Process Equipment and Plant Design
Generally, elliptical dished heads

Resist half the pressure rating compared to hemi spherical head provided on the cylindrical shell of the same thickness and diameter
Are approximately as strong as seamless cylindrical shell having the corresponding I.D and O.D
Are manufactured on 2:1 ratio of major to minor axis and is recommended to be used for pressure vessels operating above a pressure of 1.5 MN/m²
All of these

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Process Equipment and Plant Design
Bubble cap tray is the most commonly used tray in large distillation column, because

It eliminates the foaming and entrain-ment tendency during operation
It incurs less pressure drop as compared to any other try designed for the same duty
None of these
Of its flexibility and nearly constant efficiency under varying conditions of operation

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