Industrial Flare Performance at Low Flow Conditions. 2. Steam- and Air-Assisted Flares

Full-scale tests of steam- and air-assisted industrial flares were conducted using low BTU content (lower heating value) vent gases at low flow rates. A 36″ diameter steam-assisted flare with a flow capacity of 937,000 lb/h and a 24″ diameter air-assisted flare with a flow capacity of 144,000 pounds per hour were operated with mixtures of natural gas, propylene, and nitrogen or natural gas, propane, and nitrogen at flow rates less than 1% of maximum flow. Combustion efficiency (percentage of the flared gases converted to carbon dioxide and water) ranged from less than 50% to more than 99%. For the steam-assisted flare, combustion efficiency (CE) at low steam-to-vent gas flow ratios (0.5–1.0) was typically in excess of 95%. CE would gradually decrease as steam-to-vent gas ratio increased, to a point, after which CE would decrease dramatically. The steam-to-vent gas ratio at which CE would decrease dramatically depended on the heating value of the vent gas and the position of the steam injection. Higher hea...