Exergy II T. Gutowski 2.83 and 2.813 READINGS: Gutowski, T.G., et - PowerPoint PPT Presentation

Exergy II T. Gutowski 2.83 and 2.813 READINGS: Gutowski, T.G., et al., Thermodynamic Analysis of Resources Used in Manufacturing Processes, Evniron. Sci. Technol., 2009, 43 (5). Gutowski, T.G., Materials Separation and Recycling Chapter for Thermodynamics and the Destruction of Resources, B.R.Bakshi, T.G.Gutowski, and D.P.Sekulic, Camb. U. Press. 2

Exergy Accounting • The Good: • Rigorous framework • Focus on system definition • Aggregate fuel and non-fuel materials, heat and work interactions • Analysis tool 3

Exergy Accounting • The Not So Good: • Any aggregation scheme is subject to trade-offs • For fuels, many of the same answers can be obtained from LHV • It is not a well known term 4

Aggregation (Valuation) Schemes are needed, but… • Price • Weight • Lower Heating Value • “Energy Equivalent” • Exergy • Others… 5

Today: Applications • Cumulative exergy accounting – Fuels, η II , EROI – Manufacturing processes, η II & Actual MJ/kg • Minimum work of separation – Exergy of a mixture • Economic Analogies – Mining and extraction – Recycling 6

General Framework & B W , in & B W , out & B Q , in & & B Q , out B loss & B in & B out Data requirements: stoichiometrically balance reaction equation,or an inventory of inputs and outputs 7

Cumulative Exergy Accounting Energy Conversion Process & B W , in & B W , out & B Q , in & & B Q , out B loss & B in Manufacturing Process & B out & B W , in & B W , out & B W , in & B Q , in & & B W , out & B Q , out B loss & & B in B Q , in & & & B Q , out B out B loss & B in EXERGY LCA & B out Materials Production Process 8

Exergy Homework • 9. What is the maximum work one could obtain from burning the following fuels with oxygen: octane? methane? methanol? hydrogen? How much CO 2 is generated for each? 9

Burning Octane 2C 8 H 18(l) + 25 O 2(g)  16 CO 2(g) + 18H 2 O (g) 2(5413.1) + 25(3.97) - 16(19.87) - 18(9.5) = Δ B Δ B = 10,436.53 kJ 10,436.53 = 45.8 MJ 2[(8 x 12) + 18]= 228g kg 10

Exergy Value of Fuels & B W , in Useful Effect & B W , out & B Q , in & & B Q , out B loss & B in & B out Octane, Oxygen Carbon Dioxide, Water Vapor B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss 11

Gasoline Production & B W , in & B W , out Energy Inputs & B Q , in & & B Q , out Heat Out B loss & B in & B out Crude Oil Gasoline, other By-products B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss Fractional distillation and catalytic cracking require energy, (exergy), say α x100% LHV or Exergy for production 12

How to estimate α ? • If this is an established technology you can look up the research results • If this is a new technology you will need a model or an analogy • In this case gasoline production has been going on for some time. Values of α vary depending upon the the nature of the crude oil and the technology, but α ≈ 0.15 13

Cumulative exergy accounting & B W , in & & B W , in B W , out & B W , out & B Q , in & B Q , in & & B Q , out B loss & & & B Q , out B in B loss & B in & B out & B out Fuel Production Energy Production B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss Examples: energy to produce Gasoline, Ethanol, Hydrogen etc 14

Alternative Points of View (Assume α = 0.15) • exergy out/exergy in • energy out/energy in • Second law efficiency • Energy return on energy investment • Roughly, • EROI 1/0.15 = 6.7 • 1/1.15 = 0.87 • You always lose something! A gift from nature 15

EROI Accounting & B W , in & & B W , in B W , out & B W , out & B Q , in & B Q , in & & B Q , out B loss & & X & B Q , out B in B loss & B in & B out & B out Fuel Production Energy Production B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss Examples: energy to produce Gasoline, Ethanol, Hydrogen etc 16

Exergy Accounting & B W , in & & B W , in B W , out & B W , out & B Q , in & B Q , in & & B Q , out B loss & & & B Q , out B in B loss & B in & B out & B out Fuel Production Energy Production B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss B in + & & B W , in + & B Q , in = & B out + & B W , out + & B Q , out + & B loss Examples: energy to produce Gasoline, Ethanol, Hydrogen etc 17

Burning Methane CH 4 + 2O 2  CO 2 + 2H 2 O Δ B = 831.7 + 2(3.97) – 19.87 – 2(9.5) = 784.84 kJ 784.9kJ = 49 MJ 12 + 4 = 16 Kg 18

Burning Methanol 3 CH OH O CO 2 H O + � + 3 2 2 2 2 3 B 718 . 5 ( 3 . 97 ) 19 . 9 2 ( 9 . 5 ) 685 . 6 kJ � = + � � = 2 685 . 6 kJ MJ 21 . 4 = 12 4 16 kg + + 19

Burning Hydrogen 2H 2(g) + 0 2(g)  2H 2 0 (g) Δ B = 2 X 236.1 + 3.97 - 2 x 9.5; Δ B = 457kJ Maximum exergy out= 457.17kJ = 114 MJ 4g kg 20

Calculated Exergy and Reported Heating Values Chemical Calculated CO 2 Fuel Heat of Ref Max Exergy generated Combustion MJ/kg* gCO 2 /MJ MJ/kg Carbon 33 112 Coal 18-29 Smil anthracite 30-33 BCCA Octane 46 68 Gasoline 46-47 Smil Methane 49 56 Nat. gas 33-37 Smil 38-50 Web Oil 42 75 Fuel oil 42-44 Smil Hydrogen 114 0 114 Smil Methanol 21 64 21

Making Hydrogen 2H 2(g) + 0 2(g) ← 2H 2 0 (l) Δ B = 2 X 236.1 + 3.97 - 2 x 0.9; Δ B = -475kJ Minimum work required = 475kJ = 119 MJ 4g kg The minimum work to produce the hydrogen is larger than the maximum work obtainable from combustion! 22

How could hydrogen work? From an energy point of view, you From an energy point of view, you could produce H2 from wind, or PV. could produce H2 from wind, or PV. This still leaves a number of issues: leaves a number of issues: This still Infrastructure development, Infrastructure development, Storage, and Safety lead the list. Storage, and Safety lead the list. 23

Hydrogen is an energy Carrier Not an energy source 24

EROI data Cutler Cleveland, Energy, 2006 Depends on “Quality” of Resource and Technology 25

26 From Hau and Bakshi es&t 2004

Exergy equivalents, deWulf et al ES&T 08 27

Mfg Systems Manufacturing Systems as open thermodynamic systems Gutowski et al ES&T 2009 28

Balances for Mfg Process dm Mass & & MF ( N M ) ( N M ) � � = � i , in i i , out i dt i 1 i 1 MF MF = = dE & & & Q MF Q MF W MF MF � � � Energy = � � + ECMF 0 ECMF dt i & & & mat prod res H H H + � � MF MF MF & & dS Q MF Q MF � � & & & & Entropy S mat S prod S res S MF ECMF 0 = � � + � � + MF MF MF irr , MF dt T T i i 0 29

Work Rate for Mfg Process in Steady State res ) � & mat ) MF � = (( & prod + & & W ECMF H MF H MF H MF res ) � & mat ) prod + & � T 0 (( & S MF S MF S MF � � 1 � T 0 MF � + T 0 & & � Q ECMF S irr , MF � � � T i � � i > 0 30

Exergy and Work B ( H T S ) ( H T S ) = � � � o o o Branham et al IEEE ISEE 2008 res ) � & mat ) MF � = (( & prod + & & W ECMF B MF B MF B MF � � 1 � T 0 MF � + T 0 & & � Q ECMF S irr , MF � � � T i � � i > 0 Examples: plastic work, melting, vaporizing etc. 31

Work Rate for Mfg Process & & & & MF prod res mat ph W (( B B ) B ) � = + � ECMF MF MF MF n n & & ch prod ch res ( b N ) ( b N ) � � + + � i i MF i i MF i 1 i 1 = = n T � � � & & & ch mat MF ( b N ) 1 0 Q T S � � � � � � + � � i i MF ECMF 0 irr , MF T � � i 1 i 0 i = > Here all chemical exergy terms (b ch ) are at T o , P o Branham et al IEEE ISEE 2008 32

Second Law Eff i ciency; Degree of Perfection B useful output � = p B in 33

Batch Induction Melter Inputs and Outputs Ductile Iron – Batch Electric Induction Exergy Analysis Metallic Input Materials Ductile Iron Melt and Alloys 1000 kg 1024 kg Slag Input Electricity 40 kg 5,393 MJ Dust Natural Gas Preheater 0.26 kg 0.025 kg Boundaries are drawn around the entire facility so that all components are at standard pressure and temperature 34