Selection of the flare structure depends on the distance between the flare and the production platform, which in turn depends on the relief gas quantity, heating value, toxicity, and whether the flaring is intermittent or continuous. The main kinds of support structures are:
• Flare booms, which extend from the edge of the platform at an angle of 15 to 45 degrees. They are usually 100 to 200 feet long. Sometimes two booms oriented 180 degrees from each other are used to take advantage of prevailing winds. See Figure 1200-31.
• Derrick-supported flares, which are located on a derrick above the production platform. They are used when space is limited and relief quantities are moderate. The disadvantages are: a possible crude oil spill onto the platform, interference with helicopter landing, and higher radiation intensities. See Figure 1200-32.
• Bridge-supported flares, which are on a separate platform connected to the main platform by a bridge as much as 600 feet long. Bridge supports are usually spaced about every 350 feet. See Figure 1200-33.
• Remote flares are on a separate platform connected to the main platform by a subsea relief line. The main disadvantage to these flares is that any liquid carryover or subsea condensation will collect in pockets in the connecting line, so that the line acts like a liquid trap. See Figure 1200-34.
• Ground flares, which are often used on tanker based production platforms to reduce noise and to reduce the radiation levels on deck.
• Floating flares, which are supported on a barge. These are mainly used in emergency or short-term situations.