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A life cycle carbon balance for electricity produced from forest residues : a British Columbian case study

University of British Columbia

This study estimated the annual life cycle carbon emissions for a hypothetical bioenergy combustion process that generates electricity from forest residues in northern British Columbia. Net annual carbon dioxide emissions were calculated for the process life cycle, which identified and quantified each CO₂ emission source along the bioenergy supply chain. The sources identified included soil carbon, harvesting machinery, chipping, transportation, and biomass combustion. Emissions that were avoided as a result of this process were also calculated. This thesis highlighted the importance of utilizing complete accounting methodology when calculating emissions from energy processes and emphasized that the blanket assumption that all biomass is carbon neutral should not be made. While combustion emissions from the biomass source utilized in this study can be considered to be carbon neutral, a sensitivity analysis showed that emissions could increase by more than 275% if the forest residues were disposed of differently in the business-as-usual scenario. In addition, net process emissions were reduced by over 80% when it was assumed that there were no significant soil carbon emissions. Consequently, bioenergy typically appears more environmentally attractive than it actually is because combustion emissions are generally treated as carbon neutral and upstream emissions, such as from soil carbon, are not typically attributed to residues. In a British Columbian context, utilizing forest residues for bioenergy may usefully increase the provincial energy supply without incurring significant new emissions. This thesis showed that the emissions from harvesting, chipping and transporting residues are only a fraction of the emissions already produced by burning the forest residues. In addition, this thesis proposes that although utilizing forest residues for bioenergy will not result in any new soil carbon emissions, a portion of the soil emissions already incurred should be allocated to forest residues if they are used for bioenergy. Using this full emission accounting methodology, a bioenergy combustion process utilizing forest residues from the Mackenzie area of northern British Columbia would produce approximately 164 kilograms of carbon dioxide per megawatt-hour of electricity, which is significantly less than electricity produced from both coal (721 – 996 kgCO₂/MWh) and natural gas electricity (500 kgCO₂e/MWh).

Text

2011-07-04

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/35854

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/