An interesting presentation at 2011 AIChE National meeting

I’m privileged to be able to regularly attend the AIChE Spring and National (fall) meetings. I attend presentations, meet with customers and prospects, and attend division dinners. Chemstations has been a long-time exhibitor at these meetings, and often sponsors the meeting. I’m vice-chair of the admin committee for DIPPR (www.aiche.org/dippr/), which often meets during the National meeting.

One of my favorite papers at the 2011 National meeting in Minneapolis was a presentation by Dr. Becky Toghiani titled Group Contribution Methods in Undergraduate Chemical Engineering Thermodynamics. Dr Toghiani is a professor at Mississippi State; we’ve known her for years and admired the way she teaches her students the fundamentals. In her presentation, Dr Toghiani discussed one way she has her students use computer programs (CHEMCAD and Cranium*) to learn about the limitations of predicting chemical properties.

Several of the exercises involve predicting well-known chemicals and comparing the results to database values. The students start by comparing predicted pure component properties to experimental data, noticing that if Tc, Pc, and Tb are not well predicted, other properties that are correlated from these values (VP, Cp, HOV) will not be well predicted either. This shows students some of the limits of correlations.

The students then move on to mixture behavior, where they model the separation of binary mixtures using UNIFAC to predict non-ideal VLE. After modeling with predicted chemicals, they look at experimental VLE data to see how well the predicted behavior matches the system. One of the systems is a mixture of o-xylene and p-xylene. Use of a first-order subgroup model (such as Joback) to predict these chemicals will lead to these predicted isomers having the same properties and UNIFAC subgroups, which means they cannot be separated. Use of a second, order model will create slight differences in critical properties and allow for (very difficult!) separation. Naturally, the students are not warned that “cannot be separated” is the wrong answer; this is a process to help them learn to think.

These problems teach Dr Toghiani's students to remember “what is behind the curtain” when they are using modern tools and methods. The students also learn to inspect and think about their results, and ask “Should I try to approach this problem in a different way?” These are the types of lessons we really like; they show the power of a process simulator, and they also teach that a simulator is a tool, not a magical device. It’s important to understand the engineering concepts and the models underneath, even if you don’t have to do the math yourself.

* I should note that I was sitting next to a long-time friend of Chemstations during this presentation: Dr. Kevin Joback, President of Molknow (http://www.molknow.com/) and author of Cranium.

Chemical Engineering Hero: Ben Horwitz

You’ve probably caught on to the fact that we here at Chemstations are pretty proud of the chemical engineering profession. Well, I’d like to take this opportunity to recognize someone who has made some serious contributions to chemical engineering practice everywhere he’s been.

Those of you who have met Ben Horwitz know that he’s one of a kind. He’s sort of a force of nature that sweeps in and makes an impression. I’ve worked with Ben since 1995, and I owe a lot of what I know about practical process engineering to him.

Ben made a career at HK Ferguson (and then MK Ferguson) before going out on his own. He’s designed, troubleshot, de-bottlenecked, and optimized more processes that most of us will ever see; his hands-on, in-the-field techniques have made plants run when others had given up. In my experience, he doesn’t brag about the financial impact of his efforts, but I’d wager that he’s easily saved millions of dollars for his clients. Along the way, he’s educated future engineers in college process design classes and trained hundreds of engineers (and chemists!) in the use of simulation tools with his irreverent yet effective style. Ben is NOT a “click here” and “click there” instructor (as you know if you’ve taken a class!); he is a problem solver of the highest order, and he never lets you forget that process engineering is about solving problems.

If you’re interested in learning more about Ben and his myriad of engineering (and life) experiences, I invite you to take a look at his web site (www.benjaminhorwitz.com). You will very likely find his book, Portrait of a Chemical Engineer, to be a fascinating read. It spans his university years, his time in the Peace Corps, and through to his professional work; it’s told in a fast pace through a series of vignettes that capture the highlights of the events that molded and shaped him into the professional, the chemical engineer, and the hero that we’ve come to know. You can read an excerpt online, and even order your own copy.

I’m incredibly lucky to count Ben as a colleague, and I’m proud to count him as a friend.

OK, so if you’ve read this far, I’m going to tell you about Ben’s influence on me. 1994. I was pretty green (ok, very green) and just out of undergrad when Ben began teaching at our seminars. I think the first thing he said to me was, “Who are you?” I said I was the new guy; he looked me up and down and walked away. He spoke quickly. He was to the point. I had no bona fides yet, and I was unproven. I sat in the back of the seminar room and watched in amazement as Ben began by telling stories. Telling stories to teach simulation? This was an amazing sight, to be sure.

So there he is, telling stories. Setting up scenes in chemical plants. Describing characters. Replicating dialogue from other engineers, from plant managers, and from operations staff. Focusing our attention on the challenge at hand. And then he led us all down the chemical engineering, problem solving path. He often asked questions of the attendees—questions that forced us to think and really got to the heart of the challenges. He also gave quizzes. He used a flip chart to describe a problem, and he just let the class run with potential solutions. I don’t remember which quiz it was, or which day it was, but I do remember that I answered one of the quizzes in a way that caused Ben to leap up and say “YES! THAT’S RIGHT! STEVE IS EXACTLY RIGHT!” In that instant, I saw how passionate this guy was about both the challenge of process engineering and the objective of teaching its principles to the class. He cared more than anyone I have ever seen in the chemical engineering world, and with that answer, I was suddenly on Ben’s radar.

We probably worked together five or six times a year for several years after that, and I was always impressed by Ben’s ability to quickly learn every attendee’s name and background. Ben’s style is to engage everyone, keep your attention, and make it fun. He puts every ounce of his energy into the courses, and everyone comes out tired, but with new perspectives.

I don’t get to work directly with Ben as much these days, but when I get the chance I love to wander into our training room and see the class react to Ben’s stories. I know most of them by heart now, but they still sound as fresh and important as they ever did. This is because he loves what he does (and does what he loves), and that makes him a hero to me and the rest of us at Chemstations.

Great article on Heat Integration in CEP

The December 2010 issue of CEP (Chemical Engineering Progress) has a good article on heat integration. Disclaimer, I am a friend of the author (Alan Rossiter). Rossiter's article is a very understandable explanation of pinch analysis, a topic that is confusing to the uninitiated.

The concept of pinch analysis is that you don't need to use steam for all your heating needs, or cooling water for all your cooling needs. You might have 'hot' process streams that need to be cooled, and 'cold' process streams that need to be heated. Pinch analysis suggests that you will save energy if you use the 'cold' process stream as a utility for the 'hot' process stream, rather than purchasing steam and cooling water. While that may sound simple…most people find the next steps, performing the pinch analysis, difficult to understand.

Rossiter does a wonderful job showing us how to perform pinch analysis, and shows that the use of this method is not as difficult as we think. He explains how to understand the composite curve for 'heat sinks' and 'heat sources. He shows how you can perform a retrofit study, to see the potential benefits to integrating heat on an existing crude column.

Some of our customers have done pinch analysis before, some are interested in it.

Want to do it in CHEMCAD? We have the ability to generate a composite curve (fig 1, in Rossiter's article). You can specify the value for deltaTmin, the distance between the hot and cold curves. You can specify that some of the streams on the flowsheet should be ignored when you generate the composite curve; you wouldn't want to include a steam flow rate on the theoretical composite curve. When you're ready to explore alternate configurations, draw out a flowsheet with heat exchangers and match streams (Fig 3, Rossiter). We don't automatically match streams for you; we feel that an engineer needs to make that decision.

I suggest that anyone involved with utilities (or crude columns) and process simulators take the time to read Rossiter's article; it might give you money saving ideas.

PS While you are looking at recent issues of CEP, you could also take a look at page 59 of the Nov '10 issue, for a picture of the CHEMCAD Technical support team at AIChE's Process Technology Conference. Better yet, check out the back cover of January '11 CEP.