Displacement dewatering a web using compressed gas

Abstract

Displacement dewatering system, methods and apparatus, for liquid dewatering a nascent paper web in a papermaking machine nip. A press roll presents pressurized gas to the web through one or more stationary pressure zones. Each pressure zone has a seal assembly which bears on the inside surface of the outer shell of the press roll, isolating the respective pressure zone from any adjacent pressure zones. Pressurized gas passes through the one or more pressure zones, thence into and through apertures in the shell, thence into and / or through the web. A vent receptive device receives air and water exiting the web. Methods and apparatus are provided for controlling seal temperature and / or seal pressure and / or seal friction, as well as controlling light leaking past the seal.

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates to improvements in removal of water from a nascent paper web, at a water removal section of a papermaking machine. More particularly, this invention relates to improved efficiencies in removing water from such nascent paper web. Further, the invention relates to reducing water content of the nascent paper web at the water removal section, before the web reaches the thermal drying section. Yet further, the invention relates to increasing solids content of a wet nascent paper web at the water removal section of the papermaking machine.

[0002] A typical first step in removing water from the web is to pass the web through a conventional wet press nip, which mechanically squeezes the web, thus hydraulically driving a portion of the water from the web. The web can also be passed across a vacuum / suction box, either separately or in the wet press, thus to encourage further removal of water from the web. A typical final step in removing water from the web, thus to provide the finished "dried" paper product, is to pass the web through a thermal dryer.

[0003] Relative to thermal drying, use of the wet press and vacuum box are generally energy efficient in terms of the amount of water removed. However, only limited fractions of the water in the web are removed by these processes. While the thermal drying step can remove, from the web, as much water as desired, thermal drying requires changing the physical state of the water from liquid to gas / steam, which requires much more energy per unit / mass of water removed from the web than removing water in the liquid state in the conventional wet press nip. The limitation of the conventional wet press nip is that there is a known limit to the fraction of the water which can be removed in the wet press nip.

[0004] Certain embodiments of displacement dewatering are described in my co-pending application serial number 17 / 803,966, filed 02 / 10 / 2023, incorporated herein by reference in its entirety.

[0005] During displacement dewatering at a dewatering station, air or other gas, hereinafter referred to as air, is transmitted from a pressure box into and / or through the nascent paper web being dewatered, with the objective of having an optimal volume of air pass into and / or through the nascent paper web, whereby the air pushes water out of the web, thus contributing to the drying of the web. To make the best use of the air, it is desired that as much as possible of the air which is provided to the pressure box pass into and / or through the web, while the fraction of the air provided to the pressure box, which air does not pass into the web, is limited.Pressure Zone Seal Leakage

[0006] FIGURE 1 shows multiple areas inside an air dewatering station where air can be consumed / lost in the displacement dewatering process, in that such air does not pass into or through the nascent paper web 102. Since only the air which passes into and / or through the nascent paper web acts to remove water from the web, any quantity of air which does not pass into or through the web is considered to be "lost" air. In FIGURE 1, a compressed air generator or blower 23 supplies compressed air to a pressure box 24 inside a press roll 26 (see FIGURES 2 and 3) having a perforated rotating outer shell 28. Pressure box 24 feeds compressed air into one or more pressure zones 30 which supply compressed air to the outer shell. A structural, e.g. mechanical, e.g. polymeric or ceramic seal 32 is provided at the interface between the pressure box and the perforated outer shell thus to inhibit lateral leakage of the compressed air from the respective pressure zone. To the extent seal 32 allows air to leak past the seal, namely between seal 32 and outer shell 28, and thus out of the pressurized area of the liquid dewatering zone, that leaked quantity of air is air lost to the liquid dewatering process. It is an object of this invention to minimize, or at least limit, the amount of air of all sources "lost" in the displacement dewatering process.Air Entrained in Pressure Roll Leakage

[0007] Air entrained in outer shell 28 of pressurized roll 26 is pressurized air which has entered, from pressure box 24, into apertures 34, in the pressure zone which corresponds generally to at least a portion of the nip between the press roll and a vent device such as a vent roll or a vent shoe. Any such air so entrained in the press roll apertures when those apertures exit the pressure zone are released to any lower pressure atmospheres inside and / or outside the shell. Where the apertures pass beyond all pressurized zones, any air entrained in such apertures is released to those lower pressure atmospheres, e.g. ambient pressure. Such release of air, from the apertures to such lower pressure atmosphere, is also "lost" air.

[0008] The quantity of "lost" entrained air depends on the rotational speed of the outer shell and the void volume of the apertures in the outer shell.Fabric MD / CD Lateral Leakage

[0009] Lateral MD / CD leakage of air by way of an air distribution fabric 36 which receives the pressurized air from the apertures in the outer shell can be determined by direct measurement of air leakage using a tester which measures air flow while sealing out all leakage of pressurized air except for air which leaks laterally through the fabric.

[0010] Another source of air loss is the air lost due to pressurized air remaining entrained in the air distribution fabric when the air distribution fabric exits the area overlain by the respective pressure zone. When the air distribution fabric is pressurized by the pressurized perforated roll shell, voids in the fabric become pressurized. Pressurized air in the voids is released to atmosphere when the air distribution fabric leaves the influence of the pressurized pressure zone or zones. Air so released to atmosphere represents another loss of pressurized air that doesn't go into or through the nascent paper web.

[0011] In summary, air used in the dewatering process includes the following potential air applications: Air which leaks between the pressure box and the roll seal; Air entrained in the roll shell; Lateral air leakage from the air distribution fabric; Air which becomes entrained in the air distribution fabric, but does not pass through it; Air which becomes entrained in, the web being dewatered but does not pass through it; Air which passes through the nascent paper web being dewatered.

[0012] Only the air which becomes entrained in, or passes through, the nascent paper web is instrumental in removing water from the web.

[0013] Since the amount of water removed from the nascent web during displacement pressing is related to the amount of air that passes into or through the web, thus displacing water, there is a need to optimize the amount of air passing into or through the web, and limit the amount pressurized air which does not pass into or through the web

[0014] In light of the above, there remains a need, in the papermaking industry, for additional improvements in apparatus for removing water, in liquid form, e.g. without evaporating the water using heat, from nascent paper webs being formed in a papermaking machine.

[0015] There is also a need for improved methods for removing water, as liquid, from nascent paper webs in the papermaking process.

[0016] There is further a need for methods and apparatus for limiting the amount of energy required for removing water from nascent paper webs in the process of manufacturing paper products.

[0017] There is also a need for increasing solids content of a paper web before the web reaches the dryer section, in order to reduce the energy demand in the dryer section. These and other objects and needs are alleviated, or at least attenuated, by the novel apparatus, methods, and products of the invention.SUMMARY OF THE DISCLOSURE

[0018] The invention discloses novel apparatus and methods for removing water from a nascent paper web, as part of a web sandwich, in a water removal section of a papermaking machine. While mechanical pressing of the web is consistent with the invention, the invention focuses on apparatus and methods for passing air or other gas through the paper web, including through the web sandwich.

[0019] In the invention, after a nascent paper web has been formed, one or more carrier fabrics are joined with the nascent paper web, thereby defining a web sandwich. In some embodiments, carrier fabrics are disposed on opposing outer surfaces of the nascent paper web such that the resulting structure is a fabric / web / fabric sandwich. In other embodiments, one or more fabrics are disposed on one outer surface of the nascent paper web while the opposing outer surface of the nascent paper web remains exposed, without a carrier fabric thereon. Such web sandwich, having no carrier fabric on the opposing outer surface, is defined herein as an open-face sandwich.

[0020] The web sandwich is passed through a dewatering station defined by a pressure apparatus, such as a press roll, which applies air / gas pressure, and a pressure receptive vent apparatus such as a vent roll or shoe, which collectively define a nip through which the web sandwich passes. One or more optional fabrics / layers between the nascent paper web and the vent apparatus, as part of the web sandwich, receive air / gas, as well as water, which has been removed from the nascent paper web. Such fabric layer can act as an anti-rewet layer, impeding return of a rewet portion of such water to the web as the web passes through, and out of, the dewatering station.

[0021] In particular, the invention focuses on efficiently separating, away from the web, water which has been removed from the web, and reducing / limiting the loss of air to system exits other than through the web. The invention further focuses on efficient use of seals in areas being traversed by the pressurized gas / air. The invention focuses both (i) on structure and methods for using a seal to help contain and direct pressurized gas, in a pressure zone at a nip, into and through a paper web being formed, and (ii) on use of a plurality of such pressure zones along the MD length of the nip to so help contain and direct such pressurized gas.

[0022] In a first family of embodiments, the invention comprehends, in a displacement dewatering system in a papermaking machine, where a pressurized gas is being forced through apertures in an outer shell of a rotating press roll in a nip, and thence into a web sandwich comprising a nascent paper web, thereby removing liquid water from the nascent paper web, the nip having a machine direction nip length extending along the machine direction of the papermaking machine, a nip entrance, and a nip exit, a method of limiting escape of pressurized air from the displacement dewatering system at at least one of the nip entrance or the nip exit, the method comprising providing a plurality of pressure zones in the rotating press roll, the pressure zones being disposed sequentially along, and within the length of, the nip, from a first pressure zone proximate the nip entrance to an nth pressure zone proximate the nip exit, each such pressure zone having a seal which obstructs gas leakage between the respective seal and an inner surface of the press roll outer shell, in the nip; providing pressurized gas, at a first gaseous pressure, to at least one such pressurized pressure zone, the provided gaseous pressure pressurizing respective apertures in the roll shell which apertures are in gaseous communication with the pressurized pressure zone; and controlling gaseous pressure in a second such pressure zone, along the length of the nip, which is not the at least one such pressurized pressure zone, the second such pressure zone optionally being the first pressure zone or the nth pressure zone, and having a second gaseous pressure, optionally ambient pressure or near ambient pressure, lower than the first gaseous pressure.

[0023] In some embodiments, the method comprises at least one such pressurized pressure zone being displaced from both the first pressure zone and the nth pressure zone.

[0024] In some embodiments, the method comprises providing, at the nip a vented shoe press roll which receives air which has passed through the web sandwich, and also receives water which has been expelled from the web sandwich, and wherein the nip contact length between the press roll shell and the vented shoe press roll is greater than 2 inches, optionally greater than 5 inches, optionally greater than 7 inches, optionally greater than 10 inches.

[0025] In some embodiments, as the apertures in communication with the one such pressurized pressure zone rotate past the one such pressurized pressure zone, the respective apertures carry entrained pressurized gas to a next adjacent pressure zone, thereby providing the entrained pressurized gas to the next adjacent pressure zone.

[0026] In some embodiments, the method comprises recycling pressurized gas from a such pressure zone downstream in the machine direction from the one such pressurized pressure zone, to a pressure zone upstream in the machine direction from the one such pressurized pressure zone, namely toward or at the first pressure zone, or recycling the pressurized gas to an intake portion of a generator which pressurizes gas.

[0027] In some embodiments, a portion of the pressurized air passes, from the one such pressurized pressure zone, through the shell apertures and into the web sandwich, and laterally through the web sandwich and along a reverse path back into apertures in the roll shell leading to one or more pressure zones which are not the one such pressurized pressure zone.

[0028] In some embodiments, the method further comprises alternating magnitude of the gaseous pressure in at least one of the pressurized pressure zones from a relatively higher pressure to a relatively lower pressure during the course of a portion of the nascent paper web passing through the respective at least one of the pressurized pressure zones.

[0029] In some embodiments, a blanket rotates about the vented shoe press roll, the blanket having a length and a width, an inner surface proximate the press roll shoe, and an outer surface relatively more remote from the shoe, a plurality of tubes extending across the width of the blanket between the inner surface of the blanket and the outer surface of the blanket, a plurality of grooves on the outer surface of the blanket, and extending inwardly into interior locations in the blanket, and thereby intersecting with the plurality of tubes so as to provide gaseous and liquid communication between the respective outer surface of the blanket and the plurality of tubes.

[0030] In some embodiments, the method comprises directly supplying individually selected pressures of pressurized gas from a pressure generator to each such pressure zone, with optionally little or no gaseous pressure being supplied to at least one of the first pressure zone or the second pressure zone, or to the nth pressure zone or the nth-1 pressure zone.

[0031] In some embodiments, the invention comprises controlling gas pressure in a respective pressure zone thereby to limit, optionally minimize, release of gas pressure from the apertures and from the web sandwich when the web sandwich exits the nip.

[0032] In some embodiments, the method comprises controlling gas pressure in the plurality of pressure zones so as to affect noise reduction.

[0033] In some embodiments, the method further comprises providing a light source on a first side of a respective such seal, and a light sensor located, adapted and configured to detect any light leaking past the respective seal, the light sensor sending a light sensed signal to a controller, the controller adjusting pressure on the seal sufficient to eliminate leakage of light past the respective seal proximate the light sensor.

[0034] In some embodiments, the controller cycles loading pressure on the seal, seeking lesser air leakages in combination with lesser seal force at a seal interface with the outer shell.

[0035] In some embodiments, the controller adjusts the load on the seal, for seal contact pressure which limits leakage of light past the respective seal proximate the light sensor.

[0036] In some embodiments, the method further comprises providing relief zones, such as slits or cuts, in a such seal, such slits or cuts being displaced from each other along the length of the respective seal, and facilitating localized flexing of such seal in response to force urging a localized portion of the seal against the inner surface of the roll shell.

[0037] In some embodiments, the method further comprises sensing seal temperature during a break-in period of such seal, optionally at multiple locations along the length of the seal, and applying heat to the seal and thereby raising the seal temperature up to about 20 degrees C greater than the glass transition temperature of material from which the seal is made.

[0038] In some embodiments, the method further comprises sensing seal temperature during routine operation of the seal, optionally at multiple locations along the length of the seal, and applying heating and / or cooling to the seal, as applies, to maintain the seal at a temperature more than 5 degrees C, optionally more than 10 degrees C, optionally more than 20 degrees C, below the glass transition temperature of material from which the seal is made.

[0039] In some embodiments, the method comprises providing such apertures, in the outer roll shell, sized and configured such that a given aperture does not convey pressurized air to first and second adjacent such pressure zones simultaneously.

[0040] In some embodiments, the method comprises alternating magnitude of gaseous pressure applied to an element of the nascent paper web, from a relatively higher pressure to a relatively lower pressure during the course of that element of the nascent paper web passing through the nip.

[0041] In some embodiments, the method comprises such seal having an upstream portion (T1) disposed relatively toward the nip entrance and a downstream portion (T3) disposed relatively toward the nip exit, the upstream portion (T1) being relatively (MD) shorter than the downstream portion (T3).

[0042] In some embodiments, the method comprises applying water to an inner surface of the outer shell and thereby lubricating an interface between a respective such seal and the inner surface of the outer shell, and accordingly limiting friction experienced by the respective such seal.

[0043] In a second family of embodiments, the invention comprehends, in an area occupied by a compress gas, a method of managing a stationary seal which bears against an inner surface of a rotating press roll, the method comprising providing the rotating press roll; providing the stationary seal, and one or more pushers urging the seal toward or away from the inner surface at a seal interface with the rotating press roll; providing a seal controller controlling levels of force with which the seal is being urged against the moving surface; and sensing and controlling at least one parameter selected from the group consisting of seal temperature, seal pressure, seal friction, and light leaking past the seal.

[0044] In some embodiments, the controller cycles pressure on the seal, seeking lesser air leakages in combination with lesser seal force at the seal interface.

[0045] In some embodiments, the method comprises providing one or more light sources on a first side of the seal proximate the moving surface, and corresponding one or more light sensors on an opposing side of the seal, the light sensors detecting any light leaking past the seal, the controller commanding adjusting the pressure on the seal for seal contact pressure which limits leakage of light past the seal proximate the respective light sensor.

[0046] In some embodiments, the controller commands cycling of pressure on the seal, seeking a combination of limited light / air leakage and limited friction-related seal wear.

[0047] In some embodiments, the method comprises, responsive to the controller receiving input suggesting an out of range seal temperature, the controller commanding application of heating or cooling to the seal responsive to the sensed out of range seal temperature.

[0048] In some embodiments, the method comprises the controller commanding application of water e.g. mist to the moving surface as an interface lubricant.

[0049] In a third family of embodiments, the invention comprehends displacement dewatering apparatus in a papermaking machine, such displacement dewatering apparatus comprising a nip comprising a press roll and a vent receptive device, the nip having a nip entrance and a nip exit, a machine direction length extending along a machine direction of the papermaking machine, the press roll having an outer shell, the outer shell having an inner surface and an outer surface, apertures extending through the outer shell from the inner surface to the outer surface; a plurality of pressure zones extending along the length of the nip, from a first pressure zone proximate the nip entrance to an nth pressure zone proximate the nip exit, the pressure zones being disposed sequentially along, and within, the length of the nip, the pressure zones abutting the inner surface of the press roll, each such pressure zone comprising an upstream seal disposed relatively toward the nip entrance and a downstream seal disposed relatively toward the nip exit, the seals abutting the inner surface of the outer shell between respective ones of the pressure zones; and a compressed gas source, adapted and configured to supply compressed gas to an inner space in the press roll, whereby the compressed gas passes into and through respective ones of the pressure zones, thence into and through respective ones of the apertures in the outer shell, and from the apertures, into and / or through a web sandwich comprising a nascent paper web, passing through the nip, thereby to remove liquid water from the nascent paper web, the seals obstructing gas leakage from a given pressure zone to an adjacent pressure zone, by way of an interface between the respective seals and the inner surface of the outer shell, in the nip.

[0050] In some embodiments, at least first, second, and third pressure zones are arrayed along the length of the nip.

[0051] In some embodiments, the vent receptive device comprises a vented shoe press which receives gas which has passed through the web sandwich.

[0052] In some embodiments, the apparatus further comprises a blanket rotating about the vented shoe press roll, the blanket having a length and a width, an inner surface proximate the shoe press roll, and an outer surface relatively more remote from the shoe press roll, a plurality of tubes extending across the width of the blanket between the inner surface of the blanket and the outer surface of the blanket, a plurality of grooves extending along the length of the blanket, on the outer surface of the blanket, and extending inwardly into interior locations in the blanket, and thereby intersecting the plurality of tubes so as to provide gaseous and liquid communication between the respective outer surface of the blanket and the plurality of tubes.

[0053] In some embodiments, the apparatus further comprises a light source on a first side of a respective seal, and a light sensor on an opposing side of the seal, the light sensor being adapted and configured to detect light leaking past the respective seal and to send a light sensed signal to the controller.

[0054] In some embodiments, the apparatus further comprises relief zones in the seal, displaced from each other along the length of the seal, the relief zones facilitating localized flexing of the seal in response to force urging a localized portion of the seal against the inner surface of the roll shell.

[0055] In some embodiments, the apparatus further comprises temperature sensors in the seal adapted and configured to send temperature readings to the controller.

[0056] In some embodiments, the apertures in the roll shell are sized and configured such that a given aperture does not convey pressurized gas to first and second adjacent pressure zones simultaneously.

[0057] In some embodiments, the seal has an upstream portion (T1) disposed relatively toward the nip entrance and a downstream portion (T3) disposed relatively toward the nip exit, the upstream portion (T1) being shorter (MD) than the downstream portion (T3).

[0058] In some embodiments, the apparatus further comprises water apparatus in the press roll adapted and configured to apply water to the inner surface of the outer shell.

[0059] In a fourth family of embodiments the invention comprehends displacement dewatering apparatus in a papermaking machine, the displacement dewatering apparatus comprising a nip comprising a press roll and a vent receptive device, the nip having a nip entrance and a nip exit, a machine direction length extending along a machine direction of the papermaking machine, the press roll having an outer shell, the outer shell having an inner surface and an outer surface, a plurality of apertures extending through the outer shell from the inner surface to the outer surface; at least one pressure zone extending along the length of the nip, a given such pressure zone comprising a seal having an upstream seal portion disposed relatively toward the nip entrance and a downstream seal portion disposed relatively toward the nip exit, the seal abutting the inner surface of the outer shell; and a compressed gas source, adapted and configured to supply compressed gas to an inner space in the press roll, whereby the compressed gas passes into and / or through the at least one pressure zone, thence into and through respective ones of the apertures in the outer shell, and from the apertures, into and / or through a web sandwich comprising a nascent paper web passing through the nip, thereby to remove water from the nascent paper web, the seal obstructing gas leakage from a given pressure zone between the respective seal and the inner surface of the outer shell, pressure between a given seal and the inner surface of the outer shell being supported and controlled by an elongate piston operating inside a surrounding elongate cylinder, and an elongate guide plate abutting an inner wall of the elongate cylinder and thereby providing lateral support to the respective seal.

[0060] In some embodiments, the elongate guide plate comprises a soft flexible material facilitating mating of the seal to the inner surface of the outer shell.BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIGURE 1is an enlarged schematic cross section of a pressure zone in a dewatering nip, illustrating the air leakage problem. FIGURE 2is a schematic cross section illustrating using a plurality of magnitudes of pressure in a respective plurality of pressure zones. FIGURE 3is a schematic cross section of a nip employing a plurality of pressure zones, and graphically illustrating exemplary pressures in the respective pressure zones. FIGURE 4Ais a cross section of a press roll of the invention, including an outer rotating shell mounted on a hollow stationary shaft, and a seal assembly mounted on the shaft. FIGURE 4Bis a cross-section of the entire circumference of a press roll such as the press roll illustrated as a cross-section in FIGURE 4A. FIGURE 5is an elevation view of a cross-section of a seal assembly of the invention, extending in the machine direction (MD) of the papermaking machine and bearing against the inner surface of an outer shell of a press roll. FIGURE 6is a top view of a seal assembly such as that shown in FIGURES 4A, 4B, and 5. FIGURES 7 and 7Aare elevation views of seal holders and seals, including temperature sensors and heating and / or cooling elements. FIGURE 8is an elevation view taken in the cross direction, of a seal which includes slits / cuts along the length of the seal, and piston / cylinder combinations bearing on the seal between the slits / cuts. FIGURE 9is an elevation view as in FIGURE 5, illustrating use of a light source inside the seal assembly in combination with a light sensor positioned so as to detect any light leaking between the intervening seal and the inner surface of the press roll shell. DETAILED DESCRIPTION OF ILLUSTATED EMBODIMENTS

[0062] As illustrated in FIGURE 2, a pressure generator 23 feeds compressed air to pressure box 24. Pressure box 24 feeds compressed air to the plurality of pressurized pressure zones 30Z1, 30Z2, 30Z3, 30Z4, 30Z5. Air pressure in the pressure zones passes through a plurality of apertures 34 in roll shell 28, thence into and through web sandwich 58. Web sandwich 58 includes air distribution fabric 36, the paper web 102 being dewatered, and anti-rewet fabric 60.

[0063] In FIGURE 2, the roll shell, the air distribution fabric, nascent paper web / sheet and the anti-rewet layer move from left to right across the multiple stationary pressure zones being pressurized by pressure box 24. In FIGURE 2, pressure box 24 feeds multiple pressure zones. Air pressure in each pressure zone is controlled by a pressure regulator 25 in combination with a pressure valve 25V which controls the pressure in the respective pressure zone. In FIGURE 2, the pressure zones have progressively increasing pressure from pressure zone 1 to pressure zone 3, namely greater pressure in zone 2 than in zone 1 and greater pressure in zone 3 than in zone 2. Pressures decrease between pressure zone 3 and pressure zone 5. Namely pressure zone 4 has less pressure than pressure zone 3 and pressure zone 5 has less pressure than pressure zone 4. Pressure is then released to ambient as the roll shell rotates past pressure zone 5.

[0064] For each pressure zone, one or more seals 32 extend about the entirety of the respective pressure zone, thus isolating the given pressure zone from any and all other pressure zones. As illustrated, the design, configuration, and location of one or more of the respective seals enables the respective roll shell apertures 34 to be pressurized by pressurized air in the respective pressure zone while subsequently allowing the air pressure in the respective apertures to bleed into the web sandwich before exhausting the remaining air pressure to a lower e.g. atmospheric pressure.

[0065] A further advantage of providing for bleed down of pressure in the apertures before the residual air pressure is released to e.g. atmosphere is that noise made by any air being released from the respective apertures is reduced.

[0066] It is known that a seal is easier to implement if the respective seal is effected using highly cooperating surfaces, such as smooth surfaces. To that end, seals 32 are designed and configured such that the seal surfaces contacting the inside surface of the roll shell are smooth, and conform readily to the inside surface of outer shell 28. In order to provide adequate residence time in the nip to enable air pressure in a given aperture 34, from a given pressure zone, to bleed down to a specified pressure, the e.g. fabric / sheet / fabric web sandwich 58 maintains contact with the respective roll apertures for a sufficient time / distance in the nip to allow for such pressure bleed down after exposure of the given aperture to the given air pressure in the respective pressure zone has been removed.

[0067] In some cases, there may be sufficient time for acceptable water displacement to occur by simply using a 2-roll system where the press roll is pressed against a vented roll. The vented roll, opposite the press roll, can be vented structures known in the industry such as blind drilled, through drilled, a grooved tube vented roll or blanket as described in US Patent 6,884,323, a grooved suction roll, or a combination of such structures. Since it is desired to reduce vented roll backpressure, it is desired to provide vented rolls with optimal voids and flow capacity to readily accommodate air and water removed from the web. Since, in the invention, volumetric flows of air and water can be many times higher than flow from conventional wet pressing where air flow is not present except as vacuum draw, preferred vented rolls for displacement dewatering are grooved with the grooves intersecting cross-directed tubes as in the above recited '323 patent. Such rolls accept water driven by air flow, hold the water briefly and then release the water further along in the rotation of the roll, without need for use of vacuum although vacuum is contemplated as being acceptable. The vent roll can have deflectors which released water laterally away from the web. Through-drilled rolls can be used where water and air enter the roll as driven by the displacement dewatering process and are later expelled by centrifugal forces, farther along the rotation of the roll. A distinct advantage of displacement pressing is that the compressed air powers the water removal process and thus can eliminate the need for suction rolls to carry water away from the press nip. If suction rolls are used, as is an option, vacuum intensity can be reduced, compared to conventional wet pressing, thus saving energy in that element of the dewatering process as well.

[0068] In instances where more displacement dewatering time in the nip is desired, a shoe press roll can be used. Such shoe press roll mates to the press roll and provides web 102 with more residence time in the nip, which may be desirable for effective displacement dewatering to the desired level of web solids. Typical shoe presses provide MD nip lengths of 5 to 10 inches which is significantly longer than vented roll MD nip lengths, which are typically limited to 1 inch to 3 inches. Accordingly, in a nip defined between the press roll and the vented shoe roll, the MD length of the nip can be as long as the maximum MD length which the respective vented shoe roll can provide in intimate / close contact with the web sandwich.

[0069] To the extent the web sandwich is exposed to air pressure from the press roll over the entire MD length of the nip, there is a substantial release of residual such air pressure from the web sandwich as the web sandwich exits the nip, representing a substantial loss of the energy present in the so "lost" air pressure. Thus, efficiency of air pressure usage can be improved by reducing or terminating exposure of the web sandwich to air pressure before the respective portion of the web sandwich exits the nip.

[0070] Efficiency of air usage can be improved by any reduction of air pressure in the roll shell apertures before the apertures are vented to atmosphere or vented otherwise. Desirably, the roll shell apertures are sized and configured to carry at least the quantity of air required to satisfy process needs for air displacement dewatering of the respective and / or anticipated nascent paper web. The apertures are pressurized such that the air pressure in the apertures moves toward areas of lower pressure e.g. in the air distribution fabric, thence to the nascent paper web, thence to any anti-rewet layer, thereby reducing air pressure in the shell apertures. Nip length enables apertures 34 to release substantial portions of their contained pressurized air into the web sandwich before releasing any remaining pressurized air to e.g. atmosphere or otherwise when the apertures exit the nip. In some embodiments, seals in the respective pressure zones are designed and configured to isolate the apertures such that the apertures first receive air pressure on the upstream side of the pressure box due to upstream MD air leakage past or through the web sandwich, and similarly isolate / close off the apertures to air entrainment in the apertures on the downstream side of the pressure box. Once closed off from the pressure box, the apertures then bleed down a substantial portion of the pressurized air into the web sandwich before exiting the nip and releasing any remaining pressurized air into e.g. the atmosphere.

[0071] By mating press roll 26 with a receptive vented shoe press roll, the effective length of the nip between the press roll and vented shoe press roll, wherein the web sandwich can be exposed to air pressure from the roll shell, is increased in accord with the MD length of the nip which can be defined between the press roll and the vented shoe. For a given MD speed of the web sandwich, time during which the web sandwich can be subjected to pressurized air is correspondingly increased in accord with the MD length of the nip.

[0072] In FIGURE 2, the plurality of pressure zones are disposed side by side, arrayed MD from each other and interfacing with roll outer shell 28 so as to communicate with the apertures in the roll shell sequentially as the apertures enter the nip, pass through the respective pressure zone or zones, and exit the nip, consistent with rotation of the press roll. Each pressure zone is shown sealed off from all the other pressure zones and each pressure zone is sealed against the inner surface of the roll shell by the one or more seals 32. Such plurality of pressure zones are preferentially enabled in a nip provided by so mating a vent shoe press roll 56 (FIGURE 3) against a press roll 26 with an appropriate level of mechanical pressure urging press roll 26 and vented shoe roll 56 against each other with at least sufficient force to provide a desirable limit to lateral leakage of pressurized air out of the nip, between press roll 26 and an adjacent web sandwich 58.

[0073] By extending the length of the nip through which the web sandwich passes, consistent with the MD length of vented shoe press roll 56, and by correspondingly extending the residence time of web sandwich 58 in the nip, the pressure of the pressurized air contained in the web sandwich has an enhanced period of time during which the air pressure can push water out of web 102 while bleeding down air pressure, still within the confines of the nip, such that the fraction of the pressurized air which is supplied to the web sandwich and which is "lost" to ambient at either the nip entrance or the nip exit is diminished, and the fraction of the pressurized air which actually passes through the nascent paper web or remains in the web, thus contributing to removal of water from the web, is enhanced. Namely, in addition to the water which is removed from the web by the relatively higher pressure in zone 3, some fraction of the relatively lower pressure air in pressure zones 1, 2, 4, and 5 also moves into and / or through web 102, thus carrying a supplemental portion of water out of the web.

[0074] In FIGURE 2, seals between the respective pressure zones are illustrated as being urged against the inner surface of the roll shell by loading tubes 62. The loading tubes can be used to adjust loading of each seal as needed to maintain sealing contact with the inner surface of the roll shell. As seals wear, the remaining somewhat worn ends of the seals are continuously and individually urged against the roll shell by the respective loading tubes and are eventually replaced when sufficiently worn. Air cylinders are shown performing corresponding functions in FIGURES 5, 8, and 9

[0075] In FIGURE 2, the highest-pressure zone, namely zone 3, is supplied with compressed air from pressure generator 23, such as a blower or air compressor. Depending on the permeability of the system, particularly the permeability of web sandwich 58, aperture / void capacity of press roll 26, system / roll speed, and the like, the air entrained in apertures 34, or air leaked between seals 32 and the inner surface of the roll shell, or air moving laterally through air distribution fabric 36, all such sources can supply at least part of the air to zones 1, 2, 4, and 5. Additional, and typically lower pressure air, can be supplied e.g. individually to any or all of such lower pressure pressure zones to maintain the desired level of air pressure in the respective pressure zones 1, 2, 4, and 5. For example, if apertures exposed to zone 3 are pressurized and the permeability of the web sandwich is low, residual air pressure will be released into zone 4 as the respective pressurized apertures pass into that zone 4. Such transfer of air will raise the pressure in zone 4 and in succession, all zones downstream of zone 4 until all such downstream zones are pressurized by the air not yet released from the respective apertures. Typically, it is desired that the pressure fall after zone 3 until the pressure is close to zero in the last zone closest to the nip exit. Such moving of air pressure from pressure zone to pressure zone is more favored if the roll open area and roll thickness are relatively larger and web sandwich permeability is relatively lower. Similarly, if aperture density is relatively low, and roll shell thickness is low, and system permeability perpendicularly through the web sandwich and / or laterally through the air distribution layer is high, air may need to be supplied to each of the pressure zones in order to maintain the desired levels of pressure in respective ones of the pressure zones. The same pressure generator / air compressor, or one or more additional pressure generators, with corresponding pressure controls and / or pressure regulators 25, can be used to maintain the desired levels of air pressure in each of the respective pressure zones.

[0076] To maintain pressure zone pressures with a ramp up of air pressure and then a ramp down of air pressure along the MD length of the nip, as accommodated by the respective pressure box, several possible strategies are available, depending on the specific situation and system set-up.

[0077] For example and without limitation, where the air distribution fabric has low in-plane / lateral leakage, and the number of roll shell apertures is no greater than the number of apertures needed to supply the air dewatering needs of the nascent paper web, pressure zones 1 and 2 can be low pressure pressure zones since pressure zones 1 and 2 are not fed effectively by air pressure supplied to zone 3. However, once the air has pressurized the roll shell apertures in pressure zone 3, some of the air entrained in pressure zone 3 is transferred to zones 4 and 5 as the apertures in pressure zone 3 move from pressure zone 3 to pressure zones 4 and 5, thus pressurizing pressure zones 4 and 5. If residual air pressures in pressure zones 4 and are high enough, such as nip exit, the air in zones 4 and / or 5 can be piped back to pressure zones 1 and / or 2 as recycle streams, thus supplying at least part of the air requirements for pressure zones 1 and 2, and reducing the air pressure in the roll shell apertures before the respective apertures exhaust any remaining pressurized air to ambient air pressure at the nip exit.

[0078] Restated, in some embodiments where the air pressure at pressure zones 4 and / or 5 is substantial, the pressurized air in the respective pressure zone 4 and / or 5 can be recycled as an intake air supply to pressure zones 1 and / or 2, or to an air compressor such as compressor 23, or to a blower or other air handling device, thereby recycling that pressurized air into the air supply and utilizing the energy inherent in that pressurized air. Residual air pressure in pressure zone 5 is thus reclaimed / reused instead of being exhausted to ambient where such pressurized air energy would be "lost" air energy. The respective air handling device which receives the recycled air, has a control system adapted and configured to recycle / re-use the energy in the recycled compressed air from pressure zone 5. The continued containment of that pressurized air within the controlled air system reduces the amount of pressurized air which is released to ambient, thereby reducing the level of noise which would otherwise be generated by the release of pressurized air into the surrounding atmosphere at or adjacent the nip exit, which could occur as a result of such pressurized air being released from pressure zone 5. Such recycling also reduces the amount of energy consumed by the displacement dewatering system of the invention.

[0079] The number of seals can be as few as 1, or 2, or as many as "n", as defined by the user. MD lengths of all the seals can all be the same, as illustrated in FIGURES 2 and 3, or can be different. MD lengths of the pressure zones can all be the same as in FIGURES 2 and 3, or one or more of the pressure zones can have lengths which differ from the lengths of one or more others of the pressure zones.

[0080] Where a single pressure zone is used, seal structure and pressure intensity, in combination with e.g. aperture density and configuration, and fabric selection, are controlled to improve efficiency of water removal.

[0081] Where only first and second pressure zones are used, the first pressure zone, closer to nip entrance, receives a relatively higher pressure and the second pressure zone, closer to nip exit, receives a relatively lower pressure, if any, or may receive an active vacuum. The second pressure zone thus represents, to pressurized air left in the apertures entering the second pressure zone, a lower pressure reservoir into which that residual pressurized air can bleed. Any air pressure so received into the second pressure zone can then be recycled to the pressure generator or elsewhere in the pressure system.

[0082] Where a plurality of pressure zones are used, one option is to provide structure, MD downstream from any relatively higher pressure pressure zone, which blocks off any passage between inner surface 28 of press roll 26 and pressure box 24. Such blockage can take on the form of, for example and without limitation, a pressure zone free from any other supply of compressed air. Another alternative is to position a relatively longer seal downstream from, optionally adjacent, the relatively higher pressure pressure zone. Such relatively longer MD elongate seal can be, for example and without limitation, at least 25%, optionally up to 50%, optionally 100% or more, longer than another seal at the relatively higher pressure pressure zone. Such longer seal provides time for the air pressure in the respective apertures 34 to bleed down into web sandwich 58.

[0083] For example, in a system operating with only two pressure zones, zone 30Z1 near the nip entrance receives the relatively higher pressure air. The second pressure zone 30Z2 is supplied with no pressure, or an optimal vacuum. An elongate seal 34 is positioned between pressure zone 30Z1 and pressure zone 30Z2. The elongate seal can be, for example, as long as, or longer than, pressure zone 30Z1. In operation, relatively higher pressure air is supplied at pressure zone 30Z1, into the apertures 34 which are in communication with pressure zone 30Z1. As those apertures pass beyond pressure zone 30Z1, some of the air pressure in those apertures bleeds into web sandwich 58. As those apertures enter pressure zone 30Z2, any residual air pressure can continue to bleed into the web sandwich, and can also bleed into pressure zone 30Z2. Pressure zone 30Z2 is maintained at a relatively lower pressure whereby that air bleed into pressure zone 30Z2 can be recycled, and exhaust of air pressure from the apertures at the nip exit can be limited.

[0084] As an alternative, instead of using an elongate seal between pressure zones 30Z1 and 30Z2, a passive cavity can be used between the respective pressure zones.

[0085] Where more than two pressure zones are used, a such elongate seal or passive pressure zone can be employed between the nth cavity and the n-1 cavity. One or more such elongate seals or passive cavities can also be used anywhere between the first cavity and the nth cavity, while still providing that the nth cavity can be a passive cavity or a vacuum cavity.

[0086] A wide variety of pressure control devices and systems can be implemented to control and direct the pressurized air. There can be mentioned, for example and without limitation, pressure regulators, multistage blowers, slide valves, throttling valves, variable speed compressors, and the like as conditions warrant. Cost efficiencies of air dewatering systems of the invention can be enhanced by careful selection of the number of pressure zones, as well as the magnitude of the air pressure in each pressure zone, all in accord with the air permeability properties of the roll shell, the respective elements of the web sandwich, and the respective vent receptive structure.

[0087] In typical, though not limiting, implementation of the invention, a pressure zone more nearly centralized in the nip is used as the primary location where pressurized air is delivered to the roll shell apertures and thus to the air distribution fabric. Upstream and downstream of that more nearly centralized pressure zone are additional pressure zones which are typically maintained at relatively lower pressures, either by indirect / leakage pressurization or by direct addition or reduction of pressurized air to the respective pressure zones. The final pressure zone proximate the nip exit has its pressure controlled such that there is limited pressure, potentially no pressure, in the roll shell and the air distribution fabric as the web sandwich exits the nip so that little, if any, air pressure energy is lost when the respective apertures exit the nip. The air pressure in the apertures at nip exit can be controlled to the extent consistent with good papermaking machine runability; balancing papermaking productivity against energy expended in the process of dewatering web 102.

[0088] FIGURE 3 illustrates an exemplary water displacement shoe press having seven pressure zones. Press roll 26 receives pressurized air from a pressure box 24 (see FIGURE 2). A series of seals define a series of individually controllable pressure zones Z1- Z7. The loading of each seal 32 against inner surface 63 of roll shell 28 is individually controlled as needed to maintain the desired level of sealing contact with the roll shell. Air passes from the pressure box to the respective pressure zones, thence into apertures 34 in the roll shell, thence to air distribution fabric 36. In FIGURE 3, air passes from the highest pressure at pressure zone Z4 into roll shell 28, thence into air distribution fabric 36, and thence into nascent paper web 102, all under pressure zone Z4. In the pressure zones on either side of pressure zone Z4, air pressure can be controlled by pumping air in or venting air out of a respective pressure zone, thence into other ones of the pressure zones, or venting a such pressure zone into an air pump inlet. By the time the roll shell apertures and the web sandwich reach pressure zone Z7, air pressure in roll shell 28 and web sandwich 58 is substantially reduced by air bleed from the apertures into and / or through the web sandwich, and by any lateral leakage, such that air release to atmosphere after pressure zone Z7 is limited, consistent with good operation of the displacement dewatering section of the papermaking machine e.g. optimized water removal and properties, efficient nascent paper web transfer if and as needed, and limited rewet of web 102 at the nip exit.

[0089] Consistent with shoe press design, multiple layers of carrier / anti-rewet fabric can be disposed adjacent the nascent paper web, opposite distribution fabric 36. Anti-rewet fabric 60 can utilize air / gas flow being received from the web sandwich adjacent each of the pressure zones to help inhibit sheet rewet. Such anti-rewet fabric passes through the nip along with the nascent paper web and any other fabrics which are part of the web sandwich. FIGURE 3 shows the surface of anti-rewet fabric 60 against shoe press blanket 64, which facilitates passage of water and air through the nascent paper web and into the vented shoe press blanket.

[0090] Blanket 64 extends about shoe press roll 56, and serves as a primary receptacle for air passing through the web sandwich, as well as water which is removed from nascent paper web 102, as well as any additional water which is removed from web sandwich 58. The void capacity of blanket 64, which extends about shoe press roll 56, serves as an initial and temporary reservoir, adequate to receive the ongoing flow of air and water being removed from web sandwich 58, such as from nascent paper web 102 and air distribution layer 36. Voids and flow channels extend as machine direction (MD) grooves in the surface of blanket 64 which interfaces with the web sandwich. In addition, cross direction (CD) tubes 66 can be provided extending along the entire cross direction dimension of blanket 64, with the MD grooves fluidly communicating with tubes 66, whereby the combination of the MD grooves and the CD tubes provide a cross direction flow path for water leaving the web sandwich at the nip such that a substantial portion of the water leaving the web sandwich at the nip is directed away from the path of travel of web 102 leaving the nip. A deflector can be mounted after the nip between shoe press blanket 64 or the anti-rewet layer 60 and the path of the web 102, whereby the deflector can more specifically direct the water spray away from the web path, thus avoiding subjecting the departing paper web, now dryer than at the nip entrance, to any such water spray.

[0091] Tubes 66 collapse slightly when passing through the nip, and expand upon exiting the nip. Such expansion creates a level of vacuum which tends to pull water away from web 102. Such combination of structures and activity at the nip can enhance dryness of the web exiting the nip and facilitate receipt of water into the shoe and release of the water in a relatively more CD direction, thus changing the path of the water displaced from the displacement dewatering system.

[0092] The bottom portion of FIGURE 3 shows a graphic, and relative, representation exemplary of varying pressures "P" in each of the pressure zones. Namely, at steady state, pressure is zero before pressure zone 1, very low in pressure zone Z1, and is increasingly and sequentially higher in pressure zones Z2 and Z3, reaching maximum pressures in pressure zones Z4 and Z5, with pressure being less in subsequent pressure zones Z6 and Z7 and then zero gauge pressure after pressure zone Z7 as the remaining relatively low pressure is exhausted to ambient at the nip exit at the exit end of pressure zone Z7. The purpose for the relatively lower pressures in pressure zones 1 and 7 is to minimize the amount of pressurized air released at the nip entrance and the nip exit. In some embodiments, air pressure in pressure zone Z1 is greater than air pressure in pressure zone Z7.

[0093] Pressure zone pressures can be varied almost infinitely at the will of the system operator to facilitate and optimize the dewatering process and / or to optimize the properties of the nascent paper web, or to provide operational e.g. energy efficiencies. For example, high pressure can be maintained over multiple pressure zones to increase water removal from nascent paper webs 102 from which water removal is relatively more difficult. For nascent paper webs for which water removal is relatively easier, lower pressure can be used over relatively more of the pressure zones. To further increase water removal, heated air, including residual heated air from another portion of the papermaking machine, can be used as the supply air for any displacement dewatering process. As press speed changes or other operating conditions change, location and relative levels of pressure intensity in the pressure zones can be changed to affect best operation. For example, as machine speed is increased, the zone or zones of relatively higher pressure, including maximum pressure, is preferably moved closer MD to the nip entrance, and the levels of pressure intensity are preferably increased, in order to obtain optimal water removal.

[0094] To create fluid shear forces within the nascent paper web, thereby to enhance water removal, magnitude of the air pressure applied to an element of the nascent paper web can be alternated, such as vibrated, rapidly fluttered, or the like, from relatively higher pressure to relatively lower pressure during the course of that element of the nascent paper web passing through the dewatering nip. This alternating of the pressure field can enhance the directionality of flow of water as the nascent paper web flows from pressure zone to pressure zone and thereby enhance water removal, by establishing an increased number of paths by which water can pass out of the nascent paper web and reducing instantaneous flow viscosity of such water. Additionally, a high-pressure zone, properly placed, displaced from the nip exit, can give momentum to the water, accelerating an overall movement of water away from the nascent paper web, thereby reducing rewet of the nascent paper web as the nascent paper web exits the nip.Seal Assembly

[0095] FIGURE 4A shows a cross-section of a single elongate seal assembly 68 inside press roll 26, including seal 32, encompassing a single elongate pressure zone 30 which extends substantially the full length of the press roll between journaled roll ends 70. Seal assembly 68 contains seal loading piston 116 which in turn is mounted to elongate seal piston 74, elongate guide plate 84, seal base 92, and seal 32, at holes 93 (FIGURE 6). Pressurized air enters press roll 26 through centrally-located hollow shaft 72 and traverses through shaft 72, and through openings in the shaft, into seal assembly 68.

[0096] FIGURE 4B shows elongate cylinder base 80 and elongate mounting block 69 mounted to shaft 72 by bolts 82. Mounting block 69 supports seal assembly 68 from shaft and air plenum 72. Elongate cylinder 76, as part of seal assembly 68 and cylinder base 80, is mounted on mounting block 69. Elongate cylinder 76 extends upwardly from cylinder base 80. Elongate piston 74 slides inside elongate cylinder 76, sealed by O-ring 86 between the sides of the piston and the cylinder. Guide plate 84 is mounted to piston 74 with intervening O-ring 86 and rides up and down with the piston in recess 89. Seal 32 is mounted to seal base 92 with an intervening O-ring 86 and interfaces with the inner surface 63 of outer shell 28 of press roll 26. In addition to providing lateral support to the seal as the seal exits the seal holder, the elongate guide plate can also contain a soft material that flexes and allows the attached seal to better mate to the inner roll shell 63. The elongate guide plate can contain polymeric elastic materials such as neoprene, butyl or nitrile rubber and the like, either as the sole composition of the elongate guide plate or as an outer layer between the inner surface of the cylinder and a more centralized body of the guide plate.

[0097] FIGURE 5 illustrates a greatly enlarged upwardly directed MD cross-section of a single representative seal assembly 68 supported by a piston 74 / cylinder 76 combination in a pressure zone, and wherein a single pressure zone, or a plurality of pressure zones could be directed downwardly in the press roll, onto the roll shell, at the nip or in any direction as the press configuration requires. The one pressure zone represented in FIGURE 5 includes elongate oblong piston 74 which moves inside elongate oblong cylinder 76. The elongate perimeter of cylinder 76 extends along the CD width (FIGURE 4A) of seal assembly 68. FIGURE 5 is looking in the CD direction, such that T1, T2, and T3 extend, by arrows 78 shown, in the MD direction of the papermaking machine. Elongate oblong cylinder 76 extends from a cylinder base 80 which is bolted, through mounting block 69, to hollow shaft 72 of the press roll by bolts 82 (FIGURE 4B).

[0098] An exemplary MD pressurized length (T2) of the respective pressure zone, as illustrated in FIGURE 5, is 0.25 inch. The (T2) length of a given pressure zone can be varied for a given implementation and can be reduced e.g. to be as small as the cross-sections of apertures 34 in roll shell 28, typically accompanied by an increase in seal thickness (T1, T3) such that the overall seal dimension (T1, T2, T3) remains the same. Exemplary seal thickness (T1, T3) as illustrated in FIGURE 5, is 0.25 inch whereby the overall length of the respective pressure zone, as illustrated, is 0.75 inch. Dimensions T1, T2, T3 are appropriate for a press with small circular rolls, such as a pilot machine. Lengths of T1, T2, T3 can be increased where nip length is greater. Seals 32 of the respective pressure zones are urged against the inner surface of the pressurized / perforated roll shell in order to provide desired sealing against air leakages between seals 32 and inner surface 63 of roll shell 28. At minimum, the seal thickness (T1, T3) on the opposing sides of the pressure zone is sufficient to span across a given aperture in the roll shell at inner surface 63, whereby the given aperture 34 does not convey pressurized air to two adjacent pressure zones simultaneously. Similarly, seals 32 prevent routine unimpeded leakage of pressurized air between the seals and roll shell 28 from a first one of the pressure zones to a respective other adjacent pressure zone, past a seal 32.

[0099] Replaceable seal assemblies 68 can be bolted by bolts (not shown) onto elongate base piston 74 e.g. through elongate guide plate 84. Sealing between piston 74 and seal base 92 is affected by use of elongate O-rings 86 between seal base 92 and guide plate 84; and between guide plate 84 and piston 74, as shown. The O-rings follow paths around the outside edges of the elongate seal base and guide plate 84. As shown, the replaceable seal assembly is comprised of 2 elements, namely the seal 32 and the seal base 92. It is also possible to make seal 32 and seal base 92 out of a single piece of seal material.

[0100] As illustrated in FIGURE 5, pressurized air from pressure box 24 passes through air passages 85 in base plate 80 and 87 in base piston 74.

[0101] FIGURE 6 shows a top view of a single zone seal assembly.

[0102] The seal mating surfaces 98, which will interface with the inner surface of outer shell 28 are, before use, worked into a suitable shape and smoothness to match the inner surface of the roll shell. The resulting seal assembly is mounted to elongate guide plate 84 and base piston 74, both of which fit inside elongate oblong cylinder 76. Elongate guide plate 84 helps stabilize piston 74 inside cylinder 76.

[0103] Elongate oblong cylinder 76 is bolted to shaft 72 at cylinder base 80.The illustrated self-loaded seal 32 in FIGURE 5 self-loads against shell 28 due to the pressurized cross-section area below piston 74 being greater than the pressurized cross-section area T2 at the roll shell. The load at the seal can be further increased by one or more double-acting pneumatic adjusting pistons 116 disposed along the length of seal 32. The self-loading capacity of the seal increases with any increase in applied air pressure.

[0104] Seal assembly 68 (FIGURE 5) is designed and configured to uniformly and repeatably meter pressurized air into and through the respective pressure zone, thence through apertures 34 in press roll shell 28 and thence into air distribution fabric 36 and thence into the nascent paper web. Namely pressurizing the shell apertures results in the apertures conveying pressure into the air distribution layer, thence into the nascent paper web.

[0105] For minimal seal leakage, seal 32 makes continuous contact with the roll shell along the full peripheral length of the seal. To get long seal life, contact pressure between the stationary seal at the inner surface of the moving roll shell should be limited, since seal wear increases as pressure on the seal increases. In general, relatively lower seal pressure is used consistent with the seal conforming to the moving inner surface of the press roll shell which provides for limited leakage of the pressurized air past the respective seal 32 while providing for optimum seal wear life. It is an objective of this invention to make precise control changes responsive to dynamic changes in pressure box air pressure and other condition changes.

[0106] Any use of a seal against a dynamically moving surface results in the seal generating frictional heat. Accordingly, there is a need to control the temperature of the seal, by providing heat to the seal, or removing heat from the seal, when a temperature sensor reports that seal temperature is outside a specified temperature range. In addition, there is a need to limit the amount of friction between the seal and the inner surface of the outer shell irrespective of the temperature of the seal or the pressure by which the seal is being urged against the inner surface of the outer shell.

[0107] Certain polymeric seal materials soften as the material is warmed to desirable and useful temperatures. Relatively softer seal materials tend to seal better than relatively harder seal materials. But continuous use of relatively softer seal materials can lead to accelerated wear and even thermal degradation as a result of drag / friction between the seal and the surface against which the seal is bearing. Such drag / friction can increase with warming / softening of the seal, which can then lead to additional heat gain in the seal, and can lead to ultimate premature failure of the seal.

[0108] In order to avoid thermal damage to the seal, this invention provides for control of the temperature of the seal, by adding or removing heat as the situation suggests. FIGURE 7 shows temperature sensors 106 embedded in the seal system / structure. Temperature sensors 106 monitor seal temperature and report the sensed temperature to a dewatering system controller 108. Dewatering system controller 108 can use a reported temperature to control loading pressure on the seal, thus to maintain seal temperature within a specified range of temperatures. When a seal temperature sensor reports that temperature is above the specified temperature range, the temperature can be reduced by reducing the force by which the seal impinges on inner surface 63 of roll shell 28. Temperature sensors can be employed in the seal system at spaced locations along the length of the seal. Since the seal extends across the CD dimension of the web sandwich, thus across the CD dimension of the papermaking machine, such temperature sensors are incorporated into the seal system at spaced locations along the CD dimension of the papermaking machine.

[0109] Heat can also be removed, or added to the seal, by incorporating cooling coils / cooling passages and / or heating elements, collectively 110, into the seal at multiple locations about the perimeter of the seal. Frictional heat caused by pressing the seal into the moving roll shell may then be removed by controller 108 directing a flow of cool water or cool air through such cooling coils. FIGURE 7 shows incorporating cooling coils and / or heating elements 110 into seal assembly 68. In a first instance, cooling coils / tubes, heating elements 110 can extend through the seal holder as in FIGURE 7. In the alternative, cooling coils / tubes, heating elements 110 can extend through the interface between the seal holder and the seal, itself as in FIGURE 7A, or only in the seal.

[0110] Thus, in some implementations of the invention, it is desired to add heat to the seal. For example, when a seal is new, minor differences typically exist between seal surface 98 and the surface against which the seal is bearing. In such instance, the seal which bears against a dynamically-moving surface goes through a break-in period wherein localized elements of bearing / wear surface 98 of the seal wear relatively more or less heavily against minor surface variations in the surface against which the seal is bearing, such as inner surface 63 of shell 28, such that seal bearing surface 98 wears selectively at such surface variations, thereby conforming more closely, after break-in, to the surface against which the seal is bearing. And until the break-in is complete, the seal effectiveness may be less than desired / specified.

[0111] The break-in period can be enhanced / accelerated by controlling the temperature of the seal material whereby, as break-in operation of the seal material is initiated, the seal material temperature is heated to a temperature above the glass transition temperature (Tg) of the seal material. Running the seal material warmer during the break-in period softens the seal material whereby the seal more quickly becomes conformed to the respective surface variations of the inner surface of shell 28. However, allowing the seal material to get too far above Tg can result in unacceptable accelerated seal wear. By controlling the seal temperature during the break-in period, the break-in period can be accelerated whereupon the seal is more quickly readied for routine use.

[0112] Thus, in some implementations, it is desired to maintain control of seal temperature under a variety of operating conditions. Based on the properties of the seal material being used, a first, desired, routine operating temperature range is established by the user. A second, desired different break-in temperature range is also established. The routine operating temperature range is, for example and without limitation, up to about 20 degrees C below Tg for the seal material being used. The break-in temperature range is, for example and without limitation, up to about 20 degrees C above Tg for the seal material being used. Thus, heating elements can be embedded in the seal holder in locations similar to those shown for the cooling coils, thereby to enable heating the seal, e.g. at process operation start-up, to quickly raise the seal temperature to a desired minimum temperature within the respective temperature range so as to avoid excess seal wear, or excess air leakage, at start-up. Similarly, the cooling coils can be used to limit the temperature of the seal material during routine running of the process so as to not exceed the specified temperature range which has been established for a given running time / period.

[0113] During seal break-in, the heating elements temporarily increase seal temperature to a temperature range up to about 20 degrees C above Tg. The raised temperature is monitored by the temperature sensors in the seal. The temperature sensors report the seal temperature to controller 108 which controls heat input from the heating elements. As needed, temperature can be dynamically controlled, including both during the break-in period and during routine operation, by use of a combination of heating elements and cooling coils; wherein heat is applied when the seal is below the desired temperature range and cooling is applied when the seal is approaching the top of the desired temperature range, or is above the desired temperature range.

[0114] The exit temperature of the fluid ( e.g. water, air, etc.) passing through cooling coils can, for example, be monitored as a proxy for seal temperature / condition, and that temperature along with knowledge of the water flow rate or air flow rate can be used to control loading forces, to apply heat, and / or to apply heating or cooling fluid. For example, if cooling fluid / water temperature is increasing or is above the specified temperature range, loading force can be reduced and / or additional flow of cooling water may be implemented. If temperature is too low, loading force can be increased on the seal, cooling water or air flow rate can be reduced, and / or warmer water can be used to add heat to the seal, or the electric seal heaters can be engaged. The use of cooling water or flow control along with water temperature can also be used as a proxy for seal condition, seal wear, and the need for the level of force desired at various locations against the seal.

[0115] Cooling water tubes 110 can alternate between supplying cooling water and heating water depending on the temperature needs of the seal, in which case the need for electric heating elements may be obviated.

[0116] A critical time for seal operation in this invention is any start-up condition. During any such start-up, getting seal temperature to a specified temperature range facilitates efficient use of the seal during the start-up process. One such start-up time is during the break-in period where the seal is being broken in to conform to the moving surface against which the seal is bearing. During break-in, seal temperature can be allowed to rise by limiting or stopping cooling fluid flow, increasing water temperature, and / or increasing sealing force, and / or activating heating elements or flow of hot water, such that the seal quickly reaches the desired break-in temperature range, whereby seal wear is accelerated and the seal thus breaks in faster.

[0117] In general, it is desirable to select a such seal material which has a glass transition temperature Tg moderately above the desired routine operating seal temperature.

[0118] Seal stiffness may prevent the seal from conforming to the longitudinal (e.g. CD) bending, at the nip, of rotating press roll 26, namely the shell of the press roll, under operating loads being exerted on the opposing ends of the press roll. For example, when press loading is changed e.g. at the ends of the press roll, roll deflection along the length of the roll, e.g. in the middle of the roll, changes at about the same time, which can change the apparent space / gap between the seal at the pressure zones and the roll shell against which the seal is bearing. Accordingly, as the gap between the seal and the inside surface of the roll shell increases or decreases in response to changes in the mechanical loading at the ends of the press roll 26, the seal loading at respective locations along the length of the press roll needs to change accordingly in order that any gap between the seals and the roll shell be closed, or any excess pressure be reduced. Thus, for example, where mechanical loading at the ends of the press roll increases, additional loading is desirably applied to the seal in any area where a gap has developed between the seal and the roll shell. Similarly, as a gap is reduced and / or pressure between the seal and the roll shell is increased, seal deflection in that area should be dynamically reduced by reducing loading force on the seal in that area. Namely, the seal loading system of the invention is adapted and configured to locally conform to deflections of the roll shell at various and spaced locations along the length of the seal (e.g. the length of roll 26). Such local conformation capabilities can be spaced along the length of the seal at spacings determined to meet the needs for sealing against the roll shell.

[0119] For example, the seal, and the apparatus urging the seal against the shell both need to be adapted and configured to enable differential flexing the seal at spaced locations along the length of the seal. Such differential flexings are spaced sufficiently close together that forces urging the seal against the rotating inner surface of the shell can be adjusted at substantially any needed location thereby to assure and maintain a specified level of sealing against the shell at respective locations along the length of the shell. Once the shell deflection has been matched, the seal needs to be loaded lightly into the shell, in order to maintain consistent seal loading against the shell, as well as consistent sealing along the length of the shell.

[0120] As illustrated in FIGURE 8, in order to make the seal limber / flexible along the length of the seal, namely in the (CD) cross direction of the papermaking machine / web sandwich, so that the seal can flex as needed, a plurality of slits or gaps 112 can be cut in the seal on the side of the seal which is away from the seal surface 114 which is to engage the roll shell. Cutting these slits or gaps into the seal allows the seal to bend at the seal or gap such that the seal segments 119 between slits / gaps 112 can act somewhat independently of adjacent seal segments. The seal, so configured, is then attached to a series of pistons 116, for example as illustrated in FIGURE 8, through respective flexible interface pads 118. With such attachment of each piston to a respective portion of the seal through such flexible interface pad, and given the flexibility of the seal provided by the slits / gaps, each such segment of the seal can act somewhat independently by the action of the respective seal piston. Accordingly, adjusting pistons 116 provide appropriate force against the seal while the flexibility of the interface pad, and the flexibility of the seal, provide respective more refined adjustments to sealing at the seal / shell interface. Thus, by attaching the pistons to the seal itself, e.g. through the flexible interface pads, each segment 119 of a seal containing such slits can conform by an appropriate small amount independent of adjacent segments to maintain contact with the roll shell while, at the same time, maintaining contact with the piston and its flexible interface pad.

[0121] By varying the air pressures inside the respective seal cylinders, the pistons, as driven by the respective air pressures, can collectively bend the seal either up or down, as needed in order to reflect / follow corresponding deflection of the roll shell below the respective seals at the respective locations of the pistons / seal segments along the length of the seal. The cylinders typically, but not necessarily, have double acting capability, namely pneumatic pressure both above and below the respective pistons such that the pistons can either apply a pushing force urging the seal in a direction toward the roll shell, or can apply a pulling force urging the seal in a direction away from the roll shell. In the instance where the piston applies a pulling force, the actual action in the cylinder can, in some instances, be more akin to a reduction in an existing pushing force on the seal. The objective in each such instance is to dynamically and positively manage seal pressure against the roll shell so as to maintain a desired seal bending if and as needed to maintain the seal lightly loaded against the roll shell, sufficient to maintain the desired level of sealing while keeping the seal loading modest in order to provide a typical use life of the seal.

[0122] Also shown in FIGURE 8 are a plurality of the temperature sensors 106 inside seal 32 which can monitor the temperature of the seal in each seal segment. Such temperature measurements can be used as inputs related to controlling the profiling and loading process for maintaining the desired intensity of seal loading against the roll shell along the length of the seal. The general idea is to maintain consistent and low-pressure contact across the contacting surface of the seal, in order to maintain consistent, low heat generation and low wear along the length of the seal, namely along the cross machine direction of the papermaking machine / web sandwich, thereby providing for maintaining seal temperature generally constant in time and generally consistent along the length of the seal while generally optimizing seal life.

[0123] For a given papermaking machine, including a displacement dewatering system of the invention, the various operating parameters of the papermaking machine can be accounted for by the corresponding controller / computer which controls seal temperature, seal pressure, and air pressure in the pressure zone. Namely, the control system applies pressure to the seal and controls cooling fluid flow and cooling fluid inlet temperature and / or application of heat. The overall object is to maintain seal contact pressure as low as possible consistent with low seal leakage while controlling seal temperature.

[0124] The largest fraction of the leakage of air past the seal occurs when a gap / space exists between the seal and the roll shell. One way to detect such air leakage is to illuminate the seal on a first side of the seal, e.g. inside the pressure zone, and to position a light sensor on the opposite side of the seal, e.g. outside the pressure zone, directed toward the interface between the seal and the press roll shell. Air leakage is readily detected / sensed by detecting the leakage of light which accompanies such air leakage. Thus, sensing light between the seal and the roll shell is a proxy for sensing air leakage at the interface between the seal and the roll shell.

[0125] As illustrated in FIGURE 9, a light source 120 is disposed inside the respective pressure zone. Any time the displacement dewatering system is operating, the light source is illuminated. A light sensor 122 is positioned outside the respective pressure zone at a location where light emerging from the respective pressure zone, between the seal and the roll shell, can be detected by the light sensor.

[0126] Light sensor 122 reports any such detected light to system controller 108. The system controller responds by commanding increased loading force on the seal at the corresponding location. That is, in an area where light is showing between the seal and the roll shell, seal loading / force at that location along the length of the seal is increased until the light is no longer sensed by the light sensor. Thus, pressure exerted by piston 116 at the respective seal segment 119 can be adjusted until minimal or no light leakage occurs at that seal segment. The extinguishing of the light leakage is a proxy for the light / air leakage having been stopped. Once contact is occurring everywhere along the perimeter of the seal, overall loading of the seal can be reduced until light leakage is again detected. The system controller can facilitate such back and forth adjustments of force on the pistons, between leaking light / air and not leaking light / air, seeking lesser leakages and lesser seal force in each cycle and at each seal segment, until the seal force becomes stabilized at a low seal force which does not result in unacceptable levels of air leakage past the seal. Namely, through multiple iterations of the pressure being increased and decreased at a respective location along the perimeter of the seal, minimum overall loading of the seal, as well as a desired loading profile that gives the desired limited pressure along with acceptable levels of leakage which will result in extended seal life / wear, can be determined and affected. Similar adjustments / iterations can be made by controller 108 at each cylinder / piston combination along the perimeter of the seal.

[0127] To avoid issues with stray light fooling or confusing the system controller, the light source can be encoded with a specific unique data stream or pulse width which distinguishes the light received from light source 120 from other light sources which might otherwise be reported to the system controller. FIGURE 9 illustrates a CD image of a seal having a combination of the heating elements / cooling tubes 110, and light source 120, all as viewed from inside the roll shell. The number of profiling air cylinders / adjusting pistons 116 depends on the CD length / perimeter of the seal. As seal length increases in the CD direction, the number of cylinders, and respective corresponding seal segments 119, typically increases as well.

[0128] For any heat and / or pressure control applied to seal assembly 68, seal 32 still experiences friction at the seal surface which bears against inner surface 63 of outer shell 28. Such friction has a substantial influence on the tendency for lateral leakage of air between the seal and the inner surface of the press roll; as well as having a substantial influence on the wearing away of the seal surface which bears against inner surface 63, and thus the useful life of the seal.

[0129] The inventor herein has surprisingly discovered that a very fine mist, of a very small amount of water, sprayed against inner surface 63 of shell 28, FIGURE 4B, along that full length of the shell which corresponds to the length of seal assembly 68, serves to lubricate the interface between seal 32 and shell 28 such that the friction experienced by seal 32 is substantially reduced, compared to the same seal 32 bearing against a dry such inner surface 63. A suitable stress sensor (not shown) can be attached to, or embedded in, seal 32 or drive motor torque changes can be measured, and the sensed stresses or torque variations communicated to controller 108 whereupon the controller commands a change in control of the rate of lubricating water usage. FIGURE 4B shows a water conduit 124 expressing a spray 126 of water against inner surface 63 of the outer shell. The rate at which water is applied to outer shell 28 is limited / controlled so as to provide reduced friction at seal 32, thus providing potentially increased seal life, and wherein the a minimal quantity of water applied to the shell does not unacceptably impact fiber solids in web 102 exiting the dewatering nip. While some decrease in fiber solids in web 102 may be experienced, limiting the water application rate can effectively reduce friction experienced by the seal while still obtaining substantial benefit, in terms of increased fiber solids at entrance to thermal drying, from the displacement dewatering process.

[0130] The moving web sandwich is exposed to one or more substantially stationary pressure zones where air flows from the pressure box, into and through the pressure zones, thence through the outer shell, downstream (MD) of the entrance locus of the nip. The pressure zones are thus confined to an area inside the nip.

[0131] Successful displacement dewatering of the web by passing gas / air through the web has two general requirements.

[0132] The first general requirement of successful displacement dewatering is that the wet paper web be compressed in a nip at least to the extent that the web fibers are generally fixed in position relative to the remaining layers of the web sandwich, and generally preventing the fibers in the web from moving relative to each other in the nip; such that the fiber matrix is not detrimentally affected by the flow of compressed air through web 102 in that nip. The compression, where sufficient in magnitude, also reduces voids in the web and compresses / squeezes the web fibers, thus hydraulically driving at least some of the water out of interstices in the web paper fibers.

[0133] The second general requirement of successful displacement dewatering is to apply compressed air or other gas to a surface of the web, generally perpendicular to the surface of the web, which provides a pressure gradient driving the gas into and / or through the thickness of the web. Movement of the gas into or through the web displaces, pushes, carries water out of the web ahead of, and with, the air.

[0134] Thus, the second requirement of displacement dewatering using compressed gas is that air, or other gas, be passed through the paper web while the web fibers are being compressed, and thus held in position, restrained in the nip.

[0135] The spray 126 of water against inner surface 63 of shell I28 is optional, and is used as suggested by operating conditions of a particular displacement dewatering section of a respective papermaking machine making a particular paper product.

[0136] The invention is not limited in its application to the details of construction, or to the arrangement of the components set forth in the instant description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various other ways. Also, it is to be understood that the terminology and phraseology employed herein is for purpose of description and illustration and should not be regarded as limiting. Like reference numerals are used to indicate like components.

[0137] Those skilled in the art will now see that certain modifications can be made to the apparatus, products, and methods herein disclosed with respect to the illustrated embodiments, without departing from the spirit of the instant invention. And while the invention has been described above with respect to the preferred embodiments, it will be understood that the invention is adapted to numerous rearrangements, modifications, and alterations, and all such arrangements, modifications, and alterations are intended to be within the scope of the appended claims.

[0138] To the extent the following claims use means plus function language, it is not meant to include there, or in the instant specification, anything not structurally equivalent to what is shown in the embodiments disclosed in the specification.List of reference signs

[0139] 23compressed air generator 24pressure box 25pressure regulator 25Vpressure control valve 26press roll 28outer shell 30pressure zone generic 32seal 34apertures 36distribution fabric 56vent shoe press 58web sandwich 60anti-rewet fabric 62loading tubes 63inner surface of roll shell 26 64shoe press blanket 66tubes in blanket 64 68seal assembly 69mounting block 70press roll ends 72hollow shaft of press roll 26 74piston 76cylinder 78arrows FIG 5 80cylinder base plate 82bolts to shaft 72 84guide plate 85air passages in cylinder base 80 86O-ring 87air passages in piston 74 88through holes 89recess in cylinder 76 90top mold piece 92seal base 93mounting holes 94bolts 98seal mating surface 100piston seal 102web being dewatered 104lifting tube 106sensors 108system controller 110heating elements, cooling coils 112slits / gaps 114seal surface which engages shell 116adjusting pistons 118interface pads 119seal segments 120light source 122light sensor 124water conduit 126water spray

Claims

1. In a displacement dewatering system in a papermaking machine, where a pressurized gas is being forced through apertures in an outer shell of a rotating press roll in a nip, and thence into a web sandwich comprising a nascent paper web, thereby removing liquid water from the nascent paper web, the nip having a machine direction nip length extending along the machine direction of the papermaking machine, a nip entrance, and a nip exit, a method of limiting escape of pressurized air from the displacement dewatering system at at least one of the nip entrance or the nip exit, the method comprising: (a) providing a plurality of pressure zones in the rotating press roll, the pressure zones being disposed sequentially along, and within the length of, the nip, from a first pressure zone proximate the nip entrance to an nth pressure zone proximate the nip exit, each such pressure zone having a seal which obstructs gas leakage between the respective seal and an inner surface of the press roll outer shell, in the nip; (b) providing pressurized gas, at a first gaseous pressure, to at least one such pressurized pressure zone, the provided gaseous pressure pressurizing respective apertures in the roll shell which apertures are in gaseous communication with the pressurized pressure zone; and (c) controlling gaseous pressure in a second such pressure zone, along the length of the nip, which is not the at least one such pressurized pressure zone, the second such pressure zone optionally being the first pressure zone or the nth pressure zone, and having a second gaseous pressure, optionally ambient pressure or near ambient pressure, lower than the first gaseous pressure.

2. A method as in Claim 1 wherein the at least one such pressurized pressure zone is displaced from both the first pressure zone and the nth pressure zone, wherein optionally, as the apertures in communication with the one such pressurized pressure zone rotate past the one such pressurized pressure zone, the respective apertures carry entrained pressurized gas to a next adjacent pressure zone, thereby providing the entrained pressurized gas to the next adjacent pressure zone.

3. A method as in Claim 1 or 2 comprising providing, at the nip, a vented shoe press roll which receives air which has passed through the web sandwich, and water which has been expelled from the web sandwich, wherein the nip contact length between the press roll shell and the vented shoe press roll is greater than 2 inches, optionally greater than 5 inches, optionally greater than 7 inches, optionally greater than 10 inches, optionally further comprising a blanket rotating about the vented shoe press roll, the blanket having a length and a width, an inner surface proximate the press roll shoe, and an outer surface relatively more remote from the shoe, a plurality of tubes extending across the width of the blanket between the inner surface of the blanket and the outer surface of the blanket, a plurality of grooves on the outer surface of the blanket, and extending inwardly into interior locations in the blanket, and thereby intersecting with the plurality of tubes so as to provide gaseous and liquid communication between the respective outer surface of the blanket and the plurality of tubes.

4. A method as in one of claims 1 to 3 comprising recycling pressurized gas from a such pressure zone downstream in the machine direction from the one such pressurized pressure zone, to a pressure zone upstream in the machine direction from the one such pressurized pressure zone, namely toward or at the first pressure zone, or to an intake portion of a generator which pressurizes gas.

5. A method as in one of claims 1 to 4 wherein a portion of the pressurized air passes, from the one such pressurized pressure zone, through the shell apertures and into the web sandwich, and laterally through the web sandwich and along a reverse path back into apertures in the roll shell leading to one or more pressure zones which are not the one such pressurized pressure zone.

6. A method as in one of claims 1 to 5, further comprising alternating magnitude of the gaseous pressure in at least one of the pressurized pressure zones from high pressure to low pressure during the course of a portion of the nascent paper web passing through the respective at least one of the pressurized pressure zones.

7. A method as in one of claims 1 to 6, the method comprising directly supplying individually selected pressures of pressurized gas from a pressure generator to each such pressure zone, with optionally little or no gaseous pressure being supplied (i) to at least one of the first pressure zone or the second pressure zone, or (ii) to the nth pressure zone or the nth-1 pressure zone.

8. A method as in one of claims 1 to 7 comprising controlling gas pressure in a respective such pressure zone thereby to limit, optionally minimize, release of gas pressure from the apertures and from the web sandwich when the web sandwich exits the nip, wherein optionally the controller cycles pressure on the seal, seeking lesser air leakages in combination with lesser seal force at a seal interface with the outer shell, and / or comprising controlling gas pressure in the plurality of pressure zones so as to affect noise reduction or to control water removal.

9. A method as in one of claims 1 to 8, further comprising providing a light source on a first side of a respective such seal, directing light onto the seal, and a light sensor located, adapted, and configured to detect any light leaking past the respective seal, the light sensor sending a light sensed signal to a controller, the controller adjusting pressure on the seal sufficient to eliminate leakage of light past the respective seal proximate the light sensor, wherein the controller optionally adjusts the load on the seal, for seal contact pressure which limits leakage of light past the respective seal proximate the light sensor.

10. A method as in one of claims 1 to 9, further comprising providing relief zones, in a such seal, such relief zones being displaced from each other along the length of the respective seal, and facilitating localized flexing of such seal in response to force urging a localized portion of the seal against the inner surface of the roll shell.

11. A method as in one of claims 1 to 10, further comprising sensing seal temperature during routine operation of the seal, optionally at multiple locations along the length of the seal, and applying heat to the seal and thereby raising the seal temperature up to about 20 degrees C greater than the glass transition temperature of material from which the seal is made, or further comprising sensing seal temperature during routine operation of the seal, optionally at multiple locations along the length of the seal, and applying heating and / or cooling to the seal, as applies, to maintain the seal at a temperature more than 5 degrees C, optionally more than 10 degrees C, optionally more than 20 degrees C, below the glass transition temperature of material from which the seal is made.

12. A method as in one of claims 1 to 11, the method comprising providing such apertures in the roll outer shell sized and configured such that a given aperture does not convey pressurized air to first and second adjacent such pressure zones simultaneously.

13. A method as in one of claims 1 to 12 comprising alternating magnitude of gaseous pressure applied to an element of the nascent paper web, from a relatively higher pressure to a relatively lower pressure during the course of that element of the nascent paper web passing through the nip.

14. A method as in one of claims 1 to 13 comprising such seal having an upstream portion (T1) disposed relatively toward the nip entrance and a downstream portion (T3) disposed relatively toward the nip exit, the upstream portion (T1) being relatively (MD) shorter than the downstream portion (T3).

15. A method as in one of claims 1 to 14 comprising applying water to an inner surface of the outer shell and thereby lubricating an interface between a respective such seal and the inner surface of the outer shell.

16. In an area occupied by a compressed gas, a method of managing a stationary seal which bears against an inner surface of a rotating press roll, comprising: (a) providing the rotating press roll; (b) providing the stationary seal, and one or more pushers urging the seal toward or away from the inner surface at a seal interface with the rotating press roll; (c) providing a seal controller controlling levels of force with which the seal is being urged against the moving surface; and (d) sensing and controlling at least one parameter selected from the group consisting of seal temperature, seal pressure, seal friction, and light leaking past the seal.

17. A method as in Claim 16 wherein the controller cycles pressure on the seal, seeking lesser air leakages in combination with lesser seal force at the seal interface.

18. A method as in Claim 16 or 17 comprising providing one or more light sources on a first side of the seal proximate the moving surface, and corresponding one or more light sensors on an opposing side of the seal, the light sensors detecting any light leaking past the seal, the controller commanding adjusting the pressure on the seal for seal contact pressure which limits leakage of light past the seal proximate the respective light sensor, the controller optionally commanding cycling of pressure on the seal, seeking a combination of limited light leakage and limited friction-related seal wear.

19. A method as in one of claims 16 to 18 comprising, responsive to the controller receiving input suggesting an out of range seal temperature, the controller commanding application of heating or cooling to the seal responsive to the sensed out of range seal temperature.

20. A method as in one of claims 16 to 19 comprising the controller commanding application of water to the moving surface as an interface lubricant.

21. Displacement dewatering apparatus in a papermaking machine, said displacement dewatering apparatus comprising: (a) a nip comprising a press roll and a vent receptive device, the nip having a nip entrance and a nip exit, a machine direction length extending along a machine direction of the papermaking machine, said press roll having an outer shell, said outer shell having an inner surface and an outer surface, a plurality of apertures extending through said outer shell from the inner surface to the outer surface; (b) a plurality of pressure zones extending along the length of the nip, from a first pressure zone proximate the nip entrance to an nth pressure zone proximate the nip exit, the pressure zones being disposed sequentially along, and within, the length of the nip, the pressure zones abutting the inner surface of said press roll, each such pressure zone comprising an upstream seal disposed relatively toward the nip entrance and a downstream seal disposed relatively toward the nip exit, said seals abutting the inner surface of said outer shell between respective ones of the pressure zones; and (c) a compressed gas source, adapted and configured to supply compressed gas to an inner space in said press roll, whereby the compressed gas passes into and through respective ones of the pressure zones, thence into and through respective ones of the apertures in said outer shell, and from the apertures, into and / or through a web sandwich comprising a nascent paper web passing through the nip, thereby to remove liquid water from the nascent paper web, said seals obstructing gas leakage from a given pressure zone to an adjacent pressure zone, by way of an interface between the respective said seals and the inner surface of said outer shell, in the nip.

22. Displacement dewatering apparatus as in Claim 21 comprising at least first, second, and third pressure zones arrayed along the length of the nip.

23. Displacement dewatering apparatus as in Claim 21 or 22, said vent receptive device comprising a vented shoe press which receives gas which has passed through the web sandwich.

24. Displacement dewatering apparatus as in one of claims 21 to 23, further comprising a blanket rotating about the vented shoe press roll, said blanket having a length and a width, an inner surface proximate the shoe press roll, and an outer surface relatively more remote from the shoe press roll, a plurality of tubes extending across the width of the blanket between the inner surface of the blanket and the outer surface of the blanket, a plurality of grooves extending along the length of the blanket, on the outer surface of the blanket, and extending inwardly into interior locations in the blanket, and thereby intersecting the plurality of tubes so as to provide gaseous and liquid communication between the respective outer surface of the blanket and the plurality of tubes.

25. Displacement dewatering apparatus as in one of claims 21 to 24, further comprising a light source on a first side of a respective said seal, adapted and configured to shine light on said seal, and a light sensor on an opposing side of said seal, said light sensor being adapted and configured to detect light leaking past the respective said seal and to send a light sensed signal to said controller.

26. Displacement dewatering apparatus as in one of claims 21 to 25, further comprising relief zones in said seal, displaced from each other along the length of said seal, the relief zones facilitating localized flexing of said seal in response to force urging a localized portion of said seal against the inner surface of said roll shell.

27. Displacement dewatering apparatus as in one of claims 21 to 26, further comprising temperature sensors in said seal adapted and configured to send temperature readings to said controller.

28. Displacement dewatering apparatus as in one of claims 21 to 27, the apertures in said roll shell being sized and configured such that a given aperture does not convey pressurized gas to first and second adjacent such pressure zones simultaneously.

29. Displacement dewatering apparatus as in one of claims 21 to 28, said seal having an upstream portion (T1) disposed relatively toward the nip entrance and a downstream portion (T3) disposed relatively toward the nip exit, the upstream portion (T1) being shorter (MD) than the downstream portion (T3).

30. Displacement dewatering apparatus as in one of claims 21 to 29, further comprising apparatus in said press roll adapted and configured to apply water to the inner surface of said outer shell.

31. Displacement dewatering apparatus in a papermaking machine, said displacement dewatering apparatus comprising: (a) a nip comprising a press roll and a vent receptive device, the nip having a nip entrance and a nip exit, a machine direction length extending along a machine direction of the papermaking machine, said press roll having an outer shell, said outer shell having an inner surface and an outer surface, a plurality of apertures extending through said outer shell from the inner surface to the outer surface; (b) at least one pressure zone extending along the length of the nip, a given such pressure zone comprising a seal having an upstream seal portion disposed relatively toward the nip entrance and a downstream seal portion disposed relatively toward the nip exit, said seal abutting the inner surface of said outer shell; and (c) a compressed gas source, adapted and configured to supply compressed gas to an inner space in said press roll, whereby the compressed gas passes into and / or through the at least one pressure zone, thence into and through respective ones of the apertures in said outer shell, and from the apertures, into and / or through a web sandwich comprising a nascent paper web passing through the nip, thereby to remove water from the nascent paper web, said seal obstructing gas leakage from a given such pressure zone between the respective said seal and the inner surface of said outer shell, pressure between a given said seal and the inner surface of said outer shell being supported and controlled by an elongate piston operating inside a surrounding elongate cylinder, and an elongate guide plate abutting an inner wall of said elongate cylinder and thereby providing lateral support to the respective said seal.

32. Displacement dewatering apparatus as in Claim 31, said elongate guide plate comprising a soft flexible material facilitating mating of said seal to the inner surface of said outer shell.

Images