Demonstrating viable small-scale bio-LNG:
the Bio-LNG Wilp project

An important question for the transport sector is whether bio-LNG production can be scaled to meet growing demand. To achieve this, as much local waste as possible needs to be converted into biogas and then into bio-LNG. Many existing biogas plants are relatively small, located close to waste sources, and not always connected to the gas grid. Decentralised liquefaction directly at these sites makes it possible to move energy to offtakers via the LNG value chain and helps prevent existing biogas assets from becoming stranded.

Technology objectives

The process used at Wilp is based on Nordsol’s iLNG process design. It was developed specifically for small-scale, decentralised applications, rather than as a scaled-down version of large LNG plants. The main objectives of the iLNG process are:

• to reduce specific energy consumption through process integration;
• achieve high methane recovery with zero methane vent;
• maintain a compact, modular footprint suitable for industrial and agricultural biogas sites;
• minimise equipment count and apply a continuous process, without heat requirement
• ensure that automation, operability, and maintenance meet the requirements of biogas producers as well as bio-LNG off-takers.

Core process architecture

The iLNG process converts raw biogas into two main products: bio-LNG and high-purity biogenic liquid CO₂. Biogas from anaerobic digestion typically contains methane, CO₂, water vapour, hydrogen sulphide (H₂S), and traces of volatile organic compounds (VOCs). The process begins with dehumidification and removal of H₂S and VOCs to protect downstream equipment, meet LNG quality specifications, and ensure stable operation.

After pre-treatment, the bulk of the CO2 is removed by a standard biogas-to-biomethane upgrading unit. Subsequently, the remaining CO₂ and traces of water are separated from the biomethane using membranes only. Patented flash-2-sweep™ technology improves the performance of the last membrane stage by a factor of 20, creating liquefaction-ready biomethane. Flash-2-sweep boosts membrane performance by sweeping the low-pressure permeate side with flash gas and boil-off gas (BOG) from the liquefaction unit. The permeate is routed back to the biogas compressor, preventing any loss of biomethane.

The biomethane is liquefied in a cryogenic section that uses a reverse Brayton cycle based on methane gas expansion through a single turbo expander. It is a simplified version of the efficient AP-C1 process developed by Air Products4. The process uses treated biomethane as the refrigerant, rather than nitrogen, which makes it particularly efficient in the required temperature range.

CO₂ in the biogas is captured and liquefied as a high-purity product rather than vented, improving the emissions profile and enabling reuse in industrial or horticultural applications where markets exist. Biogenic CO2 will also serve as the feedstock for synthetic fuels, such as SAF or e-methane.

By integrating upgrading and liquefaction in this way, the iLNG process concentrates functionality into a compact package with low equipment count, suited to distributed biogas facilities.

Bio-LNG Wilp is the outcome of a cooperation that brings together technology, feedstock, and public support.

Nordsol developed the iLNG concept and owns and operates the biomethane liquefaction unit at Wilp. Its responsibilities include process design from biogas to bio-LNG, equipment specification, and operational control of the flash-2-sweep and liquefaction process, as well as truck loading. Attero operates the Wilp waste processing site, which includes anaerobic digestion of organic waste to produce biogas. Attero owns and operates the biogas upgrading and CO₂ liquefaction units at the site.

CINEA, the European Climate, Infrastructure and Environment Executive Agency, supports the project through the Innovation Fund, the programme that aims to accelerate the deployment of low-carbon technologies. CINEA contributes with financial support and monitors progress and results for potential replication.

Technology and production lessons

As with most first commercial applications of a new process, the Wilp plant experienced several early “child diseases” that have since been resolved and have contributed to design improvements.

In early operation, the turbo expander in the cryogenic section exhibited vibration levels that could cause trips. Through adjustments to design details, operating conditions, and start-up & shutdown sequences, the expander performance was stabilised. Future plants can incorporate these modifications from the beginning.

The plant’s ability to inject upgraded biomethane into the gas grid depended on interface conditions with the national grid. In practice, the pressure difference at the connection point was smaller than originally indicated, necessitating changes in the design and operation of the grid injection system. The experience underlines the importance of conservative assumptions and rigorous verification of external interface data for decentralised plants.

Hydrogen present in the biogas does not end up in either the bio-LNG or CO₂ products. Therefore, the hydrogen stream, which also contained methane, was used to fuel the flare pilot. However, this stream contained too much methane, leading to unnecessary carbon emissions and lower bio-LNG yield. Installing a dedicated membrane to recover methane from the hydrogen stream resolved this issue: the recovered methane is returned to the process, while the hydrogen can still be used for the pilot flame.

These experiences confirm that a thorough analysis of operational data is essential for tuning a new decentralised process and can rapidly translate into improvements for subsequent projects.

Market and regulatory lessons

The Wilp project also offers insights into market and policy dynamics for bio-LNG. At the time of the investment decision, the regulatory framework for bio-LNG – including certification rules and support mechanisms – was still evolving. This created uncertainty about which end-use segments would be most attractive over the plant’s early life. While the plant was conceived with both road and maritime transport in mind, current conditions have made the maritime sector less attractive as an outlet for Wilp’s production than initially expected. At present, the bio-LNG is used in Dutch heavy road transport. This experience highlights the value of flexible offtake strategies and the need to track regulatory developments closely when planning new decentralised liquefaction projects.

Implications for future small-scale bio-LNG developments

The main implications from Wilp for future decentralised liquefaction projects are clear. Future plants will benefit from operational data and optimisations in Bio-LNG Wilp, reducing commissioning risk and improving yield and emissions performance from the beginning. Detailed, site-specific verification of external conditions is essential.

Biogas producers with liquefaction plants can serve multiple market segments (road transport, maritime, and grid injection) and are therefore better positioned to navigate rapidly evolving regulatory and market conditions.

Plants such as Wilp show how decentralised liquefaction can complement centralised infrastructure. By converting biogas directly at the source into bio-LNG and CO₂, these facilities can feed into existing LNG supply chains while also unlocking additional value from waste and agricultural streams.

Bio-LNG Wilp illustrates how decentralised, small-scale biogas liquefaction to bio-LNG is technically mature, commercially viable, and ready for upscaling to a larger number of implementations across Europe. By combining Attero’s waste and biogas operations with Nordsol’s bio-LNG technology, and with support from CINEA through the Innovation Fund, the project has created an operational reference for onsite bio-LNG production.

Early operational experience has led to concrete technical refinements and has clarified how regulatory and market conditions influence the allocation of bio-LNG between transport segments. The Wilp case demonstrates that decentralised liquefaction can produce bio-LNG in a compact footprint, integrated directly into existing LNG logistics. As similar plants incorporate the lessons learned at Wilp, decentralised bio-LNG production can be scaled up rapidly and contribute to the decarbonisation of heavy transport across Europe.

1. Nordsol, “Bio-LNG Wilp,” project case description, available at: https://nordsol.com/cases/wilp/
2. Nordsol, “Nordsol’s iLNG process,” technology overview, available at: https://nordsol.com/articles/nordsols-ilng-process/
3. European Climate, Infrastructure and Environment Executive Agency (CINEA), official information on EU-supported alternative fuels and bio-LNG projects, available at: https://cinea.ec.europa.eu/
4. Air Products, “Leave refrigerants out in the cold”, in LNG Industry, October 2021

Disclaimer: “Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Climate, Infrastructure and Environment Executive Agency (CINEA). Neither the European Union nor the granting authority can be held responsible for them”