CHLORINE FREE PULPING AND BLEACHING SEQUENCE

摘要

23 Kraft pulp is bleached to acceptable brightness without the use of chlorinated organic compounds, yet it still has commercially acceptable strength properties. During production of the kraft pulp it is subjected to extended delignification, by adding kraft white liquor to a first recirculation loop in the digester, and a second, wash, recirculation loop in the digester. Then the pulp is subjected to hot alkali extraction; followed by two oxygen stages; then preferably acid washing to prevent the buildup of heavy metals; and then is subjected to ozone bleaching at medium consistency. The bleaching sequence after acid washing may be ZEZPZ, and the E stage may be an oxidative peroxide extraction stage.