Abstract:
Employment of one or more resealable access slots in a steam distributor apparatus affords easy access to the internal chambers of the apparatus for cleaning and maintenance. The access slots can be located on the lower walls of the steam discharge chambers where debris tend to aggregate during operation of the apparatus. The apparatus can have multiple discharge chambers that are separated by spaced-apart partitions or baffle panels. Steam that is supplied from a steam header to each chamber exits each chamber through perforations of a discharge screen plate that is permanently secured onto adjacent partition panels. Actuators can regulate the steam flow from the steam header to the individual discharge chambers thereby creating a steam curtain with uniform or non-uniform cross direction profiles as desired.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to a steam distributor for applying steam to a paper sheet moving along its side wherein one or more sealable slots located along the cross direction of the distributor permits easy access to the internal compartments or chambers for cleaning and maintenance. 
   BACKGROUND OF THE INVENTION 
   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. Apparatus are well known in the papermaking art that can sense the moisture profile of a sheet of paper. If such an 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. Unfortunately, with prior art designs, fiber and dirt tend to accumulate within the compartments and over time, the debris penetrates into the internal structures and interfere with steam flow. The steam distributor must be disassembled in order to clean the internal components; this requires that the entire screen covering the steam distributor be moved. 
   SUMMARY OF THE INVENTION 
   The present invention is based in part on the development of a steam distributor that preferably includes multiple steam discharge chambers or compartments that are separated by spaced-apart partitions or baffle panels. Steam exits each compartment through perforations in a perforated steam discharge screen plate that is permanently secured, e.g., welded, onto adjacent partition panels. The steam distributor also includes one or more resealable access slots or channels through which debris that is trapped within the internal of the compartments can be readily removed. 
   In one embodiment, the invention is directed to an apparatus to distribute steam to a moving sheet, the apparatus having a leading edge and a trailing edge relative to the moving sheet, the apparatus includes:
         (a) a steam distribution header; and   (b) a housing defining at least one steam discharge chamber that is covered with a perforated screen plate, wherein each discharge chamber is in fluid communication with the steam distribution header and the at least one steam discharge chamber has at least one sealable access slot.       

   In another embodiment, the invention is directed to an apparatus to distribute steam to a moving sheet, the apparatus having a leading edge and a trailing edge relative to the moving sheet, the apparatus includes:
         (a) a steam distribution header;   (b) housing comprising a plurality of partition panels that are spaced apart along the length of the apparatus to form a plurality of steam discharge chambers that are covered with one or more perforated screen plates, wherein each discharge chamber is in fluid communication with the steam distribution header through a conduit that has an inlet in the steam distribution header and an outlet in a discharge chamber and wherein, each discharge chamber includes a lower wall that defines a sealable access slot; and   (c) means for controlling the flow of steam from the steam distribution header to each discharge chamber.       

   Typically, each discharge chamber has an associated access slot that is located adjacent to the outer, lower portion of the discharge chamber where debris tends to congregate. The dimensions of each access slot are preferably relatively small as compared to that of the discharge chamber. Upon removal of a cleanout bar or other resealable implement that covers the access slot, the internal parts of the discharge chamber the can be cleaned of debris, dirt, and other contaminants with high pressure water that is delivered by a spray wand configured to fit through the slot. This reduces the likelihood of damage to the steam distribution apparatus since the fragile screen plates are not removed and handled. The perimeter of each access slot can be lined with a gasket to provide additional protection against steam leakage. And to facilitate precise alignment of a sealable cleanout bar over the access slot, the housing adjacent the access slot and the cleanout bar itself can have matching apertures for visual alignment. These matching apertures can accommodate dowel pins which help secure the cleanout bar to the steam distributor body. 
   Furthermore, since the discharge screen plates are permanently secured onto the partitions that separate the discharge chambers, the screen plates are an integral part of the body structure of the steam distributor. This design further prevents the thin screen plates from being twisted or otherwise damaged. Preferably, the screen plates are welded onto the partitions so that under certain abnormal operating conditions such as steam overpressure within the discharge chambers, screen plate damage is significantly reduced because of the integral design. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a perspective view of a steam distribution apparatus; 
       FIGS. 1B and 1C  are enlarged views of the discharge screen plate in the steam distributor apparatus; 
       FIG. 2  is a perspective view of a compartment in the steam distributor apparatus; 
       FIG. 3  is a cross sectional view of the compartment; 
       FIG. 4A  is another perspective view of a compartment; 
       FIG. 4B  illustrates an actuator; 
       FIG. 5  is a cross sectional view of a front portion of the discharge compartment adjacent the discharge screen plate with the cleanout bar removed; and 
       FIG. 6  is a cross sectional view of a front portion of the discharge compartment adjacent the discharge screen plate with the cleanout bar attached during normal operating conditions. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1A  illustrates the overall assembly of a steam distribution apparatus or steam shower  10  which includes an elongated housing  12  that is enclosed by end plates located at opposite ends. The length of the apparatus typically corresponds to the width of the sheet or web to which steam is to be applied. For papermaking operations the length can range, for instance, up to about 30 feet (9.1 meters). An external source of steam is connected to the steam distribution apparatus and excess steam in the form of condensate is removed through a drain  16  which is located on the side of end plate  14 . The contour of the front screen panel or plate  18  preferably matches the external shape of the product to which steam is being supplied. The concave-shaped curvature of front screen panel  18  is particularly suited for apply steam to a roll of material. The front screen panel can also have a planar configuration to match the straight run of a moving sheet. 
   As further described herein, the steam distributor apparatus  10  is separated into a plurality of steam discharge chambers or compartments along the length of the apparatus  10  so that profiling of the steam application can be accomplished. For example, the amount of steam that enters into the individual chambers can be controlled in response variations in measured properties of the sheet along its cross direction. 
     FIGS. 1B and 1C  show the arrangement of the steam outlets or perforations  20  that are formed across the entire length of the front screen panel  18 . Typically, the outlets  20  are arranged in a plurality of rows  22 ,  24 , and  26 , for instance. The individual outlets  20  can be circular or have non-circular configurations. The number and size of the outlets are designed to achieve the desired steam flow rate and velocity. The size of the outlets  20  should be sufficiently small to minimize the amount of fibers and other debris from the sheet of material being heated that enters into the discharge chambers. Nevertheless, in operation, as steam is applied through the perforations  20  onto a moving sheet of paper, for stance, the front screen plate  18  can come into contact with the sheet. As a result, fiber and dirt will clog the perforations  20  and accumulate inside the housing  12  as well. 
     FIG. 2  shows a partially disassembled exposed portion of the housing  30  of the steam distributor apparatus. The housing  30  encloses a steam distribution header  36  which is connected to at least one source of steam (not shown). Header  36  runs the length of the steam distribution apparatus. The header  36  is flanked by an interior wall  60  and an exterior wall  62 . The inner enclosure  34  shields the pneumatic actuators  32  with a removable cover that is secured by the hand tightened screws  64 . A plurality of baffles or partition panels  40 , that are laterally spaced apart are secured to the exterior wall  62  thereby creating a number of steam discharge chambers or compartments once the front screen panel segment  31  is secured to the forward part of the housing. 
   Each pneumatic actuator  32  is operatively connected to a pipe  42  which has an inlet end located within the header  36  and an outlet end that is located in a discharge chamber. In this embodiment, the inlet end of the pipe  42  is partially covered by a sleeve  44 . A piston is attached to the actuator  32  by a connecting rod to regulate the inlet into pipe  42  and thus control the steam flow between the header  36  and the control chamber. Pneumatic actuators for regulating steam flow in a steam distribution apparatus are described in U.S. Pat. No. 4,398,355 to Dove and U.S. Pat. No. 4,351,700 to Dove, which are incorporated herein by reference. 
   In operation, as shown in  FIGS. 3 and 4A , high pressure steam that is supplied to the header  36  is drawn into the pipe  42  through the annular opening between the pipe  42  and the sleeve  44 . The amount of steam drawn is controlled by the actuator  32  which is connected to a pneumatic supply  35  which tunes or regulates the actuator by pressurizing a diaphragm that is on top of a piston that is located inside the actuator  32 . The piston is connected to a measuring plug that moves inside the sleeve  44  to control the amount of steam that goes into each discharge chamber. Steam from the pipe  42  initially enters into a discharge chamber  66  through the pipe outlet  68 . The high velocity steam is dispersed within the discharge chamber  66  before exiting through the perforations of the front panel screen segment  31  and contacting a continuous moving sheet  33  located in front of the perforations. By monitoring and controlling the steam flow into each of the discharge chambers, the steam profile that is injected onto the sheet along its cross direction can be continuously regulated. 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 shown in  FIG. 2 , the front screen panel segment  31  has a concaved exterior contour; as is apparent, the individual perforations in the panel segment  31  are not shown. A backing bar  98  is secured to the lower end of the laterally spaced baffles  40 . The front screen panel segment  31  is welded onto a portion of the backing bar  98  as well as onto the baffles  40 . In this fashion, the front screen panel segment  31  forms the front perforated wall of the steam discharge chambers. The front of the backing bar  98  also defines a series of dowel pins  84  that helps align the cleanout bar  48  as it is secured with screws  50  to the body of the steam distribution apparatus as further described herein. When it is necessary to clean the steam discharge chambers between the baffles  40 , it is only necessary to remove the cleaning bar  48  to gain access to the discharge chambers through access slots that are located at the lower end of each discharge chamber. 
   The baffles  40  and front screen panel segment  31  are preferably welded onto the body of the housing as shown in  FIG. 4A . By welding the inner side of the segment  31  to the baffles  40 , steam does not leak from one discharge chamber to an adjacent one. Gaskets can be employed to further reduce leakage. As is apparent, the number of front screen panel segments  31  required to cover a steam distribution apparatus will depend on the total cross directional length of the steam distribution apparatus and the cross directional length of each panel segment  31 . 
     FIG. 5  shows a steam discharge chamber  70  that is covered by perforated screen plate  72  and that is welded onto the baffles (not shown) and onto body  76  of the steam distributor apparatus. In this embodiment, the perforated screen plate  72  is configured as a slightly curved two-sided panel. The discharge chamber  70  is partitioned from the header by the header exterior wall  74 . The body  76  and the header exterior wall  74  both extend the entire length of the steam distribution apparatus and provide structural support for the baffles and the perforated screen plate  72 . The lower end of screen plate  72  can be positioned between the projection of body  76  and a continuous backing bar  98  which provides additional support for the screen plate  72 . The backing bar  98  serves as a holding plate for the cleanout bar  78 . 
   In the lower part of the body  110  of the steam shower there is a series of fixed inserts with threaded holes. The access slot  80  can be sealed with a detachable cleanout bar  78 . Each access slot  80  is typically 1.5 in. (3.8 cm) to 2 in. (5.1 cm) wide as measured in the machine direction and 3 in. (7.6 cm) to 6 in. (15.2 cm) long as measured in the cross direction. With the bar  78  removed, the discharge chamber  70  can be cleaned. As is apparent, locating the access slot  80  in the lower part  110  substantially underneath the screen plate  72  creates an unobstructed path to maneuver a spray wand into the access slot  80  for cleaning the internal parts of the discharge chamber and for cleaning the inner surface of the screen plate  72 . Moreover, the debris inside the discharge chamber should accumulate near the access slot  80  for easy removal. When the steam distribution apparatus is equipped with a plurality of access slots along its length, it is necessary to removed only selected bars to gain access to certain discharge chambers that require maintenance. To insure a tight seal, a polymeric gasket can be positioned around the opening of the access slot  80 . To facilitate alignment of the cleanout bar  78  over the access slot  80 , the “L” shaped cleanout bar  78  can include an aperture  82  which can be visually aligned to a corresponding dowel pin  84  that is located on the bottom side of the screen plate  72 . Once the aperture  82  and dowel pin  84  are aligned, the cleanout bar  78  can be fully mounted to the steam shower body  110  using bolts  86  thereby sealing the bottom portion of the control chamber  70  (shown in  FIG. 6 ) 
   In operation, as shown in  FIG. 6 , the cleanout bar  78  is fastened to the lower wall  110  of the discharge chamber  70  with bolts  86 . High pressure steam from the header is discharged through the nozzle of a pipe  90  and into the discharge chamber  70 . Preferably, a target plate  92  which serves as a baffle, is positioned to disperse the high velocity steam uniformly throughout the discharge chamber  70  before the steam permeates through the perforations in the screen plate  72 . In this fashion, there is uniform steam distribution from the leading edge  104  to the trailing edge  106  of the steam distribution apparatus as the sheet of material moves across the screen plate  72  in the machine direction (MD). Condensate that forms on the bottom of the discharge chamber  70  seeps through a drain hole  94  and out through a condensate drain  38 . 
   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.