Technology overveiw

Theoretical part


The most effective separation possible in distillation columns takes place in the hydrodynamic regime where there is perfect displacement of the liquid and vapor streams. This can be achieved in distillation equipment with separate phase movement (SPM). Such an innovative route for process intensification in distillation is called cyclic distillation. Thus, we have come to conclusion that the maximum efficiency of the separated phase motion mode can be achieved under the following conditions:
1) If there is no inter-tray liquid flow during the steam supply;
2) If there is no agitation of liquid on the adjacent trays during liquid flow;
3) in case of the highest possible local efficiency.
The SPM mode that is the separated phase motion reflects a time separation of components (i.e., the separation in time on a contact stage) whereas the stationary mode correspondingly a spatial separation (i.e., the separation along the liquid flow on a contact stage). But under real conditions only the separated phase motion mode can ensure a perfect liquid and steam drive.

Pursuant to W.K Lewis work, the use of combinations of various hydrodynamic models of liquid and vapor phases enhances the efficiency of component separation on the tray. The greatest effect is achieved upon perfect displacement by liquid and vapor and sing-direction movement of liquid on adjacent contact degrees. In such conditions the efficiency of Murphy’s tray may significantly exceed the local efficiency and reach 200 – 300%. In a T. Sommerfeld works it was shown that upon comparison of stationary and cyclic processes both by the time of mass transfer on the tray and by the phase interaction nature, the cyclic process is similar to the stationary process upon single-direction movement of liquid on adjacent contact levels and perfect displacement by liquid and vapor. The longing for obtaining of separation efficiency above theoretical stage of McCabe-Thiele promoted the development of constructive solutions for stationary mode towards longitudinal sectioning on the tray, and for cyclic regime – provision of liquid overflow on the trays with minimum mixing of adjacent trays.

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