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

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

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Process Equipment and Plant Design
Triangular pitch tube layout as compared to square pitch in a shell and tube heat exchanger

Permits the use of more tubes in a given shell diameter
Both B and C
Facilitates comparatively easier external cleaning because of large clearance
Permits the use of less tubes in a given shell diameter

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