Abstract
AbstractProcessing biomass into multifunctional products can contribute to food, feed, and energy security while also mitigating climate change. However, biorefinery products nevertheless impact the environment, and this influence needs to be properly assessed to minimize the burden. Life cycle assessment (LCA) is often used to calculate environmental footprints of products, but distributing the burdens among the different biorefinery products is a challenge. A particular complexity arises when the outputs are a combination of energy carrying no mass, and mass carrying no energy, where neither an allocation based on mass nor on energy would be appropriate. A novel hybrid mass–energy (HMEN) allocation scheme for dealing with multifunctionality problems in biorefineries was developed and applied to five biorefinery concepts. The results were compared to results of other allocation methods in LCA. The reductions in energy use and GHG emissions from using the biorefinery's biofuels were also quantified. HMEN fairly distributed impacts among biorefinery products and did not change the order of the products in terms of the level of the pollution caused. The allocation factors for HMEN fell between mass and economic allocation factors and were comparable to energy allocation factors. Where the mass or the energy allocation failed to attribute burdens, HMEN addressed this shortcoming by assigning impacts to nonmass or to nonenergy products. Under the partitioning methods and regardless of the feedstock used, bioethanol reduced GHG by 72–98% relative to gasoline. The GHG savings were 196% under the substitution method, but no GHG savings occurred for sugar beet bioethanol under the surplus method. Bioethanol from cellulosic crops had lower energy use and GHG emissions than from sugar beet, regardless of the allocation method used. HMEN solves multifunctional problems in biorefineries and can be applied to other complex refinery systems. LCA practitioners are encouraged to further test this method in other case studies.
Highlights
To cope with population growth and the rapid depletion of fossil resources, the EU and the Unites States have proclaimed their interest in strengthening green growth in the bioeconomy (EC, 2012, The White House, 2012)
The allocation factors differed between the hybrid mass–energy (HMEN) approach and the other partitioning methods, the estimates of energy use and GHG emissions per product were in most cases within the same order of magnitude (Table 2)
The HMEN method presented in this study overcomes the limitations of allocation methods based solely on the mass or energy content of biorefinery products, which both suffer from drawbacks
Summary
To cope with population growth and the rapid depletion of fossil resources, the EU and the Unites States have proclaimed their interest in strengthening green growth in the bioeconomy (EC, 2012, The White House, 2012). The development of biorefineries is crucial for achieving the transition to a bioeconomy. Allocation in multifunctional processes has been extensively discussed in the literature (Azapagic & Clift, 1999), and several methods for solving these problems have been proposed (Jungmeier et al, 2002). The LCAs for petroleum refineries and for bioenergy and biorefinery systems are, in some cases, sensitive to allocation methods (Wang et al, 2004; Bo€rjesson, 2009; Gnansounou et al, 2009; Luo et al, 2009; Cherubini et al, 2011). The choice of an adequate method is still a contentious issue, and an arbitrary choice can lead to incorrect LCA results (Reap et al, 2008) and poor decision-making (Weidema, 2000)
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