Hydrodynamique et transfert de matière dans un contacteur gaz-liquide multicellulaire

Hydrodynamics and mass transfer in a multicellular gas-liquid contactor

¹ Laboratoire des Sciences du Génie Chimique (Nancy)
² Europoll - Techfina Engenierie

Abstract

The Techfina multicell scrubber is a new gas-liquid contactor that is presented as a regular package in three directions of elementary cells in which the gas and the liquid phases are flowing countercurrently and vertically. The results of experiments carried out first in an elementary cell, with a 80 mm length, 80 mm wideness, 20 mm heigth having a 10 mm distance at the throat and then in packages of several such cells (1 to 9) are reported. The hydrodynamics study shows that when the liquid flowrate L is kept constant while the gas flowrate G is progressively increased the following flow regimes or patterns are observed : trickling flow, surging flow, picking up the liquid by the gas, then loading and flooding. In the flow regime diagram L - G the operating zone is defined for the two-phase flowrates corresponding to an hydrodynamic operation comprised between the "picking up" point and the flooding (figure 3). Typical variations of the pressure drop with the gas flowrates for constant liquid flowrates in an elementary cell are presented in Figure 4. It is observed that the curves always show a discontinuity corresponding to the picking up phenomenum. The same trend is observed for the liquid holdup. The additivity of the pressure drop and liquid holdup in the case of the package of several elementary cells has been checked. Moreover it has been possible to correlate the liquid holdup with the values of the pressure drop corresponding to the same gas velocity at the throat of the elementary cell. This pressure drop is defined as the corrected pressure drop. The mass transfer study leads to the presentation of the performances of the scrubber characterized by the efficiency and the Number of Transfer Unit, NUT. The absorption of dilute SO₂ in air into aqueous NaOH solutions is used in the conditions of an instantaneous surface and irreversible reaction totally controlled by the mass transfer resistance in the gas phase. For an elementary cell the efficiency is approximatively comprised between 50 and 60 % (Figure 6). It has been possible to correlate the variations of NUT with the corrected pressure drop for one and several elementary cells. Experimental data show that the additivity of the performances of the cells is not satisfied because of the hydrodynamics phenomenum of liquid entrainment (priming).