Mitigating Pellet Silo Fires

Silo fires cost time, money and sometimes even lives. Minimizing the risk of, and damage from, fires should be mission-critical for responsible pellet producers.
By Ron Kotrba | July 26, 2017

In April, a wood pellet silo at a storage and shipping terminal in Port Arthur, Texas—one of five silos owned on-site by bankrupt German Pellets Texas LLC (GPTX) and Texas Pellets Inc.—began smoldering. On April 21, GPTX retained global disaster recovery specialist Cotton Commercial USA Inc. to take the lead in extinguishing the fire, extracting the pellets and restoring the site.

“Silo fires are nothing new,” says Bruce Lisle, president and CEO of Energex Corp., a pellet producer owning mills in Quebec and Pennsylvania that, combined, surpass an annual production capacity of 250,000 tons. Lisle has had the misfortune of dealing with silo fires in his 30 years of experience in this business, much like many who’ve spent any considerable time in wood pellets.

John Arsenault, director of Quebec Wood Export Bureau’s wood pellet group, is the former vice president of operations for Energex, where he was responsible for Canadian operations and overseas sales. “It’s not a question of if you’ll have a fire,” Arsenault says, “it’s when.” He recalls a story about design of a mill in New York where the engineer inquired, “Where do you want your fire?”

The realistic goal is not total elimination of fires at pellet mills and storage, Arsenault conveys, but rather to significantly reduce the potential for risk while implementing sound damage mitigation tactics when a fire or explosion occurs.

Back in Port Arthur, GPTX and Cotton Commercial USA worked with local fire officials through late April to extinguish the burn. Equipment was deployed to measure combustible gas levels in the silo, and inert gases were injected to displace combustible gases, and to reduce the risk of fire and emissions. They also established fixed water lines to cool the silo roof, and attempted to seal the vessel as completely as possible to minimize fanning the fire with oxygen.

As a result, oxygen levels inside the silo dropped to a safe enough level for GPTX to begin extracting pellets. Specially fabricated access doors were installed in the base of the silo to allow removal of the pellets, and conveyors, roads and infrastructure were built to move the extracted pellets to a location where they could be inspected, extinguished or stored.

“I remember when our silo first caught on fire,” Lisle recalls. With tens or hundreds of thousands—or even millions—of dollars in product going up in smoke, or lost to water damage, the natural response might be to ask whether some of the cache might be salvageable.

“You can’t save it,” Lisle says. “It’s a hard realization, but you have to belly up to the bar and just accept that you’ve lost it.” That’s what insurance is for, he adds. “When you’re fighting a fire in a silo, the product in the silo is gone—it’s dead,” Lisle reiterates. “You first need to face that reality and then dump it on the ground, add water to it and scoop it up. It’s done. But you need to get it out. That’s the only way to put out the fire. Every silo should have a reclaim system, just turn it on.”

A fine line exists between expeditious discharge of burning pellets from a smoldering silo to reduce impacts on residents’ health, quality of living and property damage, and keeping the safety of those involved in extraction and extinguishing efforts top of mind. “If you try to get the pellets out as quickly as possible, that can create more problems,” Arsenault says. “It’s a long process measured in weeks, not hours. It does cost money. And you may lose 20,000 tons in a silo at $150 a ton or more. The risk—and the value—is high. There’s a lot of energy accumulated in a smoldering silo.”

Meanwhile, in Port Arthur, local news outlets reported that reactions from nearby residents of the burning silo ranged from disgust that everything in their houses now smelled like a barbeque pit, to concern of the possible health effects from ongoing inhalation of the smoke.

“The amount of smoke and odor being emitted from the silo has diminished significantly,” GTPX stated April 27 on its website designed to keep locals informed of the situation. “Residents in the surrounding areas should begin to notice the reduction in smoke and odor, if they have not already. Nonetheless, GPTX is devoting significantly more resources to monitoring ambient air emissions in the surrounding area …” 

Many modern pellet storage designs have fire mitigation and suppression measures built into the vessel. “Maybe in a remote facility, nobody cares,” Lisle says, “but in a port situation, especially where you have neighbors, you’re front and center. If you have the right design, you take a lot of risk out of there.”

The silos at GPTX’s Port Arthur site are the classic, corrugated steel style of bins often used to store grains or beans. In late April, GPTX stated, “It is important to note that structural engineers have inspected the silo itself over the past several days and concluded that the silo remains structurally sound. In addition, the neighboring silos have not been impacted by this incident, and temperatures within those silos have remained within the normal range.”

On May 5, pellet extraction began after installation of the specially fabricated doors. On May 16, a calibration error in real-time air quality monitoring by GPTX led to readings of “unhealthy” air quality in the area. On May 31, GPTX halted pellet extraction through the fabricated doors and adjusted its approach to using an auger and specially installed pipes. “The auger allows us to extract pellets directly from the center of the silo,” GTPX stated. “This modified approach has resulted in a more efficient and effective method of extraction. Based on consultation with the fire department and to protect the safety of workers and the community, we are immediately soaking the pellets with water once extracted from the silo.”

On June 4, more than a month after engineers indicated the smoldering silo was structurally sound, the bin collapsed. Luckily, no injuries or fatalities occurred. “Limited flames were experienced but quickly extinguished,” GPTX stated. One of the largest cranes in the U.S. was being brought on-site to assist with demolition and removal of the collapsed silo, which must occur before removal of smoldering pellets can commence. Then, on June 16, increased heat readings were experienced in the silo next to the one that collapsed.

Upon a media request for information, Jeff Erler, general counsel for Cotton Commercial USA, told Pellet Mill Magazine, “It is Cotton’s policy not to respond to media inquiries regarding active projects unless specifically requested to do so by the company’s client. Accordingly, any media inquiries should be directed to German Pellets.”

German Pellets did not respond to multiple requests for its side of this story, outside of what is posted on its website designed to inform the public. Pellet Mill Magazine did confirm, however, with the Jefferson County, Texas, district court clerk’s office that the city of Port Arthur filed a lawsuit June 30 against GPTX, citing the public nuisance the community is experiencing over the prolonged calamity.

Proper Prevention, Damage Mitigation
Fire prevention in pellet storage begins with proper safety procedures in the mill. “You have to think about it at all levels,” Arsenault says. When pellets come off the press, they are hot, so coolers are used to bring the heat down to ambient temperatures. “That means pellets are going into whatever you’re putting them into warm,” Lisle says. “We know from our experience, if you use a warehouse and dump them onto the floor in a pile and let them sit, over time you get an ice cream cone effect. Moisture goes up the center of the pile, like a chimney, and it degrades the pellets at the top of the pile. They break down.”

Arsenault says equipment that some don’t identify as sources of ignition—dryers, grinders, pellet machines themselves—must be routinely monitored and serviced. “There’s lots of horsepower putting pressure on wood, and it can get red hot and produce sparks, so there are lots of risks in operation. It must be controlled at all levels, from mechanical failures like bearings to simple storage. Operators must, on a daily basis, look out for them and do proper maintenance and cleanup. Some are just simply not aware, and they can end up with catastrophic failures.” He adds that conveyor systems are also sources of danger, and material handling equipment must be protected so they aren’t sparking, or delivering burning pellets to the silos.

Fire damages can range from loss of product to property damage, and from injuries to fatalities. Furthermore, civil and criminal lawsuits could follow.

Energex’s Quebec plant was built decades ago under a division of Shell Petroleum, where Arsenault says safety standards from the mature refining industry included several layers of protection. Even then, accidents still happen. “In 1998, we had an explosion at the plant and an employee suffered third-degree burns,” he says. “The fire originated from a faulty bearing from the mill. The pellet cooler exploded, even though we had fire suppression equipment in the cooler. One week and $10,000 dollars later, we were running again. One of our competitors had the same problem—a bearing in the mill—and it killed an employee and burned the place completely down.”

The Wood Pellet Association of Canada is promoting safety through a new program, Arsenault says. “Right from the get-go, you have to build safety measures into the plant,” he says.

Lisle, like other pellet producers, is no stranger to the occasional fire. “The plant in Quebec has been there a long time,” he says. “Some of the fires are self-induced like a welder error, but spontaneous combustion is the real issue. In one case, we had a silo—75 feet in diameter and 60 feet tall—filled up too much. You’re supposed to be able to ventilate these silos.”

Adequate ventilation is critical. “If you’re putting pellets in a silo, you need to vent condensation out and get rid of it,” Lisle says. “If not, that moisture will condense on the roof and come back into the pile as water, and moisture plays a major role in spontaneous combustion.”

After that particular silo fire at Energex, the crew cleaned up and went back to work. But they overlooked the critical fact that the side vents on the silo were filled up with pellets from the previous incident. “We forgot to clean the vents and, five months later, bang, with no ventilation we had fire No. 2 in that silo,” Lisle says. “At that point, the silo was done. We just let the sucker burn. And it burned for a long time.” The lesson? Empty the silo once it begins burning, clean it out thoroughly, and make sure it has proper ventilation.

Large silos are often equipped with internal sensors to measure the temperature, which should be monitored on a regular basis, Arsenault says. “When you start to see the temperature rise, something is going on,” whether the hoard of pellets is being heated from a hot pellet that was transferred into the silo, or from spontaneous combustion. Moisture from leaks, humid conditions, improper ventilation and bacteria in biomass can altogether create dangerous conditions.

“Basically, the bacteria become very happy when there is 20 to 35 percent moisture,” Arsenault says. “They begin proliferating, generating heat, and generating gas, so if you let these things run out on you, and air makes its way in, you are creating conditions for a fire.”

Lisle says pellet companies should inform their local fire departments, particularly for pellet storage silos located in communities, how to fight a pellet fire in a silo. “Otherwise, if they just pour water on it, it’s like shaking a can of beer,” he says, adding that if water is added to pellets, they expand to four times their volume. “First responders—the guys who show up if you have a fire—need to be trained on what to do, and what not to do, if there’s a fire.”

Tests performed over the years have found that the ideal technique is not to water down the pellets, Arsenault says, but rather to sprinkle foam on top and inject inert gas on the bottom. “Because we didn’t have gas suppression, we stopped storing pellets in large silos,” Arsenault says. “We began storing in small silos, or in open areas like A-frame buildings. The large, enclosed silos are too large a risk. They are hard to handle. In the open, we can move material around and manage a fire easier, and there’s no explosion risk.” 

Ultimately, when handling combustible material—whether it’s natural gas, crude oil or wood pellets—adequate protection measures must be put into place, Arsenault says. “Even when you do all of that,” he says, “and you’re handling this material day-in and day-out, you can still get an occasional slip-up.” But when accidents do happen, the ability to mitigate the damage is paramount.

Author: Ron Kotrba
Senior Editor, Pellet Mill Magazine