Tracer 3 International Conference

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Recent Example of Model Building and Application
Radioactive Tracer Studies in Bubble Columns for
Dimethyl Ether (DME) Synthesis P. Chen, P.
Gupta, M. P. Dudukovic, B.A. Toseland
Tracer 3 International Conference Ciechocinek,
Poland June 22 24, 2004
Full paper submitted to Chemical Engineering
Science
http//crelonweb.wustl.edu
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Radioactive Tracer Studies in Bubble Columns for
Dimethyl Ether (DME) Synthesis
P. Chen, P. Gupta and M. P. Dudukovic Chemical
Reaction Engineering Laboratory Washington
University, St. Louis, USA Bernard. A.
Toseland Air Products Chemicals, Inc.,
USA Tracer 3 June 22 24, 2004 Ciechocinek,
Polland
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Objectives

• Determine the extent of liquid and gas backmixing
  in a pilot plant bubble column for DME synthesis
• Determine the motion of dispersed catalyst
  relative to liquid
• Evaluate the ability of phenomenological models
  developed in CREL to predict slurry and gas flow
  patterns and mixing

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Reactions and Operating Condition
Dual-catalyst system containing a commercial
proprietary methanol synthesis catalyst and a
commercial dehydration material
Operating Temperature (K) 523.0
Operating Pressure (MPa) 5.27
Inlet Superficial Gas Velocity (m/s) 0.17
Outlet Superficial Gas Velocity (m/s) 0.13
Change in Flowrate () 21.6
Average Superficial Gas Velocity (m/s) 0.15
Liquid/Slurry Superficial Velocity (m/s) 0.0
Height of Dispersed Media (m) 13.25
Mean Gas Holdup 0.43
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Reactor Set-up and Schematic Location of
Scintillation Detectors
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Individual detector responses to N2 Center and
Sidewall injections
N2 Center
N2 Center
N2 Center
N2 Sidewall
N2 Sidewall
N2 Sidewall
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Schematic representation of the experimentally
observed phenomena in bubble columns and the
basis for the gas-liquid mixing model with
interphase mass transfer
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Sample of model equations
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Determination of model parameters
Two-fluid hydrodynamic model - Continuity
Equation - Momentum Equation - Mixing length
closure (Kumar et al., 1995) - Drag force
(Tomiyama et al., 1997)
Liquid velocity profile Gas velocity
profile Bubble diameter
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Determination of model parameters

• Average gas/liquid velocity and holdup in
  compartment
• From velocity and holdup profile of gas and
  liquid phases
• Eddy diffusivity
• From Degaleesans (1997) correlation
• Interfacial area concentration
• From gas holdup and bubble diameter
• Mass transfer coefficient
• From molecular diffusivity, bubble diameter and
  gas-liquid slip velocity in compartment

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Gas and liquid backmixing parameters used in
model predictions
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Reproducibility of gas and liquid tracer responses
N2 center
N2 center
N2 center
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Comparison of model prediction and experimental
data for N2 Center and Sidewall injections of
liquid and catalyst tracers
liquid
liquid
liquid
catalyst
catalyst
catalyst
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Comparison of model prediction and experimental
data for N1 Center and Sidewall injections of
catalyst tracer
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Conclusions

• The pseudo-homogeneous assumption is valid.
  Liquid and catalyst tracers exhibit the same
  dynamics.
• The gas and liquid re-circulation with mixing
  model is able to predict the characteristic
  features of the experimental responses observed
  for gas, slurry powder and catalyst tracers at
  different reactor elevations.
• This model offers a relatively simple tool for
  assessing mixing and transport in bubble columns
  for a variety of gas conversion processes and
  provides a phenomenological framework for bubble
  column reactor modeling and design.