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IMPROVEMENTS TO DIGESTER LIQUOR RECIRCULATION

IP.com Disclosure Number: IPCOM000021069D
Publication Date: 2003-Dec-19
Document File: 4 page(s) / 27K

Publishing Venue

The IP.com Prior Art Database

Related People

Richard O. Laakso: INVENTOR [+3]

Abstract

According to the present invention, the discharge location of the extracted liquor is such that wood chip compaction within the chip column is enhanced.

This text was extracted from a Microsoft Word document.
This is the abbreviated version, containing approximately 52% of the total text.

IMPROVEMENTS TO DIGESTER LIQUOR RECIRCULATION

field of the invention

The present invention is related generally to chemical wood pulping processes and systems. More specifically, the present invention is related to liquor recirculation in continuous wood pulping digesters.

BACKground and summary of the invention

In a typical liquor-exchange digester (for example, a digester which is operating with a process design commercially available from Andritz Inc. of Glens Falls, New York and known as Lo-Solids® pulping as described in U.S. patents 5,489,363; 5,536,366; 5,547,012; 5,575,890; 5,620,562; 5,662,775; 5,824,188; 5,849,150; 5,849,151; 6,086,712; 6,132,556; 6,159,337; 6,280,568; and 6,346,167, the entirety of each being expressly incorporated hereinto by reference), liquor enters with the chips at the top of the digester and is extracted at the first set of withdrawal screens located adjacent the top of the digester near the beginning of the cook. The extracted liquor is then conventionally recirculated to a location just above the first screen set.

It has been found that conventional recirculation techniques are sometimes inadequate, especially when light weight wood (e.g., softwood) chips are employed. Particularly, it has been found that there are sometimes inadequate wood chip compaction in the chip column above the first screen set.

According to the present invention, the discharge location of the extracted liquor is such that wood chip compaction within the chip column is enhanced.

These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.

brief description of the ACCOMPANYING drawings

Reference will hereinafter be made to the accompanying drawings, wherein like reference numerals throughout the various FIGURES denote like structural elements, and wherein;

FIGURE 1 is a schematic view of a prior art digester liquor recirculation loop; and

FIGURE 2 is a schematic view of a digester recirculation loop in accordance with the present invention.

detailed description of the INVENTION

Accompanying FIGURE 1 depicts a digester 10 having a top separator 12 at the top end thereof for feeding wood chips into the digester interior. The digester includes a first set of extraction screens 14 adjacent the digester top near the beginning of the cook. Subsequent sets of extraction screens have not been depicted in the accompanying drawing FIGURES but may be present as is highly conventional in the art of continuous digesters. As shown, the first set of extraction screens 14 supports a wood chip column WC, the height of which can vary but usually extends nearly up to within a meter or so of the discharge port of top separator 12.

Liquor is extracted from the screen set 14 via pump 16 and recirculated via recirculation...