German study shows rapeseed GHG potential

By Luke Geiver | January 05, 2011

Posted Jan. 5, 2011

The German Biomass Research Center has conducted a study on optimizing greenhouse gas (GHG) emissions from rapeseed-based biodiesel. The goal of the study was to analyze the current default values for GHGs from rapeseed-based biodiesel, and to outline areas that would improve current GHG levels. Authored by Stefan Majer and Katja Oehmicen from the center, the study was conducted partially in response to the German Biofuel Sustainability Ordinance that calls for biofuels used by 2017 to reach a GHG reduction target of 50 percent when compared to fossil fuels, and 60 percent by 2018.

According to the study, most biofuels at their current default levels for GHG reductions will not be sufficient in meeting the goals set for 2017. "However," the study points out, "this raises the question of the data basis on which the default values were calculated and what reduction in GHG emissions could theoretically be achieved with a process chain optimized in terms of its GHG account."

The study found that in the cultivation process, "the production and use (field emissions) of industrial nitrate fertilizers proved to be the main influencing parameters for the overall results." By varying the industrial nitrate fertilizers and using biodiesel as opposed to diesel in the agricultural production processes, the study concluded that it is possible to make considerable improvements for reducing the overall emissions caused during rapeseed cultivation from 29 kg CO2 Eq./GJ biodiesel to roughly 21. If biodiesel were used instead of fossil fuel, emissions related to fuel use during cultivation would be reduced from 5.87 to 3.44.

At the biomass conversion stage, the study showed that heat, electricity and methanol were the main factors influencing emission numbers. By running a sensitivity calculation that inserted a biogenic source of energy into the conversion process, the analysis indicated that "the emissions from the rapeseed oil production process could be reduced from approximately 3 to approximately 1.5 kg CO2 Eq./GJ biodiesel," and, from the biodiesel production process approximately 11 to roughly 6.4 kg CO2 Eq./GJ biodiesel.

While the GHG emission levels of rapeseed-based biodiesel are roughly 28 kg CO2 Eq./GJ biodiesel, the study noted, "the maximum theoretical optimization potential which was identified by the sensitivity analysis represent an improvement of approximately 46 percent on the default value." Combined with conversion methods, the study said that the research clearly shows the influence of the use of industrial fertilizers, and as a result, "this study could provide an initial basis for the modification of fertilizer use strategies with the aim of developing GHG optimized rapeseed cultivation."

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