Mass transfer coefficient and gas holdup in rectangular air – lift columns
Advancing the chemical engineering fundamentals
Multifase Flows (T2-5P)
Keywords: Two-phase flow, gas-liquid flow, air-lift column, hold-up, mass transfer
Pretreatment of industrial wastewater is one of basic problems in many branches of industry. Air-lift columns with circular and rectangular cross sections are used successfully to pretreat wastewater near the site of its origin (Chisti 1988,1989). Columns of rectangular cross sections have many advantages in industrial applications over the columns with circular cross sections (Siegel et al. 1991, Couvert 2004, Dziubiński 2000). The most important ones include a maximum use of cubic capacity as a working volume of the column and easy connection of columns into self-supporting systems of desired capacities. In such a system many stages of wastewater pretreatment can be carried out: neutralisation, oxidation, decoloration, defoaming or removal of detergents. A system of columns was constructed and the effect of the column geometry, gas flow rate as well as viscosity and surface tension of liquid on gas hold-up in the air-lift column of rectangular cross section on technical scale with working height 4.2 m and volume exceeding 1.4 m3 was investigated. Correlations were developed which, with the accuracy sufficient for technical purposes, allow us to predict gas hold-up εGr and volumetric mass transfer coefficient kLa for these columns. They complete similar equations published in literature for small laboratory air-lift columns in the range lower by one decade of P/V0 value. A pilot-plant simulation of the pretreatment of effluents from dyestuff production achieving as a result about 90% pollutant reduction in the mixture, measured by the COD index and 72% colour reduction measured by the ABS value.
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Presented Tuesday 18, 13:30 to 15:00, in session Multifase Flows (T2-5P).
