Process Equipment and Plant Design
Pick out the wrong statement about the design of a sieve plate column.

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
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

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Process Equipment and Plant Design
Liquid gradient over a tray can be minimised by

Providing a higher skirt clearance or a higher weir
Using split flow, radial flow or cascade flow for column diameter large than 4 ft
All of these
Decreasing the number of rows of caps through which the liquid flows or by decreasing the velocity of liquid flow past the caps or by reducing the distance along the tray through which the liquid must

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Process Equipment and Plant Design
The function of manholes provided in the shell of a distillation column is to

All of these
Give access to the individual trays for cleaning, maintenance and installation
Guard against foaming & entrainment by dumping antifoaming agent through it
Keep a check on the liquid gradient over the plate by direct visual observation

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