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Singapore study highlights role and challenges of bio-LNG as future bunker fuel for shipping sector

07 Jun 2021

The Maritime Energy and Sustainable Development Centre of Excellence (MESD COE), a centre jointly funded by Singapore Maritime Institute (SMI) and Nanyang Technological University (NTU), has started investigations on the use of various alternative bunker fuels as an energy source for ships.

This article shares the main findings on bio-LNG as a marine fuel; the study ‘Bio-LNG – Its Role in Shipping Decarbonisation’ articulates the role of the material for the shipping industry and rationale behind it.

The complete study (below) has been shared with Singapore bunkering publication Manifold Times.

Bio-LNG – Its Role in Shipping Decarbonisation



Among modes of cargo transportation, maritime transport enables the regional and intercontinental movement of large quantities of cargo in the most fuel-efficient way with lower cost. Currently, there are more than 90,000 commercial vessels worldwide with around 60,000 vessels larger than 500 GT. These ships are responsible for 2-4% of the world’s annual fossil fuel consumption, accounting for approximately 250 to 300 million tonnes per year. Currently, international shipping is responsible for around 3% of total anthropogenic CO2 emission or around 11% of global transport CO2 emission. Although the CO2 emission from shipping industry currently constitute a small fraction of total anthropogenic CO2 emission, it is foreseen to increase significantly in the next few decades due to expansion of international commerce. With calls, especially to make them aligned with Paris Agreement, MEPC 72 adopted the “Initial IMO GHG Strategy” on Reduction of GHG Emission from Ships in April 2018 with the level of ambitions to reduce carbon intensity of international shipping by at least 40% by 2030 and to reduce the total annual GHG emission by at least 50% by 2050 relative to the amount of GHG emitted in 2008. The adoption of technical and operational measures (T&O measures) is likely to be the major approach, facilitating shipping industry to improve ships’ energy efficiency to meet IMO’s GHG reduction target in 2030. In contrast, it is most likely that the radical reduction in CO2 emissions to meet IMO’s target in 2050 cannot be achieved without the adoption of alternative fuels.

For shipping sector, many types of alternative fuels have been mentioned. These include liquefied natural gas (LNG), bio-LNG[1], synthetic-LNG[2], biodiesel[3], hydrotreated vegetable oil (HVO), methanol, bio-methanol, synthetic-methanol, hydrogen, and ammonia. In fact, shipping industry has witnessed the changes in energy sources throughout the past several decades. The lesson learnt from historical energy transition reveals crucial factors for the adoption of alternative fuels. The shipboard technologies (i.e., energy converters as well as fuel storage & supply system) must be available and suitable for the design and operational profile of ships. In addition, the technologies throughout the value chain must be ready, i.e., reaching Technology Readiness Level of 9 (TRL9). To enable the availability of alternative fuels for the industry, there must be an adequate amount of primary energy sources (or feedstocks) with sufficient capacity of production plants of the fuel. To enable fuel delivery to ships, there must also be bunkering infrastructure and safe & efficient practice in place. With the above components, ship owners and/or operators will be able to adopt a certain type of alternative fuels.

The Maritime Energy & Sustainable Development Centre of Excellence (MESD CoE)[4] has investigated various types of alternative fuels for international shipping. It is undeniable that the ideal approach for maritime decarbonisation appears to be the adoption of an alternative fuel, containing no carbon, i.e., hydrogen (i.e., renewable or green hydrogen). However, the technology required for hydrogen application is not matured. There is a requirement in R&D in hydrogen storage, fuel cell for marine application, safe handling & practice, establishment of renewable hydrogen supply chain and bunkering infrastructure. Therefore, it is unlikely to be ready for the entire industry within a decade. The study also reveals the potential of bio-LNG as a marine fuel. Although fossil-based LNG is a clean fuel, it will not be able to play a significant role in GHG emission reduction. For further GHG emission reduction, bio-LNG is revealed to be a good candidate for the industry as a drop-in biofuel using with LNG. It is important to note that the application of LNG and bio-LNG can pave a path for the application of synthetic methane[5] in shipping industry in the future. This paper articulates the role and the importance of bio-LNG as a green fuel for shipping industry.


In the past decade, LNG has received considerable attention from shipping industry owing to its abundance, its competitive cost, and its overall environmental performance. Fossil-based natural gas is ranked third for the abundance after coal and oil. As of 2019, the world proven reserves became 198,800 billion m3 with a reserve to production ratio of 49.8 years (BP, 2020). In the past 20 years, cost of LNG (per unit energy output from ship engine) is comparable with that of HFO. LNG is considered a cleaner fuel, and its combustion emits negligible atmospheric pollutants (i.e., SOx, NOx and PM). However, its reduction of CO2 emission is still controversial. From the carbon content in the fuels (IMO, 2012) and specific fuel oil consumption (IMO, 2014), the reduction of onboard CO2 emission by LNG could be up to ~20%. Due to methane slip, a small leakage of methane (CH4) might cancel out its beneficial effect of GHG emission reduction. It should be noted that all engine manufacturers have been putting continual R&D efforts to minimise methane slip[6]. Despite a lack of bunkering infrastructure worldwide, there are 175 LNG-fuelled ships in operation and more than 200 ships on order at the beginning of 2020 (Sea LNG, 2020). Due to the complexity of the fuel and machinery systems and the need for more safety features, LNG fuelled ships are more expensive as compared to conventional ships by as much as 30%. With additional 30% investment cost for LNG-fuelled ship, will it be worth for 20% reduction of GHG emission?


Although Bio-LNG has a similar nature with fossil-based LNG, their origins are different. Fossil-based LNG is obtained from the extraction of natural gas from the reservoirs, processing of obtained natural gas to remove non-methane hydrocarbons and impurities as well as liquefaction of treated natural gas to convert its state from gas to liquid. In contrast, bio-LNG is produced via anaerobic digestion and landfill degradation of biomass, including agricultural waste, organic waste, manure, and sewage sludge. The obtained gas, also known as biogas, consists mainly of CH4 and CO2. Biogas can be upgraded using separation technologies to achieve its final product with the same quality of fossil-based natural gas. The obtained biomethane can be distributed in either gaseous form (bio-CNG) or liquefied form (bio-LNG) by leveraging on the natural gas infrastructure.

Since bio-LNG is produced from the fourth-generation feedstock[7], its production will not cause the interference to the food chain and, at the same time, avoiding land use change. Among technologies[8] required to produce alternative fuels, the technology for biomethane production is considered as one of the most mature technologies. Unlike biodiesel (FAME), bio-LNG quality is consistent no matter which feedstock is used for its production. Bio-LNG is genuinely compatible with fossil-based LNG. The application of Bio-LNG can leverage LNG fueled ship technologies and infrastructure. Bio-LNG can be used as an alternative marine fuel in any proportion with fossil-based LNG without any modification of internal combustion engines and fuel supply system. Once the shipping industry is ready for LNG, Bio-LNG can be used as a drop-in fuel to facilitate further reduction of GHG emissions.


According to their origins, fossil-based LNG contains less fossil carbons, while Bio-LNG contains biogenic carbons. Panel on Climate Change (IPCC) differentiates between the “slow domain” of the carbon cycle, where turnover times exceed 10,000 years, and the “fast domain” (the atmosphere, ocean, vegetation and soil), vegetation and soil carbon have turnover times in the magnitude of 1-100 and 10-500 years, respectively. Fossil fuel transfers carbon from the slow domain to the fast domain, while bioenergy systems operate within the fast domain. In other words, fossil fuel use increases the total amount of carbon in the atmosphere while bioenergy system does not and operates within its system, i.e., biomass combustion simply returns the atmosphere the carbon that was absorbed as the plants grew. Biogenic CO2 emissions refer to emissions related to fast-domain carbon cycle. The CO2 emissions released from the combustion of biogenic carbon are not considered to contribute to climate change.

The above discussion is explicit that the CO2 emission resulted from the combustion of bio-LNG does not count as onboard CO2 emission contributing to climate change. However, the evaluation of GHG emission when using biofuels for energy at the point of combustion only (i.e., emissions onboard ships) might not be representative in a global level because most of GHG emission occur upstream in the production process. More appropriately, the evaluation should be performed based on the biogenic carbon flows together with any fossil GHG emission associated with the application of biofuels (IEA Bioenergy, 2019). Typically, it is known as “Life Cycle Assessment (LCA)”, a more complete evaluation of the GHG emissions associated with not only the use of the fuel, but also its production. Figure 1 provides the GHG emission resulted from the adoption of LNG and bio-LNG in comparison with other fuels. Bio-LNG could offer further GHG emission reduction to up to 70-80% in comparison with 10-20% GHG emission reduction provided by fossil-based LNG.


Availability of alternative fuels is one of the major components enabling their adoption. Although the availability of alternative fuels depends on many components (including bunkering infrastructure, fuel standard and safe bunkering operation), the adequacy of alternative fuels is of chief importance. For the shipping sector, the adequacy of alternative fuels refers to the combination of availability of feedstocks and production capacity of alternative fuels with the consideration of competing use in other sectors. In 2018, the production of biogas was estimated to be around 35 Mtoe[9] worldwide (IEA, 2020) with major producers in Europe, USA, China and Russia. Most of the biogas production in 2018 was used to generate electricity and heat. Around 30% was consumed in buildings, mainly in the residential sector for cooking and heating. The remainder (around 10% of biogas production or 3.5 Mtoe) was upgraded to biomethane and blended into the gas networks or used as a transport fuel. The above figures are from the angle of current production capacity.

As discussed earlier, the supply of alternative fuels should be considered from not only the current production capacity globally but also the availability of feedstock. For renewable feedstock, the term “technical potential” is typically used for the evaluation. It represents the estimation of achievable energy or fuel generation of a particular technology given system performance, topographic limitation, environmental and land-use constraints. The “technical potential” referred here represents the total global production potential and thus ignores competition between various sectors in the future use of such production potentials. According to the World Bioenergy Association (2013), the technical potential of biomethane is estimated to be around 35.9 EJ equivalent to 1,000 billion m3 of CH4 annually. Similarly, International Energy Agency (IEA) estimates the technical potential of biomethane to be around 30.5 EJ[10] equivalent to 850 billion m3 CH4 annually (International Energy Agency, 2020). It should be noted that the production of NG in 2018 is estimated to be 3,867 billion m3 (BP, 2019). For shipping sector, the fuel oil consumption is currently around 250 million tonnes or equivalent to the annual energy consumption[11] of around 9-10 EJ. Under business as usual, the annual energy consumption is anticipated to be around 12-13 EJ in 2030 and 20 EJ in 2050. Providing that the entire shipping sector plans to adopt LNG as marine fuel, the industry will require around 300-320 billion m3 of NG based on the current energy consumption. If we further assume that shipping industry plans to use Bio-LNG blended LNG in a ratio of 50:50 as a future fuel, the industry needs 150-160 billion m3 of biomethane, accounting for 15% of biomethane technical potential. With the energy demand in 2050 (20 EJ), the industry will require around 280 billion m3 of biomethane support the use of Bio-LNG blended LNG. The mentioned amount accounts for around 30% of technical potential of biomethane. From the estimation of potential resources for biomethane production, it seems technically that there will be sufficient amount of bio-LNG to support shipping industry (particularly in comparison with the availability of biodiesel)[12].


In the past decade, LNG has gained a lot of attention from shipping industry due to its abundance, its cost, and its overall environmental performance. LNG has been recognized as a clean fuel. However, its GHG emission reduction is still controversial due to its upstream production and potential methane slip. Although fossil-based LNG is a clean fuel, it will not be able to play a significant role in GHG emission reduction. For further GHG emission reduction, bio-LNG is revealed to be a good candidate for the industry as a drop-in biofuel using with LNG. Bio-LNG is mainly from the fourth-generation biomass feedstocks, i.e., waste and wastewater. Among technologies required to produce alternative fuels, the technology for biomethane production is considered as one of the most mature technologies. Unlike fossil-based LNG, bio-LNG contains biogenic carbon. Therefore, the CO2 emission resulted from the combustion of bio-LNG does not count as onboard CO2 emission contributing to climate change. The application of bio-LNG can leverage the mature technology of LNG with the establishment of LNG infrastructure and LNG-propulsion ships. In terms of the supply, the technical potential of bio-LNG indicates its ability to support the entire shipping industry. However, it is important to note that there are two major challenges, i.e., the competitive use of bio-LNG in the power generation sector and the establishment of bio-LNG chain development despite the mature production technology. Its allocation to shipping industry is needed to be discussed. It is undeniable that the application of hydrogen is an ideal approach for decarbonisation. However, the application of LNG and bio-LNG can also pave a path for the application of synthetic methane in shipping industry in the future. The synthetic methane is considered as a form of hydrogen carriers with recycled carbons from carbon capture.

From these, we can foresee the role and importance of Bio-LNG in reduction of GHG emission from shipping industry. Nonetheless, there are few critical questions needed to be answered by the industry. Firstly, will LNG become a major marine fuel in 10-20 years? Secondly, how to develop the value chain of bio-LNG to support its application in maritime industry? Finally, how much does it cost for end-users for the adoption of Bio-LNG blended with fossil-based LNG.

Figure 1 GHG emission resulted from LNG and Bio-LNG in comparison with other fuels (Source: MESD, 2020)

[1] In this article, Bio-LNG refers to Liquefied Bio-methane (LBM).
[2] In this article Synthetic-LNG refers to Liquefied methane produced from methanation using CO2 from carbon capture and H2 from non-bio renewable energy
[3] Biodiesel refers to fatty acid methyl esters (FAME).
[4] Launched in October 2017, Maritime Energy and Sustainable Development (MESD) Centre of Excellence is jointly funded by Singapore Maritime Institute (SMI) and Nanyang Technological University (NTU). As the first maritime research centre supported by SMI, MESD is a continual effort to deepen Singapore’s maritime R&D capability and Maritime Singapore’s position as a global maritime knowledge and innovation hub to support Singapore’s strategic maritime needs.
[5] Synthetic methane refers to methane produced from hydrogen and recycled CO2 (i.e., CO2 from carbon capture) via methanation process. The application of synthetic methane provides a low CO2 emission due to its content of recycled carbons.
[6] The methane slip could be solved by improvement of combustion process and using catalytic converter (Salem, et al., 2014). According to MAN Diesel & Turbo, low-speed diesel engines with high-pressure injection have found to have almost no methane slip (0.1% of SFOC) (Gingell, 2016). However, there are trade-offs, including cost of the complex fuel gas supply system and emission of NOx (Sharafian, et al, 2019).
[7] The biomass feedstock can be categorised based on their sources into four major groups. First-generation feedstock (1G) refers to vegetable oil & animal fats and plants containing sugar & starch. Second-generation feedstock (2G) refers to lignocellulosic biomass and inedible oils. Third-generation feedstock (3G) refers to algae (macro and microalgae). Fourth-generation feedstocks (4G) come from waste and genetically modified algae.
[8] Technologies such as gasification for hydrogen production, gasification with catalytic conversion for biomethane production, pyrolysis for bio-oil production, etc.
[9] Million tonnes of oil equivalent
[10] IEA estimated the biomethane potential of 730 Mtoe.
[11] Half of this energy is lost due to efficiency of energy converters onboard that is about 50%.
[12] Although biodiesel is the readiest alternative fuel for actual application in the shipping industry, biodiesel produced from the 1st and the 2nd generation feedstock (i.e., edible vegetable oils and inedible oils) will not be sufficient to support the shipping industry to achieve 2050’s target, especially when considering from life cycle perspective.



This project has received research funding from the Singapore Maritime Institute.


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Photo credit: Manifold Times
Published: 7 June, 2021

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