Abstract Summary (Max 250 words)
In the cooling crystallization process for potassium chloride production from seawater-derived concentrated brine, small crystal growth rate results in small crystals and poor solid–liquid separation efficiency. To address this issue, a draft tube (DT) is often placed in stirred vessels to control the vertical flow and promote particle agglomeration. Herein, the impact of the DT geometry on the solid–liquid hydrodynamics was investigated to identify the mechanisms promoting agglomeration and determine the optimal scale-up criteria. Single-phase flow was simulated using computational fluid dynamics (CFD) with the SST k-ω turbulence model. The simulations were validated by comparing the velocity profiles with particle image velocimetry measurements. The spatial crystal size distribution and crystal concentration in multiphase flow were evaluated using an Eulerian-Eulerian approach incorporating a granular model coupled with a discrete population balance model (PBM). The top-mounted impeller generated an upward flow inside the DT, enhancing particle suspension within the DT region. Compared with a straight DT, an inverted conical DT with a steeper gradient (top–bottom = Φ60–30) promoted particle suspension and internal recirculation. These flow characteristics are expected to increase the frequency of gentle particle–particle collisions, thereby promoting agglomeration. Furthermore, the upward flow rate was optimized by adjusting the rotational speed, leading to increased floating from the bottom of the vessel and greater crystal suspension inside the DT. Experimental crystallization using the Φ60–30 DT also demonstrated superior performance relative to the straight DT, indicating that the proposed simulation is a reliable tool for crystallizer design.
