Patent Application
20090173466
The present invention generally relates to a steam distributor for applying steam to a continuously moving paper sheet wherein the steam distributor includes one or more drop-out steam profiling cartridges. Each cartridge, which is attached to the steam distributor with bolts, features a number of profiling zones that are covered by a contoured, smooth profiling screen from which steam is applied. Employment of drop-out cartridges affords quick and easy removal of the profiling screens for change-out or cleaning.
The steam heating of a paper sheet is widely practiced in papermaking. The increase in sheet temperature that results provides increased drainage rates for the water thus reducing the amount of water to be evaporated in the drier section. Water drainage is improved by the application of steam principally because the heating of the sheet reduces the viscosity of the water, thus increasing the ability of the water to flow. Most of the heat transfer takes place when the steam condenses in the sheet. The condensation of the steam transforms the latent heat of the steam to sensible heat in the water contained by the sheet.
A particular advantage of the steam heating of the paper sheet is that the amount of steam applied may be varied across the width of the sheet along the cross machine direction so that the cross machine moisture profile of the sheet may be modified. This is usually carried out to ensure that the moisture profile at the reel is uniform. Techniques in the papermaking art for sensing the moisture profile of a sheet of paper are well known. If a sensing apparatus is positioned over the paper sheet, downstream of a steam distributor able to control the moisture profile, then after measuring the water profile in the sheet, steam can be applied in varying amounts on a selective basis across the sheet, thus achieving the required uniform moisture profile at the reel.
It is known to divide a steam distributor into compartments and to control the supply of steam to each compartment, thus controlling the moisture profile of the sheet. Fiber and dirt accumulate within the compartments and over time, the debris penetrates into the internal structures and interferes with steam flow. The steam distributor must be disassembled in order to clean the internal components.
U.S. Pat. No. 5,711,087 to Pazdera describes an apparatus for distributing steam to a paper web or calendar roll which includes a removable curved-shaped profile screen. The screen is mounted on the apparatus with clip members that interrupt the otherwise smooth exterior surface of the screen. In addition, the use of external clip members makes the removable screen susceptible to flexing outward with increasing steam pressure. Moreover, the clamped edge of the screens must often be separated from the clips on the frame using jarring force, then pried back into place. When they are reattached, the screens lose the intended tight fit against the baffles thereby allowing significant leakage between profiling zones. Finally, in these prior art designs where the screens are not permanently attached, the steam holes in the screen must be situated near either the leading or trailing edge of the steambox in order to minimize the machine direction (MD) length of the screen. Consequently, if a screen becomes too long in the MD, the screen tends to bow out which causes excessive and inconsistent leakage between profiling zones. These removable screen plates become warped and battered after only a few cleaning routines.
U.S. Patent Application 2006/0107704 to Passiniemi describes a steam distribution apparatus that is partitioned into a number of discharge chambers and includes screen plates which are welded to the partitions to prevent the screen plates from twisting or flexing. While the apparatus includes sealable slots for access to the internal compartments for cleaning, the slots afford only limited access.
The present invention is based in part on the development of a removable drop-out steam profiling cartridge that can be incorporated as part of a steam distribution apparatus. The cartridge is preferably fastened to the apparatus by bolts that are readily accessible from the back side of the apparatus. On its front side, the cartridge defines a plurality of isolated steam profiling zones that are separated by spaced-apart partitions or baffle panels that essentially eliminate the spilling over of steam from one profiling zone to the next. The profiling zones are covered by steam profiling screens having perforations through which steam exits. The profiling screens are welded to the baffles which enhances the structural integrity of the drop-out steam profiling cartridge. No external clamps or other devices are employed that would otherwise disrupt the smooth, curved exterior surface of the profiling screens. The drop-out cartridge design provides a rigid structure for cleaning.
Accordingly, one aspect of the invention is directed to an apparatus to distribute steam onto a moving sheet, the apparatus having a leading edge and a trailing edge relative to the moving sheet, the apparatus including:
an elongated steam chamber which has a front wall that defines a recess region;
a plurality of conduits each having an inlet located in the elongated steam chamber and an outlet;
a removable cartridge that is positioned in the recess region wherein the cartridge defines a plurality of compartments each of which is in communication with an outlet and wherein the cartridge has a front screen having a plurality of apertures through which steam can exit;
means for regulating the flow of steam through the inlet and outlet of each conduit; and
means for securing the removable cartridge to the recess region.
In another aspect, the invention is directed to an apparatus to distribute steam onto a continuously moving sheet that has an exterior contour wherein the apparatus has a leading edge and a trailing edge relative to the moving sheet, the apparatus including:
an elongated steambox header which has a front surface facing the moving sheet that defines a recess region;
a plurality of conduits each having an inlet located in the elongated steambox header and an outlet;
one or more removable cartridges that are juxtaposed along the length of the recess region wherein each cartridge comprises a frame that is partitioned along its length to form a plurality of profiling zones each of which is in communication with an outlet and wherein the frame has a front screen having apertures through which steam can exit and the screen defines an outer profiling surface with a contour conforming to the exterior contour of the moving sheet and which is flush with an exterior surface of the front surface of the elongated steambox header;
means for dependently regulating the flow of steam through the inlet and outlet of each conduit; and
means for fastening each removable cartridge to the elongated steambox header characterized in that each cartridge can be unfastened from a back side of the steambox header.
In a further aspect, the invention is directed to a method of distributing steam onto a continuously moving sheet which includes the steps of:
(a) positioning an apparatus having a leading edge and a trailing edge relative to the moving sheet, wherein the apparatus comprises:
(b) activating the actuators to allow steam through the conduits thereby delivering steam onto the moving sheet.
Apparatus 10 includes housing or steambox 2 that encloses a main steam distribution header 32 which runs the length of the apparatus and which is connected to at least one source of steam (not shown). Steam distribution header 32 includes an interior wall 6 and an exterior wall 4 which defines an exterior recess region into which is a drop-out steam profiling cartridge 42 is inserted and attached. A pair of pipes 12, 22 is welded onto interior wall 6 and exterior wall 4; each pipe is configured to provide a conduit or passageway through which a cartridge bolt can be inserted to fasten drop-out cartridge 42. Specifically, cartridge bolts 14, 24 are inserted through pipes 12, 22, respectively, and cartridge 42 includes two corresponding threaded mating nuts 18, 28, that are welded thereto, and that receive the distal ends of cartridge bolts 14, 24, respectively. Cartridge 42 is fastened by tightening cartridges bolts 14, 24 whose proximal ends 16, 26 are readily accessible through an inner enclosure 56 located at the back of steam distribution apparatus 10. By removing wing-nuts 64, 68, cover 62 can be removed from flange 60 to expose enclosure 56.
Steam exiting an opening 52 of valve sleeve 58 expands into the compartment or profiling zone 40 within cartridge 42 before being discharged through perforations in a profiling screen 38 and onto paper sheet 50 which is transported on a continuously rotating roll, for example. In this fashion, there is uniform steam distribution from a leading edge 51 to a trailing edge 53 of contoured profiling screen 38 as the sheet of material moves across profiling zone 40 in the machine direction. Condensate that forms on the bottom of profiling zone 40 seeps through a drain hole 54 and out through a condensate drain. The steam distributor apparatus is also equipped with a pressure gauge 34 and a main header condensate drain 36.
The exterior or front surface of profiling screen 38 is preferably contoured to match the shape of paper sheet 50. In this case, the concave-shaped curvature of profiling screen 38 is particularly suited for applying steam to a roll of material. The gap or distance between profiling screen 38 and paper sheet 50 typically ranges from 10 mm to 20 mm. The exterior surface of profiling screen 38 is flush with the outer, front surface of housing 2. At the perimeter where the edges of cartridge 42 meet the edge of the recess region, silicone fillers are not needed to create a smooth continuous surface.
As shown in
By monitoring and controlling the steam flow into each of a plurality of profiling zones 40, a predetermined steam profile can be injected onto a sheet along its cross direction. The steam profile, as measured along the length of the steam distribution apparatus, can be uniform or non-uniform so that the sheet or web of material can be exposed to a steam curtain having different amounts of steam in the cross direction.
As illustrated, a plurality of steam profiling zones or compartments spans the length of steam distributor apparatus 10. Steam is supplied to each compartment via an opening 86 of a valve sleeve. The compartments are isolated from one another by zone dividers or baffles 102, 104 which are spaced apart laterally and to which a stream profiling screen 38 (
The structural integrity of the drop-out cartridge allows for optimal machine-direction placement of the perforations in profiling screen 38 (
As described above, cartridge bolts are positioned along the length of the apparatus to secure the drop-out steam profiling cartridge. As shown in
The recess region is designed to accommodate one or more drop-out steam profiling cartridges. In the case where a single integral cartridge is employed, its length would essentially match that of the recess region. Alternatively, a plurality of shorter cartridges, which are individually inserted into the recess region and secured thereto, can be employed. The use of multiple smaller cartridges allows for selective removal for maintenance. For example, a sectioned cartridge that includes 9 steam profiling zones 82A through 82I is positioned in the recess region adjacent endplate 90. Other sectional cartridges are then positioned in the recess region to form a series of sectional cartridges juxtaposed from end to end.
One benefit of employing sectional cartridges is that a fixed design unit can be more readily based-lined with conventional 3-D modeling and parameterized computer-aided design (CAD) software. Furthermore, once a design unit is dimensionally fixed, it can be used in the design of various steam distribution apparatuses. Finally, employing a drop-out steam profiling cartridge simplifies the overall design of the accompanying steambox header by reducing the number of internal channels. In particular, with comparable prior art steambox headers that accommodate removable steam profiling screens, a higher number of internal channels must be welded to the steambox headers in order to allow the removable screens to be positioned properly while maintaining the required contour of the steambox front side.
The length of steam distribution apparatus 10 typically corresponds to the width of the sheet or web to which steam is to be applied. For papermaking, the length generally ranges from 5 to 12 meters and typically is about 9 meters. Each steam profiling zone, e.g., 82A in
The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.
