The Catalyst Review - May 2015 - 4

MEDIa REvIEW

The views expressed are those of the individual author and may not reflect those of The Catalyst Review or TCGR.

Energy and Process Optimization for the
Process Industries
By Frank (Xin X.) Zhu, 2014
Wiley & Sons, Hoboken, NJ, 2014

The process industries have little opportunity for product differentiation which means the focus
is on making commodity products for the minimum cost. Over the last 20 years there has been a
major investment by the sector in technologies for process modelling and optimization, distributed
control systems, and multi-variable control strategies. The area of energy and process optimization
plays a key role in maintaining margins. The subject area focuses on the fundamentals of design
and operation and, if done in the right way, opens up potentially significant profit-enhancing
opportunities. When applied, energy and process optimization can give a manufacturer real
competitive advantage.
Energy and Process Optimization for the Process Industries focuses on how to design new refinery or petrochemical processes or
modify existing ones to achieve improvements, especially in energy and throughput. The book is arranged into five sections: 1) Basic
Concepts and Theory; 2) Energy System Assessment Methods; 3) Process System Assessment and Optimization; 4) Utility System
Assessment and Optimization; and 5) Retrofit Project Evaluation and Implementation. The 23 chapters cover topics from technical
subjects such as equipment design and utility systems to site-wide energy improvement strategies.
The first section tackles the subject areas in some detail. An early chapter on how we view the value of energy presents an important
concept of fuel-equivalence from which informed decisions can be made about the relative values of plant services. Converting the
value of each utility back to a fuel-equivalent value means that the relative merits of heating using steam or fired heaters, together
with how power is generated and consumed, can more easily be assessed and therefore informed operating or design decisions can
be made. The role of energy benchmarking and how to identify and report key performance indicators is also explained.
The second section dives into some detailed engineering calculations. An interesting chapter on fired heaters explains their design.
This follows to some of the typical problems found in the field with pointers as to where operational problems might occur and what
corrective actions should be taken to improve. A significant area for focus is on instrumentation around the heaters. A chapter on
heat exchangers starts with the basic design equations. It shows how velocity and tube passes affect both heat-transfer coefficient
and pressure drop at different rates and shows how design changes impact these in the context of an overall process. Some
examples are given for heat exchangers in refinery units. Fouling represents a major problem area, especially in refining applications.
The book tackles this subject in some detail. It describes the various fouling mechanisms and shows how, with knowledge of fouling
propagation, design or operational changes can be made to mitigate its effects. It shows how to calculate cleaning cycles for fouling
exchangers based on economic criteria, which the reader may find useful. Further methods to reduce fouling such as tube inserts
and helical baffles are presented. An energy loss assessment helps an engineer identify where energy could be used within a process
and the author presents a number of specific areas for investigation, including product run-downs, hot flue gases, and fractionation
tower overheads. There is an introduction to pinch technology and energy targeting techniques, followed by a description of the
network pinch technique which was co-developed by the author. It is interesting to see the technique applied to a crude unit and
diesel hydrotreater, with some of the practical issues explained.
The third section, although headlined as process system assessment and optimization, is actually a detailed presentation of
distillation column design and improvement. After introducing the design equations for distillation column separation and hydraulics,
the author presents the capacity diagram (see Figure 1) which can be used to bound the operation of a specific column based on
spray, flooding, downcomer backup, volumetric flow, and weeping characteristics. This diagram is very useful when looking at the
effects of alternative column operation or turndown. Column integration in the context of pinch technology is reviewed, including
potentially beneficial operating changes, such as pressure and feed conditioning. Each modification is accompanied by a financial
assessment to ensure overall profitability is enhanced.
The fourth section focuses on steam/power systems, both the equations which describe individual equipment items (such as steam/
gas turbines and let-down valves) and then how to put together a steam balance. At this point, the book loses some of its own
energy. There is less practical insight here and the subject matter is presented more through a number of specific examples and the
author's personal experience rather than a general approach. As a result, there is limited external referencing about more recent
technology developments in this area. There is also little guidance in the often tricky area of instrumentation and reconciling a
continued on page 13
model against plant data, which is usually the biggest issue when developing a steam balance.
4

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