Continuous digester system.

摘要

Comminuted cellulosic fibrous material, such as wood chips, are treated in a continuous digester (11) to produce paper pulp or the like in a manner providing completely uniform treatment of the chips. The chips are introduced in a feed liquid slurry into the top (5) of the digester, with a swirling action, and establish a vertical column (52) in the digester having a substantially horizontal top (54), with some liquid (53) between the top of the digester and the top of the chips. Below the top of the chips the feed liquor is withdrawn through a first set of withdrawal screens (15), and recirculated to entrain other chips to feed them to the top of the vessel. At other vertically spaced areas of the digester other screens (16-18) are provided for withdrawing, cooking, quench, washing, and like liquors, and effecting recirculation thereof. At each screen set a plurality of nozzles (21-24) are provided circumferentially spaced around the digester, each nozzle cooperating with only a particular radial segment of the screens. Withdrawal of liquid through the nozzles is practiced so that liquid is being withdrawn substantially through only one nozzle at a time, and it is being withdrawn at the same radial segment of the digester at each screen set at any particular point in time, with progressive switching in a circumferential sequence of the nozzles through which liquor is being withdrawn. Thus deliberate channeling of treatment liquors through the chips column is provided. Treatment liquors are introduced through a vertical conduit (26) in the digester concentric with the digester shell, and discharge of treated chips (i.e. pulp) is provided at the bottom (13) of the digester utilizing sluicing liquor and a rotating outlet (72,73) which are designed to be substantially opposite the radial segment through which liquid withdrawal is being practiced at any particular time. The vertical conduit has a relatively large diameter so that treatment liquid is introduced with a relatively low velocity. A plurality of rotating valve elements (35-38) and a common driven shaft (39) preferably provide the mechanism for effecting liquid withdrawal in the desired sequence, and a rotatable shaft (70) synchronized with the valve shaft provides for the introduction of sluicing liquid and positioning of the rotatable outlet.