Optimising pulp quality in alkali profiled kraft cooks

Alkali profiling techniques have proven to be promising to enhance delignif ication, thereby reducing the bleach chemical demand and effluent treatment load. Previous studies have shown the beneficial effects of alkali profili ng in a batch digester. This kraft pulping modification utilises the princi ple of split alkali addition in a modified batch digester. Split alkali add ition results in lower levels of Effective Alkali (EA) in the initial phase of delignification, compared to a regular kraft cook. Fresh supplemental c hemical is added to maintain EA at desired levels during the bulk delignifi cation stage. The EA is monitored using an in situ conductivity sensor and controlled by adjusting the rate of alkali addition. This study focuses on cooking recipes to enhance lignin removal from pine chips, while improving or maintaining the pulp strength, as measured by viscosity. Various alkali- profiled cooks are compared to a baseline kraft cook to evaluate cooking ef ficiency, The concept of high EA profiled cooks is also introduced. The pul p characteristics for the regular kraft and modified kraft cooks are used t o develop the Kappa number-viscosity relationship for this particular wood species. This Kappa number-viscosity curve can be used to arrive at the des ired combination of pulp properties required for the particular product.