PURIFICATION OF ALKALINE WASHING LIQUID

摘要

A method for washing sulphate cellulose pulp in the washing department of a sulphate cellulose mill, in which method a first pulp flow (1) is conducted to a first washer (101), where a washing liquid (12) is combined with the first pulp flow (I). A second pulp flow (2) is conducted from the first washer (101) to a second washer (102), where a washing liquid (3) is combined with the second pulp flow (2). The washed pulp flow (5) is proceeded from the second washer (102) in the process and the filtrate (4) displaced by the washing liquid (3) is recycled to the process so that the filtrate (4) displaced by the washing liquid (3) in the second washer (102) is divided into a first part flow (6) and a second part flow (7) and the pH of the second part flow (7) is dropped by combining an acidifier (8) with the second part flow (7). The acidified part flow (9) is conducted to a process unit (103), where sludge (10) containing extractives and metals is separated from the part flow (9) and the entire process and the part flow (11) treated in the process unit (103) is combined with the first part flow (6) and is recycled to the process for use as the washing liquid (12) in the first washer (101).