Control Strategy Scheme for the Prehydrolysis Kraft Process

This paper presents a control strategy scheme for the prehydrolysis stage in the prehydrolysis kraft process. The key element of the proposed control strategy is a softsensor, which estimates the rate of the unobservable reactions based on a physicochemical dynamic model of the process. The rate of hydrolysis depends on the wood temperature and hydrogen ion concentration, which can be calculated by estimating the reaction heat due to deacetylation of wood and subsequent wood component degradation reactions. The estimated hydrogen ion concentration and reaction enthalpies are combined with dynamic temperature profile and kinetic reaction models for estimation of the main quality parameters for dissolving pulp, namely the lignin content and the content and degree of polymerization of the alpha-cellulose fraction. The developed model is tested based on parameters approximated from the literature and the feasibility of the model for testing the suggested control strategy scheme is discussed.