Grażyna Bartelmus

Hydrodynamics and mass transfer in a three-phase fixed-bed reactor with cocurrent gas—liquid downflow

Abstract The paper presents experimental results concerning dynamic liquid holdup, wetting efficiency and local mass transfer coefficients between the liquid and solid surface in a fixed-bed three-phase reactor, in which both the gas and liquid flow cocurrently downwards. The experiments were conducted for two basic regimes of operation of trickle-bed reactors, namely the gas continuous flow regime and the pulsing flow regime under atmospheric pressure. The measurements of dynamic liquid holdup have been performed for a wide range of gas and liquid flow rates, three different packing diameters, and for two systems of working media of different physical properties. The common correlation developed determines with good accuracy the holdup values in both regimes as well as in the transition region between the two hydrodynamic modes. In experiments concerning the wetting efficiency a dynamic tracer method has been employed, for which an original mathematical model has been formulated. The results are presented in the form of diagrams and appropriate correlating formulae. The experiments concerning local solid—liquid mass transfer coefficients were carried out for two diameters of spherical particles, with the flow rates of both phases and physicochemical properties of the liquid varied over a wide range. The experimental results are correlated and compared with the appropriate literature data. A mathematical model describing the time-varying solid—liquid mass transfer process is formulated for the pulsed flow regime. The time-averaged mass transfer coefficients calculated on the basis of the model developed are compared with the experimental values. A good agreement between these two sets of values fully confirms the assumptions of the model elaborated.

Hydrodynamics of a cocurrent downflow of gas and foaming liquid through the packed bed. Part II. Liquid holdup and gas pressure drop

Abstract In the present study the results of experiments have been presented whose aim was to determine the values of liquid holdup as well as gas pressure drop through the packing for systems foaming under the pulse flow regime. On the basis of 245 experimental points for the pulse flow regime the verification of the models describing the hydrodynamics of the system has been performed. Attention was focused on the models of Benkrid et al. (Chem. Eng. Sci. 52 (1997) 4021), Pina et al. (AIChE J. 47 (2001) 19) and Fourar et al. (Chem. Eng. Sci. 56 (2001) 5987). It has been concluded that none of the models analysed describes the hydrodynamics of the foaming systems with enough accuracy. Next, based on our own data-base the verification has been carried out of parameters of Benkrid et al. (Chem. Eng. Sci. 52 (1997) 4021) (‘drift flux’ model for e L and boundary layer model for Δ P / H ) and Pina et al. (AIChE J. 47 (2001) 19) models as well as the estimation of the values of F * α -functions of Fourar et al. (Chem. Eng. Sci. 56 (2001) 5987) model. Using as the criterion the accuracy of estimation of the values of (Δ P / H ) the best results have been obtained by applying Fourar et al. (Chem. Eng. Sci. 56 (2001) 5987) model (for the Ergun constants determined experimentally). The introduction of the estimated F * α -functions into the equations of the model (Eqs. 11 and 12) makes it possible to estimate the liquid holdup with the average absolute relative error not exceeding 9.8% and the pressure drop with an error less than 26%.

Hydrodynamics of cocurrent fixed-bed three-phase reactors.: Part I. The effect of physicochemical properties of the liquid on pulse velocity

The objective of the present study is to evaluate parameters that characterise the pulsing flow regime in a packed column operating with the cocurrent downflow of the gas and liquid phases. The paper presents the results of experiments aimed at determining the effect of the physicochemical properties of the liquid phase and the packing size on the velocity of liquid pulses travelling along the bed. These results are correlated and compared with the available literature data.

Hydrodynamics of a three-phase fixed-bed reactor operating in the pulsing flow regime at an elevated pressure

Abstract Results are presented for a three-phase reactor operating at an elevated pressure in the pulsing flow regime. For the system air–water and pressures of 0.1– 0.9 MPa lines are determined that define the change of the hydrodynamic model from the gas continuous flow regime (GCF) to the pulsing flow regime (PF). Also, parameters are found that characterize the pulsing flow of fluids, namely the velocity of pulses travelling along the bed, the frequency of pulsations and their structure, i.e., the length of the pulses and that of the liquid-rich zone.

Hydrodynamics of pulsing flow in three-phase chemical reactors ☆

Abstract In the present study verification is carried out of mathematical criteria that define the boundary between two hydrodynamic regimes: the gas continuous flow (GCF) regime and the pulsing flow (PF) regime. Attention is focused on the criterion derived using the model of K. Grosser, R.G. Carbonell and S. Sundaresan, AIChE J., 34 (1988) 1850–1860, and the parametric sensitivity of this criterion is analysed. Next, based on the measured values of the gas pressure drop in a reactor the verification of some selected parameters is carried out by fitting the theoretical and experimental boundary lines separating the GCF and PF regimes. Experimental results are also presented concerning the determination of parameters characterising the pulsing flow through the bed, namely the frequency of pulsations and the pulse structure. These parameters were determined for the system nitrogen–water, and also for liquids differing from water in their physicochemical properties.

Hydrodynamics and mass transfer in three-phase cocurrent reactors

Abstract The paper presents experimental results concerning mass transfer between the bulk liquid and the packing surface, along with a mathematical description of this phenomenon. Since the verification of the model proposed requires the knowledge of a number of hydrodynamic parameters which are lacking in the literature, the experiments were carried out to determine the values of these parameters. The paper also summarizes the analyses regarding a mathematical criterion that makes it possible to estimate the values of the operating parameters of the reactor at the moment when the hydrodynamic mode changes from the gas continuous to the pulsing flow regime.

Hydrodynamics of the cocurrent downflow of a gas and a foaming liquid through a packed bed. Part I. Estimation of the transition boundary between the hydrodynamic regimes from the gas continuous flow to the pulsing flow

Abstract In the study the results of investigations are presented aimed at determining such values of the operating parameters for which the change of the hydrodynamic regime occurs from the gas continuous flow (GCF) to the pulsing flow (PF). Nitrogen, helium and argon were used as the gas phase while the liquid phase was formed by the aqueous solutions of the alcohols C 1 –C 4 of the concentrations which ensured the foaming of the system. Thus a wide range of physicochemical properties of the system was covered in the experiments. The present study, as well as Part II, contain a wealth of experimental data which characterise the PF through the packing for the foam-forming systems. It is demonstrated that none of the published mathematical criteria based on the models of the flow describes the transition line between the hydrodynamic regimes (from GCF to PF) with sufficient accuracy. For these types of systems the use of the modified flow map ( Fig. 4 ) is advised or, alternatively, of the equation describing the boundary line between GCF and PF in the following form: Lλψ 0.548 / G =3.12( G / λ ) −1.16 .

Hydrodynamics of a co-current three-phase solid-bed reactor for foaming systems

The objective of the present study was to evaluate the parameters, which characterize the pulsing flow of the gas and liquid through a bed, namely the frequency of pulsation, the velocity of the pulses and the pulse structure, for foaming systems. The paper presents the results of experiments aimed at determining the effect of the foaming power and the surface tension of liquid phase on the values of the measured parameters.

Solid—liquid mass transfer in a fixed-bed reactor with concurrent flow Part II. Mathematical analysis for the pulsed flow regime

Abstract A mathematical model describing the time-varying solid—liquid mass transfer process is formulated for the pulsed flow regime. The enhancement coefficient ρ*, giving the information about how the value of the mass flux varies with time when the liquid ‘plugs’ are arising and migrating through the bed, is derived. The time-averaged mass transfer coefficients calculated on the basis of the model developed are compared with the experimental values published in the first part of the work (Chem. Eng. Process., 26 (1989) 111–120). A good agreement between these two sets of values fully confirms the assumptions of the model elaborated.

A comparative study of biodegradation of vinyl acetate by environmental strains

Four Gram-negative strains, E3_2001, EC1_2004, EC3_3502 and EC2_3502, previously isolated from soil samples, were subjected to comparative studies in order to select the best vinyl acetate degrader for waste gas treatment. Comparison of biochemical and physiological tests as well as the results of fatty acids analyses were comparable with the results of 16S rRNA gene sequence analyses. The isolated strains were identified as Pseudomonas putida EC3_2001, Pseudomonas putida EC1_2004, Achromobacter xylosoxidans EC3_3502 and Agrobacterium sp. EC2_3502 strains. Two additional strains, Pseudomonas fluorescens PCM 2123 and Stenotrophomonas malthophilia KB2, were used as controls. All described strains were able to use vinyl acetate as the only source of carbon and energy under aerobic as well as oxygen deficiency conditions. Esterase, alcohol dehydrogenase and aldehyde dehydrogenase were involved in vinyl acetate decomposition under aerobic conditions. Shorter degradation times of vinyl acetate were associated with accumulation of acetic acid, acetaldehyde and ethanol as intermediates in the culture fluids of EC3_2001 and KB2 strains. Complete aerobic degradation of vinyl acetate combined with a low increase in biomass was observed for EC3_2001 and EC1_2004 strains. In conclusion, P. putida EC1_2004 is proposed as the best vinyl acetate degrader for future waste gas treatment in trickle-bed bioreactors.