Application of Exergy-based Methods for Technical, Economic and ...

Application of Exergy-based Methods for Technical, Economic and Environmental Assessments of Nuclear Cogeneration Marc A. Rosen Past-President, Engineering Institute of Canada Professor, Faculty of Engineering & Applied Science University of Ontario Institute of Technology Oshawa, Canada

Outline     

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Exergy Exergy and efficiency Exergy and environment Exergy and economics Example: allocating cogeneration emissions Illustration: utility cogeneration in Ontario

Introduction 

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Efficiency of energy systems must be understood to increase it Energy a misleading efficiency measure Exergy can help improve  



understanding of efficiency efficiency

Exergy also helps efforts to improve economics, environment, sustainability

Objectives Improve understanding and appreciation of exergy  Show exergy can improve nuclear cogeneration 

EXERGY

What is Exergy? Maximum work obtainable in reference environment  Potential to cause change  Measure of 

quality  usefulness  value 



Merger of first and second laws

Key Exergy Feature I Not conserved (unless reversible)  “Destroyed” in real processes 

Key Exergy Feature II 

Energy forms differ: Electricity  Work  Heat  Cold  Matter 

Key Exergy Feature III All energy is equal, but not all energy is equally valuable

Exergy & Reference Environment 

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Exergy dependent on system and reference environment Exergy-environment tie has implications for environment

EXERGY AND EFFICIENCY

Exergy Analysis Helps analyse, design & improve  Clarifies: 

losses - locations, types, magnitudes  efficiencies - always approach to ideal, 

unlike for energy



Identifies margin available to design more efficient systems

Applications

All Energy Systems (and More) Use

Supply

Conversion

Illustration

Ideal Heat Engine Energy efficiency = 50% (yet device ideal)  Exergy efficiency = 100% 

Carnot engine operating between 600 K and 300 K

Illustration

Pickering Nuclear Power Plant

Illustration

Pickering Nuclear Plant Results

Energy outputs

Exergy outputs & consumptions

EXERGY AND ENVIRONMENT

Exergy and Environment 

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Exergy linked to environmental impact (measures departure from environment) Increasing exergy efficiency reduces environmental impact by reducing exergy losses  

emissions destructions

Exergy & Environment Relations

Exergy & Sustainability

EXERGY AND ECONOMICS

Exergy & Economics 

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Exergy normally consistent measure of economic value (energy sometimes is) Exergy-based economic analyses:   

recognize exergy, not energy, of value assign costs/prices to exergy variables help allocate economic resources optimally

EXAMPLE: ALLOCATING COGENERATION EMISSIONS

Cogeneration

Electricity

Fuel

Thermal Power Generation

Heat Recovery

Winter Heating Load

CO2 Allocation Methods for Cogeneration      

 

Energy content of products Exergy content of products Economic value of products Incremental fuel use to electricity production Incremental fuel use to heat production Shared emission savings between electrical and thermal energy Agreement Other factors

Allocation of emissions for Cornwall cogeneration and district heating system 120

Emissionallocation(%)

100

80

60

40

20

0 Based on exergy of products -20

Based on energy of products

Incremental fuel to electrical production

Incremental fuel to heat production

Shared emission savings

Emission allocation to thermal product Overlap for electricity/heat cost ratios of 1.5-2.5 Emission allocation to electrical product

Based on economic product values

Trigeneration Expanded Cogeneration

Electricity

Fuel

Thermal Power Generation

Heat Recovery

Winter Heating Load

Absorption Chiller

Summer Cooling Load

Extension to Economics 

Exergy can similarly be used to allocate costs among cogeneration products more rationally, yielding better pricing, for cogeneration and related processes

ILLUSTRATION: UTILITY COGENERATION IN ONTARIO

Ontario, Canada 

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13.5 million people 1 million km2 Industrial heart of Canada Large electric utilities (nuclear, hydro, fossil)

Scenarios for UtilityBased Cogeneration Basic cogeneration network Advanced cogeneration network

Residentialcommercial sector Industrial sector Combination

Results I Base-case annual energy use Base-case energy use (PJ)

Electricity

Gas & NGL's

Oil & Petrol.

Coal

Other

Utility sector Prov. (no util.) Province (total)

477 477

824 824

14 782 796

286 21 307

158 158

Uran- Total ium 640 640

940 2260 3200

% Reductions in values (Scenario A) Utility sector Prov. (no util.) Province (total)

5.3 5.3

2.8 2.8

0 0.5 0.5

17 0 17

0.5 0.5

6.8 6.8

10 2.4 4.6

Results II Base-case annual emissions to environment Material emissions (kilotons)

Utility sector Prov. (no utility) Province (total)

SO2

NOX

CO2 (1000)

CO

Particulates

VOC

Spent Uraniu m

321 1060 1380

92 526 618

32 132 164

4 3500 3504

11 837 849

0.5 775 775

1.04 1.04

Thermal Pollu -tion (PJ)

Radiation (1015 Bq)

591 591

11 11

% Reductions in values (Scenario A) Utility sector Prov. (no utility) Province (total)

17 1.2 4.9

17 0.7 3.2

17 1.2 4.2

17 0.7 0.8

17 0.3 0.5

17 0.5 0.5

6.8 6.8

15 15

6.8 6.8

Results III Heat demand satisfied by cogeneration (PJ yr-1) Scenario

A B C D E F

% reductions in some key utility parameters

% of fuel cogenerating for utility

Residen- Indust- Total Coal Uran- ElecCoal Urantial/ rial use ium tricity ium Commer use Produc-cial tion 46 206 0 0 46 206

0 0 26 54 26 54

46 206 26 54 72 260

17 41 13 16 20 47

7 30 3 5 9 35

5 24 3 6 8 30

12 77 6 13 22 100

8 49 4 2 12 49

Results IV Annual reductions in health & environmental effects/costs Cogeneration scenario

Base A

Health effects Mortality

Costs (million $)

Mor- Lost Health bidity work (1000 days)

18.9-25.7 1,043 1,691 3.0-4.2

165

286

Health and environment

Environmental effects Yield loss (%) Fish

Crops

Lost fishing (1000 days)

42.2

122.3

0.046

0.378

43.9

8.4

17.9

0.008

0.065

7.5

Implications 

Utility-based cogeneration beneficial for Ontario:     

substitute nuclear energy for other fuels increase efficiency reduce emissions and related health impacts reduce energy consumption reduce costs (observed elsewhere)

Conclusions 

Exergy can play significant role in   

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understanding and increasing efficiency improving economics reducing environmental impact

Exergy useful for  

nuclear energy systems nuclear cogeneration

Exergy Recognition