A landfill gas flare specification for a public tender should state the flare’s gas flow, combustion temperature, residence time, turndown, emission limits, noise limit and control signals, and should say how each will be proven. The tender document always takes precedence, so the supplier’s technical scope should only add detail to it. This post uses a 3,000 m³/h ground flare prepared for a landfill rehabilitation tender in South-East Asia as a worked example.
The challenge: a tender with fixed emission limits
The client was a contractor bidding for a government landfill rehabilitation scheme. The tender set emission limits for the flare and asked for a stainless steel, low-height unit with local access standards. The contractor needed a technical scope it could drop into its bid without contradicting the main contract.
The supplier’s response made one rule explicit. Its text was “additive” to the tender specification. Where the two disagreed, the tender requirement would win. That is a good habit for any bidder. It keeps the commercial risk with the party that wrote the requirement.
The approach: a low-height ground flare with a closed-loop gas analyser
Flow and turndown
The flare was rated at 3,000 normalised m³/h with a 10:1 turndown. In practice that means it keeps working down to about 300 m³/h. Turndown matters because landfill gas output falls as a site ages. A flare that only works near full load will either trip or burn poorly for most of its life.
Temperature and residence time
The flare was designed to hold at least 1,000°C in the combustion chamber when methane is above 25%, and to run cooler, down to 20% methane, as the gas weakens. Minimum residence time was 0.3 seconds. The Environment Agency’s guidance on monitoring enclosed landfill gas flares (LFTGN05) gives 1,000°C and 0.3 seconds as the indicative standard for UK enclosed flares, so the design sits at that benchmark.
Emission and noise limits
The tender limits were written straight into the specification:
| Parameter | Limit |
|---|---|
| Carbon monoxide | 100 mg/Nm³ |
| Oxides of nitrogen | 100 mg/Nm³ |
| Non-methane organic compounds | 98% destruction and removal efficiency, by weight |
| Visible emissions | Nothing darker than Ringelmann 1 more than three times in an hour |
| Noise | 85 dBA at the flare enclosure, at maximum flow |
| Outer surface temperature | No more than 100°C |
The surface temperature limit is easy to overlook. A shroud running at over 1,000°C inside needs ceramic lining and a sensible wall build-up to stay safe to approach. Here the shroud was 4.5 mm thick 316 stainless steel lined with ceramic blanket.
The gas analyser closes the loop
The specification included an on-line analyser for methane, oxygen and carbon dioxide. A coalescing filter and a hygroscopic filter dewatered the sample so liquid could not reach the sensor heads. The analyser signal was used to control the rate of gas extraction and keep the methane percentage within set limits.
This is more than a monitoring feature. If the gas field is over-pumped, air is drawn into the waste, methane falls and the flare struggles to hold temperature. Using the analyser to trim extraction protects both the flare and the gas field.
Why it works: protection and control
- Condensate removal: a stainless steel knockout pot with a polypropylene dewatering filter, a liquid seal rated to 180 mbar, a level switch and a sight glass.
- Gas mover: a 30 kW explosion-protected motor driving a stainless steel booster directly, with a variable speed controller so the flow into the flare can be adjusted automatically.
- Flame safety: flame arresters on the booster inlet and outlet, a pilot gas line with its own arrester, a UV flame sensor and a slam-shut valve ahead of the burner.
- Temperature control: a PID controller driving automated secondary air dampers, so the flare holds its set temperature as gas quality changes.
- Restart behaviour: the operator can choose “continue running on flame out” or “shut down on flame out”. In the first mode the unit tries to restart at intervals, which helps when low methane has caused a shutdown.
The PLC also exposed a list of status and alarm signals for a data logger, including flame established, booster fail, high and low flare temperature, low methane, high condensate level and low pressure. Specifying these up front makes remote monitoring much easier to set up.
What to consider for your own tender
- Write limits, not adjectives. “Low emissions” cannot be checked. “CO 100 mg/Nm³” can.
- Define turndown against your gas curve. Ask for a gas production forecast and size the lower end of the range as carefully as the upper.
- Say who supplies what. In the bid clarification, the supplier made clear that excavation, granular pipe and pipe laying were outside its price. Gaps like these cause disputes later.
- Specify local standards. Access ladders, platforms and foundations should follow the standards of the country where the flare will stand.
- Include lifting arrangements. The skid and the chimney arrived separately. The skid used four corner lifting eyes and the chimney was lifted by a telescopic crane, with lifting points designed so the hooks fall free once the jib is lowered.
For the wider regulatory picture, see the Environment Agency’s guidance on the management of landfill gas (LFTGN03).
FAQ
What temperature should a landfill gas flare operate at?
UK guidance for enclosed flares treats 1,000°C with 0.3 seconds of residence time as the indicative standard. Some projects specify higher temperatures where tighter emission control is needed.
Why does turndown matter?
Gas output declines over the life of a landfill. A flare with a 10:1 turndown can keep burning cleanly at a tenth of its rated flow, so it stays useful as the site matures.
Why fit an on-line gas analyser to a flare?
It measures methane, oxygen and carbon dioxide continuously. The signal can be used to adjust extraction so air is not drawn into the waste, which protects flame temperature and gas quality.
Which document wins if the supplier’s specification and the tender disagree?
The tender. A supplier’s technical scope should be written as an addition and say so clearly.
Need help writing a flare specification?
If you are preparing a tender or bid that includes a landfill gas flare, talk to our engineers. We can help you set limits, size the unit against your gas forecast and avoid scope gaps.