Flare management systems are an essential part of the physical infrastructure of an oil refinery. A flare in a refinery system is used to burn off the excess hydrocarbons and gases that are generated during the refining process.
Why Flare Systems are Important
Flares allow for safe and effective disposal of gases and liquids. They act as relief devices when a production plant faces an emergency situation and there is a need to quickly dispose of the excess product to avoid a possible catastrophic situation (e.g., an explosion).
Despite the best efforts of refinery engineers, it is impossible to run the unit without upsets or emergencies. For example, when critical equipment fails in the refinery or when there is a power outage, excess hydrocarbons become entrained in the system and should be fired through the flare. The flare acts as a safety system to burn the excess gases that cannot be recovered or recycled.
During flaring, excess gases are combined with steam and/or air and burned off in the flare system to produce water vapor and carbon dioxide. The process of burning these excess gases is similar to the burning of liquefied petroleum gas (LPG), which is used as a fuel for home cooking.
Types of Flare Systems
Open or elevated flare systems are widely used in the petroleum industry and in chemical plants. These systems have the capacity to handle larger loads.
An elevated refinery flare system has a flare header that collects the waste gas and entrained condensates from the plant. The condensates are unsuitable for flaring and therefore they need to be removed using a condensate knock out drum (KOD). The gases are then sent to a vertical flare stack to be burned. The height of the stack can range from 20 to 200 meters (65 to 650 feet) above ground. Any backflow of gases from the stack to the knock out drum is prevented by a water seal at the gas inlet. The elevated flare tip plays a key role in ensuring a safe and adequate dispersion of toxic or smelly gases resulting from combustion. The gases are burned in the elevated flare tip located at the top of the gas flare stack. Some challenges related to the open flare system are noise pollution and environmental issues due to carbon dioxide being dispersed. There are difficulties with open flares because some refineries have equipment sensitive to air pollution.
Another type of flaring are enclosed or ground flare systems. In typical ground flare systems, the combustion of waste gases occurs close to the ground level. The key feature of this system is that it is enclosed in a refractory lined enclosure that contains the radiation and gases from the flame. Due to the enclosure around the flame, ground flares have fewer problems relating to noise pollution and heat radiation. However, unlike the elevated flare system, gases are also released quite close to the ground and therefore ground flares can have problems if the combustion products are toxic or in the event of a flameout.
The ground flare system is primarily used where clean burning is required and noise pollution is a critical factor for consideration. But they have a limited capacity compared to elevated systems. In general, refineries use a combination in their refining processes.
Flare designs are grouped into three categories: single point flaring, multi-point flaring and enclosed flaring.
A single point flaring system is similar to the open or elevated flare system discussed above and has an upward orientation. These flare designs are generally used in onshore refining processing facilities.
The multi-point flaring system is also a variant of the open flare system, and is primarily aimed at improving the burning of the gases. The gases are routed to several burning points so that smokeless burning is achieved. These flare systems are also used in offshore exploration installations.
Enclosed flaring is similar to the ground flare system discussed above.
The type of flare determines the flare design. (Learn more about refinery design in the article Refinery Configurations: Changing Dynamics.) The major components of a flare system include a flare burner, support structure, piping and ancillary equipment. The flare pilots include pilots, pilot igniters and pilot flame detectors.
Flare design is a specialized area, and information such as what sort of gases are to be flared, their characteristics, flow rates and temperatures should be considered in the flare design process. Other important considerations in flare design include environmental and safety factors, governing regulatory provisions and local laws relating to hydrocarbon dispersal.
Flares are a Sign of Efficiency in Plant Operations
For a casual observer, a flare on the refinery premises is an uncomfortable signpost. One may mistake the flare as a fire in the refinery.
However, flares provide crucial operating information to a chemical or process engineer. For example, it is common to witness a white cloud-like formation around the flare due to excess steam injected into the combustion process. Steam is added in some instances to increase the turbulence of the flowing gas to be burned through the flare, which helps to increase the air intake and and result in clean-burning, smokeless flaring. A flare full of smoke indicates a severe plant upset or a dip in the power supply, which can lead to a temporary plant down situation. On the other hand a smokeless flare shows a steady plant with optimum efficiency. Sometimes flaring may produce a rumbling noise that may sound like thunder because of the turbulent mixing of gases, air and steam.
Flare management is an integral part of a refinery or upstream plant operation system. An experienced flare designer can design an appropriate flare system that depends on the refinery or process requirements. A holistic approach is needed to ensure the safe, secure firing of unproductive gases and hydrocarbons without causing undue harm to the environment or community at large.