jochen fricke and walter l. borst · 2013-12-28 · 11.5 hydrothermal carbonization of biomass 311...

Jochen Fricke and Walter L. Borst

Essentials of Energy Technology

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Jochen Fricke and Walter L. Borst

Essentials of Energy Technology

Sources, Transport, Storage, and Conservation

The Authors

Prof. Dr. Jochen FrickeZAE Bayern & Physikalisches Institut derUniversitat WurzburgAm Hubland97074 WurzburgGermany

Prof. Dr. Walter L. BorstTexas Tech UniversityPhysics Department11 Science BuildingLubbock TX 79409USA

Image credits for the cover illustration:1) Solar Flare:http://solarsystem.nasa.gov/multimedia/gallery/PIA03149.jpg2) Turbine: © Imaginis/fotolia.com

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V

Contents

Acknowledgments XIPreface XIIIList of Abbreviations XV

1 Introduction 11.1 Global Energy Flow 11.2 Natural and Anthropogenic Greenhouse Effect 11.3 Limit to Atmospheric CO2 Concentration 51.4 Potential Remedies 61.4.1 Energy Conservation 61.4.2 Rational Energy Production and Use 71.4.3 Carbon Capture and Storage (CCS) 71.4.4 Nuclear Energy 81.4.5 Renewable Energies 8

References 9Solutions 10

2 Energy Conservation with Thermal Insulation 112.1 Opaque Insulations 112.1.1 Conventional Opaque Insulation: Three Contributions to Heat

Transfer 142.1.2 Advanced Opaque Insulations: Vacuum Insulation Panels (VIPs) 212.1.3 Switchable Thermal Insulations 242.1.4 Thermal Measurement Methods 252.2 Transparent and Translucent Insulations 282.2.1 Radiative Transfer 282.2.2 Convective Heat Transfer 302.2.3 Windows 372.2.4 Switchable Glazings 422.2.5 Translucent Insulations 43


VI Contents

3 Thermodynamic Energy Efficiency 473.1 Carnot’s Law 473.2 Stirling Engine 493.3 Irreversibilities 523.4 Exergy and Anergy 523.5 Compression Heat Pumps and Air-Conditioning Systems 543.6 Absorption Heat Transformers 613.7 Energy and Exergy Efficiency 62


4 Fossil Fuel-Fired Energy Converters 674.1 Power Plants 674.1.1 The Rankine Steam Process 684.1.2 Gas Turbines 744.1.3 Combined-Cycle Power Plants 764.1.4 Turbine and Cooling Tower 784.1.5 Scrubber: Dust Removal, Desulfurization, and DeNOx 804.1.6 Carbon Dioxide Capture and Storage (CCS) 834.1.7 Fossil-Fired Back-Up Power Plants 894.2 Internal Combustion Engines 894.2.1 The Otto, Diesel, and Seiliger Processes 904.2.2 Fuels for Transportation 954.3 Thermoelectric Converters (TECs) 964.4 Exotic Energy Converters 1014.4.1 Thermionic Converters 1014.4.2 Alkali Metal Thermal Energy Converter (AMTEC) 1024.4.3 Magneto-Hydro-Dynamic (MHD) Converter 1034.5 Absorption Cycles 1044.6 Condensation Boilers 108


5 Nuclear Fission Energy and Power Plants 1135.1 Binding Energy and Mass Defect 1135.1.1 Volume Term 1145.1.2 Surface Term 1165.1.3 Coulomb Term 1165.1.4 Asymmetry Term 1165.1.5 Pairing Term 1175.2 Fission 1185.3 The Multiplication Factor 1245.3.1 Neutron Emission Factor k1 1245.3.2 Fast Neutron Enhancement Factor k2 1255.3.3 Resonance Escape Probability k3 127

Contents VII

5.3.4 Thermal Utilization Factor k4 1275.4 Reactor Control 1275.5 Neutron Flux 1295.6 Reactivity Changes during Power Plant Operation 1345.7 Fuel Conversion and Breeding 1355.8 Nuclear Reactor Types 1395.9 The Fuel Question 1455.10 U235 Enrichment 1465.11 Spent Fuel 1475.12 Reactor Safety and Accidents 152


6 Hydropower 1616.1 Water Runoff from Mountains 1616.2 Laminar and Turbulent Flow in Pipes 1666.3 Running Water from Oceans 1706.4 Ocean Tides 1726.4.1 Equilibrium Theory of Tides 1726.4.2 Dynamical Theory of Tides 1766.4.3 Basin Resonances and Seiches 1806.4.4 Tidal Power Plants 1836.5 Ocean Waves 1856.5.1 Characterization of Ocean Waves 1856.5.2 Energy from Ocean Waves 1896.6 Ocean Thermal Energy Conversion (OTEC) 1916.7 Energy from Osmotic Pressure 192


7 Wind Power 2017.1 Wind Velocity 2017.2 Using the Drag 2037.3 Using the Lift 2057.4 Technical Questions 2137.5 Electricity from Wind on Demand 2157.6 Small-Scale Wind Energy Conversion 2167.7 Alternative Wind Energy Converters 2187.8 Wind Energy Concentration 219


8 Photovoltaics (PV) 2238.1 Diodes and Solar Cells 2248.2 Transport Phenomena, Isc and Uoc 229

VIII Contents

8.3 Temperature Effects 2338.4 Equivalent Circuit 2348.5 Absorption Process and Transitions 2358.6 Advanced Solar Cells 2378.7 Si Production and Energy Amortization 2388.8 Other Solar Materials 2418.9 From Solar Cells to Modules 2418.10 Future Prospects for Photovoltaics 2428.11 Wet Solar Cells 244


9 Solar Space and Hot Water Heating 2499.1 Solar Radiation 2499.2 Flat Plate Collectors 2529.2.1 Gains, Losses, and Efficiency 2529.2.2 Temperature Rise along a Solar Flat Plate Collector 2589.2.3 Temperature Distribution across a Solar Flat Plate

Collector 2629.3 Evacuated Thermal Collectors 2649.4 Compound Parabolic Concentrator (CPC) 2679.5 Solar Thermal Heating Systems 2699.5.1 Active Solar Heating Systems 2699.5.2 Thermosiphon 271


10 Electricity and Fuels from Solar Heat 28110.1 Concentration of Solar Radiation 28110.2 Solar Troughs 28610.3 Fresnel Systems 28810.4 Solar Dish and Solar Tower 28910.5 Solar Thermic Power Plants 29110.6 Solar Fuels 295


11 Biomass Energy 30111.1 Growth of Biomass 30111.2 Direct Use of Solid Biomass 30411.3 Biogas 30611.4 Biofuel 30911.4.1 First Production Method 30911.4.2 Second Production Method 30911.4.3 Third Production Method 310

Contents IX

11.5 Hydrothermal Carbonization of Biomass 311References 311Solutions 312

12 Geothermal Energy 31512.1 The Origin of Geothermal Energy 31512.2 Geothermal Anomalies 31812.3 Geothermal Power Plants 31912.4 Hot Dry Rock 321


13 Energy Storage 32513.1 Mechanical Energy Storage 32513.1.1 Flywheels 32513.1.2 Compressed Air Storage 32913.2 Electric Energy Storage 33513.2.1 Capacitors 33513.2.2 Supercaps 33613.2.3 Superconducting Magnetic Energy Storage (SMES) 33713.3 Electrochemical Energy Storage 33813.3.1 General Considerations 33813.3.2 Accumulators 34113.3.2.1 Lead-Acid Accumulator 34113.3.2.2 Ni–Cd Accumulator 34213.3.2.3 Ni-Metal-Hydride Accumulator 34313.3.2.4 Li-Ion and Li-Polymer Accumulator 34313.3.2.5 Na-NiCl2 Accumulator 34413.3.2.6 Na-S Accumulator 34513.3.3 Redox Flow Systems (RFS) 34613.4 Chemical Energy Storage 34813.5 Thermal Energy Storage 35013.5.1 Sensible Heat 35013.5.2 Solid–Liquid Phase Change Materials (PCMs) 35413.5.3 Liquid–Vapor and Solid–Vapor Phase Transitions 357


14 Energy Transport 36514.1 Mechanical Energy Transport 36514.2 Transporting Electricity 36714.2.1 AC Transmission Lines 36714.2.2 DC Transmission Lines 37514.2.3 Superconductivity 37614.3 Heat Transport 382

X Contents

14.3.1 Heat Pipes 38214.3.2 District Heating 38714.3.3 Daily and Annual Temperature Variations near the Earth’s

Surface 38914.3.4 Radiative Transfer 393


15 Fuel Cells 40115.1 General Considerations 40115.2 Polymer Electrolyte Membrane Fuel Cell (PEMFC) 40415.3 Solid Oxide Fuel Cell (SOFC) 40715.4 Other Fuel Cells 408


16 Nuclear Fusion Energy 41116.1 Introduction 41116.2 Fuel for Fusion 41216.3 Break-Even and the Lawson Criterion 41316.4 Magnetic Confinement Fusion (MCF) 41616.5 International Thermonuclear Experimental Reactor (ITER) 42116.6 Inertial Confinement Fusion (ICF) 42316.7 The National Ignition Facility (NIF) 426


Index 435

XI

Acknowledgments

We wish to thank our wives, Ursula Fricke and Zwanette Borst, for their patienceduring the time we were busy writing this book. We also hope for a secure and safeenergy future for our children and grandchildren, and all persons on earth.

XIII

Preface

Back in 1980, two young physics professors – one (JF) in Wurzburg, the other(WLB) in Carbondale, Illinois – authored the German textbook ENERGIE,which was published by R. Oldenbourg Verlag, Munchen Wien. The bookgave a thorough survey of energy-related physics and technology, describedthe energy situation, discussed global energy problems, and highlightedenergy research and development. A second 600-page edition, publishedin 1984, was also sold out soon. For the next three decades, our profes-sional obligations kept us from writing a revised version of this successfultextbook.

Now, more than a quarter of a century later, we both are retired physics professors,but still teaching at our universities. We have taken a new initiative. As energyproblems during recent decades have become global and more urgent, we havewritten a new book, this time in English. We have attempted a more compacttreatment, as students today probably would despair of a 600-page book. The newtextbook treats the basic physics of present energy technology and its consequencesand discusses ideas of future interest. This new book also contains many newproblems and their solutions.

We discuss quantitatively and qualitatively the physics and technology of allenergy sources of present and likely future interest. The book can be used astextbook for advanced undergraduate and beginning graduate students. A physicsbackground will be helpful. The mathematical level is mostly algebra, but alsoincludes calculus.

General readers with a technical background should also be able to benefit fromreading parts of the book. There is sufficient narrative in the text to understand thebasic ideas without working through all the formulas and numbers. We hope thatin this way the book will serve as a survey of all important energy sources and beuseful to a broader audience.

The reader will notice that one of our concerns in the book is the anthropogenicgreenhouse effect that results from the burning of fossil fuels. It is very likely

XIV Preface

that this effect could change our world beyond recognition and threaten terrestriallife in many parts of the globe, unless changes in energy production and use aremade.

November 2012 Jochen FrickeWalter L. Borst

Wurzburg (Germany)Lubbock (USA)

XV

Abbreviations

ABB Asea Brown BoveriAC air conditionerADS accelerator-driven systemAFC alkaline fuel cellAFR air–fuel ratioAFUE annual fuel utilization efficiencyAGR advanced gas-cooled reactorAM air massaMDEA activated methyldiethanolamineAMTEC alkali metal thermal energy convertera-Si amorphous siliconATP adenosine triphosphateBMR basal metabolic rateBSCO BiSrCaCuOBSF back surface fieldBTL biomass to liquidBTU British Thermal UnitBWR boiling water reactorCAES compressed air energy storageCANDU CANadian Deuterium UraniumCCS carbon capture and storageCFL compact fluorescent lampsCIGS copper-indium-gallium-selenideCOP coefficient of performanceCPC compound parabolic concentratorc-Si crystalline siliconCSP concentrating solar powerCVD chemical vapor depositionDIN Deutsche Industrie NormDLR Deutsches Zentrum fur Luft- und RaumfahrtDMFC direct methanol fuel cellEDLC electric double layer capacitorEMEC European Marine Energy CenterEPR European Pressurized Reactor

XVI 1 Abbreviations

EPS expanded polystyreneETH Eidgenossische Technische HochschuleEVA ethyl–vinyl acetateFAME fatty acid methyl esterFFV flexible fuel vehicleFIT feed-in-tariffGWP global warming potentialHDR hot-dry-rockHP heat pumpHTC heat transmission coefficientHVDC high-voltage direct currentIAEA International Atomic Energy AgencyICF inertial confinement fusionIEA International Energy AgencyIGCC integrated gasification combined cycleIR infraredITER International Thermonuclear Experimental ReactorJET Joint European TorusKART Kumatori accelerator-driven reactor testLED light-emitting diodeLIFE laser inertial fusion energyLLNL Lawrence Livermore National LaboratoryLMFBR liquid metal fast breeder reactorMBE molecular beam epitaxyMCF magnetic confinement fusionMCFC molten carbonate fuel cellMEA methylethanolamineMEGAPIE megawatt pilot experimentMHD magneto-hydro-dynamicMOX mixed oxidempp maximal power pointMSR molten salt reactorMYRRHA multipurpose hybrid research reactor for high-tech

applicationsNADPH2 nicotinamide adenine dinucleotide phosphateNIF National Ignition FacilityNREL National Renewable Energy LaboratoryORC organic Rankine cycleOTEC ocean thermal energy converterOWC oscillating water columnPAFC phosphoric acid fuel cellPBMR pebble bed modular reactorPCM phase change materialPE polyethylenePEM polymer electrolyte membrane

Abbreviations XVII

PEMFC polymer electrolyte membrane fuel cellPET poly(ethylene terephthalate)PHWR pressurized heavy water-moderated and -cooled reactorPIUS process-inherent ultimately safePMMA poly(methyl methacrylate)PV photovoltaicsPVDF poly(vinylidene fluoride)PWR pressurized water reactorQDSL quantum dot superlatticeRBMK Reaktor Bolschoi Moschtschnosti KanalnyRF radiative forcingRFS redox flow systemRME rapeseed methyl esterRPV reactor pressure vesselSAD Subcritical Assembly DubnaSCR Selective Catalytic reactionSEER seasonal energy efficiency ratioSEGS Solar Electric Generating SystemSL superlatticeSMES superconducting magnetic energy storageSOFC solid oxide fuel cellSWU separation work unitTEC thermoelectric converterTFTR Tokamak Fusion Test ReactorTHTR thorium high-temperature reactorTiNOx titanium-nitrite-oxideTISES Texas Instrument Solar Energy SystemTMI Three Mile IslandTNT trinitrotolueneTokamak Toroidalanaya kameras magnitnymi katushkamiTRADE Triga accelerator-driven experimentTS temperature–entropyTSR tip speed ratioVRFS vanadium-redox flow systemVIG vacuum-insulated glazingVIP vacuum insulation panelWCD World Commission on DamsWEC wind energy converterWIPP Waste Isolation Pilot PlantXPS extruded polystyrineYBCO YBaCuOZAE Bayern Bayerische Zentrum fur Angewandte EnergieforschungZEBRA Zeolite Battery Research Africa

1

1Introduction

1.1Global Energy Flow

The global demand for primary energy has grown enormously during the pastdecades. It is now about 5.0 · 1020 J per year or 16 TW (Figure 1.1). Most of thisenergy is dissipated as waste heat. As the solar power reaching the Earth (insolation)is 170 000 TW, we recognize that, on a global scale, the heat dissipation causedby human activities is about 10 000 times smaller than the solar input. However,inside cities, the anthropogenic heat dissipation and the solar input can becomecomparable. This leads to a warmer microclimate.

1.2Natural and Anthropogenic Greenhouse Effect

A much more severe and global problem associated with the flow of energy isthe anthropogenic emission of greenhouse gases. Most important among these iscarbon dioxide (CO2) released by burning of fossil carbon (Table 1.1). The averagedwell time of CO2 in the atmosphere is about 120 years. CO2 is a natural constituentof the atmosphere together with water vapor, the latter being the dominantgreenhouse gas. These gases interact with a thermal radiation of 1.1 · 1017 W orabout 220 W/m2 from the Earth (Figures 1.1 and 1.2). Their molecules either havea permanent electric dipole moment, as with H2O, or are vibrationally excited, asin the case of CO2 and CH4, another greenhouse gas.

These gases thus reduce the radiative heat transfer from the Earth into space,raising the global mean temperature from −18 to +15 ◦C, a precondition for ahabitable Earth. A stable mean temperature requires a balance between solar inputand thermal output (Figure 1.3).

It is important to answer the question why the concentration of CO2 is ofany consequence. After all, the concentration of water vapor is about 100 timeslarger. Figure 1.4 shows that some of the absorption bands of CO2 coincide with‘‘windows’’ in the H2O spectrum. Thus, a relatively small amount of CO2 canreduce the thermal flow, that would otherwise escape into space through thesewindows. The effect of the other greenhouse gases on the thermal flow into space

Essentials of Energy Technology: Sources, Transport, Storage, and Conservation, First Edition.Jochen Fricke and Walter L. Borst.© 2013 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH & Co. KGaA.

2 1 Introduction

Insolation1.7 × 1017

(100)

Reflectedinsolution6 × 1016

(34)

Vaporization4 × 1016 (23)

Photosynthesis4 × 1013

(0.023)

Direct heat production7.3 × 1016 (42)

1.1 × 1017

(66)

3 × 1012

(0.0017)

1.6 × 1013

1.7 × 1012

(0.001)

2 × 1015 (1)

1.3 × 1013

1 × 1012

(0.0006)3.2 × 1013 (0.018)

Thermalenergy

Tidal energy

Earth, Moon,Sun

Earthsurface

GeothermalenergyNuclear energy

Fossileresources

Earth

Plants AnimalsOur energy

consumption

Degradation

Wind, Waves,Currents

Water vapor

Atmosphere

Infraredradiation

1.1 × 1017

(66)

(0.0075)

(0.0094)

Figure 1.1 Present global energy flow inWatt. The numbers in parentheses are rel-ative to the solar input. About 80% of ourprimary energy is provided by fossil fuels,about 10% by biomass, and 6% by nuclear

reactors. The contributions from photo-voltaics, solar thermal, wind, geothermal,and tides are not shown, as each of themstill amount to <1% of the primary energydemand. (Source: Adapted from [1].)

Table 1.1 The amount of CO2 emitted per thermal kilowatt hour depends strongly on theatomic carbon/hydrogen ratio of the fossil fuel (1 kg of C is oxidized into 3.7 kg CO2).

Carbon source Lignite Anthracite Mineral oil Methane

kg CO2/kWhthermal 0.40 0.33 0.29 0.19

is characterized by the global warming potential (GWP). For example, CH4 has aGWP ≈ 25, indicating that one molecule of CH4 is 25 times more effective thanone molecule of CO2.

CO2 and other noncondensing greenhouse gases together account for about 25%of the terrestrial greenhouse effect. Atmospheric modeling [3] shows that thesegases via feedback processes provide the necessary infrared absorption to sustainthe present levels of water vapor and clouds, which make up the remaining 75%of the terrestrial greenhouse effect. (Without CO2 and the other noncondensing

1.2 Natural and Anthropogenic Greenhouse Effect 3

Atmosphere

Greenhousegases

Without With

T = 288 K = +15 °C

T = 255 K = −18 °C

Ambientthermalradiation

Solarradiation

Figure 1.2 Hypothetical atmosphere of theEarth without infrared-active trace gases as-sumed in the left half of the figure. Abouttwo-thirds of the incoming solar radiation isabsorbed at the surface of the Earth (with analbedo or reflectivity of 0.35), reemitted asthermal radiation, and completely given offinto space. The resulting temperature wouldbe about 18 ◦C below zero, preventing life

as we know it. Greenhouse gases present inthe real atmosphere are added in the righthalf of the figure. They absorb part of theoutgoing thermal radiation and send it backto Earth. This greenhouse effect provideslife-supporting temperatures of +15 ◦C. Themost important greenhouse gas is H2O withtypically 1–2% by weight, followed by CO2,CH4, NOx, and so on.

0.5.250

1

1 2

Wavelength / μm

Rel

ativ

e ra

diat

ive

pow

er

5

Thermalradiation

Insolation

10 18

Figure 1.3 Normalized solar radiation input and thermal radiation at 300 K as a functionof wavelength. The solar blackbody spectrum at 6000 K is modified by absorption in theEarth’s atmosphere.

greenhouse gases, the atmospheric water vapor would condense. The terrestrialgreenhouse would collapse within a few decades, sending Earth into an ice-boundstate.)

In summary, the natural greenhouse effect determined the climate on the Earthin the past and supported the development of life. About 150 years of anthropogenicactivities, however, accompanied by the burning of coal, oil, and natural gas, haveled to a drastic increase in the concentration of greenhouse gases in the atmosphere.This is causing an additional, human-related reduction in the thermal radiationtransfer to space. The imbalance, also called radiative forcing, is about 1 W/m2

4 1 Introduction

0

1

0

1

1053 20 30Wavelength / μm

Rel

ativ

eab

sorp

tion

CO2

H2O

Figure 1.4 Relative spectral absorption ofwater vapor and carbon dioxide in the at-mosphere. A value of 1 means a saturatedabsorption or complete opaqueness, 0 indi-cates a ‘‘window’’ for radiative escape. Onesees, for example, that CO2 drastically re-duces the escape of thermal radiation in the

H2O-window of 4–5 μm. Note that the threeCO2-absorption bands shown are saturatedonly in their center but not in the flanks.Therefore, a further increase in CO2 in theatmosphere can definitely enhance the green-house effect. (Source: Adapted from [2].)

1960310

330

350

370

390

1970 1980 1990 2000 2010

Year

CO

2 C

once

ntra

tion

/ ppm

v

Figure 1.5 The concentration of CO2 inthe atmosphere at present is increasing bynearly two parts per million by volume peryear (ppmv) and was about 390 ppmv in2010. The oscillations on the continuousrise are about 6.5 ppmv peak-to-peak andare caused by annual variations in bioactivity

and oxidation of biomass. Photosynthesis insummer causes a relative minimum inSeptember/October, while oxidation ofbiomass in winter leads to a relative max-imum in May. The preindustrial value was280 ppmv. (Source: Adapted from MaunaLoa, Hawaii.)

today [4]. This is only a 0.5% contribution to the total radiative heat transfer fromthe Earth. Furthermore, the large thermal mass of the oceans has stored largeamounts of heat. Nonetheless, a global warming of about 0.8 K since 1870 and0.6 K since about 1960 is observed.

The main culprit for the warming of the Earth is anthropogenic CO2. Itsconcentration in the atmosphere rose from a preindustrial value of 280 to about390 ppm in the year 2010 (Figure 1.5).

In order to put the anthropogenic influence on our climate in perspective, we haveto look at the history of CO2. The CO2 concentration during the past 400 000 yearsfluctuated between about 180 and 280 ppm, and never exceeded 300 ppm. A higher

1.3 Limit to Atmospheric CO2 Concentration 5

CO2 concentration was always accompanied by warmer temperatures and viceversa. The increase to 390 ppm thus is rather dramatic. The retreat of mountainglaciers and the north polar ice sheet appear to be manifestations of the problem.

Problem 1.1A warmer atmosphere can hold more moisture [5] and thus more torrential rainscan be expected. Calculate the relative increase in water vapor pressure for anatmosphere at 20 ◦C, assuming a temperature increase of 1 K. The exponentialdependence of vapor pressure on temperature is p(T) = p0 · exp[−�E/(kB · T)]. (Inorder to find �E, start with the mass specific heat of vaporization, then find themolar mass of water and the number of water molecules per mole.)

We should mention here that aerosols in the atmosphere are responsible fora negative radiative forcing. Combustion caused by humans has increased theamount of atmospheric aerosols substantially. The interaction between theseaerosols and solar radiation leads to a direct cooling of the atmosphere. In addition,aerosols enhance the condensation of moisture and modify the optical properties ofclouds. The sign of this indirect aerosol effect – whether positive or negative – is stilluncertain. A third indirect aerosol effect involves the change of biochemical cycles[6]. All three effects may have reduced global warming substantially. Anticipatingfuture worldwide installations of scrubbing devices, much higher CO2 mitigationcosts could result than previously thought.

1.3Limit to Atmospheric CO2 Concentration

In order to prevent catastrophic climate changes in the future, causing, for example,a rise in sea level of several meters, the CO2 concentration in the atmosphere willhave to be limited. The actual limit is the subject of much discussion at present.

As an example, let us consider a maximum tolerable CO2 concentration of560 ppm, that is, twice the preindustrial value. From the known global annual useof fossil fuels and the measured CO2 increase in the atmosphere, one can obtainthe following estimate [7]: For each 4 Gt of burned carbon, the CO2 concentration inthe atmosphere increases by 1 ppm. (If about one-half of the emitted CO2 were notabsorbed in the ocean and by forests, the parts per million increase would be abouttwice as high). This amount of carbon corresponds to 4 · (12 + 32)/12 Gt = 14.7 Gtof CO2.

A limit of 560 ppm would ‘‘allow’’ an increase in CO2 concentration of(560 − 390) ppm = 170 ppm. This corresponds to a maximum total CO2 emis-sion of 170 ppm · 14.7 Gt/ppm = 2500 Gt. If we assume the present annual globalCO2 emission of 35 Gt to be constant in the future, we find a time span of about70 years for ‘‘allowed’’ CO2 emissions. After that, any CO2 emission would have tostop. If we limit the CO2 concentration to 450 ppm, as many scientists suggest, thetime span would shrink dramatically.

6 1 Introduction

Problem 1.2Calculate the remaining time span for a maximal CO2 concentration of 450 ppm.Assume that the global CO2 output due to human activities is kept at 35 Gt per year.

This type of estimate suggests how strongly the CO2 emission has to be reduced inthe near future. As a reduction of the anthropogenic CO2 emission remains ratherelusive, some concerned scientists have proposed geoengineering, the intentionallarge-scale alteration of the climate system [8]. The proposals include light shadespositioned in space, ocean fertilization, aerosol injection into the stratosphere, andcloud brightening with saltwater droplets.

Considering the CO2 problem, we find that the discussion about ‘‘peak oilproduction or consumption’’ can be misleading. The carbon limit resulting fromthe above CO2 emission limit is 2500 · (12/44) Gt ≈ 680 Gt. Releasing this amountwould severely worsen the greenhouse problem, but this amount is small comparedto the still available fossil carbon resources. It seems that we will not be able toconsume these resources.

On the other hand, we note that there are no energy or electricity sources that areentirely CO2-free. Even if a power plant emits no CO2 during operation, this green-house gas is emitted during construction of the plant. Thus electricity and thermalenergy even from nuclear reactors and renewable sources are not CO2-free, but theyhave a low CO2 ‘‘footprint.’’ Perhaps in the far future, nonfossil energy systems willprovide the energy needed for constructing power plants without a CO2 footprint.

Problem 1.3Which reactions generate heat in a coal-fired power plant and in a nuclear reactor?

1.4Potential Remedies

A compulsory lower CO2 production will be extremely difficult to accomplish in thenext few decades if we keep in mind the magnitude of 13 TW of power producedfrom fossil fuels. In the following, we discuss some possible measures for reducingthe emission of CO2 in the near term:

• Energy conservation• Rational energy production and use• Carbon capture and storage (CCS)• Nuclear energy• Renewable energies.

1.4.1Energy Conservation

A most efficient way to conserve energy is the thermal insulation of buildings. Thisespecially applies to heating in cold climates and cooling in hot climates. Here,

1.4 Potential Remedies 7

consumption could be reduced by a factor of 3 or more if existing houses wereconverted into low or ultra-low-energy houses. Many new houses in Germany are‘‘passive houses,’’ where the demand for heating is below 30 kWh per m2 of livingspace and year. In Germany, 20 cm thick conventional fiber or foam insulation isthe insulation standard for walls at the present time. In the United States, similarmeasures could be applied to a greater extent. Quite independent of this, muchenergy could be saved with more efficient and smaller cars.

Problem 1.4A rather heavy car of mass m = 2000 kg stops every 0.5 km in city traffic andthen accelerates again to v = 50 km/h. Calculate the extra number N of liters ofdiesel fuel (volume specific enthalpy h = 40 MJ/l) needed for this over a distancel = 100 km. Assume an engine efficiency of η = 0.35. If the fuel mileage of thecar is 7 l per 100 km or about 34 miles per gallon (mpg) during steady highwaydriving, what is it during city driving? Comment on alternatives to obtain a betterfuel mileage.

1.4.2Rational Energy Production and Use

Gas-fired, combined-cycle power plants employing gas and steam turbines incombination can achieve efficiencies of 60% for the generation of electricity. Fossilenergy can be converted into electricity plus useful heat with efficiencies of over80% if the power plant is connected to a district heating system. In the near future,coal-fired power plants with steam temperatures of 700 ◦C and efficiencies around50% are feasible.

Another area with a large potential for higher energy efficiency is refrigeration.Refrigerators manufactured with an innovative insulation technology, using VIPs(vacuum insulation panels) with a nearly 10-fold improved insulation capability,consume 40–60% less electricity than conventionally insulated systems.

Replacing incandescent light bulbs by compact fluorescent lamps (CFL) andlight-emitting diodes (LEDs) reduces the electricity demand for lighting by about afactor of 5.

1.4.3Carbon Capture and Storage (CCS)

The extraction of CO2 from flue gases is being tested worldwide in pilot plants[9, 10]. The CO2 is absorbed at low temperatures in an amine solution and desorbedat higher temperatures for compression and storage, for example, in saline aquifers.Another technique, the oxifuel process, uses oxygen for combustion instead of air.This renders an extraction unnecessary but requires the separation of nitrogenand oxygen. The attitude of ‘‘not in my backyard’’ characterizes the difficultiesof finding suitable underground storage sites for CO2. However, as 80% of our

8 1 Introduction

primary energy supply is still provided by fossil resources, carbon capture andstorage (CCSs) seems a must.

1.4.4Nuclear Energy

Worldwide, 437 nuclear reactors with a total installed power of about 390 GWwere operating in 31 countries as of December 2011 [11]. They provide roughly2600 TWh per year of base-load electricity. This corresponds to about 12% of theglobal annual electricity production of 22 000 TWh [12]. At present, 63 nuclearreactors with a total electric power output of 65 GW are under construction in 15countries.

The reactors under development, so-called generation IV reactors, have improvedsafety features and higher efficiencies and they produce less radioactive waste thanconventional reactors. For example, the European Union had been supportinga $400-million-a-year international effort to develop such reactors before theFukushima reactor disaster [13]. The thorium high-temperature reactor (THTR)in Germany, operated in the 1980s and decommissioned in 1989, already hadcharacteristics of a Gen IV reactor. The molten salt reactor (MSR) developed andoperated in the 1960s at Oak Ridge National Laboratory in Tennessee used thoriumfuel and had improved safety features compared to light water reactors, that is, alow pressure and a core that cools down and solidifies by itself.

After Fukushima, several countries have decided to phase out nuclear reactors,while others adhere to their commitment for more nuclear power. The Germangovernment announced in May 2011 that it would shut down all 17 Germanreactors. Italian voters opted for a non-nuclear future. On the other hand, SouthKorea announced plans in November 2012 to add 17 reactors to its 20 existingreactors by 2030 and to begin research and development on next-generationreactors. South Korean companies are preparing to build four reactors in theUnited Arab Emirates. China has 14 operating reactors and 27 reactors underconstruction. However, after Fukushima, it suspended approvals for new reactorconstruction. Vietnam, Turkey, Bangladesh, and Belarus are planning their firstnuclear reactors with imports from abraod, primarily Russia. In the United States,the Nuclear Regulatory Commission granted the first construction permits for newreactors since 1978. The price tag for a new reactor is about $10 billion todaycompared to about $2 billion then and may pose an impediment [13].

In many countries, the commitment to nuclear power is strong. Largely unre-solved is the storage or burial of the spent fuel in many parts of the world. Positiveexceptions are Switzerland, Sweden, and Finland.

1.4.5Renewable Energies

Hydroelectricity with 1000 GW installed power delivers about 3500 TWh per yearor 16% of base-load electricity [12]. It has risen since 1965 at a rate of about

References 9

50 TWh/a, and has potential for further growth. In many countries, however,the growth is being slowed by environmental concerns. Base-load electricity frombiomass amounts to about 400 TWh (2%). Wind energy with 240 GW installedpower in 2011 provides a comparable but fluctuating output [12]. Geothermalsources with an output of 11 GW deliver 70 TWh (0.3%) of base load. Nearly70 GW (fluctuating) from photovoltaics provided an amount of 70 TWh (0.3%)in 2011 [12]. Investments especially in wind turbines and photovoltaic andsolar–thermal power plants are rising steeply today. With increasing installedpower, the fluctuating electricity output of wind turbines and photovoltaic in-stallations will pose problems for the stability of the electrical grid. Supplyand demand have to be balanced on time scales ranging from seconds tomonths.

Energy storage facilities such as pumped water storage and electrochemicalbatteries are scarce. Highly dynamic power plants will have to cover the requiredloads in times of calm wind or overcast sky. Related to this is the search for suitable‘‘smart grids.’’ These are intended to switch on and off electricity-consumingdevices such as refrigerators and batteries of electric cars, depending on theavailability from the grid.

If one considers the long times necessary for changes to our energy system andthe yet very low worldwide electricity production from renewable sources, it isdifficult to assess the impact of these in the future. In the very long term, that is,a century and beyond, solar, wind, and nuclear energy are likely to dominate ourelectricity supply.

Problem 1.5The delivery of electricity from hydroelectric and photovoltaic installations differsfundamentally. Please state the difference.

References

1. Romer, R.H. (1976) Energy – An Intro-duction to Physics, W.H. Freeman andCompany, San Francisco, CA.

2. Schlegel, M. and Deutscher, W. (1985)Promet – Meteorologische Fortbildung,4/1985.

3. Lacis, A.A., Schmidt, G.A., Rind, D.,and Ruedy, R.A. (2010) Science, 330,356.

4. Trenberth, K.E. and Fasullo, J.T. (2009)Bull. Am. Meteorol. Soc., 90, 311.

5. Wentz, F.J., Ricciardulli, L., Hilburn, K.,and Mears, C. (2007) Science, 317, 2.

6. Mahowald, N. (2011) Science, 334, 794.

7. Huntingford, C.C. and Lowe, J.J. (2007)Science, 316, 829.

8. Blackstock, J.J. and Long, J.C.S. (2010)Science, 327, 527.

9. Manning, L.R., Eric Russell, J., Padovan,J.C., Chait, B.T., Popowicz, A., Manning,R.S., and Manning, J.M. (2009) Science,325, 1641–1658.

10. (2011) BWK, 63(3), 25–27.11. Weßelmann, C. (2012) BWK, 64(7+8),

31.12. Bloche, K., Witt, J., Kaltschmitt, M., and

Janczik, S. (2012) BWK, 64(5), 5.13. Normile, D. (2012) Science, 335, 1166.

10 1 Introduction

Solutions

Solution 1.1 dp/dT = p0 · exp[−�E/(kB · T)](+�E/kB · T2) = p(T) · (+�E/kB ·T2); dp/p0 = dT · �E/(kB · T0

2). With kB = 1.38 · 10−23 J/K, heat of vaporization ofone molecule �E = 7 · 10−20 J, �T = 1 K and T0 = 293 K, we obtain dp/p0 ≈ 0.06or 6% for the increase in water vapor pressure.

Solution 1.2 t(450) = (450 − 390) ppm · (14.7 Gt/ppm)/(35 Gt/a) ≈ 25 years.

Solution 1.3 The two heat-generating reactions are, respectively, C + O2 → CO2

and U235 + n(thermal) → fission products + 2.3 n(fast).

Solution 1.4 The extra number N of liters of fuel needed in the stop-and-go traffic of city driving is N = 2 · l · (m · v2/2)/(η · h) = 2 · 100 · 2000 ·(502/3.62)/(2 · 0.35 · 40 · 106) l ≈ 2.8 l. This means a fuel consumption of 9.8 l per100 km or 24 mpg in the city for this heavy car compared to 7 l per 100 km or34 mpg on the highway. Comment: Driving a smaller car would save energy.Regenerative breaking with an electric motor/generator combination would saveeven more energy.

Solution 1.5 Hydroelectricity is base-load electricity; photovoltaics provides fluc-tuating electricity with capacity factors between 10 and 20%, depending on thenumber of sunshine hours.

jochen fricke and walter l. borst · 2013-12-28 · 11.5 hydrothermal carbonization of biomass 311...

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