Development of a Task Based Crystallizer Design

Crystallisation is one of the oldest and economically most important separation technologies in chemical industry. Many interacting physical phenomena occur in crystallization processes, involving nucleation, growth, attrition, agglomeration and classification of crystals. The operating conditions and the spatial staging of the phenomena jointly determine the properties of the crystal particles in a non-uniform manner. The complex interplay between the various physical phenomena poses many challenges to the design and operation of crystallization processes.

A task based design procedure is developed aiming at improved product quality and more flexible process operation and design of industrial crystallization by creating predictive models based on first principles, improving the design of crystallizers by applying new concepts and implementation of advanced model based control. In this novel functionality driven design approach the crystallization process is decomposed into fundamental building blocks. A task is defined as an intentional transformation of matter from a given state to a desired state driven by physical phenomena. The aim of this novel task based design approach is to generate procedures to structure these fundamental tasks in a way that allows for the optimization of complex transformation process from feed stream to final product. In that perspective several experimental setups dedicated to single crystallization tasks were designed and tested. It has been shown, at laboratory scale, that it is possible to isolate a number of crystallization phenomena such as nucleation, growth and supersaturation generation in dedicated equipment.  This not only enabled the optimization of the process conditions to get the best possible results for these crystallization tasks, it also enabled in theory the design of a new generation of crystallizers with superior flexibility in product quality.

Based on the task based design approach new concepts were developed applying alternative methods for the nucleation of crystals, crystal growth and supersaturation generation.

The results show a number of new promising technologies that can be applied in a task based crystallizer approach to achieve better and flexible control of the product quality in industrial crystallization processes. Especially the laser induced nucleation and ultrasound induced nucleation might be effective technologies to control the number of seed crystals, fed into a growth crystallizer such as the airlift reactor.