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
Life cycle of a product
end of life
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
Biomass collection
Shredding
Drying
Slow pyrolysis
Syngas
heat
product
T
T
Farm equipment,
agrochemicals
Compost
(-)
T
Construction
materials
Dashed arrows with (-) indicate avoided processes.
The “T” represents transportation.
(-)
Natural gas production
& combustion
T
Soil
application
T (-)
Fertilizers
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 coproducts:




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



Yard waste




Late and early harvest (15% and 30% mcwb).
Second pass collection, harvest 50% above ground biomass.
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 landuse 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
stover
Early
stover
Switch
grass
Yard
waste
15%
30%
12%
45%
Ash content (wt.% DM)
5.6
5.6
4.6
4.5
C content of feedstock
(wt.% DM)
45
45
48
47
16000
16000
17000
18000
Property
Moisture content, wet basis
Lower heating value
(MJ t-1 DM)
Feedstock to heat energy
efficiency
37%
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
biochar
80%
Improved fertilizer use efficiency
(for N, P, K)
7.2%
Reduced soil N2O emissions
from applied N fertilizer
50%
Energy balance
Energy (MJ t -1 dry feedstock)
Late
stover
cons.
Early
stover
cons.
Switch
grass
0
cons.
2000
4000
Net = + 4116
gen.
6000
agrochems
field ops
Net = + 3044
drying
chipping
gen.
biomass trans
Net = + 4899
plant constr
other
gen.
Yard
waste
syngas heat





cons.
gen.
Net = + 4043
avoid fos fuel
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)
Yard Switch Switch
waste grass B grass A
Early
stover
Late
stover
0



emit.
300
600
900
Net = - 864
LUC & field
emiss.
agrochems
Net = - 793
field ops
reduct.
emit.
reduct.
emit.
other
Net = - 442
reduct.
emit.
Net = + 36
reduct.
emit.
Net = - 885
stable C
avoid foss fuel
gen. & comb.
land-use seq.
reduced soil
N2O emiss.
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
Early
stover
Late
stover
0
Yard Switch Switch
waste grass B grass A
GHG emissions
(cont.)
Greenhouse gases (kg CO 2e t dry feedstock)




emit.
300
600
900
Net = - 864
LUC & field
emiss.
agrochems
Net = - 793
field ops
reduct.
emit.
reduct.
emit.
other
Net = - 442
reduct.
emit.
Net = + 36
reduct.
emit.
Net = - 885
stable C
avoid foss fuel
gen. & comb.
land-use seq.
reduced soil
N2O emiss.
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.
High revenue scenario
$80 t-1 CO2e


Low revenue scenario
$20 t-1 CO2e

Late
stover
Switch
grass A
+$8
-$18
Switch
grass B

-$17
-$28
-$30
Yard
waste
Economic
analysis
+$35
-120
+$69
+$16
-80
-40
biomass collection
pyrolysis
biochar application
tipping fee
biochar P & K content
carbon value





0
40
80
cost ($ t-1 dry feedstock)
120
160
biomass transport
biochar transport
lost compost revenue
avoided compost cost
biochar improved fertilizer use
syngas heat
The high revenue of late stover (+$35 t-1 stover).
Late stover breakeven price is $40 t-1 CO2e.
Switchgrass A is marginally profitable.
Yard waste biochar is most economically viable.
Highest revenues for waste stream feedstocks with a cost associated with current
management.
200
Stable C vs. life cycle emissions
Net profits valuing stable C only ($ t-1 DM)
($ t-1 DM)


Late stover
Switchgrass A & B
Yard waste
High revenue scenario
$13
$17
$44
Low revenue scenario
-$23
$8
$10
Yard waste still most profitable
Stover and switchgrass have switched
Net revenue
-200
6000
60
5000
30
4000
-400
Net energy
3000
-600
2000
Net GHG
-800
Net energy (MJ t-1 dry stover)
Net GHG (kg CO2e t-1 dry stover)
0
0
-30
-60
Revenue ($ t-1 dry stover)
Transportation sensitivity analysis
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 $40 t-1 CO2e and further
development of pyrolysis-biochar systems will encourage sustainable
strategies for renewable energy generation and climate change mitigation.
Next steps

Preliminary results:
Mobile unit for stover biochar
Without energy capture
Net GHG = -550 kg CO2e t-1 stover
Net energy = -1000 MJ t-1 stover
Different biochar-pyrolysis sytems



Mobile unit
Small-scale non-mobile, batch units
With and without energy capture
www.biocharengineering.com
Brazilian type metal kiln, Nicolas Foidl
Next steps

Developing country scenarios




Household cook stoves
Village scale units
Central plant at biomass source
Pro-Natura in Senegal
Different feedstocks


Manures
Native grasses on
marginal lands
Cook stoves in Kenya
Acknowledgements

Cornell Center for a Sustainable Future (CCSF)

John Gaunt (Carbon Consulting)
Jim Fournier (Biochar Engineering)
Mike McGolden (Coaltec Energy)

Lehmann Biochar Research Group, especially Kelly Hanley,
Thea Whitman, Dorisel Torres, David Guerena, Akio Enders
Thank you!
Feedstock properties, pyrolysis process yields, and biochar properties for various
biomass sources
Late
stover
Early
stover
Switchgra
ss
Yard
waste
15%
30%
12%
45%
Ash content (wt.% DM)
5.6
5.6
4.6
4.5
C content of feedstock
(wt.% DM)
45
45
48
47
Lower heating value (MJ t-1 DM)
16000
16000
17000
18000
Yield of biochar (wt. %)
29.60
29.60
28.80
29.63
C content of biochar (wt.%)
67.68
67.68
63.09
65.89
Property
Moisture content, wet basis
Stable portion of total C in
biochar
80%
Improved fertilizer use efficiency
(for N, P, K)
7.2%
Reduced soil N2O emissions
from applied N fertilizer
50%
DM = dry matter
Pyrolysis facility costs
Costs (2007 USD)
Pretreatment
Operating ($ 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)
$12.14
Iron
Total Operating ($ t-1 DM)
$31.58
Total Capital ($ t-1 DM)
$16.26
Total ($ t-1 DM)
$47.84
$10.6 M Total
Costs and revenues per dry tonne of feedstock. Each feedstock has a low and high revenue scenario,
representing $20 and $80 per tonne CO2e sequestered, respectively
Late stover
Low
high
Switchgrass A
Low
High
Switchgrass B
low
High
Yard waste
low
high
Biochar
P & K content
18.39
9.68
9.68
10.01
Improved fertilizer use
1.22
1.18
1.18
1.22
C value
17.28
Energy
69.12
8.84
35.36
-0.72
-2.88
17.70
70.80
42.81
55.05
55.05
35.20
Tipping fee
NA
NA
NA
49.09
Avoided compost cost
NA
NA
NA
10.98
Lost compost revenue
NA
NA
NA
-56.03
-43.46
-36.89
-36.89
NA
Biomass
-6.24
-6.02
-6.02
NA
Biochar
-1.57
-1.53
-1.53
-1.57
Biochar application
-1.07
-1.04
-1.04
-1.07
Operating
-31.58
-31.58
-31.58
-31.58
Capital
-16.26
-16.26
-16.26
-16.26
Feedstock
Transport
Pyrolysis
Net value ($)
-17.07
34.77
-18.57
7.95
-30.29
-28.13
15.87
68.97