On the modeling of continuous kraft pulp digesters: Inclusion of wood characteristics

In order to improve the pulp quality, it is essential to understand the influence of wood characteristics in the Kraft process, highlighting the methylglucuronic (MeGlcA) and hexenuronic (HexA) acids contents, and the syringyl/guaiacyl (S/G) ratio. Since their monitoring is still inefficient, it becomes difficult to use fully data-driven modeling approaches. Therefore, it is important to improve consolidated phenomenological models. In this work, an extended Purdue model was developed to simulate a continuous kraft pulp digester. Unlike most works, we considered the formation of HexA from MeGlcA and the dissolution of both compounds. We also considered the contribution of HexA to the kappa number, an important key performance indicator. As an innovation, we proposed the addition of the S/G ratio influence on the delignification rate of hardwoods by using experimental data taken from literature. The steady-state profiles and dynamic responses were similar to those found in the base work. The blow-line kappa number was 20% higher than that obtained disconsidering HexA. By performing a sensitivity analysis, the steady-state profile of kappa number proved to be very sensitive to variations in the S/G ratio. Thus, the results confirmed the importance of wood characteristics in the kraft pulping.