The Wood Pellet Association of Canada (WPAC), in co-operation with the BC Forest Safety Council, WorkSafeBC and media partner Canadian Biomass, held the Belt Dryer Symposium on Nov. 25, 2020. As belt dryers have become more common, the pellet industry has experienced several safety incidents over the past few years. The purpose of the Belt Dryer Safety Symposium was to share the learnings from these incidents and for individual operators to share in-house safe operating procedures with their industry colleagues.
Over 70 participants, including pellet producers, dryer manufacturers, insurance companies, universities, fire detection equipment suppliers and WorkSafeBC, attended the event. The workshop was moderated by Fahimeh Yazdan Panah, WPAC’s director of research and technical director.
The symposium included presentations from all the operators of belt dryers in British Columbia. Steven Mueller, director of health and safety at Pinnacle Renewable Energy, and Nathan Bond, plant superintendent at Skeena Bioenergy, described their dryers, energy systems, the safety incidents they experienced and the results of their post-incident investigations. Jimmy Boudreau, plant manager at Canfor, presented their dryer operating procedures in Fort St. Johns and Chetwynd. Comparisons were done between direct versus indirect energy systems and Bill Laturnus, senior safety advisor at the BC Forest Safety Council, examined the use of process safety bowtie analysis as a means of systematically identifying and managing critical controls.
All the incidents that were discussed had occurred in direct-fired dryer systems. The key learnings from the speakers on some of the potential causes for incidents included:
- Investigation of some incidents showed that the contributing factor in one incident was believed to be loose debris from cleaning activities picked up in air stream, blown through burner, and ignited before being deposited on fibre mat on belt. Smolder eventually burned through the belt and was then recirculated by air flow igniting further smolders.
- In another incident, strong belief shared that the recirculation of air was a significant contributor to the build-up of flammable deposits, as well as a prime source of ignition as small bits of material could be blown into the airstream through the burner and redeposited on the dryer bed.
- Another potential cause included introduction of ignition source in fibre stream, or foreign material entering air intake and being ignited by a burner.
- Some of the incidents were not primarily dryer incidents but turned into one. One hammermill deflagration incident was likely caused by a foreign object creating sparks within the hammermill, possibly a rock or metal contaminant. All other potential causes were ruled out by investigation. In a conveyor deflagration, the entire system was inspected for possible ignition source, but no cause was identified.
- In one incident, sparks from the fire were not detected by the spark detection system and the temperature sensors above the belt were not affected by the fire’s heat.
A number of action items were executed to address the findings from these incidents. They included:
- Engaging professional fire investigators to assist in investigation and provide recommendations
- Bringing dryer manufacturers’ representatives onsite to review and approve new prevention and mitigation measures
- Increasing dryer cleaning frequency and improving cleaning practices
- Adding mesh screens in post burner airflows to catch sparks or debris
- Increasing dryer purge cycle to clear out ducting before restarting burners
- Adding additional deluge in recirculating ducting for fire suppression
- Adding man doors to allow for better cleaning and firefighting access
- Re-programming fan motors to immediately stop in upset conditions to prevent further circulation of smolders/sparks
- Re-engineering the air flow ducting and stacks to remove the recirculation air ducting system,
- Conducting Process Hazard Analysis (PHA) with process safety experts on drying systems during removal of recirculating air system
- Installing infrared cameras to detect/shut down the dryer if hot spots are found in incoming fibre
- Resetting HMI to alarm/shutdown/deluge on belt temperature increases
At the end of the symposium, participants decided to form a Belt Dryer Working Group to review the past incidents and lessons learned for safer uses of belt dryers in pellet industry.
Anyone seeking more information or interested in joining the working group should contact Fahimeh Yazdan Panah, WPAC’s director of research and technical development:
This article was originally published by Canadian Biomass, a national media brand providing coverage of the emerging biomass, bioenergy and bio-products markets. See CanadianBiomassMagazine.ca for more information.