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Could wood fired boiler ash be considered a biochar?
Kurt Spokas
USDA-ARS Soil and Water Management Unit - St. Paul, MN
What is Biochar? Solid residue remaining after the heating
of organic materials without oxygen
Pyrolysis
“Recalcitrant” carbon(charcoal)
(>10 to 1,000,000 yrs?)
Easily degradable (0-5 yrs)
Pyrolysis
➲ Pyrolysis is the chemical decomposition of an organic substance by heating
➲ Does not involve reactions with oxygen • typically in the absence of oxygen
➲ Pyrolysis is also used in everyday activity –Cooking roasting, baking, frying, grilling
➲ Also occurs in lava flows and forest/prairie fires
Wide Spectrum of Pyrolysis
High temperature pyrolysis gasification (>800 oC) {+ O2 }
“Fast” or “Slow” pyrolysis (300-600 oC)
Fast pyrolysis 60% bio-oil, 20% biochar, and 20% syngas
Time = seconds
Slow pyrolysis Can be optimized for char production
(>50% biochar yields)
Time = hours
Both temperature and time factors:
Biochar
Gaining significant attention:Carbon Storage
Biochar can store atmospheric carbon, potentially providing a mechanism for reduction in atmospheric CO2 levels
Soil Improvements Improve water quality
Improve soil fertility
Reduce GHG emissions
Bioenergy
Charcoal Timeline
10,000 (?) BC – charcoal in cave drawings
3000-4000 BC – charcoal as fuel
2000 BC – first filtration use of charcoal
10,000 BC 5,000 BC 1000 BC
1000 AD
1908 – degradation of charcoal by fungi1940-1950 – charcoal powered car in China2000’s – “Biochar”
2010 AD
1700’s
1800’s
Biochar
Not a “new” idea
Pre-Columbian Period (1,400 – 14,000 yrs ago)
Amazonian Natives:
Hypothesis : biochar was used to increase soil productivity (oxisols) by smoldering agricultural waste
Potential source of “Terra Preta” (dark) soils
What has changed?
• Pyrolysis, carbonization, and coalificationare long and well establish conversion processes with long research histories
– Except:
• Prior emphasis: – Conversion of biomass to liquids (bio-oils) or gaseous fuels
and/or fuel intermediates
– Solid byproduct (biochar) has long been considered a “undesirable side product” (Titirici et al., 2007)
• Now solid byproduct is viewed with
• carbon sequestration potential (climate change)
Byproducts from the Paper Industry
– Waste water treatment plant residuals
• ~ 6 million ton yr-1
– Boiler wood ash
• ~ 5 million ton yr-1
Large sources of biomass residuals:
Current Boiler Wood Ash Management
Estimates have been as high as 90% to landfill
•In the NE US: 80% is land applied and 5% composted with sewage sludge (85% beneficial reuse)
65 %
9 %
25 %
Landfill
Land Application
Other Uses
Greene (1988), Campbell (1990) and Vance (1996)
Direct Wood Ash Application
• Numerous agronomic studies have been conducted:– Overall beneficial effects observed:
• Increased yields
• Liming potential (increase soil pH)
• Other purposes:– Sewage amendment, scrubber systems, cement products
(Greene, 1988) and for road building (Ostrofsky,, 1983)
– Used in Finland since 1935 as a soil amendment (Hakkila, 1989; Korpilahti et al., 1999)
• Similar results obtained in the “biochar” area
Project Overview
• Examining a limited number of wood boiler ash samples for their potential use as a “biochar” material
– Moving the focus to carbon sequestration
– Seeking to identify conditions and factors that optimize the residual C content in ash samples
24
9
63
18
8480
10
10
20
30
40
50
60
70
80
90
100
101 102 103 104 105 106 107
% T
ota
l Car
bo
n
Sample ID #
Wood Ash Characteristics
Untreated biochars:40 to 75 % C
Specific Surface Area
0
200
400
600
800
1000
1200
1400
1600
1800
2000
101 102 103 104 105 106 107
Surf
ace
Are
a (m
2/g
)
Sample ID #
N/A N/A
Untreated biochars are between
0-150 m2/g
Impacts of Wood Ash on GHGProduction/Consumption
• Wood ash samples incubated with Minnesota Ag soil (Waukegan silt loam)
– 10% w/w addition at field capacity (22 oC)
Date
12/1/09 1/1/10 2/1/10 3/1/10 4/1/10
Cu
mu
lative
CO
2 C
on
ce
ntr
atio
n (
pp
m)
10000
20000
30000
40000
50000
Soil Control
Soil + Ash
Ash Alone
Preliminary GHG Impacts
Control 101 102 103 104 105 106 107
N2
O P
rod
uction (
% o
f contr
ol)
0
20
40
60
80
100
120
140
160
Control 101 102 103 104 105 106 107
CO
2 P
rod
uction (
% o
f contr
ol)
0
20
40
60
80
100
120
140
160
All wood ashes suppressed N2O
production
Majority suppressed CO2 production –
slowing over all SOMmineralization?
Impacts on N-mineralization
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30
Nit
rate
(pp
m)
Elapsed Days (d)
Control
101
102
103
104
105
106
107
5 wood ash lower than control
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 5 10 15 20 25 30
Am
mo
niu
m C
on
cen
tra
tio
n (
pp
m)
Elapsed Days (d)
Control
101
102
103
104
105
106
107
No accumulation of ammonium -- different than biochars
58
92 95
10
31
54
46
0
10
20
30
40
50
60
70
80
90
100
101 102 103 104 105 106 107
% L
oss
of
Org
inal
Car
bo
n
Sample ID #
Stability of CarbonAssessed through CTO-375 (375oC for 16-18 hours)
Chemical Thermal Oxidation test for the quantification of black carbon (recalcitrant carbon : soots, graphite, etc) in sediments (Elmquist et al., 2007)
Untreated biochars are typically between
60-90% of carbon lost during CTO-375 test
Volatile Organic (GC/MS) Fingerprints, 23-Apr-2010 + 23:27:39NRC103
5.39 7.39 9.39 11.39 13.39 15.39 17.39 19.39 21.39 23.39 25.39 27.39 29.39Time0
100
%
0
100
%
0
100
%
0
100
%
0
100
%
0
100
%
RXI5_032210_001_083 Scan EI+ TIC
9.88e615.8713.6913.10
10.188.45
11.43
18.61
17.97
29.8819.97 28.69
27.2620.72 26.56
RXI5_032210_001_120 Scan EI+ 44-2509.88e6
6.2017.5713.93
RXI5_032210_001_122 Scan EI+ 44-2509.88e6
6.21 17.57
RXI5_032210_001_124 Scan EI+ 44-2509.88e66.20
15.0412.09 13.90 17.55
RXI5_032210_001_126 Scan EI+ 44-2509.88e6
6.20 26.3124.86
RXI5_032210_001_128 Scan EI+ 44-2509.88e6
6.265.04
Trace level alkanes (C19+)
VOA Standard (1 ug of each component)
{Aldehyde compounds}Wood Ash (101)
Wood Ash (102)
Wood Ash (103)
Wood Ash (105)
Wood Ash (104)
Very low amount of volatiles observed on wood ash agrees with results of Someshwar (1996).
, 24-Apr-2010 + 00:48:10NRC104
1.01 6.01 11.01 16.01 21.01 26.01 31.01Time5
100
%
5
100
%
5
100
%
5
100
%
5
100
%
5
100
%
RXI5_032210_001_126 Scan EI+ 45-2501.27e7
RXI5_032210_001_099 Scan EI+ TIC
1.27e75.19
5.96 29.198.62 12.9411.739.87 18.2913.65
16.44 22.9518.99
21.7623.78
RXI5_032210_001_092 Scan EI+ TIC
1.27e79.29
8.37
9.8918.3012.15 16.4713.6814.82
20.56 27.4129.00
RXI5_032210_001_091 Scan EI+ TIC
1.27e77.006.005.24
10.9113.68
15.08
18.6721.75
23.81 27.1025.1027.76 29.25
RXI5_032210_001_087 Scan EI+ TIC
1.27e78.64
7.005.68
11.76
11.5413.69
12.4116.21
18.84
17.2520.02
21.81
24.16 29.7126.2027.12
RXI5_032210_001_088 Scan EI+ TIC
1.27e712.0010.419.51
5.69 7.2229.9725.8523.9423.07
21.0420.0113.09 14.41
28.9527.08
Tolu
ene
Ben
zen
e
xyle
nes
met
han
ol
Nap
hth
alen
e
1,2
-dic
hlo
rob
enze
ne
eth
ylb
enze
ne
Ace
tic
Aci
d
Wood Ash (104)
Wood pellet BC
MacadamiaShell BC
HardwoodSawdust
BC
Oak Hardwood
Bituminouscharcoal
Ace
ton
e
2-m
eth
ylb
uta
ne
eth
ano
l
Biochar typically has higher sorbed volatiles -> potential microbial inhibitors
Preliminary Conclusions• Overall, wood ash does present an interesting potential for
carbon sequestration • Converting biomass into recalcitrant carbon, while producing energy at mills• What adjustments can be made at individual mills to increase C content?
• Impacts on soil system– Similar to biochar, with some differences:
• Wood ash is cleaner from a sorbed volatile organic standpoint (lower VOC contamination)
• Concern of pH (pre-treatment?)• Lack of impact on ammonia oxidation
– Still decrease in N2O production (pH related?)
• Wood ash is typically lower in total carbon than biochars, but indications are the C is of higher stability – More resistant to oxidation
• Not all biochars (wood ashes) are created equal
Acknowledgements
• NCASI
• AECOM Environment (Doug Hermann)
• Technical support from :
– Martin duSaire, Tia Phan, Lianne Endo and
Kia Yang
• Thank you for your attention
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