Modelling, System Identification and Control of an Evaporative Continuous Crystallizer

摘要

Crystallization from solution is characterized by the production of a spectrum of differently size crystals, called the Crystal Size Distribution or CSD. In order to control the CSD, three major requirements have to be met, which are the availability of (1) reliable on-line CSD measurements, (2) an accurate model of the process dynamics in a representation suitable for control design and (3) effective process inputs. The thesis is focused on the second requirement, which involves research on physical modelling, simulation, the derivation of state space models, suitable input and output variables for control of the CSD and the assessment of experimentally validated models for the dynamics of crystalizers. It starts with a discussion of the two crystallizers used in the investigation (the 20 liter and the 970 liter crystallizer) and the measurement system available for on-line CSD measurements of the 970 liter crystallizer. The approach of system identification is investigated. This technique is applied to the experimental data of the 970 liter crystallizer and a good fit to the observed dynamics is obtained.