Transcript Biochar vs. Biofuels Factors in the Balance

Doris Hamill
October 14, 2013
Biomass
Conversion
Mass (Biochar)
• Carbon sequestration
• Agricultural productivity
• Suppression of soil
emissions
• Water retention &
filtration
Energy (Biofuels)
• Biogas for heating
• Biofuels for
transportation
• Charcoal for high
temperature (e.g.
cooking)
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• Dominic Woolf , James E. Amonette, F. Alayne Street-Perrott , Johannes
Lehmann, Stephen Joseph; Sustainable biochar to mitigate global climate
change; NATURE COMMUNICATIONS | 1:56 | DOI: 10.1038/ncomms1053
| www.nature.com/naturecommunications
“The main aim of this study is to provide an estimate of the theoretical upper
limit, under current conditions, to the climate-change mitigation potential of
biochar when implemented in a sustainable manner.”
• Dominic Woolf, Johannes Lehmann, Elizabeth M. Fisher, and Largus T.
Angenent; Biofuels from pyrolysis in perspective: trade-offs between
energy yields and soil-carbon benefits
“The aim of this study is to review the potential pathways for co-production
of transport fuels with biochar and to model how process parameters affect
the yields of biochar and fuel.”
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• Use waste biomass
– Agricultural (grains, sugar cane, manure residues)
– Forestry (harvested wood residue, mill waste, diseased
stock)
– Biomass crops on marginal lands: not agricultural, not wild
• Modern conversion technology
– Minimize black carbon particulates and potent greenhouse
gas emissions: CH4, N2O
– Capture all usable energy: heat, hydrocarbons
• Local / regional focus
– Sources, production, use
– Local market forces
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5
Beta (1.64 Pg C / yr)
Alpha (1.01 PgC / yr)
0.085
0.060.029
0.22
0.25
0.34
0.14
0.13
Maximum Sustainable
(2.27 Pg C / yr)
0.072
0.14
0.09
0.11
0.14
0.28
0.14
0.3
0.1
0.18
0.45
0.62
0.13
0.19
0.14
0.6
rice
manures
agroforestry
other cereals
biomass crops
green / wood waste
sugar cane
forestry residues
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Optimal Slow Pyrolysis
Climate change mitigation potential
1.0E+11
8.0E+10
6.0E+10
4.0E+10
2.0E+10
0.0E+00
-2.0E+10
-4.0E+10
-6.0E+10
Assuming current
carbon-intensity of
the energy supply
-8.0E+10
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Biochar
Combustion
Biochar
– Soil saturation period
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Baseline carbon
intensity mix

“… climate-change
mitigation … impact
of biochar is about
one-fourth larger, on
an average, than that
obtained if the same
biomass were
combusted for
energy.”
High C-intense
energy (e.g. coal)
favors biomass
combustion.
100 year cumulative mitigation potential from
maximizing biochar production vs. biomass combustion
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Severity of soil fertility constraints
natural baseline
gas
mix
C-intensity of offset energy (kg C GJ-1)
oil
coal
Carbon intensity of
energy being offset
Increase in mitigation of biochar relative to
bioenergy; calibrated using scant literature
from both field and greenhouse studies.
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Optimal for energy products
75-80% thermal efficiency
<5% production of biochar
(GJ/Mg Dry Mass)
Biochar Enthalpy
thermal gasification
cracking T range
not
commercially
viable
Note: biochar yield is also a function of
the lignin mass fraction of the feedstock.
Pyrolysis Temperature (C)
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18
gasification point (700C)
GJ/Mg dry mass
Biofuels energy yield
15
12
9
6
3
.1
.2
.3
Biochar carbon yield
MG carbon / MG dry mass
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“…minimum biochar price of $110
Mg-1 C to $440 Mg-1 C … before
increasing biochar production
could increase revenue ”
“… minimum biochar price of $320 Mg-1 C
would be required before slow pyrolysis FTbiofuel and biochar co-production would
increase revenues relative to fast pyrolysis
without biochar ”
“… utilizing fast pyrolysis biochar
as a soil amendment would only
become economic at a biochar
price of $580 Mg-1 C.”
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• Sustainable use of biomass for biochar has
more environmental benefits than for biofuels
– Exceptions when regional soil quality is high
and/or biofuels offsetting regional use of coal
• Conversion of biomass into biofuels is more
profitable than into biochar
– Except when / where fuel price is low
– Depends on market price for biochar
• Widespread use of biochar for environmental
remediation inhibited by market forces
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