Utility Flare

A utility flare is the right choice when the waste gas burns smokelessly on its own, or when smokeless operation is not a regulatory or community requirement at the site. It has no steam or air assist, which makes it the simplest and lowest-cost flare configuration with the fewest moving parts. It suits light hydrocarbon and hydrogen-rich streams, industrial sites with no smoke visibility constraints, sites without steam or blower infrastructure and intermittent emergency relief duty. For heavy hydrocarbon streams or sites with smoke limits, CRA offers air-assisted and steam-assisted flares instead.

Gas streams that burn smokelessly without assist are typically light hydrocarbons such as methane and ethane, hydrogen-rich streams and gases with a low carbon-to-hydrogen ratio, because there is too little heavy carbon to form soot before combustion completes. Common examples are natural gas, hydrogen and syngas purges, refinery off-gas with a high hydrogen content, biogas with sufficient methane and low siloxanes, and landfill gas with methane above 30%. Streams containing C3 and heavier hydrocarbons, aromatics or olefins generally need air or steam assist. CRA reviews the gas composition to confirm whether a stream suits unassisted flaring.

Utility flares are available as self-supported, guyed or derrick-supported structures, selected on stack height, ground footprint and the wind and seismic loading at the site. A self-supported stack is preferred for shorter heights, typically up to 30 metres, and has the smallest footprint. A guyed stack uses tensioned guy wires anchored to the ground and is a cost-effective option for tall stacks of 60 metres and more where space for the anchors is available. A derrick-supported flare uses an external lattice structure and suits very tall flares on constrained sites or in high-wind or seismic zones. CRA designs the structure to ASME and the applicable wind and seismic codes.

A utility flare relies entirely on the gas stream's own properties for clean combustion, while an assisted flare adds steam, air or pressure energy so that streams that would otherwise smoke burn smokelessly. An air-assisted flare uses a blower and is preferred where steam is unavailable. A steam-assisted flare uses high-pressure steam and gives the highest smokeless capacity, which makes it the standard choice at refineries. A high-pressure sonic flare uses the gas pressure itself. Capital cost, operating cost and complexity all rise as the design moves from utility to assisted. CRA supplies all these configurations.

Utility flares are designed to API 537 for flare design, API 521 for pressure relief systems and EPA 40 CFR 60.18 for control device requirements, the same standards that apply to assisted flares. The design checks cover tip exit velocity within stable-flame limits, combustion zone net heating value above the regulatory minimum, continuous pilot monitoring with assured ignition, radiation calculations to API 521 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 flare designs are aligned with API and CE practice.