fate of organic matter and pyrogenic char in smouldering fires: when soils burn to ash
TRANSCRIPT
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Dr Guillermo ReinDepartment of
Mechanical Engineering
KEYNOTE Fate of Organic Matter andPyrogenic Char in Smouldering Fires:
when soils burn to ash
4th Int. Meeting of Fire Effects on Soil Properties,Vilnius, July 2013
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CONTENTS:ROOTS OF HAZE
EPISODES
LARGEST FIRES ON
EARTHFATE OF ORGANIC
MATTER
PYROGENIC CHAR
Haze 2013, South East Asia
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22 Oct 1997 smoke plumeNASA TOMS satellitePage et al. Nature 420, 2002
Sign at NTU Singapore, 2011
The 1997 smouldering peat fires in Borneo released between 0.8and 2.6 billion tons of carbon into the atmosphere. That is
equivalent to 13 to 40 % of all emissions from burning fossil fuels
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The Evans Road fireSummer 2008, North Carolina, USAPocosin Lakes National Wildlife Refuge
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National Geographic 2008 / AP Photo/MODIS
The Evans Road fireburned for 7 months
During worst drought on record
16,500 ha burned (2x year avg.)1 m deep into the soilby flooding and excavation$20 million in suppression costs
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National Geographic 2008 / AP Photo/MODIS
"Think of it as one giant
charcoal briquette. It willignite and the fire will sinkinto the soil
State Forest ManagerNC, 2008
Equivalent to 1340% ofmanmade globalcarbon emissions(and not account forby IPCC yet)
salvemoslastablas.blogspot,Toms Beldad, 2009
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Russian Haze,summer 2010
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by G Rein, 2006
Rothiemurchus Wildfire, July 2006
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by G Rein, 2006
Rothiemurchus Wildfire, July 2006
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Rothiemurchus Wildfire, July 2006
by G Rein, 2006
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by G Rein, 2006
Rothiemurchus Wildfire, July 2006
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World Map of PeatlandsFrom shallow (30 m)Contain more terrestrial carbon than the forests or theatmosphere
Gore, 1983
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Organic Soils - Ignition Limits
no ignition
Ignition
Frandsen, Can. J. For. Res. 1997
dry base
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Smouldering Combustion
FlamelessLow peak temperature ~600CLow heat of combustion ~5 kJ/g
Creeping propagation ~1 mm/min
Incomplete combustion
Heterogeneous combustion on poresurfaceFuels: peat, coal, duff, organic soils
Rein, Smouldering Fires and Natural Fuels - Wiley 2013
(solid)Ash(solid)Char(gas)PyrolyzateHeat(solid)Biomass
(solid)AshgasesotherOHCOHeatO(solid)Char 222
Incomplete combustionHeterogeneous combustion on poresurfaceCocktail of emissions CO 2, CO, PM, CH4,PAH...
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igniter
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Transition to Flaming Combustion30 min1 h 1 s1 s
Torero 1992,UCB/NASA
no transition
transition
oxygen fraction
f l o w v e
l o c i t y
( m / s )
0. 3 0. 4
3
0. 35
2
1
Bar-Ilan et al, Proc. Comb. Inst. 30,
pp 2295-2302, 2005
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Most persistent fires on EarthSmouldering fires are the easiest to ignite
Ignition with much smaller heat sources (8 vs. 15 kW/m 2)Selfheating possible at ambient temperatures (ie, 30 C)
Smouldering fires are most difficult to suppressLarger amounts of water (>50% larger kg H2O/kg fuel )
Lower critical oxygen concentration (10% [O 2] vs. 16%)Much longer holding times for smothering (~months vs. min)
The oldest continuously burning fire on Earth is asmouldering coal seam in Australia ignited >6,000 years old
Rein, Smouldering Fires and Natural Fuels - Wiley 2013
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Spread over dry/wet patternsChecker board
Longitudinal split
Top view, 5 cmdeep peat layer.
20 x 20 cmsquare box
Perpendicular split
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Peat Reactivity
Huang and Rein, Combustion and Flame 2013
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Carbon Balance
Hadden et al, Proceedings of the Combustion Institute , 2012
Carbon fraction in char is ~1.5 times higher than peat Carbon fraction in ash is ~35 times lower than char During fires peat soil goes from 77 to 0.7 kgC/m 3
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Pyrogenic Char
Hadden et al, Proceedings of the Combustion Institute , 2012
Char is simultaneously product andreactant in pyrolysis and oxidationreactions, which initially results
in net char production and laterbecome net char consumption .
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Peat Reactivity TGA and Kinetics
Huang and Rein, Combustion and Flame 2013Chen et al, Energy & Fuels 2011
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Simulations of Indepth spread
Huang and Rein, Combustion and Flame 2013
The 1step drying and 4step
decomposition kinetics schemeexplains the order of the reactions
during indepth combustion:
Drying first, then Pyrolysis and last
is Oxidation
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Soil Heating vs. Soil BurningExperimental measurements of thermal severity
Medical sterilization of surgery instruments
smouldering
flaming
s o i
l d e p t h
Rein et al, Catena 2008
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Fires in the Fossil RecordCurrent science:
Char abundance is a proxy to fire abundanceImplicit assumption: char abundance increases with fire
intensity and frequencyThis is correct for flaming fires.
Bonefire example:char remains at flameout vs. ash remains the day after
Char abundance decreases with smouldering intensity and
frequencyPossible sources of lower char: a) Smouldering fire; or b)Residual smouldering postflaming fire
Suggests: In addition to char, look for ash
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Chemical Analysis of soil residue at thesmouldering front
Smouldering column tests of Sphagnum peat at different initial moisture
contents (MC) ignited at the top:, dry conditions ( MC50% ), undisturbed
conditions ( MC100% ), and wet conditions ( MC200% ).
Dry Undistr. Wet
MC50% MC100% MC200%
Zaccone et al., EGU 2012-4795, XY648
h d l l ( )
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0
40
80
120
160
0 10 20(%)
Ashcontent
100%MC
Fresh peat
0
40
80
120
160
40 60 80(%)
TC
100%MC
Fresh peat
0
40
80
120
160
0 2 4 6(%)
TN
100%MC
Fresh peat
0
40
80
120
160
0 20 40 60
C/N
ratio
100%MC
Fresh peat
0
40
80
120
160
0 10 20 30
C/Hratio
100%MC
Fresh peat
0
40
80
120
160
3 6 9
pH
100%MC
Fresh peat D e p t h f r o m
f r o n t ( m m
)
D e p t h f r o m
f r o n t ( m m
)
Ash, pH and elemental composition ( MC100% vs. FP)
h
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R = 0.9846
R = 0.8799
R = 0.192
0
5
10
15
20
25
0 10 20 30 40 50 60
C / H
C/N
C/H vs. C/N
MC50% MC100%
MC200% FP
Data show:
a higher production of aromatic and
condensed molecules, as underlined by thehigher C/H values;
the increase of the total N and decrease of
C/N ratio suggesting the incorporation of, andthe relative enrichment in, N during charring.
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Energy and Climate Crisis
World energy use and climate change sciencehas led to international concerns on:
Fossil fuel energyCarbon emissionsEnvironmental protectionSustainability
Most attention is paid to increased energyefficiency , lower resource consumption anddevelop clean energy technologies
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Accidental Sources
But accidental sources of fossil fuel burning
contributing to the problem are largely ignored
This includes nonanthropogenic sources aswell:
Smouldering Megafires in Peatlands
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Smouldering Natural Fuels
10 years 1,000 years 1,000,000 years 300,000,000 years
Most important: duff, humus, peat, coalDecayed vegetation matter, from shallow (30 m).
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National Geographic 2008 / AP Photo/MODIS
Flaming fires consumegrasslands , shrubs andforests . These take 10-10 2 yearsto grow back and sequester backthe carbon = Renewable & CarbonNeutral
Flaming vs. Smouldering
Smouldering fires consume peat ,organic soils and coal . These take 10 4
to 109
years to grow again =Not Renewable & Carbon Positive
Smouldering fires burn
ancient carbon (akin to fossil fuels)
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Feedback Mechanism in the Earth System
topics I work onPermafrost thaw are already resulting inlarge smouldering artic fires (e.g., Alaska 2010).
C l i
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ConclusionsSmouldering combustion of peatlands leads tothe largest fires on Earth
100 times higher fuel consumption per area than flamingfires
Consume organic matter and release ancientcarbon stored deep in the soil ( accidental fossil fuelburning )
Soil goes from 77 to 0.7 kgC/m 3
Pose a positive feedback mechanism to climatechange via moisture deficit, thaw and selfheating
Topic of global interest linked to ecosystem perturbation,carbon sequestration and climate change
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Thanks
Belcher et al, PNAS 2011
Rein et al, Catena 2008
Rein et al., Proc Combustion Institute 2009
Hadden et al, Proc Combustion Institute 2012
Huang and Rein, Combustion and Flame 2013
Rein, Smouldering Fires and Natural Fuels - Wiley 2013
M fi
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Megafires
320
0 3)( t S S dt mt m ld
t
t t
00
)( t S dt mt m d t
Smouldering spreads in area and indepth.
It is a volumetric phenomenon (flaming is a surface phenomenon)
Combustion Dynamics
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Combustion Dynamics
As the intensity of the fire increases (proxy via increasing oxygen
concentration), the fraction of residual char rapidly decreases to zero.
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1999 A Belenky / SPT
July 1999 Anomalous climate conditions led to first reported smouldering wild-urban interface.
Peat fires burn south of the city for weeks and haze covered five districts. That sameyear, other peat fires forced President Yeltsin to change holyday resort.
Days in July 1999
NYT Smoke Shrouds Moscow as Peat bog fire rages
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NYT Smoke Shrouds Moscow as Peat bog fire rages@ New York Times, 1972
1972:
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Sign at the sports centre of the Nanyang
Technological University, Singapore, 2012
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Mechanical Engineering Building, 2nd [email protected]
http://www.imperial.ac.uk/people/g.rein
This is home to the experimental branch of the Imperial Haze Lab, research group of Dr
Guillermo Rein at the Department of Mechanical Engineering. We study the heattransfer, condensed-phase chemistry and
thermodynamics of reactive solids. Ourcontributions help understand and solve
global environmental problems, threats toenergy resources and the protection of
infrastructure.