Best Practices for Filtration Testing for Solid-Liquid Separation

filtration testing
Photo by Pacific Northwest National Laboratory – PNNL on / CC BY-NC-SA

Testing in school has a negative connotation. Students dread tests. Parents bemoan “teaching to the test.” Teachers chafe against the curriculum parameters defined by testing expectations. Yet, the word “testing” should resonate much more positively with process engineers. After all, testing is the key for selecting the most suitable filtration tech for any individual solid-liquid separation task.

Although there is only limited theoretical background available, and even specialized engineering education at universities leaves many theoretical questions open, it is beneficial to have a minimum understanding of the theory of filtration itself. By identifying the role of each influencing part, the process engineer gains a potential tool to work with when it comes to understanding testing findings and developing a path forward in determining the best filtration procedure.

Just from experience, and for the benefit of engineers, some overview observations are necessary:

  • Don’t stop testing just because the first results suit your target
  • Don’t accept samples without verifying the parameters in the description
  • Never change more than one parameter at a time
  • One result is no result => verification is a must
  • Take a break and check the conformity of the results before you call it a day

Filtration Testing Requires Decision Making

In testing it’s essential to train yourself to stop and repeat. Don’t succumb to perceived certainty. After all, many parameters of the liquid and the solids have an influence on the filtration process.

  • Form and size of particles
  • Particle size distribution (PSD)
  • Agglomerate building behavior
  • Deformability
  • Compressibility
  • Liqiud viscosity
  • Solid content
  • Zeta-potential

While all of the above may not be known for all filtration applications, the final target is to find a theoretical approach together with a practical method of testing.

Sampling in Filtration Testing

Filtration tests need to be done with a “representative sample” defined as a sample “as close as possible” to the real production product.  Yet the specific characteristics of a slurry from the point of filtration are not obvious to everyone. That’s where testing comes in: the list of parameters is quite extensive and in many cases only a few are available.

Still, the more you can get the better. Although for the first tests, the ph-value, temperature, particle shape, size distribution, etc. are not necessary right from the beginning, these parameters are normally quickly measured and complete the picture of the suspension. It is obvious that solid content and viscosity do have an impact on the filterability.

“Suspending” Judgment in Filtration Testing

The characteristics of suspensions are not only caused by the liquid phase but also by the particles, the other half of a slurry. The solids can be of crystalline nature or amorphous, which means their structure is not really defined. They can also be organic (i.e. cell debris), fibrous, in-organic, compressible or incompressible, generate agglomerates or not, may have a zeta potential or not…. there are many possibilities.

An easy way to verify the type of solids is a sample check. If possible, the original suspension should be checked under the microscope. Then, the behavior of the solids can also be seen:

  • Do they tend to build agglomerates or stay on their own?
  • How is the distribution of the solids?
  • Is the structure of the solids needle-shape, potato shape, snow crystal or even fibrous?

The best practice in filtration testing is to consider all of these angles thoroughly before deciding on a filtration procedure.

I am a big fan of Sherlock Holmes who always warns “don’t jump to conclusions.”  This is one of the biggest risks we face during tests in the daily work of process engineering.  Let me know if you need help!

Chemical Process Optimization needs Out of the Box Thinking

Actual Unit -- Figure 2. This continuous vacuum belt filter with 9.0-m2 filter area was installed in 2016.
A continuous vacuum belt filter with 9.0-m2 filter area.

Loyal readers of this blog know how much I value innovation and creativity. So, you can’t be surprised that I want to share with you a success story in which we partnered with a client to develop an optimized filtration process for a zinc oxide product.

As discussed in a coauthored article for Chemical Processing, Madison Industries and BHS-Sonthofen Inc. worked together on laboratory and field pilot testing. Engineers from both firms showed creativity and “outside-the-box” thinking in looking at the process from new vantage points in their quest to find a better option than the installed batch filter press.

Our efforts led to the selection of continuous vacuum filtration. The continuous filter, which was installed in 2016, provides maximum filtration efficiency and improves product quality while increasing yield and reducing operating and maintenance costs.

Schematic Operation Of Filter -- Figure 1. Technology, based on fixed vacuum trays, features step-wise movement of filter media.
Figure 1. Technology, based on fixed vacuum trays, features step-wise movement of filter media.

Case Background

Madison Industries, based in Old Bridge, N.J., supplies copper and zinc compounds such as copper sulfate, copper carbonate, zinc sulfate, zinc chloride, zinc orthophosphate and phosphoric acid as well as other chemical products containing copper and zinc. Applications include animal feed, water treatment, dairy farming, food and pharmaceutical processing, and pool and wood preservative chemicals, among others.

The Madison facility was using a plate-and-frame filter press to filter a zinc oxide slurry made from a mix of various zinc feedstocks. The solids were mixed with water to form a slurry of 20% solids and then filtered. The cake was bagged in 2,000-lb totes, moved to another area of the plant and reslurried in sulfuric acid for further processing.

Madison wanted to expand production and replace the present labor-intensive process with a continuous operation.

Crucial Tests

BHS process engineers began laboratory evaluation of the process. Madison was open to all ideas and formed a team to brainstorm different approaches.

BHS conducted several weeks of testing and evaluated both pressure and vacuum filtration based upon the specific characteristics of the solids and slurries. The testing led to the following observations:

• Filtrate clarity: The most-appropriate filter cloth is a double-weave 12-micron polypropylene.
• Filtration rate: Vacuum filtration produced the maximum filtration flux rate at a cake thickness of 6 mm.
• Cake washing: Maximum displacement washing was achieved with wash ratios of 2.6:1.
• Cake moisture: Although not a critical parameter because the cake is reslurried, cake moisture is approximately 35%.

Based on its creative testing, BHS’s process engineers recommended continuous-indexing vacuum filtration as the optimum option.

Why Continuous Indexing

The BHS continuous-indexing vacuum belt filter provides for vacuum filtration, cake washing, pressing and drying of high solids slurries. The technology is based upon fixed vacuum trays, a continuously feeding slurry system and indexing or step-wise movement of the filter media (see Figure 1). In practical terms, the belt filter operates similarly to a series of Buchner funnels.

At each indexed belt position, washing and drying efficiencies are maximized with the stopped belt and the mechanism of plug flow for gases and liquids. Cake pressing and squeezing further enhance drying. Finally, the fixed trays allow for the mother liquor and the wash filtrates to be recovered individually and recirculated/recovered/reused for a more efficient operation. The design also can integrate steaming as well as counter-current washing.

Successful Switch

Madison and BHS installed the vacuum belt filter in 2016. The unit has met all product quality specifications. Madison has realized a 50% savings in wash liquids per batch as well as a reduction in labor and operating costs because the vacuum belt filter operation is fully automatic. Since the installation, Madison has optimized the operation, improving yields and minimizing costs.

The Madison and BHS collaboration illustrates a successful relationship between client and technology supplier. The BHS approach of lab and pilot testing, coupled with idea-generation, fosters identifying the optimal option for critical and difficult solid/liquid separations.

Selecting the Right Type of Filtration for Solid-Liquid Separation

solid-liquid separation
Photo by Picturepest on / CC BY

Filtration selection, if we think back to Sherlock Holmes, means “not jumping to conclusions.”  There is no “one size fits all” process solution.  Selecting a filtration technology requires a systems approach incorporated with other solids processing such as reactors, dryers, solids handling, etc.  You could gain an objective overview by filling out an application data sheet (like the ones I use for new or existing applications) that can help identify what’s involved in the specific solid-liquid separation.

Ultimately, the process has three components:

  • Material properties, which I’ll describe in more detail below
  • Separation performance objectives including, for example, filtrate quality (conductivity or residual solids) cake dryness, flowability of the cake, crystal breakage /fines generation and conditioning of the cake for further processing
  • Mechanical properties — The specification must be clear in terms of material of construction, temperatures/pressures, FDA validation, cleaning procedures, manufacturing codes, etc.  Each equipment type will have its own mechanical specifications that must be satisfied.

These three considerations are combined and ranked choices are then evaluated for operational, economic, and plant (internal and external) objectives.

Finding the Best Filtration Procedure

Your examination of material properties considers the solids and the liquids.  For solids, the engineer needs to know the total suspended solids (TSS) and solids concentration, particle size distribution (PSD), and particle shape.  The PSD should be based upon particle counts at different sizes rather than by weight or volume.

The particle shapes can vary:  spheres, rounded, angular, flaky, or thinly-flaked are among the examples.  Shape will influence the filtration rates for the process and also impact the PSD due to the nature of particle size measuring equipment.

Knowing this, the solid-liquid filtration system further requires a systems approach to incorporate other solids processing such as reactors, dryers, and solids handling, etc.  The full scope should include the actual upstream and downstream.

Consider this typical example of a chemical process including all of the associated processing steps:

  • Chemical synthesis and Crystallization:
    • Types of catalysts
    • Solvents
    • Continuous or batch
    • Temperature
    • Flashing
    • Inerting
  • Filtration
  • Drying
  • Dissolution
  • Hydrogenation
  • Secondary crystallization
  • Filtration
  • Final drying
  • Solids and slurry handling in all steps

General Guidelines to Selection

So, the question is where to begin to make the preliminary filtration technology choices for solid-liquid separation?  Here are some general guidelines to selection:

Filter Press Continuous Vacuum and Pressure Nutsche  Filter & Filter-Dryer Clarification
Solid content of the suspension (%) 5 to 30 10 to 40 10 – 40 < 5
Maximum Pressure Difference 100 bar -1 to 6 bar 6 bar 10 bar
Cake Thickness (mm) 5 to 50 5 to 150 5 to 300 20
Average Particle Size 1 to 100 micron 1 to 100 micron 5 to 200 micron 1 to 50 micron
Type of Operation Batch Continuous Batch Batch
Comments Good for slow filtration and can produce dry filter cakes; Excellent cake washing and pre-drying Good when reactor batch times equal to total cycle times Disposable for low flows; candle and plate filters for large flows

Let me know if this is helpful to you.  My idea is to do a series of types of filtration systems for solid-liquid separation for various applications.  What is troubling you?

Reflecting on Speed, and Time to Prosper

filtration technology

Welcome to 2018.

What do “Star Wars — The Force Awakens,” the New England Patriots and the Kansas City Royals and this blog all have in common?  As you might have guessed, they all had special events in 2015.  Yes, my blog has been up and running now for over three years! Plus, 2015 is when Star Wars debuted and both New England and Kansas City won their respective championships.

Before thinking about 2018, and this blog’s fourth year, I wanted to take a moment to reflect on the year 2017.  What intrigues me is what we know now that we did not know in January 2017, one year ago. There were many surprises ranging from politics, world events, social issues, to business and career, sports, food and entertainment.  In the comments below, let’s start a conversation about what you learned in 2017.

Reflecting on 2017 and 2018 Success

Of course, I have many ideas about what I learned last year. Yet, in boiling it down to one theme, I would focus on “speed.”  In all of our endeavors, the speed of information flow, decision making, world events, politics, etc., is increasing dramatically.  From a business point of view, technology, marketplace, competition, manufacturing, etc. are all changing at breakneck speed.  At BHS, for example, we addressed a marketplace request to incorporate “clean-in-place” (CIP) systems which led to changes with our rubber belt filter.

At the same time, if speed is what characterized 2017, for 2018 I’ve decided it’s time to slow down and reflect. For one thing, I have improved my yoga practice. In other areas of my day, I’m taking the time needed to review facts and data, analyze decisions, gather inspiration from many sources, and finally proceed with definite actions. Of course, I still need to be ready to change, as things will continue coming at “breakneck speed,” but I am optimistic about success.

For 2018, I’ve already started thinking with excitement about what posts my readers want to read.  There will be more blogs about “problem-solving” with topics on filtration, particle technologies, drying, and solids handling.  Yet I always invite you to make suggestions! In fact, I’d welcome guest blogger contributions to improve the chemical process industry.  Finally, read often, thick critically, and let’s all prosper in 2018.

The Technique of Technical Writing

technical writing tips
Image source:

I challenge you to think of a job in which communication skills won’t increase your chances of success. Even zoo keepers working with other species benefit from communicating non-verbally with the lions, tigers, and bears (oh my!) in their care.

In our engineering/business careers, technical writing skills are an even more important subset of communication, and highly valuable. If you follow this blog regularly, read the BHS newsletter or visit our website, you know already how much I enjoy writing and communicating ideas to the marketplace.

To me, while we may call ourselves engineers and professionals, we are also technical writers. All of us craft e-mails, white papers, reports, proposals, justifications, etc. Thinking about this made me want to share some of my thoughts on clarity of communication (with an appreciative ‘I’m not worthy’ nod to all the editors, some of whom I count as friends, of engineering magazines who have studied technical writing / journalism much more closely than I have).

Consider Your Audience

What language are you using? I do not mean to ask whether you’re utilizing a foreign language. Rather, are you employing the language of your audience? For example, many words are relative and they reflect the experience of the writer. Consider for instance the word “large.” What is a large motor, large pipe diameter, or large filter area? The answer depends upon the marketplace, application, place in the world, company, etc. A large motor for a pharmaceutical engineer is much different than for the engineer working in a refinery.   A large filter area is different in the mining industry compared to a specialty chemical. Or what about the word “high”? Think about all of the ways this one word is used…high cost, high efficiency, high pressure, high temperature….I could go on and on.

Going further, when we look at language, we should also look at our own company’s languages. Every vendor, every client, and every software device has its own acronyms and code words. It is like the United Nations without the use of the headphone translations.

Ultimately, clear and concise writing can prevent a safety accident, make a project proceed better, reduce the need for calls in the middle of the night to the process engineer (or worse to the vendor) and improve overall satisfaction. Take care with your writing.

Principles for Better Writing

How do we get better at writing? Write often. Read a lot (you’re off to a great start subscribing to this blog!). I also try to focus on the following:

  • Accuracy — Don’t get caught up in impressing people will all that you know about a subject. Instead, pay attention to accurately communicating the essential information.
  • Write to the audience — You draft for you. You revise for your audience. Always look at what you have written with fresh eyes to consider what will make sense to the person reading.
  • Conversational — Technical writing doesn’t need to be bogged down with jargon. Everything is more interesting to read when the reader is engaged in the story you are trying to tell.
  • Clear and concise — Don’t try to impress people with multisyllabic words and quotes from great classical minds. Cut the excess in favor of getting right to the point and staying there for only as long as you need — no longer.
  • Simple — There are many complex concepts we address every day in our professional lives. That’s what keeps it interesting in the office, right? Only you needn’t share all of the nuances with your reader. The job of the writer is to process the information and identify the main point and important takeaways. Do the thinking first and then share your simple observations in your writing rather than rambling on at length about all of the options you might have considered.

These are the techniques that I focus on in my writing. I hope that you’ll see my blog follows these principles.

Have you had any specific experiences or funny experiences where “language “has been confusing? Let me know. I’d love to follow this blog up with one sharing amusing stories from our field.

Get Out There and Learn!

Genchi Genbutsu
Photo credit: NASA Goddard Photo and Video via / CC BY

Years ago, when I was an MBA candidate at the University of Illinois, we were introduced to the MBWA (Management By Walking Around) principle. In Japan, the principle is known as “Genchi Genbutsu.” Toyota, in particular, is known for this “actual place, actual thing” philosophy. Ultimately, in all aspects of engineering — from operational efficiency to process development to system dynamics — this “go and see for yourself” approach is worthy of discussion. No matter how good the information may seem to be, firsthand knowledge is fundamental.

My experience is as a technology supplier, but this action-oriented principle equally applies to the production and processes of our clients. For example, we have a pharmaceutical client that moved from batch processing to continuous processing with BHS technology. The process engineer may be satisfied that the client’s goals and objectives were achieved. However, we insist the next step is to “go see ourselves” and observe the operation. What are the machine efficiencies? Is the design easy to operate and maintain? What is the operator mindset?

In another case, involving a commercial scale-up of a new chemical process, we must know the catalyst; how the scale-up is planned…step-by-step or full in; sequential or parallel technologies…vacuum or pressure; options and costs; and finally value-engineering. The best way for BHS to meet the scale-up needs is to follow the approach of “seeing for ourselves.”

Always be Learning

In looking to always be learning how to best serve customer needs, we also incorporate Jay Forrester’s system dynamics. This technique of feedback and impacts considers questions such as: How does the competition react? What are the consequences — intended or unintended?

Although system dynamics had its beginnings in the physical realm, this method of thinking has moved to areas such as leadership, operational structure, interactions of variables and making decisions for how things are changing for the future. This is easily applied to chemical engineering where “gifted all-arounders” are preferred in a world of increasing complexity.

This idea of exploring a system fully, aiming to truly understand the actual thing functioning in the actual place can greatly impact learning. It poses interesting questions too: How would a car company make pills? How would a chemical company make water bottles? How does a CEO of an airplane company succeed in begin a CEO of a car company? And so on.

Learning in one field can become applicable to others. This blog invites readers and followers to share experiences and improve engineering and innovation processes. Let’s keep this conversation going.

Business Building and Anger

Anger in business

I wouldn’t recommend anger at work, but sometimes engineers do get angry at a process, problem, or piece of equipment.  On the other side, in technical consultative sales, we try not to get angry at our clients, at least not directly. After all, in the business world, anger is often viewed as an unsavory emotion. The individual has lost self-control — a cardinal sin in business, right?

In an article addressing anger in the business world, Forbes contributor Neil Patel notes anger can:

  • hinder thought process
  • lead to rash, impulsive decisions
  • create rifts between business partners, colleagues and clients.

Yet Patel also suggested anger can have a major upside if used as fuel to build a business.

“Anger is actually useful when harnessed and controlled because it fosters useful behavioral capabilities,” according to an Inc. reporter’s summary of Emotional Intelligence experts Henry Evans and Colm Foster. Anger creates focus and generates confidence, they suggest. In fact, the highest performing people and teams tap into and express the entire spectrum of emotions.

So, how exactly might you channel anger to for positive ends?  Patel offered 10 ideas:

1. Improve Communication

2. Achieve Hyper-Focus

3. Eliminate Fear

4. Boost Your Confidence

5. Take Action

6. Ignite Your Passion

7. Show Perseverance

8. Aid in Negotiation

9. Show Your Humanness

10. Provide Self-Insight

The important thing about anger in business is to harness the emotion in a smart, controlled way. Avoid getting mad at people (focus on an action or event instead) and try not to say things you will later regret.

Ultimately, anger is one of many authentic emotions. Ignoring it, or trying to hide it, can have many negative impacts both on your professional life and personal well-being. As Inc.’s Jeff Haden pointed out, “Anger is authentic — and so are great leaders.”

Be a great leader by learning to channel your emotions — negative and positive both — in a productive way that helps your focus and drives your business success.

“Anger is authentic — and so are great leaders.”

Bringing Quality Control to Burritos

engineering process
Photo credit: jeffreyw via / CC BY

The final page of Chemical & Engineering News (C&EN), Newscripts, covers interesting scientific research. The item “Scientific Search for the Perfect Burrito” quickly caught my eye. After all, I like burritos. But what I read made me want to share the ideas with you:

Scott Cole, a neuroscience Ph.D candidate at University of California San Diego introduced a statistical burrito rating system. Why, you ask? As he suggests online, a “lack of funding to support public burrito knowledge has led millions of people to eating a burrito and subsequently feeling dissatisfied, a tragedy that can be avoided.”

He notes, “even the most experienced burrito eaters have experienced the following disappointments:”

• “I just took a bite entirely of sour cream”
• “This carne asada has the texture of rubber”
• “I am not looking forward to the leftover burrito in my fridge”
• “Where is the meat in this burrito?”
• “I need a fork”

To address the tragedy, Cole and his reviewers have set out to deploy a 10-factor rating system to evaluate the “majestic cylinder.” The considerations, per Cole’s site, are:

1. Volume
2. Tortilla quality
3. Temperature
4. Meat quality
5. Non-meat filling quality
6. Meat: the ratio between meat and non-meat.
7. Uniformity: “bites full of sour cream and cheese with no meat are disappointing.”
8. Salsa quality – and variety!
9. Flavor synergy
10. Wrap integrity

Need to see the data? It’s viewable online at Cole’s website in a Google spreadsheet.

What I love about this is the systematic way Cole has approached the problem. Just as we would do with an engineering problem, he’s talked with many people involved with producing and utilizing the burrito, developed an overarching checklist and a rating system, and created a spreadsheet to analyze the problem and formulate solutions.

While it sounds simple, we all know, it’s not so easy. After all, as Sherlock Holmes reminds us, we need to be open to investigating the basics; according to the great detective “there is nothing more deceptive than an obvious fact.”

Juiced up about Baseball Science

process engineering

Those who have followed my blog already know some about my background. For instance, I am an avid baseball fan. But here’s a new fact…I have been playing baseball since I was 5 years old. In fact, when I was 12, I was coached by the famous musical band, The Tokens, whose biggest hit was “The Lion Sleeps Tonight.” Needless to say, this was not a winning team. Success was always just “a win away, a win away…”


The Chemistry of Baseballs

With the playoffs and World Series looming, the controversy once again has arisen about the “juiced baseball.” This season the number of home runs per game has increased to 2.54 from 2.03. Hit Tracker Online provides us with all the stats and information on “how far it really went” for MLB games.

But what is really going on? There are many theories:

  • hotter temperatures due to global warming
  • strike zone changes
  • stronger and younger players
  • pitching changes.

If we focus on the data, which is what we do as chemical engineers, there are some other interesting ideas to consider.

One theory is based upon the drag coefficient (air resistance) of the ball, as discussed by Rob Arthur. His hypothesis is that the drag coefficient has decreased to 0.344 from 0.357. While this does not sound like much, it can add over five feet to the ball’s distance. This would be enough to increase the number of home runs by 10 – 15%.

Another theory by Ben Lindbergh and Mitchel Lichtman suggests an “air-ball revolution” meaning that players are swinging differently. Several MLB players have been in the news for focusing on hitting the ball harder in the air, and elevating it off the ground more.


Testing Baseball’s Stuff

Chemical & Engineering News also has weighed in on data from Rawlings, which has been the Major League Baseball (MLB) supplier for many years. Matt Davenport’s 26 June 2017 article Materials: What’s That Stuff? states the ball is the same and references the ball’s Coefficient of Restitution (COR) value, which has always been between 0.514 – 0.578. The COR refers to the ability of an object to bounce back to its original height when dropped from a certain height. The recognized standard for COR testing is an ASTM method F-1887.

Thus, why we’re seeing such a run on home runs remains a mystery and will be debated for a long time. My idea…let’s have a hot dog and a beer and share theories. As Ernie Banks said “It’s a great day for a ball game; let’s play two!”

Relating The Undoing Project to Unfiltered Thinking

decision making
Photo credit: Simon & His Camera via / CC BY-NC-ND

This summer I read The Undoing Project, by Michael Lewis. Lewis has also written Liar’s Poker, Moneyball, The Blind Side, and Flash Boys — so maybe you’re familiar with his work. His 2016 book, with the subtitle “A Friendship that Changed Our Minds” introduces us to two Israeli psychologists whose work changed everything from medicine to investing and revealed the weirdness of the human mind. This is also the story of two men with different backgrounds collaborating to create new ideas and new theories.

In the 1970s, Daniel Kahneman and Amos Tversky changed our understanding of human judgment and decision-making. In 2002, Kahneman won the Nobel Prize in Economics (Tversky would undoubtedly have won as well, if he hadn’t died of cancer several years earlier).

Kahneman and Tversky created the field of behavioral economics and showed how the human mind makes errors in judgement in uncertain situations. Their work led to the use of algorithms and big data gathering rather than relying on human intuition. Lewis’s book offers many examples of how this work is used today:

  • Index funds in the stock market
  • evidence-based medicine rather than “diagnosis from the gut”
  • sports such as basketball and baseball using algorithms to analyze players and draft choices
  • government decisions on tax policy, trade, etc. in the US, Great Britain, Australia, Germany, Scandinavia and others.

Relating Undoing to Unfiltered

While the applications of Kahneman and Tversky’s thinking are very interesting, especially data analysis, the aspect that impacts my blog readers is that of sample size. According to Lewis, the collaborators concluded that “in the search for scientific truths, [all scientists] were relying far more than they knew on chance…What’s more, because they had so much faith in the power of small samples, they tended to rationalize whatever they found in them.”

This realization, according to many in the field of measurement and statistics, was the duo’s stroke of genius. For example, a study of 40 subjects/topics gave only a 50% chance of accurately reflecting the answer while to have a 90% chance of being correct, the sample would need to be increased to over 130.

In our chemical engineering business, considering an appropriate sample is a critical point whether it’s with filtration testing, reaction chemistry, drying analysis, etc. Thinking about Kahneman and Tversky reminds us we all must remember to keep in mind our biases and get as large as sample as possible.