Task-based design techniques for crystallization processes
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Poster Session (EPIC - Poster) - P2
Keywords: Crystallization, conceptual design, attrition, crystal growth, bubble column
Crystallisation is one of the oldest and economically most important separation technologies in chemical industry. Many interacting physical phenomena occur in industrial crystallizers. This complicates model-based optimization studies and reduces flexible operation and design. The selection of crystallisation equipment is traditionally made out of a set of available crystallizers followed by optimization of that particular type of equipment. This reduces the design space and creative input of a designer. Furthermore, optimization of each individual physical phenomena is not possible because in present industrial crystallizers these phenomena are strongly interrelated.
To improve on these drawbacks a more synthesis-focused design approach is proposed called task-based design. In the task-based design approach an attempt is made to conceptually built-up the crystallization process from fundamental building blocks called physical tasks. Tasks can be connected in a network to accomplish the complete transition of a feed into a desired product. The aim is to generate alternative ways of structuring the tasks, leading to a task superstructure that contains all possible and relevant tasks and their interconnectivity. Optimization of the task superstructure can be realized based on product quality, throughput or economic evaluation of the process and can be subject to design constraints. The task based design approach is more flexible than traditional design approaches and allows for the optimization of each individual crystallisation task. In this way a much larger solution space is created which is needed to arrive at process intensification.
One of the key challenges of the task based design research is to control a certain crystallization task independently from the other tasks, which makes optimization of that particular task possible. In that perspective, a novel crystallisation configuration that mainly facilities the task crystal growth is studied. The setup consists of a bubble column in which supersaturation is created by simultaneous cooling and evaporation of the solvent (flash cooling) by sparging air. The crystals are kept in suspension by the upward velocity of the bubbles, eliminating the need for a stirrer or a circulation pump. In this way attrition caused by crystal-impeller collisions is absent. Moreover, the generation of supersaturation is nicely distributed along the complete length of the column. Experiments on lab-scale show the feasibility of the concept. Both batch-wise and continuous experiments show that both a relative low amount of seeds and a feed slurry can grow out without any significant nucleation.
Finally, the use of membranes is discussed as they can be used to optimize the generation of supersaturation independently from the other crystallization tasks.
Presented Thursday 20, 13:30 to 14:40, in session EPIC-1: Poster Session (EPIC - Poster) - P2.
