Dryer Selection and Bulk Solids Handling 

 

blindspot-analysis-toolshero-1.jpg
Image source: https://www.toolshero.com/decision-making/blindspot-analysis/

Solids handling is not a unit operation. Therefore, it’s not covered in engineering courses. This leaves process engineers struggling to understand the “flowability” of bulk solids. This blind spot is huge. So, let’s talk about dryer selection and bulk solids handling.

Recently in The Chemical Engineer, Grant Wellwood described bulk solids handling as the biggest industrial activity on the planet. The article estimated “that >70% of everything we use or consume involves bulk solids handling somewhere in its lifecycle.”

Mishandled, this process can quickly and efficiently destroy product value, careers, projects and even organizations. Yet, bulk solids flow is often an afterthought once the separation and drying equipment is selected. This article aims to bring bulk solids handling to the forefront.

Bulk Solids Handling Parameters

Bulk solids are defined as materials (solids) handled in various volumes and counts. Their flowability is impacted or controlled by friction (particle-particle or particle-surface). During the drying process, solids go through different phases such as free moisture, bound moisture, thixotropic and finally (and hopefully) free flowing.  

The selected dryer must be able to handle each phase without creating fines, balls that can trap liquids, and without adding additional heat due to friction.  

Here are some of the process and design parameters engineers need to consider for dryer selection:

  • Dryer Process: Batch, Continuous, Atmospheric/ Vacuum, Turbulent, Gentle, Ring-Layer, Feeding  (Volumetric or Gravimetric), Upstream and Downstream Equipment
  • Recipes: Number of ingredients, Frequency of campaigns, Cleaning operations, Product integrity (fines generation) after drying and  Residence time
  • Dryer Performance: Batch size, Filling levels, and  Production volume
  • Product Characteristics: Quality, Bulk density, Tendency of segregation & agglomeration, Thixotropic phase, Shape, Size, Homogeneity, Risk of separation, Flow properties, Abrasiveness, and Moisture & Temperature
  • Mixer design: Material of construction,  Surface quality, Heating/cooling, Liquid feeding, Type of mixing tools, Speed of mixing tools and degree of back mixing
  • Dryer Integration: Material flow, Physical space, Process sampling, safety requirements, etc.

It’s a lot to think about. Westwood observed in his thorough article, “When handling bulk solids, it’s always important to take a holistic or systems view because of the complex dependencies.”

BHS & Bulk Solids Handling

As my readers know, BHS provides for thin-cake filtration, cake washing and dewatering based upon pressure or vacuum, for batch or continuous operations from high solids slurries to clarification applications with solids to 1% and trace amounts.  

In 2018, BHS acquired AVA mixers and dryers based in Herrsching (Munich) Germany.  VA is in the unique position to provide both vertical and horizontal technologies providing for turbulent as well as gentle mixing, reacting and drying of wet cakes, powders and process slurries. The technologies are vacuum or atmospheric, batch and continuous, for final drying to “bone-dry” powders. The BHS technical article, Dryer Selection, explains the designs as well as selection parameters.  

We know that solids change when processed from a wet-cake to bone-dry powder. Process engineers need to do the tests and trial and error to better understand these changes. As I often say, we can’t jump to conclusions.

Our process engineers would be happy to help at the BHS test center. With an understanding of how the flow properties change, depending on “complex interactions between particle size and distribution, moisture content and distribution, process history (time and manner), mineral composition, surface texture and condition as well as ambient conditions, just to name a few…” the dryer selection can begin in an educated manner. 

Good luck and feel free to contact me for help with your bulk solids handling questions.

Engineer Checklists and Learning from Apollo

engineer checklists

Recently, I discussed the five management lessons that we can learn from the Apollo lunar landing in 1969. Continuing on this theme, an article in The Chemical Engineer, “Houston-We have a checklist” a UK magazine that I write for, had an interesting take on the lunar landing and engineer checklists.  I was intrigued, of course, as I periodically invoke Sherlock Holmes and the benefits of checklists for testing, analysis, etc.   

The magazine article, written by Mark Yates, looks at the checklists used both at Mission Control and in space. He takes us through the Apollo missions where there could be two spacecraft both operating remotely 240,000 miles from Earth and out of communications contact with Earth for significant periods of time.

Checklists and cue cards covered everything from mission rules, abort criteria, emergency procedures and activation of backup systems in the event of a total failure of a primary control system for example. These checklists and procedures went everywhere. In fact, each Moon-walking astronaut would have a book of procedures strapped to his left wrist that he could follow out on the lunar surface.

In fact, all of the Apollo crews would each log over 100 hours familiarizing themselves with the numerous procedures and checklists. Apollo 11’s Command Module Pilot Michael Collins called them the “fourth crew member.” These checklists were also one of the first examples of digital computers and man being able to operate together seamlessly.  One of the actual checklists used by the Apollo 11 crew is shown below:

Chemical Engineering Checklists

How do we use checklists in chemical engineering?  We have many uses for them. For example, if you visit an earlier blog, you’ll find checklists and application details for filtration testing.  

For AVA mixer and dryer testing, we use the following checklists:

  1. Measure bulk density
  2. Measure moisture content
  3. Measure wet cake 
  4. Make sure to ground the dryer for electrostatic charges
  5. Measure RPM
  6. Record jacket temperature and product temperature
  7. Measure vapor stream 
  8. Measure vacuum level
  9. Measure dry cake and drying time to develop drying curves 

The Apollo missions were 50 years ago, but checklists are still critical for safe and efficient operations. Whether you’re an astronaut or an engineer!

Common Myths About Engineers

common myths about engineers
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As a regular reader of Chemical Engineering Progress (CEP), I was impressed to see its Editor-in-Chief Cindy Mascone writing her monthly editorial as a poem. She mentioned that when she writes for the magazine “accuracy, clarity, and conciseness take precedence over all else.” But that doesn’t mean she can’t be creative too! Her poem got me thinking about common myths about engineers.

  1. We aren’t creative
  2. We lack social skills
  3. We want to fix everything (whether it needs it or not)
  4. We’re quantitative wonks
  5. We are boring (just in case that wasn’t clear from being a quantitative wonk)
  6. We’re not open to new areas of inquiry or interest

Get to know an engineer!

Of course, I beg to differ. I like to think of this blog as one outlet for creativity. Plus, every time we come up with a new solution or problem-solve in a new way, we’re showing not only critical, but also creative thinking.

I’ve written a lot about troubleshooting in filtration technology, but not because we do it for kicks. We do it to improve a process or solve a problem. Really, we’d rather be innovating — which, again, is just how non-boring and creative we can be.

We may know our numbers, and some of us can be a little socially awkward (but plenty of liberal arts enthusiasts are too). Still, I’d argue that we are generally creative, inquisitive, and downright interesting folks!

And now, because I know you’re curious, I can also share the poem itself:

Ode to the March 2019 Issue of CEP

This month we feature process intensification

One aspect of which may be flow augmentation

Equipment that is smaller or does more than one function

To the old paradigm, PI causes disruption.

The first article tells of three RAPID teams

Whose projects are the stuff of dreams

Microwaves, solar hydrogen, and hydrofracking

Energy-saving ideas, they are not lacking.

A dividing-wall column replaces two towers with one

It changes the way distillation is done

With a smaller footprint and lower capital cost

And on top of that, no efficiency’s lost.

So how do you optimize an intensified route?

That’s what the next article is about

Use this building block approach to process design

And watch your energy use decline.

A digital twin software tools can create

To capture the process’s every possible state

You can study alternatives and run what-if tests

To figure out which option is best.

This issue contains many other things, too

Whatever your interests, there’s something for you

The same can be said of the Spring Meeting which will

Take place in New Orleans and be quite a thrill

Check out the preview after page seventy-four

For sessions and keynotes and events galore.

I’ve run out of space so now I must stop

But if you like this poem, to the website please hop

There’s more rhyming about CEP and its staff

I hope I have made you smile and laugh.

Thank you for coming to read more of my poem

On the website or app that is our virtual home.

The authors who write for this fine magazine

Do it not for the money but to get their names seen

By thousands of people at sites far and wide

For this publication is a valuable guide.

The topics they cover in their technical articles

Range from safety and computers to fluids and particles

From water and energy, from bio to dust

From nano to columns that are resistant to rust

From instrumentation to exchangers of heat

Among chemical magazines, CEP can’t be beat.

Our readers know not what we editors do

To make the articles understandable for you

Each page is read over many times with great care

To ensure that no typos can be found anywhere

That tables and figures are in the right places

That all the text fits with no empty spaces

That references include all the necessary data

That symbol font correctly displays mu, rho, and beta

That hyphens appear everywhere hyphens are needed

That the proofreader’s comments have been fully heeded.

We take pride in our work and we love what we do

Bringing the latest technology and information to you

But now we must turn to next month’s content

And make sure every moment on the job is well spent.

Reprinted with permission from Chemical Engineering Progress (CEP), March 2019. Copyright © 2019 American Institute of Chemical Engineers (AIChE)

Inspired to write your own technical poetry? Engineering verse? I’d love to see it and share it here! Who knows, maybe there is an anthology in the works!

 

Weighing Alternative API Filtration Technologies

API filtration technologies
Image source: Google images

Being a process engineer is all about making choices. When it comes API filtration technologies, many different types of equipment can be used for removing catalyst residues. While conventional filtration equipment is operated manually, I recently worked with PharmTech on an article outlining how both candle filters and pressure plate filters are operated as automated systems. This article reviews what we discussed.

Pharmaceutical manufacturers are increasingly looking for automated equipment with in-line process control. Well, automated candle and pressure-plate filtration equipment for removing catalyst residues from API slurries are operated in a closed system. This automated filtration also meets the demand for improved safety and reliability by removing the manual operation.

First, though, you need to understand the difference between candle filters and pressure-plate filters and how they differ from tradition filters. 

Conventional or traditional filters can be defined as bag filters, cartridge filters, manual plate filters, and plate and frame filter presses. These are all manually operated filters. They are not really sealed—especially not when solids get discharged.

Candle filters and pressure plate filters are improvements over these types in terms of reproducible quality, multiple process steps, cleanable and reusable filter media, and full containment for solids recovery. 

A major difference is that the operation of plate filters and candle filters is 100% automated. Solids discharge is provided in a sealed and safe way.

When to Use Candle or Pressure Plate Filters

Deciding between candle and pressure plate filters depends largely upon the cake structure developed by the process solids. 

Cake structures that can maintain their integrity in a vertical form are suited for candle filters. If the cakes themselves are too dense or too light or tend to crack, a horizontal plate filter is the better choice of technology. Thickness of the cake structure is another decision parameter. Candle filters typically have maximum cake thickness of 20 mm, while plate filters can handle up to 75 mm.

Generally, the candle filters and pressure plate filters can be used interchangeably based upon the cake structure itself. Some cakes can be handled in either vertical or horizontal form. In that case, the process dictates the choice.

When it comes to deciding the best filtration type for continuous or semi-continuous processing, consider the upstream and downstream equipment. Both candle filters and pressure plate filters are batch operations. For continuous or semi-continuous operations, either multiple units are required or buffer/holding tanks can be installed.

Pharma Disposal or Recycling

We also discussed best practices for disposal or recycling. For non-hazardous disposal, the cakes can be first washed to remove all of the toxic or hazardous compounds and then dried to a standard of no free liquids. The cakes can be fully discharged in a contained and dust-free manner to totes or drums. 

For recycling, the process solids can be reslurried within the candle filter or pressure plate filter to be pumped back as a slurry to the process. The process liquids or filtrates can also be pumped back to the upstream reactors for reuse.

Questions about alternative API filtration technologies? Other decision parameters I didn’t think about? Let me know, I’m always ready to chat. 

Rethinking Engineering Standards: The Importance of Getting it Right

engineering standards

Normally, as my readers know, my blogs cover a wide variety of topics. I like to relate and link seemingly unrelated topics to each other in innovative ways. It keeps our critical thinking faculties sharp! However, this blog deviates from the pattern to share two fresh viewpoints on changes in engineering standards. It’s technical, but important. Science textbooks will need to be rewritten!

It doesn’t happen often, but after a November 2018 vote at the Congress Chamber in the Palace of Versailles, four fundamental units of measure have been redefined. An assembly of metrologists (those who study the science of weights and measures) voted to redefine the International System of Units (SI)’s ampere, kelvin, kilogram, and mole. 

These four units join the meter, candela, and second in being defined not in reference to physical artifacts, but in reference to fundamental physical constants. Scientists say redefining these units to be based on a physical constant will make measurements more accurate and stable. 

Science students may not be too happy about having to pay for new science textbook editions, but the unanimous vote was followed by a standing ovation by the assembly’s participants from over 60 countries.

Engineering Standards Must Be Correct

The news was followed up by a Wired blog by Rhett Allain, an Associate Professor of Physics at Southeastern Louisiana University. He agreed the “definition-based standard” was a better choice:

There is a new standard in town, and it’s sort of a big deal…It replaces the old definition of the kilogram that didn’t even have a definition. The old kilogram was an actual object. It was a cylinder made of a platinum alloy and it had a mass of 1 kilogram. It was THE kilogram. If you wanted to find the mass, you had to take it out and measure it. You could then use it to make other kilograms.  

He was behind the new standard of defining the kilogram using another constant—Planck’s constant (the details are in the Wired story). However, Allain also cautioned that there is a wrong way to define the kilogram. “Unfortunately, I have already seen some very poor explanations of this new definition of the kilogram,” he wrote. His fear, he wrote, was that “these super-simple (and technically wrong) explanations might become very popular.”

For example, he cites an example: “The new definition of the kilogram sets it equal to the mass of 1.4755214 x 1040 photons from a cesium atom.” Of this he notes, “That is so bad. I’ve even seen a diagram with a traditional balance. On one side there is a kilogram mass, on the other side a bunch of photons. Please help; please don’t share that kind of stuff. You might as well just say ‘Oh, hey—the kilogram is now defined by some magical spell.’”

For Allain, this change is another argument in favor of his number one rule about science communication:

You can rarely be 100 percent correct in your explanation, but you can be 100 percent wrong. The goal isn’t to be correct in your writing—it’s to not be wrong.

I have to agree with Allain. Scientific writing is hard, but propagating the “wrong information” can have serious consequences. 

I always encourage readers to test, test, test, and look at things with a fresh perspective. Add to my mantras an echo of Allain’s: write with care.

Clear thinking about automated clarification technologies

automated clarification technologies
Photo by SplitShire on Pexels.com

This is an edited version of an article I wrote for The Chemical Engineer. I hope you enjoy this take on automated clarification technologies.

Throughout my career in the solid-liquid separation market space, I have seen some interesting solid-liquid separation solutions. At one melamine resin facility, the slurry was in a formaldehyde process. The operators were wearing masks, opening up a manual plate filter in a room with residential floor fans, to dig out the cake from the paper filter media. 

In another case for zeolites, the client had multiple bag filters to clarify the filtrates following a vacuum belt filter. When the filtrates, the final product, remained cloudy, to my surprise, the client decided to add another set of bag filters!

A clarification system is employed after coarse-particle filtration or as a stand-alone system to remove fine particles at low concentrations. These particles are typically less than 5 µm and are in concentrations less than 5% solids down to ppm levels. 

Process engineers struggle to clarify process liquids. But there are ways to automate the clarification processes to improve filtration and minimize operator exposure. The cake solids structure and the nature of the process will determine which types of pressure-filtration, automated clarification technologies are best for you.

Candle Filters

A candle filter is a pressure vessel filled with tubular filters (called filter candles). A typical filter candle comprises a dip pipe to flow the filtrate and pressurized gas, a perforated core with supporting tie rods, and a filter sock. 

As the cake builds during operation, the candle filter’s removal efficiency increases, enabling removal of particles as small as approximately 0.5 μm. 

During operation, a feed pump or pressure from the reactor or feed tank forces the slurry into the bottom of the pressure vessel. The solids build up on the outside of the filter sock, while the liquid filtrate flows into the candle, through the registers, and out of the vessel. This process continues until the maximum pressure drop, design cake thickness, minimum flow, or maximum filtration time is reached. The cake is washed to remove impurities and residual mother liquor, and then dried by blowing gas through the cake. Next, low-pressure gas enters the individual candles and expands the filter socks.

This process breaks apart the dry cake, which detaches from the filter sock and falls into the vessel cone. Candle filters are used for thin-cake (5–20 mm) pressure filtration applications. They are best suited for filter cakes that are vertically stable.

Pressure Plate Filters

Like the candle filter, pressure plate filters comprise filter elements contained within a pressure vessel. However, instead of vertical filter candles, the vessel containshorizontal filter plates. These elements are slightly sloped, conical-shaped metal plates that support a coarse-mesh backing screen covered with filter cloth. 

An opening in the centre of the plate allows the filtrate to travel between plates and throughout the vessel. The filter cloth can be synthetic, as in the candle filter, or metallic as the cake discharge is by vibration or spinning. 

Operation is similar to that of a candle filter. For cake discharge, there are two main designs. In one, two unbalanced motors vibrate the filter plates to dislodge the cake from the filter cloth. In a second design, the plates spin so that the cake can be ‘thrown’ off the plates. Pressure plate filters are used for filtration of cakes up to 75 mm thick. 

Sintered Porous Metal Cartridges 

Another type of automated clarification technology is based upon sintered porous metal cartridges. These can be used in a variety of process flows such as inside-out filtration. After each cycle, solids are backwashed off the inside of the elements and discharged as a concentrated slurry or wet cake. They can also operate in a conventional outside-in filtration. Porous metal cartridges are used for high temperature applications greater than 200oC where the solids are well-defined hard crystalline shaped. 

Filter Aids 

Filter aids are generally the last resort. Often in clarification applications, the solids are very fine or amorphous, so can be difficult to filter. When filtered, the solids will create a thin, impermeable coating over the filter media and immediately reduce the filtration rate to an unacceptable level. In these difficult cases, filter aid pretreatment can be used to improve filtration properties and efficiently remove the fine solids from the process liquids. The types of filter aid include diatomite, perlite, and cellulose. 

In the precoat method, filter aid is used to generate a thin layer of solids on top of the filter media. Once formed, the filter aid cake functions as the primary filter media. Therefore, the filter cloth is no longer the real filter when precoat is used. For that reason, the filter cloth should be as open as possible while still retaining the filter aid material. 

The precoat process is achieved by mixing the filter aid into clear liquid or mother filtrate in a precoat tank. This slurry is then recirculated through the filter where the solids are captured by the filter media. The clean filtrate is recirculated back into the precoat tank. The precoat should be thick enough to ensure that the entire media surface is coated but thin enough so that it does not provide significant resistance to filtration. 

In body feed filtration applications, the filter aid is blended with the slurry feed either by dosing the concentrated filter aid suspension into the slurry feed with in-line mixing or by mixing the filter aid into the entire slurry batch and maintaining agitation. By adding filter aid into the slurry feed, the resulting filter cake is more porous, allowing higher and longer sustained flow rates. Body feed also helps to restrict solids movement which improves filtrate clarity. 

Needless to say, the use of filter aid improves filtration but requires more equipment, more process control, and results in more solids for disposal. 

Final Thoughts on Automated Clarification Technologies

How can the process engineer be successful? When confronted with a clarification process, don’t simple throw more bag filters at the problem. Conduct lab testing to analyze the cake structure, filter media, filtration pressure and cake thickness. With the data in hand, you can evaluate the different technologies and design a more reliable and cost-effective clarification process. Find a different approach!

 

 

P&IDs and Process Evolution

P&IDs and Process

P&IDs are par for the course in process engineering. Recently, I was poring over P&IDs and process planning for several projects. Each project was multinational, multicultural, and extremely complex. For one specialty chemical filtration application, part of a plant expansion in the southern United States, the engineering company is in the Southeast while the existing processes were from the Netherlands and Austria. In another project, with a similar scope, the plant expansion and the engineering company were both in the Northeast U.S., yet the current processes operate all throughout the UK.

As you can imagine, the piping and instrumentation diagrams (P&IDs) had many changes, each shown in a different color —the Christmas Trees of P&IDs.  There were extensive e-mail threads of comments and questions and, of course, questions/comments about the comments/questions. Plus, the projects required equally fun conference / video calls accounting for time zone differences, various languages and accents, and varied engineering cultures and operating philosophies. You’ve been in this situation too, I’ll bet.

The discussion, though, is invigorating. The idea exchange goes well beyond solid-liquid separation to encompass types of valves, types of pumps, where to put the pumps, how to handle the solids, operator safety, disposal, and on and on and on.  I even had a question about desalination and how to operate the DAF (Dissolved Air Flotation) units (that’s a topic for another blog).

Developing A New Process Path with P & IDs

After one of these calls, I had an “A-Ha” moment about the true value of our plentiful rounds with P&IDs and process. This is where the innovation happens. The P&IDs are idea development in action. This is where we, as I wrote in one of my earlier blogs, clear our path of unknowns.  

Anyone who’s read my blog consistently will recognize this is what is excites me about process engineering and all we do in this role. I’ve decided to take my own early 2019 advice and stretch myself in new directions with the birth of “P&ID-Perlmutter Idea Development” which you can find at perlmutter-ideadevelopment.com.

To me, these two sites work together like a candle filter functions better with the right filter sock. I’m excited to see how this idea develops, and eager to see what my readers, colleagues, and fellow bloggers will want to add and change and discuss (after all, it’s a P&IDs and process we’re talking about here).

What We Learn from Baseball Data

action athletes audience ball
Photo by Pixabay on Pexels.com

Readers of my blog, know that I am a big baseball fan and now-retired player due to a bad-hop broken nose years ago. Golf is generally much safer. If you look back, you can see my blogs about juiced baseballs, Moneyball and baseball in Japan. I also write a lot about safety at chemical plants.  So, here we go again…let’s talk about baseball data and safety.  

This season there has been a lot of talk about foul balls striking and injuring fans and installing netting to protect fans. But, as process engineers, we know that we need to first consider the data before making any decisions. So, let’s get the data and discuss the best way for Major League Baseball to proceed.

Annette Choi and her team recently published, “We Watched 906 Foul Balls To Find Out Where The Most Dangerous Ones Land.”  Their research gathered the following data points:

Column Description
matchup The two teams that played
game_date Date of the most foul-heavy day at each stadium
type_of_hit Fly, grounder, line drive, pop up or batter hits self
exit_velocity Recorded exit velocity of each hit — blank if not provided
predicted_zone The zone we predicted the foul ball would land in by gauging angles
camera_zone The zone that the foul ball landed in, confirmed by footage
used_zone The zone used for analysis

This data collection was no easy feat. The MLB does not keep this type of statistics, even though baseball is really a numbers game. The team watched the 10 most foul-ball-heavy games this season to gather their findings.

Armed with the baseball data, Choi and her team determined the ball parks with the most foul balls:

MOST FOUL-HEAVY DAY
STADIUM AVERAGE NO. OF FOULS PER GAME DATE MATCHUP NO. OF FOULS
Camden Yards* 57 4/20/19 Baltimore Orioles vs. Minnesota Twins 113
PNC Park 57 6/1/19 Pittsburgh Pirates vs. Milwaukee Brewers 111
Oakland Coliseum 53 6/2/19 Oakland A’s vs. Houston Astros 109
T-Mobile Park 53 5/18/19 Seattle Mariners vs. Minnesota Twins 100
Globe Life Park 55 5/3/19 Texas Rangers vs. Toronto Blue Jays 87
Dodger Stadium 51 3/29/19 Los Angeles Dodgers vs. Arizona Diamondbacks 86
Miller Park 55 5/4/19 Milwaukee Brewers vs. New York Mets 85
Citizens Bank Park 53 4/27/19 Philadelphia Phillies vs. Miami Marlins 75
SunTrust Park 53 4/14/19 Atlanta Braves vs. New York Mets 73
Yankee Stadium 51 3/31/19 New York Yankees vs. Baltimore Orioles 67

The team then looked at netted versus non-netted areas as well as the ball velocities.  Interestingly enough, they found that almost an equal number of balls went to each area but the balls with the highest velocities went into the unprotected areas. 

Choi concludes, “Even with extensive netting, no one will ever be completely safe at a baseball game. But there are ways for MLB to protect its fans from foul balls — particularly in the most dangerous areas of the park.”

What I appreciate most is her observations are based in testing and learning about baseball data!

So, enjoy the World Series and root on your team and as Ernie Banks once said “It’s a beautiful day for a ballgame… Let’s play two!”

What Type of Engineer Are You?

types of engineers
Image source

There are may different types of engineer. Recently, I read some interesting articles about defining engineers by their skills and depth of knowledge. This blog asks you to consider, what’s your skill shape: I…T…or Key?  

In the 1970’s, companies wanted staff with an I-shaped skill level. What does this mean? I-Shaped Skills reflected a person with a deep (vertical) expertise in one area and practically no experience or knowledge in other areas. This person would typically be known as a specialist. It could be one process, one type of distillation, one type of pump, etc. I remember the days when my customer, Eastman Chemical, had flange specialists, o-ring specialists, vacuum pump specialists. The other large chemical companies, such as Dow Chemical, had similarly focused engineers.

In the 1980s, McKinsey & Company developed the idea of the T-shaped professional. The vertical bar on the T represents strong knowledge in a specific discipline. The horizontal bar represents a wide yet shallow knowledge in other areas. This allows the person to collaborate across other disciplines and acquire new skills or knowledge. Chemical companies have T-shaped engineers such as filtration experts, drying experts, solids handling experts, etc. These engineers can support all types of applications across all of the operations at various sites.  

One classic T was Thomas Edison, who wanted the people around him to know a lot of different things. All his prospective employees had to take a test of 150 questions geared toward different jobs and classifications of workers.

Today, the visualization of skills concept has expanded to include the elusive key-shaped professional—a person who has several areas of expertise with varying degrees of depth. The introduction of the key-shaped professional is largely due to the rapid proliferation of technological advances and the cross-disciplinary nature of work. Across industries and professions, the ability to use technology to assimilate and apply information has created a new, broader expectation of the standard skills professionals should have.

As a result, we’re seeing new parallels between skills sought in business and process engineering.  The top skills include embracing new technology, understanding data, and thinking critically about that data. 

Becoming a Key-Shaped Engineer

types of engineers
Image source

So, how do you become a Key-shaped professional? I have made several suggestions in other blogs:

So, now you may ask, how do I describe myself? Early in my career, I was T-shaped with knowledge about solid-liquid separation. As I progressed, I became more of a Key shape with knowledge about varied topics such as centrifugation, drying, solids handling, mixing and other process operations as well as technical business marketing and startups. 

I encourage you to think about your own skills shape. It might prompt a learning opportunity, and I’d be happy to help where I can with your transformations.

Troubleshooting Filter Aids and Filtration Systems

 

filter aids
Cellulose filter: Imerys Filtration Minerals Inc.

Filter aid pretreatment can improve filtration properties and efficient removal of fine solids. Whether the filter aids are used in Plate-and-frame filter presses, horizontal and vertical pressure leaf filters, candle or tubular filters, Nutsche filters, or rotary vacuum drum filters, these practical tips can help this part of the process run smoothly.

We typically see diatomite, perlite and cellulose filter aids today. They meet the requirements of a filter aid in that they:

  • Consist of rigid, complex shaped, discrete particles;
  • Form a permeable, stable, incompressible filter cake;
  • Remove fine solids at high flow rates; and
  • Remain chemically inert and insoluble in the process liquid.

You’ll want to test different approaches to determine the best aid for your process and which of the methods — precoat or body feed — offers the greatest benefits. Once you’ve done so, though, it’s important to keep these troubleshooting tips in mind.

Practical Pointers for Using Filter Aids

Whether the process is precoating or body feeding, the filter aid slurry tank and pump are critical to the operation. 

In precoating, the mix tank should be a round, vertical tank with a height twice its diameter. Set the usable volume of the precoat tank at ≈1.25–1.5 times the volume of the filter plus the connecting lines. Use a mixer or agitator with large slow-speed impellers to avoid filter aid degradation and the creation of fines — otherwise you’ll dramatically change the filter aid process filtration.

The precoating pumps almost always are centrifugal pumps because they produce no pulsations to disturb precoat formation and their internal parts usually have hardened surfaces and open impellers to reduce wear. For body feeding, you’ll use positive displacement pumps.

Yet even when the feed tank and pump are correct, several typical issues with filtration/filter-aid systems can arise.

Bleed-through is common where the filter aid is bypassing the filter media. It may stem from mechanical, operational or process causes. Check a couple of mechanical points: 

  • Is the filter medium secured to the filter correctly? 
  • Does the filter medium have a tear or pinholes? 
  • Is the type of filter aid correct for the filter medium mesh size and the particle size distribution of the process solids? 
  • Is the pump working correctly (flow, pressure, etc.)? 
  • Is the proper amount of filter aid being added?

Another issue may be reduced filtration cycles — i.e., the time to reach the maximum pressure drop becomes shorter and shorter. This may occur:

  • if the cake isn’t being discharged completely, then each new batch has residual solids in the filter, resulting in lower capacities. Increasing precoat height or lengthening cake drying time may help improve cake discharge. 
  • if the precoat doesn’t completely cover the filter medium, then the process solids may begin to blind the medium. 
  • if you’re using body feed, inadequate mixing with the process solids may result in filter medium blinding. This also can happen if the velocity in the filter vessel is too low, which will allow the filter aid to settle out before reaching the filter elements. A bypass at the top of the filter vessel can help keep the solids suspended within the vessel.

On filters with vertical elements, precoat pump flowrate or pressure may cause loss of the precoat from the filter medium, Improper valve sequencing creating a sudden change in the pressure or flowrate may also be to blame. Finally, a mechanical issue with the filter may prompt a pulsation or pressure change that impacts the cake structure.

Apply Filter Aids Wisely

Employing filter aids to help filtration is tricky; most process operations try to eliminate or minimize their use. However, sometimes they are unavoidable.

To succeed with filter aids, a process engineer should take three essential steps:

  1. Conduct lab testing to examine the filtration operation (vacuum or pressure), cake thickness, filter aid quantities, filter medium and other parameters that are crucial to the process design;
  2. Ensure correct mechanical design to provide optimum precoat or body feed handling and distribution; and
  3. Arrange for operator training on the filtration technology as well as on filter aid operation.

This blog is an edited version of an article I co-authored with Garrett Bergquist, BHS-Sonthofen Inc. for Chemical Processing.