Formation of dissipative structures in the reaction zone of a heterogeneous reduction reactor

The problems of analysis of the hydrodynamic stability of the reaction zone of a reduction reactor are considered. It is shown that, in the course of filtration of a liquid, reaction product bubbling leads to the formation of dissipative structures in a dispersed reducing agent, which provide vortex motion of the liquid reagent and, thus, enhance heat and mass transfer. When the liquid phase contacts the gas phase flow in the countercurrent mode within the dispersed particle bed, the latter can be blocked, which is undesirable because this impairs the reliable operation of the reactor. The modeling results can be used for determining the conditions for robust operation of process apparatuses.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 146–151.Original Russian Text Copyright © 2005 by S. Panchenko, D. Panchenko, Glebova.     

Transfer processes in heterogeneous reduction reactors

The results of experimental study are presented and mathematical models are proposed for heat and mass-transfer coefficients in a packed bed layer of reacting particles immersed in a liquid through which the reaction products are bubbled. It is shown that turbulence models based on taking into account the motion of bubbles, which rise under the action of buoyancy forces and set the liquid in swirling motion, quite adequately describe the transfer processes in gas—liquid systems, including the layer of dispersed particles.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 38, No. 6, 2004, pp. 611–615.Original Russian Text Copyright © 2004 by S. Panchenko, D. Panchenko, Glebova.     

Hydrodynamics and Heat Transfer in the Bubbling of Steam Entrained by Liquid Jets Falling through a Steam Medium and Plunging into a Liquid

The hydrodynamics and heat transfer are studied in a layer of subcooled water into which vertical liquid jets plunge from a steam medium above the liquid and entrain steam from the steam space. The studies are performed as applied to the operating conditions of direct-contact jet condensers and deaerators. An equation is obtained for calculating the heat transfer in the receiving layer in the case of complete condensation of steam entrained by jets.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 362–372.Original Russian Text Copyright © 2005 by Trofimov.     

Hydrodynamics of reactive distillation tray column with catalyst containing envelopes: experiments vs. CFD simulations

We have studied the hydrodynamics of a reactive distillation sieve tray column in which catalyst containing wire-gauze envelopes are disposed along the liquid flow direction. The gas and liquid phases are in cross-current contact on the tray. Experiments were carried out to determine the clear liquid height on the tray as a function of tray geometry and operating conditions. The transient gas–liquid hydrodynamics on the tray was simulated using CFD techniques. The agreement between the experiments and CFD simulations was found to be very good, suggesting that CFD simulations can be used for design and scale-up purposes.     

Mathematical Model of Hydrodynamics of a Glass-Melting Tank

The importance of studying the hydrodynamics of the glass-melting tank is substantiated. The main equations of a numerical model of the tank hydrodynamics are given. The calculation results of temperature fields and streamlines are given for a glass-melting furnace with an output of 300 tons per day. The adequacy of the calculation results as applied to real furnace operating conditions is demonstrated. The developed model of hydrodynamics of the melting tank can be used in solving applied problems of designing glass-melting furnaces.__________Translated from Steklo i Keramika, No. 1, pp. 3 – 8, January, 2005.     

Flow of a Rheologically Complex Suspension in a Cylindroconical Hydrocyclone

A set of rheodynamic equations describing the flow of a rheologically complex suspension with a non-Newtonian dispersion medium in a cylindroconical hydrocyclone is numerically solved. The velocity and pressure fields are calculated, and the suspension film thickness as a function of the meridional coordinate is described. The effect of the rheological properties of the suspension and also the dimensionless parameters on the flow hydrodynamics is studied. The results obtained are physically interpreted.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 4, 2005, pp. 355–361.Original Russian Text Copyright © 2005 by Yablonskii, Ryabchuk.     

Bubble column with internals: Effects on hydrodynamics and local heat transfer

Local heat transfer and column hydrodynamics are investigated in a bubble column in presence of internals of different configurations. The liquid phase used is tap water and the gas phase is oil-free compressed air. The gas velocity is varied over a wide range of 0.03–0.35 m/s. The heat transfer variations are measured with a fast response probe capable of capturing bubble dynamics as well as detect local flow direction and deduce local liquid velocity. Measurements obtained in presence of internals are compared with those without internals to elucidate the effects of different internals design. Comparisons are based on average values and temporal variations obtained with the fast response probe. The average gas holdup, local liquid velocity and bubble fractions holdups obtained with and without internals are also compared to further point out the differences. The observed differences are discussed based on the insights provided by these comparisons. The results obtained show influence of internals design on column hydrodynamics which need to be considered for their proper design and modeling.     

Carbon dioxide absorption by monoethanolamine in hollow fiber membrane contactors: A parametric investigation

A mathematical and numerical investigations on the gas–liquid absorption of carbon dioxide in monoethanolamine solutions in a hollow fiber membrane contactor device is described. The reactive absorption mechanism was built based on momentum and mass transport conservation laws in all three compartments involved in the process, i.e., the gas phase, the membrane barrier, and the liquid phase. The liquid absorbing solution flows in the fiber bore in which the velocity is assumed to obey a fully developed laminar flow, and the gas mixture circulates counter‐currently to the liquid flow in the shell side where the velocity is characterized by the Navier‐Stokes momentum balance equations. The average outlet gas and liquid concentrations, the reactive absorption flux, and the gas removal efficiencies are parametrically simulated with operational parameters such as gas flow rate, fresh inlet amine concentrations, and fiber geometrical characteristics. The shell velocity was described by other flow hydrodynamics models besides Navier‐Stokes and their simulated results were favorably compared to experimental data. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Analysis of the possibility of implementing the principle of redistribution of concentration fields for reactive distillation processes

The evolution of the phase portrait for the dynamic system of open evaporation combined with a chemical reaction for a fixed liquid amount was studied as dependent on the rate constants of the reaction. A three-component azeotropic mixture whose vapor-liquid equilibrium diagram is characterized by two distillation regions was considered. The possibility of the open evaporation trajectory to transfer through the separatrix between the distillation regions was shown, as well as the possibility of implementing the principle of redistribution of the concentration fields due to chemical reactions occurring in reactive distillation columns.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 115–119.Original Russian Text Copyright © 2005 by Solokhin, Nazanskii, Timofeev.     

CFD simulation of hydrodynamics of gas-liquid-solid fluidised bed reactor

A three dimensional transient model is developed to simulate the local hydrodynamics of a gas-liquid-solid three-phase fluidised bed reactor using the computational fluid dynamics (CFD) method. The CFD simulation predictions are compared with the experimental data of Kiared et al. [1999. Mean and turbulent particle velocity in the fully developed region of a three-phase fluidized bed. Chemical Engineering & Technology 22, 683-689] for solid phase hydrodynamics in terms of mean and turbulent velocities and with the results of Yu and Kim [1988. Bubble characteristics in the racial direction of three-phase fludised beds. A.I.Ch.E. Journal 34, 2069-2072; 2001. Bubble-wake model for radial velocity profiles of liquid and solid phases in three-phase fluidised beds. Industrial and Engineering Chemistry Research 40, 4463-4469] for the gas and liquid phase hydrodynamics in terms of phase velocities and holdup. The flow field predicted by CFD simulation shows a good agreement with the experimental data. From the validated CFD model, the computation of the solid mass balance and various energy flows in fluidised bed reactors are carried out. The influence of different interphase drag models for gas-liquid interaction on gas holdup are studied in this work.     

Liquid–solid mass transfer in a three-phase stationary catalytic basket reactor

Measurements of the liquid–solid mass transfer coefficient k_S were performed in a three-phase multiple impeller and stationary catalytic basket reactor, called a Robinson–Mahoney reactor. Local coefficients were determined using naphtol particle dissolution in water and n-heptane with or without gas flow. Experiments have shown that local coefficients k_{S loc} depend on the particle position in the basket, agitation speed, and liquid properties. A correlation linking k_S to liquid velocity was established in a reactor simulating hydrodynamics in a piece of catalytic basket. Liquid velocity values were validated using a particle image velocimetry technique in a Robinson–Mahoney reactor, using water. © 2005 American Institute of Chemical Engineers AIChE J, 2005     

Computational fluid dynamics simulation of reactive absorption of CO2 in a structured packed column

In this study, multiphase Eulerian computational fluid dynamics (CFD) modelling is developed to predict the hydrodynamics, mass transfer, and chemical absorption of CO₂ using a monoethanolamine (MEA) solution in a structured packed column. First, the hydrodynamic simulation of liquid dispersion in a structured packed bed using a two-dimensional CFD is performed. The simulation results of the radial distribution of the liquid holdup are compared with the literature experimental data. The model prediction matches the experimental data at the top position of the column, whereas a slight deviation is found at the bottom position of the column. Using a validated CFD model, the reactive mass transfer is modelled to study CO₂ capture in a structured packed column with Mellapak 500.X. The model results are compared to the literature experimental results of CO₂ mole fractions along the height of the column. It is found that the model results match the experimental findings. Furthermore, CFD modelling is extended to investigate the influence of operating conditions such as gas and liquid velocities on CO₂ removal efficiency. The present CFD model demonstrates the porous media approach for reactive absorption of CO₂ in a structural packed bed.     

The hydrodynamic behavior of the liquid-solid circulating fluidized bed ion exchange system for cesium removal

In this work, experimental studies on the hydrodynamics have been carried out in a cold model liquid-solid circulating fluidized bed (LSCFB) ion exchange system where the riser is operated in the circulating fluidization regime and the downcomer in the state of slow-moving packed bed, with the aim of removing cesium from high radioactive liquid waste. Two circulating fluidization zones, the initial and the fully developed, have been observed. The solids circulation rate can be controlled merely by the primary liquid flow if the auxiliary liquid flow is set to zero and the injection tap is located at the middle of the intersection of the riser and the solid-return pipe. Therefore, it is possible to minimize the number of the liquid feed assemblies (pumps, valves, flow meters, etc.), and this is crucial to the treatment of high radioactive waste. The liquid inevitably leaks through the solid-return pipe in most cases because of the “loosening effect” of the liquid feed flow, and the direction and magnitude of the leakage vary with the operating conditions. The system geometry, including the injection tap location and the riser outlet location, plays a very important role in the hydrodynamics of the LSCFB system.     

Residue curve maps of reactive membrane separation

A batch reactive membrane separation process is analysed and compared with a batch reactive distillation process by means of residue curve maps. In both processes, the chemical reaction takes place (quasi-) homogeneously in the liquid bulk phase and vapour-liquid equilibrium is assumed to be established. Additionally, in the reactive membrane separation process, selective vapour phase permeation through a membrane is incorporated.A model is formulated which describes the autonomous dynamic behaviour of reactive membrane separation at non-reactive and reactive conditions when vacuum is applied on the permeate side. The kinetic effect of the chemical reaction is characterized by the Damköhler number Da, while the kinetic effect of multicomponent mass transfer through the membrane is characterized by the matrix of effective mass transfer coefficients. The process model is used to elucidate the effect of selective mass transfer on the singular points of reactive membrane separation for non-reactive conditions (Da=0), for kinetically controlled reaction (0<Da<∞), and for equilibrium controlled reaction (Da→∞). Scalar, diagonal and non-diagonal mass transfer matrices are considered. As examples, the simple reaction A⇔B+C in ideal liquid phase, and the cyclization of 1,4-butanediol to tetrahydrofurane in non-ideal liquid phase are investigated.     

PDA experiments and CFD simulation of a lab-scale oxidation ditch with surface aerators

Though hydrodynamic characteristic is an important parameter for the optimization of reactors, very little research deals with the hydrodynamics of oxidation ditches. This paper focuses on the hydrodynamics of an oxidation ditch from the point of view of both experiments and simulations. The three-dimensional flow field in the oxidation ditch aerated with surface aerators like inverse umbrella is simulated with computational fluid dynamics (CFD). The two-fluid model and the standard k–? model are used for the turbulent solid–liquid two-phase flow. The distributions of liquid velocity and volume fraction of solid phase are obtained. Experiments are performed in a lab-scale oxidation ditch with particle dynamic analyser (PDA). The comparison between simulations and PDA experiments confirms that the results and the methods employed in this paper are reliable. The liquid and solid have similar flow velocity, while the vertical velocity of solid phase is slightly lower than that of liquid. With the increase of aerator speed, the velocity increases and solid phase disperses more evenly. The flow in the oxidation ditch has noticeable three-dimensional features, especially between the circular channel and the straight channel. And solid phase is ready to settle in these regions. All these results form the basis for the optimization and deep research of oxidation ditches.     

Gas holdup of rotating foam reactors measured by γ‐tomography—effect of solid foam pore size and liquid viscosity

Rotating foam reactors have already shown to give high mass transfer rates compared to stirred tank reactors. For a deeper insight into the hydrodynamics of these reactors, the hydrodynamics of rotating foam reactors were studied using γ‐ray tomography. The two‐phase flow through the foam block stirrer is mainly influenced by the solid foam pore size and the liquid viscosity. For low viscosity, the optimal foam block pore size was identified in the range between 10 and 20 pores per inch (ppi). With smaller pore size, the gas holdup inside the foam block strongly increases due to bubble entrapment. For higher viscosity, pore sizes larger than 10 ppi have to be used to achieve a sufficient liquid flow rate through the foam block to avoid a strong gradient over the reactor height. The effect of the hydrodynamics on the gas–liquid and liquid–solid mass transfer and the reactor performance are discussed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 146–154, 2013     

Experimental investigation on multiscale hydrodynamics in a novel gas–Liquid–Solid three phase jet-Loop reactor

Multiphase flow hydrodynamics in a novel gas–liquid–solid jet-loop reactor (JLR) were experimentally investigated at the macroscales and mesoscales. The chord length distribution was measured by an optical fiber probe and transformed for bubble size distribution through the maximum entropy method. The impacts of key operating conditions (superficial gas and liquid velocity, solid loading) on hydrodynamics at different axial and radial locations were comprehensively investigated. JLR was found to have good solid suspension ability owing to the internal circulation of bubbles and liquid flow. The gas holdup, axial liquid velocity, and bubble velocity increase with gas velocity, while liquid velocity has little influence on them. Compared with the gas–liquid JLRs, solids decrease the gas holdup and liquid circulation, reduces the bubble velocity and delays the flow development due to the enhanced interaction between bubbles and particles (Stokes number >1). This work also provides a benchmark data for computational fluid dynamics (CFD) model validation. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16537, 2019     

Effect of bubble deformation on stability and mixing in bubble columns

The paper deals with hydrodynamics in bubble columns. The objective of the paper is to study stability and mixing in a bubble column. The modeling of parameters such as stationary drag and added mass is addressed. In addition, the effect of bubble deformation in terms of eccentricity is highlighted. In a previous paper, the transition between homogeneous and heterogeneous regimes in bubble column without liquid flow has been shown to be driven by the deformation of the bubbles associated to drag and added mass. In the present paper, this work is generalized to bubble column with liquid flow and to the transition from bubble flow to slug flow in a vertical pipe. Numerical simulations of gas-liquid reactors are presented. The numerical simulations are validated in the case of gas plume after the Becker et al. data (Becker, S., Sokolichin, A., & Eigenberg, G. (1994) Gas-liquid flow in bubble columns and loop reactors: Part II. Comparison of detailed experiments and flow simulations. Chemical Engineering Science, 49 (24B), 5747-5762. The numerical simulations are finally applied to a bubble column. The simulations of residence time distribution coupled to transient hydrodynamics are shown to be very sensitive to the modeling of interfacial transfer of momentum from the bubbles to the liquid in terms of drag and added mass, including the effect of bubble deformation.