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Life cycle assessment of biochar systems
Kelli G. Roberts, Brent A. Gloy, Stephen Joseph,
Norman R. Scott, Johannes Lehmann
Department of Crop and Soil Sciences, Cornell University
Northeast Biochar Symposium
UMass Amherst
November 13, 2009
What is Life Cycle Assessment (LCA)?
Methodology to evaluate the environmental burdens
associated with a product, process or activity throughout
its full life by quantifying energy, resources, and emissions
and assessing their impact on the global environment.
LCA has been standardized by the ISO (International
Organization for Standardization).
materials manufacture use end of life
Life cycle of a product
Goals of the LCA
To conduct a cradle-to-grave analysis of the
energy, greenhouse gas, and economic inputs
and outputs of biochar production at a large-scale
facility in the US.
To compare feedstocks (corn stover, yard waste,
switchgrass).
Scope: the functional unit
The functional unit:
A measure of the performance or requirement for a
product system.
Provides a reference so that alternatives can be
compared.
Our functional unit:
The management of one tonne of dry biomass.
System boundaries
Fossil fuels
production
Pyrolysis facility
Electricity
production Heat exhaust
Biochar T Soil
T application
Biomass collection Shredding Drying Slow pyrolysis
Syngas
T heat
T (-)
product
T
Farm equipment, Fertilizers
agrochemicals (-) T (-)
Construction Natural gas production
Compost materials & combustion
Dashed arrows with (-) indicate avoided processes.
The “T” represents transportation.
Biochar with heat co-product
Installation at Frye Poultry Farm,
West Virginia
capacity of 300 kg dry litter hr-1
www.coaltecenergy.com
LCA of biochar – industrial scale
Plant throughput 10 t dry biomass hr-1
Runs at 80% capacity
The slow pyrolysis process has four co-
products:
Biomass waste management
Biochar soil amendment
Bioenergy heat production
Carbon sequestration
Energy flows: feedstock to products
Sankey diagram, per dry tonne stover
Feedstocks
Corn stover
Late and early harvest (15% and 30% mcwb).
Second pass collection, harvest 50% above ground biomass.
Yard waste
45% mcwb
No environmental burden for production.
Assumed to be diverted from large-scale composting facility.
Switchgrass
12% mcwb
Scenarios A and B to capture range of GHG flows associated
with land-use change
Feedstocks (cont.)
Switchgrass A
Lifecycle emissions model (Deluchi), informally models land-
use change.
Assumes land conversion predominantly temperate grasses
and existing croplands, rather than temperate, tropical or
boreal forests.
Net GHG of +406.8 kg CO2e t-1 dry switchgrass harvested.
Switchgrass B
Searchinger et al (2008) global agricultural model.
Assumes land conversion in other countries from forest and
pasture to cropland to replace the crops lost to bioenergy
crops in the U.S.
Net GHG of +886.0 kg CO2e t-1 dry switchgrass harvested.
Deluchi, M. “A lifecycle emissions model (LEM)”; UCD-ITS-RR-03-17; UC Davis, CA, 2003.
Searchinger, T.; et al. Science 2008, 319 (5867), 1238-1240.
Pyrolysis and biochar parameters
Feedstock properties, pyrolysis process yields, and biochar properties for various
biomass sources
Late Early Switch Yard
Property stover stover grass waste
Moisture content, wet basis 15% 30% 12% 45%
Ash content (wt.% DM) 5.6 5.6 4.6 4.5
C content of feedstock
45 45 48 47
(wt.% DM)
Lower heating value
16000 16000 17000 18000
(MJ t-1 DM)
Feedstock to heat energy
37%
efficiency
Yield of biochar (wt. %) 29.60 29.60 28.80 29.63
C content of biochar (wt.%) 67.68 67.68 63.09 65.89
Stable portion of total C in
80%
biochar
Improved fertilizer use efficiency
7.2%
(for N, P, K)
Reduced soil N2O emissions
50%
from applied N fertilizer
Energy balance
Energy (MJ t -1 dry feedstock)
0 2000 4000 6000
stover cons. Net = + 4116
Late
agrochems
gen. field ops
Net = + 3044 drying
cons.
stover
Early
chipping
gen.
biomass trans
Switch
Net = + 4899 plant constr
grass
cons.
other
gen.
syngas heat
Net = + 4043
waste
cons.
Yard
avoid fos fuel
gen. avoid compost
All feedstocks are net energy positive.
Switchgrass has the highest net energy.
Agrochemical production and drying consume largest proportion of energy.
Biomass and biochar transport (15 km) consume < 3%.
“Other” category includes biochar transport, plant dismantling, avoided fertilizer
production, farm equipment, and biochar application.
GHG emissions balance
-1
Greenhouse gases (kg CO 2e t dry feedstock)
0 300 600 900
stover
emit. Net = - 864 LUC & field
Late emiss.
stover reduct. agrochems
Net = - 793
Early
emit. field ops
reduct. other
waste grass B grass A
Net = - 442
Yard Switch Switch
emit. stable C
reduct. avoid foss fuel
emit. gen. & comb.
Net = + 36 land-use seq.
reduct.
reduced soil
emit. N2O emiss.
Net = - 885 avoid compost
reduct.
Stover and yard waste have net (-) emissions (greater than -800 kg CO2e).
However, switchgrass A has -442 kg CO2e of emissions reductions, while B actually has
net emissions of +36 kg CO2e.
“Other” category includes biomass transport, biochar transport, chipping, plant
construction and dismantling, farm equipment, biochar application and avoided
fertilizer production.
-1
Greenhouse gases (kg CO 2e t dry feedstock)
GHG emissions
0 300 600 900
stover
emit. Net = - 864 LUC & field
Late
emiss.
(cont.)
reduct. agrochems
stover
Net = - 793
Early
emit. field ops
reduct. other
waste grass B grass A
Net = - 442
Yard Switch Switch
emit. stable C
reduct. avoid foss fuel
emit. gen. & comb.
Net = + 36 land-use seq.
reduct.
reduced soil
emit. N2O emiss.
Net = - 885 avoid compost
reduct.
Biomass and biochar transport (15 km) each contribute < 3%.
The stable C sequestered in the biochar contributes the largest
percentage (~ 56-66%) of emission reductions.
Avoided natural gas also accounts for a significant portion of reductions
(~26-40%).
Reduced soil N2O emissions upon biochar application to the soil
contributes only 2-4% of the total emission reductions.
+$35
stover
Late
Economic -$17
grass A
analysis
+$8
Switch
-$18
grass B
-$28
Switch
High revenue scenario
$80 t-1 CO2e -$30
Low revenue scenario
waste
Yard
$20 t-1 CO2e +$69
+$16
-120 -80 -40 0 40 80 120 160 200
cost ($ t-1 dry feedstock)
biomass collection biomass transport
pyrolysis biochar transport
biochar application lost compost revenue
tipping fee avoided compost cost
biochar P & K content biochar improved fertilizer use
carbon value syngas heat
The high revenue of late stover (+$35 t-1 stover).
Late stover breakeven price is $40 t-1 CO2e.
Switchgrass A is marginally profitable.
Yard waste biochar is most economically viable.
Highest revenues for waste stream feedstocks with a cost associated with current
management.
Stable C vs. life cycle emissions
Net profits valuing stable C only ($ t-1 DM)
($ t-1 DM) Late stover Switchgrass A & B Yard waste
High revenue scenario $13 $17 $44
Low revenue scenario -$23 $8 $10
Yard waste still most profitable
Stover and switchgrass have switched
Transportation sensitivity analysis
0 6000 60
Net GHG (kg CO2e t-1 dry stover) 5000 30
Net energy (MJ t-1 dry stover)
-200 Net revenue
Revenue ($ t-1 dry stover)
4000 0
-400
Net energy 3000
-30
-600
2000
Net GHG -60
-800
1000
-90
-1000 0
0 200 400 600 800 1000
Distance (km)
The net revenue is most sensitive to the transport distance, where costs
increase by $0.80 t-1 for every 10 km.
The net GHG emissions are less sensitive to distance than the net
energy.
Transporting the feedstock and biochar each 200 km, the net CO2
emission reductions decrease by only 5% of the baseline (15 km).
Biochar systems are most economically viable as distributed systems
with low transportation requirements.
Biochar-to-soil vs. biochar-as-fuel
Net GHG
Biochar-as-fuel: biochar production with biochar
combustion in replacement of coal are -617 kg
CO2e t-1 stover
Biochar-to-soil: -864 kg CO2e t-1 stover
29% more GHG offsets with biochar-to-soil
rather than biochar-as-fuel
Biomass direct combustion vs. biochar-to-soil
Net GHG
Not including avoided fossil fuels:
Biomass direct combustion: +74 kg CO2e t-1 stover
Biochar-to-soil: -542 kg CO2e t-1 stover
Emission reductions are greater for a biochar system than for
direct combustion
With avoided natural gas:
Biomass direct combustion: -987 kg CO2e t-1 stover
Biochar-to-soil: -864 kg CO2e t-1 stover
Net GHG look comparable
However, for biochar-to-soil, 589 kg of CO2 are actually
removed from the atmosphere and sequestered in soil,
whereas the biomass combustion benefits from the avoidance
of future fossil fuel emissions only
Transparent system boundaries
Conclusions
Careful feedstock selection is required to avoid unintended consequences
such as net GHG emissions or consuming more energy than is generated.
Waste biomass streams have the most potential to be economically viable
while still being net energy positive and reducing GHG emissions (~ 800
kg CO2e per tonne feedstock).
Valuing greenhouse gas offsets at a minimum of $40 t-1 CO2e and further
development of pyrolysis-biochar systems will encourage sustainable
strategies for renewable energy generation and climate change mitigation.
Preliminary results:
Mobile unit for stover biochar
Without energy capture
Next steps Net GHG = -550 kg CO2e t-1 stover
Net energy = -1000 MJ t-1 stover
Different biochar-pyrolysis sytems
Mobile unit
Small-scale non-mobile, batch units
With and without energy capture
www.biocharengineering.com Brazilian type metal kiln, Nicolas Foidl
Next steps
Developing country scenarios
Household cook stoves
Village scale units
Central plant at biomass source Pro-Natura in Senegal
Different feedstocks
Manures
Native grasses on
marginal lands
Cook stoves in Kenya
Acknowledgements
Cornell Center for a Sustainable Future (CCSF)
John Gaunt (Carbon Consulting)
Jim Fournier (Biochar Engineering)
Mike McGolden (Coaltec Energy)
Lehmann Biochar Research Group, especially Kelly Hanley,
Thea Whitman, Dorisel Torres, David Guerena, Akio Enders
Thank you!
Feedstock properties, pyrolysis process yields, and biochar properties for various
biomass sources
Late Early Switchgra Yard
Property stover stover ss waste
Moisture content, wet basis 15% 30% 12% 45%
Ash content (wt.% DM) 5.6 5.6 4.6 4.5
C content of feedstock
45 45 48 47
(wt.% DM)
Lower heating value (MJ t-1 DM) 16000 16000 17000 18000
Yield of biochar (wt. %) 29.60 29.60 28.80 29.63
C content of biochar (wt.%) 67.68 67.68 63.09 65.89
Stable portion of total C in
80%
biochar
Improved fertilizer use efficiency
7.2%
(for N, P, K)
Reduced soil N2O emissions
50%
from applied N fertilizer
DM = dry matter
Pyrolysis facility costs
Costs (2007 USD)
Pretreatment
Operating ($ t-1 DM) $4.77
Capital ($ t-1 DM) $4.12 $3.6 M Total
Pyrolysis
Operating ($ t-1 DM) $26.81
Capital ($ t-1 DM) $12.14 $10.6 M Total
Iron
Total Operating ($ t-1 DM) $31.58
Total Capital ($ t-1 DM) $16.26
Total ($ t-1 DM) $47.84
Costs and revenues per dry tonne of feedstock. Each feedstock has a low and high revenue scenario,
representing $20 and $80 per tonne CO2e sequestered, respectively
Late stover Switchgrass A Switchgrass B Yard waste
Low high Low High low High low high
Biochar
P & K content 18.39 9.68 9.68 10.01
Improved fertilizer use 1.22 1.18 1.18 1.22
C value 17.28 69.12 8.84 35.36 -0.72 -2.88 17.70 70.80
Energy 42.81 55.05 55.05 35.20
Tipping fee NA NA NA 49.09
Avoided compost cost NA NA NA 10.98
Lost compost revenue NA NA NA -56.03
Feedstock -43.46 -36.89 -36.89 NA
Transport
Biomass -6.24 -6.02 -6.02 NA
Biochar -1.57 -1.53 -1.53 -1.57
Biochar application -1.07 -1.04 -1.04 -1.07
Pyrolysis
Operating -31.58 -31.58 -31.58 -31.58
Capital -16.26 -16.26 -16.26 -16.26
Net value ($) -17.07 34.77 -18.57 7.95 -30.29 -28.13 15.87 68.97
