(353e) Novel Design Strategies for Solution Crystallization Processes
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. As a result of that, optimization of each individual physical phenomenon is not possible because of the strong interrelation of these phenomena in present industrial crystallizers. Recently a more synthesis-focused design approach is developed 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 connectivity. 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. In this contribution an overview of the current state of the art of the design of crystallization processes will be given and the prospects of this novel design approach will be discussed. In particular new operation concepts, which enable the control of certain crystallization tasks independently from the other tasks, will be examined. Results are given of a setup consisting 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 as well as feed slurry can grow out without any significant nucleation. In addition other possible realizations of individual crystallization tasks are discussed like the generation of supersaturation by the use of membranes, and the generation of viable seed crystals to control the product quality in batch and continuous operated processes. Integration of the tasks in the end leads to more flexible operation of crystallisation processes.
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