Intensification of the G/L absorption in microstructured falling film application to the treatment of chlorinated VOC's. Part III: Influence of gas thickness channel on mass transfer

A falling film micro-absorber (FFM) is used to treat gas effluents containing a chlorinated VOC. In such operation, mass transfer can be enhanced by optimizing micro-absorber geometry and operating conditions. Firstly, the influence of gas cavity thickness and gas flow rate on absorption performances, were investigated. Experimental study is performed for a range of cavity thickness between 2 and 6 mm and gas flow rate between 45 and 390 N mL/min. Results showed a significant improvement of absorption rate when cavity thickness is reduced, especially for low gas velocities. Indeed the global mass transfer coefficient K G a can be multiplied by 7 when cavity thickness is divided by a factor of 3. The mass transfer is then intensified and apparatus compactness is enhanced. The modeling of gas/liquid mass transfer ( Monnier and Falk, 2011 ) indicated that mass transport is performed mainly by diffusion. A new simulations showed an important axial dispersion in gas concentrations profile when gas flow rate and gas cavity thickness are relatively high ( t G =5–6 mm, G V >400 N mL/min). Then, to optimize micro-absorber performances, the integration of gas turbulence promoters must be considered. The second part of this paper concerns the characterization of gas-side mass transfer in the FFM. A dimensionless correlation is developed: S h G = 2.04 R e G 0.23 S c G 0.5 ( t G / Z ) 0.17 When compared to other relations found in literature, this correlation characterizes gas laminar flow in this kind of micro-structured device.