Modelling of Gas‐Liquid/Gas‐Liquid‐Solid Flows in Bubble Columns: Experiments and CFD Simulations

Abstract

Gas-liquid/gas-liquid-solid systems are widely used in the chemical process industry for a variety of applications. Recently, gas to liquid (GTL) technologies employing gas-liquid-solid systems, are receiving a wide attention. Gas-liquid flows in bubble columns are intrinsically unsteady and are composed of several flow processes occurring at different time and space scales. The presence of solids further complicates the unsteady fluid dynamics. The unsteady fluid dynamics often govern the mixing and transport processes and is inter-related in a complex way with the design and operating parameters like sparger and reactor configuration, gas flow rate and solid loading. Therefore, it is essential to develop (and validate) computational models to simulate such complex relationships for guiding the reactor design. Most of the earlier work on modelling of the gas-liquid flows was focused on predicting timeaveraged flow properties (Ranade, 1997), where the unsteady information is lost. Recently, Buwa and Ranade (2003a) have studied the role of unsteady flow structures in the liquid phase mixing in bubble columns and have shown that three-dimensional unsteady simulations are necessary for accurate prediction of mixing time. In this work, we have studied dynamics of gas-liquid and gas-liquid-solid flows in cylindrical bubble columns.In past, most of the work done on characterization of unsteady gas-liquid flows was focused on small rectangular bubble columns (Becker et al., 1994;Pfleger et al., 1999;Pan et al. 2000;Buwa and Ranade, 2002, 2003a) because of the simple geometry (lower computational demands) and well established plume oscillations. In order to transform the developed understanding and models from rectangular bubble columns to industrial bubble columns, it is essential to study the dynamics of gas-liquid flows in cylindrical bubble columns experimentally as well as computationally. Most of the earlier work on cylindrical bubble columns was carried out with an objective of measuring and predicting the time-averaged velocity and gas hold-up profiles (experimental: Yao et al., 1991;Kumar et al., 1997;Chen et al., 2001; computational: Ranade, 1997;Sanyal et al., 1999). Even though a few attempts have been made to characterize the dynamics of gas-liquid flow in cylindrical bubbles columns experimentally (Chen et al., 1994;Becker et al., 1999) and computationally (Pfleger and Becker, 2001), the agreement between measured and predicted dynamic characteristics is still qualitative and the simulations are rather restricted to lower superficial gas velocities (< 0.02 m/s). Moreover, the effect of solids on dynamic characteristics is not clearly understood and addressed before. It is therefore essential to extend present understanding and models to predict dynamic characteristics Gas-liquid/gas-liquid-solid systems are widely used in the chemical process industry for a variety of applications. In the present work, we have characterized the dynamics of gas-liquid/gas-liquid-solid flows in cylindrical bubble columns u...

Parameters measurement of hydrodynamics and CFD simulation in multi‐stage bubble columns

“…Baten and Krishna [9] ignored the added mass force and lift force for the simulation of multi-stage bubble columns. And the studies of Rampure et al [37] and Diaz et al [38] indicate that inclusion of virtual mass force does not result in any significant difference in the dynamic and time-averaged flow properties. A recent review by Sokolichin et al [39] clearly indicates the conflicting information about how the value of the lift coefficient varies with superficial gas velocity.…”

Analysis of liquid circulation in a rectangular tank with a gas source at a corner

“…The studies of Rampure et al [10] and Diaz et al [18] indicate that inclusion of virtual mass force, does not result in any significant difference in dynamic and time averaged flow properties. Therefore, virtual mass force is not considered in this present work.…”

“…G k,m is the generation of turbulence kinetic energy in the mixture, based on gradients of mean velocity and turbulent viscosity and is computed from, G k,m = t,m (∇u m + (∇u m ) T ) : ∇u m (18) Following earlier studies, we have neglected the effect of G e , the extra turbulence generation due to presence of dispersed phase [10,27]. In all the simulations, standard values of the k-ε model parameters [26] were used (C 1 = 1.44; C 2 = 1.92; C =0.09; k = 1.0; ε = 1.3).…”

“…Bubble column reactors have been simulated in the past for two different geometries, cylindrical [1,2,[8][9][10] and rectangular [4,5,[11][12][13][14][15][16][17][18]. Sokolichin et al [11] compared the results obtained using both Eulerian and Lagrangian approaches.…”

Bioreactors: Airlift Reactors

“…published showing the capability of handling the complex problem of multiphase flow in ALRs (97,133,274,(331)(332)(333)(334)(335)(336)(337)(338)(339)(340)(341)(342)(343)(344). CFD gives much more detailed information, reaching the level of local velocities and local holdup (Fig.…”