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Modeling the net greenhouse gas balance of projects that displace gasoline with wood ethanol from short rotation tree plantations

University of British Columbia

Projects that establish fast growing tree plantations and substitute gasoline with ethanol from the resulting wood biomass have the potential to reduce atmospheric carbon dioxide and other greenhouse gas (GHG) emissions and to increase terrestrial carbon (C) stocks. However, current methodologies for evaluating the net GHG balance of biofuel projects do not consider specifically the life cycle impacts of biogenic C dynamics and the emissions from decomposition of dead organic matter (DOM). This dissertation proposes the Carbon Balance and Biomass to Biofuel Optimization planning model (C3BO), which determines the net GHG balance of biofuel projects on a life cycle basis from initial land-use change, establishment of plantations and construction of biorefinery, through conversion of biomass into ethanol and final use in internal combustion engines. The novel approach of the C3BO model is the inclusion of initial C stocks, soil organic matter and biogenic C dynamics to the project GHG balance calculations. C3BO model results show that the GHG balance of biofuel projects is most sensitive to initial carbon stocks and biorefinery emissions. The potential direct land-use change impacts on initial C stocks (including the initial biomass removal and the affect of the project on the emissions from decay of soil organic matter) can affect the life-cycle net GHG balance, clearly indicating that they need to be included in life cycle analyses of biofuel projects. The magnitude of the reductions in emissions, compared with the fossil fuel baseline, is highly dependent on the length of the project time horizon: the GHG balance changes with project length, and the impact of input variables also changes with time. Biofuel projects can produce fewer emissions but they can also result in more emissions than the displaced fossil fuel system. The viability of biofuel projects as worthwhile climate mitigation strategies depends on project-specific conditions that need to be properly assessed on a project-by-project basis. This study also suggests that ethanol production cost is twice as sensitive to conversion efficiency than to biomass yield. Improving conversion efficiency will result in much larger benefits than improving biomass yield, in terms of reducing ethanol production costs.

Text

2015-04-30

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/46657

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/