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Jul 2021

Determining mixing quality in batch addition with a level change using electrical tomography

Within the pharmaceutical, consumer and agrichemical sectors, there is a frequent use of stirred tank reactors to identify differentiating materials, however they are somewhat limited by their lack of instrumentation usage. With ITS at the height of technical innovation aiding the advancement of monitoring stir tank reactor process’, we are reviewing this paper by T.L. Rodgers from the University of Manchester in partnership with Unilever.

Rogers’ aim was to monitor the mixing/ level change of barium chloride within a stir tank reactor using electrical resistance tomography (ERT). For the purpose of these experiments, Rogers chose to use ITS’ very own P2+ instrument ‘as it is the best performing ERT instrument, available to us, for experiments requiring high temporal resolution and is capable of successfully monitoring homogeneity’. Another benefit of using ERT in these particular experiments is that if the projection was only 2-dimensional, material out of the plane can be reconstructed in the plane, giving incorrect results, however using a 3-dimensional projection (result of using ERT) this side-effect is minimalised, therefore more accurate results are depicted.

The experiments were conducted using a shallow dish-based stirred tank reactor along with a cylindrical vessel which was placed into a square jacket where water can circulate for temperature control. Simultaneously, ITS’ P2+ box was connected to the computer until the end of the experiment; this allowed the equipment to operate slightly faster, allowing a faster sampling rate.


tomography output

Visualisation of the tracer mixing adjusted for the level change, with a changing finite element model showing the level change from above (top row) and from the side (bottom row). (a) 20 s, (b) 40 s, (c) 44 s, (d) 48 s, (e) 54 s, (f) 60 s, (g) 100 s, and (h) 150 s at 100 rpm.

Results showed that the mixing from the level change was following the same general pattern as the tracer with no level change, but was slightly more distributed around the vessel. This emphasised that with the use of ERT, the effect of the change in level had been compensated for and a homogeneous image at the fully mixed state was produced.

Overall, the experiments conducted by Rogers to monitor the mixing/level change of barium chloride within a stir tank reactor exemplified how significant the use of ERT can be to generate faster, more accurate results with the use of ITS’ P2+ instrument.

Reference: Rodgers, T. L. & Kowalski, A. An electrical resistance tomography method for determining mixing in batch addition with a level change. Chem. Eng. Res. Des. 88, 204–212 (2010).

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