Bio-methane

Sustainable feedstock for bio-methane is waste streams of biogenic origin such as manure, agricultural waste, and food waste. These wastes can be converted into biogas, which is then upgraded to bio-methane.

Manufacturing biogas from waste improves waste management practices and avoids methane emissions from spontaneous rotting of waste. However, not all regulatory frameworks allow for the accounting of carbon credits for improved waste management practices. The ability to account for such credits could boost the biogas industry further.

According to current estimates, the total feedstock potential for bio-methane is abundant, but it is challenged by high demand across multiple industries. At the same time, current biomass aggregation practices are costly and do not support large-scale collection of suitable waste streams.

Anaerobic digestion is a commercially established process that produces biogas, a mixture of bio-methane and CO₂. The CO₂ can then be separated from the methane or be reacted with hydrogen to make synthetic natural gas (SNG), increasing the combined bio- and e-methane yield.

To ensure a positive climate impact using this production process, special attention must be given to controlling methane slip and leakages in the production process. Operating bio-methane supply chains with low emissions is possible, and the industry needs a common, high standard on fugitive emissions for existing and new plants and processes. Further, processing certain biomass waste streams into biogas reduces methane emissions associated with poor waste management. Under the right circumstances, this means that bio-methane can have a negative greenhouse gas emissions intensity.

Some challenges to scaling up bio-methane production remain. Feedstock for biogas production tends to have a low calorific value, and the cost and emissions associated with feedstock collection and transportation often limit the scale of biogas plants. This is a concern for further processing, since upgrading and liquefaction have large economies of scale. If applicable regulations allow mass-balancing, this challenge could be mitigated by using the existing natural gas grid to aggregate methane from multiple biogas plants. Bio-methane can be transported via existing gas grids and use the existing bunkering infrastructure for liquefied natural gas (LNG).

Overall, the main bottleneck for bio-methane production in the next decade will likely be the rate of construction of new biogas plants. In the long term, we expect that sustainable biomass availability will limit bio-methane production due to competition between sectors (see also feedstock availability tile for bio-methane).

Fuel supply logistics and bunkering are well established for liquefied natural gas (LNG). Given that methane is the main constituent of LNG, bio-methane does not represent any fundamentally new challenges in fuel storage, logistics, and bunkering. Relevant safety and operating procedures are already in place to deal with e.g., explosion risk.

A remaining challenge at terminals and during bunkering is methane’s low boiling point, which creates a latent risk of boil-off. Finally, well-to-wake emissions accounting will require strict control of methane venting and release across the entire supply chain.

Liquid storage of methane requires advanced cryogenic storage systems at -163°C. Technologies for storing and converting methane on board vessels are already commercially available. Methane-fueled internal combustion engines are currently used by the existing liquefied natural gas (LNG) fleet. Different engine technologies (including dual-fuel high-pressure and low-pressure two-stroke and four-stroke) are currently used with varying cost, efficiency, and emissions. Furthermore, methane-fueled fuel cells are entering the market, with multiple small-scale demonstrations ongoing.

Hundreds of vessels primarily fueled by methane in the form of liquefied natural gas (LNG) are currently in commercial operation. If regulations and safety management practices are followed, no significant barriers exist regarding safety and onboard operations for methane as a maritime fuel (see also regulation and certification tile for bio-methane).

When assessing the overall environmental impact of bio-methane as a marine fuel, it is crucial to consider both tank-to-wake and well-to-wake emissions. Bio-methane combustion releases CO₂ tank-to-wake. However, sustainably sourced bio-methane can achieve close to net-zero well-to-wake emissions, as the CO₂ emitted is balanced by CO₂ captured in the biomass feedstock (see also tiles for feedstock availability and fuel production of bio-methane). In addition, emissions of NO_x, SO_x, and particulate matter (PM) can be effectively reduced or controlled through existing technologies, further enhancing the sustainability of bio-methane as a marine fuel.

As methane is a potent greenhouse gas, onboard emissions of uncombusted methane (methane slip) are a concern for this fuel pathway. It is crucial to address the potential negative impacts associated with methane slip, as unregulated emissions can undermine the environmental advantages of bio-methane. High-pressure two-stroke engines have very low methane slip (~0.2%). Other engine types, such as low-pressure two-stroke and four-stroke engines, have higher methane slip (1.7% and 3.1%, respectively). Methane slip should be reduced through regulations that incorporate methane into a CO₂ -equivalent methodology, combined with further development of onboard emissions reduction technologies like catalysts.

To fully realize the sustainability of bio-methane, comprehensive regulation and continued development of technology are essential. These efforts will ensure that the net-zero emissions potential of bio-methane is realized, while addressing both upstream and downstream environmental impacts.

Methane as a fuel is fully covered by mandatory regulatory text from the International Maritime Organization (IMO), notably the International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels (IGF Code). The industry has implemented bunkering guidelines and procedures for this fuel, making it scalable from a safety point of view.

The IMO is advancing its development of well-to-wake-based regulations to promote the use of sustainable fuels, including bio-methane. Regulating the climate impact of fuel use from a life-cycle (well-to-wake) perspective offers the industry the opportunity to establish sustainable fuel production and consumption patterns. Such regulation can help mitigate the risk of shifting climate impact from the downstream (tank-to-wake) segment of the value chain to the upstream (well-to-tank). This is a crucial consideration for alternative marine fuels, as a significant portion of their climate impact is associated with upstream activities (see also tiles for feedstock availability and fuel production). However, many elements of these regulations remain to be discussed and finalized, including certification, sustainability criteria, eligibility of biomass feedstocks, and implementation in the IMO mid-term measures. Despite the ongoing need for international greenhouse gas regulations from the IMO, there are no major regulatory barriers to the uptake of bio-methane as a fuel, especially in the EU.

The European Union (EU) has made progress with the introduction of the EU Emissions Trading Scheme (ETS) and the upcoming FuelEU Maritime regulation, which may promote the uptake of bio-methane. However, some aspects of bio-methane certification remain to be resolved. One such unresolved regulatory issue is the acceptance of gas grid mass-balancing for bio-methane across different regions. Currently, using methane from the natural gas grid with green attributes purchased from bio-methane produced outside the EU does not qualify as compliant for the FuelEU Maritime or EU ETS regulations. Adjusting these certification rules to recognize non-EU-sourced bio-methane could improve the supply of bio-methane available for the shipping industry, supporting a faster transition to low-carbon fuels. Another point of concern is how fugitive methane emissions are currently handled during the certification of bio-methane under the EU Renewable Energy Directive (RED), and how they will be handled when IMO regulations come into force.

More broadly, it is important for regulation to support the control of methane emissions from this fuel pathway. Therefore, bio-methane requires strong regulatory focus, including monitoring and control of fugitive methane emissions upstream as well as during onboard combustion. Regulation can also help to incentivize continued technological development and adoption of solutions that reduce methane emissions.