the retention time and the crystal mass, to obtain the optimum conditions in terms of crystal specific surface and the fastest possible growth. This is achieved by a separation – to put it simply – of the crystals from the liquid mass, in order to manage the two flows in a different way. The practical way is to perform a gravity settling to be able to extract (and possibly recycle separately) the (almost) clear liquid, while managing the mass flow around the crystallizer to obtain a precise slurry density elsewhere. A typical example is the DTB (Draft Tube and Baffle) crystallizer, an idea of Richard Chisum Bennett (a Swenson engineer and later President of Swenson) at the end of the 1950s. The DTB crystallizer (see images) has an internal circulator, typically an axial flow mixer – yellow – pushing upwards in a draft tube while outside the crystallizer there is a settling area in an annulus; in it the exhaust solution moves upwards at a very low velocity, so that large crystals settle – and return to the main circulation – while only the fines, below a given grain size are extracted and eventually destroyed by increasing or decreasing temperature, thus creating additional supersaturation. A quasi-perfect control of all parameters is achieved as DTF crystallizers offer superior control over crystal size and characteristics. This crystallizer, and the derivative models (Krystal, CSC, etc.) could be the ultimate solution if not for a major limitation in the evaporative capacity, due to the limited diameter of the vapor head and the relatively low external circulation not allowing large amounts of energy to be supplied to the system. See also Abnormal grain growth Chiral resolution by crystallization Crystal habit Crystal structure Crystallite Fractional crystallization (chemistry) Igneous differentiation Laser heated pedestal growth Micro-pulling-down Protein crystallization Pumpable ice technology Quasicrystal Recrystallization (chemistry) Recrystallization (metallurgy) Seed crystal Single crystal Symplectite Vitrification X-ray crystallography References Further reading A. Mersmann, Crystallization Technology Handbook (2001) CRC; 2nd ed. Tine Arkenbout-de Vroome, Melt Crystallization Technology (1995) CRC "Small Molecule Crystallization" (PDF) at Illinois Institute of Technology website Glynn P.D. and Reardon E.J. (1990) "Solid-solution aqueous-solution equilibria: thermodynamic theory and representation". Amer. J. Sci. 290, 164–201. Geankoplis, C.J. (2003) "Transport Processes and Separation Process Principles". 4th Ed. Prentice-Hall Inc. S.J. Jancic, P.A.M. Grootscholten: “Industrial Crystallization”, Textbook, Delft University Press and Reidel Publishing Company, Delft, The Netherlands, 1984. External links Batch Crystallization Industrial