1
Exergy and Natural Capital
Bhavik R. Bakshi
Dept. of Chemical & Biomolecular Engineering
The Ohio State University, Columbus, OH 43210
Environmentally Benign Design & Manufacturing, MIT 2.83/2.813
March 7, 2006
2
Outline
� Natural capital and its importance
� Accounting for natural capital
� Economic methods
� Biophysical methods
� Exergy and natural capital
� Thermodynamics of ecological processes
� Joint analysis of industrial and ecological systems
� Applications
3
What is Natural Capital?
� Natural capital consists of ecosystem goods and services that are essential for human well-being
RegulatingBenefits obtained from
regulation of
ecosystem processes
• climate regulation
• disease regulation
• flood regulation
• detoxification
Provisioning
Goods produced or
provided by
ecosystems
• food
• fresh water
• fuel wood
• fiber
• biochemicals
• genetic resources
Cultural
Non-material benefits
obtained from
ecosystems
• spiritual
• recreational
• aesthetic
• inspirational
• educational
• symbolic
4
Natural Capital and Human Well-Being
5
State of Natural Capital
� Findings of Millennium Ecosystem Assessment
� Humans have radically altered ecosystems in the last 50 years
� Changes have brought gains but at growing costs that threaten achievement of development goals
� Degradation of ecosystems could grow worse but can be reversed
� Effects of natural capital loss
� Nature is unable to absorb effects of human activities
� Loss of resilience - “capacity for a system to survive, adapt and grow in the face of turbulent change”
� Selected examples
6
0
50
100
150
200
250
300
1875 1925 1975 2025
Fossil Fuels
Agroecosystems
Fertilizer
Total Human
Additions
Natural Sources
Teragrams of Nitrogen per Year
Source: Millennium Ecosystem Assessment
7
Source: Millennium Ecosystem Assessment
Percent Increase in Nitrogen Flows in
Rivers
8
Source: Millennium Ecosystem Assessment
9Source: NOAA
Source: Millennium Ecosystem Assessment
Gulf of Mexico Dead Zone
10
State of Fisheries
March 2004
Cover Study of Nature Provides Startling New Evidence that Only 10% of All Large Fish are Left in Global Ocean
90 % of All Large Fish Including Tuna, Marlin, Swordfish, Sharks, Cod and Halibut are Gone
11
19002000
Source: Millennium Ecosystem Assessment; Christensen et al.2003
Biomass of Table Fish (tons per km2)
12
Loss of Wetlands
� Video of Louisiana wetlands, 1932-2050
� http://www.lacoast.gov/media/videos/index.htm
� http://www.lacoast.gov/media/videos/CWPPRA/missDelta2.rm
� http://www.lacoast.gov/media/videos/LCA/LandLossSimulation1932-2050.rm
13Washington Post,March 30, 2005
14
Loss of Natural Capital -
Reasons & Solutions� Reasons for loss of natural capital
� Natural capital is usually outside the market (public good) and not reflected in the price
� Social Cost = Costs of Production + External Costs
� Encourages overconsumption (tragedy of commons)
� Potential solutions
� Quantification of natural capital is essential
� “What is measured gets managed”
� Economic methods
� Biophysical methods
Ultimately, all environmental challenges are due to degradation or loss of natural capital
15
Outline
� Natural capital and its importance
� Accounting for natural capital
� Economic methods
� Biophysical methods
� Exergy and natural capital
� Thermodynamics of ecological processes
� Joint analysis of industrial and ecological systems
� Applications
16
Accounting for Natural Capital -
Economic Methods� Economics is anthropocentric
� Relies on human valuation
� Contingent valuation
� Travel cost
� Cost of human-made substitutes
� Sophisticated survey methods for quantifying monetary value of selected natural capital
� Main benefit of economic valuation
� Everyone understands money!
17
Results of Economic Valuation
� The total economic value associated with managing ecosystems more sustainably is often higher than the value associated with conversion
� Conversion may still occur because private economic benefits are often greater for the converted system
� Other studies� Ricketts, Daily, Ehrlich, Michener,
Economic value of tropical forest to coffee production, PNAS, 2004
� Balmford et al., Why conserving wild nature makes economic sense, Science, 2002
18
Ecosystem Services and their Value
� ECOSYSTEM SERVICES VALUE (trillion $US)
� Soil formation 17.1
� Recreation 3.0
� Nutrient cycling 2.3
� Water regulation and supply 2.3
� Climate regulation (temperature and precipitation) 1.8
� Habitat 1.4
� Flood and storm protection 1.1
� Food and raw materials production 0.8
� Genetic resources 0.8
� Atmospheric gas balance 0.7
� Pollination 0.4
� All other services 1.6
� Total value of ecosystem services 33.3
� Nearly twice as valuable as global economic product
Costanza et al., Nature, 1997
19
Shortcomings of Economic Valuation
� Diamond-Water paradox
� Water is essential to life, but not very economically valuable
� Diamonds are extremely valuable, but not important
� Economic valuation is based on marginals
� How much are people willing to pay for an additional bit
� Measure of scarcity, not importance
� Valuation surveys can be based on importance
� How do we convey the importance of ecosystems to the general public?
� Most studies are relatively narrow in spatial range or services considered
20
Accounting for Natural Capital -
Biophysical Methods� Biophysical methods are better at capturing importance of ecological goods and services
� Ecologists use such methods for understanding, assessing, and modeling ecosystems
� Mass, energy, exergy …
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Why Thermodynamics?
� Thermodynamics governs the behavior of all systems
Ecosystem
Products &
Services
Economic
Products &
Services
Sun Ecosystems Economy
� Everything is a transformed and stored form of solar
energy
� Energy available for doing useful work (exergy) is the
ultimate limiting resource
� Provides common currency for the joint analysis of
industrial and ecological systems
22
Exergy Flow in Ecosystems
� Ecosystems rely on fresh inflow of exergy
� Exergy is lost as it flows through the ecosystem
� Feedback reinforcement (autocatalytic)
� By pollinating flowers, bees reinforce the processes that produce nectar on which they feed
� Feedback is “higher quality” exergy
� Energy hierarchy
� Overall efficiency decreases witheach successive transformation
Sun Plants Herbivores Predators
105 103 102 10 1 J
102 10 1
Exergy
flow
Sun Plants Herbi-
vores
Preda-
tors
23
Global Energy Inputs� Three major inputs - solar, tidal, crustal
Mantle
Solar Insolation3.93 E24 J/yr
Atmosphere
Lithosphere
Hydrosphere
Tidal Energy5.2 E19 J/yr
Crustal Heat6.72 E20 J/yrFrom Surface
6.49 E20 J/yr
Deep Heat4.74 E20 J/yr
Crust
Radioactivity1.98 E20 J/yr
Biosphere
Sclater, Jaupart, Galson, Rev. Geophys. Space Phys., 1980; Odum, 2000
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Planetary Energy Transformation
Network
Odum, 2000; Yi, Hau, Ukidwe, Bakshi, Environmental Progress, 2004
Solar
energy
Crustal heatTidal energy
OceanOcean
HeatHeat CrustCrust
CivilizationCivilization
AtmosphereAtmosphereMinerals
Fuels
Minerals
Fuels
Power
Plant
Ammonia
Plant
RefineryCrude Oil
Air
Water
Coal
� Mining of oil and coal relies on the global land cycle
� Availability of air relies on atmospheric circulation
� Water is part of the hydrological cycle
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Products of Global Energy System
� Global latent heat 1.26 E24 J/yr
� Global wind circulation 6.45 E21 J/yr
� Global precipitation on land 1.09 E20 g/yr
� Average river flow 3.96 E19 g/yr
� Average river geopotential 3.4 E20 J/yr
� Average river chemical exergy1.96 E20 J/yr
� Average waves at shore 3.1 E20 J/yr
� Average ocean current 8.6 E17 J/yr
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Global Exergy Flow
http://www.stanford.edu/~weston/ExergyTheory.htm
27
Atmospheric Circulation
� Over ocean circulation
� Latent heat into air 9.3 E23 J/yr
� Kinetic energy used 2.33 E21 J/yr
� Cumulus land circulation 9.45 E21 J/yr
� Mesosystems (thunderstorms) 1.73 E22 J/yr
� Temperate cyclones 4.9 E21 J/yr
� Hurricanes 6.1 E20 J/yr
� Hemisphere general circulation
� Surface winds 1.61 E22 J/yr
� Average circulation 6.4 E21 J/yr
� Tropical jets 3.7 E21 J/yr
� Polar jet 1.61 E21 J/yr
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Ocean Circulation
� Surface eddies 3.0 E20 J/yr
� Mesoscale gyrals 1.78 E19 J/yr
� Sea ice 3 E19 g/yr
� Sea ice 9.0 E19 J/yr
� Ocean circulation 8.5 E17 J/yr
� Jet currents 1.67 E17 J/yr
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Earth Processes
� Earth heat flux 2.74 E20 J/yr
� Glaciers
� Mass 2.48 E18 g/yr
� Crystal heat 8.3 E20 J/yr
� Geopotential 2.11 E19 J/yr
� Available heat 1.38 E19 J/yr
� Land area sustained 1.5 E10 ha/yr
� Land, global cycle 9.36 E15 g/yr
� Continental sediment 7.4 E15 g/yr
� Volcanoes 3.05 E15 g/yr
� Mountains 2.46 E15 g/yr
� Cratons 0.81 E15 g/yr
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Natural Capital in Natural Resources
� How can knowledge about global flows be translated into contribution of NC to specific resources?
� How much does nature contribute to coal, rain, wind, water, … ?
� Use Cumulative Exergy Consumption
� Emergy analysis provides such an approach
Industrial
Processes
Industrial
Products,
Bp,l, Cp,l
Natural
Resources,
Bn,k, Cn,k
Ecological
Processes
Ecological
Inputs,
Be,j, Ce,j
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Cumulative Exergy Consumption and
Natural Capital� Cumulative exergy consumption can represent contribution of natural capital
� Allocation challenge
� Addressedin emergyanalysis
Deep
Heat
Tide
Sun
Over ocean circulation
Cumulus land circulation
Mesosystems
Temperate Cyclones
Surface eddies
Sea Ice
Ocean circulation
Earth heat flux
Wind
Rain
Pollination
Soil Nutrients
Minerals
Insects
Trees
Wetlands
Rivers
N2 Cycle ...
...
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106 106 106 106 106 sej (Emergy)
1 102 103 104 105sej/J (Trans-
formity)
Sun Plants Herbivores Predators
106 104 103 102 10 J (Exergy)
Coal Electricity
Emergy Analysis
� Emergy is available energy consumed directly or indirectly to make any product or service
� Represented in solar equivalents (sej)
� Transform ity (τ) = Emergy (M) / Exergy (B)
� Transformity indicates energy quality - ability to do many kinds of work and influence the surroundings
33
Allocation in Networks
� Need to partition the contribution of an input between multiple outputs
� Common challenge in many problems
� If structure of network and all products are known
� Allocate according to property of outputs (exergy)
� Combine by addition
10040
60
Exergy(J/yr)
1000400
600
Emergy(sej/yr)
1010
10
Transformity(sej/J)
100
40
601000
400
600
10
1010
34
Allocation in Networks
� If network structure or products are unknown
� Avoid allocation
� Combine to avoid double counting
100 4
61000
1000
1000
10250
167
3
9710 11
333200
11
333100
1000
10002000
Additive sources1000
10001000
Non-additive source
35
Approach for ECEC analysis
� Perform a traditional CEC analysis.
20
30 10
1010
(20)
(30) (15)
(15)(35)
Exergy
(Cumulative Exergy)
36
Approach for ECEC analysis
� Ecological inputs can be added through transformities from Emergy analysis.
20
30 10
1010
Eco
logic
al
Pro
cess
es
Eco
logic
al
Inputs
(20)
(30) (15)
(15)(35)
Exergy
(Cumulative Exergy)
ττττn,k = 33
ττττn,k = 20
ηηηηn,k=1/ττττn,k =1/33
ηηηηn,k=1/ττττn,k =1/20
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ηηηηn,k=1/ττττn,k =1/33
ηηηηn,k=1/ττττn,k =1/20
Approach for ECEC analysis
� Track the flow of natural resources through the network to avoid double counting.
20
30 10
1010
Eco
logic
al
Pro
cess
es
Eco
logic
al
Inputs
Exergy
(Cumulative Exergy)
(400)
(1000) (500)
(500)(500)
Cn,k=Bn,k/ηηηηn,k =20*20
Cn,k=Bn,k/ηηηηn,k =30*33
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Transformity of Global Energy Inputs
� Use global energy balance to determine conversion factors between global energy inputs
� Transformity = solar emergyexergy
� Transformities of global energy inputs
� Solar energy 1 sej/J
� Crustal heat 1.20 E4 sej/J
� Tidal energy 7.37 E4 sej/J
� Transformities represent higher quality of tidal and crustal energies than solar energy
� Total global energy input = 15.83 E24 sej/yr
� See Emergy folios at www.emergysystems.org
39
Emergy and Ecological Cumulative
Exergy� Cumulative exergy is equivalent to emergy for
� Same boundary
� Same allocation methods
� All inputs represented in solar equivalents
� Under above conditions
� Transformity = 1/ECDP
� Controversial aspects of emergy analysis need NOT be used for including ecological inputs
� Emergy theory of value
� Maximum empower (emergy/time) principle
� Using emergy/money ratio for economic inputs (addressed by thermodynamic input-output analysis)
� Transformity of ecological products and services may be used
Hau, J. L., and B. R. Bakshi, Env. Sci. Tech., 2004
40
Emergy of Selected Ecological Products� Current emergy of coal
� Based on sedimentary cycle that makes materials available near surface and compensates for erosion
� Exergy of coal = 29,302 J/g
� Global sedimentary cycle material flux = 9.36 E15 g/yr
� Transformity = (15.83 E24 sej/yr) = 5.8 E4 sej/J(9.36 E15 g/yr) x (29,302 J/g)
� Ancient emergy of global storages
� Product of replacement time and solar emergy per year
� Volcanic sedimentary rock (contains zinc, copper, lead)
� Turnover time = 1.154 E9 years
� Solar emergy per unit mass = 4.5 E9 sej/g
� Other numbers available in literature
41
Emergy of Selected Ecological Services� Surface winds (global average)
� Kinetic exergy = (1 W/m2)(3.15E7 s/yr)(5.1E14 m2/earth)= 1.61 E22 J/yr
� Transformity = (15.83 E24 sej/yr)/(1.61 E22 J/yr)= 983 sej/J
� River geopotential (global average)
� Geopotential work =(39.6E12m3/yr)(1000kg/m3)(9.8m/s2)(875m)
= 3.4 E20 J/yr
� Transformity = (15.83 E24 sej/yr)/(3.4 E20 J/yr)= 4.7 E4 sej/J
� Rain at sea level
� Amount = 1.09 E20 g/yr
� Exergy = 5 J/g (fresh water relative to sea water)
� Transformity = (15.83 E24 sej/yr)/(1.09 E20 g/yr)(5 J/g) = 2.9 E4 sej/J
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Typical Ecological Processes
� Atmospheric B (*/yr) τ (sej/*)
� Over ocean circulation 9.32 E23 J/yr 12
� Cumulus land circulation 9.45 E21 J/yr 485
� Mesosystems 1.73 E22 J/yr 912
� Temperate Cyclones 4.9 E21 J/yr 3230
� Ocean Processes
� Surface eddies 3.0 E20 J/yr 5.3 E4
� Sea Ice 9.0 E19 J/yr 1.76 E5
� Ocean circulation 8.5 E17 J/yr 1.87 E7
� Earth Processes
� Earth heat flux 2.74 E20 J/yr 5.8 E4
� Glaciers geopotential 1.38 E19 J/yr 1.38 E4
� Land, global cycle 9.36 E15 g/yr 1.69 E9
� Mountains 2.46 E15 g/yr 6.43 E9
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Emergy and Ecological Cumulative
Exergy� Cumulative exergy is equivalent to emergy for
� Same boundary
� Same allocation methods
� All inputs represented in solar equivalents
� Under above conditions
� Transformity = 1/ECDP
� Controversial aspects of emergy analysis need NOT be used for including ecological inputs
� Emergy theory of value
� Maximum empower (emergy/time) principle
� Using emergy/money ratio for economic inputs (addressed by thermodynamic input-output analysis)
� Transformity of ecological products and services may be used
Hau, J. L., and B. R. Bakshi, Env. Sci. Tech., 2004
44
Emergy-Based Metrics
� Net emergy = Y - F
� Analogous to profit
� Emergy Yield Ratio = Y/F
� Analogous to return on economic investment
� Environmental Loading Ratio = (F+N)/R
� Emergy Sustainability Index = (EYR)/(ELR)
W
Wastes
NNon-Ren
Resources
Sun EcosystemR1 Industrial
Processes
F
Y Economic
Resources
R2
Odum, 1996; Brown and Ulgiati, 1997
45
Solar vs. Coal-Based Electricity� Efficiency with ecological inputs is very different
� Indicator of sustainability?
Steam Turbine
Boiler heat exchanger
Condenser
Compressor
Parabolic through collectors
Electricity
Sunlight
271 kW
35 kW
52 kWSteam
Oil 54 kW
Exhausted
gases
Steam Turbine
Furnace
Condenser
Compressor
Coal Extraction
Electricity
35 kW
142 kW
Steam
Fuel
7 kW
Coal
142 kW
Air
0 kW
Ecological Processes
Ecosystem Inputs
6 x 106 kW
ICDPcoal= 23%
ECDPcoal= 0.0006 %
ICDPsolar= 13%
ECDPsolar= 13 %
46
Solar vs. Coal-based Electricity-
With Ecological Inputs� Ecological inputs must be considered for
� Holistic analysis
� Obtain insight into sustainability
� Transformities of natural resource inputs [Odum, 1996]
� Coal = 40,000 sej/J
� Fuel = 54,000 sej/J
� Sunlight = 1 sej/J
� CDP with ecological inputs
� CDPcoal= 0.0006% ; CDPsolar= 13 %
� Solar electricity is more efficient and sustainable
� Outstanding issues
� Ignores impact of emissions
� Uses arbitrary boundary, ignores indirect effects
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ICEC Analysis of
Chlor Alkali Water
Reservoir
Salt Mine H2SO4
Production
Brine Preparation
Plant
Electrochemical Cells
DenuderCl2 Cooler /
Drier
NaOH sol. Hydrogen Liquid
Chorine70%
H2SO4
1.455 (58) 3.305 (127)1.812
(46)0.42
(10)
0.23 (4) 0.50 (8)
0.098 (0.47) 3.08 (3.08) 60.31 (241) 3.19 (6.38)
Water Salt Coal Sulfur
0.28 (5)
1.82 (42)
0.24
(4)
1.14 (40) 1.53
(54)
3.35 (118) 1.74
(38)
0.09 (0.43)7.86
(212)
1.78
(48)
3.24 (88)
12.79 (220)3.24
(88)
0.008
(0.04)13.22 (220)
0.098 (0.47) 0.40 (3.08) 14.48 (241) 0.58
(6.38)1.26 (21)
AC
Production
Rectifier .
Cl2Compressor
CoolerCooler / .
Drier
Cooler
Legend:
Exergy in MJ
(ECEC in 1010sej)
1
10
2 3 4
5 6
7
89
11 12 13
# Unit number
� Manufacture NaOH and Cl2 from NaCl
� Exergy flow in Chlor-alkali process calculated by Szargut
� ICDP = 9.86%
Hau, J. L., B. R. Bakshi, Env. Sci. Tech., 2004
48
Application to Electricity LCA
� Considered electricity from Coal, Hydro, Wind, Geothermal, Natural Gas, Oil
� Traditional LCA indicates following order in terms of increasing life cycle impact
� Hydro
� Wind
� Geothermal
� Natural Gas
� Oil
� Coal
� Performed ThermoLCA at different scales
49
Hybrid ThermoLCA at Different Scales
- Electricity Generation
Process
Economy
Ecosystems
Exergetic Efficiency
Process Scale
Process
Economy
Ecosystems
ICDP
Economy Scale
Process
Economy
Ecosystems
ECDP
Ecosystem Scale
ECECICECExergy Anal.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
H W G N O C
Hydro
Wind
GeoNG
Oil
Coal
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
H W G N O C
Hydro
Wind
GeoNG Oil Coal
0.00
0.50
1.00
1.50
2.00
2.50
H W G N O C
x10-5
Hydro
Wind
Geo NG
Oil Coal
50
0.00
0.00
0.01
0.10
1.00
10.00
100.00
1000.00
Hydro Wind Geoth Oil Nat
Gas
Coal
Sustainability Index
Thermodynamic LCA of Electricity
� Sustainability Index = Return on Exergetic InvestmentEnvironmental load
� Results of ECEC ratios (based on inputs) match those of traditional Life Cycle Analysis (based on outputs)
� ECEC metrics do not seem to be sensitive to knowledge about emissions and their impact
51
Summary
� Accounting for natural capital is essential for sustainability
� Maintain critical natural capital
� Exergy analysis has been used for analysis of ecosystems
� Cumulative exergy consumed in ecosystems can indicate contribution of natural capital
� Ecosystems are not well understood
� Many opportunities for research and exploration