A small landfill gas flare needs the same combustion control as a large one: a temperature above 1,000°C, a proven residence time and emission limits you can measure. A 50 m³/h enclosed flare quoted for a landfill in southern Africa shows how this works at small scale, and where a blower can be left out of the package.
The challenge: small flows, full compliance
Landfills that produce modest gas volumes are often assumed to need only a simple open burner. But methane is a potent greenhouse gas, and an uncontrolled burner can emit unburned hydrocarbons and carbon monoxide. Small sites also have particular difficulties: gas flow varies as the waste ages, and the flare must still ignite and burn safely when the flow is low.
The approach: an enclosed flare sized for 10 to 50 m³/h
The proposal was for a skid-mounted enclosed (shrouded) ground flare, with this design basis:
- Flow range: 10 to 50 Nm³/h, a 5:1 turndown.
- Thermal rating: about 60 kW at minimum to 300 kW at maximum.
- Methane content: 25 to 60% by volume, with oxygen up to 5%.
- Temperature: at least 1,000°C when methane is above 25%, falling at leaner mixtures down to about 20% methane.
- Residence time: at least 0.5 seconds in the unit (the specification table gives 0.3 seconds as a minimum).
- Noise: about 70 dB(A) at 15 m.
No blower, if the gas arrives under pressure
This was a flare-only package, known as an SC/L supply. It assumed a blower or suction system elsewhere on the site could deliver the gas to the flare at a pressure of at least 5 kPa (50 mbar). Where there is no gas-moving equipment, a package with its own blower is needed instead. Check which situation you have before you ask for prices, because the two are not comparable.
Emission limits
The unit was designed not to exceed these limits, referenced to dry gas at 3% oxygen:
| Parameter | Limit |
|---|---|
| Carbon monoxide | 100 mg/Nm³ |
| Oxides of nitrogen | 200 mg/m³ |
| Unburned hydrocarbons | 20 mg/Nm³ |
It was also designed to meet TA Luft standards and the Environment Agency’s technical guidance on flaring, which is covered in LFTGN05 and LFTGN03.
Why it works
Controlled combustion air
A louvre on the combustion air inlet is moved by an actuator under PID control, driven by the flame temperature. As gas flow changes, the louvre adjusts so the temperature stays in range and combustion stays complete. The flame is hidden inside the shroud, which is lined with 100 mm of ceramic insulation.
Safe start-up and shut-down
Starting a flare is more than a spark. A PLC controls the sequence, using electric igniters, a UV flame sensor and a secondary air damper that is set mechanically during commissioning and then handed over to PID control. A biogas pilot line, with its own solenoid valve and flame arrester, lights the main burner. At the gas inlet are an ATEX flame arrester, a low-pressure switch to warn of blockage and a fail-safe slam-shut valve that closes on loss of power.
Built for sampling and service life
Four DN125 sampling ports are placed at 90-degree intervals near the top of the stack, so stack emissions can be measured. The shroud and pipework are 304 stainless steel, with a design service life of at least 10 years.
What to consider for your own project
- Decide on a blower early. If the gas will not arrive at the required pressure, you need a booster as well.
- Check the turndown. Landfill gas declines slowly. A 5:1 range gives room to operate as flows fall.
- Specify methane range. A flare designed for 25% methane and above may not stay lit on leaner gas.
- Plan the stack test. Ensure the ports are accessible and a safe platform is planned.
- Keep the spares list. A UV bulb, electrodes, thermocouple and ignition transformer cover the common failures.
For UK permits, the Environment Agency explains the requirements for managing landfill gas under an environmental permit.
FAQ
Is an enclosed flare necessary for a small landfill?
Not always, but enclosed flares give better control of temperature and emissions and keep the flame out of sight.
What does turndown mean?
It is the ratio between maximum and minimum flow the flare can handle. 5:1 means a 50 m³/h flare works down to 10 m³/h.
Can a flare burn gas below 25% methane?
This design could burn down to around 20% methane, but at a lower temperature.
Is installation included?
No. In this proposal the flare was delivered to port, with civil works, connections and installation by others.
Planning a small flare?
Send us your gas flow and methane range and we will advise on a flare and whether you need a blower.