The document discusses sizing distillation columns for azeotropic distillation. It explains that the column diameter should allow for the maximum vapor velocity to avoid flooding. The tallest column tray with the highest vapor flow sets the minimum diameter. Tray spacing is typically 0.61 m and column height includes space for piping and liquid holdup. Aspen Plus was used to size two columns, TD-101 with 24 trays, 1.53 m diameter, and 16 m height, and TD-102 with 8 trays, 1.2 m diameter, and 4.5 m height. Reflux drum sizing is also discussed.

1. AZEOTROPIC DISTILLATION
Continuing the previous Azeotropic
distillation example:
Distillation column sizing:
The column diameter should be determined
based on the maximum vapor velocity. If the
velocity is exceeded, the column liquid and
vapor hydraulics will fail and the column
will flood.
As the vapor flow rates change from tray to
tray in a non equi-molar flow system, the
tray with the highest vapor velocity will set
the minimum column diameter.
I used Aspen plus to determine the diameter
of the column. You may check the diameter
calculated by Aspen plus using the
following equation and setting f-factor equal
to 1:
𝐹 − 𝑓𝑎𝑐𝑡𝑜𝑟 = 𝑉𝑚𝑎𝑥√ 𝜌 𝑣
Vmax: Maximum vapor velocity (ft/s)
ρv: Vapor density Ib/ft3
Regarding the height of the column, it can
be determined rigorously based on the
following spacing:
1. The total tray height: The typical
distance between trays (tray spacing)
is 0.61 m (2 ft)
2. The space at the top of the column
where the reflux piping enters the
column.
3. The feed tray for feed distribution
piping.
4. The liquid height in the base of the
column that must be determined
according to NPSH of the pump.
However, the design heuristic is to provide
an additional 20% more height than that
required for the trays.
I used Aspen plus in sizing of the columns.
TD-101:
No. of stage 24
Condenser Total
Reboiler Kettle
Tray type Sieve tray
Column Diameter 1.53 m
Column height 16 m
TD-102
No. of stages 8
Condenser Total
Reboiler type Kettle
Tray type Sieve tray
Column diameter 1.2 m
Column height 4.5 m
Reflux drums:
The commonly heuristic holdup time is set
to be 5 min of liquid holdup when the vessel
is 50% full.
Assume L/D = 2.
TD-101 Reflux drum
Diameter 1.32 m
Length 2.63 m
TD-102 Reflux drum
Diameter 0.4 m
Length 0.8 m