How do we assess the efficiency and renewability of … Jo.pdf1 How do we assess the efficiency and renewability of biofuel production? An exergy-based approach J. Dewulf, H. Van Langenhove

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How do we assess the efficiency and renewability of biofuel

production? An exergy-based approach

J. Dewulf, H. Van Langenhove and B. Vande VeldeResearch group ENVOC

Ghent University, Belgium

[email protected]

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Why do we need biofuels?

- Fossil resources are depleting rapidly

- Fossil resources end up in environmental threats:- CO2 contributes to global warming- smog problems in urban areas- tropospheric ozone formation- particulates formation

- Scenarios from- academia (Graedel in Yale, Van Bekkum in Delft) - industry (Shell)

expect a 50/50 non-renewables/renewables in 2040-2050

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Are biofuels the ultimate solution?

At a first glance:

Closing cycles = reduction in resource depletion and emissions

BUT: Modern agriculture:Pesticides & Fertilizer manufacturing

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BUT: Modern agriculture:Pesticides & Fertilizer manufacturing Tractors & fuels

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Agricultural equipment

7

8



Combines

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Combines

Maintenance & Spare parts

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... and biofuel manufacturing

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Key factors in sustainability assessment of energy supply through biofuels:

- Efficiency of the supply: solar energy and land area required- Extent of use of non-renewables: renewability degree

How to do an assessment ?- Step 1: Detailed process analysis:

inventory: see LCA approach- Step 2: Quantification of resource use and products (biofuels)

in exergy analysis- Step 3: Calculation of indicators based on the exergy analysis,

taking into account allocation issues

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Key factors in sustainability assessment of energy supply:

- Efficiency of the supply: solar energy and land area required- Extent of use of non-renewables

How to do an assessment ?- Step 1: Detailed process analysis

functional unit/system boundaries-Step 2: Quantification of resource use and products (biofuels)

allocation-Step 3: Calculation of sustainability indicators

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Method of analysis: Exergy analysis

2nd law of thermodynamics: exergy is maximum amount of work that can be obtained from a resource

Process

Feeds Products

Useful heat

Power Waste heat/products

Physical

Chemical

LossPhysical

Chemical

ExergeticefficiencyExin Exout

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Exergy analysis:

- Main advantages:- universal- scientifically sound- one single scale for all type of energy, materials- allows straightforward allocation

-Main limitations:- Allows resource assessment rather than emissions

assessment- Not easy to communicate

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Analysis of three case studies:

- Ethanol from corn (Italy)

- Rapeseed Methyl Ester = RME from rapeseed (Sweden)

- Soybean Methyl Ester = SME from soybean (USA)

Important selection criterion:

Detailed accessible process data

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Step 1: Agricultural production

Agriculture

Straw Rapeseed

Seeds

Nutrients PesticidesSolar input

Fuels

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Step 2: Industrial biofuel production

RapeseedTransport

Drying, Extraction,Refining

Rape cake Rapeseed oil

Esterification

RMEGlycerol

Fuel

Electricity

Fuel

Oil

Steam

HexaneMethanol

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Agricultural Rapeseed Production: inputs and outputs related to 1 ha. All data are in GJ of exergy ha-1 yr-1

2.62

Straw

Fertilizers

Seed Solar radiation

Fuels

Pesticides

Rapeseed

32 1000.19

7.78 10³ 3.29 10³2.74

4.03 104 3.21 107 6.93 10²

0.029

86.0 62.1

Agriculture

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Agricultural Rapeseed Production: inputs and outputs related to 1 ha. All data are in GJ of exergy ha-1 yr-1

2.62

Straw

Fertilizers

Seed Solar radiation

Fuels

Pesticides

Rapeseed

321000.19

7.78 3.292.74

40.3 32100 0.69

0.029

86.0 62.1

Agriculture

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Efficiency (GJ biofuel/ha) : Corn > Rapeseed > Soybean

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Input of non-renewables :

Exergy (%)

22

7

944

18

agricultural stage

drying, cleaning andstorageextraction and refining

esterification

transport

Cumulative Exergy (%)

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4

14

57

8

agricultural stage

drying, cleaning andstorageextraction andrefiningesterification

transport

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Input of non-renewables :

Exergy (%)

22

7

944

18

agricultural stage

drying, cleaning andstorageextraction and refining

esterification

transport

Cumulative Exergy (%)

17

4

14

57

8

agricultural stage

drying, cleaning andstorageextraction andrefiningesterification

transport

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Agriculture

SolarIrradiation

Non-renewableAgriculturalresources

32100 10700

StrawNon-renewable

Agriculturalresources

Rapeseeds

Industrialconversion

Meal

RME

1.18 104 5.38

2.00 104 5.26

62.1

86.0

32.7

47.5

32100

Glycerol2.10

0.39 104 1.80

1.15 104 3.04

Non-renewableIndustrialresources

49.6

10700


Overall RME production chain: inputs and outputs related to 1 ha. All data are in GJ of exergy ha-1 yr-1

Allocation of inputsto biofuels:

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Agriculture

SolarIrradiation

Non-renewableAgriculturalresources

32100 10700

StrawNon-renewable

Agriculturalresources

Rapeseeds

Industrialconversion

Meal

RME

5.38

5.26

62.111.8

86.0

20.032.7

47.5

32100

Glycerol2.10

3.9 1.80

3.04

Non-renewableIndustrialresources11.5

49.6

10700


Overall RME production chain: inputs and outputs related to 1 ha. All data are in GJ of exergy ha-1 yr-1

Allocation of inputsto biofuels:

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15.4

4.84

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How to quantify non-renewable input:Definition of Breeding Factor:

Biofuel delivered BFex =

Allocated non-renew. Resources consumed in theagricultural and industrial biofuel production chain

Products delivered Overall BFex =

Non-renewable Resources consumed in the agricultural and industrial biofuel production chain, and agricultural and industrial supplychain

Products delivered Overall BFex =

Non-renewable Resources consumed in theoverall industrial metabolism

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Biofuel delivered Overall BFex =

All non-renew. Resources consumed in the agricultural and industrial biofuel production chain, and agricultural and industrial supplychain


All non-renew. Resources consumed in theoverall industrial metabolism

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All non-renew. Resources consumed in the agricultural and industrial biofuel production chain, and agricultural and industrial supplychain


All non-renew. Resources consumed in theoverall industrial metabolism

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Renewability : Corn > Rapeseed,Soybean

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Conclusions:

-Exergy analysis enables a straightforward efficiencyand renewability analysis

- Biofuels contribute to emission reduction and reduction of thedepletion of fossil resources

- However, from a detailed exergy analysis:Difference in efficiency

- Biofuels make use of non-renewables to a different extent

- There is a need to assess to what degree biofuels make useof non-renewables

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Thank You

Contact:

Jo Dewulf at [email protected]

Details of study:

Dewulf et al., ES&T, 39, 3878-3882, 2005
mailto:[email protected]

Documents

How do we assess the efficiency and renewability of … Jo.pdf1 How do we assess the efficiency and renewability of biofuel production? An exergy-based approach J. Dewulf, H. Van Langenhove