A model of spray drying behaviour that produces profiles for the particle moisture content, particle temperature and glass-transition temperature was used to predict crystallisation behaviour. This model has been validated in previous work. Here, the model was applied to examine the effects of varying the size of the dryer in terms of the diameter and the length of the main drying chamber, and the effects of changing the bulk gas humidity of the drying air. It was observed by the crystallisation behaviour indicator (called the impact ratio in this work) that increasing diameter and lengths increased crystallisation behaviour until a near-plateau region was reached where increased sizes provided no significant increase in predicted crystallinity. Changes in bulk gas humidity were also seen to increase predicted crystallisation behaviour although condensation effects were identified as limiting factor.