Screen Slots of Varying Width in Digester
Publication Date: 2004-Feb-23
The IP.com Prior Art Database
Carl L. Luhrmann: INVENTOR [+2]
A screening device for use in a cellulose pulp digester, wherein the screening device includes: first and second metal screen plates attachable to the digester internal surface, and individual slot regions in each of the first and second metal screen plates, wherein each slot region includes a plurality of slots having a wifth and length, wherein the width of the slot region in the first metal screen plate is narrower than the width of the slot region in the second metal screen plate.
SCREEN SLOTS OF VARYING WIDTH IN DIGESTeR
BACKground of the invention
 [lsp1] Screen plates are used in conventional digesters for the production of chemical cellulose pulp (e.g. kraft pulp) for both continuous and batch digesters. Screen plates are filters that allow liquor to be extracted from a digester but prevent the extraction of fibrous material. Screen plates are generally arranged around an inner circumference of a digester. An inner surface of the plate is exposed to the chip slurry in the digester and an outer surface of the plate forms a wall to a liquor extraction chamber. The screen plate may have multiple rows of narrow slots through which liquor (but not fiber) is extracted from the chip slurry and flows into the extraction chamber.
 The slots in screen plates tend to clog or plug with fibers and have been a source of digester operation downtime. Various types of slot designs have been developed to reduce the tendency of clogging/plugging. For example, orienting the slots diagonally to the vertical axis and horizontal planes of the digester has been found to reduce clogging/plugging. See U.S. Patent No. 6,165,323. However, clogging/plugging of the diagonal slots still occurs and there continues to be a long felt need for devices that further reduce the tendency of slot clogging/plugging.
brief description of the invention
 In one embodiment, the invention is a screening device for use in a cellulose pulp digester, wherein the screening device includes: at least a first and second sections of a metal screen plate attachable to the digester internal surface, and individual slot regions in each of the at least first and second sections of the screen plate, wherein each slot region includes a plurality of slots having a width and length, wherein the width of the slot region in the first section of the metal screen plate is narrower than the width of the slot region in the second section of the metal screen plate.
brief description of the drawings
 FIGURE 1 is a front view of a continuous digester shown schematically and partially cut away.
 FIGURE 2 is a front view of an inner screening assembly and wall of the digester, shown schematically.
 FIGURE 3 is a is a front view of several assembled screen plates in a screening assembly.
 FIGURES 4 and 5 are front and back views, respectively, of a portion of a screen plate.
 FIGURE 6 is a partial cross-section of a screen plate taken along line 6-6 in Figure 5.
detailed description of the invention
 FIGURE 1 is a side view of a prior art continuous vertical digester 10 for processing cellousic fiber material, e.g., wood chips, into fiber pulp. Though a vertical continuous digester is shown, the screen plates and screen slots described herein are applicable to other types of cylindrical continuous and batch digesters.
 A slurry of comminuted cellulosic fibrous material and cooking chemical is introduced at the top 12 of the dige...