João Malça

Uncertainty Analysis in Biofuel Systems An Application to the Life Cycle of Rapeseed Oil

Summary This article evaluates the implications of uncertainty in the life cycle (LC) energy efficiency and greenhouse gas (GHG) emissions of rapeseed oil (RO) as an energy carrier displacing fossil diesel (FD). Uncertainties addressed include parameter uncertainty as well as scenario uncertainty concerning how RO coproduct credits are accounted for (uncertainty due to modeling choices). We have carried out an extensive data collection to build an LC inventory accounting for parameter uncertainty. Different approaches for carbon stock changes associated with converting set-aside land to rapeseed cultivation have been considered, which result in different values: from −0.25 t C/ha.yr (carbon uptake by the soil in tonnes per hectare year) to 0.60 t C/ha.yr (carbon emission). Energy renewability efficiency and GHG emissions of RO are presented, which show the influence of parameter versus scenario uncertainty. Primary energy savings and avoided GHG emissions when RO displaces FD have also been calculated: Avoided GHG emissions show considerably higher uncertainty than energy savings, mainly due to land use (nitrous oxide emissions from soil) and land use conversion (carbon stock changes). Results demonstrate the relevance of applying uncertainty approaches; emphasize the need to reduce uncertainty in the environmental life cycle modeling, particularly GHG emissions calculation; and show the importance of integrating uncertainty into the interpretation of results.

Energy and Environmental Benefits of Rapeseed Oil Replacing Diesel

In this paper the benefits of rapeseed oil (RO) replacing petroleum diesel in transportation are evaluated, demonstrating that RO use displaces greenhouse gas (GHG) emissions and saves fossil energy. A systemic description of the RO chain in France has been implemented and GHG emissions and energy used throughout the life cycle have been calculated using alternative co-product credit procedures, namely a replacement method, three allocation approaches (mass, energy, economic) and ignoring co-product credits. The results show that the cultivation stage is particularly important, being responsible for 68% of the primary energy requirements and 87% of the GHG emissions of the RO “well-to-tank” system, mainly due to the use of fertilizers and related N2O emissions. Considerable reductions in fossil fuel depletion and GHG emissions can be achieved by replacing petroleum diesel with rapeseed oil (0.9 MJ and 62 g CO2eq per MJ of fossil diesel replaced), but optimum use of co-products is needed.

Impact of policy on greenhouse gas emissions and economics of biodiesel production.

As an alternative transportation fuel to petrodiesel, biodiesel has been promoted within national energy portfolio targets across the world. Early estimations of low lifecycle greenhouse gas (GHG) emissions of biodiesel were a driver behind extensive government support in the form of financial incentives for the industry. However, studies consistently report a high degree of uncertainty in these emissions estimates, raising questions concerning the carbon benefits of biodiesel. Furthermore, the implications of feedstock blending on GHG emissions uncertainty have not been explicitly addressed despite broad practice by the industry to meet fuel quality standards and to control costs. This work investigated the impact of feedstock blending on the characteristics of biodiesel by using a chance-constrained (CC) blend optimization method. The objective of the optimization is minimization of feedstock costs subject to fuel standards and emissions constraints. Results indicate that blending can be used to manage GHG emissions uncertainty characteristics of biodiesel, and to achieve cost reductions through feedstock diversification. Simulations suggest that emissions control policies that restrict the use of certain feedstocks based on their GHG estimates overlook blending practices and benefits, increasing the cost of biodiesel. In contrast, emissions control policies which recognize the multifeedstock nature of biodiesel provide producers with feedstock selection flexibility, enabling them to manage their blend portfolios cost effectively, potentially without compromising fuel quality or emissions reductions.

Capturing uncertainty in GHG savings and carbon payback time of rapeseed oil displacing fossil diesel in Europe

This article addresses different land use change scenarios, as well as uncertainty issues related to parameters and concerning how co-product credits are accounted for in the life-cycle modeling of rapeseed oil (RO). A comprehensive assessment of different land use change scenarios (rapeseed cultivation in former agricultural land and grassland) and agricultural practices has been conducted, which results in different carbon stock change values. RO GHG intensity and GHG emission implications when RO displaces petroleum diesel have been assessed in terms of probability distributions using a substitution method, three allocation approaches and ignoring co-product credits. The net GHG balance of rapeseed oil is strongly influenced by soil carbon stock variations due to land use change and by the magnitude of nitrous oxide emissions from cultivated soil. Depending on prior land use, GHG emissions may comply with the European renewable energy directive target of 35% GHG emission savings (arable land converted to rapeseed cultivation) or, conversely, may completely offset carbon gains attributed to rapeseed oil production for several decades (conversion of grassland).