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1
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
2
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
3
4
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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BUT: Modern agriculture:Pesticides & Fertilizer manufacturing Tractors & fuels
Agricultural equipment
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BUT: Modern agriculture:Pesticides & Fertilizer manufacturing Tractors & fuels
Agricultural equipment
Combines
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BUT: Modern agriculture:Pesticides & Fertilizer manufacturing Tractors & fuels
Agricultural equipment
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 (%)
17
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
Non-renewableIndustrialresources
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
Non-renewableIndustrialresources
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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27
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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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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
Biofuel delivered Overall BFex =
All non-renew. Resources consumed in the agricultural and industrial biofuel production chain, and agricultural and industrial supplychain
Biofuel delivered Overall BFex =
All non-renew. Resources consumed in theoverall industrial metabolism
31
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
Biofuel delivered Overall BFex =
All non-renew. Resources consumed in the agricultural and industrial biofuel production chain, and agricultural and industrial supplychain
Biofuel delivered Overall BFex =
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
34
Thank You
Contact:
Jo Dewulf at [email protected]
Details of study:
Dewulf et al., ES&T, 39, 3878-3882, 2005
mailto:[email protected]