A recent explosion occurred in a single burner, recirculating solids ring dryer. No one wasreported injured as a result of the explosion, however the explosion caused significant damage tothe dryer and minor damage to sections of the facility. Despite the dryer having been designedwith seven explosion doors, the explosion caused a section of the dryer recycle duct to ruptureand various doors on the dryer equipment to fail. As a result of the blast, two of the explosiondoors on the external ring duct were separated from their hinges, with one landing on the upperroof section, while the other fell back through the roof of the facility in the area of workers. Afire in the various sections of ductwork of the dryer ensued just after the explosion, which causedsignificant damage to the equipment. Fire suppression efforts using water and foam lastedapproximately 2 ? hours when the fire was ultimately extinguished.Just after the incident the facility owners thought the accident was caused by a dust explosion, asthey recently converted to a new process for treating the solid particulates prior to entering thedryer. Moreover, process data also showed that the explosion occurred seconds after a burnertrip when air was being added to the dryer to purge the system. The combustion managementsystem utilized an air-to-fuel ratio controller, along with mass flow meters for both combustionair and the natural gas for the burner. This paper describes the investigation into the cause of theexplosion and design blast venting used on the dryer. The CFD tool FLACS was used to helpevaluate the consequences associated with a dust or gas explosion during the incident. Thisincluded analysis of the process data to determine the gas mixture within the dryer at the time ofthe explosion as well as dust explosion testing of the solid particles in the dryer in order toevaluate its potential contribution. Finally, the deficiencies were identified in the blast ventdesign employed on the dryer for deflagrations associated with credible gas or dust explosions.
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