Simulation Of Bubble Column Reactors Research Articles

GPU-accelerated transient lattice Boltzmann simulation of bubble column reactors

Design parameters for Bubble Column Reactors such as backmixing and light/dark cycles of microalgae cells are pertinent to transient flow dynamics and mesoscale coherent structures. Transient simulation is therefore of practical significance. Traditional CFD solvers are generally implemented on multi-core CPU workstations, which is time-consuming and difficult to meet the requirement of industry applications. We developed a GPU-accelerated transient LBM simulation of gas-liquid flow, achieving 5000 times acceleration in comparison with the CFD simulation. A notable feature of this method, which allows a tunable and smaller dimensionless relaxation time, is the remarkable decrease of required mesh number in LBM simulation by several orders of magnitude. The solver is validated against experimental data, resolving two mechanisms of mesoscale structure, i.e., vortex rotation and radial migration, in the intensification of macromixing. The computation acceleration and resolution of mesoscale structures demonstrate the potential of this approach for fast simulation of industrial applications.

Prediction of species concentration distribution using a rigorous turbulent mass diffusivity model for bubble column reactor simulation part I: Application to chemisorption process of CO2 into NaOH solution

Rigorous prediction of species concentration distribution has been challenging in the simulation of bubble column reactors. In the present manuscript, a theoretical model of turbulent mass transfer is introduced to the numerical simulation of the process of chemisorption of CO2 into NaOH aqueous solution in a bubble column reactor. In this model the turbulent mass diffusivity was expressed as a function of the concentration variance c2‾ and its dissipation rate εc, which were modeled to close the turbulent mass transfer differential equation system. As a result, along with the fluid velocity distribution, the species concentration distribution in the bubble column can be rigorously predicted simultaneously. By using the present model, the experience relying assumption of a constant turbulent Schmidt, which has been usually adopted in a traditional species concentration simulation, can be avoided. An RNG k-ε method combined with a population balance model for predicting the bubble size distribution was used to predict the gas–liquid velocity in the turbulent flow. The simulated pH values and carbonate concentration were shown to be in satisfactory agreement with the experimental data in literature. The simulations showed that the turbulent mass diffusivity varied along axial and radial directions in the bubble column and the calculated turbulent Schmidt number was not a constant. The proposed approach can be especially useful when empirical turbulent mass diffusivity is not available for simulating a similar process in a bubble column reactor.

CFD analysis on hydrodynamic conditions of a designed spiral column photobioreactor for cultivation of microalgae

PurposeThe purpose of this study is analysis on fluid flow characteristics inside a modified designed spiral bubble column photo-bioreactor. Available fluid dynamic simulation of bubble column reactor (BCR) (which is well-known conventional photobioreactor) had shown significance contribution over the past two decades, where the fluid dynamics of the culture medium and mixing will influence the average irradiance and the light regimen to which the cells are exposed. This enhances the growth. To develop this, and also to cut down the cost parameter involving the production of biodiesel from algae, the growth rate of algae has to be enhanced.Design/methodology/approachSome design modification through a staggered spiral-path inside the bubble column design had been proposed and comparative simulation of the modified design has been reported. Three-dimensional simulations of gas–liquid flow both in the BCR and spiral path column reactor have been carried out using the Euler–Euler approach. Various graphs are plotted, and from comparing, it has been seen that the proposed reactor will enhance better mixing rate, which could help the growth rate in microalgae in the present proposed model. In this paper, an earnest attempt had made to carry out computational simulation of conventional BCR and designed reactor used for cultivation of microalgae which had analyzed using commercial code ANSYS 14.FindingsFrom this work, it was observed that the average turbulence kinetic energy fluctuates more in designed reactor over the conventional photo bioreactor, which will in turn increase diffusivity and enhance transfer of mass, momentum and energy. The results provide comprehensive information concerning effect of fluid flow characteristics inside a modified designed spiral bubble-column photo-bioreactor.Originality/valueSome of our earlier published results (www.scientific.net/AMM.592-594.2427) are also referred in this paper. This work had been performed under the financial aid from RPS project (no. 8,023/RID/RPS/27/11/12), sponsored by All India Council for Technical Education.

One‐Dimensional Modeling and Simulation of Bubble Column Reactors

AbstractReactor models that feature a practical way to design bubble columns on the semi‐industrial or even industrial scale have been published only rarely in the usual scientific literature. Creating a one‐dimensional model in the equation‐oriented simulation software ASPEN Custom Modeler™ (ACM), one can reach a compromise between model precision and modeling – i.e. computational power – based on correlations selected specifically for the application in question. The model quantitatively describes, with sufficient accuracy, the processes in a bubble column reactor. The paper discusses investigations for designing a pilot plant reactor for hydrogenating 2‐ethylhexanal as an example of its application. Geometry and operating conditions were optimized, and the results are shown in the form of spatially resolved reaction and temperature profiles.

Simulation of bubble column reactors using CFD coupled with a population balance model

Bubble columns are widely used in chemical and biochemical processes due to their excellent mass and heat transfer characteristics and simple construction. However, their fundamental hydrodynamic behaviors, which are essential for reactor scale-up and design, are still not fully understood. To develop design tools for engineering purposes, much research has been carried out in the area of computational fluid dynamics (CFD) modeling and simulation of gas-liquid flows. Due to the importance of the bubble behavior, the bubble size distribution must be considered in the CFD models. The population balance model (PBM) is an effective approach to predict the bubble size distribution, and great efforts have been made in recent years to couple the PBM into CFD simulations. This article gives a selective review of the modeling and simulation of bubble column reactors using CFD coupled with PBM. Bubble breakup and coalescence models due to different mechanisms are discussed. It is shown that the CFD-PBM coupled model with proper bubble breakup and coalescence models and interphase force formulations has the ability of predicting the complex hydrodynamics in different flow regimes and, thus, provides a unified description of both the homogeneous and heterogeneous regimes. Further study is needed to improve the models of bubble coalescence and breakup, turbulence modification in high gas holdup, and interphase forces of bubble swarms.

CFD Simulation of Bubble Column Reactor Using Population Balance

In this paper, we have presented a comprehensive analysis of the development of flow pattern in a bubble column reactor by the introduction of a population balance equation combined with the three-dimensional two-fluid model (Reynolds stress model). The multiple size group (MUSIG) model has been used to account for the nonuniform bubble size distribution in a gas−liquid mixture. The coalescence and breakage effects of the gas bubbles are modeled according to the coalescence by the random collision driven by turbulence and wake entrainment while for bubble breakage by the impact of turbulent eddies. Local radial distributions of the gas hold-up, Sauter mean bubble diameter, axial liquid velocity, turbulent kinetic energy, turbulent energy dissipation rate, and Reynolds stresses for superficial gas velocity of 20 mm/s are compared against experimental data in a bubble column reactor. The development of flow pattern were examined at six axial locations H/D = 0.2, 1.4, 2.6, 3.9, 5.0, and 6.2. Good quantitativ...

Two-Fluid Eulerian Simulation of Bubble Column Reactors with Distributors

A two-fluid Eulerian model has been used to study the effect of various sieve plate gas distributors and gas superficial velocities on the hydrodynamics of three-dimensional flow in bubble columns. Turbulence has been modelled using the k–ε turbulence model. Inclusion of gas distributors showed asymmetric flow patterns which are otherwise smoothened when modelled using a uniform gas source. The asymmetric behaviour increased with an increase in the number of holes giving better mixing. The gas hold-up increased with superficial gas velocity, and was independent of the distributor design at high superficial gas velocities. Comparison of simulation results with the experimental work from the literature has provided a successful validation of the model. This study demonstrates the significance of the real distributor in hydrodynamic studies that has been largely neglected in the past.

CFD simulation of bubble column reactors: importance of drag force formulation

CFD simulation has been presented for the flow in bubble column reactors. Procedure has been given for the specification of the drag force and the radial lift force on the basis of drift flux constants. An excellent agreement has been shown between the experimental and simulated profiles of gas hold-up and axial liquid velocity. Explanation has been provided for the enhancement in the slip velocity in the heterogeneous regime.

Heat transfer in two- and three-phase bubble column reactors with internals

Indirect and direct heat transfer is an important aspect in the design of bubble column reactors used for many industrial organic and inorganic processes. Longitudinal flow or cross-flow tube-bundle heat-exchangers, jacket cooling, direct evaporative cooling or circulation cooling are possible methods for this purpose. The existing physical and empirical models describing heat transfer in bubble columns are reviewed. The results of experimental investigations of longitudinal-flow and cross-flow tube-bundle heat-exchangers in bubble columns are presented and compared with empirical and semi-theoretical correlations. In the second part of the article the governing equations describing heat transfer in gas/liquid bubble column reactors are derived under the assumptions of the axial dispersion model and the cell model with backflow. For steady-state conditions, the axial dispersion model leads to a boundary value problem consisting of non-linear ordinary differential equations, whereas the cell model with backflow can be represented by a system of non-linear algebraic equations. Both equation systems include strong non-linearities and can be solved only by special numerical methods. As an example of the use of heat-transfer correlations in modelling bubble columns, the wet air oxidation of municipal sewage sludge carried out in a three-phase bubble column reactor (18 m in height, 2 m in diameter) is simulated considering different heat-removal methods. The simulation runs were carried out with the BCR program, which was developed at the University of Dortmund and the UMSICHT institute for the simulation of bubble column reactors operated under industrial conditions.

Simulation of bubble column reactors with the BCR computer code

BCR is a modular structured computer program for the simulation of bubble column reactors. It offers very comprehensive options for process engineering calculations for steady-state bubble columns with or without internal installations under various operation modes by determining the local pressure, temperature and concentration profiles over the column height. With the implemented computational methods, new equipment can be analyzed and optimized or the operation range of existing bubble column reactors can be checked and in some cases extended. Potential users are research and development departments in the chemical industry and universities, or research institutes with activities in the field of multiphase reaction engineering. In this contribution, the main program features are described and a short overview is given regarding the calculation methods for fluid dynamic parameters, mass- and heat-transfer coefficients and reaction kinetics in the bubble column, and about methods for considering internal installations such as sieve trays or tube bundle heat exchangers. Some examples are given showing axial temperature and concentration distributions for a bubble column reactor ( D = 2 m, H = 20 m) designed for the wet air oxidation of a sewage sludge suspension.

Modeling and simulation of bubble column reactors

The mathematical equations and a comprehensive computer program for modeling and simulating bubble column reactors with internal heat exchange installations are presented. Detailed reactor model equation systems on the basis of the axial dispersion model and the cell model with backflow are developed by linking together the mathematical description o the multiphase flow properties with the momentum, mass and energy balances of the reactor. A highly modular constructed computer program is presented summarizing a lot of theoretical and empirical knowledge about multiphase flow and heat and mass transfer processes in bubble columns. The enhanced possibilities of this new software system are demonstrated by simulating two industrial processes. The methanol synthesis in the slurry phase is chosen in oder to test the model accuracy for a multicomponent reaction system including a hermodynamically balanced chemical reaction. Secondly, the wet air oxidation of municipal sewage sludge in a large-scale slurry bubble column reactor is simulated as an example of a highly exothermic oxidation carried out at extreme pressure and temperature conditions. This chemical process requires special attention for reaction heat removal. The numerical treatment of the algebraic equation system based on the cell model with backflow is easier and leads to average computing times up to 100 times lower than for the reactor model based on the axial dispersion model. The iteration process for solving the boundary value problem runs into numerical convergence difficulties for the case of highly exothermic process conditions with considerable temperature gradients in the reactor. So the finite-difference technique cannot be recommended from a numerical point of view, whereas the cell model formulation allows computations on an IBM-compatible PC (386, 25 MHz) with tolerable computing times of the order of minutes.