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harvest residue utilization in small- and large-scale bioenergy Systems:. Life cycle results and the effects of common errors in the application of LCA methods. Julian Cleary, Post-Doctoral Fellow Faculty of Forestry

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harvest residue utilization

in small- and large-scale bioenergy Systems:

Life cycle results

and the effects of

common errors in

the application of

LCA methods

Julian Cleary, Post-Doctoral Fellow

Faculty of Forestry

University of Toronto

Bioenergy background

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

World Primary Energy Demand 2010 (IEA)

Increasing the Supply…

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

The Potential Problems…

Costs and environmental impacts

Next Step

Undertake research

LCA of forest bioenergy systems of different scales

Cogeneration vs. electricity-only systems

Here are the things we “know”…

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

Larger scale plants are more efficient

Average biomass shipping distances are longer for large-scale plants

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?

Common methodological errors boost estimated benefits

Numerous bioenergy LCAs address GHG mitigation

1) Assumption of carbon neutrality

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

3) The displaced and consumed electricity are not identical

To what extent have these errors affected GHG mitigation estimates?

LCA Assumptions

Assumed 20 year project lifespan

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

Financing – 8% int. rate

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

Time-adjusted GHG emissions

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 tonnes

Based upon estimates by Rudz

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

Biomass Collection

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

Biomass collected on 2/3 of harvest area

Cost: $16.22 per dry tonne


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

Transportation of feedstock

  • Average distance from harvest sites to:

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

Large-scale combustion system:

-hog fuel burned for drying

-equal to 15% of harvest residue inputs

S1 Cost: $9.15 per dry tonne

S2 Cost: $51.72 per dry tonne

Wood Chip Gasification

Hypothetical 250 KWe gasifier

Producer gas combustion in producer gas engine

-Electrical efficiency: 40%

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

Overall electrical efficiency


Heat from Gasification

32% of recovered heat is used for gasification reaction and wood chip drying

Available heat can dry fourteen times the Haliburton kiln capacity

Modifications to Atikokan Generating Station

$170 million (capital)

Electrical efficiency

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

-8% capacity factor


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

Non-Time-Adjusted GHG Mitigation

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

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

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

C storage effect delays GHG mitigation by approximately 4 years

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

Future Research Trajectories

Biochar and bio-oil

Thank you!

Ontario Power Generation

Haliburton Forest and Wildlife Reserve



Harvest Residue Vs. Dedicated Harvest

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

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

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