The physical properties of the fluids being processed can be studied and calculated by the methods of Edmister (2) and Maxwell (3). The API Data Book (4) is also useful.

The interrelationship between trays, reflux and fractionation requirements are discussed in Reference 5 which presents a correlation similar to Packie (6). Later independent work has suggested that, for a more realistic approach, the systems should be calculated neglect-., ing the presence of n-butane and all lighter components.

The use of pumparound reflux in these towers is almost universal. Pumpback reflux to the side sections of the tower is seldom used and, then, only in cases where a sharp separation between the cycle oils is required.

Keeping these points in mind, the tower is calculated in the same general way as is a crude tower.

Properties of Tower Feedstream (Reactor Effluent)

The composition of a catalytic cracking unit reactor product stream is usually described as a mixture of discrete light ends consisting of hydrogen through the Cs's, light t.

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