Enhancement of eucalypt pulp yield through extended impregnation cooking

The improvement caused by eucalypt chip impregnation on kraft pulping performance was assessed for terminating the cook at kappa in the range of 15-27 and at controlled residual effective alkali (REA) of 6-8 g/L NaOH. Extended impregnation cooking of eucalypt chips (EIC) increased about 10/0 lignin- and HexA-free screen yield gains in relation to conventional cooking (CC), regardless of kappa number in the range of 15-27. The EIC technology allows for cooking eucalypt wood to kappa number up to 27, without rejects production, but without significant improvement in lignin- and HexA-free screen yield and with larger chlorine dioxide (ClO2) consume during bleaching. The optimum kappa number for both CC and EIC cooking was about 19 with similar refinability and strength properties for both technologies, CC and EIC. It was concluded that extended impregnation cooking is an attractive technique for enhancing bleached eucalypt Kraft pulp yield.