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The Re-education of Chemical Engineering
Chemical Engineering research has lost its way, and it has brought its wrong turns into teaching. In attempting to turn process plant design into a problem which can be “solved” by non-practitioners it has missed the point of the exercise entirely.
To quote from Chapter 2 of An Applied Guide to Process and Plant Design:
“Douglas wrote a book called “Conceptual Design of Chemical Processes” which essentially attempts to design chemical processes, rather than process plants. Its author understands that the expert designer proceeds by intuition and analogy, aided by ‘back of the envelope’ calculations, but sees the need for a method which helps beginners to cope with all of the extra calculations they have to do whilst they are waiting to become experts.
The arguments underlying the academic approach since built on it are helpfully set out in explicit detail. There is an assumption that the purpose of conceptual design is to decide on process chemistry and parameters such as reaction yield. Choices between technologies are not considered. Pumps are assumed to be a negligible proportion of the capital (capex) and running (opex) cost, and heat exchangers are assumed to be a major proportion of capex and opex.
It is implicit in the chain of assumptions used to create the simplified design methodology that a particular sort of process is being designed. Like all design heuristics, the methodology has a limited range of applicability. Whilst it mentions other industries, it is based throughout upon an example taken from the petrochemical industry, and it is clear that the assumptions it makes are most suited to that industry.
Having declined to consider many items which are of great importance in other industries, the author finds time for pinch analysis, which was quite new when the book was written. Perhaps this really was a worthwhile exercise for the novice process designer in the petrochemical industries of the 1980s, but there are many process plant designs in 2015 which do not have a single heat exchanger. In the majority of industries, process chemistry is a job for chemists.
This book in itself offers a plausible approach to the limited problem it sets out to solve, few of whose assumptions I can argue with in the context of its chosen example. It attempts to offer a beginner a way to choose between potential process chemistries and to specify the performance of certain unit operations in a rather old-fashioned area of chemical engineering.
However, the problem which the book’s methodology seeks to address is not one I have ever been asked to find a solution for. When I am asked to offer a conceptual design, I am being asked to address different questions, on plants with a different balance of cost of plant components. Petrochemical plants of the sort used as the example in this book do not really get built in the developed world any more.
The approach in the book does however hang together coherently, in a way more recent developments based on it do not. A good amount of effort goes into constructing as rigorous a costing as is possible at the early design stage (ignoring the issue of the items which are left out).
In essence, this book seems in my view to contain the slight wrong turns and oversimplifications which, followed by successive oversimplifications and misunderstandings, led to the utterly unrealistic approaches common in academia nowadays.
The attraction of the approach to academics is presumably that it is intended to allow people who have never designed a process plant (like the majority of academics) to use the skills they do have to approximate an early stage design process.
This approach is just another design heuristic, and like all heuristics it has a limited range of applicability. It is a tool to allow a very inexperienced designer who does not have access to expert designers to simplify the design of a certain sort of petrochemical plant to the point where they can mathematically analyse the desirability of a small number of parameters such as degrees of reactor yield, and energy recovery. If its very specific assumptions are not met, its use is invalid.”
This is how the absence of Engineers in Chemical Engineering departments has led to the teaching of design practices which are worthless in practice, and consequently entirely unused by practitioners. An Applied Guide to Process and Plant Design explains how design is really done, and how real plant design can be taught.
An 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
Professor 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.
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