In Situ Measurement of 3D Crystal Size Distribution by Double-View Image Analysis with Case Study on l‑Glutamic Acid Crystallization

An in situ measurement method is proposed for monitoring three-dimensional (3D) crystal size distribution (CSD) during a crystallization process, based on a binocular microvision system. The stereo particle shape is reconstructed from double-view images captured by two microscopic cameras fixed at different angles outside the crystallizer. To overcome the influence from solution turbulence and uneven illumination background involved with in situ imaging, a microscopic double-view image analysis method is established to identify the key corners of each particle shape in the captured images, including corner detection and corner matching. Two fast algorithms are therefore given for online detection of two typical crystal morphologies of prismatic and needle-like shapes, such as α- and β-forms of l-glutamic acid (LGA) crystals, respectively. On the basis of the identified key corners for different particle shapes, a 3D geometry model is established to approximately reconstruct the 3D shape for each imaged particle, such that 3D sizes of each particle could be quantitatively estimated, along with the particle volume. Experiments on the LGA cooling crystallization are performed to demonstrate the effectiveness of the proposed method.