The Draft Tube Baffle (DTB) Crystallizer, used in applications requiring narrow crystal distribution, and larger average crystal size, has been examined widely in crystallisation theory. The basic choices of the type of crystallizer for continuous operation are few: the design engineer has to choose between a mixed tank, a fluidised bed (also known as "Growth" type or OSLO) crystallizer, and a Draft Tube Baffle (DTB) crystallizer. The nature of a mixed tank is self-explanatory, and needs no further elaboration. It is the workhorse of crystallisation processes, and is best understood, because its simple nature lends itself to practical modelling and experimentation. The bulk of batch and continuous crystallisation theory is based on work done with this type of crystallizer, the Mixed Suspension, Mixed Particle Removal (MSMPR) unit. The OSLO crystallizer has been in use for most of this century, and has been employed in cases where a large crystal size is required. It features a crystal bed, which is fluidised by a supersaturated solution. This allows for crystal growth without any mechanical mixing, and can generate very large and well-defined crystals. It is very difficult to model this type of unit in smaller scale, because of geometric limitations; also, its nature is such that basic design parameters must be based on assumptions that are difficult or impossible to verify in the field. As a result, theoretical work on the OSLO is limited, and this raises a severe handicap in scale-up or troubleshooting operations of such units. The understanding of an OSLO, therefore, is case-specific and based on empirical evidence. The third option, the DTB, is a combination of an MSMPR crystallizer and a classifier. It has been in use for about the last forty years, more or alternative to the OSLO in fulfilling large-crystal requirements. Although the DTB has been marketed by very few crystallisation designers, it has been studied well both by its creators and by Academia. While it also suffers the disadvantage of not being easily reproduced in small scale, for the same reasons as the OSLO, the design parameters are easy to define and control accurately. As a result, its understanding is based on well-proven theoretical work, and this makes the DTB easy to apply to new crystallisation systems, troubleshoot, and optimise. The simplest DTB crystallizer comprises two distinct functions and two distinct regimes : the regime