Pinch Analysis for Energy and Carbon Footprint Reduction

User Guide to Process Integration for the Efficient Use of Energy

Ian C. Kemp,Jeng Shiun Lim

• Publisher: Butterworth-Heinemann
• Year: 2020
• ISBN:
  9780081025376
• Edition: 3
• Topic: Technik & Maschinenbau
• Subtopic: Chemie- & Biochemietechnik

Pinch Analysis for Energy and Carbon Footprint Reduction is the only dedicated pinch analysis and process integration guide, covering a breadth of material from foundational knowledge to in-depth processes. Readers are introduced to the main concepts of pinch analysis, the calculation of energy targets for a given process, the pinch temperature, and the golden rules of pinch-based design to meet energy targets. More advanced topics include the extraction of stream data necessary for a pinch analysis, the design of heat exchanger networks, hot and cold utility systems, combined heat and power (CHP), refrigeration, batch- and time-dependent situations, and optimization of system operating conditions, including distillation, evaporation, and solids drying.

This new edition offers tips and techniques for practical applications, supported by several detailed case studies. Examples stem from a wide range of industries, including buildings and other non-process situations. This reference is a must-have guide for chemical process engineers, food and biochemical engineers, plant engineers, and professionals concerned with energy optimization, including building designers.

• Covers practical analysis of both new and existing processes
• Teaches readers to extract the stream data necessary for a pinch analysis and describes the targeting process in depth; includes a downloadable spreadsheet to calculate energy targets
• Demonstrates how to achieve the targets by heat recovery, utility system design, and process change
• Updated to include carbon footprint, water and hydrogen pinch, developments in industrial applications and software, site data reconciliation, additional case studies, and answers to selected exercises

Chapter 1: Introduction

Abstract

Pinch analysis is a methodology to reduce energy usage and carbon footprint by setting rigorous scientifically based energy targets. The process is then designed to achieve these targets as far as possible. Originally concentrating on heat recovery through heat exchanger networks, pinch analysis has now been extended successfully to external heating and cooling systems (utilities), optimisation of process operating conditions, and non-process aspects such as buildings and total sites.

Keywords

Flowsheet; Pinch analysis; Energy targets; Application; Onion diagram; Thermodynamics

Contents

• 1.1 What is pinch analysis?
• 1.2 Historical development and industrial experience
• 1.3 Why does pinch analysis work?
• 1.4 The concept of process synthesis
• 1.5 Hierarchy of energy reduction
• 1.6 The role of thermodynamics in process design
  • 1.6.1 How can we apply thermodynamics practically?
  • 1.6.2 Capital and energy costs
• 1.7 Learning and applying the techniques
• 1.8 A note on terminology
• References

1.1: What is pinch analysis?

Figure 1.1a shows an outline flowsheet representing a traditional design for the front end of a speciality chemicals process. Six heat transfer “units” (i.e. heaters, coolers and exchangers) are used and the energy requirements are 1722 kW for heating and 654 kW for cooling. Figure 1.1b shows an alternative design which was generated by Linnhoff et al. (1979) using pinch analysis techniques (then newly-developed) for energy targeting and network integration. The alternative flowsheet uses only four heat transfer “units” and the utility heating load is reduced by about 40% with cooling no longer required. The design is as safe and as operable as the traditional one. It is simply better.

Figure 1.1 Outline flowsheets for the front end of a speciality chemicals process.

Results like this made pinch analysis a “hot topic” soon after it was introduced. Benefits were found from improving the integration of processes, often developing simpler, more elegant heat recovery networks, without requiring advanced unit operation technology.

There are two engineering design problems in chemical processes. The first is the problem of unit operation design and the second is the problem of designing total systems. This book addresses the system problem, in particular design of the process flowsheet to minimise energy consumption.

The first key concept of pinch analysis is setting energy targets. “Targets” for energy reduction have been a key part of energy monitoring schemes for many years. Typically, a reduction in plant energy consumption of 10% per year is demanded. However, like “productivity targets” in industry and management, this is an arbitrary figure. A 10% reduction may be very easy on a badly designed and operated plant where there are many opportunities for energy saving, and a much higher target reduction would be appropriate. However, on a “good” plant, where continuous improvement has taken place over the years, a further 10% may be impossible to achieve. Ironically, however, it is the manager of the efficient plant rather than the inefficient one who could face censure for not meeting improvement targets!

Targets obtained by pinch analysis are different. They are absolute thermodynamic targets, showing what the process is inherently capable of achieving if the heat recovery, heating and cooling systems are correctly designed. In the case of the flowsheet in Figure 1.1, the targeting process shows that only 1068 kW of external heating should be needed, and no external cooling at all. This gives the incentive to find a heat exchanger network which achieves these targets.

Over the last 40 years, these initial insights have been developed into a wide-ranging methodology for energy analysis of industrial processes. As will be seen, even where little or no heat exchange is possible, pinch-based techniques still show ways to reduce energy use and carbon footprint.

1.2: Historical development and industrial experience

The next question is, are these targets achievable in real industrial practice, or are they confined to paper theoretical studies?

Pinch analysis techniques for integrated network design presented in this Guide were originally developed from the 1970’s onwards at the ETH Zurich and Leeds University (Linnhoff, 1979; Linnhoff and Flower, 1978). ICI plc took note of these promising techniques and set up research and applications teams to explore and develop them.

At the time, ICI faced a challenge on the crude distillation unit of an oil refinery. An expansion of 20% was required, but this gave a corresponding increase in energy demand. An extra heating furnace seemed the only answer, but not only was this very costly, there was no room for it on the plant. It would have to be sited on the other side of a busy main road and linked by pipe runs – an obvious operability problem and safety hazard. Literally at the eleventh hour, the process integration teams were called in to see if they could provide an improved solution.

Within a short time, the team had calculated targets showing that the process could use much less energy – even with the expansion, the targets were lower than the current energy use! Moreover, they quickly produced practical designs for a heat exchanger network which would achieve this. As a result, a saving of over a million pounds per year was achieved on energy, and the capital cost of the new furnace with its associated problems was avoided. Although new heat exchangers were required, the capital expenditure was actually lower than for the original design, so that both capital and operating costs had been slashed! Full details of the project are given as the first of the Case Studies in chapter 12 (section 12.2).

It is hardly surprising that after this, ICI expanded the use of pinch analysis throughout the company, identifying many new projects on a wide variety of processes, from large-scale bulk chemical plants to modestly sized speciality units. Energy savings averaging 30% were identified on processes previously thought to be optimised (Linnhoff and Turner, 1981). The close co-operation between research and application teams led to rapid development; new research findings were quickly tried out in practice, while new challenges encountered on real plant required novel analysis methods to be developed. Within a few years, further seminal papers describing many of the key techniques had been published (Linnhoff and Hindmarsh, 1983; Townsend and Linnhoff, 1983; Linnhoff, Dunford and Smith, 1983). From this sprang further research, notably the establishment of first a Centre and then the world’s first dedicated Department of Process Integration at UMIST, Manchester (now part of the School of Chemical Engineering and Analytical Science at Manchester University).

The techniques were disseminated through various publications, including the first edition of this User Guide (Linnhoff et al., 1982) and three ESDU Data Items (1990), and through training courses at UMIST. Applicatio...