Gas Flare - Overall Flare System in Industrial Plants

Overall Flare System in Industrial Plants

Whenever industrial plant equipment items are over-pressured, the pressure relief valves provided as essential safety devices on the equipment automatically release gases and sometimes liquids as well. Those pressure relief valves are required by industrial design codes and standards as well as by law.

The released gases and liquids are routed through large piping systems called flare headers to a vertical elevated flare. The released gases are burned as they exit the flare stacks. The size and brightness of the resulting flame depends upon the flammable material's flow rate in terms of joules per hour (or btu per hour).

Most industrial plant flares have a vapor-liquid separator (also known as a knockout drum) upstream of the flare to remove any large amounts of liquid that may accompany the relieved gases.

Steam is very often injected into the flame to reduce the formation of black smoke. In order to keep the flare system functional, a small amount of gas is continuously burned, like a pilot light, so that the system is always ready for its primary purpose as an over-pressure safety system.

The adjacent flow diagram depicts the typical components of an overall industrial flare stack system:

• A knockout drum to remove any oil and/or water from the relieved gases.
• A water seal drum to prevent any flashback of the flame from the top of the flare stack.
• As alternative gas recovery system for use during partial plant startups and/or shutdowns as well as other times when required. The recovered gas is routed into the fuel gas system of the overall industrial plant.
• A steam injection system to provide an external momentum force used for efficient mixing of air with the relieved gas, which promotes smokeless burning.
• A pilot flame (with its ignition system) that burns all the time so that it is available to ignite relieved gases whenever needed.
• The flare stack, including a flashback prevention section at the upper part of the flare stack.