Life cycle assessment of biochar systems

Kelli G. Roberts, Brent A. Gloy, Stephen Joseph, Norman R. Scott, Johannes Lehmann

Department of Crop and Soil Sciences, Cornell University

Northeast Biochar SymposiumUMass Amherst

November 13, 2009

What is Life Cycle Assessment (LCA)?

Methodology to evaluate the environmental burdens associated with a product, process or activity throughout its full life by quantifying energy, resources, and emissions and assessing their impact on the global environment.

LCA has been standardized by the ISO (International Organization for Standardization).

materials manufacture

use end of life

Life cycle of a product

Goals of the LCA To conduct a cradle-to-grave analysis of the

energy, greenhouse gas, and economic inputs and outputs of biochar production at a large-scale facility in the US.

To compare feedstocks (corn stover, yard waste, switchgrass).

The functional unit: A measure of the performance or requirement for a

product system. Provides a reference so that alternatives can be

compared.

Our functional unit: The management of one tonne of dry biomass.

Scope: the functional unit

System boundaries

Dashed arrows with (-) indicate avoided processes. The “T” represents transportation.

Biomass collection Drying Slow pyrolysis

Pyrolysis facility

TT

Soil application

Natural gas production & combustion

(-)

(-)

Farm equipment, agrochemicals

T

T

T

Compost

(-)

T

Syngas heat

product

Biochar

Heat exhaust

Fertilizers

Electricity production

Fossil fuels production

Construction materials

ShreddingBiomass collection Drying Slow pyrolysis

Pyrolysis facility

TT

Soil application

Natural gas production & combustion

(-)

(-)

Farm equipment, agrochemicals

T

T

T

Compost

(-)

T

Syngas heat

product

Biochar

Heat exhaust

Fertilizers

Electricity production

Fossil fuels production

Construction materials

Shredding

Biochar with heat co-product

www.coaltecenergy.com

Installation at Frye Poultry Farm, West Virginia

capacity of 300 kg dry litter hr-1

LCA of biochar – industrial scale Plant throughput 10 t dry biomass hr-1

Runs at 80% capacity

The slow pyrolysis process has four co-products: Biomass waste management Biochar soil amendment Bioenergy heat production Carbon sequestration

Energy flows: feedstock to products

Sankey diagram, per dry tonne stover

Dry

ing

Pyro

lysi

s

stover: 16000 MJ

Hea

t exch

an

ge

r

biochar: 8880 MJ

heat losses: 1969 MJ

stover: 16000 MJ

natural gas: 58 MJ

heat losses: 106 MJ

heat losses: 432 MJ

process heat.: 437 MJ

(Start-up)

Th

erm

al oxid

ize

r

heat losses: 80 MJ

syngas: 7958 MJ heat energy: 7878 MJ heat applications: 4591 MJ

process heat: 407 MJ

process heat: 886 MJ

Feedstocks Corn stover

Late and early harvest (15% and 30% mcwb). Second pass collection, harvest 50% above ground biomass.

Yard waste 45% mcwb No environmental burden for production. Assumed to be diverted from large-scale composting facility.

Switchgrass 12% mcwb Scenarios A and B to capture range of GHG flows associated

with land-use change

Feedstocks (cont.) Switchgrass A

Lifecycle emissions model (Deluchi), informally models land-use change.

Assumes land conversion predominantly temperate grasses and existing croplands, rather than temperate, tropical or boreal forests.

Net GHG of +406.8 kg CO2e t-1 dry switchgrass harvested.

Switchgrass B Searchinger et al (2008) global agricultural model. Assumes land conversion in other countries from forest and

pasture to cropland to replace the crops lost to bioenergy crops in the U.S.

Net GHG of +886.0 kg CO2e t-1 dry switchgrass harvested.

Deluchi, M. “A lifecycle emissions model (LEM)”; UCD-ITS-RR-03-17; UC Davis, CA, 2003.

Searchinger, T.; et al. Science 2008, 319 (5867), 1238-1240.

Feedstock properties, pyrolysis process yields, and biochar properties for various biomass sources

PropertyLate

stoverEarly stover

Switchgrass

Yard waste

Moisture content, wet basis 15% 30% 12% 45%

Ash content (wt.% DM) 5.6 5.6 4.6 4.5

C content of feedstock (wt.% DM)

45 45 48 47

Lower heating value (MJ t-1 DM)

16000 16000 17000 18000

Feedstock to heat energy efficiency

37%

Yield of biochar (wt. %) 29.60 29.60 28.80 29.63

C content of biochar (wt.%) 67.68 67.68 63.09 65.89

Stable portion of total C in biochar

80%

Improved fertilizer use efficiency (for N, P, K)

7.2%

Reduced soil N2O emissions

from applied N fertilizer50%

Pyrolysis and biochar parameters

Energy balance

All feedstocks are net energy positive. Switchgrass has the highest net energy. Agrochemical production and drying consume largest proportion of energy. Biomass and biochar transport (15 km) consume < 3%. “Other” category includes biochar transport, plant dismantling, avoided fertilizer

production, farm equipment, and biochar application.

0 2000 4000 6000

cons.

gen.

cons.

gen.

cons.

gen.

cons.

gen.

Energy (MJ t-1 dry feedstock)

agrochems

field ops

drying

chipping

biomass trans

plant constr

other

syngas heat

avoid fos fuel

avoid compost

Late

st

over

Ear

ly

stov

erS

witc

h gr

ass

Yar

d

was

teNet = + 4116

Net = + 3044

Net = + 4899

Net = + 4043

GHG emissions balance

Stover and yard waste have net (-) emissions (greater than -800 kg CO2e). However, switchgrass A has -442 kg CO2e of emissions reductions, while B actually has

net emissions of +36 kg CO2e. “Other” category includes biomass transport, biochar transport, chipping, plant

construction and dismantling, farm equipment, biochar application and avoided fertilizer production.

0 300 600 900

emit.

reduct.

emit.

reduct.

emit.

reduct.

emit.

reduct.

emit.

reduct.

Greenhouse gases (kg CO2e t-1 dry feedstock)

LUC & fieldemiss.agrochems

field ops

other

stable C

avoid foss fuelgen. & comb.land-use seq.

reduced soilN2O emiss.avoid compost

Late

st

over

Ear

ly

stov

erS

witc

h gr

ass

BY

ard

was

te

Net = - 864

Net = - 793

Net = - 442

Net = + 36

Net = - 885

Sw

itch

gras

s A

GHG emissions (cont.)

Biomass and biochar transport (15 km) each contribute < 3%. The stable C sequestered in the biochar contributes the largest

percentage (~ 56-66%) of emission reductions. Avoided natural gas also accounts for a significant portion of reductions

(~26-40%). Reduced soil N2O emissions upon biochar application to the soil

contributes only 2-4% of the total emission reductions.

0 300 600 900

emit.

reduct.

emit.

reduct.

emit.

reduct.

emit.

reduct.

emit.

reduct.

Greenhouse gases (kg CO2e t-1 dry feedstock)

LUC & fieldemiss.agrochems

field ops

other

stable C

avoid foss fuelgen. & comb.land-use seq.

reduced soilN2O emiss.avoid compost

Late

st

over

Ear

ly

stov

erS

witc

h gr

ass

BY

ard

was

te

Net = - 864

Net = - 793

Net = - 442

Net = + 36

Net = - 885

Sw

itch

gras

s A

Economic analysis

High revenue scenario $80 t-1 CO2e

Low revenue scenario $20 t-1 CO2e

The high revenue of late stover (+$35 t-1 stover). Late stover breakeven price is $40 t-1 CO2e. Switchgrass A is marginally profitable. Yard waste biochar is most economically viable. Highest revenues for waste stream feedstocks with a cost associated with current

management.

-120 -80 -40 0 40 80 120 160 200cost ($ t-1 dry feedstock)

biomass collection biomass transportpyrolysis biochar transportbiochar application lost compost revenuetipping fee avoided compost costbiochar P & K content biochar improved fertilizer usecarbon value syngas heat

+$35

-$17

Late

st

over

Sw

itch

gras

s A

Yar

d w

aste

Sw

itch

gras

s B

+$8

-$18

-$28

-$30

+$69 +$16

Stable C vs. life cycle emissions

Net profits valuing stable C only ($ t-1 DM)

($ t-1 DM) Late stoverSwitchgrass A &

BYard waste

High revenue scenario $13 $17 $44

Low revenue scenario -$23 $8 $10

Yard waste still most profitable Stover and switchgrass have switched

Transportation sensitivity analysis

The net revenue is most sensitive to the transport distance, where costs increase by $0.80 t-1 for every 10 km.

The net GHG emissions are less sensitive to distance than the net energy. Transporting the feedstock and biochar each 200 km, the net CO2 emission

reductions decrease by only 5% of the baseline (15 km). Biochar systems are most economically viable as distributed systems with

low transportation requirements.

Distance (km)

0 200 400 600 800 1000

Ne

t GH

G (

kg C

O2

e t-1

dry

sto

ver)

-1000

-800

-600

-400

-200

0

Ne

t en

erg

y (M

J t-1

dry

sto

ver)

0

1000

2000

3000

4000

5000

6000

Re

ven

ue

($

t-1 d

ry s

tove

r)

-90

-60

-30

0

30

60

Net energy

Net revenue

Net GHG

Biochar-to-soil vs. biochar-as-fuel

Biochar-as-fuel: biochar production with biochar combustion in replacement of coal are -617 kg CO2e t-1 stover

Biochar-to-soil: -864 kg CO2e t-1 stover 29% more GHG offsets with biochar-to-soil rather

than biochar-as-fuel

Net GHG

Biomass direct combustion vs. biochar-to-soil

Not including avoided fossil fuels: Biomass direct combustion: +74 kg CO2e t-1 stover Biochar-to-soil: -542 kg CO2e t-1 stover Emission reductions are greater for a biochar system than for

direct combustion

With avoided natural gas: Biomass direct combustion: -987 kg CO2e t-1 stover Biochar-to-soil: -864 kg CO2e t-1 stover Net GHG look comparable However, for biochar-to-soil, 589 kg of CO2 are actually

removed from the atmosphere and sequestered in soil, whereas the biomass combustion benefits from the avoidance of future fossil fuel emissions only

Transparent system boundaries

Net GHG

Conclusions Careful feedstock selection is required to avoid unintended consequences

such as net GHG emissions or consuming more energy than is generated.

Waste biomass streams have the most potential to be economically viable while still being net energy positive and reducing GHG emissions (~ 800 kg CO2e per tonne feedstock).

Valuing greenhouse gas offsets at a minimum of $40 t-1 CO2e and further development of pyrolysis-biochar systems will encourage sustainable strategies for renewable energy generation and climate change mitigation.

Next steps Different biochar-pyrolysis sytems

Mobile unit Small-scale non-mobile, batch units With and without energy capture

www.biocharengineering.com Brazilian type metal kiln, Nicolas Foidl

Preliminary results:Mobile unit for stover biocharWithout energy capture Net GHG = -550 kg CO2e t-1 stoverNet energy = -1000 MJ t-1 stover

Next steps Developing country scenarios

Household cook stoves Village scale units Central plant at biomass source

Different feedstocks Manures Native grasses on

marginal lands

Pro-Natura in Senegal

Cook stoves in Kenya

Acknowledgements Cornell Center for a Sustainable Future (CCSF)

John Gaunt (Carbon Consulting) Jim Fournier (Biochar Engineering)Mike McGolden (Coaltec Energy)

Lehmann Biochar Research Group, especially Kelly Hanley, Thea Whitman, Dorisel Torres, David Guerena, Akio Enders

Thank you!

Feedstock properties, pyrolysis process yields, and biochar properties for various biomass sources

PropertyLate

stoverEarly stover

Switchgrass

Yard waste

Moisture content, wet basis 15% 30% 12% 45%

Ash content (wt.% DM) 5.6 5.6 4.6 4.5

C content of feedstock (wt.% DM)

45 45 48 47

Lower heating value (MJ t-1 DM) 16000 16000 17000 18000

Yield of biochar (wt. %) 29.60 29.60 28.80 29.63

C content of biochar (wt.%) 67.68 67.68 63.09 65.89

Stable portion of total C in biochar

80%

Improved fertilizer use efficiency (for N, P, K)

7.2%

Reduced soil N2O emissions

from applied N fertilizer50%

DM = dry matter

Pyrolysis facility costs

Costs (2007 USD)

Pretreatment

Operating ($ t-1 DM) $4.77

Capital ($ t-1 DM) $4.12 $3.6 M Total

Pyrolysis

Operating ($ t-1 DM) $26.81

Capital ($ t-1 DM) $12.14 $10.6 M Total

Iron

Total Operating ($ t-1 DM) $31.58

Total Capital ($ t-1 DM) $16.26

Total ($ t-1 DM) $47.84

Costs and revenues per dry tonne of feedstock. Each feedstock has a low and high revenue scenario, representing $20 and $80 per tonne CO2e sequestered, respectively

  Late stover Switchgrass A Switchgrass B Yard waste

  Low high Low High low High low high

Biochar

P & K content 18.39 9.68 9.68 10.01

Improved fertilizer use 1.22 1.18 1.18 1.22

C value 17.28 69.12 8.84 35.36 -0.72 -2.88 17.70 70.80

Energy 42.81 55.05 55.05 35.20

Tipping fee NA NA NA 49.09

Avoided compost cost NA NA NA 10.98

Lost compost revenue NA NA NA -56.03

Feedstock -43.46 -36.89 -36.89 NA

Transport

Biomass -6.24 -6.02 -6.02 NA

Biochar -1.57 -1.53 -1.53 -1.57

Biochar application -1.07 -1.04 -1.04 -1.07

Pyrolysis

Operating -31.58 -31.58 -31.58 -31.58

Capital -16.26 -16.26 -16.26 -16.26

Net value ($) -17.07 34.77 -18.57 7.95 -30.29 -28.13 15.87 68.97