A flare without a blower suits sites where the biogas already arrives at the flare under enough pressure, such as at a sewage or water reclamation works. In a proposal for a 3,500 Nm³/h enclosed flare at a water reclamation plant in South-East Asia, the gas was supplied at 50 mbar, so the flare package left out the blower and added an inlet pressure regulator and a fail-safe shut-off valve.
The challenge: a large flare on a gas supply that already moves
A landfill flare normally pulls gas out of the ground, so it needs a blower. A biogas plant can work differently, because the gas may already reach the flare under pressure from the plant upstream. Adding a second blower then costs money and adds something else to maintain. But the flare still has to cope with the pressure it is given, and with a sudden loss of flame.
The approach: an SC/L ground flare
The duty
| Parameter | Design value |
|---|---|
| Gas flow | 700 to 3,500 Nm³/h (5:1 turndown) |
| Methane | 25 to 60% (design point 50%) |
| Temperature | At least 1,000°C, down to 20% methane at lower temperature |
| Residence time | At least 0.3 seconds |
| Methane destruction | 99.9% |
| Supply pressure | 50 mbar |
| Emission limits | CO 50 mg/Nm³, NOx 150 mg/Nm³ (at 10% oxygen, normal temperature and pressure) |
At full flow the burner releases about 17 MW. The flare is built in Thailand with European and US components and shipped in two 40-foot flat-rack containers, with final assembly on site.
Protecting the flare from the supply
Without a blower in front of it, the flare relies on a chain of devices:
- Inlet isolation valve. A wafer butterfly valve with a gear wheel for manual operation.
- Spring-loaded pressure regulator. It opens when upstream pressure reaches an adjustable limit, which is set with a screw and shown on a pointer.
- Slam-shut valve. A pneumatically actuated butterfly valve that is fail-safe and spring-closed on loss of power or an alarm. It needs a compressed air supply, which is not included, although each actuation uses less than one litre of air at 6 bar.
- Low-pressure switch. It indicates a blocked line or loss of supply.
- Thermal shut-off valve and flame arrester. This combination, designed for methane (gas group IIA1), shuts off the gas if a flame flashes back along the pipe.
Combustion control
A thermocouple measures the chamber temperature and an actuated louvre controls the combustion air. The set point is adjusted from a digital display in the panel. Ignition is automatic. A pilot line with its own solenoid valve and flame arrester is lit by an electric igniter under a burner control unit, and a UV sensor confirms the flame. The panel has a touch-screen display and volt-free contacts for remote control by others.
Why it works
The shroud is stainless steel lined with 100 mm of ceramic insulation, sprayed with a rigidiser and covered by a rain guard to prevent water getting between the insulation and the steel. The insulation keeps heat inside the shroud so that the chamber temperature can be held with low fuel use. The design follows the principles described in the Environment Agency’s guidance on enclosed flares, and it claims compliance with the TA Luft emission classes.
The trade-off is that the flare has no way of increasing gas pressure. If the supply falls below what the flare needs, it will not run properly. The design is intended for sites where a booster or the digester pressure is already in place.
What to consider for your own project
- Confirm the supply pressure at the flare inlet across the whole flow range, not only at design flow.
- Specify a compressed air source if the slam-shut valve is pneumatic, or ask for an alternative actuator.
- Decide who provides analysis. Biogas and flue gas analysis equipment were excluded.
- Plan the handover. Foundations, site delivery, installation, earthing and lightning protection were excluded.
- Check tender forms early. Public tenders ask for schedules of technical data and deviations. Prepare them early.
If your site has no gas-moving equipment, see our post on a packaged flare with blower. For the meaning of the figures in the duty table, see enclosed flare design criteria.
FAQ
Can a biogas flare run without a blower?
Yes, if the gas reaches the flare inlet at enough pressure. Here the supply was 50 mbar.
What does the pressure regulator do?
It is spring-loaded and opens when the incoming pressure reaches an adjustable limit, which is shown on a pointer.
What is a thermal shut-off valve?
It closes automatically if it detects flame heat in the gas line. Paired with a flame arrester, it prevents flashback.
What does 99.9% methane destruction mean?
It is the methane destruction efficiency stated in the design criteria.
Sizing a flare for biogas?
Tell us your gas flow, methane range and supply pressure and we will advise whether you need a blower.