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Increasing Levels of System Organization in Plant Design

By: , Posted on: July 13, 2015

The book is arranged in chapters of increasing levels of system organization. Chapter 10 of the book deals with design of system at the components and materials level. Selection criteria for pumps, valves, and other basic components are given, as well as materials selection tables. Electrical and control elements like motor control centers, cabling, and instrumentation are also covered at the level of understanding required for process plant design.

Introduction

“Engineering is the art of modeling materials we do not wholly understand, into shapes we cannot precisely analyze so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance.” – AR Dykes

The selection of the basic subcomponents of process plants is an essential part of what plant designers do. There is often a fundamental misunderstanding in academia of what constitutes the elements of a process plant.

Process plants are not made of ideas, or (at an engineer’s usual resolution of vision) even of chemicals. Process plants are made of commercially available products.

We are not usually employed to select process chemistry, but to specify the pumps and valves, pipes and tanks used to construct the plant in which those chemistries occur.

Fig 9.3 Basic Pump Curve

As a result of the composition of university departments, taught chemical engineering has overemphasized science and mathematics to the point where graduates lack the broad overview of available technologies which allows them to make such a selection.

Such qualitative knowledge may seem less intellectually rigorous than science and mathematics, but it is actually far more sophisticated to exercise multidimensional judgment in a mental space of the qualities of various process options than to grind through a rote calculation which a computer could beat you at.

In this section I will attempt to offer the broad guidance on the selection of common items which is missing from many chemical engineering programs.

What Process Engineers Design

The essence of process engineering is integration of complex systems, but in order to integrate systems, the designer has to have some knowledge of the characteristics of those systems which affect integration.

To be more specific, certain types of materials, for example, are more suited to a given range of pressures, temperatures, chemical and physical compositions than others. Matching the ranges of these parameters in the plant design envelope to suitable materials is usually thought of as the process plant designer’s job. Similarly, the selection of pumps, heat exchangers, instrumentation, valves, and so on is usually thought to be part of process plant design.Fig 9.4 Intermediate Pump Curve

The information required to make these selections is largely absent from chemical engineering degrees, justified by the idea that it is mere qualitative data which is insufficiently intellectually demanding for university level education.

Similarly, qualitative criteria used to choose between separation process and other technologies are thought too shallow and easy to be worth a student’s time. Students mostly concentrate on a few selected processes which can be used to illustrate scientific principles or mathematical techniques.

Practitioners understand that such knowledge is actually capable of forming the basis of quite subtle and sophisticated multidimensional reasoning, and that providing such judgments is one of the basic expectations of a process plant design engineer.

I will attempt in the following chapter to provide matrices showing a number of dimensions which may be used to choose between options for materials of construction, valves, pumps, blowers compressors and fans, separation processes and heat exchangers. I will also offer information on specification of electrical components and instrumentation.

This chapter should prove particularly useful to students and recent graduates, as very little of its content appears in standard texts.

Read more from Sean on SciTech Connect


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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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