Theory of Filtration and Theory of Creativity     

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Having been in the solid-liquid filtration, centrifugation, and drying marketplace since 1982, I have long said filtration is both a science and an art. I’ve witnessed the overlap of theory of filtration with theory of creativity. The practical and creative together make what we do so exciting. 

I entered the filtration business with Pall Corporation after five years with  the USEPA and receiving my MS in Environmental Science from Washington University in St. Louis. With Pall Corporation, I learned a lot about the science and art of filtration, marketing and sales, R & D, communication, and processes. It was during this time that I realized the creativity in the filtration market; every process, telephone call, e-mail was another challenge to solve a problem. 

Theory of Filtration

The theory of cake building filtration is based on Darcy’s law, describing the flow of fluids through porous materials. A practical equation was developed with a few assumptions:  

  • the build cake is (almost) incompressible
  • the pressure during the cake building is (almost) constant
  • the filtrate is clear (= (almost)) and all solids from the suspension do end up in the cake
  • the resistance created by the filter media is negligible compared with the cake resistance

 Experiences have shown that the following equation can be used:

theory of filtration

This equation describes most cases of everyday filtration testing. The most interesting parameter is alpha, the sum of all “unknowns” such as particle size distribution (PSD), porosity, solids shape and size, etc. Hence, the creativity.

Theory of Creativity

Robert J. Sternberg, Professor of Human Development at Cornell University, has developed two theories of creativity: The Investment Theory and the Propulsion Theory. What follows is a summary of Robert’s theories.

The investment theory of creativity holds that creativity is in large part a decision. Creative people generate ideas that are viewed as novel and perhaps slightly ridiculous. Creative individuals, by their nature, tend to defy the crowd. They resist merely thinking or doing what others are thinking or doing. The greatest obstacle to creativity, therefore, often is not exactly strictures from others, but rather the limitations one places on one’s own thinking.

People are not born creative or uncreative. Rather, they develop a set of attitudes toward life that characterize those who are willing to go their own way. Examples of such attitudes toward life are willingness to (a) redefine problems in novel ways, (b) take sensible risks,  (c) “sell” ideas that others might not initially accept, (d) persevere in the face of obstacles, and (e) examine whether their own preconceptions are interfering with their creative process. Such attitudes are teachable and can be ingrained in students through instruction that encourages students to think for themselves. Creativity comprises several different aspects: (a) abilities, (b) knowledge, (c) styles of thinking, (d) personality attributes, (e) motivation, and especially intrinsic motivation, and (f) environment.  

Robert continues with his propulsion theory, as follows:

Some kinds of creative contributions move forward in an already existing direction. The most basic kind of creativity is (1) conceptual replication, which is a product that basically repeats what has been done before with slight variation. (2) redefinition is a reconceptualization of a creative idea, so that an idea that was originally proposed for one purpose subsequently is used for another purpose. (3) forward incrementation is the next step in a usually long chain of ideas.  (4) advance forward incrementation is a next step that is a large leap beyond the last idea.  

Other kinds of creative contributions take a new direction from previous work. (5) redirection is a contribution that moves a field in a direction different from that in which it has been moving.  (6) regressive redirection is a contribution that takes a field in a new direction, but a direction that has been proposed earlier and perhaps discarded. (7) re-initiation is a contribution that not only moves a field in a new direction but also essentially starts a field over. Finally, (8) synthesis brings together previously divergent lines of thought, such as the invention of the seaplane.

Filtration & Creativity

Let me reiterate one of Sternberg’s observations: “The greatest obstacle to creativity, therefore, often is not exactly strictures from others, but rather the limitations one places on one’s own thinking.” I’ve written in the past about limitations that hinder our approaches to filtration. We can’t travel the same paths over and over again. We need to be willing to take a fresh look at each situation, think critically, test and test again, and innovate — with creativity.

Changing from Batch to Continuous Processing

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Our approaches to process engineering must always be evolving. Otherwise, we’ll never grow and innovate. Recently, I contributed a feature to The Chemical Engineer on making the change from batch to continuous processing. Here’s an edited version of that article for my loyal blog readers. 

As there is a push to become more efficient, many process industries have begun thinking about continuous processing. Many specialty and fine chemical operations are batch operated. It is easy and typically uses filter presses, vacuum nutsche filters, filter-dryers, plate and leaf filters, and batch centrifuges. 

Yet batch processing significantly lacks flexibility in scaling capacity, and typically requires larger manufacturing footprints and less efficient use of space. So, I’ve been seeing more of a shift from batch to continuous processing. 

In my career, I’ve helped engineers move to continuous operations for such applications in pharma and biochemical, specialty polymers, starch and cellulose, aromatic acids and fly ash wetting.

Why? In continuous processes: 

  • a filter is typically one-third the size of a batch filter
  • the process can increase yield and optimize quality
  • there are fewer reslurry/holding/buffer tanks
  • transfer pumps can be eliminated
  • complications from solids handling can be minimized
  • less agitation is used (which can impact crystal size and fines generation)
  • it can be easier to maintain constant flows, pressures and temperatures

Applications of Continuous Processing

In the article, I shared several examples of continuous processing applications in my career. I’ll recap a couple of them here too.

In a specialty chemical polymer application, a client wanted to transition to continuous processing to eliminate solids handling and reslurry tanks. Eliminating the liquid ring vacuum pump required for vacuum filtration would also cut energy costs. At BHS Filtration, we did lab and pilot testing to determine the rotary pressure filter was the best option.The continuous pressure filter saw a 16% increase in filtration rate; maintaining the temperature at -5oC resulted in a higher capacity. Secondly, we saw a more efficient washing due to less cake cracking in the thin cake (5 mm) as compared with 150 mm (6-inch) cake. 

For a pharmaceutical client, BHS was involved with a transition to fully-automated continuous processing in extracting phospholipids from egg yolk for preparation as a pet food additive. After consulting with the client and testing, the choice was a continuous-indexing vacuum belt filter for vacuum filtration, cake washing, and dewatering of the cake. The technology is based upon fixed vacuum trays, a continuously feeding slurry system, and indexing or stepwise movement of the filter media. In practical terms, the operational features of the belt filter can be viewed as a series of Buchner funnels. Making that change to the filter validated, as a GMP installation, for pharmaceutical production has increased the yield of the phospholipids by 3–5%. 

 In doing this kind of work, we’ve run into different challenges. We’ve been reminded that process scale matters and what works in the lab may not work in the plant. We’ve seen the need to silo both batch and continuous processes in the same line as a continuum. We’ve been reminded of the need to understand how one upstream decision will impact downstream processes.

We must also remember making the transition from batch to continuous processing requires more than just new equipment. The entire manufacturing operation and the mindset of staff need transformed. 

Process engineers have many choices to transition to a continuous operation. Continuous can be more challenging, but the benefits are there. Just be ready for some unexpected consequences along the way, and always test, test, test!

Of course, if you want to read the entire article, and I hope you will, it’s available! I’d be happy to discuss any of the ideas or possible applications of these insights with you. Reach out to me today!

 

Contribute to a Holistic Approach to Unit Operations!

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As the chemical industry changes and becomes more integrated worldwide, there is a need for information exchange. This must include not only principles of operation but practical knowledge transfer. That’s why I have agreed to edit a new book for Elsevier, “Integration and Optimization of Unit Operations.”

As my readers know, in 2015, I published the “Handbook of Solid-Liquid Filtration” with Elsevier, UK. This new project offers up-to-date and practical information on chemical unit operations from the R & D stage to scale-up and demonstration to commercialization and optimization.  

For this exciting and unique book to work, I need your help. I’m currently seeking contributing authors who have skills at each stage of the process from lab-scale/R&D, through pilot plants to full-scale production and finally optimization or as I call it, Putting-It-All-Together, for actual case histories / war stories.  We will also cover decommissioning of plants. Check out the preliminary Table of Contents.

Currently, most books look unit operations, each in a silo.  In this book, at each stage, the information presented differs as the technology and issues faced at the lab scale differ through commercialization and optimization. So, we will move from a silo approach to an integrated – holistic approach.

Why this Book is Needed

This book addresses a need for engineers with a broader training background. In the early 70’s, companies wanted staff with an I-shaped skill level. Someone with I-Shaped Skills is a person with a deep (vertical) expertise in one area and practically no experience or knowledge in other areas. This person is typically known as a specialist.  

Then, in the 1980s, the industry wanted T-shaped professionals. The vertical bar on the T represents strong knowledge in a specific discipline. The horizontal bar represents a wide (horizontal) yet shallow knowledge in other areas. This allows the person to be able to collaborate across other disciplines and acquire new skills or knowledge. 

Yet what we need today, with the rapid proliferation of technological advances and the cross- disciplinary nature of our work, is key-shaped engineers who can address several areas of expertise with varying degrees of depth.  

This book aims to address the needs of engineers who want to increase their skill levels in various disciplines so that they are able to develop, commercialize and optimize processes. The engineers must be able to ask questions of experts to develop creative solutions.

What Can You Contribute?

Contributing authors should be able to discuss unit operations at each stage and then relate how these technology/process decisions impacts the next stage. I am targeting the first draft by the end of the year. I will provide technical guidance and assistance as well as from my associate who is skilled in technical writing along with the Elsevier requirements.

The book will be listed on ScienceDirect, Elsevier and others and chapters will receive individual indexing so they can be searched. Review the preliminary Table of Contents and let me know what interests you to write about!

I hope you’re as excited about this opportunity to share knowledge about unit operations as I am! I look forward to hearing from you.

Dryer Selection and Bulk Solids Handling 

 

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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.

Clear thinking about automated clarification technologies

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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!

 

 

Troubleshooting Filter Aids and Filtration Systems

 

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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.

Chemical Engineers & Our Superstitions

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Superstitions surround us: Touching wood? Carrying a rabbit’s foot? Collecting lucky pennies? Not stepping on any cracks? The list goes on and on. 

On one of my many chemical filtration business trips (many people have superstitions making flights safer), I read an interesting article on superstitions in the Wall Street Journal’s (WSJ) Magazine. Six luminaries from different walks of life — photography, acting, cooking, writing, directing and music — weighed in. But, alas, there were no chemical engineers.  So, I thought I’d remedy that in a blog. 

The WSJ article featured various thoughts on superstitions. Some defined superstitions based upon religion and culture passed on from many generations. Another outlined a simple ritual such as “when hearing the title of a Scottish play, one would run outside, turn around three times, then knock on the door to come back inside the theatre.” Then, there were “routines” to keep your days identical (i.e. the same workout, the same coffee, etc.). Others talked about superstitions as an attempt at “having control of what you can control.”

However, the one overriding theme, as photographer Gregory Crewdson stated, is that a belief in superstition “comes down to order” and wanting “to clear your path of unknowns.”  

Clearing the Path for Chemical Engineers

So, how does all that relate to chemical engineering?

If you accept Crewdson’s view, all chemical engineers are superstitious. We are always trying to clear our paths of the unknown. In every chemical filtration process, it is the unknowns that give us the most headaches. Why does the pump keep plugging? Why does the filtration system not produce a clean filtrate? Why is the process not meeting the production rates?  The questions we face are endless! But our job remains the same, we must “clear our paths of the unknown.”

Regular readers will know where I’m going with this…Test! Test! Test! Testing is our way of answering questions in controlled environments. To develop a process or troubleshoot an existing one, we need to ask the correct questions, think critically, walk around the plant, etc.  

Contact me with your superstitions for solving critical filtration and drying applications.  Let’s have fun exploring what we all do in chemical filtration.  

Changing it Up with Mixer-Dryer-Reactor Acquisition

 

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Starting off 2019, I talked about push pushing ourselves personally and professionally to embrace change. Well, I’m a man of my word, and I’m proud to announce a big change in filtration technology at BHS-Sonthofen GmbH. We’re looking at 2019 as a year of growth, starting with the acquisition of the internationally active AVA-GmbH technology company.

AVA, based just outside of Munich, Germany, has 25+ years under its belt producing innovative machines and efficient processes for any industry. They tackle mixing, drying, reacting, granulating, sterilizing, evaporating, humidifying, and homogenizing to combine engineering expertise and project management know-how to provide “tailor-made solutions from a single source.”

AVA’s product portfolio is a perfect fit with BHS. Having already cooperated with them on joint projects in the past, we can be sure that our company is only strengthened by this move.

In addressing the sale, Dennis Kemmann, Managing Director of BHS-Sonthofen GmbH was enthusiastic about the opportunity to combine our products to have an “even more comprehensive offering in all of our chemical, pharmaceutical and other markets.” 

Expanding Process Filtration Technology Technologies

BHS’s latest newsletter looks at the pairing in more particular applications. You can read more about selecting AVA Vertical or Horizontal Mixer-Dryers for Batch of or Continuous Operations. The goal is a streamlined approach handling as many processes as possible in one unit to curtail investment and process costs. 

Three of AVA’s multipurpose process machines are presented as possibilities to cover the vast majority of the application spectrum of the powder and granule processing industry:

  • AVA Vertical mixer-dryers for batch operation
  • AVA Horizontal mixer-dryers for batch operation
  • AVA Horizontal mixer-dryers for continuous operation

The newsletter also mentions the AVA test center in Germany, which allows customers to scale up from 15 – 90 liter batch mixer-dryer to full scale batch and continuous operations with full scale-up reports and drying curves issued after testing. The US test center in Charlotte, North Carolina will be completed in 4Q, 2019.

Ultimately, the AVA acquisition is good news for current and prospective clients. This change means more innovative process engineering solutions as well as an expanded team to support our customers. The combination of BHS and AVA systems will provide important process benefits for turnkey projects for our clients worldwide. Let me know what we can do for you!

Application of Separation Techniques & Full Containment

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Process engineers devote their time to finding the appropriate application of separation techniques. There’s need for effective solid-liquid separation, cake washing, and drying steps across industries. In many chemical and pharmaceutical processes, the production operations are further complicated by the nature of the process, especially if the process is air-sensitive or toxic.  

The solid-liquid separation step may be accomplished by pressure, vacuum, or centrifugation in a batch or continuous mode. In this step, further choices need to be made regarding the type of filter media and the thickness of the cake or the cake depth during which the separation occurs. To optimize the production process, I’ve found value in thin-cake (2-25 mm) pressure separation technology for full containment, no residual heel.

Importance of Thin-Cake Filtration

Thin-cake solid-liquid separation can be defined as the formation of a cake in the 2-20 mm thickness range.  In this range, cake compressibility becomes less important in the cake building stage of a separation process.  Compressible cakes can be better handled at thinner cake depths and higher pressures. 

For example, an amorphous crystal that does not centrifuge well or requires long filtration times on Nutsche Filter-Dryers can be filtered at 45 psig with a cake thickness of 2 – 3 mm.  Thin-cakes also lend themselves to more effective washing and drying as there is less of a chance of channeling and the mechanism of “plug-flow” of liquids or gases is enhanced.

Impacting Filtration Performance

There are several parameters that can impact filtration performance:

  • Filtration pressure
  • Temperature
  • Particle size/Particle size distribution
  • Particle shape
  • Cake washing
  • Drying of the filter cake.

BHS’s Autopress technology can conduct filtration, cake washing, pressure and vacuum drying all in a contained environment. Cake discharge is complete. There is no residual liquid or solid heel, which is an important benefit for air-sensitive and toxic products.

Application of filtration techniques
Filter plate

Understanding Autopress Technology

This fully enclosed filter press, with circular filter plates, allows flow in forward and reverse directions. The filter plates (which can use synthetic or metal media) are contained in pressurized filter housing with a gas-inflated membrane sealing the annular space. Thus, all operations are contained from full vacuum to 150 psig.  

The operation of the AP Filter begins with slurry filling to form thin filter cakes of typically 5 – 25 mm thickness.  Pressure filtration continues operating up to 8 barg.  The cake can then be mechanically compressed to eliminate cracking to ensure maximum washing efficiency in the forward or reverse direction.  Finally, the cake can be pre-dried or fully dried either by vacuum or blowing gas through the cake. Gentle drying without agitation or tumbling is especially important for fragile crystals and thixotropic cakes.  Elastomeric knives sequentially and automatically discharge the circular cakes after which the filter begins a new cycle. 

Read more about this topic in an article I wrote for PharmaChem. My take-away is that with close collaboration between the client and the vendor, we can do the kind of creative problem-solving that applies the separation technique needed to achieve production objectives.

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:

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Photo by gemmerich on Foter.com / CC BY-SA

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!‌

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