Margaret K' Mann

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Margaret K. Mann National Renewable Energy
Laboratory Golden, Colorado USA
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Outline of Presentation

• Short discussion of life cycle assessment (LCA)
• Purpose of LCAs conducted
• System descriptions
• Biomass IGCC
• Average coal
• Coal/biomass cofiring
• Natural gas combined cycle
• Comparative Results
• Energy
• Greenhouse gases
• Other air emissions
• Resource consumption

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Life Cycle Assessment Definition

• LCA is
• a systematic analytical method
• used to quantify the environmental benefits and
  drawbacks of a process
• performed on all processes, cradle-to-grave,
  resource extraction to final disposal
• ideal for comparing new technologies to the
  status quo
• helps to pinpoint areas that deserve special
  attention
• reveals unexpected environmental impacts
  (no show-stopping
  surprises)

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System Concept in Life Cycle Assessment
Life cycle system boundary
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Three Components of LCA

• INVENTORY
• Mass and energy balances gtgt air, water, and solid
  waste emissions, energy and resource consumption
• IMPROVEMENT
• Reduce environmental burden through process
  design changes, material substitution, recycle,
  etc.
• IMPACT ASSESSMENT
• Characterize environmental effects
• Less-is-better
• Stressor categories climate change gases,
  carcinogens, resource depletion, ozone precursors
• Weighting factors e.g., methane 21 CO2
• Valuation Assign values to each effect to
  achieve an overall environmental score or set of
  scores

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Purpose of Studies

• Biomass LCA was conducted to answer common
  questions
• What are the net CO2 emissions?
• What is the net energy production?
• Which substances are emitted at the highest rate?
• What parts of the system are responsible for the
  greatest impacts?
• What should biomass RD focus on?
• Coal and natural gas LCAs the foundation for
  quantifying the benefits of biomass power.
• Direct-fired biomass system describes current
  biomass power industry.
• Cofiring LCA examined near-term option for
  biomass utilization.
• Each assessment conducted separately - common
  systems not excluded.

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Systems Examined
Indirectly-heated gasification
Biomass IGCC
Dedicated hybrid poplar feedstock
Zero carbon sequestration in base case
Pulverized coal / steam cycle
Average coal
Illinois 6 coal - moderate sulfur, bituminous
Surface mining
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Carbon Cycle (GHG Emissions)

• Example flows
• Biomass energy crop - photosynthesis, carbon
  sequestration in soil
• Biomass residue - avoided decomposition emissions
• Coal - coal mine methane, coal mine waste
• Natural gas- fugitive emissions, leaks
• General - incomplete combustion, upstream fossil
  fuel consumption

Key question On a life cycle basis, what are the
net greenhouse gas emissions of these systems?
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CH4
Particulates
SOx
NOx
CO
NMHCs
-5
-15
Average PC coal
15 Coal / biomass cofiring
Direct biomass residue
Dedicated biomass IGCC
NGCC
-41 g/kWh
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500
450
Average PC coal
400
15 cofiring
350
Direct-fired residue biomass
300
Dedicated biomass IGCC
NGCC
250
200
150
100
Coal
Limestone
Oil
Natural Gas
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Summary

• Greenhouse Gases
• Biomass IGCC nearly zero net GHGs
• Average coal system 1,000 g CO2-equiv/kWh
• NGCC system 500 g CO2-equiv/kWh
• Todays biomass systems remove GHGs from
  atmosphere
• Energy
• Coal and natural gas negative system energy
  balance
• Even neglecting the energy content of coal and
  natural gas, biomass systems are more energy
  efficient
• NGCC natural gas extraction and losses account
  for 21 of total energy
• Air emissions
• Biomass few particulates, SO2, NOx, and methane
• Coal upstream CO and NMHC emissions lower
• NGCC system methane emissions high
• Resource consumption Biomass systems ltlt fossil
  systems
• Cofiring