Compliance

Flare Systems: When Gas Goes to the Flame Instead of the Line

Flaring is what happens when gas has nowhere else to go. A well or a tank battery makes gas with the oil, and most of the time that gas goes into a sales line and earns money. Sometimes it cannot. When capture is not possible, the gas goes up a flare stack and burns. Flaring is safer than venting raw gas, because burning turns most of the gas into carbon dioxide and water instead of letting methane and other compounds straight into the air. It is also a visible sign that something is off, so operators treat it as a last resort, not a routine choice.

Why gas goes to the flare

Gas gets flared when there is no line to take it. A new well may come in before the gathering line is built, a pipeline may be full, or the sales line may be down for repairs. In those cases the well keeps producing and the gas has to go somewhere, so it goes to the flare.

Upsets also send gas to the flare. A compressor trips, a valve sticks, or pressure builds faster than the equipment can handle. Flaring protects the system by giving the gas a safe way out instead of letting pressure find a weak spot. Well tests send gas to the flare too. When a well is flowed for a test, the gas is often flared while the rate and the fluids are measured, especially when no test separator is tied to a line.

Maintenance is another common reason. When a separator or treater is opened for service, the vessel has to be blown down and the gas in it goes to the flare. Tank vapors are sometimes flared as well, though a vapor recovery unit is usually the better answer when there is enough gas to make capture worthwhile.

What a flare system is made of

A flare system is built around a few simple parts. Gas first goes through a knockout drum, a vessel that lets liquid drop out of the gas stream before the gas reaches the stack. Liquid in a flare is trouble. It can make the flame smoky, damage the tip, or turn the flare into a hazard, so the drum is sized to settle out as much liquid as it can.

From the drum, the gas goes up the flare stack to the tip, where it burns. The tip is designed to mix the gas with air so the flame burns clean. Around the tip sit the pilots, small flames meant to stay lit all the time. The pilots are what ignite the main gas the moment it arrives, so there is no wait and no unburned gas puffing out. Ignition systems back up the pilots. Some use a remote igniter that sends a spark or a flame to the tip from the ground, which matters when the stack is tall and nobody can reach the top by hand.

The federal rule for flares

The main federal rule for flares in oil and gas is 40 CFR 60.18. It sets the conditions for running a flare smokeless and for keeping the pilots burning. The rule is general on purpose, so the details that matter are the conditions written into the permit or the state plan that adopts it.

The core of the rule is that a flare has to burn the gas that is sent to it, with a pilot flame present whenever gas might flow. Flares that cannot meet the conditions have to be shut down and the gas routed somewhere else. The point of the rule is to keep flaring from becoming an uncontrolled vent, because an unlit flare is no better than a pipe open to the sky.

How pilots are watched and relit

Pilots go out. Wind, rain, a slug of liquid, or a mechanical failure can kill a pilot flame, and if nobody notices, gas can flow to an unlit tip and vent unburned. So operators watch the pilots.

The simplest watch is a person looking at the flame on rounds, but most sites use a pilot sensor or a thermocouple at the tip that reports whether the flame is there. A flame detector or a check of the pilot gas line pressure and temperature can also show the pilot is lit. Some systems relight automatically when the sensor sees the flame is out. Others raise an alarm and a field hand goes out to relight it, often with a handheld igniter.

No matter how the pilot is watched, the check is the same. The pilot has to be confirmed lit before gas can be routed to the flare, and an out pilot has to be reported and fixed.

Monitoring and records

Operators are expected to know when their flares are burning and how much gas went to them. The expectations come from the same 40 CFR 60.18 rule and from the state or federal permit that covers the site. What counts is a record that shows the flare was operated the way it was supposed to be.

Most sites keep a flare log. The log notes when gas went to the flare, why, how long the flare ran, and whether the pilot stayed lit. Meters or gauges may back the log up with flow totals, and alarm records show when the pilot dropped out and when it was relit. The records have to survive an inspection, so they are kept on paper or in a system that cannot be quietly edited.

Flare events get logged in the same field system as OpsFlo, so the ticket, the reason, and the fix all sit in one place. That makes the inspection story easy to tell: here is what flared, here is why, and here is what was done about it.

Sources and further reading

• eCFR: 40 CFR 60.18
• API Standard 521
• EPA: Oil and Natural Gas Air Pollution Standards