Michael J. Antal, Jr, Goro Uehara, Jonathan Deenik, and ... · Nov 27, 2007 3 Fuel Costs Gas...

Nov 27, 2007 www.hnei.hawaii.edu www.ctahr.hawaii.edu

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Charcoal for terra preta

Michael J. Antal, Jr, Goro Uehara, Jonathan Deenik,and Tai McClellan

Hawaii Natural Energy Institute andThe College of Tropical Agriculture & Human Resources

University of Hawaii at Manoa


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Modern Biomass Refineries• Ethanol from corn grain and biocarbons

from corn stover (USA)• Biodiesel from sunflower oil and biocar-

bons from sunflower shells and stalks (EU)• Biodiesel from coconut oil and biocarbons

from coconut shells, fronds, etc. (Malaysia)• Biodiesel from marine algae and biocarbons

from residual (dry) algal material (Hawaii)


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Fuel Costs

$18-24/GJHydrogen$6-17/GJGas$14/GJEthanol$15/GJOil$8/GJCharcoalCoal

RENEWABLEFOSSIL


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How can we use charcoal?• Potting soil (orchids and ornamentals)• Cooking (barbeque) fuel• Ultra clean coal (power production)• Activated carbon (water treatment)• Metal reductant• Terra preta (carbon sequestration!)• Biocarbon fuel cell


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Some questions concerning the pro-duction of biocarbons:1. In theory, what limits the yield of bioC

(charcoal) from biomass?2. In theory, what is the energy conversion

efficiency of biomass into bioC? 3. In practice, what yield and energy

conversion efficiency can be achieved?4. In practice, how quickly can we convert

biomass to bioC?


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Useful definitions:

1. ychar = mchar / mbio

2. 100 = % VM + % fC + % ash; where

VM = volatile matter; fC = fixed carbon

3. yfC = ychar × {% fC / (100 - % feed ash)}

4. ηchar = ychar × (HHVchar / HHVbio)


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Thermochemical equilibrium predictions for the products of cellulose pyrolysis at 400 C (Ind. Eng. Chem. Res. 2003, 42, 3690-3699).

• C, H2O, CO2, and CH4 are the only significant products.

• The theoretical charcoal (i.e. C) yield is 28 wt%.

• The gas contains significant energy (i.e. CH4).

Pressure (MPa)

0.001 0.01 0.1 1 10

Mas

s fr

actio

n (%

)

0

10

20

30

40

50

C(s)

CO2

H2O(g)

CO

CH4

(a)


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Reaction stoichiometry for the products of cellulose pyrolysis at 400 C & 1 MPa (Ind. Eng. Chem. Res. 2003, 42, 3690-3699)

C6H10O5 → 3.74 C +

2.65 H2O + 1.17 CO2 + 1.08 CH4


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Energy balance for cellulose pyrolysisfollowing thermochemical equilibrium (Ind. Eng. Chem. Res. 2003, 42, 3690-3699)

0 5000 10000 15000 20000

input

output

Energy [kJ/kg-cellulose]

cellulosespecific heat

carbongas

worksensible heat

exotherm

0 5000 10000 15000 20000

input

output

Energy [kJ/kg-cellulose]

cellulosespecific heat

carbongas

worksensible heat

exotherm


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Plot of charcoal yield from cellulose pyrolysis vs. pressure (Thermochim. Acta, 1983, 68, 165-186).

• Pressure strongly favors formation of charcoal.

• Low gas flow rates also favor the formation of charcoal.

• Elevated pressure and low flow rates together double the yield of charcoal.


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Flash CarbonizationTM reactor schematic (U.S. patent # 6,790,317; September 14, 2004).

PG

DDV

SRD

PRV

flare

IV UDV

MMV

R

H

ATW

C

A

HIC

DS

TCTC

TCTC

TCTC

TCTC

IV

TC

PT

PT

GSP

WT

WT

H


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Parity plot of Flash CarbonizationTM fixed-carbon yields from various biomass feedstocks(Ind. Eng. Chem. Res. 2003, 42, 3690-3699)

• Fixed-carbon yields from corn cob, oak, and macshellapproach the theoretical limit.

• Leucaena offers almost 90% of the theoretical limit.

yfC - experimental (%)

20 25 30 35 40 45

y fC

- th

eore

tical

lim

it (%

)

20

25

30

35

40

45

90%

80%

100%

MSLW-A1

LW-OOW-2

OW-1CC

LW-A2


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Flash CarbonizationTM demo reactor on the UH campus


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Picture source: http://www.gerhardbechtold.com/TP/gbtp.php

Terra Preta (Amazonian Dark Earths): Highly Fertile Anthropogenic Soils


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Terra Preta SoilTypical Upland Amazonian Soil

Photo source: University of Bayreuth Photo source: University of Bayreuth


16Terra Preta Unamended Soil

Effect of Terra Preta on Plant Growth

Photo source: http://tinselwing.wordpress.com/tag/terra-preta/


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Volcanic ash soil treated with flash carbonizedmacadamia nut shell charcoal

0% (w/w) 5% (w/w) 10% (w/w) 20% (w/w)


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Control 20% (w/w) charcoal


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Lettuce Shoot Biomass

0% 5% 10% 20%

Plan

t wei

ght (

gram

s/po

t)

0

20

40

60

80

100

120

140

160

a a

b

c

Charcoal Rate (w/w)


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Charcoal Effect in an Acid, Infertile Soil

0% 5% NPK + Lime


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NPK + Lime 5% + NPK + Lime


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Preliminary Conclusion:

Charcoal used in the experiment caused a negative effect on plant growth

But why?• Crop?• Soil??• Charcoal???


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• Volatile Matter (VM) content: a measure of the susceptibility of charcoal to further decompose and form carbon when heated

Hydrophobic Hydrophilic

22.5% VM Content 6.3% VM Content


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Effect of High Volatile Matter (22.5%) Charcoal on Plant Growth

0% 10% High VM


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Effect of Low Volatile Matter (6.3%) Charcoal on Plant Growth

0% 10% Low VM


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Low Volatile Matter Charcoal (6.3%) versus High Volatile Matter Charcoal (22.5%)

Low Volatile Matter

High Volatile Matter


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Combined Effect of Low Volatile Matter Charcoal Plus Fertilizer

NPK + Lime

NPK + Lime + 10% Low VM


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Volatile Matter or Feedstock?• VM content affected plant growth in macnut

shell charcoal• Does feedstock make a difference?• Repeat trial with corn cob charcoal


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Control High VM

Low VM

Effect of corn cob charcoal on soybean

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Waller-Duncan K Ratio t-test

Control HVM LVM

Soy

bean

Fre

sh W

eigh

t (g/

pot)

0

2

4

6

8

10

12

14

a

bb


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Control ControlLimeNPK

High VM

NPK

Low VM

NPK


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Waller-Duncan K Ratio t-test

Control Lime+NPK HVM+NPK LVM+NPK

Soy

bean

Fre

sh W

eigh

t (g/

pot)

0

10

20

30

40

abb

c


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Conclusions

• Volatile matter content influences a charcoal’s effectiveness as a soil amendment

• Low volatile matter charcoals are more effective soil amendments than high volatile matter charcoals


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Future Studies

• Will the positive effects observed in greenhouse tests carry over into field trials?

• Will the positive effects persist or diminish with time?

• Will the negative effects of high volatile matter charcoal persist or diminish with time?

Michael J. Antal, Jr, Goro Uehara, Jonathan Deenik, and ... · Nov 27, 2007 3 Fuel Costs Gas...

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