Device for producing crystals

An apparatus and a process for crystallizing substances from solutions or dispersions containing these substances, in a crystallizer containing a classifying zone (3), comprise a) an inner and an outer circulation system (1; 2), the inner circulation system (1) being present in the crystallizer, the inlet of the outer circulation system (2) being connected to the inner circulation system (1) via the classifying zone (3), the outer circulation system, being present outside the crystallizer, the outlet of the outer circulation system (2) being connected to the inner circulation system (1) of the crystallizer, and a means for dissolving crystals being arranged in the outer circulation system (2), before its outlet, b) an inflow (4) for solution and/or dispersion, which inflow is present on the crystallizer or on the outer circulation system, and c) an outflow (5) for dispersions, which outflow is arranged on the crystallizer or on the outer circulation system. The novel apparatus has the special feature that a line (8) connecting the outer and inner circulation systems (1; 2) to one another and intended for transporting (recycling) dispersion and/or a line (8) for transporting (recycling) dispersion are additionally present, in which both its entrance and its exit are connected to the inner circulation system (1).