Real World Examples of Particle and Cake Formation Influences

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Process engineers might love it if all of the filtration technology solutions they developed ran flawlessly, at all times, under all conditions. But, this isn’t realistic. Something might go wrong with the filtration mechanism itself. A change in the environment — upstream or downstream — could cause problems with particle or cake formation. Even the smallest shift in the operation process or procedure can prompt the dreaded phone call to the engineer: “the filtration system isn’t working.”

In my work at BHS-Sonthofen Inc., I’ve seen filtration technology impacted by particles and cake formation that weren’t predicted in designing the solid-liquid separation solutions. 

Particle Sizes Changes from Lab to Production

The existing process was a batch crystallizer operating at 0 – 5 degrees C with 13- 20% solids  to a batch vacuum filtration operation. The filter was designed for a five inch cake height. The objective of the process optimization was to move to a continuous process of continuous reaction to continuous filtration, cake washing and drying.

The BHS rotary pressure filter was installed for continuous pressure filtration.  What did the client find out?  Only the particle size has changed from lab to production!  As you can imagine, this was not a small change.

cake formation

Going back to the drawing board and testing processes again, we made the following changes to the filtration system:  new filter media, increased cloth wash pressure with a new solvent and finally a reduced cake thickness.  Yes, this trouble shooting required about 6 months of work, but problem solved!

Troubleshooting Filtration Technology

In another instance with grey water treatment units, a clarification application for the purge water treatment unit (PWTU) was installed and started up for a year of successful running. Then, inexplicably, the performance changed and the filter began plugging quickly during cycles.

cake formation

 

Troubleshooting the system we had to re-examine the filtration system under different conditions:

  • Clarifier overflow with no coagulant / no flocculants 
  • Clarifier overflow with only coagulant / no flocculants
  • Clarifier overflow with both coagulant and flocculants
  • Clarifier overflow with only flocculants / no coagulant

Taking a holistic approach to the system, we were able to determine chemical changes caused the larger particles to settle out. Only the smaller particles were reaching the filtration system, which was blinding the filter media.  By eliminating the flocculants  and reducing coagulant usage (even though this was better for the client, and not necessarily BHS as the chemical supplier, we were able to improve filtration rates and once again offer a consistent PSD.

Ultimately, with the right approach to troubleshooting, and by embracing the idea that we do on a daily basis is an art coupled with science, we can enjoy a strong sense of satisfaction when we get that filtration technology up and running again.

This blog is based on a presentation I made to the  8th World Congress on Particle Technology. View the presentation slides in full!

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