Piotr M. Machniewski

Hydrodynamics and ozone mass transfer in a tall bubble column

In the paper, major hydrodynamic parameters such as gas hold-up, phase velocities and axial dispersion as well as the ozone mass transfer coefficients in the liquid phase have been investigated in a tall bubble column for co-current, counter-current and semi-batch modes of operation. The major emphasis has been placed on evaluation of the dynamic characteristics of the combined system of experimental column and measuring sensors, which was applied in the subsequent determination of the axial dispersion and ozone mass transfer coefficients in the liquid phase. The ozone mass transfer coefficients have been estimated using two treatment methods of the recorded changes of ozone concentration in the liquid and gas phases with time during ozone absorption or stripping to an inert gas.

Performance of confined plunging liquid jet bubble column as a gas–liquid reactor

The volumetric mass transfer coefficient in a confined plunging liquid jet (CPLJ) bubble column absorber was determined during a steady-state absorption of CO 2 in sodium carbonate and bicarbonate solution with an addition of hypochlorite catalyst. Special care was paid while choosing the suitable reaction rate to account for the two different zones in the absorber (mixing zone and pipe flow zone) where the volumetric mass transfer coefficients differ by an order of magnitude. The determined mass transfer coefficients reached 0.6 s -1 and appeared to be 50% lower than those determined during physical absorption of CO 2 . Energetic efficiency of the examined CPLJ contactor was also calculated.

Mass transfer in a confined plunging liquid jet bubble column

Abstract A model of confined plunging liquid jet bubble column absorber is formulated and utilized for the interpretation of the experimental data obtained during steady-state absorption of concentrated gaseous CO 2 in water. A strong variability of molar flux of the gas phase in the contactor was observed and taken into account. Two zones differing in mass transfer and mixing characteristics are distinguished within the contactor. Volumetric mass transfer coefficient in the mixing zone beneath the impingement point, is an order of magnitude greater than in pipe flow zone and determines the overall performance of the contactor.

Liquid recirculation and bubble breakup beneath ventilated gas cavities in downward pipe flow

The dispersion of bubbles into down-flowing liquids is often encountered in a number of industrial applications involving pipe flow, bubble columns and loop reactors. Usually a gas horizontal sparging device is used to generate bubbles that are carried downward with the bulk liquid flow. At low gas flowrates discrete bubbles are formed. However, at higher gas flowrates a ventilated cavity attached to the sparger is formed. For downward pipe flow the liquid forms an annular jet, which entrains gas into the recirculation region immediately beneath the ventilated cavity. The rate of gas entrainment and the size of the bubbles produced is determined by the pipe diameter, liquid and gas volumetric flowrates and the strength of the recirculation region below the base of the ventilated cavity. In this study a model was developed to predict the liquid velocity field and bubble breakup in the recirculation region. The velocity profile was modelled using the potential flow solution of the Hills vortex, where the strength of the vortex was assumed to be directly proportional to the velocity of the annular wall jet. The proportionality constant was found to be 0.38, based on predictions obtained using the commercial code CFX. The CFX velocity profile predictions for the central part of the recirculation region were very similar to the Hills vortex velocity profile. Bubble breakup was modelled using a critical Weber number concept, based on the predicted velocity profile within the recirculation region. It was found that the prediction of bubble size was in general agreement with experimental observations when a critical Weber number of 4.7 was assumed. A digital high-speed video was used to observe the liquid and bubble motion at the base of the ventilated cavity. The video was used to obtain estimates of the recirculating liquid flow velocity, which compared reasonably well with predictions based on the Hills vortex model. The video evidence also highlighted the unsteady nature of the flow, particularly the actual gas entrainment process, and possible reasons for this behaviour are presented.

Degradation of Nitroaromatics (MNT, DNT AND TNT) by AOPs

Abstract Application of selected AOPs to degrade nitroaromatics (nitrotoluene, dinitrotoluene and trinitrotoluene) in wastewater discharged from the production of TNT has been investigated. The first stage of the experiments was devoted to test the extent of degradation and improvement in biodegradation of the pure nitroaromatics using different AOPs: ozone alone, O3 + H2O2, O3+ UV, and Fenton reaction (Fe2+ + H2O2) at the various experimental conditions (pH, ozone concentration in the inlet gas, presence of radical scavengers). In the second stage degradation of the industrial wastewaters has been examined. Simple ozonation and the Fenton oxidation process were found to be the most effective.

Modeling of Ozone Reaction with Benzaldehyde Incorporating Ozone Decomposition in Aqueous Solutions

Ozonation of benzaldehyde in its aqueous solutions based on mechanistic approach and incorporating ozone decomposition model is presented in this work. As the basis the modified and extended HSB model of ozone decomposition with phosphates and carbonates reactions included has been applied. It was then tuned with the literature data and the results of our own measurements on ozone decay in aqueous solutions. The model was extended to model benzaldehyde oxidation reactions in the aqueous solutions. Model predictions compare favorably against experimental data obtained in the range of pH 2.3 to 8 with or without radical scavenger (t-butanol).