used to replace a continuous dryer in an existing two-dryer system to save energy and reduce operating costs. It will be recognized by those skilled in the art to make paper that even when the present invention is discussed in combination with creping as shown in Figures 9, 10 and 11, the present invention can also be used in paper making processes which do not they include a creping step. The present invention can be used with the final drying after capillary drainage has been performed with continuous dryers, can dryers, high surface temperature dryers, or combinations thereof without a creping step.

On existing paper machines, the capillary drain drum 10 of the present invention can be used to reduce operating and energy costs by eliminating vacuum pumps, reducing the force of the continuous dryer fan and less use of cover gas. Potentially, a continuous dryer can be removed from the two existing ones through the continuous dryer process. By keeping both continuous dryers in place, the capillary drain drum 10 of the present invention can be used to increase the speed and productivity of the paper making machine. By adding the capillary drain drum 10 of the present invention to the conventional continuous dryer process shown in Figure 12, the total energy use of the process will be reduced by 17% to 25%. From the foregoing, it should be recognized that this invention is a well adapted to achieve all the purposes and objects set forth herein together with other advantages which are obvious and which are inherent to the apparatus and method.

It will be understood that certain features and subcombinations are useful and can be used with reference to other characteristics and subcombinations. This is contemplated by and is within the scope of the clauses.

As many possible embodiments can be made of the invention without departing from the scope thereof, it should be understood that all of the subject matter herein set forth in the accompanying drawings should be construed as illustrative and not in a limiting sense.

Claims (31)

R E I V I N D I C A C I O N S

1. A method to reduce the moisture content I'- of a fiber fabric in a process for making paper that comprises the steps of: (a) holding the fabric on an air permeable fabric; 10 (b) slightly compressing the fabric between the air permeable fabric and the capillary membrane of a capillary drain roll having defined pores therein which are configured to induce a negative capillary suction pressure; Y 15 (c) pull a vacuum inside the capillary drain roller, the vacuum not being greater than the negative capillary suction pressure of the capillary pores.

2. A method as claimed in clause 1, characterized in that the capillary pores have a diameter in the range of 0.8 microns to 10 microns.

3. A method as claimed in clause 2, characterized in that the capillary pores have a 25 diameter in the range of 2 microns to 10 microns.

4. A method as claimed in clause 1, characterized in that said air-permeable fabric comprises a continuous dryer cloth with knuckles and said light compression step only compacts the fabric in the knuckle areas of the continuous dryer cloth with knuckles .

5. A method as claimed in clause 1 characterized in that said step (c) is carried out so that the negative capillary suction pressure is not greater than Cp, where: Cp = 2s Cos? where s is the interfacial tension of water-air-solids,? is the contact angle of water-air-solids and r is the radius of the capillary pore.

6. A method for removing a portion of the liquid contained in a continuous wet porous fabric in a process for making paper without substantial overall compaction of the fabric, comprising the steps of, with steps (b) and (c) not in a particular order: (a) delivering a supply jet from a head box to a forming fabric to form an embryonic tissue; (b) vacuum draining the bionic tissue so that the embryonic tissue is in the range of from about 6% to about 32% dry; (c) transferring the fabric from the forming fabric to an open knuckle transfer fabric; (d) slightly compressing the tissue between the open knuckle transfer fabric and the capillary membrane of a rotating capillary dewatering roller, the capillary membrane has capillary pores therethrough which have a virtually straight tortuous path, the capillary pores have a pore aspect ratio of from about 2 to about 20; (e) Pulling a vacuum inside the capillary drain roll that is not larger than the negative capillary suction pressure of the capillary pores.

7. A method as claimed in clause 6, characterized in that it also comprises the step of: maintaining the tissue in contact with the capillary membrane for substantially at least 0.15 seconds.

8. A method as claimed in clause 6, characterized in that the open knuckle transfer fabric has a pattern of knuckles projecting therefrom which press the fabric during said light compression step in no more than 35% of the area of total surface of the fabric.

9. A method as claimed in clause 8, the open knuckle transfer fabric has a knuckle pattern projecting therefrom which presses the fabric during said light compression step in no more than 25% of the surface area total of the tissue.

10. A method as claimed in clause 6, characterized in that the capillary drain roller is an unseeded roller so that the vacuum pressure inside the capillary drain roller is substantially the same therethrough.

11. A method as claimed in clause 6, characterized in that it also comprises the steps of: removing the tissue from contact with the capillary membrane while continuing to hold the tissue on the transfer fabric with open knuckles; Spraying the capillary membrane with water at a pressure of from about 100 psi to about 900 psi to wash the surface of the capillary membrane and to drain any particles trapped within the capillary pores through the capillary pore into the interior of the roller. rotating capillary drain.

12. A method as claimed in clause 6, characterized in that it also comprises the steps of: drying the fabric continuously to a dryness of from about 65% to about 95%; Transfer the fabric to a Yankee dryer surface; creping the fabric of the Yankee dryer surface when the fabric is dried for about 95% to about 99%.

13. A method as claimed in clause 6, characterized in that it comprises the steps of: transferring the fabric to a dryer surface Yankee when the tissue is at a dryness from around 33% to around 43%; and creping the fabric of the Yankee dryer surface when the fabric is dry for about 95% to about 99%.

14. A method as claimed in clause 6, characterized in that it also comprises completing the drying of the fabric with a continuous air dryer.

15. A method as claimed in clause 6, characterized in that it also comprises completing the drying of the fabric with a high surface temperature dryer.

16. A method as claimed in clause 6, characterized in that it also comprises completing the drying of the fabric with can dryers.

17. A method for removing water from a wet porous tissue in a papermaking process without a virtually general compaction of the fabric, comprising the steps of: (a) placing the tissue on a capillary membrane of a rotating capillary drain roll having capillary pores therethrough which have a virtually continuous non-tortuous path, the capillary pores have a pore aspect ratio of from about 2 to around 20; (b) separating the tissue from the capillary membrane; Y (c) spraying the capillary membrane with a cleaning fluid to wash the surface of the capillary membrane and to drain any particles trapped within the capillary pores through the continuous non-tortuous capillary pores dry inside the rotating capillary drain roller sectorized

18. A method as claimed in clause 17, characterized in that step (c) comprises spraying the capillary membrane with water at a pressure of from about 100 psi to about 900 psi.

19. A method for making a creped paper product comprising the steps of, wherein steps (b) and (c) are not in a particular order: (a) delivering a supply jet from a head box to a forming fabric to form an embryonic tissue; (b) dewatering the embryonic tissue so that the embryonic tissue is in the range of from about 6% to about 32% dry; (c) transferring the fabric from the forming fabric to an air permeable fabric; (d) slightly compressing the tissue between the air permeable fabric and the capillary membrane of a rotating capillary drain roll, the capillary membrane having capillary pores therethrough which have a straight non-tortuous path, the capillary pores have a pore aspect ratio of from about 2 to about 20; (e) separating the tissue from the capillary membrane; Y (f) passing the separated ejido through a creping dryer to crepe the fabric without first passing the fabric through a conventional continuous dryer, whereby the creped paper product is produced with significant energy savings.

20. A method as claimed in clause 19, characterized in that it also comprises the steps of: keeping the tissue in contact with the capillary membrane for virtually at least 0.15 seconds.

21. A method for retrofitting a conventional paper tissue manufacturing facility of the type that includes a forming mechanism for forming an embryonic tissue on a forming mesh and at least one continuous dryer to dry the embryonic tissue to a tissue of paper dry that includes the steps of: (a) remove at least one continuous dryer; (b) replacing said continuous tumbled dryer with a rotating capillary dewatering roller having a capillary membrane with capillary pores therethrough which have a virtually continuous and straight non-tortuous trajectory, the capillary pores have a pore-like pore aspect ratio. from around 2 to around 20; Y (c) install a mechanism to compress a fabric lightly to the capillary membrane to ensure a hydraulic contact between the water contained in the fabric and the water in the pores of the capillary membrane without a general compaction of the tissue, so the system is reconfigured to be more efficient in relation to energy than what was possible here.

22. A method as claimed in clause 21, characterized in that the system comprises a crepe dryer and step (a) is carried out by means of removing any continuous dryer from the system.

23. A system for removing water from a wet tissue paper during a papermaking process, comprising: a rotating dewatering roll having a capillary membrane with capillary pores therethrough having a non-tortuous, substantially continuous and straight path, the capillary pores having a pore aspect ratio of from about 2 to about 20; Y means for compressing a tissue lightly to the capillary membrane to ensure a hydraulic contact between the water contained in the fabric and the water in the pores of the capillary membrane without a general compaction of the tissue, thus providing a draining mechanism that is more economical of energy than conventional continuous dryer mechanisms.

24. A system as claimed in clause 25, characterized in that said compression means are constructed and arranged to compress the tissue against the membrane at a linear force that is virtually within the range of less than 150 pli.

25. A system as claimed in clause 24, characterized in that said compression means are constructed and arranged to compress the tissue against the membrane at a line force that is substantially within the range of 20-50 pli.

26. A system as claimed in clause 23, characterized in that said dewatering roller is not sectoreado.

27. A system as claimed in clause 26, characterized in that it comprises means for spraying the capillary membrane with a cleaning fluid to wash the surface of the capillary membrane and to drain any particles trapped within the capillary pores through the capillary pore inside the rotating capillary drain roller.

28. A system as claimed in clause 27, characterized in that said spraying means are constructed and arranged to spray water at a pressure of from about 100 psi to about 900 psi.

29. A system for reducing the moisture content of a paper web in a process for making paper, comprising: a rotating capillary drain roll having a capillary membrane with capillary pores therethrough having a substantially straight and continuous non tortuous path, the capillary pores have a pore aspect ratio of from about 2 to about 20; means for compressing a tissue to the capillary membrane to ensure a hydraulic contact between the water contained in the tissue and the water in the pores of the capillary membrane; Y means for spraying the capillary membrane with a cleaning fluid to wash the surface of the capillary membrane and for draining any particles trapped within the capillary pores through the continuous non-tortuous capillary pores virtually straight to the interior of the rotating capillary dewatering roller.

30. A system as claimed in clause 29, characterized in that said spraying means is adapted to spray said cleaning fluid at a pressure of from about 100 psi to about 900 psi.

31. A method for retrodposing a wet compressed paper tissue manufacturing facility of the type including a forming mechanism for forming an embryonic tissue on a forming mesh and at least one press filter station for drawing water from the embryonic tissue that It includes the steps of: (a) remove the press felt station; (b) replacing said removed press felt station with a dewatering station including a rotating capillary dewatering roller having a capillary membrane with capillary pores therethrough which have a non-tortuous substantially straight and continuous path, the capillary pores they have a pore aspect ratio of from about 2 to about 20; Y (c) install a mechanism to slightly compress a tissue in the capillary membrane to ensure a hydraulic contact between the water contained in the tissue and the water in the pores of the capillary membrane without a general compaction of the tissue, so the system is reconfigured to save more energy than what was possible here. SUMMARY A method for reducing the moisture content of a paper web in a process for making paper in the range of from 10% to 32% dry to the range of 33% to 50% dry where the embryonic tissue is described is described. held on a continuous dryer cloth with knuckles and is slightly compressed between the continuous dryer fabric with knuckles and a capillary membrane of a capillary drain roller. The capillary membrane has capillary pores therethrough which have a substantially tortuous, non-tortuous path and continue with a pore aspect ratio of from about 2 to about 20. A vacuum is pulled into the capillary drain roller which it is not greater than the negative capillary suction pressure of the capillary pores.