Overcoming Challenges When Scaling-up Mixing Processes
Limitations in the data analysis of stirred systems have spurred the mixing community in Germany to search for more comprehensive measurement techniques. The main issue identified by the researchers is the detection of coarse particle suspensions (i.e biogas plants) when scaling-up mixing processes, as contemporary CFD (Computational Fluid Dynamics) models are reporting inconsistent data, particularly related to flow velocity distribution, when simulated.
To obtain a more detailed analysis into the velocity distribution of the mixing the researchers utilised ITS’ very own MIX-ITOMETER system. The system operates on the principle of Electrical Resistance Tomography (ERT), which can provide a number of detailed measurements and real-time volumetric imagery of the monitored process.
After establishing ERT as the optimum choice, the researchers set out to validate the system by testing it during the mixing of a xanthan gum solution and biogas plant (in this instance wheat straw) at both a 0.1m3 lab-scale vessel and 1.0m3 pilot plant scale vessel. Both mixing vessels were cylindrical in shape with the vessel walls fitted with a plane of sensors containing 16 electrodes.
With a consistent impeller tip speed of 5.5 m s-1, the system provides average velocities of 0.06 m s-1 and 0.54 m s-1 for the lab scale vessel and pilot plant vessel respectively. The minor deviation in velocities between the different scales can be attributed to the difference in spatial resolution in the ERT grid between the lab and pilot scale reactor.
The results gathered verify ERT as a potent processing tool, due to the accuracy of its measurements when monitoring the mixing of highly viscous, non-Newtonian and particle-loaded fluids within stirred systems and regardless of vessel size. The successful detection of the solid suspension and distribution prove ERT’s credentials as a substitute for monitoring multiphase systems when CFD is limited.
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