A flare supplied without a blower is the right choice when the site already has equipment able to push gas to the flare at the required pressure. You avoid buying and maintaining a second set of gas-moving equipment. This article looks at an enclosed flare rated for 1,450 Nm³/h at an Asian water reclamation works, and sets out what to verify before you choose between flare-only and fully packaged supply.
The challenge: gas moving equipment already in place
Suppliers commonly offer two variants of the same enclosed flare:
- Packaged (SC/P): flare plus a gas blower, knockout pot and associated controls on one skid, for sites with nothing to move the gas.
- Flare only (SC/L): a skid-mounted flare with no blower, for sites where suitable equipment already exists.
This enquiry was for the second type. The site already delivered gas at around 40 mbar g. The flare had to be sized, and designed to the right standards, to accept that gas without adding a booster.
The approach: the design basis
| Parameter | Design value |
|---|---|
| Maximum gas flow | 1,450 Nm³/h |
| Minimum gas flow | 290 Nm³/h (5:1 turndown) |
| Thermal rating | 7,320 kW at maximum |
| Methane range | 25 to 70% (design point 50%) |
| Methane destruction efficiency | 99.9% |
| Combustion temperature | At least 1,000°C |
| Residence time | At least 0.3 seconds |
| Supply pressure | 40 mbar g |
| Inlet connection | DN150 |
A methane destruction efficiency of 99.9% is the headline performance number. It means that for every 1,000 units of methane that enter the flare, only about one leaves unburned.
Where the gas pressure matters
With no blower, the whole design relies on the gas arriving at the specified pressure. If the upstream system delivers less, the burner will not operate as designed. That is why the supply pressure appears in the design criteria. Always ask the supplier of the upstream equipment to confirm the actual operating pressure across the full flow range, not just at the design point.
Why it works
Pilot and burner control
This flare uses a propane pilot line, with its own solenoid valve, flame arrester and adjustment valve. The bottles, regulators and connection were left out of the scope. A dedicated burner control unit, rather than a general PLC, handles the ignition sequence, working with igniters, a UV flame sensor and a secondary air damper.
Safety at the inlet
The inlet includes an ATEX flame arrester to EN 12874, a low-pressure switch to warn of line blockage and two electro-hydraulically actuated butterfly valves in a double block-and-bleed arrangement. The valves close on loss of power or alarm, and they do not need compressed air.
Weather protection and sampling
The ceramic insulation lining is sprayed with a rigidiser and protected by a rain guard so water cannot get between the insulation and the shell. Four DN125 sampling ports are positioned near the top of the stack, with an access platform and ladder.
Standards and responsibilities
The design followed ISO 22580 for flares. Lightning protection, the compound and its separation from buildings were left with the end user. This is common, and it needs a named owner on the project.
What to consider for your own project
- Confirm the pressure. Ensure the upstream equipment can maintain it across the full flow range.
- Check the control interface. If the flare is stopped and started by another system, agree the signals in writing.
- Decide on pilot fuel. A propane pilot needs bottle storage and a refill routine.
- Allocate lightning protection. It is easily overlooked when it sits outside the supplier’s scope.
- Allow for gas analysis. Analysis equipment was excluded, so decide how composition will be monitored.
For UK sites, LFTGN05 describes how enclosed flare performance should be monitored.
FAQ
What does SC/L mean?
It is the supplier’s designation for a shrouded combustor supplied as flare only, with no gas blower.
Is a flare-only package cheaper?
Typically, because there is less equipment. The saving is only real if the existing blowers can do the job.
What is turndown?
The ratio between maximum and minimum flow. A 5:1 flare working at 1,450 Nm³/h maximum operates down to 290 Nm³/h.
Why a propane pilot?
It gives a reliable ignition source independent of the gas quality, which can vary.
Choosing between flare-only and packaged?
Tell us what gas-moving equipment you have and we will recommend the right scope.