A mobile open flare is a single skid carrying a knockout pot, a gas blower, a flame arrester and a flare stack with a hinged tip that folds down for transport. It is designed to be delivered, connected to gas and electricity, and started without a commissioning engineer. This article describes a 500 m³/h unit quoted for an engineering contractor in Australia, and the choices behind it.

The challenge: temporary gas control that moves with the work

Engineering contractors working on landfill gas systems often need to flare gas during wellfield extension, commissioning of new collection pipework or pumping trials. These jobs are short, sites change, and the equipment must be shipped and positioned quickly. A fixed enclosed flare is overkill. A mobile unit that is simple and robust is better.

The customer was an experienced engineering company, so the flare was offered ‘plug and play’: no commissioning engineer on site, although one could be provided as an option.

The approach: everything on one frame

Design basis

• Gas: landfill gas with 20 to 50% methane, 45 to 60% carbon dioxide and up to 5% oxygen, balance nitrogen.
• Flow: up to 500 Nm³/h, down to 100 Nm³/h.
• Blower: total head of about 85 mbar g (-65 to +20 mbar g across the unit), driven by a 3 kW motor (2 kW absorbed) on a 380 V three-phase supply.

On the skid

1. DN100 manual butterfly valve on the inlet, used to trim flow and pressure.
2. Knockout pot in 304 stainless steel with a polypropylene coalescing mesh to remove condensate.
3. Centrifugal blower with aluminium casing and impeller, stainless steel shaft, anti-vibration mounts and stainless flexible connectors.
4. Low-pressure switch on the blower outlet.
5. Gas solenoid valve that closes if power is lost.
6. Sampling points on the inlet, knockout pot and blower outlet.
7. A deflagration-rated ribbon flame arrester on the riser inlet.
8. Open flare with a 310 stainless steel burner head, a high-voltage spark igniter and a UV flame sensor.
9. A local control panel with switches and lamps.

All of this is mounted on a galvanised steel base frame with lifting lugs.

Why it works

Open flare, 850°C

The flame temperature is set by manually adjusting the air-to-fuel mix at the base of the stack. It can be set to a minimum of about 850°C. This is lower than an enclosed flare, but acceptable where the flare is temporary and a permit does not demand more. See LFTGN05 for the standard expected of permanent enclosed flares in the UK.

Fold-down flare tip

The burner head is hinged. For transport it folds down into a cradle on the skid frame, so the unit can be transported on its skid. In use it stands upright.

Loss of flame protection

If the UV sensor sees no flame, the main solenoid valve closes. A fail-closed valve is a simple and reliable safeguard, which suits equipment that may be left unattended.

Optional pressure control

As standard, gas pressure and flow are adjusted by hand with the inlet butterfly valve. The option is a variable speed drive on the blower motor, controlled from a pressure transmitter on the blower inlet. The user sets the pressure they want, and the drive holds it. For a mobile unit that is moved between wells with different gas quality, this saves repeated manual adjustment.

What is not included

• Import duties, taxes and harbour charges.
• Delivery from port to site.
• Foundations or civil work.
• The electrical supply and connection, though a suitable connection point is provided.
• Servicing arrangements. Warranty is normally conditional on a service contract or on trained staff keeping full records.

Other options include a security enclosure, a trailer-mounted version and extra instrumentation.

What to consider for your own project

1. Match the gas. Check methane and oxygen ranges, especially during early extraction.
2. Plan the hook-up. Power, a gas inlet and a clear space are all the unit needs.
3. Decide on pressure control. Manual trim is cheaper, but a drive is worth it if you move often.
4. Know the permit. A temporary open flare is not a substitute for a permanent enclosed flare where one is required. See the Environment Agency’s LFTGN03.
5. Train your staff. Without a commissioning engineer, your team must understand the start-up sequence.

FAQ

What is the difference between open and enclosed flares?

An open flare burns at the top of a stack with limited air control. An enclosed flare burns inside an insulated shroud at a higher, controlled temperature.

How long does delivery take?

In this quotation, 12 weeks from the factory plus about 3 weeks for shipping.

Can a mobile flare run unattended?

The flame-out valve will shut off gas, but site rules and the permit will decide whether unattended operation is acceptable.

Need a flare that moves?

Talk to us about a mobile flare for your contract.