the green liquor tank glt is in an emptying process feeding clear green liquor to the slaker and onwards via the causticizing train ct 1 ct 2 ct 3 to the common filter apparatus glf wlf the resulting filtered white liquor is fed from the common filter apparatus glf wlf to the white liquor tank wlt in fig4 only the flows during the green liquor cycle are shown when operating the common filter apparatus glf wlf this cycle is preferably initiated during 2 5 3 hours during which the causticizing train ct 1 ct 2 ct 3 for receiving causticizised liquor is only used as buffering tank i e with no outflow of any causticizised liquor as no filtered white liquor is produced the white liquor tank wlt is in an emptying process feeding clear white to the cooking or bleaching process in the kraft pulping process raw green liquor rgl is fed from the equalizing tank eqt to the common filter apparatus glf wlf the resulting filtered green liquor is fed from the common filter apparatus glf wlf to the green liquor tank glt in fig5 are shown a number of white and green liquor cycles in sequence operated according to the inventive method typically within a 10 hour total cycle there are preferably a first white liquor cycle during 1 8 hours followed by a first green liquor cycle during 2 8 hours and repeated with a subsequent second white liquor cycle during 1 8 hours followed by a second green liquor cycle during 2 8 hours after the white liquor cycles there are preferably only an emptying of the common filter apparatus glf wlf from causticizised white liquor during the time interval a but after the green liquor cycles there are preferably not only.