| 摘要 |
<p>A method is disclosed for the continuous treatment of wood chips in a downflow vertical digester by the alkaline process. Wood chips and black liquor are introduced near the upper end of the digester and travel downwardly therethrough to a sole point at which the black liquor is discharged from the digester. Cooking liquor is introduced at a point between the lower end and black liquor discharge point of the digester and passes upwardly to the discharge point, countercurrent to the flow of wood chips, to cook the chips and leave the digester as back liquor at the discharge point. The cooked wood chips are removed from the lower end of the digester. The active chemical in the cooking liquor is maintained constant. Active chemical is further added near the upper end of the digester and the addition thereof is regulated in response to changes in the residual active chemical in the black liquor which are monitored at the discharge point of the digester, in order to keep the residual active chemical in the discharged black liquor at a substantially constant concentration. The quantity of active chemical added near the upper end of the digester does not exceed 20 percent of the total active chemical added to the digester.</p> |
