A standard enclosed flare is designed for gas containing around 25% methane or more. Below that, the flame can go out. For older landfills, where gas has weakened, a low-calorific flare with a ceramic-lined chamber and tight control of combustion air can keep burning gas down to about 12% methane. This article describes four such flares quoted for an Australian engineering contractor.
The challenge: gas below the normal limit for sustained combustion
As a landfill matures and gas collection continues, the methane fraction tends to fall, and air drawn into the waste dilutes it further. The gas may still contain enough methane to be a significant greenhouse gas emission, yet fall below the calorific value at which a flame sustains itself. Venting it is unacceptable. Burning it needs equipment designed for the job.
The approach: a shrouded combustor for weak gas
The proposal offered a low-calorific shrouded combustor (LCSC) in a packaged form, with its own blower, on a skid. Two sizes were quoted:
| LCSC100 | LCSC200 | |
|---|---|---|
| Maximum flow | 100 Nm³/h | 200 Nm³/h |
| Minimum flow | 20 Nm³/h | 40 Nm³/h |
| Thermal rating | 50 to 250 kW | 100 to 500 kW |
| Inlet connection | DN50 | DN80 |
Both accept methane from 12% up to 40%, with a design point of 20%. Flow turndown is 5:1 and thermal turndown is 10:1.
Why it works
Ceramic flame retention
The chamber is lined with at least 100 mm of ceramic blanket insulation, and a ceramic section holds the flame in place. The hot ceramic acts as a heat store that re-ignites incoming gas and helps the flame survive fluctuations.
Tight control of excess air
Gas that is already mostly inert cannot afford extra cooling air. The combustion air is controlled closely by a louvre under PID control, which keeps chamber temperature at 1,000°C or higher with residence time of at least 0.6 seconds.
A propane pilot to pre-heat the chamber
When the calorific value is too low for the gas to ignite unaided, a propane (or similar) pilot line pre-heats the chamber. This is the most distinctive difference from a standard landfill gas flare. A dedicated burner controller runs the sequence, working with igniters, a UV flame sensor and a secondary air damper.
Below 12% methane, the specification warns, flame failure is possible. That is the practical lower limit.
Blower protection
The blower is under inverter control, and pressure transmitters feed back to the PLC to protect against high and low pressure and to prevent surge. A low-pressure switch warns of a blocked line or a blower fault. A double block-and-bleed arrangement of two fail-safe valves isolates gas on loss of power.
Emissions and compliance
The units were designed to meet TA Luft emission standards and the Environment Agency’s technical guidance on flaring, covered in LFTGN05 and LFTGN03. Four sampling ports allow stack tests to be carried out.
What to consider for your own project
- Measure before you buy. Know the methane range across the year, not just a single reading.
- Plan pilot fuel. A propane pilot needs bottles or tank storage and refilling.
- Expect lower flow. Low-methane sites often produce small flows, so check the minimum turndown.
- Find the air. If methane is low because of air ingress, wellfield tuning may be cheaper than the flare. Higher oxygen also affects safety.
- Keep spares. Ignition electrodes, a UV sensor and the burner control unit are the likely wear items.
FAQ
Why does a flare go out on weak gas?
Below a certain methane concentration, the heat released is not enough to keep the flame alight against the cooling effect of combustion air.
What is the lowest methane concentration the LCSC can burn?
12% by volume. Below that, flame failure is possible.
Do low-methane flares still meet emission limits?
They were designed to meet TA Luft and UK Environment Agency flaring guidance, with sampling ports for verification.
Is the blower included?
In the packaged (LCSC/P) version, yes.
Gas getting weaker?
Send us your gas analyses and we will tell you whether a low-calorific flare is the right answer.