Agglomeration effects, observed during precipitation of barium sulphate in the unpremixed feed two-dimensional tubular precipitator, are studied experimentally and interpreted theoretically. Effects of process parameters on precipitation-agglomeration phenomena are predicted using a CFD based model that describes micromixing (the multiple-time-scale turbulent mixer model is used) and precipitation (including nucleation, growth and agglomeration of crystals). Agglomeration rate is defined as a product of the collision frequency and the probability of agglomeration.