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Related Experiment Videos

Flow pattern visualization of a simulated digester.

Khursheed Karim1, Rajneesh Varma, Mehul Vesvikar

  • 1Bioprocess and Bioreactor Engineering Laboratory (BBEL), Chemical Reaction Engineering Laboratory (CREL), Department of Chemical and Civil Engineering, One Brookings Drive, Campus Box 1198, Washington University, St. Louis, MO 63130-4899, USA.

Water Research
|September 8, 2004
PubMed
Summary

Computer automated radioactive particle tracking (CARPT) and computed tomography (CT) revealed poor mixing at the bottom of a simulated digester. Increasing gas flow did not eliminate dead zones, indicating a need for optimized reactor design.

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Area of Science:

  • Chemical Engineering
  • Fluid Dynamics
  • Process Engineering

Background:

  • Effective mixing is crucial for digester performance in various industrial processes.
  • Flat-bottom digesters can suffer from poor mixing, leading to dead zones and reduced efficiency.
  • Non-invasive imaging techniques offer advanced methods for studying complex flow patterns.

Purpose of the Study:

  • To investigate mixing patterns in a simulated flat-bottom digester using advanced non-invasive techniques.
  • To quantitatively assess the impact of gas recirculation flow rates on fluid dynamics within the digester.
  • To evaluate the effectiveness of current gas recirculation strategies in mitigating dead zones.

Main Methods:

  • Utilized computer automated radioactive particle tracking (CARPT) and computed tomography (CT) for non-invasive flow imaging.

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  • Simulated mixing using gas (air) recirculation at three distinct flow rates (28.32, 56.64, 84.96 l/h).
  • Measured time-averaged axial velocity and turbulent kinetic energy within the digester.

    • Main Results:

    • Observed improved mixing in the upper zone near the draft tube, but complete stagnation at the digester bottom across all tested flow rates.
    • Recorded a maximum axial velocity of 34.4 cm/s inside the draft tube at the highest gas flow rate (84.96 l/h).
    • Turbulent kinetic energy peaked within the draft tube and diminished radially towards the digester walls.

    Conclusions:

    • CARPT and CT are effective tools for characterizing digester flow patterns and quantifying velocity and turbulence parameters.
    • Increased gas recirculation rates did not significantly reduce dead zones in the flat-bottom digester.
    • Optimization of operating conditions and reactor configuration is necessary for achieving desired mixing and performance.