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Farrell article. Summary Evaluated potential effects of increased ethanol use Reviewed a number of previously published articles on corn ethanol Ethanol.

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Presentation on theme: "Farrell article. Summary Evaluated potential effects of increased ethanol use Reviewed a number of previously published articles on corn ethanol Ethanol."— Presentation transcript:

1 Farrell article

2 Summary Evaluated potential effects of increased ethanol use Reviewed a number of previously published articles on corn ethanol Ethanol results in less petroleum usage, but minor differences in GHGE Need for additional research in environmental metrics

3 Summary Adjusted the studies to have equivalent bounds Corrected some of the data sources in the other articles Large scale use of ethanol would require cellulosic technology

4 Methods Checked data sources of 6 current reviews on corn based ethanol Looked at net energy, but highly dependent on system boundaries Finding intuitive and meaningful units besides net energy is needed

5 Methods Add coproduct credit Apply consistent system boundary (include effluent processing energy and neglecting laborer food requirements) Account for different energy types Calculate policy metrics (not sure what this is)

6 Sensitivity Analysis Most sensitive to coproduct allocation Corn ethanol produces valuable coproducts – Studies that showed a negative energy balance for corn ethanol assumed no coproducts

7 Results Ethanol significantly reduces petroleum usage Only 5 to 26% of the energy is renewable though GHG reduction was between a 20% increase and a 32% decrease Their results – Reduce petroleum by 95% on energetic basis – Reduce GHGE by 13%

8 Uncertainty Results Uncertainty analysis suggests results are good Variation in performance by location Given appropriate policy incentives, corn ethanol could be improved Only cellulosic ethanol appears to save GHGE

9 Supplemental Data Well laid out spreadsheet (go over briefly) LHV versus HHV – LHV energy – water is evaporated from the fuel during combustion – HHV energy – recovers energy in water vapor

10 Net Energy Value Different definitions in each study Don’t define nuclear or renewable electricity Ignore differences in energy quality Very sensitive to coproducts – Are coproducts subtracted from energy inputs – Are coproducts added to energy outputs – Results in a different ratio Makes net energy ratio difficult to use

11 Metrics GHGE / MJ fuel Petroleum inputs / MJ fuel Coal inputs / MJ fuel Natural gas inputs / MJ fuel Other energy inputs / MJ fuel X – is the variable of interest A – MJ energy per l of ethanol Calculations in terms of x/a

12 Agricultural Inputs Problems with lime application Inputs to farm machinery – Used an economic input output model from Carnegie Mellon University

13 Coproducts Anything that adds value should be counted as a positive impact Looked at process, market-based, and displacement Process method – Use a tool like ASPEN to model mass and energy in process – Allocate according to the process simulation

14 Coproduct Market Based – Allocates total energy according to the relative value Displacement method (system expansion) – Preferred method – according to some other studies Most comprehensive would be market based with the displacement

15 GHGE Use IPCC on global warming potential GHGE for nitrogen fertilizers shown in S-8 to S- 10 Assume small changes on unfarmed land into cultivation Some crop shifting Importing ethanol would cause some land use changes

16 Sensitivity Analysis Determined by 1% change in input parameter Major factors – Refinery energy – Farm yield – Refinery yield – Coproduct credit – Nitrogen energy – Nitrogen application rate

17 Sensitivity Analysis N 2 O big factor Two key implications – Any feedstock that relies heavily on nitrogen will not provide significant GHGE relative to gasoline – Relatively little petroleum is used for corn or cellulosic ethanol, so large reductions in petroleum consumption are likely


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