Slurries

Containment of Slurries in Continuous and Batch Operations

Slurries
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In the 1970s, the chemical operations used acetone and benzene for the main slurries solid-liquid separation process. Next, there was a push to minimize solvent use. We looked to use water as the process liquid, but still had open filter presses and rotary drum filters; the entire plant was white from titanium dioxide or pharma stearates.
Today, we all know that processes remain open with filter presses, vacuum filters, and centrifuges. Our job is finding solid-liquid separation process solutions that can be contained for high solids slurries (greater than 10% solids) during filtration, cake washing, and dewatering/drying. This discussion considers your options for both batch and continuous operations.

Batch operations

When it comes to batch operations there are many possible ways to go.
Nutsche filter-dryers. Sized to take the complete batch from the reactor and process it to completion (final dryness). The nutsche filter contains an agitator, normally three blades, sealed to the vessel and moving up and down, clockwise and counter-clockwise. The agitated nutsche filter can conduct pressure filtration, cake smoothing, cake washing (displacement and reslurry washing), vacuum and pressure drying, and then automatic cake discharge.
The agitated nutsche filter-dryer is based upon thick cakes from 5–7 cm up to 30 cm and higher. For this type of filter to be successful, the cake permeability must be able to accept a deep cake without compression. Circular or rectangular filter media with a drainage layer is installed on a perforated filter plate.
Contained filter-presses. A contained unit does not require a process change and can operate at a cake thickness down to 2.5 cm, which is not possible in a nutsche filter-dryer. In a typical contained filter-press design a housing seals the plates. Improved designs include pressure filtration up to 1m Pa, cake washing in the forward and reverse direction, cake drying in the forward and reverse direction using pressure blowing and vacuum, as well as automatic cake discharge.
Contained centrifuges. These vary in design depending upon the operation and the type of centrifuge (such as horizontal peeler, inverting basket, and disk centrifuges). Centrifuges can be blanked or inerted for operation as well as sealed designs.

Continuous Operations

In continuous operations with slurries new options surface.
Rotary pressure filters. A continuous pressure filter designed for thin cake to deep cake filtration with cake depths from 6–150 mm. A slowly rotating drum (6–60 rph) is divided into segments (called cells) each with their own filter media (synthetic cloth or single or multilayer metal) and outlet for filtrate or gas.
The outlets are manifolded internally to a service/control head where each stream can be directed to a specific plant piping scheme or collection tank. In this way, the mother liquor can be kept separate from the subsequent washing filtrates and drying gases. This allows for better process control as well as reuse and recovery of solvents and the gases. 
Pressurized vacuum drum filters. A rotating drum inside a pressure vessel. The unit consists of a filter drum, slurry trough, agitator, wash bars, and a pressure let-down rotary valve. The process begins by closing the pressure vessel, pressurizing the vessel with compressed gas. The rotary valve is also pressurized for sealing, and the filter trough is filled via the suspension feed pipe. The agitator is started to keep the solids in suspension. Filtration, cake washing, and drying are by vacuum operation.
Indexing vacuum belt filters. 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. In practical terms, the operational features of the belt filter can be viewed as a series of Buchner funnels.
For the process operation, due to the stepwise operation of the belt, washing and drying efficiencies are maximized with the stopped belt and a plug-flow mechanism for gases and liquids. Cake pressing and squeezing further enhances drying. Finally, the fixed trays allow for the mother liquor and the wash filtrates to be recovered individually and recirculated, recovered, or reused for a more efficient operation. 

Final Thoughts

Process engineers have many choices to contain an operation. The decision is not easy:

  • Is the process batch or continuous?
  • Is it a thin-cake or thick-cake operation?
  • What is the filter media (synthetic or metal)?
  • What are the critical process steps?
  • What about maintenance and other parameters?

The design questions go on and on. In the end, whatever you choose, involve process, production, operations, and maintenance in your decisions.
This blog is an adapted version of my article for The Chemical Engineer. Read the full article here!


Engineer Checklists and Learning from Apollo

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

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!


Moonshot & Management Lessons   

2019 is the 50th anniversary of the Miracle Mets World Series-winning season, Joe Namath and the New York Jets taking the Super Bowl title, and the New York Knicks’ NBA Championship win with Bill Bradley. 1969 was quite a time for me as I was growing up a sports fan in Brooklyn. But now that I’m older, I find I’m more drawn to the management lessons we can glean from something else that happened in 1969 — Neil Armstrong, Buzz Aldrin and Mike Collins landing on the moon.  

In July, a Businessweek story presented five management lessons we can learn from the “Moonshot.” Although many of us remember the key moments, the history covered at the start of the article is interesting for the controversies we may have forgotten. Nevertheless, the bigger appeal for me is in what we can learn from the Apollo Moon Landing.

Have a clear objective.

Author Peter Coy tells us, “President John F. Kennedy vastly simplified NASA's job with his May 25, 1961, address to Congress committing to ‘the goal, before this decade is out, of landing a man on the moon and returning him safely to Earth.’'' That singular focus helped “NASA engineers [to keep] their heads down and their slide rules busy.” 

It’s the same in our work environments. If the project has a clear objective from the outset, the operating company, engineering company and vendor teams can all work together to accomplish the project from a technical and budget point of view.

Harness incongruence. 

NASA had several setbacks with the moon launch. But, as in all science, we learn from our mistakes. We must look at the problem from all angles and, as we know from Sherlock Holmes, it’s important to recognize: 

  • There is no benefit in jumping to conclusions.
  • Working with others to recreate events can be beneficial.
  • The need for problem-solving skills such as occasional silence or distancing and learning to discern the crucial from the incidental.

Delegate but decide. 

This is the essence of leadership. NASA spent over 90% of its budget on sub-contractors. Many of our projects are the same. You need to know when you need help. Then, the project team must have a strong leadership team in place to make the hard decisions, especially when teams are scattered across the world, have different cultures and languages, etc.  

Effectiveness over elegance. 

This is my favorite lesson. I’ve seen its truth often, especially when it comes to the PLC controls on a project. There is always the next best instrument, controller, valve, actuator, human-machine interface, etc. Every engineer wants that his or her project to incorporate the newest solutions, but sometimes a simpler control will allow the operators to manage the process more efficiently. Whether you go for effective or elegant, remember to involve the entire team to make the process safe and understandable.  

Improvise.

Coy shares many examples of how NASA and the astronauts improvised solutions.  We have all heard the phrase, “Hello Houston, we have a problem.” On our projects, we need listen to all team members to find the correct solution. Maybe we’ll improvise something that is a little beyond what we know; but this is how technology improves.

It’s amazing to think all of this was 50 years ago but these management lessons still hold true today! Now, if someone wants to share their thoughts on what we can learn from the Mets, Jets, and Knicks’ managers, I’d be happy to walk down that memory lane too!


Agile Project Teams in Engineering

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Engineering these days requires agility. We’re reconfiguring processes, and we need to be flexible with time zones, languages, accents, engineering cultures and operating philosophies. We cannot always select the people on our projects and must work with various teams to be successful.  How do we do this? McKinsey & Company insights into Agile Project Teams provides some interesting insights.

Let’s apply their practical observations from How to Select and Develop Individuals for Successful Agile Teams: A Practical Guide to process engineering.

First, when approaching a new process problem, it’s important for everyone to understand handling ambiguity with agreeableness leads to success. This includes the engineering and operating company teams and technology suppliers.

Processes are complex; there are many choices for the design. I have one project at the moment where the solvents/solids are toxic and hazardous, the solids polymerize immediately, and the operating conditions are severe.  There are over fifteen (15) different options for the solid-liquid separation technology design.  McKinsey’s research would suggest our project team needs to work through each option while keeping the focus on a safe and acceptable solution.

The guide suggests, Agreeableness means saying “yes, and...” instead of “yes, but.” It’s not about avoiding conflict or blindly agreeing without any thinking. It’s about testing ideas while being open to feedback.

Agility in Engineering Projects

Per McKinsey’s analysis, the agile project team’s focus must be on outcomes. “Agile teams take ownership of the product they deliver. For them, pride in the product (the outcome) sits higher than pride in the work (the process): they know that the process can and will change as they review the relationship between the process and value it achieves.”

Each step in the process moves the team closer to the desired outcome to achieve the overall objective: optimum technology selection to achieve quality while meeting environmental and safety requirements.

Finally, everyone must work as a team on successful agile projects. Sometimes different agendas must be reconciled.  Neuroticism can be an obstacle: “team members need to be able to stay calm when unexpected errors and issues arise.”

Find ways to foster a cooperative spirit. Years ago, I worked on a project where the operating company implemented a program rewarding team members that came up with ideas or creative solutions and showed cost savings. In fact, our vendor team was rewarded for including a special type of dust filter to capture solids from the vacuum dryer. As you can imagine, it’s not often the operating company provides additional compensation to the vendor!

The McKinsey study concludes, “great teams do not mean technically the best people or the most experienced.” Agility serving a shared focus on the goal can make the team even better. Next time, you’re on a project, keep these points in mind. Let me know if you are successful!

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