TOWARDS EFFLUENT-FREE TCF-BLEACHING OF EUCALYPTUS PREHYDROLYSIS KRAFTPULP

Based on Lenzing's experience in new bleaching technologies, TCF bleac hing of eucalyptus prehydrolysis kraft pulps for the production of dis solving grades with high reactivity, defined intrinsic viscosity and h igh alpha-cellulose has been developed. Prebleaching conditions have s hown to be of crucial importance for the overall selectivity, therefor e main emphasis was directed towards optimization of the prebleaching stages. Evaluation of laboratory experiments resulted in close correla tions between the conditions of TCF-bleaching and important quality pa rameters, such as alpha-cellulose content, intrinsic viscosity and bri ghtness, which is a prerequisite for the production of dissolving grad es with defined and constant quality. In a set of experiments bleachin g stages with different amounts of fresh water addition to a closed cy cle have been simulated. The effect of carry-overs of different origin on the overall bleaching efficiency and selectivity will be described in detail.