Chapter 10 - Biofuels
Introduction
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Existing standards for carbon accounting
Forestry schemes as carbon offsets
Biomass energy in place of fossil fuels
LCA role in carbon accounting
Carbon Accounting Standards and
Tools
• ISO 14064 on methods to account for carbon
• Also Greenhouse Gas Protocol
– Determining boundaries for GHG accounting
– Classification of emissions
– Identification and calculation of GHGE
– Rules for changing base year inventories
– Rules for tracking emissions over time
– Rules for assessing uncertainty
– Rules for GHGE reporting
Emissions Are Classified According
• Scope 1 – direct emissions with the boundary of
an organization, i.e. fuel combustion
• Scope 2 – indirect emissions such as purchased
electricity
• Scope 3 – other indirect emissions due to
activities in scope 1 and 2, i.e. mining,
transportation, land use changes
• Large databases are available (459 pages)
– epa.gov/climatechange/emissions/usinventoryreport.
html
Example Problems
• Difficulties with 3 scopes
– Business traveler flying for GM
– Building cars is under scope 1 and 2 (could also be
3)
– Airline burns fuel – scope 1 (this could also go out
into scope 2 and 3)
– How do we handle the business traveler?
10.2 Carbon Offsets
• Simple example – I plant trees to offset my
emissions
• Carbon cycle
– Complicated
– Uncertainty at multiple levels
– Hard to argue fallow land will not fix some carbon
(used for agriculture or go through succession)
– Assume land use change in perpetuity
– Soil changes (methane, N2O)
10.2.1 Forests as Carbon Sinks
• Continuous carbon flux
• After harvest forests are emitters for 20 to 40
years
• Only sinks when they are well established
• Land use prior to and after reforestation
– Forest land typically higher C sequestration than
ag
– Need to watch for N2O and CH4 emissions
Other Issues
• End use of forestry products
– Landfill, burning, etc.
• Increase biodiversity – unless a monoculture
• Risks of forest fire – big emitter of carbon
• Young trees use lots of water
10.3 Low Carbon and LCA
• Biomass substitute for fossil fuel systems
• Complex issue, fossil energy always needed for
biomass
• Can’t assume that burning biomass always
GHG neutral
• IPCC considers biogenic emissions do not
count towards GHG
• Considerable uncertainty though
10.3.1 Biomass in Energy
• Watch boundary
– Need full emissions
• Mining, transportation, processing, etc.
• Fertilizers, chemicals, etc.
– Site versus source
• In power generation, what does biomass
replace?
– Off-grid a little easier, whatever I am burning
– Grid system, what gets replaced?
Biomass in Power Generation
• Should biomass replace old, inefficient power
plants that generate the most expensive
electricity?
• Some studies have said the least cost fossil
energy system with lowest environmental
impacts should be compared with biomass
Biomass in Power Continued
• Could look at marginal generator
– Natural gas turbines used for peaking power
– Addition of a new biomass power plant would
displace the marginal generator (likely natural gas
with lower emissions)
• Areas with limited power supply (maybe China
or India) adding biomass power might
increase electricity consumption
– Probably no GHG reduction, would consider the
marginal effect (biomass vs fossil)
Other Arguments
• Forests sequester CO2 from fossil and biogenic
sources
• Therefore CO2 from biomass burning would
not be neutral
10.3.2 Biomass Assessment Tools
• Numerous tools (EU has some) US has GREET
developed by Argonne National Lab
• Review of biomass LCA studies for ethanol
found large variations in results
– Process residue handling and fuel combustion big
differences
– Generally resulted in resource and global warming
reductions
– Often resulted in higher acidification, human
toxicity, ecological toxicity
10.5 Future Aspects of LCA
• Several GHG accounting standards
• Still considerable uncertainty and variations in
methodology
• Issues with boundaries and co-products
• Policy and behavior issues
– Will people consume more because of planting a
tree or additional resource consumption is jutified