A gas flare, alternatively known as a flare stack, is an elevated vertical conveyance found accompanying the presence of oil wells, gas wells, rigs, refineries, chemical plants, natural gas plants, and landfills.
They are used to eliminate waste gas which is otherwise not feasible to use or transport. They also act as safety systems for non-waste gas and is released via pressure relief valve when needed to ease the strain on equipment. They protect gas processing equipment from being overpressured. Also in case of an emergency situation, the flare system helps burn out the total reserve gas.
However, flaring poses the serious problem of wasting energy uselessly. Flaring basically consists in burning precious resources instead of using them. It also plays a role in the increase of CO2 emissions.
On oil production rigs, in refineries and chemical plants, its primary purpose is to act as a safety device to protect vessels or pipes from over-pressuring due to unplanned upsets. Pressure control valves are set at predetermined pressures to release excess gas, thus allowing continued operation during upset conditions. Whenever plant equipment items are over-pressured, the pressure relief valves on the equipment automatically release gases (and sometimes liquids as well) which are routed through piping runs called flare headers to the flare stacks.
The gases and/or liquids are separated in a flare knock out drum with the gas piped to the flare stacks for burning or for lighter gases venting. The size and brightness of the resulting flame depends upon how much flammable material was released. Typically there may be more than one flare system handling high pressure gas, low pressure gas, sour or corrosive gas, cold gas and wet gas. Vents (unignited flares) are used typically on gas plants for emergency gas disposal and are designed to operate in an emergency at sonic velocity.
Flare gas recovery systems are occasionally used to collect low flows of waste gas and return it to the Process Plant as opposed to burning the gas. Steam can be injected into the flame to reduce the formation of black smoke. The injected steam does however make the burning of gas sound louder, which can cause complaints from nearby residents. Compared to the emission of black smoke, it can be seen as a valid trade off. In order to keep the flare system functional, a small amount of purge gas flows continuously, whilst there are continuously burning pilots, so that the system is always ready for its primary purpose of burning as an over-pressure safety system. Enclosed ground flares are engineered to eliminate toxic and corrosive components, reduce smoke, and contain the flame within the enclosure. Burn pits are used to dispose of waste hydrocarbon liquids and are increasingly being designed out due to their unacceptable dirty appearance.