soil carbon sequestration with biochar from waste · 1 department of agriculture & ecology lars...
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Department of Agriculture & Ecology
Lars Stoumann Jensen & Sander Bruun
Soil carbon sequestration with biochar from waste - the potential of thermo-chemical conversion technologies
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New buzzwords in a climate struck world…
”Bioenergy” … ”Biomass-fuels””CO2-neutral energy” … ”Carbon footprint”
But many derived problems…Whilst in some cases being more CO2 neutral thanfossil fuels, bioenergy may often
• compete directly with food production• divert biomass carbon from recycling to soil• lead to land use change with huge soil C
emissions as a consequence
Soil carbon sequestration with biocharrepresents a potential solution
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Kyoto article 3.4 (LULUCF additional activities)
• How much does soil C mean in Denmark?• 157 t C/ha in farmed topsoil (0-100 cm avg.) • 2,7 mio. ha farmed area = 1550 mio. t CO2-equiv.• Danish Kyoto reduction target:
70 mio. t CO2-equiv. emitted * 21 % reduction= 15 mio. t CO2-equiv.
• Total Danish CO2 target may be reached with just a relative increase in soil C by 1 % per year!
• Denmark has chosen to adopt Kyoto-protocol article 3.4• Relatively few other countries have adopted 3.4• Significant documentation monitoring and verification required• Once adopted, no step back!• Need for new soil C sequestration mechanisms
if reduction target is not met!
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Development of carbon stocks in Danish mineral soils (modelled)
(Gyldenkærne, Petersen og Olesen, 2007, MSt AR 5)
Ban on straw field burning
Ref. year 1990:∆C=-1,54 mio t C/y(5 y avg.)
Commitment period 2008-12:∆C=0,35 mio t C/y
Net change: 1,9 mio t C/year extra sequesteredLarge CO2 quota value for Denmark!
”Warm years”
Predicted with1961-90 climate
Avg. climate (1961-90)Actual climateC
arbo
nin
min
eral
soi
ls(m
io. t
C)
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Development of carbon stocks in Danish mineral soils (modelled)
(Gyldenkærne, Petersen og Olesen, 2007, MSt AR 5)
ift. klima i 2001-2004
ift. klima i 1961-1990ift. klima i 1961-1990
Most likelyscenario acc. to IPCC
However:• Increasing temperature may jeopardise article 3.4 gains!• Bioenergy will remove more C inputs = less soil C seq. • Need for technology alternatives, producing both
bioenergy and soil C sequestration
Car
bon
in m
iner
al s
oils
(mio
. t C
)
(actual climate)
Temperature:Avg. 1961-90+2 ºC/100y rel. to 1961-90+3 ºC/100y rel. to 1961-90+2 ºC/100y rel. to 2001-04
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Bioenergy with biochar – net CO2 removal?
• Bioenergy with biochar can result in a net removal of CO2 from the atmosphere, but only if• The biomass is biogenic• A significant net energy output is produced• The biochar is recalcitrant and highly stabilised in soil
(Sohi et al 2009)
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Pyrolysis and biochar from plant residues
PlantsSoil
Pyrolysis
Nutrients
Biochar
Plant resid
ues
Bio-Oil
Gas
C sequestrationSoil quality
Energy
CO2
CO2 50%
CO2 only 5%
100%
• International biochar initiative (IBI) promotes biochar as an official UNFCCC mitigation-strategy / Clean Development Mechanism (CDM)
• Discussed at COP14 in Poland and to be discussed in Copenhagen Dec 2009 at several COP15 side events
50%
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Conditions:T = 700 –1200 CAt the prese of Oand water steam
o
nce 2
Chemical conversions
BIO-OIL
GAS
FEEDSTOCK PRE-TREATMENT
Chopping indingrying (45 C)
& GrD o
XRDNRIGC/MSTGASANMRFTIR16SrDNA
ANALYSIS
SOIL AMENDMENT
Conditions:T = 350 – 650 C
Without Oo
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GasificationPyrolysisTHERMAL CONVERSION
Catalytical gasification
BIOSYNGASCO, H2
Chemicalmodification
Chemical industry
FEEDSTOCKAgricultural wastesSewage sludgesBiorefinery wastesDedicated plantations
Chemicals industry
Electricity
FT diesel
BIOCHAR
A more sustainable Carbon cycle
(W. Kwapinski, www.carbolea.ul.ie)
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More flexible outputs…
(W. Kwapinski, www.carbolea.ul.ie)
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PYROLYSIS400 - 600ºC
no O2
CONDENSATION
CATALYTIC CONVERSIONTO HYDROGEN (Optional)
Vapors
GasesH , CO, CH , C H2 4 2 4
Biochar Heat
Biomass LiquidsPOWERGENERATION
CHEMICALSEPARATION
or
COMBUSTION
Advantages of Pyrolysis:generally a simple,low-cost technology,capable of processing a wide variety of feedstocks,offers the unique advantage of giving a: liquid-fuel that can be stored and transported, Bio-char, gas-fuel.
Biomass liquefaction via pyrolysis
(W. Kwapinski, www.carbolea.ul.ie)
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Table: Typical product yields (dry wood basis) obtained by different modes of pyrolysis of wood
Mode Conditions Liquid Gas Char
Fast pyrolysis moderate temperature, around 500°C, short hot vapour residence time ~1 s 75 % 13 % 12 %
Intermediate pyrolysis
moderate temperature, around 500°C, moderate hot vapour residence time ~10-20 s 50 % 30 % 20 %
Slow pyrolysis (carbonisation)
low temperature, around 400°C, very long solids residence time 30 % 35 % 35 %
Gasification high temperature, around 800°C, long vapour residence time 5 % 85 % 10 %
75 %
35 %
85 %
Yield of Pyrolysis
(W. Kwapinski, www.carbolea.ul.ie) GreenCarbon & Stirling
pyrolysis CHP plant, Denmark
Dynamotiveplant
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What is biochar and its effects?• Biochar is the solid that remain after light gases
and tar have been released from the biomass• Charcoal like, high carbon content• Positive effects on soil quality and plant
productivity:• Increase surface area and porosity = higher water
and nutrient adsorptive capacity• Improved filtering of pollutants• Increase activity of autotrophic and symbiotic
microorganisms = increased crop productivity
• Extremely slowly degradable in soil = a way of sequestering biomass derived carbon
Fungal growth
Porous structure
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The soil carbon challenge – depletion of soil humus, especially in S. Europe
• Organic matter in soils(humus) is essential for soilfertility and influencesressource use efficiency(water, energy) and CO2storage (C sequestration)
• Worldwide soil humus levels are being depleted, due to deforestation, intensive cropping, removalof biomass for bioenergy
• In Europe especially the Mediterranean soils are lowin humus
• Biochar may serve as an important organicmatter input
(EU-JRC Soil Atlas)
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The soil carbon challenge – also on certain soils in Denmark
• Dexter Ratio = clay / org. C has been proposed as an indicator of soil C saturation
• Low values indicate soilsdepleted in complexed C
• In Denmark especially loamysoils, low in humus areidentified as depleted
• Dominant in eastern parts with few animals, close to metropolitan areas withlots of organic MSW
(Schønning et al. 2009)
OK Problem
Seriousproblem!
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00,10,20,30,40,50,60,70,80,9
1
0 100 200 300 400 500 600 700
Days of soil incubation
Frac
tion
of b
iom
ass
C re
mai
ng
00,10,20,30,40,50,60,70,80,9
1
0 100 200 300 400 500 600 700
Days of soil incubation
Frac
tion
of b
iom
ass
C re
mai
ngStability of biochar in soil
Bruun et al. (2008)
Plant material (straw)
Biochar prod. from straw at 225ºC
Biochar prod. from straw at 300ºC
Fraction of biomass C remaining
Biocharmore resitantto decaythanrawbiomass
(incl. loss during pyrolysis)
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Biochar stability and effects on decomposition- investigated using 14C labelling
Soilorganicmatter
Plant residues Biochar
CO214C
14C
14C (40 y ago)
14CO2
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Biochar degradability in soil- depends on degree of thermal alteration
Bruun et al. (2008)
dried plant mat.
pyrolysed
Respiration of plant material / biochar (14C-labelled)
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Decomposition of plant residues in soil is not affected by biochar application
Respiration from straw
00.050.1
0.150.2
0.250.3
0.350.4
0.450.5
0 50 100 150 200 250 300 350
Day
Frac
tion
of s
traw
C r
espi
red
Plant residues in soil with:no biochar addedbiochar added
(14C-labelled)
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Decomposition of biochar is not affected by plant residue addition
Respiration from biochar
00.0020.0040.0060.0080.01
0.0120.0140.0160.018
0 50 100 150 200 250 300 350
Day
Frac
tion
of b
ioch
ar C
re
spire
d
Biochar in soil with:no straw addedstraw added
(14C-labelled)
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Decomposition of soil organic matter (SOM)is not affected by biochar addition
Respiration of SOM
0
0.01
0.02
0.03
0.04
0.05
0.06
0 50 100 150 200 250 300 350
Day
Frac
tion
of S
OM
resp
ired
00.40% straw0.15% char0.77% char1.55% char
(soil humus 14C-labelled 40 y ago)
Soil onlyEquivalentamount of plant mat.
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Conclusions and final remarks
• Soil C sequestration has significant potential for climate change mitigation – but may bejeopardised by global warming
• New and more efficient waste bioenergytechnologies needed, which combine energyproduction and soil C sequestration
• Gasification / pyrolysis technology withbiochar production has significant potential
• Biochar recalcitrance depends on degree of thermal alteration
• Biochar addition to soil does not alter decomposition of other added organicresidues or old soil humus
• Still need for more system analyses in order to assess sustainability