Multiscale modeling and control of pulp digester under fiber-to-fiber heterogeneity

Abstract

In kraft pulp digester, lignin in wood chips is removed through delignification by hydroxide and sodium sulfide solution. Since both macroscopic and microscopic properties of wood pulp significantly affect the attributes of paper products, several multiscale modeling frameworks have been developed. However, these models did not consider fiber-to-fiber (F2F) heterogeneity; it is an important challenge these days as the fibers are provided from multiple sources to meet the increasing demand. Therefore, we developed a multiscale modeling framework to describe the evolution of heterogeneous fibers in a digester by running multiple kinetic Monte Carlo simulations in parallel. Specifically, the F2F heterogeneity is incorporated by introducing variation in heat capacity and dissolution rate for each fiber. Based on the developed multiscale model, we also designed an offset-free model predictive control system to regulate the cell wall thickness distribution of fibers as well as Kappa number in a pulping process.