In this article it is shown that moment models for batch crystallization processes are orbitally flat. The state dependent time scaling involved in orbital flatness is physically meaningful and leads to a notion of time that is very natural for the crystallization process. A procedure is presented to check if a desired final crystal size distribution (CSD) is achievable and to compute the temporal temperature profile that produces this desired CSD. Furthermore, the problem of dynamic optimization of the crystallizer operation is reformulated based on the system's flatness property such that the differential equations are eliminated from the optimization problem. In a case study the effectiveness of this optimization is demonstrated.