Dangers of Wood Pellet Plants | Inherently Safer Design

Excellent article below from our friends at The Harrington Group, LLC

But first, I want to make a few comments about safe design of these pellet plants:

Here in general terms are current best practices for wood pellet mills based on NFPA 664 and over 3 decades of experience protecting wood, sawdust and wood flour processes.

As a primary consideration, understand that these wood pellet plants are making fuel, that plant operations and maintenance personnel are constantly working around fuel. Consider wood flour as dangerous as gasoline. Utilize inherently safer equipment and process design. Separate, segregate and isolate various hazardous processes and equipment from each other.

Risk is defined as probability of occurrence and severity of consequence. You will want to design in various layered engineering controls to reduce risk of probability of occurrence as well as severity of consequences in pellet mill processes.

We reduce risk by reducing probability of occurrence by designing in fire prevention technology and systems. Then reduce consequences by designing in fire and explosion protection systems.

Do a process hazard risk analysis and you will find that primary ignition sources of fires are the dryers, hammermills, and pellet mills. There are of course additional secondary ignition sources. The primary areas of dust cloud explosions are the bins, coolers, dust collectors and silos.

You will want to add layers of fire and explosion prevention and protection.

The primary prevention control technology to reduce probability of fire is to utilize spark detection and extinguishing systems after all spark sources, in all ducts and conveyors with a fire hazard, and prior to all enclosures with explosion hazard, as well as black body/hot particle detection in transfer points with fire and/or explosion hazard.

The second layer of protection is to design in automatic sprinkler and deluge systems, as well as manual deluge in each process conveyor or bin with a fire hazard.

The third level or layer of protection is to add explosion protection systems utilizing venting, isolation and suppression on all conveyors, elevators, bins and silos with an explosion hazard.

Additional levels of protection should also be considered, especially CO or combustion gas detection and inerting in the silos, and bins. Other possible layers of prevention and protection include not only spark, ember and hot particle detection and suppression, but also heat, temperature, flame detection, smoke detection; and bearing temperature, run time, and belt alignment monitoring among others.

Consider that every time the product is moved or manipulated, combustible dust called fines are created. These fines can migrate around and settle in various locations around the plant. The lighter the dust, the higher it will settle. Housekeeping is of primary consideration to preventing explosions, so also consider central vacuum systems and oscillating fans to help control dust.

This is your base level hazard mitigation strategy and systems for pellet mills.

_Jeff Nichols


Fire Protection Consultants: Dangers of Wood Pellet Plants 
Harrington Group, Inc.

The Dangers of Wood Pellet Plant Facilities

 

Posted on Thursday, January 9th, 2014

Photo: Frieda Squires/The Providence Journal

An explosion occurred on August 20, 2013 at Inferno Pellets Co. in East Providence, Rhode Island and the resulting fire, which spread throughout most of the 300,000 square-foot factory, took about four hours for firefighters to bring under control. One employee was injured by the explosion and subsequently released from Rhode Island Hospital after being treated for first and second degree burns.

In September 2013, another wood pellet incident was reported. This time, a dust explosion occurred at the Nature’s Flame facility in Rotoakawa, New Zealand. Also in September, an explosion incident was reported at the Anderson Hardwoods Pellet facility in Louisville, Kentucky, where at least one person was taken to the hospital with injuries.

Going back a little further, on October 20, 2011, an explosion and fire occurred at the New England Wood Pellet facility in Jaffrey, New Hampshire, which originated in the facility’s dust conveyor system. The large ensuing fire took approximately 14 hours to extinguish by over 100 firefighters from 14 different departments. OSHA was brought in to investigate the incident, which resulted in the company being fined a total of $147,000 for safety violations including, “poor dust collection system design” and “no explosion prevention / protection”.

In June of 2011, a dust explosion and resulting fire knocked down operations for a month at the Georgia Biomass facility near Waycross, Georgia, one of the world’s largest wood pellet manufacturing facilities. The $175 million plant had only been open for about a month when the incident occurred. According to plant manager, Ken Ciarletta, an investigation cited an overheated roller/bearing assembly in a pelletizer as the likely ignition source.

Clearly, the process of manufacturing wood pellets involves all the right ingredients for explosions and fires to occur with a concerning frequency the potential to cause serious injuries, damage to property, and interruption of production.

What are Wood Pellets and Biomass Fuels?
For many years, wood pellets were referred to as, well, “wood pellets”.  Recently, wood pellets are being referred to as one form of a broader category known as biomass fuels. The term biomass refers to materials that have originated from living, or recently living, organisms. Most often, it refers to plant material. Biomass, including wood, can be used directly (through combustion) or indirectly to create heat and electricity. In order to use biomass indirectly to create heat or electricity, it must first be converted into some form of biofuel. There are various types of biomass fuels, or biofuels; however wood pellets are the most common type, and are generally made from compacted sawdust.

Wood pellets and other biofuels are considered to sustainable.  Reportedly, they can help to reduce reliance on fossil fuels, like oil, to produce heat and energy. Because of this, the industry is expected to boom in the upcoming years. As the manufacturing of wood pellets grows to meet demand, it is fair to predict that the number of explosions and fires will increase in direct proportion.
Stay tuned for part two of this series: Fire Prevention Tips for Wood Pellet Plants.

By Jeff Harrington, CEO and Founder of Harrington Group, Inc.

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