Continuous alkaline oxygen delignification of pulp, using multi reactor system with high pressure reactor part

摘要

The reactor system includes a high pressure reactor part (R 1-R 3) in which the pulp spends a predetermined dwell time. A continuous alkaline oxygen delignification of cooked and optionally washed (W 1-W 3) cellulose pulp which has been stored in a substantially atmospheric pressure tower or pit (ST), has an average consistency of 8-16% and has a kappa value of at least 15 units (preferably greater than 20) is carried out in a multi-reactor system (R 1-R 4) by adding alkali (NaOHMAIN) to obtain an initial pH greater than 9 and by adding 5-50 kg oxygen per tonne pulp in a position upstream from the first reactor. The dwell time for the pulp in the entire reactor system is greater than 45 minutes. The pulp is pressurised to an initial pressure of more than 15 bar in a high pressure part of the system, where the necessary chemicals are added and the initial mixing is carried out, then pulp is passed through at least two reactors with mixing stations (M1-M3) in between so that the pulp pressure is at least 13 bar as it leaves the final reactor in the high pressure part. The dwell time in the reactors = t 1t 2t x, where t 1is the dwell time in the reactor before the first mixing station (M1) and x is the number of high pressure reactors.