Study finds renewable fuels from hydrotreated vegetable oils outperform transesterified lipids and BTL from woody material in environmental lifecycle impacts and costs
|GHG emission comparison between fossil diesel, transesterified lipids, HVO and woody BTL. GD = HVO; RSO = Rapeseed Oil; SBO = Soybean oil; Biodiesel = Transesterified lipids. Sunde et al. Click to enlarge.|
Researchers in Norway reviewing the lifecycle impacts and costs of three renewable fuels—(1) transesterified lipids, (2) hydrotreated vegetable oils (HVO), and (3) woody biomass-to-liquid (BTL) Fischer-Tropsch diesel—and feedstocks found that HVO made from wastes or by-products such as tall oil, tallow or used cooking oil outperform transesterified lipids and BTL from woody material in both areas.
However, because those feedstocks are limited, to produce larger volumes of biofuels other raw materials must also be used, Kathrin Sunde from the Norwegian University of Life Sciences and her colleagues noted in their open access paper published in the journal Energies. To expand biofuel production and use, they found that the next preferable feedstock is likely residual woody biomass for BTL.
The relatively poor cost performance of BTL can probably be remedied through technological advancements, they suggested, noting that both the ability to not compete with food production and its environmental performance makes it a likely better option than most agricultural feedstocks.
The goal of the study was to compare and rank the renewable fuel technologies available in the short- and medium-term and combine them with the best feedstock options available in the short- and medium-term, based on environmental assessments presented in literature.
Looking at the lifecycle environmental impacts of the fuels, HVO do in most cases outperform transesterified lipids when assessing the same feedstock. Comparing HVO from different lipid feedstocks with woody BTL, the largest differences appear due to the fuel yield of the processes and the feedstock used. If HVO is produced from waste feedstocks with low upstream impacts, the high conversion efficiency of the HVO production process will make HVO the preferred fuel to BTL from any woody feedstock, even woody waste.
Fuel yield and energy efficiency is low in BTL production. When native feedstocks as palm oil and rapeseed oil is used for HVO production, BTL is mostly superior due to low feedstock impacts and high energy yields per hectare of most non-waste woody feedstocks. On the other hand, using short rotation forestry for BTL production may in some cases make HVO from native feedstock with high yields, such as palm oil, more feasible.
This is due to a combination of low energy efficiency and higher feedstock impacts of short rotation forestry than wood from waste and forestry. In a resource perspective, woody biomass is the most abundant biomass resource in Europe and in particular in Northern Europe, where large forest resources are located. Waste feedstocks available for HVO are sparse, but the availability and potential of agricultural feedstocks are higher. For HVO and transesterified lipids, improvements in agricultural practices may improve the overall environmental impacts for native feedstocks, and will be key to successful implementation of these.—Sunde et al.
Sunde, Kathrin; Brekke, Andreas; Solberg, Birger. (2011) Environmental Impacts and Costs of Hydrotreated Vegetable Oils, Transesterified Lipids and Woody BTL—A Review. Energies 4, no. 6: 845-877 doi: 10.3390/en4060845