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.
Fire Protection Consultants: Dangers of Wood Pellet Plants
Harrington Group, Inc.
The Dangers of Wood Pellet Plant Facilities
Posted on Thursday, January 9th, 2014