Minimum recommended downcomer residence time for the disengagement of entrained vapour is the same for both foaming and non-foaming liquids, which is about 20 seconds
Width of the calming section provided at the inlet and outlet sides of the plate is 75 mm for column diameter below 1.5 metres and 100 mm for larger diameter columns
For segmental downcomers, the chord length is 60-80% of the column diameter. An initial value of downcomer area of 12% is taken in the design
An increased weir height improves the tray efficiency at the cost of high plate pressure drop; optimum wear height being 40-90 mm for column pressure above atmospheric and 6-12 mm for vacuum columns
Tendency towards stable operation is increased by increasing the skirt clearance of the caps, lowering the rate of liquid flow per unit plate width or increasing the spacing between the caps
The dimensionless ratio of liquid gradient to pressure drop head caused by the bubble cap assembly should be less than 0.4
The pressure drop due to the caps & slots and the static submergence should be as high as practicable for reasonable operation
Distillation under vacuum is a substitute for steam distillation
In flash (equilibrium) distillation, a definite fraction of liquid is vaporised in such a way that the evolved vapour & residual liquids are in equilibrium with each other
Flash distillation, differential distillation & steam distillation are all continuous distillation processes
In differential (simple) distillation, the vapour is removed as soon as it is formed without appreciable condensation
EXAMIANS