Hydrodynamic performance of the ASI impeller in an aerated bioreactor containing the biopolymer solution through tomography and CFD

Abstract In this study, the performance of the ASI impeller, a new impeller designed in our research group, was assessed for the gas dispersion in the non-Newtonian fluids. The effects of volumetric gas flow rate, impeller speed, and fluid rheology on power drawn and mixing time were explored. The non-Newtonian fluids were xanthan gum solutions at different concentrations. These biopolymer solutions are pseudoplastic fluids with yield stress and their rheological behaviors were assessed using the Herschel–Bulkley model. The hydrodynamic performance of this new impeller was compared to performance of the pitched blade turbine and the Rushton impeller. The electrical resistance tomography (ERT) was employed to measure the mixing time and gas holdup. The Eulerian–Eulerian approach was employed to simulate the gas-liquid flow inside this bioreactor through computational fluid dynamics (CFD). The CFD model was successfully validated by comparing the measured gas holdup and impeller torque values to the simulation results. The data analysis indicated that the ASI exhibited minimal effect of the gassing on power consumption (36%) compared to the Rushton turbine (50%). Furthermore, the experimental and CFD results in regard to the mixing time, power consumption upon aeration, and flow field generated in the aerated reactor proved that the ASI impeller was more energy efficient compared to the pitched blade turbine and the Rushton impeller.

[1]  Leila Pakzad,et al.  Intensification of mixing of shear-thinning fluids possessing yield stress with the coaxial mixers composed of two different central impellers and an anchor , 2017 .

[2]  Philip K. Chan,et al.  Using computational fluid dynamics modeling to study the mixing of pseudoplastic fluids with a Scaba 6SRGT impeller , 2008 .

[3]  Philip K. Chan,et al.  Using electrical resistance tomography and computational fluid dynamics modeling to study the formation of cavern in the mixing of pseudoplastic fluids possessing yield stress , 2008 .

[4]  R. K. Finn,et al.  Influence of Gas Flow Rates and Gas Holdup on Blending Efficiency in Stirred Tanks , 1980 .

[5]  Alvin W. Nienow,et al.  The versatility of up-pumping hydrofoil agitators , 2004 .

[6]  Catherine Xuereb,et al.  Scale-up in laminar and transient regimes of a multi-stage stirrer, a CFD approach , 2002 .

[7]  Weeratunge Malalasekera,et al.  An introduction to computational fluid dynamics - the finite volume method , 2007 .

[8]  M. Jahoda,et al.  CFD prediction of liquid homogenisation in a gas–liquid stirred tank , 2009 .

[9]  S. S. Alves,et al.  Effect of blade shape on the performance of six-bladed disk turbine impellers , 2000 .

[10]  F. Ein‐Mozaffari,et al.  Analysis of gas phase characteristics and mixing performance in an activated sludge bioreactor using electrical resistance tomography , 2015 .

[11]  M. Fialová,et al.  Duality of the gas-liquid flow regimes in bubble column reactors , 1997 .

[12]  Leila Pakzad,et al.  Investigation of hydrodynamic performances of coaxial mixers in agitation of yield-pseudoplasitc fluids: Single and double central impellers in combination with the anchor , 2016 .

[13]  Alessandro Paglianti,et al.  Gas hold-up distribution and mixing time in gas–liquid stirred tanks , 2015 .

[14]  N. Blakebrough,et al.  Mass transfer and mixing rates in fermentation vessels , 1966 .

[15]  Alvin W. Nienow,et al.  POWER, GAS DISPERSION AND HOMOGENISATION CHARACTERISTICS OF SCABA SRGT AND RUSHTON TURBINE IMPELLERS , 1992 .

[16]  Leila Pakzad,et al.  Agitation of Herschel–Bulkley fluids with the Scaba–anchor coaxial mixers , 2013 .

[17]  Alvin W. Nienow,et al.  Mixing in large-scale vessels stirred with multiple radial or radial and axial up-pumping impellers: modelling and measurements , 2000 .

[18]  Leila Pakzad,et al.  Evaluation of the mixing of non-Newtonian biopolymer solutions in the reactors equipped with the coaxial mixers through tomography and CFD , 2013 .

[19]  A. Nienow.  Hydrodynamics of Stirred Bioreactors , 1998 .

[20]  Farhad Ein-Mozaffari,et al.  Using computational fluid dynamics modeling and ultrasonic doppler velocimetry to study pulp suspension mixing , 2007 .

[21]  Vivek V. Ranade,et al.  CFD simulation of mixing in tall gas-liquid stirred vessel: Role of local flow patterns , 2006 .

[22]  A. Lohi,et al.  A novel and energy-efficient coaxial mixer for agitation of non-Newtonian fluids possessing yield stress , 2013 .

[23]  Silvio Sicardi,et al.  HYDRODYNAMICS OF A GAS-LIQUID REACTOR STIRRED WITH A MULTI-IMPELLER SYSTEM , 1990 .

[24]  Jorge M. M. Barata,et al.  Mixing in gas-liquid contactors agitated by multiple turbines , 1995 .

[25]  Farhad Ein-Mozaffari,et al.  Effect of rheological parameters on non-ideal flows in the continuous-flow mixing of biopolymer solutions , 2015 .

[26]  D. K. Hwang,et al.  Experimental investigation of the bubble behavior in an aerated coaxial mixing vessel through electrical resistance tomography (ERT) , 2016 .

[27]  M. Mehrvar,et al.  Characterization of the continuous-flow mixing of non-Newtonian fluids using the ratio of residence time to batch mixing time , 2013 .

[28]  Alvin W. Nienow,et al.  Gas-liquid mixing studies : A comparison of Rushton turbines with some modern impellers , 1996 .

[29]  Catherine Xuereb,et al.  Effect of Axial Agitator Configuration (Up-Pumping, Down-Pumping, Reverse Rotation) on Flow Patterns Generated in Stirred Vessels , 2001 .

[30]  Alvin W. Nienow,et al.  Studies of High Solidity Ratio Hydrofoil Impellers for Aerated Bioreactors. 4. Comparison of Impeller Types , 1996 .

[31]  G. Montante,et al.  Experimental Analysis and Computational Modelling of Gas–Liquid Stirred Vessels , 2007 .

[32]  V. Murthy,et al.  Effect of palm oil on oxygen transfer in a stirred tank bioreactor , 2010 .

[33]  Václav Linek,et al.  Gas hold-up, mixing time and gas-liquid volumetric mass transfer coefficient of various multiple-impeller configurations: Rushton turbine, pitched blade and techmix impeller and their combinations , 2003 .

[34]  T. Heindel,et al.  Carbon Monoxide Mass Transfer for Syngas Fermentation in a Stirred Tank Reactor with Dual Impeller Configurations , 2008, Biotechnology progress.

[35]  A. W. Nienow,et al.  THE EFFECT OF RHEOLOGICAL COMPLEXITIES ON POWER CONSUMPTION IN AN AERATED, AGITATED VESSEL , 1983 .

[36]  Aniruddha B. Pandit,et al.  Studies in multiple impeller agitated gas–liquid contactors , 2006 .

[37]  Leila Pakzad,et al.  A new perspective in the evaluation of the mixing of biopolymer solutions with different coaxial mixers comprising of two dispersing impellers and a wall scraping anchor , 2016 .

[38]  Alvin W. Nienow,et al.  Studies of High Solidity Ratio Hydrofoil Impellers for Aerated Bioreactors. 2. Air—Water Studies , 1995 .

[39]  D. G. Cronin,et al.  An Experimental Study of the Mixing in a Proto-Fermenter Agitated by Dual Rushton Turbines , 1994 .

[40]  M. Mehrvar,et al.  Improving the dynamic performance of continuous-flow mixing of pseudoplastic fluids possessing yield stress using Maxblend impeller , 2012 .

[41]  Alvin W. Nienow,et al.  Gas—liquid mixing studies with multiple up‐ and down‐pumping hydrofoil impellers: Power characteristics and mixing time , 1998 .

[42]  D. K. Hwang,et al.  Analysis of power consumption and gas holdup distribution for an aerated reactor equipped with a coaxial mixer: Novel correlations for the gas flow number and gassed power , 2016 .

[43]  Milan Jahoda,et al.  Liquid Homogenization in Aerated Multi‐Impeller Stirred Vessel , 2000 .

[44]  Leila Pakzad,et al.  Effect of the rheological properties on the mixing of Herschel‐Bulkley fluids with coaxial mixers: Applications of tomography, CFD, and response surface methodology , 2016 .

[46]  Jules Thibault,et al.  Power consumption and mass transfer in agitated gas‐liquid columns: A comparative study , 1998 .

[47]  Václav Linek,et al.  Mass transfer correlations for multiple-impeller gas–liquid contactors. Analysis of the effect of axial dispersion in gas and liquid phases on “local”kLa values measured by the dynamic pressure method in individual stages of the vessel , 2007 .

[48]  F. Ein‐Mozaffari,et al.  The use of electrical resistance tomography for the characterization of gas holdup inside a bubble column bioreactor containing activated sludge , 2015 .

[49]  D. K. Hwang,et al.  Analysis of mixing in an aerated reactor equipped with the coaxial mixer through electrical resistance tomography and response surface method , 2016 .

[50]  Alvin W. Nienow,et al.  Studies of High Solidity Ratio Hydrofoil Impellers for Aerated Bioreactors. 1. Review , 1995 .