harvest residue utilization in small- and large-scale bioenergy Systems:

harvest residue utilizationin small- and large-scale bioenergy Systems:

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Julian Cleary, Post-Doctoral FellowFaculty of ForestryUniversity of Toronto

Life cycle results and the effects of common errors in the application of LCA methods

Bioenergy background

Bioenergy is currently the world’s largest renewable energy source and supplies 10% of primary energy demand.

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World Primary Energy Demand 2010 (IEA)

Increasing the Supply…

Moving beyond pulp and paper sector to modified coal plants and CHP systems

Costs and environmental impacts 3

The Potential Problems…

Next Step

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Undertake research

LCA of forest bioenergy systems of different scales

Cogeneration vs. electricity-only systems

Here are the things we “know”…

Larger scale plants are more efficient

Average biomass shipping distances are longer for large-scale plants

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Smaller scale plants cost more (relative to potential electricity output)

Adequate nearby heat demand is less likely next to large-scale plants

Wood pellets require more processing than wood chips but are more efficient to store due to their higher bulk density

Problems with what has been done?

Numerous bioenergy LCAs address GHG mitigation

Common methodological errors boost estimated benefits

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3) The displaced and consumed electricity are not identical

To what extent have these errors affected GHG mitigation estimates?

1) Assumption of carbon neutrality

2) Omission of climate effect of GHG emission timing on overall mitigation

LCA Assumptions

US EPA’s TRACI 2.1 LCIA method with Canada 2005 normalization

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Assumed 20 year project lifespan

Financing – 8% int. rate

US EI database, with LCA unit processes adapted to the conditions modelled

Time-adjusted GHG emissions

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Presumed source of biomass: Haliburton Forest

Annual harvest of approx. 35,400 green tonnes

Significant amounts of residue left after harvest

Approx. 7,850 dry tonnesBased upon estimates by Rudz

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Biomass Collection

Reducing the topping diameter of the cut by 5.4 cm will result in an additional 1,183 dry tonnes collected

http://www.pfla.bc.ca/wp-content/uploads/2012/07/harvest-residue.jpg

Biomass collected on 2/3 of harvest area

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Haliburton harvest residue can supply the electricity needs of almost 200 Ontario homes

Cost: $16.22 per dry tonne

Transportation of feedstock

– Mill/gasifier: 27 km• Use of self-loading truck

• High fuel use on unpaved roads, idled trucks, lower truck capacity for residue

– Atikokan: approx. 1900 km

•Average distance from harvest sites to:

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Residue Shipping Cost: $21.08/dt

Pellet Shipping Cost: $49.77/dt

Harvest residue processing

Drying, chipping and/or pelletization

Small-scale CHP system:-drying uses recovered heat

More equipment and electricity used in pelletization

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Large-scale combustion system:-hog fuel burned for drying-equal to 15% of harvest residue inputs

S1 Cost: $9.15 per dry tonneS2 Cost: $51.72 per dry tonne

Wood Chip Gasification

Hypothetical 250 KWe gasifier

39% of the energy content of the wood is lost in the conversion to producer gas

Producer gas combustion in producer gas engine-Electrical efficiency: 40%

Overall electrical efficiency-24%

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Heat from Gasification32% of recovered heat is used for gasification reaction and wood chip drying

Available heat can dry fourteen times the Haliburton kiln capacity

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Modifications to Atikokan Generating Station

Electrical efficiency-31.6% (excluding input fuel loss during drying and pelletization)

-8% capacity factor 15http://www.opg.com/power/thermal/atikokanfactsheet1009.pdf

$170 million (capital)

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Contribution of each stage of the S1 and S2 life cycles to non-biogenic Greenhouse

Gas emissions

If displacing coal, S1 emissions rise to 46 g, and S2 emissions rise to 193 g.

Time–Adjusted Cumulative GHG Mitigation

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Non-Time-Adjusted GHG Mitigation

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Timing of Emissions

Emissions do not all take place at the beginning of the selected time horizon

Time-adjusted GHG mitigation is at a far lower magnitude (omitting time-adjustment boosts GHG mitigation by 51% over 50 yrs).

This change in GHG modelling does not alter the position of S1 relative to S2 in terms of GHG mitigation.

Carbon Neutrality

Incorrect assumption of C neutrality boosts GHG mitigation estimate by over 50% over a 50 year time horizon

Other findings

The average area subject to residue removal was 3.7 m2/kWh

The small-scale system has a far greater potential to reduce impacts than is indicated in the results because 63% of the potentially recoverable heat remains unused

Average annual costs per kWh generated over the 20 year lifespan of each project

(in 2010 dollars)

Key Findings

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C storage effect delays GHG mitigation by approximately 4 years

Electrical efficiency disadvantage of small-scale CHP system can be overcome even at low levels of heat recovery

The avoided propane use in the lumber kiln compensates for all of the non-biogenic GHGs of the small-scale CHP system.

S1, but not S2, can surpass even the non-biogenic GHG benefits from renewable electricity generation alternatives

Future Research Trajectories

Biochar and bio-oil

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Thank you!

NSERC

MITACS-Accelerate

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Haliburton Forest and Wildlife Reserve

Ontario Power Generation

Harvest Residue Vs. Dedicated Harvest

• Unlike a dedicated harvest, residue collection does not affect carbon sequestration from trees

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• Unlike fossil fuels, harvest residue decomposes if left in place