Abstract:
A steam distributor for applying steam to a continuously moving paper sheet employs one or more drop-out steam profiling cartridges. Each cartridge is connected to a steam distribution apparatus and includes a number of profiling zones that are covered by a contoured, smooth profiling screen from which steam is applied. The profiling screens are welded to baffles which enhances the structural integrity of the cartridge. No external clamps or other devices are employed that would otherwise disrupt the smooth, curved exterior surface of the profiling screens. The spaced-apart baffles also eliminate the spilling over of steam from one profiling zone to the next which has the effect of minimizing the response width for steam profiling control. The use of the drop-out cartridges permits quick and easy removal of the profiling screens for change-out or cleaning.

Description:
FIELD OF THE INVENTION 
       [0001]    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. 
       BACKGROUND OF THE INVENTION 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
       SUMMARY OF THE INVENTION 
       [0007]    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. 
         [0008]    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: 
         [0009]    an elongated steam chamber which has a front wall that defines a recess region; 
         [0010]    a plurality of conduits each having an inlet located in the elongated steam chamber and an outlet; 
         [0011]    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; 
         [0012]    means for regulating the flow of steam through the inlet and outlet of each conduit; and 
         [0013]    means for securing the removable cartridge to the recess region. 
         [0014]    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: 
         [0015]    an elongated steambox header which has a front surface facing the moving sheet that defines a recess region; 
         [0016]    a plurality of conduits each having an inlet located in the elongated steambox header and an outlet; 
         [0017]    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; 
         [0018]    means for dependently regulating the flow of steam through the inlet and outlet of each conduit; and 
         [0019]    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. 
         [0020]    In a further aspect, the invention is directed to a method of distributing steam onto a continuously moving sheet which includes the steps of: 
         [0021]    (a) positioning an apparatus having a leading edge and a trailing edge relative to the moving sheet, wherein the apparatus comprises:
       (i) an elongated steam chamber that is in communication with a source of steam and which has a front wall that defines a recess region;   (ii) a plurality of conduits each having an inlet located in the elongated steam chamber and an outlet;   (iii) 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;   (iv) actuators for regulating the flow of steam through the inlet and outlet of each conduit; and   (v) means for securing the removable cartridge to the recess region; and       
 
         [0027]    (b) activating the actuators to allow steam through the conduits thereby delivering steam onto the moving sheet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1A  is a cross sectional side view of a partially exposed portion of the steam distributor apparatus as steam is applied onto the surface of a moving sheet of paper that is supported on a roller; 
           [0029]      FIG. 1B  is a cross sectional side view of a partially exposed portion of the steam distributor apparatus showing the drop-out steam profiling cartridge removed; 
           [0030]      FIG. 2  is a cross sectional side view of a partially exposed portion of the steam distributor apparatus showing an actuator; and 
           [0031]      FIG. 3  is front view of the steam distribution apparatus illustrating the profiling compartments or zones and the positions of the cartridge bolts and steam discharge conduits. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]      FIG. 1A  illustrates a steam distributor apparatus  10  that is particularly suited for applying steam to a paper web or calendar roll in a sheet making process. Papermaking devices are well known in the art and are described, for example, in U.S. Pat. No. 5,539,634 to He and U.S. Pat. No. 5,022,966 to Hu, U.S. Pat. No. 4,982,334 to Balakrishnan, U.S. Pat. No. 4,786,817 to Boissevain et al., and U.S. Pat. No. 4,767,935 to Anderson et al. which are incorporated herein by reference. 
         [0033]    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 . 
         [0034]    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 . 
         [0035]    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. 
         [0036]      FIG. 1B  shows the steam distribution apparatus with cartridge  42  removed from recess region  8  that is configured within exterior wall  4 . This can be readily accomplished by loosening cartridge bolts  14 ,  24  to disengage the bolts from threaded nuts  18 ,  28 , respectively. Cartridge  42  is preferably configured as a U-Shaped frame  30  that is covered by profiling screen  38  that has perforations or apertures that are sized and distributed to allow steam to discharge through in a predetermined pattern. Steam distributor apparatus  10  also includes a plurality of actuators each of which regulates the amount of steam which is discharged through an opening  52  of valve sleeve  58 . The use of cartridge bolts  14 ,  24  to secure drop-out cartridge  42  and to maneuver profiling screen  38  into U-Shaped frame  30  permits design and manufacturing tolerances to be flexible without sacrificing performance of the steam distributor apparatus. The manufacturing process can be more readily streamlined. 
         [0037]    As shown in  FIG. 2 , high pressure steam that is supplied to main steam distribution header  32  is drawn into valve sleeve  58  through an annular opening  55  that is located between the valve sleeve  58  and pipe  74 . The amount of steam drawn is controlled by actuator  70  which is connected via connector  72  to a pneumatic supply which tunes or regulates the actuator by pressurizing a diaphragm that is on top of a piston that is located inside actuator  70 . The piston is connected to a measuring plug that moves inside pipe  74  to control the amount of steam that goes into a profiling zone  40  within cartridge  42 . Pneumatic actuators for regulating steam flow in a steam distribution apparatus are described, for instance, in U.S. Pat. Nos. 4,398,355 to Dove and 4,351,700 to Dove, which are incorporated herein by reference. 
         [0038]    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. 
         [0039]      FIG. 3  illustrates a front view of steam distributor apparatus  10  exposing the compartment of the drop-out steam profiling cartridges without the profiling screens. Housing  2 , which is flanked by endplates  90 ,  92 , forms an elongated structure having a front wall configured to serve as a recess region into which one or more drop-out steam profiling cartridges are secured. An external source of steam is connected through steam line  94  to steam distribution apparatus  10  and excess steam in the form of condensate exits through drain  96 . 
         [0040]    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  ( FIG. 1B ) is welded. Baffles  102 ,  104  also serve as internal gussets onto which U-Shaped frame  30  ( FIG. 1B ) of the drop-out steam profiling cartridge  42  ( FIG. 1B ) is welded. In this fashion, the steam profiling screen is held in place so as not to flex or expand outwardly and possibility come into contact with the paper sheet should the pressure in the compartment increase suddenly. In addition, the baffles prevent the spill-over of steam between steam profiling zones which minimizes the overall response width in the process of monitoring and controlling the steam profile. Since the steam profiling screen is welded to the cartridge, the screen can withstand a higher pressure from the steam jet at the actuator outlet than with conventional designs. For example, steam jet  52  may be allowed to impact steam profiling  38  screen directly without the need for a protective plate as illustrated in  FIGS. 1A and 1B . As a result, a higher range of pressure distribution within the profiling zones or compartments can be achieved. 
         [0041]    The structural integrity of the drop-out cartridge allows for optimal machine-direction placement of the perforations in profiling screen  38  ( FIG. 1B ). In particularly, unlike prior designs where the perforations are restricted primarily to the leading or trailing edges of the steambox, with the drop-out steam profiling cartridge, the screen holes can be moved to the center of the contoured surface. This feature may be beneficial in reducing the cross-directional response width (fanning out) of the process. 
         [0042]    As described above, cartridge bolts are positioned along the length of the apparatus to secure the drop-out steam profiling cartridge. As shown in  FIG. 3 , the bolts are connected to nuts, such as nuts  84 A and  84 B located in compartment  82 A. As depicted, pairs of bolts are spaced apart along the length of the apparatus; however, in order to fasten a cartridge to steam distributor apparatus  10 , it is not necessary that a pair of bolts be associated with each compartment. 
         [0043]    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  82 A through  82 I 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. 
         [0044]    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. 
         [0045]    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.,  82 A in  FIG. 3 , has a width of about 3 in. (7.6 cm) to 4 in. (10.2 cm). A typical steam distribution apparatus has up to about 90 steam profiling zones in total. In operation, the steam pressure in each profiling zone ranges up to about 80 kPa. 
         [0046]    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.