Why I Needed to Write "An Applied Guide To Process and Plant Design" #2

The loss of professional engineers from engineering education has had a profound impact on the way in which engineering is taught in universities.

The vague messiness of real engineering problems has had to be transformed into a collection of unambiguous tasks which will meet learning objectives; comply with miscellaneous administrative requirements; prove straightforward to teach and assess by busy academic staff who are almost never engineering practitioners; and garner appropriate levels of student satisfaction.

However, these requirements militate against educators’ ability to foster a total system-level approach to design, as Pugh (1991) has explained. Added to this, academic culture believes that the best teaching is ‘research-led’ (even though pedagogic research suggests that this plausible idea does not actually work in practice (Prince et al, 2007). This ethos can lead to an over-emphasis on design approaches related to areas of research interest, of which modelling and simulation are the key examples. The research ethos also favours design novelty, as opposed to the constrained creativity which is a key characteristic of professional practice.

Thus, in a typical student engineering design exercise, a great deal of data is provided to students, the problems are so tightly framed as to be mere tasks, and in a ‘successful’ example, (as judged by student satisfaction) it is very clear to students that they are being assessed on carrying out a number of the sub-tasks which would have been covered in recent lectures. Whilst such exercises are very often undertaken at least in part in groups, they are structured such that the group can readily split them into a number of standalone elements to be undertaken as individual exercises.

This approach to the student design exercise correlates strongly with texts such as Biegler et al’s ‘Systematic Methods of Chemical Process Design’ (1997), Turton et al’s ‘Analysis, Synthesis and Design of Chemical Processes’ (2012), and Smith’s ‘Chemical Process: Design and Integration’ (2016). All three titles refer to ‘chemical process design’, like Douglas, rather than to ‘process plant design’, its real-world counterpart. Despite their great popularity in academia, in my opinion these books have limited value in demonstrating how process plants (as opposed to chemical processes) are designed.

My experience of examining several cohorts of students who carried out this type of design exercise demonstrated that only the most able have any understanding of the ‘big picture’ - the majority are essentially grinding through the textbook method (or operating the simulation program) for the sub-task which they have been assigned. Neither do the majority have any appreciation of the complexity of the sub-structures of a process plant. Thus, the typical student design exercise produces neither a total design approach, nor a grasp of detailed considerations.

Pugh's ‘Total Design’ (1991) offers an excellent analysis of the issue, though his designs are for products rather the processes. Pugh labels the approach taught in universities ‘partial design’, resulting from the necessity to dismantle a complex and holistic discipline into distinct parts which can be taught in an academic setting by non-practitioners, an example of assessment drift. Or, as Kahneman (2013) puts it: "when faced with a difficult question, we often answer an easier one instead, usually without noticing the substitution".

Pugh discusses the importance of placing this simplification in context in order to emphasise that it represents just a small part of the real-world total design activity, and of spelling out that what is being taught is not really design itself.

The greatest problems with the simplified approach occur when we mistake the bricks for the building; many universities unfortunately teach process design as if processes did not happen in process plants. The consequence of this simplification is that academia promotes approaches which ignore all of the real difficulties of total design. Instead, design becomes a sort of applied mathematics in which one or two elements of partial design are combined to make what is mistakenly considered to be an integrated model.

In such approaches, the three most important measures of a design’s quality (its cost, safety and robustness) are glossed over, in favour of optimisation of a small number of parameters in a greatly simplified model of just part of the plant.

Research quality is a major contributor to wider indices of quality in university education such as the THES and QS rankings. This has led to a problem in the case of engineering, where the majority of staff in UK departments have academic backgrounds and research interests in the physical sciences and mathematics as opposed to the practice of engineering (as can be seen from the website of any such department). Taken with the IChemE’s requirement for exposure to research in the final year of the typical undergraduate chemical engineering degree (IChemE, 2017) this has led to an increase in curriculum time being devoted to the types of science and mathematics beloved of scientific researchers (as opposed to the fundamentals of engineering), often of limited applicability at best in professional practice.

We also see an increased generalized promotion within academia of modelling and simulation methodologies used as research tools, the ramifications of which I explore in some detail in An Applied Guide. Some of my fellow engineering practitioners call the products of such an engineering education ‘Hysys Monkeys’, implying that they have merely been taught to operate the most commonly used program, Aspen Hysys.

As Pugh explains, teaching design as it is practised by professionals is harder than teaching science and mathematics. I would also argue that it is too complex ever to be practically replaceable with software. When we allow our students to use such software without a proper understanding of its limitations, they develop a narrower understanding of the process. Simulation programmes may generate very precise answers, but hidden in the software are hundreds of tiny assumptions which no-one (perhaps not even the programmer) really understands.

The key skill of the process engineer, which cannot be supplanted by simulation technologies, is an intuitive grasp of the ways in which a complex system fits and works together. If process design were ever to be handed over to software, process plants would be produced that no-one really understood. This would be of great concern from a safety point of view.

Academics love the precision of mathematics, and the certainty of pure science, but professional engineers know that there is far more to reality than these disciplines can usefully express, and we can meet society’s needs better with rough calculations and our mind’s eye than scientists and mathematicians ever will.

In the 1980s Mecklenburgh (1985) speculated that computer programmes would soon be laying out plants, just as there are those now who think that process design will soon be done by computer programmes. With sufficient effort, I imagine some sort of programme could be written to lay out plant and make process design choices and I am aware that some already exist. They are not used much by practitioners because they are inferior to the art of a real engineer (and always will be) - they are at best only as good as their programmers, who are not professional process engineers.

A second consequence of the research-led ethos in engineering education is related to creativity. In the research arena, novel concepts are valued highly. Whilst creativity is an important element in professional process design, excessive novelty is not. Engineers exercise a limited form of creativity bounded by considerations of cost, safety and robustness.

At an individual level, the process designer must nonetheless forge a personal style, as advocated by Gibbs,(1998), which bears specific distinct hallmarks. The constrained creativity of professional designers is often grounded in a particular method of recombination of elements they have used before, or have seen others use.

For example, when designing systems for dosing acids and alkalis into water under control of a pH probe, I will use a particular combination of static mixers, piston-diaphragm pumps, loading and pressure relief valves which, I have found, provides a robust, economical and reliable solution.

I know, from multiple applications of this design, which elements need the greatest attention in order to construct a system which controls pH to within 0.1 pH units.

I (and other professional designers) can reliably develop such designs based on very sketchy information about the water which is to be treated. Virtually never will there be sufficient sampling data even to generate a statistically significant estimate of the values of key parameters. Furthermore, for this type of design, the buffering capacity of the water is a key determinant of how much acid or alkali will be required. No scientifically valid estimate of a representative range of buffering capacities will ever be available to the professional designer.

The professional designer’s methodology is based in part on mathematical analysis, and in part on a very old scientific paper, but the end result is also based at least as much on a feel for the data and certain qualitative aspects of a situation. My choice of technology is based on a personal style, grounded in repeated experience, and to some extent influenced by the personal style and preferences of those who taught me the art of engineering. 

The ultimate fine detail of my design - how I put the system together in space, considering that it contains strongly corrosive chemicals under pressure, requires manual interventions and maintenance from time to time, and carries a client expectation of a neat and professionally designed appearance – thus has very little at all to do with science and mathematics.

As a professional engineering designer, I would assert that one learns process design by doing it. In doing so, the designer will develop a reliable understanding of both complex system level issues and finer details. They will develop and progressively refine their own individual approaches to problems. They will develop an almost intuitive feel for optimum combinations and sub-assemblies of components, for appropriate margins of error and so on.

I teach process design in this way. I attempted to teach formal approaches to creativity, but I see now that I am already teaching real engineering creativity by teaching process design based on my professional experience. This is how I learned, so this is how I teach.

My early discussions with fellow chemical engineering academics suggested that there was a widely held belief in those parts of academic chemical engineering interested in the area that process plant design practice had changed radically since the 1980s. However, from my continuing professional practice as a plant designer and as an expert witness, I knew that this was not the case. The core activities and interrelationship of parts of the design process have scarcely changed at all in the last thirty years or more.

Supporting scientific research in this area is unavailable, because the professional process plant design process is not an area of modern research interest. However, it is my strong belief that the divergence between academic engineering and professional practice has been caused by gradual ongoing change in engineering education, rather than the profession.

The ultimate consequence of this divergence has been the loss of the professional design philosophy from the engineering curriculum and its replacement with a simulated and incomplete version of design. The teacher of engineering in academia will thus find a range of textbooks to support what might be labelled ‘researcher-led process design’, but very little to describe and support the teaching of a professional design philosophy.

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