Simple analytical expressions are developed to model the steady-state operation of a chemical plant with a continuous crystallizer. The equations show analytically how uncontrolled variables change with the changing production rate depending on the values of key kinetic parameters and the choice of controlled variables. Because the results are derived, their validity and limitations are more apparent than heuristics that are suggested based on case studies. Furthermore, because the equations are simple and analytic, it is possible to develop insight and understanding about the behavior of the process. Finally, these results can be readily taught to process engineers and used to rapidly screen alternative control structures for operability problems. Results are illustrated with a case study process to produce adipic acid. (C) 2007 American Institute of Chemical Engineers.