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

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101 102 103 104 105 106 107

% T

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Sample ID #

Wood Ash Characteristics

Untreated biochars:40 to 75 % C

Specific Surface Area

0

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101 102 103 104 105 106 107

Surf

ace

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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

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uction (

% o

f contr

ol)

0

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All wood ashes suppressed N2O

production

Majority suppressed CO2 production –

slowing over all SOMmineralization?

Impacts on N-mineralization

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Nit

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m)

Elapsed Days (d)

Control

101

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104

105

106

107

5 wood ash lower than control

0

0.2

0.4

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Am

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pp

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Elapsed Days (d)

Control

101

102

103

104

105

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107

No accumulation of ammonium -- different than biochars

58

92 95

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31

54

46

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101 102 103 104 105 106 107

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oss

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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

%

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%

5

100

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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

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1,2

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Ace

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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