Typical flare system in industrial plants

 Diagrammatic representations of a typical vertical, elevated flare stack system in an industrial plant.

During operations, when industrial plant equipment items are over-pressured, the pressure relief valve is an essential safety tool that automatically releases gases and sometimes liquids. Those pressure relief valves are essential by industrial design codes and standards as well as by law.

The released gases and liquids are directed through large piping systems known as flare headers to a vertical elevated flare. The escaped gases are burned as they exit the flare stacks. The size and brightness of the resulting flame is determined by the flammable material's flow rate in joules per hour (or btu per hour).

Majority of industrial plant flares have a vapour-liquid separator(also called a knockout drum) upstream of the flare to remove any large amounts of liquid that may go along with the relieved gases.

Steam is frequently injected into the flame to reduce the formation of black smoke. When steam added is too much, a condition known as "over steaming" can take place resulting in reduced combustion efficiency and higher emissions. And to ensure 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 typical components of an overall industrial flare stack system include:

(i)                 A knockout drum to eliminate any oil or water from the relieved gases.

(ii)               A water seal drum to avoid any flashback of the flame from the top of the     flare stack.

(iii)             An alternative gas recovery system for use during partial plant startups and       shutdowns as well as any time when necessary. The recovered gas is directed into the fuel gas system of the overall industrial plant.

(iv)             A steam injection system to provide an external momentum force used for efficient mixing of air with the relieved gas, which aids smokeless burning.

(v)               A pilot flame (with its ignition system) that burns always  so that it is available to ignite relieved gases when required.