Tomographic imaging during reactive precipitation in a stirred vessel: Mixing with chemical reaction

Abstract Electrical resistance tomography (ERT) allows the user to non-invasively ‘see inside their process’ through the manipulation and measurement of electrical properties enabling a powerful real-time visualisation of the time evolving three-dimensional conductivity distributions within the process unit. A 4-plane 16-sensor ERT array retrofitted to a 7.5 l stirred vessel has been used to rigorously interrogate the single feed semi-batch precipitation of barium sulphate, providing over 1000 spatially varying data points per ‘captured’ frame. A variety of reactant concentrations and agitation intensities were investigated. The results obtained reflect both the hydrodynamics and complex reaction kinetics involved with reactions and detail a number of very distinct regions during the experimental runs. This is achieved through the direct visualisation of the induced feed plume, quantification of the homogeneity (‘mixedness’) within the vessel, time evolving conductivity trends and a further analysis into the rates of conductivity changes as the reaction proceeds. For some experimental runs the predicted conductivity trends for a perfectly mixed state have been calculated using a conductivity–concentration correlation. ERT offers many spatially varying data points as opposed to point wise measurements which offers a significant improvement for the validation of mathematical models which attempt to deal with reactive crystallisation. As well as data collection, specifically for model validation, ERT may offer the means to control the spatio-temporal distributions of reactants and phases within the reactor to aid the suppression of unwanted by-products for industrial processes whilst offering a means to monitor the process unit to ensure the required mixing intensity is always achieved. Also included is an analysis of the mean volume diameter of the precipitate for each experimental run with scanning electron microscope (SEM) images.

[1]  David Wong,et al.  Effect of ion excess on particle size and morphology during barium sulphate precipitation: an experimental study , 2001 .

[2]  Alan Jones,et al.  Mixing effects on product particle characteristics from semi-batch crystal precipitation , 2000 .

[3]  Ken Primrose,et al.  Interrogation of a precipitation reaction by electrical resistance tomography (ERT) , 2005 .

[4]  Mi Wang,et al.  Electrical Process Tomography: Simple and Inexpensive Techniques for Process Imaging , 1997 .

[5]  M. S. Beck,et al.  Imaging system based on electromagnetic tomography (EMT) , 1993 .

[6]  Sohrab Rohani,et al.  Micromixing in a single‐feed semi‐batch precipitation process , 1999 .

[7]  W. B. Gilboy,et al.  Imaging large vessels using cosmic-ray muon energy-loss techniques. , 2007 .

[8]  Alberto Brucato,et al.  ON THE SIMULATION OF STIRRED TANK REACTORS VIA COMPUTATIONAL FLUID DYNAMICS , 2000 .

[9]  Mi Wang,et al.  Inverse solutions for electrical impedance tomography based on conjugate gradients methods , 2002 .

[10]  Reg Mann,et al.  Augmented-reality visualization of fluid mixing in stirred chemical reactors using electrical resistance tomography , 2001, J. Electronic Imaging.

[11]  Mi Wang,et al.  Measurements of gas-liquid mixing in a stirred vessel using electrical resistance tomography (ERT) , 2000 .

[12]  Podd,et al.  Model-based parameterisation of a hydrocyclone air-core , 2000, Ultrasonics.

[13]  Tomasz Dyakowski,et al.  Applications of electrical tomography for gas-solids and liquid-solids flows : a review , 2000 .

[14]  R. Mann,et al.  Effects of convection, feed-separation and macro-mixing on particle size distributions for double-jet semi-batch precipitation in a stirred vessel , 2005 .

[15]  Lynn F. Gladden,et al.  Transition to pulsing flow in trickle‐bed reactors studied using MRI , 2005 .

[16]  R. David,et al.  A simultaneous determination of nucleation and growth rates from batch spontaneous precipitation , 1999 .

[17]  O. Söhnel,et al.  Precipitation: Basic Principles and Industrial Applications , 1992 .

[18]  Hristo Hristov,et al.  Reconciling Electrical Resistance Tomography (ERT) Measurements with a Fluid Mixing Model for Semi‐Batch Operation of a Stirred Vessel , 2008 .

[19]  S. J. Stanley,et al.  Tomographic Imaging of Fluid Mixing in Three Dimensions for Single-Feed Semi-Batch Operation of a Stirred Vessel , 2002 .

[20]  Rainer Krebs,et al.  The future of mixing research , 2004 .

[21]  Richard A Williams,et al.  Process tomography : principles, techniques and applications , 1995 .