Novel Dissolved Lignin Carryover Measurement in O₂ and D₀ Stages Brings Opportunities for Significant Improvements in Fiberline Operations

Abstract

Conventional fiberline control is solely based on the lignin content of the pulp fibers expressed as kappa number combined with brightness measurement in the bleaching stages. The kappa number is measured using a traditional multipoint analyzer with several sample locations sharing the limited capacity of one central analyzer thus resulting in low update rate and lack of redundancy. Some mills still only use manual sampling and laboratory kappa measurement which inevitably means very low update rate and typically also poor repeatability. While the fiber lignin content and brightness indeed are critical parameters for the unit operations' control, it has been shown that the dissolved lignin in liquor phase, often referred to as black liquor carryover, plays a keyrole due to its impact on the occurring reactions. This carryover measurement has been a critical missing link in having a fully automated optimum fiberline process control.

This study presents results from evaluations of two new sensors for capturing the dissolved lignin carryover in the pulp stock, to properly account for its impact in oxygen delignification and chlorine dioxide stages. Mill data is combined with laboratory data which confirms the benefits of these novel control concepts, employing the new sensor tools.

Recent research and mill studies have revealed that if appropriately implemented, these new measurement and control capabilities bring significant improvement potential in fiberline operations, in terms of optimizing pulp yield and quality, production rate, and consumption of bleaching chemicals.