Mass transfer analysis in ozone bubble columns

Abstract

An impinging-jet bubble column has been tested for the ozone mass transfer applications in water treatment. Two venturi injectors were utilized to create turbulent gas-liquid jets in the ambient fluid by placing them at an intersecting angle of 125°. The intersecting of the jets caused an increase in the turbulence produced in the ambient fluid and therefore, increased the gas–liquid mass transfer rate. The steady-state one-phase axial dispersion model (1P-ADM) was applied to analyze the dissolved ozone concentration profiles measured in the bubble column by fitting these profiles to the predicted profiles, using the 1P-ADM, to determine the column-average overall mass transfer coefficient (kLa) and liquid-phase axial dispersion coefficient (DL). Two minimization approaches were applied to solve the differential equation representing the 1P-ADM: two-parameter (kLa and DL) and one-parameter (kLa) minimization techniques. To examine the sensitivity of the predicted kLa to changes in DL, DL was estimated first from the tracer experiments. Then, the one-parameter minimization technique was applied to determine kLa. As a result, kLa varied only slightly (<11%) between the two types of minimization techniques. Using the two-parameter minimization technique, kLa and DL values were correlated to the superficial gas and liquid velocities uG and uL, respectively) by power-law relationships. The following correlations were obtained: kLa = 20.54 uG1.13uL0.07 and DL = 2.94 x 10–2uG0.03uL0.18. The 1P-ADM has proven to be an accurate and easy-to use tool for describing the ozonation process in the impinging-jet bubble column as an excellent conformity between the measured and the predicted dissolved ozone concentration profiles was observed. Key words: axial dispersion model, impinging-jet bubble column, mass transfer, ozone.