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!

Troubleshooting When the Filtration System is Not Working

 

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These are five dreaded words that no engineer wants to hear on a Saturday night or Sunday morning: “The filtration system is not working.” Of course, we never seem to get this call at 10 in the morning on a work day!

No matter the time of day, let’s not panic, take a deep breath and begin the analysis.  

There are normally three main areas that must be examined when you learn the filtration system is not working:

  1. The filter itself for mechanical reasons
  2. The equipment around the filter is not working
  3. The filter operational procedures are not correct.  

To fully understand the problem, it’s necessary to separate the symptoms from the causes. So, let’s examine each of these groups in more detail.

Troubleshooting Filter Problems

The first thing that should be checked is the filter itself. There could be a failure of the equipment mechanics such an internal components, seals, etc. Many of these issues will be described normally in the preventative maintenance section of the filter’s O & M manual. 

Second, keeping in mind, the filtration system is part of the entire process it’s important to examine the upstream and downstream equipment. For example, you might check:

  • Are the reactors performing correctly in terms of agitation, temperature control, etc. in order to produce the specified crystals?  
  • Are the precoat and body feed systems in tune for mixing, feeding, flow rates, solids loading, etc.?  
  • Are the valves and instruments operating correctly and reading the correct variables (calibrations), etc.?  

Next, take a look at the pumps that feed the slurry and washing liquids as well as the compressors the feed the gas streams for drying and cake discharge.  The pumps must produce the required pressure, flow rates, etc.  The compressors must also produce a certain gas flow at a specific pressure for a certain amount of time.  Are their interlocks in the control system or a control communication problem that are not being recognized that are causing the filter problem.  Finally, if flocculants and chemicals are being used, have these changed?  

Process Engineering Problems? 

The last place to look is the process or operational procedures. These could be responsible for the filtration problems.  For example, the particle size distribution may have changed, the amount of solids in the slurry may have changed, the cake compressibility may have changed, etc.  In terms of the operation, has the filtration pressure changed, timers changes, speed changed, etc.?  Finally, determine whether or not a process parameter has changed.  

Trouble shooting is not easy, but solving the problem brings a great sense of satisfaction. 

Let me know some of your troubleshooting horror stories! I’d love to share some in a future blog. Together, we can make it easier to handle the situation next time we hear those five dreaded words.  

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4 Key Differences between Filtration and Centrifugation

I’m always looking to collaborate and explore ideas with others in our filtration technology business. Happily, director of Oriental Manufacturers Jigar Patel, has offered this guest blog discussing differences between filtration and liquid solid centrifugation. I hope you enjoy Patel’s perspective:

liquid solid centrifugation
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Filtration and centrifugation are two distinct separation techniques used for isolating the required components from the mixture. The major difference between the techniques is the nature of the force employed and the separation method used. While filtration uses a sieve or filter media to strain undesired constituents, centrifugation leverages the power of the centrifugal force for the separation.

What is Filtration?

Filtration is a physical separation technique, by pressure, vacuum or gravity, used for segregating one or more components from a mixture for different applications. Depending on the application, the process may employ one or multiple metal perforated layers or filter mesh for solid-liquid separation. 

What is Centrifugation? 

Centrifugation is a process that employs a centrifugal force to separate the elements of the liquid slurry.  The remaining liquid (supernatant) is then transferred from the centrifuge tube or removed without disturbing the precipitate. The precipitating particles left behind depend on the speed of the machine, the shape and size of the particles and their volume, viscosity, and density.

4 Major Differences between Filtration and Centrifugation

#1 Nature of Operation 

  • Filtration 

Large particles in a mixture are unable to pass through the perforated layers of the filter. Yet fluids and small particles easily pass through the filter mesh under the pressure, vacuum, or gravitational force. 

  • Liquid Solid Centrifugation 

The centrifugal machine forces the heavier solids to the bottom creating a firm cake. The lighter mixture that stays above the cake is then decanted. 

#2 Separation Techniques

  • Filtration 

Filtration uses different techniques depending on the expected outcome which can be classified as pressure, vacuum, or gravitational.

  • Centrifugation 

Centrifugation techniques can be classified as micro-centrifuges, high-speed centrifuges and ultra-centrifugations. Microcentrifuge is typically used for research studies that require the processing of biological molecules in very small volumes. High-speed centrifugal machines are designed to handle bigger batches and are mainly used for processing industrial mixtures on a large scale. The ultra-centrifugation technique is used to study the properties of biological particles.

#3 Function 

  • Filtration 

The main function of filtration is getting the desired output by eliminating impurities from any given liquid or isolating solids from a mixture. 

  • Centrifugation 

The main purpose of centrifugation is fast, efficient separation of solids from a liquid solution or slurry.

#4 Efficiency 

  • Filtration 

Simple filtration techniques take time separating the desired materials, which makes the separation method less efficient. 

  • Centrifugation 

Centrifugation techniques employ machines that run with the aid of power, so the separation method is faster and more efficient. 

Both filtration and centrifugation are solid-liquid separation techniques that use different equipment and have different applications.

My two cents: Deciding which one is best suited to your process will take work. No matter the process in question, engineers are well served by taking the time to gather the information, make their own comparisons, and then develop a process solution.

Thanks to Jigar Patel. The director of Oriental Manufacturers believes in the power of good functional designs and their ability to boost productivity and drive growth. Fueled by his passion for innovation and all things EPC, Jigar writes on topics related to process plant equipments, process machinery production, turnkey solutions, best industry practices, liquid solid centrifugation, and his personal insights!‌

Keep the sharing going — let me know what you want to write about in this spot next!

Cookies are yummy, but avoid cookie-cutters.

filtration tests
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We can all agree that cookies are yummy. Cookie monster is not the only creature out there who loves to chow down on a tasty chocolate chip or oatmeal raisin (my favorite are Thin Mints).

What is not so good, though, is using a cookie-cutter approach to problem solving and filtration tests.

In filtration testing and scaling-up to commercial size, it’s important to not “jump to conclusions” that the familiar approach is going to work best.

Laboratory/bench top filtration testing is critical in the problem analysis, technology selection, and pilot and demonstration scale-up stages.

As I’ve blogged about, and discuss at length in my Practical Guide to Solid-Liquid Filtration, we can learn a lot from sleuths Holmes and Watson. They would argue it’s important to train yourself to be a better decision maker. Your best bet is to use checklists, formulas, and structured processes.

It’s also essential to train yourself to stop and repeat. Don’t succumb to certainty. Discuss your options with technology suppliers that can provide different filtration solutions. Partnering with suppliers with a proven track record in similar applications will shorten your technology scale-up cycle.

Ultimately, what matters are your premises (process definition, requirements and testing objectives) how the testing unwinds the crucial from the incidental (what is the critical process parameter) and ending up with a logical conclusion (optimum process filtration solution). With caution and clear thinking you can better manage the stress of a scale-up.

This blog marks the one year anniversary of “Perlmutter Unfiltered.”  I would like to thank everyone for their feedback and responses.  Let me know your ideas and thoughts; guest bloggers are always welcomed, whether it’s about filtration tests or something else for our industry.