Industrial and Process Furnaces: Principles, Design and Operation

By Peter Mullinger and Barrie Jenkins

Industrial and Process Furnaces: Principles, Design and Operation, Third Edition?continues to provide comprehensive coverage on all aspects of furnace operation and design, including topics essential for process engineers and operators to better understand furnaces. New to this edition are sections on production, handling and utilization of alternative fuels such as biomass, hydrogen and various wastes, modeling of the process, combustion and heat transfer, their benefits, advantages and limitations, mitigation and removal of CO2 , the role of solar and other renewable energy, recent research, and the practical approach of the Whyalla steelworks for harnessing solar energy for sustainable steelmaking, hydrogen and as a "clean fuel".

The book also includes a discussion on the limitations of hydrogen supply owing to fresh water supply constraints, the difficulty of storing and transporting hydrogen, and the current sociopolitical impetus of CO2.

• Covers the manufacture and utilization of hydrogen as a clean fuel
• Includes process modeling and expands on computational fluid dynamics (CFD), with a special focus on flames and burners, costs, efficiencies and future trends
• Expands on future trends, including sociopolitical impacts on CO2 emissions and control

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 26, 2022
• ISBN: 9780323984911

Peter Mullinger

Peter Mullinger held senior management roles with both equipment suppliers and end users before joining the University of Adelaide as Associate Professor in 1999. Now semi-retired, he continues to teach process design and process safety.

Book preview

Industrial and Process Furnaces

Principles, Design and Operation

Third Edition

Barrie Jenkins

Engineering Director, Origen Powers Ltd., London, and Consulting Engineers, High Wycombe, United Kingdom

Peter Mullinger

Visiting Research Fellow, School of Chemical Engineering, University of Adelaide, Adelaide, SA, Australia

Table of Contents

Cover image

Title page

Copyright

Dedication

Foreword to third edition

Foreword to second edition

Foreword to first edition

Preface to third edition

Preface to the second edition

Preface to first edition

Acknowledgements

List of figures

List of tables

Chapter 1. Introduction

1.1. What is a furnace?

1.2. Where are furnaces used? Brief review of current furnace applications and technology

1.3. Drivers for improved efficiency

1.4. Concluding remarks

Chapter 2. The combustion process

2.1. Simple combustion chemistry

2.2. Combustion calculations

2.3. Chemical reaction kinetics

2.4. The physics of combustion

Chapter 3. Fuels for furnaces

Determining the calorific value of a fuel

3.1. Manufactured gaseous fuels

3.2. Natural gas

3.3. Properties of gaseous fuels

3.4. Liquid fuels

3.5. Solid fuels

3.6. Biomass based fuels

3.7. Waste fuels

3.8. Choice of fuel

3.9. Safety

3.10. Emissions

Nomenclature for chapter 3

Chapter 4. An introduction to heat transfer in furnaces

4.1. Conduction

4.2. Convection

4.3. Radiation

4.4. Electrical heating

Chapter 5. Flames and burners for furnaces

5.1. Types of flame

5.2. Function of a burner and basics of burner design

5.3. Gas burners

5.4. Oil burners

5.5. Pulverised coal burners

5.6. Burners for biomass and waste-based fuels

5.7. Furnace aerodynamics

5.8. Combustion system scaling

5.9. Furnace noise

Chapter 6. Combustion and heat transfer modelling

6.1. Physical modelling

6.2. Mathematical modelling

6.3. Application of modelling to furnace design

Nomenclature

Chapter 7. Fuel preparation and handling systems

7.1. Gas valve trains

7.2. Fuel oil handling systems

7.3. Pulverised coal handling and firing systems

7.4. Waste fuel handling

Chapter 8. Furnace control and safety

8.1. Process control

8.2. Furnace instrumentation

8.3. Flue gas analysis

8.4. Combustion control

8.5. Ensuring furnace safety

8.6. Burner management systems

Chapter 9. Furnace efficiency

9.1. Furnace performance charts

9.2. Mass and energy balances

9.3. Energy conversion

9.4. Heat recovery equipment

9.5. Identifying efficiency improvements

Chapter 10. Emissions and environmental impact

10.1. Formation of carbon monoxide

10.2. Formation of nitrogen oxides

10.3. Formation of sulphur oxides

10.4. Formation of intermediate combustion products

10.5. Particulate emissions

10.6. Environmental control of emissions

Chapter 11. Furnace construction and materials

11.1. Basic performance requirements of the furnace structure

11.2. Basic construction methods

11.3. Practical engineering considerations in the use of refractories

11.4. Ceramic refractory materials

11.5. Heat resisting and refractory metals

11.6. Practical engineering considerations in the use of high temperature metals

11.7. Concluding remarks

Chapter 12. Furnace design methods

12.1. Introduction

12.2. Conceptual design

12.3. Furnace sizing

12.4. Burner Selection

12.5. Detailed analysis and validation of the furnace design

12.6. Furnace instrumentation and controls

Chapter 13. Economic evaluation

13.1. Cost accounting

13.2. Distinction between capital and revenue

13.3. Profit and profitability

13.4. Financial ratios

13.5. Project costing

13.6. Investment evaluation

13.7. Determining financial benefits

13.8. Post project analysis

Chapter 14. Selected examples of real furnace applications

14.1. Design of a new burner for a lime sludge kiln

14.2. Optimising flash furnace design

14.3. Contribution to the design of a new reforming process for fuel cell applications

14.4. Resolving tube internal coking and premature tube failure in a refinery heater

14.5. Unsuccessful attempts to resolve severe problems with a preheater cement kiln

14.6. Investigation and elimination of coal firing system problems

14.7. Concluding remarks on implementation

Chapter 15. Future trends and concluding remarks

15.1. Trends in new materials

15.2. Trends in furnace emissions and fuels for furnaces

15.3. Trends in carbon capture from furnaces

15.4. Trends in furnace controls

15.5. New applications for furnaces

15.6. Concluding remarks

Index

Copyright

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This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

ISBN: 978-0-323-91629-5

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Cover Designer: Mark Rogers

Typeset by TNQ Technologies

Cover photos: Top Left: Tapping an electric arc furnace in a steelworks

Top Right: A premix burner firing a high hydrogen gas in a methane reforming furnace

Bottom Left: A multi-fuel burner on a lime recovery kiln in a kraft mill

Bottom right: An existing kiln burner adapted to fire thermally stable wastes in moderate temperature environments

Dedication

To the Late Frank David Moles who showed us a better way of thinking about furnaces, especially those where the product was directly heated by the flame.

Foreword to third edition

This 3rd edition of the book by Barrie Jenkins and Peter Mullinger has had many additions and modifications from the previous 2 editions to match the needs of a rapidly changing world with the expectation that significant changes are going to be needed in our behaviour and usage of energy. I have known Peter Mullinger for 50 and Barrie Jenkins for close to 40 years and have always had great respect for their work in the field of process engineering. The book really summarizes their joint 100+ years of experience and how the techniques and strategies developed can be widely applied.

Hydrogen is of course a fuel very much in the headlines and this book provides an excellent background to the problems of changing mixed radiative/ convective heat transfer systems to ones where convective heat transfer dominates, similar comments apply to mass transfer systems, The authors experience in such work lends itself to a wide range of processes, both existing and under development. Of course, it is probable that CO2 sequestration will also become extremely important, enabling existing industries to continue with efficiency upgrades and the addition of CO2 separation equipment to the exhaust gas systems. Industries such as cement where the calcination of carbonaceous feedstock leads to quite high CO2 exhaust gas concentrations are one example. Again, this work is of considerable value

In the context of speed of change and implementation of science and technology; the authors discuss 40 year implementation periods. I feel that if climate change becomes perceived as a global emergency the pressure to speed up technological advance will be unstoppable. Good examples of this are the effects of WW1 and 2 and the following Cold War, leading to very rapid advance in technologies and their implementation, including radar, electronic computing, jet engines, aircraft design (think of Spitfire C 1940 to MIG 15 and F86 Sabre C 1951) etc. In this atmosphere the value of this book is considerable

The book is of direct use not only to practitioners in the area, but also to a wider section of the Engineering and Scientific Community at an Undergraduate and Post graduate level. Chapter 15 is a must read for many persons in the political/environment fields who often push forward concepts and policies which cause untold damage to a future capabilities. A good example of this is the Civil Nuclear Engineering Industries in the Western World, where ‘stop go’ policies have literally decimated industries and made resurrection difficult and expensive. Similar comments apply to the Oil and Gas Industries where careful balances are needed between running these industries down too quickly (for CO2 reduction) and the development and implementation of other replacement technologies including renewables of various types including green and other sources of hydrogen, nuclear and possibly fusion. Into this equation is of course CO2 sequestration and what its role should be in a future world.

Nick Syred

Hon Professor

School of Engineering

Cardiff University

Foreword to second edition

Additional chapters in this second edition focus attention on a range of actual combustion related projects and the economic issues related to furnaces. In doing so, it also highlights that industrial problems can be quite complex and multi-faceted. In the past, and even today, many of these issues would almost certainly be addressed by trial and error, simply due to the lack of adequate technical knowledge, which can now be found in this book.

Combustion related projects generally require a wide range of ancillary equipment ranging from valve trains and pumping systems, blowers/fans and ducting, refractory lining, electric motors, boilers and heat exchangers, exhaust gas cleaning etc. As this book addresses all of these aspects it also provides useful information, which can be applied outside the field of combustion. I have successfully used a section in chapter 5 to assess the design of a twin fluid atomiser installed in a water spray system used for gas cooling.

To me the most important thing highlighted in the second edition through the practical examples, is that the solutions to complex combustion and heat transfer problems do exist and all we have to do is correctly apply the science but better still, use this science to get the design right in the first place!

Greg Mills

Engineering Consultant

Perth, Western Australia

Foreword to first edition

Furnaces have been used by humans for thousands of years and yet, beyond the basic chemical reactions and heat release calculations, engineers rarely have any formal training in relation to furnace design, combustion and their integration into industrial processes. It is therefore not surprising that the solution to issues of emissions, throughput and performance related problems have relied heavily on trial and error and experience. Within industry in general equipment would be more successful designed using the principles outlined in this book rather than relying on correlations and scale up factors that have little or no scientific basis to support them.

In the early 1970s the authors set themselves the goal of applying more scientific methods to burner design than were currently used. This led to the realisation that heat release from flames needed to be closely matched to the process requirements and that this was intimately related to the design of the furnace itself. Now, more than ever before, the need to reduce ongoing energy costs and greenhouse gas emissions requires decisions to be made on the basis of knowledge rather than guesswork and past experience. This book, being one of only a few ever published on the subject, highlights the applicable science which can be used to take much the guesswork out of furnace design. This book also emphasises the importance of ensuring that individual pieces of equipment are appropriate for the whole process and not simply selected on the basis of capacity or lowest capital cost.

Alcoa’s alumina refineries operate a range of processes and equipment including boilers, rotary kilns, gas suspension alumina calciners and regenerative thermal oxidisers and, like many other industries, have needed to address emissions, throughput, performance and safety issues without a clear understanding of the science and underlying design basis. This makes it difficult to undertake reliable root cause analysis when problems occur.

In the early 1980s I was a mechanical engineer in Alcoa’s Equipment Development Group. I had insufficient knowledge of, and certainly no experience with, combustion processes and was faced with having to address throughput and emissions related issues with alumina calciners. Fortunately I met the authors of this book, Peter Mullinger and Barrie Jenkins, and was delighted to discover that a scientific approach to furnace design is possible and methods are available to investigate and optimise many aspects of the combustion and associated processes.

It was highlighted through physical modelling of the flow patterns and acid alkali modelling of the combustion process mixing that both the throughput and emissions could be significantly improved by simply relocating fuel injection points. These modifications proved to be effective and have now been employed on all applicable alumina calciners at Alcoa’s refineries around the world saving otherwise significant capital expenditure with potentially ineffective outcomes.

Since those early days the science as described in this book has been employed over a wide range of process issues, from the design of new equipment and in the solution of problems with existing equipment, positively impacting on performance and reliability. More recently there has been a major application in relation to the design of safety systems.

In particular the application of CFD modelling has highlighted to me that CFD doesn’t replace the need for a deep understanding of the science of combustion and furnace heat transfer processes as there are many traps for the unwary and the uninformed.

Whether you are engaged in modelling, design of original equipment, or equipment or equipment upgrades or operation of combustion and heat transfer processes, this book provides much of the essential understanding required for success.

Greg Mills

Senior Consultant – Calcination

Technology Delivery Group

Alcoa World Alumina

Preface to third edition

In the eight years that have passed since the second edition was prepared much has happened, not so much in furnace development, but in the environment in which they are designed and operate. On the technical side, significant improvements in computerised fluid dynamic modelling have occurred. Fortunately, these improvements should make the task of adapting furnaces to the new environment a little easier.

Emissions of CO2 have continued to increase despite the pledges made at Kyoto in 2005 and Paris in 2015. There was a small drop in emissions with the reduction in economic activity at the onset of the Covid-19 pandemic but pre-Covid levels have already been exceeded.

Despite little overall progress in reducing emissions of greenhouse gases, localised efforts in specific jurisdictions, by commercial, industrial and government organisations are likely to affect furnace users in the near future. In addition, the application of alternative, low emission fuels, such as hydrogen and those that benefit the environment in other ways, such as waste derived fuels, are already affecting furnace designers and users. Hydrogen with its low emissivity, may mean radical redesigns of furnace to utilise convective heat transfer much more effectively than most current furnaces. Much work is also occurring to enable the use of hydrogen as a reductant, a task far from straightforward, as demonstrated by at least one spectacular failure.

There has been significant engineering progress in the development of greenhouse gas removal technologies suitable for integration with current furnaces, and through the capture of atmospheric CO2, which may be offset against emissions. A number of these systems are currently at pilot and demonstration plant scale and are proving their technical viability. Unfortunately, there are generally no incentives in place to encourage the major emitters to advance them to full implementation. Neither is there any significant global infrastructure available to receive the captured and sequestrated CO2. We are currently experiencing what has been a common historical scenario, where we have recognized the risks, developed the technological solutions to solve a problem, but have not yet created a sufficiently attractive range of financial incentives required to apply them.

We have taken the opportunity to update the book and cover as many of these developments as we are able.

Peter Mullinger, Adelaide

Barrie Jenkins, High Wycombe

2021

Preface to the second edition

In the five years since the original publication of this book, feedback from readers of the original book suggested that more information on CFD modelling would be helpful, particularly examples of its application, together with case studies and worked examples to demonstrate more application of the theory. Other areas where additional information was requested was in connection with flames and burners for furnace, costing, efficiencies, optimisation, future trends and the properties of slag.

We have attended to these requests by providing a couple of examples of CFD modelling in chapter 6. However, because we rarely used one modelling technique in isolation, we have included a new chapter of selected real furnace applications, which also includes CFD modelling, together with new chapters on furnace economics and future trends. Unfortunately, we could not find sufficient data on slag properties to include anything worthwhile.

The chapter on furnace economics includes a case study where seven options for rebuilding or upgrading a furnace are considered. The cost of each option is derived, the potential fuel savings are determined and a cost-benefit analysis prepared.

The chapter on selected real furnace applications provides detailed descriptions of six real projects, which have been chosen to demonstrate the application of the techniques to completely different industrial processes. Three of these projects also included site data collection, which is described in some detail. Most of these projects involved the application of more than one modelling technique.

Finally in the chapter on future trends, we look at trends in furnace design, construction, and control, furnace applications and emission limits. We expect the latter to drive most future developments. However, as in the 1960’s and 70’s, major disruptions to fuel supply could also have a significant disruptive influence. Forecasting is by its definition an uncertain exercise, and unlike the timescale used by Nostradamus, we are likely to be around to witness our failures.

Peter Mullinger, Adelaide

Barrie Jenkins, High Wycombe

2013

Preface to first edition

This book has been more than twenty years in gestation; its lineage can be traced back to Barrie’s lecturing at the University of Surry in the late 1970s and early 1980s and Peter’s first combustion course, provided internally to the Rugby Cement’s engineers in 1981.

We are not attempting to explain how to design any particular furnace but are advocating a more scientific approach to furnace design than the traditional methods of scaling from the last design. New approaches are essential if we are to make the advances needed to develop new processes for the twenty first century and to significantly reduce industrial energy consumption and emissions.

We have worked together to improve the efficiency of furnaces since 1977, starting with rotary kilns in the cement industry when Roger Gates, Technical Director of Rugby Cement, allowed Peter Mullinger to try the techniques developed by Fuels and Energy Research Group at the University of Surrey (FERGUS) on Rugby’s South Ferriby No 3 Kiln. This work was strongly encouraged by the Plant Manager, the late Jim Bowman. The project was an immediate success and let to significantly increased production and reduced fuel consumption. The success of that project encouraged Rugby to sign a research agreement with the late Frank Moles, founder of FERGUS which committed Barrie Jenkins and the rest of the FERGUS team to support Rugby Cement’s efforts to improve the production capacity, product quality and fuel economy of their twenty one kilns.

Following time in senior technical management roles with a company supplying combustion equipment into the petrochemical industry, we founded our own business to apply more scientific methods to combustion and heat transfer problems in all industries but principally those where the product was directly heated by the flame.

We commercialised techniques that had been successfully developed and used in-house by organisations such as by British Gas, CEGB, British Steel’s Swinden Laboratories, Rotherham. We added acid/alkali modelling as a means of determining fuel/air mixing and flame shape, a technique that had seen little application outside of research institutions at that time.

We built a successful business on this philosophy that continues today, managed by our successors. During the time we managed it we applied these techniques to over 250 projects in a wide range of furnace types in the alumina, cement, ceramic, chrome, copper, lead, lime, steel, mineral sands, nickel, petrochemical, pulp and paper and even the nuclear industry.

The idea for this book arose from the short course we provided on behalf of the International Kiln Association to industry and to the Portland Cement Association where we were regularly asked to recommend a book. We would have suggested Professor Thring’s book The science of flames and furnaces but it was long out of print so all that we could offer were the course notes. We hope that this book goes some way to filling the gap. It is the culmination of thirty years of working together, albeit for the last few years from across the globe.

Peter Mullinger, Adelaide

Barrie Jenkins, High Wycombe

2007

Acknowledgements

Over the years it has been our privilege to work with many engineers, process operators and other people who have encouraged and cooperated with us. Those who are mentioned below are but a small selection, whose influence has strongly encouraged the preparation of this book or who have directly contributed to it. Of special influence was the late Frank Moles, founder of the Fuels and Energy Research Group at the University of Surrey (FERGUS), who changed our thinking about industrial combustion, and Roger Gates, Technical Director of Rugby Cement, who allowed us to implement Frank’s and our ideas on the company’s plants.

We would like to thank many of the engineers at the former Midlands Research Station of British Gas, especially Neil Fricker, Malcolm Hogarth, Mike Page, Rachel Palmer, Jeff Rhine and Bob Tucker all of whom encouraged us to found Fuel and Combustion Technology Ltd. (FCT), in 1984 and to apply modelling techniques to industrial combustion and heat transfer problems. We believe that we were the first to use these techniques commercially on a large scale.

We owe a special debt of gratitude to those who were brave enough to give us our early work at FCT, including Len May, Terry Henshaw and John Salisbury of ARC Ltd., Erik Morgensen and Lars Christiansen of Haldor Topsoe A/S, Greg Mills of Alcoa Australia, Ian Flower and Con Manias of Adelaide Brighton Cement, Philip Alsop of PT Semen Cibinong, Terry Adams and Peter Gorog of the Weyerhaeuser Company, all of whom were very influential in providing FCT with its early projects. We should also like to thank Alcoa World Alumina and Hador Topose A/S for permission to publish descriptions of their projects.

Peter Mullinger would also particularly like to thank late Emeritus Professor Sam Luxton who strongly supported his change of direction to an academic career in 1999. Without that change, it is unlikely that time would have ever been available to complete this task. Peter would also like to thank his colleagues at the University of Adelaide who, either contributed directly to the book, or who covered his teaching duties during the first half of 2005 and first half of 2007, when the majority of this book was written, particularly Prof Keith King, Dr Peter Ashman, Prof. Gus Nathan and Dr Yung Ngothai, A.Prof Dzuy Nguyen and the late A.Prof Brian O’Neill.

We should also like to thank those commercial companies who provided data, photographs and drawings (who are acknowledged in the captions) but special thanks are due to Adam Langman, who tuned our woeful sketches into artistic masterpieces and Dave Crawley of DCDesign Services, who produced the process and instrument drawings and flow diagrams. We would especially like to thank Mr Brian Haggerty of Alcoa and Mr Tommy Hansen together with Mads Cordt Gyldenkærne of Haldoe Topsoe for their contribution to obtaining approval to publish examples of practical applications involving projects with those companies.

Grateful thanks are also due to Dr. Christine Bertrand, Mr Dennis Butcher and the late Dr John Smart for their invaluable contribution to the sections on 'CFD modelling', 'Furnace control and safety' and 'NOx formation and control' respectively.

We hope that the errors are minimal, but there would be many more but for the excellent proofreading of Victoria Jenkins and Sheila Kelly, to whom very special thanks are due. We could not have managed without you. Sheila, in particular, has read every word but maintains that it is not as much fun as Harry Potter!

Finally to all those who attended our industrial combustion short courses and asked, What book is available? It is available at last; we hope that you won’t be disappointed.

List of figures

Figure 1.1 The iron bridge at Coalbrookdale 2

Figure 1.2 The basic elements of a furnace 4

Figure 1.3 Classification of furnaces 5

Figure 1.4 Cross section through a traditional downdraught pottery batch kiln 8

Figure 1.5 Schematic of a mixed feed vertical shaft lime kiln and a battery of six oil fired vertical shaft lime kilns 9

Figure 1.6 Twin shaft regenerative lime kiln 9

Figure 1.7 Modern cement kiln technology showing the cyclone preheater tower and the satellite cooler 10

Figure 1.8 Schematic of a regenerative glass tank 11

Figure 1.9 Schematic of a modern blast furnace with Abraham Darby’s pioneering furnace 13

Figure 1.10 A reverberatory furnace for smelting copper sulphide ores 13

Figure 1.11 A Pierce-Smith converter 14

Figure 1.12 Outokumpu flash smelter for copper smelting 15

Figure 1.13 Cross section through a copper anode furnace showing the blowing, slag skimming and casting operations 15

Figure 1.14 The crucible steel furnaces at Abbydale showing the charging and firing floors 16

Figure 1.15 A hydrogen atmosphere furnace for de-sulphurisation of nickel briquettes 17

Figure 1.16 Fluid bed furnace for roasting copper ore 18

Figure 1.17 Flash furnace for alumina, lime or cement raw material calcination 19

Figure 1.18 A large billet re-heating furnace 20

Figure 1.19 Crucible furnace in use at Liquid Metal Studios, Adelaide showing the crucible casting process 21

Figure 1.20 Continuous rapid heating furnace for small billets 22

Figure 1.21 Schematic of slab re-heating furnace 22

Figure 1.22 Two large gearbox cases entering a large annealing furnace 23

Figure 1.23 A small incinerator designed by the authors to recover energy from methanol contaminated water 24

Figure 1.24 Reducing kiln used in the mineral sands industry 25

Figure 1.25 Herreschoff multiple hearth roaster 26

Figure 1.26 Two types of refinery heater showing a cylindrical heater and a cabin heater 27

Figure 1.27 Heat transfer coils for refinery heaters showing a coil for a cabin heater and cylindrical heater 28

Figure 2.1 Effect of temperature on reaction rate in the extended Arrheneus Equation 39

Figure 2.2 Consequence of extended Arrhenius equation on temporal consumption of species A 39

Figure 2.3 Extracted reactions from the 'chemical soup' of fossil fuel combustion 40

Figure 2.4 Relationship between reactedness and mass consumption of fuel and oxidant 41

Figure 2.5 Dependence of fuel reaction rate on the reactedness of a flame 42

Figure 2.6 Equilibrium rate values for combustion reactions 43

Figure 2.7 Stages in the combustion of a fuel particle 44

Figure 2.8 Entrainment of secondary fluid into a free jet 47

Figure 2.9 Entrainment of fluid into a high momentum confined jet with external recirculation 49

Figure 2.10 Entrainment of fluid into a swirling free jet with internal recirculation 50

Figure 2.11 Typical aerodynamics in a rotary kiln associated with a grate cooler, obtained by water-bead and air modelling 59

Figure 2.12 Typical aerodynamics in a flash calciner – obtained using water-bead modelling 60

Figure 2.13 The effect of excess air on heat consumption (i.e. fuel efficiency) for a cement kiln 60

Figure 2.14 The effect of excess air on flue gas heat losses 61

Figure 3.1 Schematic of bomb calorimeter 67

Figure 3.2 Examples of three types of gasifier 70

Figure 3.3 Examples of sidewall and down-fired tubular steam reformers 72

Figure 3.4 Schematic of an electrolyser to produce hydrogen 73

Figure 3.5 Combustion characteristics of methane 80

Figure 3.6 Effect of Carbon/Hydrogen ratio on flame emissivity 82

Figure 3.7 Viscosity temperature relationship for petroleum-based fuels 84

Figure 3.8 Effect of fuel type on heat transfer in a rotary kiln 93

Figure 4.1 Representation of section through compound refractory furnace wall 101

Figure 4.2 Representation of ingot shape and reheating furnace firing pattern 102

Figure 4.3 Gurnie-Lurie chart for long cylinder 104

Figure 4.4 Ingot heating predictions using Gurnie-Lurie chart 104

Figure 4.5 Representation of slab showing slice details 105

Figure 4.6 Graphical solution of slab heating problem 107

Figure 4.7 Representation of slab showing slice details with surface heat transfer 108

Figure 4.8 Development of boundary layer over a flat plate 109

Figure 4.9 Temperature profile through a tube wall 114

Figure 4.10 The electromagnetic spectrum 122

Figure 4.11 Diagrammatic representation variation of E with λ for various types of emitter 124

Figure 4.12 Evaluation chart for approximate flame gas emissivity calculations 128

Figure 4.13 Radiative exchange between large, closely spaced parallel Lambert surfaces 130

Figure 4.14 Radiative exchange between two finite surfaces 131

Figure 4.15 Example of crossed string evaluation of exchange area between curved surfaces 133

Figure 4.16 Rectilinear surface relationship 134

Figure 4.17 Complete geometry system 134

Figure 4.18 Sub division of radiating planes 134

Figure 4.19 A refractory backed row of tubes 135

Figure 4.20 Mean beam length values for two geometric systems 136

Figure 4.21 Regions of an arc 139

Figure 4.22 Induction heating of plasma 140

Figure 5.1 Premixed and diffusion flames produced by a Bunsen burner 152

Figure 5.2 Schematic diagram of the stability limits of a premixed flame 153

Figure 5.3 Carbon monoxide concentrations in an 8 MW rotary kiln flame 155

Figure 5.4 Effect of final droplet size on the additional surface area created by atomising a 10 mm sphere 156

Figure 5.5 Mechanism of spray formation from a typical atomiser 157

Figure 5.6 Rosin Rammler distribution for four different oil atomisers 159

Figure 5.7 Optimum combustion intensities for selected rotary kiln processes 161

Figure 5.8 Predicted temperatures and heat flux profiles in a cabin heater 161

Figure 5.9 Examples of stable and unstable flames on the same burner which is to the extreme left in each photograph 163

Figure 5.10 Schematic diagrams illustrating the presence of external and internal flow recirculation 164

Figure 5.11 Flame stabilisation using flow deviation caused by bluff body 165

Figure 5.12 Typical nozzle premix as applied to a tunnel burner and venturi mixer 167

Figure 5.13 Effect of excess air on adiabatic flame temperature for natural gas 169

Figure 5.14 Partial premix radiant wall burner used in side wall reformer and other furnaces 170

Figure 5.15 Principle of flame arrestor fuel gas nozzle 171

Figure 5.16 Principle of turbulent jet diffusion flame 172

Figure 5.17 Recirculation in confined flames 173

Figure 5.18 Principle of precessing jet gas burner nozzle 175

Figure 5.19 Typical industrial turbulent jet burner gas nozzle arrangements with gas pokers and central gas gun 178

Figure 5.20 The main components of a typical furnace oil burner – water cooled version shown 181

Figure 5.21 General mechanism of spray combustion 182

Figure 5.22 Solid and hollow cone sprays 182

Figure 5.23 Illustration of flame stabilisation by internal recirculation zone caused by air entrainment into a hollow cone spray 183

Figure 5.24 Classification of oil burners by atomiser type 184

Figure 5.25 Schematic of simple and spill return pressure jet atomisers 185

Figure 5.26 Calibration curve for wide turndown spill return pressure jet atomiser 187

Figure 5.27 Schematic and exploded view of duplex wide turndown pressure jet atomiser 187

Figure 5.28 A low pressure air atomising burner 188

Figure 5.29 Examples of medium and twin fluid atomisers 189

Figure 5.30 Typical calibration curve for a high-pressure twin fluid atomiser 190

Figure 5.31 Typical open ended pipe kiln burner arrangement 192

Figure 5.32 Typical pulverised coal burner with auxiliary oil firing for rotary kilns 193

Figure 5.33 Waste liquid fuel sprayer developed by the authors to handle contaminated liquids 195

Figure 5.34 An existing burner modified with external waste conveying tubes suitable for use with stable wastes in low to moderate temperature environments 196

Figure 5.35 A multi-fuel burner designed to handle waste petroleum coke as well as natural gas and fuel oil 197

Figure 5.36 Flames produced by each fuel at full load 199

Figure 5.37 Frontal view of gas and pulverised coal burners capable of firing solid and liquid wastes simultaneously 200

Figure 5.38 Schematic of the principal combustion air supply systems 202

Figure 5.39 Examples of how poor secondary airflow adversely affects kiln flames 206

Figure 5.40 Typical combustion air duct supplying multiple burners 207

Figure 5.41 Poor combustion air distribution caused by inadequate duct design 208

Figure 5.42 Example of constant velocity combustion air ducting 209

Figure 5.43 Example of constant velocity combustion air ducting with weirs 209

Figure 5.44 Effect of single blade damper/air door on airflow 210

Figure 5.45 Combustion air distribution following modelling and installation of flow correction devices 210

Figure 5.46 Typical Register oil burner - note the radial airflow distribution required for optimum performance 211

Figure 5.47 Schematic and graphical representation of a sound wave 216

Figure 5.48 The Clyde Refinery flares in normal mode and oscillation mode 221

Figure 5.49 Schematic of gas supply pipework for Clyde Refinery flares 222

Figure 6.1 Physical modelling facility set up for water modelling 229

Figure 6.2 Flow visualisation in an arched furnace roof using water bead modelling 230

Figure 6.3 Simulation of fuel/air mixing in rotary kiln using acid-alkali modelling 230

Figure 6.4 Effect of furnace shape on thermal efficiency 235

Figure 6.5 Thermal performance of well-stirred furnace chambers 238

Figure 6.6 Effect of wall loss factor on well-stirred efficiency equation 239

Figure 6.7 The effect of flame emissivity and excess air on furnace efficiency in a rotary kiln 242

Figure 6.8 Construction of a one-dimensional cylindrical furnace model with jet mixing 243

Figure 6.9 Cement kiln flame temperature calculation using 3-D zone model 246

Figure 6.10 Cement kiln measured flame temperatures 246

Figure 6.11 Comparison of measured and predicted flame temperatures 247

Figure 6.12 3-D, 1-D and well stirred furnace model predictions of wall heat flux 247

Figure 6.13 Co-ordinate grid systems used in CFD modelling 251

Figure 6.14 Effect of burner spacing in a high alumina cement shaft kiln 252

Figure 6.15 Effect of poor windbox design on flames in a four burner water tube boiler 253

Figure 6.16 Modelling inter-relationship for engineering design 256

Figure 7.1 Typical Gas valve safety shutoff system - double block and bleed type 263

Figure 7.2 Oil system typical ring main with multiple furnace off-takes and steam heating 267

Figure 7.3 Typical pumping and heating unit with shell and tube oil heaters and standby electric heating 269

Figure 7.4 Typical oil valve train arrangement 270

Figure 7.5 Rat hole and mass flow 272

Figure 7.6 Raw coal bunker and feeder 273

Figure 7.7 Coal drying curves 275

Figure 7.8 Ball mill for grinding coal with integral drying chamber 276

Figure 7.9 Two types of vertical spindle mill for grinding coal 278

Figure 7.10 Coal mill throughput vs fineness 281

Figure 7.11 Schematic of typical direct firing system applied to a cement kiln 283

Figure 7.12 Schematic of typical indirect firing system 284

Figure 7.13 Coal mill heat balance 288

Figure 7.14 Coal mill inlet temperatures required to dry coal from various raw coal moistures to a fine coal moisture of 2% for various mill airflows showing the effect of false air 289

Figure 7.15 Coal mill throughput vs coal moisture 290

Figure 7.16 Schematic of a typical fine coal storage bin showing the principal instrumentation 292

Figure 7.17 Examples of volumetric fine coal feeders showing screw feeder and rotary valve 294

Figure 7.18 Schematic of an impact weigher 296

Figure 7.19 Schematic of a loss in weight fine coal feeder system 296

Figure 7.20 Schematic of the rotor weigh-feeder showing the principal of operation 297

Figure 7.21 Simplified process flow diagram for hazardous liquid waste 302

Figure 7.22 A small hammer mill capable of drying and pulverising brittle materials 308

Figure 7.23 A schematic of a single shaft waste shredder 309

Figure 7.24 Simplified schematic of a chain hammer mill for pulverising shredded garbage with an example of the product 310

Figure 7.25 A single chamber A TEC Rocket Mill showing feed and product conveyers 311

Figure 7.26 Simplified schematic showing the principle of the walking floor discharge system 312

Figure 7.27 Multiple screw feeders allowing a wide bin opening 313

Figure 7.28 Schematic of a blow through rotary valve for feeding fluff waste to a burner 313

Figure 8.1 Sources of error in temperature measurement using thermocouples and resistance thermometers 322

Figure 8.2 Suction pyrometer 323

Figure 8.3 Venturi-pneumatic pyrometer 324

Figure 8.4 Principle of remote temperature measurement using infrared radiation 325

Figure 8.5 Principle of ultrasonic temperature and flow measurement 326

Figure 8.6 Schematic of a Schenck type belt weigher 327

Figure 8.7 Schematic of a conventional flue gas sampling system 334

Figure 8.8 Typical flue gas sampling probe installation 335

Figure 8.9 Water-cooled hot gas portable sampling probe designed by the authors 335

Figure 8.10 A water-cooled probe employing automatic pneumatic cleaning 336

Figure 8.11 the principle of the dilution extractive gas sampling probe 337

Figure 8.12 Schematic of cross-duct optical obscuration dust monitor and backscatter device 338

Figure 8.13 A high temperature (700-1700oC) zirconia analyser for flue gas oxygen measurement showing a cross section of the cell 339

Figure 8.14 Procal folded beam in-situ flue gas analyser 341

Figure 8.15 Schematic of a cross-duct multi-component optical spectrometer gas analyser 342

Figure 8.16 The fire triangle 344

Figure 8.17 Typical furnace start sequence 346

Figure 8.18 Principle of fail-safe relay logic employed in BMS systems 351

Figure 8.19 Example of fault tree analysis 357

Figure 8.20 Example of two flow transmitters (4-20 mA) are used to prove combustion air flow using redundancy 358

Figure 8.21 Logic associated with three flow transmitters (4-20 mA) used to prove combustion air flow and reduce spurious trips 358

Figure 8.22 Ultra-violet and infra-red wavelength compared with visible light 359

Figure 8.23 Principle of flame ionisation showing half wave rectification of the current 361

Figure 9.1 Schematic diagram of a generic furnace process showing flows through the system 364

Figure 9.2 Plot of typical furnace performance 367

Figure 9.3 Distribution of thermal quantities data 368

Figure 9.4 Plant trials using a suction pyrometer to measure combustion air temperature and an optical pyrometer to measure product discharge temperature 370

Figure 9.5 Process flowsheet with envelopes 375

Figure 9.6 Energy conversion trianges 385

Figure 9.7 Temerature–enthalpy data for cement, lime and alumina production 388

Figure 9.8 Composite curves for hot and cold streams for pinch analysis 389

Figure 9.9 Types of flow path configurations through recuperative heat exchangers 391

Figure 9.10 Relationship between heat transfer rate and surface area for different recuperative heat exchanger flow regimes 392

Figure 9.11 Types of flow path configurations through regenerative heat exchangers 395

Figure 9.12 Process flowsheet with air preheat option 397

Figure 9.13 Process flowsheet with air preheat and convection section options 399

Figure 10.1 The structures in which nitrogen is commonly bound in heavy oil and coal fuels 407

Figure 10.2 A simplified schematic representation of the paths of NOx formation 408

Figure 10.3 A schematic representation of the role of HCN in the NOx formation process 408

Figure 10.4 The temperature dependence of the NOx formation process 409

Figure 10.5 The structure of Dioxins 413

Figure 10.6 Soot burning times for 500 Å particle at an oxygen partial pressure of 0.05 bar 418

Figure 10.7 Tendency of fuels to smoke in relation to their composition 418

Figure 10.8 Schematic mechanism for soot formation, showing the influence of reaction time and temperature 419

Figure 10.9 Typical ash structures 420

Figure 10.10 Mechanisms for ash formation 421

Figure 10.11 An example of the trade-off between NO and CO emissions, here from an internal combustion engine, which operates as pre-mixed flame 426

Figure 10.12 Effect of stoichiometry on NOx emissions for diffusion and premixed flames 427

Figure 10.13 The effect of FGR on NOx emissions in an oil-fired boiler 428

Figure 10.14 An aerodynamically air staged burner 429

Figure 10.15 The principal of reburn illustrated schematically 430

Figure 10.16 The principal of reburn applied to an entire boiler 431

Figure 10.17 Atypical tangential inlet cyclone 432

Figure 10.18 The range of processes for CO2 capture 435

Figure 11.1 Basic types of furnace showing direct fired and indirect fired 440

Figure 11.2 Typical brick lining construction showing alternative layers of bricks and expansion joints with casing reinforcing 441

Figure 11.3 Typical monolithic lining held to the shell by anchors 442

Figure 11.4 Typical ceramic fibre lining showing fixing details on the right 442

Figure 11.5 Brick failure caused by inadequate allowance for expansion 444

Figure 11.6 Tapered brick being installed in a rotary kiln; note the purpose-built support frame to facilitate quick and accurate installation 444

Figure 11.7 Typical anchors for installation of castable refractory 446

Figure 11.8 Use of split mould formwork to cast refractory on a burner pipe 447

Figure 11.9 Gunning refractory into place in a rotary kiln 448

Figure 11.10 Strength development during curing of castable refractory 449

Figure 11.11 Failure of an A 316 spun cast burner tube 451

Figure 11.12 Typical furnace arch construction 452

Figure 11.13 An example of an internally tiled furnace flat roof 452

Figure 11.14 Simplified schematic of closed cooling system and open circuit cooling system 455

Figure 11.15 Effect of raw materials on refractory properties 456

Figure 11.16 Example of alloying element providing strength to a metal by distortions of the crystal structure. 463

Figure 11.17 Schematic illustration of how a passive oxide layer protects the metal 464

Figure 12.1 Design Constraints 484

Figure 12.2 Evolutionary development of the rotary kiln cement making process 486

Figure 12.3 The design process 487

Figure 12.4 Furnace process functions within the overall manufacturing process 489

Figure 12.5 Schematics of cross flow and counter flow recuperators and regenerative heat wheel for preheating combustion air 502

Figure 12.6 Time-temperature-enthalpy diagram for metal slab heating 505

Figure 12.7 Time-temperature-enthalpy diagram for multi-component oil heating 506

Figure 12.8 Time-temperature-enthalpy diagram for mineral aggregate processing 506

Figure 12.9 Temperature-enthalpy relationships for metal slab. Oil and aggregate heating processes 507

Figure 12.10 Schematic diagram of a typical single zone re-heating furnace 512

Figure 12.11 Effect of slab length on principal parameters in the design of a heating furnace 514

Figure 12.12 Schematic diagram of a typical rectangular tube-still heater 516

Figure 12.13 Effect of furnace height on principal parameters in the design of a rectangular oil heating furnace 519

Figure 12.14 Effect of furnace height on principal parameters in the design of a cylindricaloil heating furnace 519

Figure 12.15 Effect of kiln diameter on principal parameters in the design of a shaft kiln 521

Figure 12.16 Schematic of shaft kiln with integral product cooling and air preheating 522

Figure 12.17 Surface heat flux profile for slab heating 524

Figure 12.18 Surface heat flux to outside of tube for oil heating 525

Figure 12.19 Surface heat flux to lump for aggregate processing 525

Figure 12.20 Effect of adjacent burners on measured flame temperature of the centre burner of a set of three 527

Figure 13.1 General arrangement of 3 zone slab reheating furnace 544

Figure 14.1 The Everett lime sludge kiln with a schematic of the internal fittings 569

Figure 14.2 Typical temperature profiles in a lime sludge kiln 570

Figure 14.3 The multi-fuel burner nozzle with a cross section of a gas port 573

Figure 14.4 Isometric sketch of the multi-fuel burner 574

Figure 14.5 Everett kiln flames for all fuels 575

Figure 14.6 Simplified process flow diagram of the Alcoa calciner system showing the sampling points 577

Figure 14.7 The double valve lock and seal system allowing safe probe insertion and withdrawal 579

Figure 14.8 Acid Alkali Model of main furnace combustion showing normal operation on the left and intermittent unstable conditions in the centre and to the right 581

Figure 14.9 The 3-dimensional grid used for the CFD modelling 583

Figure 14.10 Photograph of the computer screen showing two CFD Modelling results 584

Figure 14.11 Example of the air and particle velocity profiles in the flash furnace showing a slice model and 3-D model 584

Figure 14.12 Example of the particle concentration profiles in the flash furnace 585

Figure 14.13 Schematic of typical tubular steam reforming plant 586

Figure 14.14 Schematic of a phosphoric acid fuel cell 588

Figure 14.15 Simplified schematic of the convective heat exchange reformer 589

Figure 14.16 Multi-fuel burner for convective heat exchange reformer 591

Figure 14.17 The acid alkali model set up 592

Figure 14.18 Typical flames simulated using acid alkali modelling 595

Figure 14.19 Typical plot of flame length versus excess oxygen predicted by acid alkali modelling 595

Figure 14.20 Predicted heat flux profile for normal operation with anode off-gas 596

Figure 14.21 Likely failure mechanism of silicon carbide burner nozzle 597

Figure 14.22 The temporary test facility for the tri-fuel burner 598

Figure 14.23 Simplified process flow diagram for a typical fuel cell stationary PAFC system 600

Figure 14.24 Residual oil cabin heater supplying delayed coker plant showing the visually observed flame pattern 600

Figure 14.25 Predicted heat flux profiles for current operation and for proposed low excess air operation 603

Figure 14.26 The physical model set up for airflow measurement following the installation of windbox entry splitters 604

Figure 14.27 Existing air distribution determined using physical modelling 605

Figure 14.28 The improved air distribution achieved by physical modelling 606

Figure 14.29 Schematic of the existing swirl burners 607

Figure 14.30 Schematic of the modified burners 608

Figure 14.31 Simplified process flow diagram for dry process cement manufacture 610

Figure 14.32 View of the cooler offset elbows showing the resulting airflow pattern 613

Figure 14.33 Model of coolers and burner shown with kiln tube removed 618

Figure 14.34 Model of existing firing conditions, note the dark region of unmixed alkali in the vortex core 618

Figure 14.35 Predicted heat flux profile for exiting gas-firing conditions 619

Figure 14.36 Acid alkali model simulation for high momentum swirled primary air 621

Figure 14.37 Predicted heat flux profile for the proposed gas-firing conditions 622

Figure 14.38 Comparison of existing and scaled up cement kiln dimensions 623

Figure 14.39 Schematic of the submerged combustion direct reduction smelter 625

Figure 14.40 Simplified process flow diagram of rotary drum coal drying system 626

Figure 14.41 The original coal firing system installed on the plant 629

Figure 14.42 Location of sample points used to measure operational data with portable instrumentation 629

Figure 14.43 The overall mass and energy balance for the preheater kiln 630

Figure 14.44 Cooler mass and energy balance 630

Figure 14.45 Process and instrument diagram of revised coal grinding and firing system 631

Figure 14.46 Performance of the preheater kiln prior to and following the upgrade 632

Figure 15.1 CO2 capture processes 648

Figure 15.2 The principle of CO2 sequestration using oxy-fuel combustion 651

Figure 15.3 Post-combustion gas composition from coal burned in a mixture of oxygen and recycled flue gas 652

Figure 15.4 Overview of typical technology selection for combustion applications of oxygen source 653

Figure 15.5 Costs for transportation of CO2 654

Figure 15.6 Geological storage options 657

Figure 15.7 Ocean Storage Options for CO2 658

List of tables

Table 1.1 Examples of furnaces meeting the classifications specified in figure 1.3 6

Table 2.1 The characteristics of furnace flames with and without external recirculation 50

Table 2.2 The comparative characteristics of simple enclosed jet theories 53

Table 3.1 Raw compositions of a few manufactured gases at 15oC 75

Table 3.2 Typical natural gas compositions as supplied to customers 76

Table 3.3 Flammable limits for gases at room temperature 79

Table 3.4 Typical properties of selected petroleum-based furnace fuels 83

Table 3.5 Characteristic properties of selected solid fuels 85

Table 4.1 Convective heat transfer correlations for a range of common geometries 115

Table 4.2 Total emissivity of some common materials at room temperature 127

Table 4.3 Materials used for resistance heating elements 138

Table 5.1 Comparison between original and new scaled-up kilns 214

Table 6.1 Hierarchy of turbulence models 249

Table 6.2 Typical diffusion coefficients and source terms 250

Table 6.3 Comparative merits of modelling methods 256

Table 7.1 General comparison between ball, vertical spindle and high-speed mills 276

Table 7.2 Comparison between direct and indirect firing systems 286

Table 7.3 An example of a liquid waste fuel specification 301

Table 8.1 Typical flue gas analysis for heavy fuel oil showing the difference between wet and dry oxygen proportions 330

Table 8.2 Summary of flue gas species analysis techniques 332

Table 8.3 Comparison between basic extractive gas sampling and in-situ gas analysis systems 333

Table 8.4 Safety integrity level defined by IEC standard 61508 354

Table 9.1 Energy flows relating to Figure 9.1 364

Table 9.2 Process measurements 374

Table 9.3 Selected fuel data 375

Table 9.4 Mass balance for the process 377

Table 9.5 Energy balance for the process 379

Table 9.6 Mass Balance for the furnace 381

Table 9.7 Energy balance for the furnace 383

Table 9.8 Energy balance for the process with reduced in-leakage and balanced burner flows 384

Table 9.9 Maximum energy conversion efficiency for various processes based on Figure 9.6 386

Table 9.10 Common types of recuperative heat exchangers used in furnace operations 393

Table 9.11 Common types of regenerative heat exchangers used in furnace operations 396

Table 9.12 Energy balance for the process with combustion air preheating 398

Table 9.13 Energy balance for the process with combustion air preheating 399

Table 10.1 Rate constants for thermal NOx equations 406

Table 10.2 Occurrence of prompt NOx for some combustion processes 410

Table 10.3 Chemical pathways to the formation of acid mist 411

Table 10.4 World Health Organisation total equivalence factors for human risk assessment of PBCs, dioxins and furans 414

Table 10.5 Estimated Dioxin and Furan Emissions in the UK 415

Table 10.6 Dimensional ratios for various cyclone designs 433

Table 11.1 Characteristics of the main classifications of stainless steels 465

Table 12.1 Ash analysis for several South Australian lignites 496

Table 12.2 Furnace design data derived from figures 12.6, 12.7 and 12.8 508

Table 12.3 Calculation of heat transfer areas and average furnace heat flux for design examples 510

Table 12.4 Input data for well-stirred furnace model analysis 512

Table 12.5 Well-stirred furnace analysis of slab heating furnace designs 513

Table 12.6 Well-stirred furnace analysis of rectangular oil heating furnace designs 517

Table 12.7 Well-stirred furnace analysis of cylindrical oil heating furnace designs 518

Table 12.8 Well-stirred furnace analysis of aggregate processing shaft furnace designs 520

Table 12.9 Analyses of the effect of kiln diameter on pressure drop through packed bed of aggregate 521

Table 12.10 Well-stirred furnace analysis of aggregate processing shaft furnace designs including integral product cooling by combustion air 523

Table 12.11 Manufacturer’s technical data on nozzle mixing gas burner for slab heating furnace 526

Table 13.1 Methodology of categorising detailed cost analysis 534

Table 13.2 Financial performance ratios 537

Table 13.3 Levels of cost estimation 539

Table 13.4 Typical scaling factors for costs of standard equipment 541

Table 13.5 Determination of Lang factor for a heat exchanger 542

Table 13.6 Summary of WSF modelling of reheating furnace – oil fired base case 545

Table 13.7 Summary of modelling for case 1- re-brick with no insulation 547

Table 13.8 Summary of modelling for case 2 - conversion to natural gas 547

Table 13.9 Summary of modelling for case 3 – conversion to natural gas with new calcium silicate lining 548

Table 13.10 Summary of modelling for case 4 – reinstate stack recuperators 549

Table 13.11 Summary of modelling for case 5 – conversion to blast furnace gas with stack recuperators 549

Table 13.12 Summary of modelling for case 6 – install self-recuperative burners 550

Table 13.13 Summary of modelling for case 7 – Oxygen enrichment 551

Table 13.14 Summary of process modelling data required for economic study 552

Table 13.15 Summary of process operating cost data required for economic study 553

Table 13.16 Base case costing sheet 554

Table 13.17 Re-brick with no insulation costing sheet 554

Table 13.18 Conversion to natural gas costing sheet 555

Table 13.19 Conversion to natural gas with new lining costing sheet 556

Table 13.20 Reinstate stack recuperators costing sheet 557

Table 13.21 Conversion to blast furnace gas with stack recuperators costing sheet 558

Table 13.22 Install self-recuperative burners costing sheet 559

Table 13.23 Oxygen enrichment costing sheet 560

Table 13.24 Variable cost analysis for case options 561

Table 13.25 Analysis of investment potential for projects 562

Table 13.26 Relationship between capital cost and project payback 564

Table 14.1 Typical dewatered catalytic steam reformer gas properties 587

Table 14.2 Acid and alkali concentrations used to represent the different fuels 594

Table 14.3 Typical cement kiln raw mix feed 610

Table 14.4 Comparison between existing wet kilns and the new large dry process kilns 612

Table 14.5 Operational data collected from temporary and plant instrumentation 615

Table 14.6 Comparison of existing and scaled up cement kiln operating parameters 615

Table 15.1 Absorption options for CO2 capture 649

Table 15.2 Variation of CO2 control cost predictions for a large scale project 653

Table 15.3 Existing carbon dioxide pipelines 656

Chapter 1: Introduction

Abstract

Chapter 1 briefly reviews the historical development of furnaces and notes their position at the heart of our industrial society. The concept of a furnace and furnace efficiency is defined together with a classification of the types of furnace based on energy source and product type. The designer’s basic objectives are outlined and the importance of achieving satisfactory product quality as the over-riding key objective is explained.

The remainder of the chapter examines the industries in which furnaces are used and the types of furnaces used in those industries. This includes ceramics, cement & lime, glass, metal ore smelting and refining, metal processing, furnaces with reducing atmospheres, oil refining and petrochemical applications as well as incineration and resource recovery furnaces. The chapter concludes with a discussion on the drivers for improved efficiency.

Key Words

furnace definition; classification; furnace efficiency; furnace applications; reducing atmospheres; drivers for improved efficiency

Combustion and furnaces are the very heart of our society. Furnaces and kilns are used to produce virtually everything we use and many of our food and drink items, either directly such as the metal products used in everyday life, the packaging for our food and drink or indirectly such as the tools that are used to grow that food. Even a natural product, such as timber, requires drying to make it suitable for most uses, and that drying occurs in a kiln.

From the earliest days of human existence food was cooked over open fires and sticks were charred to harden them. However, open fires provided little control over the heating process, and the birth of the Bronze Age some 5000-6000 years ago would have required the construction of a forced draft furnace to achieve the temperature required to smelt the ore and produce liquid metal for casting. Metal production remained small scale for centuries owing to the scarcity of suitable fuel (charcoal) and the high cost of its production. The breakthrough came as a result of the determination and tenacity of Abraham Darby who worked much of his life to reduce the cost of cast iron by using coke in place of charcoal. He finally succeeded and a lasting testament to his work is the world’s first iron bridge, completed in 1779 crossing the River Seven at Coalbrookdale in North West England, figure 1.1.

Darby’s pioneering work laid the foundations for the industrial revolution because iron production was no longer constrained by fuel supply and blast furnaces proliferated in the Severn Valley and even changed the way artists perceived the landscape, as exemplified in Philip James de Loutherbourg’s famous landscape Coalbrookdale by Night now exhibited in the Science Museum, London. In addition to pioneering the use of coke, Darby also utilised steam engines for powering his furnace bellows and hence make the operation far less dependent on water power and less reliant on local rainfall, which was problematic and, on many occasions, drought had interrupted production for long periods. By establishing his furnaces independence of the vagaries of the charcoal burners and the weather, Darby triggered an industrial revolution that is continuing to this day.

Figure 1.1  The iron bridge at Coalbrookdale

The vast majority of the materials we use, and the food and drink we consume, have been heated at some stage during the production process. Combustion processes are conveniently divided into high and low temperature process. Although there is no strict dividing line between the two, processes with wall temperatures below 400-500oC are often considered low temperature, while those above 500-800oC are generally considered high temperature. High temperature processes include, cement and lime manufacture, brick and ceramic manufacture, most metal processing, glass making, etc., while low temperature processes include drying processes, food processing and sterilisation, steam raising, oil refining, etc..

It is much more difficult to ensure efficient use of the fuel’s energy in high temperature processes than their low temperature counterparts. For low temperature processes, such as steam raising, efficiencies of over 80% are commonly obtained, whereas for high temperature processes, efficiencies exceeding 50% are rare. Furnace design engineers of the future will be required to maximise overall process efficiency in a carbon constrained world. This requirement will be driven both, by the community need to achieve greenhouse gas reduction, as well as the process economics owing to high fossil fuel costs, especially for processes requiring premium fuels, such as oil and gas. The aim of this book is to assist engineers to achieve higher performance both from existing, and from new furnace designs, by providing the readers access to the tools that assist with gaining an in-depth understanding of the fundamentals of the individual processes. The book does not attempt to provide an in-depth understanding of any individual process because that would require a book in itself, for each industry, as can be seen from the wide variety of furnaces outlined in this introduction. In any case, we consider that the weakness of that approach is that the knowledge remains confined to that particular industry. For example, the excellent kiln efficiencies achieved by the lime industry were almost unknown in the pulp and paper industry in the early 1980s hence their lime kilns used some 30-50% more fuel than those in the mainstream industry at that time.

1.1. What is a furnace?

The Oxford English Dictionary defines a furnace as "an enclosed structure for intense heating by fire, esp. of metals, or water", whereas a kiln is described as as furnace or oven for burning, baking or drying, esp. for calcining lime or firing pottery. In reality, there is little difference between the two, kilns and furnaces both operating within a similar temperature range. The two names owe more to tradition than to functional differences.

Furnaces are the basic building block of our industrial society, indeed they are the foundation of our entire civilisation, as shown above. The principal objective of a furnace is to attain a higher processing temperature than can be achieved in the open air. Although some processes could be carried out in the open air, to do so would be far less efficient, the fuel consumption would be much higher and control of the process would be much more difficult.

Furnaces can be used to facilitate a wide range of chemical reactions, or in some cases simply for physical processes, such as annealing or drying. Design of the former is normally more complex than the latter but not exclusively so. One of the challenges of furnace design is to determine the critical rate determining step(s) and to ensure that these are effectively addressed in the design. By achieving this, smaller more efficient furnaces and more cost effective designs can often be developed.

In this book we shall be dealing with furnaces for processing materials at high temperatures, that is, above 400oC, especially those where the product is directly exposed to the flame. We shall not discuss steam boilers, the design and manufacture of which is a highly specialised subject. In any case steam boilers have reached such high efficiencies that only marginal gains are possible. Future gains in the efficiency of electricity generation, for example, depend on improving the cycle efficiency; while this will impact on boiler design that is not where the gains will originate. Readers should consult Babcock and Wilcox (2005) for further information on boiler design.

1.1.1. Furnace outline

The basic concept of a furnace is shown in figure 1.2, below.

Heat is liberated by burning fuel with air (or oxygen), or from electrical energy, and some of this heat is transferred to the product. The remaining heat leaves in the flue gas and through openings such as charging doors, or is lost from the external surface. The efficiency of the furnace can be defined as:

[1.1]

Where: = furnace efficiency

= heat embedded in the final product

= heat supplied by combustion

The heat embedded in the product is often quite small compared with the overall heat supplied, much heat being lost in the flue gases and by-products or waste materials such as slag. While equation 1.1 is a general expression for efficiency and is equally applicable to boilers etc, it has many limitations with respect to determining the effectiveness of a furnace. Later we shall examine other, more useful, measures of furnace performance.

1.1.2. Furnace classification

There are an almost infinite number of ways of classifying furnaces, e.g. by shape, industry, product, etc., but a very simple classification based on the heat transfer concepts of the type heat source and the type of heat sink is shown in figure 1.3. This classification system is highly simplified but it is useful because the nature of the product, the type of fuel, and the heat transfer mechanism all have a major influence on the physical arrangement of the furnace. It should be noted that many furnaces have multiple heat sinks and use several fuels, either concurrently of alternatively, which also affects the furnace design. Examples of furnaces falling in the classifications shown in figure 1.3 are provided in table 1.1 . Descriptions and illustrations of a wide range of furnaces meeting the classification shown in figure 1.3 follow later in this chapter. We will also refer to figure 1.3 when considering the design of furnaces in chapter 12.

Figure 1.2  The Basic Elements of a Furnace

Figure 1.3  Classification of Furnace

1.1.3. Principal objectives of furnace designers and operators

1. Obtain a satisfactory product

2. Use minimum fuel and energy to achieve that product

3. Construct the furnace for the lowest capital cost

4. Operate with the lowest possible manning levels

5. Achieve a satisfactorily long life with low maintenance costs

Objective 1 overrides all others because, if the product is unsatisfactory, then it cannot be sold or must be sold for an inferior price. While safety has not been mentioned in the above objectives, it can be taken as a given in today’s environment and is covered extensively in chapter 8.

The art of furnace design involves achieving the best combination of these five objectives over the entire life of the furnace, in other words to produce a high quality product at the lowest achievable cost. Although these five objectives may seem self evident, in our experience they are not always achieved. Furnace users have generally purchased on the basis of capital cost, understandably so, given that the other objectives are much more difficult to assess at the tendering stage. This approach has led to relatively little engineering effort being expended on improving existing designs because engineering time