A low visual impact landfill gas flare is a horizontal, enclosed ground flare that burns gas at 1,000°C inside a low shroud, hidden behind a slatted screen, instead of on a tall stack. In a proposal for a remediated landfill in East Asia, a 1,000 Nm³/h horizontal flare was designed to fit a footprint of roughly 5 m by 6 m and to act as an emergency standby if the site’s gas treatment plant failed.
The challenge: a flare that must exist but should not be noticed
The site was a remediated landfill, now a public-facing asset with neighbours and stakeholders who care how it looks. The main gas treatment plant would normally deal with the landfill gas. The flare was needed mainly for emergencies, so that gas could still be destroyed safely if that plant stopped.
A standby flare is rarely used, but it has to work first time when it is. It also stands on site every day of the year. An elevated flare with a visible flame and a tall stack would have been a constant reminder of the landfill. The brief was therefore to keep the emission performance of a proper enclosed flare while minimising visual impact and the risk of complaint.
The approach: a horizontal ground flare behind a screen
How the horizontal layout works
Instead of firing upwards inside a tall chimney, the burner fires along a horizontal shroud. A forced-draught burner mixes gas and air properly, and the gas is destroyed as it travels through the horizontal sections. The length of the shroud is set to give the gas time at temperature, which is what controls the emissions. The design residence time is more than 0.5 seconds.
The key design values were:
- Capacity: up to 1,000 Nm³/h of landfill gas at 50% methane, with a normal operating range down to about 250 Nm³/h. That is a 4:1 turndown, so the same unit can handle a decaying gas supply as well as a full-flow emergency.
- Temperature: at least 1,000°C while methane is above about 25%. With weaker gas it burns cooler, down to about 20% methane, before the flare can no longer sustain stable combustion.
- Feed pressure: about 140 mbar gauge at the flare, supplied by a stainless-steel centrifugal blower with a head of about 150 mbar. The burner itself accepts gas between 100 and 500 mbar gauge.
- Burner rating: roughly 3.8 MW thermal, which is the energy in 1,000 Nm³/h of gas at 50% methane.
Controlling the flame temperature
A thermocouple measures the temperature in the combustion chamber and a PID controller adjusts a combustion air blower to hold it. Too little air and combustion is incomplete. Too much air cools the chamber and the residence time shortens. Automatic control keeps the flare within its window as the gas quality changes, with no operator needed.
Built to be left alone
A standby unit may sit idle for months in a wet climate, so the materials matter:
- A shroud made of 304 stainless steel, lined with 100 mm of ceramic block on non-surface-mounted fixings, so there are no exposed metal fixings in the hot zone.
- A rain guard on the flare tip to protect the insulation blanket from excess water.
- A hot-dip galvanised skid and carbon steel pipework, with stainless steel offered as an upgrade for a longer life.
- A condensate knockout pot at the inlet with a polypropylene mesh demister that removes about 99% of droplets larger than 6 microns, for a clean pressure drop of under 3 mbar.
- Pressure gauges on the inlet and after the demister, so a blocked mesh shows up as a rising pressure drop, and a sample point on the feed line.
The visual part
The whole flare is enclosed in a slatted aluminium frame, painted dark green by default so that it blends into planting and the surrounding landscape. The frame screens the unit from view without blocking the air the flare needs. The structure is designed for wind loading and to comply with relevant British Standards for fixing to the concrete base, and radiation at ground level is kept within acceptable limits.
Why it works: emissions first, appearance second
A screen would be pointless if it were hiding a poor flare. The design is based on conditions that are known to give good destruction of landfill gas: high temperature, controlled combustion air and sufficient residence time. The proposal states that it is designed to meet the German TA Luft emission standard and the Environment Agency’s guidance on flaring landfill gas, which expects enclosed flares to reach at least 1,000°C. See the Environment Agency’s guidance on monitoring enclosed flares (LFTGN05).
| Elevated flare | Low visual impact horizontal flare | |
|---|---|---|
| Flame visible from outside | Yes, at the stack tip | No, enclosed in the shroud |
| Height | Tall stack | Low, behind a slatted screen |
| Typical temperature control | More limited | Automatic, 1,000°C minimum |
| Best suited to | Remote sites | Sites near neighbours or public access |
The trade-off is footprint and cost. A horizontal flare takes more ground area than a vertical one, and a screened, enclosed unit costs more than a simple open flare. For a site where appearance is part of the planning conditions or the community relationship, that is usually a fair price.
What to consider for your own project
- Decide the duty. A standby flare for emergencies has different needs from a duty flare running every day. Ask how often it will run and for how long.
- Define the gas range. Give the maximum flow, the lowest flow you expect, and the methane range. Here the unit was designed for 20% to 70% methane.
- Check the footprint early. The horizontal layout is compact in height, but you still need the plan area, access for maintenance and a safe distance to boundaries.
- Plan the supporting works. Electrical supply, foundations, condensate drainage and any telemetry link were outside this supply, as is normal. They need to be ready on time.
- Arrange servicing. A warranty normally depends on a service arrangement being in place, and a standby unit still needs periodic inspection so it is ready when needed.
FAQ
What is a low visual impact flare?
It is an enclosed ground flare designed to reduce how much of the flare can be seen. The flame is inside a low shroud, and the unit is screened by a frame in a colour that suits its surroundings.
Is a horizontal flare as effective as a vertical ground flare?
The orientation does not change the principle. What matters is temperature, mixing and residence time. This design used a forced-draught burner and held at least 1,000°C with over 0.5 seconds of residence time.
Why use a flare as a standby unit?
If the main gas treatment plant stops, landfill gas is still being produced. A flare gives a safe, controlled way to destroy it rather than venting methane to the atmosphere.
How long does delivery take?
The proposal allowed 12 to 14 working weeks after receipt of the deposit, delivered to port, plus commissioning and training for the operator’s staff.
Need a flare that blends in?
Tell us about your site, gas flow and planning constraints and we will recommend a flare layout.