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1

Exergy and Natural Capital

Bhavik R. Bakshi

Dept. of Chemical & Biomolecular Engineering

The Ohio State University, Columbus, OH 43210

bakshi.2@osu.edu

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 …

21

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

24

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

25

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

26

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 ...

...

32

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

37

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

38

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

42

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

43

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

47

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