Open Elevated Flare

An open elevated flare is the right choice for high-volume relief and emergency service where the gas flow can far exceed normal venting rates and elevation is needed to disperse heat and combustion products safely away from personnel and equipment. It is the standard relief device for refinery and petrochemical flare headers. It fits best when peak relief flows are very high, when heat dispersion at height is needed for personnel safety, when the plant footprint cannot accommodate an enclosed ground flare at peak flow, and when flame visibility is acceptable at the site. For sites near residential areas or where flame visibility is unacceptable, CRA offers enclosed ground flares.

An elevated flare burns the gas at a height above the surrounding plant so that thermal radiation and hot combustion products dissipate before they reach areas where personnel work. The stack height is calculated for the worst-case relief flow and ambient wind so that ground-level radiation stays within the API 521 limits, typically 1.58 kW/m² for areas where personnel may be present. An exclusion zone is defined around the base, the tip design controls flame length, lift-off and direction, and an optional windshield or shroud improves flame stability at windy sites. CRA carries out radiation and dispersion assessment to confirm the safety distances under worst-case conditions.

The three configurations differ in how smokeless combustion is achieved on heavy or fuel-rich streams. An unassisted (utility) flare is the simplest and lowest-cost design and is used where the gas burns smokelessly on its own, such as light hydrocarbons and hydrogen-rich gas, or where smoke is not a regulatory concern. An air-assisted flare uses a blower to inject combustion air and suits sites without steam or moderate flows. A steam-assisted flare uses high-pressure steam and gives the highest smokeless capacity, which makes it standard in refineries and petrochemical plants where steam is available. CRA manufactures all three and selects on gas composition, peak flow, utilities and emissions requirements.

Open elevated flares are designed to API 537 for flare design, API 521 for relief and depressuring systems and EPA 40 CFR 60.18 for control device requirements. International projects add the EU IED, ATEX where it applies, and local environmental standards. Design checks cover tip exit velocity within smokeless and stable-flame limits, net heating value of the combustion zone gas above the regulatory minimum, continuous pilot monitoring with redundant ignition, radiation calculations for safe ground-level exposure, and structural design to ASME and the applicable wind and seismic codes. CRA is ISO 9001 certified through TÜV NORD, and its designs are aligned with API and CE practice.

In LNG and petrochemical plants, open elevated flares handle large emergency relief volumes from compressors, storage tanks and process units, and also take routine purge and vent flows. Wide turndown and large peak capacity make them the standard relief device in these industries. Typical duty includes LNG storage tank and ship-loading vapour relief, compressor and turbine blowdown during start-up, shutdown or trip, process unit relief from reactors, columns and separators, pipeline and pig launcher depressuring, and routine purge gas that keeps air out of the flare header. CRA selects materials and tip design for the specific gas mix, with upgraded metallurgy for sour or acid service.