MARINE BIOFUELS: PRACTICAL DECARBONISATION FOR OPERATING SHIPS

Biofuels represent a significant opportunity for the maritime industry to advance decarbonisation with minimal disruption to existing fleets. Derived from renewable organic material — ranging from plant matter and algae to industrial and municipal waste — marine biofuels provide an adaptable, low-emission alternative to traditional fossil fuels. While biofuels are available in solid, liquid, and gaseous forms, liquid biofuels are taking centre stage in maritime applications due to their compatibility with current ship technology, fuel infrastructure, and regulations. For shipowners and operators, they offer a practical pathway to reducing emissions while extending the value of existing vessels.

This article explores what marine biofuels are, which biofuel types are suitable for ships, what regulations apply, and what operators should consider when integrating biofuels into existing fuel supply systems.

REGULATORY DRIVERS AND RETROFITTING FOR MARINE BIOFUELS

Industry analysts estimate that a significant portion of the current global fleet — potentially up to two-thirds — may not undergo major retrofits for next-generation fuels such as LNG, methanol, or ammonia, primarily due to vessel age and economic constraints. For these vessels, SOLAS-compliant marine biofuels offer a practical path to achieving IMO carbon reduction targets with minimal capital expenditure (CAPEX).

These fuels operate within existing safety and environmental frameworks, as outlined in SOLAS Chapter II-2 and MARPOL Annex VI, with requirements covering minimum flash point, sulphur content, and fuel quality. SOLAS Chapter II-2 mandates a minimum flash point of 60°C for marine fuels, while MARPOL Annex VI governs sulphur content and emissions. Compliance is verified through documentation such as the Bunker Delivery Note (BDN) and Safety Data Sheets (SDS), which form part of the operator’s ISM obligations, while national port authorities verify supplier compliance.

Beyond IMO regulations, regional frameworks such as the EU’s FuelEU Maritime and the EU Emissions Trading System (ETS) are also driving biofuel adoption by requiring greenhouse gas intensity reductions and emissions reporting for ships calling at European ports.

PROPERTIES FOR BIOFUELS FOR MARITIME USE

Biofuels suitable for marine engines must meet strict statutory, technical, and safety requirements. Below are key categories:

RAW VEGETABLE OILS:

Extracted from oil-bearing crops such as rapeseed, soybean, and sunflower, these oils are characterised by high viscosity (30–40 cSt at 40°C) and moderate energy density. Use requires fuel pre-heating and careful material selection due to acidity and possible corrosion risks. In addition, fuel consumers may require MGO mixed in with raw vegetable oils (typically 5-20%) to work as a combustion and ignition promoter.

HYDROTREATED VEGETABLE OIL (HVO):

Produced via hydrotreatment of vegetable oils or animal fats, HVO closely resembles conventional diesel in performance, with low viscosity (2–4 cSt at 40°C) and superior cold-flow properties. This premium, drop-in biofuel meets ISO 8217:2024 and EN15940 requirements and is often called also renewable diesel. EN15940 HVO can be used in existing engines without modification, though due to the paraffinic nature of HVO, filtration needs in the fuel circulation may be increased during fuel changeovers from HVO to asphaltene rich fuels, as high concentrations of paraffins can promote asphaltene precipitation of the heavy fuel oils.

FATTY ACID METHYL ESTER (FAME):

Manufactured through transesterification of vegetable oils or fats, FAME is also included at up to 100% in ISO 8217:2024 marine fuel standards, RF and DF grades. FAME is low in viscosity (4–6 cSt at 40°C) and may require fuel oil cooling. FAME is also called biodiesel (including blends such as B20 and B30) but usage requires FAME compatibility of engine elastomers and seals.

EMULSION AND ADVANCED BIOFUELS:

Blending bio-derived water-soluble feedstocks such as glycerin from FAME production processes and sugars from pyrolysis processes with water and further emulsification of fine fuel droplets to the water base produces cost-effective fuels like bioMSAR™, offering substantial CO₂ reductions versus HFO. These solutions are being tested in full-scale sea trials and may become mainstream options for existing vessels.

HYDROTREATED PYROLYSIS OIL (HDPO) AND F-T BIODIESELS:

HDPO and Fischer-Tropsch biodiesels that can utilize even solid bio-feedstocks and do not require oils and fats as one offer technical promise but remain in the early stages of adoption due to production complexity and high costs.

SYSTEM INTEGRATION AND OPERATIONAL CONSIDERATIONS

Biofuels generally require only minor modifications to fuel supply systems in case of SOLAS-compliant types. Engineers may retrofit existing biofuel handling units to be able to handle a given set of biofuels, or modify fuel supply lines to incorporate a so called fuel split system, where one fuel system is for biofuels and the other for traditional fuels. Key integration considerations include:

HEATERS:

Required for high-viscosity fuels to attain optimal injection properties. Surface temperature and surface power control are important for some biofuels to avoid fuel degradation or coking, such as emulsion fuels or pyrolysis oils, respectively.

COOLERS:

Particular consideration often necessary for biofuels with higher temperature cold flow properties to maintain suitable viscosity and prevent wax formation and cold filter plugging.

HOMOGENIZERS:

Used to reduce sludge and particulate content, enhancing fuel stability and engine performance. Especially for systems running with mixtures of paraffinic diesels and asphaltene rich HFO’s, for example during changeovers.

BIO-MIXER/BLEND-ON-BOARD:

Facilitate precise mixing of biofuels and distillates, enabling multiple operational and efficiency benefits through ignition and combustion promoting, or even enabling water emulsion fuels with water soluble fuel components.

SAFETY, COMPLIANCE AND COMPETITIVE ADVANTAGES

SOLAS and MARPOL Annex VI ensure that biofuel adoption is both safe and seamless. With proper product selection and system integration, vessels can use biofuels with minimal change to tanks, machinery, and bunkering processes. Those fuels that fall outside SOLAS requirements, to be designed under the IMO IGF Code, require more extensive retrofits and certification. For operational vessels, SOLAS-compliant biofuels are the most cost-effective and least disruptive way to achieve sustainability objectives.

CONCLUSION

Marine biofuels are an essential component of the shipping industry’s decarbonisation toolkit, particularly for fleets not suited for conversion to alternative fuels. They leverage existing infrastructure, meet evolving regulatory demands, and can be deployed with minimal operational disruption. As technological development and regulatory support continue, biofuels will play an increasingly important role in achieving maritime sustainability targets and supporting a global low-carbon transition.

Join our biofuel webinar on 7th of May to learn more about biofuel options and biofuel supply solutions. Find the link to registration on the beneath.