Landfill gas flare monitoring turns a flare from a machine you visit into one you can watch. Adding on-line gas analysers, a data-logger and an autodialer lets an operator see gas quality and flare status in real time and be alerted to a fault without being on site. This post uses a 750 m³/h ground flare package specified for an Irish local authority landfill to explain what each element does and what routine maintenance still has to be done by people.
The challenge: a flare that must perform and prove it
A landfill gas flare is often at a remote site, running unattended for days. The operator still has to demonstrate that it burns gas at the right temperature, and has to know quickly when something goes wrong. The specification in this example asked for a flare that would meet TA Luft emission standards and the UK Environment Agency’s interim technical guidance on best-practice flaring of landfill gas, with the monitoring to support it.
The approach: flare, booster and monitoring on one skid
The gas path
The package is skid-mounted. Gas first passes through a condensate knockout pot, which contains a polypropylene dewatering filter so that no airborne liquid reaches the gas booster. The pot’s liquid seal holds a maximum head of about 180 mbar. The booster is driven by an ExN (Zone 2) motor through a direct-drive arrangement and delivers 750 m³/h at a total head of about 150 mbar, with a star-delta starter. Noise at 1 m is about 80 dB(A) without an acoustic enclosure, which is offered as an option. Flame arresters sit on the booster inlet and outlet.
The flare
The ground flare burns at a minimum of 1,000°C when methane is above 25%, and runs cooler at lower methane concentrations down to 20%. Minimum residence time is 0.6 seconds. Turndown is 5:1, so the minimum flow is around 150 m³/h. The shroud has 100 mm of ceramic blanket lining. A PID controller, a combustion air louvre and an 80-second actuator control flame temperature automatically.
The monitoring layer
This is where the package goes beyond a basic flare:
- Orifice plate flow meter: flow data is signalled to the PLC and available at a remote location through the specified software.
- SCADA system: an autodialer alerts a remote receiver of alarm conditions, on-line real-time monitoring covers gas composition and flare status, and a data-logger records historical data on gas composition and flare performance.
- Three on-line analysers: a chemical-cell oxygen analyser, an infra-red methane analyser and an infra-red carbon dioxide analyser, each with an operator-adjustable alarm.
What each analyser tells you
| Measurement | What it indicates |
|---|---|
| Methane | Whether the gas is rich enough to burn at full temperature and whether flow needs to be cut back |
| Carbon dioxide | Together with methane, the balance of the bulk gases in the field |
| Oxygen | Air entering the gas collection system, a safety and efficiency concern |
Commissioning included analysing both the inlet gas composition and the exhaust gas emissions on site, to verify compliance with the specification.
Why it works: maintenance still matters
Monitoring does not replace maintenance. The package pairs it with a two-level regime:
- Regular checks, weekly: visual inspection of the booster and motor, control panel readouts, and gauges, valves and other fittings, as set out in the instruction manual. The manual also gives troubleshooting steps for alarm conditions, such as checking for a power cut after a motor shutdown.
- Servicing at four-monthly intervals: an engineer shuts down the flare and services the inlet demister and condensate removal equipment, the booster and motor, the flame arresters, the main gas valve, and the ignition and burner equipment.
The supply also covered one year of servicing support (three visits) and a three-year warranty covering parts, materials and labour.
What to consider for your own project
- Decide what you need to prove. If you must show temperature and gas composition to a regulator, specify a data-logger from the start. The Environment Agency’s guidance on monitoring enclosed flares (LFTGN05) is the starting point for the UK.
- Choose alarm set points deliberately. Each analyser has an adjustable alarm. Agree the values before commissioning.
- Plan the alert route. An autodialer is only useful if someone is always on the receiving end.
- Keep the people routine. Weekly visual checks and scheduled servicing remain essential.
- Consider noise. Around 80 dB(A) at 1 m will matter near neighbours or operators. Acoustic options exist.
FAQ
What does SCADA do on a flare?
It gives remote monitoring of flare status and gas composition, logs historical data and alerts a remote receiver when an alarm condition occurs.
Which gases should be monitored at the flare inlet?
This package monitored methane, carbon dioxide and oxygen on-line.
How often should a flare be serviced?
This package specified weekly operator checks and a four-monthly engineer service.
What is turndown?
It is the range between maximum and minimum flow a flare can burn properly. Here, 5:1 meant a minimum around 150 m³/h.
Planning flare monitoring?
Tell us what your permit requires you to record and we will specify the right analysers and data-logging. For related reading, see our guide to writing a flare specification and flare running costs and lifespan.