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SYSTEM AND METHOD FOR SCREENING IN A BATCH DIGESTER VESSEL

IP.com Disclosure Number: IPCOM000021066D
Publication Date: 2003-Dec-19
Document File: 8 page(s) / 37K

Publishing Venue

The IP.com Prior Art Database

Related People

Nam Hee Shin: INVENTOR [+2]

Abstract

A method for batch digesting in a vessel have a plurality of vertical screens arranged in an annular array around a circumference of the vessel, wherein the method comprises: injecting a slurry of cellulosic fiber material and cooking liquor into an interior of the vessel; ceasing the injection of the slurry and allowing the liquor to react with the fiber material in the interior of the vessel; extracting a portion of the liquor through the vertical screens and into a chamber on an opposite side of the screens from the interior of the vessel; passing the extracted liquor through a plurality of orifices at a bottom side of the chamber, and the liquor flowing through the orifices passing into a head and out through a port of the vessel.

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SYSTEM AND METHOD FOR SCREENING IN A BATCH DIGESTER VESSEL

background of the invention

[0001]                           [lsp1] In the art of chemical pulping of comminuted cellulosic fibrous material, for example wood chips, the cellulose material is typically treated with cooking chemicals under pressure and temperature in one or more cylindrical vessels, known as digesters. This treatment can be performed continuously or in a batch mode. In the batch method, one or more batch digesters are filled with chips and cooking chemical, capped and then treatment commences. Once the treatment is finished the contents of the batch digester are discharged. In either batch or continuous digesters, a slurry of comminuted cellulosic fibrous material and cooking chemical is treated in one or more a cylindrical vessels.

[0002]                           In batch digesters, the cooking chemical liquids are circulated in the digester vessel while the chips remain relatively stagnate in the vessel. In the design of a batch digester, consideration must be given as to how to make the cooking liquid flow uniformly through the digester and how to control the concentration of cooking liquid in the vessel by extraction or injection of liquid to or from the vessel. It is particularly difficult to ensure uniform distribution of cooking liquids through out the pool of stagnate chips in a batch digester. In contrast, chips flow downward through a continuous digesting vessel through various stages of screens used to extract or inject cooking liquid from the flow of chips. The flow of chips in a continuous digester assists in achieving uniform distribution of cooking liquids. However, the continuous digester vessel is designed to allow for a smooth flow of chips and avoid having clumps of chips obstructing the flow through the vessel. Accordingly, the design issues to be addressed in a batch digester differ in several respects to the issues that are addressed in designing a continuous digester.

[0003]                           In both continuous and batch digesters, cooking liquor is typically circulated through the slurry of chips and liquor, typically referred to as "the chip column" to uniformly distribute both temperature and cooking chemical. The chip column flows down through the vessel of a continuos digester and remains stagnate during cooking in a batch digester. This circulation is typically facilitated by some form of screen, located along the internal surface of the cylindrical vessel, and a pump, a heater, and a return conduit. The screen retains the material within the digester as the liquor is removed, augmented with other liquors and/or a portion thereof removed, pressurized, heated, and then returned to the slurry in the vicinity of the screen or elsewhere. The proper operation of the digester and the production of uniform product having the best or optimum properties, for example, strength, are highly dependent upon the efficiency and uniformity of this liquid circulation process.

[0004]                           Typically, digester screen assemblies compr...