EFFECT OF PULP DELIGNIFICATION DEGREE AND BLEACHING PROCESS ON AN EUCALYPTUS FIBER LINE PERFORMANCE AND ECONOMICS

摘要

Industrially made kraft pulps obtained by a modified cooking process may contain 60-75 mmol/kg of hexenuronic acids (HexAs),which represents 6-7.5 kappa units.HexAs do not react with oxygen and very little of it is actually removed across the oxygen delignification stage,causing low efficiencies in the range of 25-35%.In this study,a thorough economical evaluation of the ECF bleaching processes was carried out,having none and double-stage oxygen delignification,when applied to eucalyptus pulps of kappa varying in the range of 14-21.The bleaching processes included sequences containing specific stages for HexAs removal (Z,A/D and D_(HT)).The results indicated that fiber lines already equipped with oxygen delignification will benefit from terminating the cook at higher kappa numbers (17.5-21) and proceeding with the sequence D_(HT)(PO)DP.A more thorough economic analyses for a green field mill,using WinGEMS simulation,suggested that cooking to lower kappa numbers generated higher revenue free cash value and IRR at 40/MWH power sale value.Oxygen delignification showed a slightly higher revenue and IRR.The sequence O/OD_(HT)(PO)DP at 14.1 kappa number had the highest IRR (14.28%) and A/D(PO)DP a 20.9 kappa number had the lowest IRR (13.52%).