Air Assist Flares

An air-assisted flare is the right choice when waste streams contain heavy hydrocarbons that would smoke under unassisted combustion, but the site has no high-pressure steam available. Forced-air injection provides the mixing energy needed for smokeless burn while remaining cheaper to operate than steam-assist on sites without existing utility steam.

Best fit when:

• Waste gas contains heavy hydrocarbons (C3+, aromatics, olefins) prone to smoking
• Site lacks reliable high-pressure steam supply
• Operating profile includes large variations in flow (turndown) and BTU content
• Tank vapors, loading emissions, or low-pressure relief streams are involved
• Smokeless operation is required for compliance or community impact

Air-assisted flares achieve smokeless combustion by using a high-velocity blower to inject combustion air directly into the flame zone, generating turbulence that fully mixes oxygen with heavy hydrocarbons before they thermally crack into soot. Without that mixing, fuel-rich pockets form, producing visible smoke.

How the system works:

• Blower delivers controlled air flow matched to gas flow and BTU content
• Multi-stage tip design distributes air around and into the flame envelope
• Staged air injection allows efficient operation across full turndown range
• CFD-modelled tip geometry ensures uniform mixing without excess air

The result is destruction efficiency above 98% with no visible smoke, even on heavy hydrocarbon streams.

Air-assisted flares achieve destruction and removal efficiency (DRE) above 98% for hydrocarbons and VOCs, meeting EPA 40 CFR 60.18 and API 537 requirements. Performance depends on tip design, air-to-gas ratio, and flame stability across the operating range.

Performance drivers:

• Properly sized blower for the design air-assist ratio
• Tip geometry that delivers air into the flame envelope, not just around it
• Stable pilot system to maintain ignition during low-flow conditions
• Adequate residence time at flame temperature for full oxidation

CFD modelling is used to verify mixing and combustion efficiency before fabrication, ensuring the design meets DRE targets across normal, turndown, and emergency relief conditions.

Air-assisted flares typically handle gas flows from a few hundred to several hundred thousand kg/hr, with turndown ratios of 50:1 or higher when staged air systems are used. Exact range is sized to the application, since tip diameter, blower capacity, and staging strategy all scale with peak flow.

Operating range characteristics:

• Pilot flow — continuous low burn for ignition reliability
• Routine venting — typical day-to-day relief streams
• Emergency relief — sized for peak upset or blowdown event
• Staged air control modulates blower output to match instantaneous gas flow, avoiding excess air at low flows

Sizing is driven by peak relief case (typically a fire scenario or vessel blowdown), not normal operating flow.

The three flare types differ in how they handle heavy hydrocarbons that would otherwise produce smoke. Air-assist uses a blower, steam-assist uses high-pressure steam injection, and utility (unassisted) flares rely on the gas itself to burn cleanly.

• Air-assisted — uses a blower; preferred when steam isn't available; lower operating cost than steam at moderate flows; well-suited to tank vapors and low-pressure streams.
• Steam-assisted — uses high-pressure steam; highest smokeless capacity and turndown; preferred at very high flows in refineries/petrochemicals where steam is already available.
• Utility (unassisted) — no assist medium; lowest capital and operating cost; only suitable for streams that burn smokeless on their own (light hydrocarbons, hydrogen-rich gases) or where smoke is not a regulatory concern.

Air-assisted flares are designed to meet API 537 (flare details for general refinery and petrochemical service) and EPA 40 CFR 60.18 (general control device requirements). International projects typically also require compliance with the EU Industrial Emissions Directive (IED) and local regulatory frameworks.

Common compliance items:

• Net heating value of combustion zone gas above the regulatory minimum
• Exit velocity within limits for stable, smokeless combustion
• Continuous pilot monitoring and assured ignition
• Records of operating parameters for emissions reporting

CRA flare designs follow ISO 9001, ASME, API, and CE marking requirements, with project-specific certifications added when local regulations require.

Air-assisted flares require routine maintenance focused on the blower, flare tip, pilot system, and ignition controls. With proper maintenance, the structure and tip last 15–25+ years; the blower, pilots, and ignition components are replaceable items.

Typical maintenance schedule:

• Routine (monthly/quarterly): blower bearing inspection, pilot flame check, ignition system verification, instrumentation calibration
• Annual: tip inspection for erosion or corrosion, blower performance test, control system check, refractory or shroud condition (where applicable)
• Multi-year: tip replacement if eroded (typically 10–15+ years), blower motor or impeller refurbishment, full structural inspection per local code

Continuous monitoring of pilot flame, blower current, and gas flow allows early detection of degradation before performance is affected.