In a previous article, ‘Air Intake Flame Arrestors are Non-Negotiable’, we explored important industry regulations for the use of gas-fired equipment in the oil and gas industry – specifically, the rules surrounding the use of Enclosed Vapor Combustor (EVC) technology.
The key takeaway from the article is that because flashback from a combustor source can be dangerous – even lethal – for operators present on-site, all air intakes on combustors must be equipped with a flame arresting device to help ensure the safety of workers.
However, while the article provided a high-level overview of the potentially catastrophic consequences of improperly functioning flame arrestors, there is much more to delve into regarding the manufacturing and performance testing processes of these devices, which also affect operational safety on site.
Manufacturing & Applications
An Air Intake Flame Arrestor is an essential safety device for any gas-burning appliance on an oil and gas facility. This device stops a flame from entering an atmosphere where combustible gases may be present to prevent explosions, burns, or other hazards. These devices are typically constructed of crimped or corrugated aluminum ribbon that is rolled tightly into a cell. Depending on the application, however, additional screens, slotted plates, or meshes can be used to supplement the rolled cell.
Under normal operating conditions, the construction of the cell allows for combustion air to flow freely from the protected side of the system toward the unprotected side. This protected side is typically the exposed area on a facility where operators and wellsite workers may be present. The unprotected side of the system, in many cases, is the stable and continuous combustion source.
There are a wide variety of applications where a flame arrestor would be required – such as line heaters, reboilers, dehydrators, and enclosed vapor combustors. Each of these pieces of equipment requires an air intake flame arrestor in order to operate safely and consistently in the event of a flashback scenario.
What happens during a flashback?
A flashback occurs when combustible gases pass through the flame arrestor and are spontaneously ignited at the combustion source. The resulting explosion can create a knock-on effect where the flame front propagates back toward the flame arrestor to escape into the protected side of the system.
Once a flashback has occurred, the flame arrestor must perform two tasks:
- Slow the speed of the flame front.
The small openings, or channels, in the flame arrestor must allow for air to flow freely but must also slow the speed of a flame that may be travelling in the opposing direction. The flame cell takes advantage of the principle that the speed of the flame decreases with the reduction in diameter of the pipe.
- Absorb as much heat as possible from the flame front.
Flame arrestors must be manufactured of materials that absorb as much heat as possible. The combustion process requires fuel to burn, air to supply oxygen, and there must be heat (ignition temperature) to start and continue the combustion process. Metal materials, such as aluminum, are great for absorbing heat from the combustion process. When a flame front is in contact with an aluminum flame arrestor, the heat from the flame will be transferred to the aluminum. If enough heat can be transferred and absorbed by the arrestor, the flame front will be extinguished before reaching a protected area.
A crucial factor to consider is that not all flame arrestors perform the same in a flashback scenario.
Testing is the only way manufacturers can ensure flame arrestor safety
Unfortunately, there are currently no industry-wide performance and design standards for the construction of air intake flame arrestors. This means that not all flame arrestors in use today may be sufficiently function and/or safety tested to perform the tasks for which they are designed.
The American Petroleum Institute (API) has proposed a method of conducting routine testing of installed air intake flame arrestors. This test involves leaking a small amount of propane gas from the protected side toward the combustion source. If any flame can burn back through the flame arrestor or through a seal on the housing, the flame arrestor is not suitable for use and must be replaced. This testing method is sufficient in determining how a flame cell performs under normal operation, but it is not intended to test the ability to prevent flashbacks through the arrestor if combustible gas builds up in the fire tube and is ignited. Therefore, without fully testing the ability of a flame arrestor to extinguish a flame in a flashback scenario, the safety of everyone on a work-site may be put at risk under the assumption that a flame arrestor is fully and properly functioning.
Clear Rush Co. conducts routine testing of every flame arrestor that we manufacture, including flashback scenario testing, to ensure our products are proven safe and reliable for our clients and everyone on-site.
Watch our video “Air Intake Flame Arrestors: Testing & Comparing at Clear Rush Co.” to see how testing is done and how alternative flame arresting methods, such as stainless steel mesh, compare.
As demonstrated in the video, a crimped ribbon aluminum flame arrestor is the only proven way to guarantee the safety of equipment and personnel in a flashback scenario.
What can be determined
The performance of a flame cell is determined by two key factors:
- The size of the openings in the aluminum ribbon and;
- The overall thickness of the cell that the flame must travel through.
A flame cell that has larger openings will allow for more air to pass through, but will also allow for a flame to travel more easily and more quickly through the cell. Similarly, a flame cell that is thicker will have more exposure to the flame as it tries to travel through it.
A slower moving flame that is in contact with the cell for a longer period will have more opportunity to be cooled and extinguished before it reaches the other side.
The key takeaway is that air intake flame arrestors are intrinsically safe pieces of equipment that must be installed properly on any gas-fired appliance found in the oil and gas sector. There is no substitute for a well-designed and fully tested flame arrestor. The safety of everyone on-site depends upon them working properly.
Clear Rush Co. never compromises when it comes to safety.
Find out more about Clear Rush Co.’s trusted clean technology products and services for the global energy sector: www.clearrushco.com