Dictaat spm4510Version 2.1 - Year 2013-2014

Design of Innovative Energy and Industry Systems - Part II

Gerard P.J. Dijkema and R. Praet

Delft University of TechnologyDepartment of Technology, Policy and Management

MSc SEPAM© 2014 TU Delft

Dictaat spm4510Version 2.1 - Year 2013-2014

Design of Innovative Energy and Industry Systems - Part IIG.P.J. Dijkema and R. Praet

This is the Reader spm4510. This document forms an integral part together with the literature prescribed(Reader, part I) and the lecture slides.

These can be accessed via blackboard or directly viahttps://svn.eeni.tbm.tudelft.nl/Education/spm4510

An electronic version of this PDF can be downloaded fromhttps://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_

Design/Electronic_Reader_Q2/spm4510_Part_II_reader.pdf

TU DelftFaculteit Techniek, Bestuur en Management

Program M.Sc. SEPAM© 2014 TU Delft

Colofon

Titel: Design of Innovative Energy and Industry Systems - Part II

Auteurs: G.P.J. DijkemaR. Praet

ISBN:

Program: M.Sc. SEPAMCourse code: spm4510

e-mail: g.p.j.dijkema@tudelft.nl.

Published and distributed by:Technische Universiteit DelftFaculteit Techniek, Bestuur en ManagementP.O. Box 50152600 GA Delft-NLT: +31 15 278 2727F: +31 15 278 3422I: www.tbm.tudelft.nl

Copyright © 2014 TU Delft

DISCLAIMER. This is the second version of this Reader. An effort has been made to use reliablesources, and to offer a complete record through proper citing of sources used. As a third version andwork-in-progress, the bibliography may not be complete and may contain errors. Please contact thefirst author if you think there is an error in the text, or material used has not been appropriately cited.

LIMITED LIABILITY This reader has been compiled for M.Sc SEPAM student use. In no event shallthe author(s) be liable for any found errors contained in this Reader or for any direct, indirect orconsequential damages in connection with the furnishing or use of this material. The informationcontained within this reader may be subject to change without notice.

This work is published under the Creative Commons Attribution-Noncommercial-Share Alike 3.0Unported License – http://creativecommons.org/licenses/by-nc-sa/3.0/

Typeset by the author using LATEX.

Contents

Contents iii

1 System Design Theory 31.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Design and Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 System definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4 Design of Innovative Systems - Why? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Design Methods for Innovative System Design 92.1 Overview of Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 The nature of (conceptual) design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3 Process System Innovation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.4 Functional Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.5 Problem specification: the Meta-Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.6 Superstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3 Natural Gas Infrastructure Systems 173.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.2 About Natural Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.3 Gas Production & Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.4 Natural Gas Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.5 Dutch Gas Infrastructure Design and Development, 1959-2009 . . . . . . . . . . . . . . . . 39

4 Electricity Infrastructure Systems 454.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.2 Design of Energy Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.3 Electricity Production Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474.4 Co- & TriGeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.5 Power Supply in the Netherlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Bibliography 57

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Contents

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Preface

This reader is about the design of innovative large-scale systems: energy infrastructures and indus-trial networks. The focus is on the conceptual technological system design.Functional modelling anddecomposition are introduced, as are engineering problem formulation and the use of the superstruc-ture method. These are introduced through, illustrated by and applied to natural gas infrastructuresystems and the electricity infrastructure system design.

While in this course the focus is on conceptual technological system design, we know that today’sinfrastructures and industrial networks can be viewed at large-scale complex socio-technical systems(Nikolic et al., 2009; Dijkema. and Basson, 2009; Herder. et al., 2008). Innovative system design, there-fore must relate and interface effectively with the socio-economic context a system is designed in. Sub-sequently, it must take into account that the power of decision may be distributed over multiple actors,that each control and manage only part of the system. And finally, that a process is needed to bringthe system-into-being. This leads to a requirement of TIP-design - Technology, Process and InstitutionalDesign, which is the objective of spm5920, the SEPAM design project.

The course spm4510 will provide students with methods, theories, tools and knowledge to completea conceptual technological system design, and will let the students bring their designs to a more detailedlevel of specificity in certain domains (e.g. chemical process design, separations systems, gas infrastruc-ture and power conversion systems).

Gerard P.J. Dijkema, Delft, December 2013

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Contents

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Chapter 1

System Design Theory

1.1 Introduction

This course is about design of energy and industry systems. In this chapter we will address whatis design, how system thinking and various methods from system design can help us to develop newsystem designs for energy infrastructure and industry. In this chapter we will discuss the necessity ofinnovative system design and various approaches to get there. This text is accompanied by a series oflectures and lecture slides 1.

1.2 Design and Engineering

Design is not the same as engineering. To make matters even more complicated, an acknowledged in-troductory textbook is titled Engineering Design (Dym and Little, 2009). In their first chapter, theydefine design as ”‘an activity that intends to produce a ”‘description of an artifice in terms of its orga-nization and functioning” – its interface between inner and outer environments”’(Dym and Little, 2009,p.13). Thus, design is an activity of the mind or of many minds, its end product being a description ofsomething, an artifice, and how that is supposed to function and organized (embodied, realized). Theend product of design we label as ”‘a conceptual design”’. This is then where engineering begins: theconceptual design needs to be further specified and detailed. An example may serve to illustrate thedifference between design and engineering.

A design team may be asked to come up with a zero-energy tomato greenhouse for the Netherlands.After a couple of expert meetings, creative workouts, brainstorm sessions and hard design thinking theteam has developed its novel concept: the greenhouse will be developed as a single system connectedto its subsurface for heat storage and heat withdrawal. To this end, a water circulation system will beset up that connects greenhouse and subsurface hot water reservoir. The greenhouse will only use CO2and electricity from renewable sources. In the design process, we may go one step further, and state,for example, that this greenhouse will obtain electricity (for internal transport, automation etcetera)from solar panels, using the grid as backup; similarly, that CO2 (needed for tomato plant growth) isobtained from a local CO2-grid. The final step in design may be some estimates of the system scale

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• Introduction to Systems Thinking: https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_1_1_Introduction_large_system_design_nov_18_2013.pdf

• The Meta Model: https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_2_1_the_meta_model_Nov_18_2013.pdf

• Superstructure Method: https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_3_2_superstructure_method_Nov_28_2013.pdf

• Degrees-of-Freedom: https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_3_1_degrees-of-freedom_nov_24_2013.pdf

• Functional Modeling: https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_x_1_functional_modeling_NOT_PRESENTED_2013.pdf

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1.3. System definition

and volumes of flows involved. For example, the heat flow for a typical tomato greenhouse may beknown - in and around summer the greenhouse will absorb excess solar heat that can be stored, whilein and around winter, the stored heat must be used. Both for storage and withdrawal, seasonal anduse patterns translate into maximum heat flows per hectare. These may be converted in heat storagecapacity, in [MWh], but if entry and exit temperatures of the water are known, this also translates intoa size of the subsurface heat storage. Similarly, initial estimates for CO2 and electricity requirementsmay be derived. Engineering now starts by specifying more precisely how this zero energy tomatogreenhouse system will be realized. It will be specified how heat will be extracted from or supplied tothe greenhouse. Questions such as ’what kind and size of heat-exchanger’, ’where to place them in thegreenhouse’, ’single system (summer and winter) or multiple system’, ’backup system or not’ etcetera.

The tomato greenhouse example also illustrates that there is a caveat when we attempt to distinguishbetween design and engineering: the engineers (!) engaged in the activity of engineering the subsys-tems will perceive their activities as design activities! And they are right: what is design and what isengineering also is determined by the system scope. Using the perspective of the zero-energy tomatogreenhouse design team, the activities to detail and design the subsystems are engineering; the engi-neers involved, however, preferably (should) start their activity by treating the problem given to themas a design problem – e.g. for the ’heat’ subsystem, they are supposed to come up with a design: howto get heat in and out of a greenhouse? The difficulty of delineating between engineering and designis also reflected in the second part of Dym and Little’s definition of design – design not only relates tofunctioning but also to organization, and thus to internal and external system interfaces and linkages.

We can conclude system design can be executed at various system aggregation levels (see also § 1.3),and always focuses on functioning and organization, not on implementation and realization details.

1.3 System definition

There are numerous definitions of systems, which necessitates the adoption of a working definitionthat avoids ambiguity and is suitable for the purpose of devising conceptual system models and inno-vative system design.

We define a system as ”a structured assemblage of elements and subsystems, which interact through inter-faces. The interaction occurs between system elements and between the system and its environment. The elementsand their interactions constitute a total system, which satisfies functional, operational, and physical characteris-tics, as defined by the user and customer needs and requirements, over a defined total system life cycle of the systemexistence, including the life cycle of bringing the system into being” (Asbjornsen, 1992).

Note that this definition is essentially content or technology-free. It stipulates description if not for-malization of a system by describing what it should do, not how the conversion between inputs andoutputs is to be realized. Thus, the adoption of this system definition opens the way to develop new(technological) concepts to bring about the targeted transformation between inputs and outputs (Di-jkema, 2004). Starting from an existing system realization, we may abstract and describe this systemin terms of its function and organization. Once we have completed this step, we may then think ofalternative realization, filling in technical details.

Adopting the definition also implies one has to somehow develop a system decomposition, a partic-ular way to break down the system in its constituting parts. In case we also make sure that in suchdecomposition the system’s lowest level is a system element that is again only defined by functionalcharacteristics, we have arrived at a technology-free decomposition.

Exercise: define and describe the tomato greenhouse as a system

1.4 Design of Innovative Systems - Why?

There exists a variety of reasons why there is a need for innovative systems and innovative systemdesign. These include, but are not limited to a series of mega-trends, Sustainability and increasingconnectivity around the globe.

1.4.1 Mega-trends

Taking a helicopter view of global society, we can observe a number of megatrends:

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Chapter 1. System Design Theory

• From trade (Dutch:”‘ambachten”’) (19th century) to industrial productivity (20th century) to knowl-edge intensive products and services (21st century) (Peter Drucker)

• The Economic Center of Gravity shifts towards South-East Asia• A shrinking world (ICT) - The world is flattening (Th. Friedman)• A quest for sustainability - the pressure is certainly on!

– Global resource scarcity and competition– System Earth: increasing global environmental stress– Equity: a widening gap between the rich and the poor

The first three of these mega-trends profoundly impact the structure of the global economy, whilesustainability requires a fundamental change if not transition of society and the systems we use to satisfyour needs. Each region (the European Union, the US, Japan, South-America, India, China) needs todevelop a response to these trends, to ensure competitiveness and market niche, maintain affluence,and realize sustainability.

The first mega-trends of course build upon developments in the (19th century) and (20th century),which saw the development of a tremendous industrial infrastructure that provides people in the “de-veloped” countries with continuously available drinking water, electric power, natural gas, transportfuels, chemicals, fertilizer, plastics and pharmaceuticals.

The other mega-trends, however, may put this foundation at risk, because the production by thesesectors is resource and capital intense and many a production technology and system is considered tobe mature and locked-in to their technology or system.

1.4.2 Connectivity at a global scale

Since 1850 (yes, the mid-19th century!), world-wide webs have been developed fostering mass-communication,mass-mobility and mass-production. In communication, the telegraph was followed by the telephone,and later internet. Mass-mobility was enabled by the steam-engine, powering huge ships and notablyrail roads. Mass-production also took off because of the arrival of the steam engine and the availabilityof coal, to be followed by the bonanza in oil production in the second half of the 19th century. The 20th

century is the age of electricity and of the automobile, enabled by gasoline, diesel, engines and mass pro-duction developed by Henry Ford. Electricity was popularized by the inventions of Edison around theturn of the century, which led to ”‘electrification”’ of society, both in household appliances and industry.

All of these developments required massive inputs of primary energy sources - first coal, subse-quently oil products, and today also natural gas. With time, electricity and gas networks turned intoinfrastructure systems that shape society.

The impact of humanity on the natural environment can be seen as the product of Population,Affluence and Technology (Equation 1.1)(Ehrlich and Holdren, 1971, 1972).

I = P ∗A ∗ T (1.1)

Population During the 20th century alone, global population has increased from 1.65 billion to 6 billion.Projections indicate we will cross the 7 billion mark in 2013, the 8 billion mark in 2028 and the 9billion mark in 2054 before human population stabilizes at just above 10 billion after 2200 (UN,1999).

Affluence Affluence is a measure for the welfare/well-being of each individual, which translates to con-sumption. A commonly used proxy is the Gross Domestic Product (GDP) per capita. Accordingto the World Bank, global average GDP per capita equalled 445 US$ in 1960 and increased to 9,042US$ in 2008 (expressed in US$ of 2008). Although technically the GDP is a measure of the pro-duction it is generally assumed is a good enough proxy for consumption - with no stockpiling,everything that is produced in a year approximately is consumed.

Technology The Technology variable is an indicator of the resource intensity required for Affluence.One indicator for this is the energy use per US$ GDP produced Figure 1.1. In 1980 this indicatorwas 239 kilogram of oil equivalent for each 1000 US$ GDP. In 2007, it had dropped to 186 kilogramof oil equivalent. Another indicator is the CO2 intensity of our technology. The World Bank notesthat it took 1.296 kilogram of CO2 emissions to produce 2000 US$ GDP in 1960 versus 0.7491 kilo-gram in 2006. The changes in these indicators reflect the advancement in technological capability,and the shift from a product to a product and services economy.

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1.4. Design of Innovative Systems - Why?

Figure 1.1: World Real GDP 1950-2002 $billions (Real Gross Domestic Product per Capita from the PennWorld Tables (Alan Heston, Robert Summers and Bettina Aten, Penn World Table Version 6.1, Center for Inter-national Comparisons at the University of Pennsylvania (CICUP), October 2002.)

While in post-industrial economies (US, Canada, EU), more and more GDP is generated via services,governments in Brazil, Russia, India and China (BRIC) and other developing countries are advancingtheir societies to improve the affluence of their citizens. Inevitably, this involves industrialization similarto the 20th century development in the “developed” countries. Thus, in the BRIC countries one enablesmass-communication, mobility and production, which requires large amounts of resources. To avoidglobal depletion of resources and over stressing the carrying capacity of our Spaceship Earth (Fuller,1968) requires innovative, effective, sustainable infrastructure systems and industrial systems.

1.4.3 A Changing Engineering Agenda?

Traditional engineering is characterized by a ’fixed’ scope and mono disciplinary complexity whereascurrent engineering needs to operate in a socio-economic context that sets more fluid boundaries andrequires a interdisciplinary approach to deal with increased complexity and interdependencies.

Sustainable development, for instance, is not just an environmental challenge. Sustainability is aboutbalance between the environmental, the social and economic.

Ashford (2004) argues that ”competitiveness, environment, and employment are the operationally-important dimensions of sustainability and these three dimensions together drive sustainable develop-ment along different pathways and go to different places than environmentally-driven concerns alone,which may otherwise require trade-offs, for example, between environmental improvements and jobs”.Table 1.1 illustrates that the sustainable agenda is a proactive one – it is aimed at system change, whereasthe traditional agenda is reactive – it is aimed at system optimization. Pursuing a sustainable agenda willrequire a multi-disciplinary (i.e. several or many disciplines) or interdisciplinary (i.e. across disciplines)approach that is able to address the many facets of sustainability.

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Chapter 1. System Design Theory

Figure 1.2: Sustainability (source: Wikipedia)

Agenda Competitiveness Environment Employment

Current Improve performance Control pollution/make Ensure supply of/cut costs simple substitutions or adequately trained people;

changes dialogue with workersConserve energy and Provide safe workplaces

resourcesSustainable Change nature of Prevent pollution Radical improvement

meeting market needs through system changes in human-technologythrough radical or Change resource and interfaces (a systems change)

disrupting innovation energy dependence(a systems change)

Table 1.1: Current versus Sustainable Engineering Agenda Ashford (2004)

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1.4. Design of Innovative Systems - Why?

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Chapter 2

Design Methods for Innovative SystemDesign

There are many approaches available to help one arrive at innovative design. The objective of thiscourse, however, is to offer structured methods for innovative system design. Since we are after in-novative system design, the emphasis is on conceptual design - finding a balance between abstractingfrom reality and (obvious) technological or system solutions, and maintaining relevance, and providingrecipes for collecting, ordering and interpreting information that will help us explore multidimensionaldesign space.

2.1 Overview of Design

Figure 2.1 gives an overview of ”‘design”’ as an activity. In the center column, the overall design processis depicted. The expansion to the left depicts the ”‘problem of problem formulation”’, an activity thatmay be structured further using functional modelling and the meta-model. The right hand expansionexpands the development of a solution space, which is further detailed in the section on superstructures.The drawing indicates that qualitative superstructure development is an iterative, evolutionary process.Once a specific set of alternatives has been developed, one will attempt to select the optimum - maybethrough some optimisation algorithm.

In this section we will discuss functional modelling, the meta-model of design, the superstructureapproach. Finally, we will devote some attention to a ”‘recipe”’ for sustainability. In this way, wegradually move from conceptual to more specific, from addressing an open problem to developing aclosed problem formulations.

2.2 The nature of (conceptual) design

Conceptual design is what is says: a process that leads to a concept. Since this concept is to become anartefact - a product, production system, or infrastructure, we call it a design. Since it only exists in ourminds, as a collection of thoughts, possibly organized and embodied as a text, a collection of schemes,but NOT as a physical entity; we call it a conceptual design.

Conceptual design has been addressed in numerous disciplines. Douglas has addressed concep-tual process design is his seminal book. Dunki-Jacobs and Davis address the importance of conceptualdesign in power systems design (Dunki-Jacobs. and Davis, 1994).

When you are asked to develop a conceptual design, realize that you are NOT asked to address aclosed engineering problem, but to engage in a much tougher challenge - you are facing an open designproblem.

An example open problem, for example, is ”‘develop a conceptual design to provide an Eskimo com-munity with electric power”’. A more closed problem would be ”‘develop a design for an Eskimo com-munity’s floating power plant that runs on (otherwise wasted) whale fat and makes use of off-the-shelftechnology only”’. A really closed problem formulation, for example, would be ”‘determine the maindesign parameters for an Eskimo communitys cogeneration unit, that provides at least 10 [MW] electric

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2.2. The nature of (conceptual) design

Figure 2.1: General Design Paradigm (Dijkema, 2004)

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Chapter 2. Design Methods for Innovative System Design

power and 20 [MW] thermal for district heating and that runs preferably on whale fat, and uses onlygas oil as a backup fuel. The total cost of ownership must be less than 100.000 US$ per year.”’ You mayalso recognize that in this example the open problem is a design problem, while the maximum closedproblem really is about engineering.

The first problem challenges you to develop your concept. The second introduces a number of con-straints. The third adds a boundary for the solution-space. It effectively requires you to engineer asolution, given a set of ingredients. If you are a professional, this should be obvious - you work yourselfthrough the appropriate theories, develop and combine equations, and solve whatever you get. This isnot to belittle engineering - the described process can be very difficult, not-straightforward, and maydemand involvement of some of the brightest minds. It is, however, an activity that is fundamentallydifferent from addressing the open problem - how to provide Eskimo’s with electric power? This openproblem challenges you to design, to be creative, while respecting the Laws of Nature and Thermody-namics. It may make you think of exploiting the wind, the tide, the melting of ice, the migration ofcaribou or flying kites.

The trick in conceptual design thus is to allow yourself to “selectively and temporarily forget” - forgetabout the known and proven ways to do things, accepted combinations and applications of technology.Invent new uses, combinations, environments where known concepts may find a new lease on life. Itrequires, no challenges you to rethink the commonly accepted functions of well-known systems. Is asubway system only about moving as many passengers from A to B, or is it for a great many passengersa cocoon that provides them space and time in transit, where they can work, relax, sleep etcetera? Andwhat would these functions beyond moving from A to B then imply for the subway rail car and carriagedesign?

When you do this, when you have stepped out of the ordinary, have been rethinking and creative,allowed associative thinking on design, a zillion times you will conclude that indeed what others havedesigned already is a perfect, good or a good-enough solution. But once every while, new concepts,combinations, embodiments, even new functions are identified: innovative design!

2.3 Process System Innovation

Process System Innovation can be defined as ”a change in system structure or system design of (aparticular) industry, its industrial complexes, or individual plants...These can be enabled by technologi-cal inventions or vice versa” (Dijkema, 2004). It concerns the transformation of a need into a (technical)object or system solution. It is unlikely, for example, that the current dependency on fossil fuels and theresulting CO2-emissions are resolved by sound environmental management alone. The use of carbonfuels simply implies the formation of CO2In other words, the CO2-intensity of fossil fuels and the maxi-mum efficiencies of their use imply a CO2-floor for our current energy system. To reduce this CO2-floorrequires us to change the system structure and the system content – the system design – of the industry,its industrial complexes, or individual plants. While the system function remains the same, its unwantedby product, CO2 must be drastically reduced, which may imply a change of technology, of system con-tent and of resources used. Such developments must be enabled by technological inventions, such assuper-efficient solar photovoltaic technology. The development of innovative system designs may alsofoster technological development. The characteristics of the electric power grid, for example, imply thatreplacing fossil fuels with renewables require technology for the affordable, efficient large-scale storageof electricity that presently does not exist. Similar technology and system challenges exist to let us har-vest solar energy instead of depleting fossil resources; to let us arrange for the continued, safe, secureand affordable supply of water, minerals and metals. And of course, in sustainable agriculture and foodsupply.

2.4 Functional Modeling

Functional modelling is about the functions of systems, products and services. What is it that a systembrings about? What are the functions of a system, existing or to be designed and realized? Thesequestions can be addressed in a variety of ways - by an expert, who is reconsidering and re-framingher knowledge on a particular system or class of systems, by multidisciplinary teams, in workshopsetcetera.

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2.4. Functional Modeling

An ammonia plant’s function, for example, obviously is to produce ammonia. Since the overallprocess of converting natural gas to ammonia is exothermic, inevitably, ammonia plants produce a lotof heat, which is wasted to the environment and requires significant investment in cooling facilities. Sowhy not adapt the design of ammonia plants and shift this function - from producing waste heat to letthe ammonia plant co-produce a useful heat product?

Functional modelling thus is about establishing a proper inventory and description of a system’sfunction or functions. As a matter of course, this can be done at multiple system levels, which leads tosystem decomposition - breaking down systems into constituting parts conceptually.

In design, we want to establish the requirements of a system. ”a requirement is a singular, docu-mented physical and functional need that a particular design, product or process must be able to per-form” (Wikipedia, http://en.wikipedia.org/wiki/Requirement, 2013).

We distinguish two types of requirements: functional and non-functional requirements. ”Functionalrequirements define what a system is supposed to do, while non-functional requirements define how asystem is supposed to be” (after Wikipedia, http://en.wikipedia.org/wiki/Non-functional_requirement, 2013). The former translates into functions or objectives (e.g. a system that providesheat to a building), the latter may be translated into constraints (e.g. the system should be sufficientlysafe, the number of incidents should be less than 1 in a million hours of operation).

In functional modelling, a system is broken down in subsystems, each of which have specific sub-functions. The decomposition is not trivial - it should preferably be done in such a way that each sub-system identified corresponds to a sub-set of system operations that achieve one of the intermediate orfinal (system) functions. To do this, the concept of objective-defined functions needs to be introducedBaylin (1990) in Dijkema (2004)). These are functions that can be defined through thinking of the ob-jective that is to be achieved. To use the ammonia plant, for example, to the owner or shareholders ofthe ammonia company, it’s main function may be the continued generation of cash flow and profit, butthe objective-defined function of the installation is ”‘produce ammonia”’. The previously unwanted,not-valorized by-product ”‘waste-heat”’ may be included in the set of objective-defined functions of thefacility, by stating these are ”‘produce ammonia and utilize as much of the heat liberated while produc-ing ammonia”’.

In order to open the way towards innovative system designs - a selection of system elements, con-necting linkages, together providing system structure, we can try to achieve a functional decomposition(of an existing or intended system). This involves system abstraction and decomposition in an iterativeprocedure involving trial and error.

We then need to know when to stop - when have we formulated an adequate functional decompo-sition, if not functional model? For this we can use the functional cohesion principle, as developed for(information) system decomposition. Functional cohesion involves keeping together related system el-ements, and keeping apart unrelated system elements while at the same time avoiding both duplicationand conflict (Baylin (1990) in Dijkema (2004)). This definition indicates that decomposition is in partsubjective. Recognizing that a single system may have multiple functionality and may serve multipleobjectives, Baylin extended his definition of an objective-defined function to sub-set of the operations ofa system, consisting of only those operations directly necessary to the achievement of the same specificobjective, or the same mutually contingent specific set of objectives (Baylin (1990) in Dijkema (2004)).

”When in functional modelling the condition of mutual contingency is met the decomposition adoptedis functionally cohesive.”(Dijkema, 2004). Mutual contingency is used to express a condition where thereexists no way of changing the decomposition to improve the functional cohesion - keeping together re-lated system elements, keeping apart unrelated elements. Or, in other words, achieve ’loose coupling’between system elements. ”‘Functional modelling of the system is then successfully completed whenfunctional cohesion has been achieved at each (sub) system level. If not, the model and the decompo-sition must be modified. Thus, mutual contingency provides both the foundation for a definition offunctional cohesion and a stop-criterion for the functional decomposition procedure” (Dijkema, 2004).

The functional decomposition procedure consists of the following four process steps:

1 Identify intermediate objectives of the parent system, and then group all (cluster) together all thesystem elements closely related to each intermediate objective, or to the final objective;

2 eliminate from each group (identified in #1) those elements not closely related to the objective(s)of the group (cluster);

3 separate sub-groups of system elements into distinct subsystems of their own which are;

– 3.1 Insufficiently coupled within the group

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Chapter 2. Design Methods for Innovative System Design

– 3.2 Common to a number of different groups already identified– 3.3 Tightly coupled to a number of different groups already identified

4 check for functional cohesion at system, subsystem(s) and system element levels.

 

Figure 2.2: The Functional Decomposition Procedure (Dijkema, 2004)

This procedure can be used when an new, innovative design has to developed for ”‘known”’ tech-nology, for example, a new ammonia plant, a new refinery, a new power plant. Applying functionalmodelling then provides a structured procedure for abstraction, for rethinking well-established andproven system designs. The existing designs and body-of-knowledge is thereby used as a source forinspiration rather than a constraining template.

Functional modelling is introduced in (Dijkema et al., 2003) 1. The concept of trigeneration (simul-taneous production of electricity, heat and chemical products from an integrated system or productioncomplex) was developed using functional modelling. Trigeneration, its functions, and design is dis-cussed in more detail in (Dijkema, 2001) 2

Exercise Superstructure - MSW in Kolkata, India In the lecture slides 3 the issue of municipal solidwaste management is introduced. MSW is processed by an infrastructure. In the case of Kolkata, thisinfrastructure includes the Dhapa site, a large landfill site, where waste from Kolkata is brought to. Thisis one of the largest landfills in the world. While it causes local pollution problems, it also provides aliving for local people who scavenge the waste and recycle valuable materials such as plastics, paperand metals. Part of the organic waste collected in Kolkata is processed on the site to compost. Thepast few years, initiatives to develop a waste-to-energy facility have not yet been successful, despite theinvolvement of renown international consultants and waste management companies.

Exercise: develop a superstructure for a Kolkata MSW infrastructure

2.5 Problem specification: the Meta-Model

The meta-model of design (Figure 2.3) provides a straightforward overview of the activities and de-cisions that need to be undertaken to arrive at a design problem specification (Herder and Stikkelman,

1(Dijkema et al., 2003) is included in the spm4510 electronic reader (see blackboard)2(Dijkema, 2001) is included in the spm4510 electronic reader (see blackboard)3SlidesadaptedfromSaptakGhosh,https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_

Focus_Large_Systems_Design/Electronic_Reader_Q2/spm4510_Reader_13_14_Kolkata_MSW_System.pdf

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2.5. Problem specification: the Meta-Model

2004).As indicated in figure 2.3 the meta-model suggests a design problem specification must start with

engaging with the stakeholders, or at least with an analysis/activity targeted at identifying their needsand requirements. These are then used to develop design objectives and constraints. For each of these,performance indicators are to be compiled which can be used in testing design alternatives.

The meta-model can be used in two ways:

• as a procedure to guide largely qualitative activities, where stakeholder requirements and soci-etal norms (rules, regulations) are the input of the activity; the output is a set of objectives andconstraints, which ideally is agreed upon between relevant stakeholders. This set then serves asinput for the development of a conceptual design (§2.1). Typically, this mode is applied when atruly open problem is addressed, e.g. when addressing issues, such as ”‘we want to develop azero-emission transport system for the Netherlands”’

• as a procedure to specify and make design activities as specific and quantified as possible. Thisuse of the model typically is made when the scope of the system or product design as well as itsfunctions are known. For example when a new chemical plant is the subject of the design team

The meta-model does not prescribe how one is to arrive at objective and constraints. Preferably,however, any set of objectives and constraints is arrived at in a recorded process. Since this more oftenthan not will involve teams of engineers, marketeers, business developers and the like, the outcomealmost never will be reproducible. The set up and organization of the process, however, should beaccording some template, that can be re-used, for example involving different representatives of thesame stakeholders.

One purpose of using the meta-model is to make the qualitative part of a design problem formulationexplicit. In other words, it is a process that guides participants towards a specific description of thedesign problem. After a number of sessions, typically, the core problem and its essential characteristicsshould emerge. The process is recorded; in a commercial development project a specific amount of timeand budget should be allocated to it. More often than not, its use and completion in particular designprojects lead to increased understanding of the system requirements. The explicit demand to developtests (qualitative OR quantitative) often will lead to iteration and reformulation of objectives and tests.

The meta-model suitably links with functional modelling and the superstructure method. The firststep in using the meta-model may be preceded, replaced by or integrated with the use of functionalmodelling (§ 2.4). ”‘Stakeholders”’ may be replaced by ”‘Functional Modelling”’ to ’Develop a list offunctional requirements’. These may then be further developed into (functional) objectives and con-straints. The solution space development may be done using the the superstructure approach, which isonly one method to develop a solution space, from which we can then select alternatives and combina-tions using the tests developed.

A high level conceptual Basis of Design (cBoD) is to be developed by walking through the entireprocess of formulation of the objectives, constraints, tests and evaluating options in the solution space.This cBoD subsequently may serve as the input for more specific (engineering) design activities.

 

Figure 2.3: Meta Model (Herder and Stikkelman, 2004)

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Chapter 2. Design Methods for Innovative System Design

The meta-model is introduced and applied in (Herder and Stikkelman, 2004)4.

2.6 Superstructures

The dictionary defines a superstructure as ”an entity, concept, or complex based on a more funda-mental one”. In chemical process system design, the superstructure is an approach for systematic rep-resentation of design alternatives (per system element). It is an organized representation of all possiblestructures that may materialize - a generalized representation of all instances of a system, derived froma superset that includes all alternatives that can be selected for each and every system element and theconnections between system elements.

In process system engineering, ideally, the superstructure should be formulated in such a way, thata suitable algorithm could be used to select the best or optimal alternative (assuming we know how todefine ”‘optimal”’ in each and every design case). To date, this ’holy grail’ of process system engineer-ing has remained beyond the horizon, but in determining optimal separation systems, there has beenconsiderable advancement. For example (Hernandez-Suarez et al., 2004) use the superstructure decom-position in combination with parametric optimization for the design of waste water treatment networks.Within this methodology, ”a typical complex network superstructure for simultaneous design is decom-posed into a set of basic network superstructures, which partitions the design search space. The besttreatment network design embedded in each of the basic network superstructures is determined bysolving a set of linear programming problems that is generated from a structured non-convex mathe-matical model by fixing a small number of key problem variables. Under the most generally acceptedassumptions, the systematic exploration of the parametric space defined by the key problem variablesrenders, from the solution space spanned by the basic network superstructures, a most certainly globallyoptimal network design” (Hernandez-Suarez et al., 2004). The use of the superstructure decompositionmethod / optimization combination, however, requires one to exclude parts of the design space, suchas recirculation or recycle loops between the various basic network superstructures.

As the work quoted here is targeted at arriving at some optimal solution, it may be seen that this isa ’closed engineering problem formulation’ approach. The superstructure approach is very well suited,however, for addressing an open design problem. In this chapter, we suggest to combine it with func-tional modelling and incorporate it into the work flow suggested by the meta-model.

Indeed, Siirola and Douglas (1996) notes that ”This analysis-dominated approach starts with a largersuper-flowsheet which contains embedded within it many redundant alternatives and interconnectionsamong them and then systematically strips the less desirable parts of the superstructure away. Thissuperstructure optimization offers the promise of simultaneous optimization of structural as well asother design parameters”.

We suggest that the superstructure approach is used in a functional design approach, where onefirst identifies the functions of a system (that is to be designed), second develops a functional systemdecomposition (e.g. from existing knowledge and designs), and third then develops the superstructureas a list of possible technical embodiments or realizations per functional system element. The result ofsuch an exercise, completed for a waste incineration facility, is shown in figure 2.4.

As illustrated in figure 2.4, the functional decomposition of the MSW system leads to a set of func-tional elements that includes

• pretreatment• combustion• energy recovery• byproduct processing• flue gas cleanup

These have been labelled in such a way that they are ”‘technology-free”’. An additional functionalelement is “connections and recycle”.

If we now want to realize the design, the figure illustrates that for each and every functional ele-ments, we have a range of options. These are the degrees-of-freedom for the system design. “Connec-tions and recycle” is somewhat difficult to delineate, because they constitute both a functional element,and upon realization, provide a degree-of-freedom.

4The paper (Herder and Stikkelman, 2004) is included in the spm4510-Reader part I).

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2.6. Superstructures

Figure 2.4: SuperStructure - Example Waste Incineration

In continuous process systems, recycles can be used to intensify operations and reduce equipmentsize - you can build a large reactor with low flow-rate, or a smaller one with high flow rate, and recyclethe mixture a couple of times. In many cases, the inclusion of a recycle in the process system designis mandatory because of low conversion in a chemical reactor – conversion of synthesis gas (syngas) tomethanol, for example is only 10%. So typically, after separation of the product (e.g. methanol), theunconverted raw materials (e.g. syngas) is recycled back to the inlet of the reactor. Thus, each mole ofsyngas passes the reactor multiple times, and an acceptable conversion can be achieved.

Another degree-of-freedom5 beyond technology selection per functional element and connectionand recycle structure is the number of items installed per functional element for a given capacity. Or,in other words, at each system level in the installation, one must ask: one single item, or multiple. Thedecisive criteria are flexibility, reliability and cost. Many types of equipment can only run between 50-110% of rated capacity. If this offers insufficient flexibility, two items must be installed. If demand is low,one item can then be put on standby (0 %). Inevitably, this will reduce reliability when using similarcomponents, because more equipment items, controls, valves etc. are introduced, each of which can bea source of system failure. The solution then is to use parts with a lower failure rate (but which come ata higher cost). Finally, economy-of-scale more often than not dictates that a single large device will havelower unit costs that multiple smaller devices that add up to the same capacity.

In a municipal waste incineration plant we typically find multiple furnaces - the turndown ratio ofa single furnace is limited, while demand for furnace capacity fluctuates. In most Dutch facilities 2-8furnaces typically are connected to a single ’train’ for energy-recovery and flue gas cleaning. Again,most MSW facilities will have two of these trains. This way, the entire MSW system is maintainable– one train can be shut down for maintenance, e.g. in the summer months, while the other continuesrunning (only at the risk of a somewhat higher chance of system failure).

5For an introduction to this concept, see the corresponding lecture, https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_3_1_degrees-of-freedom_nov_24_2013.pdf

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Chapter 3

Natural Gas Infrastructure Systems

3.1 Introduction

Natural gas is an important fossil energy resource that consists largely of methane, CH4. At the endof 2008, global natural gas reserves exceeded 6,500 trillion cubic feet (Tcf) or 185 trillion cubic meters(Tcm), while global annual consumption equalled slightly more than 3,000 billion cubic meters (Bcm)(BP, 2009). As a consequence, the R/P -ratio for natural gas is around 62 years - at the present rate ofconsumption, reserves will last for 62 years. To put things in perspective: the R/P -ratio for crude oil is42 years, and for coal around 300 years.

Not only does the relative abundance of gas provide a stable and economic alternative to burningcoal and oil products as fuel, natural gas also is intrinsically less CO2-intense compared to hard coal.Generation of 1 [MWh] of electricity in a modern, state-of-the-art gas-fired power plant co-producessome 0.4 ton of CO2; a modern coal-fired station, would emit about 2.5 times as much CO2.

For end-users, natural gas is a clean-burning fuel, which requires little flue gas cleaning. Due tothe high-adiabatic flame-temperature of natural gas, the formation of NOx needs special attention. Indecentralized, small-scale use, e.g. in households, low-NOx burner design should be adopted. Largerpower plants, boilers, cogeneration facilities should include special precautions to minimize NOx in theflue gas. Methods in use include low-NOx burners, steam-injected gas turbines (STIG) and selectivecatalytic reduction (SCR) of flue gas.

Natural gas is found in in underground reservoirs far beneath the earth’s surface. Some of the largestgas fields are found in Russia (Siberia), Norway, Trinidad and Tobago, the Middle-East and the Nether-lands. Each and every gas field has a unique composition that is the result of the particularities of itsformation and geological history.

Most of the world’s natural gas reserves are located far from its consumers. In 2006, for example, theOrganization of Economic Co-operation and Development (OECD) countries accounted for 50 % of theglobal gas consumption, only for some 38 % of the global gas production, making them dependent onimports from non-OECD sources for 25 percent. An extensive overview of gas per country can be foundon http://enipedia.tudelft.nl/wiki/GasOverview .

The limited OECD gas reserves and increased OECD gas consumption imply that this supply gap isset to increase. Estimates of the EIA show that in 2030 the OECD accounts for only 31 percent of globalgas production whereas the OECD gas consumption will reach 42 percent of the world total and thedependability on non-OECD sources 27 percent (EIA, 2009).

Natural gas is relatively cheap compared to its main substitute, refined petroleum products fromcrude oil. In order to compare the prices for natural gas and crude oil it is necessary to look at the energycontent of these fuels. When thus comparing the dollar price of a barrel of oil with the oil-equivalentcost of natural gas, as a matter of course we should take into account the cost of crude-oil refining. Acommon approximation is that the energy content of 1 barrel of oil [bbl] is equivalent to 5.800 cubic feet[cf] of natural gas. Under this rule of thumb, the crude oil price of $81.75 [bbl] on April 19th, 2010 would mean a natural gas price of $14 [Mcf], while the actual natural gas priceequalled only $4 per [Mcf] on that very day. Apparently, while the connection between oil and gas (andcoal) markets is complex, the relation between $ per [GJ] remains relatively weak. This is only one ofthe ratio’s for Shell to develop their Gas-to-liquids (GTL) technology (§ 3.4.3 on a large-scale, with the

17

3.2. About Natural Gas

recent development and start-up of the 2.5 million barrel equivalent Qatar operations.This chapter 3 views ’bringing natural gas to the consumer market’ as the Objective Defined Func-

tion of any Natural Gas Infrastructure System. Accordingly, it will discuss the design and layout ofthe Natural Gas Infrastructure System from the point of production to the point of consumption. Thetechnical system comprises the subsystems gas production, treatment, transport and gas utilization. §3.2 explains the basics of natural gas and acts as the point of departure for the remainder of this chapter.The natural gas production and initial processing are discussed in § 3.3. Further processing of methaneas pipelined natural gas, liquefied natural gas and synthesis gas (syngas) is assessed in § 3.4. Thischapter concludes with discussing 50 years of Dutch natural gas infrastructure system development inparagraph §3.5.

3.2 About Natural Gas

In this section some natural gas terminology is introduced. It addresses how the future of natural gasis shaped by its technology drivers. Finally the functional modelling approach is applied to the naturalgas system.

3.2.1 Natural Gas Terminology

Each natural gas reservoir contains a unique composition of gas. Generally speaking, natural gas isa combustible mixture of hydrocarbons, of which the primary constituent is methane (CH4). In therange of simple hydrocarbons methane has the shortest carbon-skeleton. It is also the lightest of thesehydrocarbons with a molecular weight of 16 [g/mol]. In most gas fields, CH4 accounts for 70 to 90percent of the mixture. Commonly found constituents are the heavier, saturated hydrocarbons: ethane(C2H6), propane (C3H8) and butane (C4H10), may account for as much as 0-20 % of the mixture. Higher,heavier, hydrocarbons may also be present in some cases - sometimes up to C5-C9. Since their boilingpoint is at or below ambient temperature, these are generally labelled Natural Gas Liquids or NGL’s.

Apart from higher hydrocarbons, quite a few gas reservoirs also contain CO2 - up to 8 % CO2 hasbeen recorded. Long-distance gas transport for a variety of reasons requires the gas essentially to befree of CO2, notably because CO2 exhibits some nasty behaviour at elevated pressure, which can bedetrimental for the operation and safety of long-distance pipeline systems.

In case natural gas from a particular reservoir contains significant amounts of sulphur impurities,COS and notably hydrogen-disulfide, H2S, it is termed “sour gas”. Since H2S is an extremely toxicnerve gas (lethal concentration being as low as 200 parts per million or less, any sour gas must be treatedbefore it can safely be transported over longer distances and applied by end-users. Direct combustionof sour gas is environmentally damaging, because of the inevitable production of SO2, the precursor ofacid-rain. The product gas of a desulphurisation operation, which is essentially free of sulphur impuri-ties, is commonly labelled “sweet gas”.

In case natural gas is co-produced from an oil reservoir, it is labelled “Associated gas”. Since in thegeological reservoir it has been “associated with crude-oil”, such associated gas almost inevitably con-tains higher hydrocarbons, sometimes even light aromatics, and more often than not sulfur compounds,including H2S. The flaring (combustion via a flare system) of large-amounts of such associated gas fromoil fields around the gulf have contributed to the acidification of the Red Sea.

Natural gas from gas reservoirs or associated gas can also be classified as “wet” gas, which impliesthat the gas contains small to significant amounts of water H2O.

An important characteristic of natural gas used is the Wobbe number or Wobbe index, which isan indicator of the gas behaviour in gas burners. The index derives its name from Goffredo Wobbe, aphysicist in Bologna who in 1927 observed that

• the heat rate of a burner is proportional to the flow volume per unit of time• the flow velocity through an orifice at constant pressure is proportional to the specific gravity of

the gas• the calorific value of a gas is proportional to its specific gravity

The following explanation of the Wobbe index is obtained from the American Gas Association: ”TheWobbe number, or Wobbe index, of a fuel gas is found by dividing the higher heating value of the gas in Btu per

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Chapter 3. Natural Gas Infrastructure Systems

standard cubic foot by the square root of its specific gravity with respect to air. The higher a gases Wobbe number,the greater the heating value of the quantity of gas that will flow though a hole of a given size in a given amount oftime. It is customary to give a Wobbe number without units even though it has the dimensions [Btu/scf] becauseto do so would lead to confusion with the volumetric heating value of the gas. In almost all gas appliances, theflow of gas is regulated by making it pass through a hole or orifice. The usefulness of the Wobbe number is that forany given orifice, all gas mixtures that have the same Wobbe number will deliver the same amount of heat. Puremethane has a Wobbe number of 1363; natural gas as piped to homes in the United States typically has a Wobbenumber between 1310 and 1390” (Halchuk-Harrington and Wilson, 2006).

These observations led him to below equation (Formulas 3.1 and 3.2).

Wobbe Index =calorific value

root of relative density(3.1)

W =∆Hc√d

(3.2)

In Europe the Wobbe-index is also widely used. There, however, it is not expressed in [Btu/scf] butin units commonly used in Europe, namely the Lower Heating Value ∆Hc per standard cubic meter andthe relative density compared to air.

Any equipment for the firing of natural gas will have been designed for gas with a particular WobbeIndex. In case gas is used with a Wobbe Index that deviates too much from the design value, an unsafesituation will result:

• Wobbe too high due to the calorific value of the gas having increased. In this case, the heat rateincreases, equipment may be damaged.

• Wobbe too high due to a decrease of the relative density of the gas. If this situation occurs, thevelocity of the gas flame will decrease, up to the point where the flame will attempt to move intothe burner. The flame dies, and the equipment is filled with an explosive mixture of natural gasand air.

• Wobbe too low after the calorific value has gone down. The heat rate decreases, and the tempera-tures achieved in the system will drop. The control system will increase the flow, with the dangerof blowing the flame of the tip of the burner.

• Wobbe too low after relative density has gone up. In this case, the velocity of the gas flame willincrease, possibly up to a point where the flame will be blown of the burner. The equipment isfilled with an explosive mixture of natural gas and air.

This dominant characteristic of gas fired equipment has created a vast “lock-in” effect - the operatorof any gas infrastructure system must ensure that the gas quality (expressed as Wobbe) remains withinthe design limits of the fired-equipment in use with end users. In the built environment, these aremillions of gas-fired heaters and boilers.

Both in the United States and Europe, continents with extensive natural gas systems that evolvedover a number of decades, the Wobbe index is back on the agenda because of the large-scale arrival ofLiquified Natural Gas (LNG), essentially pure methane, which if no moderation and polishing of gasquality is applied, will result in a largely different Wobbe in the Hi-Cal pipeline network.

Also, without any provisions in the system, the Wobbe may start to wobble, because the feed of LNGinto the existing network is not centrally controlled, but the result of market parties deciding when touse their LNG facilities and dispatch re-gasified LNG into the network. This thus begs the question howand where best protect and ensure system integrity and safety, for operators and end users alike. Shouldthis be done by all end-users, taking steps to enable them to safely use gas with a greater Wobbe range,by the Transmission System Operator (TSO) who then should have the technical means and authorityto maintain the gas quality (Wobbe) within prescribed (narrow) limits? Or should this be arranged bythe dispatcher of re-gasified LNG?

3.2.2 From Production to Consumer

Natural gas accounts for almost a quarter of the world’s energy consumption (24% in 2008 (BP, 2009))a characteristic which makes the design of the Natural Gas Infrastructure System highly relevant tosociety at large. Already the discussion on Wobbe above illustrates that the design of Natural Gas

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3.2. About Natural Gas

Infrastructure Systems in a changing societal, political, economical and environmental context translatesto shifting design variables, objectives and constraints. The schematic and strongly simplified overviewof the natural gas supply chain (Figure 3.1) is divided in three major components: Upstream, Midstreamand Downstream.

Production

Exploration

BusinessHousehold

Application

Distribution

Transport

Refinement

Industry Utilities

Upstream

Midstream

Downstream

Figure 3.1: Natural Gas Infrastructure

Because there exists a considerable variety of natural gas compositions, more often than not naturalgas from a reservoir must be treated to reach international standards and recover valuable byproducts.

The function of initial gas processing is to treat the raw gas obtained from the reservoir, with theobjective to create a gas that can be transported using a pipeline or refrigerated to become LNG, whilerecovering any valuable by-products. Or, in other words, the function of the treatment system is to makethe gas suitable for transport.

Typically, on off-shore operations the amount of processing is reduced to the absolute minimumbecause of the high-cost of platform space. Thus, treatment is limited to the extent that it must onlyallow the gas to be transported on-shore, where subsequent treatment will take place to adjust the gasto the required quality and composition standards of the receiving grid.

The design objectives of natural gas processing thus are twofold: to adjust the natural gas to therequired quality standard and to ensure the recovery of byproducts (Hammer et al., 2006).

After treatment, the gas thus enters a system with the main function “transport”. Methane (CH4)can be transported by pipeline, by liquefaction to LNG and subsequent shipping, or by converting itto GTL, methanol or ammonia. The latter three involve conversion of methane into ”‘synthesis gas”’ orsyngas (a mixture of CO and H2) the feedstock for Fischer-Tropsch synthesis to GTL-products, methanolproduction and ammonia manufacture (Figure 3.2).

Long distance pipeline infrastructure for CH4 typically consist of cross country transmission pipelinesoperated at high pressure (50-90 [bar]) and compressor stations. They connect to national or regionaldistribution lines or mains § 3.4.1, through which the gas is eventually distributed to the consumer.These typically are elaborate networks operated at medium pressure (regional: 15-25 bar; local 6-10 bar)down to the consumer who is served by pipelines operated at only : 10-20 [mbar] overpressure, or 1,010[bar]).

Bringing otherwise ’stranded’ natural gas to the market as LNG involves the more comprehensiveseries of processes - a system that incorporates methane liquefaction, LNG-shipping, storage and re-gasification § 3.4.2.

The CH4 can be converted into syngas (§ 3.4.3) by means of Steam Methane Reforming (SMR), PartialOxidation (POX), Autothermal Reforming (ATR) or Ceramic Membrane Technology. In the chemicalindustry, syngas is further processed to ammonia (NH3) (a process invented in 1908), the main precursorof NPK-fertilizer, to methanol (MeOH), GTL fuels or olefin’s respectively.

As a matter of course natural gas can also be used directly at the reservoir site to generate electricity- an option that was elected for the utilization of the gas from the (now largely depleted) Bergumer-meer gas field in Friesland. With the availability of efficient long-distance Direct-Current (DC) power-

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Chapter 3. Natural Gas Infrastructure Systems

transmission lines, this may become an option for more gas fields in the future. A variety of this conceptis the Eemshaven power plant, which runs on Norwegian gas, which is piped to the Eemshaven througha 600 km dedicated gas pipeline from Norway.

(Remote) Natural Gas Production

MeOH Plant

Liquefaction Plant

Fischer Tropsch Plant

Natural Gas Processing Plant

NG

Ammonia Plant

CO2, H2S, Sand, Water

CH4

GTL Fuels (naphta,kersone, diesel)

LNG

NH3MeOH

Fertilizer Plant

Fertilizer

Pipeline Distribution

Cargo Ship

LNG Tanker

Cargo Ship MTO Plant

Cargo Ship

Olefins

Regasification

CH4

CH4

Utilities Agriculture Transport Sector

Cargo Ship

Syngas

Chemical Industry

Natural Gas Liquids (Alkanes)

MTG Plant

Cargo Ship

Transport Sector

Gasoline

GasifierSMR

ATR POXHeat Exchanger

Membrane Technology

Figure 3.2: Natural Gas System Superstructure

3.2.3 Natural Gas Scenarios

In 2008, natural gas accounted for 24 percent of the global primary energy consumption, behind oiland coal with 35 and 29 percent respectively (BP, 2009). Due to the lower carbon intensity of naturalgas and the availability of highly efficient application technologies it is widely expected that the shareof natural gas will rise. Worldwide, the total natural gas consumption in 2006 amounted to 104 [Tcf] andis expected to increase by an average of 1.6 percent per year to 153 [Tcf] in 2030 (IEA, 2009). Accordingto the IEA reference case, liquid fuels remain the largest source of energy with a projected share of 32percent of world marketed energy consumption in 2030 (down from 34 percent in 2010) while the shareof natural gas remains stable at 23 percent. Coal is the only fossil fuel with a higher growth rate thannatural gas, 1.7 percent per year, while its share of the global energy consumption equals 28 percent inboth 2010 and 2030.

One company that is well-known for its use of scenarios to explore the future is Royal Dutch Shell.According to Shell ”Scenarios provide alternative views of the future. They identify some significantevents, main actors and their motivations, and they convey how the world functions. We use scenariosto explore possible developments in the future and to test our strategies against those potential develop-ments” (Shell, 2010). In their latest scenarios on energy, Shell recognizes four key drivers: demand, re-sources, technology and environment Shell (2008). The driver ”‘technology”’, for instance, breaks downinto innovation, implementation, mobility, power and IT (Table 3.1). The main differences between theScramble and Blueprint scenarios are the way in which governments secure the energy supply to theirrespective countries. In Scramble governments focus on a national energy security while Blueprint en-visions a new energy framework that emerges from coalitions between various levels of (inter)nationalsocieties and governments. In Scramble nuclear energy is strongly guarded and reluctantly shared with

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3.3. Gas Production & Treatment

non-friendly states with a corresponding small contribution of nuclear power to the energy mix. In or-der to meet rising demand the world turns to coal instead. In Blueprint on the other hand technologytransfer is facilitated by the international community. The resulting projections for the development ofthe primary energy demand and the source from which it is obtained are illustrated in Figures 3.3a and3.3b. The corresponding projections for the share of natural gas in the primary energy demand show apeak in 2030 when Scramble shows a gas demand 134 [EJ] (from a total of 734 [EJ]) per year and Blueprint143 EJ (from a total of 692 [EJ]) per year. This subsequently declines to 108 [EJ] (from a total of 880 [EJ])and 122 [EJ] (from a total of 769 [EJ]) respectively.

3.3 Gas Production & Treatment

There exist large variations in natural gas compositions between one location and another whichnecessitate the treatment of natural gas to remove contaminants mentioned (§ 3.2) to appropriate levels.Typically these levels are determined by the market for which the natural gas is destined and specifiedby contract as well as safety and operability considerations (Mallison, 2004). The production of naturalgas is discussed first after which the treatment of feed gas from a processing plant to ”pipeline quality”standards is assessed. This involves gas dehydration (water removal), sweetening (acid gas removal)and hydrocarbon recovery & fractionation. Note that the exact specifications of each processing step(presence, order, seize) are dependent on the composition of the produced natural gas.

3.3.1 Gas Production

Natural gas is found in rocks with favourable porosity and permeability that are sealed with a imper-meable cap (typically shales, salts and clays). The decision of whether or not to drill a well depends ona variety of factors including technical issues such as the nature of the potential formation, subsurfacecharacteristics, depth and size of the field. Once the optimal location has been identified it is necessaryto obtain the required juridical authorization to actually drill. This includes required permits, royaltiesarrangements that allow the natural gas to be extracted and the design of distribution infrastructure.Some important reservoir characteristics are illustrated in Figure 3.4b.

The Bottom Hole Pressure (BHP) is usually measured in pounds per square inch (psi), at the bot-tom of the hole is an important concept for well control. It is important that the BHP gradient exceedsthe formation pressure as to avoid an influx of formation fluid into the well-bore. If on the other handthe BHP is to high this may cause a formation fracture and cause a loss of welbore fluids.

As the production of natural gas declines over time it is important to determine the optimal pro-duction rates. Using a geological and technical perspective, a reservoir can be considered a “balloon”filled with gas, that through driving holes in it, can be emptied, “produced”. Drilling production wellsthen involves deciding on the number of wells, their size (capacity per well) and geographical distribu-tion. Almost without exception, gas (and oil) reservoirs will suffer when produced at too fast a rate. TheBHP will go down when to many production wells are drilled; when extraction occurs at too fast a rate,the reservoir rock may collapse, rendering part of the gas locked, a dead pocket of gas that cannot bebrought to the surface any more.

From an economic viewpoint the limit of a well is the time when the gross revenues that are de-rived from the production are equal to the cost of operations. The economic limit is calculated by withequation 3.3. In which ”P(t) denotes the average, quality-adjusted price of the hydrocarbon stream inyear (t), Q(s,t) is the annual production of structure (s) in year (t), and (R) is the royalty rate, usually afixed percentage of the gross revenues adjusted for the cost of gathering, compression, dehydration, and

Technology Drivers Scramble Blueprint

Innovation Strongly guarded Extensively sharedImplementation National docking points International tipping pointsMobility Hybrids & downsizing Hybrids & electrificationPower Efficiency Carbon capture & storageIT Supply optimization Demand load management systems

Table 3.1: Scenario Technology Drivers (Shell (2008))

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Figure 3.3a: Primary Energy by Source Scramble((Shell, 2008))

Figure 3.3b: Primary Energy by Source Blueprint((Shell, 2008))

 

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3.3. Gas Production & Treatment

sweetening. Capital expenditures and depreciation are generally negligible toward the end of the life-time of a structure, with the operating expenses OPEX(s,t) accounting for the bulk of the expenditures”Kaiser (2008).

te(s) = t|P(t)Q(s, t)[1− R] = OPEX(s, t) (3.3)

3.3.2 Gas Treatment

Before natural gas that is produced at the wellhead is fed into the mainline gas transportation systemit must be cleaned from contaminants and natural gas liquids. A generalized scheme of natural gasprocessing is given in figure 3.5, where this processing is decomposed to a set of functions to be realizedby these systems (and not through single columns always as the scheme in figure 3.5 suggests!!).

Some forms of gas treatment are required for all types of natural gas such as the removal of smallamounts or traces of water (dehydration), condensate and H2S (sweetening). Water is removed to pre-vent corrosion, clogs and unwanted chemical reactions while H2S is removed to prevent corrosion andthe emittance of SO2. Higher hydrocarbons are also removed (hydrocarbon removal and fractioning) toprevent clogging and the degrading of the polymer coating of infrastructure while CO2 is removed toprevent corrosion and lesser burning properties.

In accordance with the Douglas hierarchy, whenever confronted with the question to design a gastreatment system, the first question is: should the separation be implemented as a batch or a continuoussystem? That is, at the contaminant receiving end; the gas of course must flow continuously. A secondquestion is whether it is feasible to condense the impurities, and thus employ gas-liquid separation.More often than not, distillation is NOT an option, because of the very low boiling points of gaseousconstituents like CO2, H2S ethane and N2.

Options thus include:

• using a device to exploit the differences in specific gravity and boiling points. A simple flash vesselmay for example allow one to remove the greater part of water or hydrocarbon liquids from a gasstream; oil/water separators use specific gravity differences also.

• using a filter. This is typically done when gaseous impurities present at very low levels (10-1000ppm) are present. For example, a zinc oxide (ZnO) filter may be applied to capture traces of H2S.This is a batch solution at the receiving end, as such filters typically are replaced every 1-3 years.The used filter typically is disposed off in a controlled way. If the filter loading increases, one maydecide to use a parallel set up, with one filter on standby. In such cases, any frequency (beyondonce a day) in principle is possible (but of course, then alternatives may be more economic, reliableand safe)

• use filter or adsorbent devices that can be regenerated. This is typically done when impurity levelsare higher. To date, only for some impurities, suitable adsorbent materials exist. The (physical)adsorbent needs to be selective, and should remain its adsorptive capacity over a large numberof cycles. Molecular sieves for water meet this criterion, but can only be used when no other

Figure 3.4a: Natural Gas Production

 

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Figure 3.4b: Well Characteristics

 

impurities (like CO2, H2S, hydrocarbons) are present – these would clog and damage the device.Regeneration is typically done with a (very) small amount of clean gas at low pressure; this gasis then sent to a flare or used in a local furnace or turbine. Advancing this concept has led toPressure-Swing Adsorption (PSA).

• use a continuous extraction process. These typically consist of contacting the gas with some chem-ical absorbent that binds the impurities. The loaded solvent is regenerated in a separate unit.These kinds of plants typically are used when water, H2S, CO2 quantities are relatively high (say0.1-10 vol.%), the amount of gas processed is large and the quality targets are severe (separationefficiency ¿ 99.5 %). The gas industry employs hundreds of glycol units, and many large-scalecontinuous sour gas treatment plants based on this principle.

In the above description, we can discern several sub-functions of gas processing and treatment (EIA(2006)):

 

Figure 3.5: Generalized Natural Gas Processing Schematic (EIA (2006)).Please note that this is only anillustration if not system decomposition of the required treatment functions! By no means are all these stepsimplemented as extraction towers always! Many alternatives exist!!

A) Gas-Oil Separation: ”In many instances pressure relief at the well head will cause a natural sepa-

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ration of gas from oil (using a conventional closed tank, where gravity separates the gas hydrocarbonsfrom the heavier oil). In some cases, however, a multi-stage gas-oil separation process is needed to sep-arate the gas stream from the crude oil. These gas-oil separators are commonly closed cylindrical shells,horizontally mounted with inlets at one end, an outlet at the top for removal of gas, and an outlet atthe bottom for removal of oil. Separation is accomplished by alternately heating and cooling (by com-pression) the flow stream through multiple steps. Some water and condensate, if present, will also beextracted as the process proceeds”.

B) Condensate Separation: ”Condensates are most often removed from the gas stream at the wellhead through the use of mechanical separators. In most instances, the gas flow into the separator comesdirectly from the well head, since the gas-oil separation process is not needed. The gas stream entersthe processing plant at high pressure (600 pounds per square inch gauge [psig] or greater) through aninlet slug catcher where free water is removed from the gas, after which it is directed to a condensateseparator. Extracted condensate is routed to on-site storage tanks”.

C) Dehydration: ”A dehydration process is needed to eliminate water which may cause the for-mation of hydrates. Hydrates form when a gas or liquid containing free water experiences specifictemperature/pressure conditions. Dehydration is the removal of this water from the produced naturalgas and is accomplished by several methods. Among these is the use of (tri-) ethylene glycol (glycolinjection) systems as an absorption 1 mechanism to remove water and other solids from the gas stream.Alternatively, adsorption dehydration may be used, utilizing dry-bed dehydrators towers, which con-tain desiccants such as silica gel and activated alumina, to perform the extraction”. Figure 3.6 presentsa process flow diagram for a glycol dehydration system in which the glycol solution is introduced atthe top of the column while water-containing natural gas is introduced at the bottom of the column.As the glycol flows across each tray and down to the next and the natural gas flows upwards throughperforations or caps in the trays both liquids get highly mixed. ”This mixing provides good contactbetween the gas and the liquid to allow the transfer of the water from the gas to the liquid. This countercurrent flow pattern provides the best approach to equilibrium for the removal of water from the gasphase. The gas has less water remaining at each successive tray until it leaves the column at the top.The liquid increases its water content as it flows down through the column until it is discharged at thebottom” Mallison (2004).

D) Contaminant Removal: ”Removal of contaminates includes the elimination of hydrogen sulfide,carbon dioxide, water vapor, helium, and oxygen. The most commonly used technique is to first directthe flow though a tower containing an amine solution. Amines absorb sulfur compounds from naturalgas and can be reused repeatedly. After desulphurization, the gas flow is directed to the next section,which contains a series of filter tubes. As the velocity of the stream reduces in the unit, primary sep-aration of remaining contaminants occurs due to gravity. Separation of smaller particles occurs as gasflows through the tubes, where they combine into larger particles which flow to the lower section of theunit. Further, as the gas stream continues through the series of tubes, a centrifugal force is generatedwhich further removes any remaining water and small solid particulate matter”.

E) Nitrogen Extraction: ”Once the hydrogen sulphide and carbon dioxide are processed to accept-able levels, the stream is routed to a Nitrogen Rejection Unit (NRU), where it is further dehydrated usingmolecular sieve beds. In the NRU, the gas stream is routed through a series of passes through a columnand a brazed aluminum plate fin heat exchanger. Using thermodynamics, the nitrogen is separated in acryogenic process and vented. Another type of NRU unit separates methane and heavier hydrocarbonsfrom nitrogen using an absorbent solvent. The absorbed methane and heavier hydrocarbons are flashedoff from the solvent by reducing the pressure on the processing stream in multiple gas decompressionsteps. The liquid from the flash regeneration step is returned to the top of the methane absorber as leansolvent. Helium, if any, can be extracted from the gas stream in a Pressure Swing Adsorption (PSA)unit”.

F) Methane Separation: ”The process of demethanizing the gas stream can occur as a separate oper-

1Adsorption is the binding of molecules or particles to the surface of a material, while absorption is the filling of the pores in asolid. The binding to the surface is usually weak with adsorption, and therefore, usually easily reversible.

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Figure 3.6: Glycol Dehydration Process DiagramMallison (2004)

ation in the gas plant or as part of the NRU operation. Cryogenic processing and absorption methodsare some of the ways to separate methane from NGLs. The cryogenic method is better at extractionof the lighter liquids, such as ethane, than is the alternative absorption method. Essentially, cryogenicprocessing consists of lowering the temperature of the gas stream to around -120 degrees Fahrenheit.While there are several ways to perform this function the turbo expander process is most effective, usingexternal refrigerants to chill the gas stream. The quick drop in temperature that the expander is capa-ble of producing condenses the hydrocarbons in the gas stream, but maintains methane in its gaseousform.The absorption method, on the other hand, uses a clean absorbing oil to separate the methane fromthe NGLs. While the gas stream is passed through an absorption tower, the absorption oil soaks up alarge amount of the NGLs. The enriched absorption oil, now containing NGLs, exits the tower at thebottom. The enriched oil is fed into distillers where the blend is heated to above the boiling point ofthe NGLs, while the oil remains fluid. The oil is recycled while the NGLs are cooled and directed to afractionation tower. Another absorption method that is often used is the refrigerated absorption methodwhere the lean oil is chilled rather than heated, a feature that enhances recovery rates somewhat”.

G) Fractionation: ”Fractionation, the process of separating the various NGLs present in the remain-ing gas stream, uses the varying boiling points of the individual hydrocarbons in the stream, by nowvirtually all NGLs, to achieve the task. The process occurs in stages as the gas stream rises throughseveral towers where heating units raise the temperature of the stream, causing the various liquids toseparate and exit into specific holding tanks”.

The above functions, embodied in specific operations and technologies commercially available, canbe implemented in a specific gas treatment plant for a particular gas field. The last operation, fractiona-tion, strictly speaking is not part of gas treatment, but can be seen as upgrading of the NGLs.

Finally, any gas treatment system design will be completed taking into account the downstreamoptions and constraints. For example, because of the ubiquity of the Groningen-quality gas grid inthe Netherlands and North-West Europe, a nitrogen removal unit will never be considered. In the US,ethane removal is often very profitable, as it is a sought resource for the petrochemical industry. InEurope, however, most steam-crackers are built for butane, naphtha or gas-oil feedstock, principallyproviding less incentive for ethane removal - ethane is a gas, that needs its own pipeline infrastructure,or it must be used on the site of production.

Pending on the characteristics of the natural gas the treatment itself can take place directly at the

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well or in centralized treatment plants. Table 3.2 shows the different design objectives that are applicableto the treatment of natural gas.

In the lecture slides 2 two illustrations of possible embodiments of water removal have been in-cluded:

• an advanced Tri-Ethylene Glycol unit, or TEG-unit. This is an example state-of-the-art processsystem design, integrating system functions in the design to arrive at minimum cost and maximumperformance

• injection of TEG into a high-pressure gas pipeline. Here, the high-pressure of the gas is usedto advantage. The TEG will absorb any water. After Joule-Thomson expansion, the liquid canbe removed from the gas and subject to regeneration. Bringing the lean liquid solvent to high-pressure with a pump is straightforward.

The last slide illustrates the common absorber/stripper combination used for H2S removal in sourgas treatment plants - absorption of contaminant H2S into lean solvent - usually an amine -, rendering aclean gas that can be send into the pipeline grid, and loaded solvent that needs to be regenerated. Thisis done by stripping of the H2S using steam. Concentrated H2S is sent to a Claus furnace to convert itinto elemental sulphur,the lean solvent is used in the absorber.

Design requirements for the solvent include:

• high H2S (or other contaminant) absorption capacity, low to zero absorption affinity for naturalgas. This then allows highly selective absorption.

• easy desorption, either through stripping with steam, or via simple pressure reduction. Solvent re-generation is an process that requires net input of work (exergy). If the affinity of the contaminantto the absorbent is too large, exergy use (usually in the form of medium pressure steam) becomesexcessively high, and the column excessively large for a given capacity.

• low affinity for other trace contaminants, that certainly should not “neutralize” the solvents ad-sorption capacity

• chemical stability - the solvent must withstands thousands of (pressure. temperature) cycles with-out major degradation. Degradation products may accumulate in the system, and always requirefor addition of make-up solvent, or full replacement

3.4 Natural Gas Transportation

The distance between gas resources and gas markets creates the biggest challenge (save for the fielddiscovery) in the natural gas system: transportation. Recall that gas infrastructure’s main ObjectiveDefined Function is ’bringing natural gas to the consumer market’ and that the main component CH4 istransported in a gaseous state as Pipelined Natural Gas (PNG), in the liquid state as Liquefied NaturalGas (LNG) or processed to syngas and subsequent syngas-derived products.

2https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_Design/Slides_Q2/spm4510_13_14_Week_5_1_Gas_Production_and_treatment_dec_9_2013.pdf

Type of Plant Design Objectives

Installation at Individual Well To guarantee trouble-free gas flow in the production pipes and surface equipmentTo separate or, if necessary, treat co-produced liquidsTo condition the gas for transportation to the processing plantTo meet the required feed quality for the pipeline distribution networkTo protect the production pipes and field installations from corrosion

Centralized Treatment Plant Type and concentration of accompanying substances in the gasBehaviour of the gas during pipeline transportationApplicable sales specifications

Table 3.2: Design Objectives Natural Gas Treatment (adopted from Hammer et al. (2006)

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Figure 3.7a: Natural Gas Transport Options by Smith (2004)

Figure 3.7b: Natural Gas Transport Options by Wood et al. (2008)

3.4.1 Pipelined Natural Gas

Pipelined Natural Gas or PNG is the preferred option for the transportation of large volumes of nat-ural gas over relatively short distances. The PNG transmission system that transports natural gas fromthe producer to the market areas is composed of pipelines, valves, compressor stations, metering sta-tions, city gate stations, pig launching/receiving facilities and storage facilities. The following pipelinetechnology overview is adopted from (Folga, 2007).

Pipelines: ”coating mills apply pipe coatings to ensure that the pipe does not corrode once placedin the ground. Often, the coating mill is located adjacent to the pipe mill, so line pipe moves directlyfrom the pipe manufacturer to the coating facility. The purpose of the coating is to protect the pipe frommoisture, corrosive soils, and construction-induced defects, which cause corrosion and rusting”.

Compressor station: ”natural gas is highly pressurized as it travels through an interstate pipelineto expedite the flow of gas. To ensure that the natural gas flowing through any one pipeline remainspressurized, compression of the natural gas occurs periodically along the pipe. This is accomplished bycompressor stations, which are usually placed at 40- to 100-mile intervals along the pipeline. The naturalgas enters the compressor station, where it is compressed by either a turbine, motor, or engine”. Thenumber of compressors that are installed at each compressor station impacts the availability, reliability,fuel consumption, and the pipeline capacity. Some of the planning issues for a new pipeline include thefollowing Lubomirsky et al. (2010):

• capabilities and requirements of the pipeline system: involves the capability to cope with changesin flow capacity on all time scales (i.e., hourly, daily, seasonally) as well as changes in availablepower. The pipeline hydraulics relate pressure losses to the flow through the pipeline, determinethe compressor operating conditions in terms of head and actual flow, and subsequently determinethe required power from the driver. Contractual requirements and obligations, such as pressures

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and volumes at transfer points, have to be considered.• growth requirements and capabilities: deals with the fact that the nominal capacity of a pipeline

may grow when additional customers demand a higher supply of natural gas. In fact, manynew pipelines start out with 50% and less capacity and grow to full capacity over several years,or are sized for easy expansion. Often, the prediction of the rate of growth shows a significantdegree of uncertainty. The growth scenarios, if foreseeable, drive a station layout to possibly allowadditional power to be installed at the station level later or additional stations along the pipeline.The alternative scenario, where the pipeline usage declines over the years (e.g., because the gassupply from the field declines), is also a possibility.

• availability and total cost of ownership; plays a significant role in determining the requirement forspare units in a station or along the pipeline. If units become unavailable, either due to plannedmaintenance, or due to unplanned failures, the pipeline capacity is reduced. This will cause lessprofit for the operator. Since many pipeline operations have to guarantee a certain minimumflow, this minimum flow becomes a planning criteria for the spare unit requirements, based on thereliability and availability of individual units and components. Total cost of ownership and lifecycle cost are influenced by first cost, but also by the efficiency of operation.

• delivered cost to markets;

The investment of transmission pipelines is largely determined by the costs that are related to thepipeline subsystem and those that are related to the costs of the compressor subsystem. In order tominimize the total costs a balance must be reached between these two systems that satisfies both thepipeline flow equation and allowed maximum pressure that is related to the pipeline strength. Whengas flows through a pipeline it needs to overcome frictional forces which result in a pressure drop. TheColebrook-White correlation is commonly used to calculate this friction factor Equation 3.4. f representsthe friction factor which is based on roughness ε, Reynols number Re and the inner diameter D. Thiscorrelation can be estimated with a Moody-diagram, which is a semi-logarithmic diagram.

1√f

= −2 log(2.51

Re√

f+

ε

3.7D) (3.4)

A number of options thus exits to increase the capacity of existing pipeline systems:

• use the adaptability built-into the compressor stations. Increase the pressure-ration delivered ina compressor station. This can be done by adding compressor stages and/or operating speed(revolutions per minute, [rpm]) of the machines. In both cases, more drive-power is required. Theflow through the system will increase, as a larger pressure-drop, and thus a larger flow betweenstations can be accommodated

• add compressor stations. Again, the flow can increase, since after a shorter distance the pressureis boosted. The flow may be increased up to the point where the pressure drop over the shorteneddistance equals the original pressure drop.

• build an additional pipeline system. Both previous options suffer from the fact that adding com-pressor stations or stages to an existing pipeline system has its limits (see Slides). Each new stationor stage will add less additional capacity per compressor or stage.

Metering station: ”are placed periodically along interstate natural gas pipelines. These stations al-low pipeline and local distribution companies to monitor, manage, and account for the natural gas intheir pipes. Essentially, these metering stations measure the flow of gas along the pipeline, allowingpipeline companies to track natural gas as it flows along the pipeline. Metering stations employ special-ized meters to measure the natural gas as it flows through the pipeline without impeding its movement.In essence, the metering station is the company’s cash register”.

City Gate Station: ”the natural gas for most distribution systems is received from transmissionpipelines and fed through one or more city gate stations, sometimes called town border or tap stations.The basic function of these stations is to meter the gas and reduce its pressure from that of the pipelineto that of the distribution system”.

Valves: ”interstate pipelines include a great number of valves along their entire length. These valveswork like gateways; they are usually open and allow natural gas to flow freely, but they can be used

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to stop gas flow along a certain section of pipe. There are many reasons why a pipeline may need torestrict gas flow in certain areas, including for emergency shutdown and maintenance”.

Pig Launching/Receiving Facilities: ”consist of pig launching or receiving equipment and allow thepipeline to accommodate a high-resolution internal inspection tool. Pigs are devices that are placed intoa pipeline to perform certain functions. Some are used to clean the inside of the pipeline or to monitorits internal and external condition. Launchers and receivers are facilities that enable pigs to be insertedinto or removed from the pipeline”.

Pipes are subject to economy-of-scale (see Slides): the larger a pipeline, the lower the unit cost oftransportation ($ per Nm/super3 per kilometre).

3.4.2 Liquefied Natural Gas System

Liquefied Natural Gas (LNG) provides a means of transporting natural gas if pipeline transport is in-feasible or undesirable. Typically this involves the transport of natural gas over long distances (e.g. over2.000 kilometres) and/or from political unstable regions. The LNG value-chain requires natural gas tobe cooled to a temperature of minus 161 ◦C to convert it to a liquid form that takes approximately 1

600th

of its original volume. As such the LNG value chain consists of five different components: exploration& production, liquefaction, shipping, storage and re-gasification (Figure ??).

Figure 3.8: LNG Value Chain (Ball et al., 2004)

The first commercial shipment of LNG took place in 1964, delivering Algerian gas to the UK andFrance. One of the most important motivations for importing natural gas as LNG is that it offers thepossibility to increase natural gas imports in a diversified manner. Consequently, the LNG trade soonmoved away from the specialized niche business it once was to become a mainstream natural gas mar-keting alternative. In fact LNG accounted for about 6 percent of the world natural gas consumptionand about 26 percent of internationally traded gas volumes in 2002 EIA (2003). Currently there are twomajor LNG importing regions: the Atlantic Basin and the Pacific Basin. Japan is the world’s largestLNG importer and accounted for almost half the world imports in 2002. The dominance of the PacificBasin is strengthened by major importers as South Korea and Taiwan, resulting in a 66 percent shareof world LNG imports in 2005 EIA (2005). This leaves the Atlantic basin responsible for the remainingLNG imports of 34 percent.

The LNG value-chain comprises of three main segments: the upstream (production, transportation toliquefaction, liquefaction), midstream (LNG sales and shipping) and downstream (LNG re-gasification,storage and transportation to the market, consumption) segment (Figure 3.9)

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Natural Gas Production

Natural Gas Transportation

Natural Gas Liquefaction

Liquefied Natural Gas Shipping

LNG Regasification and Regas Storage

Regas Transportation

Regas Realisation

Loading Port Access

Unloading Port Access

Upstream

Midstream

Downstream

Figure 3.9: LNG Value Chain Graphic (Griffin, 2006)

Exploration: natural gas reserves usually are located in remote areas of the world or in countriesthat do not have a large domestic consumption of gas. Natural gas is produced in areas with abundant,stable reserves and is transported to a liquefaction facility by pipeline.

Liquefaction: when produced from underground reservoirs, natural gas contains other gases andcomponents such as CO2, H2S and mercury. These other gases and components are removed from thenatural gas resulting in an extremely clean-burning fuel. The natural gas is then cooled to -161 ◦C (-256F) where it becomes a liquid known as liquefied natural gas (LNG). Condensing natural gas into a liquidat 1

600th of its volume as a gas permits safe and efficient storage and transport over long distances.

Because of the high critical pressure of methane, LNG must be produced commercially by refriger-ation rather than pressurization. A number of processes have been commercialized for LNG production.Common to all natural gas liquefaction processes is the need to pre-treat the gas feed for removal of com-ponents that would freeze out (thus restricting the flow of the process), cause corrosion, or lead to pollu-tion upon combustion of the re-vaporized LNG. The AP −XTM process cycle that is depicted in figure3.10 makes use of a cycle that is similar to the pre-cooled mixed-refrigerant process which incorporates apropane refrigerant loop in series with a mixed-refrigerant cycle. The logic behind this configuration isthat natural gas is pre-cooled in the propane loop while simultaneously acting as a intermediate refrig-erant for heat rejection from the mixed-refrigerant to cool airing air or water. This pre-cooling of naturalgas in the propane loop minimizes the range of cooling that must be achieved by the mixed-refrigerant.An important economical advantage of this configuration is that the propane section can be fabricatedfrom lower cost carbon steel, whereas the lower temperature sections require aluminium or nickel steels.

TheAP−XTM process differs from the mixed-refrigerant cycle in that liquefied LNG is sub-cooledin a nitrogen refrigeration closed-loop process cycle. ”Nitrogen gas is compressed, cooled to near am-bient conditions with cooling water or ambient air, and then further cooled to cryogenic conditions byexpansion to lower pressure. The gaseous nitrogen is then used to sub-cool LNG, after which it is re-turned to be re-compressed, completing the refrigeration cycle. By employing the nitrogen refrigerationcycle to sub-cool the LNG, the mixed-refrigerant only has to cool the LNG to about 115 ◦C (versus 150◦C to 160 ◦C for the typical pre-cooled mixed-refrigerant process). This allows for a larger productioncapacity without a substantial increase in equipment size” (adopted from (Hammer et al., 2006)).

Storage: LNG Storage is an important part of the LNG value-chain and is present at both the lique-faction and re-gasification part. At the receiving end, storage facilities at the terminal is the single largestexpense as it accounts for around 40-50 percent of total terminal costs (Inc, 2007). The strong economiesof scale for this part of the terminal also imply that the optimal size for a storage tank is the largestone available on the market. Hammer et al. (2006) notes that one of the earliest efforts in tank designwas dedicated at proper material selection to overcome the low temperatures (and high temperaturevariations). Whereas the single-integrity LNG storage tank of Figure 3.11 is equipped with an internalcryogenic liquid tank that is enclosed by an outer insulation tank made of carbon steel and a roof thatwas not necessarily gas tight but merely supported insulation. Low dikes were also added to containpossible LNG spills that could create a large product vapour cloud that could drift, ignite, and causedamage. These risks were countered by using materials which are less prone to failure and by placingtaller dikes closer to the tank. The advent of external risks such as a crashing air plane and the resulting

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Figure 3.10: Liquefaction AP − XTM , A) Propane precooled mixed-refrigerant process; B) Nitrogenrefrigeration closed-loop process Hammer et al. (2006)

tightening of the safety rules mean that double-integrity tankage (i.e. a liquid spill from a failure of theinner tank is contained by a second concentric tank that is structurally independent of the first) and full-height earthen berms or in-ground storage have become the industry standard (adopted from (Hammeret al., 2006).

 

Figure 3.11: LNG Storage, a) Suspended deck; b) Outer tank; c) Sidewall insulation; d) Inner tank; e)Load-bearing insulation; f ) Foundations; g) Dike (Hammer et al., 2006)

Shipping: a typical tanker measures some 275 [m] in length, about 43 [m] in width and 11 [m] inwater draft and transports about 125,000-138,000 [m3] of LNG. In order to economize on scale, the newgenerations of LNG tankers that are used at the Rasgas and Qatargas projects are able to transport215,000-245,000 [m3] of LNG. These tankers are equipped with double-hulled well-insulated storagetanks to take the LNG to the point of consumption. Two types of containment systems dominate theLNG tanker fleet: spherical ship tanks and membrane ship tanks. For tankers that employ a sphericaltank design, each tank is insulated and located between bulkheads in a separate section of the ship. Thecompartments are blanketed with inert nitrogen gas, which is sampled periodically to detect any LNGleakage.

Tankers that use membrane tanks feature a hull that is insulated and equipped with a secondary bar-

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rier (see Figure 3.13). ”A metallic membrane containment barrier is then installed over the surface of theinsulation. The membrane may consist of Invar (highly alloyed steel with an extremely low coefficientof thermal expansion)or of a waffle structure (made of nickel steel), where the cross section of the waffleallows two-dimensional thermal movement while maintaining intimate contact with the load-bearinginsulation. Membrane tanks are also compartmentalized and enable more efficient storage use of thehull volume. This manifests itself in a flattop deck and a lower center of gravity, whereas sphericaltanks extend up through the deck and require domed covers” (adopted from (Hammer et al., 2006)).

Legenda to above two diagrams:

• Spherical ship tank (Figure 3.12): a) Weather cover;b) Tank; c) Insulation; d) Support skirt;e) Thermal break; f) Inner hull;g) Ballast tank; h) Outer hull;

• Membrane ship tank: (Figure 3.13): a) Membrane liner;b) Insulation; c) Inner hull;d) Ballast tank; e) Outer hull.

Both types of tankers run their ship engines on natural gas - during the voyage, inevitably some gaswill evaporate, even withing the insulated storage hulls. Using continuous pressure control, this gas isled to the engine-room, pre-heated and used to fuel the ship engines.

Re-gasification: LNG is transferred to a receiving facility where it is stored as a liquid in well-insulated tanks at atmospheric pressure until natural gas is needed. When needed, the LNG is warmedto normal temperatures, returning it to its original gaseous state, and natural gas is delivered into a gaspipeline system. This is often achieved in heat exchangers or vaporizers that use seawater of naturalgas to provide the required heat. Yang and Huang (2004) notes that the following five types of LNGvaporizers have either been used or demonstrated in LNG receiving terminals:

1 Open Rack Vaporizers (ORV);2 Submerged Combustion Vaporizers (SCV);3 Shell and Tube type Vaporizers (STV) including modified designs such as the Reli-Vap type vapor-

izer;4 Combined Heat and Power unit with Submerged Combustion Vaporizer (CHP-SCV);5 Other type of Vaporizers - Ambient Air-Heated Vaporizers.

Key selection criteria are the availability and quality of seawater, capital and fuel costs and envi-ronmental issues such as air and water emissions. The most commonly used vaporizers are the ORVand SCV. ”In general, the ORV system uses seawater as the heat medium. It has a lower operating costthan the SCV, but normally a higher capital cost because of the vaporizer equipment cost, the added sea-water intake/outfall system, the large diameter seawater pipes, and the seawater pumping and treatingsystems The SCV requires fuel for the LNG vaporization, and the fuel consumption is about 1.5% of thesend-outgas. Thus, it has a higher operating cost than the ORV as the fuel has a significant economic

 

Figure 3.12: LNG Shipping Characteristics; Spherical ship tank Hammer et al. (2006)

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Figure 3.13: LNG Shipping Characteristics Membrane ship tank Hammer et al. (2006)

value at the LNG terminals” (Yang and Huang, 2004).

 

Figure 3.14: Possible Design of a Receiving Terminal – Simplified Process Flow Diagram (Tarlowski andSheffield, n.d.)

In the Port of Rotterdam, waste heat from the new E.On coal-fired power plant will be used to va-porize LNG.

Distribution: the final component of the LNG value-chain is the distribution of the natural gas fromregional supply centers to residential, commercial and industrial users. Distribution systems consists ofhigh, medium and low pressure grids where the latter is normally tied into medium-pressure or high-pressure distribution systems from which they receive gas at special supply stations. Because of theevolutionary development of the natural gas grid it often consists of mains of different diameter andmaterials. Consequently there are substantial differences in the operating pressure with 2-8 kPa for oldlines and 100 kPa for new ones.

More often than not LNG projects - from gas reservoir development to dispatch of the re-gasifiednatural gas to national gas grids - are completely organized before design and investment in the entireinfrastructure and its constituent components begins. Gas reservoir production capacity and market de-mand pose the obvious constraints. These determine the continuous operating capacity of liquefactionand re-gasification facilities. Distance, speed, loading and off-loading time and number of LNG-carriersthen determines storage capacity at both ends. Reliability requirements, economics, and contract ar-rangements (penalties for late-delivery etcetera) then determine the optimal storage volume and num-ber of LNG-carriers. These decisions further will be determined by the maximum-size achievable forboth storage and tankers, because of economy-of-scale.

Notably the location of LNG terminals is carefully assessed, as in many countries and harbours it isdifficult to find a spot where the risk to shipping traffic, other facilities and nearby communities or cities

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Figure 3.15: Possible Design of an Open Rack Vaporizer (Tarlowski and Sheffield, n.d.)

is acceptable.

3.4.3 Syngas Production and Derivatives

The CH4 component of natural gas has been a major feedstock for the production of chemicals sincethe early 20th century. The intrinsic stability of CH4 to date has resisted development of commercial pro-cesses that perform, for example, direct partial oxidation of methane to methanol. As a consequence, ifCH4 is to be used as a feedstock, it must be converted to syngas - a mixture of hydrogen, H2 and carbonmonoxide, CO). The syngas can then be used in further processing and converted to useful chemi-cals. These included methanol, ammonia, NH3and so-called middle-distillates, the GTL fuels (naphtha,kerosene, diesel) using Fisher-Tropsch synthesis (FTS). Figure 3.16 illustrates the chemical pathways toform primary and secondary industrial chemicals from CH4 via synthesis gas as an intermediate.

Figure 3.16: Chemical Pathways for Gas Conversion Mallison (2004)

Four well established gasification options may be used to convert CH4 to syngas. These includeSteam Methane Reforming (SMR), Partial Oxidation (POX), Autothermal Reforming (ATR) and CeramicMembrane Technology. The following descriptions are adopted, adapted and extended from Vosloo(2001)

SMR: methane is reacted with steam through the addition of large amounts of heat, required for theendothermic reaction. Using a system design perspective, an obvious advantage of steam reforming isthat it does not require pure oxygen, and thus no air separation plant. Steam-reforming is an established,much applied technology. In the last two decades of the twentieth century, however, new technologiesarrived at the scene that out compete steam-reforming in many occasions: POX and auto-thermal re-

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forming. Typically, steam reformers are more costly than either POX or autothermal reformers andexhibit an intrinsically lower thermodynamic efficiency. As a consequence, there is a minimum plantsize above which the economy of scale of a cryogenic oxygen plant in combination with a POX or auto-thermal reformer is cheaper than a steam reformer on its own. Other characteristics of steam reformingthat may limit its application or suitability in specific cases are:

• A steam reformer produces syngas with a H2/CO-ratio of around 3. This is much higher thanneeded in FischerTropsch synthesis (a little over 1) and methanol (a little over 2). This requires anaddition system function: correction of this ratio, or utilization of the excess hydrogen.

• Relatively low methane conversion due to a maximum operating temperature of around 900 ◦C ;• High use of water, which may render the technology unsuitable for arid regions.

The methane conversion is a function of the operating pressure, decreasing the operating pressureof the reformer can increase the methane conversion.

Adjusting the syngas H2/CO-ratio can be done two ways: by adding CO2 to the mixture BEFOREreforming or by removal of excess H2 produced AFTER reforming. The latter can be done by means ofmembranes will lower the H2/CO-ratio and optimize the process for use in Fischer Tropsch synthesis ora methanol plant. Alternatively, the synthesis gas can be used as is, and a hydrogen-rich purge gas canbe subject to membrane separation for hydrogen recovery. Adding CO2 will reduce the H2/CO-ratio,because the CO2 will react with H2 to produce CO and H2O - somewhat less steam thus is required, asthe CO2 replaces some of the steam as a source of oxygen. The CO2 can be extracted from the flue gasof the furnace used to heat the pipes wherein the steam reforming reaction takes place.

Due to the costs involved with these steps, it is most likely that steam reforming will only be consid-ered when one or more of the following conditions are met:

• A relatively small GTL plant with a capacity of well below 10 000 bpd;• The excess H2 can be sold as a valuable byproduct;• The natural gas has a high CO2 content;• Suitable water can be obtained at a low cost.

POX: the non-catalytic partial combustion of methane produces syngas with a H2/CO-ratio (smallerthan 2) close to the optimum needed by the FischerTropsch synthesis. This low H2/CO-ratio gas resultsfrom the very little, if any, steam that is used in the process. Due to the absence of catalyst, the reformeroperates at an exit temperature of about 1400 ◦C . This high temperature and the absence of catalysthave the following disadvantages as compared to an auto-thermal reformer.

• Formation of soot and much higher levels of ammonia and HCN, which necessitates the use of ascrubber to clean the gas;

• Higher oxygen consumption;• Due to the absence of the watergas shift reaction, the unconverted methane as well as the methane

produced by the FischerTropsch reaction cannot be recycled to the reformer without removing theCO2 from the FischerTropsch tail gas.

Depending on the energy needs of the plant, the syngas from the reformer can either be cooled bymeans of a water quench (a quench is a rapid cooling down) or by the production of steam in a heatexchanger. A quench system is the less costly of the two, but is also less thermodynamically efficient. Indesigning a POX-based GTL plant, the choice between a quench or a waste heat reboiler will depend onthe relative cost of capital and energy.

ATR: Unlike partial oxidation reforming, auto-thermal reforming uses a catalyst to reform the nat-ural gas to syngas in the presence of steam and oxygen. Due to the milder operating conditions (exittemperature of approximately 1000 ◦C ) and the use of steam (steam/carbon (S/C) ratio normally morethan 1.3), the syngas is soot-free and less ammonia and HCN are produced as compared to a POX. How-ever, at a S/C ratio of 1.3 the syngas will have a H2/CO-ratio of about 2.5, which is higher than the rationeeded by Fischer Tropsch. Similar to steam reforming, the H2/CO-ratio can be controlled by a combi-nation of lowering the S/C ratio and recycling the CO2 to the reformer. Although S/C ratios below 1.3

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are not commercially used, Haldor Topse and Sasol have successfully completed low S/C ratio tests ona commercial scale at Sasol’s synfuels plant in South Africa. Some of the other design parameters of thesyngas section that influence the cost and thermal efficiency of the GTL plant are as follows.

• The preheat temperatures of oxygen and natural gas. The higher these temperatures are, the lessoxygen will be used. The maximum preheat temperatures are determined by safety factors and bythe need to prevent soot formation.

• The pressure of the steam generated in the waste heat reboiler. The higher the steam-pressure, themore efficient energy can be recovered from the steam, but the more costly the steam and boilerfeed water treatment systems become. The optimum steam pressure will be determined by therelative cost of capital and energy.

Ammonia is produced by the reaction of hydrogen with nitrogen and is the basic intermediate forall nitrogen fertilizers. Its uses are illustrated in figure 3.17.

Figure 3.17: Use of Ammonia

Methanol is used in the production of a range of chemicals and as a transportation fuel. ”The largestchemical use of methanol is in the production of formaldehyde which is primarily used in produc-ing construction material such as foam insulation and as a resin binder for plywood and compositionboard...Acetic acid is the second largest chemical use. It is used in the making of paints, adhesives, coat-ings and other products”.

Methanol finds major use in the production of MTBE, a gasoline additive.GTL fuels are produced through Fischer Tropsch based technology - a technology that has been

developed and use since the 1930’s. In Fischer-Tropsch, higher hydrocarbons are assembled from thesmallest building blocks, CO and H2. Dry (2002) notes ”that there are two FT operating modes. Thehigh-temperature (300 − 350 degrees Celsius) process with iron-based catalysts is used for the produc-tion of gasoline and linear low molecular mass olefin’s. The low-temperature (200240 ◦C ) process witheither iron or cobalt catalysts is used for the production of high molecular mass linear waxes. Since theFT reactions are highly exothermic it is important to rapidly remove the heat of reaction from the catalystparticles in order to avoid overheating of the catalyst which would otherwise result in an increased rateof deactivation due to sintering and fouling and also in the undesirable high production of methane.High rates of heat exchange are achieved by forcing the syngas at high linear velocities through longnarrow tubes packed with catalyst particles to achieve turbulent flow, or better, by operating in fluidizedcatalyst bed reactor”.

In a continued research, development and commercialization effort, Shell has further developed theirmiddle-distillates synthesis technology, where they use syngas to produce synthetic naphtha, keroseneand gas-oil components. Experimental reactors in their KSLA laboratories in the late seventies where

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upscaled to a first demonstration plant in Bintulu, Malaysia. Recently, a full-scale plant went on-streamin Qatar.

3.5 Dutch Gas Infrastructure Design and Development, 1959-2009

In this section, we attempt to review 50 years of Dutch gas infrastructure development from a sys-tem design perspective. What, in retrospect, could have been the major system design objectives andconstraints for this system? And how have these shaped this system over the years? This review isonly presented for educational purposes - it is a qualitative re-interpretation of Dutch gas infrastructuredevelopment based on a limited set of sources, with the objective to stimulate re-thinking of gas infras-tructure design and learning, not a reconstruction of the case.

In January 2007, Dutch proven natural gas reserves equalled 1.439 [bcm] which at the 2008 produc-tion levels suffices for 17 years of additional production. Figure 3.5 illustrates that the Dutch reserveshave declined since the 1980s (with the exception of 1992). The Dutch gas infrastructure is clearly impor-tant to the Dutch economy as the domestic consumption equalled 33.1 billion cubic meters [bcm] whilethe export volume amounted to 50.9 [bcm] in 2008 (Figure 3.5) from which the Dutch state receivedapproximately 10 billion Euros in revenue. The design of the gas infrastructure in the Netherlands isstrongly related to its historical evolution and the changing context (e.g. societal, political, economic,geological) in which it operates. Understanding these changing conditions and their impact on the(shifting) design variables, objectives and constraints are a prerequisite to the consolidation of the cur-rent Dutch position in the gas business. Figure 3.5 illustrates the Dutch production outlook for thecoming decades. The discovery of new fields is unlikely due to the saturation of both the prospectiveonshore and offshore areas. Consequently, the peak in gas production is already over while gas reservesare in decline and gas imports on the rise.

After the discovery of the Groningenfield (Slochteren) in 1959 the consensus at the time appearedto be to concentrate the production efforts on this field and to extract the available natural gas as fast aspossible (e.g. in 30 to 35 years time). This policy was motivated by the high expectations about nuclearenergy, which at the time was expected to become a cheaper and more reliable energy source than fossilfuels. This in turn would render the gas left in the ground after say 1990 worthless. As a consequence,the national gas grid was rolled-out at an - in retrospect - incredible pace. Main design objective was tocreate demand quickly by hooking up as many users as quickly as possible. To this end, users wherelured by the prospect of safe, reliable and affordable gas supply to their homes and businesses.

The Dutch gas infrastructure system design objective - beyond bringing gas from Groningen to con-sumers - were reliability and safety, the system outage allowed to be once every 50 years; reliabilitysimply said: no gas explosions, which was realized through a combination of technology, stringentspecifications of end-user equipment, and institutions. In this case, although explicitly expressed, safetywas clearly not a constraint, but an objective of system design. In this respect, Dutch gas infrastructuredesign resembles the design of Dutch dikes that togehter form the primary flood defence system. These

 

Figure 3.18: Dutch Gas Reserves (source: EZ (2008))

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3.5. Dutch Gas Infrastructure Design and Development, 1959-2009

 

Figure 3.19: Dutch Gas Exports (source: GasTerra (2010))

 

Figure 3.20: Dutch Gas Production Outlook (source: EZ (2008))

must be designed (and maintained) such, that the chance of flooding in dike-ring 14 (the greater partof the Randstad) is less than once every 10.000 years. This is the dike system main design objective,translated into a very specific criterion for design, not a constraint.

In the seventies a shift in public opinion and the oil crisis of 1973 (and 1979) meant a dramaticshift in perspective - natural gas became a valuable, strategic national asset. The past policy of sellingthe gas quickly and cheaply was completely outdated. Dutch gas reserves needed to be maintained aslong as possible to ensure safe, secure gas supply, and a steady source of supplemental national income.The unique characteristics of the Groningen field - notably its extreme flexibility - should be maintained.Thus, the Dutch government introduced the ’small-fields policy’, which aimed to maintain the gas re-serves of the Groningen field as long as possible by shifting production to smaller and scattered onshoreand offshore gas-fields. The “Herenakkoord” was concluded, where the energy companies and the gov-ernment agreed upon exploitation of the Groningen field and the development of smaller gas fields.

Thus the function of the Groningen field was transformed from sole producer of natural gas to acushion for supply and demand imbalances. The function of the gas grid shifted from “bringing Gronin-gen gas to consumers” to “connecting gas fields to consumers”. This “broader” function brought a newobjectives: “maintain gas quality (Wobbe)” and “prolong the life of Slochteren to the maximum extent.

In the nineties, the EU and the Dutch Government where liberalizing many an energy market. In1998, this led to a new Gas Law, where large (industrial) consumers could seek out alternative suppliers.To maintain production capacity of the Groningen field, the first large-scale underground storage wasdeveloped (in Norg), and re-compression facilities installed (Grijpskerk). The function of the gas griddoes not change much - if only where it that more players and more dynamics and more gas needs tobe accommodated.

In the beginning of the 21st century, it is obvious that the declining Dutch natural gas reserves re-quire yet another change of course. With most of the natural gas extracted from the small gas fields andthe pressure of the Groningen field reduced to a level where it can no longer fully support its balancing

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role, the dependence on natural gas imports will rise. The excellent geographical location of the Nether-lands, its widespread natural gas transportation infrastructure and the availability of now or soon tobe depleted gas-fields create opportunities to retain a strong position in the European gas business. Inorder to secure regional energy supplies the Dutch government envisions the Netherlands to become agas hub to enable the North West European gas markets, by offering storage, quality adjustment andtransport of gas to make sure gas trade transactions are converted into gas dispatch and delivery.

The function of the gas grid changes once again - with the last stages of the new gas law in force, ithas become a transmission system, where shippers dispatch their gas to their clients, the transmissionsystem operator maintaining the system, making the gas flow and ensuring that molecules dispatchedmatch molecules received. And on the back of this system, a new function, the gas hub, should material-ize: routing gas flows, information flows, making a profit in the process. Meanwhile, the “old” functionsstill need to be performed too - Dutch households still expect reliable, affordable and safe supply of theirgas.

3.5.1 The Groningen Field

The huge size of the Groningen field necessitated the production through ’clusters’ of closely spacedwells which serve to equalize the reservoir pressure. There are now about 300 wells, spread over 29production clusters. Each of these may have gas treatment, power supply and (remote) control facilities.The maximum production of the entire Groningen field per day is approximately 350 million Nm3. Thelayout of the Groningen field is illustrated in Figure 3.5.1 while its location among the Dutch gas fieldsis depicted in Figure 3.5.1.

3.5.2 Design Objectives

Politico-economic aspects are an important part of the context in which the Groningen gas is pro-duced. The Minster of Economic Affairs established the Nota inzake het aardgas in 1962 of which theprinciple objective was to generate a maximum of revenues for the state and the holder of the conces-sion, the NAM 3. The ’market-value’ principle was introduced as the basis on which the gas shouldbe produced. (Correlje and Odell, 2000) notes that, the price for gas to be sold to the various types ofconsumers was linked to the price of alternative fuels most likely to be substituted, viz. to gas oil forsmall-scale users and to fuel oil for large-scale users. Accordingly, consumers would never have to paymore for gas than for alternative fuels, but the market value principle also ensured that they would notpay less. The Groningen field initially enjoyed the role of sole (monopoly) producer of natural gas formuch of Northern Europe, a position that proved to be untenable with the emergence of alternative pro-ducers (most notably new discoveries (UK and Norway), pipelined Soviet gas and LNG imports fromNorth Africa). Resultantly, ”In terms of the Dutch contribution to mainland Western Europe’s demand(outside the Netherlands itself), the decline was steep and continuing from 54% in 1971, to 36% in 1981,to under 19% in 1991 and to only 16% by 1998. Groningen, in particular, as, in effect, a supplier of lastresort (given the preference extended by the Dutch government to the exploitation of small fields), waseven more significantly affected: so much so, in fact, that it can be described as having lost its role asa catalyst in the system” Correlje and Odell (2000). Another important milestone in the Dutch energypolicy was 1998 when the Minstery of Economic Affairs drafted the Gas Law. ”The 1998 draft Gas Law(MEZ, 1998a) provided that customers would have free choice regarding their gas supplier(s). Largeconsumers, accounting for around 46% of Gasunie’s home market sales, were explicitly allowed to seekalternative suppliers immediately. In 2002, medium-sized users, representing 16% of the market, willfollow. Eventually, in 2007, it is suggested that the small users will be allowed to shop around freely”Correlje and Odell (2000).

Looking forward the Dutch government is committed to utilizing its extensive infrastructure toonce again become the gas hub of Northwest Europe. Connections to different European markets, itsgeographical position and flexible storage capabilities should enable a Dutch gas ’roundabout’ whichmanages incoming and outgoing gas flows from a variety of sources. Further important developmentsin this respect are the demand increase of wind power capacities (which calls for backup power sources),

3The emphNederlandse Aardolie Maatschappij is a 50/50 joint-venture of Shell and Exxon)

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Figure 3.21: GroningenFieldCharacteristics (source: NAM (2010), Breunese et al. (2005))

 

Figure 3.22: Gas Fields in the Netherlands (source: NAM (2010), Breunese et al. (2005))

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the creation of LNG terminals and the existence of the Title Transfer Facility (or TTF) which is a virtualtrading point for natural gas.

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Chapter 4

Electricity Infrastructure Systems

4.1 Introduction

World net electricity generation amounted to 18.0 trillion kiloWatthours (kWh) in 2006 and is expectedto increase to 23.2 trillion [kWh] in 2015 and 31.8 trillion [kWh] in 2030 in the reference case scenario ofthe EIA (2009). To put this number into perspective the 2006 net electricity production of the Netherlandsequalled 92.6 billion [kWh] (EIA, 2010a). Electricity generation also outpaced the growth in total energyconsumption (2.9% per year versus 1.9% per year, respectively). Coal is responsible for the majority ofthis electricity generation with a global share of 41 percent, followed by natural gas (20%), renewables(19%), nuclear (15%) and liquids (5%).

By 2030 the relative importance of electricity fuels are expected to be more or less equal to 2006 withcoal (43%), natural gas (21%), renewables (21%), nuclear (12%) and liquids (3%) (EIA, 2009). The loca-tion of the electricity supply however will differ from the current distribution with non-OECD countriesresponsible for the majority of the world’s electricity supply (from 45% in 2006 to 58% in 2030).

Chapter 4 views ’meeting the increased electricity demand’ as the Objective Defined Function of anyElectricity Infrastructure System. As such, it will commence with the principles of electric power sys-tems design §4.2. Different electricity production techniques and their design principles are discussed in§4.3. Modern power systems may have multiple Objective Defined Functions, which leads to the Co-&Trigeneration concept - combined production of power, heat and industrial products. These conceptsare discussed in §4.4. The chapter concludes with a discussion of the Dutch Electricity System in §4.5.

4.2 Design of Energy Systems

The conversion of potential energy to electrical energy can be direct (for example through solar energyor fuel cells) or indirect through mechanical energy. Figure 4.1 illustrates the possibilities for the creationof electrical energy. The importance of combustion (and to a lesser extend nuclear energy conversion)is exemplified by the fact that 80% of the 2006 electricity generation originates from non-renewables(fossil fuels and uranium). The heat that results from this combustion process is usually converted toelectrical energy via mechanical energy. The preferred conversion will depend on a variety of designcriteria including: costs, availability, efficiency and legislation.

Electricity generation in thermal power plants always involves three technical processes:

(1) combustion (or nuclear reaction)(2) heat to (mechanical) power conversion(3) conversion of mechanical to electrical power.

In the design of energy systems it is important to maximize the efficiency of the available technologyand budget, which makes it essential that the heat to power conversion proceeds in a cyclical process.We classify the electricity production through fuel source and assess the design of their respective tech-nologies. The main thermodynamic cycles in power generation are the steam (Rankine) cycle and gas

45

4.2. Design of Energy Systems

������������������� �������������� ����������������������������������������������������������������������� ��������������� ���� ���������������� ���� ��������� ����������� ��!�"!���������������� #����������������"�������#�������������

Figure 4.1: Trias Energetica (Verkooijen and Boersma, 2009)

turbine (Brayton) cycle. Beer (2004) notes that ”In the Rankine cycle, steam is created in a boiler, and partof the enthalpy of the high-pressure superheated steam is converted to shaft work in a steam turbinethat drives an electric generator. In the Brayton cycle, high-pressure and high-temperature gaseous com-bustion products enter directly a gas turbine, where part of their enthalpy is converted to shaft work.The gas turbine drives a compressor and the electric power generator. Because of the direct entry of thecombustion products into the turbine, the gas turbine cycle is highly sensitive to the quality of fuel andis restricted to the use of natural gas or distillate fuel oil. Boilers in the steam cycle are, by contrast, fairlytolerant to fuel quality and are capable of being fuelled even by low-quality coal or waste fuels”. In theBrayton cycle, ambient air is pressurized (isentropic compression) before it runs through the combus-tion chamber where it is heated (constant pressure heat addition). The hot air is then passed througha turbine where it performs work (isentropic expansion) before being returned to ambient conditions(constant pressure heat rejection). In the Rankine cycle the working fluid is pressurized before it entersa boiler and converted to a saturated vapour. Next the vapour expands through a turbine and returnedto a saturated liquid.

4.2.1 Thermodynamics

The First Law of Thermodynamics (often called the Law of Conservation of Energy) states that energycan be transformed (changed from one form to another) but cannot be destroyed. Equation 4.1 demon-strates that the increase in internal energy of the system dU equals the amount of heat energy added tothe system δQ minus the amount of work done by the system on its environment δW .

dU = δQ− δW (4.1)

The Second Law of Thermodynamics is an expression of the universal principle of entropy, statingthat the entropy of an isolated system which is not in equilibrium will tend to increase over time, ap-proaching a maximum value at equilibrium; and that the entropy change dS of a system undergoing anyinfinite small reversible process is given by δq / T, where δq is the heat supplied to the system and T isthe absolute temperature of the system. Or in the words of the originator of concept of entropy, Germanphysicist Rudolf Clausius ”The entropy of the universe tends to a maximum” (equation 4.2).∫

δQ

T≥ 0 (4.2)

For electricity generation this implies that there exists a limit to the conversion of heat Q to powerW . The most efficient cycle capable of converting a given amount of thermal energy into work (orconversely for refrigeration purposes) is the Carnot cycle (equation 4.3). Where T is the temperature inKelvin and Tc represents the cold sink and Th the heat source. Increasing the maximum efficiency of theconversion can thus be achieved by either increasing the Th and/or lowering Tc.

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W = δQh(1− Tc/Th) (4.3)

Figure ?? illustrates the Carnot cyle acting as a heat engine on a temperature-entropy and pressure-volume diagram Figure 4.2 and Figure 4.3 respectively. The following processes can be identified:

• 1-2: isotropic compression with power addition;

• 2-3: isothermal expansion at constant upper process temperature Tu and heat addition q;

• 3-4: isotropic expansion with power production;

• 4-1: isothermal compression at constant lower temperature Tl with heat extraction q.

Note that the Carnot cycle is an idealization, as in reality there do not exist heat engines that operatein a reversible process and there exist no physical processes that proceed at finite speed without entropyincrease. It is useful however in the determination of the theoretical maximum efficiency of a heat enginethat operates between Th and Tl (Equation 4.3). Note that the Second Law relates to the Universe - inpart of the Universe, of course entropy can be reduced. Inevitably, however, elsewhere entropy willhave been increased, to meet the criterion ∆S > 0.

4.3 Electricity Production Systems

This section will discuss the most widely used forms of electricity generation by energy source. As such,it will commence with the design of coal based electricity production before turning focus to natural gas,renewables and nuclear.

4.3.1 Coal

Coal is and continues to be the fuel of choice for electricity generation because of its broad availability(large reserve base in several countries around the world), low costs and the attractive economics thatare related to its use. At the end of 2008, global estimated coal reserves equalled 826.000 million tons,which at present consumption leads to an R/P-ratio of 122 years (BP, 2009).

Although there are different classifications of coal the most important ones for power generationare lignite, sub-bituminous and bituminous coals. It is mined from surface and underground minesaround the world with particular high productions in China and the US, which together accounted forapproximately 60% of the 2008 global production.

The basic principle of converting coal to electricity is to burn it in a boiler, heat water and producesteam that subsequently flows into a turbine that spins a generator and produces electricity. The maindisadvantage of coal utilization concerns the CO2 -emissions and pollutants such as SO2, NOx and fineparticulates. There are several technologies to convert coal to electric power, the most important ofwhich are Pulverized Coal Combustion (PC) and Fluidized Bed Combustion (FBC). The following are

Figure 4.2: Carnot Cycle Acting as Heat Engine – T,s Diagram

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Figure 4.3: Carnot Cycle Acting as Heat Engine – P,V Diagram

the basic important reactions that summarize the combustion process (equation 4.4 - 4.8 Nowak et al.(2004)).

C + O2 −− > CO2 (4.4)

H2 + 1/2O2 −− > 2O2 + H2O (4.5)

S + O2 −− > SO2 (4.6)

N(fuel−bound) + O2 −− > NOx (4.7)

N2(atmospheric) + O2 −− > NOx (4.8)

The first two reactions (Equation 4.4, Equation 4.5) are important because they account for nearlyall the heat and CO2 -emissions released in the combustion process. Reaction 4.6, 4.7 and 4.8 are impor-tant because of the production of pollutants that must be controlled. In order to reduce CO2-emissionsof coal combustion Carbon Capture and Sequestration (CCS) is being developed.

PC, the workhorse of today’s coal-fired generation, and FBC are illustrated in figure 4.5. PC is sim-ilar to gas combustion as small particles of coal (d50 = 50 µ m) are combusted to give temperatures ofup to 1600 ◦C . Since the adiabatic flame temperature of coal is in excess of 2200 ◦C , in PC a large excessof combustion air is used to achieve lower furnace temperatures. With time, as materials and furnacedesigns have advanced, this temperature has gone up, and so has the steam pressure and ultimatelyplant efficiency.

FBC makes use of larger particles that are up to 5000 times as large (1-50 mm) which combust totemperatures of maximum 900 ◦C . Important parameters for the design of coal fired furnaces include(Verkooijen and Boersma, 2009) fixed parameters such as the fuel, fuel range (heating value, water con-tent, ash content, volatiles, grind-ability, melting behavior). Other requirements include a stable igni-tion, complete burnout, the avoidance of slagging, fouling and corrosion in the furnace and convectiveheat exchangers and the part load behaviour. Together these requirements determine the type of firingsystem, geometry of the furnace their number and arrangement. Some of the (dis)advantages of bothFBC and PC are illustrated in Table 4.1

4.3.2 Natural Gas

The previous chapter discussed how natural gas is delivered from the point of production to the pointof consumption. This section will discuss how natural gas is used for electricity generation. The mostbasic natural gas fired electric generation is similar to the design of a coal fired power plant: it involvessteam generation units where natural gas is burned in a boiler to generate steam and power a turbine(Rankine cycle). Although natural gas can be used for this process, basic steam generation is morecommonly used for power production from coal or nuclear facilities and delivers efficiencies in the order

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Figure 4.4: Pulverized Coal Combustion

Figure 4.5: Fluidized Bed Combustion

of 45% and 35% respectively. Modern gas fired power plants are almost without exception combined-cycle units (see below). Gas turbines can also be used as stand-alone power conversion units. Becausegas turbines can easily be switched on and off they are traditionally used for peak-load demands. If itdecided not to co-produce steam, the (large amount of ) waste heat needs to be disposed off in anotherway (typically, GT efficiency is around 25-30 %.

Combined-Cycle units combine the Rankine (steam turbine) and Brayton (gas turbine) thermody-namic cycles by using the waste heat from the latter to generate steam, which is then used to generateelectricity in a steam cycle. This efficient use of heat enables combined-cycle plants to reach efficienciesof up to 50% to 60% (see Table 4.3), far higher than stand-alone gas or steam turbines. The derivationfor gas turbine efficiencies (ratio of electrical output to energy of the steam) is illustrated by equation4.9, while the Gas Turbine Combined Cycle (GTCC) efficiency is illustrated by equation 4.10 (Verkooijenand Boersma, 2009).

ηT = ηth,o, ηi,T, ηGen, ηm (4.9)

with:

Fluidized Bed Pulverized Fuel

Advantages low fuel preparation requirements high availabilityno flue gas cleaning for high boiler capacitiesSOx and NOx required high power density

good burnoutash utilization

Disadvantages high lime stone demand complex fuel preparationfor desulphurization secondary flue gas cleaning required

ash not usable

Table 4.1: Fluidized bed and Pulverized fuel firing compared (Verkooijen and Boersma, 2009)

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• ηth,o efficiency of thermodynamic cycle with isentropic expansion;• ηi,T internal turbine efficiency;• ηGen Gen generator efficiency;• ηm mechanical efficiency of the turbine shaft.

ηtot = ηb, ηT, ηaux, ηp (4.10)

with:

• ηb boiler efficiency;• ηT turbine efficiency;• ηaux auxiliary power efficiency;• ηp efficiency of connecting pipes.

The production of electricity at a GTCC involves three main sections: the compressor, combustionsystem and the turbine. The compressor draws air into the engine and pressurizes it. Compressed air isfed into the combustion system where it mixes with fuel and burned at temperatures in excess of 1100◦C . The high temperature, high pressure gas stream expands through the turbine next where it drivesthe rotation of blades that spin a generator to produce electricity and draw more pressurized air into thecombustion section.

4.3.3 Biomass

The burning of wood and other solid biomass is the oldest energy technology used by man. Severalenergy carriers are subsumed under the umbrella term biomass, these include wood-based fuels such asbales, log, wood-chips, pellets, saw chips and dust but also biogas and biogenous fuels. The importanceof traditional biomass is hard to overestimate, as 2.4 billion people in so-called developing countriescontinue to rely on it to meet their residential needs (e.g. for cooking and heating). Victor and Vic-tor (2002) notes that ”Biomass energy is mainly used in the household sector in developing countries,where on average it accounts for about 75 percent of the total final energy use”. Generally speaking theimportance of traditional biomass diminishes as socio-economical development increases.

Biomass was the single largest source of renewable energy with a share of 53% with renewableenergy accounting for 7% of the total U.S. energy consumption in 2007. Wood and wood-derived fuelsaccounted for 60 percent of the total biomass energy consumption. Waste (consisting of municipal solidwaste from biogenic sources, landfill gas, sludge waste, agricultural by-products, and other biomass)accounted for 12% and the remaining 28% through biofuels (Fuel ethanol (minus denaturant) and bio-diesel) (Data derived from (EIA, 2010b)).

Energy is produced from biomass through combustion, gasification or liquefaction. Figure 4.6 il-lustrates the efficiencies of the different conversion techniques for electrical power. It should be notedthat the co-combustion of biomass in modern coal power plants, reaching efficiencies of up to 45%,provides the most cost effective biomass utilization. Co-firing also makes it possible to accommodateseasonal demand/supply swings of biomass by adjusting the coal/biomass ratio. The IEA (2007) notesthat dedicated biomass plants for combined heat & power (CHP), are typically of smaller size andlower electrical efficiency compared to coal plants (30%-34% using dry biomass, and around 22% formunicipal solid waste) while biomass integrated gasification in gas-turbine plants (BIG/GT) is not yetcommercially available. Far more efficient is the biomass conversion through cogeneration where totalefficiencies may reach 85%-90%. Table ?? provides typical data and figures for power generation frombiomass and acts as the point of departure for the discussion of the respective technologies.

Biomass combustion consists of several steps: drying, pyrolysis, gasification, and finally full com-bustion. An important characteristic of biomass is the presence of water as this significantly impacts theoverall system performance. Faaij (2004) notes that it is generally impossible to maintain the combustionprocess at moisture contents over 60 %. This makes the heating value an important quality indicator forbiomass fuels. Equation 4.11 indicates that the lower heating value (LHV) is equal to the energy contenton dry basis, i.e. the higher heating value (HHV), minus the energy that is required for the evaporationof water. Note that this equation allows the LHV to drop below zero at certain moisture contents.

LHVwet = HHVdry(1−W)− Ew(W + H ∗mH2O (4.11)

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Figure 4.6: Energy Production from Biomass (Verkooijen and Boersma, 2009)

Technologies Efficiency (% LHV) Typical Size (MWe) Capital Costs ($/kW) Electricity Costs ($/kWh)

Co-firing 35-40 10-50 1100-1300 0.05Dedicated Steam Cycle 30-35 5-25 3000-5000 0.11

IGCC 30-40 10-30 2500-5500 0.11-0.13Gasification & Engine CHP 25-30 0.2-1 3000-4000 0.11

Stirling engine CHP 11-20 0.001-0.1 5000-7000 0.13

Table 4.2: Typical Data and Figures for Power Generation from Biomass (IEA, 2007)

with:

• Ew is the energy required for evaporation of water;• W is the moisture content;• H is the hydrogen content (weight percent of wet fuel);• mH2O is the weight of water created per unit of hydrogen.

In order to increase the LHV, drying is a possible way to decrease the moisture content W . Se-lection of the appropriate dryer depends on many factors including the size and characteristics of thefeedstock, capital cost, operation and maintenance requirements, environmental emissions, energy effi-ciency. Roos (2008) notes that there are many types of dryers in use to dry biomass, including direct- andindirect fired rotary dryers, conveyor dryers, cascade dryers, flash or pneumatic dryers, superheatedsteam dryers and microwave dryers.

Drying is followed by pyrolysis which is ”the thermal decomposition occurring in the absence ofoxygen. It is always also the first step in combustion and gasification processes where it is followed bytotal or partial oxidation of the primary products. Lower process temperature and longer vapour resi-dence times favour the production of char coal. High temperature and longer residence time increasethe biomass conversion to gas and moderate temperature and short vapor residence time are optimumfor producing liquids” (Bridgwater, 2004).

Gasification of biomass enables its conversion to more convenient gaseous and/or liquid fuelsfor the generation of heat and electricity. Bauen (2004) notes that ”‘Gasification is a total degradationprocess consisting of a sequence of thermal and thermochemical processes that converts practically allthe carbon in the biomass to gaseous form, leaving an inert residue. The gas produced consists of carbonmonoxide (CO), hydrogen (H2), carbon dioxide (CO2), methane (CH4), and nitrogen (N2) (if air is usedas the oxidizing agent) and contains impurities, such as small char particles, ash, tars, and oils. The solid

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residue will consist of ash (composed principally of the oxides of Ca, K, Na, Mg, and Si) and possiblycarbon or char”’. Circulating Fluidized Bed Gasification are particularly good in converting biomassto a high quality, low calorific value gas with a high carbon conversion efficiency while allowing highcapacity, good tolerance to variations in fuel quality and reliable operations (Bauen, 2004). The producedgas is subsequently burned to generate electricity, the options for which include (IEA, 2007):

• Co-Firing; ”In general, combustion efficiency of biomass can be 10 percentage points lower thanfor coal at the same installation, but co-firing efficiency in large-scale coal plants (35%-45%) ishigher than the efficiency of biomass-dedicated plants. In the case of co-combustion of up to5%-10% of biomass (in energy terms) only minor changes in the handling equipment are neededand the boiler is not noticeably degraded. Traditionally, co-firing of biomass cannot exceeding10% of coal input.” If the biomass fraction increases, changes to the system are needed becauseof the different composition of biomass and coal. The furnace, steam pipes, flue gas treatmentmaterials and arrangement may need to be modified. ”In addition, coal ashes that are used toproduce construction materials should not be contaminated with tar and alkali metals-rich ashfrom biomass” .

• Dedicated Steam Cycle; ”Biomass can be burned to produce electricity and CHP via a steam tur-bine in dedicated power plants. The typical size of these plants is ten times smaller (from 1 to100 MW) than coal-fired plants because of the scarce availability of local feedstock and the hightransportation cost. A few large-scale such plants are in operation. The small size roughly dou-bles the investment cost per kW and results in lower electrical efficiency compared to coal plants.Plant efficiency is around 30% depending on plant size. This technology is used to dispose of largeamounts of residues and wastes (e.g bagasse). Using high-quality wood chips in modern CHPplants with maximum steam temperature of 540 degrees Celsius, electrical efficiency can reach33%-34% (LHV), and up to 40% if operated in electricity-only mode”.

• ”Integrated Gasification Combined Cycle (IGCC); The first integrated gasification combined cycle(IGCC) running on 100% biomass (straw) has been successfully operated in Sweden. Technicalissues appear to have been overcome. IGCC plants are already economically competitive in CHPmode using black-liquor from the pulp and paper industry as a feedstock”.

The slide package contains a presentation from Wartsila, detailing their biomass-cogeneration tech-nology https://svn.eeni.tbm.tudelft.nl/Education/spm4510/Q2_Part_2_Focus_Large_Systems_

Design/Slides_Q2/spm4510_13_14_Week_7_Wartsila_Biopower_jan_6_2014.pdf . This includes arevolutionary combustion and boiler, and provision to connnect to district-heating. The thermal ratingis some 22 MW, with an electric output of some 5 MW and thermal output of 15 MW.

From a technical perspective, issues addressed when developing biomass power infrastructure in-clude

• biomass storage. Biomass that is wet may start to ferment, and ignite spontaneously. Also, theenergy density of biomass is relatively low. Already for a moderately sized biomass plant, largestorage facilities are needed to ensure e.g. one or three days of interrupted operation when thebiomass supply chain is interrupted.

• conversion efficiency. Since the LHV of biomass is low (max. 15 [GG/ton], efficiency for conver-sion to electric power is limited to may as little as 20%. Thus, any biomass conversion for powergeneration almost always will be a cogeneration facility.

• flexibility and dynamic load. A biomass cogen delivering heat to a district-heating system in-evitably will face seasonal and daily variations in load. Heat storage may be considered (in theform of hot water, underground storage etcetera)

• flue gas cleaning. Biomass contains the entire periodic system, and may be rich in al kinds ofmetals and salts. Also, incomplete combustion will lead not only to COemission, but possiblynasty organic compounds. This should be taken care of in system design.

From a sustainability perspective, what is known as the food-or-fuel debate has led to general accep-tance (at least in the EU) that only biomass that in no way can ameliorate the food chain, or be recycledin agriculture, should be used in power generation. This also holds true for land-use - only land not fitfor agriculture should be used, excluding of course the unsustainable practice of cutting down rainforestand other old-stock forests for timber, pulp and biomass. This leaves only uneconomic strips of land,

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and the well-known northern regions of the northern hemisphere for sustainable forest-based biomassproduction: Canada, North-US, Scandinavia, Russia etcetera.

Around the globe, forestry and agriculture research is being conducted, to enable exploitation ofpreviously unusable land. Another development is the production of algae in coastal seas and oceans.

4.4 Co- & TriGeneration

Cogeneration refers to the combined production of electric energy and heat whereas trigeneration alsoinvolves the production of cooling.

Figure 4.7: Co-generation versus Reference Boiler and Power Plant

”A cogeneration system is the sequential or simultaneous generation of multiple forms of useful en-ergy (usually mechanical and thermal) in a single, integrated system. CHP systems consist of a numberof individual components prime mover (heat engine), generator, heat recovery, and electrical intercon-nection configured into an integrated whole. The type of equipment that drives the overall system (i.e.the prime mover) typically identifies the CHP system. Prime movers for CHP systems include recipro-cating engines, combustion or gas turbines, steam turbines, micro-turbines, and fuel cells. These primemovers are capable of burning a variety of fuels, including natural gas, coal, oil, and alternative fuels toproduce shaft power or mechanical energy. Although mechanical energy from the prime mover is mostoften used to drive a generator to produce electricity, it can also be used to drive rotating equipmentsuch as compressors, pumps, and fans. Thermal energy from the system can be used in direct processapplications or indirectly to produce steam, hot water, hot air for drying, or chilled water for processcooling”UNEP (2006). Figure 4.7 shows the efficiency advantage of CHP compared to the referenceboiler and power plant. When both thermal and electrical processes are compared, the CHP systemrequires approximately 75% of the primary energy compared to the reference system that comprises aseparate boiler and power plant. The reduced primary fuel consumption is the main environmentalbenefit of CHP and is illustrated as the CO2-free produced electricity.

4.4.1 Applied Example: The Production of Chemicals

Please consult (Dijkema, 2001).

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4.5 Power Supply in the Netherlands

Dutch electricity demand in 2007 equaled 119 TerraWatt-hour (TWh) and is expected to grow to ap-proximately 156 TWh in 2020 which itself represents a growth of 2.2% per year. In addition to thisexpansion of the production capacity a further 24 TWh is expected to be added for export (Seebregtsand Snoep, 2009). An overview of the planned expansion of the Dutch power supply is illustrated inTable 4.3. In terms of planned production capacity approximately 60% is gas fired versus 40% coalfired. Interesting to note in this respect are the European climate and energy targets for 2020 which arecollectively known as the 20-20-20 targets:

• A reduction in EU greenhouse gas emissions of at least 20% below 1990 levels;• 20% of EU energy consumption to come from renewable resources;• A 20% reduction in primary energy use compared with projected levels, to be achieved by improv-

ing energy efficiency.

This climate and energy package for the EU was first endorsed in March 2007 before being proposedas binding legislation in January 2008. An agreement was reached by the European Parliament andCouncil to make the energy package law in June 2009. The Netherlands pursuits even more ambitiousclimate and energy targets for 2020 to become one of the cleanest and most efficient energy countries inthe world. These targets include:

• to cut emissions of greenhouse gases by 30% in 2020 compared to 1990 levels;• to double the rate of yearly energy efficiency improvement from 1 to 2% in the coming years;• to reach a share of renewable energy of 20% by 2020.

Dutch energy policy is thus aimed at developing a energy supply that is affordable, sustainable andreliable, the design of which is discussed next.

4.5.1 Design of the Future Power Supply

Where the stated objective of the Balkenende-IV government was to achieve a share of 20% renewablesin 2020, the new coalition led by Prime Minister Rutte has reduced this target to 14 % by 2020. In thelong run, this share must increase. While the Dutch government has stated its vision to be that by 2050,40% of all energy originates from sustainable energy sources (Uyterlinde et al., 2007), in Europe it isthe UK who is presently accelerating its transition to a low carbon economy, with stated targets by theliberal/conservative government. To achieve this vision the Netherlands will Hennekens (2010):

• Create a good investment climate for large scale energy production, further integration of elec-tricity markets, streamlining procedures for infrastructure projects, develop a clear framework forCarbon Capture and Storage and develop clear sustainability criteria for the use of biomass;

• Strengthen the role of the Netherlands as main hub for gas distribution in the world and work onthe development of the North-Sea as (sustainable) energy source;

Company Location Capacity (MWe) Operational Fuel Type Efficiency

Delta Sloegebied 870 2009 gas STEG 58%Electrabel Flevocentrale 870 2009 gas STEG 59%Enecogen Rijnmond 870 2010 gas STEG Cogen 58%

Essent Moerdijk 400 2011 gas STEG, Cogen 58%Essent Maasbracht +635 2011 gas Upgrade to STEG 58%

Intergen Rijnmond 419 2010 gas STEG 58%Nuon Eemshaven 1300 2012 gas STEG 56%E.ON Maasvlakte 1070 2012 Pulverized coal conv. 46%

Electrabel Maasvlakte 800 2009 Pulverized coal conv. 58%RWE Eemshaven 1600 2013 Pulverized coal conv. 58%

Table 4.3: New large-scale power plants 2009-2015 Seebregts and Snoep (2009)

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• Foster innovation to develop small scale techniques and develop the accompanying policies tomake the energy grind smarter, flexible and more efficient.

Innovation is central to the realization of Energy Vision 2050 which is why the government hasformulated seven themes on which the energy transition should focus:

• Sustainable Mobility;• Biobased Raw Materials;• New Gas;• Chain Efficiency;• Sustainable Electricity Supply;• Energy in the Built Environment;• The Greenhouse as Energy Source.

We will discuss the themes that are relevant for the future power supply in more detail. The aim forbio-based raw materials is that they constitute 30% of the raw materials in the total energy supply ofthe Netherlands by the year 2030. In order to meet this target biomass will have to be imported as theavailability from waste and domestic production is limited. New gas refers to the ambition of creating asustainable gas supply which is clean, affordable, reliable and socially acceptable. While these issues areclearly important, the realization of a sustainable electricity supply is expected to be key for the futurepower supply. According to the Sustainable Electricity Supply Platform there are four complementaryroutes to make the electricity supply in the Netherlands sustainable:

• Increasing the share of renewable energy sources;• Improving the sustainability of traditional electricity production (e.g. through CO2 storage and

cogeneration);• Modifying the electrical infrastructure;• Achieving electricity savings.

4.5.2 Expansion of Electric Power Generation

Renewable energy accounted for 4% of the domestic energy consumption in the Netherlands (upfrom 3.4% in 2008) and is a long way off the 2020 target of 20%. Biomass accounts for 2.5% of therenewable energy while wind power accounts for 1%. In a recent report from the Innovatieplatformto the Dutch House of Representatives it is recommended that the renewable energy policy shouldfocus on biomass fuels, offshore wind, solar and micro-chp to take advantage of its knowledge positionand structural strengths in these areas. In addition to a strong knowledge position these include thefollowing (Innovatieplatform, 2010):

• Biomass

- Potentially large direct and indirect economic contributions through the existing presenceand activities of Dutch companies and spill over effects into other sectors like (petro) chemistry,agriculture, food, pharmaceutical and transportation and logistics;

- Geographically strength Netherlands: Rotterdam is the largest fuel port, existing gas infras-tructure and build on the development of the Netherlands as a gas roundabout. Moreover, theNetherlands has a competitive advantage in the removal of barriers in this area: e.g. throughknowledge and experience in the field of biotechnology, infrastructure and experience in naturalgas.

• Offshore wind

- Potentially large economic contribution towards 2020 due to the current strong competitiveposition of Dutch companies (i.e. foundation, installation and maintenance and assembly offshore,maritime strengths). The value-weighted market share of Dutch companies in 2008 equals 15%;

- Netherlands Geographical location: lots and lots of coastal port capacity;

- Building on the existing strong position of the Netherlands in the maritime and offshoreindustry.

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• Solar PV

- Great economic potential after 2020, this global market will accelerate. Opportunities forthe Netherlands are primarily in production equipment, components & materials and integratedapplications and systems within the built environment. However, it should also be noted thatother nations already have very strong global positions in the field;

- There are limited social and economic obstacles;

- In all likelihood solar PV is about to play an important role in alternative energy in theNetherlands, regardless of whether the Netherlands are a key player in this field with the associ-ated economic potential for the Netherlands.

• Micro CHP

- The Netherlands is a leader in developing micro-CHP;

- The Netherlands is a leader in research;

- Connect to industrial strengths in heating and strengthened role of Dutch distribution;

- Geographic: dense gas and electricity networks;

- The Netherlands has the ambition to develop a gas hub.

This advise illustrates also for the Netherlands there exist numerous alternatives for electricity ifnot energy supply. As with natural gas, for electric power, the available options can be combined ina superstructure. If we would develop this, we would see, contrary to natural gas, that in electricpower there is a basic system characteristic that needs to be decided upon whether or not to stimulate orfacilitate through the grid and its regulation. Decentralized power supply, enabled through the grid, orcentral, large-scale power supply, channelled through the grid. Or combining the best of both? The latteris the dominant model since the 1920s; the former is the newly emerging model. For it to materialize, thepower grid needs to change - to enable safe, secure and reliable local exchange of electricity (and heat),using the national grid as a backup. Meanwhile, with the long list of new large power plants (table 4.3,the national Dutch grid is reinforced. More of the old model?

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