Crystallization processes are characterized by close interaction between particle formation and fluid flow. A detailed physical description of these processes leads to complicated high-order models whose numerical solution is challenging and computationally expensive. For advanced process control and other model based real-time applications, reduced order models are required. In this work, a reduced model for a urea crystallizer is derived from a detailed reference model with two external and one internal coordinate. Proper orthogonal decomposition is applied to all three coordinates to obtain a low-order representation of the system. Nonlinear terms are treated efficiently by best points interpolation. Simulations are carried out to show the good agreement between reduced model and reference model. (C) 2011 Elsevier Ltd. All rights reserved.