Dealing with Combustible Dust

Flamex and IEP Technologies equip customers with the knowhow and tools they need to protect assets and employees.
By Anna Simet | October 28, 2019

Spark Detection Pioneer
To combat the common problem of dust collector fires and explosions often experienced in the woodworking industry, Flamex pioneered utilization of a new technology in North America by introducing its spark detection and extinguishing system in 1977, and it became the first of its kind to become FM Approved. Since that time, thousands of Flamex Systems have been installed in woodworking facilities across North America and beyond.

When the wood pellet industry entered a period of rapid growth over a decade ago, it was a natural fit for the company. “We specialize in industries that handle combustible dust, so we’re germane to the wood pellet industry—there are many fire hazards associated with the processes,” says Allen Wagoner, Flamex president.

Today, Flamex has thousands of installations in applications of all kinds across North America, belonging to global fire protection industry company Minimax-Viking. “We have systems in wood shavings plants and smaller-sized pellet manufacturing operations, but we’re also supporting large-scale pellet producers—we have some unique features and capabilities, and that’s appealing to them.”

One example is Flamex’s recently introduced YMX 5000 Detector series, which represents a unique and technologically advanced generation of infrared spark and flame sensors for industrial applications.  An industry-exclusive self-monitoring optics feature provides through-the-lens testing for each detector in real time to immediately alert the user of a reduction of detector capability caused by damage or lens contamination.

While Flamex is working with new-build pellet plants, much of its current work is helping existing plants protect assets and correct problems. “Some have gotten by for a while, but realized they have a problem—or could have a problem—and need to seek a solution.”

Wagoner emphasizes that it isn’t uncommon for local jurisdictions—whether it be fire marshals or insurance companies—to be inconsistent or unaware of hazards specific to wood pellet manufacturing, so onboarding a company to assist in identifying and correcting risks will allow for facilities not only to meet local codes and regulations but, meet or exceed industry safety standards. “A lot of what we do is educate people about the hazards under which they operate,” he says. “The wood pellet industry brings special hazards from drying to hammermilling, size reduction and other downstream aspects, and what’s done in one part of the mill is different than another. In an industrial-sized pellet mill for example, we can supply multiple systems and tie them all together to be monitored from one control room, and one computer using our Inveron HMI system.  The controller at the computer can see exactly where the problem is, and what’s going on.”

Wagoner emphasizes the importance of across-the-board operator training. “At some facilities—not specific to the wood pellet industry—some customers put the system in and don’t want to touch it, but they need to be able to maintain and operate it on a day-to-day basis,” he says. “They often assign one person to take care of it, and when they leave the company, nobody knows anything about it. We provide that training to operate and maintain systems. We’ll perform inspections and maintenance as needed, but on a day-to-day basis, they should understand and maintain the system. It will function a lot better if operators stay on top of preventative maintenance so that down the road, it’s reliable.”

Saving Lives, Protecting Assets 
IEP Technologies formed from four leading explosion protection companies in the U.S., United Kingdom, Germany and Switzerland. Part of the Hoerbiger Safety Solutions Network, IEP’s mission, according to David Grandaw, vice president of sales, is to save lives and protect assets by assisting customers in devising customized explosion protection solutions.

“Companies handling cellulose dust, including wood pellet plants, face the risk of dust explosions daily,” Grandaw says. “Sometimes, these explosions are confined to the original process vessel, but often, there are secondary explosions with devastating results. Having a comprehensive plan to prevent explosions from happening under normal circumstances, as well as mitigation under upset conditions, is critical.”

In wood processing plants, equipment most typically associated with dust explosions include dust collectors, cyclones, storage hoppers or silos, mechanical and pneumatic conveying, milling systems, pellet coolers and bucket elevators, according to Grandaw. “All of these vessels can have suspended wood dust, and all it takes is an ignition source to initiate deflagration. Deflagration pressure travels at the speed of sound, while the growing fireball inside the process vessel propagates at a much slower speed. When the shock wave from the ruptured vessel liberates and suspends process area dust that has accumulated on horizontal surfaces, the dust is ignited by the escaping fireball, causing a secondary explosion that can destroy the building,” Grandaw says.

Installing ignition prevention and control measures such as spark detection and suppression, static control and magnetic separators should be considered to minimize explosion risks under normal operating conditions. And because abnormal and upset conditions can happen, Grandaw says, both passive and active explosion protection should be considered.

One explosion protection option is relief venting, which requires one or more vents installed on a process vessel wall. “During a dust explosion’s incipient stage, the vent ruptures and directs the explosion’s overpressure, flame, and burnt and unburnt material away from the vessel to a safe location,” Grandaw explains. “The explosion relief vent is designed to ensure the explosion's pressure rise doesn't exceed the vessel's pressure shock resistance.”

Flameless venting protects indoor equipment by combining an explosion relief venting principle with a metal ribbon or mesh trap that arrests flame and retains particles. Like an explosion relief vent, Grandaw says, the flameless vent opens to relieve pressure during a deflagration. “But unlike with a rupture-style vent, the EVN valve from IEP Technologies utilizes a reusable, spring-loaded plate to relieve the pressure through a flame arresting material, which prevents a flame from ejecting into the surrounding area.”

Another protection alternative is explosion suppression systems, often installed in applications where it isn’t possible to safely vent an explosion away from process equipment, Grandaw continues. Explosion isolation devices  prevent deflagration from propagating through a connection such as a duct, chute or conveyor to other equipment, causing subsequent explosions.

There is much to seriously consider when working with combustible dust, and IEP’s experience in understanding and addressing deflagration risks is some of the most extensive in the explosion protection industry. “The risk of a combustible dust explosion is an ever-present threat at any facility that processes or handles combustible particulate solids or vapors,” Grandaw adds. “Assessing these risks and implementing proper explosion prevention and protection is a must for these facilities.”