Scale up of Algae Biofuels: Challenges and Opportunities
Christopher HartoArgonne National Laboratory
Purpose
Take a very wide perspective look at algae biofuel systems Identify major challenges to scale up propose potential pathways for overcoming them
Environmental Science Division, IPEC 17th International Petroleum & Biofuels Environmental Conference
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(DOE)(DOE)
Outline
Economic Input-Output LCA Nutrient mass balance (C, N, P) Challenges and future research areas
Environmental Science Division, IPEC 17th International Petroleum & Biofuels Environmental Conference
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Algae Growth Requirements
Land/solar energy Water Energy Carbon Nitrogen Phosphorus
Environmental Science Division, IPEC 17th International Petroleum & Biofuels Environmental Conference
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Economic Input-Output LCA
Analysis based upon 1996 technoeconomic analysis by NREL at the conclusion of aquatic species program (Benemann and Oswalt 1996)
Uses 1997 US model in EIOLCA.net Co-Products allocated based on energy content Impacts Considered
– CO2
– Energy
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System Specifications
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400 ha, unlined, open pond Paddle wheel mixing Harvest through flocculation and settling along with
3 phase centrifuge Extraction through hot oil emulsion in centrifugation
step Non-lipid biomass converted to methane through
anaerobic digestion Energy output 25% methane, 75% lipids N recycle 50%, P recycle 75% Productivity 30 g/m2/day and 50% lipids content
Results
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GWP g CO2e/gal Energy MJ/gal
Capital Impacts 149 1.7
Operating Impacts 3389 34.2
Total Impacts 3539 35.9
Diesel Fuel 10100 146
Output/Input 0.35 4.1
Results Breakdown
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Global Warming Potential
4%
53%20%
5%
1%
4%
13%
Capital powernutrientsmaintainancelaborflocculantwaste disposal
Energy Consumption
5%
61%
18%
6%
1%5%
4%
Capital powernutrientsmaintainancelaborflocculantwaste disposal
Sensitivity Studies
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Scenario Name Productivity Lipid % Allocation Method N Recycle % P Recycle %
Baseline 30 50 Energy (methane) 50 75
No Recycle 30 50 Energy (methane) 0 0
Displacement 30 50 Displacement (electricity) 50 50
Electricity Co-Product 30 50 Energy (electricity) 50 50
Double Productivity 60 50 Energy (methane) 50 75
Half Productivity 15 50 Energy (methane) 50 75
Half Lipids 30 25 Energy (methane) 50 75
Achievable EA 15 25 Energy (methane) 50 75
Achievable DA 15 25 Displacement (electricity) 50 75
Achievable NR 15 25 Energy (methane) 0 0
Sensitivity Studies
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Sensitivity Studies
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Nutrient Mass Balances
Look at impact of scale up on flows and availability of C, N and P Use simple mass balance approach Assumptions:
– 100% utilization efficiency
Environmental Science Division, IPEC 17th International Petroleum & Biofuels Environmental Conference
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Source C% N% P%
shastri 2005 (Synechocystis) 51 11.3
Grobbelaar 2004 (microalgae) 51 6.6 1.3
Powell 2008 (Scenedesmus spp.) 0.4 to 3.2
Carbon
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Carbon Analysis
Due to day/night cycle and fraction point sources likely only 20-30% of total emissions viable for feedstock
Global carbon agreements may reduce total by as much as 80% of current flows
Only 4-6% of current carbon emissions likely available for long run algae fuels production
Realistic long term US algae fuel production ~ 1,000,000 barrels per day (5% of current liquid fuels consumption)
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Carbon Mass Transfer
In absence of point sources, growth likely to be mass transfer limited
At current atmospheric CO2 concentration and 30% lipids content, CO2 from 1,100,000 m3 of air must be extracted to produce 1 barrel of algae oil
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Algae Lipid Concentration Volume of Air at STP Required to Supply Carbon to Produce One Gallon of Fuel (m3)
15% 52,00030% 26,00050% 16,00070% 11,000
Nitrogen
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Nitrogen Analysis
Nitrogen probably a soft limit as fertilizer production can be scaled up reasonably easily using Haber-Bosch process– H2 for process from methane produced by biomass or solar electrolysis
Alternative N sources from NOx in flue gas, wastewater or nitrogen fixing organisms
Increasing demand will probably spill over and affect agricultural markets through fertilizer price increases
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Phosphorus
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Phosphorus Analysis
P uptake can vary by order of magnitude depending on conditions
Typically must be supplied in excess due to tendency to complex with metal ions and become unavailable to organisms
P is mined with limited supplies in very few places – 50% global reserves in Morocco
Total P reserves maybe 50-100 years Like N, competes with agriculture for nutrient supply
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Key Research Areas
Nutrient utilization efficiency and recycling processes– Use of organisms that excrete product– Organisms with low N and P demands
Better understand potential for atmospheric carbon mass transfer
Improve understanding and management of global P cycle Seek synergies and ways to close loops, use waste streams as
nutrient sources
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Agricultural Run Off and Ocean Dead Zones? Opportunities? Rivers concentrate agricultural runoff w/ high N and P
concentration– Can they act as a water AND nutrient source?
Massive Algal blooms occur which subsequently die – Can they be harvested?
Dead organisms sink to bottom and decompose using up O2 supply creating anoxic conditions– If nutrients or organisms removed before death, is there still harm to
the ecosystem?
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Thank You!
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