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Scale Up Case Study

Process Air Flow Rate Determination

Problem

Determine the hydrodynamically equivalent process in a 32" tapered bowl for a process that was developed in a cylindrical 18" bowl.

Problem Categories

Hydrodynamics, scale up, Wurster, and PCTSWurster .
Solution

Duplicate U/Ut in the spout, U/Umf in the annulus, and mechanical forces (momentum).
Analysis of the Small Scale Process
Enter the process conditions in PCTSWurster to determine U/Ut in the spout, U/Umf in the annulus, and momentum.
Design of the Large Scale Process
Update the equipment and batch information.  Vary the column pressure drop until the U/Ut in the spout, U/Umf in the annulus, and momentum are duplicated in the large scale. 

The bed was bubbling in the smaller scale (i.e., U/Umf > 1) throughout the annulus due to its cylindrical shape.  In the larger bed, considerably more air needs to flow through the annulus in order to bubble the entire annulus due to the expanded bed area of the tapered bowl towards the top of the bed.  In many cases it is not possible to fluidize the entire bed for the tapered bowl.  For the purposes of this example, an arbitrary flow rate was chosen for the annulus that was bubbling at the bottom of the annulus, but not at the top.  The results are shown in the window below (second window below).  Note that 5% open area in the 32” was used to increase the air flow through the annulus. 

Conclusions
The process air flow rate that resulted in the same spout condition (i.e., U/Ut) using the 5% open area in the distributor plate above was 1980 SCFM.  This flow rate can now be used to hone in on the thermodynamic condition forthe scaled up process.