Flare Management system is an essential part of the physical infrastructure of an oil refinery. A flare in a refinery system is used to burn excess hydrocarbons and gases generated during the refinery process. 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 in order to avoid a possible catastrophic situation like an explosion.
Refinery operation engineers strive hard to maintain steady condition of the production plant, though 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 get entrained in the system and they should be fired through the flare. The flare acts as a safety system to burn the excess gases which cannot be recovered or recycled.
During flaring, excess gases are combined with steam and/or air and burnt 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 gases (LPG), which is used as fuel for home cooking.
Different types of flare systems
Open or elevated flare systems are widely used in the petroleum industry and in chemical plants. These systems have bigger capacities to handle higher loads. An elevated refinery flare system consists of flare header collecting the waste gas and entrained condensates from the plant. The condensates are not suitable for flaring and hence they need to be removed using a condensate knock out drum (KOD). The gases are then sent to a vertical flare stack to be burnt. The height of the stack can range from 20 to 200 meters above ground. Any backflow of gases from the stack to the knock out drum is prevented by the use of a water seal at the gas inlet. The elevation plays a key role in ensuring adequate and safe dispersion of toxic or smelly gases resulting from combustion through the flare tip. The gases are burnt in the elevated flare tip located at the top of the gas flare stack. There some challenges related to the open flare system such as noise pollution and environmental issues due to carbon dioxide dispersion when the gases are being burned. Since it is an open flare, in some refinery areas, there are difficulties in the installation of equipment sensitive to pollution.
Another type of flaring is known as enclosed or ground flare system. In typical ground flare systems the combustion of waste gases takes place close to the ground level. The key feature of this system is that it is close to the ground and enclosed in a refractory lined enclosure to contain the radiation and gases originating from the flame. Due to the enclosure around the flame, ground flare has lower or no problems relating to noise pollution and heat radiation. However, unlike the elevated flare system, gases are also released quite close to the ground and hence ground flare can have problems in case the combustion products are toxic in nature or in the event of a flame-out. The ground flare system is primarily used where clean burning is required and noise pollution is a critical factor for consideration. But they have limited capacity compared to elevated system. In general, refineries use combination of both these systems in their refining processes.
Flare designs are grouped into three categories, i.e., single point flaring, multi-point flaring and enclosed flaring. A single point flaring system is similar to an open or elevated flare system discussed above and has an upward orientation. Flare designs are generally used in onshore refining processing facilities. The multi-point flaring is also a variance of open flare system which is primarily aimed at improved burning of the gases. The gases are routed to many burning points so that smokeless burning is achieved. These flare systems are also used in offshore exploration installations. The enclosed flaring is similar to the ground flare system discussed above.
The type of flare decides the flare design and 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 specialist area and lots of information such as what sort of gases would be flared, their characteristics, flow rate, temperatures, etc., 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 hydrocarbons dispersion.
Flare is a signpost of efficiency in plant operations
For a normal human being, a flare in refinery premises is an uncomfortable signpost. One may mistake the flare as fire in the refinery. However, flares provide crucial operating information to a chemical or process engineer in a refinery. For example, it is not unusual to witness a white cloud-like formation around the flare. This is because of excess steam injected in the combustion process. Steam is added in some instances to increase the turbulence in the gas flow which would be burnt through the flare. This helps to increase the air intake and aid in complete clean burning of gases and result in smokeless flaring. A flare full of smoke indicates a severe plant upset or a dip in power supply, and this 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 which may sound like thunder because of the turbulent mixing of gases, air and steam.
Flare management is an integral part of the refinery or upstream plant operations systems. An experienced flare designer is required to design the flare system depending on the refinery or process requirements. A holistic approach is needed while deciding the flare management system from conceptual design to equipment required for flare installation strictly complying with the statutory regulations. It is an important function to ensure safe, secure firing of unproductive gases and hydrocarbons without causing any harm to the environment and community at large.