The gas booster is sized by two numbers: the flow it must move and the pressure head it must develop to pull gas through the wellfield and push it into the flare. For a landfill ground flare handling 3,000 m³/h, a head of about 300 mbar, a two-impeller stainless steel booster and an acoustic box giving 60 dBA at 1 metre met the client’s needs. This post shows how those choices were reached as a project grew from 1,000 m³/h to 3,000 m³/h.
The challenge: head, noise and growth
A landfill operator in the Midlands began with a budget enquiry for a 1,000 m³/h ground flare. Two requirements shaped the early discussion:
- a total head of 300 mbar across the booster, which is higher than some standard units are built for;
- quiet operation, because the fan would be heard from outside the site.
The supplier had to find a booster able to develop the head. At one point the operator asked for 1 bar across the fan assembly, and that was priced as a separate, higher-cost variant. The lesson is that head drives booster cost, so it should be set from calculation, not habit.
The approach: scale up, then specify the details
From 1,000 m³/h to 3,000 m³/h
Over about two years the project was re-scoped to 3,000 m³/h. By then the scheme was seen at a trade exhibition and a revised quotation followed. The final specification was issued with the order, together with a confirmation that the flare would meet the Environment Agency’s March 1999 interim guidance on best practice flaring of landfill gas.
The booster
The final booster assembly has two stainless steel impellers on a single shaft, driven by an explosion-protected electric motor with a star-delta starter. It delivers 3,000 m³/h at about 300 mbar (120 inches water gauge). Using two impellers on one shaft is a common way to reach a higher head than a single impeller gives at the same speed.
Turndown and control
The client asked whether the blower could turn down all the way. The answer was yes: the blower has an infinite turndown ratio, from full flow to pilot flow. The flare itself holds 1,000°C above 25% methane, burns cooler down to 20% methane, and has a 5:1 turndown (about 600 m³/h at the low end).
These two turndowns do different jobs. The blower’s turndown lets you throttle extraction as gas production falls. The flare’s turndown sets the range over which it burns to specification.
Noise, filtration and the panel
- Acoustic box around the fan, giving 60 dBA at 1 metre.
- 50 micron coarse filter upstream, to protect the booster from particles that pass the knockout pot.
- Fully waterproof control panel, chosen for an outdoor site.
Why it works
The booster is the heart of the system. If its head is too low, gas will not reach the flare from the far end of the field. If its flow is too small, wells further out will be starved. If it is too noisy, it becomes a planning problem.
The flare then does what the booster cannot, which is to destroy the gas cleanly. Temperature is held by a PID controller and a combustion air louvre, with a minimum residence time of 0.5 seconds. For guidance on how flaring fits with wider gas control, see the Environment Agency’s LFTGN03.
What to consider for your own project
- Calculate head from the system. Include pipe losses, wellhead vacuum and the pressure the flare needs at its inlet.
- Allow for growth. A flare that started at 1,000 m³/h was later specified at 3,000 m³/h. Ask what your expected gas peak is.
- Set the noise target early. The acoustic box was part of the specification, not an afterthought.
- Ask about blower turndown. A fan that can throttle to pilot flow gives you more room as the site ages.
- Protect the booster. A coarse filter is inexpensive relative to an impeller replacement.
- Tie payments to milestones. The project used staged payments linked to order, drawing approval, delivery and commissioning, which keeps both sides aligned.
FAQ
What does a landfill gas booster do?
It creates suction on the gas field and delivers gas to the flare at the pressure the burner needs.
What pressure head do I need?
It depends on pipe length, wellhead vacuum and flare inlet pressure. In this example it was about 300 mbar.
How do you reduce booster noise?
An acoustic enclosure around the fan. In this project it brought noise to 60 dBA at 1 metre.
What is the difference between blower turndown and flare turndown?
Blower turndown is how far you can reduce extraction. Flare turndown is the range over which the flare holds its design temperature.
Sizing a flare and booster?
Send us your gas forecast and we will help you size flow, head and noise.