Choose a high-temperature ground flare when exhaust emissions matter most, and an elevated flare when a lower combustion temperature is acceptable and cost is the priority. In a 2,600 m³/h enquiry from a process engineering contractor, the supplier quoted a ground flare holding at least 1,000°C and offered an elevated alternative at a minimum of 850°C. The temperature difference, and a substantial price reduction, were the trade-off.
The challenge: a specification that did not state a temperature
A contractor was preparing a tender for a waste treatment scheme in Ireland. Its enquiry asked for an ex-works flare rated at 2,600 normalised m³/h but did not specify a combustion temperature. That left the supplier to decide what to quote.
Where a specification is silent, a sensible supplier quotes the more capable option and offers a cheaper alternative. That is what happened here.
The approach: quote the ground flare, offer the alternative
The base offer: SC Range ground flare
The gas had a calorific value of about 15 MJ/m³, and the flare was designed around that:
- Temperature: at least 1,000°C when calorific value is above 9 MJ/m³, falling as it weakens, down to 7 MJ/m³.
- Residence time: at least 0.5 seconds.
- Feed pressure: at least 10 mbar at the flare inlet. No booster was part of this supply, so the gas has to arrive at the flare under its own pressure.
- Shroud: 9 m high, hot-dip galvanised steel lined with 100 mm of ceramic insulation.
- Control: a PID controller with combustion air louvres and an actuator, plus a thermocouple to detect the flame and electric ignition run by a PLC.
- Safety: a flame arrester on the inlet, a pressure switch to detect flow interruption and a single-block slam-shut valve.
The operator can choose between continuing to run on flame-out, shutting down on flame-out, or venting only.
The alternative: AC Range elevated flare
An AC Range elevated flare was offered as a lower-specification option. It would meet every other aspect of the specification, with a minimum combustion temperature of 850°C. The supplier quantified the saving in the quotation, which was a substantial reduction on the ground flare price.
Why the choice matters
| Ground flare (SC Range) | Elevated flare (AC Range) | |
|---|---|---|
| Minimum combustion temperature | 1,000°C | 850°C |
| Combustion air control | Automatic, tight | More limited |
| Flame visibility | Hidden in the shroud | Visible at the stack tip |
| Destruction of trace gases | Maximised | Lower |
| Typical use | Where emission control is of senior importance | Remote sites or lighter requirements |
Higher temperature gives a higher destruction and removal efficiency for toxic trace gases. In the UK, regulators expect enclosed flares to reach at least 1,000°C with 0.3 seconds of residence time, according to the Environment Agency’s guidance on monitoring enclosed flares (LFTGN05). If your project is in the UK and subject to a permit, the 850°C option is unlikely to be enough on its own.
What to consider for your own project
- State a temperature in the enquiry. It avoids pricing the wrong option and saves a revision cycle.
- Know your gas calorific value. The flare’s lower operating limit depends on it. This one was designed to run down to 7 MJ/m³.
- Check inlet pressure. Without a booster, the gas must reach the flare at the pressure it needs. Here that was at least 10 mbar.
- Ask for the alternative. A lower-spec price helps the client judge what the extra performance costs.
- Check the regulator’s view first. A cheaper flare that fails a permit is not a saving.
FAQ
What is the difference between a ground flare and an elevated flare?
A ground flare burns gas inside an enclosed shroud with controlled combustion air. An elevated flare burns it at the top of a stack, usually at a lower temperature.
Why does combustion temperature matter?
Higher temperatures destroy toxic trace gases more completely, which is why enclosed flares are specified where emission control is important.
Can a flare run without a booster?
Yes, if the gas arrives at the flare inlet at enough pressure. This design needed a minimum of 10 mbar.
What happens when the flame goes out?
The operator selects the response in advance: keep running, shut down, or vent only.
Choosing a flare type?
Tell us about your gas and your permit and we will recommend a flare type.