Fig. 5 refers to a direct comparison between an external and
an internal reflux column, both operating at 12.2 MPa and with
S/F = 100. The former column is isothermal and operates at 50 ◦C.
The same temperature was fixed for stages 2 – N in the internal
reflux column. The behaviour of the two columns was studied
varying the reflux ratio (L0/D) or the top temperature (T1), respectively.
As can be observed from Fig. 5, an increase of the top stage
temperature in the range (7–15) ◦C can generate an internal reflux
with effects similar to external reflux ratios from 1.7 to 5.5. Furthermore,
for a stated Xhr, the internal reflux gives better results
in terms of recovery. This fact is also observed in process simulations
referred to other operating parameters (data not shown), such
as different pressure and/or S/F and/or temperature. In all cases
the internal reflux column leads to better or approximately same
recovery, given the other process parameters.