The term “bio-oils” refers to a range of biogenic fuels with oil-like physical properties. More specifically, bio-oils typically indicate the products of pyrolysis (Pyr.) or hydro-thermal liquefaction (HtL), which are thermochemical conversion processes. Fatty Acid Methyl Esters (FAME) and Hydrotreated Vegetable Oil (HVO) are not included in the bio-oil category.
Feedstock for bio-oils are waste biomass streams such as agricultural waste, wet waste, and manure. These are abundant according to current estimates, but their availability is challenged by high demand across multiple industries.
First generation bio-oils such as Fatty Acid Methyl Esters (FAME) and Hydrotreated Vegetable Oil (HVO) are also considered bio-oils but are not included in this category. These fuels are biofuels obtained from fats, greases, and oils with diesel-like properties. While FAME and HVO are already commercial products, the availability of sustainable feedstock is small and the competition from road transport and aviation is intense and are therefore not expected to contribute significantly to the energy transition of the shipping sector.
While conventional (slow) pyrolysis technology is well-known, optimizing the technology to maximize the production of biofuels with suitable properties require further development. Fast Pyrolysis, Flash Pyrolysis, Catalytic Pyrolysis and hydrothermal liquefaction (HtL) are expected to become available technologies by the end of this decade.
The status on fast pyrolysis (FP) is:
- Few small FP crude plants in operation today
- FP oil upgrading is still in pilot scale
The status on hydrothermal liquefaction (HtL) is:
- No full-scale HtL plants in operation today
- HtL oil upgrade technology in pilot scale
Competition from other industries on biomass feedstock could drive fuel costs up. However, it is expected that shipping engines will not need the same level of upgrade compared to engines used in other industries. Therefore, shipping might have an advantage of being able to start using bio-oils as soon as the conversion technology is ready, even if there are uncertainties on the upgrading part for other applications.
The bottleneck for short-term impact from bio-oils is mainly the conversion technology readiness. As soon as the technology is commercially ready, the rate of construction of new production plants per year and, in longer term, the availability of biomass will define an upper limit of impact.
Fuel storage, logistics & bunkering
Managing a variety of bio-oil specifications in the supply chain, including potential mixing of different bio-oils can prove to be challenging. Bio-oil storage stability, fuel system corrosion and NOx emissions are currently uncertain. Logistics and bunkering must be established for bio-oils, and here bio-oils could benefit from existing infrastructure if fully upgraded or blended into established fuel. Other challenges include bacterial growth at the oil/fuel and water interface, and oxidative stability that can lead to breakdown of the fuel and formation of harmful components, potentially leading to corrosion and filter blockages. This must be managed for wide-scale implementation of bio-oils.
Onboard energy storage & fuel conversion
Combusting bio-oils in existing engines appears feasible, but the impact of varying fuel properties (e.g. stability, acidity, corrosion) requires attention. As bio-oil products are made more readily available, engine and onboard storage and testing is needed to better understand potential impacts.
Onboard safety & operations
Bio-oils are high flash-point fuels and are like conventional fuels in many ways. Safe operation is not considered a challenge.
Local air pollutants including SOx and PM are reduced due to their low sulfur content and high oxygenation. Varying quality and feedstock of bio-oils may lead to different emission profiles and levels (e.g. NOX emissions).
Increased NOx emissions can lead to non-compliance with MARPOL Annex VI Regulation 13. Technology for NOx reduction is mature and available. Engines are currently certified on fuel derived from petroleum refining.
Regulation & certification
Standardization is still required around bio-oil including rules for emissions for comparable, but not identical, bio-products. Bio-oils will vary with feedstock and process and the development of standards and certification is therefore complex.
Well-to-wake greenhouse gas quantification for bio-oils not developed in key regulatory bodies such as the European Union (EU) or International Maritime Organization (IMO).
Life-cycle assessment and policy to be developed, particularly certification of CO2 point sources considered renewable. Regulating the climate impact of fuel use from a life cycle perspective offers the industry the opportunity to establish sustainable fuel production and consumption patterns. By regulating the upstream (well-to-tank) climate impact, fuel users can select fuels with solid sustainability credentials. Regulation from a life cycle perspective also reduces the risk of burden shift of climate impact from the downstream (tank-to-wake) part of the value chain to the upstream. This is an important consideration for alternative marine fuels whereby much of the climate impact resides in well-to-tank activities.
Bio-oils as marine fuel: Prospects for the shipping industry - Documentation of assumptions for NavigaTE 1.0 (2021)