Towards Real-Time Control of a Semibatch Crystallization Process by Electrical and Ultrasound Tomographic Techniques

This research work presents a feasibility study to demonstrate the application of Electrical Resistance Tomography and transmission-based Ultrasound Computed Tomography for monitoring and control of micron-sized calcium carbonate crystallization process. Herein, precipitated calcium carbonate production is bind to a carbon dioxide absorption process based on hollow-fiber membrane contactor.
ERT acquisition system is equipped with 16 electrodes with operating frequency of 156 KHz and image capturing frame rate of 2 Hz. The ultrasound tomography equipment consists of 32 piezoelectric transducers at a frequency of 200 KHz. These sensors are sensitive to changes in suspension density and conductivity. Furthermore, a process control framework is developed by utilizing the fundamental relations of settling velocity of particles. Through simulations in the LabVIEW software, the PI-based feedback controller demonstrates a possibility of setpoint tracking by manipulating the control variable (mixing speed). Upon further investigations, this approach can be used as a multi-dimensional process analytical technology tool for quality assurance and malfunction diagnosis when out-of-specification events occur throughout the entire process.