Landfill sites, anaerobic digesters, and coal mines all produce a valuable but often underused resource: methane-rich gas. Rather than flaring this gas or letting it escape into the atmosphere, it can be captured, cleaned, and converted into a high-value cryogenic liquid fuel. Methane liquefaction systems make this possible — providing an efficient way to recover energy from sources that might otherwise be wasted.
What Is Methane Liquefaction?
Methane liquefaction is the process of taking raw biogas or mines gas, removing impurities such as oxygen, nitrogen, and trace contaminants, and then cooling the purified methane to cryogenic temperatures until it condenses into a liquid. The resulting product — liquefied methane — is far easier to store in bulk and transport than gaseous methane, and it can be dispensed in precise, measured quantities at the point of use.
This approach is particularly attractive for remote or distributed gas sources, such as landfill sites or coal mines, where connecting directly to a gas grid isn’t practical. Instead, the liquefied fuel can be transported by road to wherever it’s needed.
How the System Works
Compact gas cleaning and liquefaction units take raw gas from landfill, digester, or coal-mine sources and process it through several key stages:
- Gas cleaning – removal of oxygen, nitrogen, and trace gases, integrated as standard within the system
- Compression and cooling – using an integrated cryogenic refrigeration cycle
- Liquefaction – condensing the purified methane into a cryogenic liquid
- Optional by-product recovery – industrial-grade carbon dioxide can be recovered alongside the liquid methane
Removal of oxygen, nitrogen, and trace gases is built into the standard system — no separate cleaning circuit is required.
Refrigeration Cycle Options
There are, in principle, many possible refrigeration cycles for driving liquefaction, but in practice these narrow down to two proven options: nitrogen refrigeration and methane refrigeration. Multi-stage or cascading cycles, while common in very large industrial plants, are not considered appropriate for either mobile or full-scale methane liquefaction units of the type described here.
Nitrogen Refrigeration Cycle
In this configuration, nitrogen is compressed and passed through an expansion engine to generate the low temperatures needed within the fractionation column, operating as a separate, self-contained circuit from the methane process gas.
Advantages:
– A pure, separately contained nitrogen cycle operates reliably for many years without degradation from the process gas itself
– Standard equipment, readily available from small-scale liquid nitrogen plants, can be used
Disadvantages:
– Requires its own dedicated nitrogen compressor in addition to the landfill/biogas compressor, adding both energy consumption and capital cost
Methane Refrigeration Cycle
Here, methane recovered from the landfill or biogas source itself is recycled through the system to provide the cooling needed for liquefaction.
Advantages:
– The main gas compressor already used for the landfill gas can also supply the pressure needed for the expansion engine, reducing capital costs
– The output is purified methane, so no separate gas-handling circuit is required
Disadvantages:
– The purified gaseous methane stream from the main heat exchanger is recycled back into the unpurified feed gas at the compressor inlet
– There is a small methane loss during purification (approximately 5%), and recycling increases overall losses somewhat
– Trace contaminants can build up gradually over time, although removal efficiency remains high (around 99%) and can be managed with routine maintenance
System Scale and Specifications
Organics offers methane liquefaction systems across a wide range of scales, from small mobile units suited to individual landfill or digester sites, up to large fixed installations for major gas recovery projects.
| System Type | Methane Output | Approx. Gas Flow | By-product CO₂ Output |
|---|---|---|---|
| Mobile units (standard range) | 2–15 tonnes/day | ~250–1,750 Nm³/hr | 4–30 tonnes/day |
| Fixed installations (standard range) | 30–400 tonnes/day | ~1,750–50,000 Nm³/hr | 30–800 tonnes/day |
Fixed installations can scale up to 400 tonnes of methane per day — equivalent to roughly 50,000 Nm³/hr of gas throughput.
Key Benefits
- Optimum use of energy resources through integrated cooling systems
- High-purity methane gaseous product suitable for a range of downstream uses
- Optional recovery of industrial-grade carbon dioxide as a valuable by-product
- Mobile, packaged units for flexible deployment at different sites
- Fully integrated cryogenic support systems, reducing the need for separate infrastructure
- Purified compressed gas take-off points for convenient use on-site
- Designed specifically for biogas and mines gas applications
Typical Applications
Methane liquefaction systems are well suited to:
- Landfill gas recovery, converting decomposition gas into transportable liquid fuel — see landfill gas for background on this energy source
- Anaerobic digester gas, capturing biogas from agricultural or wastewater treatment digesters
- Coal-mine gas, recovering methane that would otherwise present a safety hazard or be vented
The resulting cryogenic liquid — often referred to in general terms as liquefied natural gas (LNG) when composed primarily of methane — can be transported from the point of production to wherever it is needed, making it ideal for sites without direct pipeline access.
Key Takeaways
- Methane liquefaction converts landfill, digester, and coal-mine gas into a storable, transportable cryogenic liquid fuel
- Systems range from 2–15 tonnes/day mobile units up to 30–400 tonnes/day fixed installations
- Industrial-grade CO₂ can be recovered as an optional by-product
- Two proven refrigeration cycles — nitrogen and methane — each offer distinct cost and operational trade-offs
- Integrated gas cleaning removes oxygen, nitrogen, and trace gases as standard, delivering high-purity methane product
Get in Touch
If you’re exploring ways to capture and monetize methane from a landfill, digester, or mining operation, our team can help you assess which liquefaction configuration — mobile or fixed, nitrogen-cycle or methane-cycle — best fits your site and production goals. Contact us today to discuss your project requirements and get a tailored recommendation.