Efficiencies Flashcards
(14 cards)
Name four factors on how fluid viscosity and surface tension affect efficiency in a distillation column.
Bubble size (SA)
Rising and settling velocity (vapour/liquid contact time)
Diffusivity (mass transfer)
Flow regime (froth, spray)
How do bubble cap trays work?
Vapour rises through risers under bubble caps, then flows sideways and bubbles up through the liquid on the tray. This forces good vapour–liquid contact.
How do sieve trays work?
Vapour rises directly through holes in a flat tray plate and bubbles through the liquid. There are no moving parts.
How do valve trays work?
Vapour flows through holes that have movable or liftable caps (valves). The valves lift with vapour flow and regulate passage to maintain efficient contact.
3 advantages of bubble cap trays?
Very good vapour–liquid contact
Work well at low vapour flowrates
Less prone to weeping or dumping
3 advantages of sieve trays?
Simple design and cheap to manufacture
Low maintenance (no moving parts)
Low pressure drop
3 advantages of valve trays?
Self-adjusting for different flowrates
Wider operating range than sieve trays
More efficient than sieve at low-to-medium loads
3 disadvantages of valve trays?
More complex than sieve trays
Slightly higher cost
Moving parts may wear over time, get jammed or have higher potential to foul
3 disadvantages of sieve trays?
Can weep at low vapour flowrates
Narrow operating range
Less flexible for varying loads
3 disadvantages of bubble cap trays?
Most expensive and mechanically complex
Higher pressure drop
Harder to clean and maintain
Name 3 factors that affect stage efficiencies.
Liquid and vapour flow rates
Stage geometry (weir height, hole size, flow paths)
Physical properties (viscosity and surface tension)
Name 5 hydraulic regimes on tray.
Bubble
Cellular Foam
Froth
Spray
Emulsion
What happens if vapour flow rate is too low?
Weeping
Liquid drops
What happens if vapour flow rate is too high?
Flooding and entrainment
When vapour flow is too high, it can carry liquid upwards (entrainment) or block liquid from flowing down (flooding).
