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Decarbonisation developments and challenges: Plugging the gap with bridging fuels

News & Insights 14 November 2022

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IMO 2030 is already looming large. Putting aside 2050’s longer-term targets, shipowners already face a tough task to comply with the sizeable reductions required in carbon dioxide (CO2) and greenhouse gas (GHG) emissions. As members continue their transition to decarbonisation, our 2022 Alternative Fuels survey reveals their current thinking.

In our third of six blog posts highlighting the survey’s main talking points, we focus on which bridging fuels are gaining ground with members, their benefits – and their challenges.

Decarbonisation developments and challenges: Plugging the gap with bridging fuels

IMO 2030 and IMO 2050

Under IMO’s initial strategy, the shipping industry needs to reduce carbon intensity (CO2 emissions per transport work) by at least 40% by 2030. This figure almost doubles to 70% by 2050 and targets a complete phasing out by the end of the century. IMO-2050 sets out a reduction in total annual GHG emissions of at least 50% by 2050 and eventual phasing out. However, a strategy review planned for 2023 may move these goalposts – potentially bringing forward the net-zero requirement to 2050. 

For more information on the latest regulations and amendments to MARPOL VI, see our ‘Looking to 2023’ blog post.

Exploring bridging fuels

While it is clear shipowners need to act fast, there’s an inertia in the industry. This is mainly down to a lack of clarity about which alternative(s) are likely to be the best. Greater detail is also needed on the potential safety of each fuel, the likely cost of implementation, the emissions efficiency of each fuel on ship and onshore, and the ‘well to wake’ carbon impact.

Each fuel has a unique set of benefits and challenges. But two are currently setting the pace in the short and mid-term while the industry explores and develops more permanent means of complying with IMO-2050. These ‘bridging fuels’ are biofuels and liquified natural gas (LNG). 

Our 2022 Alternative Fuels survey revealed that most members currently favour biofuels for their existing vessels, and LNG as a preferred option for newbuilds. This is subject to the price and availability of the fuel, which would be dependent on the geopolitical situation and market factors. Other barriers and challenges gathered from our 2022 Alternative Fuels survey have been highlighted in our previous blog post.


Biofuel is a general term encompassing a wide variety of liquids or gases derived from biomass or bio-waste. It is categorised based on the feedstock and production technique.

  • First generation biofuels are produced from conventional feedstock, such as food crops, sugar/starch, and vegetable oils, e.g., Fatty Acid Methyl Ester (FAME)
  • Second generation biofuels are produced from waste, residues, or non-food crop feedstocks, including used cooking oil using hydrogenation process, e.g., Hydrotreated Vegetable Oil (HVO)
  • Third generation biofuels are produced by farming algae. Oil is extracted from these microorganisms for use as biofuel - a process that offers high yields and require little maintenance.
  • Fourth generation biofuels are produced by bioengineered organisms, i.e., genetically modified algae and cyanobacteria, that enhances biofuel production. This method of biofuel production is currently at research level.

Interest in using biofuels and biofuel blends has increased, particularly after IMO MEPC-78 (in June-2022) approved a Unified Interpretation (MEPC.1/Circ.795/Rev.6) that clarifies that fuels with a biofuel content of 30% by volume or less can be considered as a conventional marine fuel oil derived from petroleum refining.

Biofuels offer a number of benefits, including:

  • Carbon-neutral – as derived from biologically-renewable resources such as plant-based sugars, etc.
  • Usually blended with traditional marine fuels or used as a ‘drop-in’ (replacement) fuel, and compatible with current conventional marine engines.
  • Non-toxic, biodegradable properties and reduced GHG emissions when burned.
  • Biodegradable in the event of a spill.
  • Potentially widely available through a variety of production methods.

However, while trials with biofuels have shown good operating results, adopting biofuel does throw up several barriers for the industry to overcome. These include:

  • Higher cost compared to conventional fossil fuels.
  • Biofuel feedstock is currently limited due to competition from existing industries such as agriculture.
  • Various production methods may be used to generate variety of biofuels, which can affect fuel quality, cost, and overall life-cycle emissions. While ISO 8217 is a fossil fuel standard, and it could be used as a guideline, there are missing parameters that are relevant to biofuels and others which are not relevant.
  • Potential compatibility issues with some conventional fuels.
  • Biofuels have higher acid content, which can lead to corrosion in the fuel system. The mitigation is relatively easily solved by selecting the materials that are compatible with higher acid contents. Seals must be replaced more regularly when some biofuels are adopted.
  • The energy density of FAME biofuels can be lower than conventional fossil fuels. The Lower Calorific Value (LCV) of a fuel is an indication of the amount of heat released by combusting a specified quantity of that fuel; this directly affects the power output of the engine. The LCV of FAME is lower than conventional fossil fuel, due to its higher oxygen content.
  • There is a risk of microbial growth when water is present in certain grades of biofuels. This risk can be mitigated by storing the fuel in a clean fuel tank, preventing water ingress, regular sample testing and frequently draining the tanks. Alternatively, biocide or anti-microbial additives can be added to the biofuel or biofuel blend to avoid microbial build-up.
  • Higher oxygen content in biofuels as compared to conventional fuels also can lead to lower oxidation stability, making the fuel more prone to degrade over time. The long-term storage of some biofuels may result in bacterial and fungal growth and coagulation in storage tanks, leading to clogging of filters. More frequent bunkering, or perhaps the application of new tank coatings that prevent bacterial growth, can solve these issues. Alternatively, antioxidant additives can be used to slow-down this process.
  • Biofuels have poor cold flow properties, i.e., at low ambient temperatures, the fuel tends to cloud and gel. If fuel temperatures are not properly controlled, they may accelerate instability, impact shelf life and the fuel’s suitability for use. It is recommended to heat fuel-storage tanks, piping, and filters. If temperatures cannot be kept above the cloud point, it is recommended to treat the fuel with cold-flow improvers or anti-gel additives.

Most of the challenges faced by biofuels can be addressed by implementing fuel management procedures with due regards to the selected biofuel characteristics. It is recommended to consult with the fuel supplier and machinery manufacturers for specific recommendations for using biofuels.

Biofuels’ carbon-neutral nature clearly makes it an attractive proposition for shipowners, especially following the IMO’s adoption of the Carbon Intensity Indicator (CII) regulation. However, organisations will also need to monitor their supply chains for quality, reliability, and sustainability.

Currently, there is no globally accepted standard or certification for verifying green end-to-end production. However, there are voluntary schemes for biofuels management enabling companies to prove compliance with directives and demonstrate their commitment to sustainable biofuels/biomass production, processing and purchasing.


LNG is a fossil fuel, primarily consisting of methane (CH4). Compared to heavy fuel oil, it allows substantial reduction of air emissions - more than 99% of sulphur oxides (SOx), 80% for nitrogen oxides (NOx), particulate matter (PM), and up to 20% for CO2.

While other emerging alternative fuel options are unproven and under development, industry trends suggest a surge in LNG-fuelled newbuilding orders.

Other potential benefits of LNG are:

  • Already in practical use and readily available.
  • Bunkering infrastructure is rapidly growing.
  • High energy density.
  • Specific regulations for LNG already exist in the IMO’s International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code).

While LNG is seen to have some beneficial features it also has some challenges, such as:

  • Storage required at cryogenic state (-162C) to stay in liquid state.
  • Low volumetric density requires almost 2x storage compared to traditional marine fuels.
  • Bunkering, storage and handling require much more care.
  • Risk of methane slip, which is the discharge of unburned methane from an engine, with a potential GHG impact 25x greater than CO2 emissions.
  • Possible criticism for using fossil fuels.
  • Currently limited to major ports.

When liquefied at approximately -162° C, the volume required for natural gas is reduced to about 1/600th of that required when in the gaseous state. Although the tanks are insulated, a small amount of warming will occur, causing the LNG cargo to evaporate as it reaches its boiling point. This natural evaporation, known as boil-off, is unavoidable, and the generated boil-off gas (BOG) must be removed to preserve the tank pressure within acceptable limits.

Whichever route members decide to take, they will need to focus on some key factors to ensure they comply with the regulations. Investment in training personnel onboard and ashore will be vital, as will close collaboration with partners and peers.

We also recommend members review their overall fuel management strategy and procedures and adopt a culture that embraces regular and effective management oversight and auditing of their compliance procedures. 

Support from Standard Club

We are committed to helping our members and shipowners across the globe make a safe, sustainable and successful transition to greener energy, in line with the IMO’s goals.

Our focus on a supportive role aims to provide members and brokers with all the information needed to make an informed choice and decision.

Visit our dedicated Alternative Fuels webpage for a range of alternative fuels information, including greener fuels – bridging and emerging, articles, advice and support tools from videos and podcasts, to events and webinars, and access to contacts with considerable expertise and experience in the alternative fuels arena.

Category: Alternative Fuels

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