Population balance modeling and passivity-based control of particulate processes, applied to the Silgrain® process

• Main Author: Dueñas Diéz, Marta
• Format: Dissertation
• Language: English

This thesis deals with the systematic development of mechanistic models of particulate processes for the purposes of nonlinear controller design and implementation.The methods investigated in this thesis were illustrated with an industrial hydrometallurgical process called the Silgrain® process (Elkem ASA), for which a model and a controller strategy have been developed from scratch. The class of processes studied in this thesis, particulate processes,has attracted and still attracts a great deal of interest from the international research community. Particulate processes are characterized by the presence of a continuous phase and a dispersed phase comprised of entities that have a distribution of properties. Such a distribution of properties has an important impact on the process operation and quality of the final products. Moreover, most of process industries contain one or more stages that involve particulate processes, among them the major Norwegian companies: Elkem, Hydro, Borealis, Statoil, etc. A systematic method to PBE modeling was suggested, consisting of the following stages: establishment of model purpose and model foundations, building of the model structure, determination of the constitutive relations, selection of a solution method, parameter estimation and model validation. Such an approach is general to any type of process, but when dealing with particulate processes special care should be placed on some of these stages. The method was thoroughly illustrated with the development of the model of the tworeactors of the Silgrain® process. The model was based on the traditional balance equations of mass, energy, and momentum, and on a balance of the distribution of properties, called the population balance equation (PBE). This is the first time PBE is used to model a hydrometallurgical leaching reactor where disintegration takes place. An experimental laboratory campaign had to be carried out in order to determine the constitutive equations of the disintegration event. Another experimental campaign at the plant level was carried out to gather data for parameter estimation and model validation. The results of the fitting were satisfactory. Besides the particular contribution of developing a detailed model for the case study, some general contributions of this research were: • it was shown how dividing the model into compartments according to the regions that are observed in practice in the reactors is key to obtaining realistic models; • it was