A semi-continuous crystallizer configuration that combines continuous seeding using a dual impinging jet with growth rate control in a stirred tank was experimentally demonstrated for the manufacture of L-asparagine monohydrate (LAM) crystals with the objective of obtaining a target flattop size distribution. The dual impinging jets combined hot and cold saturated solutions to generate highly uniform 20-mu m crystals that were further grown to a desired size in the stirred tank with suppressed nucleation that was instrumented with attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and focused beam reflectance measurement (FBRM). The construction of calibration models and the measurement of solubility and metastable limit were obtained by an automated system that followed preset supersaturation profiles using feedback control. The experiments confirm that greatly enhanced control of the crystal size distribution can be achieved using continuous seeding. (C) 2012 Elsevier Ltd. All rights reserved.