Load and vapour velocity

The term load is used to denote the amount of substance which reaches the column head as condensate in unit time, and is composed of the quantity of reflux plus the amount of distillate removed. In industrial usage it is customary to express the load on a column in terms of the vapour velocity, referred to the free column cross-section. In laboratory practice this figure is calculated only if a comparison with a semi-technical or industrial installation is required. It may be usefully expressed as ml/cm h. 

If it is desired to compare laboratory columns with semi-technical or industrial columns, account should be taken of the fact that the vapour velocities in the former are generally very much lower, and lie in the range of 0.02 to 0.5 m/sec, whilst in 

Specific stage number ( th P i ) a. a function of the load for various packings according to Stage (Refs. chap. 1 [39]) 

Curves 1 — 12 Test mixture benzene-1.2-dichloroethane Curves 13—23 Test mixture n-heptane-methylcyclohexane 

4 = glass Raschig rings, 4.5 x 4.5 mm 0 0 = small glass spheres, 3 mm 0 

---