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Simplicity and Sophistication in Plant Design

By: , Posted on: June 11, 2015

 

rube goldberg device

In Chapter 7 of the book I attempt to address some key aspects of the feel for complexity which is the difference between the master and the beginner in engineering. To take a few sections at random:

“Simple/Robust vs Complicated/Fragile Design

There are so many quotes about the importance of this that I am spoilt for choice, but how about starting with someone who many consider the first engineer?

“Simplicity is the ultimate sophistication.”

– Leonardo Da Vinci

Complex designs shouldn’t be ruled out, sometimes they are needed, but they should be evaluated bearing in mind the fact that simple plants are easier to understand, easier to analyse (as Popper points out), more robust, more likely to be getting to the root of design challenges rather than piling afterthoughts on top of each other. More operable, more maintainable, more commissionable, more reliable, more available, more robust. What’s not to like?

A classicist turned computer scientist puts it well:

“There are two ways of constructing a… design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.”

– CAR Hoare

There is however an unexamined axiom in Koolen’s formal “simple and robust” approach similar to that in academic approaches, the optimization of a small number of variables. Do we really need all process plants to be operable by the general public? Or are we shooting for a simpler design than is necessary if we blindly apply this approach?

“It seems that perfection is reached not when there is nothing left to add, but when there is nothing left to take away”

– Antoine de Saint Exupéry

animated rube

Lessons from the slide rule

Before computers or even electronic calculators, engineers had slide rules. They couldn’t easily add and subtract, only worked to three significant figures, and you had to guess where the decimal point was. This meant that engineers needed to be quite adept at mental arithmetic, and only worked to three significant figures.

Simplicity is the ultimate sophistication. – Leonardo DaVinci

My students get nervous when I round things up, do rough sums in my head and so on like engineers of my generation.  They believe that all ten of the figures on their calculator displays are significant, even when I have set them a problem with two significant figures in the question data.

Process plant design engineers are probably kidding themselves if they think that they are working beyond three significant figures. Their underlying data is probably at best to this degree of precision. The extra decimal places on calculator and computer screen are spurious precision.

A feel for the sensibleness and reliability of our numbers is what really matters. Our modern tools seem to be taking this judgment away from new engineers.

Estimation/ Feel

“He … (the real engineer) insists that no mathematical formula, however exact it may appear to be, can be of greater accuracy than the assumptions on which it is based, and he draws the conclusion that experience still remains the great teacher and final judge.”

– James Kip Finch

A feel for the potential error associated with your answer, and its consequent meaningful precision is very important in engineering, (even those who are not Finch’s assumed he’s). It is related to the margin of safety and turndown required to make a plant which will work.”

Modern design software is always in practice checked against the intuitions of those who were trained as engineers before it came into common usage.  Many of those I have spoken to in preparing this book expressed great concern as to how today’s young engineers will gain this intuition. This book should help point them in the right direction.


applied guide to process and plant designAn Applied Guide to Process and Plant Design is available for pre-order on the Elsevier Store.

Use discount code “STC215” at checkout and save up to 30% on your very own copy!

About the Author

sean moranProfessor Moran is a Chartered Chemical Engineer with over twenty years’ experience in process design, commissioning and troubleshooting. He started his career with international process engineering contractors and worked worldwide on water treatment projects before setting up his own consultancy in 1996, specializing in process and hydraulic design, commissioning and troubleshooting of industrial effluent and water treatment plants.

In his role as Associate Professor at the University of Nottingham, he co-ordinates the design teaching program for chemical engineering students. Professor Moran’s university work focuses on increasing industrial relevance in teaching, with a particular emphasis on process design, safety and employability.

Connect with Sean on LinkedIn here, check out his Facebook page here and stay up-to-date on his thoughts, research and practice at his personal blog here.

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