Landfill sites generate methane-rich gas as organic waste decomposes, and safely destroying that gas is both an environmental necessity and, in many jurisdictions, a legal requirement. The US AC Series open flare stack — also known as a candle or utility flare — was purpose-built to meet the specific demands of the North American market, where taller, elevated burners are the industry preference.
This data sheet overview explains how the US AC Series works, what makes its combustion approach different from conventional diffusion flares, and the technical specifications that engineers and site operators need to know.
What Is an Open (Candle) Flare Stack?
An open flare, sometimes called a candle or utility flare, burns landfill gas in an elevated, exposed flame rather than inside an enclosed combustion chamber. Unlike enclosed “ground” flares, open flares don’t provide precise control over secondary combustion air — the ambient air that mixes with combustion gases after they leave the burner port. Instead, they rely on wind and atmospheric conditions to complete the combustion process.
The US AC Series distinguishes itself through its burner tip design, which uses pre-aerated combustion. This means air is mixed with the landfill gas before it exits the burner, producing a short, sharp, high-intensity, low-luminosity flame — a marked contrast to the long, lazy, yellow-tipped flame typical of standard diffusion burners.
Flame temperatures in the US AC Series are controlled within a range of 800 to 1,000°C (1,500 to 1,800°F), depending on methane concentration, flow rate, and prevailing wind conditions.
How the System Works
At the core of the design is a control panel that manages ignition, flame monitoring, and safety shutdowns automatically. Key operational features include:
- Automatic ignition on start-up, powered by a landfill gas-fired pilot — no on-site propane required
- Self-checking UV flame detection, with automatic re-ignition attempts for an operator-settable period following flame failure
- “Run-on” mode, which allows the unit to continue operating as a vent (rather than shutting down entirely) if re-ignition fails — keeping gas migration control active even when combustion isn’t sustained
- Dispersal and vent station mode, for situations where methane concentration is too low to support combustion
This flexibility is particularly valuable at landfill sites where gas quality fluctuates over time, ensuring that migration control remains active regardless of whether the flame is lit.
Blower and Flow Control
Flow rate into the unit is regulated by chemical duty butterfly valves across two standard flanged inlets (additional inlets are available on request). The gas booster provides turn-down to zero flow without surging, giving operators fine control across a wide operating range.
An inlet knock-out pot fitted with a filter de-mister element protects the gas booster by removing condensate and debris before the gas reaches the impeller chamber.
Technical Specifications
| Parameter | Specification |
|---|---|
| Flow rate range | 150 to 25,000 SCFM (100 to 15,000 m³/h) |
| Pressure rise across gas booster | 60″ WG (150 mbar) |
| Flame temperature | 1,500 to 1,800°F (800 to 1,000°C) |
| Minimum methane concentration for sustained combustion | 20% |
| Number of inlets (standard) | 2 flanged inlets |
| Pipework finish | Hot dip galvanised to industry standard |
| Burner material | High temperature stainless steel |
| Flame arrestor | Fitted on gas booster inlet and outlet |
| Flame detection | Self-checking UV sensor |
| Standard colour | Battleship Grey (or customer specification) |
| Destruction Efficiency Rating (DRE) | Greater than 98% |
Instrumentation and Monitoring
The pipework system is designed to accommodate a range of flow meters depending on budget and site requirements, and comes fitted with pressure and temperature gauges at key points in the flow stream. Access points are also included for hand-held anemometers and pitot static flow meters, giving operators flexibility in how they verify performance.
Optional additions include:
- Flow rate and gas concentration measurement instrumentation
- Remote access and datalogging capability
- Programmable timers, gas analysis alarms, and telemetry for power failure, flame failure, and high oxygen alerts
Construction and Site Practicalities
The entire unit is skid-mounted, simplifying transport and on-site repositioning — a practical advantage as landfill gas collection fields expand or wellfields are reconfigured over time. Fully stainless steel construction is available as an option for sites requiring extra corrosion resistance.
The unit’s stainless steel burner and galvanised pipework are engineered for durability in the harsh, corrosive environment typical of active landfill gas fields.
Performance and Limitations
Because it’s an elevated, open flare, the US AC Series cannot match the flame temperature stability or extended residence times achievable with an enclosed ground flare system. Secondary combustion air is essentially uncontrolled, and dilution varies with wind speed and direction. In calm conditions with strong methane concentration, a flame temperature of 1,000°C can be maintained with reasonable stability — but during high wind and low methane periods, reaching that figure becomes far more difficult.
Despite this inherent limitation — shared by all elevated flare designs — the US AC Series reliably achieves Destruction Efficiency Ratings (DREs) greater than 98%, satisfying the baseline regulatory standards required across the United States.
Typical Applications
The US AC Series is best suited to:
- Municipal and industrial landfill sites requiring landfill gas destruction to meet environmental compliance
- Sites where tall, elevated flares are preferred over enclosed ground flares, whether for space, cost, or regulatory reasons
- Operations needing a mobile, skid-mounted solution that can be relocated as gas wellfields develop
- Facilities wanting a proven, propane-free, landfill-gas-fired pilot ignition system
Key Takeaways
- The US AC Series is an open (candle/utility) flare stack designed for the North American landfill gas market’s preference for tall burners.
- Pre-aerated combustion produces a high-intensity, low-luminosity flame with flame temperatures between 800–1,000°C (1,500–1,800°F).
- The system handles flow rates from 150 to 25,000 SCFM and reliably achieves DREs greater than 98%.
- Automatic ignition, self-checking UV flame detection, and a “run-on” vent mode ensure continuous gas migration control even during flame failure.
- Skid-mounted construction, optional stainless steel build, and a wide range of instrumentation options make it adaptable to diverse landfill site requirements.
Get in Touch
Looking to specify a reliable, code-compliant flare stack for your landfill gas management project? Contact our team to discuss how the US AC Series can be configured to match your site’s flow rates, gas composition, and regulatory requirements.