A Modelling Tool for Dynamic Simulation of Solution Crystallization Processes
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Abstract
The design of current industrial crystallizers is strongly focused on optimisation of known types of crystallization equipment. To get a better control over the physical events governing crystalline product quality the TU Delft started with the development of a task based design (TBD) strategy, which is an example of a phenomena based approach. Task-based design uses physical phenomena to construct tasks, which are used as building blocks for design. In this research, a modelling tool for dynamic simulation of task based solution crystallization processes is developed. This is an important step towards the long term aim of model-based optimisation driven process synthesis. The developed TBD model can be applied to a wide range of crystallization processes: various crystallization methods, operation modes, configurations and a variety in number of streams, compartments and crystallization tasks. The modelling structure is based on compartmental modelling. A new way to connect tasks to this compartment model is developed. This framework supports rapid generation of consistent process models and facilitates analysis of the influence of individual tasks. The model is implemented in gPROMS. To show the ability to quickly construct networks of units representing all kinds of crystallization processes, three different cases are simulated with the new model. Already existing innovative task based equipment from the TU Delft is also implemented, such as an airlift crystallizer, a membrane unit for solvent removal and an ultrasound vessel for the creation of primary nuclei. The first case simulates batch cooling crystallization experiments of ammonium sulphate in an airlift crystallizer with tasks Growth and Seeding and a cooling curve. The results are in agreement with experimental values. Case 2 shows the effect of individual tasks on a batch adipic acid crystallization system using a membrane unit for solvent removal. To demonstrate the future potential of TBD, in the third case a crystallization process is modelled which is never experimentally tested: continuous crystallization of adipic acid in a cascade of airlift crystallizers. Influence of the crystallizers in series on the CSD width is investigated. As expected, more larger crystals with a narrower CSD are produced in the cascade of airlifts. The results show that the developed structure works well. Using the task-function framework, newly developed tasks can be easily added, such that innovative Process Intensifications can be included in the model. The developed TBD model offers potential for model based process design of innovative task based crystallizers.