Drive past an oilfield at night and you may see a flame burning at the top of a tall stack.
To someone outside the industry, it can look incredibly wasteful.
Natural gas is valuable.
Why would an oil company deliberately set it on fire?
That question comes up regularly among people trying to understand oil and gas operations, and the answer is more complicated than simply saying the company has too much gas.
A flare is first and foremost a safety system.
It gives an oil and gas facility somewhere to safely send combustible gases when those gases cannot remain inside the process equipment.
Sometimes that happens during an emergency.
Sometimes it happens during startup or shutdown.
Sometimes gas cannot temporarily be processed or exported.
And in some producing regions, gas has historically been routinely flared because there was no economic way to get it to market.
Those situations may all produce the same visible flame, but the reasons behind it are very different.
What Is a Flare?
A flare is a controlled combustion system used to dispose of combustible gases.
Instead of releasing hydrocarbons directly into the atmosphere, the gas is routed to a designated location and burned.
A typical elevated flare is positioned away from normal working areas and releases the combustion products high above the facility.
The flame you see is only the final part of a much larger system.
A flare system can include:
A flare header
Relief piping
A knockout drum
Liquid seals or gas seals
Purge gas
The flare stack
Flare tip
Pilot burners
Ignition equipment
Instrumentation and controls
Some facilities have multiple flare systems serving different pressure levels or process areas.
Why Does a Refinery Need a Flare?
Imagine a refinery processing thousands of barrels of hydrocarbons every hour.
The equipment contains flammable fluids under pressure.
Now imagine something goes wrong.
A compressor suddenly stops.
Cooling water is lost.
A control valve fails.
A process vessel begins experiencing excessive pressure.
The hydrocarbons inside the equipment cannot simply be allowed to continue increasing pressure indefinitely.
Pressure relief valves provide a controlled escape path.
But releasing large quantities of hydrocarbons directly beside operating equipment would create another hazard.
Instead, relief systems can route suitable gases into the flare header.
The flare provides a controlled location where combustible material can be burned.
That is one of its most important jobs.
A Flare Is Not a Gas Storage Tank
This is a surprisingly common misconception.
A facility does not normally send gas into the flare stack and store it there until someone decides to burn it.
The flare system is a disposal route.
Gas enters the flare header and travels toward the flare.
The system has to remain available because an emergency release may occur with little warning.
That is why flare headers are treated differently from ordinary process piping.
Blocking the path to a required flare could prevent pressure relief equipment from doing its job.
What Is a Flare Header?
A flare header is the piping system that collects gases from different parts of a facility and carries them toward the flare.
Think of it as a drainage system for gas.
Instead of water flowing downhill into a sewer, relief gases from different equipment items enter a common piping network.
That network eventually leads toward the flare system.
The header has to be designed for potentially large flows because several relief devices may discharge during a major plant upset.
Pressure drop matters too.
A relief valve cannot protect equipment properly if excessive backpressure develops in the system it is discharging into.
What Is a Relief Valve?
A pressure relief valve is designed to protect pressurized equipment from excessive pressure.
Suppose a vessel has a maximum allowable working pressure.
Under normal conditions, controls keep the vessel safely below that limit.
But controls can fail.
A downstream valve might accidentally close.
A fire could heat the vessel.
A process reaction could generate unexpected pressure.
A compressor or pump could create abnormal conditions.
If pressure reaches the relief valve’s set point, the valve opens and provides another path for fluid to leave.
In many hydrocarbon services, that path ultimately leads to a flare system.
The relief valve protects the individual equipment.
The flare system safely handles the released material.
Why Not Just Vent the Gas?
Burning hydrocarbons produces emissions, so it is reasonable to ask why the gas cannot simply be released without burning.
One reason is safety.
A large release of unburned combustible gas can create a flammable cloud.
If that cloud reaches an ignition source, the consequences can be severe.
Flaring converts combustible gases through controlled combustion at a location specifically designed for it.
There is also an environmental reason.
Methane itself is a potent greenhouse gas.
Burning methane converts much of it into carbon dioxide and water.
Carbon dioxide is also a greenhouse gas, but releasing methane directly can have a much greater warming effect per unit of mass over relevant time periods.
This does not make flaring environmentally harmless.
It explains why flaring can be preferable to directly venting combustible gas when recovery is not practical and a release is necessary.
Why Is the Flare Always Burning?
Sometimes what appears to be continuous flaring is actually the pilot flame.
The flare needs a reliable ignition source.
If a large quantity of hydrocarbon gas suddenly enters the flare system, you do not want it leaving the stack unburned while someone tries to find a way to ignite it.
Pilot burners therefore maintain an ignition source at the flare tip.
The pilot flame is much smaller than the large flame produced during significant flaring.
From a distance, however, even a relatively small flame can be very visible at night.
What Is Purge Gas?
There is another problem flare designers need to prevent.
Air entering the flare system.
If oxygen travels backward into piping containing combustible gas, a flammable mixture can develop inside the system itself.
That is obviously undesirable.
A small continuous flow of purge gas can be used to help prevent air from entering the flare stack.
Depending on the system, natural gas, fuel gas, nitrogen, or another suitable gas may be used.
Specialized seals can also help reduce the amount of purge gas required.
What Is a Flare Knockout Drum?
Before gas reaches the flare stack, it commonly passes through a vessel called a flare knockout drum.
Its purpose is extremely important.
The flare is primarily intended to handle gas.
But relief streams can contain liquid droplets.
Hydrocarbon vapor can also cool and condense while travelling through the flare header.
The knockout drum gives those liquids somewhere to separate from the gas before the gas continues toward the flare.
Liquid collects in the vessel and can then be handled through the facility’s appropriate liquid recovery or disposal system.
Why Is Liquid in the Flare Dangerous?
Imagine sending a large slug of liquid hydrocarbons all the way to the top of a flare stack.
The liquid may not burn cleanly like a gas.
Burning droplets could potentially fall from the flare.
Combustion can become unstable.
Smoke can increase.
The flare may not behave as intended.
This is why flare knockout drums and their liquid level controls are important.
Operators monitor these vessels carefully, particularly during significant process upsets when the flare system may receive unusually large quantities of material.
Why Does a Flare Sometimes Produce Black Smoke?
A clean burning natural gas flame may produce little visible smoke.
Heavier hydrocarbons are different.
When the flare receives hydrocarbon streams that do not mix sufficiently with air, incomplete combustion can produce soot.
That soot creates the black smoke people associate with some flare events.
The composition and flow rate of the flare gas matter.
A flare handling relatively light gases can look very different from one receiving heavier hydrocarbons during a process upset.
Why Is Steam Injected Into Some Flares?
Some refinery and petrochemical flare tips use steam to improve mixing between the flare gas and surrounding air.
Better mixing can improve combustion and reduce soot formation.
This is why you may see steam lines running all the way to the flare tip.
The objective is not to extinguish the flame.
The steam helps create turbulence and improves mixing.
Some flare designs use air assistance rather than steam.
The appropriate design depends on the facility and the gases being handled.
Why Does a Flare Suddenly Get Huge?
A facility that normally has only a small pilot flame can suddenly produce an enormous flare.
That usually means much more gas has entered the flare system.
One possible cause is a process upset.
Suppose a major compressor trips.
Gas that was supposed to continue through the process may temporarily have nowhere to go.
Pressure begins increasing.
Controls respond.
Relief or depressurization systems may send gas to the flare.
The visible flame can increase dramatically within a short period.
To someone driving past the facility, it may look alarming.
For the operators, however, the fact that the gas is reaching the flare and burning may mean an important safety system is functioning as designed.
The underlying process upset still needs attention.
What Is Emergency Depressurization?
Sometimes the safest response to an emergency is intentionally removing hydrocarbon inventory from process equipment.
Consider equipment exposed to a serious fire.
As the equipment heats, pressure can increase and the metal itself can lose strength.
A depressurization system can reduce the quantity and pressure of hydrocarbons inside affected equipment.
Those gases need a safe destination.
The flare system may provide it.
This can result in very large temporary flare loads.
The flare therefore has to be designed for more than normal operating conditions.
Engineers evaluate credible emergency scenarios when determining how much gas the flare system may need to handle.
Why Do Oil Wells Flare Gas?
The reason can be different from refinery flaring.
Crude oil often contains natural gas.
Some gas exists separately in the reservoir.
Additional gas can come out of solution as pressure decreases during production.
Once the fluids reach the surface, the gas is separated from the oil.
Now the operator has to do something with it.
Ideally, useful gas can be captured.
It may be processed and sold.
It may be used as fuel.
It may generate electricity.
It may be compressed and reinjected.
But all of those options require equipment and infrastructure.
Why Not Sell Every Cubic Foot of Gas?
Because producing gas and selling pipeline quality natural gas are not the same thing.
Gas coming from an oil well may contain water, heavier hydrocarbons, hydrogen sulfide, carbon dioxide, or other components.
It may need treatment.
It may need compression.
A gathering pipeline has to reach the location.
That pipeline needs available capacity.
A processing plant may be required downstream.
Now imagine a remote oil well producing a relatively small amount of associated gas.
Building kilometres of pipeline and installing compression for that one gas stream may cost more than the gas will ever be worth.
Historically, operators in some regions simply flared it.
That does not mean flaring is technically the only option.
It means infrastructure and economics influence what is practical.
What Is Associated Gas?
Associated gas is natural gas produced along with crude oil.
An oil producer may therefore produce two valuable hydrocarbons from the same well.
The difficulty is that oil and gas are transported differently.
Oil can often be stored in tanks and moved by truck if necessary.
Natural gas is much more difficult to handle that way.
Without a gathering pipeline, compression, processing, or another use at the location, gas can become stranded.
That is one reason rapid oil development can sometimes outpace gas infrastructure.
Pipeline Capacity Can Matter Too
Having a pipeline nearby does not necessarily mean every cubic foot of produced gas can enter it.
The gathering system has capacity limits.
Compressors have capacity limits.
Processing plants have capacity limits.
Gas also needs to meet specifications.
A facility can therefore be physically connected to gas infrastructure and still encounter situations where gas cannot be accepted.
This is one reason understanding actual flare behavior requires more information than simply looking at a map and noticing a pipeline nearby.
Why Not Shut the Oil Well Down Instead?
Sometimes operators do reduce or stop production when gas cannot be handled.
But the decision depends on regulations, contracts, well behavior, economics, duration of the problem, and available alternatives.
Shutting in an oil well means losing oil production too.
Restarting certain wells can also require additional work.
Modern regulations in many producing regions place restrictions on routine flaring, which changes the economics of producing oil without adequate gas handling infrastructure.
Flaring is increasingly treated as something to minimize rather than a normal destination for valuable gas.
Can Flare Gas Be Used to Generate Electricity?
Yes.
Associated gas can be used as fuel where its quantity and quality make that practical.
Oilfield facilities themselves require energy.
Electricity may be needed for pumps, compressors, instrumentation, buildings, artificial lift systems, and other equipment.
Gas engines or turbines can convert suitable produced gas into useful power.
The economic question is whether the volume, consistency, gas quality, equipment cost, and power demand justify the installation.
A gas stream that exists today but disappears as the well declines may not support an expensive long term project.
Can Flare Gas Be Reinjected Underground?
In some fields, yes.
Gas compression systems can inject gas into suitable wells or reservoirs.
Gas injection may be used for disposal, pressure maintenance, enhanced recovery, or other reservoir management objectives depending on the project.
Again, compression costs money.
High pressure injection can require substantial equipment and energy.
The reservoir must also be suitable.
There is no single gas disposal method that makes sense for every field.
Why Are Companies Trying to Reduce Routine Flaring?
The most obvious reason is that flaring wastes a potentially useful energy resource.
There are also emissions concerns.
Even when a flare burns properly, combustion produces carbon dioxide.
Real flares may also have incomplete combustion under some conditions, allowing a portion of hydrocarbons to remain unburned.
Reducing routine flaring can therefore lower emissions while potentially creating value from gas that would otherwise be destroyed.
Companies and regulators have consequently placed increasing emphasis on gas gathering, utilization, reinjection, improved flare measurement, and other methods of reducing unnecessary flaring.
Does Seeing a Flare Mean Something Has Gone Wrong?
Not necessarily.
A small stable flame may simply be the pilot.
A facility may also have legitimate operating reasons for temporary flaring.
Startup and shutdown can produce flare activity.
Maintenance can produce flare activity.
Equipment trips can produce flare activity.
Emergency depressurization can produce much larger flare activity.
The key question is not whether a flare ever burns.
It is why material is being sent there and how frequently that happens.
A facility that requires a flare for emergency protection may operate for long periods with almost nothing entering it.
Why Do Refineries Flare During Startup?
Starting a refinery unit is not like switching on a household appliance.
Temperatures, pressures, flows, and equipment have to be brought into operation in a controlled sequence.
Products may not initially meet specifications.
Compressors and other systems may not yet be available.
Temporary gas streams can therefore need a safe destination.
The flare can provide that destination while the process reaches stable operation.
Once normal conditions are established, flare flow should generally decrease.
Why Do Plants Flare During Shutdown?
Shutdown creates the opposite transition.
Equipment containing hydrocarbons has to be taken out of service.
Depending on the reason for the shutdown, some systems may need to be depressurized.
Hydrocarbon gases removed from the process may be routed to the flare.
A planned shutdown can therefore create visible flaring without necessarily indicating an uncontrolled emergency.
What Happens If the Flare Goes Out?
The flare needs reliable ignition.
Pilot systems are therefore monitored.
Multiple pilots may be installed to improve reliability.
Ignition systems allow pilots to be relit when necessary.
The precise design depends on the facility.
The important point is that sending a large hydrocarbon release through an unlit flare could allow combustible gas to enter the atmosphere rather than being burned.
Pilot reliability is consequently an important part of flare system design and operation.
Why Is the Flare So Tall?
Putting the flame high above the ground provides separation from personnel and equipment.
A large flare releases significant heat.
Combustion products also need to disperse safely.
Stack height, flare location, expected gas flow, radiation, surrounding equipment, and other factors are considered during design.
That spectacular flame hundreds of feet in the air is intentionally located far away from the people operating the plant.
Are All Flares Tall Stacks?
No.
Ground flare systems also exist.
Some use multiple burners located inside an enclosure.
The surrounding structure can reduce visible flame and help manage radiation.
Different designs are appropriate for different facilities.
An elevated flare is simply the version most people recognize because it can be seen from far away.
Why Does the Flame Sometimes Make Noise?
Large quantities of gas moving through a flare tip at high velocity can produce substantial noise.
Combustion itself adds to it.
Steam assisted flares can be particularly noticeable when large amounts of steam are being used.
During a major relief event, the sound can be significant.
Again, the flare is handling energy that would otherwise remain inside process equipment or be released somewhere less suitable.
What Do Operators Watch During Flaring?
A flare may be physically distant from the main process, but operators still need to understand what is happening in the system.
Depending on the facility, they may monitor conditions including flare header pressure, knockout drum level, pilot status, flare gas flow, purge conditions, and other instrumentation.
More importantly, they monitor the equipment sending material to the flare.
A rapidly increasing flare load is a symptom.
The real operational question is:
What is causing it?
Maybe a compressor has tripped.
Maybe a pressure controller is malfunctioning.
Maybe a relief valve has opened.
Maybe a unit is being intentionally depressurized.
Stopping the flame is not the immediate objective.
Correcting the condition that is sending unnecessary hydrocarbons to the flare is.
The Flare Is Something You Hope You Rarely Need
A large refinery flare can look dramatic, but its purpose is fairly straightforward.
Oil and gas facilities contain large quantities of combustible material.
Sometimes that material has to leave process equipment quickly.
When it does, engineers want a controlled path available.
The flare provides that path.
Under ideal normal operation, valuable hydrocarbons remain in the process and eventually become useful products.
When normal operation cannot be maintained, the priorities change.
Protect people.
Protect equipment.
Control pressure.
Keep hydrocarbons from accumulating in dangerous places.
Sometimes that means deliberately burning valuable gas.
Seen from that perspective, a flare is less like a waste burner and more like an emergency exit for a process plant.
Most of the time, you hope it does very little.
When something goes seriously wrong, you are very glad it is there.
Frequently Asked Questions
Why do oil companies burn natural gas instead of selling it?
Gas may be flared when gathering, compression, processing, or pipeline capacity is unavailable or uneconomic. Gas can also be flared temporarily during process upsets, maintenance, startup, shutdown, or emergency pressure relief.
Is flaring natural gas wasteful?
Routine flaring destroys gas that could potentially have value, so reducing unnecessary flaring is an important industry objective. Safety flaring is different because the flare provides a controlled destination for gases that need to be released from process equipment.
Is a flare always burning?
Many flare systems maintain small pilot flames so incoming gas can be ignited immediately. That does not mean large quantities of process gas are continuously being flared.
Why is there black smoke from a flare?
Black smoke generally indicates soot formation. Heavier hydrocarbon streams and insufficient mixing with combustion air can increase smoking. Some flare systems use steam or air assistance to improve mixing.
What does a flare knockout drum do?
It removes entrained or condensed liquids from the flare gas before the gas reaches the flare stack. This helps prevent liquid hydrocarbons from reaching the flare tip.
What is the difference between flaring and venting?
Flaring burns combustible gas in a controlled system. Venting releases gas without combustion. The safety and environmental consequences are therefore different.
Can natural gas from oil wells be used instead of flared?
Yes. Depending on the project, associated gas can be processed and sold, used as fuel, used to generate electricity, reinjected, or handled through other recovery systems. Whether those options are practical depends on gas volume, composition, infrastructure, regulations, and economics.
Does a large refinery flare mean the plant is on fire?
No. A large flare can result from startup, shutdown, equipment trips, depressurization, or other operating events. The flare itself is specifically designed to burn hydrocarbons at a controlled location away from the main process equipment.
Why are flare stacks so tall?
Height helps keep the flame and thermal radiation away from workers and process equipment while allowing combustion products to disperse.
Why can’t a refinery operate without a flare?
Some facilities use different relief and disposal arrangements, but large hydrocarbon processing facilities generally need reliable systems for safely handling gases released during pressure relief, depressurization, and abnormal operating conditions. A flare is one widely used way to provide that protection.