Using Life Cycle Assessment to
Determine Greenhouse Gas Emissions
from Bioenergy Systems
Timothy A. Volk
SUNY – ESF
SURE 2010, Syracuse, NY
November 4, 2010
Overview
• Brief overview of LCA
• LCA of willow biomass crops
• LCA of electricity generating systems
using different feedstocks:
– hybrid poplar
– wood residues
– coal
– natural gas
Assessing GHG Balances
• Need to use a consistent framework
• To compare systems need to:
– agree on the goal and scope
– use the same functional units
– have common boundaries
– use the same life cycle inventory and calculation
techniques
» Computation and quantification of inputs and outputs
» Allocation of inputs and outputs
» Conversion and weighting factors
(McMillan 2006)
(McMillan 2006)
(McMillan 2006)
Willow Biomass Production Cycle
Three-year old after
coppice
Site Preparation
Planting
Harvesting
One-year old after
coppice
Coppice
First year growth
Early spring after coppicing
LCA of Willow Crops - Boundaries
(Heller et al. 2003)
(Heller et al. 2003)
Primary Energy Use
Management Scenarios
sulfur coated urea requires more energy to manufacture than ammonia
(76 MJ kg−1 N vs.55 MJ kg−1)

(Heller et al. 2003)
GHG Flows in Willow Biomass Crops
LCA Results from Heller et al. (2003)
Current Study
CO2
(Mg CO2 ha-1)
Other GHG
(Mg CO2 eq ha-1)
Total
(Mg CO2
eq ha-1)
Diesel fuel
3.1
0.1
3.2
Agriculture Inputs
2.9
0.4
3.4
N2O from N fertilizer
3.9 (+ 3.2)
3.9
N2O from foliage
7.3 (+ 5.8)
7.3
Emissions
C Sequestration
Below ground
Soil C
Net Total
Harvested Biomass
-14.1
-14.1
0
0
-8.0
-499.2
11.7 (+ 9.0)
3.7
-499.2
CO2
(Mg CO2 eq ha-1)
Changes in Soil Carbon in Willow in
Biomass Crops Across a 19 Year
Chronosequence
Mg ha-1 in top 45 cm
200
180
160
140
120
100
80
60
40
20
0
0-yr old
5-yr old
12-yr old
14-yr old
19-yr old
(Pacaldo et al. 2010)
Above and Below Ground Biomass
60
belowground
biomass
50
aboveground
biomass
Mg ha-1
40
30
20
10
Previous estimate was 7.6 Mg ha-1
0
5-yr old
12-yr old
14-yr old
19-yr old
(Pacaldo et al. 2010)
Change in Below Ground Biomass
• 21 Mg ha-1 of below ground biomass
equated to 38.5 Mg CO2eq
– woody biomass is about 50% C
– Convert from Mg C to Mg CO2 by
multiplying by 44/12
• Previous estimate of 7.6 Mg ha-1 (14.1
Mg CO2eq) below ground biomass was
based on measurements in young
willow biomass crops
GHG Flows in Willow Biomass Crops
Current Study
LCA Results from Heller et al. (2003)
CO2
(Mg CO2 ha-1)
Other GHG
(Mg CO2 eq ha-1)
Total
(Mg CO2
eq ha-1)
Total
(Mg CO2 eq ha-1)
Diesel fuel
3.1
0.1
3.2
3.2
Agriculture Inputs
2.9
0.4
3.4
3.4
N2O from N fertilizer
3.9 (+ 3.2)
3.9
3.9
N2O from foliage
7.3 (+ 5.8)
7.3
7.3
-14.1
-14.1
-38.5
0
0
0
3.7
-20.8
-499.2
-499.2
Emissions
C Sequestration
Below ground
Soil C
Net Total
Harvested Biomass
-8.0
-499.2
11.7 (+ 9.0)
(Pacaldo et al. 2010)
A Comparison of the Environmental
Consequences of Power from Biomass,
Coal, and Natural Gas
Margaret K. Mann
National Renewable Energy Laboratory
Golden, Colorado USA
Purpose of Studies
• 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.
Systems Examined
Biomass IGCC
Indirectly-heated gasification
Dedicated hybrid poplar feedstock
Zero soil carbon sequestration in base case
Average coal
Pulverized coal / steam cycle
Illinois #6 coal - moderate sulfur, bituminous
Surface mining
Systems Examined
Biomass / coal 15% cofiring by heat input
cofiring Biomass residue (urban, mostly) into PC boiler
0.9 percentage point efficiency derating
Credit taken for avoided operations including
decomposition (i.e., no biomass growth)
Direct-fired biomass Biomass residue
Avoided emissions credit as with cofiring
Natural gas Combined cycle
Upstream natural gas losses = 1.4% of gross
Scope of Systems Studied
• Different studies
used common
–
–
–
–
Goal and scope
Boundaries
functional unit
life cycle inventory
and calculation
techniques
• Allows for a direct
Boundaries and material and energy flows in
electricity generation systems with coal and
biomass feedstocks (Mann and Spath 1999)
comparison of the
different processes
Energy Balance
• The total energy consumed by each
system includes the fuel energy
consumed plus the energy contained in
raw and intermediate materials that are
consumed by the systems
Net Energy Ratios
Life Cycle Energy Balance
30
net energy ratio
25
external energy ratio
20
15
10
5
0
Dedicated
biomass
IGCC
Average
PC coal
Coal/biomass
cofiring
Direct-fired
biomass
residue
NGCC
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?
Life Cycle Greenhouse Gas Emissions
1200
GWP (g CO2-equivalent / kWh)
1000
800
600
400
200
0
-200
-400
-600
Wind and
solar GHG
emissions
are in the
range of 10 –
60 g CO2equiv/kWh
Dedicated
biomass
IGCC
Direct-fired
biomass
residue
Average
PC coal
Coal/biomass
Cofiring
NGCC
Other Air Emissions
15
5
CH4
-5
Particulates
SOx
NOx
CO
NMHCs
-15
Average PC coal
15% Coal / biomass cofiring
Direct biomass residue
Dedicated biomass IGCC
NGCC
-41 g/kWh
Biomass IGCC also emits isoprene at 21 g/kWh
Summary
• Need to use a consistent and reliable method for
•
•
•
assessing GHG emissions from different energy
systems
Biomass systems based on short rotation woody
crops are C neutral or C sinks based on recent data
In a side by side comparison of electricity generating
systems, biomass has GHG emissions that are ~95%
lower than coal and ~90% less than natural gas
GHG emissions from biomass to electricity are similar
to wind and solar electricity generating systems
Questions