ENCHANCEMENT OF TRAY EFFICIENCY IN COLUMN MASS-EXCHANGE APPARATUS

Abstract

     Technological calculations of the column mass–exchange apparatus assume instantaneous transfer of volatile components of vapour and liquid phases, without considering the residence time the liquid on the trays. There is a threshold below which the contact time between the phases is insufficient to reach equilibrium, and as a result, the efficiency of commonly used tray types does not exceed 0.4-0.6.

    The aim of the work was to study the phase equilibrium between liquid and vapour in the ethanol-water system under subatmospheric pressure; to select appropriate methods for thermodynamic thermodynamic validation of experimental data; to develop approaches for modeling mass transfer between liquid and vapour in cyclic column apparatuses in order to increase  tray efficiency; and to evaluate their effectiveness in processing of ethanol–containing fractions under industrial conditions.

      Research methods included analytical, computational, physicochemical and chromatographic techniques using instruments and methodologies applied in the production of rectified ethanol. The custom-designed experimental apparatus was developed, which allowed to increase the accuracy measurements and reduced the time required to achieve phase equilibrium to 30–40 min. Experimental data on phase equilibrium in the ethanol-water system were obtained in the pressure range of 103 to 50.6 kPa specifically in the low ethanol concentration region (below 3.0 mоl. %), which corresponds to the operation conditions in the lower sections of distillation and rectification columns. Based on the experimental data, phase equilibrium modeling was performed for the specified pressure. The Tsuboko-Katayama equation was used for modeling. Thermodynamic validation of the results demonstrated a satisfactory level of agreement between calculated and experimental data. Phase equilibrium curves were constructed, the relationship between ethanol evaporation coefficients and pressure was established, and the inversion of equilibrium curves was identified.

       Mass transfer methods between liquid and vapor under controlled cycles of liquid holdup and overflow have been developed, along with designs of mass-exchange apparatus for their implementation. The hydrodynamic operating modes of trays under cyclic conditions have been determined. Experimental results have shown that the extending the contact time between phases on the trays to 30-60 seconds significantly increases the efficiency and reduces steam consumption up to 40%.