Open Elevated Flare

Open elevated flares are the right choice for high-volume relief and emergency service where the gas flow can far exceed normal venting rates and elevation is required to disperse heat and combustion products safely away from personnel and equipment. They're the standard for refinery and petrochemical flare headers.

Best fit when:

• Peak relief flows are very high (e.g., refinery main flare, vessel blowdowns)
• Heat dispersion at elevation is needed for personnel safety
• Plant footprint is too constrained for an enclosed ground flare at peak flow
• Flame visibility is acceptable for the site (industrial location, no community impact constraints)
• Wide operating range from pilot flow to large emergency relief

For sites near residential areas or where flame visibility is unacceptable, enclosed ground flares are preferred.

Open elevated flares can achieve turndown ratios of 100:1 or higher when designed with multi-stage flare tips and proper pilot systems. This wide range is what makes them suitable for handling everything from continuous low-flow venting to massive emergency relief in a single device.

How it's achieved:

• Continuous pilot flame ensures ignition reliability at lowest flows
• Multi-tip or staged-tip design distributes peak flow across multiple combustion points
• Purge gas system maintains positive pressure in the stack to prevent air ingress at low flow
• Tip geometry is optimized for stable flame across full velocity range

Wide turndown is critical for refinery applications where the same flare must handle routine fugitive emissions and 100+ kg/s upset relief.

Elevated flares disperse combustion heat by burning the gas at a height above the surrounding plant, allowing thermal radiation and hot combustion products to dissipate before reaching personnel-accessible areas. Stack height is calculated specifically to keep ground-level radiation within safe limits during peak relief.

Design considerations:

• API 521 radiation limits — typically 1.58 kW/m² (500 BTU/hr·ft²) for personnel areas
• Stack height calculated for worst-case relief and ambient wind conditions
• Exclusion zone defined around the base for radiation and dispersion safety
• Tip design controls flame length, lift-off behaviour, and direction
• Optional windshield or shroud improves flame stability in high-wind sites

Design verification uses radiation and dispersion modelling to confirm safety distances under worst-case conditions.

Open elevated flares are available in three configurations based on how smokeless combustion is achieved on heavy or fuel-rich streams.

• Unassisted (utility) — simplest design, lowest cost. Used when waste gas burns smokeless on its own (light hydrocarbons, hydrogen-rich gas) or where smoke is not a regulatory concern.
• Air-assisted — blower injects combustion air for smokeless burn of heavy hydrocarbons. Best when steam isn't available or for moderate flows where steam-assist would be over-engineered.
• Steam-assisted — high-pressure steam injection enables smokeless combustion at the highest flows. Standard in refineries and petrochemical plants where steam is already available; offers the highest smokeless capacity.

Selection depends on gas composition, peak flow, available utilities, and emissions requirements. CRA evaluates all three during early design.

Open elevated flares are designed to meet API 537 (flare design), API 521 (relief and depressuring systems), and EPA 40 CFR 60.18 (control device requirements). International projects add EU IED, ATEX (where applicable), and local environmental standards.

Key compliance items:

• Tip exit velocity within smokeless and stable-flame limits
• Net heating value of combustion zone gas above regulatory minimum
• Continuous pilot monitoring with redundant ignition
• Radiation calculations confirming personnel-safe ground levels
• Structural design per ASME and applicable wind/seismic codes

Manufacturing follows ISO 9001 and CE; API certification is included where required by project specs.

In LNG and petrochemical service, open elevated flares handle large emergency relief volumes from compressors, storage tanks, and process units, while also covering routine purge and vent flows. The combination of wide turndown and large peak capacity makes them the standard relief device for these industries.

Typical service:

• LNG storage tank and ship-loading vapour relief
• Compressor and turbine blowdown during start-up, shutdown, or trip
• Process unit relief from reactors, distillation columns, separators
• Pipeline and pig-launcher depressuring
• Routine purge gas to prevent air ingress in the flare header

Materials and tip design are selected for the specific gas mix; sour or acid service requires upgraded metallurgy and corrosion-resistant tip components.

An elevated flare structure (stack and supports) typically lasts 25+ years with proper maintenance, while wear components like the flare tip, pilot system, and ignition components have shorter service lives and are designed to be replaced.

Component service life:

• Stack and structural supports — 25+ years; carbon steel with periodic recoating
• Flare tip — 10–15+ years depending on service severity (sour, acid, high-temperature streams shorten life)
• Pilot burners and ignition — 5–10 years; replaceable items
• Steam or air injection components — 10–15 years
• Purge reduction seals — 10+ years; refurbishable

Long-term service agreements and scheduled inspections extend overall system life and prevent unplanned failures.