Calcination of diatomite is an expensive process frequently resulting in products with unpredictable structure. Alternatively, calcination in swirling flow is an energy-saving option. Computational fluid dynamics modeling of an experimental calcination process unit is presented. Experimental results and systematic collection of process data were used to define boundary condition for steady-state and transient simulation runs. The comparison of experimental and simulation results shows the complexity of the calcination process. The results can be used for further process optimization.