The document discusses different types of distillation trays including sieve, valve, and bubble-cap trays, highlighting their design features, operational efficiency, cost, and maintenance aspects. Sieve trays are identified as the cheapest and suitable for most applications, while bubble-cap trays are more efficient at low vapor rates but more expensive. Additionally, structured packing is presented as an alternative to trays for higher efficiency in vapor-liquid contact and reduced height in columns.

2.  TRAYS
 BUBBLE CAP TRAYS
 SIEVE TRAYS
 VALVE TRAYS
 PARAMETERS FOR TRAY DESIGN
 STRUCTURED PACKAGING
 TRAYS VS PACKAGING

3.  To provide liquid holdup in order to achieve the
proper vapor-liquid mass transfer that the distillation
process requires for separation.
 The function of a tray is to facilitate contact between
the vapour phase and liquid phase so that mass
transfer between the two phases can take place.
 Each tray can be considered as being made up of
three sections: weir, bubbling area, and downcomer.

4.  The function of a weir is to maintain a desired liquid level
on the tray.
 Downcomers are used to guide liquid flow from an upper
tray to a lower tray.
 The bubbling area is the place where vapour-liquid
contact takes place. Vapour flows through the openings on
the tray from below, and into the liquid flowing across the
tray, forming a foaming, turbulent mixture.
 In the simplest design, sieves are provided for vapour-
liquid contact.
 Alternatively, valves or bubble-caps may be used.
During this foaming process, a high interfacial area for
efficient vapour-liquid mass transfer is produced.

5.  Trays are supported in a vessel by means of support rings
or beams.
On the operating principles, there are three common types
of trays:
1. Sieve
2. Valve
3. Bubble-cap

6.  Riser or chimney fitted over each hole, and a cap that
covers the riser.
 The cap is mounted so that there is a space between riser
and cap to allow the passage of vapour.
 Vapour rises through the chimney and is directed
downward by the cap, finally discharging through slots in
the cap, and finally bubbling through the liquid on the
tray.

8.  Sieve trays are simply metal plates with holes in them.
 Vapour passes straight upward through the liquid on the
plate.
 The arrangement, number and size of the holes are design
parameters.

10.  Perforations are covered by liftable caps.
 Vapour flows lifts the caps, thus self creating a flow area
for the passage of vapour.
 The lifting cap directs the vapour to flow horizontally into
the liquid, thus providing better mixing than is possible in
sieve trays.

12. Cost
 Bubble-caps are appreciably more expensive than sieve or
valve trays
 The relative cost will depend on the material of
construction used.
 Due to its simple design, sieve trays are normally the
cheapest.

13. Operating Range
 Bubble-cap trays have a positive liquid seal and can
therefore operate efficiently at very low vapour rates.
Sieve trays rely on the flow of vapours through the holes
to hold the liquid on the tray, thus cannot operate at very
low vapour rates.
 Valve trays are intended to give greater flexibility than
sieve trays at a lower cost than bubble-caps.
 Thus, bubble-cap trays have the widest operating range,
followed by valve tray, and sieve tray.

14. Pressure Drop
 This factor will be important in vacuum operations.
 The tray pressure drop will depend on the detailed design
of the tray, but in general, sieve trays give the lowest
pressure drop, followed by valves, with bubble-caps giving
the highest.
Maintenance
For dirty services, bubble-caps are not suitable as they are
most susceptible to plugging.
Sieve trays are the easiest to clean.

15. SUMMARY
Sieve trays are the cheapest and are satisfactory for most
applications.
 Valve trays should be considered if the specified turndown
ratio cannot be met with sieve trays.
 Bubble-caps should only be used where very low vapour
rates have to be handled and a positive liquid seal is
essential at all flow rates.

16.  Structured packing is formed from corrugated sheets of
perforated embossed metal or wire gauze.
 The result is a very open honeycomb structure with
inclined flow channels giving a relatively high surface
area but with very low resistance to gas flow.
 The surface enhancements have been chosen to maximize
liquid spreading.
 These characteristics tend to show significant
performance benefits in low pressure and low irrigation
rate applications.

17. A tray column that is facing throughput problems may be
de-bottlenecked by replacing a section of trays with
packings. This is because:
packings provide extra inter-facial area for liquid-vapour
contact
efficiency of separation is increased for the same column
height
packed columns are shorter than trayed columns
Packed columns are called continuous-contact columns
while trayed columns are called staged-contact columns
because of the manner in which vapour and liquid are
contacted.

18. [1] R. Perry, D. Green and R. Perry, Perry's Chemical
Engineers' Handbook. New York: McGraw-Hill, 2008.
[2] Distillation Tray Fundamentals. Cambridge University
Press, 2009.
[3] A. Górak and Z. Olujic, Distillation. 2014.
[4]E. Ludwig, Applied Process Pesign for Chemical and
Petrochemical Plants. Houston, Tex. [u.a.]: Gulf Publ, 1997.

19. THANKS TO ALL OF YOU