Air Assist Flares

An air-assisted flare is the right choice when the waste gas contains heavy hydrocarbons that would smoke in an unassisted flare and the site has no high-pressure steam. A blower injects combustion air into the flame zone to provide the mixing energy for smokeless combustion at lower operating cost than steam assist where there is no utility steam. It fits best when the gas contains C3 and heavier hydrocarbons, aromatics or olefins, when flow and calorific value vary widely, when tank vapours or low-pressure relief streams are involved, and when smokeless operation is needed for compliance or community reasons. CRA designs each tip for the actual gas and flow range.

Air assist makes a flare smokeless by using a blower to inject combustion air directly into the flame zone, creating turbulence that mixes oxygen with the heavy hydrocarbons before they crack thermally into soot. Without that mixing, fuel-rich pockets form and produce visible smoke. The blower delivers air matched to the gas flow and calorific value, the multi-stage tip distributes air around and into the flame envelope, and staged air injection keeps the flare efficient across the turndown range. CRA uses CFD modelling of the tip geometry during design to check that mixing is uniform without excess air. The result is destruction efficiency above 98% with no visible smoke.

An air-assisted flare achieves destruction and removal efficiency above 98% for hydrocarbons and VOCs and is designed to meet EPA 40 CFR 60.18 and API 537 requirements. Performance depends on tip design, the air-to-gas ratio and flame stability across the operating range. The main design points are a blower sized for the design assist ratio, a tip geometry that delivers air into the flame envelope as well as around it, a stable pilot that holds ignition at low flow, and enough residence time at flame temperature for full oxidation. CRA checks mixing and combustion with CFD modelling before fabrication so the design covers normal, turndown and emergency relief conditions.

The three flare types differ in how they deal with heavy hydrocarbons that would otherwise smoke. An air-assisted flare uses a blower, is preferred where steam is unavailable, costs less to run than steam at moderate flows and suits tank vapours and low-pressure streams. A steam-assisted flare uses high-pressure steam, gives the highest smokeless capacity and turndown, and is preferred at very high flows in refineries and petrochemical plants where steam already exists. A utility flare has no assist medium, has the lowest capital and operating cost and suits only streams that burn smokelessly on their own or sites where smoke is acceptable. CRA manufactures all three.

Air-assisted flares are designed to API 537 for flare details in refinery and petrochemical service and EPA 40 CFR 60.18 for general control device requirements. International projects often add the EU Industrial Emissions Directive (IED) and local regulatory frameworks. Design checks cover the net heating value of the combustion zone gas above the regulatory minimum, exit velocity within the limits for stable and smokeless combustion, continuous pilot monitoring with assured ignition, and records of operating parameters for emissions reporting. CRA is ISO 9001 certified through TÜV NORD, and its flare designs are aligned with API and CE practice, with site-specific regulatory requirements built into the design basis.