Gas Flare System Product

Overview

A flare is the last line of defense of a process plant. Every relief valve, blowdown valve and emergency depressurization line in a refinery or gas plant discharges into a common collection system that ends at an elevated burner. When a vessel overpressures or a unit must be emptied in a hurry, the gas has somewhere safe to go: up the Riser & Stack Structure and into a flame anchored at the Flare Tip, where it burns at high destruction efficiency instead of forming a vapor cloud at grade. The flare must accept anything from a few kilograms per hour of purge to hundreds of tonnes per hour during a total plant depressurization, and it must be ready without warning, around the clock, for decades.

Gas path

Relief discharges enter the Flare Header, a large sloped main fed by Subheader Lateral from each process unit. The header runs continuously downhill (at least 1:500) to the Knockout Drum so liquids can never pocket; Expansion Loop absorb the contraction when auto-refrigerating blowdowns chill the pipe far below ambient.

The knockout drum exists because a flare can burn gas but not rain fire. Liquid slugs and droplets bigger than a few hundred micrometers would pass through the flame partially burnt and fall to grade as burning droplets. The horizontal KO Drum Shell is sized per API 521 so vapor velocity is low enough for droplets above 300–600 µm to settle; an Inlet Diverter breaks slug momentum, Level Instrumentation trip on high-high level, and Pumpout Pump units return condensate to slops. From the drum the gas climbs the Riser Pipe to the tip.

Keeping air out

A stack open to atmosphere is a chimney in reverse: hot days, wind and gas buoyancy all pull air down into it, and air mixed with hydrocarbon inside the stack is an internal explosion waiting for the next ignition. Two measures prevent this. The Purge Gas System sweeps a continuous trickle of fuel gas or nitrogen up the stack — 0.03–0.06 m/s is enough — metered at the Purge Control Skid. And just below the tip sits the Molecular Seal, an annular trap whose internal Seal Baffle forces the gas through a 180° reversal. A buoyant layer of light gas held in the inverted trap blocks heavier air from diffusing past it, which lets the purge rate be cut by an order of magnitude. A small Seal Drain Line weeps rainwater out of the trap.

Pilots and ignition

Three Pilot Burner units ring the tip, each shielded to stay lit in 160 km/h wind and proven by its own Pilot Thermocouple. If a pilot drops out, the operator fires the Flame-Front Generator Panel: the panel charges a 25 mm Ignition Line with a stoichiometric air-gas mix and sparks it, and the flame front travels up the tube — sometimes 150 m or more — to relight the pilot at the tip. Ground-mounted IR Flame Scanner units provide non-contact backup flame proving, since thermocouples eventually burn out in service.

Smokeless operation and the tip

Heavy hydrocarbons burn sooty in a simple diffusion flame. The Steam Injection Ring injects steam at up to 0.4 kg per kg of gas, which entrains air into the flame core and shifts combustion toward premixed, eliminating visible smoke for routine flaring rates (typically the first 15–20% of capacity). The Flame Retention Ring keeps the flame attached at exit velocities approaching Mach 0.5, and the Wind Fence stops crosswind from folding the flame down over the Tip Barrel — flame lick is the main tip killer, which is why the barrel is 310 stainless or Incoloy and still has a 5–10 year replacement life.

Stack and siting

Stack height is set by thermal radiation, not dispersion: API 521 limits radiation to 4.73 kW/m² where personnel may be briefly exposed and lower levels at the fence line, and for a 600 t/h flame that pushes the tip to 60–120 m. The structure is built from flanged Stack Section held by three levels of Guy Wire Set, with Aircraft Warning Light beacons and a caged Access Ladder & Platforms for shutdown maintenance. Flared quantities are measured by the Ultrasonic Flare Meter, whose 1:2000 turndown spans purge flow to full relief, feeding the Monitoring Cabinet for emissions reporting under 40 CFR 60.18 and local equivalents.