August 2005 – Due to the azeotrope, an ethanol-water mixture cannot be
concentrated into pure ethanol by simple distillation. Various processes exist
for the production of dehydrated ethanol including entrainer distillation,
pervaporation and dehydration by adsorption of water molecules.
Molecular sieve technology is particularly suited for the dehydration
of ethanol and is therefore being more frequently applied in recent times. GEA
Wiegand has improved this process, offering significant possibilities for
energy integration and heat recovery.
The figure depicts a model
showing the load of a molecular sieve in relation to flow (z axis) and over
time. The foreground shows the active zone (blue) which has the greatest
potential to adsorb water. The water content in the adsorbent then rapidly
rises in the mass transfer zone (green) before passing into the equilibrium
(saturation) zone, shown in red. In this region, no more water molecules can be
adsorbed.
If concentrated ethanol is to be processed, it is sensible to
use the plant configuration shown in the process flow diagram opposite. The
latent heat of the dehydrated alcohol vapours flowing from the molecular sieve
(S 01) is used to generate flash steam (W 01). The flash vapour produced is
recompressed to a higher pressure by means of a jet pump (V 01). This steam is
then used for heating the column (K 01) and rectifying the raw ethanol.
Depending on the boundary conditions, energy savings of up to 40 % are achieved
in this way.
Other concepts can be combined where the dehydration
system is to be integrated within an overall process. GEA Wiegand therefore
specializes in achieving optimum energy consumption levels, significantly
reducing operating costs for the benefit of plant operators at a time of rising
energy prices.
