DSS249: What is flameless venting efficiency and what is its importance with Dimitrios Kakogiannis

In today’s episode of the Dust Safety Science podcast, we’re talking about flameless venting- in particular, its efficiency and importance. Joining us is Dimitrios Kakogiannis, Explosion Protection Application Scientist from Fike Europe.

Dimitrios has a master’s degree from the University of Patras and a Ph.D in engineering from Free University in Brussels. He also has several years’ experience with the Royal Royal Military Academy in Belgium and over five years experience with Fike Europe in this explosion protection application scientist role. In this episode, he answers the following questions:

What is flameless venting?
What is flameless venting efficiency?
What are some of the key factors involved?
What should we start to be asking our explosion protection manufacturers?

What is Flameless Venting?

Dimitrios explained that flameless venting is a type of venting system consisting of a vent panel and a flame filter. It is used to create a flame towards the outside.

“With conventional venting we would have combustion and burning particles, a cloud of burning particle particles and a flame front would escape on the outside of the vessel with the flameless venting we blocked. Its advantages is that we have increased safety. So since there is no flame, there is no risk of fire spreading. Damage in general is reduced to the equipment and the surroundings, and we could classify it as environmentally friendly because it uses the gases’ particulates into the environment during an explosion.”

It is used in processes that involve potentially explosive dust to maintain a safe working environment. Flameless venting may seem simple as a concept, but in reality it is a very, very complex process.

“I will describe it by using a quote from a journal paper entitled Flameless Venting of Dust Explosions, Testing and Modeling,” Dimitrios said. “It’s a very interesting paper and I recommend it to the audience. And it says the flameless venting device does not behave as a standard vent. There is a highly complicated fluid mechanics problem of the fluid particle flow passing through a porous media, which in that case is the filter, which passing surface is progressively reduced.”

What is Flameless Venting Efficiency?

Efficiency in venting is defined as the ratio between the effective venting area and the physical vent area. In an ideal scenario, a vent would be like a massless block that disappears during combustion, allowing gases to escape freely. However, in reality, vents often have a membrane, usually metallic, which is less efficient than this ideal because it has mass and needs to open.

Flameless venting efficiency is different and more complex. It’s not the same as standard venting efficiency and should not be confused with it. In flameless venting, combustion occurs more extensively inside the vessel, affecting the explosion’s physics. The efficiency of a flameless venting device is influenced by the combustible dust’s burning properties and physical characteristics. Unlike standard vents, which have a single efficiency number, flameless venting efficiency varies and cannot be represented by just one number. It depends on several factors:

Particle Size Distribution: Coarse or fine dust affects how the filter clogs.
Dust Morphology: The type of dust, whether fibrous or melting, changes how quickly blockage occurs during combustion.
Dust Concentration: The amount of dust present influences combustion and how particles, both burned and unburned, pass through the vent.
Maximum Flame Length: This depends on the vessel’s shape and the location of the flameless venting device relative to the ignition point.

Clogging is a significant factor in flameless venting efficiency. Over time, as the filter clogs, the efficiency decreases. The device’s mesh can quench a fixed amount of energy, and the volume of the vessel is linked to this capacity. This description aims to provide a clearer understanding of the variable nature of flameless venting efficiency.

How Can We Maximize Flameless Venting Efficiency?

From the perspective of a manufacturer, maximizing efficiency in flameless venting systems involves optimizing the filter. The challenge lies in balancing several factors: the filter’s porosity, its ability to quench flames, the spectrum of dust it needs to protect against, and the cost. It’s difficult to create a one-size-fits-all design due to these varying needs.

When designing a flameless venting device, if the filter allows too many particles through, the system may be more efficient but less capable of quenching flames, risking flames escaping. Conversely, a very restrictive design may lead to rapid clogging, requiring a larger mesh area. Therefore, manufacturers must strike a balance between these numerous parameters.

From the perspective of a facility owner who wants to install flameless venting devices, a deep understanding of their specific process is crucial. They need to be aware of dust concentrations and other relevant factors. Often, this requires consulting services to optimize explosion protection solutions. The more detailed the process information, the more accurate and targeted the flameless venting solution can be.

Efficiency calculations should take into account various factors previously discussed. By considering these factors, less conservative and more efficient designs can be achieved. This approach can improve practical efficiency in flameless venting systems.

What Happens When the System is Inefficient?

There are potential dangers associated with flameless venting devices, which emphasizes the importance of accurate efficiency calculations.

One common failure mode is flame escaping outside the mesh enclosure. If this occurs near people, it poses a risk of injury. Information on different designs can be found online, which typically involve a casing holding the mesh.

A second scenario is more severe and relates directly to miscalculations of the device’s efficiency. If a device is thought to have higher efficiency than it actually does and clogs quickly, it may lead to increased pressure inside the vessel. This could cause the casing to break and turn into projectiles, posing a significant danger. These pieces, often made of heavy materials like iron, can move rapidly after a dust combustion, becoming dangerous projectiles due to their inertia.

This highlights the critical nature of having a range of efficiency estimates for these devices, rather than a single number. It’s also essential to gather as much information as possible about the specific process in use. In the absence of detailed data, worst-case scenarios must be considered, such as maximum dust concentration, coarse particles, and flame length. This approach is vital for safety and effective functioning of flameless venting systems.

What is Their Certification Process?

In recent years, there has been a significant development in the understanding of flameless venting systems. “Flameless Venting of Dust Explosion Testing and Modeling” was the first to clearly address the concept of multiple efficiencies in flameless venting devices, challenging the previous notion that a single efficiency number could adequately describe a device.

Before this paper, the certification process, particularly under the European ATEX certification for safety in explosive environments, involved testing in closed vessels and often used the lowest efficiency number to represent the device’s efficiency. However, this approach did not always provide a complete picture, as sometimes the types of dust used in testing were not specified.

The EN Standard, which sets guidelines for these processes, has been vague and doesn’t offer a clear methodology. Recently, however, there has been a shift in approach by notified bodies responsible for certification. These bodies are moving away from providing a single efficiency number based on a series of tests. Instead, they are beginning to offer a more detailed description, including the number of tests conducted, the range of particle sizes, and the range of dust concentrations. However, this is a recent development, and not many manufacturers have obtained such detailed certifications yet.

The EN Standard itself is under discussion for potential changes, although the timeline for these changes is unclear. Currently, there is a transitional period where some manufacturers still use a single efficiency number for their devices, especially if the devices were certified a few years ago. Other manufacturers, like Fike, have started to consider the factors discussed in the recent findings and provide more detailed descriptions of what their devices can do. This change in the certification process reflects a growing understanding and sophistication in how flameless venting devices are evaluated and described.

Conclusion

At the end of the interview, Dimitrios said, “Users need to be reminded that behind the functioning of flameless venting devices is hidden complex problem: a fluid particle flow with heat transfer that happens within milliseconds. The application of such a device to mitigate an explosion requires more information than traditional venting. And now a more general statement is that the AP community should be an inquiry community, and we should keep learning from each other.”

If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Dimitrios Kakogiannis directly:

Email: [email protected]
LinkedIn: https://www.linkedin.com/in/dimitrioskakogiannis/
Website: https://www.fike.com/

If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.