Real-time monitoring and insights into process control of micron-sized calcium carbonate crystallization by an in-line digital microscope camera

Abstract

In the present study, a crystallization monitoring unit consisting of an in-situ digital microscope camera and real-time image analysis is utilized for monitoring and control of a micron-sized, liquid-liquid crystallization of calcium carbonate. The crystallization process is integrated with a membrane contactor-based carbon dioxide capture process to demonstrate a sustainable CO2-to-chemical unit operation. The measurement probe transilluminates the crystal suspension and provides a live view from the crystallizer. In a series of open-loop experiments, the effects of several operating conditions such as feed flow rate and volumetric power on crystal size and particle count are investigated. For comparison purposes, solid product crystals are assessed with an offline laser diffraction technique. In the closed-loop experiments, the controlled variable is average particle diameter, and the manipulated variable is mixing intensity. The implemented set-point tracking PI controller generates actuating signals based on real-time image analysis measurement of the crystal size. Experimental results demonstrate a practical approach for measuring micron-sized particle suspensions, which is a challenge for particles with a mean diameter smaller than 15–20 μm, provides insights into the mixing intensity-based particle size controllability in fast-reaction precipitation systems and offers a framework to implement a direct design feedback control policy.